The synthesis of new ‘bulky yet flexile’ N-heterocyclic carbenes (NHC’s) are reported. The NHC’s salts described in the study include IPrMe●HCl, and 6-, 7-, and 8- membered IPr, IPaul and IPr* NHC’s. All NHC’s were synthesized through a two step process starting from the appropriate IPr, IPaul and IPr* aniline. Amidinium salt, IPrMe●HCl, was synthesized through the creation of an intermediate diimine before preforming cyclization. Various methods were attempted to synthesizes the the 6-, 7- and 8- membered IPr, IPaul and IPr* NHC’s. These methods included intermediates of either a formamide or a diamine. Products from each synthesis were determined through the use of NMR and LCMS data. The study was unable to determine if IPrMe●HCl was correctly synthesized due to contradictory data from the NMR and the LCMS. Due to steric strain, 6-, 7- and 8- membered NHC’s proved harder to synthesis than expected. The study was only able to produce the NHC’s with the least amount of steric strain, 6- and 7- IPr NHC. The remaining NHC’s (8-IPr, 6-, 7- and 8-IPua and 6-, 7-, and 8-IPr*) were all synthesized; however, NMR and LCMS data confirmed that cyclization to close the NHC ring did not occur leaving the products as the intermediate forms of a formamide or a diamine. The best method for synthesizing NHC’s with heavy steric strain is through synthesizing a diamine before preforming cyclization to produce the N-heterocyclic carbene salt.

Synthesis of new N-heterocyclic carbenes

2019 Spring National Meeting

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