Ferrocenyl (P,N)-diphosphines incorporating pyrrolyl, imidazolyl or benzazaphospholyl moieties: Synthesis, coordination to group 10 metals and performances in palladium-catalyzed arylation reactions

Three novel symmetrical ferrocenyl diphosphines with tertiary phosphorus atoms holding respectively nitrogen-containing heterocyclic derivatives of pyrrole, imidazole and benzazaphosphole were synthesized and characterized. Up to now, integration of heteroaromatic fragments, or more generally hetero-cycles, as substituents on the tertiary phosphines of symmetrical ferrocenyl diphosphines has been limited to the furyl motif. Their coordination to palladium and platinum group 10 transition metals was exemplified, and analyzed using single crystal X-ray diffraction. The performances obtained in palladium-catalyzed copper-free Sonogashira and Suzuki cross-coupling reactions using bromoarenes and chloroarenes are reported for the most efficient system. The unprecedented combination of a tert-butyl group and of an imidazolyl motif on the phosphorus atoms led to an air-stable ferrocenyl diphosphine, which allowed in combination with 0.1–0.2 mol% of palladium to generate catalytic systems able to couple some activated chloroarenes and most of the bromoarenes examined.