Oxygen Activation by Co(II) and a Redox Non-Innocent Ligand: Spectroscopic Characterization of a Radical–Co(II)–Superoxide Complex with Divergent Catalytic Reactivity

Bimetallic (Et4N)2[Co2(L)2], (Et4N)2[1] (where (L)3– = (N­(o-PhNC­(O)iPr)2)3–) reacts with 2 equiv of O2 to form the monometallic species (Et4N)­[Co­(L)­O2], (Et4N)­[3]. A crystallographically characterized analog (Et4N)2[Co­(L)­CN], (Et4N)2[2], gives insight into the structure of [3]1–. Magnetic measurements indicate [2]2– to be an unusual high-spin CoII-cyano species (S = 3/2), while IR, EXAFS, and EPR spectroscopies indicate [3]1– to be an end-on superoxide complex with an S = 1/2 ground state. By X-ray spectroscopy and calculations, [3]1– features a high-spin CoII center; the net S = 1/2 spin state arises after the Co electrons couple to both the O2•– and the aminyl radical on redox non-innocent (L•)2–. Dianion [1]2– shows both nucleophilic and electrophilic catalytic reactivity upon activation of O2 due to the presence of both a high-energy, filled O2– π* orbital and an empty low-lying O2– π* orbital in [3]1–.双金属配合物二(四乙基铵) (Et4N)₂[Co₂(L)₂]，即(Et4N)₂[1]（其中(L)³⁻ = (N(o-PhNC(O)iPr)₂)³⁻）与2当量的O₂反应，生成单金属物种(Et4N)·[Co(L)O₂]，即(Et4N)·[3]。经晶体学表征的类似物二(四乙基铵) (Et4N)₂[Co(L)CN]，即(Et4N)₂[2]，可为[3]¹⁻的结构提供关键解析依据。磁学测量结果表明，[2]²⁻是一种罕见的高自旋Co²⁺-氰基物种（自旋量子数S=3/2）；而红外光谱、扩展X射线吸收精细结构（EXAFS）与电子顺磁共振（EPR）光谱表征显示，[3]¹⁻为端基超氧配合物，基态自旋为S=1/2。通过X射线光谱学与理论计算可知，[3]¹⁻具有一个高自旋Co²⁺中心；其净自旋S=1/2的形成，源于Co的电子同时与超氧自由基O₂•⁻以及氧化还原非 innocent配体(L•)²⁻上的氨基自由基发生自旋耦合。二阴离子[1]²⁻在O₂活化过程中同时展现出亲核与亲电催化活性，这一特性源于[3]¹⁻中同时存在高能占据的O₂⁻ π*轨道与低能未占据的O₂⁻ π*轨道。