Group 3 metal complexes based on a chiral tetradentate diamine-diamide ligand: Synthesis and use in polymerization of (d,l)-lactide and intramolecular alkene hydroamination catalysis

Heck, Romain; Schulz, Emmanuelle; Collin, Jacqueline; Carpentier, Jean‐François

doi:10.1016/j.molcata.2006.12.030

Cited by 66 publications

(44 citation statements)

References 47 publications

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“…We have studied the precatalyst structures, pursued structure/activity/selectivity relationships for precatalysts and substrate combinations, and correlated these observations with kinetic effects to better understand this highly active and highly enantioselective system for C−N bond formation. [7] (eq 2). However, the conditions for synthesis and the complex stability vary significantly for the metal−ligand pairs.…”

Section: ■ Introductionmentioning

confidence: 99%

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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Section: ■ Introductionmentioning

confidence: 99%

Highly Enantioselective Zirconium-Catalyzed Cyclization of Aminoalkenes

et al. 2013

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“…Yttrium complex 4 allows the 94% complete conversion of 1000 equiv of lactide within 1 h at room temperature in toluene at [rac-LA] ¼ 1.0 mol L À1 (Table 4, entry 2). Polymerizations with this yttrium initiator/catalyst proceed much more slowly in THF (Table 4, entry 6), presumably due to the competitive coordination between the monomer and this donor solvent, as often observed in this type of ROP reactions promoted by oxophilic meta-based systems [44,87]. This difference in activity between toluene and THF solvent is not observed with complexes 3 and 5 (Table 4, entries 1, 3, 5 and 7); however, the ytterbium complex 5 is less active than yttrium complex 4 in toluene medium (Table 4, entries 2 and 3).…”

Section: Catalytic Activitymentioning

confidence: 78%

Synthesis, structure, and catalytic activity of organolanthanides with chiral biphenyl-based tridentate amidate ligands

Wang

Zhang

Song

et al. 2011

Journal of Organometallic Chemistry

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“…reported low enantioselectivities of 11% ee combined with remarkable conversions (95-100%) for the asymmetric intramolecular hydroamination of aminoalkenes 1a-b into the corresponding chiral pyrrolidines 2a-b performed at 25°C and catalyzed with 5-7 mol% of complex 3 (Scheme 1) [17]. The catalyst was readily prepared prior to the reaction by mixing the corresponding chiral tetradentate nitrogen ligand with Y[N(TMS) 2 ] 3 in toluene at room temperature.…”

Section: Intramolecular Hydroaminationsmentioning

confidence: 99%

“…2a: R,R = (CH 2 ) 5 , n = 1: > 95% conversion, 42% ee (S) 2b: R = Me, n = 1: > 95% conversion, 25% ee (S) 2d: R = Ph, n = 1: > 95% conversion, 11% ee (S) Cl Ar = 2,6-i-Pr 2 C 6 H 3 2b: R = Me, n = 1: 95% conversion, 90% ee (S) 2d: R = Ph, n = 1: 90% conversion, 64% ee (S) 2e: R = Me, n = 2: 87% conversion, 73% ee (S) 2f: R,R = (CH 2 ) 4 , n = 1: 90% conversion, 78% ee (S) [17,18,19,20]. (87-100%) were reported by these authors for the synthesis of pyrrolidines 2a-b,d,g by using at 25°C 6 mol% of another type of yttrium catalyst, such as chiral amido alkyl complex 9 [23].…”

Section: (3-4 Mol%) 60°cmentioning

confidence: 99%

Recent developments in enantioselective yttrium-catalyzed transformations

Pellissier

2016

Coordination Chemistry Reviews

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Group 3 metal complexes based on a chiral tetradentate diamine-diamide ligand: Synthesis and use in polymerization of (d,l)-lactide and intramolecular alkene hydroamination catalysis

Cited by 66 publications

References 47 publications

Highly Enantioselective Zirconium-Catalyzed Cyclization of Aminoalkenes

Highly Enantioselective Zirconium-Catalyzed Cyclization of Aminoalkenes

Synthesis, structure, and catalytic activity of organolanthanides with chiral biphenyl-based tridentate amidate ligands

Recent developments in enantioselective yttrium-catalyzed transformations

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