Catalytic Asymmetric Hydrogenation of Imines with a Chiral Titanocene Catalyst: Scope and Limitations

Willoughby, Christopher A.; Buchwald, Stephen L.

doi:10.1021/ja00099a012

Cited by 279 publications

(125 citation statements)

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“…The rate-determining step in the titanium-catalyzed hydrogenation of imines has been proposed to be cleavage of the Ti±N bond in the intermediate amido complex through a sbond metathesis pathway; [7] we presume that the same applies to the hydrosilylation reaction. [8] Our previous work implies that this metathesis, which takes place in the crowded wedge of the bis(tetrahydroindenyl) scaffold, is quite sensitive to steric effects.…”

Section: Dedicated To Professor Satoru Masamunementioning

confidence: 99%

“…[8] Our previous work implies that this metathesis, which takes place in the crowded wedge of the bis(tetrahydroindenyl) scaffold, is quite sensitive to steric effects. [7] Specifically, the rate of Ti ± N cleavage for imine substrates with moderate to large nitrogen substituents is very low.…”

Section: Dedicated To Professor Satoru Masamunementioning

confidence: 99%

“…Although a detailed mechanistic study has not yet been undertaken, one possible pathway is the catalytic cycle shown in Scheme 1 a. Amines are obtained with the same absolute configuration as in the case of titanium-catalyzed hydrogenation, which suggests a chirality-transfer step in which the imine is inserted into the TiÐH bond of the titanocene hydride 5 in analogy to the hydrogenation case. [7] The additive would then react with the sterically encumbered titanium ± amido complex 6 to release a chiral amine and to generate the new amido complex 7. Finally, reaction of the less hindered complex 7 with silane regenerates 5.…”

Section: Dedicated To Professor Satoru Masamunementioning

confidence: 99%

“…[4b, 6] At best two substituents could be introduced with electrophilic or nucleophilic reagents, and the methods were limited with regard to the starting porphyrin or the introduction of different substituents. [7] To date, no general method exists for the direct meso substitution of unactivated porphyrins with alkyl or aryl residues or for the introduction of more than two substituents.…”

Section: Dedicated To Professor Satoru Masamunementioning

confidence: 99%

See 3 more Smart Citations

Amine Additives Greatly Expand the Scope of Asymmetric Hydrosilylation of Imines

Verdaguer

Lange

Buchwald

1998

Angewandte Chemie International Edition

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175

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Section: Dedicated To Professor Satoru Masamunementioning

confidence: 99%

Section: Dedicated To Professor Satoru Masamunementioning

confidence: 99%

Section: Dedicated To Professor Satoru Masamunementioning

confidence: 99%

Section: Dedicated To Professor Satoru Masamunementioning

confidence: 99%

See 2 more Smart Citations

Amine Additives Greatly Expand the Scope of Asymmetric Hydrosilylation of Imines

Verdaguer

Lange

Buchwald

1998

Angewandte Chemie International Edition

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175

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show abstract

“…[7] In addition, the less active TiA C H T U N G T R E N N U N G (ebthi)-catalyst displays excellent selectivity in the asymmetric hydrogenation of some cyclic imines. [8] However, for our catalyst screening we selected iridium catalysts as they are the most promising candidates for the reduction of 1.…”

Section: Introductionmentioning

confidence: 99%

Evolutionary Catalyst Screening: Iridium‐Catalyzed Imine Hydrogenation

Kluwer¹,

Detz²,

Abiri³

et al. 2012

Adv Synth Catal

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A high throughput catalyst screening is presented employing an evolutionary approach. The method comprises the optimization of initial leads by subjecting the catalysts to iterative rounds of optimization, including structural elaboration of the ligands by creating new focused libraries. Highly modular supramolecular ligands, robotized synthesis combined by high throughput experimentation creates a platform for fast catalyst development. An illustrative example for the asymmetric hydrogenation of cyclic 2,3,3-trimethyl-3H-indole using iridium catalysts is presented. The kinetic investigation of the best catalyst yields an unusual second order in iridium, first order in hydrogen and zeroth order in substrate. Under optimized reaction conditions a TOF of 100 mol mol À1 h À1 with 96% ee could be obtained with the best catalyst. A full catalyst screening and kinetic study was conducted within a three-week time-frame.

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Formation and Structures of [1,2–Bis(N-tert-butylcarbamoyl)cyclopentadienyl]zirconium Complexes – Coordination Chemistry of a “Fulvenologous” Malonic Amide Anion Ligand System

Klaß¹,

Duda²,

Kleigrewe³

et al. 1999

Eur. J. Inorg. Chem.

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Treatment of sodium cyclopentadienide with two molar equivalents of tert‐butyl isocyanate yields sodium 1,2‐bis(N‐tert‐butylcarbamoyl)cyclopentadienide (6). The [C5H3(1,2‐CONHCMe3)2]Na reagent 6 adds to Cp2Zr(CH3)Cl (8) to yield Cp2Zr(CH3)[C5H3(CONHCMe3)2] (9). In 9 the C5H3(CONHCMe3)2 ligand is bonded to zirconium through one of its carboxamido‐oxygen atoms (ĸO‐coordination). Treatment of 6 with CpZrCl3(THF)2 yields CpZrCl2[C5H3(CONHCMe3)2](THF) 11. In 11 the 1,2‐bis(N‐tert‐butylcarbamoyl)cyclopentadienide moiety serves as a Cs‐symmetric chelate ligand, binding to zirconium through both carbamoyl oxygens (ĸ2O,O′‐coordination). The same seven‐membered metallacyclic structural type is found in the reaction products of 6 with ZrCl4(THF)2 in 1:1 and 2:1 molar ratios. The former yields the distorted octahedral complex ZrCl3[C5H3(CONHCMe3)2](THF) (12), the latter gives the chiral octahedral system ZrCl2[C5H3(CONHCMe3)2]2 (13). In solution, complex 13 undergoes a thermally induced enantiomerization process (Λ → Δ interconversion), for which a Gibbs activation energy of ΔG‡enant = 14.0 ± 0.3 kcal mol−1 was determined by dynamic 1H‐NMR spectroscopy. The ĸ2O,O′‐coordination of the [C5H3(1,2‐CONHCMe3]− ligand in the complexes 11, 12, and 13 was secured by X‐ray crystal structure analyses.

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Catalytic Asymmetric Hydrogenation of Imines with a Chiral Titanocene Catalyst: Scope and Limitations

Cited by 279 publications

References 0 publications

Amine Additives Greatly Expand the Scope of Asymmetric Hydrosilylation of Imines

Amine Additives Greatly Expand the Scope of Asymmetric Hydrosilylation of Imines

Evolutionary Catalyst Screening: Iridium‐Catalyzed Imine Hydrogenation

Formation and Structures of [1,2–Bis(N-tert-butylcarbamoyl)cyclopentadienyl]zirconium Complexes – Coordination Chemistry of a “Fulvenologous” Malonic Amide Anion Ligand System

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