Structure and Bonding Properties of the Complex (η⁵-Diphenylfulvene)Mn(CO)₃⁺

Reaction of cymantrene (6) with n-butyllithium followed by benzophenone and subsequent hydrolysis yielded 1-(diphenylhydroxymethyl)(η⁵-cyclopentadienyl)(tricarbonyl)manganese (7). Treatment of 7 with HBArF·2Et₂O in methylene chloride affords the blue cation 2b. Investigations of single crystals of 2b by means of the X-ray technique showed a displacement of the exo carbon by 6.6° toward the metal and a pronounced bond alternation of the C−C bonds of the fulvene moiety. DFT calculations on the parent system 2a and on a system with a planar fulvene moiety (2a‘) yielded an energy difference of 23 kJ/mol in favor of 2a. As a result of the bending of the exo methylene group the positive charge at the metal is increased and at C9 decreased.