cis-W(CO)4(PPh3)2 (1c) or trans-W(CO)4(PR3)2 (1t) (R = C6H5, p-CH3C6H4) reacted with NOPF6 in methylene chloride to give cis,mer-[W(CO)3(NO)(PR3)2][PF6] (2-PF6); BF4- and ClO4- salts (2-BF4; 2-ClO4) were also prepared. Halide anions (X = Cl-, Br-, I-) reacted with 2 first to give mer-WX(CO)3(NO)(PPh3) (7a, X = Cl; 7b, X = Br; 7c, X = I) and PPh3, then cis,cis-WX(CO)2(NO)(PPh3)2 (6a, X = Cl; 6b, X = Br; 6c, X = I), and finally trans,trans-WX(CO)2(NO)(PPh3)2 (3a, X = F; 3b, X = Cl; 3c, X = Br; 3d, X = I). Further reaction of 3c with NOPF6 and n-Bu4NX gave WXBr(NO)2(PPh3)2 (4c, X = Br; 4f, X = F). Upon reaction with NO+, trans-Cr(CO)4(PPh3)2 gave good yields of trans-[Cr(CO)4(PPh3)2][PF6] (5), but trans-Mo(CO)4(PPh3)2 produced complex mixtures. Acetate reacted with 2 to form trans,trans-W(η1-CH3CO2)(CO) 2(NO)(PPh3)2 (8) and then trans-W(η2-CH3CO2)(CO)(NO)(PPh 3)2 (11) and CO. Dimethyldithiocarbamate reacted with 2 to form cis-W-(η2-S2CNMe2)(CO) 2(NO)(PPh3) (13) and PPh3 and then trans-W(η2-S2CNMe2)(CO)(NO)(PPh 3)2 (14). In the presence of LiBH4 and PPh3 in tetrahydrofuran, both 3c and 2 were transformed into the tungsten(0) hydride trans,trans-WH(CO)2-(NO)(PPh3)2 (15). This hydride underwent α-insertion reactions with RN3 and RN2+, forming trans-W(η2-RN3H)(CO)-(NO)(PPh3)2 (19a, R = Ph; 19b, R = To) and trans,trans-[W(RN2H)(CO)2(NO)(PPh3) 2]+ (23, R = Ph; 24, R = To), and it underwent β-insertion reactions with RNCNR, CO2, and CS2, forming trans-W(η2-RNCHNR)(CO)(NO)(PPh3)2 (21, R = To), trans,trans-W(η1-HCO2)(CO)2(NO)(PPh 3)2 (9), and trans,trans-W(η1-HCS2)(CO)2(NO)(PPh 3)2 (22). Heating the hydride with RN=NNHR and RN=CHNHR produced trans-W(η2-RN3R)(CO)(NO)(PPh3)2 (20) and 21, respectively. When allowed to react with acids (HX; X = Cl, Br, I, CH3CO2, HCO2, OClO3), 15 gave trans,trans-WX(CO)2(NO)(PPh3)2 (3b, 3c, 3d, 8, 9, 16 (X = OClO3)). The perchlorato ligand in 16 was rapidly displaced by halide and pseudohalide anions but not by CO even at 1000 psi (20-80°C).