Direct insertion of sulfur, selenium and tellurium atoms into metallaborane cages using chalcogen powders

Reaction of [(η5-C5Me5)MCl4], 1–2 (1: M = Mo and 2: W) with six fold excess of [LiBH4·thf] followed by thermolysis with excess chalcogen powders (S, Se and Te) yielded dichalcomolybda- and tungstaboranes, [(η5-C5Me5M)2B4H4E2], 5–8 (5: M = Mo, E = S; 6: M = Mo, E = Se; 7: M = Mo, E = Te; 8: M = W, E = Se) in modest yields. The geometry of 5–8 resembles a hexagonal bipyramid with a missing connectivity of two chalcogen vertices and a very short cross cage metal–metal bonding. All these new dichalcometallaboranes have been characterized by mass, 1H, 11B, 13C NMR spectroscopy, and the structural types were unequivocally established by crystallographic analysis of compound 6.