Photochemical reactions with phosphines, metal-carbonyl

CO substitution in heteronuclear cobalt carbonyl complexes has also been studied. Several phosphines were used in exchange reactions with CO in the complex CpMo(CO)3-Co(CO)4. Both a CO dissociative pathway, leading to substitution, and a radical chain pathway, initiated by associative attack of the phosphine and subsequent disproportionation (see Disproportionation), were found depending on reaction conditions (thermal or photochemical treatment) and the basicity and sterics of the phosphine ligands. As seen in substitution reactions with Co2(CO)g, strongly basic phosphines add to the complex via disproportionation, while less basic phosphines add via substitution. However, the metal centers help determine where the phosphine adds because the rates of substitution on each metal center differ depending on which pathway, dissociative or radical chain, is operative. ... 

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