N-Heterocyclic carbenes (NHCs) have become one
of the most widely studied class of ligands in molecular chemistry
and have found applications in fields as varied as catalysis, the
stabilization of reactive molecular fragments, and biochemistry. More
recently, NHCs have found applications in materials chemistry and
have allowed for the functionalization of surfaces, polymers, nanoparticles,
and discrete, well-defined clusters. In this review, we provide an
in-depth look at recent advances in the use of NHCs for the development
of functional materials.
Herein, we describe
the synthesis of a toroidal Au
10
cluster stabilized by
N
-heterocyclic carbene and
halide ligands
via
reduction of the corresponding
NHC–Au–X complexes (X = Cl, Br, I). The significant
effect of the halide ligands on the formation, stability, and further
conversions of these clusters is presented. While solutions of the
chloride derivatives of Au
10
show no change even upon heating,
the bromide derivative readily undergoes conversion to form a biicosahedral
Au
25
cluster at room temperature. For the iodide derivative,
the formation of a significant amount of Au
25
was observed
even upon the reduction of NHC–Au–I. The isolated bromide
derivative of the Au
25
cluster displays a relatively high
(
ca
. 15%) photoluminescence quantum yield, attributed
to the high rigidity of the cluster, which is enforced by multiple
CH−π interactions within the molecular structure. Density
functional theory computations are used to characterize the electronic
structure and optical absorption of the Au
10
cluster.
13
C-Labeling is employed to assist with characterization of
the products and to observe their conversions by NMR spectroscopy.
We present isolable examples of formal zinc hydride cations supported by N-heterocyclic carbene (NHC) donors, and investigate the dual electrophilic and nucleophilic (hydridic) character of the encapsulated [ZnH](+) units by computational methods and preliminary hydrosilylation catalysis.
The extremely bulky N-heterocyclic carbene (NHC), ITr (ITr=[(HCNCPh ) C:]) featuring sterically shielding umbrella-shaped trityl (CPh ) substituents was prepared. This NHC features the highest percent buried volume (%V ) to date, and was used to form a thermally stable quasi one-coordinate thallium(I) cation [ITr-Tl] . This Tl adduct and the corresponding lithium complex [ITr⋅Li(OEt )] are versatile "all-in-one" transmetalation/ligation reagents for preparing low-coordinate inorganic species inaccessible by pre-existing routes.
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