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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.
IMes is a free NHC that can be used as a ligand. Other NHCs have been isolated as the free ligands. [6] Aside from IMes, another important NHC ligand is IPr, which features diisopropylphenyl groups in place of the mesityl groups. [1] [7] NHCs with saturated backbones include SIMes and SIPr.
This suggests an origin for the efficacy of NHC transfer chemistry from Ag NHC complexes, with weaker M-NHC bonds in addition to the straightforward synthetic route described previously. [5] Further charge-decomposition analysis of the three model complexes suggests that the- major contribution to covalent bonding arises from the NHC to M σ ...
NHC boryl anions have stronger electron-releasing character when compared to normal NHCs. [3] These characteristics make NHC boryl anions key ligands in many applications, such as polycyclic aromatic hydrocarbons, and more commonly low oxidation state main group element bonding.
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.
One quintessential dinitrogen complex of a main group element is Gernot Frenking’s triphenylphosphinazine, first reported in 2013 in Angewandte Communications. [6] This compound was notable for demonstrating the double Lewis acid behavior of dinitrogen, as the publication describes the N 2 moiety in the doubly excited 1 Γ g state with four lone pairs on N—N fragment.
This process can be used in conjunction with the in situ generation of free carbenes. Pd-NHC complexes can also be synthesized through transmetalation with silver-NHC complexes. The transmetallated NHCs can either be isolated for subsequent reaction with palladium in a two-step method, or generated in the presence of palladium in a one-pot ...