Iridium and Ruthenium Complexes with Chelating N-Heterocyclic Carbenes: Efficient Catalysts for Transfer Hydrogenation, β-Alkylation of Alcohols, and N-Alkylation of Amines

Gnanamgari, Dinakar; Sauer, Effiette L. O.; Schley, Nathan D.; Butler, Chase H.; Incarvito, Christopher D.; Crabtree, Robert H.

doi:10.1021/om800821q

Cited by 357 publications

(203 citation statements)

References 65 publications

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“…5 The overall transformation is based on a process called "borrowing hydrogen" 6 or "hydrogen autotransfer" 7 The first use of homogeneous catalysts for the alkylation of amines with alcohols was described in 1981, and since then a 30 number of metal-containing catalysts, including complexes of ruthenium, rhodium and iridium, have been evaluated in this transformation. 4 Elegant results from the groups of Beller, 8 Williams, 9 Kempe, 10 Fujita, 11 Martín-Matute, 12 Crabtree 13 and Yus 14 have made the alkylation of amines with alcohols an 35 efficient method for the synthesis of a variety of amines. In the past few years, research in this field has focused mainly on iridium-and ruthenium-containing catalysts.…”

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confidence: 99%

Room temperature and solvent-free iridium-catalyzed selective alkylation of anilines with alcohols

Andersson

2013

Chem. Commun.

121

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PostprintThis is the accepted version of a paper published in Chemical Communications. This paper has been peer-reviewed but does not include the final publisher proof-corrections or journal pagination. Citation for the original published paper (version of record):Li, J., Andersson, P. (2013) Room temperature and solvent-free iridium-catalyzed selective alkylation of anilines with alcohols. water is the only byproduct, making it atom-economical. Also, the replacement of toxic alkylating agents by readily available alcohols makes this a greener route for amine synthesis. 5 The overall transformation is based on a process called "borrowing hydrogen" 6 or "hydrogen autotransfer" 7 (Scheme 1). ChemicalScheme 1 "Borrowing hydrogen" or "hydrogen autotransfer" in the alkylation of an amine with an alcohol.The first use of homogeneous catalysts for the alkylation of amines with alcohols was described in 1981, and since then a 30 number of metal-containing catalysts, including complexes of ruthenium, rhodium and iridium, have been evaluated in this transformation. 4 N-Heterocyclic carbenes (NHCs) have found widespread applications as versatile ligands and experienced significant development in transition-metal catalysis in the past few years. 20 The high activity of the iridium catalysts in N-alkylation 55 reactions, combined with the excellent performance of NHCs as ligands in homogeneous catalysis, inspired us to seek an easily accessible and highly active NHC-based iridium catalyst for Nalkylation with alcohols. Here, we report a highly reactive bidentate iridium NHC/phosphine complex that catalyzes the N-60 alkylation of aromatic amines with primary alcohols under mild conditions. Some reactions could even be carried out at room temperature and without solvent.The three-step synthesis of the triphenylphosphinefunctionalized imidazolium salt 1 was reported by Zhou and co-65

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confidence: 99%

Room temperature and solvent-free iridium-catalyzed selective alkylation of anilines with alcohols

Andersson

2013

Chem. Commun.

121

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“…Air-stable Ir and Ru complexes of a chelating pyrimidinefunctionalized N-heterocyclic carbene were synthesized [21] and found to be catalytically active for transfer hydrogenation, and N-alkylation of amines with primary alcohols. The Ir complexes were found to catalyze the N-alkylation of amines using 55 Scheme 8.…”

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confidence: 99%

Important Industrial Procedures Revisited in Flow: Very Efficient Oxidation and N-Alkylation Reactions with High Atom-Economy

Sipos¹,

Gyóllai²,

Sipőcz³

et al. 2013

J Flow Chem

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The atom economy concept is one of the earliest recognition for green and sustainable aspects of organic synthesis. Over the years, novel technologies emerged that made this important feature of reactions into practice. Continuousflow devices increased the efficiency of the chemical transformations with novel process windows (high T, high p and heterogeneous packed catalysts etc.) and increased safety which turned the attention to reexamine old, industrial processes. Oxidation can be performed under flow catalytic conditions with molecular oxygen; alcohols can be oxidized to carbonyl compounds with high atom economy (AE=87 %). Using O 2 and 1 % Au/TiO 2 , alcohol oxidation in flow was achieved with complete conversion and >90 % yield. N-alkylation is another good example for achieving high atom economy. Under flow catalytic conditions (Raney Ni), amines were successfully reacted with alcohols directly (AE=91 %) with >90 % conversion and selectivity. In both examples, the effective residence time was less than 1 min. These two examples demonstrate the significant contribution of flow technology to the realization of key principles in green and sustainable chemistry.

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“…We compared our catalysts in transfer hydrogenation reactions following protocols found in literature [23,24]. We focused on the reduction of acetophenone to 1-phenylethanol using potassium hydroxide (0.1 equiv.)…”

Section: Catalysismentioning

confidence: 99%

Cationic Protic Imidazolylidene NHC Complexes of CpIrCl+ and CpRhCl+ with a Pyridyl Tether Formed at Ambient Temperature

et al. 2018

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Protic NHC (PNHC) complexes with N 1 H, N 2 -alkyl/aryl imidazolylidene ligands are relatively rare, and routes for their synthesis differ from what is used to make non-protic analogs. Prior work from our group and others showed that in the presence of a tethering ligand (phosphine or in one case, pyridine), CpM and Cp*M (M = Ir, Ru) PNHC complexes could be made by heating. Here, we find that the use of ionizing agents to activate [Cp*M III Cl(µ-Cl)] 2 (M = Ir, Rh) allows for what we believe is unprecedented ambient temperature formation of PNHC complexes from neutral imidazoles; the product complexes are able to perform transfer hydrogenation.

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Iridium and Ruthenium Complexes with Chelating N-Heterocyclic Carbenes: Efficient Catalysts for Transfer Hydrogenation, β-Alkylation of Alcohols, and N-Alkylation of Amines

Cited by 357 publications

References 65 publications

Room temperature and solvent-free iridium-catalyzed selective alkylation of anilines with alcohols

Room temperature and solvent-free iridium-catalyzed selective alkylation of anilines with alcohols

Important Industrial Procedures Revisited in Flow: Very Efficient Oxidation and N-Alkylation Reactions with High Atom-Economy

Cationic Protic Imidazolylidene NHC Complexes of CpIrCl+ and CpRhCl+ with a Pyridyl Tether Formed at Ambient Temperature

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Iridium and Ruthenium Complexes with Chelating N-Heterocyclic Carbenes: Efficient Catalysts for Transfer Hydrogenation, β-Alkylation of Alcohols, and N-Alkylation of Amines

Cited by 357 publications

References 65 publications

Room temperature and solvent-free iridium-catalyzed selective alkylation of anilines with alcohols

Room temperature and solvent-free iridium-catalyzed selective alkylation of anilines with alcohols

Important Industrial Procedures Revisited in Flow: Very Efficient Oxidation and N-Alkylation Reactions with High Atom-Economy

Cationic Protic Imidazolylidene NHC Complexes of Cp*IrCl+ and Cp*RhCl+ with a Pyridyl Tether Formed at Ambient Temperature

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Cationic Protic Imidazolylidene NHC Complexes of CpIrCl+ and CpRhCl+ with a Pyridyl Tether Formed at Ambient Temperature