Cross-coupling reactions monodentate ligands

The formation of the endo adduct suggests that complex X with 1 as an endo bidentate ligand is an intermediate. The order of coordination strength for each component, PPhj > > 1 (as bidentate) > 2 > 1 (as monodentate), was used to rationalize the clean cross-coupling reaction in the presence of PPhj. 

Tremendous effort has been made to develop ligands that control and improve the selectivity, stability, and reactivity of palladium and nickel complexes for cross coupling. Initially, ligandless palladium complexes and triphenylphosphine-palladium complexes were used for these processes. Subsequently, bidentate ligands and monodentate ligands have been developed that possess particular electronic and steric properties that increase reaction rates, scope, and turnover numbers. 

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