Reactions of Low-Coordinate Cobalt(0)-N-Heterocyclic Carbene Complexes with Primary Aryl Phosphines.

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)2 Co(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)2 Co(vtms)] with H2 PDmp (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 [Cp2 Fe][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 H2 PC6 H2 -2,4,6-Me3 (H2 PMes) at room temperature, whereas [(ICy)2 Co(vtms)] can react with H2 PMes at room temperature to produce the cobalt(II) phosphido alkyl complex trans-[(ICy)2 Co(CH2 CH2 SiMe3 )(PHMes)] (5). At 80 °C, the cobalt(0) alkene complexes [(IPr)Co(vtms)2 ] and [(ICy)2 Co(vtms)] and also the cobalt phosphido complexes, 1, 2, and 5 can serve as precatalysts for the dehydrocoupling reaction of H2 PMes to afford MesHPPHMes. NHC-Co(I)-phosphido species are proposed as the in-cycle intermediates for these cobalt-catalyzed dehydrocoupling reactions.