Hydrosilylation Of Acetophenone Research Articles

Palladium and Rhodium Complexes with Planar-Chiral Carborane Ligands

Base degradation of the prochiral 1-diphenylphosphanyl-2-phenyl-1,2-dicarba-closo-dodecaborane (1) affords the planar-chiral 7-diphenylphosphanyl-8-phenyl-7,8-dicarba-nido-undecaborate anion (2). Resolution of the racemic anion carried out using a well-established procedure, gave the internally diastereomeric palladium complexes 3R-R and 3R-S. These complexes were separated by fractional crystallization. A single-crystal X-ray analysis of 3R-R established the exo-nido bonding of the carborane ligand via the phosphorus atom and the adjacent BH group, and the (R) configuration of the carborane ligand. The enantiomerically pure anions of 2 were liberated from the diastereomerically pure palladium complexes 3R-R and 3R-S, respectively, by subsequent addition of HCl and NaCN. The exo-nido-rhodium−carborane complexes 4−8 were prepared by heating 2eR or 2eS with [Rh(COD)Cl]2 and/or a chiral chelating phosphane, such as DIOP and BINAP, under reflux. The chiral complexes were tested under enantioselective catalysis conditions such as hydrogenation of acetamidocinnamic acid, hydrogenation of ketopantolactone, and hydrosilylation of acetophenone.

New chiral 2,2′:6′,2″-terpyridines as ligands for asymmetric catalysis: cyclopropanation and hydrosilylation reactions

A number of new chiral 2,2′:6′,2″-terpyridines were prepared and the corresponding rhodium and ruthenium complexes were assessed as chiral catalysts for the enantioselective hydrosilylation of acetophenone with diphenylsilane and for the cyclopropanation of styrene with ethyl diazoacetate. Enantioselectivities up to 59% in the cyclopropanation and up to 13% in the hydrosilylation were obtained.

Chiral ligands with pyridine donors in transition metal catalyzed enantioselective cyclopropanation and hydrosilylation reactions

Copper(I) and rhodium(I) complexes prepared in situ from [Cu(OTf)(C 6H 6) 0.5] and [Rh(cod)Cl] 2 with a range of chiral 2,2′-bipyridines, 5,6-dihydro-1,10-phenanthrolines, 1,10-phenanthrolines and 2,2′:6′,2′′-terpyridines were assessed as chiral catalysts for the enantioselective cyclopropanation of styrene with diazoacetates and for the hydrosilylation of acetophenone with diphenylsilane. Enantioselectivities up to 68% in the cyclopropanation and up to 32% in the hydrosilylation were obtained.

Mixed donor ligands based on sp2-hybridized nitrogen donors: asymmetric hydrosilylation catalyzed by rhodium complexes that contain the 2-(2-oxazolin-2-ylmethyl)pyridine system

The synthesis and coordination chemistry of a mixed pyridine–oxazoline bidentate ligand, 2-(2-oxazolin-2-ylmethyl)pyridine, are described. Crystal structure data along with variable temperature NMR studies establish the structures of achiral and chiral versions of this ligand system. In addition, the catalytic asymmetric hydrosilylation of acetophenone has been examined.

Enantioselective catalysis. Part 119: New chiral 2-(2-pyridinyl)oxazoline ligands containing an additional optically active substituent in the pyridine system

The synthesis of novel chiral nitrogen ligands and their precursors is described. They consist of an optically active oxazoline bound to pyridine in the 2-position. In addition, another optically active substituent is attached to the pyridine ring. The effect of the two independent stereogenic units in one ligand was studied in the Rh(I)-catalysed enantioselective hydrosilylation of acetophenone with diphenylsilane.

Synthesis of New Chiral P,S Hybrid Ligands and Their Use in Asymmetric Hydrosilylation of Ketones.

Novel chiral P,S-hybrid ligands bearing 1,2-cis phosphinomethyl (or thiomethyl) and thio (or phosphino) groups on a cyclopentane skeleton were prepared by using borane as a protecting group for the phosphino group. Asymmetric hydrosilylation of acetophenone with 1 mol% of rhodium complex catalysts prepared in situ from [Rh(COD)Cl] 2 and P,S ligands, (1R,2R)-2-(diphenylphosphino)methyl-1-(phenylthio)cyclopentane (TPCP) and (1R,2S)-1-diphenylphosphino-2-[(phenylthio)methyl]cyclopentane (PTCP) gave the corresponding alcohols. The asymmetric hydrosilylation with the ligand TPCP showed higher enantioselectivity than that with PTCP or a diphosphine ligand (1R,2R)-1-(diphenylphosphino)-2-[(diphenylphosphino)methyl]cylopentane (PPCP).

Novel C2-symmetric chiral bisoxazoline ligands in rhodium(I)-catalyzed asymmetric hydrosilylation

Novel C 2-symmetric chiral bisoxazoline ligands with four asymmetric centers were readily synthesized from the two enantiomers of tartaric acid and several aminoacids via the corresponding bis(β-hydroxylamide)s and dimesylates as successive intermediates. With these novel chiral bisoxazoline ligands, rhodium(I)-catalyzed hydrosilylation of acetophenone was carried out and the effects of the combination of the four asymmetric centers as well as the substituent on oxazoline ring of the ligands on the reaction were studied.

ChemInform Abstract: Enantioselective Catalysis. Part 94. The “Diphenyl Effect” in the Enantioselective Hydrosilylation of Acetophenone with Diphenylsilane Using Rh/5,5‐Diphenyl‐2‐(2‐pyridinyl)oxazoline Catalysts.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Enantioselective catalysis 94. The “diphenyl effect” in the enantioselective hydrosilylation of acetophenone with diphenylsilane using Rh/5,5-diphenyl-2-(2-pyridinyl)oxazoline catalysts

The 5,5-diphenyl-2-(2-pyridinyl)oxazolines 2a-e give ee values 9.6 – 34.2 % higher than their unsubstituted counterparts 1a-e in the Rh-catalyzed enantioselective hydrosilylation of acetophenone with diphenylsilane.

Enantioselective addition of diethylzinc to aldehydes catalyzed by pyridineoxazolinealcohols

Chiral 2-pyridylcarbinols carrying chiral oxazolyl substituents in the 6-position of the pyridine ring catalyze the enantioselective addition of diethylzinc to aromatic aldehydes. The absolute configuration of the product alcohol is determined by the configuration at the stereogenic center bearing the alcohol group, the effect of the oxazoline ring being to increase the stereoselectivity. Attempts to use methyl ether derivatives of the same ligands in the rhodium-catalyzed hydrosilylation of acetophenone did not result in any observed enantioselectivity.

Asymmetrische Katalysen, 76. Rh-katalysierte enantioselektive Hydrosilylierung von Acetophenon mit einem polymergebundenen Pyridinoxazolin / Asymmetric Catalysis, 76. Rh-Catalyzed Enantioselective Hydrosilylation of Acetophenone by a Polymer-Bound Pyridineoxazoline

In the enantioselective hydrosilylation of acetophenone with diphenylsilane, a polystyrenebound heterogeneous Rh/pyridineoxazoline catalyst achieved higher optical inductions than a comparable homogeneous catalyst. After using the polymeric catalyst 8—10 times, the catalytic activity decreased markedly and an inversion of the product configuration was observed, the enantiomeric excess rising to 92% ee. These results indicate that the polymeric catalyst contains several catalytically active species with different enantioselectivity and stability.

Enantioselektive Katalysen: LXXVIII. Der optisch aktive Phosphido-verbrückte Eisenkomplex [(η 5C 5H 5) 2Fe 2(μ-H)(μ-PMen 2)(CO) 2] — Synthese, Isome

The hydrido-phosphido-bridged complex [(η 5-C 5H 5) 2Fe 2(μ-H)(μPMen 2)(CO) 2] ( 3) is prepared from [(η 5-C 5H 5)Fe(CO) 2] 2 ( 1) and dimenthylphosphine HPMen 2 in boiling toluene. The reaction proceeds via the intermediate [(η 5-C 5H 5) 2Fe 2(HPMen 2)(CO) 3] ( 2). 2 forms a pair of cis- trans isomers, whereas 3 consists of three isomers, the meso-isomer cis- 3 and the two diastereomers trans- 3a and trans- 3b. In hot toluene, 2 gives 1 and 3. In solution, 3 undergoes a photochemical cis- trans isomerization reaction. 3 is an enantioselective catalyst in the photochemical hydrosilylation of acetophenone with diphenylsilane to give 1-phenylethanol in up to 33% ee.

ChemInform Abstract: Enantioselective Catalysis. Part 74. Ligand Excess and Intermediates in the Rhodium‐Catalyzed Enantioselective Hydrosilylation of Acetophenone with Pyridineoxazoline Ligands.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Enantioselektive Katalysen: LX . Addition von optisch aktiven Aminen an P-substituierte Olefine

The Addition of the optically active amines (−)-1-phenylethylamine, (+)-1-phenylethylamine, and (+)-3-aminomethylpinane to diphenylvinylphosphine oxide or 1,1-bis(diphenylphospino)ethene sulfide gives new PN compounds which were used as cocatalysts in the cross coupling of 1-phenylethyl Grignard with vinylbromide and in the hydrosilylation of acetophenone with diphenylsilane.

Asymmetrische Katalysen: LXXV. Enantioselektive Hydrosilylierung von Acetophenon mit Pyridinyloxazolin-kobalt(I)-Komplexen als Katalysatoren

In situ catalysts cobalt(I)/pyridinyloxazoline give satisfactory enantioselectivities and high chemical yields in the asymmetric hydrosilylation of acetophenone with diphenylsilane.

Asymmetrische Katalysen, 71 / Asymmetric Catalyses, 71

The enantioselective hydrosilylation of acetophenone with diphenylsilane in the solvents toluene and CCl4 was catalysed with a [Rh(COD)Cl]2/2-pyridineoxazoline catalyst. The “CCl4-effect” (higher enantioselectivity and reactivity) was already confirmed with stoichiometric quantities of CCl4 with respect to the Rh-catalyst. The influence of other halogenated solvents on the hydrosilylation was investigated.

Enantioselektive Katalysen: LIX. Addition von optisch aktiven P-H-Verbindungen an P-substituierte Olefine

The base-catalyzed addition of the optically active P-H phospholanes tarpholane and diopholane to olefins activated by diphenylphosphino or diphenylphosphinoyl groups gives unsymmetrical chelate phosphines which are used as cocatalysts in the hydrogenation of ( Z)-α- N-acetamidocinnamic acid, in the cross-coupling of 1-phenylethyl Grignard with vinylbromide, and in the hydrosilylation of acetophenone with diphenylsilane.

Synthesis of (C 5H 5)Fe(CO)(SiHPh 2) 2H, a catalytically active intermediate in the hydrosilylation of acetophenone by diphenylsilane

The well-known iron complex (η-C 5H 5)Fe(CO) 2(CH 3), 3, is an efficient catalyst for the hydrosilylation of acetophenone by diphenylsilane. During the reaction the new complex (C 5H 5)Fe(CO)(SiHPh 2) 2H, 6, is formed. This complex is a catalytically active intermediate in the hydrosilylation reaction; it has been characterised by elemental analysis, IR and 1H-NMR spectroscopy. The observed magnetic equivalence of the two SiH protons is interpreted in terms of classical bonding of the H ligand and the SiHPh 2 groups to the metal centre.

Enantioselective metal complex catalysis. 6. Rhodium catalysts for asymmetric hydrosilylation based on chiral phosphites

A study has been made of the asymmetric hydrosilylation of acetophenone by diphenylsilane under the influence of rhodium complexes with chiral phosphites. The enantioselective nature of the reaction depends on the phosphite structure, the acetophenone/rhodium and ligana/rhodium ratios, and the temperature. The maximum optical yield (24%) is attainod on the complex [Rh(COD)Cl]2/(S, S)-2-ethoxy-4,5-dicarbisopropoxy-1,3-2-dioxophiospholane.

Enantioselective catalysis 74.: Ligand excess and intermediates in the rhodium-catalyzed enantioselective hydrosilylation of acetophenone with pyridineoxazoline ligands

The enantioselective hydrosilylation of acetophenone and diphenylsilane with [Rh(COD)Cl] 2 and the cocatalysts L1 - L4 was investigated. The substitution of hydrogen in the 6-position of the pyridine ring dramatically reduces the dependence of the optical induction on ligand excess, solvent, and concentration of diphenylsilane, acetophenone, and catalyst. The 6-substituents on the pyridine ring are assumed to block one of the coordination sites of rhodium, preventing further interaction with additional ligands, solvents, substrates, and additives.