THE VERSATILITY OF LITHIUM REAGENTS IN SYNTHETIC ORGANOMETALLIC CHEMISTRY - THEIR DIFFERING REACTIONS WITH [(CPMO)-MO-ASTERISK(NO)(CH2SIME3)(2)]

[CpMo(NO)(CH2SiMe3)(2)] exhibits three principal types of reaction wi th 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, l eads ultimately to the formation of the alkylidene ''ate'' complex [Cp Mo(NO)(CH2SiMe3)(=CHSiMe3)](2)[Li-2(thf)(3)] (1). While LiN(SiMe3)(2) effects this conversion directly with no detectable intermediates, re action with 1 equiv of LDA in THF for 15 min deprotonates the Cp liga nd to form the lithium salt of the ''tucked-in'' ate complex (1)C(5)Me (4)CH(2))Mo(NO)(CH2SiMe3)(2)][Li(thf)(3)] (2) in 40% isolated yield, C omplex 2 slowly converts to the thermodynamically more stable 1 when l eft as a THF or C6D6 solution at ambient temperature fbr 48 h. Reactio n of the dialkyl starting material with either tBuLi or PhLi leads to the production of the alkylidene complex 1 in irreproducible yields (1 0-50% NMR; not isolable). A kinetic analysis of the reaction of [CpMo (NO)(CH2SiMe3)(2)] with LiN(SiMe3)(2) indicated that the reaction was first-order in both the lithium and molybdenum reagents, and the activ ation parameters of Delta H-double dagger = 7,3 +/- 1.0 kcal mol(-1) a nd Delta S (double dagger) = -34 +/- 3 e.u. suggest an associative pro cess. Treatment of the neutral dialkyl with 1 equiv of LiPPh2, in THF results in a one-electron reduction and production of {[CpMo(NO)(CH2S iMe3)(2)][Li(thf)]}(2) (3). If left in solution, the 17e(-) dialkyl an ion 3 is converted to the 18e(-) alkylidene anion 1 by the Ph2P-PPh2 c oproduct, which effects the requisite hydrogen-atom abstraction. Final ly, 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 [CpMo(NO)(CH2SiMe3)(2)(Me)][Li(thf)(3)] ( 4). Warming of 4 in a C6D6 solution results in loss of methane and pro duction of 1. In most cases, the chemistry exhibited by the Mo system is duplicated by the analogous W congener, [CpW(NO)(CH2SiMe3)(2)]. Th e solid-state molecular structures of complexes 1 and 4 have been esta blished by single-crystal X-ray crystallographic analyses.