Bonding in clusters. Part 2. Hexaborane(10) and related metalloboranes

Abstract

Investigation of the bonding in Fe(CO)₃ derivatives of hexaborane(10) by self-consistent charge calculations provides a rationalisation for the formation of the only observed isomer 4-[B₅H₉Fe(CO)₃]. The highest occupied molecular orbital (h.o.m.o.) of this isomer is directly comparable to that in B₆H₁₀. Calculations on [C₂B₃H₇Fe(CO)₃] and observations on Co(η-C₅H₅) derivatives of B₆H₁₀ are used to suggest possible reasons for the stability of the known compounds. These results are used to predict that the most favourable structure of [C₄BH₅Fe(CO)₃] should contain adjacent Fe(CO)₃ and BH units in the basal plane. Previously reported photoelectron spectra are reasonably well reproduced by the calculations. Metalloborane derivatives of unknown isomers of B₆H₁₀ with B subrogated by Mn(CO)₃ or Fe(η-C₅H₅) units are similarly treated. Analysis of the bonding leads to an understanding of why the reported isomers are formed. Finally, the µ-bonded complex µ-[Fe(CO)₄]B₆H₁₀ has been analysed. Consideration of the frontier orbitals of B₆H₁₀ and Fe(CO)₄ leads to the construction of a unique bridged bond between the previously non-bonding electron density in the h.o.m.o. of B₆H₁₀ and an Fe 3d orbital.