Alkene and alkyne insertion into the Ir–H bond: Synthesis of new mono- and dinuclear alkyl and alkenyl iridium–pybox complexes

The treatment of the complex [Ir(η2-C2H4)2(L)][PF6] (L = κ3-N,N,N-(S,S)-iPr-pybox) with acetic acid (1:1 molar ratio) at −10 °C affords the complex [Ir(C2H5)(κ2-O,O-O2CCH3)(L)][PF6] (1). The dinuclear iridium(III) complex [Ir2(μ-Cl)2(C2H5)2(L)2][PF6]2 (2) is stereoselectively obtained by spontaneous intramolecular insertion of ethylene into the iridium-hydride bond of the mononuclear complex [IrClH(η2-C2H4)(L)][PF6]. The single bridging chloride dinuclear derivative [Ir2(μ-Cl)(C2H5)2Cl2(L)2][PF6] (3) is prepared by reaction of 2 with one equivalent of NaCl. The intramolecular insertion reaction of methyl and ethyl propiolate into the Ir–H bond of the complex [IrClH(MeCN)(L)][PF6] gives stereoselectively the dinuclear complexes [Ir2(μ-Cl)2(HCCHCO2R)2(L)2][PF6]2 (R = Me (4), Et (5)). The reaction of the complexes 4, 5 with one equivalent of NaCl or with an excess of sodium acetate yields the dinuclear [Ir2(μ-Cl)(HCCHCO2R)2Cl2(L)2][PF6] (R = Me (6), Et (7)) or the mononuclear [IrCl(HCCHCO2Et)(κ1-O-O2CMe)(L)] (8) complexes, respectively. The structure of the dinuclear complex 3 · CH2Cl2 has been determined by an X-ray monocrystal study.

The complex [IrClH(η2-C2H4){κ3-N,N,N-(S,S)-iPr-pybox}][PF6] evolves spontaneously to give the dinuclear complex [Ir2(μ-Cl)2(C2H5)2{κ3-N,N,N-(S,S)-iPr-pybox}2][PF6]2 which in turn reacts with NaCl to afford the complex [Ir2(μ-Cl)(C2H5)2Cl2{κ3-N,N,N-(S,S)-iPr-pybox}2][PF6]. The X-ray crystal structure of the latter is reported. Novel mono and dinuclear alkyl and alkenyl iridium–pybox complexes are stereoselectively prepared through the insertion reaction of olefins and activated alkynes into the Ir–H bond of the mononuclear hydride precursors.Figure optionsDownload as PowerPoint slide