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

• Facile nucleophilic substitution at metal bound phosphorus.
• The first cationic alkoxy and aryloxyphosphinidenes.
• A computational study on the role of heteroatom substituents in stabilizing cationic phosphinidene complexes.

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 [Ph3PPPPh3][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.

Attempted chloride abstraction from a molybdenum PCl2 complex leads to nucleophilic substitution and P–P bond formation, but not to a chlorophosphinidene. The PCl2 complex does serves as a precursor to alkoxyphosphido complexes, which can be converted to alkoxy phosphinidene complexes via chloride abstraction.Figure optionsDownload as PowerPoint slide