Titanium thiolates

Mono-Cp alkoxo and aryloxo titanium thiolates and sulfides have been widely reported. These complexes show an interesting reactivity, including C-H and G-S bond activation and reduction of Ti(iv) to Ti(m). The incorporation of bulky aryloxo ligands in the coordination environment of the titanium center limits some of this reactivity and alters the chemistry of the compounds considerably. The implications of the electronic and steric effects of these ancillary ligands have been considered.1005-1008... 

Carmalt CJ, Dinnage CW, Parkin IP (2000) Thio sol-gel synthesis of titanium disulfide from titanium thiolates. J Mater Chem 10 2823-2826... 

The regioselectivity of Michael additions of thiolates to 2,4-dienones can be altered drastically by variation of the reaction conditions and addition of Lewis acids to the reaction mixture. Lawton and coworkers examined the reaction of 2-mercaptoethanol with l-(3-nitrophenyl)-2,4-pentadien-l-one and observed a high regioselectivity in favor of the 1,6-addition product at 45 °C (equation 42)123,124. Lowering of the reaction temperature caused an increase in the amount of 1,4-adduct, and at —40°C, a product ratio of 40 60 was found. These events suggest that kinetic control favors the 1,4-addition product whereas the 1,6-adduct is thermodynamically more stable. If, however, the reaction was carried out with a complex of the dienone and titanium tetrachloride, only the 1,4-adduct was isolated after hydrolytic workup123. Obviously, this product is trapped as a metal chelate which prevents formation of the 1,6-adduct by retro-Michael/Michael addition. In the absence of the chelating Lewis acid, the 1,4-addition product can indeed be converted... 

Thiolato titanium complexes have been developed supported by Cp and phosphinimido ligands, in an attempt to compare their chemical behavior with the corresponding bis-Cp derivatives, using the steric and electronic analogy between Gp and imido functionalities. Compounds of the type CpTi(N=PPr13)(SR2)2 (Scheme 244) are prepared by reaction of the dichloro complex with the corresponding lithium thiolates LiSR, or alternatively by protonolysis of Ti-Me... 

Efficient immobilization of aptamers on surfaces is necessary for the construction of tongh, stable sensors and assay systems as one necessary step to overcome limitations for practical applications (Bini et al., 2007). Bini et al. (2007) have compared thrombin aptamers immobilized on a gold snrface by chemisorption (thiolated aptamer) and by biotin-streptavidin interaction (biotinylated aptamer carrying a linker) on a gold surface modified by a thiol-dextran-streptavidin layer. The linker-modified aptamer immobilized via streptavidin-biotin showed better reproducibility and sensitivity results for the quartz crystal sensor. Aptamers can be used for the functionalization of titanium-alloy surfaces (e.g., implant material, scaffolds) to enhance cell adhesion. The aptamers directed to osteoblasts are fixed electrochemically on the snrface of the alloy and promote cell adhesion (Gno et al., 2005, 2007). 

Figure 1 (A) Schematic section through a chemically microstructured TSG sample after pCP with reactive DSU, formation of a HUT SAM and immobilization of proteins. Primary amines of proteins react with the end groups of the DSU crosslinker (11, ll -dithio-bis(succinimi-dylundecanoate), Fig. 1C bound DSU (thiolate form) with the formation of an amide bond. (B) Schematic section through a microstructured silicon/gold structure after pCP, etching the gold, titanium and silicon, removal of the etch-resistant monolayer, formation of a reactive monolayer and finally reaction with protein.

The convenient preparation of thiolates of titanium " and uranium from their respective dialkylamides, but not from alkoxide analogues, demonstrates the oxophilic nature of these metals in their higher oxidation states. 

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