THE ROLE OF NEUTRAL AND RADICAL ANIONIC ORGANOZINC COMPLEXES IN THE ALKYLATION REACTIONS OF 1,4-DIAZA-1,3-BUTADIENES WITH DIORGANOZINC COMPOUNDS

We have earlier postulated the intermediacy of organozinc radical spec ies in the regioselective alkylation reactions of 1,4-di-tert-butyl-1, 4-diaza-1,3-butadiene (t-BuNCHCHN-t-Bu) with diorganozinc compounds (Z nR2). To verify these postulates, we have prepared and studied the neu tral organozinc radical complex MeO(CH2)(3)Zn(t-BuNCHCHN-t-Bu) (A) and two diorganozinc radical-anionic complexes, M[R2Zn(t-BuNCHCHN-t-Bu)] (R = Me (8a), Et (8b)). A was prepared in situ by the reaction of t-Bu NCHCHN-t-Bu with bis(methoxypropyl)zinc. Complexes 8 were prepared by reducing the 1:1 coordination complex ZnMe2(t-BuNCHCHN-t-Bu) (1a) with potassium or by the nucleophilic addition of K(t-BuNCHCHN-t-Bu) to Zn R2 (R = Me, Et). The resulting radical-anionic complexes are thermally unstable and readily undergo an intermolecular single-electron transf er, giving a mixture of the metallacyclic heteroleptic zincate complex es K[ZnR(t-BuNCHCHN-t-Bu)] (9) and K[ZnR(t-BuNC(R)CHN-t-Bu)] (10). The ratio in which the latter complexes are formed depends on the R group and on the concentration and the temperature. Alternatively, 9 has be en prepared separately from the reduction of [ZnR(t-BuNCHCHN-t-Bu)](2) (4) with 2 equiv of potassium. The crystal structures of two complexe s of 9, i.e. {9a(THF)}(n) and {9c(Et2O)(1/2)}(n), have been determined , Both complexes form linear coordination polymers containing alternat ing potassium cations and zinc-diazabutadiene anions.