Stoichiometric and catalytic reactivity of the N-heterocyclic carbene ruthenium hydride complexes [Ru(NHC)(L)(CO)HCl] and [Ru(NHC)(L)(CO)H(eta2-BH4)] (L=NHC, PPh3)

Thermolysis of [Ru(AsPh3)3(CO)H2] with the N-aryl heterocyclic carbenes (NHCs) IMes (1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), IPr (1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) or the adduct SIPr.(C6F5)H (SIPr=1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene), followed by addition of CH2Cl2, affords the coordinatively unsaturated ruthenium hydride chloride complexes [Ru(NHC)2(CO)HCl] (NHC=IMes , IPr , SIPr ). These react with CO at room temperature to yield the corresponding 18-electron dicarbonyl complexes . Reduction of and [Ru(IMes)(PPh3)(CO)HCl] () with NaBH4 yields the isolable borohydride complexes [Ru(NHC)(L)(CO)H(eta2-BH4)] (, L=NHC, PPh3). Both the bis-IMes complex and the IMes-PPh3 species react with CO at low temperature to give the eta1-borohydride species [Ru(IMes)(L)(CO)2H(eta1-BH4)] (L=IMes , PPh3), which can be spectroscopically characterised. Upon warming to room temperature, further reaction with CO takes place to afford initially [Ru(IMes)(L)(CO)2H2] (L=IMes, L=PPh3) and, ultimately, [Ru(IMes)(L)(CO)3] (L=IMes , L=PPh3). Both and lose BH3 on addition of PMe2Ph to give [Ru(IMes)(L)(L')(CO)H2](L=L'=PMe2Ph; L=PPh3, L'=PMe2Ph). Compounds and have been tested as catalysts for the hydrogenation of aromatic ketones in the presence of (i)PrOH and H2. For the reduction of acetophenone, catalytic activity varies with the NHC present, decreasing in the order IPr>IMes>SIMes.     

Activation of two C-H bonds of NHC N-methyl groups on triosmium and triruthenium carbonyl clusters

The thermolysis of the NHC triosmium cluster [Os3(Me2Im)(CO)11] (1a; Me2Im = 1,3-dimethylimidazol-2-ylidene) in toluene at reflux temperature sequentially affords the edge-bridged cluster [Os3(micro-H)(micro-kappa2-MeImCH2)(CO)10] () and the face-capped derivative [Os3(micro-H)2(micro3-kappa2-MeImCH)(CO)9] (3a). These products result from the sequential oxidative addition of one (2a) and two (3a) N-methyl C-H bonds of the original NHC ligand. The related face-capped triruthenium cluster [Ru3(micro-H)2(micro3-kappa2-MeImCH)(CO)9] (3b) has been prepared by heating the NHC triruthenium cluster [Ru3(Me2Im)(CO)11] (1b) in THF at reflux temperature. In this case, the pentanuclear derivatives [Ru5(Me2Im)(micro4-kappa2-CO)(CO)14] (4b) and [Ru5(Me2Im)2(micro4-kappa2-CO)(CO)13] (5b) are minor reaction products, but a ruthenium cluster analogous to has not been obtained. The face-capped oxazole-derived NHC triruthenium cluster [Ru3(micro-H)2(micro3-kappa2-OxCH)(CO)9] (3c; MeOx = N-methyloxazol-2-ylidene) is the only isolated product of the thermolysis of [Ru3(MeOx)(CO)11] (1c) in THF at reflux temperature.     

Dithiocarboxylate complexes of ruthenium(II) and osmium(II)

The ruthenium(II) complexes [Ru(R)(κ(2)-S(2)C·IPr)(CO)(PPh(3))(2)](+) (R = CH=CHBu(t), CH=CHC(6)H(4)Me-4, C(C≡CPh)=CHPh) are formed on reaction of IPr·CS(2) with [Ru(R)Cl(CO)(BTD)(PPh(3))(2)] (BTD = 2,1,3-benzothiadiazole) or [Ru(C(C≡CPh)=CHPh)Cl(CO)(PPh(3))(2)] in the presence of ammonium hexafluorophosphate. Similarly, the complexes [Ru(CH=CHC(6)H(4)Me-4)(κ(2)-S(2)C·ICy)(CO)(PPh(3))(2)](+) and [Ru(C(C≡CPh)=CHPh)(κ(2)-S(2)C·ICy)(CO)(PPh(3))(2)](+) are formed in the same manner when ICy·CS(2) is employed. The ligand IMes·CS(2) reacts with [Ru(R)Cl(CO)(BTD)(PPh(3))(2)] to form the compounds [Ru(R)(κ(2)-S(2)C·IMes)(CO)(PPh(3))(2)](+) (R = CH=CHBu(t), CH=CHC(6)H(4)Me-4, C(C≡CPh)=CHPh). Two osmium analogues, [Os(CH=CHC(6)H(4)Me-4)(κ(2)-S(2)C·IMes)(CO)(PPh(3))(2)](+) and [Os(C(C≡CPh)=CHPh)(κ(2)-S(2)C·IMes)(CO)(PPh(3))(2)](+) were also prepared. When the more bulky diisopropylphenyl derivative IDip·CS(2) is used, an unusual product, [Ru(κ(2)-SC(H)S(CH=CHC(6)H(4)Me-4)·IDip)Cl(CO)(PPh(3))(2)](+), with a migrated vinyl group, is obtained. Over extended reaction times, [Ru(CH=CHC(6)H(4)Me-4)Cl(BTD)(CO)(PPh(3))(2)] also reacts with IMes·CS(2) and NH(4)PF(6) to yield the analogous product [Ru{κ(2)-SC(H)S(CH=CHC(6)H(4)Me-4)·IMes}Cl(CO)(PPh(3))(2)](+)via the intermediate [Ru(CH=CHC(6)H(4)Me-4)(κ(2)-S(2)C·IMes)(CO)(PPh(3))(2)](+). Structural studies are reported for [Ru(CH=CHC(6)H(4)Me-4)(κ(2)-S(2)C·IPr)(CO)(PPh(3))(2)]PF(6) and [Ru(C(C≡CPh)=CHPh)(κ(2)-S(2)C·ICy)(CO)(PPh(3))(2)]PF(6).     

Isolation of N-Heterocyclic Carbene-Stabilized Phosphorus and Arsenic Mononitride

Phosphorus mononitride (PN) and arsenic mononitride (AsN) species supported by two different N-heterocyclic carbenes were prepared: The reaction of [(IDipp)NSiMe₃] [IDipp = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene] with PCl₃ or AsCl₃ afforded the dichlorides [(IDipp)NECl₂] (E = P, As) and, after the addition of IMes [IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene], the cationic chloro species [(IDipp)NE(Cl)(IMes)]Cl (E = P, As), which were reduced with potassium graphite (KC₈) to yield the neutral compounds [(IMes)PN(IDipp)] and [(IMes)AsN(IDipp)], which exhibit the typical trans-bent geometry of dicarbene-dielement species in the solid state according to single-crystal X-ray diffraction.     

Reactivity of diaminogermylenes with ruthenium carbonyl: Ru3Ge3 and RuGe2 derivatives

The nature of the products of the reactions of [Ru(3)(CO)(12)] with diaminogermylenes depends upon the volume and the cyclic or acyclic structure of the latter. Thus, the triruthenium cluster [Ru(3){μ-Ge(NCH(2)CMe(3))(2)C(6)H(4)}(3)(CO)(9)], which has a planar Ru(3)Ge(3) core and an overall C(3h) symmetry, has been prepared in quantitative yield by treating [Ru(3)(CO)(12)] with an excess of the cyclic 1,3-bis(neo-pentyl)-2-germabenzimidazol-2-ylidene in toluene at 100 °C, but under analogous reaction conditions, the acyclic and bulkier Ge(HMDS)(2) (HMDS = N(SiMe(3))(2)) quantitatively leads to the mononuclear ruthenium(0) derivative [Ru{Ge(HMDS)(2)}(2)(CO)(3)]. Mixtures of products have been obtained from the reactions of [Ru(3)(CO)(12)] with the cyclic and very bulky 1,3-bis(tert-butyl)-2-germaimidazol-2-ylidene under various reaction conditions. The Ru(3)Ge(3) and RuGe(2) products reported in this paper are the first ruthenium complexes containing diaminogermylene ligands.     

Structure, reactivity, and computational studies of a novel ruthenium hydrogen sulfide dihydride complex

Addition of 1 atm of H(2)S to [Ru(IMes)(2)(CO)(EtOH)H(2)] (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) affords the air-stable hydrogen sulfide dihydride complex, [Ru(IMes)(2)(CO)(H(2)S)H(2)] 2. Treatment of 2 with excess H(2)S leads to formation of the 16-electron bis-hydrosulfido complex, [Ru(IMes)(2)(CO)(SH)(2)] 3. Preliminary studies show that 3 reacts with both H(2) and CO in solution as well as in the solid state. Both 2 and 3 have been structurally characterized     

Synthesis of N-heterocyclic carbene rhenium(I) carbonyl complexes

Reaction of aminophosphinimine [RHN(CH(2))(2)N[double bond, length as m-dash]PPh(3)] (R = H, Et) with Re(2)(CO)(10) provided the NH-functionalized carbene rhenium complex [Re(2)(CNHCH(2)CH(2)NR)(CO)(9)] (3a, R = H, 3b, R = Et). Treatment of 3 with Br(2) provided the mono nuclear [Re(CNHCH(2)CH(2)NR)(CO)(4)Br] (1, R = H, 2, R = Et). However, NH-functionalized carbene complexes 1-3 did not undergo N-alkylation with alkyl halides to yield the N-substituted NHC complexes. The direct ligand substitution of [Re(CO)(5)Br] with a carbene donor was employed to prepare [Re(IMes(2))(CO)(4)Br] (6a, IMes(2) = 1,3-di-mesitylimidazol-2-ylidene; 6b, IMes(2) = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene). Analyses of spectroscopic and crystal data of 6a and 6b show similar corresponding data among these complexes, suggesting the saturated and unsaturated NHCs have similar bonding with Re(I) metal centers. Reduction of 6a and 6b with LiEt(3)BH yielded the corresponding hydrido complexes 7a-b [ReH(CO)(4)(IMes(2))], but not 1 and 2. Ligand substitution of 1, 6a and 6b toward 2,2'-bipyridine (bipy) was investigated. Crystal structures of 1, 3a-b, 6a-b and 7b were determined for characterization and comparison.     

Stabilisation of iridium(III) fluoride complexes with NHCs

The first neutral, [IrClF(2)(NHC)(COD)] and [IrClF(2)(CO)(2)(NHC)] (NHC = IMes, IPr), and cationic, [IrF(2)py(IMes)(COD)][BF(4)] and [IrF(2)L(CO)(2)(NHC)][BF(4)] (NHC = IMes, L = PPh(2)Et, PPh(2)CCPh, py; NHC = IPr, L = py), NHC iridium(III) fluoride complexes, have been synthesised by the xenon difluoride oxidation of iridium(I) substrates. The stereochemistries of these iridium(III) complexes have been confirmed by multinuclear NMR spectroscopy in solution and no examples of fluoride-trans-NHC arrangements were observed. Throughout, CO was found to be a better co-ligand for the stabilisation of the iridium(III) fluoride complexes than COD. Attempts to generate neutral trifluoroiridium(III) complexes, [IrF(3)(CO)(NHC)], via the ligand substitution reaction of [IrF(3)(CO)(3)] with the free NHCs were unsuccessful.     

Reactivity of triruthenium thiophyne and furyne clusters: competitive S-C and P-C bond cleavage reactions and the generation of highly unsymmetrical alkyne ligands

The synthesis and reactivity of the thiophyne and furyne clusters [Ru3(CO)7(mu-dppm)(mu3-eta2-C4H2E)(mu-P(C4H3E)2)(mu-H)] (E = S, O) is reported. Addition of P(C4H3E)3 to [Ru3(CO)10(mu-dppm)] (1) at room temperature in the presence of Me3NO gives simple substitution products [Ru3(CO)9(mu-dppm)(P(C4H3E)3)] (E = S, 2; E = O, 3). Mild thermolysis in the presence of further Me3NO affords the thiophyne and furyne complexes [Ru3(CO)7(mu-dppm)(mu3-eta2-C4H2E)(mu-P(C4H3E)2)(mu-H)] (E = S, 4; E = O, 6) resulting from both carbon-hydrogen and carbon-phosphorus bond activation. In each the C4H2E (E = S, O) ligand donates 4-electrons to the cluster and the rings are tilted with respect to the mu-dppm and the phosphido-bridged open triruthenium unit. Heating 4 at 80 degrees C leads to the formation of the ring-opened cluster [Ru3(CO)5(mu-CO)(mu-dppm)(mu3-eta3-SC4H3)(mu-P(C4H3S)2)] (5) resulting from carbon-sulfur bond scission and carbon-hydrogen bond formation and containing a ring-opened mu3-eta3-1-thia-1,3-butadiene ligand. In contrast, a similar thermolysis of 3 affords the phosphinidene cluster [Ru3(CO)7(mu-dppm)(mu3-eta2-C4H2O)(mu3-P(C4H3O))] (7) resulting from a second phosphorus-carbon bond cleavage and (presumably) elimination of furan. Treatment of 4 and 6 with PPh3 affords the simple phosphine-substituted products [Ru3(CO)6(PPh3)(mu-dppm)(mu3-eta2-C4H2E)(mu-P(C4H3E)2)(mu-H)] (E = S, 8; E = O, 9). Both thiophyne and furyne clusters 4 and 6 readily react with hydrogen bromide to give [Ru3(CO)6Br(mu-Br)(mu-dppm)(mu3-eta2-eta1-C4H2E)(mu-P(C4H3E)2)(mu-H)] (E = S, 10; E = O, 11) containing both terminal and bridging bromides. Here the alkynes bind in a highly unsymmetrical manner with one carbon acting as a bridging alkylidene and the second as a terminally bonded Fisher carbene. As far as we are aware, this binding mode has only previously been noted in ynamine complexes or those with metals in different oxidation states. The crystal structures of seven of these new triruthenium clusters have been carried out, allowing a detailed analysis of the relative orientations of coordinated ligands.     

Transformation of mu4-phosphinidenes at an Ru5 center: isolation and structural characterization of hydroxyphosphinidene cluster acids, fluorophosphinidenes, and a novel mu5-phosphide

Acid hydrolysis of [Ru(5)(CO)(15)(mu(4)-PN(i)Pr(2))] (2) or protonation of the anionic PO cluster [Ru(5)(CO)(15)(mu(4)-PO)](-) (3) affords the hydroxyphosphinidene complex [Ru(5)(CO)(15)(mu(4)-POH)].1.[H(2)N(i)()Pr(2)][CF(3)SO(3)], which cocrystallizes with a hydrogen-bonded ammonium triflate salt. Reaction of [Ru(5)(CO)(15)(mu(4)-PN(i)Pr(2))] (2) with bis(diphenylphosphino)methane (dppm) leads to [Ru(5)(CO)(13)(mu-dppm)(mu(4)-PN(i)Pr(2))] (4). Acid hydrolysis of 4 leads to the dppm-substituted hydroxyphosphinidene [Ru(5)(CO)(13)(mu-dppm)(mu(4)-POH)] (5), which is analogous to 1, but unlike 1, can be readily isolated as the free hydroxyphosphinidene acid. Compound 5 can also be formed by reaction of 3 with dppm and acid. The cationic hydride cluster [Ru(5)(CO)(13)(mu-dppm)(mu(3)-H)(mu(4)-POH)][CF(3)SO(3)] (6) can be isolated from the same reaction if chromatography is not used. Compound 4 also reacts with HBF(4) to form the fluorophosphinidene cluster [Ru(5)(CO)(13)(mu-dppm)(mu(4)-PF)] (7), while reaction with HCl leads to the mu-chloro, mu(5)-phosphide cluster [Ru(5)(CO)(13)(mu-dppm)(mu-Cl)(mu(5)-P)] (8).     

New insights into catalytic hydrogenation by phosphido-substituted triruthenium clusters: confirmation of intact cluster catalysis by parahydrogen NMR

The phosphido-substituted triruthenium cluster Ru(3)(CO)(9)(mu-H)(micro-PPh(2)) is shown to react with H(2) to form the trihydride cluster Ru(3)(CO)(9)(H)(mu-H)(2)(mu-PPh(2)), which undergoes a number of re-arrangement reactions on heating to yield other phosphido-substituted triruthenium clusters. In the presence of alkyne substrates, heating the system leads to catalytic hydrogenation via CO loss and the formation of a Ru(3)(eta(2)-PhC[double bond, length as m-dash]CHPh)(CO)(8)(micro-H)(PHPh(2)) resting state, in a reaction affected by the polarity of the solvent. No mononuclear fragments are observed in the catalytic transformation, confirming directly that the phosphido ligand is able to exert a stabilising influence on the cluster core.     

Oxidation states and CO ligand exchange kinetics in a self-assembled monolayer of a triruthenium cluster studied by in situ infrared spectroscopy

Oxidation states and CO ligand exchange kinetics in a self-assembled monolayer (SAM) of an oxo-centered triruthenium cluster [Ru(3)(mu3-O)(mu-CH3COO)6(CO)(L1)(L2)] (L1 = [(NC5H4)CH2NHC(O)(CH2)10S-]2, L2 = 4-methylpyridine) have been extensively investigated on the surface of a gold electrode in aqueous and nonaqueous solutions. The SAM exhibits three consecutive one-electron transfers and four oxidation states, which have been characterized by electrochemistry, in situ infrared spectroscopy, and in situ sum frequency generation (SFG) vibrational spectroscopy measurements. The original electron-localized state of the Ru cluster center was changed to electron delocalization states by oxidation or reduction of the central Ru ions. These changes are revealed by the IR absorptions of the CO ligand and the bridging acetate ligands of the triruthenium cluster in the SAM. The IR absorptions of the two kinds of ligands are strongly dependent on the oxidation state of the Ru cluster center. One-electron oxidation of the central Ru ion in the SAM triggers a CO ligand liberation process. Solvent molecules may then occupy the CO site to result in a CO-free SAM. One-electron reduction of this CO-free SAM in a CO-saturated solution leads to re-coordination of the CO ligand into the SAM. Both processes can be precisely controlled by tuning the electrode potential. The kinetics of the CO exchange cycle in the SAM, including liberation and coordination, has been investigated by in situ IR and SFG measurements for the first time. The CO exchange cycle is significantly dependent on the temperature. The reaction rate greatly decreases with decreasing solution temperature, which is an important factor in the CO ligand exchange process. The activation energies of both CO liberation and coordination have been evaluated from the reaction rate constants obtained at various temperatures.     

Formation and reactivity of the cyclometallated N-heterocyclic carbene complexes [Ru(NHC)'(dppe)(CO)H

Thermolysis of [Ru(PPh(3))(dppe)(CO)HCl] (dppe = 1,2-bis(diphenylphosphino)ethane) with the N-heterocyclic carbenes I(i)Pr(2)Me(2) (1,3-diisopropyl-4,5-dimethyl-imidazol-2-ylidene), IEt(2)Me(2) (1,3-diethyl-4,5-dimethyl-imidazol-2-ylidene) or ICy (1,3-dicyclohexylimidazol-2-ylidene) gave the cyclometallated carbene complexes [Ru(NHC)'(dppe)(CO)H] (NHC = I(i)Pr(2)Me(2), 4; IEt(2)Me(2), 5; ICy, 6). Dissolution of 4 in CH(2)Cl(2) or CHCl(3) gave the trans-Cl-Ru-P complex [Ru(I(i)Pr(2)Me(2))'(dppe)(CO)Cl] (7), which converted over hours at room temperature to the trans-Cl-Ru-CO isomer 7'. Chloride abstraction from 7 by NaBPh(4) under an atmosphere of H(2) produced the cationic mono-hydride complex [Ru(I(i)Pr(2)Me(2))(dppe)(CO)H][BPh(4)] (9), which could also be formed by protonating 4 with 1 eq HBF(4)·OEt(2). Treatment of 4 with excess HBF(4)·OEt(2) followed by extraction into MeCN produced the dicationic acetonitrile complex [Ru(I(i)Pr(2)Me(2))(dppe)(CO)(NCMe)(2)][BF(4)](2) (10). The structures of 6, 7, 7' and 10 have been determined by X-ray crystallography.     

Synthesis of mixed tin-ruthenium and tin-germanium-ruthenium carbonyl clusters from [Ru3(CO)12] and diaminometalenes (M = Sn, Ge)

Diaminostannylenes react with [Ru(3)(CO)(12)] without cluster fragmentation to give carbonyl substitution products regardless of the steric demand of the diaminostannylene reagent. Thus, the Sn(3)Ru(3) clusters [Ru(3){μ-Sn(NCH(2)(t)Bu)(2)C(6)H(4)}(3)(CO)(9)] (4) and [Ru(3){μ-Sn(HMDS)(2)}(3)(CO)(9)] (6) [HMDS = N(SiMe(3))(2)] have been prepared in good yields by treating [Ru(3)(CO)(12)] with an excess of the cyclic 1,3-bis(neo-pentyl)-2-stannabenzimidazol-2-ylidene and the acyclic and bulkier Sn(HMDS)(2), respectively, in toluene at 110 °C. The use of smaller amounts of Sn(HMDS)(2) (Sn/Ru(3) ratio = 2.5) in toluene at 80 °C afforded the Sn(2)Ru(3) derivative [Ru(3){μ-Sn(HMDS)(2)}(2)(μ-CO)(CO)(9)] (5). Compounds 5 and 6 represent the first structurally characterized diaminostannylene-ruthenium complexes. While a further treatment of 5 with Ge(HMDS)(2) led to a mixture of uncharacterized compounds, a similar treatment with the sterically alleviated diaminogermylene Ge(NCH(2)(t)Bu)(2)C(6)H(4) provided [Ru(3){μ-Sn(HMDS)(2)}(2){μ-Ge(NCH(2)(t)Bu)(2)C(6)H(4)}(CO)(9)] (7), which is a unique example of Sn(2)GeRu(3) cluster. All these reactions, coupled to a previous observation that [Ru(3)(CO)(12)] reacts with excess of Ge(HMDS)(2) to give the mononuclear complex [Ru{Ge(HMDS)(2)}(2)(CO)(3)] but triruthenium products with less bulky diaminogermylenes, indicate that, for reactions of [Ru(3)(CO)(12)] with diaminometalenes, both the volume of the diaminometalene and the size of its donor atom (Ge or Sn) are of key importance in determining the nuclearity of the final products.     

Reactions of mu3-alkenyl triruthenium carbonyl clusters with alkynes: synthesis of trinuclear mu-//-alkyne, mu-vinylidene, and mu-dienoyl derivatives

The reactions of doubly face-capped triruthenium cluster complexes of the type [Ru(3)(mu(3)-kappa(2)-HNNMe(2))(mu(3)-kappa(2)-R(2)CCHR(1))(mu-CO)(2)(CO)(6)] (HNNMe(2) = 1,1-dimethylhydrazide; R(2)CCHR(1) = alkenyl ligand) with terminal and internal alkynes have been studied in refluxing toluene. The following derivatives have been isolated from these reactions: [Ru(3)(mu(3)-kappa(2)-HNNMe(2))(mu(3)-kappa(2)-R(2)CCHR(1))(mu-kappa(2)-//-HCCH)(CO)(7)] (R(1) = R(2) = H, 5; R(1) = Ph, R(2) = H, 6; R(1) = CH(2)OMe, R(2) = H, 7 a; R(1) = H, R(2) = CH(2)OMe, 7 b) from acetylene, [Ru(3)(mu(3)-kappa(2)-HNNMe(2))(mu(3)-kappa(2)-HCCH(2))(mu-kappa(2)-//-PhCCPh)(CO)(7)] (11) from diphenylacetylene, and three isomers of [Ru(3)(mu(3)-kappa(2)-HNNMe(2))(mu(3)-kappa(2)-HCCH(2))(mu-kappa(2)-//-PhCCH)(CO)(7)] (14, 15 a, and 15 b) from phenylacetylene. These products result from substitution of a CO ligand by the alkyne and contain an Ru--Ru edge bridged by the alkyne ligand in a parallel manner. DFT calculations on selected isomeric products have helped to establish that the type of Ru--Ru edge bridged by the alkyne depends more on kinetic factors related to the size of the alkyne substituents than on the thermodynamic stability of the final products. The preparation of triruthenium cluster complexes with mu-//-alkyne ligands is unprecedented and seems to relate to the fact that the starting trinuclear complexes have their two triangular faces protected by capping ligands. The clusters bearing mu-//-acetylene (5-7) are thermodynamically unstable with respect to their transformation into edge-bridging vinylidene derivatives, [Ru(3)(mu(3)-kappa(2)-HNNMe(2))(mu(3)-kappa(2)-HCCHR)(mu-kappa(1)-CCH(2))(CO)(7)] (R = H, 8; Ph, 9; CH(2)OMe, 10). DFT calculations have shown that complex 8 is 11.2 kcal mol(-1) more stable than its precursor 5. The thermolysis of compound 11 leads to [Ru(3)(mu(3)-kappa(2)-HNNMe(2))(mu-kappa(4)-H(2)CCHCPhCPhCO)(mu-CO)(2)(CO)(5)] (12), which contains a novel edge-bridging dienoyl ligand that arises from an unusual coupling of diphenylacetylene, carbon monoxide, and the ethenyl ligand of complex 11. A chloro-bridged dimer of trinuclear clusters, [Ru(6)(mu-Cl)(2)(mu(3)-kappa(2)-HNNMe(2))(2)(mu(3)-kappa(2)-HCCH(2))(2)(mu-kappa(2)-PhCCHPh)(2)(mu-CO)(2)(CO)(10)] (13), has been prepared by treating compound 11 with hydrogen chloride. Therefore, edge-bridging parallel alkynes are susceptible to protonation to give edge-bridging alkenyl ligands. Compound 13 is the first complex to contain two alkenyl ligands on a trinuclear cluster, one face-capping and the other edge-bridging.     

Easy activation of two C-H bonds of an N-heterocyclic carbene N-methyl group

The first trinuclear clusters containing NHC ligands are described; the compound [Ru3(Me2Im)(CO)11](Me2Im=1,3-dimethylimidazol-2-ylidene) is easily converted into [Ru3(mu-H)2(mu3-MeImCH)(CO)9] by a process involving the activation of two C-H bonds of a methyl group that is an example of degradation of a metal-coordinated NHC ligand under mild conditions.     

Cubane-type heterometallic sulfido clusters: incorporation of two metal fragments into a dinuclear ReS(mu-S)2ReS core affording bimetallic M2Re2(mu 3-S)4 clusters (M = Ru,Pt, Cu) or trimetallic MM'Re2(mu 3-S)4 clusters via incomplete cubane-type MRe2(mu 3-S)(mu 2-S)3 intermediates (M = Ru,Rh, Ir; M' = Mo,W, Pd,Ru, Rh)

Reactions of a dirhenium tetra(sulfido) complex [PPh(4)](2)[ReS(L)(mu-S)(2)ReS(L)] (L = S(2)C(2)(SiMe(3))(2)) with a series of group 8-11 metal complexes in MeCN at room temperature afforded either the cubane-type clusters [M(2)(ReL)(2)(mu(3)-S)(4)] (M = CpRu (2), PtMe(3), Cu(PPh(3)) (4); Cp = eta(5)-C(5)Me(5)) or the incomplete cubane-type clusters [M(ReL)(2)(mu(3)-S)(mu(2)-S)(3)] (M = (eta(6)-C(6)HMe(5))Ru (5), CpRh (6), CpIr (7)), depending on the nature of the metal complexes added. It has also been disclosed that the latter incomplete cubane-type clusters can serve as the good precursors to the trimetallic cubane-type clusters still poorly precedented. Thus, treatment of 5-7 with a range of metal complexes in THF at room temperature resulted in the formation of novel trimetallic cubane-type clusters, including the neutral clusters [[(eta(6)-C(6)HMe(5))Ru][W(CO)(3)](ReL)(2)(mu(3)-S)(4)], [(CpM)[W(CO)(3)](ReL)(2)(mu(3)-S)(4)] (M = Rh, Ir), [(Cp*Ir)[Mo(CO)(3)](ReL)(2)(mu(3)-S)(4)], [[(eta(6)-C(6)HMe(5))Ru][Pd(PPh(3))](ReL)(2)(mu(3)-S)(4)], and [(Cp*Ir)[Pd(PPh(3))](ReL)(2)(mu(3)-S)(4)] (13) along with the cationic clusters [(Cp*Ir)(CpRu)(ReL)(2)(mu(3)-S)(4)][PF(6)] (14) and [(Cp*Ir)[Rh(cod)](ReL)(2)(mu(3)-S)(4)][PF(6)] (cod = 1,5-cyclooctadiene). The X-ray analyses have been carried out for 2, 4, 7, 13, and the SbF(6) analogue of 14 (14') to confirm their bimetallic cubane-type, bimetallic incomplete cubane-type, or trimetallic cubane-type structures. Fluxional behavior of the incomplete cubane-type and trimetallic cubane-type clusters in solutions has been demonstrated by the variable-temperature (1)H NMR studies, which is ascribable to both the metal-metal bond migration in the cluster cores and the pseudorotation of the dithiolene ligand bonded to the square pyramidal Re centers, where the temperatures at which these processes proceed have been found to depend upon the nature of the metal centers included in the cluster cores.     

Mixed nitrosyl/phosphinidene and nitrene/phosphinidene clusters of ruthenium

Reaction of the aminophosphinidene complex [Ru5(CO)15(mu 4-PNPri2)] 1 with [PPN][NO2] (PPN = Ph3P=N=PPh3) led to the mixed nitrosyl/phosphinidene cluster complex [PPN][Ru5(CO)13(mu-NO)(mu 4-PNPri2)] 2 which is transformed into the novel nitrene/phosphinidene cluster [Ru5(CO)10(mu-CO)2(mu 3-CO)(mu 4-NH)(mu 3-PNPri2)] 3 via treatment with triflic acid.     

NHCs as Neutral Donors towards Polyphosphorus Complexes

The first adducts of NHCs (=N-heterocyclic carbenes) with aromatic polyphosphorus complexes are reported. The reactions of [Cp*Fe(η⁵-P₅)] ( 1 ) (Cp*=pentamethyl-cyclopentadienyl) with IMe (=1,3,4,5-tetramethylimidazolin-2-ylidene), IMes (=1,3-bis(2,4,6-trimethylphenyl)-imidazolin-2-ylidene) and IDipp (=1,3-bis(2,6-diisopropylphenyl)-imidazolin-2-ylidene) led to the corresponding neutral adducts which can be isolated in the solid state. However, in solution, they quickly undergo a dissociative equilibrium between the adduct and 1 including the corresponding NHC. The equilibrium is influenced by the bulkiness of the NHC. [Cp′′Ta(CO)₂(η⁴-P₄)] (Cp′′=1,3-di-tert-butylcyclopentadienyl) reacts with IMe under P atom abstraction to give an unprecedented cyclo-P₃-containing anionic tantalum complex. DFT calculations shed light onto the energetics of the reaction pathways.     

Ruthenium and osmium carbonyl clusters incorporating stannylene and stannyl ligands

The reaction of [Ru(3)(CO)(12)] with Ph(3)SnSPh in refluxing benzene furnished the bimetallic Ru-Sn compound [Ru(3)(CO)(8)(mu-SPh)(2)(mu(3)-SnPh(2))(SnPh(3))(2)] which consists of a SnPh(2) stannylene bonded to three Ru atoms to give a planar tetra-metal core, with two peripheral SnPh(3) ligands. The stannylene ligand forms a very short bond to one Ru atom [Sn-Ru 2.538(1) A] and very long bonds to the other two [Sn-Ru 3.074(1) A]. The germanium compound [Ru(3)(CO)(8)(mu-SPh)(2)(mu(3)-GePh(2))(GePh(3))(2)] was obtained from the reaction of [Ru(3)(CO)(12)] with Ph(3)GeSPh and has a similar structure to that of as evidenced by spectroscopic data. Treatment of [Os(3)(CO)(10)(MeCN)(2)] with Ph(3)SnSPh in refluxing benzene yielded the bimetallic Os-Sn compound [Os(3)(CO)(9)(mu-SPh)(mu(3)-SnPh(2))(MeCN)(eta(1)-C(6)H(5))] . Cluster has a superficially similar planar metal core, but with a different bonding mode with respect to that of . The Ph(2)Sn group is bonded most closely to Os(2) and Os(3) [2.786 and 2.748 A respectively] with a significantly longer bond to Os(1), 2.998 A indicating a weak back-donation to the Sn. The reaction of the bridging dppm compound [Ru(3)(CO)(10)(mu-dppm)] with Ph(3)SnSPh afforded [Ru(3)(CO)(6)(mu-dppm)(mu(3)-S)(mu(3)-SPh)(SnPh(3))] . Compound contains an open triangle of Ru atoms simultaneously capped by a sulfido and a PhS ligand on opposite sides of the cluster with a dppm ligand bridging one of the Ru-Ru edges and a Ph(3)Sn group occupying an axial position on the Ru atom not bridged by the dppm ligand.