Palladium(II) Complexes Bearing an Indazole-Derived N-Heterocyclic Carbene and Phosphine Coligands as Catalysts for the Sonogashira Coupling and the Hydroamination of Alkynes

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• 作者：Jan C. Bernhammer ; Ning Xi Chong ; Ramasamy Jothibasu ; Binbin Zhou ; Han Vinh Huynh
• 刊名：Organometallics
• 出版年：2014
• 出版时间：July 14, 2014
• 年：2014
• 卷：33
• 期：13
• 页码：3607-3617
• 全文大小：469K
• ISSN：1520-6041

文摘

Indazolin-3-ylidenes (indy) are among the most strongly donating N-heterocyclic carbenes, but the structural diversity of their complexes is still limited. Two dimeric palladium(II) complexes, [PdBr₂(indy-5)]₂ (2a) and [PdBr₂(indy-6)]₂ (2b) (indy-5 = 2,3-dihydro-1H-pyrazolo[1,2-a]indazolin-3-ylidene, indy-6 = 6,7,8,9-tetrahydropyridazino[1,2-a]indazolin-3-ylidene], bearing indazolin-3-ylidene ligands with different sizes of the fused aliphatic ring can be obtained by silver carbene transfer. The reaction of these dimers with pyridine yielded trans-[PdBr₂(indy)(pyridine)] complexes (3a,b), while the poorly soluble monophosphine complexes cis-[PdBr₂(indy)(PPh₃)] (4a,b) were obtained by reaction with triphenylphosphine. Ligand substitution of the latter with silver trifluoroacetate afforded cis-[Pd(O₂CCF₃)₂(indy)(PPh₃)] complexes (5a,b) with improved solubilities, allowing for their detailed characterizations. In the presence of sodium tetrafluoroborate, cationic bis(phosphine) complexes trans-[PdBr(PPh₃)₂][BF₄] (6a,b) could be obtained. Similarly, cis-[PdBr(dppe)][BF₄] (7a,b) and cis-[PdBr(dppp)][BF₄] (8a,b) were obtained (dppe = bis(diphenylphosphino)ethane; dppp = bis(diphenylphosphino)propane) with the respective chelating diphosphines. A preliminary catalytic study revealed that the complexes incorporating monodentate phosphine ligands are good catalysts for the Sonogashira cross-coupling, while moderate to good yields were achieved with all complexes for the hydroamination of carbon鈥揷arbon triple bonds.