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

The synthesis, spectroscopic and structural characterization of the bromo-boryl complexes (eta(5)-C(5)R(4)R')Fe(CO)(2)-B(2,4,6-Me(3)C(6)H(2))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. (eta(5)-C(5)H(5))Fe(CO)(2)B(2,4,6-Me(3)C(6)H(2))OC(6)H(4)(t)Bu-4, 6], and bridging borylene complexes {e.g. [(eta(5)-C(5)H(4)R)Fe(CO)(2)](2) B(2,4,6-Me(3)C(6)H(2)), 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 [(eta(5)-C(5)H(5))Fe(CO)(2)](2)B(2,4,6-Me(3)C(6)H(2)) yields the complex [(eta(5)-C(5)H(5))Fe(CO)](2)(mu(2)-CO)[mu(2)-B(2,4,6-Me(3)C(6)H(2))] (11), which features a supported bridging borylene ligand.