Photochemical Carbene Transfer Reactions of Aryl/Aryl Diazoalkanes—Experiment and Theory. Issue 24 (5th May 2021)

• Record Type: Journal Article
• Authors: Jana, Sripati; Pei, Chao; Empel, Claire; Koenigs, Rene M.
• Is Part Of: Angewandte Chemie international edition. Volume 60:Issue 24(2021)
• Page Start: 13271
• Page End: 13279
• Publication Date: 2021-05-05
• Subjects: carbene -- DFT calculations -- photochemistry -- singlet -- triplet; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.202100299
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: Controlling the reactivity of carbene intermediates is a key parameter in the development of selective carbene transfer reactions and is usually achieved by metal complexes via singlet metal‐carbene intermediates. In this combined experimental and computational studies, we show that the reactivity of free diaryl carbenes can be controlled by the electronic properties of the substituents without the need of external additives. The introduction of electron‐donating and ‐withdrawing groups results in a significant perturbation of singlet triplet energy splitting of the diaryl carbene intermediate and of activation energies of consecutive carbene transfer reactions. This strategy now overcomes a long‐standing paradigm in the reactivity of diaryl carbenes and allows the realization of highly chemoselective carbene transfer reactions with alkynes. We could show that free diaryl carbenes can be readily accessed via photolysis of the corresponding diazo compounds and that these carbenes can undergo highly chemoselective cyclopropenation, cascade, or C−H functionalization reactions. Experimental and theoretical mechanistic analyses confirm the participation of different carbene spin states and rationalize for the observed reactivity. Abstract : Aryl/aryl diazoalkanes undergo distinct, chemoselective reactions with alkynes upon blue light photolysis. This report showcases how electronic properties and spin state influence the reaction outcome of metal‐free carbene transfer reactions by experimentation and theory.