STRUCTURE OF A CARBON-MONOXIDE ADDUCT OF A CAPPED PORPHYRIN - FE(C2-CAP)(CO)(1-METHYLIMIDAZOLE)

The structure of Fe(C2-Cap)(CO)(1-Melm) has been determined by single-crystal X-ray diffraction methods. It consists of the packing of two crystallographically independent porphyrin molecules and solvate molecules. Both porphyrin molecules display the expected connectivity in which the benzene caps are slanted with respect to the mean porphyrin planes (dihedral angles of 15.5 and 11.5-degrees for molecules 1 and 2, respectively). The centroids of the cap atoms are 5.57 and 5.68 angstrom from the mean porphyrin planes. Since this distance is 3.96 angstrom in H-2(C2-Cap), the cap moves 1.6-1.7 angstrom further away from the porphyrin upon binding a CO ligand inside the cavity. The coordinated CO ligand is slightly but detectably distorted from linearity, being both bent and tilted off the axis normal to the porphyrin. The Fe-C-O bond angle and the off-axis displacements for the C and O atoms of CO are 173.1 (9)degrees, 0.17 angstrom, and 0.41 angstrom, respectively, for molecule 1, and 175.8 (8)degrees and 0.12 and 0.28 angstrom, respectively, for molecule 2. Crystallographic data: triclinic P1BAR, Z = 4, a = 18.022 (2) angstrom, b = 20.017 (1) angstrom, c = 20.691 (2) angstrom, alpha = 70.507 (7)degrees, beta = 76.232 (10)degrees, gamma = 82.549 (7)degrees at -150-degrees-C, 18 468 observations, 1740 variables, R(F) = 0.096 (F0(2) > 3-sigma(F0(2))).