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