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A new series of binary mononuclear complexes were prepared from the reaction of the hydrazone ligand, 2-carboxyphenylhydrazo-benzoylacetone (H2L), with the metal ions, Cd(II), Cu(II), Ni(II), Co(II), Th(IV) and UO2(VI). The binary Cu(II) complex of H2L was reacted with the ligands 1,10-phenanthroline or 2-aminopyridine to form mixed-ligand complexes. The binary complexes of Cu(II) and Ni(II) are suggested to have octahedral configurations. The Cd(II) and Co(II) complexes are suggested to have tetrahedral and/or square-planar geometries, respectively. The Th(IV) and UO2(VI) complexes are suggested to have octahedral and dodecahedral geometries, respectively. The mixed-ligand complexes have octahedral configurations. The structures of all complexes and the corresponding thermal products were elucidated by elemental analyses, conductance, IR and electronic absorption spectra, magnetic moments, 1H NMR and TG-DSC measurements as well as by mass spectroscopy. The ligand and some of the metal complexes were found to activate the enzyme pectinlyase.

Catalytic H/D-exchange reactions were studied with [Ru(dtbpmp)(η2-H2)(H)2] (1) as catalyst. Under mild reaction conditions (25–75 °C) a wide range of arenes and olefins undergo H/D exchange with [D6]benzene. A preference for protons at sp2 carbons was observed with conversions up to >90 % and significant regioselectivity in certain cases. For more reaction insights NMR-based kinetic studies were performed with naphthalene as substrate, revealing an activation energy of 15.8 kcal mol–1 for the H/D exchange at the β-position. Furthermore, the key steps of the reaction mechanism were investigated by means of DFT calculations for both model complexes (PMe2 donor sites) and real catalysts (PtBu2 donor sites). The calculations resulted in Gibb's free activation energies in the range of 10–16 kcal mol–1, indicating H/D exchange at the β-position of naphthalene to be clearly favoured over the α-position, which is in full accordance with the experimental observations.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Exposure of a series of zirconocene amido and hydrazido hydride complexes, (η5-C5Me4H)2Zr(NHR)H (R = tBu, NMe2, Me, H), to 4 atm of D2 gas at 56 °C produced isotopic exchange in both the N−H and Zr...

The study in the area of luminescent d10 complexes has been developing rapidly. The metals with d10 electronic configuration have a closed d-shell, therefore the nature of the complexes are quite different from regular transition metal complexes. The complexes show a diversity of the electronic excited states. This paper reviews the characteristic nature of the d10 metal complexes with interesting examples. Copper(I), silver(I), gold(I), nickel(0),palladium(0) and platinum(0) complexes are discussed. Luminescent copper(I) complexes are classified into two groups; the first includes the complexes bearing halogen ligands, and the second have no halogen ligands. In the second group, the complexes with phosphine and diimine type ligands are mainly discussed. As for the silver(I) and gold(I) complexes, multinuclear complexes are mostly described. For the palladium(0) and platinum(0) complexes, although a small number of works have been published so far, some interesting studies including our works have been described. In addition to the recent studies on the photophysical properties of the complexes, some applications are described in this review.

A series of new dicationic dihydrogen complexes of the type trans-$[Ru(\eta^2-H_2)(L)(dppm)_2][X]_2 (L=CH_3CN, CH_2=CHCN, C_6H_5CN, C_6H-5NC, CO; X 5 BF_4, OTf; dppm = Ph_2PCH_2PPh_2)$ have been prepared by protonating the precursor hydrides using either $HBF_4 . Et_2O or HOTf$. The variable temperature spinlattice relaxation times $(T_1, ms)$ and the H, D coupling constants of the $\eta^2-HD$ isotopomers indicate the intact nature of the H-H bond in these derivatives. The H-H distances of the dihydrogen complexes bearing trans-nitrile ligands are not significantly affected by the sterics and the electronics of the nitrile. On the other hand, the H-H distances of the dihydrogen complexes bearing either isonitrile or CO ligand are comparable to those possessing chelating diphosphine ligands of greater bite angle. Also, the thermal stabilities of these complexes are significantly less than those bearing diphosphines of greater bite angle. The trans- $[Ru(H)(CH_3CN)(dppm)_2][BF_4]$ complex has been characterized by X-ray crystallography.

Reaction of [OsCl6]2- with a pincer-type ligand, (S)-But2PCH2CH(NMe2)C3H6PBut2, afforded a chiral square-pyramidal 16-electron carbene complex, OsCl(PGP) (1), PGP = [κ4-But2PCH2CH(N(Me)CH)CHC2H4PBut2], in excellent yield. Reactions of 1 with hydrogen under different conditions resulted in the hydride and dihydrogen species OsH2Cl(PGP), [Os(H2)2(PGP)]+, and OsH3(PGP), which have been characterized by a combination of spectroscopic and DFT computational techniques.

The unimolecular isomerization mechanism from a secondary 2,1 → 3,1 propene unit promoted by the prototype zirconocene system H2SiCp2Zr+(P) (P = polymeryl chain) has been investigated by using density functional theory calculations (B3LYP) for both gas and solvent phases. The typical route occurring through β-hydrogen elimination to the metal, olefin rotation around the metal center and olefin reinsertion into the metal hydrogen bond has been calculated by using QM/MM calculations with the ONIOM model in the presence of the counterion CH 3 B(C 6 F 5 ) 3 - and compared to the alternative intramolecular reversible formation of a zirconocene allyl dihydrogen complex. Our calculations show that the alternative route remains energetically less accessible, at least for the prototype metallocene system used here.

The transfer of the hydrogen atoms from the η 2 -H 2 ligand to the cis -disposed olefin ligand in a ruthenium olefin–dihydrogen complex is discussed. It is realized that H 2 O and NEt 3 exhibit promoting effects in the catalytic hydrogenation of olefins with a couple of hydro(trispyrazolyl)borate (Tp)-supported ruthenium complexes. A reaction mechanism that accounts for the promoting effect has been proposed. A Tp-supported ruthenium solvento hydride complex TpRu(PPh 3 )(CH 3 CN)H was found to react with H 2 and R 3 SiH to form the fluxional dihydrogen–hydride, and η 2 -silane–hydride complexes, respectively. Although no stable and isolable σ-complex was formed with CH 4 , the solvento hydride complex was found to be active in catalyzing H/D reactions of CH 4 with some deuterated common organic solvents. In the catalytic CO 2 hydrogenation reactions in THF/H 2 O or alcohol, the complex TpRu(PPh 3 )(CH 3 CN)H generates the metal-ligand bifunctional catalyst TpRu(PPh 3 )(ROH)H (R = H or alkyl) which transfers the hydride and a proton from ROH to the CO 2 molecule in a concerted manner, without coordination of the latter to the metal center. Aminocyclopentadienyl ruthenium complexes, which exhibit intramolecular Ru–H⋯H–N dihydrogen-bonding interactions were synthesized and characterized. These complexes provide good models for the study of heterolytic cleavage of η 2 -H 2 ligand and its reverse-protonation of metal hydride to form dihydrogen complex. An indenyl ruthenium hydride complex was synthesized and found to be good catalyst for nitrile hydration reactions to give amides; these reactions nicely demonstrate the principle of utilizing dihydrogen bond to promote catalytic reactions.

Mixed-ligand OsCl(Tp)L(PPh3) complexes 1 [Tp = hydridotris(pyrazolyl)borate; L = P(OMe)3, P(OEt)3 and PPh(OEt)2] were prepared by allowing OsCl(Tp)(PPh3)2 to react with an excess of phosphite. Treatment of chlorocomplexes 1 with NaBH4 in ethanol afforded hydride OsH(Tp)L(PPh3) derivatives 2. Stable dihydrogen [Os(η2-H2)(Tp)L(PPh3)]BPh4 derivatives 3 were prepared by protonation of hydrides 2 with HBF4 · Et2O at −80 °C. The presence of the η2-H2 ligand is supported by short T1 min values and JHD measurements on the partially deuterated derivatives. Treatment of the hydride OsH(Tp)[P(OEt)3](PPh3) complex with the aryldiazonium salt [4-CH3C6H4N2]BF4 afforded aryldiazene [Os(4-CH3C6H4NNH)(Tp){P(OEt)3}(PPh3)]BPh4 derivative 4. Instead, aryldiazenido [Os(4-CH3C6H4N2)(Tp)[P(OEt)3](PPh3)](BF4)2 derivative 5 was obtained by reacting the hydride OsH(Tp)[P(OEt)3](PPh3) first with methyltriflate and then with aryldiazonium [4-CH3C6H4N2]BF4 salt. Spectroscopic characterisation (IR, 15N NMR) by the 15N-labelled derivative strongly supports the presence of a near-linear Os–NN–Ar aryldiazenido group. Imine [Os{η1-NHC(H)Ar}(Tp){P(OEt)3}(PPh3)]BPh4 complexes 6 and 7 (Ar = C6H5, 4-CH3C6H4) were also prepared by allowing the hydride OsH(Tp)[P(OEt)3](PPh3) to react first with methyltriflate and then with alkylazides.

The hydrido σ-dihydrogen complex RuClH(η2-H2)(PCy3)2 (2) reacts with the chlorosilanes HSiMe3-nCln (n = 1−3) to form the corresponding silyl σ-dihydrogen complexes RuCl(SiMe3-nCln)(η2-H2)(PCy3)2 (3Me3-nCln). These complexes display a 16-electron configuration, as shown by NMR, by X-ray data in the case of 3MeCl2, and by theoretical calculations. The σ-H2 ligand in 3MeCl2 has been located by X-ray diffraction, and the H−H distance of 1.05(3) A compares well with the value obtained by DFT/B3PW91 (1.073 A) as well as with the value of 1.08 ± 0.01 A derived from the measurement of the JHD coupling constant of 17.5 Hz for the deuterated isotopomer RuCl(SiMeCl2)(η2-HD)(PCy3)2. The series of model complexes RuCl(SiMe3-nCln)(η2-H2)(PMe3)2 (S3Me3-nCln) was investigated by DFT at the B3PW91 level. The most stable isomers have a structure that resembles the X-ray structure of 3MeCl2: i.e., a silyl σ-dihydrogen formulation. In the case of S3Me2Cl and S3MeCl2 a second minimum very close in energy was optimized and fo...

Treatment of RuCl2(PPh3)3 in benzene at room temperature with 2-vinylpyridine produces the vinylpyridine complex RuCl2(2-CH2CHC5H4N)(PPh3)2. In the presence of Cs2CO3, RuCl2(PPh3)3 reacts with 2-vinylpyridine at room temperature to give the cyclometalated complex RuCl(CHCHC5H4N)(CH2CHC5H4N)(PPh3), which is also produced from the reaction of RuHCl(PPh3)3 with 2-vinylpyridine. OsCl2(PPh3)3 reacts with 2-vinylpyridine/Cs2CO3 at room temperature to give the analogous cyclometalated complex OsCl(CHCHC5H4N)(CH2CHC5H4N)(PPh3). In the presence of NaBF4, the reaction produces [Os(CHCHC5H4N)(CH2CHC5H4N)(PPh3)2]BF4. The dihydrogen complex Os(H2)Cl(CHCHC5H4N)(PPh3)2 is produced from the reaction of OsHCl(PPh3)3 with 2-vinylpyridine. The mechanism of the cyclometalation reactions has been investigated by computational chemistry.

Equilibrium constants (K) for reactions between acids and the conjugate base forms of a number of phosphonium salts, [HPR 3 ][BF 4 ], and iron hydrides, [Fe(CO)3H(PR 3 ) 2 ][BF 4 ], in CD 2 Cl 2 have been determined by means of 31 P and 'H NMR spectroscopy at 20 °C. The anchor compound chosen for pK CD 2 Cl 2 determinations was [HPCy 3 ][BF 4 ] with a pK CD 2 Cl 2 value of 9.7, as assigned by literature convention (Cy: cyclohexyl). A continuous scale of pK CD 2 Cl 2 values covering the range from 9.7 to -3 was created and correlated with the ΔH values reported by Angelici and co-workers and literature pK a values. The pK CD 2 Cl 2 values for 15 other hydride or dihydrogen complexes of the iron group elements and of diethyl ether were also placed on this scale. The crystal structures of [Fe(CO) 3 H(PCy2Ph) 2 ][BF 4 ] and [Fe(CO) 3 (PCy 2 Ph) 2 ] revealed that the trans-oriented, bulky, unsymmetrical phosphane ligands distort the equatorial plane of the complexes. The acidity of iron carbonyl hydrides is an important feature of the reactions of iron hydrogenase enzymes.

B3LYP/6-31++G(d,p) and MP2/6-31++G(d,p) calculations for a series of hydrogen- and dihydrogen-bonded systems have been carried out in order to analyze the topology of the electron density and the energy densities at the respective energy-optimized bond critical points. Even though there are no significant differences when these properties are represented as a function of the dimerization energy, they can be separated into two well-defined sets if those properties are correlated with intermolecular distances. When analyzing the dependence of various properties with equilibrium bond lengths, the specific trends of dihydrogen bond systems consist of (a) lower electron density at the bond critical point, and (b) lower concentration/depletion of that density which can be translated in a different behavior for the Laplacian components. Furthermore, the sets of molecules form two different plots which allow for a valuable classification between hydrogen- and dihydrogen-bonded systems.

Protonation of the osmium(IV) trihydrides (C5Me5)OsH3(L) with HBF4 in diethyl ether affords the molecular dihydrogen complexes [(C5Me5)Os(H2)H2(L)][BF4], where L is PPh3 (1), AsPh3 (2), or PCy3 (3)...

The synthesis and characterisation of nonclassical ruthenium hydride complexes containing bidentate PP and tridentate PCP and PNP pincer-type ligands are described. The mononuclear and dinuclear ruthenium complexes presented have been synthesised in moderate to high yields by the direct hydrogenation route (one-pot synthesis) or in a two-step procedure. In both cases [Ru(cod)(metallyl)(2)] served as a readily available precursor. The influences of the coordination geometry and the ligand framework on the structure, binding, and chemical properties of the M--H(2) fragments were studied by X-ray crystal structure analysis, spectroscopic methods, and reactivity towards N(2), D(2), and deuterated solvents.

The complexes [(C5R5)RuH(dippae)] [R = H (1a), Me (2a); dippae = 1,2-bis(diisopropylphosphinoamino)ethane] and [(C5R5)RuH((R,R)-dippach)] [R = H (1b), Me (2b); (R,R)-dippach = (R,R)-1,2-bis(diisopropylphosphinoamino)cyclohexane] have been prepared and characterized. The cationic ruthenium(IV) dihydride derivatives [(C5R5)RuH2(dippae)][BPh4] [R = H (3a), Me (4a)] and [(C5R5)RuH2((R,R)-dippach)][BPh4] [R = H (3b), Me (4b)] are also reported. No significant intramolecular interaction between the amino protons and the hydrogen atoms bound to the metal has been observed in any of these compounds. The X-ray crystal structure of 4a was determined. The proton-transfer processes over the monohydrides 2a and 2b with HBF4.OEt2 have been studied by NMR spectroscopy. Dicationic dihydride complexes [CpRuH2(LH)]2+ [LH = dippaeH+ (5a), (R,R)-dippachH+ (5b)] and [Cp*RuH2(LH)]2+ [LH = dippaeH+ (6a), (R,R)-dippachH+ (6b)] result respectively from the protonation of either the monohydrides 1a,b or 2a,b or the dihydrides 3a,b or 4a,b at one of the NH groups of the phosphinoamine ligands by an excess of HBF4. These dicationic derivatives exhibit fluxional behavior in solution. In the course of the protonation of 1a with HBF4.OEt2, a cationic dihydrogen complex and a dihydrogen-bonded derivative have been identified as intermediates by NMR spectroscopy. Another dihydrogen species, namely, [CpRu(H...HOOCPh)((R,R)-dippach)], was also identified in the course of the reaction of 1b with benzoic acid in toluene-d8. The reaction of 1a with 0.5 equiv of 1,1,1,3,3,3-hexafluoroisopropanol generates a hydride species having a very short (T1)min of 6.5 ms at 400 MHz, an experimental fact for which no satisfactory explanation has yet been found.

Complexation of dihydrogen to transition metal centers was discovered by Kubas and coworkers in 1984. The notion that the simplest molecule in chemistry can act as a ligand to form relatively stable transition metal complexes has led to a paradigm shift in coordination chemistry. Crucial to the exploration of this intriguing new chemistry has been the use of isotope substitution. Several aspects of the coordination chemistry of dihydrogen have revealed fascinating isotope effects on reactivity, spectroscopy and in some cases structure. Complexation of HD has been used to diagnose bond distances from measurements of JHD and isotope effects for D2 versus H2 binding have been evaluated. Examples of quantum mechanical exchange coupling in H2 complexes have been described. These effects disappear when one of the H atoms is replaced by D. In molecules with bound hydrogen adjacent to a hydride ligand, non-statistical occupancy of hydrogen versus hydride sites by deuterons has been observed. In some cases, isotope-dependent structures have been established by the study of HD, HT and DT complexes using NMR spectroscopy. Copyright © 2007 John Wiley & Sons, Ltd.

The interaction between Cp ∗ RuH(dppe) and a series of proton donors (HA) of increasing strength: CFH 2 CH 2 OH (MFE), CF 3 CH 2 OH (TFE), (CF 3 ) 2 CHOH (HFIP), p -nitrophenol, CF 3 COOH and HBF 4 has been investigated spectroscopically by variable-temperature IR, UV–Vis, and NMR spectroscopy in solvents of differing polarity ( n -hexane, dichloromethane and their mixture). The low-temperature IR study shows the establishment of a hydrogen-bond which involves the hydride ligand as the proton accepting site. The basicity factor E j for the hydride was found to be 1.39. All techniques indicate that an equilibrium exists between the dihydrogen-bonded complex and the cationic dihydrogen complex, [Cp ∗ Ru(η 2 -H 2 )(dppe)] + , the formation of which is shown here for the first time. The proton transfer from HFIP is characterized by Δ H ∘ = −8.1 ± 0.6 kcal mol −1 and Δ S ∘ = −17 ± 3 eu. The activation parameters for the subsequent irreversible isomerization leading to the classical dihydride complex, [Cp ∗ Ru(H) 2 (dppe)] + , are Δ H ‡ = 20.9 ± 0.8 kcal mol −1 and ΔS ‡ = 9 ± 3 eu as determined from 1 H NMR spectroscopy for protonation by HBF 4 . Computational results at the DFT/B3PW91 level confirm the experimentally observed hydride basicity increase on descending the Group from iron to ruthenium and also the formation of the non-classical complex as an intermediate, prior to the thermodynamically favored dihydride.

The hexahydride complex OsH6(PiPr3)2 (1) reacts with the BF4-salts of 1-phenyl-3-methyl-1-H-benzimidazolium, 1-phenyl-3-methyl-1-H-5,6-dimethyl-benzimidazolium, and 1-phenyl-3-methyl-1-H-imidazolium to give the respective trihydride-osmium(IV) derivatives OsH3(κ2-Caryl,CNHC)(PiPr3)2 (2–4). The protonation of these compounds with HBF4·OEt2 produces the reduction of the metal center and the formation of the bis(dihydrogen)-osmium(II) complexes [Os(κ2-Caryl,CNHC)(η2-H2)2(PiPr3)2]BF4 (5–7). DFT calculations using AIM and NBO methods reveal that the Os–NHC bond of the Os-chelate link tolerates a significant π-backdonation from a doubly occupied dπ(Os) atomic orbital to the pz atomic orbital of the carbene carbon atom. The π-accepting capacity of the NHC unit of the Caryl,CNHC-chelate ligand, which is higher than those of the coordinated aryl group and phosphine ligands, enhances the electrophilicity of the metal center activating one of the coordinated hydrogen molecules of 5–7 toward the heterolysis. As a result, these compounds are strong Brønsted acids with pKawater values between 2.5 and 2.8. In acetonitrile the hydrogen molecules of 5 and 6 are displaced by the solvent, the resulting bis(solvento) compounds [Os(κ2-Caryl,CNHC)(CH3CN)2(PiPr3)2]BF4 (8, 9) react with acetylacetonate (acac) and cis-1,2-bis(diphenylsphosphino)ethylene (bdppe) to give Os(κ2-Caryl,CNHC)(acac)(bdppe) (10, 11) as a mixture of the two possible isomers, namely with P trans to the aryl group or to the NHC moiety., Financial support from the Spanish MINECO (Projects CTQ2011-23459 and CTQ2013-44303-P), the Red de Excelencia Consolider (CTQ2014-51912-REDC), the DGA (E35), the European Social Fund (FSE) and FEDER, and Universal Display Corporation is acknowledged. T.B. thanks the Spanish MINECO for funding through the Juan de la Cierva programme.

Anion binding properties of a quinoline-based tripodal tris-thiourea receptor have been studied for several oxoanions including perchlorate, nitrate, hydrogen sulfate, and dihydrogen phosphate by H-1 NMR and UV-vis titrations in DMSO. Results show that the receptor selectively binds dihydrogen phosphate with a 1:1 stoichiometry. Ab initio calculations based on density functional theory (DFT) suggest that the dihydrogen phosphate is encapsulated within the host's cavity via six NH center dot center dot center dot O and two N center dot center dot center dot OH interactions. (C) 2014 Elsevier Ltd. All rights reserved.

In the present study, the inorganic analogues of alkanes as well as their isoelectronic BN/CC counterparts that bridge the gap between organic and inorganic chemistry are comparatively studied on the grounds of static DFT and Car-Parrinello molecular dynamics simulations. The BN/CC butanes CH3 CH2 BH2 NH3 , BH3 CH2 NH2 CH3 , and NH3 CH2 BH2 CH3 were considered and compared with their isoelectronic counterparts NH3 BH2 NH2 BH3 and CH3 CH2 CH2 CH3 . In addition, systematical replacement of the NH2 BH2 fragment by the isoelectronic CH2 CH2 moiety is studied in the molecules H3 N(NH2 BH2 )3-m (CH2 CH2 )m BH3 (for m=0, 1, 2, or 3) and H3 N(NH2 BH2 )2-m (CH2 CH2 )m BH3 (for m=0, 1, or 2). The DFT and Car-Parrinello simulations show that the isosteres of the BN/CC butanes CH3 CH2 BH2 NH3 , BH3 CH2 NH2 CH3 , and NH3 CH2 BH2 CH3 and of larger oligomers of the type (BN)k (CC)l where k≥l are stable compounds. The BN/CC butane H3 NCH2 CH2 BH3 spontaneously produces molecular hydrogen at room temperature. The reaction, prompted by very strong dihydrogen bonding NH⋅⋅⋅HB, undergoes through the neutral, hypervalent, pentacoordinated boron dihydrogen complex RBH2 (H2 ) [R=(CH2 CH2 )n NH2 ]. The calculations suggest that such intermediate and the other BN/CC butanes CH3 CH2 BH2 NH3 , BH3 CH2 NH2 CH3 , and NH3 CH2 BH2 CH3 as well as larger BN/CC oligomers are viable experimentally. A simple recipe for the synthesis of CH3 CH2 BH2 NH3 is proposed. The strength of the dihydrogen bonding appeared to be crucial for the overall stability of the saturated BN/CC derivatives.

Covalent X–H bonds, particularly where X is H, C, B, and Si, can act as Lewis base ligands in forming metal complexes of general type L n M(H–X), where the M–H–X angle is strongly bent so that the coordination can best be considered as side-on. The binding is greatly enhanced by back donation from the metal into the X–H σ* orbital. This elongates and eventually breaks the X–H bond, leading to characteristic structural, physicochemical characteristics and alteration of the reactivity of the ligand. The requirement for back donation means that the appropriate L n M fragment must usually have appreciable π donor character. Since the binding of the X–H bond to the metal center is relatively weak, and the binding of the deprotonated X− group left behind is much stronger, the binding also facilitates proton loss from the X–H bond. This electron redistribution results in reactivity differences which may be exploited. The case of H2 is treated in most detail in this review, because of its central place in the field.

Density functional theory (DFT) calculations using the KMLYP method on a series of pincer PCP−rhodium dihydrogen complexes have been employed to model and examine the proposed mechanisms for the pincer PCP−rhodium complexes mediated hydrogenation of carbon dioxide (CO2). The relative energies of dihydrogen rotamers and dihydride isomers were evaluated together with T1 values to determine the molecular structures of these complexes. We have investigated possible pathways for the CO2 reduction processes involving the formation of rhodium dihydride species. Although the dihydrogen complexes are more stable than the corresponding dihydride isomers, the reduction of CO2 has to proceed through the dihydride structures.

Three new monocationic molecular hydrogen complexes of ruthenium of the type trans- $[RuC1(\eta2-H_2)(PP)_2][BF_4]$ (PP = bis-1,2(diarylphosphino)ethane, aryl = p-fluorobenzyl, benzyl, p-methylbenzyl) have been prepared by protonating the precursor hydride complexes trans-$[RuC1(H)(PP)_2]$ using $HBF_4.Et_2O$. These three dihydrogen complexes are quite stable and have been isolated in the solid state. The intact nature of the H–H bond in these derivatives has been established from the short spin-lattice relaxation times ($T_1$, ms) and the observation of substantial H, D couplings in the HD isotopomers. The H–H bond distances $(d_{HH}$, \AA) increase from 0.97 to 1.01 \AA as the electron donor ability of the diphosphine ligand increases from the p-fluorobenzyl to the benzyl to the p-methylbenzyl moiety. These dihydrogen complexes constitute the initial stages of elongation of the H–H bond enroute to its cleavage along the reaction coordinate for the oxidative addition of $H_2$ to a metal centre.

In many transition metal dihydrides and dihydrogen complexes the hydrogens are relatively weakly bound and exhibit a fairly high mobility, in particular with respect to their mutual exchange. Part of this high mobility is due to the exchange symmetry of the two hydrogens, which causes an energy splitting into even and odd spatial energy eigenfunctions, resulting in the typical coherent tunneling of a two-level system. Owing to the quantum mechanical symmetry selection principles the eigenfunctions are connected to the possible nuclear spin states of the system. If the tunneling frequency is in the proper frequency window it is thus possible to observe these tunneling transitions by NMR at very low temperatures, where no thermally induced exchange reactions overshadow the tunneling. The first part of this review gives an introduction into the interplay of chemical kinetics and tunneling phenomena in general, rotational tunneling of dihydrogen in a two-fold potential in particular and the Bell tunnel model, followed by a summary of solid state NMR techniques for the observation of these tunnel processes. Then a discussion of the effects of these processes on the 2H NMR line shape is given. The second part of the review reports results of a 2H-solid state NMR spectroscopy and T1 relaxatiometry study of trans-[Ru(D2)Cl(PPh2CH2CH2PPh2)2]PF6, in the temperature regime from 5.4 to 320 K. In the Ru-D2 sample coherent tunneling and incoherent exchange processes on the time scale of the quadrupolar interaction are observed. From the spectra and T1-data the height of the tunneling barrier is determined. Next results of 2H-spin–lattice relaxation measurements for a selectively η2 − D2 labeled isotopomer of the complex W(PCy3)2(CO)3)(η2 − D2) are presented and discussed. The relaxation measurements are analyzed in terms of a simple one dimensional Bell tunnel model and comparison to incoherent neutron scattering (INS) data from the H2 complex. The comparison reveals a strong isotope effect of 2 × 103 for the exchange rates of the deuterons versus hydrons.

The air-sensitive DMF-containing intermediate [RuTp(PR3)(Cl)(DMF)] is formed by refluxing a DMF solution of [RuTp(COD)Cl] (1) in the presence of at least 1 equiv. of PR3 (PR3 = PPh3, PPh2iPr, PiPr3, and PCy3). On exposure to air in the presence of CCl4, this complex is readily converted into the respective RuIII complexes [RuTp(PR3)Cl2] (2a–d). These compounds are air-stable, readily accessible, permit easy variations as far as the electronic and steric properties of the PR3 co-ligands are concerned, and are reducible to a variety of RuIITp complexes. Treatment of 2 with NaBH4 affords dihydrogen compounds of the type [RuTp(PR3)(H)(η2-H2)]. Reduction of 2 can also be accomplished with Zn in the presence of CH3CN and pyridine, which affords the diamagnetic RuII compounds [RuTp(PR3)(CH3CN)2]+ (4a–c) and [RuTp(PR3)(py)Cl] (5). X-ray structures of representative complexes are presented. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

The reaction of the cycloheptatrienyl-toluene sandwich complex [(η7-C7H7)Mo(η6- C6H5Me)]BF4 with tricyclohexylphosphine in acetonitrile furnishes the cationic half-sandwich cycloheptatrienyl complex {(η7-C7H7)Mo[P(C6H11)3](CH3CN)2}BF4 (1). Treatment of 1 with NaBH4 in ethanol results in the formation of the tetrahydroborate complex {(η7-C7H7)Mo(η2- BH4)[P(cyclo-C6H11)3]} (2), in which the borohydride ligand is coordinated to the molybdenum atom through two three-center, two-electron bonds. The complex is stable in ethanol and water. The expected formation of a metal trihydride of the type {(η7-C7H7)MoH3[P(cyclo-C6H11)3]} as a hydrolysis product could not be observed. Since this behaviour differs from the reactivity reported for related cyclopentadienyl-ruthenium complexes, a comparative computational study on the model complexes [(η5-C5Me5)RuH3(PMe3)] (4) and [(η7-C7H7)MoH3(PMe3)] (5) was performed revealing that the classical trihydride form [MH3] represents the global minimum for the ruthenium complex 4, whereas the dihydrogen-hydride form [MH(η2-H2)] is more stable for the molybdenum counterpart.

Aminocyclopentadienyl ruthenium hydride complexes were optimized at the second-order Moller−Plesset (MP2) level of theory with 6-31G(d) and 6-311++G(d,p) basis sets to investigate the nature of intramolecular interactions. The computations show that both Ru−H···H−N dihydrogen bond interactions and Ru···H−N interactions are responsible for the stability of these complexes. The BSSE-corrected interaction energies, computed at the B3LYP and MP2 levels of theory with 6-31G(d), 6-311++G(d,p), and 6-311++G(2d,2p) basis sets, indicate that the dihydrogen bond interaction energy accounts for only 20% of the total interaction energy. Therefore, the Ru···H−N interactions play a key role in stabilizing the aminocyclopentadienyl ruthenium hydride complexes. Topological analysis of electron density at bond critical points confirms the formation of the dihydrogen bonds between oppositely charged hydrogen atoms. Analysis of charge distributions (Mulliken charges) shows there is a strong electronic attraction between Ru ...

A computational study on the structure and reactivity of (η1-allyl)-Pd complexes has been performed on model systems containing different neutral and cyclometalating ligands. A comparison of the reactivity of these compounds with the usually proposed (η3-allyl)-Pd derivatives has been performed to investigate the feasibility of the participation of the former as intermediates in Pd-catalyzed reactions. These complexes are more stable than (η3-allyl)-Pd derivatives with a cyclometalated PCP tridentate ligand. Intermediates, transition states, and activation and reaction energies have been calculated for several reactions of cationic and neutral complexes: (a) nucleophilic attack of NH3 on the allyl system, (b) nucleophilic attack of the γ-allyl carbon on formaldehyde, (c) pallada-ene reactions of σ-allyl complexes with ethylene, and (d) pallada-ene type reactions of σ-allyl complexes with acetylene. Our results show that (η1-allyl)-Pd complexes are probably not involved as intermediates in the Tsuji−Trost...

The complex OsCl(NH=C(Ph)C 6 H 4 )(PiPr 3 ) 2 (H 2 ) (1) has been characterized by Esteruelas and coworkers (Organometallics 1998, 17, 4065-4076) as an elongated dihydrogen complex based on relaxation time measurements and observation of J H-D = 6.3 Hz in 1-d 1 . Variable-temperature NMR studies were reported in which the single hydride resonance observed at ambient temperature decoalesced into two signals at low temperature (193 K), which was attributed to hindered rotation of the bound H 2 ligand. Reinvestigation of the low-temperature NMR spectra of 1 reveals a more complex situation. Examination of the 1 H and 31 P NMR spectra of 1 and 1-d 1 at lower temperatures than previously studied demonstrates that quantum mechanical exchange coupling is observed between the metal-bonded hydrogen atoms. This coupling is quenched in 1-d 1 . Hindered rotation around Os-P bonds in 1 also contributes to the observed NMR spectra.

The ruthenium(II) hexaaqua complex [Ru(H2O)6]2+ reacts with dihydrogen under pressure to give the h2-dihydrogen ruthenium(II) pentaaqua complex [Ru(H2)(H2O)5]2+.The complex was characterized by 1H, 2H and 17O NMR: d H = -7.65 ppm, J HD = 31.2 Hz, d O = -80.4 ppm (trans to H2) and d O = -177.4 ppm (cis to H2).The H-H distance in coordinated dihydrogen was estd. to 0.889 .ANG. from J HD, which is close to the value obtained from DFT calcns. (0.940 .ANG.). Kinetic studies were performed by 1H and 2H NMR as well as by UV-Vis spectroscopy, yielding the complex formation rate and equil. consts.: k f = (1.7 +- 0.2) * 10-3 kg mol-1 s-1 and K eq = 4.0 +- 0.5 mol kg-1.The complex formation rate with dihydrogen is close to values reported for other ligands and thus it is assumed that the reaction with dihydrogen follows the same mechanisn (I d).In deuterated water, one can observe that [Ru(H2)(H2O)5]2+ catalyzes the hydrogen exchange between the solvent and the dissolved dihydrogen.A hydride is proposed as the intermediate for this exchange.Using isotope labeling, the rate const. for the hydrogen exchange on the h2-dihydrogen ligand was detd. as k 1 = (0.24 +- 0.04) * 10-3 s-1.The upper and lower limits of the pK a of the coordinated dihydrogen ligand have been estd.:3 < pK a < 14.

The reaction of the isostructural anions of group 13 hydrides EH4- (E = B, Al, Ga) with proton donors of different strength (CH3OH, CF3CH2OH, and CF3OH) was studied with different theoretical methods [DFT/B3LYP and second-order Møller-Plesset (MP2) using the 6-311++G(d,p) basis set]. The results show the general mechanism of the reaction: the dihydrogen-bonded (DHB) adduct (EH...HO) formation leads through the activation barrier to the next concerted step of H2 elimination and alkoxo product formation. The structures, interaction energies (calculated by different approaches including the energy decomposition analysis), vibrational E-H modes, and electron-density distributions were analyzed for all of the DHB adducts. The transition state (TS) is the dihydrogen complex stabilized by a hydrogen bond with the anion [EH3(eta2-H2)...OR-]. The single exception is the reaction of BH4- with CF3OH exhibiting two TSs separated by a shallow minimum of the BH3(eta2-H2)...OR- intermediate. The structures and energies of all of the species were calculated, leading to the establishment of the potential energy profiles for the reaction. A comparison is made with the mechanism of the proton-transfer reaction to transition-metal hydrides. The solvent influence on the stability of all of the species along the reaction pathway was accounted for by means of polarizable conductor calculation model calculations in tetrahydrofuran (THF). Although in THF the DHB intermediates, the TSs, and the products are destabilized with respect to the separated reactants, the energy barriers for the proton transfer are only slightly affected by the solvent. The dependence of the energies of the DHB complexes, TSs, and products as well as the energy barriers for the H2 release on the central atom and the proton donor strength is also discussed.

The addition of H2 on (sulfur, phosphorus, sulfur)-pincer-based 16-VE complexes was studied from both experimental and theoretical points of view. The reaction of H 2 with [M(SPS)(PPh 3 )] (M = Rh, Ir) led to the formation of dihydride M(III) complexes, which was fully characterized with iridium as metal. No reaction occurred with the isoelectronic 16-VE Pt(II) [Pt(SPS)Cl] complex. This reaction was also studied by means of DFT/B3PW91 calculations on the model complexes [M(SPS)(PH 3 )] (M = Rh, Ir) and by B3PW91//ONIOM(B3PW91:UFF) calculations on real systems. The regioselectivity observed and the greater reactivity of the Ir compound were properly reproduced and related through a thermodynamic cycle to the electronic properties of the metal complex and to the energetics of the M-H bonds under formation. For both Rh and Ir complexes, the transition state for the formation of the dihydride product is a molecular dihydrogen complex located about 9 kcal mol -1 above the reactants. The reactivity of Pd(II) and Pt(II) analogues ([M(SPS)(X)], X = Cl, PH 3 + ) was also studied, and the formation of M(IV) dihydrides was found to be much less favorable, especially for M = Pd. Non-oxidative-addition processes leading to molecular dihydrogen complexes or to an heterolytic cleavage of H 2 were also explored, but none of them were found to be favored on AG grounds.

Photolysis of solutions of M(CO)(6) (M = Cr, W) at low temperature in the presence of hydrogen gas affords Cr(CO)(5)(H(2)) (1) and W(CO)(5)(H(2)) (2). Complexes 1 and 2 are characterized as dihydrogen complexes based on short T(1) values for the hydride resonances and the observation of a large HD coupling in the HD derivatives. Irradiation of a phosphine-substituted derivative (PMe(3))Cr(CO)(5) in the presence of hydrogen gas gave similar results. Thus cis-(PMe(3))Cr(CO)(4)(H(2)) (3) and trans-(PMe(3))Cr(CO)(4)(H(2)) (4) were prepared and characterized by (1)H and (31)P NMR spectroscopy. When the photolysis reactions were carried out in methylene chloride, solvent binding competitive with hydrogen binding was observed. This was not observed in less coordinating solvents such as alkanes. Subsequent displacement of solvent by H(2) leads to the dihydrogen complexes. Complexes 1 and 2 are moderately acidic, with deprotonation effected by mild bases.

The preparation and isolation of the first palladium dihydrogen complex is described. NMR spectroscopy reveals a very short H-H bond length, but the hydrogen molecule is activated toward heterolytic cleavage. An X-ray crystal structure suggests that proton transfer to the (tBu) PCP (κ(3)-2,6-((t)Bu2PCH2)2C6H3) pincer ligand is possible. The basicity of the ipso-carbon atom of the pincer ligand was investigated in a related complex.

Octahedral metal complexes are attractive structural templates for the design of enzyme inhibitors as has been demonstrated, for example, with the development of metallo-pyridocarbazoles as protein kinase inhibitors. The octahedral coordination sphere provides untapped structural opportunities but at the same time poses the drawback of dealing with a large number of stereoisomers. In order to address this challenge of controlling the relative metal-centered configuration, the synthesis of rhodium(III) pyridocarbazole complexes with facially coordinating acyclic tridentate ligands was investigated. A strategy for the rapid synthesis of such complexes is reported, the diastereoselectivities of these reactions were investigated, the structure of several complexes were determined by X-ray crystallography, the high kinetic stability of such complexes in thiol-containing solutions was demonstrated in (1)H-NMR experiments, and the protein kinase inhibition ability of this class of complexes was confirmed. It can be concluded that the use of multidentate ligands is currently maybe the most practical strategy to avoid a large number of possible stereoisomers in the course of exploiting octahedral coordination spheres as structural templates for the design of bioactive molecules.

The trifunctional ligand, 2,6-bis(diphenylphosphorylmethyl)-4-methylphenol (L2), forms complexes with cerium(III) nitrate having a ligand to metal ratio of 1: 1, 2: 1, and 3: 1. The structures of these complexes in the solid state and in solution were studied by X-ray diffraction, IR and NMR (1H and 31P) spectroscopy, and conformational analysis (molecular mechanics). The 2: 1 complexes of L2 with lanthanum(III) and neodymium(III) nitrates were synthesized and characterized. In all complexes, the neutral ligand is coordinated through both phosphoryl oxygen atoms. The hydroxy oxygen atom is coordinated only in some complexes, and the hydrogen atom of the hydroxy group is involved in hydrogen bonding. The compositions and structures of the resulting complexes depend on the method of synthesis and the nature of solvent. The ligand was found to undergo easy inner-sphere oxidation. The structure of one of the transformation products was established by X-ray diffraction. Unlike the coordinated ligand, the free ligand is very stable to oxidation.

Bromotricarbonylrhenium(I) complexes [ReBr(CO) 3 L] [L = Ph 2 PO(CH 2 ) 3 OPPh 2 ( L 1 ), i Pr 2 PO(CH 2 ) 2 OP i Pr 2 ( L 2 ), Cy 2 PO(CH 2 ) 2 OPCy 2 ( L 3 )] were prepared by reaction of [ReBr(CO) 5 ] with L. X-ray crystallography showed them all to be mononuclear, with the CO ligands fac . Subsequent reaction with AgOTf gave fac -[Re(OTf)(CO) 3 L], as shown by IR and NMR spectra. By contrast, reaction of [ReH(CO) 5 ] with L 1 – 3 gave hydrido complexes, the nuclearity and stereochemistry of which depended on the identity of L, as was confirmed by X-ray crystallography of mer -[ReH(CO) 3 L 1 ], fac -[ReH(CO) 3 L 2 ] and [{ReH(CO) 4 } 2 (μ- L 3 )]. Protonation of the hydrido compounds at 183 K with HBF 4 · OMe 2 gave the corresponding non-classical cationic dihydrogen complexes ( T 1(min) ∼ 15 ms at 400 MHz), which released H 2 at temperatures above critical temperatures (243–263 K) that depended on the co-ligands.

The existence of a dihydrogen bond (S-H...H-B) and its combination with a C-H...S hydrogen bond in an unusual cooperative effect are demonstrated from a combination of experimental and theoretical methods. This cooperative effect seems to be responsible for self-assembly of mercaptane-metallacarborane complexes such as closo-[3-Ru(eta6-C6H6)-8-HS-1,2-C2B9H10] (1) and closo-[3-Co(eta5-C5H5)-8-HS-1,2-C2B9H10] (3), which present identical supramolecular two-dimensional polymeric networks. The findings, besides documenting structurally the first S-H...(H-B)2 dihydrogen bond and the unconventional cooperative ability of a boron-attached SH group, prove that substituted carboranes have the potential to serve as building blocks for assembling complex structures.

To be able to propose experimental tests to distinguish elongated dihydrogen transition-metal complexes from compressed dihydride transition-metal complexes, a thorough density functional study of the electronic structure in combination with quantum nuclear dynamics calculations have been performed for complexes [Cp*Ru(H2PCH2PCH2(H2)]+ and [CpRe(CO)2H2]. The results of this study suggest that elongated dihydrogen complexes and compressed dihydride complexes have different properties and that it should be possible to distinguish between them experimentally. In particular, different behavior is predicted with respect to 1) the sign of the isotope geometric effect on the H-H distance at 0 K, 2) the temperature dependence of the H-H distance, and 3) the temperature dependence of the H-D spin-spin coupling constant in 1H NMR spectroscopy.

Single-crystal neutron diffraction, inelastic neutron scattering, and density functional calculations provide experimental and theoretical analyses of the nature of the osmium-bound, "elongated" dihydrogen ligands in [Cp*OsH(4)(L)][BF(4)] complexes (L = PPh(3), AsPh(3), or PCy(3)). The PPh(3) and AsPh(3) complexes clearly contain one dihydrogen ligand and two terminal hydrides; the H(2) ligand is transoid to the Lewis base, and the H-H vector connecting the central two hydrogen atoms lies parallel to the Ct-Os-L plane (Ct = centroid of Cp* ring). In contrast, in the PCy(3) complex the H-H vector is perpendicular to the Ct-Os-L plane. Not only the orientation of the central two hydrogen atoms but also the H-H bond length between them depends significantly on the nature of L: the H...H distance determined from neutron diffraction is 1.01(1) and 1.08(1) A for L = PPh(3) and AsPh(3), respectively, but 1.31(3) A for L = PCy(3). Density functional calculations show that there is a delicate balance of electronic and steric influences created by the L ligand that change the molecular geometry (steric interactions between the Cp* and L groups most importantly change the Ct-Os-L angle), changing the relative energy of the Os 5d orbitals, which in turn govern the H-H distance, preferred H-H orientation, and rotational dynamics of the elongated dihydrogen ligand. The geometry of the dihydrogen ligand is further tuned by interactions with the BF(4)(-) counterion. The rotational barrier of the bound H(2) ligand in [Cp*OsH(4)(PPh(3))](+), determined experimentally (3.1 kcal mol(-)(1)) from inelastic neutron scattering experiments, is in reasonable agreement with the B3LYP calculated H(2) rotational barrier (2.5 kcal mol(-)(1)).

A new series of Fe(II) complexes, FeCl2[N(R)=C(Me)C(Me)=N(R)], containing diimine ligands with hemilabile sidearms R (R = CH2(CH2)2NMe2, 1, CH2(CH2)2OMe, 2, CH2(CH2)2SMe), 3) were synthesized. The crystal structure of 1 showed 6-coordination where both amine arms were attached, whereas 2 was a 5-coordinate 16e species with one methoxy arm dangling free. Extensive attempts were made to bind CO to these species to synthesize precursors for dihydrogen complexes but were unsuccessful. Reaction of 1 with 1 or 2 equiv of AgOTf under CO atmosphere resulted in isolation of only a 6-coordinate bis(triflate)-containing product [Fe[N(R)=C(Me)C(Me)=N(R)](OTf)2] (R = CH2(CH2)2NMe2), 5. Reaction of 5-coordinate 2 with AgSbF6 under CO did not give a CO adduct but afforded instead a dicationic dinuclear complex [Fe[N(R)=C(Me)C(Me)=N(R)](mu-Cl)]2[SbF6]2 (R = CH2(CH2)2OMe), 4, containing a weakly bound SbF6. Thus coordination of hard-donor anions to iron was favored over CO binding. The unexpected rejection of binding of CO is rationalized by the iron being in a high-spin state in this system and energetically incapable of spin crossover to a low-spin state. Theoretical calculations on CO interaction with Fe(II) centers in spin states S = 0, 1, and 2 for both the 16e complexes and their CO adducts aid further understanding of this problem. They show that interaction of CO with a high-spin 5-coordinate Fe model diimine complex is essentially thermoneutral but is exergonic by about 48 kcal/mol to a comparable but low-spin diphosphine fragment. Spin crossover is thus disfavored thermodynamically rather than kinetically (e.g. a "spin block" effect); i.e., the ligand field strengths of the primarily N-donor groups are apparently insufficient to give a low-spin CO adduct.

The discovery of dihydrogen complexes, L n M(H2), pointed to direct transfer of hydrogen from coordinated H2 ligands to substrates as an operable pathway in catalysis both in homogeneous and heterogeneous systems. Sigma complexes, L n M(η2-H–X) (X=H, Si, C, etc), are indeed relevant in hydrogenation as well as silane alcoholysis and methane conversion.

The bonding and geometries of H2Fe(CO)3, H2Fe(CO)3(C2H4), and HFe(CO)3(C2H5), which are species relevant to iron carbonyl-catalyzed olefin hydrogenation, are analyzed using density functional theory (DFT). These calculations indicate that H2Fe(CO)3 and H2Fe(CO)3(C2H4) are respectively triplet and singlet dihydrogen complexes with H2Fe(CO)3(C2H4) lower in energy than HFe(CO)3(C2H5) by a modest amount (10.2 kcal/mol with BP86/LACV3P**). Further, it is likely that when H2Fe(CO)3(C2H4) forms, it can rearrange to form the HFe(CO)3(C2H5) complex. The reductive elimination of C2H6 from HFe(CO)3(C2H5) is exothermic, whether it is accompanied by or precedes ethylene addition.

The diastereomerically pure complexes [TpRuX(R,R-dippach)] (X = Cl (1a), H (2a); R,R-dippach = (R,R)-1,2-bis((diisopropylphosphino)amino)cyclohexane) as well as the nonchiral derivatives [TpRuX(dippae)] (X = Cl (1b), H (2b); dippae = 1,2-bis((diisopropylphosphino)amino)ethane) have been prepared and characterized. The reaction of either 1a or 1b with H2 and NaBAr‘4 (Ar‘ = 3,5-bis(trifluoromethyl)phenyl) in fluorobenzene yields the corresponding stable dihydrogen complexes [TpRu(H2)(R,R-dippach)][BAr‘4] (3a) and [TpRu(H2)(dippae)][BAr‘4] (3b). No significant intramolecular interaction between the amino protons and the hydrogen atoms bound to the metal has been observed in any of these compounds. Both 3a and 3b react readily with dinitrogen, furnishing the complexes [TpRu(N2)(R,R-dippach)][BAr‘4] (4a) and [TpRu(N2)(dippae)][BAr‘4] (4b). The X-ray crystal structures of 3b and 4b were determined. The proton-transfer processes over the monohydrides 2a and 2b with HBF4·OEt2 have been studied by NMR spectroscopy...

Reaction of [Cp*Ir(CH3CN)3][PF6]2 with methylenebis(N-methylimidazolium) iodide in the presence of Et3N affords [Cp*Ir(C−C)I]PF6 (1) (C−C = bis-carbene). The structure of complex 1 was confirmed by X-ray crystallography. The chloride analogue [Cp*Ir(C−C)Cl]X (2) was similarly prepared from [Cp*Ir(CH3CN)3][PF6]2 (X = PF6) or [Cp*IrCl2]2 (X = Cl) and methylenebis(N-methylimidazolium) chloride. Reaction of 2 (X = Cl) with Et3SiB(C6F5)4 under hydrogen gas gives the dicationic dihydrogen complex [Cp*Ir(C−C)(H2)]2+ (3). Complex 3 is identified as a dihydrogen complex based on T1(min) = 37 ms for the hydride resonance (240 K, 750 MHz) and JHD = 23.5 Hz in the partially deuterated analogue.

Chloro phosphite complexes RuClTpL(PPh 3 ) ( 1a , 1b ) [L = P(OEt) 3 , PPh(OEt) 2 ] and RuClTp[P(OEt) 3 ] 2 ( 1c ) [Tp = hydridotris(pyrazolyl)borate] were prepared by allowing RuClTp(PPh 3 ) 2 to react with an excess of phosphite. Treatment of the chloro complexes 1 with NaBH 4 in ethanol yielded the hydride RuHTpL(PPh 3 ) ( 2a , 2b ) and RuHTp[P(OEt) 3 ] 2 ( 2c ) derivatives. Protonation reaction of 2 with Bronsted acids was studied and led to thermally unstable (above 10 °C) dihydrogen [Ru(η 2 - H 2 )TpL(PPh 3 )] + ( 3a , 3b ) and [Ru(η 2 -H 2 )Tp{P(OEt) 3 } 2 ] + ( 3c ) complexes. The presence of the η 2 -H 2 ligand is indicated by short T 1 min values and J HD measurements of the partially deuterated derivatives. Aquo [RuTp(H 2 O)L(PPh 3 )]BPh 4 ( 4 ), carbonyl [RuTp(CO)L(PPh 3 )]BPh 4 ( 5 ), and nitrile [RuTp(CH 3 CN)L(PPh 3 )]BPh 4 ( 6 ) derivatives [L = P(OEt) 3 ] were prepared by substituting H 2 in the η 2 -H 2 derivatives 3 . Vinylidene [RuTp{ C C(H)R}L(PPh 3 )]BPh 4 ( 7 , 8 ) (R = Ph, t Bu) and allenylidene [RuTp( C C CR1R2)L(PPh 3 )]BPh 4 ( 9 – 11 ) complexes (R1 = R2 = Ph, R1 = Ph R2 = Me) were also prepared by allowing dihydrogen complexes 3 to react with the appropriate HC CR and HC CC(OH)R1R2 alkynes. Deprotonation of vinylidene complexes 7 , 8 with NEt 3 was studied and led to acetylide Ru(C CR)TpL(PPh 3 ) ( 12 , 13 ) derivatives. The trichlorostannyl Ru(SnCl 3 )TpL(PPh 3 ) ( 14 ) compound was also prepared by allowing the chloro complex RuClTpL(PPh 3 ) to react with SnCl 2 · 2H 2 O in CH 2 Cl 2 .

Reaction of RuHCl(PPh(3))(2)(diamine) (1a, diamine = (R,R)-1,2-diaminocyclohexane, (R,R)-dach; 1b, diamine = ethylenediamine, en) with KO(t)Bu in benzene quickly generates solutions of the amido-amine complexes RuH(PPh(3))(2)(NHC(6)H(10)NH(2)), (2a'), and RuH(PPh(3))(2)(NHCH(2)CH(2)NH(2)), (2b'), respectively. These solutions react with dihydrogen to first produce the trans-dihydrides (OC-6-22)-Ru(H)(2)(PPh(3))(2)(diamine) (t,c-3a, t,c-3b). Cold solutions (-20 degrees C) containing trans-dihydride t,c-3a react with acetophenone under Ar to give (S)-1-phenylethanol (63% ee). Complexes t,c-3 have lifetimes of less than 10 min at 20 degrees and then isomerize to the cis-dihydride, cis-bisphosphine isomers (OC-6-32)-Ru(H)(2)(PPh(3))(2)(diamine) (Delta/Lambda-c,c-3a, c,c-3b). A solution containing mainly Delta/Lambda-c,c-3a reacts with acetophenone under Ar to give (S)-1-phenylethanol in 20% ee, whereas it is an active precatalyst for its hydrogenation under 5 atm H(2) to give 1-phenylethanol with an ee of 50-60%. Complexes c,c-3 isomerize to the cis-dihydride, trans-bisphosphine complexes (OC-6-13)-Ru(H)(2)(PPh(3))(2)(diamine) (c,t-3a, c,t-3b) with half-lives of 40 min and 1 h, respectively. A mixture of Delta/Lambda-c,c-3a and c,t-3a can also be obtained by reaction of 1a with KBH(Bu(sec))(3). A solution of complex c,t-3a in benzene under Ar reacts very slowly with acetophenone. These results indicate that the trans-dihydrides t,c-3a or t,c-3b along with the corresponding amido-amine complexes 2a' or 2b' are the active hydrogenation catalysts in benzene, while the cis-dihydrides c,c-3a or c,c-3b serve as precatalysts. The complexes RuCl(2)(PPh(3))(2)((R,R)-dach) or 1a, when activated by KO(t)Bu, are also sources of the active catalysts. A study of the kinetics of the hydrogenation of acetophenone in benzene catalyzed by 3a indicates a rate law: rate = k[c,c-3a](initial)[H(2)] with k = 7.5 M(-1) s(-1). The turnover-limiting step appears to be the reaction of 2a' with dihydrogen as it is for RuH(NHCMe(2)CMe(2)NH(2))(PPh(3))(2) (2c'). The catalysts are more active in 2-propanol, even without added base, and the kinetic behavior is complicated. The basic cis-dihydride c,t-3a reacts with [NEt(3)H]BPh(4) to produce the dihydrogen complex (OC-14)-[Ru(eta(2)-H(2))(H)(PPh(3))(2)((R,R)-dach)]BPh(4) (4) and with diphenylphosphinic acid to give the complex RuH(O(2)PPh(2))(PPh(3))(2)((R,R)-dach) (5). The structure of 5 models aspects of the transition state structure for the ketone hydrogenation step. Complex 2b' decomposes rapidly under Ar to give dihydrides 3b along with a dinuclear complex (PPh(3))(2)HRu(mu-eta(2);eta(4)-NHCHCHNH)RuH(PPh(3))(2) (6) containing a rare, bridging 1,4-diazabutadiene group. The formation of an imine by beta-hydride elimination from the amido-amine ligand of 2a' under Ar might explain some loss of enantioselectivity of the catalyst. The structures of complexes 1a, 5, and 6 have been determined by single-crystal X-ray diffraction.

Treatment of RuHCl(CO)(PPh3)3 with 1,3,5-triethynylbenzene produces the trimetallic complex 1,3,5-[Cl(CO)(PPh3)2RuCHCH]3C6H3, which reacts with PMe3 to give 1,3,5-[Cl(CO)(PMe3)3RuCHCH]3C6H3. 1,3,5-[Cl(CO)(PPh3)2RuCHCH]3C6H3 also reacts with pyridine (Py) and 4-phenylpyridine (PhPy) to give 1,3,5-[Cl(CO)(L)(PPh3)2RuCHCH]3C6H3 (L = Py, PhPy). Reactions of OsHCl(CO)(PPh3)3 with ArC⋮CH (Ar = Ph, p-tolyl) produce the six-coordinated insertion products OsCl(CHCHAr)(CO)(PPh3)3. Reaction of OsHCl(CO)(PPh3)3 with 1,3,5-triethynylbenzene produces the bimetallic complex 1-HC⋮C-3,5-[Cl(CO)(PPh3)3OsCHCH]2C6H3, which reacts with PMe3 to give 1-HC⋮C-3,5-[OsCl(CO)(PPh3)2(PMe3)OsCHCH]2C6H3. The electrochemical and second-order NLO properties of some of the new complexes have been investigated.