The use of “new” catalytic systems working in reactions that were previously known to be possible only by transition-metal complexes has attracted growing interest. Organocatalysis, a catalytic approach based on using small organic compounds, such as N-heterocyclic carbenes (NHC), to promote reactivity, has become a powerful tool in organic synthesis, polymer synthesis and other areas, thanks to several advantages it can offer, as compared to other modes of catalysis. Following our work in the NHC promoted polymerization of cyclic and acyclic acrylates [1-2], here we present an account of theoretical studies into the mechanism of polymerization of polar cyclic monomers promoted by N-heterocyclic carbenes (NHC). In particular, the mechanism of polymerization of N-substitued N-carboxy-anhydrides to poly(a-peptoid), promoted by NHC has been investigated, see Chart 1. The general mechanism goes through the monomer activation carried up by the NHC species, acting like an initiator; afterwards the propagation occurs on the anionic center. In each step one monomer is added and one molecule of CO2 is released [3-4]. Recent experimental findings strongly suggested the presence of two initiation pathways. Encouraged from these experimentally results, a DFT investigation has been performed with the aim to rationalize the possible occurring activation, propagation and termination mechanisms, figuring out which is the mechanism energetically favored. Chart 1. [1] Zhang Y., Miyake G. M., Falivene L., Caporaso L, Cavallo L., Chen E. Y.-X. , J. Am. Chem. Soc., 135 (47), 2013, pp 17925–17942. [2] Zhang Y., Miyake G. M., John M.G., Falivene L., Caporaso L, Cavallo L., Chen E. Y.-X., Dalton Trans., 41, 2012, pp 9119-9134. [3] Guo L. and Zhang D., J. Am. Chem. Soc, 131 (50), 2009, pp 18072-18074. [4] Guo L., Lahasky S. H., Ghale K.and Zhang D., J. Am. Chem. Soc, 134 (22), 2012, pp 9163-9171.

N-heterocyclic carbenes in the organopolymerization of N-substitued N-carboxy-anhydrides to polypeptoid

249th National Meeting (2015)

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