Oleg V. Ozerov - 1:00 p.m.
Associate Professor of Inorganic Chemistry, Brandeis University

"Oxidative Addition Reactions at PNP Supported Metal Centers"

Abstract: Diarylamido-based PNP pincer ligands serve as robust platforms for support of reactive transition metal centers. Unsaturated (PNP)Rh and (PNP)Ir species can be generated in solution, although they are too reactive to be observed directly. (PNP)Rh reacts preferentially via oxidative addition of carbon-heteroatom (C-Hal, C-S, C-O) bonds whereas the analogous iridium fragment prefers to attack C-H bonds in aromatic substrates. The selectivity for the C-H bonds over C-Hal bonds with iridium is kinetic in nature. (PNP)Ir displays high selectivity for aromatic (vs. benzylic) C-H bonds in methylated arenes. However, this selectivity is unexpectedly reversed in the presence of additional donor ligands. The relevance of the reactivity of (PNP)Rh and (PNP)Ir to catalytic bond-breaking and –making processes will be discussed. In addition, we will discuss the binuclear oxidative addition of small molecules to a bimetallic Pd complex.

Lisa M. Berreau - 1:45 p.m.
Associate Professor of Chemistry, Utah State University

"Chemistry of Ni(II) Complexes of Relevance to Intermediates in the Catalytic Cycle of Acireductone Dioxygenases"

Abstract: Acireductone dioxygenases (ARDs) catalyze oxidative carbon-carbon bond cleavage reactions involving an intermediate at a branch point in the methioine salvage pathway. A Ni(II)-containing ARD enzyme catalyzes the O 2-dependent breakdown of acireductone into methylthiopropionic acid, formic acid, and carbon monoxide. This reaction is a shunt out of the methioine salvage pathway. X-ray absorption and 1H NMR spectroscopic studies of Ni(II)-ARD in the presence of substrate under anaerobic conditions indicate the formation of an enzyme/substrate adduct wherein the acireductone substrate is coordinated to the Ni(II) center. This adduct undergoes reaction with O 2 to generate products. To date, the structural features of the enzyme/substrate adduct remain speculative. As an approach toward elucidating structure/reactivity relationships relevant to the enzyme/substrate adduct in Ni(II)-ARD, we have prepared and characterized novel Ni(II) complexes of a bulky acireductone analog substrate. These complexes undergo reaction with O 2 to produce products of an ARD-type reaction (carboxylates and CO) as well as small amounts of additional side products. Details of the synthetic, spectroscopic, and reactivity portions of this research will be presented.

John C. Gordon - 3:00 p.m.
Group Leader, Chemistry Division, Los Alamos National Laboratory

"Chemical Hydrogen Storage at Los Alamos"

Abstract: One of the major technical barriers to the use of clean-burning hydrogen as a transportation fuel is on-board fuel storage. Current storage technologies include liquid or high pressure gas tanks, adsorbent materials, and metal hydrides. The Department of Energy has set gravimetric density (0.09 kg hydrogen per kg of storage weight; at least 9 wt% H 2) and volumetric density (0.081 kg H 2 per liter of storage volume) research goals for 2015, which generally preclude the use of current storage technologies by virtue of their weight. Chemical hydrides, in which hydrogen is stored as covalent E-H bonds (E = main group element), offer advantages for production, transportation and storage of hydrogen for transportation applications. DOE's Chemical Hydrogen Storage Center of Excellence is taking a coordinated approach to identify, research, develop and validate advanced on-board chemical hydrogen storage systems to overcome technical barriers. Some recent technical results from LANL in support of the development of a hydrogen based economy will be presented.

Gregory S. Girolami - 3:45 p.m.
Professor of Chemistry, University of Illinois at Urbana-Champaign

"New Chemistry of Osmium Alkyls and Hydrides: Toward a Stable Methane Complex in Solution"

Abstract: The activation of hydrogen and alkanes is a topic of significant interest to the catalysis community. This talk will describe our studies of new metal hydrides and alkyl complexes, including efforts to prepare kinetically stabile coordination complexes in which one of the ligands is an alkane. We have found that the protonation of certain metal alkyl complexes affords a metal alkyl hydride species that is in rapid equilibrium with a metal alkane complex: the hydrogen atoms of the M-H and M-CH 2R groups are exchanging 100 times per second at -100 ºC, by means of the alkane intermediate M(CH 3R). Related studies of metal dihydrogen complexes will also be discussed.