Reactivity of P₂N₂ and P₂N₂H₄ towards C₇H₈M(CO)₄ (M = Cr, Mo). X-ray structure of fac-(CO)₃Mo[PN₂P(O)]

The interaction of C₇H₈M(CO)₄(M = Cr, Mo) with half an equivalent of P₂N₂ (P₂N₂ = N,N′-bis[o-(diphenylphosphino)benzylidene]ethylenediamine) in THF at ambient temperature gives [cis-(CO)₄M]₂(P₂N₂) (I, M = Cr; II, M = Mo) in high yield. The interaction of C₇H₈M(CO)₄ with 1 equivalent of P₂N₂ in refluxed THF gives [cis-(CO)₄M]₂(P₂N₂), fac-(CO)₃M(PN₂P) (III, M = Cr; IV, M = Mo) and fac-(CO)₃M [PN₂P(O)] (V, M = Mo). The yield of the products depends on the length of the reaction time. For a short reaction time the major product is [cis-(CO)₄M]₂(P₂N₂), whereas for a long reaction time fac-(CO)₃M(PN₂P) is the major product. However, the interaction of C₇H₈Cr(CO)₄ with 1 equivalent of P₂N₂H₄ (P₂N₂H₄ = N,N′-bis[o-(diphenylphosphino)benzyl]ethylenediamine) in refluxed THF produces [cis-(CO)₄Cr]₂(P₂N₂H₄) (VI as the only isolated product in high yield. Prolonged refluxing of [cis-(CO)₄M]₂(P₂N₂) with P₂N₂ in THF does not give fac-(CO)₃M(PN₂P). In solution IV slowly oxidizes to V, whose structure has been determined by X-ray crystallography.