Syntheses of 2H,1,3,2-diazaphosphole, 2H-1,4,2-diazaphosphole, and Δ3-1,3,2-Oxazaphospholene complexes;: First examples of 2H-azaphosphirene complex formation by [2+1] cycloaddition

Thermal ring-opening of {[2-bis(trimethylsilyl)methyl-3-phenyl-2H-azaphosphirene-kappa P]pentacarbonyltungsten(0)} (1) in the presence of various nitriles is investigated, in which toluene and/or the nitriles are used as solvents. In toluene, for example: the 3-(1-piperidino)-substituted 2H-azaphosphirene complex 5b, 4-(1-piperidino)-5-phenyl- and 4,5-bis(1-piperidino)-substituted 2H-1,3,2-diazaphosphole complexes 6b,d are obtained if 1-piperidino nitrile (2b) is employed as trapping reagent. Furthermore, a new three-component reaction is presented, using the 2H-azaphosphirene complex 1 and a mixture of two different nitriles, thus giving access to 4,5-mixed-substituted 2H-1,3,2-diazaphosphole complexes 6a,b and 6e-h. The chemo- and regioselectivity of such reactions is rationalized by [3+2] cycloadditions of transiently formed C-dialkylamino-substituted nitrilium phosphane ylide complexes 3b,c to nitriles. Use of two equivalents of dialkyl cyan amides and four equivalents of either ethyl cyanoformate or phenyl glyoxonitrile resulted in dual trapping reactions of complexes 3b,c, forming 2H-1,3,2-diazaphosphole complexes 6i-k and Delta(3)-1,3,2-oxazaphospholene complexes 8a-g. Reaction of the 2H-azaphosphirene complex 1 with ethyl cyanoformate in toluene gave exclusively the 4,5-bis(ethoxycarbonyl)-2H-1,3,2-diazaphosphole complex 61; even in benzonitrile, the mixed-substituted 2H-1,3,2-diazaphosphole complex 6m is formed only as a by-product. The first 2H-1,4,2-diazaphosphole complex 9 was synthesized along with the regioisomeric 2H-1,3,2-diazaphosphole complex 6n (ratio of 9:6n:6:1) through thermal ring-opening of 2H-azaphosphirene complex 1 in neat benzonitrile. The structures of 2H-1,3,2-diazaphosphole complex 6c, 2R,5S-Delta(3)-1,3,2-oxazaphospholene complex 8a and 2H-1,4,2-diazaphosphole complex 9 were determined by single-crystal X-ray diffraction.