Absolute Configurations of Organometallic Compounds. 3. Structure and Absolute Configuration of the Square-Pyramidal Complex [(+)_579-(C₅H₅)Mo(CO)₂(NN*)]PF₆(NN*=Schiff Base Derived from Pyridine-2-carbaldehyde and-(S)-(-)-α-Phenylethylamine)

The structure of [FORMULA OMMITED] the Schiff base derived from pyridine-2-carbaldehyde and (S)-(-)-α-phenylethylamine was determined using standard single-crystal x-ray diffraction methods. The absolute configuration was determined by refinement of the data using the anomalous scattering contributions of Mo and P to a final R(F)=0.056 for 2634 independent reflections having I>3σ(I). The substance crystallizes in the space group P212121 with unit cell dimensions of a=12.249 (4), b=9.236 (3), and c=20.692 (9) Å and Z=4 molecules/unit cell. The square-pyramidal coordination of the Mo atom is defined by two carbonyl carbons and two Schiff base nitrogens occupying the four basal plane sites and the five carbons of the η5-C5H5 ligand in the axial position. The Mo-ligand distances and the bond lengths and angles within the ligands are normal and compare closely with those of recent structure determinations of comparable precision. The Mo atom is 0.95 Å above the plane formed by the four basal plane ligands. The conformation of the (S)-α-phenylethyl group with respect to the ligand plane, defined by the pyridine ring, the imine system, and the Mo atom, is discussed. The configuration at the metal atom in the (+)579 isomer is specified as (S). The PF6- anion executes large amplitude torsional motion in the lattice, as is commonly the case for this anion when not hydrogen bonded.