99639-27-7Relevant academic research and scientific papers
Metal alkoxides - Models for metal oxides. 11. Synthesis and properties of mixed alkyl/aryl/benzyl alkoxides of formula 1,2-W2R2(OR′)4 and W2R(OR′)5(M≡M)
Chisholm, Malcolm H.,Eichhorn, Bryan W.,Folting, Kirsten,Huffman, John C.,Tatz, Robert J.
, p. 1599 - 1606 (2008/10/08)
Hydrocarbon solutions of 1,2-W2R2(NMe2)4 compounds (R = Me, Et, n- and i-Pr, i-Bu, CH2CMe3, CH2SiMe3, Ph, p-tolyl, and CH2Ph) react with alcohols, R′OH, to give initially 1,2-W2R2(OR′)4 compounds. The latter may be isolated provided the combination of R and R′ has sufficient combined steric bulk to guard against further protolysis with successive elimination of RH and formation of W2(OR′)6 compounds. In the presence of Lewis bases HNMe2 or pyridine, the adducts W2Ar2(O-i-Pr)4(HNMe2), where Ar = Ph and p-tolyl, and W2Me2(O-t-Bu)4(py)2 have been isolated. The former compounds provide rare examples of four-coordinate tungsten atoms united to three-coordinate tungsten atoms by triple bonds: (i-PrO)2-(Ar)(HNMe2)W≡W(Ar)(O-i-Pr)2. When R contains (β-hydrogen atoms, the initially formed compounds W2R2(OR′)4 show evidence for reversible β-hydrogen/deuterium abstraction and this can result in an isomerization of the alkyl ligands, e.g., i-Pr→n-Pr. The compound W2(i-Bu)2(O-i-Pr)4 has been isolated as an air- and heat-sensitive crystalline material and characterized by a single-crystal X-ray study. In the solid state there is a central W2C2O4 moiety having virtual C2h symmetry, i.e., the anti rotamer with W-W = 2.309 (1) A?, W-C = 2.141 (9) A?, and W-O = 1.88 (1) A? (averaged) and W-W-C = 100.2 (3)° and W-W-O = 107 (1)° (averaged). The molecule has a crystallographically imposed center of inversion, and the i-Bu ligand is arranged such that the W-C-C-H moiety has the anti conformation with the β-hydrogen lying distal to the W≡W bond. In solution the W2R2(OR′)4 compounds, where R contains β-hydrogen atoms, are reactive toward elimination of alkane and alkene and toward protolysis. In the reactions between W2(CH2CD3)2(NMe2) 4 and i-PrOH (and W2(CH2CH3)2(NMe2) 4 and i-PrOD) there is evidence from 1H and 2H NMR spectroscopy for the formation of a W2(μ-H/D) moiety. These observations are compared to previous studies of alcoholyses involving Mo2R2(NMe2)4 compounds with the following conclusions. (1) Reactions proceed faster for M = W relative to Mo. (2) When R = a β-hydrogen containing alkyl, β-hydrogen atom abstraction is reversible for W but not for Mo. (3) Reductive elimination of alkane and alkene occurs more readily for Mo than for W. (4) No reduced W24+-containing compounds have been isolated. Crystal data for W2(p-tolyl)2(O-i-Pr)4(HNMe2) at -155°C: a = 17.836 (8) A?, b = 9.955 (4) A?, c = 19.822 (9) A?, β = 113.72 (2)°, Z = 4, dcalcd = 1.714 g cm-3, and space group P21/c. Crystal data for W2(i-Bu)2(O-i-Pr)4 at -167°C: a = 9.618 (2) A?, b = 9.077 (2) A?, c = 8.198 (2) A?, α = 99.96 (1)°, β = 92.29 (1)°, γ = 65.52 (1)°, Z = 1, dcalcd = 1.860 g cm-3, and space group P1.
