Bear, John - University of Houston - Department of Chemistry

个人简介

M.A. Southwest Texas State University, 1956 B.S., Southwest Texas State University, 1955

研究领域

Over the past few years our research has been aimed at understanding structure reactivity relationships of several group VIII-B dinuclear transition metal complexes and to use this information to control the chemical and electrochemical reactivity at the metal centers. Among these complexes, the dirhodium and diruthenium compounds are the most sensitive to the nature of the axial and bridging ligands with respect to variation in their chemical and electrochemical behavior. The reactivity at a metal center depends on the sigma donor-pi acceptor properties of the bridging ligand, the geometric bonding arrangement, and the steric environment about the reactive site of the metal. For example the Rh24+/Rh25+ redox couple can be controlled over the range from approximately 2.0 V for Rh2(tfac)4 to -0.63V for Rh2(ap)4(CCH)2 (tfac = trifluoroacetate ion; ap = 2-anilino-pyridinate ion). The same type of control is true for other dirhodium redox couples corresponding to the formation of (MI - MII), (MII - MII), (MII - MIII), (MIII - MIII), and (MIII - MIV) oxidation states. The objectives of our current research are: (i) to investigate the mechanism of bridging ligand exchange reactions and determine the factors that control the different geometric isomers formed; (ii) to investigate structure-reactivity relationships of dirhodium and dirhuthenium transition metal complexes with a variety of homo- and hetero-do nor bridging ligand and use this information to understand and control metal centered reactivity; (iii) to investigate the chemistry of the three geometric isomers of the family of complexes with the formula Ru2(F(5-x)Hxap)4Cl. These complexes exhibit a very different chemistry which is related to their unique structural and electronic features. (iv) to investigate the factors that determine the electronic electronic structure of diruthenium complexes.

近期论文

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"John L. Bear, Baocheng Han, Shurong Huang and Karl M. Kadish, ""The Effect of Axial Ligands on the Oxidation State, Structure and Electronic Configuration of Diruthenium Complexes. Synthesis and Characterization of Ru2(dpf)4Cl, Ru2(dpf)4(CCC6H5),Ru2(dpf)4(CCC6H5)2 and Ru2(dpf)4(CN)2 where dpf = N,N'-diphenylformamidinate,"" Inorg. Chem., 35, 3012 (1996). John L. Bear, Yulan Li, Baocheng Han, Eric Van Caemelbecke, and Karl M. Kadish, ""Synthesis and Characterization of a new Strucural Type of Di-ruthenium(III) Complex,"" Inorg. Chem., 35, 3053, (1996). John L. Bear, Yulan Li, Baocheng Han, Eric Van Caemelbecke, and Karl M. Kadish, ""Synthesis, Molecular Structure and Electrochemistry of a Paramagnetic Diruthenium(III) Complex.Characterization of Ru2(hpp)4(Cl)2, Where hpp is the 1,3,4,6,7,8-Hexahydro-2H-pyrim-ido[1,2-a] pyrimidinate ion,"" Inorg. Chem., 35, 1395, (1996). John L. Bear, Yulan Li, Baocheng Han, Eric Van Caemelbecke, and Karl M. Kadish, ""Isomer Effect on the Structure and Chemical Reactivity of Diruthenium Complexes. Synthesis and Characterization of the (4,0), (3.1) and (2,2) trans Isomers of Ru2(F5ap)4Cl and Ru2(F5ap)4-(CCC 6H5)2, where F5ap is the 2-(2,3,4,5,6-pentafluoroanilino)pyridinate Anion,"" Inorg. Chem., 36, 5449 (1997). John L. Bear, Yulan Li, Jing Cui, Boacheng Han, Eric Van Caemelbecke, Tuan Phan and Karl M. Kadish, ""The Reaction Between the (3,1) Isomer of Ru2(F5ap)4Cl and CN-. Synthesis, Structural, Determination and Electrochemistry of Ru2(F5ap)3[m-(o-NC)F4ap](m-CN) and Two Geometric Isomers of Ru2(F5ap)4[m-CN)2,"" Inorg. Chem., 39, 857, (2000). John L. Bear, Yulan Li, Boacheng Han, Eric Van Caemelbecke and Karl M. Kadish, ""Syntheses and Characterization of the Diruthenium(III) Complexes Ru2(F4Oap)2(F5ap)2 and Ru2(F4Oap)(F4NCNap)(F5ap)2 (where F4Oap is 2-(3,4,5,6,-tetrafluoro-2-oxonilino)-pyridinate Anion, F4NCNap is the 2-(3,4,5,6,-Tetrafluoro-2-cyanim-adoanilino) pyridinate Anion),"" Inorg. Chem. 40, 182, (2001)."