Facile Synthesis of Silver(I)−Carbene Complexes. Useful Carbene Transfer Agents

Abstract

[Ag(Et2-Bimy)2][AgBr2] (1; Et2-Bimy = diethylbenzimidazol-2-ylidene) was obtained readily from the reaction of [Et2-BimyH]Br with Ag2O. Compound 2, [Ag(Et2-Bimy)2]PF6, was prepared by the reaction of [Et2-Bimy]PF6 with Ag2O under basic phase transfer catalysis conditions. Both compounds 1 and 2 are good carbene transfer agents. Thus, Pd(Et2-Bimy)2Cl2, Au(Et2-Bimy)Br, and [Au(Et2-Bimy)2]PF6 were obtained in high yields using 1 and 2 as carbene sources. The byproduct AgBr or AgCl can be reused to generate 1 under basic phase transfer catalysis conditions. The crystal structure of compound 1 revealed that linear [Ag(Et2-Bimy)2]+ and [AgBr2]- groups were associated through a short AgI−AgI contact (2.956 Å). FAB/mass spectrometry and molar conductivity measurements indicate the existence of ligand-unsupported AgI−AgI interactions in the gas phase and acetonitrile solution. 13C NMR studies suggest that the two Bimy ligands in 1 are fluxional in solution.

Platinum(ii) N-heterocyclic carbene complexes: coordination and cyclometallation.

“…Silver NHC salts were then prepared via the reaction of imidazolium salt with silver oxide in DCM. 5,6,8 …”

“…3 Relatively simple synthetic procedures leading to precursor imidazolium salts have been elucidated, 4 and many routes that allow the introduction of an NHC ligand to a metal centre have been developed. The reaction of imidazolium salts with silver oxide giving an NHC complex of silver, which serves as a useful trans-metallating reagent, has proved particularly popular, [5][6][7][8] and we use it in this paper. Other interesting methods include the utilisation of an electron-reservoir complex, together with air, to generate NHCs, 9 or the use of imidazolium-2-carboxylates which lose CO 2 to generate NHCs, 10 though, increasingly, direct reaction of the imidazolium salt with the metal has found favour.…”

Polymer precursors from catalytic reactions of natural oils

“…The direct NHC transfer from one metal centre to another, in one reaction, appears most practical and straightforward. As an example of this transmetallation approach, the silver-mediated reaction is the most common method for NHC transfer, 279,280 and in this manner, transmetallation can be achieved successfully with numerous metals. 281,282 However, the NHC transfer from silver does not always proceed correctly.…”

Efficient Electronic Communication of Two Ruthenium Centers through a Rigid Ditopic N‐Heterocyclic Carbene Linker

“…Therefore, formation of the carbene silver intermediate was performed in MeOH and the solvent was then changed to CH 2 Cl 2 for the transmetalation, without any purification or characterization of the probably polymeric silver complex. [23] Complex 5 is an air-stable orange solid. While HPLC-MS analysis suggests a pure compound, NMR spectroscopic analysis shows two distinct sets of signals that were attributed to the rac and meso diastereoisomers of 5 as a consequence of the chirality of the complex at each ruthenium center.…”