TUNGSTEN-CARBON, CARBON-CARBON, AND CARBON-HYDROGEN BOND ACTIVATIONS IN THE CHEMISTRY OF 1,2-W(2)R(2)(OR')(4) (W-W)COMPLEXES .4. PHOSPHINE-AND AMINE-PROMOTED LIGAND MIGRATIONS AND ALPHA-CH ACTIVATIONS IN THE FORMATION OF ALKYLIDYNEHYDRIDODITUNGSTEN C

摘要

Lewis bases [PMe(3) or quinuclidine (Quin)] and 1,2-W-2(CH(2)Ph)2(O-i-Pr)(4) react in toluene and hexane at room temperature to give benzylidyne hydride compounds, W-2(mu-H)(mu-CPh)(O-i-Pr)(4)L(x), where L = Quin, x = 2, and L = PMe(3), x = 3 and 2, by way of a double alpha-CH activation and elimination of toluene. Similarly, 1,2-W-2(i-Bu)(2)(O-i-Pr)(4) and PMe(3) yields the alkylidyne hydride W-2(mu-H)(mu-C-i-Pr)(O-i-Pr)(4)(PMe(3))(3) and isobutane. By contrast, addition of bisdimethylphosphinomethane (dmpm) yields adducts 1,2-W-2(CH(2)R)(2)(O-i-Pr)(4)(dmpm), where R = Ph and i-Pr, that are relatively inert in solution at room temperature with respect to alpha-CH activation and formation of alkylidyne bridge complexes. The rate of formation of the benzylidyne hydride compounds has been studied in the presence of excess L. The formation of W-2(mu-H)(mu-CPh)(O-i-Pr)(4)(Quin)(2) was approximately half-order in [Quin], while for PMe(3) there was an inverse dependence on [PMe(3)]. These observations are attributed to differences in the relative equilibria involving the reversible uptake of L by 1,2-W-2(CH(2)Ph)(2)(O-i-Pr)(4) to give 1,2-W-2(CH(2)Ph)(2)(O-i-Pr)(4)L(2) by way of a monoligated intermediate 1,2-W-2(CH(2)Ph)(2)(O-i-Pr)(4)L. The kinetic isotope effects, k(HH)/k(DD) Of 5.0(6) at 25 degrees C and 3.4(4) at 22 degrees C were observed for the liberation of toluene and toluene-d(8) for the reactions employing Quin and PMe(3), respectively, and the protio- and perdeuteriobenzyl-containing compounds. A discussion of the likely mechanism of formation of the hydride alkylidyne bridged complexes is presented with emphasis on ligand induced benzyl/alkyl migration across the W equivalent to W bond as reported in a previous paper for the reaction between 1,2-Mo-2(CH(2)Ph)(2)(O-i-Pr)(4) and PMe(3) to give (PMe(3))(PhCH(2))(2)(i-PrO)Mo equivalent to Mo(O-i-Pr)(3) (Chisholm, M. H.; et al. Organometallics 1992, 11, 4029). Support for elimination of toluene from one metal center is seen in the formation of the kinetic product (PMe(3))(3)(i-PrO)W(mu-H)(mu-CPh)W(O-i-Pr)(3) which, by dissociation of PMe(3) and alkoxide migration, yields (PMe(3))(i-PrO)(2)W(mu-H)(mu-CPh)W(O-i-Pr)(2)(PMe(3)). All the new compounds have been characterized by NMR studies, infrared spectroscopy, elemental analyses, and single crystal X-ray crystallography. The mu-alkylidyne hydride complexes contain a central W-2(8+) core With W-W distances typical of a W=W bond, similar to 2.5 Angstrom, while the dmpm adducts contain W equivalent to W bonds of distance similar to 2.3 Angstrom. Crystal data: (i) For W-2(mu-H)(mu-CPh)(O-i-Pr)(4)(PMe(3))(3) at -157 degrees C, a = 23.786(5) Angstrom, b = 10.946(2) , c = 14.153(3) Angstrom, Z = 4, d(caled) = 1.66 g/cm(3) and space group P2(1)2(1)2(1) For W-2(mu-H)(mu-CPh)(O-i-Pr)(4)(PMe(3))(2) at -143 degrees C, a = 11.441(4) Angstrom, b = 13.223(6) Angstrom, c = 21.892(8) A, beta = 94.21(2)degrees, Z = 4, d(caled) = 1.70 g/cm(3), and space group P2(1)/c. For W-2(mu-H)(mu-CHP)(O-i-Pr)(4)(Quin)(2) at -152 degrees C, a = 17.942(6) Angstrom, b = 9.976(3) Angstrom, c = 19.788(8) Angstrom, beta = 94.82(2)degrees, Z = 4, d(caled) = 1.725 g/cm(3), and space group P2(1)/c. (ii) For W-2(mu-H)(mu-C-i-Pr)(O-i-Pr)(4)(PMe(3))(3) at -170 degrees C, a = 19.122(4) Angstrom, b = 20.749(3) Angstrom, c = 19.817(3) Angstrom, beta = 114.45(1)degrees, Z = 8, d(caled) = 1.65 g/cm(3), and space group P2(1)/a. (iii) For W-2(i-Bu)(2)(O-i-Pr)(4)(dmpm) at -168 degrees C, a = 9.855(2) Angstrom, b = 18.832(4) Angstrom, c = 18.176(3) Angstrom, beta = 94.87(1)degrees, Z = 4, d(caled) = 1.69 g/cm(3), and space group P2(1). (iv) For W-2(CH(2)Ph)(2)(O-i-Pr)(4)(dmpm) at -172 degrees C, a = 15.020(2) Angstrom, b = 29.207(4) Angstrom, c = 17.774(2) Angstrom, beta = 111.63(1)degrees, Z = 8, d(caled) = 1.69 g/cm(3), and space group P2(1). [References: 25]