Titanium porphyrins

Although it is just 50 years since Treibs obtained vanadyl deoxophylloerythroetioporphyrin, the major metalloporphyrin in petroleum and shales,145 it is only relatively recently that Tsutsui obtained the first titanium porphyrin, (meso-DME)Ti=0.146 A review of this general area is available 147 the nomenclature is given in Table 7. 

H. J. Ledon, F. Varescon, Role of peroxo vs. alkylperoxo titanium porphyrin complexes in the epoxidation of olefins, Inorg. Client. 23 (1984) 2735. 

VIV. As with the titanium porphyrins, these complexes occur as vanadyl complexes with an axial oxo group and produce a "normal electronic spectrum which changes to a hematin spectrum when trifluoroacetic acid is added [Bonnett (9)]. The vanadyl porphyrins contain a single unpaired electron (/i=l,4B.M.) and their esr spectra have been studied in some detail [Kivelson (113a), Roberts (152)]. The rich redox chemistry of the inorganic vanadium salts is not reflected in the vanadyl porphyrins, where the +4 state seems to be exceptionally stable. 

The use of porphyrin complexes for the electrocatalytic detection of 8O2 is limited. Iron and titanium porphyrin peroxo complexes (TPPFe-O-FeTPP or TiP(02)) interact with 8O2 to give sulfato complexes of the porphyrins or to give free sulfate Carballo et al. showed that NiPPIX polymerized on GCE catalyzed the oxidation of 8O2, and the modified electrode was stable under hydro-dynamic conditions of a flow cell . ... 

Miksztal, A.R. and J.S. Valentine (1984). Reactivity of the peroxo hgand in metal-loporphyrin complxes Reaction of sulfur dioxide with iron and titanium porphyrin peroxo complxes to give sulfato complexes or sulfate. Inorg. Chem. 23(22), 3548-3552. 

Recent developments in the studies of titanium and vanadium porphyrins with special emphasis on oxygen adducts, low valent metalloporphyrins and related systems of sulphur and selenium. R. Gui-lard and C. Lecomte, Coord. Chem. Rev., 1985, 65, 87 (76). 

Considerable attention has been directed to dehalogenation mediated by corrinoids and porphyrins in the presence of a chemical reductant (references in Gantzer and Wackett 1991 Glod et al. 1997 Workman et al. 1997). Illustrations are provided by the dechlorination and elimination reactions carried out by titanium(III) citrate and hydroxocobala-min (Bosma et al. 1988 Glod et al. 1997). The involvement of corrinoids and porphyrins is consistent with the occurrence of analogous mechanisms for biological reactions that... 

There has recently been much work in this area using Ru-based catalysts, particularly with porphyrin-based catalysts, following the work by Sharpless et al. on asynunetric epoxidation of allylic alcohols by a titanium-based tartrate system. There are reviews on asymmetric epoxidations catalysed by chiral Ru porphyrins [5, 18]. 

Some of the metallic constituents were somewhat soluble in the propane-oil portion, but all tended to be concentrated in the asphaltic portion. Although vanadium (0.02% by weight in the original crude petroleum) was present in all fractions, the greater part was found in the cyclohexane and benzene fractions. From the similarity of the absorption spectra of the vanadium concentrates from petroleum and those of synthetic vanadium porphyrin complexes, Skinner arrived at the conclusion that vanadium compounds from the petroleum of the Santa Maria Valley Field in California exist as porphyrin complexes. Additional metallic constituents were detected by Skinner as these became concentrated in the various solvent fractions, including aluminum, titanium, calcium, and molybdenum. 

The lack of adequate experimental data on chelates of germanium, boron, titanium, and vanadium prevents a similar comparison for these elements however, their high ionic potentials do indicate that they should form stable chelates. Vanadium does occur naturally in the very stable vanadium porphyrin complex. For similar reasons, molybdenum and tin are not discussed further. 

Dioxygen binds to metal porphyrins in the three expected modes, i.e. u-superoxo, peroxo and bridging peroxo. In contrast to die simple complexes discussed previously, dioxygen coordination occurs with a wide range of transition metals from titanium and niobium through to the Group VIII metals. 

Titanium can be inserted into a porphyrin by heating TiPh2Cl2, TiO(acac)2 or TiCL, in high boiling solvents.17 The complex is isolated as TiO(Por), which serves as a precursor of halide derivatives.36 The reaction of an oxotitanium porphyrin with benzoyl peroxide or hydrogen peroxide gives a peroxy compound (v(0—O) 895 cm-1). X-Ray structure analyses confirmed the triangular side-on structure with the O—O bond ( 1.45 A) parallel to one of the —Ti—directions. 

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