A homobimetallic complex of chromium(0) with a σ-borane component

Abstract

The synthesis, characterization, and reactivity of a chromium(0) complex bearing an amine–borane moiety (η⁶-C₆H₅CH₂NMe₂·BH₃)Cr(CO)₃ (2) is reported. Photolysis of complex 2 results in the elimination of a CO ligand followed by the formation of an intramolecular σ-borane complex (η¹-(η⁶-C₆H₅CH₂NMe₂·BH₂–H))Cr(CO)₂ (3). This species was characterized in solution by NMR spectroscopy. Reaction of complex 2 with photochemically generated (OC)₅Cr(THF) affords a novel homobimetallic σ-borane complex (OC)₃Cr(η⁶-C₆H₅CH₂NMe₂·BH₂–H–Cr(CO)₅) (4), wherein one of the BH moieties is bound to the chromium center in an η¹-fashion. The σ-borane complex 4 was isolated in moderate to good yield (72%). The BH₃ fragment in the complexes 3 and 4 are highly dynamic involving exchange of the BH hydrogen bound to the metal with the terminal BH hydrogen atoms. The dynamics has been studied using variable-temperature NMR spectroscopy. Complexes 2 and 4 have been characterized by X-ray crystallography.