Synthetic Principles for Bandgap Control in Linear pi-Conjugated Systems.

The increasing demand to produce enantiomerically pure pharmaceuticals, agrochemicals, flavors, and other fine chemicals has advanced the field of asymmetric catalytic technologies.1,2 Among all asymmetric catalytic methods, asymmetric hydrogenation utilizing molecular hydrogen to reduce prochiral olefins, ketones, and imines, have become one of the most efficient methods for constructing chiral compounds.3 The development of homogeneous asymmetric hydrogenation was initiated by Knowles4a and Horner4b in the late 1960s, after the discovery of Wilkinson’s homogeneous hydrogenation catalyst [RhCl(PPh3)3]. By replacing triphenylphosphine of the Wilkinson’s catalystwithresolvedchiralmonophosphines,6Knowles and Horner reported the earliest examples of enantioselective hydrogenation, albeit with poor enantioselectivity. Further exploration by Knowles with an improved monophosphine CAMP provided 88% ee in hydrogenation of dehydroamino acids.7 Later, two breakthroughs were made in asymmetric hydrogenation by Kagan and Knowles, respectively. Kagan reported the first bisphosphine ligand, DIOP, for Rhcatalyzed asymmetric hydrogenation.8 The successful application of DIOP resulted in several significant directions for ligand design in asymmetric hydrogenation. Chelating bisphosphorus ligands could lead to superior enantioselectivity compared to monodentate phosphines. Additionally, P-chiral phosphorus ligands were not necessary for achieving high enantioselectivity, and ligands with backbone chirality could also provide excellent ee’s in asymmetric hydrogenation. Furthermore, C2 symmetry was an important structural feature for developing new efficient chiral ligands. Kagan’s seminal work immediately led to the rapid development of chiral bisphosphorus ligands. Knowles made his significant discovery of a C2-symmetric chelating bisphosphine ligand, DIPAMP.9 Due to its high catalytic efficiency in Rh-catalyzed asymmetric hydrogenation of dehydroamino acids, DIPAMP was quickly employed in the industrial production of L-DOPA.10 The success of practical synthesis of L-DOPA via asymmetric hydrogenation constituted a milestone work and for this work Knowles was awarded the Nobel Prize in 2001.3k This work has enlightened chemists to realize * Corresponding author. 3029 Chem. Rev. 2003, 103, 3029−3069

New Chiral Phosphorus Ligands for Enantioselective Hydrogenation

Color Control in π-Conjugated Organic Polymers for Use in Electrochromic Devices

The gas sensors fabricated by using conducting polymers such as polyaniline (PAni), polypyrrole (PPy) and poly (3,4-ethylenedioxythiophene) (PEDOT) as the active layers have been reviewed. This review discusses the sensing mechanism and configurations of the sensors. The factors that affect the performances of the gas sensors are also addressed. The disadvantages of the sensors and a brief prospect in this research field are discussed at the end of the review.

/pdf/gas-sensors-based-on-conducting-polymers-4l6i49715q.pdf

Gas Sensors Based on Conducting Polymers

3.2. Thienothiophenes 1216 3.2.1. Thieno[3,4-b]thiophene Analogues 1216 3.2.2. Thieno[3,2-b]thiophene Analogues 1217 3.2.3. Thieno[2,3-b]thiophene Analogues 1218 3.3. , ′-Bridged Bithiophenes 1219 3.3.1. Dithienothiophene (DTT) Analogues 1220 3.3.2. Dithieno[3,2-b:2′3′-d]thiophene-4,4-dioxides 1221 3.3.3. Dithienosilole (DTS) Analogues 1221 3.3.4. Cyclopentadithiophene (CPDT) Analogues 1221 3.3.5. Nitrogen and Phosphor Atom Bridged Bithiophenes 1222

Functional oligothiophenes: molecular design for multidimensional nanoarchitectures and their applications.

The synthesis and application of three examples of a new class of chiral (C2) atropisomeric diphosphines characterized by two interconnected five-membered heteroaromatic rings, with hindered rotation around the interanular bond, are described. Optically pure (+)- and (−)-2,2‘-bis(diphenylphosphino)-4,4‘,6,6‘-tetramethyl-3,3‘-bibenzo[b]thiophene (tetraMe-bitianp) (1a) and the parent unsubstituted system (+)- and (−)-bitianp (1b) were synthesized. They were found to be optically stable at 100 °C and were successfully employed as ligands in the Ru(II)-catalyzed hydrogenation of α- and β-oxo esters to the corresponding α- and β-hydroxy esters and in the hydrogenation of olefinic substrates. The optical and chemical yields were comparable with those reported for the same Ru(II)-binap-catalyzed reactions carried out under the same experimental conditions. The 2,2‘-bis(diphenylphosphino)-3,3‘-bibenzo[b]furan (1c), the oxygenated analogue of bitianp, was found to be configurationally unstable at room temperature....

New Class of Chiral Diphosphine Ligands for Highly Efficient Transition Metal-Catalyzed Stereoselective Reactions: The Bis(diphenylphosphino) Five-membered Biheteroaryls.

The four-step straightforward synthesis of enantiopure (+)- and (−)-2,2‘,5,5‘-tetramethyl-4,4‘-bis(diphenylphoshino)-3,3‘-bithiophene (tetraMe-BITIOP), a new C2-symmetry chelating ligand for transition metals, is described, starting from 2,5-dimethylthiophene. The complexes of this electron-rich diphosphine with Ru(II) and Rh(I) were used as catalysts in some homogeneous hydrogenation reactions of prostereogenic carbonyl functions of α- and β-ketoesters, of prostereogenic carbon−carbon double bonds of substituted acrylic acids, and of N-acetylenamino acids. The enantiomeric excesses were found to be excellent in all the experiments and comparable with the best results reported in the literature for the same reactions, carried out under similar experimental conditions, with the metal complexes of the most popular chiral diphosphine ligands as catalysts.

2,2',5,5'-tetramethyl-4,4'-bis(diphenylphoshino)-3,3'-bithiophene: a new, very efficient, easily accessible, chiral biheteroaromatic ligand for homogeneous stereoselective catalysis

The First “Charm Bracelet” Conjugated Polymer: An Electroconducting Polythiophene with Covalently Bound Fullerene Moieties

Chiral atropisomeric five-membered biheteroaromatic diphosphines: new ligands of the bibenzimidazole and biindole series

Racemic (±)-3,3‘-bis(diphenylphosphinyl)-1,1‘-dimethyl-2,2‘-biindole (1c) (N-Me-2-BINPO) and (±)-3,3‘-bis(diphenylphosphinyl)-1,1‘-bis(methoxymethyl)-2,2‘-biindole (1d) (N-MOM-2-BINPO) were synthesized in satisfactory yields following a three-step reaction sequence, starting from indole. Resolution of racemic 1c and 1d was achieved through fractional crystallization of their diastereomeric adducts with optically active dibenzoyl tartaric acids, followed by alkaline decomplexation of the diastereomerically pure salts. Their trichlorosilane reduction gave enantiopure phosphines (+)- and (−)-(1a) (N-Me-2-BINP) and (+)- and (−)-(1b) (N-MOM-2-BINP). The electrochemical oxidative potential of 1a and 1b was found to be 0.52 and 0.60 V, respectively. Both the enantiomers of (1a) were tested as ligands of Ru(II) in asymmetric hydrogenation reactions of α- and β-oxoesters. Reactions were found to be outstandingly fast and enantioselection quite good. Comparative kinetic experiments on the hydrogenation reaction of ...

https://pubs.acs.org/doi/pdf/10.1021/jo004011m

3,3‘-Bis(diphenylphosphino)-1,1‘-disubstituted-2,2‘-biindoles: Easily Accessible, Electron-Rich, Chiral Diphosphine Ligands for Homogeneous Enantioselective Hydrogenation of Oxoesters

Franco Sannicolò

Papers

New Class of Chiral Diphosphine Ligands for Highly Efficient Transition Metal-Catalyzed Stereoselective Reactions: The Bis(diphenylphosphino) Five-membered Biheteroaryls.

2,2',5,5'-tetramethyl-4,4'-bis(diphenylphoshino)-3,3'-bithiophene: a new, very efficient, easily accessible, chiral biheteroaromatic ligand for homogeneous stereoselective catalysis

The First “Charm Bracelet” Conjugated Polymer: An Electroconducting Polythiophene with Covalently Bound Fullerene Moieties

Chiral atropisomeric five-membered biheteroaromatic diphosphines: new ligands of the bibenzimidazole and biindole series

3,3‘-Bis(diphenylphosphino)-1,1‘-disubstituted-2,2‘-biindoles: Easily Accessible, Electron-Rich, Chiral Diphosphine Ligands for Homogeneous Enantioselective Hydrogenation of Oxoesters