Hydrosilylation Of Imines Research Articles

Titanocene-Catalyzed Hydrosilylation of Imines: Experimental and Computational Investigations of the Catalytically Active Species

In this paper we communicate mechanistic investigations of the asymmetric catalytic hydrosilylation of imines using (R,R)-ethylene-1,2-bis(η5-4,5,6,7-tetrahydro-1-indenyl)titanium (R)-1,1′-binaphth-2-olate (1) and (S,S)-ethylene-1,2-bis(η5-4,5,6,7-tetrahydro-1-indenyl)titanium dichloride (2) as catalyst precursors. After activation with RLi (R = alkyl, aryl) and a silane, these complexes are well-known catalysts for hydrosilylation reactions. However, the exact nature of the catalytic active species is still a subject of debate and was therefore investigated by us using experimental (IR, NMR, EPR, GC/MS) and computational methods. Our results indicate an EBTHITiRSiH2Ph compound (EBTHI = ethylene-1,2-bis(η5-4,5,6,7-tetrahydro-1-indenyl), R = alkyl, aryl) as the catalytically active species. This Ti(IV) species is postulated to be responsible for the lower activities of 1 and 2 in contrast to hydrosilylations with ethylene-1,2-bis(η5-4,5,6,7-tetrahydro-1-indenyl)titanium difluoride (3), for which a Ti(III)-H compound was postulated to be the active species.

Development of highly enantioselective new Lewis basic N-formamide organocatalysts for hydrosilylation of imines with an unprecedented substrate profile

l-Pipecolinic acid derived N-formamides have been developed as new Lewis basic organocatalysts that promote the asymmetric reduction of N-aryl ketimines using trichlorosilane as the reducing agent. The substituent on N4 of the piperazinyl backbone and the 2-carboxamide group both proved to have profound effects on the efficacy of the catalyst. The reductions of both N-aryl acyclic methyl ketimines and non-methyl ketimines were catalyzed to afford the desired amines in good to high yield and enantioselectivity. In particular, catalyst 6e enabled the reduction of the difficult bulky ketimines to be highly efficient and enantioselective, affording up to 99% yield and 97% ee. This catalyst proved to prefer the relatively bulkier non-methyl acyclic ketimines to the methyl ketimines as substrate, which is so far unprecedented in catalytic asymmetric reduction of imines.

Zinc‐Catalyzed Enantioselective Hydrosilylation of Imines.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Zinc-Catalyzed Enantioselective Hydrosilylation of Imines

The authors report a nice example of hydrosilylation of imines using inexpensive polymethylhydrosiloxane. This reagent must be used in a mixed solvent system (THF-MeOH) to obtain good selectivity. The use of simple, modular diamines also makes this protocol attractive for future use. N-Diphenylphosphinyl imines were formed stereoselectively and afforded appropriate reactivity for the reduction.

Zinc‐Catalyzed Enantioselective Hydrosilylation of Imines

AbstractThe highly enantioselective reduction of imines is achieved by employing chiral Zn/diamine catalysts. This new catalytic protocol offers attractive features such as use of a non‐precious metal and an inexpensive silane, easy modification of chiral diamine ligands and provides ready access to chiral amines in good yields and with excellent enantioselectivities.

Hydroamination/Hydrosilylation Sequence Catalyzed by Titanium Complexes

A single precatalyst is used for the sequential combination of the Ti-catalyzed hydroamination of alkynes with the Ti-catalyzed hydrosilylation of imines. In this way alkynes and primary amines are converted efficiently into secondary amines in a fully catalytic one-pot process (see scheme).

Synthesis of lanthanide(II)–imine complexes and their use in carbon–carbon and carbon–nitrogen unsaturated bond transformation

Ytterbium and samarium metals reduced aromatic ketimines to give directly divalent azalanthanacyclopropane complexes 1 quantitatively, the structure of which was characterized by X-ray analysis. The imine complexes 1 catalyzed dehydrogenative silylation of terminal alkynes, hydrosilylation of imines and alkenes, and intermolecular hydrophosphination of alkynes. Moreover, dehydrogenative double silylation of conjugated dienes was achieved with 1.

Stoichiometric Hydrosilylation of Nitriles and Catalytic Hydrosilylation of Imines and Ketones Using a μ-Silane Diruthenium Complex

The novel μ-iminosilyl complexes Ru2(CO)4(μ-dppm)(μ-SiTol2)(μ-R‘CHNSiTol2) (2) were obtained in high yields during the stoichiometric reactions of a diruthenium complex having Ru−H−Si interactions, {Ru(CO)2(SiTol2H)}2(μ-dppm)(μ-η2:η2-H2SiTol2) (1), with nitriles R‘CN (R‘ = Me, Ph, t-Bu, CHCH2). The catalytic hydrosilylation of various ketones and imines with dihydrosilanes were achieved using 1 as a catalyst. A novel reaction cycle involving the cooperative functions of the two Ru metals is proposed for the related hydrosilylation of various ketones and imines catalyzed by 1.

Efficient kinetic resolution in the asymmetric hydrosilylation of imines of 3-substituted indanones and 4-substituted tetralones.

Kinetic resolution of the N-methyl imines of 3-substituted indanones and 4-substituted tetralones could be accomplished by hydrosilylation with a chiral titanocene catalyst. N-Methyl imines of 4-substituted tetralones were resolved to yield, after hydrolysis of the unreacted starting materials, ketones with high ee's and the amine products with high diastereomeric and enantiomeric purity. The utility of this process was demonstrated in the synthesis of sertraline.

Dehydrogenative Silylation of Amines and Hydrosilylation of Imines Catalyzed by Ytterbium−Imine Complexes

Dehydrogenative silylation of primary and secondary amines with triphenylsilane was catalyzed by ytterbium−imine complexes, [Yb(η2-Ph2CNAr)(hmpa)n], to give aminosilanes in good yields. In the reaction with diphenyl- and phenylsilanes, diaminosilanes were formed as major products. Whereas n- and sec-alkylamines were readily silylated, tert-alkylamines and aromatic amines exhibited lower reactivities. Moreover, hydrosilylation of imines has been achieved by using phenylsilane and the imine complexes (Ar = Ph, C6H4F-4), giving rise to mono- and diaminosilanes. The two reactions were in agreement as regards the product selectivities and yields.

Iridium-Catalyzed Asymmetric Hydrosilylation of Imines Using Chiral Oxazolinyl-Phosphine Ligands

Chiral oxazolinylphosphines are effective ligands for the Ir(I)-catalyzed asymmetric hydrosilylation of imines to afford the corresponding sec-amines with high enantioselectivities (up to 89% ee) after hydrolysis in almost quantitative yields. The structure of an Ir(I)−oxazolinylferrocenylphosphine complex was determined by X-ray analysis.

Synthesis of NPS R-568 utilizing titanium-catalyzed asymmetric hydrosilylation

The enantioselective hydrosilylation of imines catalyzed by an (EBTHI) Ti (EBTHI=ethylene-bis(η 5-tetrahydroindenyl)) species was applied to the synthesis of NPS R-568, an active compound for the treatment of hyperparathyroidism.

ChemInform Abstract: Short Enantioselective Total Syntheses of the Piperidine Alkaloids (S)‐Coniine and (2R,6R)‐trans‐Solenopsin A via Catalytic Asymmetric Imine Hydrosilylation.

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.

ChemInform Abstract: Amine Additives Greatly Expand the Scope of Asymmetric Hydrosilylation of Imines.

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.

Amine Additives Greatly Expand the Scope of Asymmetric Hydrosilylation of Imines.

Slow addition of a primary amine to the reaction mixture greatly increases the scope of the titanium-catalyzed asymmetric reduction of imines 1. An important added feature of this method is that chiral secondary amines 2 can be obtained in much higher optical purity (up to 99 % ee) than would be predicted from the E:Z ratios of the starting imines 1.

Preparation of Novel Titanium Complexes Bearing o-Phosphinophenol Ligands

The preparation of novel titanium complexes bearing o-phosphinophenol ligands is reported. The feature of this ligand system is that its electronic and steric properties can be independently tuned. The complexes were found to be fluxional by 1H NMR analysis at low temperature. An X-ray structural analysis showed that in the solid state the molecule is chiral at the metal center. These complexes were shown to be effective catalysts for olefin hydrogenation and imine hydrosilylation.

Enantiomerically selective metal complex catalysis. 7. Asymmetric hydrosilylation of imines and oximes on the catalyst [Rh(COD)Cl]2/(S)-phephos

Asymmetric hydrosilylation of acetophenoxime and cyclic and acyclic imines (with subsequent hydrolysis to amines) was investigated using as catalyst a rhodium complex with the chiral phosphinamino ligand (S)-Phephos. With this method the chiral analog of the antidepressant Pyrazidol was synthesized with an optical yield of 73%.

Reduction asymetrique catalysee par des complexes de metaux de transition IV. synthese d'amines chirales au moyen d'un complexe de rhodium et d'isopropylidene dihydroxy-2,3 bis(diphenylphosphino)-1,4 butane (diop)

A chiral rhodium complex with (+)-diop as ligand is used as a catalyst in asymmetric synthesis leading to amines and N-acyl derivatives. Two kinds of reactions are investigated: asymetric hydrogenation of enamides and hydrosilylation of imines. Good optical yields are observed in the synthesis of N-acetyl α-phnenylethylamine (e.e. 45%) and N-acetyl α-phenylpropylamine (e.e. 83%). A strong solvent effect is observed, which can reverse the absolute configuration of tN-acetyl-α-phenylethylamine obtained by reduction of its enamide precursor. N-Benzyl-α-phenyl ethylamine is prepared by hydrosilylation with 65% optical purity. An asymmetric synthesis of 1,2,3,4-tetrahydropapaverine (e.e 38%) and related compounds is described.