Carl D. Hoff
Professor, Inorganic Chemistry

Ph.D., University of Missouri-Kansas, 1977
Research Associate, University of Georgia,
1977-79

E-mail: choff@jaguar.ir.miami.edu

There are a number of challenging problems in the inorganic chemistry of catalytic processes. The synthesis, structure, reactivity, and physical chemistry of chromium, molybdenum, and tungsten is the main area of our research. The development and utility of active catalysts requires understanding fundamental reactions at the individual molecular level. In inorganic chemistry that remains a challenge for many simple molecules. In particular our recent work focuses on how metal based radicals interact with S8, H2S, and NO. Hydrodesulfurization is a major industrial catalytic process catalyzed by molybdenum/sulfur complexes. Nitrogen fixation is a major biochemical process also catalyzed by molybdenum/sulfur complexes. A number of enzymes from nitrogenase to xanthine oxidase contain the molybdenum-sulfur bond. Many ligands bound to a metal are "innocent" in the sense that they modify the metal complex properties but are not themselves the site of reactivity. That is not the case with sulfur. The ability to bind and store hydrogen as coordinated thiols, and to undergo coupling to form coordinated disulfides, as well as a other reactions give the molybdenum sulfur enzymes a complex nature. The authors laboratory has made a number of advances in understanding how third order and radical reactions activate the sulfur-hydrogen bond. Work in progress will give insight into how highly reactive radicals can be generated and utilized in design of catalytic reactions. The final steps in design of real world catalysts will involve proper choice of supramolecular assembly of the individual component reactions. It is the authors view that the role of the complex structures of enzymes may be less that of facilitating reactions needed in catalysis, than eliminating those that are not.

• Kiss, G.; Nolan, S. P.; Hoff, C. D. "Direct Solution Calorimetric Measurements of Proton and Electron Transfer Reactions for Transition Metal Complexes. Thermochemical Study of Metal-Hydride and Metal-Metal Bond Energies." Inor. Chim. Acta., 1994. 227, 285.

• Lang, R. F.; Ju, T. D.; Kiss, G.; Hoff, C. D.; Bryan, J. C.; Kubas, G. J.; "Oxidative Addition of Disulfides, Thiols, and Hydrogen Sulfide to the Complex W(CO)3(phen)(EtCN). Synthesis, Structure, and Reactivity of W(CO)2(phen)(SPh)2, a Coordinatively Unsaturated W(II) Complex that Reversibly Binds CO and Other Ligands." Inorg. Chem., 1994, 33, 3899.

• Lang, R. F.; Ju, T. D.; Kiss, G.; Hoff, C. D.; Bryan, J. C.; Kubas, G. J.; "Oxidative Addition of Thiols, Disulfides, Iodine, and Hydrogen Iodide to W(CO)3(PiPr3)2. Preparation of Stable 17 Electron Tungsten-Thiolate Radicals from Complexes with Weak W-H Bonds." J. Amer. Chem. Soc., 1994, 116, 7917.

• Kiun, J.; Zhang, S.; Basolo, F.; Ju, T. D.; Lang, R. F.; Kiss, G.; Hoff, C. D.; "Ground State Versus Transition State Effects in Arene Displacement Reactions of Complexes AreneCr(CO)3: Arene = Benzene, Naphthalene, Anthracene, Pyrene, Triphenylene, Thiophene, and Dimethylthiophene." Organometallics, 1994, 13, 3692.

• Lang, R. F.; Ju, T. D.; Hoff, C. D.; Bryan, J. C.; Kubas, G. J.; "Synthesis and Structure of W(CO)(phen)(SPh)2(n2-SO2)-A W(II) Sulfur Dioxide Complex that Spontaneously Extrudes Sulfur to Form the W(VI) Dioxo Complex W(phen)(SPh)2(=O)2." J. Amer. Chem. Soc., 1994, 116, 9747.

• Mukerjee, S. L.; Gonzales, A. A.; Nolan, S. P.; Ju, T. D.; Lang, R. F.; Hoff, C. D.; "Heats of Reaction of HMo(CO)3(C5R5)(R = H, CH3) wotj Diphenyldisulfide, and of Formation of the Clusters [PhSMo(CO)x(C5H5)]2. Thermodynamic Study of Molybdenum-Sulfur Bond Strengths." Inorg. Chim. Acta.; 1995, 240, 175.

• Ju, T. D.; Lang, R. F.; Hoff, C. D.; "Oxidative Addition of Butanethiol and Thiophenol to the Cr(CO)3C5Me5 Radical. Thermodynamic and Kinetic Study of a Third Order Reaction and its Catalysis." J. Amer. Chem. Soc.; 1996, 118, 5328.

• Lang, R. F.; Ju, T. D.; Bryan, J. C.; Kubas, G. J.; Hoff, C. D.; "Reaction of the Complexes M(PR3)2(CO)3(M = Cr, Mo, W, R = iPr, Cy) with Thiols, Hydrogen Sulfide, Disulfides, Hydrogen Iodide, and Iodine. The Role of Heteroatoms in Determining the Metal-Hydrogen Bond Strength at a Sterically Crowded Metal Center." Inorg. Chim. Acta.; 1997, 259, 317.

• Bender, B. R.; Jones, L. H.; Swanson, B. I.; Eckerd, J.; Capps, K. B.; Hoff, C. D.; "Why Does D2 Bind Better than H2? A Theoretical and Experimental Study of the Equilibrium Isotope Effect for the Binding of H2 in a M(n2-H2) Complex. Normal Coordinate Analysis of W(CO)3(PCy3)(H2)." J. Amer. Chem. Soc.; 1997, 119, 9179.

• Ju, T. D.; Capps, K. B.; Rober, G. C.; Lang, R. F.; Hoff, C. D.; "Reaction of Phenyl and Methyl Disulfude with Cr(CO)3C5Me5 and HCr(CO)3C5Me5. Metal Radical and Metal Hydride Reactivity at the Sulfur-Sulfur Bond. Different Mechanisms for Oxidative Addition on Alkyl and Aryl Disulfides." Inorg. Chem.; 1997, 36, 614.

• Ju, T. D.; Capps, K. B.; Roper, G. C.; Lang, R. F.; Hoff, C. D.; "First and Second Order Mechanisms for Oxidative Addition of Bound Methyl Disulfide in the Complex W(CO)3(phen)(MeSSMe)." Inorg. Chim. Acta., 1998, 270, 488.

• Capps, K. B.; Wixmerten, B.; Bauer, A.; Hoff, C. D.; "Thermochemistry of Sulfur Atom Transfer. Enthalpies of Reaction of Phosphines with Sulfur, Selneium, and Tellurium and of Desulfurization of Triphenylarsenic Sulfide, Triphenyl Antimony Sulfide, and Benzyl Trisulfide." Inorg. Chem.; 1998, 37, 2861.