Novel Class of Heterometallic Cubane and Boride Clusters Containing Heavier Group 16 Elements

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