A Convenient Approach for the Synthesis of Multidentate N-Heterocyclic Carbene Ligand Precursors.

Multidentate bis-NHCs ligands with various spacers are expected to combine the advantages of coordination chemistry and catalysis. These offer opportunities to construct various organometallic frameworks involving transition metals and main group elements. Therefore, developing a general procedure for synthesizing a variety of carbene salt precursors using a convenient technique is key in this context. The extended protocol of a solvent-free approach for synthesizing various bridged bis-imidazolium carbene salts, including tris and tetrakis-imidazolium precursors, is reported here. This method can be performed in the laboratory, leading to high yields (80-95 %) and isolated as analytically pure, multigram, bench-stable compounds.