The catalysis of multi-electron redox reactions is a fundamental problem that has been solved in certain biological systems through the agency of multimetallic enzymes (cytochrome c oxidase, laccase, and nitrogenase). The detailed mechanisms by which these metalloenzymes function are still obscure. Our research is directed towards the synthesis of functional biomimetic catalysts for the electrochemical reduction of dioxygen to water (a 4e- process), nitrogen to ammonia (a 6e- process), and the oxidation of hydrogen (a 2e- process). Recently we have developed several functional models for the active site in cytochrome c oxidase. These complexes reduce O2 by 4e- at pH 7. The complex that is structurally closest to "the real thing," is the best catalyst. By studying the electrocatalytic reduction of dioxgen in lipid layers under conditions of slow electron delivery, we have shown that Cub is necessary to afford selective 4e reduction of dioxygen at physiological potentials.

The enzyme family cytochrome P-450 catalyzes the incorporation of one oxygen atom from O2 into a variety of organic substrates. We are developing chiral porphyrin catalysts for asymmetric, catalytic oxygenation of olefins and hydrocarbons. We have also developed Fe porphyrins that have normal O2, but low CO affinities. We are exploring an alternative mechanism by hydrocarbon C-H oxygenation.

We are exploring the synthesis, structural characterization, spectroscopic properties (Raman, IR, NMR), electrochemistry, magnetic properties and chemical reactions of 4d and 5d metalloporphyrin dimers. These manifest the entire range of M-M bond orders: 1, 1.5, 2, 2.5, 3, 3.5, and 4. Recently we have prepared and structurally characterized multiple bonds between metals in different triads of the periodic table.

1) "Heterodinuclear Transition Metal Complexes with Multiple Metal-Metal Bonds," J.P. Collman and R. Boulatov, Angew. Chem., Int. Ed., 41, 3948-3961 (2002).

2) "Functional analogs of the dioxygen reduction site in terminal oxidases: mechanistic aspects and possible effects of CuB." R. Boulatov, J.P. Collman, I.M. Shiryaeva, and C.J. Sunderland, J. Am. Chem. Soc., 124, ASAP (2002).

3) "Electrocatalytic O2 reduction by synthetic analogs of the heme/Cu site of cytochrome oxidase incorporated in a lipid film," J.P. Collman and R. Boulatov, Angew. Chem. Int. Ed., 41, 3489-3491 (2002).

4) "Electrochemical metalloporphyrin-catalyzed reduction of chlorite," J.P. Collman, R. Boulatov, C.J. Sunderland, I.M. Shiryaeva, and K.E. Berg, J. Am. Chem. Soc., 124, 10670-10671 (2002).

5) "Functional Analogues of Cytochrome c Oxidase, Myoglobin and Hemoglobin," J.P. Collman, R. Boulatov, C.J. Sunderland, and L. Fu, Chem. Rev., 104, 561-588 (2004).

6) "Radical Autoxidation and Autogenous O2 Evolution in Manganese Porphyrin Catalyzed Alkane Oxidations with Chlorite," J.P. Collman, L.M. Slaughter, T.A. Eberspacher, and J.I. Brauman, Inorg. Chem., 43, 5198-5204 (2004).

7) "The Mechanism of Dihydrogen Cleavage by High-Valent Metal Oxo Experimental and Computational Studies," J.P. Collman, L.M. Slaughter, T.A. Eberspacher, T. Strassner, and J.I. Brauman, Inorganic Chemistry, 40, 6272-6280 (2001).

8) "The First Quadruple Bond Between Elements of Different Groups," J.P. Collman, R. Boulatov, and G.B. Jameson, Angew. Chem. Int. Ed., 40, (7) 1271-12744 (2001).

9) "Multiple Active Oxidants in Cytochrome P-450 Model Oxidations," J.P. Collman, A.S. Chien, T.A. Eberspacher, and J.I. Brauman, J. Am. Chem. Soc., 122, 11098-11100 (2000).

10) "Synthetic Models for Hemoglobin and Myoglobin: Issues and Recent Success," J.P. Collman and L. Fu, Acc. Chem. Res., 32, 455-463 (1999).

11) "Clicking Functionality onto Electrode Surfaces," J.P. Collman, N.K. Deveraj, C.E.D. Chidsey, Langmuir, 20(4), 1051-1053 (2004).

12) "Functional Analogs of Heme Protein Active Sites," J.P. Collman, Inorg. Chem., 36, 5145-5155 (1997).