title: C(sp3)-H activation without a directing group: regioselective synthesis of N-ylide or N-heterocyclic carbene complexes controlled by the choice of metal and ligand.
abstract: N-Ylide complexes of Ir have been generated by C(sp(3))-H activation of α-pyridinium or α-imidazolium esters in reactions with [Cp*IrCl2]2 and NaOAc. These reactions are rare examples of C(sp(3))-H activation without a covalent directing group, which-even more unusually-occur α to a carbonyl group. For the reaction of the α-imidazolium ester [3H]Cl, the site selectivity of C-H activation could be controlled by the choice of metal and ligand: with [Cp*IrCl2]2 and NaOAc, C(sp(3))-H activation gave the N-ylide complex 4; in contrast, with Ag2O followed by [Cp*IrCl2]2, C(sp(2))-H activation gave the N-heterocyclic carbene complex 5. DFT calculations revealed that the N-ylide complex 4 was the kinetic product of an ambiphilic C-H activation. Examination of the computed transition state for the reaction to give 4 indicated that unlike in related reactions, the acetate ligand appears to play the dominant role in C-H bond cleavage.
authors.affiliation: School of Science and Technology, Nottingham Trent University, Nottingham, NG11 8NS (UK). warren.cross@ntu.ac.uk.
authors.forename: Warren B
authors.initials: WB
authors.lastname: Cross
authors.forename: Sunnah
authors.initials: S
authors.lastname: Razak
authors.forename: Kuldip
authors.initials: K
authors.lastname: Singh
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Warner
keywords: CH activation; cooperative effects; iridium; synthetic methods; ylides