Synthesis and dehydrocoupling reactivity of iron and ruthenium phosphine–borane complexes

Abstract

The Fe and Ru phosphine–borane complexes CpM(CO)₂PPh₂·BH₃ (1, M = Fe, 4, M = Ru) were synthesized utilizing the reaction of the phosphine–borane anion Li[PPh₂·BH₃] with the iodo complexes CpM(CO)₂I. The Fe complex 1 reacted with PMe₃ to yield CpFe(CO)(PMe₃)(PPh₂·BH₃) (2) and CpFe(PMe₃)₂(PPh₂·BH₃) (3) whereas the Ru species 4 gave only CpRu(CO)(PMe₃)(PPh₂·BH₃) (5). The complexes 1–5 were characterized by ¹H, ¹¹B, ¹³C and ³¹P NMR spectroscopy, MS, IR and X-ray crystallography for 1 to 4, and EA for 1, 2 and 4. The reactivity of 1 and 4 towards PPh₂H·BH₃ was explored. Although no stoichiometric reactions were detected under mild conditions, both 1 and 4 were found to function as dehydrocoupling catalysts to afford Ph₂PH·BH₂·PPh₂·BH₃ in the melt at elevated temperature (120 °C). The carbonyl Fe₂(CO)₉ also functioned as a dehydrocoupling catalyst under similar conditions. Complex 1 and Fe₂(CO)₉ represent the first reported active Fe complexes for the catalytic dehydrocoupling of phosphine–borane adducts.