Silver salts complex hydrides

In general the complexes are mild reducing agents and in solution will reduce silver nitrate to silver (86). The hydrides are not acidic in solution, nor will they form sodium salts analogous to those of the carbonyl hydrides... 

The normal neutral pathway (22 24 25 27) was ruled out by conducting the reaction with monodentate phosphine BINAP ligand mimics (Scheme 12.5). The products obtained were of low enantiomeric excess relative to reactions employing BINAP. The direct cationic pathway (24-> 26) was also eliminated due to the fact that the opposite stereochemistry was obtained under cationic conditions with the addition of silver salts. The switch in stereoselectivity in the presence of silver salts, moreover, indicates that oxidative insertion is not the enantioselective step. j8-Hydride elimination was also discounted as the enantioselective step due to the influence of the double-bond geometry of the starting material on the enantioselectivity of the cyclization. The proposed enantioselective step is the formation of the cationic intermediate 26 by an associative displacement (24-> 28-> 26). In the case of square planar pafladium(n) complexes, substitution chemistry can occur through associative processes. Axial coordination of the alkene would form the pentacoordinate pafladium(II) complex 28. Reports of isolated and characterized pentacoordinate palladium(II) species provide support for this proposed intermediate. 

Pyridine-functionalized N-heterocyclic carbene Rh and Ir complexes have also been described as active precatalysts for C=0 bond TH. For example, Peris and coworkers observed the formation of metal hydrides by C—H oxidative addition of a pyridine-N-substituted imidazolium salt such as N-"Bu-N -(2-pyridylmethyl-imidazolium) hexafluorophosphate in the reaction leading to M-pyNHC complexes, that is [lr(cod)H(pyNHC)Cl] (58) [54]. Transmetallation from silver carbene... 

In this process, carboxylic acids and olefins are converted to vinylarenes in the presence of palladium in catalytic amounts and silver in overstoichiomettic amounts (Scheme 4). It is initiated by formation of a silver arenecarboxylate salt, which then reacts with a palladium(ll) halide complex (a) to give the silver halide and palladium carboxylate b. The extrusion of carbon dioxide, and thus the conversimi of the carboxylate to the organometallic species c, occurs within the ligand sphere of palladium. The subsequent steps, i.e., insertion of the olefin into the palladium-carbon bond, internal rotation, and (3-hydride elimination, correspond to the classical Heck reaction [26]. An additional oxidation step converts the palladium(0) species f back to palladium(ll). It is this oxidation by silver that... 

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