Phosphinoferrocene Amidosulfonates: Synthesis, Palladium Complexes, and Catalytic Use in Pd-Catalyzed Cyanation of Aryl Bromides in an Aqueous Reaction Medium
Abstract
The reaction of pentafluorophenyl 1'-(diphenylphosphino)ferrocene-1-carboxylate (4) with omega-aminosulfonic acids H2N(CH2)nSO3H (n = 1-3) in the presence of 4-(dimethylamino)pyridine and triethylamine affords the respective phosphinoferrocene amidosulfonates as crystalline triethylammonium salts, viz., (Et3NH)[Ph2PfcCONH(CH2)nSO3] (1, n = 1; 2, n = 2; 3, n = 3; fc = ferrocene-1,1'-diyl), in good yields. These ligands react smoothly with [PdCl2(cod)] (cod = eta(2):eta(2)-cycloocta-1,5-diene) to give the anionic square-planar bis-phosphine complexes trans-(Et3NH)2[PdCl2(Ph2PfcCONH(CH2)nSO3-kappa P)2] (5, n = 1; 6, n = 2; and 7, n = 3).
The chloride-bridged dimer [LPdCl]2, where L is 2-[(dimethylamino-kappa N)methyl]phenyl-kappa C-1 auxiliary ligand, is cleaved with 1 to give (Et3NH)[LPd(Ph2PfcCONHCH2SO(3)-kappa P)] (8), in which the amidosulfonate coordinates as a simple phosphine. A similar reaction of [LPd(OAc)]2 and 1 proceeds under a partial elimination of (Et3NH)OAc to afford a mixture of zwitterionic bis-chelate [LPd(Ph2PfcCONHCH2SO3-kappa O-2,P)] (9) and another Pd(II) complex tentatively formulated as [LPd(OAc)(Ph2PfcCONHCH2SO3-kappa P)] (9a), from which the former complex separates as an analytically pure crystalline solid.
All compounds have been characterized by spectroscopic methods and elemental analysis. The crystal structures of 1, 3, 5.2.5CH2Cl2, and 9.2CHCl3 were determined by single-crystal X-ray diffraction analysis.
In addition, complexes 5-7 were tested as defined precatalysts for Pd-catalyzed cyanation of aryl bromides with K4[Fe(CN)6].3H2O in aqueous dioxane. Complex 5 proved the most active and generally applicable, affording the nitrile products in good to excellent yields.