C-S bond activation

Metal Insertion into the C-S Bond C-S Bond Activation 823... 

These studies indicate once more the importance of multimetallic cooperative effects for desulfurization to be accomplished. In another clear case of bimetallic cooperative C-S bond activation, Bianchini and coworkers have provided very pertinent information involving a complex containing a Group 8/Group 6 metal couple (RhAV). The reaction of BT with [(triphos)RhH] leads to ring-opening followed by hydride transfer as shown in Eq. 4.18 ... 

The fact that the Curtis clusters are capable of cleaving carbon-sulfur bonds at temperatures several hundred degrees below those employed in the commercial heterogeneous process has been taken to suggest that it is removal of sulfur from the catalyst surface rather than C-S bond activation that is the rate-determining step in the heterogeneous system. ... 

C-S Bond Activation, Hydrogenolysis, and Desulfurization of Thiophenes by Metal Complexes... 

Another case of bimetallic cooperative C-S bond activation involves the reaction the triphos-Rh BT-derived metallacycle with W(CO)s to yield the heterobimetallic sulfur-bridged species 47, which upon thermolysis under H2 (30 atm) induced HDS of BT to ethylbenzene, plus [(triphos)RhH(CO)] together with an insoluble W-S material (Equation (9)). This shows that the S-bridged Rh-W couple switches the reactivity from hydrogenolysis... 

New photochemical methods for the synthesis of esters and ketones have been also established. For instance, the visible-light mediated photoredox reaction of a-brominated carboxylates with enamines allowed to obtain y-ketoesters in good yields, under very mild conditions. Symmetrical and unsymmetrical 1,4-diketones could be synthesised from p-ketosulfones by visible light-induced C-S bond activation using... 

Elimination of Benzylic Phenyl Thioethers. That C-S bond activation by CuOTf is not limited to substrates that can generate sulfur-stabilized carbocation intermediates is illustrated by a C-C connective synthesis of trans-stilbene (eq 56). The elimination of thiophenol under mild conditions is favored by benzylic stabilization of a carbocation intermediate or an E2 transition state with substantial carbocationic character. 

Palladium(II)-promoted reaction of 2-arylthiophenes with alkynes gives access to IH-isothiochromenes in moderate to good yields, via C-H and C-S bond activations (Scheme 90) (130L282). 

More recently, a general procedure for the preparation of coumestans from 2-(methylthio)benzofuran-3-carboxyl-ates and 2-hydroxyphenylboronic acids has been described (Scheme 43) [142]. The annulation process involves the initial cross-coupling of the benzofurans with the boronic acids, via Pd-catalyzed C-S bond activation, followed by intramolecular transesterification in the resulting coupling products. 

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