Facile synthesis and structural variation of novel heterobimetallic alkali metal–zinc-alkoxide and -siloxide clusters

Abstract

The novel alkali metal zinc-alkoxide and the first -siloxide aggregates [(thf)M(MeZn)(O^tBu)₂]₂1a (M = Li), 1b (M = Na), [(thf)₂K(MeZn)(OSiMe₃)₂]₂2 and [(tmeda)KZn(OSiMe₃)₃]₂3 are easily accessible from the reaction of Me₂Zn with MOR (molar ratio 1 ∶ 1; M = Li, Na, K; R = ^tBu, SiMe₃) in boiling thf and tmeda, respectively. While 1a, 1b and 2 possess distorted M₂Zn₂O₄ heterocubane frameworks, compound 3 consists of a K₂Zn₂O₆ core of a strongly distorted, face-fused double-heterocubane with two missing corners. In contrast, heating a mixture of Me₂Zn and KO^tBu in the molar ratio of 1 ∶ 1 in toluene affords the donor solvent-free K–Zn–O cluster [K(MeZn)₃(O^tBu)₄] 4 which crystallizes as a polymer of strongly distorted [KZn₃O₄] heterocubanes via intermolecular agostic K⋯MeZn interactions. The formation of the clusters may be rationalized in terms of alkali metal ion- and donor solvent-dependent ligand exchange reactions of methyl(alkoxide)- and methyl(siloxide)-zincates as initial products. Some of the initial products have been detected by means of electro spray ionisation (ESI) mass spectrometry.