Binary catalytic systems constructed by porphyrin cobalts(II) with confining nano-region and Zn(OAc)2 for oxygenation of cycloalkanes with O2 in relay mode

Abstract

To produce partly oxygenated products of cycloalkanes utilizing O2 in high-efficiency and high-selectivity, binary catalytic systems possessing bimetallic centers were constructed based on porphyrin cobalts(II) and Zn(OAc)2. Porphyrin cobalts(II) possessing bulky substituents had been synthesized to construct confining nano-regions to inhibit the spread of free radical in shambolic state, and Zn(OAc)2 was utilized to catalyze transformation of oxygenation intermediates cycloalkyl hydroperoxides. For cycloalkanes oxygenation using O2, binary system constructed by T2-NaPBr8Co(II)&Zn(OAc)2 exhibited superior catalytic performance. Both conversion and total selectivity to partly oxygenated products were raised. Compared with metalloporphyrin TPPBr8Co(II) with small substituents, conversion was increased from 5.13 to 6.21% and selectivity to partly oxygenated products was raised from 86.9 to 95.8% in classical cyclohexane oxygenation. The excellent performance of binary catalytic system constructed by T2-NaPBr8Co(II) and Zn(OAc)2 was mainly due to lower temperature, inhibited spread of free radical in confining catalytic region of T2-NaPBr8Co(II) and catalytic conversion of cycloalkyl hydroperoxides. The relay oxygenation path and catalytic mechanism were systematically investigated via EPR analyses and control experiments. This study is not only a significant contribution to construction of efficient and selective catalytic systems for cycloalkane oxygenation, but also a useful reference for other chemical conversion containing free radicals.