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In coordination chemistry, a transition metal NHC complex is a metal complex containing one or more N-heterocyclic carbene ligands. Such compounds are the subject of much research, in part because of prospective applications in homogeneous catalysis. One such success is the second generation Grubbs catalyst. [1] IMes is a popular NHC ligand.
Ever since the first crystalline carbene structure was isolated by Arduengo ins 1990, tuning different properties of NHCs has been a popular area of study in main group chemistry. [4] The first NHC boryl anion was synthesized by Segawa in 2006. [1]
When a dimethyl group was added to C exo, the reaction no longer proceeds this way, and was able to polymerize lactide, δ-valerolactone, and ω-pentadecalactone. While this broadened the scope and speed of the polymerization, the reaction was difficult to control due to the formation of an enolate intermediate.
When the alkyl group bridges two main group elements, the bonding is called three-center two-electron bonds. This pattern is seen for dimethyl beryllium and trimethylaluminium. In the case of methyl lithium, the methyl group can be shared (bonded to) three Li centers. These bonding aspects influence the structures: Trimethylaluminium, dimethyl ...
This effect can be used to stabilize highly reactive main group and transition metal compounds. [6] [22] Because excessive steric hindrance can be an issue for some reactivity, NHCs and CAACs bearing substituents with multiple spatial conformations (e.g. cyclohexyl) offer "flexible steric bulk" for catalysis.
The success of normal NHCs is greatly attributed to their superior σ-donating capabilities as compared to phosphines, which is even greater in abnormal NHC counterparts. Employed as ligands in palladium complexes, NHCs contributed greatly to the stabilization and activation of precatalysts and have therefore found application in many areas of ...
Adding "steric hindrance" to a molecule's reactive site through bulky groups is a common strategy in molecular chemistry to stabilize reactive moieties within a molecule. [3] In this case bulky ligands like terphenyls , bulky alkoxides , aryl-substituted NHCs , etc. serve as a protective wrapper on the molecule. [ 1 ]
In chemistry the polyhedral skeletal electron pair theory (PSEPT) provides electron counting rules useful for predicting the structures of clusters such as borane and carborane clusters. The electron counting rules were originally formulated by Kenneth Wade , [ 1 ] and were further developed by others including Michael Mingos ; [ 2 ] they are ...