The Catalyst Review July 2020 - 16

EXPERIMENTAL
impedes the reaction
entirely (entries 5-7).
Change of ligand from
L1 to other similar N,Ndonor ligands (L2-L4) did
not provide any product
formation signifying that
the presence of - OH
group is critical (entries
8-10). Changes in
concentration or use of
methanol/water mixture
did not improve secondary
alcohol (2a) formation
(entries 11-12). Among
the bases screened, KOH
was found to be the best
in combination with L1
and Cp*Ir(III) for efficient
transfer hydrogenation
of ketone (1a) using
methanol as LOHS.

Table 1. Reaction optimization.

Scheme 1. Scope of ketones. Reaction conditions: 1/[Ir]/L1/KOH in
0.4/0.008/0.02/0.04 mmol using methanol (2.0 mL) as solvent at
60°C for 24 h. [a] 1/[Ir]/L1/KOH in 0.4/0.016/0.04/0.08 mmol. [b]
Reaction performed with 0.2 mmol scale with respect to 1u. [c] 1am/
[Ir]/L1/KOH in 0.2/0.008/0.02/0.04 mmol using methanol (1.0 mL)
as solvent at 60°C for 24 h. All the numbers given here are isolated
yields after column chromatography.

With optimal conditions
in hand, the authors then
investigated a wide variety
of ketones, as depicted in
Scheme 1. These results
suggest that the described
catalytic system is a
well-defined metal-ligand
system that works well under moderately basic conditions capable of demonstrating high chemo-selectivity and does not require
any additional organic solvent or special equipment. Source: Garg N, Paira S and Sundararaju B. (2020). ChemCatChem. doi.
org/10.1002/cctc.202000228.
Impact of Alkali and Alkali-Earth Cations on Ni-Catalyzed Dimerization of Butene...
The steam cracking of butenes from naphtha to synthesize branched dimers, for gasoline additives, or into linear dimers as
feedstock relies on the use of catalysts comprised of Ni dispersed on amorphous silica-alumina (ASA). The ASA support provides
both Lewis and Brønsted acid sites, enabling the dispersion and strong interaction of the Ni2+ cations, which, in turn, serve as
the active sites for the dimerization of 1-butene. However, isolated Brønsted acid sites (BAS) catalyze the synthesis of branched
dimers via the formation of secondary carbenium ions, as well as by isomerization of 1-butene to 2-butene. Herein, the authors
explore the role of the cations in the absence of pore confinement to differentiate between intrinsic catalytic properties of Ni2+
cations in the absence of Brønsted acid sites without constraints of a microporous environment.
To this end, they first assessed the concentration of Ni2+ and respective cocations in impregnated samples of amorphous silica-alumina (Table 1). The
catalytically active sites for 1-butene dimerization were then identified as
accessible Ni2+on ASA (Ni-LAS). Ni2+ cations in NiO supported on SiO2 did not
have a sufficiently high catalytic activity to lead to measurable conversions.
Furthermore, the presence of alkali (Na+ or Li+) and alkali-earth (Ca2+ or Mg2+)
co-cations on Ni/ASA blocks BAS that catalyze 1-butene dimerization which
the authors attribute to an increase in the local base strength. As a negative
side effect, the particle size of the supported NiO particles increases, leading
to a decrease in the concentration of Ni2+ cations at exchange positions of
the ASA support. Although the alkali- and alkali earth cations increase the
16

Table 1. Loadings of Ni and the respective co-cations of
the catalysts used in this work. (Determined by AAS).

The Catalyst Review											

July 2020


https://chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/cctc.202000228 https://chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/cctc.202000228

The Catalyst Review July 2020

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