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Reed, Christopher A
Distinguished Professor of Chemistry
Christopher Reed began research in 1968 at The University of Auckland with Warren R. Roper F.R.S. His M.Sc. and Ph.D. theses on the oxidative addition chemistry of iridium complexes resulted in 11 original papers in journals of The Chemical Society. In postdoctoral work with James. P. Collman at Stanford University he synthesized “picket fence porphyrin”, a model for hemoglobin that has found its way into most biological and inorganic textbooks. In his independent career, he went on to develop the principles that underlie spin state/structure relationships in all hemoproteins. His 1981 article on this subject in Chemical Reviews with crystallographer W. Robert Scheidt (publication # 50) remains definitive and continues to be heavily cited (>350 citations to date). During these studies, Reed synthesized the first model compound for the quantum mechanically admixed spin state proposed for cytochrome c (publication # 35; 277 citations). Conceptually distinct from a spin state equilibrium, this phenomenon has yet to be found outside of iron(III) chemistry. More recently, it has been used to develop a “Magnetochemical Series” alternative to the familiar Spectrochemical Series (publication # 130). The magnetochemical approach offers a considerably more sensitive indicator of ligand field strength and is also more fundamentally rooted in s rather than p bonding effects. During the 1980’s, the Reed labs made many original contributions to bioinorganic chemistry, particularly with iron and copper. Highlights include model compounds for cytochrome c and an understanding of the factors that control cytochrome redox potentials (publication # 52), extensive imidazolate chemistry (e.g. publication # 43), spectroscopically accurate model compounds for hemocyanin (publication # 59) and orbital symmetry arguments to rationalize spin-spin coupling phenomena (publications # 66, 103). The decade-old question of metal versus ligand oxidation in oxidized iron(III) porphyrins was resolved in favour of a porphyrin p-cation radical formulation following new synthetic work, the discovery of an infrared marker band (publication # 48; >140 citations) and the application of other spectroscopies (publication # 66; >100 citations). In the late 1980’s, Reed proposed carboranes as candidates for the most inert, least coordinating anions in chemistry (publications # 67, 88, 147). With icosahedral carboranes of the type CB11H6Cl6-, this was realized in the synthesis of the closest approach to the long sought trialkylsilylium ion (R3Si+) (publications # 108, 148). His arguments on the nature of these controversial species have prevailed over those of G. A. Olah. More recently, carborane anions have allowed the isolation and X-ray structural characterization of protonated arenes, so-called Wheland intermediates in electrophilic aromatic substitution, which were previously amenable to study only at sub-ambient temperatures (publications # 147, 149). The salt of protonated benzene is a weighable, crystalline superacid stable to 170° C. Superacid chemistry, which has not changed significantly in the last 25 years, is being taken to new levels by the production of clean, non-oxidizing, Lewis acid-free superacids. Conceptually critical to this development is the strict separation of Bronsted-Lowry acidity from oxidation and anion nucleophilicity, a combination that destroys many reactive cations in traditional superacid media such as HF/SbF5. In this way, carborane anions have not only allowed the development of a new level of non-oxidizing acidity, they have also given access to a new level of non-acidic oxidation. Very strong, electron-abstracting oxidants, the synthetic equivalents of controlled potential coulommetry, have been synthesized with a level of anion inertness not currently available in electrochemistry. They have led to the synthesis of the first fullerenium cations, C76+ and C60+, the first all-carbon carbocations (publication # 135; Chem. & Eng. News May 4, 1998, p. 49; Chem. in Britain, 1998, 24 (8), p 19). In parallel to these developments with very weakly coordinating anions, new weak interactions of neutral ligands have been observed. These include the first X-ray structure of a free alkane complex (publication # 138) and the coordination of benzene to hard transition metals such as iron(III). These studies have given widespread pause to use of the terms “non-coordinating anion” and “non-nucleophilic solvent”. Reed has also made substantial contributions to the field of fullerene chemistry. His studies on discrete C60n- fullerides (publications # 106, 113, 124) have revealed that the C603- ion, active in superconducting phases with alkali metals, does not obey Hund’s rule. This poses a challenge for theory because its (t1u)3 configuration is not subject to a Jahn-Teller distortion. Studies on the C602- ion gave rise to the first ordered structure of a fulleride ion (publication # 113) allowing the first experimental assessment of Jahn-Teller distortions in fullerides. Contributions in other areas of fullerene chemistry include the synthesis of covalently linked fullerene/porphyrin conjugates for photophysical studies, solvatochromism studies, vibrational assignments, analysis of the factors affecting redox potentials and more recently, the identification of a new supramolecular recognition element – the spontaneous attraction of a fullerene to the centre of a porphyrin, at unusually close van der Waals approach (2.7 – 2.9 Å).
University of Southern California (1973-1998)
Alfred P. Sloan Research Fellow (1976-78)
Professor Reed is primarily an inorganic chemist who specializes in making molecules that haven't been made before. Current research targets include a new class of superacids, a new class of ionic liquids, self assembling fullerene/porphyrin supramolecular conjugates, hemoprotein model compounds, novel carbon-based materials, complexes of xenon, inert anions and reactive cations across the periodic table. These systems are applied to problems of acid catalysis, bioinorganic chemistry and materials science.
147. "Carboranes: A New Class of Anions for Strong Electrophiles, Oxidants and Superacids," Reed, C. A., Accounts Chem. Res., 1998, 31, 133-139.