Formation of a Chelate Bis(phosphino)[3]ferrocenophane Ligand and Its Use in Palladium-Catalyzed Alternating CO/Ethene Copolymerization

Treatment of 1,1‘-diacetylferrocene ( 1 ) with dimethylamine, catalyzed by titanium tetrachloride, proceeded in a Mannich-type C−C coupling reaction to yield the unsaturated [3]ferrocenophane 2 . Subsequent catalytic hydrogenation gave the saturated [3]ferrocenophane derivative [(C 5 H 4 CHMeCH 2 CH(NMe 2 )C 5 H 4 )Fe] ( trans - 3) . Directed Cp metalation of trans - 3 was carried out by treatment with n -BuLi, followed by reaction with ClPPh 2 to yield the “ortho-phosphorylated” P, N -[3]ferrocenophane chelate ligand 4 . Its treatment with HPPh 2 in acetic acid resulted in a clean substitution of the −NMe 2 group by −PPh 2 with overall stereochemical retention to yield the P, P -[3]ferrocenophane ligand 5 . The stereochemical pathway of such substitution reactions at the [3]ferrocenophane framework, which proceed cleanly by a double-inversion route with participation of the metal center, was modeled by computational chemistry and its reactive cationic intermediate 14 characterized by a DFT calculation. Reaction of 4 with (cod)PdCl 2 gave the chelate complex 6 . The analogous reaction of 5 with (cod)PdCl 2 furnished the P, P -[3]ferrocenophane−PdCl 2 chelate complex 7 . Both the complexes 6 and 7 and the ligand 5 were characterized by X-ray diffraction. Treatment of 7 with AgBF 4 in dichloromethane or alternatively of 5 with palladium acetate, followed by BF 3 addition, gave very active catalyst systems for alternating carbon monoxide/ethene copolymerization.