11/14/17 - 9:45 AM to 11:00 AM
Student Seminar Series: Professor Robert H. Crabtree
Student Seminar Series
"Iridium Catalysts for Water Oxidation, CH Hydroxylation and Alcohol Dehydrogenation"
Alternative energy requires electrocatalysis, for example of water oxidation. Homogeneous oxidation catalysis is harder to arrange than reduction or redox-neutral cases. For one thing the ligands must be oxidation-resistant, hence our choice of pyalk (1). In the protonated form, pyalkH, this binds to the low valent metal precursor but on oxidation it loses the proton to become an exceptionally strong donor, both σ and π. Another feature of our best complexes is coplanar binding of the alkoxides or other anionic ligands. By raising the energy of just one of the dπ orbitals, filled in d6 octahedral Ir(III), we destabilize one pair of electrons so that oxidation with loss of these two electrons gives d4 octahedral Ir(V). We also apply the same ideas to Rh, but here only Rh(IV) was accessible. Our catalytic solutions for water oxidation to O2 are too complex to characterize but model compounds were fully characterized in III, IV and V states. A Cu(pyalk)2 catalyst has also proved effective but this is still under study. The Ir catalyst can be attached to surfaces but depending on the case, the activity is sometimes reduced. Several new techniques for crystallizing these intermediates have proved valuable. These complexes are also active for CH oxidation in alkanes (or alkyl groups) with retention of configuration at carbon. Finally, we look at oxidation by dehydrogenation as applied to biomass conversion.
At Yale since 1977, Robert “Bob” Crabtree is now Whitehead Professor. In early work, he reversed homogeneous catalytic alkene hydrogenation to attain the goal of alkane dehydrogenation. The so-called Crabtree catalyst has proved useful for certain challenging cases and has therefore seen broad use. This was followed by work on complexation of molecular hydrogen to metals and finding a new type of hydrogen bonding that he called dihydrogen bonding. Recently, he developed water oxidation and C-H bond conversion to C-OH with iridium catalysts in connection with the problem of green catalysis and alternative energy production. He has been an American Chemical Society (ACS) and Royal Society of Chemistry (RSC) organometallic chemistry awardee, Baylor Medallist, Dow, Williams and Mond lecturer, Centenary awardee, has chaired the ACS Inorganic Division and is the author of an organometallic textbook in its 6th edition. He is a Fellow of the ACS, RSC,International Union of Pure and Applied Chemistry, and the American Academy as well as a member of the National Academy of Sciences.
Professor Crabtree's research encompasses the design and synthesis of inorganic, coordination or organometallic molecules with unusual structures and properties. These are typically catalytic properties for atom economic (green) transformations, bioinorganic relevance or utility in alternative energy strategies, such as solar energy and hydrogen storage. Molecular recognition is applied to homogeneous catalysis to obtain high selectivity. Computational and physicochemical insights are obtained from collaborative work.