Deprotonation of the diruthenium μ-methylidyne complex [(Cp*Ru)2(μ-NtBu)(μ-CH)][BF4] (Cp* = η5-C5Me5) with 2 equiv of KN(SiMe3)2 in the presence of CuCN, AgOTf, or AuCl(SMe2) afforded the trigonal planar bridging carbido complexes [(Cp*Ru)2(μ-NtBu)(μ3-C)M{N(SiMe3)2}] (M = Cu (4), Ag (5), and Au (6)). Complexes 4 and 6 were characterized crystallographically. The M–C bonding in these complexes showed considerable similarity with that in the N-heterocyclic carbene (NHC) derivatives (NHC)M{N(SiMe3)2} (M = Cu and Au), illustrating the analogy between the diruthenium carbido ligand [(Cp*Ru)2(μ-NtBu)(μ-C)] and NHCs. The reaction of 4 with 2,6-di-tert-butylphenol allowed derivatization via protonolytic exchange of the disilazide moiety, yielding the aryloxo complex [(Cp*Ru)2(μ-NtBu)(μ3-C)Cu(OAr)] (7; Ar = 2,6-tBu2C6H3), which was also structurally characterized. The electron donor ability and steric bulkiness of the diruthenium carbido ligand were studied by computational methods.

The first catalytic dehydrative condensation of the benzylic C–H bonds of toluene and p-xylene with aromatic aldehydes is reported herein. This protocol provides highly atom-economical access to stilbene and p-distyrylbenzene derivatives, whereby water is the sole byproduct. The reaction is based on the deprotonation–functionalization of benzylic C–H bonds through η6-complexation of the arenes, which is realized for the first time using a catalytic amount of a transition metal activator. The key to the success of this method is the use of a sulfonamide anion as a catalyst component, which appears to facilitate not only the deprotonation of the benzylic C–H bonds but also the formation of a C–C bonds via an electrophilic tosylimine intermediate.

•Metal-ligand cooperative reactivity of a diruthenium imido complex is reported.•The diruthenium imido complex activates a variety of element-hydrogen bonds.•The amido complexes produced display interesting variation in the Ru–Ru distance.The diruthenium imido complex [(Cp*Ru)2(μ-NPh)(μ-CH2)] (1; Cp* = η5-C5Me5) reacts with a variety of Brønsted acidic element-hydrogen bonds to give amido complexes of the type [(Cp*Ru)2(μ-NHPh)(X)(μ-CH2)]. Single-crystal X-ray structures are reported for products with X = OTf, μ-Cl, μ-κ2-O,O′-O2CPh, μ-NHSO2Ph, μ-H (from i-PrOH), and μ-CCC6H4Me-p, where the Ru–Ru distance ranges from 2.46 Å to 2.68 Å depending on the nature of the ligand X. Additionally, the reaction of 1 with BH3·THF produces the imido-borane adduct [(Cp*Ru)2(μ-H3BNPh)(μ-CH2)], in which two B–H bonds are weakened through the formation of B–H–Ru bridging hydride structures.

•Aminolysis of [Cp*Ru(μ-OEt)]2 with sulfonamides has been studied.•The first terminal sulfonamido derivatives of the Cp*Ru fragment have been isolated.•Anionic complexes of the type [Cp*Ru(sulfonamido)2]– are readily accessible.The reaction of [Cp*Ru(μ-OEt)]2 (1) with sulfonamides affords terminal sulfonamido complexes via alkoxo-sulfonamido exchange and either symmetrical or unsymmetrical cleavage of the dimeric structure. The neutral phosphine-ligated monomeric complexes [Cp*Ru(NHTs)(PR3)n] (R = Cy, n = 1; R = Me, n = 2) are obtained by sequential treatment of 1 with TsNH2 and PR3 in THF. When the above reaction is conducted in the absence of PR3, a formally zwitterionic dinuclear complex [Cp*Ru−(NHTs)(μ-κ1:η6-NHTs)Ru+Cp*] is isolated. When the aminolysis of 1 with TsNH2 is conducted in toluene, trapping of a Cp*Ru+ fragment by a solvent molecule occurs to give the fully ionic complex salt [Cp*Ru(η6-toluene)][Cp*Ru(NHTs)2] (4a). The 16-electron anionic bis(tosylamido) complex in 4a reacts with CO or CNtBu, yielding the neutral 18-electron complexes [Cp*Ru(NHTs)(L)2] (L = CO, CNtBu) and a free tosylamide anion, the latter of which is isolated in the form of the complex salt [Cp*Ru(η6-toluene)][NHTs]. Mesylamido and N,N′-ditosylethylenediamido complexes analogous to 4a have also been synthesized.

Low-temperature deprotonation of the cationic μ-methylidyne complex [(Cp*Ru)2(μ-NPh)(μ-CH)][BF4] (Cp* = η5-C5Me5) with KN(SiMe3)2 affords a thermally unstable μ-carbido complex [(Cp*Ru)2(μ-NPh)(μ-C)] (2), as evidenced by trapping experiments with elemental S or Se and 13C NMR spectroscopic observation. The reactivity of 2 toward CO2, Ph2S+CH2–, EtOH, and an intramolecular C–H bond indicates that the μ-carbido carbon in 2 has an ambiphilic (nucleophilic and electrophilic) nature consistent with the formulation of 2 as the first example of a transition-metal-substituted singlet carbene. DFT study suggests that the Ru substituents in 2 are stronger σ-donor and weaker π-donor to the carbene center than amino substituents in N-heterocyclic carbenes.

Ruthenium has an extensive coordination chemistry with carbido ligands, forming diverse array of structures ranging from low-coordinate carbido complexes with Ru–C multiple bonds to high-nuclearity clusters with interstitial carbon atoms. These complexes have a close relationship to ruthenium carbene and carbyne complexes and have relevance to important catalytic processes such as the Fischer–Tropsch reaction and olefin metathesis. Ruthenium carbido clusters are versatile building blocks for high-nuclearity mixed-metal clusters of interesting structures and applications. This review aims to give an overview of recent progress in ruthenium carbido coordination chemistry with detailed coverage of the literature from 2000 to 2010.Highlights► Progress of ruthenium carbido coordination chemistry in 2000–2010. ► Low-coordinate carbido derivatives with Ru–C multiple bonds. ► High-nuclearity clusters with interstitial carbido ligands. ► Relationship to ruthenium carbene and carbyne complexes. ► Relevance to olefin metathesis and Fischer–Tropsch reaction.

New amido- and alkoxo-bridged dinuclear cobalt complexes [Cp*Co(μ-X)]2 (X = NHTol (2), NHBoc (3), OBn (4); Cp* = η5-C5Me5; Tol = p-tolyl; Boc = t-BuOCO; Bn = CH2Ph) have been prepared by the reaction of [Cp*Co(μ-Cl)]2 (1) with LiX and characterized by X-ray analysis. The amido complexes 2 and 3 are diamagnetic and feature a folded Co2N2 butterfly structure with a Co−Co single bond. In contrast, the alkoxo complex 4 is paramagnetic and contains a planar Co2O2 core with a long Co···Co separation. Dynamic stereochemical processes in 2 and 3 were investigated by NMR spectroscopy, and cis−trans isomerization in 2 and Co2N2 ring inversion in 2 and 3 were identified. Complexes 2 and 4 reacted with carbon monoxide to give N,N′-di-p-tolylurea and dibenzyl carbonate, respectively, along with [Cp*Co(CO)2] and [Cp*Co(μ-CO)]2. Oxidation of 2 with iodine and ferrocenium triflate afforded the Co(III) complexes [(Cp*Co)2(μ-I)(μ-NHTol)2]I (5) and [(Cp*Co)2(μ-OH2)(μ-NHTol)2][OTf]2 (6), respectively, the latter being characterized by X-ray analysis.

[Cp*Ru(μ-NHPh)]2 (Cp* = η5-C5Me5) reacted with CO, t-BuNC, Ph2S═CH2, or Me3SiC≡CH to give the dinuclear ruthenium bridging imido complexes [(Cp*Ru)2(μ-NPh)(μ-L)] (2a, L = CO; 2b, L = t-BuNC; 2c, L = CH2; 2d, L = CCHSiMe3). Protonolysis of 2d with t-BuOH produced the parent vinylidene complex [(Cp*Ru)2(μ-NPh)(μ-CCH2)] (2e). Treatment of 2e with HOTf or MeOTf afforded the cationic alkylidyne complexes [(Cp*Ru)2(μ-NPh)(μ-CR)]OTf (2f, R = Me; 2g, R = Et). Hydride abstraction from 2c with Ph3CBF4 gave the methylidyne complex [(Cp*Ru)2(μ-NPh)(μ-CH)]BF4 (2h). X-ray structures of 2a−c and 2f revealed short Ru−N distances (1.876−1.894 Å) consistent with Ru−N multiple bonds, and the μ-alkylidyne 2f also featured short Ru−C bonds (1.929(7) and 1.914(7) Å). In addition to giving simple Lewis base adducts such as [(Cp*Ru)2(μ-NPh)(μ-CO)(PMe3)] and [(Cp*Ru)2(μ-NPh)(μ-CH2)(t-BuNC)2], these imido complexes provided an array of novel ligand coupling reactions. Thus, 2b underwent a tandem imido−isocyanide coupling and C−H activation reaction to give an amidinate complex. Complexes 2c and 2e mediated imido−CO−methylene and imido−CO−vinylidene coupling to give [{Cp*Ru(CO)2}2(μ-PhNCOCH2)] (6) and [{Cp*Ru(CO)}2(μ-PhNCOC═CH2)] (7), respectively. Complex 2c also underwent a selective coupling reaction with 2 equiv of Me3SiC≡CH to give the μ-allenylimine complex [(Cp*Ru)2{μ-Me3SiCH═C═C(SiMe3)C(Me)═NPh}] (8). The imido methylidyne complex coupled with 2 equiv of alkynes to give [(Cp*Ru)2{μ-HC(R1CCR2)(R2CCR1)NPh}]OTf (9a−c), a product of double alkyne cycloaddition to the Ru−N and Ru−C multiple bonds and C−C coupling of the resulting ruthena- and azaruthenacyclobutene moieties.

The bimetallic Ru2Pt complex [(Cp*Ru)2(μ2-NHPh)(μ2-H)(μ3-C)PtMe(PMe3)2][OTf] (3; Cp* = η5-C5Me5) containing a planar three-coordinate carbido ligand has been prepared in 93% yield by thermal isomerization of the bridging methylene precursor [(Cp*Ru)2Me(μ3-NPh)(μ2-CH2)Pt(PMe3)2][OTf] (2) via cleavage of the methylene C−H bonds. Exposure of the carbido complex 3 to carbon monoxide (1 atm) induced coupling of the carbido ligand with the nearby methyl and hydride ligands to produce the diruthenium ethylidene complex [(Cp*Ru)2(μ2-CHMe)(μ2-NHPh)(CO)2][OTf] (4) and the known triplatinum complex [Pt(CO)(PMe3)]3. The crystal structures of 2, 3, and 4 (BPh4 salt) are reported.