Novel class of heterometallic cubane and boride clusters containing heavier group 16 elements

Abstract

Thermolysis of an in situ generated intermediate, produced from the reaction of [Cp*MoCl₄] (Cp* = η⁵-C₅Me₅) and [LiBH₄.THF], with excess Te powder yielded isomeric [(Cp*Mo)₂B₄TeH₅Cl] (2 and 3), [(Cp*Mo)₂B₄(μ₃-OEt)TeH₃Cl] (4), and [(Cp*Mo)₄B₄H₄(μ₄-BH)₃] (5). Cluster 4 is a notable example of a dimolybdaoxatelluraborane cluster where both oxygen and tellurium are contiguously bound to molybdenum and boron. Cluster 5 represents an unprecedented metal-rich metallaborane cluster with a cubane core. The dimolybdaheteroborane 2 was found to be very reactive toward metal carbonyl compounds, and as a result, mild pyrolysis of 2 with [Fe₂(CO)₉] yielded distorted cubane cluster [(Cp*Mo)₂(BH)₄(μ₃-Te){Fe(CO)₃}] (6) and with [Co₂(CO)₈] produced the bicapped pentagonal bipyramid [(Cp*MoCo)₂B₃H₂(μ₃-Te)(μ-CO){Co₃(CO)₆}] (7) and pentacapped trigonal prism [(Cp*MoCo)₂B₃H₂(μ₃-Te)(μ-CO)₄{Co₆(CO)₈}] (8). The geometry of 8 is an example of a heterometallic boride cluster in which five Co and one Mo atom define a trigonal prismatic framework. The resultant trigonal prism core is in turn capped by two boron, one Te, and one Co atom. In the pentacapped trigonal prism unit of 8, one of the boron atoms is completely encapsulated and bonded to one molybdenum, one boron, and five cobalt atoms. All the new compounds have been characterized in solution by IR, ¹H, ¹¹B, and ¹³C NMR spectroscopy, and the structural types were unambiguously established by crystallographic analysis of 2 and 4–8.