Alkyl dehydrogenation in iridium tri-cyclopentyl phosphines

The iridium cyclooctadiene complex incorporating a tricyclopentyl phosphine ligand (PCyp3), Ir(η2:η2-C8H12)(PCyp3)Cl, has been prepared. Removal of the chloride from this complex using Na[BArF4][ArF=C6H3(CF3)2] in CH2Cl2/arene solvent results in dehydrogenation (C–H activation followed by β-H transfer) of one of the alkyl phosphine rings and formation of the complexes [Ir(η6-C6H5X){PCyp2(η2-C5H7)}][BArF4] (X = H, F) which contain a hybrid phosphine–alkene ligand. These complexes are formed alongside another product (5–20% yield) that has been identified as [Ir(η2:η2-C8H12){PCyp2(η2-C5H7)}][BArF4], which can be prepared in high yield by an alternative, and slightly modified, route. This complex is with a minor isomer that has been tentatively identified as [Ir(η2:η3-C8H11)(H){PCyp2(η2-C5H7)}][BArF4], which results from allylic C–H activation of cyclooctadiene. Addition of H2 to [Ir(η2:η2-C8H12){PCyp2(η2-C5H7)}][BArF4] and its isomer in arene solvent (C6H5X, X = F, H) forms the dihydrido η6-arene Ir(III) complexes [Ir(H)2(η6-C6H5X)(PCyp3)][BArF4]. In contrast, hydrogenation in CH2Cl2 alone results in the formation of Ir(H)2(PCyp3){η6-(C6H3(CF3)2)BArF3} in which the [BArF4]- anion is now acting as a ligand through one of its aryl rings. The fluorobenzene complex [Ir(H)2(η6-C6H5F)(PCyp3)][BArF4] can be cleanly converted to [Ir(η6-C6H5F){PCyp2(η2-C5H7)}][BArF4] by addition of the hydrogen acceptor tert-butylethene (tbe).

Graphical abstractDehydrogenation of cyclopentylphosphine occurs in Ir-complexes, to afford Ir(I) system ligated with hybrid phosphines.Figure optionsDownload full-size imageDownload as PowerPoint slide