Planar triple-decker and capped octahedral clusters of group-6 transition metals

Abstract

Recent isolation and structural characterization of a planar triple-decker metallaborane complex of tungsten prompted us to synthesize its molybdenum analogue. Therefore, we have explored the thermolysis reaction of the intermediates obtained from the low-temperature reaction of [Cp*MoCl4] (Cp* = η5-C5Me5) and LiBH4 with Co2(CO)8. The reaction indeed produced the analogous triple-decker complex of molybdenum with a planar middle-deck [(Cp*Mo)2{µ-η6:η6-B4H4Co2(CO)5}(H)2], 1, along with the formation of the reported [(Cp*Mo)2B5H9] metallaborane. In an effort to isolate multi-decker complexes with a different geometries, we have also further explored the thermolysis reaction of the intermediates obtained from the low-temperature reaction of [Cp*WCl4] and LiBH4 with Co2(CO)8. The reaction afforded an octahedral cluster, [{Cp*W(CO)2}2(µ-H)2B3H3Co2(CO)4], 2, along with the formation of the bimetallic cluster [(Cp*W)2B3H3(µ-H)2Co2(CO)4(µ-CO)2], 3. The cage geometry of compound 2 is based on an octahedron with one additional vertex capping a trigonal face. That of compound 3 is a bicapped trigonal-bipyramidal analogue to the parent compound [(Cp*W)2B5H9]. While compound 1 has been characterized by various spectroscopic analyses, compounds 2 and 3 have been characterized by multiple spectroscopic and single-crystal X-ray diffraction analyses. Density-functional theory (DFT) calculations account for their stability and structural variation.