Absolute configurations of organometallic compounds : V. X-ray study of (−)578-(η5-C5H5)Mo(CO)2SC(CH3NR′ with R′ = (S-CH(CH3)(C6H5)

The structure and absolute configuration of the thioamido complex (?)₅₇₈-(η⁵-C₅H₅Mo(DO)₂SC(CH₃NR′ with R′ = (S)CH(CH₃)(C₆H₅) have been determined by single-crystal X-ray diffraction. The substance crystallizes in the orthorhombic system; space group P2₁2₁2₁ with cell constants of a = 8.314(1), b = 9.020(1), and c = 22.352(2) Å, and Z = 4 molecules/unit cell. The absolute configuration was determined using Bijvoet's method. Refinement of the data using the anomalous scattering contributions of Mo and S yields a final R(F = 0.036 for 2715 independent reflections having I > 3σ(I). The distorted square pyramidal coordination of the Mo atom is defined by two carbonyl carbons and the S and N atoms of the thioamido ligand occupying the four basal plane sites and the five carbons of the η⁵-C₅C₅ ligand in the axial position. The Mo—ligand distances and most of the bond lengths and angles within the ligands are normal and compare closely with those of recent structure determinations. However, the distances and angles within the thioacetamide ligand show, distinctly, the effect of chelate binding to the Mo atom. In particular, the angles at the central thioacetamide carbon differ markedly from those of free thioacetamide and monodentate, S-bound metal thioacetamido complexes. The Mo atom is 1.041 Å above the plane formed by the four basal ligands. The conformation of the (S)-α-phenylethyl group with respect to the ligand plane, defined by the thioamido system and the Mo atom, is discussed. The configuration at the metal atom in the (?)₅₇₈-isomer of (η⁵-C₅H₅)Mo(CO)₂SC(CH₃)NR′ is specified as (S).