SYNTHESES AND REACTIONS OF HYDRAZINE AND DIAZENE COMPLEXES OF TUNGSTEN - THE 1ST EXAMPLE OF MONODENTATE COORDINATION OF NH=NH

Reaction of trans,trans-W(H)(CO)2(NO)(PR3)2 (2a, R = Ph; 2b, R = Cy) w ith triflic acid gives trans,trans-W(eta1-OSO2CF3)(CO)2(NO)(PR3)2(3a, R = Ph; 3b, R = Cy) and dihydrogen in excellent yield. The weakly coor dinated triflato ligands of 3a and 3b are cleanly displaced by hydrazi ne to give yellow tungsten-hydrazine coordination complexes [trans,tra ns-W(NH2NH2)(CO)2(NO)(PR3)2+][SO3CF3-] (4a, R = Ph; 4b, R = Cy). React ion of 4a and 4b with Pb(OAc)4 at -78-degrees-C results in selective o xidation of the hydrazine ligands to give [trans,trans-W(NH=NH)(CO)2(N O)(PR3)2+][SO3CF3-] (5a, R = Ph; 5b, R = Cy). By using (N2H4)-N-15, th e isotopically labeled derivatives ans,trans-W(15NH215NH2)(CO)2(NO)(PP h3)2+][SO3CF3-] ([N-15(2)]4a) and [trans,trans-W(15NH=15NH)(CO)2(NO)(P Ph3)2+] [SO3CF3-] ([N-15(2)]5a) have been prepared. The magnitudes of the 3J(HH) (27.0 Hz) and the two 1J(NH) (-46.0, -65.0 Hz) exhibited by the NH=NH ligand suggest that diazene is coordinated to tungsten (i) via a single nitrogen atom and (ii) with trans-NH=NH geometry. Variabl e-temperature H-1 NMR data for 5a and 5b also support the trans-NH=NH assignment. Although 5a undergoes slow decomposition in solution, exch ange of the noninnocent triflate anion with sodium tetraphenylborate r esults in a more robust salt, [trans,trans-W(NH=NH)(CO)2(NO)(PPh3)2+][ BPh4-] (5c). Nucleophilic displacement of NH=NH from 5a by bromide ion at 0-degrees-C gives N2 and N2H4, the known products of the bimolecul ar disproportionation of diazene. In the presence of excess diphenylac etylene, bromide displacement of NH=NH from 5a gives cis-stilbene and N2 in addition to hydrazine.