Phosphinoferrocenyl Carboxamides Bearing Glycine Pendant Groups: Synthesis, Palladium(II) Complexes, and Catalytic Use in Polar and Aqueous Reaction Media

Abstract

The reaction of 1′-(diphenylphosphino)-1-ferrocenecarboxylic acid (Hdpf) with H2NCH2CO2CR3 mediated by peptide coupling agents (EDC/HOBt) afforded novel glycine phosphino-carboxamides Ph2PfcCONHCH2CO2CR3 (fc = ferrocene-1,1′-diyl; R = H (1) and Me (2*)). Compound 1 was converted to its corresponding phosphine oxide (3*) and sulfide (4*), to N-acyl glycine Ph2PfcCONHCH2CO2H (5), and to bis-amide Ph2PfcCONHCH2CONH2 (6*). Compounds 1 and 6 reacted with [PdCl2(cod)] (cod = η2:η2-cycloocta-1,5-diene) and 5 reacted with Na2[PdCl4] to afford the respective, mostly solvated bis-phosphine complexes trans-[PdCl2(L-κP)2] (7: L = 1; 8: L = 5, 9: L = 6). Two different solvatomorphs of 9 were isolated in crystalline form and structurally characterized (9* and 9a*). Furthermore, bridge cleavage reaction of [{Pd(μ-Cl)(LNC)}2] (LNC = 2-[(dimethylamino-κN)methyl]phenyl-κC1) with 1 gave [(LNC)Pd(Cl)(1-κP)] (10*), which was further reacted with AgClO4 or KOt-Bu to afford bis-chelate complexes [(LNC)Pd(1-κ2O,P)]ClO4 (11*) and [(LNC)Pd(L-κ2N,P)] (12*; L = 1 deprotonated at the NH group), respectively. All compounds were characterized by spectroscopic methods (multinuclear NMR, MS, and IR) and by elemental analyses; the asterisk indicates that the crystal structure has been determined. Compounds 1, 3−6, and 10−12 were studied by electrochemical methods, while phosphines 1, 5, and 6 in combination with palladium(II) acetate were shown to be highly active catalysts for the Suzuki−Miyaura cross-coupling of aryl bromides with phenylboronic acid in polar solvents (ethanol and dioxane), in their aqueous mixtures, and in pure water.