91229-84-4Relevant academic research and scientific papers
Metathesis of acetylenes by triphenoxytungstenacyclobutadiene complexes and the crystal structure of W(C3Et3) [O-2,6-C6H3(i-Pr)2]3
Churchill, Melvyn Rowen,Ziller, Joseph W.,Freudenberger, John H.,Schrock, Richard R.
, p. 1554 - 1562 (2008/10/08)
The reaction between W(CCMe3)(1,2-dimethoxyethane)Cl3 and LiO-2,6-C6H3(i-Pr)2 (LiOR) yields yellow, crystalline W(CCMe3)(OR)3 (1). 3-Hexyne reacts with 1 to give Me3CC≡CEt and W(C3Et3)(OR)3 (2) quantitatively. W(C3Et3)[O-2,6-C6H3(i-Pr) 2]3 crystallizes in the monoclinic space group P21/c with a = 19.271 (6) ?, b = 13.000 (3) ?, c = 17.195 (6) ?, β = 96.55 (2)°, and Z = 4. Diffraction data were collected with a Syntex P21 diffractometer, and the structure was refined to RF = 4.67% for all 3873 data with 2θ = 4.5-40.0° (Mo Kα). This sterically crowded molecule is approximately a trigonal bipyramid in which the planar tungstenacyclobutadiene ring is located in the equatorial position with the two W-Cα bond lengths being 1.883 (10) and 1.949 (9) ? and the W?Cβ bond distance being 2.159 (10) ?. Both 2 and an analogous W(C3Pr3)[O-2,6-C6H3(i-Pr) 2]3 complex (3) catalyze the metathesis of 3-heptyne or 4-nonyne. They each react with 3-hexyne-d10 at a rate that is independent of the concentration of 3-hexyne-d10, characteristic of rate limiting loss of 3-hexyne from 2 or 4-octyne from 3: ΔHDagger; ? 26 kcal mol-1 and ΔS? ? 16 eu in each case. Related studies employing O-2,6-C6H3Me2 suggested that this ligand is not bulky enough to yield metathesis catalysts, while use of O-2,6-C6H3(CMe3)2 led to a neopentylidene complex through addition of a tert-butyl CH bond to the W≡C bond.
