2 research outputs found
Macrocyclic Platforms for the Construction of Tetranuclear Oxo and Hydroxo Zinc Clusters
The
design of ligands that can act as platforms for the controlled,
“bottom-up” synthesis of transition-metal clusters is
a promising approach to accessing enzymatic mimics and new small-molecule
reaction chemistry. This approach is exemplified here through the
coordination chemistry of two compartmental Schiff-base calixpyrroles
(H<sub>4</sub>L) that usually act as dinucleating ligands for transition
metals. While reactions between H<sub>4</sub>L and ZnÂ{NÂ(SiMe<sub>3</sub>)<sub>2</sub>}<sub>2</sub> form the expected dinuclear Zn “Pacman”
complexes Zn<sub>2</sub>(L), reactions with ZnEt<sub>2</sub> result
in the tetranuclear Zn alkyl complexes Zn<sub>4</sub>Et<sub>4</sub>(THF)<sub>4</sub>(L), in which open, “bowl-shaped”
structures are adopted due to the flexibility of the macrocyclic platform.
The outcome of hydrolysis reactions of these tetranuclear complexes
is found to depend on the macrocyclic cavity size, with the smaller
macrocycle favoring oxo formation in Zn<sub>4</sub>(ÎĽ<sub>4</sub>-O)ÂEt<sub>2</sub>(L) and the larger macrocycle favoring complete
hydrolysis to form the hydroxide-bridged cluster Zn<sub>4</sub>(ÎĽ<sub>2</sub>-OH)<sub>4</sub>(L). This latter complex reacts with carbon
dioxide at elevated temperature, re-forming the free macrocycle H<sub>4</sub>L and eliminating ZnCO<sub>3</sub>
Catalytic α‑Arylation of Imines Leading to N‑Unprotected Indoles and Azaindoles
A palladium N-heterocyclic
carbene catalyzed methodology for the
synthesis of substituted, N-unprotected indoles and azaindoles is
reported. The protocol permits access to various, highly substituted
members of these classes of compounds. Although two possible reaction
pathways (deprotonative and Heck-like) can be proposed, control experiments,
supported by computational studies, point toward a deprotonative mechanism
being operative