Novel mixed donor N-Heterocyclic carbene complexes

Abstract

A series of novel silver (1) and copper (1) N-heterocyclic carbene complexes functionalised with nitrogen, oxygen and phosphorus donors have been synthesised.

A series of novel palladium carbene complexes functionalised with nitrogen and oxygen donors have been synthesised.

Novel mixed donor picolyl-carbene complexes of nickel, rhodium and ruthenium have been synthesised. The mixed donor carbene complexes of nickel, rhodium and ruthenium are: (3-Ar'-1-pic-ylidene) NiBr₂; (3-Ar'-l-pic-ylidene) RhCl (COD); (3-Ar'-1-pic-ylidene) RhCl(p-cymene).

A number of the palladium complexes were shown to be extremely good pre-catalysts for the Heck reaction. Subtle differences in the complexes are shown to affect their effectiveness as catalysts: for the bidentate ligands larger bite angles give higher turnover frequencies but smaller bite angles increase stability of the active catalyst, for tridentate ligands less bulky substituents enable the reaction to proceed faster but do not affect the stability of the catalyst. Turnover numbers comparable to the best-known systems were achieved with aryl iodides. The chiral palladium carbene complexes were shown to catalyse the Heck reaction at temperatures bellow that of enantiomer interconversion. These chiral complexes also catalyse the Heck reaction effectively with aryl chlorides.

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