Chemistry of molybdaboranes: synthesis, structures, and characterization of a new class of open-cage dimolybdaheteroborane clusters

Abstract

Reaction of [Cp*MoCl₄], 1 (Cp* = η⁵-C₅Me₅), with [LiBH₄·thf] in toluene at −70 °C, followed by pyrolysis with excess dichalcogenides RE-ER (R = Ph, CH₂Ph, 2,6-(^tBu)₂-C₆H₂OH, (CH₃)₃C = ^tBu); E = S, Se) yielded a new class of hybrid clusters, 3−8: (3, [(Cp*Mo)₂ (μ-η¹-SPh)₂(μ₃-S)(H₂BSPh)]; 4, [(Cp*Mo)₂B₅H₈ (SPh)]; 5, [(Cp*Mo)₂B5H₈ (SePh)]; 6, [(Cp*Mo)₂B₂S₂H₂ (μ-η¹-S)]; 7, [(Cp*Mo)₂B₂H₅ (BSR)₂ (μ-η¹-SR)], (R = 2,6-(tBu)₂-C₆H₂OH); and 8, [(Cp*Mo)₂B₂H₅ (BSePh)₂ (μ-η¹-SePh)]. Compounds 3−8 have been isolated in modest yields as green or brown crystalline solids. In parallel with 3−8, [(Cp*Mo)₂B₅H₉] was isolated as a major product in all cases. The isolation and structural characterization of compounds 3 and 6−8 provided the first direct evidence of the existence of [(Cp*Mo)₂B₄H₈], 2, an intermediate in the formation of [(Cp*Mo)₂B₅H₉]. These new compounds have been characterized in solution by mass spectrometry, ¹H, ¹¹B, ¹³C NMR, and IR spectroscopy, and elemental analysis. The structural types were unequivocally established by X-ray crystallographic analysis of compounds 3−8.