Redox induced oxidative C-C coupling of non-innocent bis(heterocyclo)methanides

• Published in: Dalton transactions : an international journal of inorganic chemistry Vol. 5; no. 45; pp. 16647 - 16659
• Main Authors: Panda, Sanjib, Baliyan, Rupal, Dhara, Suman, Huang, Kuo-Wei, Lahiri, Goutam Kumar
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 23.11.2021
• Subjects: Coupling (molecular); Covalent bonds; Mathematical analysis; Oxygen; Oxygenation; Ruthenium
• ISSN: 1477-9226; 1477-9234; 1477-9234
• DOI: 10.1039/d1dt03310g

Redox driven C-C bond formation has gained recent attention over the traditional sequence of oxidative addition, insertion and reductive elimination reactions. In this regard, the transient radical mediated diverse reactivity profile of bis(heterocyclo)methanes (H-BHM: HL1-HL4) has been demonstrated as a function of varying metal ions and ligand backbones. It highlighted the following events: (a) redox induced homocoupling of deprotonated HL1 and HL4 on coordination to M(OAc) 2 precursors (M = Cu II , Zn II , Pd II , Ag I ), including the effective role of molecular oxygen in the transformation process; (b) steric inhibition of C-C coupling of HL1 or HL4 on inserting the substituent at the bridged methylene centre (Ph in HL2 or CH 3 in HL3); (c) competitive C-C coupling versus oxygenation of free HL1 with varying concentrations of Pd II (OAc) 2 as the ease of oxygenation over dimerisation of the deprotonated HL1 was corroborated by the DFT calculated lower activation barrier and greater thermodynamic stability of the former; and (d) redox non-innocence of BHMs on a coordinatively inert ruthenium platform, which in turn favored the involvement of a radical pathway for the aforestated coupling or oxygenation process. A combined structural, spectroscopic and DFT calculated transition state analysis demonstrated the mechanistic outline for the metal assisted oxidative coupling of BHMs. Redox driven oxidative homocoupling versus oxygenation of bis(heterocyclo)methanides (BHMs) has been shown to be a function of varying BHM backbones and metal precursors.