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

Abstract

Strong evidence for a strictly intramolecular rearrangement process leading to 2 H -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 2 H -azaphosphirene complex 4 and another product 5 , which could not be isolated, but showed 31 P-NMR characteristics of a σ 4 λ 5 -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 -2 H -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 2 H -azaphosphirene complex. These results provide strong evidence for non-participation of the metal atom center in the ring-closure process giving the three-membered 2 H -azaphosphirene ring system.