Titanyl complexes

A review on the chemistry of low-valent titanium has appeared which deals with some aspects of the chemistry of titanium sulfoxide complexes (397). Titanyl complexes of the type [Ti0L5][C104]2 have... 

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... 

O—Ti) suggests that they are polymeric, and not titanyl complexes. Conductivities of the acid adducts indicate that they are 1 1 electrolytes in methanol, but are much lower in pyridine and much higher in water the adducts can also be formed from TiOSB by treatment with acid. Ligand conformations as indicated by c.d. spectra are both solvent- and acid-dependent. 

OC-Hydroxycarboxylic Acid Complexes. Water-soluble titanium lactate complexes can be prepared by reactions of an aqueous solution of a titanium salt, such as TiCl, titanyl sulfate, or titanyl nitrate, with calcium, strontium, or barium lactate. The insoluble metal sulfate is filtered off and the filtrate neutralized using an alkaline metal hydroxide or carbonate, ammonium hydroxide, amine, or alkanolamine (78,79). Similar solutions of titanium lactate, malate, tartrate, and citrate can be produced by hydrolyzation of titanium salts, such as TiCl, in strongly (>pH 10) alkaline water isolation of the... 

Similar complexes are formed between poly(viayl alcohol) and titanium lactate (96,101), titanyl sulfate (102), or vanadyl compounds (103). 

Douglas investigated heats of formation of dimethyl sulphoxide (and also of the sulphone) and proposed in a footnote that it could be determined by 5-min reaction with potassium permanganate/sulphuric acid, then adding excess iron(II) sulphate and finally titrating with permanganate. The same principle was used by Krishnan and Patel to determine dimethyl sulphoxide in various complexes (with perchlorates of titanyl, zirconyl and thorium), and by Krull and Friedmann to determine the same compound but using only dilute sulphuric acid and 5-min reaction. 

The first attempts concerned the grafting of TiCl4 and Ti(OEt)4 onto the surface of silica 145 this reaction was followed by an oxidation at 400 °C. The surface complex is presumed to be a titanyl species in which a Ti=0 2+ unit is connected to the surface by two Si — O—Ti linkages. 

In the envisaged titanium oxo complex, the Ti atom is side-bound to the peroxy moiety (02H), consistent with all the spectroscopic results mentioned in Section III in Scheme 27, between the two O atoms that are side-bound to Ti4+, the O atom attached to both the Ti and H atoms is expected to be more electrophilic than the O atom attached to only the Ti atom and is likely to be the site of nucleophilic attack by the alkene double bond. The formation of the Ti-OH group (and not the titanyl, Ti=0, as proposed by Khouw et al. (221)) after the epoxidation and its subsequent condensation with Si-OH to regenerate the Ti-O-Si links had been observed (Section III.B) by FTIR spectroscopy by Lin and Frei (133). Because this is a concerted heterolytic cleavage of the 0-0 bond, high epoxide selectivity and retention of stereochemistry may be expected, as indeed has been observed experimentally (204). 

It is proposed that hydrated or dehydrated titaniumperoxo compounds are formed in TS-1 by H2O2 chemisorption on the titanyl (Ti 0) group, and that these complexes constitute the actual oxidants [96]. In the particular case of alkane oxidation, a homolytic reaction mechanism is proposed, as is tentatively represented in scheme 6 [114]. 

The latest experimental evidence suggest the presence of titanyl groups (Ti=0) in the structure188 (Scheme 9.3). H202 is activated via chemisorption on these groups with the formation of a surface titanium peroxo complex (13). It may exist in the hydrated or open diradical form and initiates hydrogen abstraction. Rapid... 

Mazur et al. described the organization of vanadyl oxide 2,9,16,23-tetraphenoxy-29H, 31//-phthalocyanine (V02+PcPhO) on highly oriented pyrolytic graphite (HOPG) [47], They focused on the fact that the adsorption geometry of nonplanar Pc complexes of titanyl and vanadyl (TiOPc and VOPc) is not well understood... 

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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