Rhodium-Mediated Stereoselective Polymerization of “Carbenes”

Unprecedented rhodium-catalyzed stereoselective polymerization of “carbenes” from ethyl
diazoacetate (EDA) to give high molecular mass poly(ethyl 2-ylidene-acetate) is described. The mononuclear,
neutral [(N,O-ligand)MI(cod)] (M = Rh, Ir) catalytic precursors for this reaction are characterized by (among
others) single-crystal X-ray diffraction. These species mediate formation of a new type of polymers from
EDA:  carbon-chain polymers functionalized with a polar substituent at each carbon of the polymer backbone.
The polymers are obtained as white powders with surprisingly sharp NMR resonances. Solution and solid
state NMR data for these new polymers reveal a highly stereoregular polymer, with a high degree of
crystallinity. The polymer is likely syndiotactic. Material properties are very different from those of atactic
poly(diethyl fumarate) polymer obtained by radical polymerization of diethyl fumarate. Other diazoacetates
are also polymerized. Further studies are underway to reveal possible applications of these new materials.