Synthesis, Structure, Fluxional Behavior, and Addition Reaction ofthe Metal-Metal-Bonded Heterobimetallic Phosphido-Bridged Complex CpW(CO)2(.mu.-PPh2)Mo(CO)5

The heterobimetallic phosphido-bridged complex CpW(C0)2(p-PPh2)Mo(C0)5 (1) was prepared by the reaction of CpW(C0)3PPh2 with M o ( C ~ ) ~ ( C ~ H ~ ) . Treatment of 1 with CO produced CpW(C0)3(p-PPhz)Mo(C0)5 (2). The structures of 1 and 2 were determined by singlecrystal X-ray diffraction. Crystal data for 1: C ~ ~ H I ~ M O O ~ P W , space group P21/n, a = 14.464(7) A, b = 11.6743(12) A, c = 14.7639(14) A, p = 97.916(12)', V = 2469.3(6) A3, 2 = 4. The structure was refined to R = 0.054 and R, = 0.055. Crystal data for 2: C ~ ~ H I ~ M O O ~ P W , space group P21/n, a = 9.6322(16) A, b = 12.4673(21) A, c = 20.813(3) A, /3 = 94.476(12)', V = 2472.7(7) A3, 2 = 4. The structure was refined to R = 0.035 and R, = 0.044. The W-Mo distance was 3.2056(16) A in 1, indicative of a W-Mo bond. The long distance between W and Mo (4.5192(14) A) in 2 indicates tha t no metal-metal bond exists in the complex. Fluxional behavior involving the exchange of four Mo CO ligands cis to the phosphido bridge in 1 was studied by variabletemperature 13C NMR spectroscopy. Addition reactions between 1 and Lewis bases L (L = PPh2H, PMe3, P(OMe)3) produced CpW(CO)&.-PPh2)Mo(C0)4(L) (3) with L regiospecifically and stereospecifically coordinating to the Mo cis to the phosphido bridge. The structure of CpW(C0)3(p-PPh2)Mo(C0)4(PMe3) ( a) was determined by single-crystal X-ray diffraction. Crystal data for 3a: C27H24M007PzW, space group P21/n, a = 11.756(4) A, b = 16.423(6) A, c = 14.968(3) A, /3 = 98.397(20)', V = 2858.8(14) A3, 2 = 4. The structure was refined to R = 0.026 and R, = 0.031. Reaction of 1 with PPh3 produced C~W(CO)~(~-PP~~)MO(CO)~(PP~~) with a metal-metal bond and with PPh3 occupying the position trans to the phosphido bridge. Complexes with similar structures were synthesized by removal of one CO from 3 to regenerate