Title of Talk

Electrophilic Activation or Oxidative Addition? A Curious Case of C-H Cleavage

 

Abstract

A clear understanding of C−H activation processes is central to improve the existing strategies for organic transformations. Depending on the electronic nature of the metal and the set of ligands in the active metal species, C−H activation mechanisms are classified into different categories. Oxidative addition (OA) is favoured for electron-rich low-valent transition metals, whereas electrophilic activation (EA) is likely to occur for electron-deficient late transition metals. Detailed experimental work supported by DFT calculations allowed us to delineate the exact mechanism.^1-3 For example, C-H activations of hetero-aryl naphthyridines on a solvated dipalladium(I) complex are shown to proceed via oxidative addition followed by electrophilic activation.⁴ Though it is possible to ascribe C−H activation mechanism in some cases, the distinction is not always straightforward. We encountered an intriguing reactivity of heteroaryl substituted naphthyridines with metal-metal singly bonded [Ru^I−Ru^I] unit. N-methylpyrrolyl naphthyridine undergoes C−H bond cleavage via an electrophilic mechanism that involves C(pπ)−H → σ* [Ru−Ru] interaction.^5,6 On the contrary, imidazolyl naphthyridine results in oxidation addition of C(sp²)−H σ bond on the same [Ru−Ru] core. The rational for the differential behaviour of pyrrolyl and imidazolyl C−H on a [Ru^I−Ru^I] platform will be discussed. The oxidative route to imidazolyl C−H activation affords a unique synthetic method to access metal-N-heterocylic carbene complexes from dimetal precursors.^7,8

 

 

References:

1. Daw, P.; Ghatak, T.; Doucet, H.; Bera, J. K. Organometallics 2013, 32, 4306.

2. Rahaman, S. M. W.; Dinda, S.; Sinha, A.; Bera, J. K. Organometallics 2013, 32, 192.

3. Rahaman, S. M. W.; Dinda, S.; Ghatak, T.; Bera, J. K. Organometallics 2012, 31, 5533.

4. Sarkar, M.; Doucet, H.; Bera, J. K. Chem. Commun. 2013, 49, 9764.

5. Sinha, A.; Majumdar, M.; Sarkar, M.; Ghatak, T.; Bera, J. K. Organometallics 2013, 32, 340.

6. Patra, S. K.; Bera, J. K. Organometallics 2006, 25, 6054.

7. Sinha, A.; Daw, P.; Rahaman, S. M. W.; Saha, B.; Bera, J. K. J. Organomet. Chem. 2011, 696, 1248.

8. Sinha, A.; Sarbajna, A.; Dinda, S.; Bera, J. K. J. Chem. Sci. 2011, 123, 799.

Jitendra K. Bera, Professor

 

Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, INDIA

e-mail: jbera@iitk.ac.in

 

Profile. Bera received his M. Sc. from the University of Kalyani in 1993 and his Ph. D. from the Indian Institute of Science in 1999. After a couple of postdoctoral stints at Purdue University and at Texas A&M University, he joined the faculty at IIT Kanpur in 2003 where he is presently a Professor. He is the recipient of the Ramanna fellowship and the Swarnajayanti fellowship from DST, India, and has received the CRSI bronze medal for the year 2011. Bera's research interests span synthetic, structural and mechanistic organometallic chemistry. Recent efforts are directed toward bifunctional activation of small and abundant molecules and their catalytic transformations to useful and value-added chemicals.

 

 

Selected Publications

1. Chem. Commun. 2013, 49, 9764.

2. Organometallics 2013, 32, 340.

3. Inorg. Chem. 2013, 52, 1432.

4. Organometallics 2013, 32, 192.

5. Organometallics 2013, 32, 4306.