The Catalyst Review September 2017 - 16

EXPERIMENTAL
been developed for the preparation of
important esters and derivatives thereof.
Of interest is the recently reported
palladium-catalyzed Markovnikov
methoxycarbonylation of 1-alkenes -
considered to be the first example of the
preparation of branched esters.

Scheme 2. A) Ruthenium-catalyzed methylation of amines and sulfo-namides using
methanol. B) Proposed reaction mechanism.

Finally, mention is made of the oxidation
of alcohols to carbonyl compounds
and esters - a crucial transformation
in synthetic chemistry. Specifically, the
oxidative formation of methyl esters from
alcohols constitutes a direct and green
approach for the preparation of aromatic,
aliphatic, and heterocyclic methyl esters.
Source: Natte K, Neumann H, Beller M,
Jagadeesh RV. (2017). Angew. Chem. Int.
Ed., 56, 6384-6394.

Tuning the Ti3+ and Al3+ Synergy in an Al2O3/TiClx Catalyst to Modulate the Grade of the Produced
Polyethylene...
The authors previously reported the synthesis of a new alumina-supported Ziegler−Natta (Z-N) catalyst capable of producing
branched polyethylene using ethylene as the only feed and which does not require the use of an activator. The Al2O3/TiClx catalyst
was obtained through thermal reduction of the Al2O3/ TiCl4 pre-catalyst in H2, leading to a completely dehydroxylated and chlorinated
alumina surface exposing highly acidic Al3+ sites and reduced Tilt species. The Al3+ Lewis acid sites oligomerize ethylene to branched
oligomers via a carbocationic mechanism and activate the reduced titanium chloride species for copolymerizing the in situ-produced
branched oligomers with ethylene. Herein, they describe an alternative strategy for activating the Al2O3/TiCl4 precatalyst using AlEt3
(TEA), a classical co-catalyst
Figure 1. (A) FT-IR spectra of δ-Al2O3−600
Figure 2. (A) DR UV−vis spectra of δ-Al2O3−600
in Ziegler−Natta catalysis.
(spectrum 1), theδ-Al2O3−600/TiCl4 precatalyst
(spectrum 1), theδ-Al2O3−600/TiCl4 precatalyst
The formation of the catalyst
(spectrum 2), and the δ-Al2O3−600/TiCl4/TEA and
(spectrum 2), and the δ-Al2O3−600/TiCl4/TEA and
was investigated using a
δ-Al2O3−600/TiCl4/H2−400 catalysts (spectra
δ-Al2O3−600/TiCl4/H2−400 catalysts (spectra 3a and
3a and 3b, respectively). (B) FT-IR spectra of
3b, respectively). (B) Experimental (thick line)
series of complementary
δ-Al2O3−600/TiCl4/H2−400 and δ-Al2O3−600/TiCl4/
and simulated (thin line) X-band CW EPR spectra
spectroscopic techniques
TEA catalysts after subtraction of spectrum 2,
of the δ-Al2O33−600/TiCl4/TEA (spectrum 3a) and
aimed at identifying the
compared to the FT-IR spectrum of liquid TEA
δ-Al2O3−600/TiCl4/H2−400 (spectrum 3b) catalysts.
electronic structure and the
collected in ATR mode. Spectra 1, 2, and 3b are
The EPR spectra were recorded at 77 K. Spectra
the same spectra discussed in ref 14 and are
1, 2, and 3b are the same spectra discussed
coordinative environment
reproduced here for sake of comparison with
in ref 14 and are reproduced here for sake of
of the reduced Ti sites and
spectrum 3a.
comparison with spectrum 3a.
3+
their interaction with the Al
sites. These studies included
FT-IR Spectroscopy (Figure
1), Diffuse Reflectance (DR)
Ultraviolet−Visible−NearInfrared (UV−vis−NIR)
Spectroscopy (Figure 2),
Electron Paramagnetic
Resonance (EPR), and
Differential Scanning
Calorimetry (DSC).
Analysis of the data collected
using these techniques indicates that activation by TEA induces the formation of small reduced TiClx clusters that coexist with
chemisorbed HCl species, which is responsible for the production of a highly crystalline HDPE. In contrast, thermal activation in H2
leads to the formation of isolated Ti3+ sites (responsible for olefin polymerization via coordination) on an extensively chlorinated
16

The Catalyst Review

September 2017

The Catalyst Review September 2017

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