Mercury(II)- and silver(I)-N-heterocyclic carbene complexes of CNC pincer-type ligands: Synthesis, crystal structures and Hofmann-type elimination studies

A series of Hg(II)- and Ag(I)-NHC complexes of N-alkyl/N-alkyl-aryl substituted CNC pincer-type ligands composed of bis-(benz)imidazolium core were synthesized and characterized using different spectral and analytical techniques. Bis-nitrile functionalized (benz)imidazolium salts (8) undergoes rapid hydrolysis to form 1H-bis-(benz)imidazolium salts, which readily experience the Hofmann-type elimination in presence of basic metal sources. Due to elimination reaction, cationic N-coordinated metal complexes were formed in good yields. Structure of 4a, 4d, 6b·2H2O, 9b and Hg(II)-NHC complex 11a was established by the X-ray diffraction studies. Structural studies reveal the existence of diverse hydrogen bonding patterns that involve the (benz)imidazolium-CH units and the anions. Crystallographic study on 11a reveals linear C–Hg–C arrangement for the complex.

Graphical abstractA series of Hg(II)-carbene complexes of CNC pincer ligands having pyridine core were prepared. 2-Cyanoethyl-substituted pyridine derivative undergoes rapid hydrolysis to form N-protonated azolium salt.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► A series of pyridine-linked (benz)imidazolium salts were prepared. ► Hg(II)- and Ag(I)-NHC complexes of CNC pincer ligands were synthesized. ► 3H-(benz)imidazolium salts were prepared upon hydrolysis of dicyanoethyl derivative. ► These salts experience Hofmann-type elimination when treated with basic metal salts.