Synthesis of Phosphanylferrocenecarboxamides Bearing Guanidinium Substituents and Their Application in the Palladium-Catalyzed Cross-Coupling of Boronic Acids with Acyl Chlorides
Abstract
Phosphanylferrocene donors bearing polar guanidinium substituents, namely acylguanidinium chloride, [Ph(2)PfcCONHC(NH2)NH2]Cl (1), and amidoguanidinium chloride, [Ph(2)PfcCONHCH(2)CH(2)NHC(NH2)NH2]Cl (2; fc = ferrocene-1,1-diyl), have been prepared and characterized. As functional phosphane donors, they were employed in the synthesis of Pd-II complexes bearing 2-[(dimethylamino)methyl-kappa N]phenyl-kappa C-1 (L-NC) and (3)-allyl supporting ligands, [(L-NC)PdCl(L-kappa P)] and [(eta(3)-C3H5)PdCl(L-P)] (L = 1 and 2), respectively.
These defined complexes as well as their surrogates generated in situ from the respective palladium(II) precursor and the phosphanylferrocene ligand were evaluated as catalysts for the coupling of boronic acids with acyl chlorides to give ketones in an aqueous biphasic system. The coupling reaction proceeded best with a simple catalyst formed from Pd(OAc)(2) and ligand 2, which (at 0.2 mol-% Pd loading) produced substituted benzophenones from benzoyl chlorides and benzeneboronic acids in very good yields.
These yields could then be further improved by a proper choice of the reaction partners. Analogous reactions involving aliphatic substrates generally afforded lower yields.