Redox-Switchable Hydroelementation of a Cobalt Complex Supported by a Ferrocene-Based Ligand

The first crystallographically characterized tetrahedral cobalt salen (salen = N,N′-ethylenesalicylimine) complex was synthesized by using a 1,1′-ferrocene derivative, salfen (salfen = 1,1′- di­(2,4-di-tert-butyl-6-salicylimine)­ferrocene). The complex undergoes two oxidation events at low potentials, which were assigned as ligand centered by comparison to the corresponding zinc complex. The cobalt complex was found to catalyze the hydroalkoxylation of styrenes, similarly to related square planar cobalt salen complexes, likely due to its fluxional behavior in alcoholic solvents. Furthermore, the one-electron-oxidized species was found to be inactive toward hydroalkoxylation. Thus, the hydroalkoxylation reactivity could be turned on/off in situ by redox chemistry.首例经晶体学表征的四面体钴salen配合物（salen即N,N′-乙叉双水杨亚胺，对应英文为N,N′-ethylenesalicylimine），通过1,1'-二茂铁衍生物salfen（1,1'-二(2,4-二叔丁基-6-水杨亚胺)二茂铁）合成得到。该配合物在低电位下可发生两次氧化过程，通过与对应锌配合物的对比分析，将其归属为配体中心氧化反应。研究发现，该钴配合物可催化苯乙烯的氢烷氧基化反应，这与相关平面正方形钴salen配合物的催化行为一致，其原因可能是该配合物在醇溶剂中具有流变行为。此外，单电子氧化后的物种对氢烷氧基化反应无催化活性。由此，可通过氧化还原化学在原位实现该氢烷氧基化反应活性的可控开关。