Synthesis and chemistry of the open-cage cobaltaheteroborane cluster [{(η⁵-C₅Me₅)Co}₂B₂H₂Se₂]: a combined experimental and theoretical study

Abstract

Reaction of [(η⁵-C₅Me₅)CoCl]₂ with a two-fold excess of [LiBH₄·thf] followed by heating with an excess of Se powder produces the dicobaltaselenaborane species [{(η⁵-C₅Me₅)Co}₂B₂H₂Se₂], 1, in good yield. The geometry of 1 resembles a nido pentagonal [Co₂B₂Se₂] bipyramid with a missing equatorial vertex. It can alternatively be seen as an open cage triple-decker cluster. Isolation of 1 permits its reaction with [Fe2(CO)9] to give heterometallic diselenametallaborane [{(η⁵-C₅Me₅)Co}Fe(CO)₃B₂H₂Se₂], 2. The geometry of 2 is similar to that of 1 with one of the [(η⁵-C₅Me₅)Co] groups replaced by the isolobal, two-electron fragment [Fe(CO)₃]. Both new compounds have been characterized by mass spectrometry, and by ¹H, ¹¹B and ¹³C NMR spectroscopy. The structural architectures have been unequivocally established by crystallographic analysis. In addition, density functional theory calculations were performed to investigate the bonding and electronic properties. The large HOMO–LUMO gaps computed for both clusters are consistent with their thermodynamic stability. Natural bond order calculations predict the absence of metal–metal bonding interaction.