Alkyne adducts of mixed chloro-dimethylamido ditungsten compounds

Article abstract of DOI:10.1021/om00142a002

Alkyne adducts of formula W₂Cl₂(NMe₂)₄(μ-C ₂RR′)(py)₂ (R = R′ = H; R = R′ = Me; R = Me, R′ = H; R = Ph, R′ = H) have been isolated from the reactions of alkynes with W₂Cl₂(NMe₂)₄ in the presence of pyridine. These compounds, with the exception of W₂Cl₂(NMe₂)₄(μ-C ₂H₂)(py)₂ (III), undergo thermal ligand redistribution reactions in hydrocarbon solvents to produce compounds having the general formula W₂Cl_x(NMe₂)_6-x(μ-alkyne)(py) ₂, where x = 3 and 4, and W₂(NMe₂)₆. Thus, W₂Cl₂(NMe₂)₄(μ-PhC ₂H)(py)₂ reacts in toluene at ca. 50°C to produce W₂Cl₃(NMe₂)₃(μ-PhC ₂H)(py)₂·1/2C₇H₈ (V) in good yields. Compound V is very sparingly soluble in hydrocarbon solvents, and no further decomposition has been observed. By contrast, W₂Cl₂(NMe₂)₄(μ-C ₂Me₂)(py)₂ undergoes ligand redistribution in toluene and, at ca. 55°C, yields W₂Cl₄(NMe₂)₂(μ-C ₂Me₂)(py)₂ (VI) presumably via the initial formation of W₂Cl₃(NMe₂)₃(μ-C ₂Me₂)(py)₂. No further decomposition of compound VI has been observed. Single-crystal X-ray studies reveal pseudotetrahedral W₂(μ-C₂) cores in both III and V, arising from the perpendicular addition of the alkynes to the (W≡W)⁶⁺ centers. The C-C (1.38 (1) A? in III, 1.40 (1) A? in V) and the W-W (2.597 (1) A? in III, 2.657 (1) A? in V) distances approach C-C and W-W single bond distances and conform closely to the description of dimetallatetrahedranes. The overall geometry around each of the tungsten atoms, in III and V, can be considered pseudooctahedral, and these octahedra are joined together through the agency of the μ-C₂H₂ and two μ-NMe₂ ligands in III and by the ligands μ-PhC₂H and μ-Cl and one μ-NMe₂ in V. Compound VI, on the other hand, contains a μ-C₂Me₂ moiety which shows a large deviation, θ = 35°, from being in an ideal perpendicular orientation, θ = 0. There are two significantly different W-C distances, 2.02 (1) and 2.44 (1) A?, approaching W-C double and nonbonding distances, respectively. These data, coupled with the observed short W-W distance of 2.436 (1) A?, indicate incipient 1,2-dimetallacyclobutadiene characteristics within the W₂(μ-C₂) core in VI. These studies are compared with the related alkyne adducts of W₂(OR)₆ compounds. Crystal data for (i) W₂Cl₂(NMe₂)₄(μ-C ₂H₂)(py)₂-CH₂Cl₂ at -160°C: a = 17.123 (5) A?, b = 12.012 (3) A?, c = 7.410 (1) A?, α = 105.80 (1)°, β = 94.71 (1)°, γ = 101.93 (1)°, Z = 2, d_calcd = 2.069 g cm^-3, and space group P1. (ii) W₂Cl₃(NMe₂)₃(μ-PhC ₂H)(py)₂·1/2C₇H₈ at -161°C: a = 14.701 (7) A?, b = 12.137 (6) A?, c = 17.632 (9) A?, β = 103.15 (3)°, Z = 4, d_calcd = 1.979 g cm^-3, and space group P2₁/n. (iii) W₂Cl₄(NMe₂)₂(μ-C ₂Me₂)(py)₂ at -160°C: a = 10.918 (4) A?, b = 13.440 (5) A?, c = 16.558 (7) A?, β = 104.45 (2)°, Z = 4, d_calcd = 2.287 g cm^-3, and space group P2₁/n.