[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.