Mediumeffekte in Palladium‐katalysierten Kreuzkupplungen und Implikationen bezüglich der katalytisch aktiven Spezies

Proutière, Fabien; Schoenebeck, Franziska

doi:10.1002/ange.201101746

Cited by 58 publications

(11 citation statements)

References 55 publications

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“…However, work is ongoing to fully capitalize on the properties of these new ligands, such as their exceptional solubility in non-polar media that might offer new horizons in cross-coupling and related catalysis. [34] The initial catalytic results with the ITent ligand family have permitted the identification of more active Pd-NHC precatalysts for Suzuki-Miyaura and Buchwald-Hartwig cross-couplings and have given precious information for improved understanding of Pd-NHC catalysis. [35] The remarkable steric suppleness of the large yet flexible ligand set is currently being further explored in late transition metal catalysis.…”

Section: Resultsmentioning

confidence: 99%

Large yet Flexible N‐Heterocyclic Carbene Ligands for Palladium Catalysis

Meiries

Duc

Chartoire

et al. 2013

Chemistry A European J

126

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A straightforward and scalable eight‐step synthesis of new N‐heterocyclic carbenes (NHCs) has been developed from inexpensive and readily available 2‐nitro‐m‐xylene. This process allows for the preparation of a novel class of NHCs coined ITent (“Tent” for “tentacular”) of which the well‐known IMes (N,N′‐bis(2,4,6‐trimethylphenyl)imidazol‐2‐ylidene), IPr (N,N′‐bis(2,6‐di(2‐propyl)phenyl)imidazol‐2‐ylidene) and IPent (N,N′‐bis(2,6‐di(3‐pentyl)phenyl)imidazol‐2‐ylidene) NHCs are the simplest and already known congeners. The synthetic route was successfully used for the preparation of three members of the ITent family: IPent (N,N′‐bis(2,6‐di(3‐pentyl)phenyl)imidazol‐2‐ylidene), IHept (N,N′‐bis(2,6‐di(4‐heptyl)phenyl)imidazol‐2‐ylidene) and INon (N,N′‐bis(2,6‐di(5‐nonyl)phenyl)imidazol‐2‐ylidene). The electronic and steric properties of each NHC were studied through the preparation of both nickel and palladium complexes. Finally the effect of these new ITent ligands in Pd‐catalyzed Suzuki–Miyaura and Buchwald–Hartwig cross‐couplings was investigated.

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Section: Resultsmentioning

confidence: 99%

Large yet Flexible N‐Heterocyclic Carbene Ligands for Palladium Catalysis

Meiries

Duc

Chartoire

et al. 2013

Chemistry A European J

126

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“…[6] Computational Details All geometries were optimized at the B3LYP/LACVP* level [14,15] by using Jaguar 7.6. [22] Gibbs free energies were calculated by the following equation G(kJ mol À1 ) = E(DFT/basis set) + G solv + ZPE + H 298 + S 298 + 7.9 (concentration correction to the free energy of solvation from 1 M(g) ! 1 M(aq) to 1 atm(g) !…”

mentioning

confidence: 99%

Dispersion and Back‐Donation Gives Tetracoordinate [Pd(PPh₃)₄]

Ahlquist¹,

Norrby²

2011

Angewandte Chemie

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Palladium-catalyzed coupling reactions have received enormous attention in recent years, as illustrated by the Nobel Prize in 2010. [1] Despite this, there are many questions remaining to be answered in the field. One concerns the nature and activation of Pd 0 precatalysts that are frequently employed in couplings. Taking [Pd 0 (PPh 3 ) 4 ] as a common example, it is generally agreed that this complex must lose two phosphine ligands to enter catalytic cycles as a [Pd 0 (PPh 3 ) 2 ] complex. [2] However, why would the complex do a rare double dissociation from the 18-electron tetrakis complex to reach a doubly unsaturated state? Furthermore, why is the 18electron complex preferred, when it is well known that Pd 0 has a full shell of d orbitals and only the 5s orbital available for accepting dative bonds? [3] To illuminate some of these issues, we have undertaken a detailed study of the energies and electronic structures of the different [Pd(PPh 3 ) n ] complexes.The 18-electron rule has been an important guideline for studying the coordination chemistry of transition metals. The theory behind it is that each ligand can donate its electron pair(s) to one of nine available valence orbitals (s, p, or d) on the transition metal. However, it is now generally accepted that for most transition metals, the p orbitals are too high in energy to participate in valence bonding, removing a theoretical foundation for the 18-electron rule. [3,4] Inorganic chemists have also long been able to rationalize complex geometries using ligand field theory (LFT) based solely on d orbitals. [5] Using valence bond concepts, Landis and Weinhold have shown that transition metal coordination can be understood in terms of 6 valence orbitals (s and d only) in combination with 3-center-4-electron bonds, so-called w bonds. [3] The Landis-Weinhold theory can rationalize observed geometries not only of most 18-electron complexes, but also well-known exceptions to the 18-electron rule like the square planar d 8 complexes (e.g., Pd II ) and linear d 10 complexes (e.g., Au I ). However, [Pd 0 (PPh 3 ) 4 ] follows the 18-electron rule and apparently violates the Landis-Weinhold theory, which instead predicts the catalytically competent [Pd 0 (PPh 3 ) 2 ] as the preferred state, and in fact defines this complex as hypervalent.In the current study, we will use the labels P 1 -P 4 to designate the number of phosphine ligands bound to Pd 0 (e.g., P 2 means [Pd 0 (PPh 3 ) 2 ]), with the addition "Cl" showing an anionic complex with a chloride ligand in addition to the phosphines. Our starting point for the current study was a previous investigation at the B3LYP level, where P 2 was identified as the preferred state, [6] in violation of crystal data [7] as well as studies of the ligation preference in solution. [8] However, recent improvements allowing inclusion of dispersion interactions into DFT calculations [9,10] have shown that it is now possible to quantify binding energies to transition metals, [11] as well as model processes like the oxidative additi...

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“…2000 berichteten Fu und Mitarbeiter über den Einsatz des sperrigen elektronenreichen pyrophoren PtBu 3 und des weniger luftempfindlichen PCy 3 als Liganden in Suzuki-Miyaura-Kupplungen von Arylboronsäuren mit C(sp 2 )-Halogeniden bzw. [128] Ein Jahr nach seiner richtungsweisenden Arbeit berichtete Fu über den vorteilhaften Einsatz des weniger sperrigen Liganden PCy 3 in der Kupplung von Alkylhalogeniden mit Alkyl-oder Vinylborreagentien. [126] Durch die Auswahl eines geeigneten Liganden erreichten sie eindrucksvolle Chemoselektivitäten, weil sich die Reaktivitätsabfolge für Ar-OTf und Ar-Cl beim Wechsel zwischen den beiden Liganden ändert.…”

Section: Die Bedeutung Der Liganden Und Ihrer Eigenschaftenunclassified

“…Schoenebeck zeigte allerdings später durch theoretische und experimentelle Studien, dass auch alleine mit PtBu 3 in polaren Lçsungsmitteln in Gegenwart koordinierender Kupplungspartner oder Additive infolge der Bildung anionischer Pd-Spezies ein Selektivitätswechsel zwischen C-Cl und C-OTf eintreten kann. [128] Ein Jahr nach seiner richtungsweisenden Arbeit berichtete Fu über den vorteilhaften Einsatz des weniger sperrigen Liganden PCy 3 in der Kupplung von Alkylhalogeniden mit Alkyl-oder Vinylborreagentien. [129] Zwar war Suzuki schon 1986 die Kupplung von B-Alkyl-9-BBN mit Aryliodiden gelungen, [130] doch durch den Einsatz von Alkylhalogeniden als Kupplungspartnern konnte Fu die Substratpalette deutlich erweitern.…”

Section: Die Bedeutung Der Liganden Und Ihrer Eigenschaftenunclassified

Palladiumkatalysierte Kreuzkupplungen: eine historische Perspektive im Kontext der Nobel‐Preise 2010

et al. 2012

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Im Jahr 2010 wurden Richard Heck, Ei‐ichi Negishi und Akira Suzuki in den illustren Kreis der Chemie‐Nobelpreisträger aufgenommen. Begründet wurde diese Auszeichnung mit ihrer Rolle bei der Entdeckung und Entwicklung von praktischen Methoden zur C‐C‐Bindungsbildung. Ausgelöst durch ihre Beiträge über höchst nützliche palladiumkatalysierte Kreuzkupplungen, hat sich seit den frühen 1970er Jahren die Auswahl an verfügbaren Strategien und Methoden in der modernen organischen Synthese grundlegend verändert – sowohl für Chemiker an Hochschulen wie auch in der Industrie. Dieser Aufsatz vollzieht die historische Entwicklung dieser leistungsstarken Reaktionen nach: von den bahnbrechenden Entdeckungen bis hin zu den Kreuzkupplungsverfahren, die heute in der Synthese angewendet und hoch geschätzt werden.

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Mediumeffekte in Palladium‐katalysierten Kreuzkupplungen und Implikationen bezüglich der katalytisch aktiven Spezies

Cited by 58 publications

References 55 publications

Large yet Flexible N‐Heterocyclic Carbene Ligands for Palladium Catalysis

Large yet Flexible N‐Heterocyclic Carbene Ligands for Palladium Catalysis

Dispersion and Back‐Donation Gives Tetracoordinate [Pd(PPh₃)₄]

Palladiumkatalysierte Kreuzkupplungen: eine historische Perspektive im Kontext der Nobel‐Preise 2010

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Mediumeffekte in Palladium‐katalysierten Kreuzkupplungen und Implikationen bezüglich der katalytisch aktiven Spezies

Cited by 58 publications

References 55 publications

Large yet Flexible N‐Heterocyclic Carbene Ligands for Palladium Catalysis

Large yet Flexible N‐Heterocyclic Carbene Ligands for Palladium Catalysis

Dispersion and Back‐Donation Gives Tetracoordinate [Pd(PPh3)4]

Palladiumkatalysierte Kreuzkupplungen: eine historische Perspektive im Kontext der Nobel‐Preise 2010

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Dispersion and Back‐Donation Gives Tetracoordinate [Pd(PPh₃)₄]