Synthesis, Crystal Structure, and Stereoisomerism of the Alkylidene Complex (η⁵-C₅H₅)WOS₃(CO)₉(μ-O)(μ-Cl)(μ-CHCH₂Tol) and Related Complexes

The reaction of CpWOs₃(CO)₉(μ-O)(μ³-CCH₂Tol) (1) with HC1 or BC1₃/H₂0 at ambient temperatures generates the alkylidene complex cpwos3(co)9( μ -o)( μ -c1)( μ -chch2to1) (3, isomer b) isolated in 65-90% yield. Complex 3b crystallizes in the triclinic space groups PI with a = 9.2724 (32) Å, b = 11.3130 (43) Å, c = 14.0040 (62) Å, α = 69.790 (31)°, β = 77.236 (30)°, γ = 83.700 (20)°, V = 1343.6 (9) ų, and Z = 2. Convergence of the structure solution was reached with R_F= 3.7% for all 3526 unique data (R_F= 3.1% for those 3085 data with |F₀| > 6σ(|F₀|). The metal atoms adopt the “butterfly” configuration typical of 62-electron clusters, with the chlorine atom bridging the wing-tip osmium atoms (Os(l)-Cl = 2.488 (3) Å, Os(3)-Cl = 2.463 (3) Å; Os(l)-Cl-Os{2) = 98.4 (1)°). Three carbonyl groups are bound to each Os atom, while the Cp ligand is bound to W. The oxygen atom is involved in a W=O:→Os bridge, with W═O(1) = 1.786(9) Å, Os(3)—O(1) = 2.126 (8) Å, and <W—O(1)—Os(3) = 99.2 (4)°. The μ-alkylidene moiety bridges W and Os(l), with W-C(l) = 2.064 (11) A, Os(l)-C(l) = 2.196 (11) Å, and <W-C(l)-Os(l) = 85.0 (4)°; the -CH₂Tol substituent is oriented anti to the triply edge-bridged W-Os(l)-Os(3) face. Pyrolysis of 3b in refluxing toluene generates an isomeric alkylidene complex 3c isolated in 71% yield and characterized spectroscopically. Treatment of 1 with HBr or HSPh generates analogous alkylidene compounds CpWOs₃(CO)₉(μ-O)(μ-X)(μ-CHCH₂Tol) (X = Br (4) or SPh (5)); in these cases both stereoisomers are obtained directly. The substitution of a carbonyl ligand in 3b by ¹³CO or PPh₂Me is shown to be stereoselective; activation by both the bridging oxo and the bridging chloro ligands is proposed.