Synthesis, Coordination Properties, and Catalytic Use of Phosphinoferrocene Carboxamides Bearing Donor-Functionalized Amide Substituents
Abstrakt
Phosphinoferrocene carboxamides bearing donor-functionalized substituents at the amide nitrogen, Ph2PfcCONH(CH2)nY (Y/n = NMe2/2 (1), NMe2/3 (2), PPh2/2 (3), and PPh2/3 (4); fc = ferrocene-1,1'-diyl), were obtained by amide coupling reactions of 1'-(diphenylphosphino)ferrocene-1-carboxylic acid (Hdpf) with the respective amines and structurally characterized. Amide 1 was further converted to the corresponding omega-azoniaalkyl amidophosphine [Ph2PfcCONHCH2CH2NMe3]X (7; X = Cl/I).
Amides 1 and 3, possessing the shorter ethane-1,2-diyl linker, reacted smoothly with [PdCl2(cod)] (cod = cyclocta-1,5-diene) to give the respective trans-chelate complexes, trans-[PdCl2(L-kappa P-2,Y)] (8: L = 1; 9: L = 3). The homologous donors 2 and 4 showed more complicated coordination behavior, affording mixtures of several Pd(II) complexes under similar conditions.
Compounds 1, 3, and 7 were further evaluated as ligands for Pd-catalyzed Suzuki-Miyaura cross-coupling using 4-bromoacetophenone and phenylboronic acid as model substrates. In dioxane, the yields of the coupling product decreased in the order 3 > 1 > 7, presumably due to different donor ability of these ligands (type of donor atoms; PP > PN > PN+).
The catalytic performance in pure water was different: The yields were generally lower and the order of ligands changed to 3 > 7 > 1.