THERMAL AND PHOTOCHEMICAL SUBSTITUTION AND DISPROPORTIONATION REACTIONS OF THE HETERODINUCLEAR COMPOUND CPMO(CO)(3)-CO(CO)(4)

The thermal and photochemical substitution and disproportionation reactions of the heterodinuclear CpMo(CO)(3)-Co(CO)(4) complex (1) with phosphorus-donor ligands in 3-methylpentane (3MP) and CH2Cl2 were investigated. A CO dissociative pathway, leading to substitution, and a radical chain pathway initiated by associative attack of the ligand, leading to disproportionation, have been found to be operative in the thermal reactions. Reaction products differ, depending on the electronic and steric requirements of the ligand. Substitution on Co is observed foe all the phosphorus ligands. For P(n-Bu)(3), PPh(3), P(OMe)(3), and P(OPh)(3), small amounts of substitution on Mo have also been observed in addition to the major Co substitution. For ligands such as PPh(3), P(i-Pr)(3), P(c-Hx)(3), and P(OPh)(3), monosubstitution is the only observable process in 3MP; it occurs exclusively on Co for very bulky ligands P(i-Pr)(3) and P(c-Hx)(3). Reactions with P(n-Bu)(3) and P(OMe)(3) under normal thermal conditions favor a disproportionation pathway, forming the ionic product [CpMo(CO)(2)L(2)](+)[Co(CO)(4)](-) (L = P(n-Bu)(3) or P(OMe)(3)). Trace quantities of oxygen in the solution quench the thermally-induced radical chain processes. Upon photochemical initiation of the disproportionation reaction in CH2Cl2, small amounts of [Co(CO)(3)L(2)](+) and [CpMo(CO)(3)](-) are also formed in addition to [CpMo(CO)(2)L(2)](+) and [Co(CO)(4)](-) (L = PPh(3), P(i-Pr)(3), or P(c-Hx)(3)). The X-ray crystal structure of [CpMo(CO)(2)(P(n-Bu)(3))(2)][Co(CO)(4)] is reported.