Titanyl porphyrinates

Atropisomers arising from hindered rotation of meso-aryl have been used in studies of metalloporphyrins. Barriers for a series of para and meta aryls in titanyl porphyrins and... 

The Group 4 porphyrins, represented by complexes with M = Ti, 2r, and Hf, have been studied in detail, but again, with the exception of the Ti complexes, most of these porphyrins exist as (P)2M and (P)(Pc)M complexes, where P = OEP or TPP and M = Zr or Hf [127]. A number ofTi porphyrins with 0X0, peroxo [129-132], halogen [133-134] or chalcogen [135-137] axial ligands have been synthesized and many of these compounds have been studied as to their electrochemical properties. The Ti porphyrins can exist with the metal ion in a -1-4, -1-3 or -1-2 oxidation state, and in most cases, other than for the titanyl porphyrins, the electrode reactions of these compounds are accompanied by chemical reactions involving a loss of the axial ligand [7]. 

A. N. Sidorov, Russ. Chem. Rev. (Engl. Transl.) 35,152-166(1966). Porphyrin-titanyl complexes ... 

However, there are a few true titanyl examples, mostly porphyrins and related complexes that do have Ti=0 bonds. The Ti=0 bond appears to be short 1.62 A while ir bands are in the region 890 to 972 cm 1 (Raman, v = 975 in 2 M HC1) consistent with a Ti=0 double bond. Octahedral titanyl complexes, such as (Me3tacn)Cl2TiO, are readily available from Tim precursors by oxidation with dioxygen in an aprotic solvent.17 A cationic titanyl complex which is stable in aqueous media18 can be made according to... 

A n.m.r. study of the substituted titanyl tetraphenylporphyrin complexes TiO(p-Pr -TPP) and TiOfp-CFj-TPP) showed that at 9 and 17 °C, respectively, rotation of the phenyl rings is slow enough to render the two sides of each ring non-equivalent. Peroxotitaniumoctaethylporphyrin has been prepared and its structure determined (see p. 14) the structure of titanyl octaethylporphyrin has also been determined. The Ti=0 bond is perpendicular to the porphyrin ligand... 

TiIv. Diamagnetic Ti porphyrins have been isolated and characterized as titanyl (Ti =0) complexes [Fuhrhop (71), Tsutsui (181), (183)]. An esr spectrum of a Tim state has been mentioned, but no detailed data are available on this oxidation state nor on the potential of the Ti111/ TiIV couple [Tsutsui (183)]. The "normal electronic spectrum of titanyl OEP [573 (28,000), 535 (14,000) 405 (350,000)] [Fuhrhop (71)] is replaced by a hematin spectrum [582 (8,500) 480 (24,000) 359 (105,000)] [Fuhrhop (71)] and the fluorescence of the original titanyl compound disappears when the axial oxo group is protonated. The influence on the redox potential of the intramolecular n- dxz,yz charge transfer, which occurs similarly in the hematins (see IV.6), has not been investigated. 

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