Alkali metal salts of ditopic carbanionic carbenes as reagents for the synthesis of novel complexes of group 12 and 14 metals.

Reaction of the lithiated N-heterocyclic carbene [:C[N(2,6-(i)Pr2C6H3)]2(CH)CLi]n (LiIPr) with KO(t)Bu in diethylether (Et2O) afforded the novel organo-potassium compound [:C[N(2,6-(i)Pr2C6H3)]2(CH)CK(THF)2] (KIPr·2THF). Both LiIPr and KIPr can be interpreted as ditopic carbanionic carbenes (or alkali metal salts of anionic "dicarbenes") and are interesting precursors for the synthesis of novel metal complexes bearing carbanionic carbenes as ligands. Reaction of KIPr with M[N(SiMe3)2]2 (M = Zn, Sn) afforded salts of the anionic three coordinate complexes [M{C(CH)[N(2,6-(i)Pr2C6H3)]2C:}{N(SiMe3)2}2](-) (M = Zn (1) and Sn (2)). Contrasting reactivity was observed for the other group 14 bis-amide compounds M[N(SiMe3)2]2 (M = Ge, Pb), which initially appear to yield analogous 1 : 1 complexes (M = Ge (3) and Pb (4)), however over time give rise to compounds bearing two ditopic carbanionic carbenes ([M{C(CH)[N(2,6-(i)Pr2C6H3)]2C:}2{N(SiMe3)2}](-); Ge (5) and Pb (6)) and the tris-amide anions ([M{N(SiMe3)3}](-)), presumably via a Schlenk-type equilibrium. Compounds 5 and 6 can be directly synthesized by reacting M[N(SiMe3)2]2 (M = Ge, Pb) with two equivalents of KIPr, respectively.