Aiming to get knowledge on the reactivity of low-coordinate cobalt(0) species toward primary phosphines, the reactions of [(IPr)­Co­(vtms)2] and [(ICy)2Co­(vtms)] (IPr = 1,3-bis­(2′,6′-diisopropylphenyl)­imidazol-2-ylidene, ICy = 1,3-dicyclohexylimidazol-2-ylidene, and vtms = vinyltrimethylsilane) with several primary aryl phosphines have been examined. The reactions of [(IPr)­Co­(vtms)2] and [(ICy)2Co­(vtms)] with H2PDmp (Dmp = 2,6-dimesitylphenyl) at 80 °C furnish the diamagnetic cobalt­(I) phosphido complexes [(NHC)­Co­(PHDmp)] (NHC = IPr, 1; ICy, 2) that feature the Co–(η6-mesityl) interaction. Complex 1 can coordinate CO to generate the terminal phosphido complex [(IPr)­Co­(CO)3(PHDmp)] (3) and can be oxidized by [Cp2Fe]­[BArF 4] to yield the cobalt­(II) phosphido complex [(IPr)­Co­(PHDmp)]­[BArF 4] (4, BArF 4 = tetrakis­(3,5-di­(trifluoromethyl)­phenyl)­borate). For the reactions with sterically less-hindered primary phosphines, [(IPr)­Co­(vtms)2] is inert toward H2PC6H2-2,4,6-Me3 (H2PMes) at room temperature, whereas [(ICy)2Co­(vtms)] can react with H2PMes at room temperature to produce the cobalt­(II) phosphido alkyl complex trans-[(ICy)2Co­(CH2CH2SiMe3)­(PHMes)] (5). At 80 °C, the cobalt(0) alkene complexes [(IPr)­Co­(vtms)2] and [(ICy)2Co­(vtms)] and also the cobalt phosphido complexes, 1, 2, and 5 can serve as precatalysts for the dehydrocoupling reaction of H2PMes to afford MesHPPHMes. NHC–Co­(I)-phosphido species are proposed as the in-cycle intermediates for these cobalt-catalyzed dehydrocoupling reactions.

The reactions of nitrosoarenes with transition-metal species are fundamentally important for their relevance to metal-catalyzed transformations of organonitrogen compounds in organic synthesis and also the metabolization of nitroarenes and anilines in biology. In addition to the well-known reactivity of metal-mediated N−O bond activation and cleavage of nitrosoarenes, we present herein the first observation of a nitrosoarene C−N bond oxidative addition reaction upon the interaction of a three-coordinate cobalt(0) species [(IPr)Co(vtms) 2 ] with 2,4,6-tri(tert-butyl)-1-nitroso-benzene (Ar*NO). The reaction produces a cobalt nitrosyl aryl complex, [(IPr)Co-(Ar*)(NO)] (1), with a bis(nitrosoarene)cobalt complex, [(IPr)Co(η 2 -ONAr)(κ 1 -O-ONAr)] (2), as an intermediate. Spectroscopic characterizations, DFT calculations, and kinetic studies revealed that the redox non-innocence of nitrosoarene induces a stepwise pathway for the C−N bond oxidative addition reaction.

Among the great efforts of developing cobalt-based catalysts for hydrosilylation reactions, cobalt (II) and cobalt(I) complexes are the extensively studied ones. In contrast, explorations on cobalt(0) complexes are relatively rare. Presented herein is the investigation on the catalytic performance of low-coordinate cobalt(0) N-heterocyclic carbene (NHC) complexes in the hydrosilylation reaction of alkynes, which disclosed the fine performance of [(CyIDep)Co(η 2 -CH 2 CHSiMe 3 ) 2 ] (CyIDep denotes for a 1,3-bis (2 0 ,6 0 -diethylphenyl)imidazole-2-ylidene that bears fused cyclohexyl group on the imidazole backbone) in catalyzing the syn-addition of a series of symmetric and unsymmetric internal alkynes with H 2 SiPh 2 , producing vinylsilanes with high regio-selectivity. Mechanistic study indicates that the catalytic reaction likely proceeds on a cobalt(0)/cobalt(II) cycle and that the high selectivity is governed by the steric nature of the NHC ligand.