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]c hlorophosphane (2) and triethylamine under CO atmosphere; the byproducts, d inuclear 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 triethylamin e in dichloromethane afforded 2H-azaphosphirene complex 4 and another produ ct 5, which could not be isolated, but showed P-31-NMR characteristics of a sigma (4)lambda (5)-phosphorus center posses sing a P-H function. {cis-[et hoxy/amino(aryl)carbene](triorganylphosphane)chromium(0)) and -tungsten(0) complexes 6a,b, 7a,b and 11, 12 were synthesized, 6a and 7b additionally ch aracterized by X-ray crystallography, and reacted also with methylene(chlor o)phosphane 2 in the presence of triethylamine, thus yielding cis-2H-azapho sphirene triorganylphosphane complexes 8a,b and 13a,b, which were unambiguo usly confirmed by act spectroscopy. The latter reactions proceeded with cis -stereospecificity. Significant chiral induction was not observed in the re action leading to 13a,b, and racemization occured, most probably, at the ph osphorus of the 2H-azaphosphirene complex. These results provide strong evi dence for non-participation of the metal atom center in the ring-closure pr ocess giving the three-membered 2H-azaphosphirene ring system. (C) 2001 Els evier Science B.V. All rights reserved.