Mechanistic Investigation of Intramolecular Aminoalkene and Aminoalkyne Hydroamination/Cyclization Catalyzed by Highly Electrophilic, Tetravalent Constrained Geometry 4d and 5f Complexes. Evidence for an M−N σ-Bonded Insertive Pathway

Stubbert, Bryan D.; Marks, Tobin J.

doi:10.1021/ja0675898

Cited by 195 publications

(168 citation statements)

References 72 publications

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“…The {S-2}-related resonances are broad, and the zirconium-containing product is not characterized. The lack of activity for this zirconium monoamido chloride complex is remarkable in comparison to the related constrained geometry (CG = Me 2 Si(C 5 Me 4 )Nt-Bu) system, 25 in which the mixed {CG}Zr(NMe 2 )Cl is more reactive than the corresponding diamide complex for cyclizations.…”

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confidence: 84%

Highly Enantioselective Zirconium-Catalyzed Cyclization of Aminoalkenes

et al. 2013

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Aminoalkenes are catalytically cyclized in the presence of cyclopentadienylbis(oxazolinyl)borato group 4 complexes {PhB(C5H4)(OxR)2}M(NMe2)2 (M = Ti, Zr, Hf; OxR = 4,4-dimethyl-2-oxazoline, 4S-isopropyl-5,5-dimethyl-2-oxazoline, 4S-tert-butyl-2-oxazoline) at room temperature and below, affording five-, six-, and seven-membered N-heterocyclic amines with enantiomeric excesses of >90% in many cases and up to 99%. Mechanistic investigations of this highly selective system employed synthetic tests, kinetics, and stereochemistry. Secondary aminopentene cyclizations require a primary amine (1-2 equiv vs catalyst). Aminoalkenes are unchanged in the presence of a zirconium monoamido complex {PhB(C5H4)(Ox4S-iPr,Me2)2}Zr(NMe2)Cl or a cyclopentadienylmono(oxazolinyl)borato zirconium diamide {Ph2B(C5H4)(Ox4S-iPr,Me2)}Zr(NMe2)2. Plots of initial rate versus [substrate] show a rate dependence that evolves from first-order at low concentration to zero-order at high concentration, and this is consistent with a reversible substrate-catalyst interaction preceding an irreversible step. Primary kinetic isotope effects from substrate conversion measurements (k′obs(H)/k′obs(D) = 3.3 ± 0.3) and from initial rate analysis (k2(H)/k2(D) = 2.3 ± 0.4) indicate that a N-H bond is broken in the turnover-limiting and irreversible step of the catalytic cycle. Asymmetric hydroamination/cyclization of N-deutero-aminoalkenes provides products with higher optical purities than obtained with N-proteo-aminoalkenes. Transition state theory, applied to the rate constant k2 that characterizes the irreversible step, provides activation parameters consistent with a highly organized transition state (ΔS⧧ = −43(7) cal·mol-1 K-1) and a remarkably low enthalpic barrier (ΔH⧧ = 6.7(2) kcal·mol-1). A six-centered, concerted transition state for C-N and C-H bond formation and N-H bond cleavage involving two amidoalkene ligands is proposed as most consistent with the current data. ABSTRACT: Aminoalkenes are catalytically cyclized in the presence of cyclopentadienylbis(oxazolinyl)borato group 4 complexes {PhB(C 5 H 4 )(Ox R ) 2 }M(NMe 2 ) 2 (M = Ti, Zr, Hf; Ox R = 4,4-dimethyl-2-oxazoline, 4S-isopropyl-5,5-dimethyl-2-oxazoline, 4S-tert-butyl-2-oxazoline) at room temperature and below, affording five-, six-, and seven-membered N-heterocyclic amines with enantiomeric excesses of >90% in many cases and up to 99%. Mechanistic investigations of this highly selective system employed synthetic tests, kinetics, and stereochemistry. Secondary aminopentene cyclizations require a primary amine (1−2 equiv vs catalyst). Aminoalkenes are unchanged in the presence of a zirconium monoamido complex {PhB(C 5 H 4 )(Ox 4S-iPr,Me 2 ) 2 }Zr(NMe 2 )Cl or a cyclopentadienylmono(oxazolinyl)borato zirconium diamide {Ph 2 B(C 5 H 4 )-(Ox 4S-iPr,Me 2 )}Zr(NMe 2 ) 2 . Plots of initial rate versus [substrate] show a rate dependence that evolves from first-order at low concentration to zero-order at high concentration, and this is consistent with a reversible substrate−catalyst interac...

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confidence: 84%

Highly Enantioselective Zirconium-Catalyzed Cyclization of Aminoalkenes

et al. 2013

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“…[64] Both authors proposed that the new C À N bond forms by migratory insertion. In addition, Majumder and Odom reported the intramolecular hydroamination of primary aminoalkenes catalyzed by titanium and zirconium dipyrrolylmethane complexes.…”

Section: Catalytic Reactions Involving Insertions Into the Metal-nitrmentioning

confidence: 99%

Migratory Insertion of Alkenes into Metal–Oxygen and Metal–Nitrogen Bonds

Hanley

Hartwig

2013

Angew Chem Int Ed

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The insertion of an unsaturated ligand into a MC or MH bond proceeds through migratory insertion, a fundamental organometallic reaction. Recent literature documents evidence of the migratory insertion of alkenes into an MO and MN bonds for alkene alkoxylation and alkene amination reactions, respectively. Herein we provide an overview of the literature and a perspective on how these recent experiments relate to classic experiments on CO and CN bond formation with alkene complexes of the late transition metals.

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“…The desired mixed cyclopentadiene-bis(2-oxazoline) proligands are synthesized by reaction of nucleophilic lithium bis(2-oxazolinyl)methylcarbide and iodocyclopentadiene reagents. In the first example, reaction of C 5 (Figure 1).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…4 This reactivity contrasts with that reported for constrained-geometry group 4 catalysts in hydroamination, which require more forcing conditions. 5 Trivalent rare earth catalysts supported by constrainedgeometry-type ligands are highly reactive for hydroamination/ cyclization reactions, 6 in contrast to the group 4 examples. Monoanionic constrained-geometry-like cyclopentadienyl phosphazene or 2,2-bis(pyrazol-1-yl)ethyl lutetium dialkyl compounds (bpzcp)Lu(CH 2 SiMe 3 ) 2 (bpzcp = 2-[2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethyl]-1,3-cyclopentadiene) also catalyze the cyclization of aminoalkenes to 2-alkylpyrrolidines.…”

Section: ■ Introductionmentioning

confidence: 99%

Cyclopentadienyl-bis(oxazoline) Magnesium and Zirconium Complexes in Aminoalkene Hydroaminations

Eedugurala

Hovey

et al. 2015

Organometallics

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A new class of cyclopentadiene-bis(oxazoline) compounds and their piano-stool-type organometallic complexes have been prepared as catalysts for hydroamination of aminoalkenes. The two compounds MeC(Ox Me2 ) 2 C 5 H 5 (Bo M CpH; Ox Me2 = 4,4-dimethyl-2-oxazoline) and MeC-(Ox Me2 ) 2 C 5 Me 4 H (Bo M Cp tet H) are synthesized from C 5 R 4 HI (R = H, Me) and MeC(Ox Me2 ) 2 Li. These cyclopentadienebis(oxazolines) are converted into ligands that support a variety of metal centers in piano-stool-type geometries, and here we report the preparation of Mg, Tl, Ti, and Zr compounds. Bo M CpH and Bo M Cp tet H react with MgMe 2 (O 2 C 4 H 8 ) 2 to give the magnesium methyl complexes {Bo M Cp}MgMe and {Bo M Cp tet }MgMe. Bo M CpH and Bo M Cp tet H are converted to Bo M CpTl and Bo M Cp tet Tl by reaction with TlOEt. The thallium derivatives react with TiCl 3 (THF) 3 to provide [{Bo M Cp}TiCl(μ-Cl)] 2 and [{Bo M Cp tet }TiCl(μ-Cl)] 2 , the former of which is crystallographically characterized as a dimeric species. Bo M CpH and Zr(NMe 2 ) 4 react to eliminate dimethylamine and afford {Bo M Cp}Zr(NMe 2 ) 3 , which is crystallographically characterized as a monomeric four-legged piano-stool compound. {Bo M Cp}Zr(NMe 2 ) 3 , {Bo M Cp}MgMe, and {Bo M Cp tet }MgMe are efficient catalysts for the hydroamination/cyclization of aminoalkenes under mild conditions.

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Mechanistic Investigation of Intramolecular Aminoalkene and Aminoalkyne Hydroamination/Cyclization Catalyzed by Highly Electrophilic, Tetravalent Constrained Geometry 4d and 5f Complexes. Evidence for an M−N σ-Bonded Insertive Pathway

Cited by 195 publications

References 72 publications

Highly Enantioselective Zirconium-Catalyzed Cyclization of Aminoalkenes

Highly Enantioselective Zirconium-Catalyzed Cyclization of Aminoalkenes

Migratory Insertion of Alkenes into Metal–Oxygen and Metal–Nitrogen Bonds

Cyclopentadienyl-bis(oxazoline) Magnesium and Zirconium Complexes in Aminoalkene Hydroaminations

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