Stereoselective Synthesis of Tertiary Allylic Amines by Titanium‐Catalyzed Hydroaminoalkylation of Alkynes with Tertiary Amines

Kaper, Tobias; Geik, Dennis; Fornfeist, Felix; Schmidtmann, Marc; Doye, Sven

doi:10.1002/chem.202103931

Cited by 10 publications

(13 citation statements)

References 41 publications

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“…While significant advances in the field of alkene hydroaminoalkylation catalysis with early transition-metal complexes have been realized, catalytic hydroaminoalkylation of alkyne substrates has only been recently reported. − Stoichiometric alkyne hydroaminoalkylation was pioneered by the Buchwald group and further developed by Norton and others (Scheme ). ,,, In these reports, insertion of alkynes into the Zr–C bond of zirconaaziridine complexes, supported by cyclopentadienyl-derived ligands (e.g., A ), resulted in the formation of isolable five-membered metallacyclic complexes ( B ).…”

Section: 3-(no) Zirconium Complexes For Hydrofunctionalization Reactionsmentioning

confidence: 99%

From Stoichiometric to Catalytic E–H Functionalization by Non-Metallocene Zirconium Complexes─Recent Advances and Mechanistic Insights

Bahena

Schafer

2022

ACS Catal.

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The chemistry of group 4 elements has historically been dominated by the use of metallocene complexes in stoichiometric transformations. While this area continues to be widely explored, the development of non-cyclopentadienyl-based ligands has substantially contributed to the increase in applicability of group 4 metals in catalysis during the last 15 years. In addition to their application in polymerization catalysis, zirconium complexes supported by nitrogen-based anionic ligands have been useful as catalysts for a variety of E–H functionalization reactions. Two particular zirconium systems, (1) bis(ureate)-supported zirconium complexes reported by the Schafer group and (2) tripodal triamidoamine-supported zirconium complexes employed by the Waterman group, promote a variety of E–E′ bond-forming catalytic processes upon E/E′–H activation. The former system has been exploited for catalytic hydroamination, hydroaminoalkylation, and hydroalkynylation (alkyne dimerization) reactions, and the latter system has been used in hydrophosphination and dehydrocoupling reactions. This Perspective focuses on the bountiful reactivity of these catalytic systems with an emphasis on mechanistic insights of these transformations gained from a combination of kinetic analyses, isolation of reaction intermediates, stoichiometric reactivity studies, and computational calculations. The insights generated from this approach have revealed a series of features that enable catalytic E–E′ bond formation and that can contribute to guided efforts in early transition-metal ligand design. For the zirconium bis(ureate) system, the expanded coordination sphere promoted by the multidentate ligand facilitates the coordination of neutral amine donors that are essential for realizing innersphere E–H bond formation in hydrofunctionalization catalysis. For the triamidoamine-supported zirconium complexes, the noninnocent tripodal ligand mediates E–H bond formation/activation during catalysis. For both zirconium systems, the highly ionic nature of the chelating ligands has been shown to induce significant polarization of reactive Zr–E bonds (E = N, C, P). This bond polarization translates into exceptionally reactive Zr–E bonds, akin to those of rare earth metals, enabling σ-bond insertion reactions for E–E′ bond formation. The goal of this Perspective is to highlight examples where compelling evidence has been gathered demonstrating ligand design effects to promote zirconium catalysis. Lessons learned from the featured zirconium systems aim to highlight ligand design features that will advance new directions in early transition-metal catalysis.

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Section: 3-(no) Zirconium Complexes For Hydrofunctionalization Reactionsmentioning

confidence: 99%

From Stoichiometric to Catalytic E–H Functionalization by Non-Metallocene Zirconium Complexes─Recent Advances and Mechanistic Insights

Bahena

Schafer

2022

ACS Catal.

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“…Finally, we tested several other homoleptic early transition metal alkyl complexes that are known hydroaminoalkylation catalysts, such as Ti(CH2SiMe3)4 and ZrBn4, 22,27,65 With L1 ligand, none of them gave no observable photo reactivity (Entry 11-13), suggesting the unique reactivity of Ta complex under photonic excitation.…”

Section: Early Transition Metal Complex Reactivity Screeningmentioning

confidence: 99%

“…Also, less toxic and less expensive early-transition metals (ETM) from groups 3, 4 and 5, including earth abundant metals like titanium can be used as catalysts. [22][23][24][25][26] In recent years this strategy has proven to be an efficient, thermally promoted reaction. However, like many other C-H functionalization reactions, this transformation often requires very high reaction temperatures of up to 180 °C.…”

Section: Introductionmentioning

confidence: 99%

Tantalum Ureate Complexes for Photocatalytic Hydroaminoalkylation

Hao,

Manßen,

Schafer

2022

Preprint

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Using a tantulum ureate pre-catalyst, photocatalytic hydroaminoalkylation of unactivated alkene with unprotected amine at room temperature is demonstrated. The conbination of Ta(CH2SiMe3)3Cl2 and ureate ligand with saturated cyclic backbone resulted in unique reactivity. The substrate scope of Ta photocatalytic hydroaminoalkylation (β-alkylation of amine) was evaluated. Preliminary investigation on reaction mechanism suggests both similarities and differences with Ta catalyzed hydroaminoalkyaltion under thermo conditions

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“…Early transition-metal-catalyzed hydroaminoalkylation of unsaturated substrates other than alkenes has recently been shown to expand the scope of nitrogen-containing molecules that can be synthesized through this C–C bond-forming strategy. − For example, intermolecular hydroaminoalkylation of allenes enables the formation of allylic amines, with a homoallylic amine isomer as a minor side-product. , To assemble allylic amines in a more selective manner and from commercially available feedstocks, the catalytic hydroaminoalkylation of alkynes was disclosed by our group using a bis(ureate)-supported zirconium catalyst and by the Doye group using titanium-based catalysts. , Preliminary studies of these catalyst systems have suggested that alkyne hydroaminoalkylation proceeds through an analogous mechanism to that of the alkene variant (Scheme b). , …”

Section: Introductionmentioning

confidence: 99%

“…23,24 To assemble allylic amines in a more selective manner and from commercially available feedstocks, the catalytic hydroaminoal-kylation of alkynes was disclosed by our group using a bis(ureate)-supported zirconium catalyst 25 and by the Doye group using titanium-based catalysts. 26,27 Preliminary studies of these catalyst systems have suggested that alkyne hydroaminoalkylation proceeds through an analogous mechanism to that of the alkene variant (Scheme 1b). 29,30 In this mechanism, a catalytically active metallaaziridine intermediate A is formed upon N−H/C−H activation from the corresponding bis(amido) precatalyst (Scheme 1b).…”

Section: ■ Introductionmentioning

confidence: 99%

Mechanistic Investigation of Zirconium-Catalyzed Hydroaminoalkylation of Alkynes: Substrate and Ligand Effects

2023

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The mechanism of zirconium-catalyzed hydroaminoalkylation of diphenylacetylene, and the origin of the contrasting reactivity with N-benzylaniline or N-(trimethylsilyl)benzylamine substrates, have been investigated. Isolated intermediates have revealed that the nature of the C−H activation and C−C bondforming steps in alkyne hydroaminoalkylation are analogous to those of the alkene variant, regardless of the amine substrate. In the zirconium-catalyzed hydroaminoalkylation of alkynes, the open coordination sphere at the zirconium center, supported by the bis(ureate) ligand, enables the coordination of neutral protic donors. This is essential for promoting catalytic turnover in these reactions. Under catalytic conditions, dimethylamine acts as a proton source for releasing the allylic amine products while minimizing the formation of side products. Additionally, we identified the formation of a homoleptic tetra(ureate) zirconium complex as the main catalyst decomposition pathway in catalytic alkyne hydroaminoalkylation. The formation of similar homoleptic structures is further favored when employing smaller bis(urea) proligands, thus explaining the poor performance of some ligands in catalysis. However, further increasing the bis(urea) proligand size to minimize such catalyst decomposition favors isomerization side-products resulting in reduced yields of the desired product. This study provides ligand design principles that guide the development of coordinatively flexible catalysts to achieve catalytic turnover in systems that rely upon protonolysis steps, as in hydroaminoalkylation.

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Stereoselective Synthesis of Tertiary Allylic Amines by Titanium‐Catalyzed Hydroaminoalkylation of Alkynes with Tertiary Amines

Cited by 10 publications

References 41 publications

From Stoichiometric to Catalytic E–H Functionalization by Non-Metallocene Zirconium Complexes─Recent Advances and Mechanistic Insights

From Stoichiometric to Catalytic E–H Functionalization by Non-Metallocene Zirconium Complexes─Recent Advances and Mechanistic Insights

Tantalum Ureate Complexes for Photocatalytic Hydroaminoalkylation

Mechanistic Investigation of Zirconium-Catalyzed Hydroaminoalkylation of Alkynes: Substrate and Ligand Effects

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