Synthetic, structural and reaction chemistry of transition metal complexes containing the mesitylborylene ligand

Abstract

The synthesis, spectroscopic and structural characterization of the bromo-boryl complexes (η⁵-C₅R₄R′)Fe(CO)₂B(2,4,6-Me₃C₆H₂)Br (R = R′ = H, 2; R = H, R′ = Me, 3; R = R′ = Me, 4) are reported. These are shown to be versatile substrates for the synthesis of both asymmetric boryl complexes [e.g. (η⁵-C₅H₅)Fe(CO)₂B(2,4,6-Me₃C₆H₂)OC₆H₄^tBu-4, 6], and bridging borylene complexes {e.g. [(η⁵-C₅H₄R)Fe(CO)₂]₂B(2,4,6-Me₃C₆H₂), R = H, 7; R = Me, 8} via substitution chemistry with retention of the metal–boron bond. Complexes 7 and 8 are the first reported examples of structurally characterized bridging borylene complexes without a supporting M–M bond. Photolytically induced CO loss from [(η⁵-C₅H₅)Fe(CO)₂]₂B(2,4,6-Me₃C₆H₂) yields the complex [(η⁵-C₅H₅)Fe(CO)]₂(μ₂-CO)[μ₂-B(2,4,6-Me₃C₆H₂)] (11), which features a supported bridging borylene ligand.