Dicarbonyl(η-cyclopentadienyl)iron(II) derivatives of pentaborane(9)

Abstract

The [B₅H₈]^– anion reacts with [Fe(η-C₅H₅)(CO)₂I] to give [Fe(2-B₅H₈)(η-C₅H₅)(CO)₂](1). This can be deprotonated with KH to give the anion [Fe(2-B₅H₇)(η-C₅H₅)(CO)₂]^– which can react with another equivalent of [Fe(η-C₅H₅)(CO)₂I] to give [{Fe(η-C₅H₅)(CO)₂}₂(2,4-B₅H₇)](3); this is the first example of a compound with two transition-metal atoms bound to the pentaborane skeleton. Boron-11 and ¹H n.m.r. and mass spectroscopic data confirm the structures assigned to (1) and (3); these are consistent with the hypothesis that nido-penta-borate anions act as 2–3-η ligands in 16-electron transition metal compounds and as 2-σ ligands in 18-electron species. The electron-impact fragmentation of the compounds is briefly discussed.