Activation of coordinated benzonitrile upon reduction of the dimolybdenum nitrosyl complex [Mo2Cp2(μ-Cl)(μ-PtBu2)(NO)2]. Azavinylidene, amido, imido, and carbyne derivatives

Reaction of [Mo 2 Cp 2 ( μ -Cl)( μ -P t Bu 2 )(NO) 2 ] with Na(Hg) in benzonitrile for ca. 15 min followed by protonation with (NH 4 )PF 6 gave the azavinylidene complex [Mo 2 Cp 2 ( μ - κ:κ -NCHPh)( μ -P t Bu 2 )(NO) 2 ] and the benzoylamido complex [Mo 2 Cp 2 { μ - κ N : κ N -HNC(O)Ph}( μ -P t Bu 2 )(NO) 2 ]. These are thought to follow from H- and OH-abstraction reactions of radical [Mo 2 Cp 2 ( μ -P t Bu 2 )( μ -NCPh)(NO) 2 ] with traces of water present in the solvent. In contrast, extension of the reduction time to ca. 1 h before protonation yielded as major products the above amido complex and [Mo 2 Cp 2 { μ - κ:κ -NC(OH)Ph}( μ -P t Bu 2 )(NCH 2 Ph)(NO)]PF 6 , the latter involving the activation of two molecules of benzonitrile, converted into hydroxylazavinylidene and terminal benzylimido ligands, respectively. The latter ligand might arise from double protonation of the coordinated nitrile in the intermediate anion [Mo 2 Cp 2 ( μ -P t Bu 2 )( μ -NCPh)(NO) 2 ] − , followed by H-shift in the resulting imine ligand, while the hydroxylazavinylidene ligand here might stem from nitrosyl displacement by a second nitrile molecule that would generate radical intermediates undergoing OH-abstraction. A minor product in the latter reaction was the benzylidyne complex [Mo 2 Cp 2 ( μ -CPh)( μ -P t Bu 2 )(NO) 2 ]. Attempts to generate it from the benzyl complex [Mo 2 Cp 2 (CH 2 Ph)( μ -P t Bu 2 )(CO)(NO) 2 ] were unsuccessful. While photolysis of this precursor efficiently yielded the agostic benzyl-bridged complex [Mo 2 Cp 2 ( μ - κ:η 2 -CH 2 Ph)( μ -P t Bu 2 )(NO) 2 ], no dehydrogenation could be further induced on it. Its protonation with HBF 4 ·OEt 2 promoted partial dehydrogenation yielding the benzylidene-bridged cation [Mo 2 Cp 2 ( μ - κ:η 3 -CHPh)( μ -P t Bu 2 )(NO) 2 ] + , but the latter could not be successfully deprotonated.