The propensity of alkoxide and aryloxide derivatives of tungsten carbonyls to aggregate in solution.: Synthesis and X-ray structures of dinuclear, trinuclear and tetranuclear complexes derived from the MeOW(CO)5- anion

The complex [Et4N] [W(CO)(5)OMe] (1) has been prepared from the reaction of the photochemically generated W(CO)(5)THF adduct and [Et4N] [OH] in methanol. Complex 1 was shown to undergo rapid CO dissociation in THF to quantitatively provide the dimeric dianion, [W(CO)(4)OMe](2)(2-). The resulting THF insoluble salt [Et4N](2)[W(CO)(4)OMe](2) (2) has been structurally characterized by X-ray crystallography, with the doubly bridging methoxide ligands being in an anti configuration. Complex 2 was found to subsequently eact with excess methoxide ligand in a THF slurry to afford the face-sharing octahedron complex [Et4N](3)[W-2(Co)(6)(OMe)(3)] (3) which contains three doubly bridging methoxide groups. In the absence of excess methoxide ligand complex 2 cleanly yields the tetrameric complex [Et4N](4)[W(CO)(3)OMe](4) (4) which has been structurally characterized as a cubane-like arrangement with triply bridging mu(3)-methoxide groups and W(CO), units. Although complex 3 was not characterized in the solid state, the closely related glycolate derivative [Et4N](3) [W-2(CO)(6)(OCH2CH2OH)(3)] (5) was synthesized and its structure determined by X-ray crystallography. The trianions of complex 5 are linked in the crystal lattice by strong intermolecular hydrogen bonds. Crystal data for 2: space group P2(1)/n, a = 7.696(2), b = 22.019(4), c = 9.714(2) Angstrom, beta = 92.22(3)degrees, Z = 4, R = 6.43%. Crystal data for 4: space group Fddd, a = 12.433(9), b = 24.01(2), c = 39.29(3) Angstrom, Z = 8, R = 8.13%. Crystal data for 5: space group P2(1)2(1)2(1), a = 11.43(2), b = 12.91(1), c = 29.85(6) Angstrom, Z = 8, R = 8.29%. Finally, the rate of CO ligand dissociation in the closely related aryloxide derivatives [Et4N] [W(CO)(5)OR] (R = C6H5 and 3,5-F2C6H3) were measured to be 2.15 x 10(-2) and 1.31 x 10(-3)s(-1), respectively, in THF solution at 5 degrees C. Hence, the value of the rate constant of 2.15 x 10(-2)s(-1) establishes a lower limit for the first-order rate constant for CO loss in the W(CO)(5)OMe- anion, since the methoxide ligand is a better pi-donating group than phenoxide. (C) 1998 Elsevier Science S.A.