Cleavage of Ether, Ester, and Tosylate C(sp3)–O Bonds by an Iridium Complex, Initiated by Oxidative Addition of C–H Bonds. Experimental and Computational Studies,Journal of the American Chemical Society

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Cleavage of Ether, Ester, and Tosylate C(sp3)–O Bonds by an Iridium Complex, Initiated by Oxidative Addition of C–H Bonds. Experimental and Computational Studies
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2013-03-21 , DOI: 10.1021/ja312464b
Sabuj Kundu ₁ , Jongwook Choi ₁ , David Y. Wang ₁ , Yuriy Choliy ₁ , Thomas J. Emge ₁ , Karsten Krogh-Jespersen ₁ , Alan S. Goldman ₁

Affiliation

A pincer-ligated iridium complex, (PCP)Ir (PCP = κ(3)-C6H3-2,6-[CH2P(t-Bu)2]2), is found to undergo oxidative addition of C(sp(3))-O bonds of methyl esters (CH3-O2CR'), methyl tosylate (CH3-OTs), and certain electron-poor methyl aryl ethers (CH3-OAr). DFT calculations and mechanistic studies indicate that the reactions proceed via oxidative addition of C-H bonds followed by oxygenate migration, rather than by direct C-O addition. Thus, methyl aryl ethers react via addition of the methoxy C-H bond, followed by α-aryloxide migration to give cis-(PCP)Ir(H)(CH2)(OAr), followed by iridium-to-methylidene hydride migration to give (PCP)Ir(CH3)(OAr). Methyl acetate undergoes C-H bond addition at the carbomethoxy group to give (PCP)Ir(H)[κ(2)-CH2OC(O)Me] which then affords (PCP-CH2)Ir(H)(κ(2)-O2CMe) (6-Me) in which the methoxy C-O bond has been cleaved, and the methylene derived from the methoxy group has migrated into the PCP Cipso-Ir bond. Thermolysis of 6-Me ultimately gives (PCP)Ir(CH3)(κ(2)-O2CR), the net product of methoxy group C-O oxidative addition. Reaction of (PCP)Ir with species of the type ROAr, RO2CMe or ROTs, where R possesses β-C-H bonds (e.g., R = ethyl or isopropyl), results in formation of (PCP)Ir(H)(OAr), (PCP)Ir(H)(O2CMe), or (PCP)Ir(H)(OTs), respectively, along with the corresponding olefin or (PCP)Ir(olefin) complex. Like the C-O bond oxidative additions, these reactions also proceed via initial activation of a C-H bond; in this case, C-H addition at the β-position is followed by β-migration of the aryloxide, carboxylate, or tosylate group. Calculations indicate that the β-migration of the carboxylate group proceeds via an unusual six-membered cyclic transition state in which the alkoxy C-O bond is cleaved with no direct participation by the iridium center.

中文翻译：

铱络合物对醚、酯和甲苯磺酸酯 C(sp3)-O 键的裂解，由 C-H 键的氧化加成引发。实验和计算研究

发现钳形连接的铱络合物 (PCP)Ir (PCP = κ(3)-C6H3-2,6-[CH2P(t-Bu)2]2) 发生 C(sp(3) )-O 键的甲酯 (CH3-O2CR')、甲苯磺酸甲酯 (CH3-OTs) 和某些缺电子的甲基芳基醚 (CH3-OAr)。DFT 计算和机理研究表明，反应是通过 CH 键的氧化加成和氧化物迁移进行的，而不是通过直接添加 CO 进行。因此，甲基芳基醚通过添加甲氧基 CH 键进行反应，然后 α-芳基氧化物迁移得到顺式-(PCP)Ir(H)(CH2)(OAr)，然后铱到亚甲基氢化物迁移得到（ PCP)Ir(CH3)(OAr)。乙酸甲酯在甲氧基上发生 CH 键加成得到 (PCP)Ir(H)[κ(2)-CH2OC(O)Me]，然后得到 (PCP-CH2)Ir(H)(κ(2)-O2CMe ) (6-Me) 其中甲氧基 CO 键已被裂解，来自甲氧基的亚甲基已迁移到 PCP Cipso-Ir 键中。6-Me 的热解最终得到 (PCP)Ir(CH3)(κ(2)-O2CR)，这是甲氧基 CO 氧化加成的净产物。(PCP)Ir 与 ROAr、RO2CMe 或 ROTs 类型的物质反应，其中 R 具有 β-CH 键（例如，R = 乙基或异丙基），导致形成 (PCP)Ir(H)(OAr)，（ PCP)Ir(H)(O2CMe) 或 (PCP)Ir(H)(OTs)，以及相应的烯烃或 (PCP)Ir(烯烃) 络合物。与 CO 键氧化加成一样，这些反应也通过 CH 键的初始活化进行；在这种情况下，在 β 位添加 CH 之后是芳基氧化物、羧酸酯或甲苯磺酸酯基团的 β-迁移。

更新日期：2013-03-21

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