Originated as chemical curiosity, N-heterocyclic carbenes have played an important role as transient
intermediates over the last few decades and very limited information was available about their properties.
The isolation of stable NHC was the key for their detailed characterizations including quantification of their
various chemical/structural properties. Afterwards, they have been successfully applied in various fields
such as homogeneous catalysis, supramolecular chemistry, material science etc. NHC based metal
complexes have opened a new dimension of homogeneous catalysis due to their strong σ-donating/weak π-
accepting nature, ability to stabilize multiple oxidation states of metals, and the formation of non-labile
bonds with most of the metals. Incorporation of NHC donors within the chelating system imparts extra
stability in addition to the strong M-NHC bond. Among all the known NHCs, imidazole based NHC
(ImNHC) is the most studied one whereas another form of NHC where metal is bonded to C4/C5 position
(abnormal ImNHC) have been relatively under developed.1 Further, the triazole based analogue of the
classical ImNHC, 1,2,3-triazole (tzNHC) have gained specific attention due to their unique σ-donor/π-
accepting nature2 and direct access of their diverse family through well-known click reaction. Several
chelated bis(ImNHC) ligands have been reported but due to the symmetrical nature, their steric and
electronic profiles cannot be modified as per the requirements. To overcome this, heteroditopic ligands
where ImNHC coupled to tzNHC have recently been emerged as a better alternative.3 Variety of
homo/heteroditopic chelating bis(NHC) ligands have been extensively studied for various basic organic
transformations but in majority of complexes precious metals (Ir, Rh, Pd, Ru etc.) are used. However, the
metal complexes of these types of ligands with highly abundant and cost-effective base metals (Fe, Co, Ni,
Mn etc.) are rather limited.4 Inspired from the literature findings, our research objectives focus on two new
ligand systems and their metalations with base metals (Fe, Co, Ni, Mn etc.) followed by their applications
in various organic transformations. The first ligand accommodates an abnormal NHC coupled to a tz-N
donor while the second ligand contains an abnormal NHC with a tzNHC donor and importantly, their
electronic/steric profiles can easily be tuned as per the need by changing their backbone and N-substitutions.
Along with this, some preliminary outcomes will also be presented during the seminar.
References:
1. Arnold, P. L.; Pearson, S. Coord. Chem. Rev. 2007, 251, 596-609.
2. Nguyen, T. V. Q.; Yoo, W. J.; Kobayashi, S. Angew. Chem. Int. Ed. 2015, 54, 9209-9212.
3. Sluijter, S. N.; Elsevier, C. J. Organometallics 2014, 33, 6389-6397.
4. Velazquezd, H. D.; Verpoort, F. Chem. Soc. Rev. 2012, 41, 7032-7060.