Reactions Leading to Formation and Cleavage of Metal-Metal and Metal-μ-Phosphido Bonds in Binuclear Molybdenum and Tungsten Complexes. Structural Analyses of W2(CO)8(μ-PPh2)2 and Its Two-Electron Reduction Product, 2

Article abstract of DOI:10.1021/ja00246a018

Reduction of M2(CO)8(μ-PPh2)2 (M= Mo (1-Mo) or W (1-W)) and reactions of various binuclear molybdenumand tungsten anionic products were found generally to proceed with a remarkably facile scission or formation of M-M and M-(μ-PPh2) bonds.Thus, complexes 1 are converted by M'BR3H (M'= Li, R= Et; M'= K, R= sec-Bu) or LiAlH4 in THF to the M-M bond cleaved ^2- (2) or to <*> (3) depending on the nature and, usually the amount of the reductant.Reactions of 1 with LiR (R= Me (a), N-B (b), Ph (c)) afford the acyl anions <*> (4a-c), of which yield the carbene complexes <*> (5a,c) when treated with Me3OBF4.The M-M bond of 3 is readily broken by CO and n-BuLi to give <(CO)5M(μ-PPh2)M(CO)4(PPh2H)>^- (6) and 2, respectively.Treatment of 3 with CF3COOH leads to a fragmentation of the binuclear unit with the formation of cis-M(CO)4(PPh2H)2 and M(CO)5(PPh2H).The dianions 2 are converted to the M-M bonded 3 and 4a when reacted with 1 equiv of CF3COOH and MeI (in THF or DMF), respectively.Possible mechanisms of these reactions are discussed.The structures of 1-W and its 2-electron reduction product,Li(THF)3⁺>₂2-W, were determined by single-crystal X-ray diffraction analyses.Both crystals are monoclinic of space group P2₁/c, with a= 9.830 (2) Angstroem, b= 19.802 (4) Angstroem, c= 16.889 (5) Angstroem, β= 103.72 deg, and Z= 4 for 1-W and a= 11.265 (5) Angstroem, b= 19.546 (3) Angstroem, c= 16.446 (5) Angstroem, β= 122.07 (3) deg, and Z= 2 for +>₂2-W.The structure of 1-W was solved and refined to R= 0.030 and R_W= 0.33 by using 5206 independent reflections, whereas the structure of +>₂2-W was solved and refined to R= 0.051 and R_W= 0.062 by using 3987 independent reflections.Both structures possess a planar W2P2 core.The W-W distance of 3.0256 (4) Angstroem in 1-W increases to a nonbonding value of 4.1018 (4) Angstroem in 2-W, and the W-P-W bond angles of 75.14 deg (mean) in 1-W widen to 104.20 deg in 2-W.The Li⁺ ion in +>₂2-W possesses an almost regular tetrahedral oxygen environment, being attached to three THF molecules and an equatorial CO of 2-W.