METALLOPORPHYRINS CONTAINING SIGMA-BONDED NITROGEN AXIAL LIGANDS .2. SYNTHESIS AND CHARACTERIZATION OF IRON(III) TETRAZOLATO AND TRIAZOLATO PORPHYRIN COMPLEXES - MOLECULAR-STRUCTURE OF (5-METHYLTETRAZOLATO)(2,3,7,8,12,13,17,18-OCTAETHYLPORPHINATO)IRON(III)

The first synthesis and characterization of iron(III) porphyrins with sigma-bonded tetrazolato or triazolato axial ligands are reported. These compounds are represented as (P)Fe[N4C(R)] or (P)Fe(N3C6H4) where P = the dianion of octaethylporphyrin (OEP) or tetramesitylporphyrin (TMP) and R = C6H5, p-CH3C6H4, m-CH3C6H4, or CH2CH3. Each metalloporphyrin may exist in two different isomeric forms, which are labeled as isomer I and isomer II for the case of (P)Fe[N4C(R)]. The linkage mode of the tetrazolato group (and the type of isomer) was determined for two representative complexes by single-crystal X-ray diffraction. (OEP)Fe[N4C(CH3)].1/2C6H5CH3 crystallizes as isomer I in the monoclinic system, space group P2(1)/c (a = 15.967 (2) angstrom, b = 17.464 (4) angstrom, c = 14.726 (2) angstrom, beta = 66.59 (2)-degrees, Z = 4, V = 3765 angstrom-3, rho = 1.27 g cm-3, R(F) = 5.97%, R(w)(F) = 5.82%). (OEP)Fe[N4C(C6H5)] also crystallizes in the monoclinic space system, space group P2(1)/c (a = 12.798 (2) angstrom, b = 12.748 (3) angstrom, c = 24.301 (5) angstrom, beta = 78.93 (2)-degrees, Z = 4, V = 3891 angstrom-3, rho = 1.25 cm-3) but exists as isomer II. Altogether, eight different tetrazolato and triazolato complexes were synthesized, and each was characterized by UV-visible, IR, ESR, and H-1 NMR spectroscopy, as well as by electrochemistry. Variable-temperature magnetic susceptibility measurements were also performed and give data consistent with a high-spin-state Fe(III) central metal. An analysis of the isotropic chemical shifts shows that the electronic structures of the high-spin-state complexes are virtually independent of the specific sigma-bonded nitrogen axial ligand.