Investigation of Active Palladium Catalyst Based on Novel Ruthenocenylphosphine Ligand and its Application to Cross-Coupling Reaction

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A highly general, active, and stable catalytic system was realized in the palladium-catalyzed Suzuki-Miyaura reactions of sterically and/or electronically deactivated aryl chlorides and aminochloropyridines with arylboronic acids using a palladium precatalyst prepared from di-cyclo-hexylruthenocenylphosphine(CyR-Phos), Pd(dba)_2, and ethyl 4-bromobenzoate. The relatively weak basicity and highly steric hindrance of R-Phos, di-tert-butyl analogue of CyR-Phos, was disclosed on the basis of the JP-Se coupling constant and the crystal structure of the phosphine selenide derivative. These results suggest that not the electron donation but the steric bulkiness is the key element of the ligand architecture of R-Phos family to activate the palladium catalyst.