Studies of Metal-Nitrogen Multiple Bonds. III. The Crystal and Molecular Structures of Trichloro(p-methoxyphenylimino)bis(diethylphenylphosphine)rhenium(V) and Trichloro(p-acetylphenylimino)bis(diethylphenylphosphine)rhenium(V)

The crystal and molecular structures of two arylimino complexes of rhenium(V)-trichloro(p-methoxyphenylimino)bis-(diethylphenylphosphine)rhenium(V), ReC₃(NC₆H₄OCH₃)(P(C₂H₂)₂C₆H₅)₂, and trichloro(p-acetylphenylimino)bis(diethylphenylphosphine)rhenium(V), ReC₃(NC₆H₄OCH₃)(P(C₂H₂)₂C₆H₅)₂-have each been determined from three-dimensional X-ray data collected by counter methods. The structure of the methoxy compound has been refined by least-squares techniques to a final R factor on F of 2.7% for the 2952 independent reflections above background. The material crystallizes in space group C_2h⁶-C2/c of the monoclinic system in a cell of dimensions a = 15.427 (6) Å, b = 13.998 (6) Å, c = 17.062 (7) Å, β = 126.55 (2)°. The density of 1.60 g/cm³ calculated for four formula units in the cell agrees well with the observed density of 1.61 ± 0.01 g/cm³. The well-separated individual molecules are required crystallographically to possess C₂ symmetry. The over-all structure around Re is octahedral with P atoms trans to one another and Cl atoms trans to one another in the basal plane and the third Cl at the one vertex and the arylimino group (coordinated to Re via the N atom) at the other. Neither the Re-N-C angle nor the C-O-CH₃ angle is 180° and so the imposition of C₂ symmetry on the molecule requires that the C₆H₄-O-CH₃ portion of the molecule be disordered. The Re-Cl distance in the equatorial plane is 2.421 (1) Å while the Re-Cl distance trans to the N ligand is 2.432 (2) Å. The Re-P distance is 2.470 (1) Å. The acetyl compound has been refined by least-squares techniques to give a final R factor of 3.0% on F for the 3027 independent reflections above background. The compound crystallizes in the monoclinic space group C_2h⁵-P2₁/c. The cell dimensions are a = 10.52(2) Å, b = 16.06 (3) Å, c = 18.15 (3) Å, β = 91.65 (5)°. The calculated density for four molecules per unit cell is 1.64 g/cm⁸; the observed density was 1.63 ± 0.01 g/cm³. No crystallographic symmetry is imposed on the molecule. The over-all molecular structure is the same as that found for the methoxy compound. The Re-Cl distance trans to the N atom is 2.410 (3) Å and the cis distances are 2.433 (3) and 2.399 (3) Å. The Re-P distances are 2.457 (4) and 2.461 (4) Å. The octahedral configurations in both complexes are slightly distorted; the atoms in the equatorial plane are bent toward the axial Cl atom. The Re-N distances in the methoxy and acetyl complexes are 1.709 (4) and 1.690 (5) Å, respectively. Both of these bonds are significantly shorter than the value 1.788 (11) Å found previously in ReNCl₂(P(C₂H₆)₂C₆H₅)₃. Hence, formal double bonds in the arylimino complexes are shorter than the formal triple bond in the related nitrido complex.