Solid-state structure, solution-state behaviour and catalytic activity of electronically divergent C,N-chelating palladium–N-heterocyclic carbene complexes

Abstract

A family of electronically diverse pyridyl-and picolyl-substituted imidazolium salts have been prepared and coordinated to palladium in a single step, to deliver a variety of palladium(II)-N-heterocyclic carbene (NHC) complexes. Neutral Pd(NHC)X2, cationic [Pd(NHC)2X]X and dicationic [Pd(NHC)2]X2-type complexes have been isolated and fully characterised, with singlecrystal X-ray analysis revealing a variety of coordination environments around the palladium centres. The pre-formed complexes have been employed in a model Suzuki-Miyaura cross-coupling reaction to yield a sterically congested tetraortho-substituted biaryl product, showcasing turnover numbers comparable to Pd-PEPPSI-IPr catalyst.

Cross coupling reactions catalyzed by (NHC)Pd(II) complexes

“…Pyridyl-and picolyl-substituted imidazol-2-ylidene palladium(II) complexes, neutral Pd(NHC)X 2 (C40), cationic [Pd(NHC) 2 X]X (C41 and C42), and dicationic [Pd(NHC) 2 ]X 2 (C43) have been employed in a model Suzuki cross-coupling reaction to yield a sterically congested tetra-orthosubstituted biaryl product, with comparable activity to Pd-PEPPSI-IPr catalyst (Table 4, entries 43-46). 73…”

Synthesis and structures of 4,5-dimethyl-1,3-bis(pyridin-2-ylmethyl)-1H-imidazolium chloride and 1,1′-bis(pyridin-2-ylmethyl)-2,2′-bis(4,5-dimethylimidazole)

“…Numerous complexes of different transition metals with tridentate N-hetero cyclic ligands of this type were described in the literature. [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] Here we report an attempt to synthesize a new N-hetero cyclic carbene pincer ligand containing picolyl sub stituents.…”