Groups 9 and 10 Complexes of C–Donor Ligands Derived from Pyridinium-Stabilized Phosphorus Ylides

Abstract

The design and synthesis of η 1 -C-donor ligands that combine nucleophilic 4-alkylidene dihydropyridines with phosphorus ylides is reported. Positioning of a phosphonium group at the picolyl carbon of 4-alkylpyridinium salts allows for conversion to phosphonium-stabilized alkylidene dihydropyridine ligands under mildly basic conditions. The resulting (Me-N-Py-CH-PPh 2 -R)(BF 4 ) ligands coordinate Pd(II)Cl 2 as monodentate (R = Ph) or bidentate ligands (R = 2-Py, CH 2 PPh 2 , or CH 2 CH 2 PPh 2 ), and six new Pd(II) complexes were spectroscopically characterized. Structural features of four of the complexes were further defined through single-crystal X-ray diffractometry. The ligands in these complexes are best described as phosphorus ylide C-donors that are stabilized by adjacent N-methylpyridinium rings. In addition, two Rh(I) complexes were successfully prepared and characterized, including a Rh(I) carbonyl complex which exhibited a low ν CO of 1984 cm −1 , indicative of the strong σ-donor properties of these ligands. The ability of a Pd complex to catalyze Suzuki cross-coupling reactions was examined.