Phosphinoferrocene amidosulfonates: Synthesis, palladium complexes, and catalytic use in pd-catalyzed cyanation of aryl bromides in an aqueous reaction medium

Article abstract of DOI:10.1021/om2011529

The reaction of pentafluorophenyl 1-(diphenylphosphino) ferrocene-1-carboxylate (4) with -aminosulfonic acids H₂N(CH ₂)nSO₃H (n = 13) in the presence of 4-(dimethylamino)- pyridine and triethylamine affords the respective phosphinoferrocene amidosulfonates as crystalline triethylammonium salts, viz., (Et3NH)[Ph ₂PfcCONH(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 = ²:²-cycloocta-1,5-diene) to give the anionic square-planar bis-phosphine complexes trans-(Et3NH)2- [PdCl₂ (Ph2PfcCONH(CH2)nSO3-κP)2] (5, n = 1; 6, n = 2; and 7, n = 3). The chloride-bridged dimer [LNCPdCl]2, where LNC is 2-[(dimethylamino- κN)methyl]phenyl-κC1 auxiliary ligand, is cleaved with 1 to give (Et3NH)[LNCPd(Ph₂PfcCONHCH₂SO₃-κP)] (8), in which the amidosulfonate coordinates as a simple phosphine. A similar reaction of [LNCPd(OAc)] ₂ and 1 proceeds under a partial elimination of (Et3NH)OAc to afford a mixture of zwitterionic bis-chelate [LNCPd(Ph ₂PfcCONHCH₂SO₃-κ2O,P)] (9) and another Pd(II) complex tentatively formulated as [LNCPd(OAc)- (Ph ₂PfcCONHCH2SO3-κP)] (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, 52.5CH₂Cl₂, and 92CHCl3 were determined by single-crystal X-ray diffraction analysis. In addition, complexes 57 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.