Stereochemically defined metal carbene complexes as chemical probes for studies of the ring formation of 2H-azaphosphirene complexes

Strong evidence for a strictly intramolecular rearrangement process leading to 2H-azaphosphirene complex 4 was obtained by reactions of {[amino(phenyl)carbene]pentacarbonyltungsten(0)} (1) with [bis(trimethylsilyl)methylene]chlorophosphane (2) and triethylamine under CO atmosphere; the byproducts, dinuclear carbene complexes 3a,b, were obtained and characterized as E,E- and E,Z-isomers. Reaction of a 5:2 mixture of complexes 3a,b with triethylamine in dichloromethane afforded 2H-azaphosphirene complex 4 and another product 5, which could not be isolated, but showed 31P-NMR characteristics of a σ4λ5-phosphorus center possessing a P–H function. {cis-[ethoxy/amino(aryl)carbene](triorganylphosphane)chromium(0)} and -tungsten(0) complexes 6a,b, 7a,b and 11, 12 were synthesized, 6a and 7b additionally characterized by X-ray crystallography, and reacted also with methylene(chloro)phosphane 2 in the presence of triethylamine, thus yielding cis-2H-azaphosphirene triorganylphosphane complexes 8a,b and 13a,b, which were unambiguously confirmed by NMR spectroscopy. The latter reactions proceeded with cis-stereospecificity. Significant chiral induction was not observed in the reaction leading to 13a,b, and racemization occured, most probably, at the phosphorus of the 2H-azaphosphirene complex. These results provide strong evidence for non-participation of the metal atom center in the ring-closure process giving the three-membered 2H-azaphosphirene ring system.