Angewandte
Research Articles
Chemie
How to cite: Angew. Chem. Int. Ed. 2021, 60, 10964–10970
International Edition:
German Edition:
Metal-Organic Frameworks
Amino Acid-Functionalized Metal-Organic Frameworks for
Asymmetric Base–Metal Catalysis
Rajashree Newar+, Naved Akhtar+, Neha Antil+, Ajay Kumar, Sakshi Shukla, Wahida Begum,
Abstract: We report a strategy to develop heterogeneous
single-site enantioselective catalysts based on naturally occur-
ring amino acids and earth-abundant metals for eco-friendly
asymmetric catalysis. The grafting of amino acids within the
pores of a metal-organic framework (MOF), followed by post-
synthetic metalation with iron precursor, affords highly active
and enantioselective (> 99% ee for 10 examples) catalysts for
hydrosilylation and hydroboration of carbonyl compounds.
Impressively, the MOF-Fe catalyst displayed high turnover
numbers of up to 10000 and was recycled and reused more
than 15 times without diminishing the enantioselectivity. MOF-
Fe displayed much higher activity and enantioselectivity than
its homogeneous control catalyst, likely due to the formation of
robust single-site catalyst in the MOF through site-isolation.
commercial supply chain planning. Immobilization of cata-
lytically active species on solid supports may results in
enhanced catalyst stability, activity and recyclability,[4] but
traditional heterogenization of homogeneous catalysts onto
oxide supports has met limited success owing to the presence
of multiple active-sites, difficulty in characterization and
complication in optimizing and uniformly distributing the
catalytic species. Therefore, the development of highly active
and enantioselective heterogeneous catalysts from earth-
abundant metals and cheap chiral feedstocks is crucial for
sustainable asymmetric synthesis.
Amino acids or protected amino acids are an important
class of chiral ligands from synthetic and industrial viewpoints
as they are cheap, naturally occurring, scalable, easily tunable
and air-stable.[5] However, the application of amino acids as
chiral ligands to prepare robust single-site base-metal cata-
lysts is very limited due to their lack of steric bulkiness and
limited solubility in organic solvents. Constructed from metal-
cluster secondary building units (SBUs) and organic linkers,
metal-organic frameworks (MOFs) provide a unique plat-
form for the simple preparation of single-site chiral catalysts
via site-isolation owing to their porous and crystalline nature
as well as modular and tunable properties.[6] Unlike the
traditionally supported catalysts, MOF-catalysts combine
both the advantages offered by heterogeneous catalysts such
as high stability, facile catalyst separation and recovery, less
leaching of active metals, and those provided by their
homogeneous counterparts such as homogeneity of the active
sites, reproducibility and selectivity.[7] Inspired by the recent
reports on the development of amino acid- or peptide-
functionalized-MOFs,[8] we surmised that the post-synthetic
metalation of chiral amino acid grafted MOF with base-
metals would afford single-site amino acid ligated earth-
abundant metal catalysts for asymmetric organic transforma-
tions (Figure 1). Herein, we report a synthetic strategy of
developing highly active, enantioselective and easily tunable
heterogeneous iron catalysts based on MOFs having chiral
pores derived from naturally occurring amino acids for
asymmetric reduction of ketones.
Introduction
Owing to the growing demand of optically pure com-
pounds, as well as the increasingly strict safety, quality and
environmental requirements of industrial synthetic processes,
the development of sustainable strategies for the synthesis of
chiral molecules is still a challenge in chemical and pharma-
ceutical industries. Heterogeneous catalysis is a cornerstone
of the chemical industry, as heterogeneous reactions are
recyclable and are typically less step-, solvent- and energy-
intensive than their homogeneous counterparts. However, the
production of optically active ingredients in industries
typically relies on solvent-intensive optical resolution or
homogeneous catalysts made of precious and toxic late
transition metals,[1] primarily because of the lack of efficient
heterogeneous and chiral first-row metal catalysts.[2] Homo-
geneous chiral earth-abundant metal catalysts typically con-
stitute bulky phosphine- or nitrogen-donor chiral ligands to
avoid intermolecular decomposition.[3] Unfortunately, several
factors such as high cost, lack of commercial availability, poor
scalability of its synthesis or intellectual property restrictions
render the use of many such chiral ligands impractical on
a bulk scale, and thus presents a significant problem in
[*] R. Newar,[+] N. Akhtar,[+] N. Antil,[+] Dr. A. Kumar, S. Shukla, W. Begum,
Prof. Dr. K. Manna
Results and Discussion
Department of Chemistry, Indian Institute of Technology Delhi
Hauz Khas, New Delhi, 110016 (India)
Three chiral MOF-iron catalysts were synthesized follow-
ing a multi-step post-synthetic modifications of easily afford-
able amine-tagged zirconium UiO-68 MOF of Zr6O4(OH)4-
(L-NH2)6 (L-NH2 = 2’-amino-[1,1’:4’,1’’-terphenyl]-4,4’’-dicar-
boxylate) as shown in Figure 2a. UiO-type MOFs built from
E-mail: kmanna@chemistry.iitd.ac.in
[+] These authors contributed equally to this work.
Supporting information and the ORCID identification number(s) for
the author(s) of this article can be found under:
10964
ꢀ 2021 Wiley-VCH GmbH
Angew. Chem. Int. Ed. 2021, 60, 10964 –10970