Prof. AnnMarie O’Donoghue
Department of Chemistry
11:00 - 12:00,
Weds 29 March, 2023
Prof. O'Donoghue joins as an invited guest.
This is a departmental lecture for all students and staff. Please come along. Tea, coffee and refreshments will be provided from 10:45.
From Stable N-Heterocyclic Carbenes to Organic Radicals: Synthesis, Mechanism and Biocatalysis
Our research is focused on the synthesis, mechanistic evaluation and applications of stable carbenes as organo- and biocatalysts. As part of this work, we recently reported the unusual rearrangement of a C(3)-anilino-1,2,4-triazolium ion, commonly known as Nitron, to new C(3)-amido and anilino Blatter-type organic radicals.1 These stable benzotriazinyl organic radicals have seen successful application as switchable signal enhancement agents for NMR spectroscopy.2 Prior to this work, only the synthesis of the parent Nitron was reported, which we used to access radical derivatives with simple alkyl substituents.1 Nitron exists in both zwitterionic and N-heterocyclic carbene (NHC) tautomeric forms. In the first part of the talk we report a new improved synthetic route to Nitron, which permits access to a broader range of C(3)-anilino-1,2,4-triazolium derivatives encompassing both strong electron donating and withdrawing substituents. The range of Nitron derivatives were evaluated in the Nitron to Blatter radical rearrangement, with radical formation proving to be dependent on the zwitterion to carbene equilibrium position (KT). Determination of NH and C(3)-H pKas enabled access to KT values for zwitterion-NHC tautomerization (KT). We also report the evaluation of the series of Nitron derivatives as NHC organocatalysts of the archetypal benzoin condensation. In the second part of the talk, we will report our recent results on the synthesis, mechanistic evaluation and applications of 1,2,4-triazolium mimics of Vitamin B1 (thiamine) as non-native co-factors for biocatalysis.
1. J. A. Grant, Z. Lu, D. E. Tucker, B. M. Hockin, D. S. Yufit, M. A. Fox, R. Kataky, V. Chechik and A. C. O'Donoghue, Nat. Commun., 2017, 8, 6-11.
2. F. Saenz, M. Tamski, J. Milani, C. Roussel, H. Frauenrath and J.-P. Ansermet, Chem. Commun., 2022, 58, 689-692.