Synthesis and reactivity of subvalent compounds

Denk, Michael; Rodezno, José M.

doi:10.1016/s0022-328x(00)00390-9

Cited by 29 publications

(20 citation statements)

References 12 publications

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“…21 The lattice water is bound to the chloride via interaction of H(1B), rendering a H(1B) … Cl(1) contact of 2.28(3) A ˚(sum of van der Waals radii 2.80 A ˚), 21 From a survey of other imidazolium halides in the CCDC, it appears IMes is relatively unique in its ability to furnish this 'anion' binding ensemble whereby both heterocycle and N-substituent protons participate. Thus, whilst the acidity of 4,5-position hydrogens has been noted, 23 and that of the 2-position imidazolium hydrogen made the subject of several studies, 19,20 in the absence of alternate acidic hydrogen atoms, e.g. those of included lattice solvent, 24 other imidazolium halides display a decreased tendency to coordinate halides (in the solid state) as convincingly as [IMesH] imidazolium species.…”

Section: Resultsmentioning

confidence: 99%

Facile purification of the N-heterocyclic carbene precursor [IMesH][Cl] and chloride binding in the solvates [IMesH][Cl]·acetone and [IMesH][Cl]·H₂O (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene)

Cole

Junk

2004

CrystEngComm

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Section: Resultsmentioning

confidence: 99%

Facile purification of the N-heterocyclic carbene precursor [IMesH][Cl] and chloride binding in the solvates [IMesH][Cl]·acetone and [IMesH][Cl]·H₂O (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene)

Cole

Junk

2004

CrystEngComm

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“…Moderate warming to 60 ºC accelerated the exchange considerably and reached 72% in 4 after the same reaction time (83% in 7). Mechanistically, the deuterium incorporation may be strongly related to the isotope exchange observed in free normal carbenes, 31 and may thus involve complex 2c is indeed instable towards such a strong acid. Performing the reaction in the presence of 1,8-bis(dimethylamino)naphthalene as proton-sponge did not completely prevent decomposition, yet a selective decrease of the signal due to the C5-bound proton to 32% with respect to 5 the other ligand signals was noted, indicating a substantial degree of deprotonation.…”

mentioning

confidence: 99%

Smooth C(alkyl)–H bond activation in rhodium complexes comprising abnormal carbene ligands

et al. 2011

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Rhodation of trimethylene-bridged diimidazolium salts induces the intramolecular activation of an alkane-type C-H bond and yields mono-and dimetallic complexes containing a formally monoanionic C,C,C-tridentate dicarbene ligand bound to each rhodium centre. Mechanistic 10 investigation of the C alkyl -H bond activation revealed a significant rate enhancement when the carbene ligands are bound to the rhodium centre via C4 (instantaneous activation) as compared to C2-bound carbene homologues (activation incomplete after 2 days). The slow C-H activation in normal C2-bound carbene complexes allowed intermediates to be isolated and suggests a critical role of acetate in mediating the bond activation process. Computational modelling supported by 15 spectroscopic analyses indicate that halide dissociation as well as formation of the agostic intermediate is substantially favoured with C4-bound carbenes. It is these processes that discriminate the C4-and C2-bound systems rather than the subsequent C-H bond activation, where the computed barriers are very similar in each case. The tridentate dicarbene ligand undergoes selective H/D exchange at the C5 position of the C4-bound carbene exclusively. A mechanism has 20 been proposed for this process, which is based on the electronic separation of the abnormal carbene ligand into a cationic N-C-N amidinium unit and a metalla-allyl type M-C-C fragment.

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“…The deuterated carbene 1,3 -ditert -butyl -4,5 -dideutero -imidazol -2 -ylidene was isolated from the reaction mixture [ 108 ] (see Figure 1. 19 ).…”

Section: Basicity Of Nhcmentioning

confidence: 99%

The Nature of N‐Heterocyclic Carbenes

Kühl

2010

Functionalised N‐Heterocyclic Carbene Complexes

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There are essentially three different types of transition metal carbene complexes featuring three different types of carbene ligands. They have all been named after their fi rst discoverers: Fischer carbenes [ 27 -29 ], Schrock carbenes [ 30 , 31 ] and Wanzlick -Arduengo carbenes (see Figure 1.1 ). The latter, also known as N -heterocyclic carbenes (NHC), should actually be named after three people: Ö fele [ 2 ] and Wanzlick [ 3 ], who independently synthesised their fi rst transition metal complexes in 1968, and Arduengo [ 1 ] who reported the fi rst free and stable NHC in 1991. Fischer carbene complexes have an electrophilic carbene carbon atom [ 32 ] that can be attacked by a Lewis base. The Schrock carbene complex has a reversed reactivity. The Schrock carbene complex is usually employed in olefi n metathesis (Grubbs ' catalyst) or as an alternative to phosphorus ylides in the Wittig reaction [ 33 ].The NHC are different from both other types. They form transition metal complexes that are essentially inert, although exceptions are known. Their exceptional stability derives from their intrinsic stabilisation from the N -C p π -p π bonding interaction of the nitrogen atoms fl anking the carbene carbon atom. The p orbital of the carbon is thus partially fi lled and no longer available for nucleophilic attack. Also, it does not have a lone pair of its own with which it could possibly engage in a nucleophilic interaction of its own. Hence, it remains unreactive taking the middle ground between the opposing reactivities of Fischer and Schrock carbenes. It is this apparent lack of reactivity that meant that the transition metal NHC complexes received little attention in their early history. Functionalised N-Heterocyclic Carbene ComplexesOlaf Kühl

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Synthesis and reactivity of subvalent compounds

Cited by 29 publications

References 12 publications

Facile purification of the N-heterocyclic carbene precursor [IMesH][Cl] and chloride binding in the solvates [IMesH][Cl]·acetone and [IMesH][Cl]·H₂O (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene)

Facile purification of the N-heterocyclic carbene precursor [IMesH][Cl] and chloride binding in the solvates [IMesH][Cl]·acetone and [IMesH][Cl]·H₂O (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene)

Smooth C(alkyl)–H bond activation in rhodium complexes comprising abnormal carbene ligands

The Nature of N‐Heterocyclic Carbenes

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Synthesis and reactivity of subvalent compounds

Cited by 29 publications

References 12 publications

Facile purification of the N-heterocyclic carbene precursor [IMesH][Cl] and chloride binding in the solvates [IMesH][Cl]·acetone and [IMesH][Cl]·H2O (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene)

Facile purification of the N-heterocyclic carbene precursor [IMesH][Cl] and chloride binding in the solvates [IMesH][Cl]·acetone and [IMesH][Cl]·H2O (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene)

Smooth C(alkyl)–H bond activation in rhodium complexes comprising abnormal carbene ligands

The Nature of N‐Heterocyclic Carbenes

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Product

Resources

About

Facile purification of the N-heterocyclic carbene precursor [IMesH][Cl] and chloride binding in the solvates [IMesH][Cl]·acetone and [IMesH][Cl]·H₂O (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene)

Facile purification of the N-heterocyclic carbene precursor [IMesH][Cl] and chloride binding in the solvates [IMesH][Cl]·acetone and [IMesH][Cl]·H₂O (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene)