Electronically Dissymmetric DIPHOS Derivatives Give Higher n:i Regioselectivity in Rhodium-Catalyzed Hydroformylation Than Either of Their Symmetric Counterparts

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• 作者：Charles P. Casey ; Evelyn Lin Paulsen ; Eckart W. Beuttenmueller ; Bernd R. Proft ; Brock A. Matter ; and Douglas R. Powell
• 刊名：Journal of the American Chemical Society
• 出版年：1999
• 出版时间：January 13, 1999
• 年：1999
• 卷：121
• 期：1
• 页码：63 - 70
• 全文大小：113K
• 年卷期：v.121,no.1(January 13, 1999)
• ISSN：1520-5126

文摘

Electronic effects on rhodium-catalyzed hydroformylation of 1-hexene with electronically dissymmetric DIPHOS derivatives [3,5-(CF₃)₂C₆H₃]₂PCH₂CH₂PPh₂ = [DIPHOS-(3,5-CF₃,H)] (1), [2-(CF₃)C₆H₄]₂PCH₂CH₂PPh₂ = [DIPHOS-(2-CF₃,H)] (2), [3,5-(CF₃)₂C₆H₃]₂PCH₂CH₂P[2-(CH₃)C₆H₄]₂ = [DIPHOS-(3,5-CF₃,2-CH₃)] (3), and [2-(CF₃)C₆H₄]₂PCH₂CH₂P[2-(CH₃)C₆H₄]₂ = [DIPHOS-(2-CF₃,2-CH₃)] (4) wereinvestigated. Two apical-equatorial chelate isomers were observed for model (diphosphine)Ir(CO)₂H complexesof dissymmetric diphosphines 1-4. In each case, the equatorial phosphine of the major isomer (96-60%) hadelectron-withdrawing aryl substituents. These dissymmetric DIPHOS derivatives were used to test the hypothesisthat an electron-withdrawing substituent on an equatorial phosphine increases the hydroformylation n:i ratiowhile an electron-withdrawing substituent on an apical phosphine decreases the n:i ratio. In agreement withthe predictions of this hypothesis, hydroformylation with the dissymmetric diphosphine ligand DIPHOS-(3,5-CF₃,H) (1), gave an n:i ratio of 4.2:1, higher than either of the symmetric ligands DIPHOS, 2.6:1, andDIPHOS-(3,5-CF₃), 1.3:1. Similar observations were made for hydroformylations with 2-4.