Background:

• Councilor, ACS Division of Inorganic Chemistry, 1986-88
• Program Chairman, Inorganic Division, ACS, 1989-92
• Chair, Inorganic Division, ACS, 1998

We are attempting to explore and exploit a class of compounds of the transition metals, M, of general formula MHxCl4Ln where L is a bulky phosphine PR3. The metal is "unsaturated," meaning it has empty orbitals that can bind substrate for subsequent catalytic reaction. The function of the hydride ligands H is to migrate easily and transform the substrate. The function of the chloride (or any halide) is to "tune" rationally the reactivity of the molecule. For example, we have found that fluoride, in place of chloride, enables transfer of H between the relatively unreactive hydrogens of benzene and ethylene; no other halide can make that claim!

Recently, we have discovered how to create metal complexes that have two empty orbitals, "14-electron complexes," which enhance their catalytic potential for substrate binding. A detailed look at the structure and bonding of such 14-electron species shows that they are so hungry for donor groups that they bind the aliphatic H of C-H bonds in the R substituent of PR3. The enhanced reactivity of one example, RuHCl(PiPr3)2, is shown by its ability to isomerize an olefin, H2C=C(H)(OR), into a carbene C(CH3)(OR)!

By systematic comparative study of two transition metals from the iron group, we have shown that 4d vs. 5d metals can have dramatically different stability preferences:

These species, isomeric by virtue of locating H on carbon (Ru case) or on the metal (Os), completely change the electronic structure of the molecules, and thus their catalytic activity for olefin metathesis. We are currently exploring applications of this concept of "redox isomerism."

The final step in production of metallic aluminum is reduction at a carbon electrode in a fluoride electrolyte, and a side product of this creates undesirable CF4. We are exploring transition metal complexes as a way to transform these C-F bonds into more valuable products. When we introduce CF3 in place of F in RuHF(CO)L2, the product, at 20°C, is the already CF-cleaved product RuHF(CO)(CF2)L2, the carbene complex illustrated. Hydrogen converts the carbene ligand to CF2H2, thus showing the potential of this methodology.

Selected Publications:

Facile alkane functionalization in copper-[2.1.1]-(2,6)-pyridinophane-PhINTs systems, Andrei N. Vedernikov and Kenneth G. Caulton, Chem. Commun., 2004, 162-163.

Reactivity of the hydrido/nitrosyl radical MHCl(NO)(CO)(PⁱPr₃)₂, M = Ru, Os, Alexei V. Marchenko, Andrei N. Vedernikov, David F. Dye, Maren Pink, Jeffrey M. Zaleski, and Kenneth G. Caulton, Inorg. Chem., 2004, 43, 351-360.

Facile C(sp²)/O₂CR bond cleavage by Ru or Os, German Ferrando, Joseph N. Coalter, Helene Gerard, Dejian Huang, Odile Eisenstein, and Kenneth G. Caulton, N. J. Chem., 2003, 27, 1451-1462.

Double C(sp³) dehydrogenation as a route to coordinated Arduengo carbenes: Experiment and computation on comparative p-acidity, Victoria M. Ho, Lori A. Watson, John C. Huffman, and Kenneth G. Caulton, N. J. Chem., 2003, 27, 1446-1450.

A p-basic rhenium center that effects cyclohexene isomerization to a β-agostic carbene ligand, Oleg V. Ozerov, Lori A. Watson, Maren Pink, Kenneth G. Caulton, J. Am. Chem. Soc., 2003, 125, 9604-9605.

Angular ligand constraint yields an improved olefin aziridination catalyst, Andrei Vedernikov and Kenneth G. Caulton, Org. Lett., 2003, 5, 2591-2594.

Four-coordinate, planar Ru(II). A triplet state as a response to a 14-valence electron configuration, Lori A. Watson, Oleg V. Ozerov, Maren Pink, Kenneth G. Caulton, 2003, 125, 8426-8427.

Conversion of ethylene to hydride and ethylidyne by an amido rhenium polyhydride, Oleg V. Ozerov, John C. Huffman, Lori A. Watson, Kenneth G. Caulton, Organometallics, 2003, 22, 2539-2541.

Design and synthesis of tridentate facially chelating ligands of the [2.n.1]-(2,6)-pyridinophane family, Andrei N. Vedernikov, Maren Pink, Kenneth G. Caulton, J. Org. Chem., 2003, 68, 4806-4814.

Evaluation of energies of isomeric SO₂ complexes, Alexei V. Marchenko, Andrei N. Vedernikov, John C. Huffman, and Kenneth G. Caulton, New J. Chem., 2003, 27, 680.

[2.1.1]-(2,6)-Pyridindophane(L)-controlled alkane C-H bond cleavage: (L)PtMe2H as a precursor to the geometrically "tense" transient (L)PtMe, Andrei N. Vedernikov, John C. Huffman, and Kenneth G. Caulton, New J. Chem., 2003, 27, 665.

N-PtIV-H/N-H---PtII intramolecular redox equilibrium in a product of H-C(sp²) cleavage and unusual alkane/arene C-H bond selectivity of ([2.1.1]pyridinophane)PtII(CH₃) , Vedernikov, A.N. and Caulton, Kenneth G., Chem. Commun., 2003, 358-359.

Amido/phosphine pincer hydrides of ruthenium, Watson, L. A., Coalter, J.N., III, Ozerov, O., Pink, M., Huffman, J.C., and Caulton, K.G., New J. Chem., 2003, 27, 263-273.

Control of H-C(sp³) bond cleavage stoichiometry: clean reversible alkyl ligand exchange with alkane in [LPt(alk)(H)₂](L=[2.1.1]-(2,6)-pyridinophane), Vedernikov, A.N. and Caulton, K.G., Angew. Chem., Int. Ed., 2002, 41, 4102-4104.

Vinyl C-F Cleavage by Os(H)₃Cl(PiPr₃)₂, Ferrando-Miguel, G., Gerard, H., Eisenstein, O., and Caulton, K.G., Inorg. Chem., 2002, 41, 6440-6449.

Coordination Chemistry of Tripyridinedimethane, Vedernikov, A.N., Huffman, J.C., and Caulton, K.G., Inorg. Chem., 2002, 41, 6244-6248.

[n.1.1]-(2,6)-Pyridinophanes: A New Ligand Type Imposing Unusual Metal Coordination Geometries, A.N. Vedernikov, J.C. Huffman, and K.G. Caulton, Inorg. Chem., 2002, 41, 6867.

An Electron-Excessive Nitroxyl Complex: Reactivity of a Ligand-Centered Radical Leading to Coordinated HNO, A.V. Marchenko, A. N. Vedernikov, D.F. Dye, M. Pink, J.M. Zaleski, and K.G. Caulton, Inorg. Chem. Comm., 2002, 41, 4087-4089.

Condensation of 2-pyridylmethyllithium nucleophiles and pyridine electrophiles as a convenient synthetic route to polydentate chelating N-donor ligands, A.N. Vedernikov, R. Miftakhov, S.V. Borisoglebski, K.G. Caulton, B.N. Solomonov, Chemistry of Heterocyclic Compounds, 2002, 38, 406-416.

Evolving approaches to integration of computational with experimental chemistry: an example from osmium hydrido (h¹/h²-)nitrosyl/nitroxyl chemistry, Vedernikov, A.N. and Caulton, K.G., New J. Chem., 2002, 26, 1267-1269.

Double Silyl Migration Converting Ore[N(SiMe₂CH₂PCy₂)²] to NRe[O(SiMe₂CH₂PCy₂)²] Substructures, Ozerov, O.V., Gerard, H.F., Watson, L.A., Huffman, J.C., and Caulton K.G., Inorg. Chem., 2002, 41, 5615-5625.

Conventional Lithium Bases as Unconventional Sources of Methyl Anion: Facile Me-Si and Me-C Bond Cleavage in RLi, R₂NLi, and BR₄-by an Electrophilic Osmium Dihydride, Organometallics, 2002, 21, 4030-4049.

Geminal dehydrogenation of ether and amine C(sp³)H₂ groups by electron-rich Ru(II) and Os, Ferrando-Miguel, G., Coalter, J.N., III, Gerard, Helene, Huffman, J.C., Eisenstein, O., and Caulton, K.G., New J. Chem., 2002, 26, 687-700.

Assessing isomeric structures of pincer-ligand ruthenium and osmium polyhydrides using density functional calculations, Watson, L.A. and Caulton, K.G., Molecular Physics, 2002, 100, 385-395.

Electrophilic (Li) acceleration of C-H reductive elimination and oxidative addition reactions of Os(II)/Os(0) nitrosyl complexes, Dmitry V. Yandulov and Kenneth G. Caulton, New J. Chem., 2002, 26, 498.

Cu(I) and Cu(II) complexes of a pyridine-based pincer ligand. Andrei N. Vedernikov, Peng Wu, John C. Huffman, Kenneth G. Caulton, Inorganica Chimica Acta, 2002, 330, 103.