Page 7 - Periodic ISSUE 8

Pr
ofessor N ew Research

Malcolm Green Professor
Malcom Green FRS.
Thomas Player reports on some exciting new
FRS research highlights

(1936 – 2020) complexes. Likely
after a fun dinner Anderson Group
The Department was sad to announce the death of with colleagues at
Professor Malcolm Green FRS in July 2020. Malcolm Balliol, he coined the Large aromatic rings
was a global figure in the field of organometallic name “agostic” for
chemistry and was known for his creativity in devising these relatively weak electronic interactions. Agostic
new compounds and in pioneering new ways of making “bonds” play roles in many C-H activation processes Harry Anderson’s group has been exploring the upper
them. He was awarded the prestigious Davy Medal of great importance in the chemical industry. size-limits of aromaticity, whereby certain ring-
of the Royal Society in 1995 “In recognition of his shaped molecules have special electronic and magnetic
contribution to organometallic chemistry with particular We are greatly indebted to Malcolm for his brilliant characteristics compared to non-aromatic compounds,
application to catalytic reactions”. He was an inspiration development of scalable metal vapor synthesis and exhibit distinctive electric currents when in a
to the huge number of undergraduates, Part II & D.Phil. methods to obtain useful quantities of organometallic magnetic field. It can be important to know whether or
students and postdocs whom he taught or guided, and compounds of titanium and other early transition not a particular molecule will be aromatic: but how can
all will have their own fond memories of him. metals. He and I spent many enjoyable hours we tell?
discussing applications of his game changing work All organic chemistry textbooks will tell you to use
Malcolm graduated from Acton Technical College in during my year in Oxford. I also was greatly impressed Hückel’s rule for counting pi-electrons. This simple rule
1956 and obtained his PhD from Imperial College by his development of scalable methods for the is very reliable for small molecules. What was not clear
in 1959 in the group of Geoffrey Wilkinson. He was syntheses of carbon nanotubes. His work, which led was whether it can be extended to far larger rings that
briefly an Assistant Lecturer in Cambridge before to single walled nanotubes that can include metals and contain many more electrons.
moving to Oxford for the rest of his career, becoming other materials, made a huge impact on the course of The molecular structure of one of the large ring complexes over
Fellow of Inorganic Chemistry at Balliol College in nanoscience. The Anderson group’s research into these larger which the aromatic electrons are delocalised.
1963 and a University Lecturer in Inorganic Chemistry rings was recently featured on the cover of Nature
in 1965. He was a Royal Society Senior Research Malcolm had many close friends at Caltech. There was Chemistry, where they measured ring currents in Most textbooks say aromaticity is limited to rings
Fellow from 1979-86, and in 1989 he was elected never a dull day during the year he and Jenny spent nanoscale porphyrin ring structures containing up to with less than about 22 pi-electrons, which makes it
to the Statutory Professorship of Inorganic Chemistry with us. Both in the lab or mixing it up with students 162 pi-electrons, corresponding to n = 40 in Hückel’s interesting to study this effect in much larger rings. It is
and Headship of the Inorganic Chemistry Laboratory, and faculty at the Green house on Hill Avenue in the rule. They observed the presence of aromatic (and also intriguing because, at low temperatures, small non-
becoming a Fellow of St Catherine’s College, until his late afternoon and evening, he was in his element. No anti-aromatic) ring currents for various oxidation states molecular rings of metal display persistent ring currents
retirement in 2004. He was elected Fellow of the one here will ever forget the hugely positive impact he of these nanorings, and were able to control whether and behave like aromatic molecules. This research is
Royal Society in 1985 and was the recipient of many had on our science. or not the molecules were aromatic by varying their exploring to what extent molecular wire rings behave
other major awards and prizes from learned societies structure, oxidation state, and conformation. like small rings of wire.
around the world. He will be sadly missed by all those I have lost a great friend, one who put his stamp on Professor Anderson has recently been awarded an
who knew him. my field as no other. This work involved many NMR oxidation titrations,
some of which threw up results that were at first Advanced Grant from the European Research Council
confusing. It eventually came good though, and with “all (ERC), which will be used to continue exploring the
Harry B Gray, Arnold O. Beckman Professor of boundaries of aromaticity in nanoscale structures.
Chemistry at Caltech, pays tribute to Malcolm’s the observations falling into place, we knew we had just
life and work: proved the validity of Hückel’s rule”. This is how former References: Rickhaus, M. et al., Nature Chemistry
group member Michel Rickhaus, now leading his own
Malcolm Green was a towering figure in inorganic and research group at the University of Zurich, described 12 (2020) 236–241 (doi.org/10.1038/s41557-019-
organometallic chemistry. His work on metal-alkyl the team effort he, Michael Jirasek, and other group 0398-3); Behind the Paper (2020) https://go.nature.
compounds led to the discovery of noncovalent members made to reach their conclusions. com/30CS7pa.
interactions between C-H bonds and empty orbitals
in coordinatively unsaturated early transition metal
Hückel’s rule: if a delocalised loop of p orbitals in a flat molecule contains 4n + 2 electrons (where n is an integer),
then the molecule is expected to be aromatic. Benzene is the classic example with six pi electrons, meaning n = 1.

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