Synthesis, Characterization, and Molecular Structure of Oxo(porphyrinato)chromium(IV) Complexes

The reaction of chloro(5,10,15,20-tetraphenylporphyrinato)chromium(III) [Cr(TPP)Cl] with iodosylbenzene and base (tert-butyl hydroperoxide, m-chloroperoxybenzoic acid, or sodium hypochlorite) produced the corresponding oxochromium(IV) complex (2). This diamagnetic compound had an intense band in the IR at 1025 cm⁻¹, which shifted to 981 cm⁻¹ upon ¹⁸O substitution. The visible spectrum showed bands at 430 and 544 nm. The oxochromium(IV) complex reacted with triphenylphosphine to give triphenylphosphine oxide and chromium(II), which reacted with methylene chloride to give Cr(TPP)Cl or with 2 to give a μ-oxo chromium(III) dimer, 5. Crystallization of oxo(5,10,15,20-tetra-p-tolylporphyrinato)chromium(IV) from benzene-hexane gave diffractable single crystals: space group P2₁/c, Z = 4, a = 17.342 (6) Å, b = 16.964 (7) Å, c = 15.804 (6) Å, β = 112.52 (3), V = 4295 (3) ų. Least-squares refinement based on 2309 observed data with I > 3σ(I) gave R₁ = 0.068, R₂ = 0.072. The CrO bond length was 1.572 (6) Å, the average CrN distance was 2.032 (7) Å and the chromium cation was 0.469 Å above the average pyrrole nitrogen plane. The porphyrin ring was distinctly saddle shaped with the pyrrole β-carbons displaced 0.340 and 0.568 Å above and below the mean pyrrole nitrogen plane.