14561-12-7Relevant academic research and scientific papers
Cyclometalation of aryl-substituted phosphinines through C-H-bond activation: A mechanistic investigation
Broeckx, Leen E. E.,Güven, Sabriye,Heutz, Frank J. L.,Lutz, Martin,Vogt, Dieter,Müller, Christian
supporting information, p. 13087 - 13098 (2013/10/01)
A series of 2,4,6-triarylphosphinines were prepared and investigated in the base-assisted cyclometalation reaction using [Cp*IrCl2] 2 (Cp=1,2,3,4,5-pentamethylcyclopentadienyl) as the metal precursor. Insight in the mechanism of the C-H bond activation of phosphinines as well as in the regioselectivity of the reaction was obtained by time-dependent 31P{1H}NMR spectroscopy. At room temperature, 2,4,6-triarylphosphinines instantaneously open the Ir-dimer and coordinate in an η1-fashion to the metal center. Upon heating, a dissociation step towards free ligand and an Ir-acetate species is observed and proven to be a first-order reaction with an activation energy of ΔE A=56.6kJ mol-1 found for 2,4,6-triphenylphosphinine. Electron-donating substituents on the ortho-phenyl groups of the phosphorus heterocycle facilitate the subsequent cyclometalation reaction, indicating an electrophilic C-H activation mechanism. The cyclometalation reaction turned out to be very sensitive to steric effects as even small substituents can have a large effect on the regioselectivity of the reaction. The cyclometalated products were characterized by means of NMR spectroscopy and in several cases by single-crystal X-ray diffraction. Based on the observed trends during the mechanistic investigation, a concerted base-assisted metalation-deprotonation (CMD) mechanism, which is electrophilic in nature, is proposed. Finely tuned: A series of substituted 2,4,6-triarylphosphinines were prepared and investigated in a base-assisted cyclometalation reaction using [Cp*IrCl 2]2 (Cp=1,2,3,4,5-pentamethylcyclopentadienyl) as the metal precursor M (see figure). Insight into the mechanism of the C-H bond activation of phosphinines as well as into the regioselectivity of the reaction was obtained by using time-dependent 31P{1H}NMR spectroscopy and single-crystal X-ray diffraction. Copyright
