[2]Ferrocenophanes with Nitrogen in Bridging Positions

Three [2]ferrocenophanes ([2]FCPs) bridged by nitrogen and silicon (7SiMe2) and nitrogen and tin (7SnMe2, 7SntBu2) were synthesized by salt metathesis between a dilithioferrocene derivative, prepared in situ from 1-bromo-1′-(trimethylsilylamino)ferrocene (6), and Me2SiCl2, Me2SnCl2, and tBu2SnCl2, respectively. A multistep synthesis of precursor 6 is described. Only 7SiMe2 and 7SntBu2 could be prepared as analytically pure compounds. The molecular structures of all three [2]FCPs were determined by single-crystal X-ray analysis. Expectedly, the tilting of the Cp ligands in the silicon species 7SiMe2 is larger [α = 15.73(13)°] than in the tin compounds 7SnMe2 [α = 9.36(17) and 9.45(18)°] and 7SntBu2 [α = 10.13(11)°]. Ring-opening polymerizations of 7SiMe2 and 7SntBu2 were attempted using the common methods of thermal, transition-metal-catalyzed, anionic, and photocontrolled ring-opening polymerization, but none of the experiments gave polymeric materials.