The Versatility of Lithium Reagents in Synthetic Organometallic Chemistry: Their differing reactions with [Cp^*Mo(NO)(CH₂SiMe₃)₂]

Abstract

Abstract [Cp * Mo(NO)(CH 2 SiMe 3 ) 2 ] exhibits three principal types of reaction with the various lithium reagents investigated during this study, namely: regioselective deprotonation, reduction, and addition. Deprotonation of the reactant, achieved by treatment with lithium amide reagents, leads ultimately to the formation of the alkylidene „ate”︁ complex [Cp * Mo(NO)(CH 2 SiMe 3 ) 2 (CHSiMe 3 )] 2 ‐[Li 2 (thf) 3 ] ( 1 ). While LiN(SiMe 3 ) 2 effects this conversion directly with no detectable intermediates, reaction with 1 equiv of LDA in THF for 15 min deprotonates the Cp * ligand to form the lithium salt of the „tucked‐in”︁ ate complex [(η 5 ,η 1 ‐C 5 Me 4 CH 2 )Mo(NO)(CH 2 SiMe 3 ) 2 ]‐[Li(thf) 3 ] ( 2 ) in 40% isolated yield. Complex 2 slowly converts to the thermodynamically more stable 1 when left as a THF or C 6 D 6 solution at ambient temperature for 48 h. Reaction of the dialkyl starting material with either t BuLi or PhLi leads to the production of the alkylidene complex 1 in irreproducible yields (10–50% NMR; not isolable). A kinetic analysis of the reaction of [Cp * Mo(NO)(CH 2 SiMe 3 ) 2 ] with LiN(SiMe 3 ) 2 indicated that the reaction was first‐order in both the lithium and molybdenum reagents, and the activation parameters of Δ H * = 7.3∓1.0 kcal mol −1 and Δ S * = − 34∓3 e.u. suggest an associative process. Treatment of the neutral dialkyl with 1 equiv of LiPPh 2 in THF results in a one‐electron reduction and production of {[Cp * Mo(NO)(CH 2 SiMe 3 ) 2 [Li 2 (thf) 3 ] ( 3 ). If left in solution, the 17e − dialkyl anion 3 is converted to the 18e − alkylidene anion 1 by the Ph 2 P–PPh 2 coproduct, which effects the requisite hydrogen‐atom abstraction. Finally, addition of a sterically undemanding alkyllithium reagent such as MeLi to the 16e − dialkyl reactant leads to the formation of the 18e − trialkyl anionic complex [[Cp * Mo(NO)(CH 2 SiMe 3 ) 2 (CHSiMe 3 )] 2 ‐[Li 2 (thf) 3 ](Me)][Li(thf) 3 ] ( 4 ). Warming of 4 in a C 6 D 6 solution results in loss of methane and production of 1 . In most cases, the chemistry exhibited by the Mo system is duplicated by the analogous W congener, [Cp * Mo(NO)(CH 2 SiMe 3 ) 2 (CHSiMe 3 )] 2 ‐[Li 2 (thf) 3 ]. The solid‐state molecular structures of complexes 1 and 4 have been established by single‐crystal X‐ray crystallographic analyses.