Titanium, thiolate complexes

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... 

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... 

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