The Catalyst Review October 2019 - 6

PROCESS NEWS
Losing the Metal to Make Organoboron Bonds...
Creating new carbon-carbon bonds is the backbone of synthesizing drugs and natural products. Ultimately, many chemists do this
through a Suzuki coupling reaction, which marries an organohalide to an organoboron to beget the desired C-C bond. Now, two
independent groups have come up with a simpler way to insert the necessary B atoms, an advance that could make it easier to
make organoboron compounds. Both groups used indoles, bicyclic compounds made up of a benzene ring fused to a pyrrole ring,
to figure out their new coupling reactions. Indoles are important precursors to many biomolecules and drugs, and their chemistry is
well understood. Chemists know how to get a boron atom onto the pyrrole's C-2 and C-3 positions of an indole, but they have had
a harder time cracking the benzyl backbone. "Reactivity in the pyrrolic unit has lower barriers," says Michael Ingleson, a chemist
from the University of Edinburgh and an author
on the Angewandte Chemie International Edition
paper. "It's been historically challenging to get the
other side," he says. Chemists have traditionally
made indoles substituted on the benzyl ring from
aryllithiums via lithium-halogen exchange or
directed ortho metalation, says Nanjing University
chemist Zhuangzhi Shi, an author on the Nature
paper. Expensive transition-metal catalysts can
install a boron in a C-H bond, but they are a source of contamination and have to be removed to create, for example, pure batches
of pharmaceuticals. Both groups sought to remove these metals. Each team found that it could eliminate the catalysts by using BBr3
as a boron source on a variety of N-pivaloyl indoles. The acyl oxygen attached to the pyrrole ring directs the boron group to the
C-7 position to make a chelate-supported intermediate (shown). The chemists then added pinacol to remove the bromine groups,
yielding the borylated indole. In addition, the researchers found that this reaction also works well with analines, a class of aromatic
amines. The new method is elegant and can compete with many transition-metal systems, says Frédéric-Georges Fontaine, a greencatalysis chemist from Laval University. He says the method's efficient selection of boron sites is impressive and opens a new door to
the benzyl end of an indole, which has always been elusive. Source: Chemical & Engineering News (C&EN), 10/9/2019.

Industry Perspectives (continued from page 1)

The American Chemistry Council (ACC) (Washington, DC) estimates the potential economic impact of plastic recycling and
recovery technologies in the United States at about $10 billion. Details are in the report "Economic Impact of Advanced Plastics
Recycling and Recovery Facilities in the U.S." (February 2019). The ACC also created the Chemical Recycling Alliance.
Government research laboratories are stepping up R&D on technical solutions to plastic waste challenges. For example, the
Alliance for Sustainable Energy, LLC, the manager and operator of the National Renewable Energy Laboratory (NREL) of the US
Department of Energy (DOE), has been developing a process to make fiber-reinforced plastics (FRPs) by combining reclaimed
PET with bio-based monomers. This PET upcycling process saves energy and reduces greenhouse gas emissions compared to
standard petroleum-based FRPs.
Catalysis has played a vital role in the plastics industry from the beginning, e.g., Ziegler-Natta, olefin metathesis, metallocene,
and single-site catalysis. Catalysis will continue to enable innovation throughout the plastics life-cycle, from monomers to
polymers, and in chemical recycling. Catalysis R&D traditionally has been focused on product selectivity, but for recycling mixed
plastics, feedstock selectivity is also important. Catalyst separation from the reaction mixture and reuse requires creative
technology, such as ionic liquids and organic catalysts.
In conclusion, plastic waste is a serious global environmental problem. Comprehensive technical solutions that are practical and
economical at commercial scale need to be developed and deployed soon. Efforts are under way, but substantial investments
in R&D, recycling facilities, infrastructure, and supply chains will be needed over the next several decades. Companies need to
anticipate future regulations and customer preferences regarding plastics, and to have the technical capabilities to satisfy them.
About the Author

Dr. Sorab R. Vatcha is a consultant and author in catalysis, chemicals, energy, and environmentally sustainable
("green") products and technologies. His career in consulting, industry, and academia spans four decades. He
has contributed to The Catalyst Review and the Catalytic Advances Program (CAP) of TCG/TCGR. He has an SM
in management of technology from MIT and a PhD in chemical engineering from Caltech. He is a Registered
Professional Engineer (PE), a member of several professional societies, and the author of numerous publications and
presentations.
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The Catalyst Review

October 2019

The Catalyst Review October 2019

Table of Contents for the Digital Edition of The Catalyst Review October 2019