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The tungsten-tungsten triple bond. 11. Ligand redistribution reactions involving chloride and dimethylamide ligands at dimolybdenum and ditungsten (M≡M) centers induced by added tertiary phosphines. Preparations and characterizations of W2Cl2(NMe2)4(Me2PCH 2PMe2), W2Cl3(NMe ...
Ahmed, Kazi J.,Chisholm, Malcolm H.,Folting, Kirsten,Huffman, John C.
, p. 4039 - 4044 (2008/10/08)
Full title: The tungsten-tungsten triple bond. 11. Ligand redistribution reactions involving chloride and dimethylamide ligands at dimolybdenum and ditungsten (M≡M) centers induced by added tertiary phosphines. Preparations and characterizations of W2Cl2(NMe2)4(Me2PCH 2PMe2), W2Cl3(NMe2)3(PMe2Ph) 2, and W2Cl4(NMe2)2(PMe2Ph) 2. Tertiary phosphines react with M2Cl2(NMe2)4 (M≡M) compounds (M = Mo and W) in hydrocarbon solvents to give a variety of products depending upon the metal and the phosphine. The bidentate phosphines L-L (L-L = Me2PCH2PMe2 and Me2PCH2CH2PMe2) give isolable and kinetically stable 1:1 adducts: M2Cl2(NMe2)4(L-L). The monodentate phosphines L (L = PMe3 and PMe2Ph) induce ligand redistribution reactions to give M2Cl3(NMe2)3L2, M2Cl4(NMe2)2L2, and M2(NMe2)6 compounds. The compounds M2Cl4(NMe2)2L2, where M = Mo and L = PMe3 and PMe2Ph but not where M = W, were found to undergo reductive elimination (by way of β-hydrogen elimination from a NMe2 ligand) in the presence of added phosphine to give Mo2Cl4L4 (M-4M) compounds. The compounds M2Cl2(NMe2)4(L-L) and M2Cl4-n(NMe2)2+nL2, where n = 0 or 1, are formulated as compounds containing four-coordinate metal atoms united by M-M triple bonds. This has been verified by single-crystal X-ray diffraction studies for the compounds W2Cl3(NMe2)3(PMe2Ph) 2 (at -160°C, a = 11.909 (3) A?, b = 13.271 (4) A?, c = 11.551 (3) A?, α = 104.76 (1)°, β = 108.64 (1)°, γ = 71.09 (1)°, Z = 2, dcalcd = 1.916 g cm-3, and the space group is P1) and W2Cl4(NMe2)2(PMe2Ph) 2 (at -158°C, a = 17.624 (8) A?, b = 11.995 (5) A?, c = 14.397 (6) A?, β = 114.29 (3)°, Z = 4, dcalcd = 2.093 g cm-3, and the space group is P21/c). In both molecules the W-W distances, 2.33 (2) A? (averaged), and W-P distances, 2.53 (1) A? (averaged), are similar while the W-N distances are notably shorter when N is bonded to W atoms having two Cl ligands and one PMe2Ph ligand, 1.93 (1) A? (averaged), relative to W-N distances, 1.99 (1) A? (averaged), involving W atoms bonded to two NMe2, one Cl, and one PMe2Ph. In both compounds, the NMe2 ligands contain trigonal-planar nitrogen atoms and the W-NC2 units are aligned along with the W-W axis such that the nitrogen lone pairs may interact with the W dxy atomic orbital, the one d orbital not used in either the M≡M bond or the four M-L σ bonds. In a formal sense the W-N distance of 1.93 A? corresponds to a W-N double bond and the W-N distance of 1.99 A? to a W-N bond order of 1 1/2.
