Perfluoroalkyl Cobaloximes: Preparation Using Hypervalent Iodine Reagents, Molecular Structures, Thermal and Photochemical Reactivity

• Published in: Organometallics Vol. 37; no. 4; pp. 570 - 583
• Main Authors: Liebing, Phil, Oehler, Florian, Wagner, Mona, Tripet, Pascal F, Togni, Antonio
• Format: Journal Article
• Language: English
• Published: American Chemical Society 26.02.2018
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/acs.organomet.7b00892

Treatment of cobaloximes­(II), [Co­(Hdmg)2­(L)2] (Hdmg = dimethylglyoximate, L = neutral ligand), with perfluoroalkyl iodane reagents leads to the formation of perfluoroalkyl cobaloximes­(III), [Co­RF­(Hdmg)2­(L)] (RF = CF3, C2F5, n-C3­F7, CF2­CF2­Ph; L = Py, NH3, Me­NH2, PhNH2, MeOH). The synthetic protocol can be significantly simplified to a one-pot procedure starting from cobalt­(II) acetate–tetrahydrate. The products have been fully characterized by NMR, IR, and UV/vis spectroscopy as well as single-crystal X-ray diffraction, and the thermal and photochemical reactivity has been studied. According to the Co–L distances in the crystal, the trans influence of the RF – ligands can be rated as C2F5 – ≈ n-C3F7 – < CF2CF2Ph– ≈ CF3 – < CH3 –. The thermal decomposition of the complexes is different from that of nonfluorinated analogues, probably including perfluoroalkylation of an Hdmg– ligand as the initial step. In the CF3 complexes, the Co–C bond is very resistant against photolysis, but the ligand L is readily exchanged by MeOH upon exposure to blue light. In the complexes with longer RF chains, the Co–C bond is more readily cleaved, and the product distribution depends strongly on the presence of O2. Thus, the alkane RFH is the main product under exclusion of O2, while a fluorinated methyl ester and HF are formed in a methanol solution exposed to air.