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Chemistries of Nb(V) and Ta(V) compounds are essentially identical as a result of lanthanide contraction. Hydrolysis of M(NMe

Treatment of the tetrahedral cluster H2Ru3(CO)9(μ3-S) (1) with 2-(diphenylphosphino)thioanisole (PS) furnishes the cluster H2Ru3(CO)7(κ2-PS)(μ3-S) (2). Cluster 2, which exhibits a chelated thiophos...

The reaction of [Mo(CO)3(NCMe)3] with added thiol in the presence of a phosphine auxiliary has been investigated. Treatment of [Mo(CO)3(NCMe)3] with pyrimidine-2-thiol (pymSH) and PPh3 at 60 °C in MeCN afforded the known mononuclear compounds cis-[Mo(CO)4(PPh3)2] (1) and [Mo(к2-pymS)4] (2), and the new binuclear compound [Mo2(CO)4(μ,к2-pymS)2(PPh3)2] (3), which possesses idealized C2 symmetry. A different product distribution was found when dppm was employed as the phosphine ligand. Of the five reaction products isolated, three consisted of mononuclear compounds, [Mo(CO)4(к2-dppm)] (4), [Mo(CO)3(κ2-dppm)(κ1-dppm)] (5) and [Mo(CO)(к2-pymS)2(к2-dppm)] (6), with the remaining two products corresponding to dinuclear compounds, [Mo2(CO)6(μ,к1-pymS)2(μ,к2-dppm)] (7) and [Mo2(CO)4(μ,к2-pymS)2(к2-dppm)] (8). Products 6–8 are new and have been fully characterized in solution by IR and NMR spectroscopy, and by X-ray crystallography in the case of 6 and 7. The reaction of [Mo(CO)3(NCMe)3] with PhSH and dppm at 60 °C in MeCN was also examined to assess the effect of thiol on the product distribution. The two principal products isolated were identified as the mononuclear compound [Mo(CO)2(κ1-PhS)2(κ2-dppm)] (9) and the dinuclear compound [Mo2(CO)6(μ,κ1-PhS)2(μ,κ2-dppm)] (10). The bonding in compounds 3, 6 and 7 was also examined by DFT, and highlights between the computational and experimental structures are discussed.

Chalcogenide-capped triiron clusters [Fe3(CO)7(μ3-CO)(μ3-E)(μ-dppm)] and [Fe3(CO)7(μ3-E)2(μ-dppm)] (E = S, Se) have been examined as proton-reduction catalysts. Protonation studies show that [Fe3(CO)9(μ3-E)2] are unaffected by strong acids. Mono-capped [Fe3(CO)7(μ3-CO)(μ3-E)(μ-dppm)] react with HBF4.Et2O but changes in IR spectra are attributed to BF3 binding to the face-capping carbonyl, while bicapped [Fe3(CO)7(μ3-E)2(μ-dppm)] are protonated but in a process that is not catalytically important. DFT calculations are presented to support these protonation studies. Cyclic voltammetry shows that [Fe3(CO)9(μ3-Se)2] exhibits two reduction waves, and upon addition of strong acids, proton-reduction occurs at a range of potentials. Mono-chalcogenide clusters [Fe3(CO)7(μ3-CO)(μ3-E)(μ-dppm)] (E = S, Se) exhibit proton-reduction at ca.-1.85 (E = S) and -1.62 V (E = Se) in the presence of p-toluene sulfonic acid (p-TsOH). Bicapped [Fe3(CO)7(μ3-E)2(μ-dppm)] undergo quasi-reversible reductions at -1.55 (E = S) and -1.45 V (E = Se) and reduce p-TsOH to hydrogen but protonated species do not appear to be catalytically important. Current uptake is seen at the first reduction potential in each case, showing that [Fe3(CO)7(μ3-E)2(μ-dppm)]- are catalytically active but a far greater response is seen at ca.-1.9 V being tentatively associated with reduction of [H2Fe3(CO)7(μ3-E)2(μ-dppm)]+. In general, selenide clusters are reduced at slightly lower potentials than sulfide analogues and show slightly higher current uptake under comparable conditions. peerReviewed

Coordinatively and electronically unsaturated square-pyramidal Fe(CO)(κ2-dppn)(κ2-tdt) (2) is shown to be amongst the most efficient proton-reduction catalysts reported to date. It is formed from the reaction of Fe2(CO)6(μ-tdt) (tdt = 3,4-toluenedithiolate) with 1,8-bis(diphenylphosphino)naphthalene (dppn) in presence of Me3NO·2H2O affording Fe2(CO)4(κ2-dppn)(μ-tdt) (1) as the major product, together with smaller but reproducible amounts of 2. Both have been characterized by single crystal X-ray diffraction. The electrochemistry of 2 is solvent dependent but in both CH2Cl2 and a 1:1 mixture of CH2Cl2/MeCN it shows a reversible reduction at E1/2 = –1.54 V and E1/2 = –1.68 V respectively. While 2 degrades in the presence of the strong acid HBF4·2H2O it is catalytically active for proton-reduction using CF3CO2H. Catalysis occurs at the first reduction potential and it displays an impressive icat/ip ratio of 33 after addition of 20 equivalents CF3CO2H. It is amongst the most efficient molecular proton-reduction catalysts reported to date.

The reaction of thiosaccharin (tsacH) with the triosmium cluster [Os3(CO)10(NCMe)2] furnishes the decacarbonyl isomers [HOs3(CO)10(μ-S-tsac)] (1) and [HOs3(CO)10(μ-N,S-1,3-tsac)] (2) in a 3:1 ratio at room temperature. These isomers differ by the coordination mode displayed by tsac ligand. The tsac moiety functions as an edge-bridging ligand via the sulfur atom in 1 while in 2 the bridging of adjacent osmium centers is achieved through the sulfur and nitrogen groups. The ancillary hydride in both products shares the Os Os edge that is bridged by the heterocyclic ligand. Heating 1 at 80 °C affords 2 and demonstrates that the former cluster is the product of kinetic control. The conversion of 1 → 2 has been investigated by DFT and the isomerization pathway elucidated. The DFT calculations confirm cluster 2 as the thermodynamically preferred isomer in this pair of products. Thermolysis of 2 in refluxing toluene affords the hexanuclear cluster [H2Os6(CO)17(μ-C,N-1,2-C6H4CNSO2)2(μ3-S)(μ4-S)] (3) via carbon-sulfur bond scission and subsequent capture of the extruded sulfur by the cluster core. The molecular structures for the three new clusters have been determined by single-crystal X-ray diffraction analyses.

Bis(phosphinidene)-capped triiron carbonyl clusters, including electron rich derivatives formed by substitution with chelating diphosphines, have been prepared and examined as proton reduction catalysts. Treatment of the known cluster [Fe3(CO)9(µ3-PPh)2] (1) with various diphosphines in refluxing THF (for 5, refluxing toluene) afforded the new clusters [Fe3(CO)7(µ3-PPh)2(κ2-dppb)] (2), [Fe3(CO)7(µ3-PPh)2(κ2-dppv)] (3), [Fe3(CO)7(µ3-PPh)2(κ2-dppe)] (4) and [Fe3(CO)7(µ3-PPh)2(µ-κ2-dppf)] (5) in moderate yields, together with small amounts of the corresponding [Fe3(CO)8(µ3-PPh)2(κ1-Ph2PxPPh2)] cluster (x = -C4H6-, -C2H2-, -C2H4-, -C3H6-, -C5H4FeC5H4-). The molecular structures of complexes 3 and 5 have been established by X-ray crystallography. Complexes 1–5 have been examined as proton reduction catalysts in the presence of p-toluenesulfonic acid (p-TsOH) in CH2Cl2. Cluster 1 exhibits two one-electron quasi-reversible reduction waves at –1.39 V (ΔE = 195 mV) and at –1.66 V (ΔE = 168 mV; potentials vs. Fc+/Fc). Upon addition of p-TsOH the unsubstituted cluster 1 shows a first catalytic wave at –1.57 V and two further proton reduction processes at –1.75 and –2.29 V, each with a good current response. The diphosphine-substituted derivatives of 1 are reduced at more negative potentials than the parent cluster 1. Clusters 2–4 each exhibit an oxidation at ca. +0.1 V and a reduction at ca. –1.6 V; for 4 conversion to a redox active successor species is seen upon both oxidation and reduction. Clusters 2–4 show catalytic waves in the presence of p-TsOH, with cluster 4 exhibiting the highest relative catalytic current (icat/i0 ≈ 57) in the presence of acid, albeit at a new third reduction process not observed for 2 and 3. Addition of the dppf ligand to the parent diphosphinidene cluster 1 gave cluster 5 which exhibited a single reduction process at –1.95 V and three oxidation processes, all at positive values as compared to 2–4. Cluster 5 showed only weak catalytic activity for proton reduction with p-TsOH. The bonding in 4 was investigated by DFT calculations, and the nature of the radical anion and dianion is discussed with respect to the electrochemical data. peerReviewed

Reaction of [MoO2Cl2(dmso)2] with the tetradentate O2N2 donor ligand papy [H2papy = N-(2-hydroxybenzyl)-N-(2-picolyl)glycine] leads to formation of the dioxomolybdenum(VI) complex [MoO2(papy)] (1) as a mixture of cis and trans isomers. Recrystallization from methanol furnishes solid cis-1, whereas the use of a dichloromethane-hexane mixture allows for the isolation of the trans-1 isomer. Both isomers have been structurally characterized by X-ray crystallography and the energy difference between the isomeric pair has been investigated by electronic structure calculations. Optimization of two configurational isomers in the gas phase predicts the trans isomer to lie 2.5 kcal/mol lower in energy (ΔG) than the cis isomer, which is inconsistent with the solution NMR data in d3-MeCN that exhibit a Keq of ca. 3 at 298 K for the trans ⇌ cis equilibrium. The DFT-computed energy difference is significantly improved (Keq = 5.4) by the inclusion of the MeCN solvent using the polarization continuum model (PCM). Density functional calculations reveal that the isomerization proceeds via a Ray-Dutt twist mechanism with a barrier of 14.5 kcal/mol, which is in accordance with the 1H NMR spectral data and the rapid equilibration of these isomers in solution. The catalytic reactivity of [MoO2(papy)] in the epoxidation of cis-cyclooctene is described, as well as its ability to effect oxo transfer from DMSO to PPh3.

Refluxing equimolar amounts of 1-ferrocenyl-1,3-butanedione (Fcacac) with BrRe(CO)5 in THF yielded the labile solvent complex fac-Re(CO)3 (THF)[κ2-O,O-FcC(O)CHC(O)Me] (1) in 80% isolated yield. 1 may also be prepared in quantitative yield using fac-BrRe(THF)2(CO)3 as the starting rhenium complex. The THF molecule in 1 is replaced by H2O during chromatographic purification to furnish the corresponding aqua complex fac-Re(CO)3(H2O)[κ2-O,O-FcC(O)CHC(O)Me] (2) while the reaction of 1 with PPh3 gives fac-Re(CO)3(PPh3)[κ2-O,O-FcC(O)CHC(O)Me] (3). Treatment of 1 with the terminal alkynes phenylacetylene and methyl propiolate proceeds rapidly at room temperature to give the π intermediates fac-Re(CO)3 (alkyne)[κ2-O,O-FcC(O)CHC(O)Me] [4 (PhC≡CH); 6 (MeO2CC CH)] that are not stable and undergo a 1,4-addition with regiospecific alkyne attack at the γ-methine site of the Fcacac moiety to afford fac-Re(CO)3 [κ3-C,O,O-FcC(O)CH(E-PhC = CH)C(O)Me] (5) and fac-Re(CO)3 [κ3-C,O,O-FcC(O)CH(Z-HC=CCO2Me)C(O)Me] (7). The solid-state structure for 5 and 7 was established by X-ray crystallography, and the computed mechanisms that account for the formation of these two products from 1 and alkyne are presented. 1 reacts with the internal alkyne dimethyl acetylenedicarboxylate (DMAD) to furnish the novel dimeric compound [fac-Re(CO)3{FcC(O)CH2C(CO2Me)C(CO2Me)}]2 (9). The structure of 9 confirms the linking of the monomeric fac-Re(CO)3{FcC(O)CH2C(CO2Me)C(CO2Me)} fragments through the intermolecular coordination of the ester oxygen atom associated with the α-carbomethoxy moiety of the E-metalated alkene; the latter moiety is traced to the initial DMAD insertion into the 6-membered metallocyclic ring in the π precursor fac-Re(CO)3 (MeO2CC CCO2Me)[κ2-O,O-FcC(O)CHC(O)Me].

Heating the 50-electron cluster [Fe3(CO)9 (μ3-Te)2] (1) with the diphosphines Ph2P-R-PPh2 [R = -CH2CH2- (dppe), Z-CH=CH- (dppv), 1,2-C6H4 (dppb), -CH2CH2CH2- (dpp), ferrocenyl (dppf), naphthalenyl (dppbn)] in benzene affords the 52-electron diphosphine-containing tellurium-capped triiron clusters [Fe3(CO)8 (μ3-Te)2 (κ2-diphosphine)] (diphosphine = dppe, dppv, dppb, dpp, dppf, dppnd) (2–7) in moderate yields, resulting from both phosphine addition and carbonyl loss. With 1,2-bis(diphenylphosphino)benzene (dppb) a second product is the cubane cluster [Fe4(CO)10(μ3-Te)4 (κ2-dppb)] (8). Cyclic voltammetry measurements on 2–7 reveal that all clusters show irreversible reductive behaviour at ca. −1.85 V with a series of associated small back oxidation waves, suggesting that reduction leads to significant structural change but that this can be reversed chemically. Oxidation occurs at relatively low potentials and is diphosphine-dependent. The first oxidation appears at ca. +0.35 V for 2–6 with a small degree of reversibility but is as low as +0.14 V for the bis(diphenylphosphino)naphthalene derivative 7 and in some cases is followed by further closely-spaced oxidation. Addition of [Cp2Fe][PF6] to 2–7 results in the formation of new clusters formulated as [Fe3(CO)8(μ3-Te)2(κ2-diphosphine)]+, with their IR spectra suggesting oxidation at the diiron centre. This is supported by computational studies (DFT) of the bis(diphenylphosphino)propane cluster 5 showing that the HOMO is the Fe Fe σ-bonding orbital, while the LUMO is centered on the diphosphine-substituted iron atom and has significant Fe Te σ∗-anti-bonding character consistent with the irreversible nature of the reduction. Complexes 2–7 have been examined as proton reduction catalysts in the presence of para-toluenesulfonic acid (TsOH). All are active at their first reduction potential, with a second catalytic process being observed at slightly higher potentials. While their overall electrocatalytic behaviour is similar to that noted for [Fe2(CO)6{μ-E(CH2)3E}] (E = S, Se, Te), the DFT results suggest that as the added electron is localised on the unique iron atom. The mechanistic aspects of hydrogen formation are likely to be quite different from the more widely studied diiron models.

The reactions of the MeCN-substituted compounds [Re2(CO)9(NCMe)] and [H3Re3(CO)11(NCMe)] with SbPh3 are described. Treatment of [Re2(CO)9(NCMe)] with SbPh3 in refluxing benzene furnished [Re2(CO)9(SbPh3)] (1) in good yield. Complex 1 reacts with SbPh3 in the presence of Me3NO in acetonitrile to give [Re2(CO)8(σ-C6H5)(µ-SbPh2)(NCMe)] (2), which on further reaction with additional SbPh3 in refluxing benzene afforded the known complex [Re2(CO)8(σ-C6H5)(µ-SbPh2)(SbPh3)] (3). Heating 1 with SbPh3 at 110 °C yields 3, which on prolonged heating at 110 °C in the presence of SbPh3 furnished the known stibene-bridged compound [Re2(CO)7(µ-SbPh2)2(SbPh3)] (4). Complex 2 is a rare example of a dirhenium complex containing a sigma-bonded phenyl group and a labile acetonitrile ligand in the same molecule. The stibene-bridged dirhenium complexes (2−4) result from the cleavage of antimony-carbon and Re–Re bonds. Heating [H3Re3(CO)11(NCMe)] with SbPh3 in refluxing toluene afforded the new compounds [H3Re3(CO)11(SbPh3)] (5), [H2Re3(CO)11(µ-SbPh2)(SbPh3)] (6), and [HRe2(CO)6(µ-SbPh2)(SbPh3)2] (8) together with previously reported compound [HRe2(CO)7(µ-SbPh2)(SbPh3)] (7). Compound 5 is a simple monosubstituted product, while 6 contains a terminally coordinated SbPh3 ligand and a bridging SbPh2 group formed by Sb–Ph bond scission. Compound 8 results from cluster fragmentation and SbPh3 ligand activation by Sb–Ph bond cleavage. A series of separate thermolysis experiments have been performed in order to establish the relationship between the different products. Compounds 1, 2, 5, 6, and 8 have been structurally characterized by X-ray crystallography. The bonding in these new compounds has been investigated by electronic structure calculations.

A series of new cationic dioxidomolybdenum(VI) complexes [MoO2(Ln)]PF6 (2–5) with the tripodal tetradentate pyridyl aminophenolate ligands HL2-HL5 have been synthesized and characterized. Ligands HL2-HL4 carry substituents in the 4-position of the phenolate ring, viz. Cl, Br and NO2, respectively, whereas the ligand HL5, N-(2-hydroxy-3,5-di-tert-butylbenzyl)-N,N-bis(2-pyridylmethyl)amine, is a derivative of 3,5-di-tert-butylsalicylaldehyde. X-ray crystal structures of complexes 2, 3 and 5 reveal that they have a distorted octahedral geometry with the bonding parameters around the metal centres being practically similar. Stoichiometric oxygen atom transfer (OAT) properties of 5 with PPh3 were investigated using UV–Vis, 31P NMR and mass spectrometry. In CH2Cl2 solution, a dimeric Mo(V) complex [(µ-O){MoO(L5)}2](PF6)2 6 was formed while in methanol solution an air-sensitive Mo(IV) complex [MoO(OCH3)(L5)] 7 was obtained. The solid-state structure of the µ-oxo bridged dimer 6 was determined by X-ray diffraction. Complex 7 is unstable under ambient conditions and capable of reducing DMSO, thus showing reactivity analogous to that of DMSO reductases. Similarly, the OAT reactions of complexes 2–4 also resulted in the formation of dimeric Mo(V) and unsaturated monomeric Mo(IV) complexes that are analogous to complexes 6 and 7. Catalytic OAT at 25 °C could also be observed, using complexes 1–5 as catalysts for oxidation of PPh3 in deuterated dimethylsulfoxide (DMSO‑d6), which functioned both as a solvent and oxidant. All complexes were also tested as catalysts for sulfoxidation of methyl-p-tolylsulfide and epoxidation of various alkene substrates with tert-butyl hydroperoxide (TBHP) as an oxidant. Complex 1 did not exhibit any sulfoxidation activity under the conditions used, while 2–5 catalyzed the sulfoxidation of methyl-p-tolylsulfide. Only complexes 2 and 3, with ligands containing halide substituents, exhibited good to moderate activity for epoxidation of all alkene substrates studied, and, in general, good activity for all molybdenum(VI) catalysts was only exhibited when cis-cyclooctene was used as a substrate. No complex catalysed epoxidation of cis-cyclooctene when an aqueous solution of H2O2 was used as potential oxidant.

The reaction of Os3(CO)12 with the tripodal ligand 1,1,1-tris(diphenylphosphinomethyl)ethane, triphos, results in the formation of the 48e trinuclear cluster complex Os3[μ-Ph2PCH2C(Me)(CH2PPh)CH2PC6H4](CO)7(η1-Ph). This new complex has been characterized by X-ray crystallography as well as by IR and NMR spectroscopy. The activation of the triphos ligand to yield the novel 9e donor ligand Ph2PCH2C(Me)(CH2PPh)CH2PC6H4 is unprecedented. The triphos ligand does not cap the triangular Os3 face; instead, the three phosphorus atoms are coordinated to only two of the metal atoms with the remaining osmium atom coordinated by an ortho-metalated aryl group. The triphos ligand is also transformed in several ways. Two C–P bonds are cleaved during the reaction, yielding an η1 phenyl ligand in the product and free benzene. The bonding in 1 has been examined by electronic structure calculations.

The activation of Ph3GeH at the dppm-bridged cluster Ru3(CO)10(μ-dppm) [dppm = bis(diphenylphosphino)methane] has been investigated. Ru3(CO)10(μ-dppm) reacts with Ph3GeH at room temperature in the presence of Me3NO to give the new cluster products Ru3(CO)9(GePh3)(μ-dppm)(μ-H) (1) and Ru3(CO)8(GePh3)2(μ-dppm)(μ-H)2 (2) via successive oxidation-addition of two Ge–H bonds. Refluxing 1 in THF furnishes the diruthenium complex Ru2(CO)6(μ-GePh2)(μ-dppm) (3) as the major product (44%), in addition to Ru3(CO)7(μ-CO)(GePh3){μ3-PhPCH2P(Ph)C6H4}(μ-H) (4) and the known cluster Ru3(CO)9(μ-H)(μ3-Ph2PCH2PPh) (5) in 7 and 8% yields, respectively. Heating samples of cluster 2 also afforded 3 as the major product together with a small amount of Ru3(CO)7(GePh3)(μ-OH)(μ-dppm)(μ-H)2 (6). DFT calculations establish the stability of the different possible isomers for clusters 1, 2, and 6, in addition to providing insight into the mechanism for hydride fluxionality in 2. All new compounds have been characterized by analytical and spectroscopic methods, and the molecular structures of 1, 3, and 6 have been established by single-crystal X-ray diffraction analyses.

Heating a benzene solution of the unsaturated cluster Os3(CO)8(μ-dppm)(μ-H)2 (1) [dppm = bis(diphenylphosphino)methane] with MeO2CC CCO2Me (DMAD) or EtO2CC CCO2Et (DEAD) at 80 °C furnished the dinuclear compounds Os2(CO)4(μ-dppm)(μ-η2;η1;к1-RO2CCCHCO2R)(μ-H) (3a, R = Me, 3b, R = Et) and the saturated trinuclear complexes Os3(CO)7(μ-dppm)(μ3-η2;η1;η1-RO2CCCCO2R)(μ-H)2 (4a, R = Me, 4b, R = Et). In contrast, similar reactions using unsaturated Os3(CO)8(μ-dppf)(μ-H)2 (2) [dppf = bis(diphenylphosphino)ferrocene] afforded only the trinuclear complexes Os3(CO)8(μ-dppf)(μ-η2;η1-RO2CCHCCO2R)(μ-H) (5a, R = Me; 5b, R = Et) and Os3(CO)7(μ-dppf)(μ3-η2;η1;η1-RO2CCCCO2R)(μ-H)2 (6a, R = Me; 6b, R = Et). Control experiments confirm that 5a and 5b decarbonylate at 80 °C to give 6a and 6b, respectively. Both 5a and 5b exist as a pair of isomers in solution, as demonstrated by 1H NMR and 31P{1H} NMR spectroscopy. DFT calculations on cluster 5a (as the dppf-Me4 derivative) indicate that the isomeric mixture derives from a torsional motion that promotes the conformational flipping of the cyclopentadienyl groups of the dppf-Me4 ligand relative to the metallic plane. VT NMR measurements on clusters 6a and 6b indicate that while the hydride ligand associated with the dppf-bridged Os-Os bond is nonfluxional at room temperature, the second hydride rapidly oscillates between the two non-dppf-bridged Os-Os edges. DFT examination of this hydride fluxionality confirms a “windshield wiper” motion for the labile hydride that gives rise to a time-average coupling of this hydride to both phosphorus centers of the dppf ligand. Thermolysis of 6a and 6b in refluxing toluene yielded Os3(CO)7(μ-dppf)(μ-η2;η1;к1-CCHCO2R) (7a, R=Me; 7b, R=Et). The vinylidene moieties in 7a and 7b derive from the carbon-carbon bond cleavage of coordinated alkyne ligands, and these two products exhibit high thermal stability in refluxing toluene.

The oxidation reactions of alkanes with hydrogen peroxide and peracids (peracetic acid (PAA) and m-chloroperoxybenzoic acid (mCPBA)) catalysed by two Fe(II) complexes of pentadentate {N5}-donor ligands have been investigated. Kinetic isotope effect experiments and the use of other mechanistic probes have also been performed. While the total yields of oxidized products are similar regardless of oxidant (e.g. 30–39% for oxidation of cyclohexane), the observed alcohol/ketone ratios and kinetic isotope effects differ significantly with different oxidants. Catalytic reactions in H2O2 medium are consistent with the involvement of hydroxyl radicals in the Csingle bondH bond cleavage step, and resultant low kinetic isotope effect values. On the other hand, catalytic reactions performed using peracid media indicate the involvement of an oxidant different from the hydroxyl radical. For these reactions, the kinetic isotope effect values are relatively high (within a range of 4.2–5.1) and the C3/C2 selectivity parameters in adamantane oxidation are greater than 11, thereby excluding the presence of hydroxyl radicals in the Csingle bondH bond cleavage step. A low spin Fe(III)-OOH species has been detected in the H2O2-based catalytic system by UV/Vis, mass spectrometry and EPR spectroscopy, while an Fe(IV)-oxo species is postulated to be the active oxidant in the peracid-based catalytic systems. Computational studies on the Csingle bondH oxidation mechanism reveal that while the hydroxyl radical is mainly responsible for the H-atom abstraction in the H2O2-based catalytic system, it is the Fe(IV)-oxo species that abstracts the H-atom from the substrate in the peracid-based catalytic systems, in agreement with the experimental observations. (Less)

The dinitrogen donor N,N’-diisopropylformamidine [PriN=C(H)NHPri] reacts with the triosmium cluster Os3(CO)10(NCMe)2 at room temperature to yield the isomeric clusters HOs3(CO)9[μ-C(O)NPriC(H)NPri] (1) and HOs3(CO)10[μ-NPriC(H)NPri] (2) in a 1:2.8 ratio. 1 contains an edge-bridging iminocarbamoyl ligand, while 2 contains a bridging formamidinate ligand. Thermolysis of 1 yields 2 plus the face-capped cluster HOs3(CO)9[μ3-NPriC(H)NPri] (3). The decarbonylation of 2 to 3 + CO confirms the molecularity of the observed reaction steps. The three products have been fully characterized in solution by IR and NMR spectroscopies, and the solid-state structures for 1-3 have been determined by X-ray crystallography. The kinetics for the thermolysis reaction were investigated over the temperature range 342–383 K, and the concentration versus time profiles for the conversion of 1 → 2 → 3 + CO have been successfully modeled using two consecutive, irreversible first-order reactions. The bonding in clusters 1-3 have been examined by DFT, and these data support cluster 1 as the kinetic substitution product and cluster 2 as the thermodynamically favored isomer.

Four new triosmium carbonyl complexes containing multiple dppm ligands were produced by microwave heating of solutions containing Os3(CO)12 and excess dppm. Three of these complexes, Os3(μ-H)2(CO)6(μ-dppm)[μ3-Ph2PCHP(C6H4)Ph] (2), Os3(CO)6[μ3-Ph2PCH2P(C6H4)Ph]2 (3), and Os3(μ-H)(CO)6[μ3-PhPCH2P(C6H4)Ph][μ3-PhPCH(C6H4)PPh] (4), contain two dppm ligands per Os3 unit, while the fourth, Os3(μ-H)(CO)5(dppm)[μ3-PhPCH2P(C6H4)Ph][μ3-PhPCH(C6H4)PPh] (5), is the first example of an Os3 cluster containing three dppm ligands. Microwave heating was also used to prepare the known complex Os3(μ-dppm)2(CO)8 (1) more efficiently than previously reported. The new complexes 2–5 have been characterized by IR, NMR, mass spectrometry, and X-ray crystallography. In addition, the bonding in these complexes has been examined by electronic structure calculations. All of the new complexes contain at least one dppm ligand that has undergone C H and/or C P bond activation. Complex 2 is a 48e cluster that contains one intact dppm ligand and one face-capping dppm ligand that coordinates all three osmium sites through the phosphine moieties and cyclometalated and ortho-metalated carbon atoms. Complex 3 is a 48e cluster with two ortho-metalated dppm ligands while complexes 4 and 5 are 50e clusters that possess a common metallic framework with one cyclometalated dppm ligand and one ortho-metalated dppm ligand.

Reaction of Ru 3 (CO) 12 with tris(2-thienyl)phosphine (PTh 3 ) in CH 2 Cl 2 at room temperature or in THF in the presence of a catalytic amount of Na[Ph 2 CO] furnishes the carbonyl substitution products Ru 3 (CO) 11 (PTh 3 ) ( 1 ), Ru 3 (CO) 10 (PTh 3 ) 2 ( 2 ), and Ru 3 (CO) 9 (PTh 3 ) 3 ( 3 ). Heating 1 in toluene affords the cyclometalated cluster Ru 3 (CO) 9 {μ-Th 2 P(C 4 H 2 S)}(μ-H) ( 4 ) resulting from carbonyl loss and carbon–hydrogen bond activation, and both 4 and the substituted derivative Ru 3 (CO) 8 {μ-Th 2 P(C 4 H 2 S)}(PTh 3 )(μ-H) ( 5 ) resulted from the direct reaction of Ru 3 (CO) 12 and PTh 3 at 110 °C in toluene. Interestingly, thermolysis of 2 in benzene at 80 °C affords 5 together with phosphido-bridged Ru 3 (CO) 7 (μ-PTh 2 ) 2 (μ 3 -η 2 -C 4 H 2 S) ( 6 ) resulting from both phosphorus–carbon and carbon–hydrogen bond activation of coordinated PTh 3 ligand(s). Cluster 6 is the only product of the thermolysis of 2 in toluene. Heating cyclometalated 4 with Ru 3 (CO) 12 in toluene at 110 °C yielded the tetranuclear phosphinidine cluster, Ru 4 (CO) 9 (μ-CO) 2 (μ 4 -η 2 -C 4 H 2 S)(μ 4 -PTh) ( 7 ), resulting from carbon–phosphorus bond scission, together with the pentaruthenium sulfide cluster, Ru 5 (CO) 11 (μ-PTh 2 )(μ 4 -η 4 -C 4 H 3 )(μ 4 -S) ( 8 ), in which sulfur is extruded from a thiophene ring. All the new compounds were characterized by elemental analysis, mass spectrometry, IR and NMR spectroscopy, and by single crystal X-ray diffraction analysis in case of clusters 4 , 6 , 7 , and 8 . Cluster 4 consists of a triangular ruthenium framework containing a μ 3 -Th 2 P(C 4 H 2 S) ligand, while 6 consists of a ruthenium triangle containing η 2 -μ 3 -thiophyne ligand and two edge-bridging PTh 2 ligands. Cluster 7 exhibits a distorted square arrangement of ruthenium atoms that are capped on one side by a μ 4 -phosphinidene ligand and on the other by a 4e donating μ 4 -η 2 -C 4 H 2 S ligand. The structure of 8 represents a rare example of a pentaruthenium wing-tip bridged-butterfly skeleton capped by μ 4 -S and μ 4 -η 4 -C 4 H 3 ligands. The compounds 4 , 6 , 7 , and 8 have been examined by density functional theory (DFT), and the lowest energy structure computed coincides with the X-ray diffraction structure. The hemilabile nature of the activated thienyl ligand in 4 and 6 has also been computationally investigated.

Reaction of TaCl2(═NSiMe3)[N(SiMe3)2] (1) with alkylating reagents form the alkyl amide imide complexes TaR2(═NSiMe3)[N(SiMe3)2] (R = Me (2), CH2Ph (3)) and mixed amide imide compounds Ta(NR′2)2(═NSiMe3)[N(SiMe3)2] (R′ = Me (4), Et (5)). The reaction of 2 and 0.5 equiv of O2 leads to preferential oxygen insertion into one Ta–Me bond, yielding the alkoxy-bridged alkyl dimer Ta2(μ-OMe)2Me2(═NSiMe3)2[N(SiMe3)2]2 (6) as cis and trans isomers. Crystallization of the cis-6 and trans-6 mixture gave only crystals of trans-6. When the crystals of trans-6 were dissolved in benzene-d6, conversion of trans-6 to cis-6 occurred until the trans-6 ⇌ cis-6 equilibrium was reached with Keq = 0.79(0.02) at 25.0(0.1) °C. Kinetic studies of the exchange gave the rate constants k = 0.018(0.002) min–1 for the trans-6 → cis-6 conversion and k′ = 0.022(0.002) min–1 for the reverse cis-6 → trans-6 conversion at 25.0(0.1) °C. Complex 6 reacts with additional O2, forming the dialkoxy dimer Ta2(μ-OMe)2(OMe)2(═NSiMe3)2[N(SiMe3)2]2 (7)...

Thermolysis of [HOs3(CO)8{µ3-Ph2PCH2P(Ph)C6H4}] in refluxing xylene has been investigated, and three new polynuclear osmium compounds containing an activated dppm ligand(s) as a result of multiple C H bond cleavages have been isolated. The new complexes are [H2Os3(CO)8{µ3-Ph2PCHP(Ph)C6H4}] (1), [H2Os3(CO)6(µ3-Ph2PCHPPh2){µ3-Ph2PCH2P(Ph)C6H4}] (2) and [Os2(CO)6{µ-H4C6(Ph)PCH2P(Ph)C6H4}] (3), each of which exhibits a different coordination mode involving the activated diphosphine ligand. Cluster 1 is formed by C H bond oxidative addition of the backbone methylene spacer and an ortho site at an ancillary aryl ring. Control experiments confirm that cluster 2 is formed from cluster 1 and dppm. The dinuclear compound 3 is formed via metalation of two phenyl rings on the dppm ligand and is accompanied by the release of an osmium atom. The molecular structure of each new complex has been established by single-crystal X-ray diffraction analysis, and the bonding in compounds 1–3 has been examined by DFT calculations.

The reaction of the labile triosmium cluster [Os3(CO)10(NCMe)2] with tetramethylthiuram disulfide [(Me2NCS2)2, tmtd] has been investigated at room temperature. Conducting the reaction under mild conditions has permitted the isolation of the three new polynuclear osmium complexes [Os3(CO)10{κ2(S,S)-S2CNMe2}2] (1), [Os4(CO)12{κ2(S,S)-S2CNMe2}2{μ3-η1(C),κ2(O,O)-CO2)}(μ3-S)] (2) and [Os3(CO)9{μ3-η1(C),κ1(S)-SCNMe2}{μ-κ1(S)-SC(O)NMe2}] (3) in 20, 16 and 10% yield, respectively, in addition to the known mononuclear complex [Os(CO)2{κ2(S,S)-S2CNMe2}2] (4) in 10% yield. The triosmium complex 1 has a linear arrangement of osmium atoms with each terminal osmium center containing a chelating Me2NCS2 ligand. The tetraosmium complex 2 also possesses a μ3-CO2 ligand in addition to capping sulfido and chelating Me2NCS2 ligands. Complex 3 contains an open triosmium core with the open Os···Os edge bridged by a Me2NC(O)S ligand and a capping Me2NCS ligand. A similar reaction between the unsaturated cluster [Os3(CO)10(μ-H)2] and [(Me2NCS2)2] yielded the triosmium complexes [Os3(CO)10{μ-κ1(S)-S2CNMe2}(μ-H)] (5) and [Os3(CO)9{μ3-κ2(S,S)-S2CNMe2}(μ-H)] (6) in addition to compounds 1 and 4 and the known hydroxyl cluster [Os3(CO)10(μ-OH)(μ-H)] (7) in 7, 14, 14, 10, and 6% yield, respectively. Both 5 and 6 possess a triosmium core, and the Me2NCS2 ligand acts in edge-bridging capacity in the former while it serves as a face-capping ligand in the latter. All new complexes have been characterized by combustion analyses and IR and NMR spectroscopies, and the solid-state structures of 1–3, and 6 have been established by X-ray crystallography. The bonding in clusters 1-3 and 6 has been examined by electronic structure calculations, and the thermodynamics for the formation of 1 and MeCN (two equiv) from [Os3(CO)10(MeCN)2] and tmtd, relative to other chelated and bridged isomers of [Os3(CO)10(tmtd)] are discussed.

Reactions of [Ru3(CO)12] with thiosaccharin (tsacH) at different temperatures have been investigated. At 40 °C, the diruthenium complex [Ru2(CO)6(μ-N,S-tsac)2] (1) is produced and whose ruthenium atoms are bridged by two tsac ligands that are oriented in a head-to-tail fashion. When this reaction is carried out at 66 °C, the tri-, tetra- and penta-ruthenium complexes [H2Ru3(CO)7(μ-N,S-tsac)(μ-C,N–C6H4CNSO2)(μ3-S)] (2), [Ru4(CO)12(μ-N,S-tsac)2(μ4-S)] (3) and [H2Ru5(CO)13(μ-N,S-tsac)(μ-C,N–C6H4CNSO2)(μ3-S)(μ4-S)] (4), respectively, are also isolated in addition to 1. The triruthenium complex 2 exhibits an arachno SRu3 polyhedron containing edge-bridging tsac and C6H4CNSO2 ligands. The tetraruthenium complex 3 consists of two [Ru2(CO)6(μ-N,S-tsac)] fragments linked via a μ4-S ligand, while the pentaruthenium complex 4 is composed of individual Ru3 and Ru2 units linked via a μ4-S ligand. At 81 °C, the same reaction furnishes the pentaruthenium complex [HRu5(CO)15(μ-N,S-tsac)(μ5-S)] (5) containing tsac and μ5-S bridging ligands. The molecular structures of the new complexes have been determined by single-crystal X-ray diffraction analyses, and the bonding in each product has been examined by DFT.

Reactions of binuclear [Re(CO)3(μ,κ2-S,N-thpymS)]2 (1) with diphosphines have been investigated. At 298 K, dppm reacts to give mononuclear [Re(CO)3(κ1-dppm)(κ2-S,N-thpymS)] (2) through a phosphine-promoted scission of the dithiolate bridges that leaves one of the phosphine moieties free (dangling). Refluxing 2 in toluene leads to CO loss and formation of dinuclear [Re2(CO)4(μ-dppm)(μ,κ2-S,N-thpymS)2] (3) whose rhenium centers are bridged by two thiolate groups and the dppm ligand. Treatment of 1 with dppe at room temperature furnishes [Re(CO)3(κ2-S,N-thpymS)]2(μ,κ1,κ1-dppe) (4) where each phosphine center ligates the respective d6-ML5 rhenium fragment. Complex 4 exists as two distinct configurational isomers (4a and 4b) that have been isolated and the solid-state structures characterized crystallographically. The principal difference in the stereoisomeric products is the orientation of the two [Re(CO)3(κ2-S,N-thpymS)] moieties at the anti-staggered Newman projection involving the P-C-C-P backbone of the dppe ligand. Both stereoisomers retain their identity in solution at ambient temperatures but equilibrate to a 1:1 mixture upon heating at 363 K for 1 h. The reaction of 1 with dppe in toluene at 383 K affords [Re(CO)2(κ1-dppe)2(κ2-S,N-thpymS)] (5) containing two monodentate (dangling) diphosphine ligands. Thus, these seemingly simple reactions afford a range of different products whose composition is highly dependent upon the experimental conditions employed and the nature of the diphosphine backbone. The reaction of 1 with dppe and the process responsible for the equilibration of the two configurational isomers of 4 have been investigated by electronic structure calculations.

The redox behaviour and electrocatalytic proton reduction ability of the thiolate-capped triiron clusters [Fe3(CO)9(μ3-SR)(μ-H)] (1, R = iPr; 2, R = tBu) have been investigated. In CH2Cl2, both show a quasi-reversible reduction and an irreversible oxidation. The thiol substituent has a significant influence on their reduction potentials (E1/2 = −1.24 V for 1 and E1/2 = −1.40 V for 2 vs. Fc+/Fc) but less impact on oxidation potentials (E1/2 = 0.99 V for 1 and E1/2 = 0.93 V for 2 vs. Fc+/Fc). Reduction is quasi-reversible and DFT studies reveal that this is due to scission of an iron-iron bond. While the clusters are not protonated by CF3CO2H or HBF4·Et2O, they can catalyse proton reduction of these acids at their corresponding reduction potentials following an ECEC mechanism.

Three new molybdenum complexes have been synthesized from one-pot reactions between Mo(CO) 3 (NCMe) 3 and pyridine-2-thiol (pySH) in the presence of different P-donors. Reaction with P(OMe) 3 in MeCN at ca. 55 °C gives Mo(CO) 2 [P(OMe) 3 ](κ 2 -pyS) 2 ( 1 ) and Mo(CO) 4 [P(OMe) 3 ] 2 ( 2 ). A similar reaction involving bis(diphenylphosphino)methane (dppm) furnishes the dinuclear species Mo 2 (CO) 4 (μ,κ 2 -pyS) 2 (κ 2 -dppm) ( 3 ) together with the mononuclear complexes Mo(CO)(κ 2 -pyS) 2 (κ 2 -dppm) ( 4 ) and Mo(CO) 4 (κ 2 -dppm) ( 5 ). With bis(diphenylphosphino)ethane (dppe) only the mononuclear complexes Mo(CO)(κ 2 -pyS) 2 (κ 2 -dppe) ( 6 ), Mo(CO) 4 (κ 2 -dppe) ( 7 ), and Mo(CO) 3 (κ 1 -dppe)(κ 2 -dppe) ( 8 ) resulted. Complexes 1 , 3 , and 6 have been characterized by single-crystal X-ray diffraction analyses and the bonding in 1 and 3 has been evaluated by density functional theory (DFT) calculations, optimized structures being discussed relative to the observed solid-state structures.

The electronically unsaturated dimolybdenum complex [CpMo(CO)2]2 (1) reacts with the π-excessive heterocycle 2-mercapto-1-methylimidazole at 110 °C to afford the mononuclear molybdenum complex CpMo(CO)2(κ2-C4H5N2S) (2) and the trimolybdenum cluster Cp3Mo3(μ-CO)2(μ-κ2-C4H5N2)(μ-S)(μ3-S) (3) in 22% and 20% yields, respectively. A similar reaction between 1 and the benzoannulated heterocycle 2-mercaptobenzothiazole furnishes CpMo(CO)2(κ2-C7H4NS2) (4) and Cp3Mo3(μ-CO)2(μ-κ2-C7H4NS)(μ-S)(μ3-S) (5) in 17% and 20% yields, respectively. Compounds 2 and 4 consist of a single molybdenum atom with two carbonyl groups, a cyclopentadienyl ligand, and a chelating heterocyclic thiolato ligand. The trimolybdenum clusters 3 and 5 consist of three cyclopentadienyl ligands, a metalated heterocyclic ligand, edge-bridging and face-capping sulfido ligands, and a pair of semi-bridging carbonyl ligands. All new compounds have been fully characterized in solution by IR and NMR spectroscopy, and the solid-state structures of 3 and 4 have been determined by single-crystal X-ray diffraction analyses. The bonding in cluster 3 has been computationally investigated by Density Functional Theory (DFT), and the data support a cluster that is electronically saturated with 48e and where both sulfido ligands function as 4e donor groups.

The reaction of the heterocycle ethyl (2Z)-cyano-6-methoxyquinolin-2(1 H )-ylidene-ethanoate ( L ) with different rhenium carbonyls to give cis -BrRe(CO) 4 L ( 1 ) is reported. X-ray crystallography reveals that the heterocyclic ligand coordinates to the rhenium center via the nitrile moiety and cis to the bromine group in 1 . Compound 1 has been characterized in solution by IR and NMR (1D and 2D) spectroscopy, and the complete assignment of the 1 H and 13 C NMR resonances associated with the coordinated heterocycle established. The redox properties and the bonding in 1 have been explored by cyclic voltammetry and DFT calculations, respectively. The mechanism for the formation of 1 , starting from BrRe(CO) 5 and L , has been studied computationally, and the cis product is computed to be 16.8 kcal/mol more stable than trans -BrRe(CO) 4 L.

Os3(CO)12 reacts with phenazine in refluxing xylene to yield the monohydride cluster Os3(CO)9(μ3,η2-C12H7N2)(μ-H) (1) in 18% yield and the dihydride cluster Os3(CO)9(μ3,η2-C12H6N2)(μ-H)2 (2) in 21% yield. Compound 1 reacts reversibly with CO to give the decacarbonyl compound Os3(CO)10(μ,η2-C12H7N2)(μ-H) (3) and with PPh3 to afford the addition product Os3(CO)9(μ,η2-C12H7N2)(PPh3)(μ-H) (4). Compounds 1, 2, and 4 have been structurally characterized. 1 contains a C-metalated phenazine ligand that is coordinated to the cluster by a dative nitrogen bond and a benzylidene-type bond, the latter which bridges the same cluster edge as the bridging hydride. The activated phenazine ligand in 2 derives from a double C–H bond metalation sequence, affording a face-capping heterocyclic ligand that binds adjacent osmium centers through two σ–Os–C bonds and the third osmium atom via an aryl π bond in an η2 fashion. Compound 4 exhibits a closed trimetallic Os3(CO)9 core that contains edge-bridging phenazine (C,N coordination) and hydride moieties, and a triphenylphosphine ligand that is coordinated at the non-phenazine-ligated osmium center. These compounds represent rare examples of polynuclear osmium clusters containing C-metalated phenazine ligands. The potential energy surfaces that afford clusters 1 and 2 from Os3(CO)12 and phenazine have been modeled by DFT calculations, and these data indicate that both product clusters originate from the unsaturated cluster Os3(CO)11.

Rhodium(I) and Iridium(I) borate complexes of the structure [Me2B(2-py)2]ML2 (L2 = (tBuNC)2, (CO)2, (C2H4)2, cod, dppe) were prepared and structurally characterized (cod = 1,5-cyclooctadiene; dppe = 1,2-diphenylphosphinoethane). Each contains a boat-configured chelate ring that participates in a boat-to-boat ring flip. Computational evidence shows that the ring flip proceeds through a transition state that is near planarity about the chelate ring. We observe an empirical, quantitative correlation between the barrier of this ring flip and the π acceptor ability of the ancillary ligand groups on the metal. The ring flip barrier correlates weakly to the Tolman and Lever ligand parameterization schemes, apparently because these combine both σ and π effects while we propose that the ring flip barrier is dominated by π bonding. This observation is consistent with metal–ligand π interactions becoming temporarily available only in the near-planar transition state of the chelate ring flip and not the boat-configured ground state. Thus, this is a first-of-class observation of metal–ligand π bonding governing conformational dynamics.

Novel dppm-ligated ruthenium-tin clusters have been prepared from the reaction of [Ru3(CO)10(μ-dppm)] with Ph3SnH. At room temperature and in the presence of Me3NO, [Ru3(CO)9(SnPh3) (μ-dppm) (μ-H)] (1) is produced from the formal loss of CO and Sn-H bond oxidative-addition. Treatment of 1 with a further two equivalents of Ph3SnH (in the presence of Me3NO) gave [Ru3(CO)7(SnPh3)2(μ-SnPh2)(μ-dppm)(μ-H)(μ3-H)] (2) which results from both Sn–H and Sn–C bond scission and contains two different hydride environments (μ and μ3) and a μ-SnPh2 moiety. Cluster 2 has 48 CVE (cluster valence electron) with three formal ruthenium-ruthenium bonds; two of those are very long and fall at the extreme end of distances attributed to ruthenium-ruthenium bonds. Thermolysis of 2 at 66 °C liberates benzene to give [Ru3(CO)8(SnPh3)(μ-SnPh2)(μ3-SnPh2)(μ-dppm)(μ-H)] (3). DFT calculations confirm that the hydride bridges one of the Ru-μ-SnPh2 bonds in 3. The solid-state structures of 2 and 3 have been determined by X-ray crystallography, and the bonding and ligand distribution have been investigated by DFT studies. The geometry-optimized structures are consistent with the solid-state structures.

Reactions of Ru 3 (CO) 10 (μ-dppf) ( 1 ) (dppf = 1,1′-bis(diphenylphosphino)ferrocene), Ru 3 (CO) 10 (μ-dppm) ( 2 ) (dppm = bis(diphenylphosphino)methane), and the orthometalated derivative Ru 3 (CO) 9 {μ 3 -PPhCH 2 PPh(C 6 H 4 )} ( 3 ) with silanes (Ph 3 SiH, Et 3 SiH, Ph 2 SiH 2 ) are reported. Treatment of 1 with Ph 3 SiH and Ph 2 SiH 2 at room temperature leads to facile Si–H bond activation to afford Ru 3 (CO) 9 (μ-dppf)(SiPh 3 )(μ-H) ( 4 ) (60% yield) and Ru 3 (CO) 9 (μ-dppf)(SiPh 2 H)(μ-H) ( 6 ) (53% yield), respectively. The reaction of 1 with Ph 3 SiH has been investigated by electronic structure calculations, and these data have facilitated the analysis of the potential energy surface leading to 4 . Compound 1 does not react with Et 3 SiH at room temperature but reacts at 68 °C to give Ru 3 (CO) 9 (μ-dppf)(SiEt 3 )(μ-H) ( 5 ) in 45% yield. Reaction of 2 with Ph 3 SiH at room temperature yields two new products: Ru 3 (CO) 9 (μ-dppm)(SiPh 3 )(μ-H) ( 7 ) in 40% yield and Ru 3 (CO) 6 (μ 3 -O)(μ-dppm)(SiPh 3 )(μ-H) 3 ( 8 ) in 15% yield. Interestingly, at room temperature compound 7 slowly reverts back to 2 in solution with decomposition and liberation of Ph 3 SiH. Complex 8 can also be prepared from the direct reaction between 7 and H 2 O. Similar reactions of 2 with Et 3 SiH and Ph 2 SiH 2 give only intractable materials. The orthometalated compound 3 does not react with Ph 3 SiH, Et 3 SiH and Ph 2 SiH 2 at room temperature but does react at 66 °C to give Ru 3 (μ-CO)(CO) 7 {μ 3 -PPhCH 2 PPh(C 6 H 4 )}(SiR 2 R 1 )(μ-H)]( 9 , R = R′ = Ph, 71% yield; 10 , R = R′ = Et, 60% yield; 11 , R = Ph, R′ = H, 66% yield) by activation of the Si–H bond. Compounds 4 and 8 – 11 have been structurally characterized. In 4 , both the dppf and the hydride bridge a common Ru–Ru vector, whereas NMR studies on 7 indicate that two ligands span different Ru–Ru edges. Compound 8 contains a face-capping oxo moiety, a terminally coordinated SiPh 3 ligand, and three bridging hydride ligands, whereas 9 – 11 represent simple oxidative addition products. In all of the compounds examined, the triruthenium framework retains its integrity and the silyl groups occupy equatorial sites.

The new clusters [Ru-3(CO)(9)(mu-dppf){P(C4H3E)(3)}] (1, E = O; 2, E = S) have been prepared from the Me3NO-induced decarbonylation of [Ru-3(CO)(10)(mu-dppf)] in the presence of PFu(3) (E = O) and PTh3 (E = S), respectively. Upon thermolysis in benzene, the major products are the cyclometalated clusters [(mu-H) Ru-3(CO)(7)(mu-dppf){mu(3)-(C4H3E)(2)P(C4H2E)}] (3, E - O; 4, E - S). This thermolytic behavior is in marked contrast to that previously noted for the analogous bis(diphenylphosphino) methane (dppm) complexes [Ru-3(CO)(9)(mu-dppm){P(C4H3E)(3)}], in which both carbon-hydrogen and carbon-phosphorus bond activation yields furyne- and thiophyne-capped clusters. The crystal structures of 1, 3 and 4 are presented and reveal that phosphine migration has occurred during the transformation of 1,2 into 3,4, respectively. The possible relation of the observed reactivity to the relative flexibilities of the diphosphine ligands is discussed. Density functional calculations have been performed on the model cluster [Ru-3(CO)(9)(mu-Me-4-dppf){ P(C4H3O)(3)]}], and these data are discussed relative to the ground-state energy differences extant between the different isomeric forms of this cluster. The dynamic NMR behavior displayed by the metalated thienyl ring in cluster 4 has also been investigated by computational methods, and the free energy of activation for the "windshield wiper" motion of the activated thienyl moiety determined. (C) 2013 Elsevier B.V. All rights reserved. (Less)

The syntheses of novel dimethylbis(2-pyridyl)borate nickel(II) complexes 4 and 6 are reported. These complexes were unambiguously characterized by X-ray analysis. In dichloromethane solvent, complex 4 undergoes a unique square-planar to square-planar rotation around the nickel(II) center, for which activation parameters of ΔH⧧ = 12.2(1) kcal mol–1 and ΔS⧧ = 0.8(5) eu were measured via NMR inversion recovery experiments. Complex 4 was also observed to isomerize via a relatively slow ring flip: ΔH⧧ = 15.0(2) kcal mol–1; and ΔS⧧ = −4.2(7) eu. DFT studies support the experimentally measured rotation activation energy (cf. calculated ΔH⧧ = 11.1 kcal mol–1) as well as the presence of a high-energy triplet intermediate (ΔH = 8.8 kcal mol–1).

Reactions of the lightly stabilized triosmium cluster [Os-3(CO)(8){mu(3)-Ph2PCH2P(Ph)C6H4}(mu-H)] with tri(2-thienyl)phosphine (PTh3) and tri(2-furyl)phosphine (PFu(3)) are described and compared to analogous reactions with PPh3. At room temperature, a number of products are isolated: [Os-3(CO)(10)(mu-dppm)] from CO addition, [Os-3(CO)(8)(PR3){mu(3)-Ph2PCH2P(Ph)C6H4}(mu-H)] from phosphine addition, [Os-3(CO)(9)(PR3)(mu-dppm)] from phosphine and CO addition and [Os-3(CO)(8)(PR3)(2)(mu-dppm)] from addition of two equivalents of phosphine. The latter are shown by NMR and X-ray diffraction to exist as 1,2-isomers, whereby one phosphine is bound to the non-dppm-substituted center and the second shares an osmium atom with one end of the diphosphine. Heating 1,2-[Os-3(CO)(8)(PTh3)(2)(mu-dppm)] at 100 degrees C results in its clean isomerization to the 1,1-isomer in which both monodentate phosphines are located on the same osmium atom. Prolonged heating of [Os-3(CO)(8)(PR3)(2)(mu-dppm)] (R = Th, Ph) at 110 degrees C gives [Os-3(CO)(9)(PR3)(mu-dppm)] and the new lightly stabilized clusters [Os-3(CO)(7)(PR3){mu(3)-Ph2PCH2P(Ph)C6H4}(mu-H)], the latter being formed by loss of phosphine and CO with concurrent metalation of a phenyl ring. Heating [Os-3(CO)(8)(PFu(3))(2)(mu-dppm)] at 110 degrees C gives [Os-3(CO)(9)(PFu(3))(mu-dppm)] together with the carbon-phosphorus bond cleavage products [Os-3(CO)(7)(mu-PFu(2))(mu(3)-eta(2)-C4H2O)(mu-H)(mu-dppm)] and [Os-3(CO)(7)(mu-PFu(2))(mu(3)-eta(2)-C6H3CH3)(mu-H)(mu-dppm)]. All new compounds were characterized by analytical and spectroscopic techniques together with single crystal X-ray diffraction analysis of nine clusters. Density functional theory (DFT) calculations have been carried out on isomers of [Os-3(CO)(8)(PR3)(2)(mu-dppm)] in order to understand the observed isomer ratios. (C) 2013 Elsevier B.V. All rights reserved. (Less)

Reaction of N-(2′,6′-dimethylphenyl)pyrrole-2-aldimine (L-Me2) with Ir(PPh3)3Cl in refluxing toluene affords two organometallic complexes (1 and 2), where the imine-ligand (L-Me2) is coordinated to the metal center, via N–H and methyl C–H activations, as a di-anionic tridentate NNC-donor, along with two triphenylphosphines. In 1 the sixth coordination site is occupied by a hydride, while in 2 by a chloride. In both cases the hydride or chloride is trans to the coordinated imine-nitrogen, and the two triphenylphosphines are mutually trans. Similar reaction of N-(2′-methylphenyl)pyrrole-2-aldimine (L-Me) with Ir(PPh3)3Cl affords 3, where the imine-ligand is coordinated to the metal center as a mono-anionic bidentate NN-donor, along with two triphenylphosphines, a hydride and a chloride. Structures of 1, 2 and 3 have been determined by X-ray crystallography. DFT analyses have been carried out to understand the formation of the complexes. All the complexes show characteristic 1H NMR signals and, intense transitions in the visible and ultraviolet regions. Cyclic voltammetry on all three complexes shows two irreversible oxidations within 0.89–1.34 V vs. SCE and a reduction within −1.31 to −1.40 V vs. SCE. Complexes 1, 2 and 3 have been found to efficiently catalyze the Oppenauer oxidation of alcohols.

Addition of 2,2’-bis(diphenylphosphino)propane, Ph2PC(Me)2PPh2 (dppmMe2), to Os3(CO)10(MeCN)2 at room temperature affords Os3(CO)10{m-Ph2PC(Me)2PPh2 }( 1-Me2), whose X-ray diffraction has been established and found to contain a bridging diphosphine ligand. Heating 1-Me2 in toluene results in the formation of the expected orthometalated addition product Os3(CO)8{m3-Ph2PC(Me)2P(Ph)C6H4}(m-H) (2Me2) in only trace amounts, with the face-capped cluster Os3(CO)9{m3-PhPC(Me)2P(Ph)C6H4 }( 3-Me2) formed as the major product as a result of elimination of benzene. The conversion of 1-Me2 to 2-Me2 has been investigated by density functional theory (DFT) calculations and the potential energy surface has been mapped out. The observed reactivity in the dppmMe2-substituted cluster 1-Me2 is compared with the related dppmH2- and dppmHMe-substituted triosmium complexes.

Products of the addition of Ph3SnH to the unsaturated triosmium clusters [(μ-H)2Os3(CO)8(μ-dppm)] (1) and [(μ-H)2Os3(CO)8(μ-dppf)] (2) are highly dependent on the nature of the diphosphine. With the rigid bis(diphenylphosphino)methane (dppm), the stannylene complex [H2Os3(CO)7(μ-SnPh2)2(μ-dppm)] (3) is the major cluster product (35% yield), resulting from both Sn–H and Sn–C bond activation, while two previously reported triphenyltin complexes, [(μ-H)2Os3(CO)8(SnPh3)2(μ-dppm)] (4) (10% yield) and [(μ-H)2Os3(CO)8(SnPh3){μ-Ph2PCH2P(Ph)C6H4}] (5) (11% yield) also result. Biphenyl is also a co-product of this reaction and it is postulated to be formed concomitantly with 3. A similar reaction with the highly flexible 1,1′-bis(diphenylphosphino)ferrocene (dppf) complex leads to the formation of four tin-containing complexes: two previously reported compounds [HOs(CO)4(SnPh3)] (6) (8% yield) and [Os2(CO)6(SnPh3)2(μ-SnPh2)2] (8) (5% yield), and the new triphenyltin and hydrostannylene clusters [H(μ-H)2Os3(CO)8(SnPh3)(μ-dppf)] (10) (22% yield) and [(μ-H)Os2(CO)4(SnPh3)2(μ-HSnPh2)(μ-dppf)] (9) (12% yield) respectively, together with the dihydroxy cluster [Os3(CO)8(μ-OH)2(μ-dppf)] (7). Two of these new clusters have been characterized by X-ray crystallography. Cluster 3 consists of a central Os3 triangle with two stannylene groups, each bridging one Os–Os edge, a dppm ligand that bridges the third Os-Os edge, and two terminal hydride ligands. Cluster 10 consists of an Os3 triangle with a terminal SnPh3 group, one terminal and two bridging hydride ligands, and a bridging dppf ligand. The new compounds 3, 7, 9, and 10 have been investigated by electronic structure calculations, and the computed ground-state structures are discussed relative to the X-ray crystallographic structures.

The reactivity of the triosmium clusters [Os 3 (CO) 10 (μ-dppm)] [dppm = bis(diphenylphosphino)methane] and [HOs 3 (CO) 8 {μ 3 -Ph 2 PCH 2 P(Ph)C 6 H 4 }] with tributylgermanium hydride (Bu 3 GeH) has been investigated. Oxidative addition of Bu 3 GeH to [Os 3 (CO) 10 (μ-dppm)] at 110 °C affords [HOs 3 (CO) 9 (GeBu 3 )(μ-dppm)] ( 1 ) which undergoes further decarbonylation upon prolonged heating to yield [H 2 Os 3 (CO) 7 (GeBu 3 ){μ 3 -Ph 2 PCH 2 P(Ph)C 6 H 4 }] ( 2 ) and [HOs 3 (CO) 8 (GeBu 3 )(μ-GeBu 2 )(μ-dppm)] ( 3 ). Control experiments confirm the bimodal formation of 2 and 3 from 1 during thermolysis. Cluster 2 reacts with additional Bu 3 GeH at 140 °C to give [Os 3 (CO) 6 (μ-GeBu 2 ) 2 {μ 3 -PhP(C 6 H 4 )CH 2 P(Ph)C 6 H 4 }] ( 4 ), a thermolysis product also produced from 3 . In contrast, oxidative addition of Bu 3 GeH to [HOs 3 (CO) 8 {μ 3 -Ph 2 PCH 2 P(Ph)C 6 H 4 }] occurs at room temperature to afford [H 2 Os 3 (CO) 8 (GeBu 3 ){μ 3 -Ph 2 PCH 2 P(Ph)C 6 H 4 }] ( 5 ), which decarbonylates at 110 °C to yield 4 . All new clusters have been characterized by elemental analyses and spectroscopic methods, and the molecular structures established by X-ray crystallography. Electronic structure calculations on the different hydride isomers based on 1 and 5 are reported.

Thermolysis of BrRe(CO) 5 with 4-(2,2-dimethylhydrazino)dimethylhydrazone-3( Z )-penten-2-one in toluene at 70 °C furnishes the new β-diketimine-substituted complex fac -BrRe(CO) 3 [(Me 2 NNCMe) 2 CH 2 ] ( 1 ) in 50–70% isolated yield. Product 1 is also obtained in comparable yield when the same reactants are irradiated at 366 nm at room temperature in fluid solution. Treatment of the parent ligand with the “lightly stabilized” rhenium compound fac -BrRe(CO) 3 (THF) 2 affords 1 as the sole observable rhenium product. Complex 1 has been characterized in solution by IR and 1 H NMR spectroscopy, and the molecular structure has been determined by single-crystal X-ray diffraction analysis. The solid-state structure confirms that the ancillary nitrogen ligand in 1 coordinates to the rhenium center as a chelating β-diketimine moiety, making this the first structurally characterized example of a β-diketimine derivative containing the parent ligand. Complex 1 has been examined by DFT analysis, and the ground-state structure computed for 1 is in agreement with the X-ray diffraction structure. Treatment of 1 with the phosphines Ph 2 PH and 1,2-( Z )-Ph 2 PCH CHPPh 2 (dppen) leads to loss of the β-diketimine ligand and formation of fac -BrRe(CO) 3 (Ph 2 PH) 2 ( 2 ) and fac -BrRe(CO) 3 (dppen) ( 3 ), respectively. Both of these products have been isolated, and the X-ray diffraction structure of the Ph 2 PH-substituted derivative determined. The relative energies of the different tautomeric forms of the 4-(2,2-dimethylhydrazino)dimethylhydrazone-3( Z )-penten-2-one ligand and 4-(2,2-dimethylhydrazino)-3( Z )-penten-2-one, the precursor to the parent ligand, have been investigated by DFT analyses. The most stable tautomer for each compound contains a six-membered ring and exhibits an intramolecular N–H bond to the imine and keto moiety, respectively.

The reaction of 2-[(diphenylphosphino)methyl]-6-methylpyridine (PN) with Os3(CO)12−n(MeCN)n [where n = 0 (1), 1 (2), 2 (3)] has been investigated. Os3(CO)12 reacts with PN in the presence of Me3NO to afford the clusters Os3(CO)11(κ1-PN) (4) and 1,2-Os3(CO)10(κ1-PN)2 (5). X-ray diffraction analyses confirm the equatorial coordination of the phosphine(s) in 4 and 5, with the two phosphines in the latter cluster exhibiting a 1,2-trans orientation about the Os–Os vector that contains the two ligands. Treatment of the MeCN-substituted cluster Os3(CO)11(MeCN) and PN (1:1 ratio) in CH2Cl2 gives clusters 4 and 5, in addition to HOs3(η1-Cl)(CO)10(κ1-PN) (6) as a result of competitive activation of the reaction solvent. Cluster 6 contains 48e and the diffraction structure reveals the presence of axial chloride and equatorial phosphine ligands which are located on adjacent osmium atoms. The bridging hydride ligand in 6 spans the Cl,P-substituted Os–Os vector. The reaction of Os3(CO)10(MeCN)2 with PN furnishes 5, 6, and 1,1-Os3(CO)10(κ2-PN) (7) in yields that are dependent on the reagent stoichiometry and reaction solvent. The solid-state structure of 7 confirms the chelation of the PN ligand to a single osmium atom via the pyridine and phosphine moieties at axial and equatorial sites, respectively. The bonding in 7 relative to other possible stereoisomers has been explored by DFT calculations, and the diffraction structure is computed as the thermodynamically most stable form of this cluster. Cluster 4 is photosensitive and CO loss gives 7, in addition to the formation of the dihydride H2Os3(CO)8[μ-CH(NC5H3)CH2PPh2] (8), whose origin derives from the double metalation of the C-6 methyl group of the PN ligand in 7. Photolysis of 7 yields 8 without detectable observation of the expected intermediate hydride HOs3(CO)9[μ-CH2(NC5H3)CH2PPh2]. The PN ligand in 7 undergoes P–C bond activation in toluene at 110 °C to afford the 50e cluster Os3(CO)9(μ-C6H4)(μ-PPh) (9), which contains face-capping benzyne and phosphinidene moieties. The bonding between the benzyne moiety and the opened Os3 frame in 9 has been examined computationally, and these data are discussed relative to σ and π bonding contributions from the metalated aryl ring to the cluster polyhedron.

The dirhenium complexes Re2(CO)6(μ-thpymS)2 (1) and eq-Re2(CO)9{κ1-(S)-SN2C4H8} (2) are obtained from the reaction of tetrahydropyrimidine-2-thiol (thpymSH) with Re2(CO)8(NCMe)2 or Re2(CO)10. Complex 1 proves to be an excellent precursor to a range of monometallic and cluster complexes acting as a source of “Re(CO)3(thpymS)”. Thus, reactions with triphenylphosphine (PPh3) and bis(diphenylphosphino)methane (dppm) afford mononuclear fac-Re(CO)3(PPh3)(κ2-thpymS) (3) and fac-Re(CO)3(κ1-dppm)(κ2-thpymS) (4), respectively. A crystal structure of 3 reveals that the pyrimidine-2-thiolate binds in a chelating fashion. Reactions with M3(CO)12 (M = Ru, Os) at moderate temperatures afford mixed-metal clusters. With Ru3(CO)12 in boiling thf isomeric tetranuclear butterfly clusters ReRu3(CO)13(μ3-thpymS) (5–6) result which differ in the position of the capping pyrimidine-2-thiolate ligand on the cluster surface. Thus in the kinetic isomer 5, the pyrimidine-2-thiolate caps the ReRu2 face while in the thermodynamic isomer 6 it caps the Ru3 face. A similar reaction with Os3(CO)10(NCMe)2 in boiling benzene affords predominantly the ReOs2-capped tetranuclear cluster ReOs3(CO)13(μ3-thpymS) (7), together with small amounts of (μ-H)Os3(CO)9(μ3-thpymS) (8) resulting from loss of rhenium. Cluster 7 is stable in refluxing toluene but slowly converts to isomeric 9 in xylene at 140 °C but only in low yields. The crystal structures of isomeric 5–6 have been solved and show only small variations in the cluster core geometry. Density functional calculations show that clusters 6 and 9 are slightly more stable than 5 (ΔG 2.0 kcal mol−1) and 7 (ΔG 1.5 kcal mol−1), respectively, and a mechanism is proposed for these conversions in which the pyrimidine-2-thiolate becomes bidentate after release of the pyrimidine group.

Reaction of [Fe2(CO)6(μ-pdt)] with the small bite-angle diphosphine 2,2′-bis(diphenylphosphino)propane gave the chelated complex [Fe2(CO)4{κ2-Ph2PC(Me2)PPh2}(μ-pdt)]. This exists in solution as a mixture of non-interconverting dibasal and apical-basal isomers which slowly rearrange to the bridged isomer, [Fe2(CO)4{μ-Ph2PC(Me2)PPh2}(μ-pdt)], upon heating. X-ray structures of the dibasal and bridged isomers reveal an increase of ca. 19° in the PCP bond angle upon diphosphine movement from chelated to bridged positions. To probe the relative stability of these isomers, DFT calculations have been carried out and the bridged isomer is found to lie 3.8 and 1.3 kJ mol-1 lower in energy than the dibasal and apical-basal chelated isomers respectively. Protonation of the bridged isomer with HBF4·Et2O is slow and gives an unstable product. In contrast, both chelated isomers protonate rapidly and cleanly to initially yield apical-basal [Fe2(CO)4(μ-H){κ2-Ph2PC(Me2)PPh2}(μ-pdt)][BF4], which rearranges slowly to the dibasal isomer. The latter has been crystallographically characterized, protonation resulting in only very minor metric changes with the iron-iron bond length and diphosphine coordination being essentially unchanged. Electrochemical studies have been carried out in MeCN, and for the chelated isomers separate redox features are seen for the dibasal and apical-basal isomers. The chelated isomers are proton reduction catalysts in acetonitrile in the presence of HBF4·Et2O. Proton reduction occurs at -1.58 V via the kinetically favoured apical-basal hydride cation. DFT calculations have been used to study the mechanism of formation of H2 and are consistent with competing CECE and CEECC mechanisms, the branch point being the protonation or one-electron reduction of the 35-electron species [Fe2(CO)4(μ-H){κ2-Ph2PC(Me2)PPh2}(μ-pdt)].

The rearrangement of the phosphine-thioether ligand in 1,2-(Peq,Seq)-Os3(CO)10(Ph2PCH2CH2SMe) to 1,1-(Peq,Sax)-Os3(CO)10(Ph2PCH2CH2SMe) was investigated by electronic structure calculations. The chelated isomer lies 2.5 kcal/mol lower in energy than its bridged counterpart, and the barrier computed for the mechanism is in agreement with the results from our earlier experimental study. Phosphine-thioether isomerization occurs via three distinct steps that involve the migration of the CO and SMe groups in a plane that is perpendicular to the trimetallic core. One of the intermediates on the reaction surface corresponds to the 50e cluster Os3(CO)9(μ-CO)(μ-Ph2PCH2CH2SMe), whose edge-bridging thioether moiety functions as a 4e donor ligand. Alternative mechanisms involving ligand dissociation/association and merry-go-round sequences are energetically prohibitive.

The reactivity of the unsaturated dimer H{sub 2}Re{sub 2}(CO){sub 8} (1) with the ambiphilic phosphinoborane Ph{sub 2}PCH{sub 2}CH{sub 2}BR{sub 2} (2; where BR{sub 2} = 9-borabicyclo[3.3.1]nonanyl) has been explored. Coordination of the ambiphilic ligand to 1 is rapid at room temperature, leading to the fragmentation of 1 and formation of HRe(CO){sub 4}({kappa}B,P-Ph{sub 2}PCH{sub 2}CH{sub 2}BR{sub 2}) (3) in high yield. 3 has been characterized in solution by IR and NMR spectroscopy, and the molecular structure established by X-ray diffraction analysis. The solid-state structure confirms the presence of a chelated phosphinoborane ligand through coordination of the phosphine to the rhenium center and the formation of a three-center, two-electron (3c,2e) Re-H-B interaction. The nature of the Re-H-B interaction in 3 has been investigated by DFT, and the energetics for borane dissociation and hydride abstraction by the coordinated Lewis acid in 3 have also been computationally evaluated. The coordination of an oxygen in one of the ancillary CO groups by the pendant borane in HRe(CO){sub 4}({kappa}P-Ph{sub 2}PCH{sub 2}CH{sub 2}BR{sub 2}) is thermodynamically unfavorable relative to the formation of the 3c,2e Re-H-B bond.

The molecular structure of cis-2,6-(E,E)-bis(ferrocenylidene)-N-methyl-4-piperidone (1) has been determined by X-ray crystallography. Compound 1 crystallizes in the monoclinic chiral space group P2(1), a = 6.0055(17) A, b = 12.802(4) A, c = 14.465(4) A, β = 95.438(4)°, V = 1107.1(5) A3, Z = 2, and Dcalc = 1.516 Mg/m3; R = 0.0335, Rw = 0.0682 for 4230 reflections with I > 2σ(I). The substituents at the vinyl group of each chalcone moiety exhibit a trans (entgegen) disposition, and the two ferrocene moieties adopt a syn orientation and are located on the side of the piperidone ring opposite of the nitrogen lone electron pair. Molecules of 1 pack in chains along the a axis and exhibit weak intermolecular C-H⋯O hydrogen bonds involving the ferrocene and carbonyl moieties of adjacent molecules. The energy difference between the ferrocene rotational isomers in 1 has been evaluated by DFT, and the lowest energy structure is represented by the solid-state structure. The barriers for the rotational isomerization of the ferrocene groups have been evaluated and are discussed in the context of polymorphic modifications available to 1.

Treatment of TaCl(NMe2)4 (1) with allylMgCl furnishes the allyl-substituted compound Ta(NMe2)4(η1-allyl) (2) in moderate yield. The X-ray structure of 2 reveals a trigonal-bipyramidal geometry at t...