Aldehydes and ketones influence reactivity and selectivity in nickel-catalysed Suzuki-Miyaura reactions

A Bench-Stable Fluorophosphine Nickel(0) Complex and Its Catalytic Application

We herein present a fluorophosphine-based nickel(0) complex [Ni(PFPh2)4] (1), which is highly stable in air and water. [Ni(PFPh2)4] can be obtained from a one-pot reaction of [Ni(MeCN)4](BF4)2 with Ph2P(═O)-PPh2, involving a unique in situ reduction of Ni(II) to Ni(0) and a simultaneous fluorination by the BF4 - anion. This complex does not only incorporate a nickel center in the zero-oxidation state, resulting from a Ni(II) precursor, but also includes fluorophosphine ligands, which typically disproportionate immediately in solution. The application of [Ni(PFPh2)4] as highly stable Ni(0) pre-catalyst in combination with additional phosphine ligands, such as dppf (1,1'-bis(diphenylphosphino)ferrocene), in various coupling reactions uncovers its high catalytic activity and versatility, which is superior to [Ni(COD)2] (COD═cycloocta-1,5-diene) as conventional Ni(0) source.

π-Lewis Base Activation of Carbonyls and Hexafluorobenzene

We report hitherto elusive side-on η2-bonded palladium(0) carbonyl (anthraquinone, benzaldehyde) and arene (benzene, hexafluorobenzene) palladium(0) complexes and present the catalytic hydrodefluorination of hexafluorobenzene by cyclohexene. The comparison with respective cyclohexene, pyridine and tetrahydrofuran complexes reveals that the experimental ligand binding strengths follow the order THF Collapse

Key Words

• Catalysis
• Chemical Bonding
• Intermediates
• Organometallic Chemistry
• Spectroscopy

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MESH Headings Collapse

Grants

• 948185 H2020 European Research Council
• 256/506-1 Deutsche Forschungsgemeinschaft
• 256/582-1 Deutsche Forschungsgemeinschaft
• 440719683 Deutsche Forschungsgemeinschaft
• 2008-390540038 Deutsche Forschungsgemeinschaft

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Affiliation(s)

Aditesh Mondal Coordination Chemistry, Saarland University, Campus C4.1, D-66123, Saarbrücken, Germany
Kevin Breitwieser Coordination Chemistry, Saarland University, Campus C4.1, D-66123, Saarbrücken, Germany
Sergi Danés Departament de Química, Institut de Química Computacional I Catàlisi, Universitat de Girona, c/m. Aurelia Capmany 69, 17003, Girona, Spain
Annette Grünwald Coordination Chemistry, Saarland University, Campus C4.1, D-66123, Saarbrücken, Germany Inorganic and General Chemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstr. 1, D-91058, Erlangen, Germany
Frank W Heinemann Inorganic and General Chemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstr. 1, D-91058, Erlangen, Germany
Bernd Morgenstern Solid State Chemistry, Saarland University, Campus C4.1, D-66123, Saarbrücken, Germany
Frank Müller Experimental Physics and Center for Biophysics, Saarland University, Campus E2.9, D-66123, Saarbrücken, Germany
Michael Haumann Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195, Berlin, Germany
Maximilian Schütze Institut für Chemie, Humboldt-Universität zu Berlin, Brook-Taylor-Straße 2, 12489, Berlin, Germany
Dustin Kass Institut für Chemie, Humboldt-Universität zu Berlin, Brook-Taylor-Straße 2, 12489, Berlin, Germany
Kallol Ray Institut für Chemie, Humboldt-Universität zu Berlin, Brook-Taylor-Straße 2, 12489, Berlin, Germany
Dominik Munz Coordination Chemistry, Saarland University, Campus C4.1, D-66123, Saarbrücken, Germany

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Mapping Electrophile Chemoselectivity in DalPhos/Nickel N-Arylation Catalysis: The Unusual Influence of Remote Sterics

We disclose herein our evaluation of competitive (hetero)aryl-X (X: Br>Cl>OTf) reactivity preferences in bisphosphine/Ni-catalyzed C-N cross-coupling catalysis, using furfurylamine as a prototypical nucleophile, and employing DalPhos and DPPF as representative ancillary ligands with established efficacy. Beyond this general (pseudo)halide ranking, other intriguing structure-reactivity trends were noted experimentally, including the unexpected observation that bulky alkyl (e. g., R=tBu) substitution in para-R-aryl-X electrophiles strongly discourages (pseudo)halide reactivity relative to smaller substituents (e. g., nBu, Et, Me), despite being both remote from, and having a similar electronic influence on, the reacting C-X bond; such effects on nickel oxidative addition have not been documented previously and were not observed in our comparator reactions presented herein involving palladium. Density functional theory modeling of such PhPAd-DalPhos/Ni-catalyzed C-N cross-couplings revealed the origins of competitive turnover of C-Br over C-Cl, and possible ways in which bulky para-alkyl substitution might discourage net electrophile uptake/turnover, leading to inversion of halide selectivity.

Characterization of non-covalent contacts in mono- and di-halo substituted acetaldehydes: probing the substitution effects of electron donating and withdrawing groups

In the current work, a systematic evaluation of the different types of non-covalent interactions (NCIs) in acetaldehyde dimers, including dimers of mono-halo (XCH₂CHO)₂, di-halo (X₂CHCHO)₂ and tri-halo substituted (X₃CCHO)₂ acetaldehydes via the associated stabilization energy of these dimers has been performed. Furthermore, a topological analysis of the electron density based on the quantum theory of atoms in molecules (QTAIM) and non-covalent interaction reduced density gradient (NCI-RDG) isosurfaces has also been performed to evaluate the nature of these NCIs. The geometrical and electronic characteristics have been evaluated via the presence of different electron-donating groups (EDGs) and electron-withdrawing groups (EWGs) or substituents in dimers of these molecules, namely, XCH(Y)CHO and X₂C(Y)CHO (wherein X = -F, -Cl, and -Br and Y = -SO₃H, -CN, -NO₂, -NH₂, -CH₃, -OCH₃, and -SMe₃). The C-H⋯O, C-H⋯X, X⋯X, X⋯O and C⋯O tetrel bonded contacts have been recognized to play an important role in the stabilization of the formed dimers. This study also establishes the fact that the overall stability of the dimeric assemblies is governed by the contributions from the mutual and complex interplay of a variety of interactions in the investigated dimers. Hence considerations based on strong H-bond donor-acceptor characteristics hold relevance for simple systems only, but slight alteration in the electronic environment can affect the overall stabilization energies of the system being investigated and the nature of the interactions that contribute towards the same.

Inhibition of (dppf)nickel-catalysed Suzuki-Miyaura cross-coupling reactions by α-halo-N-heterocycles

A nickel/dppf catalyst system was found to successfully achieve the Suzuki-Miyaura cross-coupling reactions of 3- and 4-chloropyridine and of 6-chloroquinoline but not of 2-chloropyridine or of other α-halo-N-heterocycles. Further investigations revealed that chloropyridines undergo rapid oxidative addition to [Ni(COD)(dppf)] but that α-halo-N-heterocycles lead to the formation of stable dimeric nickel species that are catalytically inactive in Suzuki-Miyaura cross-coupling reactions. However, the corresponding Kumada-Tamao-Corriu reactions all proceed readily, which is attributed to more rapid transmetalation of Grignard reagents.

The Effect of Added Ligands on the Reactions of [Ni(COD)(dppf)] with Alkyl Halides: Halide Abstraction May Be Reversible

The reactions of dppf-nickel(0) with alkyl halides proceed via three-coordinate nickel(0) intermediates of the form [Ni(dppf)(L)]. The effects of the identity of the added ligand (L) on catalyst speciation and the rates of reactions of [Ni(COD)(dppf)] with alkyl halides have been investigated using kinetic experiments and density functional theory calculations. A series of monodentate ligands have been investigated in attempts to identify trends in reactivity. Sterically bulky and electron-donating ligands are found to decrease the reaction rate. It was found that (i) the halide abstraction step is not always irreversible and the subsequent recombination of a nickel(I) complex with an alkyl halide can have a significant effect on the overall rate of the reaction and (ii) some ligands lead to very stable [Ni(dppf)(L)₂] species. The yields of prototypical (dppf)nickel-catalyzed Kumada cross-coupling reactions of alkyl halides are significantly improved by the addition of free ligands, which provides another important variable to consider when optimizing nickel-catalyzed reactions of alkyl halides.

Concise catalytic asymmetric synthesis of (R)-4-amino Uhle's ketone

A practical and asymmetric synthesis of (R)-4-amino-5-oxo-1,3,4,5-tetrahydrobenz[cd]indole, an enantiopure framework shared by most ergot alkaloids, was accomplished. Our method involves a Rh(i)-catalyzed 6-exo-trig intramolecular cyclization of an appropriate 4-pinacolboronic ester d-tryptophan aldehyde followed by the oxidation of the resulting secondary benzylic alcohol with a Cu(i)-ABNO catalyst and final deprotection under acidic conditions. This new procedure offers significant advantages over previous synthetic approaches, including brevity, mild reaction conditions, preservation of chiral integrity, and high overall yield and avoids the use of stoichiometric amounts of strongly basic and pyrophoric organometallic reagents.

Reactions of nickel(0) with organochlorides, organobromides, and organoiodides: mechanisms and structure/reactivity relationships

The reactions of nickel(0) complexes with phosphine, bipyridine-type, and N-heterocyclic carbene ligands with aryl, vinyl, and alkyl halides is reviewed.

Unexpected Nickel Complex Speciation Unlocks Alternative Pathways for the Reactions of Alkyl Halides with dppf-Nickel(0)

The mechanism of the reactions between dppf-Ni0 complexes and alkyl halides has been investigated using kinetic and mechanistic experiments and DFT calculations. The active species is [Ni(κ2-dppf)(κ1-dppf)], which undergoes a halide abstraction reaction with alkyl halides and rapidly captures the alkyl radical that is formed. The rates of the reactions of [Ni(COD)(dppf)] with alkyl halides and the yields of prototypical nickel-catalyzed Kumada cross-coupling reactions of alkyl halides are shown to be significantly improved by the addition of free dppf ligand.

Nickel-Catalyzed Mono-Selective α-Arylation of Acetone with Aryl Chlorides and Phenol Derivatives

The challenging nickel-catalyzed mono-α-arylation of acetone with aryl chlorides, pivalates, and carbamates has been achieved for the first time. A nickel/Josiphos-based catalytic system is shown to feature unique catalytic behavior, allowing the highly selective formation of the desired mono-α-arylated acetone. The developed methodology was applied to a variety of (hetero)aryl chlorides including biologically relevant derivatives. The methodology has been extended to the unprecedented coupling of acetone with phenol derivatives. Mechanistic studies allowed the isolation and characterization of key Ni⁰ and Ni^II catalytic intermediates. The Josiphos ligand is shown to play a key role in the stabilization of Ni^II intermediates to allow a Ni⁰ /Ni^II catalytic pathway. Mechanistic understanding was then leveraged to improve the protocol using an air-stable Ni^II pre-catalyst.

Terpyridine-based Pd(ii)/Ni(ii) organometallic framework nano-sheets supported on graphene oxide-investigating the fabrication, tuning of catalytic properties and synergetic effects

Tailoring the structures of catalysts and the arrangement of organic bimetallic catalysts are essential in both fundamental research and applications. However, they still impose enormous challenges such as size and active species distribution, ordered uniformity, and controllable composition, which are critical in determining their specific activities and efficiency. Herein, a novel terpyridine-based hetero-bimetallic Ni/Pd nanosheet supported on graphene oxide (denoted as GO@Tpy-Ni/Pd) was fabricated, which exhibited higher catalytic activity, substrate applicability and recyclability for the Suzuki coupling reaction under mild conditions. The catalytic mechanism was heterogeneous catalysis at the interface and the synergetic effect between Pd and Ni resulted in a little Ni(0)/Pd(0) cluster including Pd(ii)/Ni(ii) as a whole being formed through electron transfer on the catalytic surface. This phenomenon could be interpreted as the nanoscale clusters of Ni/Pd being the real active centre stabilized by the ligand and GO and the synergetic effect. The absorption and desorption of different substrates and products on Ni/Pd clusters, as calculated by DFT, was proved to be another key factor.

The synergistic effect between Ni and Pd atom was the crucial factor for enhancing catalytic activity.

Direct Synthesis of Chain-end-functionalized Poly(3-hexylthiophene) without Protecting Groups Using a Zincate Complex

Chain-end-functionalized poly(3-hexylthiophene)s (P3HTs) with benzyl alcohol (─PhCH₂ OH), phenol (─PhOH), and benzoic acid (─PhCOOH) groups are directly synthesized based on the Negishi catalyst-transfer polycondensation method utilizing the zincate complex of ^t Bu₄ ZnLi₂ . In this system, neither protection nor deprotection steps are required, and also providing a living polymerization system to control the molecular weight while maintaining a low molar mass dispersity (Ð_M ) of the obtained P3HT derivatives. Indeed, the chain-end-functionalized P3HTs can be synthesized along with controlled number-average molecular weights (M_n = 5100-20 000), low Ð_M (1.06-1.14), and high chain-end functionality (Fn = 46-86%). The Fn values for the alcohol and phenol groups are found to be high (86% for ─PhCH₂ OH and 71% for ─PhOH based on ¹ H NMR, respectively), as also confirmed by matrix-assisted laser desorption/ionization time of flight mass spectroscopy. The easily synthesizable chain-end-functionalized P3HTs will be applicable for the facile synthesis of block and branched polymers containing P3HT as well as its related semiconducting polymer segments.