Synthesis and Interconversion of V4, V7, and V8 Oxide Clusters: Unexpected Formation of Neutral Heptanuclear Oxido(alkoxido)vanadium(V) Clusters [V7O17(OR)(4,4′-tBubpy)3] (R = Et, MeOC2H4)

The octanuclear oxidovanadium(V) complex [V8O20(4,4'-(t)Bubpy)4] (1; 4,4'-(t)Bubpy = 4,4'-di-tert-butyl-2,2'-bipyridine) was synthesized in multigram-scale quantities by the reaction of VOSO4 with 4,4'-(t)Bubpy in the presence of sodium benzoate under O2. The reaction of 1 with MeOH under air afforded the tetranuclear oxidovanadium(V) complex [V4O8(OMe)4(4,4'-(t)Bubpy)2] (2) selectively. In contrast, treatment of 1 with EtOH or MeOC2H4OH under air gave the heptanuclear oxidovanadium(V) complexes [V7O17(OR)(4,4'-(t)Bubpy)3] (R = Et (3a), MeOC2H4 (3b)) having an unprecedented neutral V7O17(OR) core. Although 3a and 3b are relatively stable in CH2Cl2, slow diffusion of Et2O into the solution of 3a in CH2Cl2 afforded 1 as yellow crystals. Complex 2 was also converted into 1 by recrystallization from CHCl3-CH2Cl2/Et2O. (1)H and (51)V NMR as well as electrospray ionization mass spectrometry studies of the behavior of 2 in CD2Cl2 suggested the formation of the methoxido analogue of 3 (3c, R = Me), which is considered to be an intermediate species in the conversion of 2 to 1. The present results provide a rare example of interconversion among neutral vanadium(V) oxide cluster complexes by changing the solvent systems.