The tungsten-tungsten triple bond. XV. Synthesis, structure and reactivity of 1,2-W 2[CH(SiMe 3) 2] 2(NMe 2) 4: the remarkable inertness of a sterically-encumbered tungsten-amido complex

Abstract

Addition of 1,2-W 2Cl 2(NMe 2) 4(W≡W) to a toluene slurry of LiCH(SiMe 3) 2(2 equiv) results in the formation of 1,2-W 2[CH(SiMe 3) 2] 2(NMe 2) 4(W≡W) ( I) in 79% isolated yield. Compound I has been characterized by 1H and 13C NMR, IR, elemental analysis and single-crystal X-ray diffraction. The molecule exists exclusively in the gauche conformation in solution and in the solid state with WW = 2.320(1) Å. Compound I is very sterically encumbered as evidenced by: (1) large WWC angles, 110°, at the disyl ligand; (2) skewing of the NC 2 planes of the NMe 2 ligands off the WW vector; (3) anomalously large barriers to WNM 2 bond rotation in solution; (4) the inertness of I towards CO 2 and alcohols. However, compound I reacts with acetic anhydride to form 1,2-W 2[CH(SiMe 3) 2] 2(O 2CMe) 4(W≡W) ( II) in 31% isolated yield. Compound II has been characterized by 1H and 13C NMR, IR, and elemental analysis. The mechanistic implications of these studies with regard to alcoholysis and CO 2 insertion reactions of other 1,2-W 2R 2(NMe 2) 4 compounds are discussed. Crystal data for 1,2-W 2[CH(SiMe 3) 2] 2(NMe 2) 4 at −140°C: space group P2 1/ n, a = 12.555(3), b = 18.699(5), c = 15.214(4) Å, β = 95.24(1)° and Z = 4.