Electron-precise 1,3-bishomocubanes - a combined experimental and theoretical study

Abstract

A combined experimental and quantum-chemical study of a series of homometallic metallaheteroboranes [(Cp*M)₂E₆B₂H₂] (M = Rh or RuH; E = S or Se; Cp* = η⁵-C₅Me₅), which are analogues of 1,3-bishomocubane, is reported. The thermolysis of nido-[(Cp*Rh)₂B₃H₇] (1) in the presence of S or Se powder in toluene yielded bishomocubane clusters [(Cp*Rh)₂(μ-E)₂(μ₃-E)₄B₂H₂], (3: E = S; 4: E = Se). In a similar fashion, the treatment of nido-[(Cp*RuH)₂B₃H₇] (2) with S or Se powder in p-xylene yielded [(Cp*Ru)₂(μ-E)₂(μ₃-E)₄B₂H₂] (5: E = S; 6: E = Se) and [(Cp*Ru)₂(μ₃-Se)(μ₄-Se)B₃H₅] (7). One of the noteworthy features of 3–6 is the presence of an electron-precise trichalcogenoborato ligand. All of the compounds have been characterized by mass spectrometry; IR spectroscopy; and ¹H, ¹¹B, and ¹³C NMR spectroscopy. The structures of 3, 4, 6, and 7 were established unequivocally by X-ray crystallographic analysis. Quantum-chemical calculations by DFT methods for 3, 4, and 6 showed reasonable agreement with the experimentally observed structural parameters. The large HOMO–LUMO gaps are consistent with the high stabilities of these complexes.