Rhodium(III) Complexes Containing C4-Bound N-Heterocyclic Carbenes: Synthesis, Coordination Chemistry, and Catalytic Activity in Transfer Hydrogenation

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• 作者：Liangru Yang ; Anneke Kr&#xfc ; ger ; Antonia Neels ; Martin Albrecht
• 刊名：Organometallics
• 出版年：2008
• 出版时间：July 14, 2008
• 年：2008
• 卷：27
• 期：13
• 页码：3161 - 3171
• 全文大小：899K
• 年卷期：v.27,no.13(July 14, 2008)
• ISSN：1520-6041

文摘

Direct metalation of C2-protected diimidozolium salts with RhCl₃ or [RhCl(cod)]₂ and KI afforded a series of new rhodium(III) complexes with abnormally C4-bound, cis-chelating NHC ligands. The complexes were isolated as dimetallic species containing two (μ²-I)₃-bridged rhodium(III) centers. In the presence of coordinating ligands such as CH₃CN, PPh₃, or dppe, the dimeric structure is readily cleaved and yields monometallic complexes. Crystallographic analysis of representative structures indicates a higher trans influence of abnormally C4-bound carbenes as compared to normal NHCs. The exceptionally strong donor ability of carbenes in such a C4 coordination mode increases the catalytic activity of the rhodium center and allows for efficient transfer hydrogenation of ketones in iPrOH/KOH.