NHC Ruthenium Complexes as Second Generation Grubbs Catalysts

Guerra, Javier Miguel Martín

doi:10.1055/s-2003-37132

Cited by 6 publications

(3 citation statements)

References 2 publications

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“…11 The most successful example is probably the second generation Grubbs catalysts, where substituting one phosphine with a carbene greatly increases catalytic reactivity. 12 Although similar, N-heterocyclic carbenes do have several differences from phosphines as ligands. The steric presence of a carbene is different.…”

Section: Introductionmentioning

confidence: 99%

Electronic structure and ionization energies of palladium and platinum N-heterocyclic carbene complexes

Green¹,

Herbert²

2005

Dalton Trans.

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Density functional methods have been used to calculate the geometries, electronic structure and ionization energies (IE) of N-heterocyclic carbene complexes of palladium and platinum, [M(CN2R2C2H2)2](M = Pd, Pt; R = H, Me, Bu t). Agreement with X-ray structures (R = Bu t) was good. Calculated IE agreed well with the photoelectron (PE) spectra (R = Bu t); metal bands were calculated to be within 0.25 eV of the experimental values, whereas the higher lying ligand bands deviated by up to 0.9 eV. Spin-orbit methods were needed to achieve this level of agreement for the Pt complex, but the calculations were found to underestimate the spin-orbit splitting somewhat. The principal metal-ligand bonding is between the carbene lone pair HOMO and a (d(z2)+ s) hybrid on the metal. The metal p(z) orbital contributes very little to the bonding. The metal d(xz,yz) orbitals mix primarily with the filled pi3 orbitals on the ligands and secondarily with the empty pi5 orbitals. Consequently they are little stabilized in comparison to the metal d(xy,x2- y2) orbitals, which are non-bonding in the complex. The first PE band for both the Pd and Pt complexes is from ionization of a (s - d(z2)) hybrid orbital. The IE is greater for Pt than for Pd on account of the post-lanthanide relativistic stabilization of the Pt 6s orbital.

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Section: Introductionmentioning

confidence: 99%

Electronic structure and ionization energies of palladium and platinum N-heterocyclic carbene complexes

Green¹,

Herbert²

2005

Dalton Trans.

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“…On the other hand, Pd–N(pyridine) bond length 2.120(9) Å is longer than the sum of the individual covalent radii of Pd and N (Pd–N=1.983 Å) and comparable to those found in related complexes . The longer Pd–N(pyridine) distance is attributed to the greater trans effect of the NHC ligand residing diagonally opposite to the pyridine …”

Section: Resultsmentioning

confidence: 57%

2‐Hydroxyethyl‐Substituted Pd‐PEPPSI Complexes: Synthesis, Characterization and the Catalytic Activity in the Suzuki‐Miyaura Reaction for Aryl Chlorides in Aqueous Media

et al. 2018

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In recent years, PEPPSI (Pyridine‐Enhanced Precatalyst Preparation Stabilization and Initiation) complexes have attracted attention in organometallic chemistry. This study contains the synthesis of the 2‐hydroxyethyl‐substituted Pd‐PEPPSI complexes and their catalytic activity in the Suzuki‐Miyaura reaction aryl chlorides in aqueous media. The Pd‐PEPPSI complexes have been prepared from the 2‐ hydroxyethyl‐substituted N‐heterocyclic carbene (NHC) precursors, palladium chloride and 3‐chloropyridine. The Pd‐PEPPSI complexes have been characterized by using 1H NMR, 13C NMR, FTIR spectroscopy and elemental analysis techniques. The Pd‐PEPPSI complexes have been examined as catalysts in the Suzuki‐Miyaura reactions in aqueous media with arylboronic acid derivatives. Also, they have demonstrated excellent activity in these reactions. Molecular and crystal structure of one of the 2‐hydroxyethyl substituted Pd‐PEPPSI complex was determined by single crystal X‐ray diffraction method. X‐ray studies show that the molecular structure adopts a slightly distorted square‐planar geometry with the palladium (II) center.

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“…110 Inhibiting syn-b-hydride elimination is essential, and it is no surprise to find that a screen of a Second generation NHC ruthenium catalysts 106 have been briefly highlighted. 120 Based on the general structure 106, Grubbs continues to expand upon the range of catalysts available for metathesis reactions (they are readily accessible in two steps from commercially available 106) (Scheme 25).…”

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confidence: 99%

5 Transition metals in organic synthesis

Fairlamb

2004

Annu. Rep. Prog. Chem., Sect. B: Org. Chem.

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A selection of transition metal mediated reactions from the chemical literature of 2003 are reviewed. Reactions involve a metal component either catalytically or stoichiometrically. The review is divided into reaction types. The author has endeavoured to emphasise reactions of great current interest in academic and industrial sectors in the fields of organic, organometallic and bioorganic chemistry. The review combines the separate catalytic and stoichiometric reviews written previously, 1 focusing more on general transition metal mediated coupling processes, cyclisation and alkene metathesis reactions. Transition metal coupling reactions (catalytic and stoichiometric)Metal-catalysed carbon-carbon and carbon-heteroatom bond formations represent important reactions in synthetic chemistry. The metal of choice for cross-coupling processes is still palladium. The recent focus on increasing catalyst efficiency, longevity, reactivity and selectivity, has led to more detailed mechanistic studies being carried out on a number of highly active catalysts for key reactions, particularly Suzuki and Hartwig-Buchwald amination reactions. Highlights of these studies are presented below. More unusual electrophilic and nucleophilic substrates, particularly heteroaromatic derivatives, for cross-coupling reactions are illustrated, which are shown to provide a greater challenge for cross-coupling reactions than simple biaryl compounds. Medicinal chemists have made a significant contribution in this respect. It is quite clear that the development of new catalysts should focus on utilising such substrates for benchmarking purposes, which could/should promote more widespread use of newly developed catalyst systems, particularly in target-directed synthesis. Allylic substitution (alkylation) reactionsTransition metal catalysed allylic substitution continues to be the benchmark asymmetric reaction by which novel chiral bidentate and monodentate ligands, particularly for palladium, are screened and tested. Bidentate ligands with two different donor atoms (hybrid ligands) represent one of the most effective classes. An

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NHC Ruthenium Complexes as Second Generation Grubbs Catalysts

Cited by 6 publications

References 2 publications

Electronic structure and ionization energies of palladium and platinum N-heterocyclic carbene complexes

Electronic structure and ionization energies of palladium and platinum N-heterocyclic carbene complexes

2‐Hydroxyethyl‐Substituted Pd‐PEPPSI Complexes: Synthesis, Characterization and the Catalytic Activity in the Suzuki‐Miyaura Reaction for Aryl Chlorides in Aqueous Media

5 Transition metals in organic synthesis

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