Synthesis, Coordination Properties, and Catalytic Use of Phosphinoferrocene Carboxamides Bearing Donor-Functionalized Amide Substituents

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 ω-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-κ2P,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.