871710-97-3Relevant academic research and scientific papers
An anion-dependent switch in selectivity results from a change of C-H activation mechanism in the reaction of an imidazolium salt with IrH 5(PPh3)2
Appelhans, Leah N.,Zuccaccia, Daniele,Kovacevic, Anes,Chianese, Anthony R.,Miecznikowski, John R.,Macchioni, Alceo,Clot, Eric,Eisenstein, Odile,Crabtree, Robert H.
, p. 16299 - 16311 (2005)
Changing the counteranion along the series Br, Bp4, PF 6, SbF6 in their ion-paired 2-pyridylmethyl imidazolium salts causes the kinetic reaction products with IrH5(PPh 3)2 to switch from chelating N-heterocyclic carbenes (NHCs) having normal C2 (N path) to abnormal C5 binding (AN path). Computational work (DFT) suggests that the AN path involves C-H oxidative addition to Ir III to give IrV with little anion dependence. The N path, in contrast, goes by heterolytic C-H activation with proton transfer to the adjacent hydride. The proton that is transferred is accompanied by the counteranion in an anion-coupled proton transfer, leading to an anion dependence of the N path, and therefore of the N/AN selectivity. The N path goes via IrIII, not IrV, because the normal NHC is a much less strong donor ligand than the abnormal NHC. PGSE NMR experiments support the formation of ion-pair in both the reactants and the products. 19F,1H-HOESY NMR experiments indicate an ion-pair structure for the products that is consistent with the computational prediction (ONIOM(B3PW91/UFF)).
