Metal-Coordinated Ligand Radicals. Molecular and Electronic Structure, and Reactivity

Abstract : Generation of ligand radicals can lead to interesting ligand-centered reactivity, with the mechanism of galactose oxidase serving as an inspiration for synthetic inorganic chemists. The design of metal complexes to promote or catalyze multielectron reactions usually relies on one or more transition-metal ions capable of two-electron changes in a formal oxidation state. An alternative strategy to multielectron chemistry employs redox-active ligands as reservoirs of electrons to supply reducing or oxidizing equivalents for bond-making and bond-breaking reactions at coordinatively unsaturated metal complexes. The determination of molecular structure, investigating the magnetic, spectral and redox properties, and correct assignment of electronic structure of metal complexes of 2-anilino-4,6-di-tert-butylphenol-derived ligands in their deprotonated forms have drawn the attention of inorganic chemists due to redox-active nature of such ligands [1]. From the standpoint of modeling galactose oxidase activity [2,3], we have directed our attention to designing new ligands of 2-anilino-4,6-di-tert-butylphenol-appended with azo, benzylthioether, ethylthioether, and thioalkylpyridines functionality [4-6], to investigate their coordination behavior towards transition metal ions, and to investigate radical coupling-driven reactions. In this presentation, an account of detailed molecular (X-ray), spectroscopic and magnetic, and redox properties of a number of ligand radical-coordinated metal complexes involving a group of redox-active ligands to correctly assign the spin-state of the metal and redox-level of the coordinated ligands will be discussed. The electronic structure of the complexes is rationalized by the Density Functional Theory (DFT) calculations. Radical-driven reactivity aspects (C–N, N–N, and –O–C–O– bond formation) will be discussed.

References : [1] Mukherjee, A.; Mukherjee, R. N. Indian J. Chem. 2011, 50A, 484–490 (Special Issue  on Bioinorganic Chemistry; R. N.Mukherjee acted as one of the editors of this issue). [2] Mukherjee, A.; Lloret, F.; Mukherjee, R. N. Inorg. Chem. 2008, 47, 4471–4480. [3] Mukherjee, A.; Lloret, F.; Mukherjee, R. N. Eur. J. Inorg. Chem. 2010, 1032–1042. [4] Rajput, A.; Sharma, A. K.; Barman, S. K.; Koley, D.; Steinert, M.; Mukherjee, R. N. Inorg. Chem. 2014, 53, 36–48. [5] Ali, A.; Barman, S. K.; Mukherjee, R. N. Inorg. Chem. 2015, 54, 5182–5194.  [6] Ali, A.; Dhar, D.; Barman, S. K.; Lloret F.; Mukherjee, R. N. Inorg. Chem. 2016, 55, 5759–5771.

About the speaker : Prof. Mukherjee is a Chemistry Professor at the Department of Chemistry, IIT Kanpur. He is a Fellow of several national and international academies including Indian Academy of Sciences, Bangalore (1999), Indian National Science Academy, New Delhi (2008), J. C. Bose National Fellow, Department of Science & Technology, Government of India (2008–2018), Royal Society of Chemistry, UK (2003), Vice President, Chemical Research Society of India, Bangalore (2008–2013). He is a recipient of several national and international awards such as Bronze/Silver Medal, Chemical Research Society of India (CRSI), Bangalore (2001/2011), Priyadaranjan Ray Memorial Award, Indian Chemical Society, Kolkata (2010), A. V. Rama Rao Foundation Prize Lecture in Chemistry, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore (2005), RSC Journals Grants for International Authors, UK (2001). He is also member of several scientific bodies such as Planning Committee Member, International Conference on Coordination Chemistry (2004 –), Asian Coordination Chemistry Conference (2007–), Advisory Board-Dalton Transactions (RSC) (2008–), Editorial Board of Inorganica Chimica Acta (Elsevier) (2011–2013), Editorial Advisory Board of Inorganic Chemistry (ACS) (2017–2020). He is also a visiting professor at the Departament de Química, Universitat de Girona, Spain (2004) and Department of Chemistry, Stanford University, USA (2005 – 2006). His research activities include systematic development of synthetic coordination chemistry of transition metal ions with designed organic ligands to address diversified research problems. Emphasis is directed to bioinorganic modeling, metal-coordinated ligand radicals, coordination polymers, multi-metal clusters etc.