Ligand Substituent Effects on Asymmetric Induction. Effect of Structural Variations of the DIOP Ligand on the Rh-Catalyzed Asymmetric Hydrogenation of Enamides

2000 ◽  
Vol 2 (26) ◽  
pp. 4137-4140 ◽  
Author(s):  
Yuan-Yong Yan ◽  
T. V. RajanBabu
Keyword(s):  
Substituent Effects ◽  
Asymmetric Hydrogenation ◽  
Asymmetric Induction ◽  
Induction Effect ◽  
Structural Variations

Ruthenium-Catalyzed Asymmetric Hydrogenation of 3-Oxoglutaric Acid Derivatives: A Study of Unconventional Solvent and Substituent Effects

2012 ◽  
Vol 18 (51) ◽  
pp. 16531-16539 ◽  
Author(s):  
Wanfang Li ◽  
Xiaoming Tao ◽  
Xin Ma ◽  
Weizheng Fan ◽  
Xiaoming Li ◽  
...  
Keyword(s):  
Substituent Effects ◽  
Asymmetric Hydrogenation

scholarly journals Rhodium-catalyzed asymmetric hydrogenation using self-assembled chiral bidentate ligands

2006 ◽  
Vol 78 (2) ◽  
pp. 501-509 ◽  
Author(s):  
James M. Takacs ◽  
Kittichai Chaiseeda ◽  
Shin A. Moteki ◽  
D. Sahadeva Reddy ◽  
Di Wu ◽  
...  
Keyword(s):  
Self Assembly ◽  
Metal Forming ◽  
Asymmetric Hydrogenation ◽  
Catalyst System ◽  
Asymmetric Induction ◽  
Bidentate Ligands ◽  
Catalytic Metal ◽  
Preliminary Study ◽  
Self Assembled ◽  
Heteroleptic Complex

The chirality-directed self-assembly of bifunctional subunits around a structural metal - typically, zinc(II) - is used to form a heteroleptic complex in which a second set of ligating groups are suitably disposed to bind a second metal, forming a heterobimetallic catalyst system. We find that subtle changes in the structural backbone (i.e., ligand scaffold) of such chiral bidentate self-assembled ligands (SALs) can be used to manipulate the ligand topography and chiral environment around catalytic metal; thus, the scaffold can be optimized to maximize asymmetric induction. Using this combinatorial strategy for ligand synthesis, a preliminary study was carried out in which a library of 110 SALs was evaluated in the rhodium-catalyzed asymmetric hydrogenation of a simple N-acyl enamide. The level of enantioselectivity obtained varies from near racemic to greater than 80 % ee as a function of the ligand scaffold, with the possibility of further improvement yet to be explored.

Structural influences impacting the role of the 9-ylidene bond in the electronic tuning of structures built upon 9-fluorenylidene scaffolds

2013 ◽  
Vol 91 (11) ◽  
pp. 1059-1071 ◽  
Author(s):  
Galen L. Eakins ◽  
Matthew W. Cooper ◽  
Nikolay N. Gerasimchuk ◽  
Terry J. Phillips ◽  
Bryan E. Breyfogle ◽  
...  
Keyword(s):  
Electronic Properties ◽  
Substituent Effects ◽  
Effect Study ◽  
Semiconducting Materials ◽  
Structural Variations ◽  
Steric Strain ◽  
Exciton Coupling ◽  
Electronic Tuning ◽  
Homo Lumo

A structure–effect study is presented pertaining to the HOMO–LUMO tuning of compounds built upon the 9-fluorenylidene scaffold frequently incorporated as a moiety within organic-based semiconducting materials. The results represent the first reported analysis employing an ensemble of spectroscopy, electrochemistry, and crystal structure data to elucidate and compare the electronic properties of 9-fluorenones, 9-fluorenylidenes, and 9-fluorenimine derivatives. The results also provide the first spectroscopically and crystallographically measured description of exciton coupling within 9,9′-bifluorenylidenes. The 9-ylidene bond is seen to play a key role impacting the electronic properties, and an examination of the effects of substituents, conjugation, heteroatoms, and steric strain on the 9-ylidene bond in a diverse set of structures with representative structural variations relevant to the HOMO–LUMO tuning is presented. Increasing conjugation decreased the HOMO–LUMO gap (HLG), increased the HOMO energy (EHOMO), but decreased the LUMO energy (ELUMO). Substituent effects were observed to produce only slight changes that tended to decrease the HLG and increase both EHOMO and ELUMO, while heteroatom inclusion at the 9-ylidine bond tended to decrease the HLG, EHOMO, ELUMO, and the extinction coefficient. In the sterically hindered 9,9′-bifluorenylidenes, increased steric strain that promoted either an increase in the torsion angle or bond length of the 9-ylidene bond was seen to decrease the HLG via exciton coupling. These results elucidate the HOMO–LUMO tuning of systems containing a 9-fluorenylidene moiety and may assist in developing materials with specifically tuned HLGs and HOMO–LUMO levels for a variety of applications.

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