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μ-Carbido diporphyrinates and diphthalocyaninates of general formula [{Mp²⁻}₂(μ-C)] (p²⁻ = tpp (M = Fe), oep (Fe), pc (Fe, Ru); H₂tpp: 21H,23H-5,10,15,20-tetraphenylporphine; H₂oep: 21H,23H-2,3,4,8,12,13,17,18-octaethylporphine; H₂pc: 29H,31H-phthalocyanine) of formally Fe^IV and Ru^IV are prepared by a new and improved ‘one-pot’ synthesis. The corresponding chloro complexes of the tervalent metal ions react successively with potassium hydroxide in boiling 2-propanol and then with trichloromethane. Potassium hydroxide is proven to be a very versatile and powerful reductant in tetrapyrrolic chemistry. As evidenced from electron spin resonance and UV vis spectral measurements, the precursor is reduced primarily to an ate-complex of type [M^Ip²⁻]⁻ of a formally monovalent metal ion. This active species is assumed to react with trichloromethane via a dichlorocarbene complex of type [M^II(CCl₂)p²⁻] to yield the actual -carbido complex. [{Feoep²⁻}₂(μ-C)] is crystallographically characterized. It is monoclinic, space group C12/c1 (15), with a = 18.279(3) Å, b = 15.005(2) Å, c = 23.392(7) Å, β = 107.12(2)°, Z = 4, R₁ = 0.0773. The iron atom is displaced by 0.192(3) Å out of the centre (Ct) of the (N_p)₄ plane toward the (μ-C) atom. Average d(Fe-N_p) is 1.986(5) Å; d(Fe-(μ-C)) is 1.6638(9) Å. The Fe-C-Fe skeleton is linear (179.5(3)°). The two slightly waving porphyrinato cores are in a staggered conformation, the (N_p-Fe-Fe″-N_p″) torsion angle being 21.0(3)°. Solutions of each μ-carbido complex in pyridine/dichloromethane show four distinct quasi-reversible redox processes in their differential-pulse voltammograms and these are assigned to the successive one-electron reduction and oxidation of the macrocyclic ligands. ¹³C CP MAS NMR spectra indicate effective four-fold symmetry within the series of the μ-carbido complexes with isotropic shifts occurring at similar fields to those of the corresponding macrocyclic complex of a closed-shell metal ion. Resonances of the bridging carbon atom are not detected. A characteristic increase of line broadening within the series tpp²⁻ > oep²⁻ > pc²⁻ may be due to Fermi contact interactions with the strongly coupled low-spin M^IV centres. The magnetic susceptibility studies show that the complexes all display non-zero μ values at 295 K increasing from pc²⁻ to tpp²⁻. Mössbauer spectra confirm the low-spin Fe^IV oxidation state for the iron centres. Isomer shift, δ, and quadrupole splitting, ΔE_Q, for [{Fepc²⁻}₂(μ-C)] and [{Fetpp²⁻}₂(μ-C)] are identical to those previously reported. Data for [{Feoep²⁻}₂(μ-C)] are essentially the same as for the pc and tpp complex. Thus the order of δ is tpp ≈ oep > pc whilst that of ΔE_Q is pc >> oep > tpp. Small impurity lines are observed which help explain the magnetic data. UV vis/NIR spectra of the μ-carbido complexes show the characteristic π-π* transitions. These are shifted with respect to the corresponding mononuclear complexes to higher energy because of excitonic interactions. Vibrational spectra are discussed in detail ν_as(M-C-M) (in cm⁻¹) is at 937 (M = Fe; tpp) < 976 (Fe/oep) < 997 (Fe/pc) < 1050 (Ru/pc), ν_s(M-C-M) (in cm⁻¹ at 433 (Fe/tpp) < 460 (Fe/oep) < 477 (Fe/pc). Hence, valence force constants increase significantly in the order tpp < oep < pc. ν_s(Fe-C-Fe) of [{Fepc²⁻}₂(μ-C)] is selectively resonance Raman enhanced. As evidenced from the excitation profile a C→Fe charge transfer, not detected in the vis spectrum, is assumed to be present at 22 000 > ν > 25 000 cm⁻¹.

The synthesis and characterization of new alkali-soluble osmium tetraphenylporphyrinates, complexes of the 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin Os(tH₄cpp)L₂ and Os(tH₄cpp)LL' (2a–j), is described. 2a–j are obtained from the corresponding new osmium porphyrinates Os(tmecpp)L₂ and Os(tmecpp)LL'(1a–k) by alkaline saponification and precipitation with hydrochloric acid. In fact, the osmium(II) porphyrinates 2c–f as well as 2i–j are oxidized to the osmium(III) porphyrinates Os(tH₃cpp)L₂(3c–f) and Os(tH₃cpp)LL'(3i–j) in the presence of air, as confirmed by UV-vis spectroscopy.