Carbene complexes

Çetinkaya, Engin; Hitchcock, Peter B.; Küçükbay, Hasan; Läppert, Michael F.; Al-Juaid, Salih S.

doi:10.1016/0022-328x(94)85013-5

Cited by 90 publications

(42 citation statements)

References 17 publications

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“…The synthesis of carbenes of type 4 containing an annelated N-heterocyclic five-membered ring by methods described by Arduengo et al [4a,b] or Kuhn et al [4c] is hampered by two factors; i) the deprotonation of sterically less bulky substituted N,N'-dialkylated benzimidazolium ions with strong bases like nBuLi, tBuLi, or NaH in THF, in contrast to the corresponding imidazolium ions, does not yield stable carbenes but instead C2ÀC2 connected olefins, [12] and ii) the preparation of bulky (tBu, neopentyl) substituted N,N'-dialkylated benzimidazolium salts starting from benzimid-azole, which cannot dimerize after C2 deprotonation, proved unsuccessful to date.…”

Section: Resultsmentioning

confidence: 99%

N,N′-Bis(2,2-dimethylpropyl)benzimidazolin-2-ylidene: A Stable Nucleophilic Carbene Derived from Benzimidazole

et al. 1999

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N,N'-Dialkylated benzimidazol-2-thiones 6 can be prepared in a three-step procedure from o-phenylenediamine. Thione 6 a was reduced with sodium/potassium under desulfurization leading to carbene 4. Compound 4 is the first stable free carbene derived from benzimidazole. It exhibits the topology of an unsaturated carbene including a short C4 À C5 bond. Its observation that the unsaturated carbene 4 behaves like a saturated imidazolidin-2-ylidene is corroborated by the tendency of the sterically less bulky N,N'-dialkylated thione 6 b to yield the olefin 8 after reduction with Na/K. Carbene 4 can be coordinated to a W(CO) 5 fragment yielding the complex 9, which contains a nonplanar carbene ring.

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Section: Resultsmentioning

confidence: 99%

N,N′-Bis(2,2-dimethylpropyl)benzimidazolin-2-ylidene: A Stable Nucleophilic Carbene Derived from Benzimidazole

et al. 1999

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“…3 ]. 56 The latter shows a υ 103 Rh of 2874 ppm, which is very different from the former at 642 ppm and is higher than for any other Rh(I) compound. Together with the fact that only one 13 C resonance was observed for all three carbene carbon atoms, it was suggested that the halide is dissociated in solution.…”

Section: Ligand Class and Donor Atommentioning

confidence: 92%

¹⁰³Rh NMR spectroscopy and its application to rhodium chemistry

Ernsting

Gaemers

Elsevier

2004

Magnetic Reson in Chemistry

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Rhodium is used for a number of large processes that rely on homogeneous rhodium-catalyzed reactions, for instance rhodium-catalyzed hydroformylation of alkenes, carbonylation of methanol to acetic acid and hydrodesulfurization of thiophene derivatives (in crude oil). Many laboratory applications in organometallic chemistry and catalysis involve organorhodium chemistry and a wealth of rhodium coordination compounds is known. For these and other areas, 103Rh NMR spectroscopy appears to be a very useful analytical tool. In this review, most of the literature concerning 103Rh NMR spectroscopy published from 1989 up to and including 2003 has been covered. After an introduction to several experimental methods for the detection of the insensitive 103Rh nucleus, a discussion of factors affecting the transition metal chemical shift is given. Computational aspects and calculations of chemical shifts are also briefly addressed. Next, the application of 103Rh NMR in coordination and organometallic chemistry is elaborated in more detail by highlighting recent developments in measurement and interpretation of 103Rh NMR data, in relation to rhodium-assisted reactions and homogeneous catalysis. The dependence of the 103Rh chemical shift on the ligands at rhodium in the first coordination sphere, on the complex geometry, oxidation state, temperature, solvent and concentration is treated. Several classes of compounds and special cases such as chiral rhodium compounds are reviewed. Finally, a section on scalar coupling to rhodium is provided.

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“…A similar twist of the double bond was found in the enetetramine (3 b) 2 , although the twist angles were nearly identical (16.8(1)8 and 14.4(1)8, respectively). [10] On the other hand, both molecules show a regular length for the double bond (3 c: 1.345(2); (3 b) 2 1.344(4) ). NMR spectroscopic studies did not indicate the dissociation of 3 c into two bridged N-heterocyclic carbenes.…”

Section: F Ekkehardt Hahn* Lars Wittenbecher Duc Le Van and Rolanmentioning

confidence: 98%

“…[9] Despite the unsaturated nature of the N-heterocyclic ring, this carbene shows structural and spectroscopical properties which are typical for saturated carbenes of type 2. In addition, the fast dimerization of the N-methylated derivative, which is sterically less crowded, to form (3 b) 2 [9,10] is characteristic for saturated N-heterocyclic carbenes. Unsaturated derivatives of type 1 seldom form enetetramines, [1b] or only after suitable double bridging.…”

Section: F Ekkehardt Hahn* Lars Wittenbecher Duc Le Van and Rolanmentioning

confidence: 99%

Evidence for an Equilibrium between an N-heterocyclic Carbene and Its Dimer in Solution

Hahn¹,

Wittenbecher

Van

et al. 2000

Angewandte Chemie International Edition

281

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Carbene complexes

Cited by 90 publications

References 17 publications

N,N′-Bis(2,2-dimethylpropyl)benzimidazolin-2-ylidene: A Stable Nucleophilic Carbene Derived from Benzimidazole

N,N′-Bis(2,2-dimethylpropyl)benzimidazolin-2-ylidene: A Stable Nucleophilic Carbene Derived from Benzimidazole

¹⁰³Rh NMR spectroscopy and its application to rhodium chemistry

Evidence for an Equilibrium between an N-heterocyclic Carbene and Its Dimer in Solution

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Carbene complexes

Cited by 90 publications

References 17 publications

N,N′-Bis(2,2-dimethylpropyl)benzimidazolin-2-ylidene: A Stable Nucleophilic Carbene Derived from Benzimidazole

N,N′-Bis(2,2-dimethylpropyl)benzimidazolin-2-ylidene: A Stable Nucleophilic Carbene Derived from Benzimidazole

103Rh NMR spectroscopy and its application to rhodium chemistry

Evidence for an Equilibrium between an N-heterocyclic Carbene and Its Dimer in Solution

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¹⁰³Rh NMR spectroscopy and its application to rhodium chemistry