3 research outputs found
Nitration Under Continuous Flow Conditions: Convenient Synthesis of 2‑Isopropoxy-5-nitrobenzaldehyde, an Important Building Block in the Preparation of Nitro-Substituted Hoveyda–Grubbs Metathesis Catalyst
Herein, we describe the use of continuous flow chemistry
for selective,
efficient and reproducible nitration of 2-isopropoxybenzaldehyde to
produce the desired 2-isopropoxy-5-nitrobenzaldehyde, an important
building block in the preparation of a ligand of nitro-substituted
Hoveyda–Grubbs metathesis catalyst. Nitration was done with
red fuming HNO<sub>3</sub>, and this challenging and hazardous process
was performed using a flow-through silicon-glass microreactor equipped
with a set of temperature sensors, and with a productivity of 13 g/h,
providing us with a reproducible chemical process amenable for production
of sufficient quantities of 2-isopropoxy-5-nitrobenzaldehyde for ongoing
large-scale synthesis of nitro-substituted Hoveyda–Grubbs metathesis
catalyst
Ru-Based Complexes with Quaternary Ammonium Tags Immobilized on Mesoporous Silica as Olefin Metathesis Catalysts
Ruthenium olefin metathesis catalysts
bearing a polar quaternary
ammonium group in N-heterocyclic ligand were immobilized on silica
and siliceous mesoporous molecular sieves with different pore sizes
(SBA-15 and MCM-41). The activity of the heterogeneous catalysts was
found to increase with an increase in pore size of the support used,
with the best results observed for SBA-15-supported catalyst. The
influence of reaction conditions (temperature, solvent, catalyst,
and substrate concentration) on the efficiency of new heterogeneous
catalysts was established. A significant influence of the counterion
present in the ruthenium complex on the activity of immobilized catalysts
was also found: those derived from chloride containing ion exhibited
the highest activity. High activity in ring-closing metathesis of
substrates as citronellene, 1,7-octadiene, and diallyl compounds as
well as in cross-metathesis of unsaturated aliphatic compounds with
methyl acrylate was observed under optimized conditions. In some cases,
heterogenization led to catalysts with efficiency higher than those
observed for corresponding homogeneous complexes
Carboxyl Graphene as a Superior Support for Bulky Ruthenium-Based Olefin Metathesis Catalyst
A Hoveyda-type catalyst decorated
with two quaternary ammonium
tags was synthesized and noncovalently grafted on SiO<sub>2</sub>,
SBA-15, and on carboxyl graphene. A comparative study showed that
the efficiency of the dual-anchored heterogeneous catalysts was highly
dependent on the properties of the supporting material with graphene
outperforming silicate supports. The graphene-immobilized complex
exhibited excellent efficiency reflected in turnover numbers obtained
in ring-closing metathesis and in self-metathesis of 1-decene. Importantly,
the solid-supported catalyst assured increased recyclability with
no ruthenium leaching as confirmed by inductively coupled plasma mass
spectrometry