Synthesis of NHC-Oxazoline Pincer Complexes of Rh and Ru and Their Catalytic Activity for Hydrogenation and Conjugate Reduction

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• 作者：Jun-ichi Ito ; Kanae Sugino ; Satoru Matsushima ; Hiroki Sakaguchi ; Hiroshi Iwata ; Takahiro Ishihara ; Hisao Nishiyama
• 刊名：Organometallics
• 出版年：2016
• 出版时间：June 13, 2016
• 年：2016
• 卷：35
• 期：11
• 页码：1885-1894
• 全文大小：610K
• 年卷期：0
• ISSN：1520-6041

文摘

We describe the preparation and catalytic reactions of new CCN pincer Rh and Ru complexes containing NCH-oxazoline hybrid ligands. Oxazolinyl-phenyl-imidazolium derivatives (3) were suitable ligand precursors for the CCN pincer scaffold. C–H bond activation of 3 with RhCl₃·3H₂O in the presence of NEt₃ yielded the desired CCN pincer Rh complexes 5 in 13–27% yields. The related CCN pincer Ru complexes 8–10 were synthesized in good yields by C–H bond activation of p-cymene Ru complexes 7 in the presence of NaOAc in DMF. The chiral complexes 8 and 9 had two diastereomers according to the coordination of CO and OAc ligands. The CCN Rh complexes showed catalytic activity for conjugate reduction of ethyl β-methylcinnamate with hydrosilane, with moderate enantioselectivity. The CCN Ru complexes were found to be active in the hydrogenation of aromatic ketones. In particular, hydrogenation of 9-acetylanthracene took place at not only the C═O bond but also the anthracene ring. The Ru complexes were also used as catalysts in the transfer hydrogenation of 9-acetylanthracene with 2-propanol; again, both the C═O bond and the anthracene ring were hydrogenated.