Metal-Diazo Radicals of ?-Carbonyl Diazomethanes.

ABSTRACT: Metal-diazo radicals of ?-carbonyl diazomethanes are new members of the radical family and are precursors to metal-carbene radicals. Herein, using electron paramagnetic resonance spectroscopy with spin-trapping, we detect diazo radicals of ?-carbonyl diazomethanes, induced by [Rh(I)Cl(cod)]2, [Co(II)(por)] and PdCl2, at room temperature. The unique quintet signal of the Rh-diazo radical was observed in measurements of ?-carbonyl diazomethane adducts of [Rh(I)Cl(cod)]2 in the presence of 5,5-dimethyl-pyrroline-1-N-oxide (DMPO). DFT calculations indicated that 97.2% of spin density is localized on the diazo moiety. Co- and Pd-diazo radicals are EPR silent but were captured by DMPO to form spin adducts of DMPO-N? (triplet-of-sextets signal). The spin-trapping also provides a powerful tool for detection of metal-carbene radicals, as evidenced by the DMPO-trapped carbene radicals (DMPO-C?, sextet signal) and 2-methyl-2-nitrosopropane-carbene adducts (MNP-C?, doublet-of-triplets signal). The transformation of ?-carbonyl diazomethanes to metal-carbene radicals was confirmed to be a two-step process via metal-diazo radicals.

SUBMITTER: Li F 

PROVIDER: S-EPMC4785408 | biostudies-literature | 2016 Mar

REPOSITORIES: biostudies-literature