Hill Andrew G, Castillo Mariah C, Bacsa John, Otte Kaitlyn S, Soper Jake D
School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, United States.
X-ray Crystallography Center, Department of Chemistry, Emory University, 1515 Dickey Drive, Atlanta, Georgia 30322, United States.
J Am Chem Soc. 2025 Apr 23;147(16):13356-13369. doi: 10.1021/jacs.4c18305. Epub 2025 Apr 8.
A five-coordinate chlorovanadium species supported by two redox-active -phenyl aminophenol ligands was prepared. Experimental and computational data support formulation of this complex as [(ap)(isq)VCl], containing one dianionic [ap] amidophenolate and one monoanionic [isq] iminosemiquinonate radical. Exposure of [(ap)(isq)VCl] to O readily cleaves the O═O bond to generate [(isq)(ibq)V(O)Cl], containing an [ibq] iminobenzoquinone, so the 2e oxidation is entirely ligand centered. [(isq)(ibq)V(O)Cl] is reduced by net H abstraction from 9,10-dihydroanthracene, or in reactions with main-group nucleophiles, such as PPh and MeS, which form a new bond to oxygen and regenerate [(ap)(isq)VCl]. Accordingly, the dioxygenase-type O activation and O-atom transfer cycling are a direct consequence of ligand redox noninnocence and covalency in the vanadium─aminophenol bonding. The reactions with O-atom donor and acceptor substrates establish a V≡O BDE of 73 ± 14 kcal mol in [(isq)(ibq)V(O)Cl]. Reported V≡O BDEs in redox-innocent vanadyl complexes typically fall in the range of 120-170 kcal mol. Unlike later 3d metals, where M═O species are typically high energy and activated by, for instance, occupancy of M-O π* antibonding MOs, the exceptionally weak V≡O bond in [(isq)(ibq)V-(O)Cl] reflects stabilization of the reduced product. Thus, this research highlights an alternative pathway to generating strong oxidants that are not strong outer-sphere electron acceptors, with implications for the design of early metal catalysts for aerobic oxidations of weak O-atom acceptors or strong X-H bonds.
制备了一种由两个具有氧化还原活性的对苯基氨基酚配体支撑的五配位氯钒物种。实验和计算数据支持将该配合物表述为[(ap)(isq)VCl]，其包含一个二价阴离子的[ap]酰胺酚盐和一个一价阴离子的[isq]亚氨基半醌自由基。[(ap)(isq)VCl]与O接触会很容易地切断O═O键，生成[(isq)(ibq)V(O)Cl]，其中包含一个[ibq]亚氨基苯醌，因此2e氧化完全以配体为中心。[(isq)(ibq)V(O)Cl]通过从9,10 - 二氢蒽净提取H或在与主族亲核试剂（如PPh和MeS）的反应中被还原，这些亲核试剂与氧形成新键并再生[(ap)(isq)VCl]。因此，双加氧酶型O活化和O原子转移循环是钒 - 氨基酚键合中配体氧化还原非无辜性和共价性的直接结果。与O原子供体和受体底物的反应确定了[(isq)(ibq)V(O)Cl]中V≡O的键解离能为73±14 kcal/mol。在氧化还原无辜的钒氧基配合物中报道的V≡O键解离能通常在120 - 170 kcal/mol范围内。与后期的3d金属不同，其中M═O物种通常具有高能量并通过例如占据M - O π*反键分子轨道而被活化，[(isq)(ibq)V-(O)Cl]中异常弱的V≡O键反映了还原产物的稳定性。因此，本研究突出了一种生成强氧化剂的替代途径，这些强氧化剂不是强外层球电子受体，这对设计用于弱O原子受体或强X - H键的需氧氧化的早期金属催化剂具有启示意义。
