[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.
A series of gold(I)−carbene complexes of the type [Au(R2-bimy)L] (R = Et, Me; bimy =
benzimidazol-2-ylidene; L = Cl, Br, I, bimy, thiophenolate, phenylacetylide) have been
prepared. These carbene complexes are luminous in acetonitrile solution and in the solid
state with long lifetimes at room temperature. Multiple emissions have been observed for
different R and L. The crystal structure of [Au(Me2-bimy)Cl] shows a relatively short
intermolecular AuI−AuI contact of 3.1664(10) Å and an intermolecular ring π−π interaction
with a ring−ring distance of 3.45 Å. The structure of [Au(Et2-bimy)Cl], however, shows only
intermolecular ring−ring interactions with a distance of 3.53 Å. Crystal structure data
suggest that bimy is a high-trans-influence ligand.
Gold(I) carbene complexes of the type [Au(NHC)Cl], where NHC represents N-heterocyclic carbenes, have been synthesized. Two crystal structures of this type show that the molecules are stacked to form a linear polymer with Au‚‚‚Au interactions. Luminous [Au(NHC)(cbz)] (cbz ) carbazolate) were synthesized from [Au(NHC)Cl]. The crystal structure of one of this series indicates that the carbene and cbz rings are coplanar and two molecules are arranged pairwise in a head-to-tail fashion. While all the compounds prepared exhibit high-energy emission bands at ∼400 nm, [Au(NHC)Cl] complexes display additional low-energy emission bands at 580-650 nm, which are attributed to Au-centered transitions involving Au‚‚‚Au interactions. On the other hand, the low-energy emission bands of the [Au(NHC)(cbz)] complexes, which appear at 584-592 nm with fine structures, are likely to arise from the transitions involving mainly carbazolate tuned by Au, as also suggested by the density functional calculations. Crystal structures of Au(I)-dicarbenes are also reported.
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