Titanium complexes with porphyrins

Convergent dendrimers, with their versatile three-dimensional scaffold, may be tailored to mimic, perhaps crudely, some elements of enzymatic structures. Numerous catalytic moieties, including manganese porphyrins,253,254 bis(oxazoline) copper complexes,304 305 tertiary amines,306 binaphthol titanium complexes,285 307 titanium taddolates,292,308 thiazolio-cyclophanes,309 and fullerene-bound bisoxazoline copper complexes,310 have been incorporated at the core of dendritic molecules to determine the effect of dendritic encapsulation on their catalytic activity. 

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. 

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. 

TV-phenylbenzohydroxamic acid, 506, phthalocyanines, 865 polypyrazolylborates, 248 porphyrins, 823 pseudohalides, 228 Titanium(III) complexes octaethylporphyrin reaction with dioxygen, 325 Titanium(IV) complexes 1,3-diketones, 376 triazines... 

Titanium(IV)-porphyrin [TiO(TPP)] as well as molybdenum(V)-porphyrin [MoO(OMe)(TPP)] complexes were found to be active for the catalytic epoxidation of alkenes by alkyl hydroperoxides, whereas their peroxo derivatives are inactive.632 Iron(III)-porphyrin-peroxo complexes such as Fe(TPP)02NMe4 did not react with hydrocarbons, but form sulfato complexes upon reaction with S02.632 Manganese(III)-porphyrin-peroxo complexes Mn(02)(TPP) K+ were recently characterized by X-ray crystallography.634... 

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. 

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