SYNTHESIS AND CHARACTERIZATION OF NOVEL COBALT ALUMINUM COFACIAL PORPHYRINS - 1ST CRYSTAL AND MOLECULAR-STRUCTURE OF A HETEROBIMETALLIC BIPHENYLENE PILLARED COFACIAL DIPORPHYRIN

The synthesis of the novel family of heterodinuclear complexes (DP)CoAl(OR) (where DP4- is the tetraanion of the diporphyrin biphenylene DPB or the diporphyrin anthracene DPA, and R = CH3, CH2CH3, or CH2C6H5) is reported. These complexes were obtained by selective metalation of the cofacial diporphyrins with cobalt and aluminum. Each (DP)CoAl(OR) complex was characterized by mass spectrometry and UV-vis, IR, ESR, and H-1 NMR spectroscopies. Unusually large paramagnetic shifts were observed for the protons on axial ligands bound to aluminum and for the porphyrinic N-H protons of the monocobalt DPB and DPA complexes. Analysis of the paramagnetic shifts indicates that the main contribution to isotropic shifts arises from a through space (or dipolar) interaction of an unpaired electron on cobalt(II). Structural data were deduced from the H-1 NMR study. In addition, the molecular structure of the cobalt(II) aluminum(III) ethoxide diporphyrin biphenylene (DPB)CoAl(OCH2CH3) was determined by X-ray diffraction. This is the first crystal structure of a heterobimetallic cofacial diporphyrin. (DPB)CoAl(OCH2CH3) (C78H81N8OCoAl.C7H8) crystallizes in the triclinic system, space group P1BAR. Its lattice constants are as follows: a = 13.095 (4) angstrom, b = 16.836 (3) angstrom, c = 16.986 (3) angstrom, alpha = 87.47 (1)-degrees, beta = 70.40 (3)-degrees, gamma = 85.90 (2)-degrees, V = 3516 angstrom3, Z = 2, R(F) = 5.30%, R(w)(F) = 5.27%, GOF = 2.5 for 6800 reflections with I greater-than-or-equal-to 3sigma(I). No metal-metal interaction occurs (Co-Al = 4.370 (1) angstrom), and both porphyrin moieties are slipped by a = 29.8-degrees. Finally, the tedious synthesis of the (DPA)H-4 free-base porphyrin has been extensively modified, and several new reaction steps are presented leading to significant increases in both scale and yield.