Javier A. Cabeza

The N-heterocyclic carbene chemistry of transition-metal carbonyl clusters.

In the last decade, chemists have dedicated many efforts to investigate the coordination chemistry of N-heterocyclic carbenes (NHCs). Although most of that research activity has been devoted to mononuclear complexes, transition-metal carbonyl clusters have not escaped from these investigations. This critical review, which is focussed on the reactivity of NHCs (or their precursors) with transition-metal carbonyl clusters (mostly are of ruthenium and osmium) and on the transformations underwent by the NHC-containing species initially formed in those reactions, shows that the polynuclear character of these metallic compounds or, more precisely, the close proximity of one or more metal atoms to that which is or can be attached to the NHC ligand, is responsible for reactivity patterns that have no parallel in the NHC chemistry of mononuclear complexes (74 references).

From an N-methyl N-heterocyclic carbene to carbyne and carbide ligands via multiple C-H and C-N bond activations.

Ruthenium complexes containing N-heterocyclic carbene (NHC) ligands, and particularly 1,3-disubstituted imidazol2-ylidenes, are among the most active catalysts for important organic reactions, such as olefin metathesis and various C C bond-forming processes. However, recent reports have shown that the N–R arms of some NHC–ruthenium complexes may be involved in intramolecular C H, C C, and/or C N bond-activation reactions. Some NHC ligand degradation processes have important implications in catalyst activation or deactivation. In fact, a ruthenium complex with an N-alkyl-metalated NHC ligand has been shown to be a more efficient catalyst than the nonmetalated precursor for a tandem oxidation/Wittig/reduction reaction that gives C C bonds from alcohols. On the contrary, the deactivation of the second and third generations of Grubbs alkene metathesis catalysts occurs through intramolecular C H bond-activation processes. Therefore, the design of new NHC–ruthenium complexes, the study of their thermal intramolecular transformations, and the understanding of the factors that control such processes are currently relevant themes of research. The interest in combining ruthenium complexes with NHC ligands and the absence of reports describing the reactivity of triruthenium clusters with NHCs led us to study the reactivity of [Ru3(CO)12] with NHCs. [10] We previously reported the synthesis of the trinuclear derivative [Ru3(Me2Im)(CO)11] (1; Me2Im= 1,3-dimethylimidazol-2-ylidene) and its transformation into [Ru3(m-H)2(MeImCH)(CO)9] (2) through a process that involves the unusual reversible cleavage of two C Hbonds of anN-methyl group (Scheme 1). We have now discovered that an N-methyl group of Me2Im can not only be transformed into a bridging methylene group (complex 2), but also into bridging carbyne and carbide ligands. The thermolysis of compound 2 in toluene at reflux temperature led to an approximately 1:1 mixture of [Ru6(m3H)(m5-MeImC)(m3-MeImCH)(m-CO)2(CO)13] (3) and [Ru5(m5-C)(m-H)(m-MeIm)(Me2Im)(CO)13] (4), which were separated by chromatographic methods (Scheme 2).

Mononuclear η6-p-cymeneosmium(II) complexes and their reactions with Al2Me6 and other methylating reagents

An improved-yield synthesis of the η6-p-cymeneosmium(II) chloride complex [(p-MeC6H4CHMe2)2Os2Cl4](1) has allowed the development of the chemistry of the mononuclear complexes, [(p-MeC6H4CHMe2)OsLCl2](2)[L = CO, CNCMe3, Me2SO, PMe3, PPh3, or P(OPh)3]. These gave [(p-MeC6H4CHMe2)OsL(Me)Cl](3)(L = CO, CNCMe3, Me2SO, or PMe3) with Al2Me6. Reaction of [(p-MeC6H4CHMe2)Os(Me2SO)(Me)Cl] with L′[PPh3 or P(OPh)3] gave the complex [(p-MeC6H4CHMe2)OsL′(Me)Cl]. Al2Me6 reacted with [(p-MeC6H4CHMe2)OsL′Cl2] to give chiefly the ortho-metallated complexes [(p-MeC6H4CHMe2)Os{PPh2(o-C6H4)}X](5)(X = Cl), (6)(X = Me), and [(p-MeC6H4CHMe2)Os{P(OPh)(OC6H4-o)2}](8); however, the triphenylphosphine complex also gave the mono- and the di-methyl complexes [(p-MeC6H4CHMe2)Os(PPh3)(Me)X](X = Cl or Me). The complexes have been characterised by their i.r., 1H, 13C, and 31P n.m.r. spectra and their e.i. mass spectra. The p-cymene ring remains η6-bonded throughout these reactions and appears quite difficult to displace.

A Simple Preparation of Pyridine‐Derived N‐Heterocyclic Carbenes and Their Transformation into Bridging Ligands by Orthometalation

Cat-ionic nickel(II) or palladium(II) complexes that have beenprepared in the laboratories of Raubenheimer, Herrmann, orFrenking by oxidative addition (or oxidative substitution) ofthe C X(X=halogen) bond of N-alkyl (or N-aryl) halopyr-idinium (or haloquinolinium, haloacridinium, etc.) salts toappropriate metal(0) precursors.

Triruthenium and triosmium carbonyl clusters containing chiral bidentate NHC-thiolate ligands derived from levamisole

The trinuclear complexes [M3(mu-Cl)(mu-S approximately CH)(CO)9] (M=Ru, Os; S approximately CH=1-ethylenethiolate-3-H-4-(S)-phenylimidazolin-2-ylidene) and [M3(mu-H)(mu-S approximately CMe)(CO)9] (M=Ru, Os; S approximately CMe=1-ethylenethiolate-3-methyl-4-(S)-phenylimidazolin-2-ylidene) have been prepared by treating [Ru3(CO)12] and [Os3(CO)10(MeCN)2] with levamisolium chloride or [M3(mu-H)(CO)11]- with methyl levamisolium triflate, respectively. The chiral N-heterocyclic carbene-thiolate ligands S approximately CH and S approximately CMe arise from the oxidative addition of the C-S bond of levamisolium or methyl levamisolium cations to anionic trinuclear clusters.

The different reactivity of 2-aminopyridines and 2-pyridone with [Ru3(CO)12]. X-Ray crystal structure of [Ru3(µ-H)(µ3-anpy)(CO)9](hanpy = 2-anilinopyridine)

The complex [Ru3(CO)12] reacts with 2-aminopyridines [2-aminopyridine, 2-amino-4-methylpyridine, -5-methylpyridine, and -6-methylpyridine, 2-(methylamino)pyridine, and 2-anilinopyridine] to give hydrido trinuclear clusters of the type [Ru3(µ-H)(µ3-L)(CO)9](1)–(6)(L = a 2-aminopyridinate-type ligand). Although the presence of substituents on the pyridine ring or on the aminic nitrogen has no influence on the reactivity of the ligands towards [Ru3(CO)12], it affects the fluxionality of the complexes they form. The solid-state structure of [Ru3(µ-H)(µ3-anpy)(CO)9](6)(Hanpy = 2-anilinopyridine) has been determined by X-ray diffraction methods: monoclinic, space group P21/n, Z= 4, a= 12.705(1), b= 10.621 (2), c= 18.427(2)A, and β= 107.349(7)°. The structure was solved by direct and Fourier methods and refined by full-matrix least squares to R= 0.019, R′= 0.021, for 3 621 observed reflections. The reaction of [Ru3(CO)12] with 2-(dimethylamino)pyridine (dmapy) gives [Ru3(µ-dmapy)(µ-CO)3(CO)7]. However, with 2-pyridone (HOpy) the polymer [{Ru2(µ-Opy)2(CO)4}n](8) or the dimer [Ru2(µ-Opy)2(CO)4(HOpy)2](13) are formed depending on the ratio of the reactants. The reactivity of the polymer (8) with neutral ligands to give the binuclear ruthenium(I) dimers [Ru2(µ-Opy)2(CO)4L2][L = CO, (9); MeCN, (10); PPh3, (11); P(OPh)3, (12); or HOpy, (13)] is also reported.

The reactions of [Ru3(CO)12] with nitrogen-containing heterocycles. Crystal structures of [Ru3(µ-H)(µ3-ppy)(CO)9] and [Ru3(µ-napy)(µ-CO)3(CO)7]

The reactions of [Ru3(CO)12] with several nitrogen-containing heterocycles under thermal conditions have been studied. 1H-Pyrrolo[2,3,-b]pyridine (Hppy) and benzimidazole (Hbzim) give the trinuclear clusters [Ru3(µ-H)(µ3-ppy)(CO)9](1a) and [Ru3(µ-H)(µ-bzim)(CO)10](2a), respectively. However, benzotriazole (Hbztz) affords the dinuclear complex [Ru2(µ-bztz)2(CO)6](3a). 1,8-Naphthyridine(napy) produces the carbonyl-bridged cluster [Ru3(µ-napy)(µ-CO)3(CO)7](4). Complex (4) reacts with HBF4 to give the cationic complex [Ru3(µ-H)(µ-napy)(CO)10][BF4](5) which has all terminal carbonyls. Complex (5) regenerates complex (4) on reaction with NEt3, 1,10-Phenanthroline(phen),2,2′-biquinoline(biquin) or 2,2′-bipyrimidine (bipym) react with [Ru3(CO)12] to give [Ru3(L–L)(µ-CO)2(CO)8][L–L = phen (6a), biquin (6b), or bipym (6c)], in which the L–L ligand chelates one ruthenium, and two carbonyl groups bridge the same edge of the tringle. The structures of compounds (1a) and (4) have been established by X-ray diffraction studies. Complex (1a) crystallizes in the monoclinic space group P21/a with a= 14.688(5), b= 16.251(7), c= 8.594(5)A, β= 97.64(2)°, and Z= 4. Crystals of (4) are monoclinic, space group P21/c with a= 15.374(7), b= 17.336(6), c= 16.167(7)A, β= 98.02(3)°, and Z= 8. Both structures were solved from diffractometer data by direct and Fouier methods and refined by full-matrix [(1a)] and block-matrix [(4)] least-squares to R= 0.0349 for 3 211 observed reflections for (1a) and to R= 0.0405 for 4 205 observed reflections for (4). In (1a) the pyrrolopyridinate ligand is co-ordinated to three Ru atoms, through the pyridinic N atom to one metal and through the pyrrolic N atom symmetrically bridging the other two, which are involved also in a hydridic bridge. In (4) there are two independent, but very similar, complexes in which three carbonyls bridge the three edges of a triangular metal array; the 1,8-naphthyridine ligand bridges two metal atoms through the two N atoms.

Diaminogermylene and diaminostannylene derivatives of gold(I): novel AuM and AuM2 (M = Ge, Sn) complexes.

The reactions of [AuCl(THT)] (THT = tetrahydrothiophene) with 1 equiv of the group 14 diaminometalenes M(HMDS)(2) [M = Ge, Sn; HMDS = N(SiMe(3))(2)] lead to [Au{MCl(HMDS)(2)}(THT)] [M = Ge (1), Sn (2)], which contain a metalate(II) ligand that arises from insertion of the corresponding M(HMDS)(2) reagent into the Au-Cl bond of the gold(I) reagent. While compound 1 reacts with more Ge(HMDS)(2) to give the germanate-germylene derivative [Au{GeCl(HMDS)(2)}{Ge(HMDS)(2)}] (3), which results from substitution of Ge(HMDS)(2) for the THT ligand of 1, an analogous treatment of compound 2 with Sn(HMDS)(2) gives the stannate-stannylene derivative [Au{SnCl(HMDS)(2)}{Sn(HMDS)(2)(THT)}] (4), which has a THT ligand attached to the stannylene tin atom and which, in solution at room temperature, participates in a dynamic process that makes its two Sn(HMDS)(2) fragments equivalent (on the NMR time scale). A similar dynamic process has not been observed for the AuGe(2) compound 3 or for the AuSn(2) derivatives [Au{SnR(HMDS)(2)}{Sn(HMDS)(2)(THT)}] [R = Bu (5), HMDS (6)], which have been prepared by treating complex 4 with LiR. The structures of compounds 1 and 3-6 have been determined by X-ray diffraction.

The Important Role of Some Ancillary Ligands in the Chemistry of Carbonylmetal Cluster Complexes − Selected Reactivity of Triruthenium Clusters Containing Deprotonated 2‐Aminopyridines

The presence of deprotonated 2-aminopyridines (apy ligands) as face-capping ancillary ligands in carbonyltriruthenium cluster complexes facilitates their reactivity (mild reaction conditions) and increases the regioselectivity of their reactions. This is probably due to the hemilabile character of the apy ligands that help maintain the cluster nuclearity and also provides reaction pathways of low activation energy. Thus, the presence of apy ligands in triruthenium cluster complexes of the type [Ru3(µ-H)(µ3-apy)(CO)9] has allowed an extensive and regioselective derivative chemistry that is surveyed in this review. A comparative study of the reactivity

Ruthenium(I) complexes containing bridging N-donor ligands: structure, synthesis and reactivity patterns

Abstract The article reviews the chemistry of binuclear ruthenium(I) complexes containing bridging N-donor ligands. The introduction is followed by a survey of compounds, which is classified in alphabetical order according to the type of organic molecule that gives rise to each particular bridging ligand (amides, diamines, imidazoles, oximes, pyrazoles, pyridines, thiazoles, triazenes, triazoles), and covers the literature published up to the end of 1992. The article finishes with some comments on structural, synthetic and reactivity aspects of this class of compound.