(^(OMe)bipy)Cu^(I)/ABNO催化体系催化氧化苄醇的反应机理研究

DFT Studies on the mechanism of benzyl alcohol oxidation catalyzed by(OMe bipy)Cu^(I)/ABNO complexes

采用密度泛函理论(DFT)研究了(^(OMe) bipy)Cu^(I)/ABNO(^(OMe) bipy∶4,4′-二甲氧基-2,2′-联吡啶;ABNO∶9-氮杂双环[3.3.1]壬烷-N-氧基自由基)催化体系催化氧化苄醇的反应机理,提出了3种可能的反应路径(路径A、B和C)。计算结果表明,路径B为最优反应路径,即(^(OMe) bipy)Cu^(I)/ABNO反应体系中,底物苄醇PhCH_(2)OH分别发生H质子和C_(α)-H原子转移,生成苄醛PhCHO和ABNOH,随后ABNOH被O_(2)氧化,最终形成的ABNO和(^(OMe) bipy)Cu^(I)-OH,促使体系中大量的PhCH_(2)OH被氧化。其中C_(α)-H原子转移过程为速控步骤,反应活化能为19.4 kcal mol^(-1)。分析结果说明,由于ABNO空间位阻较小,仅在室温条件下即可与惰性的脂肪醇发生反应,且反应体系生成的ABNOH很容易被O_(2)氧化,生成ABNO被重复利用,使得整个反应中,将ABNO减少到1 mol%仍未影响反应速率。

The reaction mechanism of the oxidation of benzyl alcohol to benzyaldehyde by a(^(OMe) bipy)Cu^(I)/ABNO catalytic system(MeObipy∶4,4-dimethoxyl-2,2-bipyridine;ABNO∶9-nitrogen-hetero-duplexring[3.3.1]azananeN-oxyl radical)was fully investigated using density functional theory(DFT).Three possible reaction pathways(pathways A,B and C)are proposed.Calculations show that path B is the optimal reaction path,i.e.,the(^(OMe) bipy)Cu^(I)/ABNO reaction system in which the substrate benzyl alcohol PhCH_(2)OH undergoes H-proton and C_(α)-H atom transfer,respectively,to produce benzyl aldehyde PhCHO and ABNOH,then ABNOH is oxidized by O_(2),and finally forms ABNO and(^(OMe) bipy)Cu^(I)-OH,prompting a large amount of PhCH_(2)OH in the system.The C_(α)-H atom transfer process is the rate-determining step with a reaction activation energy of 19.4 kcal mol^(-1).The analysis of the findings shows that due to the small spatial site resistance of ABNO,it can react easily with inert fatty alcohols even at room temperatures,and the ABNOH generated by the reaction system can be easily oxidized by O_(2) to produce ABNO which is reused,making the rate of reaction not being affected even when ABNO is reduced to 1 mol%.