Organometallic Chemistry
(The A-Team)
Hydroelementation
Lanthanides and actinides offer a new frontier in organometallic chemistry. Our interests include tuning electrophilic f-element centers to effect unusual types of transformations. Closely coordinated are computational and thermochemical investigations of bonding and bond energies. These offer deeper insight into bonding and aid in designing new reactions.
With recent advances in lanthanide-mediated catalysis and bond-energy studies, we are developing f-element catalysts for hydrosilation, hydroalkoxylation, hydroamination, and hydrothiolation. We are also investigating the use of “green” solvents, including ionic liquids, as media for hydroelementation reactions. Hydrothiolation of terminal alkynes and aromatic and aliphatic thiols is efficiently carried about with lanthanide and actinide catalysts. This transformation is clean, highly selective, and typically quantitative. Mechanistic studies implicate a turnover-limiting insertion of the alkyne into the metal-sulfur bond, followed by rapid cleavage of product from the metal. These reaction systems are also being explored as chain transfer agents to effect polymer molecular weight and microstructure.
Bimetallic Catalysis
We are synthesizing group 4 and group 10 bimetallic polymerization catalysts. A ligand system has been designed to keep two metal centers in close proximity. The resulting catalysts have high functional group tolerance and activity. Compared with monometallic analogues, the bimetallic systems have 2x the ethylene polymerization activity, 2x the branch density, and 3x greater selectivity for comonomer enchainment.
Supported Catalysis
Our group is exploring the use sulfated metal oxides as supports for group 4 metallocene-based catalysts. The sulfated metal oxides have sufficient acidity to activate as well as support the catalysts, and the resulting catalysts can be more active then homogeneous catalysts. These supported catalysts have been used for olefin polymerization as well as benzene hydrogenation. We are currently studying the effects of the support on catalyst activity, as well as performing EXAFS measurements to determine surface interactions.
Lanthanides and actinides offer a new frontier in organometallic chemistry. Our interests include tuning electrophilic f-element centers to effect unusual types of transformations. Closely coordinated are computational and thermochemical investigations of bonding and bond energies. These offer deeper insight into bonding and aid in designing new reactions.
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Bimetallic Catalysis
We are synthesizing group 4 and group 10 bimetallic polymerization catalysts. A ligand system has been designed to keep two metal centers in close proximity. The resulting catalysts have high functional group tolerance and activity. Compared with monometallic analogues, the bimetallic systems have 2x the ethylene polymerization activity, 2x the branch density, and 3x greater selectivity for comonomer enchainment.
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Supported Catalysis
Our group is exploring the use sulfated metal oxides as supports for group 4 metallocene-based catalysts. The sulfated metal oxides have sufficient acidity to activate as well as support the catalysts, and the resulting catalysts can be more active then homogeneous catalysts. These supported catalysts have been used for olefin polymerization as well as benzene hydrogenation. We are currently studying the effects of the support on catalyst activity, as well as performing EXAFS measurements to determine surface interactions.
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We are studying organometallic grafting reactions for the development of selective oxidation catalysts. Using well-defined molecular precursors, we prepare structurally defined heterogeneous catalyst species. These catalysts are characterized by a variety of analytical techniques including solid state NMR, UV-Raman, UV-Vis DRS, and X-ray absorption spectroscopies. Catalytic studies are currently underway.
Nanocomposites
We support polymerization catalysts on surfaces of inorganic nanoparticles and then in situ
polymerization produce polymers surrounding the nanoparticles to form nanocomposites. These
nanocomposites combine the best properties of both inorganic fillers and polymer matrix. They are
used as dielectrics with high dielectric permittivity, high breakdown strength, low loss, and fast
response.
- Rodriguez, B.A.; Delferro, M.; Marks, T.J. Enchainment Cooperativity Effects in Neutrally Charged Bimetallic Nickel (II) Phenoxyiminato Polymerization Catalysts, and Enhanced Selectivity for Polar Comonomer Enchainment, J. Am. Chem. Soc., 2009 , 131, 5902-5919.
- Weiss, C.J.; Wobser, S.D.; Marks T.J. Organoactinide-Mediated Hydrothiolation of Terminal Alkynes with Aliphatic, Aromatic, and Benzylic Thiols, J. Amer. Chem. Soc., 2009, 131, 2062-2063.
- Dzudza, A.; Marks, T.J. Efficient Intramolecular Hydroalkoxylation/Cyclization of Unactivated Alkenols Mediated by Lanthanide Triflate Ionic Liquids, Organic Letters, 2009 , 1846-1848.
- Yuen, H.F.; Marks, T.J. Phenylene-Bridged Binuclear Organolanthanide Complexes as Catalysts for Intramolecular and Intermolecular Hydroamination, Organometallics, 2009 , 28, 2423-2440.
- Williams, L.A.; Marks, T.J. Chemisorption Pathways and Catalytic Olefin Polymerization Properties of Group 4 Mono- and Binuclear Constrained Geometry Complexes on Highly Acidic Sulfated Alumina, Organometallics, 2009, 28, 2053-2061.
- Seo, S.Y.; Yu, X.; Marks, T.J. Intramolecular Hydroalkoxylation/Cyclization of Alkynyl Alcohols Mediated by Lanthanide Catalysts. Scope and Reaction Mechanism, J. Am Chem. Soc, 2009, 131, 263-276.
- Salata, M.R.; Marks, T.J. Catalyst Nuclearity Effects in Olefin Polymerization. Enhanced Activity and Incorporation of Comonomers in Ethylene + Olefin Copolymerizations Mediated by Bimetallic Group 4 Phenoxyiminato Catalysts, Macromolecules, Macromolecules , 2009, 42, 1920-1933.
- Motta, A.; Fragala, I.L.; Marks, T.J. Proximity and Cooperativity Effects in Binuclear d0 Olefin Polymerization Catalysts. Theoretical Analysis of Structure and Mechanism, J. Amer. Chem. Soc. , 2009, 131, 3974-3984.
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