Homoleptic chelating N-heterocyclic carbene complexes of palladium and nickel

Herrmann, Wolfgang A.; Schwarz, J.; Gardiner, Michael G.; Spiegler, Michael

doi:10.1016/s0022-328x(98)00980-2

Cited by 143 publications

(96 citation statements)

References 11 publications

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“…Crystals suitable for crystal structure determination were obtained by slow diffusion of Et 2 O into a DMSO solution. The analytical data are identical to those reported previously [12,13].…”

Section: [Pdi 2 (Biscarbenepr 2 )] (2b)supporting

confidence: 84%

“…This reaction scheme represents a further simplification of the preparation of homoleptic carbene complexes. Initially, 6a was prepared in low yields from 1a with BuLi as the base [12], later a two-step procedure was reported using NaOAc [13]. Both complexes 6a and 6b appeared to be virtually insoluble in organic solvents such as CH 2 Cl 2 or CHCl 3 , though very soluble in polar solvents like DMSO.…”

Section: Tetracarbene Palladium Complexesmentioning

confidence: 99%

“…Notably, 6 can be obtained from the bisimidazolium precursor 1 either directly (see above) or in a sequential reaction via initial formation of 2 in the absence of an external base, and subsequent reaction of 2 and another equivalent of ligand in the presence of a base such as NaOAc [13] or NEt 3 . In order to check whether 2 is an intermediate during the direct formation of 6, the reaction of [Pd(OAc) 2 ] with 2 moleq.…”

Section: Role Of the Basesmentioning

confidence: 99%

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Synthesis and structural analysis of palladium biscarbene complexes derived from bisimidazolium ligand precursors

Heckenroth

Neels

Stœckli-Evans

et al. 2006

Inorganica Chimica Acta

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Dedicated to Gerard van Koten with deep appreciation for his outstanding contribution to the organometallic chemistry of late transition metals. AbstractThe palladation of potentially chelating bisimidazolium ligand precursors with palladium acetate gives bridging bimetallic, chelating monometallic, and homoleptic tetracarbene complexes. The coordination mode of the biscarbene ligand has been identified by spectroscopic analysis and crystallographic characterization of representative complexes, including the first example of a biscarbene A-frame structure. Substantial concentrations of free acetate favor the formation of tetracarbene over biscarbene palladium complexes, while in the absence of a base, the concentration of reactants influences the selectivity for bridging bimetallic versus chelating monometallic species. Preliminary kinetic and mechanistic studies indicate that chelating biscarbene palladium acetate complexes are intermediates in the formation of the homoleptic tetracarbene complexes. Probably due to the high trans effect of the biscarbene ligand, such complexes are more efficient palladating agents for bisimidazolium salts than palladium acetate.

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Section: [Pdi 2 (Biscarbenepr 2 )] (2b)supporting

confidence: 84%

Section: Tetracarbene Palladium Complexesmentioning

confidence: 99%

Section: Role Of the Basesmentioning

confidence: 99%

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Synthesis and structural analysis of palladium biscarbene complexes derived from bisimidazolium ligand precursors

Heckenroth

Neels

Stœckli-Evans

et al. 2006

Inorganica Chimica Acta

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“…27 Anion exchange was recently reported to yield a dimeric structure that is closely related to that of 7. 28 However, the Pd ◊ ◊ ◊ Pd distance in the C2-bound analogue (3.1683(6) Å ) is substantially larger than that of 7.…”

Section: Impact Of C4 Bonding On Reactivitymentioning

confidence: 99%

Palladation of diimidazolium salts at the C4 position: access to remarkably electron-rich palladium(ii) centers

et al. 2008

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a Palladation of C2-protected diimidazolium salts with Pd(OAc) 2 afforded complexes comprising C4-bound N-heterocyclic dicarbene ligands. The reactivity of these complexes towards Lewis acids (AgBF 4 , AgOAc) and Brønsted acids (H 2 SO 4 , H 3 PO 4 , HOAc) revealed that abnormal C4 bonding of the carbenes markedly increases the nucleophilicity of the coordinated palladium center as compared to C2 bonding. Despite its formal +2 charge, the palladium center in these complexes is best described as a Lewis base. The abnormal carbene bonding mode induces new reaction patterns such as the formation of a Pd-Ag adduct. Based on metallation studies including the palladation of a dissymmetric diimidazolium salt, a rationale for the selective activation of the C4-H bond in the diimidazolium precursor salts is proposed.

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“…The bis-NHC complexes were synthesized according to procedures reported in the literature. 1,2 Standard procedure for H/D exchange reaction. The metal compound was weighed directly into the NMR tube in a N 2 filled glovebox.…”

Section: Methodsmentioning

confidence: 99%

Proton or Metal? The H/D Exchange of Arenes in Acidic Solvents

Munz

Webster‐Gardiner

et al. 2014

ACS Catal.

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The H/D exchange of arenes in acidic media by transition-metal and main-group-metal complexes and common inorganic salts was studied. The influence of Lewis acidity, anions, charge, and ligands was evaluated. The results indicate that the determination of H/D exchange activity in acidic media is not related to the formation of metal−carbon bonds (i.e., C−H activation). The combined experimental data (regioselectivity, activation energy, kinetics, isotope effects, solvent effects) and DFT calculations point toward a proton catalysis mechanism. Thus, highly Lewis acidic metal compounds, such as aluminum(III) triflate, were extraordinarily active for the H/D exchange reactions. Indeed, the degree of H/D exchange reactivity allows for a comparative measurement of Lewis acidities.

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Homoleptic chelating N-heterocyclic carbene complexes of palladium and nickel

Cited by 143 publications

References 11 publications

Synthesis and structural analysis of palladium biscarbene complexes derived from bisimidazolium ligand precursors

Synthesis and structural analysis of palladium biscarbene complexes derived from bisimidazolium ligand precursors

Palladation of diimidazolium salts at the C4 position: access to remarkably electron-rich palladium(ii) centers

Proton or Metal? The H/D Exchange of Arenes in Acidic Solvents

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