Temperature Dependence of the Crystal Structure of Ru4(µ4-C2H2)(CO)9(η-PhMe)

Abstract

The thermal reaction between Ru₄(µ₄-C₂H₂)(CO)₁₂ and toluene afforded Ru₄(µ₄-C₂H₂)(CO)₉(η-PhMe), whose crystal and molecular structures, determined at c. 300 and 153 K, are reported [triclinic, P 1; a ≈ 8 . 0; b ≈ 10 . 4; c ≈ 13 . 7 Å, a ≈ 87; b ≈ 89 . 7; γ ≈ 70°, Z = 2; conventional R values on |F| at convergence were 0 . 027 (300 K), 0 . 020 (153 K) for 4561, 4761 independent ‘observed’ [F >4σ(F)] reflections, respectively]. At low temperature, the structure is a nicely ordered Ru₄ butterfly with a C₂H₂ ligand sitting between the wing tips and an η⁶ -PhMe ligand attached to one of the wing-tip atoms along the extension of the axis between them. At 300 K, a disordered component is evident, 9% occupancy of the wing-tip atom appended to toluene being displaced by 0 . 701(8) Å so that the bonding to the toluene approaches η²; this is accompanied by a counterpart displacement of one of the hinge Ru atoms. It is suggested that this is the first stage of a putative migration of the arene from wing-tip to hinge Ru atoms.