非血基質三價鈷超氧化物搭配氯取代之五配位配位基的合成與反應性

Abstract

此研究以本實驗室自製之氯取代配位基H2BDPClP鍵結鈷金屬，合成出二價鈷錯合物Co(BDPClP) (1)，鑑定後進行反應性測試，用以比較不同取代基之間的差異，錯合物1在-90 ℃下與氧氣反應可形成三價鈷超氧化物Co(BDPClP)(O2˙) (2)，所形成的錯合物 2與TEMPOH在-90 ℃反應，會進行氫原子轉移形成Co(BDPClP)(OOH) (3)。欲得到錯合物 3之OO-H鍵能，需將錯合物 2在加入HOTf後，以proton sponge進行滴定，求得錯合物 2質子化後的的pKa，再以循環伏安法測得錯合物 3的還原電位E1/2，最後將兩數值代入Bordwell方程式便可求得。將錯合物 2和多種酚類反應，得知極少數酚類有較明顯反應變化，其中二甲氨基苯酚的O-H鍵能較小，因此反應較顯著，藉由UV-vis觀測，我們判斷其反應在-120 ℃時有氫鍵作用力產生，而升溫到-90 ℃後，會進行鹼性不同步之質子耦合電子轉移(Basic asynchronous concerted proton electron transfer)反應；然而，其餘酚類則大多都只與錯合物 2上配位基的氧產生氫鍵作用力，鮮少有後續反應，唯有EPR的A值能觀察到些微變化。A recent develpoed ligand, H2BDPClP, with a Cl substituent on the para-position of phenyl rings was employed to synthesize a CoⅡ complex, Co(BDPClP) (1). After bubbling O2 into THF solutions of 1 at -90 ℃, a CoIII-superoxo complex, Co(BDPClP)(O2˙) (2) was formed. Reactions of 2 with TEMPOH gave a CoIII-hydroperoxo complex, Co(BDPClP)(OOH) (3), via a hydrogen atom transfer reaction. In order to obtain the OO-H bond dissociation free energy (BDFE) of 3 by Bordwell equation, we need the pKa value acquired by using proton sponge to perform titration of protonated complex 2 by HOTf, and the redox potential (E1/2) of 3 obtain from cyclic voltammetry. Reactions of 2 with various phenols monitored by UV-vis spectroscopy revealed that only the one with 4-dimethylaminopyridine displayed an obvious change because of its smaller O-H BDFE. We found that there is a hydrogen bond interaction between complex 3 and 4-dimethylaminopyridine at -120 ℃ and the reaction followed by basic asynchronous CPET as the reaction solution warming up to -90 ℃.On the other side, the reactions of 2 with rest phenols only show a hydrogen bonding interaction with complex 2, demonstrated by their EPR spectras of the resulting solutios displaying a settle change of hyperfine coupling constant (A).