SOLID-STATE STRUCTURE AND DYNAMICS OF A CHIRAL METALLACYCLIC (ZIRCONOXYCARBENE)TUNGSTEN COMPLEX

The reaction of the (π-allybzirconoxycarbene complex [inline-formula omitted] (3a) with pinacolone affords the chiral nine-membered metallacyclic carbene complex [inline-formula omitted] (5), featuring a trans C=C double bond in the ring. In solution only one diastereoisomer is detected, being characterized by relative configurations of R* and p-S* at the chiral center and at the adjacent planar chirality element within the ring system, respectively. In contrast, the diastereomer 5’, having relative configurations R* and p-R*, is detected as a minor component of the 3a/pinacolone addition product in the solid state by13C CP/MAS NMR spectroscopy. Complex 5 crystallizes in space group P⥘ with cell parameters a = 8.447 (2) Å, b = 11.257 (3) Å, c = 15.224 (3) Å, α = 102.78 (2)°, β = 103.16 (2)°, γ = 99.69 (2)°, and Z = 2. Temperature-dependent13C CP/MAS NMR spectroscopy revealed hindered rotation of the W=C(carbene) bond of 5 in the crystalline state (ΔG*rot(350 K) ≈ 16.5 kcal/mol). The corresponding nine-membered metallacyclic (zirconoxycarbene)tungsten complex [inline-formula omitted] (4), formed by treatment of 3a with 1 molar equiv of acetone, exhibits a W=C(carbene) rotational barrier of ΔG*rot(260 K) ≈ 13.5 kcal/mol in the solid state. © 1990, American Chemical Society. All rights reserved.