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

The thermal and photochemical substitution and disproportionation reac tions of the heterodinuclear CpMo(CO)(3)-Co(CO)(4) complex (1) with ph osphorus-donor ligands in 3-methylpentane (3MP) and CH2Cl2 were invest igated. A CO dissociative pathway, leading to substitution, and a radi cal chain pathway initiated by associative attack of the ligand, leadi ng to disproportionation, have been found to be operative in the therm al reactions. Reaction products differ, depending on the electronic an d steric requirements of the ligand. Substitution on Co is observed fo e 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 ob servable process in 3MP; it occurs exclusively on Co for very bulky li gands 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 quen ch the thermally-induced radical chain processes. Upon photochemical i nitiation 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), o r P(c-Hx)(3)). The X-ray crystal structure of [CpMo(CO)(2)(P(n-Bu)(3)) (2)][Co(CO)(4)] is reported.