title: Metal-Diazo Radicals of α-Carbonyl Diazomethanes.
abstract: Metal-diazo radicals of α-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 α-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 α-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 α-carbonyl diazomethanes to metal-carbene radicals was confirmed to be a two-step process via metal-diazo radicals.
authors.affiliation: Department of Polymer Science, College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, China.
authors.forename: Feifei
authors.initials: F
authors.lastname: Li
authors.affiliation: Department of Polymer Science, College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, China.
authors.forename: Longqiang
authors.initials: L
authors.lastname: Xiao
authors.affiliation: Department of Polymer Science, College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, China.
authors.forename: Lijian
authors.initials: L
authors.lastname: Liu