Ligand synthesis phosphorus-palladium complexes

Palladium-complex-promoted asymmetric Diels-Alder reaction stereoselective synthesis of a new sulfinyl-substituted phosphine ligand containing three carbon, one phosphorus and one sulfur stereogenic centres <95CC1747>. 

Phosphine ligands based on the ferrocene backbone are very efficient in many palladium-catalyzed reactions, e.g., cross-coupling reactions,248 Heck reaction,249 amination reaction,250 and enantioselective synthesis.251 A particularly interesting example of an unusual coordination mode of the l,l -bis(diphenylphosphino)ferrocene (dppf) ligand has been reported. Dicationic palladium(II) complexes, such as [(dppf)Pd(PPh3)]2+[BF4 ]2, were shown to contain a palladium-iron bond.252,253 Palladium-iron bonds occur also in monocationic methyl and acylpalladium(II) complexes.254 A palladium-iron interaction is favored by bulky alkyl substituents on phosphorus and a lower electron density at palladium. 

Because of its potential application to the synthesis of estersfor lubricating oils, the dimerization-carbonylation of butadiene has received special attention. Basic phosphines such as PBun3 and weakly basic tertiary amine solvents (quinoline, N, N-diethylaniline) were found to improve both the stability and activity of the catalyst system.S3° In a further report in which PPr 3 was used as phosphorus ligand it was found that the addition of maleic anhydride caused a marked increase in the catalytic activity. It was believed that through coordination it stabilized the palladium(O) complexes formed against precipitation as metal.s 1... 

Cyclometalation is one of the most reliable and versatile methods for the synthesis of stable Pd-C a-bonds. In this reaction, a palladium (or other metal) complex is reacted with a ligand possessing a donor atom. The metal is directed by the donor atom to insert into a C-H bond, forming a chelate ring. This donor is usually the nitrogen of a tertiary amine, heterocyclic amine, or imine, or a phosphorus in a tertiary phosphine or phosphite. Other donor atoms, such as O and S, are occasionally encountered. The chelate ring size is normally five. ... 

Olefin hydrocyanation using palladium catalysts has been less well studied than with nickel. Nevertheless, zerovalent complexes of palladium, particulrly triarylphosphite complexes, hydrocyanate a wide range of olefins in useful yields (see Table 1). Early work reported the merit of excess phosphorus ligand to promote the reaction, and further paralleling the observations with nickel, Lewis acids have been used to improve catalytic activity. However, addition of ZnClj fails to improve nitrile product yield . Asymmetric induction in hydrocyanation results in optical yields of 30% in the synthesis of exo-2-cyanonorbomane using the chiral ligand DIOP, and studies on the stereochemistry of HCN and DCN addition to terminal alkenes and a substituted cyclohexene with the same catalyst have been reported. ... 

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