Bond-selective nitrile insertion into the 2H-azaphosphirene ring system as induced by tetracyanoethylene

Competitive reactions of 2H-azaphosphirene metal complexes 1a-c (M =Cr, Mo, W) with 1-piperidinonitrile and tetracyanoethylene in toluene have been observed at elevated temperatures. For the case of complex 1c, the delta5-1,2-azaphospholene complex 2c (as main product) and the 2H-1,4,2-diazaphosphole complex 3c (as by-product) were separated from the product mixture. At ambient temperature and using 1-piperidinonitrile as solvent, bond and regioselective insertion of 1-piperidinonitrile into the P-N bond of 2H-azaphosphirene metal complexes 1a-c (M = Cr, Mo, W) has been achieved in the presence of tetracyanoethylene (TCNE), yielding 2H-1,4,2-diazaphosphole metal complexes 3a-c, analogous reactions in benzo- or acetonitrile afforded the 2H-1,4,2-diazaphosphole tungsten complexes 3d, e. A preliminary study with the 2H-azaphosphirene tungsten complex 1c and 1-piperidinonitrile as solvent has revealed that substoichiometric amounts of TCNE (0.3 equiv) induce approximately 70% conversion of complex 1c. NMR data of the complexes 2c and 3a-e and the X-ray structure of complex 3c are discussed.