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Investigations on incorporating an N-flanking anthracenyl moiety to [Rh(Cp*)(NHC)Cl2] complexes surprisingly led to the formation of an intramolecular C-C bond between the Cp* and anthracenyl moieties, with additional auxiliary interactions between the metal and the anthracenyl ring system. In silico modeling supports a reaction mechanism whereby Rh(η4-tetramethylfulvene) intermediates undergo metallocycloaddition and the abstraction of a chlorido ligand, affording unique cationic complexes that feature Rh centers coordinated by a nonadentate ligand with exclusively carbon donor atoms. Some Rh-C interactions were extremely weak but nevertheless exhibited covalent bonding character. These weak Rh-C interactions were readily displaced by stronger electron donors, and the nonadentate ligand reverted to the heptadentate coordination mode observed in the intermediate. As far as we are aware, this study provides the first conclusive evidence of complexes bearing a single nonadentate κ9-coordinating ligand that features only carbon donors bound to a metal center.

Organometallic Rh(Cp*) (Cp* = η

In comparison to β-diketiminates, a highly exploited class of N,N-chelating ligands, the corresponding β-thioketoiminates, monothio-substituted analogues, have received only minor attention. β-Thioketoiminates are straightforwardly prepared through treatment of an appropriate β-ketoiminate with Lawesson’s reagent. Employing standard synthetic techniques for η6-arene Ru(II) and Os(II) β-diketiminate complexes, an analogous series of chlorido-metal complexes supported by different sized N-aryl substituted β-thioketoiminate ligands is reported. However, metal ligation of a β-thioketoiminate bearing an electron-withdrawing CF3 group was not possible. The metal–chlorine bond in these complexes is readily activated by various sodium or silver salts of weakly coordinating anions, affording coordinately unsaturated cationic formally 16-electron species. All η6-C6H6 metal β-thioketoiminate complexes were characterized by NMR and in the solid state using single crystal X-ray diffraction techniques. Structural studi...

Ruthenium complexes of the type [RuCl(eta(6)-arene)-(NN)]X (X = BF4 or BPh4) featuring an eta(6)-arene ligand modified with an imidazolium ring and incorporating the bis(azo) chelating (NN) ligands 2-hydroxyphenylbis(3,5-dimethylpyrazol-1-yl) methane or 2-nitrophenylbis(3,5-dimethylpyrazol-1-yl) methane are reported. The catalytic activities of the complexes were evaluated in the transfer hydrogenation of benzaldehyde to benzyl alcohol with iPrOH as the hydrogen donor in the absence of a base and under biphasic conditions; one of the two phases was iPrOH, and the other was an ionic liquid. The catalysts featuring the imidazolium-modified eta(6)-arene could be recycled and reused with only a minor decrease in substrate conversion after multiple reaction cycles. The reaction rate was strongly influenced by the type of ionic liquid employed in the biphasic system.

This paper describes the preparation and comprehensive characterization of a series of water-soluble cationic silver(I)-centered complexes featuring the hemilabile P, N-ligand known as 3,7-dimethyl-1,3,5-triaza-7-phosphabicyclo[3.3.1]nonane (herein abbreviated as PTN(Me)) and differing types of monoanionic counterions including known biologically active sulfadiazine and triclosan. The complexes primarily differed though the number of coordinating PTN(Me) ligands. The bis-substituted Ag(I) complexes revealed P, N bidentate coordination, while the only P-monocoordination of the metal center was observed for the tris-substituted systems. The bis-ligated silver compounds were observed to quickly degrade upon photoexposure or in contact with air. In contrast, the tris-ligated complexes demonstrated greater stability, in particular, a high resistance to photo-decomposition. Calculated geometry optimized models using the density functional theory method (BP86) revealed for the bis-substituted PTN(Me) Ag(I) species that the total enthalpy of the tetrahedral C

Attempted deprotonation of 1,2-di(fluorenylidene)cyclobutane, 8, using n-butyl or tert-butyl-lithium led instead to 1,4-addition across the 1,3-butadiene unit to yield the 1-(9H-fluorenyl-2-(9-butyl-9H-fluorenyl)cyclobutene 10 or 11, respectively; analogously, n-butyl-lithium and trans-3,4-bis(trimethylsilyl)-1,2-di(fluorenylidene)cyclobutane, 12, furnished the corresponding 1,4-adduct 13. Bromination of 8 with N-bromosuccinimide led to mono-, di- and tri-bromo derivatives whereby, in the trans-di-bromo systems, the helical character of the trans bromines could either match (in 16) or oppose (in 17) the helicity of the fluorenylidenes. In accordance with DFT calculations, the diastereomer 17 is the favoured product, and a pure sample of 16 in solution underwent equilibration via cleavage of the C(3)–C(4) linkage such that 17 became the major isomer. Attempted addition of bromine to 3,4-di(fluorenylidene)-1,2-diphenylcyclobutene, 24, unexpectedly yielded the diketone 2,3-di(9H-fluoren-9-ylidene)-1,4-diphenylbutane-1,4-dione, 25. The structures of 10, 11, 13, 16, 17 and 25 were determined by X-ray crystallography.

The strongly chelating anionic beta-diketiminate ligand has been employed to formulate complexes involving almost every metal of the periodic table; however, the heavier metals of the d block remain relatively unexplored. This paper describes the synthesis and characterization of the first two osmium, beta-diketiminato compounds, including a coordinatively unsaturated cationic complex. In parallel to the analogous Ru(II) complexes, the cationic (eta(6)-arene)osmium(II) complex demonstrates bifunctional behavior through [4 + 2] cycloaddition with ethylene, cleavage of dihydrogen under mild conditions, and protonation/chloride addition with [Et2OH]Cl. Metal-centered activity in both the Ru(II) and Os(II) beta-diketiminates has until now remained elusive, as the cationic Os complex is shown to readily coordinate an aryl isonitrile. The applicability of Os(II) beta-diketiminato complexes in catalytic olefin hydrogenation demonstrates significantly greater activity in terms of conversion and TOF for a range of substrates, including styrene, cyclohex-1-ene, and 1-methylcyclohex-1-ene. Moreover, selective hydrogenation of the exocyclic alkenyl group in limonene was observed, whereas the corresponding isostructural Ru(II) complexes are inactive. In contrast, the cationic (eta(6)-arene)ruthenium(II) beta-diketiminato complex proved more active for the catalytic dehydrogenation of N,N-dimethylamine borane (Me2NBH3) than the equivalent Os(II) species. A detailed DFT study of the Ru(II) and Os(II) beta-diketiminato species using charge decomposition analysis (CDA) demonstrates differences in metal ligand interactions, which in turn considerably influences the extent of bifunctional reactivity.

Ammonia borane (AB) was loaded onto a range of mesoporous materials (MCM-41, SBA-15 and MCF) by wet impregnation from THF solutions and its thermal dehydrogenation studied using TGA/MS. The interactions between the AB and the surfaces were characterised using difference FTIR spectroscopy. The presence of mesoporous materials promotes lower temperature H 2 release, and greater selectivity towards the formation of H 2 , i.e. decreased formation of gaseous boron-containing side products. D-FTIR results confirm interactions between isolated silanol groups or surface Si-O-Si species and AB and this supports the proposal that a H-bonding interaction between the surface and deposited AB is important in promoting decomposition at lower temperature. AB interacting with silanol groups decomposes more readily than that coordinated to Si-O-Si. The effect on the temperature of H 2 release is greater for materials of larger pore size (rather than materials of larger surface area), i.e. MCF > SBA-15 > MCM-41. This suggests that access to the internal surface of the mesoporous material (where the majority of surface silanols are located) is important, and this in turn suggests that polymeric species, which may have restricted access to the internal surface of the different materials, form when AB is dissolved in THF. Decomposition of B-N-containing gaseous materials (to AB(g)) following their formation, on the silanol groups of the SiO 2 , is suggested as the reason for the increased selectivity of the reaction to H 2 (and decreased release of unwanted side products) in the presence of mesoporous material.

Amine borane type substrates show significant potential as safe and effective chemical hydrogen storage materials. β-Diketiminato(η6-arene)-Ru(II) complexes have shown the ability to rapidly perform the heterolytic cleavage of H2 under mild conditions through bifunctional metal-ligand interaction. The presented work explores the applicability of such complexes toward the catalytic dehydrogenation of different substituted amine boranes, in particular, ammonia borane (AB) and N,N-dimethylamine borane (DMAB). Complex [(η6-C6H6)-Ru(2,6-(CH3)2-C6H3NC(CH3))2CH]OTf (1) showed excellent activity in the catalytic release of a single equivalent of H2 within 0.5 h from a concentrated DMAB solution in THF (3.2 M) at near ambient temperatures. Studies involving structural analogues of 1 allowed insight into the operational dehydrocoupling mechanism. It is concluded from this preliminary work that in solution, 1 forms a homogeneous bifunctional active species that does not undergo deactivation, even after prolonged exp...

Five different types of β-diketiminate ligands, bearing electron-donating to strongly electron-withdrawing substituents, were synthesized and used in the synthesis of Cp* ruthenium complexes (Cp* = η5-C5Me5). One series consists of complexes with a covalent RuIII–Cl bond, and the other series features a reduced RuII center, where the chloride is abstracted by treatment of the corresponding RuIII compounds with Zn or Mg. All compounds were characterized by single-crystal X-ray diffraction, UV–visible spectroscopy, and cyclic voltammetry. In the case of RuII complexes, solution NMR techniques provided key information regarding the electronic and structural differences induced by the different β-diketiminate ligands employed. Capitalizing on the facile reduction–oxidation cycle of the Cp* ruthenium β-diketiminato complexes, catalytic atom transfer radical addition (ATRA) and cyclization (ATRC) reactions were performed on relevant substrates. The turnover rates are strongly dependent on the type of β-diketimi...

Utilizing the aza-Wittig reaction involving the ylid 3,5-(CF3)2C6H3NPPh3 and 1,1,1,5,5,5-hexafluoro-2,4-pentanedione, a highly fluorinated and electron-withdrawing β-diketiminate was obtained. Using strong bases, nBuLi, Ag2O, or TlOEt, the corresponding β-diketiminato-Li, -Ag, or -Tl chelated complexes were prepared. Subsequent in situ transmetalation with (Ru(η6-C6H6)Cl2)2 or (Ru(η6-p-cymene)Cl2)2 afforded the half-sandwich chloro-substituted Ru(II) β-diketimino complexes in high yield. The synthesis of the Lewis acidic catalysts featuring a vacant coordination site at the metal center was accomplished using [Na]BArF (BArF = tetrakis[3,5-bis(trifluoromethyl)phenyl]boron). These complexes are active for the Lewis acid catalyzed Diels–Alder reaction between α,β-unsaturated aldehydes, that is, methacrolein, acrolein, and dienes, that is, cyclopentadiene and 2,3-dimethyl-1,3-butadiene, with conversions in the range of 66–98% under mild conditions. Whereas the herein described catalysts generally promote exo ...

A series of ruthenium-benzene complexes with β-diketiminate ligands modified with electron-withdrawing groups were prepd. and characterized by NMR spectroscopy, mass spectrometry, and single-crystal x-ray diffraction. The complexes are stable in air and undergo controlled hydrolysis in water. The complexes were evaluated for anticancer activity in vitro, and two of them proved to be highly cytotoxic, comparable or even superior to cisplatin. This work shows the potential utility of the β-diketiminate ligand in the rational design of new anticancer metal-contg. drugs. A related complex with a η6-C6H5CF3 ligand was prepd. and found to undergo a nucleophilic addn. reaction at the coordinated arene ring to afford a substituted η5-cyclohexadienyl deriv.

A series of salts composed of the coordinatively unsatd. areneruthenium β-diketiminato cation and different anions, [(η6-C6H6)Ru(ArN:CMeCHCMe:NAr)][X] (1-4; Ar = 2,6-dimethylphenyl; X = OTf-, BF4-, PF6-, BPh4-) and [(η6-C6H6)Ru(ArN:CMeCHCMe:NAr)][BArF4] [5, ArF = 3,5-(CF3)2C6H3], were prepd. and characterized. The solid state structures of 1, 2, and 5 have also been detd. using single-crystal x-ray crystallog. Both soln. and solid state data reveal the presence of anion-cation interactions, the extent of which depends on the nature of the anion, which have been further rationalized via computed charge d. profiles using DFT energy optimized models. The catalytic activity of 1-5 in the hydrogenation of styrene was found to be highly dependent on the nature of the counteranion, as inferred from investigations based on high-pressure soln. NMR, pulsed gradient spin-echo (PGSE) NMR diffusion, and Overhauser NMR spectroscopy. A good correlation between catalytic activity and the extent and nature of ion pairing was found, and the structure of the active catalytic species is proposed.

A series of compounds of general formula [Ru(η6-fluoroarene)(pta)Cl2] (fluoroarene = C6H5F, C6H5CF3, and 1,4-C6H4CH3F; pta = 1,3,5-triaza-7-phosphatricyclo[3.3.1.1]decane) have been prepared and characterized spectroscopically. Additionally, X-ray diffraction was employed to characterize two of the complexes and the corresponding precursors, i.e., [Ru(acac)2(η4-cod)] and Ru(η6-fluoroarene)(η4-cod)] (cod = cycloocta-1,5-diene). The solubility, pKa’s, and the stability toward hydrolysis of the [Ru(η6-fluoroarene)(pta)Cl2] complexes were studied, and DFT calculations were performed to assist in rationalizing the observed properties at a molecular level. The cytotoxicities of the pta-based compounds were evaluated in A2780 ovarian cancer cells, and the observed activities were correlated to the above-mentioned properties. The rate of hydrolysis of the Ru−Cl bonds in the C6H5CF3 derivative was found to increase significantly at low pH, which represents a possible method of tumor targeting based on the reduced ...

Dimeric arylgallium/indium chalcogenides 7−10 of formula [Ar′ME]2 (Ar′ = C6H3-2,6-(C6H3-2,6-Pri2)2; M = Ga or In, E = O or S) were synthesized by the treatment of Ar′MMAr′ with N2O or elemental sulfur and characterized by NMR spectroscopy and X-ray crystallography. Their structures feature three-coordinate, +3 oxidation state metal centers with planar M2E2 cores. The cores were almost perfectly square for E = O, but for E = S, they were distorted parallelograms in 7−10. The M–E bond lengths were shorter than those in the higher aggregated species [RME]n (n ≥ 4) but comparable to those in M3+ aryloxides or thiolates featuring three-coordinate metals. Short M···M separations [2.553(1) A in 7, 2.8882(4) A in 8, 2.8276 A (avg.) in 9, and 3.1577(8) A in 10] are observed. Low oxidation heavier group 13/group 16 chalcogenolate isomers 16−19 of formula [Ar′EM]2 (M = In or Tl, E = O or S) were also synthesized and characterized. In the +1 compounds [Ar′EIn]2 (O, 16; S, 19) together, with the In +3 species [Ar′InE]...

A new zwitterionic bidentate ligand was synthesized incorporating a 4,4'-bipyridine core with a carboxylate group as a single building block, specifically designed for the rational construction of supramol. structures (metal-org. frameworks) that are capable of encapsulating and aligning water aggregates leading to the formation of extended polymeric networks. In particular, both the terminal N' end and a carboxylate oxygen of the monosubstituted 4,4'-bipyridine was found to readily coordinate in a straightforward manner with different transition metal halides in water, affording heterocyclic complexes featuring various structural motifs. However, crit. to the stability and shape of the incorporated water structures is the presence of strong hydrogen bonding resulting from the directional influence exerted by an unbound oxygen center of the metal-bonded carboxylate groups. A search of the Cambridge Structural Database reveals that only a small no. of complexes that feature a free carboxylate oxygen strongly interact with a hydrogen atom assocd. with a cis-bonded aqua ligand.

Imidazolium- and pyridinium-based ionic liquids with ether/polyether substituents have been evaluated as solvents for palladium-catalyzed Suzuki C−C coupling reactions. In general, reactions proceed more efficiently in these solvents compared to other ionic liquids, which is believed to be due to better stabilization of the palladium catalyst, involving weak interactions with the ether groups. The position and the number of oxygen atoms in the ether side chain strongly influence the outcome of the coupling reactions in the imidazolium-based ionic liquids, whereas for the pyridinium-based liquids no influence is observed. Carbene derivatives, generated from the imidazolium-based ionic liquids, are believed to play a role by terminating the catalytic cycle, and representative species have been isolated and characterized from stoichiometric reactions.

The water-soluble iridium(III) complexes [Cp*Ir(PTA)Cl(2)] (1) and [Cp*Ir(PTA)(2)Cl]Cl (2) (PTA = 1,3,5-triaza-7-phosphaadamantane) have been synthesised and characterised by spectroscopy and X-ray crystallography. The complexes were evaluated as catalyst precursors for the hydrogenation of CO2 and hydrogen carbonate in aqueous solutions, in the absence of amines or other additives, under relatively mild conditions. Complex I performed poorly while 2 catalyses the hydrogenation with moderate activity. The catalytically active monohydride [Cp*Ir(PTA)(2)H](+) was identified by multinuclear NMR spectroscopy and its nature confirmed by independent synthesis.

The new mixed-metal complex {anti-[(p-cymene)RuCl]-μ-[κ 2-P,P′;κ 1-P′′-(PPh2CH2)3CMe]-[AuCl]}PF6 and its cluster derivative {anti-[(p-cymene)RuCl]-μ-[κ 2-P,P′;κ 1-P′′-(PPh2CH2)3CMe]-[AuPt3(CO)3(PCy3)3]}(PF6)2 have been prepared and characterized. Notably, NMR spectroscopy and high resolution FT-ICR mass spectrometry, including a tandem mass spectrometric analysis, demonstrated the formation of these compounds that was also confirmed by single crystal X-ray diffraction analysis.

The α-diimino chelating ligand 1,4-diaza-1,3-butadiene, or its dianionic enediamido form (generically defined as DAD), forms a variety of complexes with group 4 transition metals either with or without other co-ligands. The known species are either pseudo-octahedral [L4M(DAD)] or tetracoordinate [L2M(DAD)] with a lower degree of metal saturation in the latter case. Additionally, there are a number of known CpMLn species and homoleptic complexes with the formula [M(DAD)3] or [M(DAD)2]. The M-DAD metallacycle is generally either planar or folded at the N···N vector, the latter arrangement being observed when the number of co-ligands is reduced and hence there is insufficient saturation at the metal. The conformation also depends on the relative electron population of DAD, which is a noninnocent ligand and exists as a continuum between the neutral and dianionic resonance forms. Herein some theoretical concepts, that have previously been developed to describe the bonding capabilities of DAD toward different triads of transition metals, are extended to complexes of the group 4 metals. New electronic aspects of the [M(DAD)3] complexes are described together with a completely new analysis of the [M(DAD)2] complexes. These exhibit the planar/bent conformational dichotomy, which may have an electronic and/or steric origin as it is affected by the type of substituent at the nitrogen atoms. A reasonable justification of the observed conformational preferences is found from a combination of density functional and QTAIM analyses. The latter clearly demonstrates that a peculiar intramolecular hydrogen bonding can contribute to the stabilization of planar-type structures.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Ten complexes of general formula [Ru(η6-arene)Cl2(L)], [Ru(η6-arene)Cl(L)2][X], and [Ru(η6-arene)(L)3][X]2 (η6-arene = benzene, p-cymene; L = imidazole, benzimidazole, N-methylimidazole, N-butylimidazole, N-vinylimidazole, N-benzoylimidazole; X = Cl, BF4, BPh4) have been prepd. and characterized by spectroscopy. The structures of five representative compds. have been established in the solid state by single-crystal X-ray diffraction. All the new compds. were assessed by the same in vitro screening assays applied to [imidazole-H][trans-RuCl4(DMSO)(imidazole)] (NAMI-A) and [Ru(η6-arene)Cl2(1,3,5-triaza-7-phosphaadamantane)] (RAPTA) compds. It was found that the new compds. show essentially the same order of cytotoxicity as the RAPTA compds. toward cancer cells. Several of the compds. were selective toward cancer cells in that they were less (or not) cytotoxic toward nontumorigenic cells that are used to model healthy human cells. Thus, two of the compds., [Ru(η6-p-cymene)Cl(vinylimid)2][Cl] (vinylimid = N-vinylimidazole) and [Ru(η6-benzene)(mimid)3][BF4]2 (mimid = N-methylimidazole), have been selected for a more detailed in vivo evaluation.

The synthesis and characterization of three new organothallium(I) compounds are reported. Reaction of (Ar‘Li)2 (Ar‘ = C6H3-2,6-(C6H3-2,6-Pri2)2) and Ar‘ ‘Li (Ar‘ ‘ = C6H3-2,6-(C6H3-2,6-Me2)2) with TlCl in Et2O afforded (Ar‘Tl)2 (1) and (Ar‘ ‘Tl)3 (2). The “dithallene” 1 is the heaviest group 13 dimetallene and features a planar, trans-bent structure with Ar‘Tl−Tl = 119.74(14)° and Tl−Tl = 3.0936(8) A. Compound 2 is the first structurally characterized neutral, three-membered ring species of formula c-(MR)3 (M = Al−Tl; R = organo group). The Tl3 ring has Tl−Tl distances in the range ca. 3.21−3.37 A as well as pyramidal Tl geometries. The Tl−Tl bonds in 1 and 2 are outside the range (2.88−2.97 A) of Tl−Tl single bonds in R2TlTlR2 compounds. The weak Tl−Tl bonding in 1 and 2 leads to their dissociation into Ar‘Tl and Ar‘ ‘Tl monomers in hexane. The Ar‘Tl monomer behaves as a Lewis base and readily forms a 1:1 donor−acceptor complex with B(C6F5)3 to give Ar‘TlB(C6F5)3, 3. Adduct 3 features an almost linear th...

Chloro-, bromo-, iodo-, and trifluoromethylsulfonyloxy-(2,4,6-tri-tert-butylphenylimino)phosphines (MesNPX; X = Cl, Br, I, OTf) react quantitatively with 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (Im) to give Lewis acid-base complexes with the general formula MesNP(Im)X. The dichlorophosphetidine (DippNPCl)(2) (Dipp = 2,6-diisopropylphenyl) represents a formal cyclodimer of an iminophosphine and reacts with Im to give a similar complex. The process represents a ligand induced dissociation of the phosphetidine framework and is reversed by the introduction of an appropriate Lewis acid. Solid state structures of RNP(Im)X complexes show that the closest contact between acid and base occurs between phosphorus and carbon in all cases, highlighting them as compounds that contain examples of C-->P coordinate bonds. Association of Im with phosphorus also effects a substantial increase in the P-X distance, but all derivatives maintain a short NP bond, indicating the presence of NP pi-bonding.

The cage-like water-soluble monodentate phosphine 1,3,5-triaza-7-phosphaadamantane (PTA) has received renewed interest in the recent literature due to its properties to solubilize transition metal complexes in aqueous phase. This property has allowed application of Rh, Ru and Pd-PTA complexes in aqueous phase or biphasic homogeneous catalysis, antitumoral tests (Ru- and Pt-PTA) and photoluminescence (Au-PTA). This paper reviews the synthesis and structural properties of PTA and derivatives, their transition metal complexes, catalytic, medicinal and photoluminescence uses.

The reaction of LiPh with Ar*SnPh (Ar* = C 6 H 3 -2,6-Trip 2 ; Trip = C 6 H 2 -2,4,6-Pr i 3) afforded either the monomeric etherate (Et 2 O)LiSnPh 2 Ar* (1) or the dimer (LiSnPh 2 Ar*) 2 (2). The reaction of 2 with SnCl 2 in a 1:1ratio in Et 2 O yielded the monomeric distannylstannylene Sn(SnPh 2 Ar*) 2 (3). The compounds 1-3 were characterized by 1 H, 7 Li, 1 3 C, and 1 1 9 Sn NMR and UV-vis spectroscopy. Complete single-crystal X-ray crystal structures of 2 and 3 were determined as well as a partial structure for 1. The structure of 1 showed that the tin was pyramidally coordinated by the three organic groups as well as by lithium. The lithium was found to be ligated by ether and η 6 -coordinated by one of the phenyl rings. The structure of 2 showed that it was dimerized through η 6 -interactions of a tin-coordinated lithium with a phenyl group of a partner monomer rather than through tin-tin bonding. The structure of 3 featured a central, two-coordinate tin(II) bound to two SnPh 2 Ar* groups with long Sn-Sn distances near 2.96 A and a very wide Sn-Sn-Sn angle of 115.19(2)°. The 1 1 9 Sn NMR chemical shift of the central tin is 3752 ppm, which is the furthest downfield 1 1 9 Sn NMR chemical shift recorded for a stannylene.

The very bulky phenols Ar*OH (1) and Ar′OH (2), where Ar* = C6H3-2,6-Trip2 (Trip = C6H2-2,4,6-iPr3) and Ar′ = C6H3-2,6-Dipp2 (Dipp = C6H3-2,6-iPr2), as well as their lithium and sodium derivatives (LiOAr*)2 (3), (LiOAr′)2 (4) and (NaOAr*)2 (5) have been synthesized and characterized. The terphenols 1 and 2 were obtained by the reaction of the aryllithium reagents with nitrobenzene and were isolated in ca. 70% yield. The lithium or sodium salts 3−5 were isolated by the reaction of 1 or 2 with nBuLi or sodium metal. All compounds were characterized spectroscopically, and by X-ray crystallography in the case of 1, 2, 4 and 5. The large terphenyl substituents prevent hydrogen-bonded association of the phenols 1 and 2. Instead, the O−H hydrogens interact with the π-electron cloud on one of the flanking Trip or Dipp rings. The dimeric structures of 4 and 5 are relatively rare examples of structurally characterized alkali metal phenoxides that are unsolvated by internal electron pair donors or classical Lewis bases such as ethers or amines. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The reduction of terphenylgermanium(II) or terphenyltin(II) chlorides with alkali metals was investigated. Treatment of Ar'GeCl or ArGeCl (Ar' = C(6)H(3)-2,6-Dipp(2), Dipp = C(6)H(3)-2,6-Pr(i)(2); Ar = C(6)H(3)-2,6-Trip(2), Trip = C(6)H(2)-2,4,6-Pr(i)(3)) with lithium, sodium, or potassium afforded the neutral alkyne analogues Ar'GeGeAr', 1, ArGeGeAr, 2, the singly reduced radical species NaArGeGeAr, 3, or KAr'GeGeAr', 4, or the doubly reduced compounds Li(2)Ar'GeGeAr', 5, Na(2)ArGeGeAr, 6, or K(2)ArGeGeAr, 7. Similarly, reduction of Ar'SnCl or ArSnCl afforded the neutral Ar'SnSnAr', 8, or ArSnSnAr, 9, the radical anions [(THF)(3)Na[rSnSnAr]], 10, [K(THF)(6)][Ar'SnSnAr'], 11, [K(THF)(6)][ArSnSnAr], 12, [K(18-crown-6)(THF)(2)] [ArSnSnAr], 13, or the doubly reduced Na(2)ArSnSnAr, 14, K(2)Ar'SnSnAr', 15, or K(2)ArSnSnAr, 16. The compounds were characterized by UV-vis, (1)H and (13)C NMR or EPR spectroscopy. The X-ray crystal structures of all compounds were determined except those of 2 and 9. The neutral 1 and 8 displayed planar, trans-bent CMMC (M = Ge and Sn) cores with M-M-C angles of 128.67(8) and 125.24(7) degrees, respectively. The M-M bond lengths, 2.2850(6) and 2.6675(4)A, indicated considerable multiple character and a bond order approaching two. Single and double reduction of the neutral species resulted in the narrowing of the M-M-C angles by ca. 12-32 degrees and changes in the Ge-Ge and Sn-Sn bond lengths. One-electron reduction afforded a slight (ca. 0.03-0.05A) lengthening of the Ge-Ge bonds in the case of germanium species 3 and 4 and a greater lengthening (ca. 0.13-0.15A) for the Sn-Sn bonds in the tin compounds 10-13. The addition of another electron yielded salts of the formal dianions [Ar'MMAr'](2)(-) and [ArMMAr](2)(-) which are isoelectronic to the corresponding doubly bonded, neutral arsenic and antimony derivatives. All the dianion salts were obtained as contact ion triples with two alkali metal cations complexed between aryl rings. The Ge-Ge bonds in the dianions of 5-7 were longer, whereas the Sn-Sn distances in the dianions in 14, 15, and 16 were shorter than those in the monoanions. Unusually, the Li(2)Ar'GeGeAr' salt, 5, displayed a longer Ge-Ge bond (by ca. 0.06A) than those of its Na(+) or K(+) analogue salts which was attributed to the greater polarizing power of Li(+). It was concluded that the M-M bond lengths in 3-7 and 10-16 are dependent on several factors that include M-M-C angle, Coulombic repulsion, alkali metal cation size, and the character of the molecular energy levels. The M-M bonding in the neutral compounds was accounted for in terms of a second-order Jahn-Teller mixing of sigma- and a pi-orbital which afforded bond orders near two for the neutral compounds, 1, 2, 8, and 9. Calculations on MeMMMe (M = Ge or Sn) model species showed that the LUMO corresponded to an orbital that had n(+) lone pair character. The slight Ge-Ge bond length increase upon one-electron reduction is consistent with these results, and the further bond lengthening upon double reduction is consistent with increased Coulombic repulsion. The greater Sn-Sn bond length increase seen for one-electron reduction of the tin species is probably due to the increased p-character of orbitals comprising the Sn-Sn sigma-bond when the Sn-Sn-C angle is decreased by ca. 30 degrees. Upon further reduction, the slight decrease in the Sn-Sn bond is probably a result of the reduced importance of Coulombic repulsion due to the larger size of tin and a widening of the Sn-Sn-C angles which may shorten the Sn-Sn sigma-bond.

The synthesis, structure, and properties of several new organogallium(I) compounds are reported. The monovalent compounds GaAr* (Ar* = C(6)H(3)-2,6-Trip(2), Trip = C(6)H(2)-2,4,6-Pr(i)()(3), 1), GaAr# (Ar# = C(6)H(3)-2,6(Bu(t)Dipp)(2), Bu(t)Dipp = C(6)H(2)-2,6-Pr(i)(2)-4-Bu(t)(), 4), and the dimeric (GaAr')(2) (Ar' = C(6)H(3)-2,6-Dipp(2), Dipp = C(6)H(3)-2,6-Pr(i)(2), 6) were synthesized by the reaction of "GaI" with (Et(2)O)LiAr*, (Et(2)O)LiAr# (3), or (LiAr')(2). Compounds 1 and 4 were isolated as green crystals, whereas 6 was obtained as a brown-red crystalline solid. All three compounds dissolved in hydrocarbon solvents to give green solutions and almost identical UV/visible spectra. Cryoscopy of 1 and 6 showed that they were monomeric in cyclohexane. Crystals of 1 and 4 were unsuitable for X-ray crystal structure determinations, but an X-ray data set for 6 showed that it was weakly dimerized in the solid with a long Ga-Ga bond of 2.6268(7) A and a trans-bent CGaGaC core array. The 1,2-diiodo-1,2-diaryldigallane compounds [Ga(Ar*)I](2) (2), [Ga(Ar#)I](2) (5), and [Ga(Ar')I](2) (7) were isolated as byproducts of the synthesis of 1, 4, and 6. The crystal structures of 2 and 7 showed that they had planar ICGaGaCI core arrays with Ga-Ga distances near 2.49 A, consistent with Ga-Ga single bonding. Treatment of 1, 4, and 6 with B(C(6)F(5))(3) immediately afforded the 1:1 donor-acceptor complexes ArGa[B(C(6)F(5))(3)] (Ar = Ar*, 8; Ar#, 9; Ar', 10) that featured almost linear gallium coordination, Ga-B distances near the sum of the covalent radii of gallium and boron, as well as some close Ga...F contacts. Compound 1 also reacted with Fe(CO)(5) under ambient conditions to give Ar*GaFe(CO)(4) (11), which had been previously synthesized by the reaction of GaAr*Cl(2) with Na(2)Fe(CO)(4). Reaction of 1 with 2,3-dimethyl-1,3-butadiene afforded the compound [Ar*GaCH(2)C(Me)C(Me)CH(2)]2 (12) that had a 10-membered 1,5-Ga(2)C(8) ring with no Ga-Ga interaction. Stirring 1 or 6 with sodium readily gave Na(2)[Ar*GaGaAr*] (13) and Na(2)(Ar'GaGaAr') (14). The former species 13 had been synthesized previously by reduction of GaAr*Cl(2) with sodium and was described as having a Ga-Ga triple bond because of the short Ga-Ga distance and the electronic relationship between [Ar*GaGaAr*](2-) and the corresponding neutral group 14 alkyne analogues. Compound 14 has a similar structure featuring a trans-bent CGaGaC core, bridged by sodiums which were also coordinated to the flanking aryl rings of the Ar' ligands. The Ga-Ga bond length was found to be 2.347(1) A, which is slightly (ca. 0.02 A) longer than that reported for 13. Reaction of Ga[N(Dipp)C(Me)](2)CH, 15 (i.e., GaN(wedge)NDipp(2)), which is sterically related to 1, 4, and 6, with Fe(CO)(5) yielded Dipp(2)N(wedge)NGaFe(CO)(4) (16), whose Ga-Fe bond is slightly longer than that observed in 11. Reaction of the less bulky LiAr"(Ar"= C(6)H(3)-2,6-Mes(2)) with "GaI" afforded the new paramagnetic cluster Ga(11)Ar(4)" (17). The ready dissociation of 1, 4, and 6 in solution, the long Ga-Ga distance in 6, and the chemistry of these compounds showed that the Ga-Ga bonds are significantly weaker than single bonds. The reduction of 1 and 6 with sodium to give 13 and 14 supplies two electrons to the di-gallium unit to generate a single bond (in addition to the weak interaction in the neutral precursor) with retention of the trans-bent geometry. It was concluded that the stability of 13 and 14 depends on the matching size of the sodium ion, and the presence of Na-Ga and Na-Ar interactions that stabilize their Na(2)Ga(2) core structures.

Various stoichiometric combinations of PCl3 with DippNH2 (Dipp = 2,6-di-isopropylphenyl) have been examined using 31P NMR spectroscopy. The dehydrochloride coupling reaction is mediated by the moderate steric bulk of the Dipp substituent. Isolation procedures and characterization data are reported for the aminodichlorophosphine (1), the aminotetrachlorodiphosphine (4), and the dichlorophosphetidine (7). The observations offer new appreciation of dehydrochloride coupling products of halophosphines with primary amines.Key words: phosphorus, nitrogen, phosphazanes, phosphetidines, iminophosphine.

Computational data for the tetragallium clusters K2Ga4(C6H3-2,6-Trip2)2 and Na2Ga4Trip6 (Trip=C6H2-2,4,6-i-Pr3) showed that significant Ga–Ga multiple bonding exists only in the latter species. The data for the M2Ga4R2 (M=Li, Na or K; R=H, Me or Ph) models of K2Ga4(C6H3-2,6-Trip2)2, which has a distorted octahedral K2Ga4 core structure incorporating an almost square Ga4 moiety, showed that they have an occupied bonding π-orbital that is delocalized over the four galliums, thereby conferring formal aromatic character by the [4n+2] Huckel rule. However, the Ga–Ga bond order is approximately one, and the hypothetical free [Ga4H2]2− dianion is unstable toward electron dissociation. For the cluster Na2Ga4Trip6, calculations for the model compounds Ga4H6 and [Ga4H6]2−, which involve a central gallium trigonally substituted by three GaH2 units, confirmed that no multiple bonding exists in the neutral species Ga4H6 but that, upon reduction to [Ga4H6]2−, a π-bond is formed which is delocalized over the Ga4 unit. The Ga–Ga distances that were calculated for all model species listed above are longer than those experimentally observed. This was attributed to the absence of alkali metal-aryl interactions in the model species.

Density functional theory (DFT) has been applied to study potential ammonia borane (AB) dehydrogenation pathways via new bifunctional ruthenium-based catalysts, alongside their computationally-designed iron-based counterparts (i.e., four catalysts), using the wB97XD (dispersion-included) functional. The efficiency of each catalyst was under scrutiny based on the addition of ammonia borane, with a focus on the associated activation-energy barriers, whilst hydrogen release from the catalyst was also studied in detail. Here, natural-population analysis charges were key quantities of interest. It was found that the iron-based catalysts display more promising dehydrogenation energy barriers vis

This article covers the progress of β-diketiminates as supporting ligands in transition metal complexes from the seminal review published by Lappert et al. in 2002 to the middle of 2013.1 Due to the tremendous number of reports since 2002 involving this class of ligand, this review focuses on the early transition metals, with elements from groups 3 to 5. β-diketiminate ligands are sterically demanding and thus stabilise highly reactive metal environments engendering both low-coordinate and multiply-bonded motifs. Recent publications also demonstrate the utility of this ligand class to build early transition catalysts with unique and interesting reactivity.

Spectroscopic and structural features are presented for the first homologous series of diazadipnictetidines, which have the general formula [DipNPnN(H)Dip]2 (Pn = P, As, Sb, Bi; Dip = 2,6-diisopropylphenyl). The compounds are obtained from a general reaction of the corresponding halopnictine with excess LiN(H)Dip, which was previously reported for [DipNBiN(H)Dip]2. However, isolation is improved by the introduction of LiN(H)-t-Bu (at the appropriate stoichiometry) following the addition of LiN(H)Dip. The intermediate steric presence of the Dip substituent is suitable to support the heterocatenate framework for all homologues. This is in contrast to the small substituents (e.g. alkyl), which enable both bis- and tris-amination, and the larger substituent (Mes* = tri-tert-butylphenyl), which can impose coordinative unsaturation (aminoiminopnictine) for the smaller congeners (P and As).Key words: phosphorus, arsenic, antimony, bismuth, phosphazanes, phosphetidines, synthesis, structures, spectroscopic characterization.

Formation of a vacant coordination site on a Ru center permits an unusual binding of small molecules such as ethylene, acetylene, and dihydrogen, resulting in the transformation of the chelating β-diketiminate ligand to a β-diimine. These representative species are observed during the catalytic hydrogenation of styrene.

The solid-state structural analysis of the title compound, Me4C2N2C--B(C6F5)3 or C25H12BF15N2, provides useful metric parameters for the qualitative comparison of the donor strength with other mono- and dicoordinate main-group compounds which feature distinctive lone-pair character.

Electronic-structure density functional theory calculations have been performed to construct the potential energy surface for H2 release from ammonia-borane, with a novel bifunctional cationic ruthenium catalyst based on the sterically bulky β-diketiminato ligand (Schreiber et al., ACS Catal. 2012, 2, 2505). The focus is on identifying both a suitable substitution pattern for ammonia-borane optimized for chemical hydrogen storage and allowing for low-energy dehydrogenation. The interaction of ammonia-borane, and related substituted ammonia-boranes, with a bifunctional η6-arene ruthenium catalyst and associated variants is investigated for dehydrogenation. Interestingly, in a number of cases, hydride-proton transfer from the substituted ammonia-borane to the catalyst undergoes a barrier-less process in the gas phase, with rapid formation of hydrogenated catalyst in the gas phase. Amongst the catalysts considered, N,N-difluoro ammonia-borane and N-phenyl ammonia-borane systems resulted in negative activation energy barriers. However, these types of ammonia-boranes are inherently thermodynamically unstable and undergo barrierless decay in the gas phase. Apart from N,N-difluoro ammonia-borane, the interaction between different types of catalyst and ammonia borane was modeled in the solvent phase, revealing free-energy barriers slightly higher than those in the gas phase. Amongst the various potential candidate Ru-complexes screened, few are found to differ in terms of efficiency for the dehydrogenation (rate-limiting) step. To model dehydrogenation more accurately, a selection of explicit protic solvent molecules was considered, with the goal of lowering energy barriers for H-H recombination. It was found that primary (1°), 2°, and 3° alcohols are the most suitable to enhance reaction rate. © 2014 Wiley Periodicals, Inc. Science Foundation Ireland Author has checked copyright

The crystal structure of Cl3Al–O–PCl3 contains covalent molecular units with an essentially linear Al–O–P axis, and a similar solution structure is indicated by NMR spectroscopy.

Polynuclear compounds are a relatively new and successful approach in metal-based cancer chemotherapy as typified by the trinuclear Pt compound BBR3464 which was evaluated in clinical trials. In this review, we discuss newer developments of polynuclear ruthenium, osmium and gold complexes, focusing on their anticancer activity. The compounds presented are often supposed to exert their anticancer activity by different modes of action as compared to established drugs, including newly proposed mechanisms such as enzyme inhibition, crosslinking of biomacromolecules or through photo-activation, though many of the examples are also capable of binding to DNA nucleobases. Important metabolization and chemical characteristics of such compounds are discussed, and if the appropriate data is available, molecular modes of action are highlighted.

A series of compounds of the general formula [M(eta6-arene)(ptn)Cl]X (M = Ru, Os; arene = p-cymene, benzene, toluene, hexamethylbenzene; ptn = 3,7-dimethyl-7-phospha-1,3,5-triazabicyclo[3.3.1]nonane; X = Cl-, BF4-) have been prepared and characterized spectroscopically. X-ray diffraction was additionally used to characterize four of the complexes in the solid state. The hydrolysis of the compounds was studied, and their cytotoxicity was evaluated in A2780 ovarian cancer cells and found to be comparable to that of known RAPTA complexes based on 7-phospha-1,3,5-triazatricyclo[3.3.1.1]decane (pta). The reactivity of the complexes toward double-stranded oligonucleotides and the model protein ubiquitin was investigated using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and gel electrophoresis, demonstrating a strong preference for the formation of covalent adducts with the protein. Correlations among compound structure, hydrolysis, biomolecular interactions, and cytotoxicity are established.

Organometallic ruthenium(II) complexes of the general formula [Ru(η6-p-cymene)Cl2(L)] and [Ru(η6-p-cymene)Cl(L)2][BPh4] with modified phenoxazine- and anthracene-based multidrug resistance (MDR) modulator ligands (L) have been synthesized, spectroscopically characterized, and evaluated in vitro for their cytotoxic and MDR reverting properties in comparison with the free ligands. For an anthracene-based ligand, coordination to a ruthenium(II) arene fragment led to significant improvement of cytotoxicity as well as Pgp inhibition activity. A similar, but weaker effect was also observed when using a benzimidazole-phenoxazine derivative as Pgp inhibitor. The most active compound in terms of both Pgp inhibition and cytotoxicity is [Ru(η6-p-cymene)Cl2(L)], where L is an anthracene-based ligand. Studies show that it induces cell death via inhibition of DNA synthesis. Moreover, because the complex is fluorescent, its uptake in cells was studied, and relative to the free anthracene-based ligand, uptake of the complex is accelerated and accumulation of the complex in the cell nucleus is observed.

A DFT study using a "discrete-continuum" modeling of the reaction medium, employed to unravel the role of water in the activation of dihydrogen by [CpRu(PTA)2Cl] (PTA ) 1,3,5-triaza-7-phosphaadamantane), has revealed that the solvent takes an active part in lowering the energy barriers of the overall heterolytic splitting of the H-H bond. PTA itself promotes the heterolytic activation of the Ru(eta2-H2) bond through one of its nitrogen atoms via a solvent-mediated intramolecular proton transfer