非血基質三價鈷超氧及過氧氫化物之合成與反應性

Abstract

本研究以修飾過的配位基H2BDPFP和H2BDPMeP合成出二價鈷錯合物Co(BDPFP) (1)和Co(BDPMeP) (2)，並進行鑑定與比較推拉電子基對鈷金屬錯合物的影響。錯合物1和2與氧氣反應可形成三價鈷超氧化物Co(BDPFP)(O2˙) (3)和Co(BDPMeP)(O2˙) (4)，藉由與具較弱的氫氧鍵受質TEMPOH進行奪氫反應會形成Co(BDPFP)(OOH) (5)和Co(BDPMeP)(OOH) (6)。另外，可藉由proton sponge與TEA滴定求得pKa值與從循環伏安法得到的還原電位E1/2，利用Bordwell方程式求出兩者的OO-H鍵能。利用錯合物3和4與不同鍵能的酚類反應，得知只有鍵能較小的酚類可先進行質子轉移，再進行電子轉移的反應。錯合物3和4與二甲氨基苯酚反應時，透過不同溫度的UV-vis及EPR光譜偵測，可以判斷出是先進行質子轉移再進行電子轉移。而與對硝基苯酚反應則只進行質子轉移的步驟。並且錯合物3和4也可以對2-PPA進行親核反應生成苯乙酮。Two modified ligands, H2BDPFP and H2BDPMeP, were prepared for the synthesis of Co(II) complexes, Co(BDPFP) (1) and Co(BDPMeP) (2). Reactions of 1 and 2 with O2 forming superoxo complexs, Co(BDPFP)(O2˙) (3) and Co(BDPMeP)(O2˙) (4). Two Co(III)-hydroperoxo complexs, Co(BDPFP)(OOH) (5) and Co(BDPMeP)(OOH) (6), were formed by reactions of 3 and 4 with TEMPOH, which has a weak O-H bond, via hydrogen atom transfer reaction. In addition, the bond dissociation free energies of the OO-H bond in 5 and 6 were determined by the pKa values confirmed by proton sponge and TEA titration and the redox potentials (E1/2) from cyclic voltammetry via Bordwell equation.Reactions of 3 and 4 with phenols having different O-H bond energies revealed that only phenols with a relatively small O-H bond energies can proceed proton transfer followed by electron transfer reaction. Reactions of 3 and 4 with 4-dimethylaminopyridine, monitored by UV-vis and EPR spectroscopies at different temperatures revealed that proton transfer occurred first at 153 K and electron transfer proceeded when temperature raised up to 193 K. Reactions with 4-nitrophenol only performed proton transfer reaction. Complexes 3 and 4 can also carry out the nucleophilic reaction on 2-PPA to generate acetophenone.