Comparison of carbene and imidazole bonding to a copper(I) center

Wyer, Elsbeth; Gucciardo, Gabriele; Leigh, Vivienne; Müller‐Bunz, Helge; Albrecht, Martin

doi:10.1016/j.jorganchem.2011.02.012

Cited by 15 publications

(10 citation statements)

References 46 publications

(17 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…With the exception of the iodo adduct ( E = 0.24 V, L = I), these oxidation potential values [0.68 (L = pyridine), 0.80 (L = NCMe, CNCy) and 0.81 V (L = pyrazole)] are much higher than that (0.18 V) of the NHC adduct 6 , which suggests that the NHC ligand at the dirhodium(II) centre behaves as a markedly stronger electron donor than pyridine, NCMe, pyrazole and CNCy ligands. This contrasts with previous reports that indicate that related N‐heterocyclic carbenes at a tetracoordinate (1,4,7‐trithiacyclononane)Cu I complex21 or at half‐sandwich carbonyl cyclopentadienyl‐iron(II) complexes22 have an electron‐releasing ability similar to that of pyridine.…”

Section: Resultscontrasting

confidence: 99%

“…A value of the electrochemical E L Lever parameter (a measure of the net electron‐donor character of a ligand, the stronger this property the lower the value of E L )23 for the studied NHC ligands of ca. +0.30 V vs. NHE (normal hydrogen electrode) was proposed21–22 on the basis of the redox potential of the limited number of investigated complexes. Although our results do not allow us to estimate with confidence the E L parameter of IPr, in view of the limited number of complexes and the irreversibility of the oxidation wave of the iodide adduct Rh 2 (OAc) 4 (IPr)(I) (which does not allow us to have access to the thermodynamic potential), they suggest that, at the dinuclear Rh II centre of our study, the NHC ligand appears to exhibit an E L value much lower (stronger‐electron releasing character) than the above (ca.…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

N‐Heterocyclic Carbene Dirhodium(II) Complexes as Catalysts for Allylic and Benzylic Oxidations

Coelho

Trindade

Wanke³

et al. 2013

Eur J Org Chem

View full text Add to dashboard Cite

The experimental conditions (solvent, base, temperature and oxidant) for allylic and benzylic oxidation reactions catalyzed by dirhodium(II)/N‐heterocyclic carbene (NHC) complexes were optimized for the first time in this work. The oxidations of cyclohexene and fluorene were used as model reactions. Two optimized experimental conditions for both types of oxidations were found, which resulted in their ketone [aerobic conditions, 40 °C, 1 equiv. tBuOOH (TBHP)] or tert‐butyl peroxide derivatives (anaerobic conditions, 25 °C, 2 equiv. TBHP). The dirhodium(II) complexes undergo a single‐electron reversible oxidation by cyclic voltammetry in CH2Cl2, which is assigned to the Rh24+/Rh25+ redox couple at an oxidation potential that is lowered upon sequential axial coordination of further ligands to the Rh–Rh centre. The oxidation potential is discussed in terms of the electron‐donor character of the NHC ligand, which was shown to act as an effective electron‐releaser to the Rh24+ centre, and the electrochemical behaviour is compared to the observed catalytic activity.

show abstract

Section: Resultscontrasting

confidence: 99%

Section: Resultsmentioning

confidence: 99%

N‐Heterocyclic Carbene Dirhodium(II) Complexes as Catalysts for Allylic and Benzylic Oxidations

Coelho

Trindade

Wanke³

et al. 2013

Eur J Org Chem

View full text Add to dashboard Cite

show abstract

“…[28,29] Dimethylimidazolium carboxylate is the ideal precursor for the generation of an N-heterocyclic carbene [32,33] at the Cu center. Previous studies have demonstrated that carbene bonding to small molecule Cu I complexes is established via the decarboxylation of this precursor, [34] and we have now demonstrated the suitability of this decarboxylation protocol for the formation of high-valent Cu II NHC complexes. [30] Therefore, we adopted this approach to install an exogenous carbene ligand at the Cu center of Azu H117G (H117G~NHC) by the decarboxylation of N,N'dimethylimidazolium carboxylate (Scheme 1).…”

mentioning

confidence: 71%

“…We used an excess of the pure imidazolium-carboxylate (250 equivalent) [30] to promote the binding of the carbene to the mutagenized Cu site. This methodology is highly tolerant to water, [34] and the reaction was conveniently performed in an aqueous MES buffer. The addition of the carbene precursor rapidly induced a color change of the protein in solution from colorless to blue, essentially identical to the change observed when reconstituting the T1 Cu center of the H117G~H2O mutant by adding exogenous NMI (see above).…”

mentioning

confidence: 99%

Carbene in Cupredoxin Protein Scaffolds: Replacement of a Histidine Ligand in the Active Site Substantially Alters Copper Redox Properties

et al. 2018

Self Cite

View full text Add to dashboard Cite

N-heterocyclic carbene (NHC) ligands have had a major impact in homogeneous catalysis, however, their potential role in biological systems is essentially unexplored. Here we replaced a copper-coordinating histidine (His) in the active site of azurin with exogenous dimethyl-imidazolylidene; this NHC rapidly restores the type-1 Cu center with spectroscopic properties (EPR, UV-vis) that are identical to those from Ncoordination of the His in the wild type. However, the introduction of the NHC markedly alters the redox potential of the metal, key functionality of this blue copper protein. These results suggest that C-bonding for histidine is plausible and a potentially relevant bonding mode of redox-active metalloenzymes in their (transient) active states.

show abstract

“…84 It was also employed for the formation of copper, cobalt, and silver complexes. [85][86][87][88] Thus, complex 126 was formed in 90% yield.…”

mentioning

confidence: 99%

Recent advances in neutral and anionic N-heterocyclic carbene – betaine interconversions. Synthesis, characterization, and applications

Schmidt¹,

Wiechmann²,

Freese³

2013

Arkivoc

View full text Add to dashboard Cite

Some mesoionic compounds, i.e. five-membered representatives of the class of conjugated mesomeric betaines (CMB), are in equilibrium with their tautomeric normal N-heterocyclic carbenes (nNHC). In addition, anionic N-heterocyclic carbenes, generated by deprotonation of mesoionic compounds, have been described. The first examples of conversions of crossconjugated mesomeric betaines (CCMB), 6-oxopyrimidinium-4-olates, into normal Nheterocyclic carbenes have been reported as well. CCMB such as imidazolium-4-carboxylate and pyrazolium-4-carboxylate can decarboxylate to form abnormal (aNHC) or remote N-heterocyclic carbenes (rNHC). Most conversions of betaines into N-heterocyclic carbenes start from pseudocross-conjugated mesomeric betaines (PCCMB) which can be regarded as heterocumulene adducts of nNHC. Thus, decarboxylations of imidazolium-2-carboxylates, 1,2,4-triazole-3-carboxylates, pyrazolium-3-carboxylates or indazolium-3-carboxylates yield N-heterocyclic carbenes which have been used in catalysis, complex chemistry, heterocyclic synthesis, and organocatalysis.

show abstract

Comparison of carbene and imidazole bonding to a copper(I) center

Cited by 15 publications

References 46 publications

N‐Heterocyclic Carbene Dirhodium(II) Complexes as Catalysts for Allylic and Benzylic Oxidations

N‐Heterocyclic Carbene Dirhodium(II) Complexes as Catalysts for Allylic and Benzylic Oxidations

Carbene in Cupredoxin Protein Scaffolds: Replacement of a Histidine Ligand in the Active Site Substantially Alters Copper Redox Properties

Recent advances in neutral and anionic N-heterocyclic carbene – betaine interconversions. Synthesis, characterization, and applications

Contact Info

Product

Resources

About