Iron-SNS and -CNS Complexes: Selective C<sub>aryl</sub>–S Bond Cleavage and Amine-Borane Dehydrogenation Catalysis

Elsby, Matthew R.; Ghostine, Karine; Das, Uttam Kumar; Gabidullin, Bulat; Baker, R. Tom

doi:10.1021/acs.organomet.9b00524

“… 13 − 19 Prevalent examples of such systems are metal complexes based on ligands bearing secondary amine donors, 20 which are capable of getting involved in reversible metal-amine/metal-amido interconversion ( Figure 1 a). 13 − 15 , 17 , 18 …”

Section: Introductionmentioning

confidence: 99%

“…Catalysts based on transition metals have provided fast kinetics and a large extent of H 2 release under relatively mild reaction conditions . Particularly, metal complexes stabilized by pincer ligands have been widely investigated because of the enhanced catalyst stability provided by the κ 3 –tridentate ligand coordination. − Moreover, since ammonia–borane is a polar molecule with hydridic (BH) and acidic (NH) hydrogen atoms, transition-metal complexes based on ligands containing Brønsted basic sites have been shown to be particularly adequate to promote H 2 release from AB through the transfer of the hydridic BH to the acidic metal center and the NH proton to the basic ligand functionality (bifunctional catalysts). − Prevalent examples of such systems are metal complexes based on ligands bearing secondary amine donors, which are capable of getting involved in reversible metal-amine/metal-amido interconversion (Figure a). − ,, …”

Section: Introductionmentioning

confidence: 99%

Ammonia–Borane Dehydrogenation Catalyzed by Dual-Mode Proton-Responsive Ir-CNN^H Complexes

Ortega-Lepe

¹

,

Rossin

²

,

Sánchez

³

et al. 2021

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Metal complexes incorporating proton-responsive ligands have been proved to be superior catalysts in reactions involving the H 2 molecule. In this contribution, a series of Ir III complexes based on lutidine-derived CNN H pincers containing N-heterocyclic carbene and secondary amino NHR [R = Ph ( 4a ), t Bu ( 4b ), benzyl ( 4c )] donors as flanking groups have been synthesized and tested in the dehydrogenation of ammonia–borane (NH 3 BH 3 , AB) in the presence of substoichiometric amounts (2.5 equiv) of t BuOK. These preactivated derivatives are efficient catalysts in AB dehydrogenation in THF at room temperature, albeit significantly different reaction rates were observed. Thus, by using 0.4 mol % of 4a , 1.0 equiv of H 2 per mole of AB was released in 8.5 min (turnover frequency (TOF 50% ) = 1875 h –1 ), while complexes 4b and 4c (0.8 mol %) exhibited lower catalytic activities (TOF 50% = 55–60 h –1 ). 4a is currently the best performing Ir III homogeneous catalyst for AB dehydrogenation. Kinetic rate measurements show a zero-order dependence with respect to AB, and first order with the catalyst in the dehydrogenation with 4a (−d[AB]/d t = k [ 4a ]). Conversely, the reaction with 4b is second order in AB and first order in the catalyst (−d[AB]/d t = k [ 4b ][AB] 2 ). Moreover, the reactions of the derivatives 4a and 4b with an excess of t BuOK (2.5 equiv) have been analyzed through NMR spectroscopy. For the former precursor, formation of the iridate 5 was observed as a result of a double deprotonation at the amine and the NHC pincer arm. In marked contrast, in the case of 4b , a monodeprotonated (at the pincer NHC-arm) species 6 is observed upon reaction with t BuOK. Complex 6 is capable of activating H 2 reversibly to yield the trihydride derivative 7 . Finally, DFT calculations of the first AB dehydrogenation step catalyzed by 5 has been performed at the DFT//MN15 level of theory in order to get information on the predominant metal–ligand cooperation mode.

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“…16 In another finding relevant to this work, we showed that electron-rich ancillary ligands led to selective C aryl −S bond cleavage with subsequent formation of a coordinated dianionic CNS pincer ligand (Scheme 2). 15,20 For nickel, there are three relevant previous reports. Bouwman et al prepared Ni(κ 2 -SNS t-Bu ) 2 from Ni acetate and showed that heating in toluene effected selective C−S tBu bond cleavage, affording dithiolate-bridged [Ni(μ-κ 3 -SNS)] 2 presumably by release of isobutene and the protonated ligand (Scheme 3A).…”

Section: ■ Introductionmentioning

confidence: 99%

“…Transition metal complexes bearing “pincer” ligands tend to exhibit improved thermal stability, reactivity, and catalytic activity/selectivity when compared to their monodentate analogs. − Inspired by a plethora of multiple N,S coordination geometries in metallo-enzymes − and their synthetic models, , we have been preparing new first row metal SNS complexes (Figure ) − in order to assess and compare the roles of “hard” amido and “soft” thiolate donors as cooperative ligands in catalysis …”

Section: Introductionmentioning

confidence: 99%

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Nickel(II)-SNS Thiolate Complexes: Reactivity and Solution Dynamics

Albkuri

¹

,

Ovens

²

,

Martin

³

et al. 2021

Self Cite

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Nickel coordination chemistry with a biomimetic thiolate-imine-thioether SNSMe ligand is accompanied by diverse reactivity and multidentate ligand dynamics. Reaction of Ni(acac)2 with 2 equiv of 2-(methylthio)-phenyl-benzothiazolidine (MPB) affords the bis(arylimino-phenylene-thiolate) complex Ni(κ2-SNSMe)2 (1; acac = acetylacetonate). Thermolysis of 1 in refluxing toluene is accompanied by imine C–C bond formation, yielding [Ni(N2S2)] (2) with a redox-active ligand. Protonation of 1 with NHTf2 at a low temperature released 1 equiv of MPB, yielding crystals of the dimeric dication {[Ni(μ-κ3-SNSMe)]2}(NTf2)2 (3; Tf = SO2CF3) in high yield. In contrast, the same reaction at room temperature gave also paramagnetic complexes {Ni[μ-Ni(κ3-SNSMe)2]2}(NTf2)2 (4) and {Ni[μ-Ni(κ3-SNSMe)2]3}(NTf2)2 (5) that feature coordination of two or three pseudo-octahedral, paramagnetic Ni(κ3-SNSMe)2 units to a central Ni(II) dication via thiolate bridges. Remarkably, dissolution of 3 in a variety of solvents, including weakly coordinating CH2Cl2, rapidly generates a mixture of 4 and Ni(NTf)2. Treatment of this mixture with Lewis bases L gave high yields of dimers {[Ni(μ-κ3-SNSMe)L]2}(NTf2)2 for L = CNXylyl (6a) and {[Ni(μ-κ3-SNSMe)]2(μ-dmpm)}(NTf2)2 (6b; dmpm = bis(dimethylphosphino)methane) or monomers [Ni(κ3-SNSMe)L](NTf2) for L = PMe3 (7a) and P(OMe)3 (7b). Addition of 2 equiv of the strong donor N-heterocyclic carbene ligand, IPr, to 3, however, led to thioether demethylation, affording neutral dithiolate complex Ni(κ3-SNS)(IPr) (8). Reaction products were characterized by NMR and mass spectrometry and complexes 1–5, 6a, 6b, 7a, and 8 by single-crystal X-ray diffraction.

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Symmetrical and Non‐symmetrical Pd (II) Pincer Complexes Bearing Mesoionic N‐heterocyclic Thiones: Synthesis, Characterizations and Catalytic Properties

Yan

¹

,

Zhang

²

,

Zhang

³

et al. 2020

Applied Organom Chemis

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In contrast to well‐established symmetrical pincer complexes, non‐symmetrical metal pincers with the loss of C2v symmetry are much less studied. In this work, mesoionic NHTs (NHTs = N‐heterocyclic thiones), which can be viewed as the sulfur adducts of mesoionic carbenes, are incorporated into pincer complexes for the first time. Two symmetrical and non‐symmetrical phenylene‐bridged bis (NHT) compounds 3a/3b were synthesized as proligands via a “cycloaddition‐alkylation‐thionation” reaction sequence. In a case to access bis (NHT) compound 3c, N‐dealkylation reactions occurred. The carbene NMR signals of NHTs are only partially correlated to the π‐accepting abilities of carbenes, which is different from Bertrand's carbene‐phosphinidene system. The structural analysis of 3a/3b indicates that they possess C‐S partial double bonds. 3a and 3b served as the precursors to access two aryl anion‐linked [SCS/S′] pincer complexes 6a/6b. An external base proved to be essential for this cyclopalladation process. The catalytic properties of 6a/6b in the cycloisomerizations of alkynoic acids have been examined. Finally, non‐symmetrical complex 6a shows superior catalytic performance in such transformations contrasting to its symmetrical counterpart 6b.

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Iron-SNS and -CNS Complexes: Selective C_aryl–S Bond Cleavage and Amine-Borane Dehydrogenation Catalysis

Cited by 19 publications

References 80 publications

Ammonia–Borane Dehydrogenation Catalyzed by Dual-Mode Proton-Responsive Ir-CNN^H Complexes

Ammonia–Borane Dehydrogenation Catalyzed by Dual-Mode Proton-Responsive Ir-CNN^H Complexes

Nickel(II)-SNS Thiolate Complexes: Reactivity and Solution Dynamics

Symmetrical and Non‐symmetrical Pd (II) Pincer Complexes Bearing Mesoionic N‐heterocyclic Thiones: Synthesis, Characterizations and Catalytic Properties

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Iron-SNS and -CNS Complexes: Selective Caryl–S Bond Cleavage and Amine-Borane Dehydrogenation Catalysis

Cited by 19 publications

References 80 publications

Ammonia–Borane Dehydrogenation Catalyzed by Dual-Mode Proton-Responsive Ir-CNNH Complexes

Ammonia–Borane Dehydrogenation Catalyzed by Dual-Mode Proton-Responsive Ir-CNNH Complexes

Nickel(II)-SNS Thiolate Complexes: Reactivity and Solution Dynamics

Symmetrical and Non‐symmetrical Pd (II) Pincer Complexes Bearing Mesoionic N‐heterocyclic Thiones: Synthesis, Characterizations and Catalytic Properties

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Product

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Iron-SNS and -CNS Complexes: Selective C_aryl–S Bond Cleavage and Amine-Borane Dehydrogenation Catalysis

Ammonia–Borane Dehydrogenation Catalyzed by Dual-Mode Proton-Responsive Ir-CNN^H Complexes

Ammonia–Borane Dehydrogenation Catalyzed by Dual-Mode Proton-Responsive Ir-CNN^H Complexes