Synthesis and NMR study of N-heterocyclic carbenes (NHC) precursors derived from Tröger’s Base

Abstract

Since the discovery of olefin metathesis reactions, various catalysts have been developed but those based on Ruthenium and N-heterocyclic carbenes (NHC) ligands are particularly more efficient. Herein, we report a synthesis of NHC precursors derived from the Tröger's base and its analogues which can be used in the synthesis of the new kind of metathesis catalysts. The NHC derived from the Tröger's base present a particular chirality that could affect stereoselectivity of catalysis, and the form "V" of these ligands implies that the aromatic substituents point totally outside the coordination sphere of the metal, where would be no steric hindrance unlike what happens with the usual NHC.

Hoveyda–Grubbs catalysts with an N→Ru coordinate bond in a six-membered ring. Synthesis of stable, industrially scalable, highly efficient ruthenium metathesis catalysts and 2-vinylbenzylamine ligands as their precursors

“…Several approaches have been described earlier for the preparation of the “chloroform adduct” ( 9 ) [51–55]. Even though these approaches provide good yields they have some drawbacks such as the use of expensive reagents, difficulties in the purification process, and data analysis.…”