Catalysts through self-assembly for combinatorial homogeneous catalysis (original) (raw)
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Angewandte Chemie International Edition, 2005
A new concept for generation of chelating ligand libraries for homogeneous metal complex catalysis based on self-assembly is presented. Thus, self-assembly of structurally simple monodentate ligands in order to give structurally more complex bidentate ligands is achieved employing hydrogen bonding. Based on this concept and on the 2-pyridone/hydroxypyridine tautomeric system, a new rhodium catalyst was identified which operated with excellent activity and regioselectivity upon hydroformylation of terminal alkenes. In order to generate defined unsymmetrical heterodimeric ligands, an A-T base pair analog-the aminopyridine/isoquinolone system-was developed which allows for complementary hydrogen bonding. Based on this platform, a 4 × 4 phosphine ligand library was screened in the course of the rhodium-catalyzed hydroformylation of 1-octene. A catalyst operating with outstanding activity and regioselectivity in favor of the linear aldehyde was discovered.
Angewandte Chemie International Edition, 2007
A new concept for generation of chelating ligand libraries for homogeneous metal complex catalysis based on self-assembly is presented. Thus, self-assembly of structurally simple monodentate ligands in order to give structurally more complex bidentate ligands is achieved employing hydrogen bonding. Based on this concept and on the 2-pyridone/hydroxypyridine tautomeric system, a new rhodium catalyst was identified which operated with excellent activity and regioselectivity upon hydroformylation of terminal alkenes. In order to generate defined unsymmetrical heterodimeric ligands, an A-T base pair analog-the aminopyridine/isoquinolone system-was developed which allows for complementary hydrogen bonding. Based on this platform, a 4 × 4 phosphine ligand library was screened in the course of the rhodium-catalyzed hydroformylation of 1-octene. A catalyst operating with outstanding activity and regioselectivity in favor of the linear aldehyde was discovered.
Hydrogen-Bonding-Assisted Supramolecular Metal Catalysis
Chemistry-an Asian Journal, 2018
The process of catalyst screening and discovery still relies on traditional ligand designing approaches, which suffer from complex synthesis and offer limited structural diversity. While supramolecular chemistry harnesses multiple weak secondary interactions to deliver self-assembled catalysts with diverse structures or orients substrates to achieve enzyme like activity and selectivity. Application of hydrogen bonding (Hbonding) as a construction element and as a directing group in "supramolecular transition metal catalysis" is critically reviewed and the state of the art in the field is presented. H-bonding empowers structurally simple ligands to deliver complex selfassembled catalysts, which were found to catalyse hydroformylation, hydrogenation, allylation and a gamut of other organic transformations. As we discuss, on many occasions these supramolecular catalysts outperform their parent covalently linked catalytic systems. The potential of H-bonding as directing group has been lately recognized by the scientific community and this review presents the role of hydrogen bonding in directing the substrate to obtain excellent selectivities and activities in a spectrum of catalytic transformations.
A Supramolecular Catalyst for Regioselective Hydroformylation of Unsaturated Carboxylic Acids
Angewandte Chemie International Edition, 2008
Natural enzymes efficiently combine molecular recognition and catalysis in one functional assembly. Reactions within enzyme-substrate complexes have much higher rate constants than corresponding bimolecular reactions. High degrees of regio-and stereoselectivity are achieved by orientation of the substrate and precise positioning of the reaction site in a favorable orientation relative to the catalytic center. Of particular importance for substrate binding by enzymes is the guanidine functional group of arginine. Over 70 % of enzyme substrates and cofactors are anions, and the guanidinium group forms strong ion pairs with oxoanions, such as carboxylates and phosphates. Through multiple noncovalent interactions within the active site, enzymes can achieve astonishing levels of substrate selectivity. This specificity, however, can also be a problem. Very often, enzymes have a narrow substrate specificity and lack the generality required for synthetic applications.
Enhancing the Enantioselectivity of Novel Homogeneous Organometallic Hydrogenation Catalysts
Angewandte Chemie International Edition, 2003
The exigent need to develop new asymmetric hydrogenation catalysts is universally acknowledged, and many new feasible strategies for the design and synthesis of such catalysts continue to be proposed. Herein, in addition to describing a new set of efficient, diamino-type ligands for a central rhodium or palladium ion that leads to good enantioselective (ee) performance, homogeneously, we also show that significant improvement in the stereoselectivity of the organometallic catalyst may be achieved by heterogenizing it at the inner walls of a mesoporous silica so that advantage is taken of the spatial restrictions imposed by the concave surface at which we have located the active center.
ChemInform, 2006
Preparation of aminopyridinyl phosphines S-3 2 Preparation of aminopyridinyl phosphonites S-8 3 Preparation of isoquinolinyl phosphonites S-12 III General procedure for asymmetric hydrogenation S-16 IV Heterodimeric platinum complexes S-17 V Heterodimeric cationic rhodium complexes S-19 VI Literature S-24 I General Bisdiethylamino-chloro-phosphine, [1] 2-(trimethylsilyl)ethanol, [2] the BINOL-derivatives, [3] 2amino-6-bromopyridine, [4] 2-bromo-6-N-pivaloylaminopyridine [5] and 1,3-dibromoisoquinoline [6] were synthesized according to literature procedures. The unsymmetrical disubstituted chlorophosphines can be prepared according to literature. [7] Methyl-2acetamidoacrylate and dimethylitaconate were purchased from Aldrich and Jansen Chimica, methyl-α-acetylamino cinnamate [8] was synthesized according to literature procedures. All reactions were carried out in dried glassware under an argon atmosphere 5.0 (Südwest-Gas). Air and moisture sensitive liquids and solutions were transferred via syringe. All reagents were obtained commercially unless otherwise noted. All solvents were dried and distilled by standard procedures. Organic solutions were concentrated under reduced pressure by rotary evaporation. Chromatographic purification of products was accomplished using flash chromatography [9] on a Merck silica gel Si 60 (200-400 mesh). S-2 Nuclear magnetic resonance spectra were acquired on a Varian Mercury spectrometer (300 MHz, 121 MHz and 75 MHz for 1 H, 31 P and 13 C respectively), on a Bruker AMX 400 (400 MHz, 162 MHz and 100 MHz for 1 H, 31 P and 13 C respectively) and on a Bruker DRX 500 (500 MHz, 202 MHz and 125 MHz for 1 H, 31 P and 13 C respectively) and are referenced according to residual protio solvent signals. Data for 1 H-NMR are recorded as follows: chemical shift (δ in ppm), multiplicity (s, singlet; br s, broad singlet; d, doublet; t, triplet; q, quartet; m, multiplet; p, pseudo), coupling constant (Hz) , integration. Data for 13 C-NMR are reported in terms of chemical shift (δ in ppm), multiplicity (if not a singlet), coupling constant (Hz). High-resolution mass spectra were obtained on a Finnigan MAT 8200 instrument and ESI mass spectrometry was performed on a Finnigan LCQ Advantage. Elementary analysis was performed on an elementar vario (Fa. Elementar Analysensysteme GmbH). Optical rotations were measured on a Perkin-Elmer 241 polarimeter. Separation of the enantiomers was achieved on a Chiralpak AD-H column using a Knaur K-2501 UV-detector. The enantiomeric excess of the triarylphosphine ligands was determined by HPLC using a Chiralpak AD-H column. Hydrogenation experiments were performed following the general procedure using hydrogen gas 5.0 (Südwest-Gas). S-3 II Experimental procedures and characterizations 1 Preparation of aminopyridinyl phosphines (rac)-6-(o-Anisylphenylphosphino)-2-pivaloylaminopyridine (4a) N N O H P O C 23 H 25 N 2 O 2 P Mol. Wt.: 392.43 To a solution of 2.42 g 2-bromo-6-N-pivaloylaminopyridine (9.4 mmol, 0.8 eq.) in 30 ml THF was added at-100°C 11.7 ml n-butyl-lithium (1.60 M in hexane, 18.8 mmol, 1.6 eq.) during 20 min. The mixture was stirred for 1 h, then a solution of 2.95 g o-anisylchlorophosphine (11.8 mmol, 1.0 eq.) in 10 ml THF was added slowly. After stirring 30 min at-100°C, the yellow solution was allowed to warm to room temperature and stirred 24 h at this temperature. The solvent was removed under reduced pressure and the residue was filtrated through a plug of silica to remove salts. The filtrate was concentrated in vacuo and purified via flash chromatography (Cy:EtOAc 10:1) to yield 1.84 g of the title compound 4a (4.7 mmol, 50%) as a white foam.