Tautomerization of Pyridine and 2-Substituted Pyridines to Pyridylidene Ligands by the Iridium(I)–Diene Complex TpMe2Ir(η4-CH2═C(Me)C(Me)═CH2)

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• 作者：Florencia Vattier ; Verónica Salazar ; Margarita Paneque ; Manuel L. Poveda ; Eleuterio álvarez
• 刊名：Organometallics
• 出版年：2014
• 出版时间：January 27, 2014
• 年：2014
• 卷：33
• 期：2
• 页码：498-510
• 全文大小：702K
• ISSN：1520-6041

文摘

The complex Tp^Me2Ir(畏⁴-CH₂鈺怌(Me)C(Me)鈺怌H₂) (3; Tp^Me2 = hydrotris(3,5-dimethylpyrazolyl)borate) reacts with pyridines NC₅H₄-2-R (R = H, Me, SiMe₃, F, OMe, NMe₂, C(鈺怬)Me) in cyclohexane, with formation of Ir(III) products whose natures depend strongly on the reaction conditions and on the R substituent. The simplest case is for R = NMe₂, C(鈺怬)Me, where 魏²:蟽²-but-2-enediyl N鈥揌 pyridylidenes, i.e. the result of the metal-promoted tautomerization of the pyridines, are the only species obtained from 60 to 150 掳C. For R = Me, F the N-bonded adducts Tp^Me2Ir(魏²-CH₂C(Me)鈺怌(Me)CH₂)(NC₅H₄-2-R) are formed at 60 掳C but, under harsher conditions (120鈥?50 掳C), the observed products are, exclusively and respectively, the N鈥揌 pyridylidene and a bicyclic carbene compound derived from the formal, trans-stereospecific transfer of the N鈥揌 hydrogen of the corresponding (not observed) pyridylidene onto one of the carbons of the C鈺怌 double bond of the but-2-enediyl moiety, the other experiencing C鈥揘 formation. For R = OMe, the N adduct formed at 60 掳C transforms, at higher temperatures, into a mixture of the N鈥揌 pyridylidene and the bicyclic carbene, with no further evolution. More complex behavior is observed for the rest of the pyridines studied. Thus, when R = SiMe₃, in addition to the expected N鈥揌 pyridylidene, two isomeric N鈥揌 pyridylidenes containing a 魏²:蟽²-but-1-enediyl coligand are also formed under kinetic control (60 掳C) but with both cleanly transforming into the former compound at higher temperatures. Finally, for R = H only the N adduct is formed under kinetic control at 25 掳C but this species transforms almost completely into a mixture of the N鈥揌 pyridylidene and two epimeric, N鈥揅 bicyclic carbenes after prolonged heating at 150 掳C. A detailed study of the temperature-dependent behavior of 3 in C₆H₆ has also been undertaken, revealing the interesting deuteration of its 鈺怌H₂ termini by C₆D₆.