A Flexible and Modular Approach to Ferrocenophanes with Nitrogen in Bridging Position
[n]Ferrocenophanes are interesting because these strained sandwich compounds can be polymerized to metallopolymers by ring-opening polymerization reactions. Although there are many strained [n]ferrocenophanes known, only few of them can be polymerized with controlled molecular weight and molecular weight distribution. Among them, the Me2¬Si-bridged ferrocenophane is the mostly explored species. To expand the possibility of accessible monomers we synthesized a new class of strained ferrocenophanes. Although there are plenty of examples of symmetrically bridged ferrocenophanes known, similar species with two different bridging elements are comparatively rare. In order to induce a difference in polarity over the diatomic bridge, nitrogen was introduced in the bridging position. Via a known synthetic methodology, one bromine of 1,1'-dibromoferrocene was selectively replaced by an amino group. The resulting compound was then modified into a class of easily synthesizable starting materials which were cleanly lithiated under optimized condition and in-situ reacted with different elemental dihalides to produce unsymmetrically bridged azaferrocenophanes. This is the first reported development of a modular synthetic approach towards this class of strained sandwich compounds. Azaferrocenophanes with boron, gallium, silicon, tin, and phosphorus as the second bridging element were prepared and characterized. Among these strained compounds, only the silicon- and tin-bridged species have been investigated for ring-opening polymerizations. However, no polymeric materials were obtained from these reactions. The preparation of azaphosphaferrocenophanes was surprisingly difficult and led to unexpected products like 1,1'-disubstituted ferrocenes and azacarbaphosphaferrocenophane.
Metallocenophane, Ferrocenophane, Silicon, Tin, Phosphorus, Boron, Ring-Opening Polymerization, Metallopolymers.
Doctor of Philosophy (Ph.D.)