C−H Activation of Inert Arenes using a Photochemically Activated Guanidinato‐Magnesium(I) Compound
Abstract
UV irradiation of solutions of a guanidinate coordinated dimagnesium(I) compound, [{(Priso)Mg}2]3(Priso=[(DipN)2CNPri2]−, Dip=2,6‐diisopropylphenyl), in either benzene, toluene, the three isomers of xylene, or mesitylene, leads to facile activation of an aromatic C−H bond of the solvent in all cases, and formation of aryl/hydride bridged magnesium(II) products, [{(Priso)Mg}2(μ‐H)(μ‐Ar)]4–9. In contrast to similar reactions reported for β‐diketiminate coordinated counterparts of3, these C−H activations proceed with little regioselectivity, though they are considerably faster. Reaction of3with an excess of the pyridine,p‐NC5H4But(pyBut), gave [(Priso)Mg(pyButH)(pyBut)2]10, presumably via reduction of the pyridine to yield a radical intermediate, [(Priso)Mg(pyBut⋅)(pyBut)2]11, which then abstracts a proton from the reaction solvent or a reactant. DFT calculations suggest two possible pathways to the observed arene C−H activations. One of these involves photochemical cleavage of the Mg−Mg bond of3, generating magnesium(I) doublet radicals, (Priso)Mg⋅. These then doubly reduce the arene substrate to give “Birch‐like” products, which subsequently rearrange via C−H activation of the arene. Circumstantial evidence for the photochemical generation of transient magnesium radical species includes the fact that irradiation of a cyclohexane solution of3leads to an intramolecular aliphatic C−H activation process and formation of an alkyl‐bridged magnesium(II) species, [{Mg(μ‐Priso−H)}2]12. Furthermore, irradiation of a 1 : 1 mixture of3and the β‐diketiminato dimagnesium(I) compound, [{(DipNacnac)Mg}2] (DipNacnac=[HC(MeCNDip)2]−), effects a “scrambling” reaction, and the near quantitative formation of an unsymmetrical dimagnesium(I) compound, [(Priso)Mg−Mg(DipNacnac)]13. Finally, the EPR spectrum (77 K) of a glassed solution of UV irradiated3is dominated by a broad featureless signal, indicating the presence of a doublet radical species.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Sep 26, 2022
- Source ID
- 10.1002/chem.202202103
Entities
People
- Asim Maity
- Cameron Jones
- David C Powers
- Gerard P. Van Trieste Iii
- Jeremy C. Mullins
- K Yuvaraj
- Yixiao Jiang
Organizations
- Air Force Office of Scientific Research
- Australian Research Council
- Monash University
- Office of Science
- Robert A. Welch Foundation
- Yusuf Hamied Department of Chemistry