Formation of phosphorus heterocycles using a cationic electrophilic phosphinidene complex

• Cycloaddition reactions of a stable cationic terminal phosphinidene complex.
• Facile formation of a wide variety of phosphorus heterocycles via complex.
• Simple removal and separation of heterocycles from metal.
• Transformation from amino to chloro substituted P heterocycles.

The electrophilic terminal aminophosphinidene complex [CpFe(CO)2P{N-i-Pr2}][X] (Cp = cyclopentadienyl, i-Pr = isopropyl, X = AlCl4 or NaBPh4), generated from [CpFe(CO)2{P(Cl)N-i-Pr2}] by chloride abstraction, reacts with alkynes and alkenes via (1 + 2) cycloaddition to form phosphirenes and phosphiranes respectively. Conjugated alkenes react with [CpFe(CO)2P{N-i-Pr2}]+ to form phosphirane intermediates, which then rearrange to 3-phospholenes. The phosphinidene complex reacts with benzylideneacetone to give an oxo-3-phospholene complex. Azobenzene reacts with [CpFe(CO)2P{N-i-Pr2}]+ to form a benzodiazophosphole via C–H activation. Addition of HCl or HBF4·Et2O to the iron diphenylphosphirene complex and iron benzodiazophosphole complex results in P–N bond cleavage, yielding the respective chlorophosphorus heterocyclic complexes. The heterocycles can be removed from the metal complexes to make metal free phosphorus heterocycles by addition of trimethyl- or triethylphosphine.

The cationic terminal phosphinidene complex [CpFe(CO)2{PN-i-Pr2}]+ reacts with a wide variety of unsaturated substrates, making it a versatile reagent for the formation of P-heterocycles.Figure optionsDownload as PowerPoint slide