Reactivity of Cationic Molybdenum(II) Complexes. Part 2. Electrochemical Reduction of the Eighteen-electron Complexes [Mo(CO)3(eta-5-C5Me5)L] + [L=CO, p-MeC6H4NC, or P(OMe)3]. Crystal Structure of [Mo2(CO)6(eta-5-C5Me5)]

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)-(Ph-CC-Ph)2]+ indicates that it can be reduced in two sequential one-electron quasi-reversible steps, [Mo(CO)(η5-C5Me5)(Ph-CC-Ph)2] and [Mo(CO)(η5-C5Me5)(Ph-CC-Ph)]– however being stable only for short times (t½≈ 50 s).