Electrophilic (Li+) acceleration of C–H reductive elimination and oxidative addition reactions of Os(II)/Os(0) nitrosyl complexes

Abstract

The reductive elimination of methane from cis,trans-Os(H)₂(CH₃)(NO)L₂ (L = PⁱPr₃) in benzene is accelerated by added LiN(SiMe₃)₂, with ¹H NMR and IR evidence for binding of the lithium electrophile to NO oxygen. Oxidative addition of benzene to the transient OsH(NO)L₂, to give cis,trans-Os(H)₂(C₆H₅)(NO)L₂, is also accelerated by LiN(SiMe₃)₂. DFT calculations of the reaction path with and without LiNMe₂ show the rate acceleration is due to preferential stabilization of the oxidative addition/reductive elimination transition state, due to the greater back donation to NO in the TS. This is traced, in turn, to the relief of the filled–filled repulsion between the occupied Os d and C–H σ-orbitals by the Li electrophile on NO oxygen.