Modular N,O‐Chelating Ligands: Group‐4 Amidate Complexes for Catalytic Hydroamination

Lee, Alison V.; Schafer, Laurel L.

doi:10.1002/chin.200732267

Cited by 9 publications

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“…A key experimental trend in Ta-catalyzed HAA is the observation that a more electrophilic metal center offers enhanced reactivity. The unsymmetric N , O -chelating ligand of complex I presents computational challenges in that multiple coordination geometries can be readily accessed in the κ 2 binding mode. , Furthermore, these strained 4-membered metallacycles are also known to readily adopt κ 1 binding modes. , To begin, computational work focused on simplified 5-coordinate tantalum complexes Cl 2 TaR(NPhMe) 2 , with R as either an electron-withdrawing (chloro) ( II ) or electron-donating (methyl) ( III ) ligand to explore σ-donor effects upon catalysis (Figure ). For ease of computational resources, N -methyl aniline and propene were selected as model substrates.…”

Section: Resultsmentioning

confidence: 99%

Ta-Catalyzed Hydroaminoalkylation of Alkenes: Insights into Ligand-Modified Reactivity Using DFT

et al. 2018

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Density functional theory (DFT) calculations were performed to probe the mechanism of tantalum-catalyzed hydroaminoalkylation, a reaction that affords Csp3–Csp3 bond formation via α-alkylation of a secondary amine with an alkene. Electronic effects in catalyst design were probed to reveal key features in the energy profile of the proposed mechanism, corroborating experimental trends in which electrophilic metal centers demonstrate enhanced reactivity. Modeling of the energy profile with an N,O-chelating amidate Ta catalyst (I) revealed profound differences in relative energetics, rationalizing improvements that have been observed using sterically and electronically varied ligands. N,O-Chelating ligands electronically promote preferential reactivity in the equatorial plane. The turnover-limiting step can be completely changed depending upon the ligand; for sterically bulky monoamidate complexes, the protonolysis of an intermediate metallacycle is the turnover-limiting step rather than C–H activation, as has been found for systems lacking steric bulk. Unproductive off-cycle pathways were also modeled to compare with experimental studies. These insights contribute to a theoretical understanding of key features in ligand design for developing improved catalysts for hydroaminoalkylation.

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Section: Resultsmentioning

confidence: 99%

Ta-Catalyzed Hydroaminoalkylation of Alkenes: Insights into Ligand-Modified Reactivity Using DFT

et al. 2018

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“…Our goal was to introduce a versatile and hemilabile ligand system that could act as a σ-donor and δ-acceptor at discrete binding sites, thereby facilitating the stabilization of structurally related uranium complexes across multiple oxidation states and enabling us to probe their single- and multielectron reactivity. To address these considerations, we turned to amidates, as this class of ligands is highly tunable, both sterically and electronically, and capable of adopting multiple binding modes. − By using an amidate ligand with an N -aryl substituent, the ligand is capable of binding to the metal center through the tethered arene moiety in addition to the more conventional O- and N-donor sites . Through these efforts, we have isolated three new actinide arene complexes, including a U(II) bis(arene) complex containing a monoreduced arene ligand, and explored the reactivity and electronic structure of these unusual molecules.…”

Section: Introductionmentioning

confidence: 99%

A Uranium(II) Arene Complex That Acts as a Uranium(I) Synthon

et al. 2021

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Two-electron reduction of the amidate-supported U(III) mono(arene) complex U(TDA) 3 (2) with KC 8 yields the anionic bis(areneEPR spectroscopy, magnetic susceptibility measurements, and calculations using DFT as well as multireference CASSCF methods all provide strong evidence that the electronic structure of 3 is best represented as a 5f 4 U(II) metal center bound to a monoreduced arene ligand. Reactivity studies show 3 reacts as a U(I) synthon by behaving as a twoelectron reductant toward I 2 to form the dinuclear U(III)−U(III) triiodide species 6) and as a three-electron reductant toward cycloheptatriene (CHT) to form the U(IV) complex [K[2.2.2]cryptand][U(η 7 -C 7 H 7 )(TDA) 2 (THF)] ( 7). The reaction of 3 with cyclooctatetraene (COT) generates a mixture of the U(III) anion [K[2.2.2]cryptand][U(TDA) 4 ] (1-crypt) and U(COT) 2 , while the addition of COT to complex 2 instead yields the dinuclear U(IV)−U(IV) inverse sandwich complex [U(TDA) 3 ] 2 (μ-η 8 :η 3 -C 8 H 8 ) (8). Two-electron reduction of the homoleptic Th(IV) amidate complex Th(TDA) 4 (4) with KC 8 gives the mono(arene) complex [K[2.2.2]cryptand][Th-(TDA) 3 (THF)] (5). The C−C bond lengths and torsion angles in the bound arene of 5 suggest a direduced arene bound to a Th(IV) metal center; this conclusion is supported by DFT calculations.

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“…Therefore, catalytic methods for the preparation of amines are highly desirable. The hydroamination reaction − represents a highly attractive process in which an amine N–H functionality is added to an unsaturated carbon–carbon linkage, because it is 100% atom economical without formation of any waste byproduct. As many of the targeted amine products are chiral, the development of chiral catalyst systems for asymmetric hydroamination reactions has been the focus of a large number of studies over the last two decades .…”

Section: Introductionmentioning

confidence: 99%

Asymmetric Intra- and Intermolecular Hydroamination Catalyzed by 3,3′-Bis(trisarylsilyl)- and 3,3′-Bis(arylalkylsilyl)-Substituted Binaphtholate Rare-Earth-Metal Complexes

et al. 2018

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The series of novel 3,3′-bis(trisarylsilyl)-and 3,3′-bis(arylalkylsilyl)-substituted binaphtholate rare-earthmetal complexes 2a−i (SiR 3 = Si(o-biphenylene)Ph (a), SiCyPh 2 (b), Si-t-BuPh 2 (c), Si(i-Pr) 3 (d), SiCy 2 Ph (e), Si(2-tolyl)Ph 2 (f), Si(4-t-Bu-C 6 H 4 ) 3 (g), Si(4-MeO-C 6 H 4 )Ph 2 (h), SiBnPh 2 (i)) have been prepared via arene elimination from [Ln(o-C 6 H 4 CH 2 NMe 2 ) 3 ] (Ln = Y, Lu) and the corresponding 3,3′-bis(silyl)-substituted binaphthol. The complexes exhibit high catalytic activity in the hydroamination/ cyclization of aminoalkenes, with activities exceeding 1000 h −1 for (R)-2f-Ln, (R)-2g-Ln, and (R)-2h-Ln in the cyclization of 2,2-diphenylpent-4-enylamine (3a) at 25 °C, while the rigid dibenzosilole-substituted complexes (R)-2a-Ln and the triisopropylsilyl-substituted complexes (R)-2d-Ln exhibited the lowest activity in the range of 150−270 h −1 . Catalysts (R)-2b-Lu, (R)-2c-Lu, (R)-2f-Lu, and (R)-2i-Lu provide the highest selectivities for the majority of the substrates, while the yttrium congeners are usually less selective. The highest enantioselectivities of 96% ee were observed using (R)-2a-Lu and (R)-2c-Lu in the cyclization of (4E)-2,2,5-triphenylpent-4-enylamine (9). The reactions show apparently zero-order rate dependence on substrate concentration and first-order rate dependence on catalyst concentration, with some reactions exhibiting a slightly accelerated rate at high conversion due to a shift in the equilibrium between a less active, higher coordinate catalyst species in favor of a more active, lower coordinate species as a result of weaker binding of the hydroamination product in comparison to the aminoalkene substrate. The shift in equilibrium from the higher to the lower coordinate species is also entropically favored at elevated temperatures, which results in an unusual increase in selectivity in the cyclization of 2,2-dimethylpent-4-enylamine (3d), presumably due to a higher selectivity of the lower coordinate catalyst species. All binaphtholate yttrium complexes, except (R)-2a-Y, are catalytically active in the intermolecular hydroamination of benzylamines with terminal alkenes. The highest selectivity of 66% ee was observed for the reaction of benzylamine with 4-phenyl-1-butene using (R)-2h-Y at 110 °C.

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Modular N,O‐Chelating Ligands: Group‐4 Amidate Complexes for Catalytic Hydroamination

Abstract: ChemInform 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.

Cited by 9 publications

References 0 publications

Ta-Catalyzed Hydroaminoalkylation of Alkenes: Insights into Ligand-Modified Reactivity Using DFT

Ta-Catalyzed Hydroaminoalkylation of Alkenes: Insights into Ligand-Modified Reactivity Using DFT

A Uranium(II) Arene Complex That Acts as a Uranium(I) Synthon

Asymmetric Intra- and Intermolecular Hydroamination Catalyzed by 3,3′-Bis(trisarylsilyl)- and 3,3′-Bis(arylalkylsilyl)-Substituted Binaphtholate Rare-Earth-Metal Complexes

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