Linked and Fused Tungstaborane Clusters:  Synthesis, Characterization, and Electronic Structures of<i>bis</i>-{(η⁵-C₅Me₅W)₂B₅H₈}₂and (η⁵-C₅Me₅W)₂{Fe(CO)₃}<i>_n</i>B_6-<i>_n</i>H_10-<i>_n</i>,<i>n</i>= 0, 1

Abstract

In addition to (η 5 -C 5 Me 5 W) 2 B 5 H 9, (η 5 -C 5 Me 5 W) 3 (μ-H)B 8 H 8, and (η 5 -C 5 Me 5 W) 2 B 7 H 9 reported earlier, thermolysis of {η 5 -C 5 Me 5 W}H 3 B 4 H 8 ( 1 ) with BH 3 ·THF leads to the formation of bicapped closo -{η 5 -C 5 Me 5 W} 2 B 6 H 10 ( 2 ) in parallel with a B−B linked dimer of {η 5 -C 5 Me 5 W} 2 B 5 H 9 ( 4 ) and bis-{(η 5 -C 5 Me 5 W) 2 B 5 H 8 } 2 ( 3 ). Reaction of 4 with a 3-fold excess of Fe 2 (CO) 9 in hexane generates an iron analogue of 2, (η 5 -C 5 Me 5 W) 2 B 5 H 9 Fe(CO) 3 ( 5 ) in 46% yield. All the metallaboranes, 2, 3, and 5, have been characterized by 1 H, 11 B 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 [{η 5 -C 5 Me 5 Re} 2 B 7 H 7 ], 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, W 2 B 5, are joined by an exopolyhedral boron−boron bond.