Linked and Fused Tungstaborane Clusters: Synthesis, Characterization, and Electronic Structures of bis-{(η5-C5Me5W)2B5H8}2 and (η5-C5Me5W)2{Fe(CO)3}nB6-nH10-n, n = 0, 1
Résumé
In addition to (η5-C5Me5W)2B5H9, (η5-C5Me5W)3(μ-H)B8H8, and (η5-C5Me5W)2B7H9 reported earlier, thermolysis of {η5-C5Me5W}H3B4H8 (1) with BH3*THF leads to the formation of bicapped closo-{η5-C5Me5W}2B6H10 (2) in parallel with a B−B linked dimer of {η5-C5Me5W}2B5H9 (4) and bis-{(η5-C5Me5W)2B5H8}2 (3). Reaction of 4 with a 3-fold excess of Fe2(CO)9 in hexane generates an iron analogue of 2, (η5-C5Me5W)2B5H9Fe(CO)3 (5) in 46% yield. All the metallaboranes, 2, 3, and 5, have been characterized by 1H, 11B NMR spectra and crystal structure determinations. The structures of 2 and 5 appear to follow the regular electron counting rules as they possess seven skeletal electron pairs (sep) appropriate for bicapped octahedral structures. However, their electronic structures revealed by a molecular orbital analysis is more closely related to that of [{η5-C5Me5Re}2B7H7], a cluster that does not obey the classical electron counting rules. Clusters 2 and 5 are notable examples of closo clusters containing four bridging hydrogens. 3 is a coupled-cage structure in which two bicapped trigonal bipyramidal frameworks, W2B5, are joined by an exopolyhedral boron−boron bond.