Reactivity of cationic molybdenum(II) complexes. Part 2. Electrochemical reduction of the eighteen-electron complexes [Mo(CO)3(η5-C5Me5)L]+[L = CO, p-MeC6H4NC, or P(OMe)3]. Crystal structure of [Mo2(CO)6(η5-C5Me5)2]

Abstract

The 18-electron cationic complexes [Mo(CO)₃(η⁵-C₅Me₅)L]⁺[L = CO, p-MeC₆H₄NC, or P(OMe)₃] undergo, in dichloromethane solvent, a one-electron cathodic process, which gives rise to different products depending upon the nature of L. Through an e.c.c. electrode mechanism, the irreversible one-electron reduction of [Mo(CO)₄(η⁵-C₅Me₅)]⁺ and [Mo(CO)₃(η⁵-C₅Me₅)(p-MeC₆H₄NC)]⁺ affords the dimer [Mo₂(CO)₆(η⁵-C₅Me₅)₂], whereas [Mo(CO)₃(η⁵-C₅Me₅){P(OMe)₃}]⁺ leads to [Mo₂(CO)₄(η⁵-C₅Me₅)₂{P(OMe)₃}₂]. The dimer [Mo₂(CO)₆(η⁵-C₅Me₅)₂] has been characterized by an X-ray structure determination. A preliminary electrochemical investigation on [Mo(CO)(η⁵-C₅Me₅)-(PhCCPh)₂]⁺ indicates that it can be reduced in two sequential one-electron quasi-reversible steps, [Mo(CO)(η⁵-C₅Me₅)(PhCCPh)₂] and [Mo(CO)(η⁵-C₅Me₅)(PhCCPh)]^– however being stable only for short times (t_½≈ 50 s).