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

Abstract

The design and synthesis of η1-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-PPh2-R)(BF4) ligands coordinate Pd(II)Cl2 as monodentate (R = Ph) or bidentate ligands (R = 2-Py, CH2PPh2, or CH2CH2PPh2), 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 νCO 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.