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)((OBu)-Bu-t)(2)](2) 1a (M = Li), 1b (M = Na), [(thf)(2)K(MeZn)(OSiMe3)(2)](2) 2 and [(tmeda)KZn(OSiM3)(3)](2) 3 are easily accessible from the reaction of Me2Zn with MOR (molar ratio 1 : 1; M = Li, Na, K; R = Bu-t, 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 (KOBu)-Bu-t in the molar ratio of 1 : 1 in toluene affords the donor solvent-free K-Zn-O cluster [K(MeZn)(3)((OBu)-Bu-t)(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.