Cleavage of Ether, Ester, and Tosylate C(sp3)鈥揙 Bonds by an Iridium Complex, Initiated by Oxidative Addition of C鈥揌 Bonds. Experimental and Computational Studies

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• 作者：Sabuj Kundu ; Jongwook Choi ; David Y. Wang ; Yuriy Choliy ; Thomas J. Emge ; Karsten Krogh-Jespersen ; Alan S. Goldman
• 刊名：The Journal of the American Chemical Society
• 出版年：2013
• 出版时间：April 3, 2013
• 年：2013
• 卷：135
• 期：13
• 页码：5127-5143
• 全文大小：1163K
• 年卷期：v.135,no.13(April 3, 2013)
• ISSN：1520-5126

文摘

A pincer-ligated iridium complex, (PCP)Ir (PCP = 魏³-C₆H₃-2,6-[CH₂P(t-Bu)₂]₂), is found to undergo oxidative addition of C(sp³)鈥揙 bonds of methyl esters (CH₃鈥揙₂CR鈥?, methyl tosylate (CH₃鈥揙Ts), and certain electron-poor methyl aryl ethers (CH₃鈥揙Ar). DFT calculations and mechanistic studies indicate that the reactions proceed via oxidative addition of C鈥揌 bonds followed by oxygenate migration, rather than by direct C鈥揙 addition. Thus, methyl aryl ethers react via addition of the methoxy C鈥揌 bond, followed by 伪-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鈥揌 bond addition at the carbomethoxy group to give (PCP)Ir(H)[魏²-CH₂OC(O)Me] which then affords (PCP-CH₂)Ir(H)(魏²-O₂CMe) (6-Me) in which the methoxy C鈥揙 bond has been cleaved, and the methylene derived from the methoxy group has migrated into the PCP C_ipso鈥揑r bond. Thermolysis of 6-Me ultimately gives (PCP)Ir(CH₃)(魏²-O₂CR), the net product of methoxy group C鈥揙 oxidative addition. Reaction of (PCP)Ir with species of the type ROAr, RO₂CMe or ROTs, where R possesses 尾-C鈥揌 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鈥揙 bond oxidative additions, these reactions also proceed via initial activation of a C鈥揌 bond; in this case, C鈥揌 addition at the 尾-position is followed by 尾-migration of the aryloxide, carboxylate, or tosylate group. Calculations indicate that the 尾-migration of the carboxylate group proceeds via an unusual six-membered cyclic transition state in which the alkoxy C鈥揙 bond is cleaved with no direct participation by the iridium center.