Non-chelating polydentate N-heterocyclic carbenes through assembly approaches

GRAPHICAL ABSTRACT

ABSTRACT

Bridging-type polydentate N-heterocyclic carbene (NHC) ligands are valuable building blocks for organometallic supramolecules. In order to quickly expand the ligand library of poly-NHC, we have assembled several bi-functional carbene precursors with spiroborate, phthalimide and metal-carboxylate to yield poly-NHC ligands with various denticities and geometries. Condensation of 4,5-dihyxdroxy-N,N′-diaryl-benzimidazolium and arylboronic acids leads to a spiroborate-linked bis-benzimidazolium salt, which can be further deprotonated to give a linear anionic bis-NHC. The second approach utilizes the dehydrative condensation of phthalic anhydride functionalized benzimidazole with poly-anilines to afford a series of poly-benzimidazole compounds, which can be converted into the corresponding poly-nuclear metal-NHC complexes after alkylation and metalation. The introduction of a benzoate group to bi-functional carbene precursor facilitates the assembly of poly-benzimidazolium salts with metal salts leading to MCl₂ (M=Zn, Co)-linked C_2h symmetric bis-benzimidazoliums and a penta-Zn cluster-linked tetra-benzimidazolium.

KEYWORDS:

• N-Heterocyclic carbine
• multi-dentate ligands
• non-chelating

Acknowledgment

We would like to thank Dr. G.-H. Lee, Y.-H. Liu, and Prof. S.-M. Peng for structural determinations.

Funding

We would like to thank the Ministry of Science and Technology of Taiwan for funding (MOST 103-2113-M-002-005 and MOST 104-2811-M-002-130).