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

The novel alkali metal zinc-alkoxide and the first -siloxide aggregates [(thf)M(MeZn)(OtBu)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 KOtBu in the molar ratio of 1 :1 in toluene affords the donor solvent-free K-Zn-O cluster [K(MeZn)3 (OtBu)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.