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.
