REACTIONS OF COORDINATED DIAZENE IN RHENIUM AND TUNGSTEN COMPLEXES - DEPROTONATION OF LIGATED NH=NH AND SUBSEQUENT H-MIGRATION TO CARBONYL LIGANDS TO GIVE METAL FORMYLS

The tungsten diazene complex [trans,trans-W(NH=NH)(CO)2(NO)(PPh3)2+] [SO3CF3-] (1) reacts with NH2R (R = H, CH3, NH2) to give trans,trans-W(eta1-OSO2CF3)(CO)2(NO)(PPh3)2 (2), trans,trans-W(H)(CO)2(NO)(PPh3)2 (3), and [trans,trans-W(NH2NH2)(CO)2(NO)(PPh3)2+] [SO3CF3-] (4). If the reaction of NH2R with 1 is monitored at -78-degrees-C, intermediates in the formation of 3 can be observed, which have been characterized as the neutral 6-coordinate formyl complexes trans-W(CH=0)(CO)(NO)(NH2R)(PPh3)2 (5a, R = H; 5b, R = CH3; 5c, R = NH2) on the basis of multinuclear (H-1, C-13, P-31) NMR spectroscopy and H-2 and C-13 labeling experiments. The noncoordinating Bronsted base NaN(SiMe3)2 reacts with 1 to give 3 in 47% isolated yield, but because of the absence of a coordinating Lewis base, no formyl intermediate was observed. A reaction mechanism for the formation of hydride 3 is proposed involving (i) deprotonation of the diazene ligand in 1 by NH2R, (ii) H-migration from nitrogen to a carbonyl ligand to give the formyl complexes 5, and (iii) H-migration from the formyl ligand to the metal to give the neutral hydride product 3. The isoelectronic rhenium diazene complex [trans,mer-Re(NH=NH)(CO)3(PPh3)2+][SO3CF3-] (9) has been prepared and shown to undergo a similar reaction with NH2CH3 to give trans,mer-Re(H)(CO)3(PPh3)2 (6) in 80% yield.