Phosphine ligands hydrometallation

Hydrometallation is catalyzed by Pd. Hydroboration of l-buten-2-methyl-3-yne (197) with catecholborane (198) gives the 1,4-adduct 199 with 84% selectivity. The ratio of Pd to phosphine (1 1.5) is important[l 10]. The vinyl sulfide 201 is prepared by a one-pot reaction of the thioalkyne 200 via a Pd-catalyzed hydroborution-coupling sequence using dppf as a ligand[l 11]. 

The resulting <7 alkyl bond in such complexes is very reactive, especially towards carbon-carbon bonds. Thus an alkene in the reacting system will lead to coordination followed by migratory inser tion into the palladium-carbon a bond. This process is like hydrometallation and is called carbo palladation as carbon and palladium are attached to the ends of the alkene system. There is nc change in oxidation state during this process, although the ligands (often phosphines) must dissociate to allow coordination of the alkene and associate to provide a stable final 16-electron product. 

A number of cyclometallated Rh complexes have been prepared with ligands such as 2-phenylpyridine,361 2-benzylpyridine,362 l-phenylpyrazole,363 6-(2-thienyl) bipy, and 2,6-diphenylthiophenol.364 The photophysical properties of some phenylpyridinate complexes have been studied.365 The hydrometallation of vinylcyclopropane with a cyclometallated Rh complex gave quinolyl pentenyl ketones,366 and the insertion of CO into the Rh-C bond of a cyclometallated phosphine has been reported.367... 

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