Stereochemically matched (and mismatched) bisphosphine ligands: DIOP-DIPAMP hybrids
- Additional Document Info
- View All
The three diastereomers of (R,R)-2,3-O-isopropylidene-2,3-dihydroxy-1,4-bis([2-methoxyphenyl]-phenylphosphino)butane (1) and of (R,R)-2,3-O-isopropylidene-2,3-dihydroxy-1,4-bis([2-(dimethylammo) phenyl]phenylphosphino)butane (2) have been prepared and isolated. Advanced intermediates in the preparation and isolation of diastereomers of (R,R)-2,3-O-isopropylidene-2,3-dihydroxy-1,4-bis([2,6-dimethoxyphenyl]phenylphosphino)butane (3) are also described. Absolute configurations of four of the chiral phosphine ligands were determined via single-crystal X-ray diffraction studies of molybdenum tetracarbonyl derivatives ((RP,RP)-6, (RP,RP)-7, (RP,RP)-8, and (SP,SP)-8); this facilitated assignments of absolute configurations for all the isomers of ligands 1-3. These bisphosphine ligands are rare insofar as they have chiral phosphorus centers supported on an asymmetric carbon framework. Several reactions were performed to test for “cooperativity” between chiral centers in these ligands with respect to asymmetric induction in transition-metal-catalyzed processes. Matching and mismatching effects were observed, but there are some irregular trends in the data. The enantioselectivities obtained were moderate but greater than that for the parent ligand DIOP in some cases. The o-dimethylamino functionality of ligands 2 may play an active role in the coordination of these isomeric bisphosphine ligands. Trends and factors influencing the performance of ligands 1–3 in asymmetric catalysis are discussed. Crystal data for the compounds analyzed via X-ray diffraction are as follows. (RP,RP)·6: monoclinic, space group P21 (No. 4), a = 11.621 (3) Å, b = 10.676 (2) Å, c = 14.850 (2) Å, β = 101.59 (2)°, V = 1804.8 (6) Å3, Z = 2, R = 0.029. (RP,RP)-7•0.5CH2Cl2: monoclinic, space group P21 (No. 4), a = 11.013 (6) Å,b = 21.134 (5) Å, c = 18.555 (6) Å, β = 101.32 (3)°, V = 4235 (2) Å3, Z = 4, R = 0.111. (RP,RP)-8: triclinic, space group P1 (No. 1), a = 11.64 (1) Å,b = 16.05 (1) Å, c = 10.760 (7) Å, α = 94.06 (6)°, β = 97.05 (6)°, γ= 97.10 (7)°, V = 1973 (5) Å3, Z = 2, R = 0.098. (SP,SP)-8: orthorhombic, space group P212121 (No. 19), a = 14.007 (3) Å, b = 27.419 (8) Å, c = 10.394 (3) Å, V = 3992 (2) Å3 Z = 4,R = 0.052. © 1992, American Chemical Society. All rights reserved.
author list (cited authors)
Burgess, K., Ohlmeyer, M. J., & Whitmire, K. H.