Reactivity of ether- and amine-complexed dimers and tetramers of alkyllithiums towards triphenylmethane

Kinetics of Lewis base (LB) complexed primary and secondary sigma-alkyllith iums (RLi) with triphenyl methane (TPMH) are reported. RLis in which one or two LB groups (-OMe, -NMe2, -NMeR) are part of the molecule form, in benze ne, intramolecularly complexed tetramers, for example, 2(4), or dimers, for example, 4(2), They are used as models for their intermolecular congeners R4Li4,. 4LB and R2Li2. 4LB (LB = NR3' OR2'). Nonunity reaction orders in [R Li] are in line with reactions via as yet unidentified 1:1 complexes formed in an equilibrium (K(stat. corr.)approximate to 1) between aggregated RLi and TPMH. In some cases, a tetramer/dimer equilibrium mixture undergoes com plexation/reaction. Reaction rates correlate linearly with calculated conce ntrations of the complexes. Relative rates of complexes range from 1 [prim- R4Li4. 3LB . TPMH (presumed)] to 4250 [sec-R2Li2. 3LB . TPMH (presumed)]. A major role in the reactivity enhancement owing to LB-induced conversion of tetramers into dimers is ascribed to increased LBI participation in LB-ric her dimer transition states. Amine and ether complexes have practically equ al reactivities, Lithiation of TPMH by dimeric RCH2Li is retarded by a fact or of 24000 if a silyl group is linked to the alpha-carbon.