Degradation Chemistry of Dimetallaboranes, [(Cp*M)₂B₅H_9+x ] with [Ph₂Se₂] (x=2 or 0, M = V or Cr)

The synthesis and structural characterization of new divanadaborane clusters are reported. The pressure tube thermolysis of an intermediate formed by the reaction of [(Cp*VCl2)(3)] with [LiBH4THF] and [BH3THF] in diglyme at 160 degrees C yielded 6-sep, 7-vertex oblato-nido cluster, [(Cp*V)(2)B5H11], 2 (Cp* = pentamethyl-eta(5)-cyclopentadienyl). In an attempt to test the reactivity of this cluster with chalcogenide ligands, thermolysis of 2 with [Ph2E2] (E = S, Se, or Te) in toluene was carried out. While the reaction of 2 with [Ph2Se2] resulted in the formation of [(Cp*V)(2)B4H8(SePh)(mu-SePh)], 3, via cluster degradation reaction, [Ph2S2] and [Ph2Te2] did not generate analogous clusters. Compound 3 is an example of a tetraborane cluster being stabilized by two SePh fragments, one bridging the two Cp*V fragments while the other forming a terminal bond with one of the boron atoms. In an attempt to explore the cluster degradation reaction with analogous group 6 metallaborane [(Cp*Cr)(2)B5H9], 5, we treated it with [Ph2Se2] that led to the formation of terminally substituted [(Cp*Cr)(2)B5H7(SePh)(2)], 6. All the clusters were characterized by using various spectroscopic studies and X-ray diffraction analysis. Quantum chemical calculations using density functional theory methods were carried out to gain more insight into the bonding and electronic structure of 3 and 6.