Abstract
The living ring-opening metathesis polymerization (ROMP) of an unsaturated twisted amide using the third-generation Grubbs initiator is described. Unlike prior examples of ROMP monomers that rely on angular or steric strain for propagation, this system is driven by resonance destabilization of the amide that arises from geometric constraints of the bicyclic framework. Upon ring-opening, the amide can rotate and rehybridize to give a stabilized and planar conjugated system that promotes living propagation. The absence of other strain elements in the twisted amide is supported by the inability of a carbon analogue of the monomer to polymerize and computational studies that find resonance destabilization accounts for 11.3 kcal mol-1 of the overall 12.0 kcal mol-1 ring strain. The twisted amide polymerization is capable of preparing high molecular weight polymers rapidly at room temperature, and post-polymerization modification combined with 2D NMR spectroscopy confirms a regioirregular polymer microstructure.
Highlights
Ring-strain is a common driving force for chemical reactions in both small molecule and macromolecular synthesis
The absence of other strain elements in the twisted amide is supported by the inability of a carbon analogue of the monomer to polymerize and computational studies that find resonance destabilization accounts for 11.3 kcal molÀ1 of the overall 12.0 kcal molÀ1 ring strain
An initial ring-opening metathesis polymerization (ROMP) experiment with monomer 1 was performed with G3 in DCM at room temperature targeting a degree of polymerization (DP) of 100 (Table 1, entry 4)
Summary
Ring-strain is a common driving force for chemical reactions in both small molecule and macromolecular synthesis. The living ring-opening metathesis polymerization (ROMP) of an unsaturated twisted amide using the thirdgeneration Grubbs initiator is described.
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