Reactivity of a dichlorophosphido complex. Nucleophilic substitution reactions at metal coordinated phosphorus

Reaction of the dichlorophosphido complex [Cp*Mo(CO) ₃(PCl₂)] (1) with AlCl₃ leads to the bimetallic bridging P₂Cl₃ complex [{Cp*Mo(CO) ₃}₂(μ-P₂Cl₃)][AlCl₄] (2), which is formed via a Lewis-acid assisted nucleophilic substitution reaction, and not via a chlorophosphinidene intermediate. A similar reaction with external nucleophile PPh₃ leads to [Cp*Mo(CO) ₃(P(Cl)PPh₃)][AlCl₄] (3), which can be viewed as a phosphine coordinated chlorophosphinidene complex. Addition of two equivalents each of PPh₃ and AlCl₃ leads a double chloride displacement, and formation of the known triphosphenium salt [Ph ₃PPPPh₃][AlCl₄]. In this reaction the dichlorophosphido complex effectively act as a source of P⁺. Reaction of 1 with alkoxides leads to alkoxyphosphido complexes [Cp*Mo(CO) ₃{P(OR)Cl}] (R = p-t-butyl phenoxy, menthoxy). These complexes serve as precursors to transient alkoxy phosphinidenes [Cp*Mo(CO) ₃{POR}]⁺, which can be trapped with alkynes. A computational study on the chloro, alkoxy, and related amino and alkyl phosphinidenes shows that chloro and alkoxy phosphinidenes have minimal π-donation to P from Cl or OR, in contrast to stable aminophosphinidenes, which have significant N to P π-donation.