title: Modulating reactivity in iridium bis(N-heterocyclic carbene) complexes: influence of ring size on E-H bond activation chemistry.
abstract: The changes in the steric and electronic properties of N-heterocyclic carbenes (NHCs) as a function of ring size have a profound effect on the reactivity of their late transition metal complexes. Comparison of closely related complexes featuring either a saturated 5- or 6-membered NHC, reveals that the larger ring is associated with an increased propensity towards intramolecular C-H activation, but with markedly lower reactivity towards external substrates. Thus, systems of the type [IrL2(H)2](+) give rise to contrasting chemical behaviour, primarily reflecting the differing possibilities for secondary stabilization of the metal centre by the N-bound aryl substituents: highly labile [Ir(5-Mes)2(H)2](+) can only be studied by trapping experiments, while [Ir(6-Mes)2(H)2](+) is air and moisture stable, and unreactive towards many external reagents. With appropriate substrates, this heightened reactivity can be exploited, and in situ generated [Ir(5-Mes)2(H)2](+) is capable of intermolecular B-H and N-H activation chemistry. In the case of H3B·NMe2H, this affords a rare opportunity to study amine/aminoborane coordination via single crystal neutron diffraction methods.
authors.affiliation: Inorganic Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford, OX1 3QR, UK. SimonAldridge@chem.ox.ac.uk.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Phillips
authors.forename: Christina Y
authors.initials: CY
authors.lastname: Tang
authors.forename: Rémi
authors.initials: R
authors.lastname: Tirfoin
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Kelly
authors.forename: Amber L
authors.initials: AL
authors.lastname: Thompson
authors.forename: Matthias J
authors.initials: MJ
authors.lastname: Gutmann
authors.forename: Simon
authors.initials: S
authors.lastname: Aldridge