Synthesis, Palladium(II) Complexes, and Catalytic Use of a Phosphanylferrocene Ligand Bearing a Guanidinium Pendant

A polar phosphanylferrocene donor equipped with a hydrophilic guanidinium pendant, Ph(2)PfcCH(2)NHC(NH)NH2 center dotHCl (1HCl; fc = ferrocene-1,1'-diyl), has been prepared from the corresponding amine hydrochloride, Ph(2)PfcCH(2)NH(2)HCl (2HCl), and studied as a ligand for Pd-II. The reactions of 1HCl with [PdCl2(MeCN)(2)] in 1:1 and 1:2 Pd/ligand ratios led to an unexpected zwitterionic complex, [PdCl3(1H-P)] (3), and the expected bis(phosphane) complex, trans-[PdCl2(1H-P)(2)]Cl-2 (4), which were structurally characterized. The defined and air-stable solvated complex 3Me2CO and the in situ generated Pd(OAc)(2)/1HCl system were found to be active catalysts for the Suzuki-Miyaura cross-coupling of anionic triolborates with aryl bromides, giving the corresponding biphenyls. These reactions, which do not require the presence of an additional base, were advantageously performed in aqueous ethanol, and the coupling products were isolated in good to excellent yields.