Picolinamide as a Directing Group on Metal Sandwich Compounds: sp<sup>2</sup> C–H Bond Activation and sp<sup>3</sup> C–H Bond Oxidation
作者:Susanta Hazra、Mayukh Deb、Jatinder Singh、Anil J. Elias
DOI:10.1021/acs.organomet.7b00143
日期:2017.5.8
Palladium catalyzed bis-arylations, -alkylations, and -allyl-ations on the Cp ring of iron and cobalt sandwich compounds have been achieved using the bidentate picolinamide directing group. This directing group along with catalytic Pd(OAc)(2) was found to be highly efficient for C-H functionalization, giving up to 87% yields. The palladacyclic intermediate for the C-H activation of the Cp ring has been isolated and structurally characterized for the cobalt sandwich compound [eta(5)-C5H5]Co(eta(4)-C4Ph4). Attempted C-H annulation reactions using picolinamide-derived sandwich compounds did not yield the expected annulated products and instead oxidized the Cp- and picolinamide-bound CH2 unit to aldehydes. Detailed studies on this novel and unprecedented oxidation indicated that this happens only with the assistance of the picolinamide directing group. We have also shown that the sp(2) C-H functionalization and the sp(3) C-H oxidation can be effectively carried out as a one-pot reaction.