Reactivity of Nitric Oxide and Nitrosonium Ion with Copper(II/I) Schiff Base Complexes: Mechanistic Aspects of Imine C═N Bond Cleavage and Oxidation of Pyridine-2-aldehyde to Pyridine-2-carboxylic Acid,Inorganic Chemistry

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Reactivity of Nitric Oxide and Nitrosonium Ion with Copper(II/I) Schiff Base Complexes: Mechanistic Aspects of Imine C═N Bond Cleavage and Oxidation of Pyridine-2-aldehyde to Pyridine-2-carboxylic Acid
Inorganic Chemistry ( IF 4.3 ) Pub Date : 2022-04-22 , DOI: 10.1021/acs.inorgchem.1c04038
Saikat Mishra ₁ , Shibaditya Kumar ₁ , Anirban Bhandari ₁ , Aniruddha Das ₁ , Pallav Mondal ₁ , Geeta Hundal ₂ , Marilyn M Olmstead ₃ , Apurba K Patra ₁

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Four Schiff base ligands of the general formulas [6-(R)-2-pyridyl-N-(2′-methylthiophenyl)methylenimine] (^RL1) and 6-p-chlorophenyl-2-pyridyl-N-(2′-phenylthiophenyl)methylenimine (^RL2), where R = H, Me, p-ClPh, and their bis-ligand copper(II) and copper(I) complexes, 1–4 and 1′–4′, respectively, were synthesized and characterized. The reactivities of 1–4 with nitric oxide (NO) gas and of 1′–4′ with solid NOBF₄ (NO⁺) were examined in dry acetonitrile in the presence and absence of water (H₂O). The results revealed that, in the absence of H₂O, complexes 1–4 (or 1′–4′) reacts with NO (or NOBF₄), leading to imine C═N bond cleavage of both (or one) Schiff base(s) that generates 2 (or 1) equiv of 2-(methyl/phenyl)thiobenzenediazonium perchlorates (5/6) and the corresponding picolaldehyde (^RPial) via a copper nitrosyl of a {CuNO}¹⁰-type intermediate. In the presence of H₂O, the in situ formed ^RPial get oxidized to the corresponding picolinic acid (^RPicH) via an in situ formed LCu^IOH intermediate (LCu^I + HO-NO → LCu^IOH + NO⁺; L = ^RL1/^RL2/^RPic^– and ν_O–H of Cu^IOH = 3650 cm^–1) and subsequently produces, with the aid of NO⁺ oxidant, the picolinate-ligated copper(II) complexes (i) [(^HPic)₂Cu] (7), [(^MePic)₄Cu₃(NO₃)₂]_n·H₂O (8·H₂O), or [(^ClPhPic)₂Cu] (9) when NO reacts with 1–4 or (ii) [(^RPic)Cu^II(^RL1/^RL2)]⁺ when NO⁺ reacts with 1′–4′. The Cu^II to Cu^I reduction of [(^RPic)Cu^II(^RL1/^RL2)]⁺ is essential for C═N cleavage of the remaining ^RL1/^RL2 Schiff base; excess NO can do it. The X-ray structures (1, 1′, 3′, 5, 7, and 8) and spectroscopic results revealed the role of Cu^II/I, NO, NO⁺, and H₂O, shedding light on the mechanism of C═N bond cleavage and the oxidation of pyridine-2-aldehyde to pyridine-2-carboxylic acid. The reaction of 1 with ¹⁵NO revealed that the terminal N of the N₂⁺ group of 5 originates from ¹⁵NO [ν_{¹⁴N¹⁴N–} = 2248 cm^–1 and ν_{¹⁵N¹⁴N–} = 2212 cm^–1].

中文翻译：

一氧化氮和亚硝基离子与铜 (II/I) 席夫碱配合物的反应性：亚胺 C=N 键断裂和吡啶-2-醛氧化成吡啶-2-羧酸的机理方面

通式 [6-( R )-2-吡啶基-N- (2'-甲基硫苯基)亚甲基亚胺] ( ^R L1) 和 6-对- 氯苯基-2-吡啶基- N - (2'-) 的四个席夫碱配体苯硫基苯基）亚甲基亚胺 ( ^R L2)，其中 R = H、Me、p -ClPh，以及它们的双配体铜 (II) 和铜 (I) 配合物，分别为1 – 4和1' – 4'，被合成并表征。1 – 4与一氧化氮 (NO) 气体的反应性以及1' – 4'与固体 NOBF ₄ (NO ⁺) 在存在和不存在水 (H ₂ O) 的情况下在无水乙腈中进行检查。结果表明，在没有 H ₂ O的情况下，配合物1 – 4（或1' – 4'）与 NO（或 NOBF ₄）反应，导致两个（或一个）席夫碱的亚胺 C=N 键断裂(s)通过 {CuNO} ¹⁰型中间体的亚硝基铜生成 2（或 1）当量的 2-（甲基/苯基）硫代苯重氮高氯酸盐 ( 5 / 6 ) 和相应的吡啶甲醛 ( ^{R Pial)。}在 H ₂ O的存在下，原位形成^R Pial 通过原位形成的 LCu ^I OH 中间体 (LCu ^I + HO-NO → LCu ^I OH + NO ⁺ ; L = ^R L1/ ^R L2/ ^R Pic ^–和 ν )被氧化成相应的吡啶甲酸 ( ^R PicH) Cu ^I OH = 3650 cm ^{–1 ) 的}_O–H并随后在 NO ⁺氧化剂的帮助下生成吡啶配位铜 (II) 配合物 (i) [( ^H Pic) ₂ Cu] ( 7 ), [ ( ^Me Pic) ₄ Cu ₃ (NO ₃) ₂ ] _n ·H ₂ O ( 8 ·H ₂ O)，或 [( ^ClPh Pic) ₂ Cu] ( 9 ) 当 NO 与1 – 4或 (ii) [( ^R Pic)Cu ^II ( ^R L1/ ^R L2)] ⁺当 NO ⁺与1' – 4'反应时。[( R ^Pic )Cu II ⁽^R^L1 / R ^L2⁾ ] ⁺^{对于剩余的R} L1/ ^R L2 席夫碱的 C =N 裂解是必不可少的；过量的NO可以做到。X射线结构（1、1 '、3'、5、7和8 ）和光谱结果揭示了Cu ^II/I、NO、NO ⁺和H ₂O的作用，揭示了C的机制＝N键断裂和吡啶-2-醛氧化成吡啶-2-羧酸。1与¹⁵ NO的反应表明，N ₂⁺基团5的末端 N来源于¹⁵NO [ν _{¹⁴ N ¹⁴ N–} = 2248 cm ^–1和 ν _{¹⁵ N ¹⁴ N–} = 2212 cm ^–1 ]。

更新日期：2022-04-22

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