Poulten Rebecca C, López Isidoro, Llobet Antoni, Mahon Mary F, Whittlesey Michael K
Department of Chemistry, University of Bath , Claverton Down, Bath BA2 7AY, U.K.
Inorg Chem. 2014 Jul 21;53(14):7160-9. doi: 10.1021/ic500213h. Epub 2014 Jun 27.
Activation of O2 by the three-coordinate Ni(I) ring-expanded N-heterocyclic carbene complexes Ni(RE-NHC)(PPh3)Br (RE-NHC = 6-Mes, 1; 7-Mes, 2) produced the structurally characterized dimeric Ni(II) complexes Ni(6-Mes)(Br)(μ-OH)(μ-O-6-Mes')NiBr (3) and Ni(7-Mes)(Br)(μ-OH)(μ-O-7-Mes')NiBr (4) containing oxidized ortho-mesityl groups from one of the carbene ligands. NMR and mass spectrometry provided evidence for further oxidation in solution to afford bis-μ-aryloxy compounds; the 6-Mes derivative was isolated, and its structure was verified. Low-temperature UV-visible spectroscopy showed that the reaction between 1 and O2 was too fast even at ca. -80 °C to yield any observable intermediates and also supported the formation of more than one oxidation product. Addition of O2 to Ni(I) precursors containing a less electron-donating diamidocarbene (6-MesDAC, 7) or less bulky 6- or 7-membered ring diaminocarbene ligands (6- or 7-o-Tol; 8 and 9) proceeded quite differently, affording phosphine and carbene oxidation products (Ni(O═PPh3)2Br2 and (6-MesDAC)═O) and the mononuclear Ni(II) dibromide complexes (Ni(6-o-Tol)(PPh3)Br2 (10) and (Ni(7-o-Tol)(PPh3)Br2 (11)) respectively. Electrochemical measurements on the five Ni(I) precursors show significantly higher redox potentials for 1 and 2, the complexes that undergo oxygen atom transfer from O2.
通过三配位镍（I）环扩展N-杂环卡宾配合物Ni（RE-NHC）（PPh₃）Br（RE-NHC = 6-Mes，1；7-Mes，2）对O₂的活化产生了结构表征的二聚镍（II）配合物Ni（6-Mes）（Br）（μ-OH）（μ-O-6-Mes'）NiBr（3）和Ni（7-Mes）（Br）（μ-OH）（μ-O-7-Mes'）NiBr（4），其中一个卡宾配体的邻位均三甲苯基基团被氧化。核磁共振和质谱提供了在溶液中进一步氧化生成双-μ-芳氧基化合物的证据；分离出了6-Mes衍生物并验证了其结构。低温紫外-可见光谱表明，即使在约-80°C下，1与O₂之间的反应也太快，无法产生任何可观察到的中间体，并且还支持形成不止一种氧化产物。将O₂添加到含有供电子性较弱的二氨基卡宾（6-MesDAC，7）或体积较小的6元或7元环二氨基卡宾配体（6-或7-o-Tol；8和9）的镍（I）前体中，反应过程大不相同，分别得到膦和卡宾氧化产物（Ni（O═PPh₃）₂Br₂和（6-MesDAC）═O）以及单核镍（II）二溴化物配合物（Ni（6-o-Tol）（PPh₃）Br₂（10）和Ni（7-o-Tol）（PPh₃）Br₂（11））。对这五种镍（I）前体的电化学测量表明，对于1和2这两种经历O₂氧原子转移的配合物，其氧化还原电位明显更高。
