REACTIONS OF CHROMIO, TUNGSTENIO, AND PLATINIO NITRILE YLIDES WITH ARYLDIAZONIUM SALTS - TRIAZOLIN-5-YLIDENE COMPLEXES VS CLEAVAGE OF THE N-EQUIVALENT-TO-N(AR) BOND AND FORMATION OF N-CYANAMIDINES

The metallo nitrile ylides [M]CNCHR- ([M] = W(CO)5, R = Tos; [M] = [Pt(Cl)(PPh3)2]+, R = CO2Et) have been regenerated by deprotonation with LiBu(n) or NEt3 of the metal-coordinated alpha-CH-acidic isocyanides TOSMIC and ethyl isocyanoacetate and reacted regiospecifically with the aryldiazonium salts [4-XC6H4N2]BF4 (X = H, Cl, Me, NO2, NMe2), [4-MeOC6H4N2]PF6, and [2,4,6-Me3C6H2N2]BF4 to give the carbenoid and carbanionic 1,2,4-triazoles 1-10. In the case of the nitrile ylides [M{CNCHCO2Et}(CO)5]- (M = Cr, W), however, two isomeric products, 1,2,4-triazolin-5-ylidene (11a-15a) and N-cyanamidine complexes (11b-15b) were obtained. The latter can formally be described as products of insertion of isocyanide into the N=N triple bond of the diazonium component. The structural assignments are made on the basis of IR, NMR (H-1, C-13), and mass spectroscopy data as well as X-ray structure analyses of Cr(CO)5-{CN(H)C(CO2Et)NNPh} (11a) and Cr(CO)5{N=CN=C(CO2Et)N(H)-C6H4Cl-4}(12b).