Ken Caulton received a B.A. at Carleton College in 1962. He was awarded his Ph.D. Ph.D. at the University of Wisconsin in 1968. Caulton studied molecular orbital theory for his PhD thesis under Dick Fenske, then did an experimental postdoctoral at MIT with Al Cotton, before joining IU.
Caulton’s research has been in the areas of transition metal hydride chemistry as it relates to homogeneous catalysis and photochemistry. His work has been directed towards making exceptionally unsaturated metal complexes where the several empty orbitals enable reactivity with fast rates (hence less energy-consuming), and with high capabilities for attacking even the most inert of bonds, such as C-H and C-F. A topic of special interest is learning the characteristic reactivities of transition metal radical molecules, including those where significant spin density “leaks” onto the ligand. Can there be reactions which are "spin forbidden?"
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.
[Ni{N(SiMe2CH2PtBu2)2}]+: direct observation of transannular Si-C(sp3) bond coordination. Fan, H.; Fullmer, B. C.; Pink, M.; Caulton, K. G., Angewandte Chemie, International Edition, 2008, 47(47), 9112-9114.
Reactivity of the Radical NO With a Masked Form of 14 Valence Electron (PNP)Rh: Forming Rh(0, I or II)?. Verat, A. Y.; Pink, M.; Fan, H.; Fullmer, B. C.; Telser, J.; Caulton, K. G., Eur. J. Inorg. Chem., 2008, (30), 4704-4709.
Spin state, structure, and reactivity of terminal oxo and dioxygen complexes of the (PNP)Rh moiety. Verat, A. Y.; Fan, H.; Pink, M.; Chen, Y.-S.; Caulton, K. G., Chem.—A Eur. J., 2008, 14(25), 7680-7686.
Influence of the Metal Orbital Occupancy and Principal Quantum Number on Organoazide (RN3) Conversion to Transition-Metal Imide Complexes. Walstrom, A. N.; Fullmer, B. C.; Fan, H.; Pink, M.; Buschhorn, D. T.; Caulton, K. G., Inorg. Chem., 2008, 47(19), 9002-9009.
[(tBu2PCH2SiMe2)2N]RhI? Rapidly reversible H-C(sp3) and H-C(sp2) bond cleavage by rhodium(I). Verat, A. Y.; Pink, M.; Fan, H.; Tomaszewski, J.; Caulton, K. G., Organometallics, 2008, 27(2), 166-168.
Coupling of terminal alkynes by RuHXL2 (X = Cl or N(SiMe3)2, L = PiPr3). Lee, J.-H.; Caulton, K. G., J. Organometallic Chem., 2008, 693(8-9), 1664-1673.
Mechanism of alkyne conversion to carbyne by 14- or 16-electron Os(H)2ClL2X (L = PiPr3; X = OTf or B(C6H3(CF3)2)4). Lee, J.-H.; Pink, M.; Smurnyy, Y. D.; Caulton, K. G., J. Organometallic Chem., 2008, 693(8-9), 1426-1438.
Nitrogen-Ligated Iron Complexes: Photolytic Approach to the FeN+ Moiety. Buschhorn, D.; Pink, M.; Fan, H.; Caulton, K. G., Inorg. Chem., 2008, 47(12), 5129-5135.
O/C Bond Cleavage of CO2 by Ni. Fullmer, B. C.; Fan, H.; Pink, M.; Caulton, K. G.. Inorg. Chem., 2008, 47(6), 1865-1867.
The Effect of One Valence Electron: Contrasting (PNP)Ni(CO) with (PNP)Ni(NO) to Understand the Half-Bent NiNO Unit. Fullmer, B. C.; Pink, M.; Fan, H.; Yang, X.; Baik, M.; Caulton, K. G., Inorg. Chem., 2008, 47(9), 3888-3892.
Redox Chemistry of the Triplet Complex (PNP)CoI. Ingelson, M. J.; Pink, M.; Fan, H.; Caulton, K. G., J. Amer. Chem. Soc., 2008, 130(13), 4262-4276.
Influence of the d-Electron Count on CO Binding by Three-Coordinate [(tBu2PCH2SiMe2)2N]Fe, -Co, and –Ni. Ingleson, M. J.; Fullmer, B. C.; Buschhorn, D. T.; Fan, H.; Pink, M.; Huffman, J. C.; Caulton, K. G., Inorg. Chem., 2008, 47(2), 407-409.
Metal-Dependent Reactivity Differences for Transients Formed by Flash Photolysis of (PNP)M(CO), M=Co and Rh. Rimmer, R. Dale; Grills, David C.; Fan, Hongjun; Ford, Peter C.; and Caulton, Kenneth G., J. Amer. Chem. Soc., 2007, 129(50), 15430-15431.
Exploring the Reactivity of Four Coordinate PNPCoX with Access to Three Coordinate, Spin Triplet PNPCo. Ingelson, M. J.; Pink, M.; Fan, H.; Caulton, K. G., Inorganic Chemistry, 2007, 46(24), 10321-10334.
2-Electron reduction of N2O yields a new ligand binding mode: N-Nitrosoimide. Fan, Hongjun; and Caulton, Kenneth G., Polyhedron, 2007, 26, 4731-4736.
Radical (NO) and Nonradical (N2O) Reagents Convert a Ruthenium (IV) Nitride to the Same Nitrosyl Complex. Walstrom, Amy; Pink, Maren; Fan, Hongjun; Tomaszewski, John; and Caulton, Kenneth G., Inorg. Chem., 2007, 46, 7704-7706.
Facile Hydrogenation of N2O by an Operationally Unsaturated Osmium Polyhydride. Lee, Joo-Ho; Pink, Maren; Tomaszewski, John, Fan, Hongjun; and Caulton, Kenneth G., J. Amer. Chem. Soc., 2007, 129, 8706-8707.
NO Binds to Unsaturated Os(IV) Polyhydrides as a Redox Reagent. Lee, Joo-Ho; Vedernikov, Andrei N; Dye, David; and Caulton, Kenneth G., J. Organometallic Chem., 2007, 692, 3121-3132.
Reactivity of NO with an Osmium Polyhydride: Reductive Elimination and Reductive Nitrosylation on the Path from Odd- to Even-Electron Molecules. Lee, Joo-Ho; Fan, Hongjun; Pink, Maren; and Caulton, Kenneth G., New J. Chem., 2007, 31, 838-840.
Influence of Chelate Substituents on Structure and Spin-State of Unsaturated [N(SiMe2CH2PtBu2)2]Ru-X. Yang, Xiaofan; Walstrom, Amy; Tsvetkov, Nikolay; Pink, Maren; and Caulton, Kenneth G., Inorg. Chem., 2007, 46, 4612-4616.
Operationally Unsaturated Pincer/Rhenium Complexes Form Metal Carbenes from Cycloalkenes and Metal Carbynes From Alkanes. Ozerov, Oleg V.; Watson, Lori A.; Pink, Maren; and Caulton, Kenneth G., J. Amer. Chem. Soc., 2007, 129, 6003-6016.
Si-N Bond Hydrolysis Furnishes a Planar 4-coordinate 14-Electron Ru(II) Complex with a Triplet Ground State. Walstrom, Amy; Pink, Maren; and Caulton, Kenneth G., Inorg. Chem., 2006, 45, 5617-5620.
Reducing Power of Three-Coordinate Cobalt (I). Ingleson, Michael J.; Pink, Maren; and Caulton, Kenneth G., J. Am. Chem. Soc., 2006, 128(13), 4248-4249.
[(tBu2PCH2SiMe2)2N]RuMe2: Synthesis and Reactivity of an Unsaturated Ruthenium Dialkyl Radical Species. Ingleson, Michael; Pink, Maren; Huffman, John C.; Fan, Hongjun; and Caulton, Kenneth G., Organometallics, 2006, 25(5), 1112-1119.
Cleavage of F-C(sp2) bonds by MHR(CO)(PtBu2Me)2 (M = Os and Ru; R = H, CH3 or Aryl): Product Dependence on M and R. Huang, Dejian; Renkema, Kenton B.; and Caulton, Kenneth G., Polyhedron, 2006, 25(2), 459-468.
Three-coordinate Co(I) Provides Access to Unsaturated Dihydrido-Co(III) and Seven-Coordinate Co(V). Ingleson, Michael; Fan, Hongjun; Pink, Maren; Tomaszewski, John; and Caulton, Kenneth G., J. Am. Chem. Soc., 2006, 128(6), 1804-1805.
Triple Benzylic Dehydrogenation by Osmium in an Amide Ligand Environment. Lee, Joo-Ho; Pink, Maren; Caulton, Kenneth G., Organometallics, 2006, 25(4), 802-804.
N2 Provides Insight into the Mechanism of H-C(sp3) Bond Cleavage. Walstrom, Amy; Pink, Maren; Tsvetkov, Nikolai P.; Fan, Hongjun; Ingleson, Michael; Caulton, Kenneth G., J. Am. Chem. Soc., 2005, 127(48), 16780-16781.
[(tBu2PCH2SiMe2)2N]RuCH3: The Origin of Extremely Facile, Double H-C(sp3) Activation Generating a "Hydrido-Carbene" Complex. Ingleson, Michael J.; Yang, Xiaofan; Pink, Maren; Caulton, Kenneth G., J. Am. Chem. Soc., 2005, 127(31), 10846-10847.
A facile approach to a d4 Ru≡N: moiety. Walstrom, Amy; Pink, Maren; Yang, Xiaofan; Tomaszewski, John; Baik, Mu-Hyun; and Caulton, Kenneth G., J. Am. Chem. Soc., 2005, 127(15), 5330-5331.
Exceptionally facile CO addition to a saturated ruthenium complex. Bibal, Christine; Smurnyy, Yegor D.; Pink, Maren; and Caulton, Kenneth G., J. Am. Chem. Soc., 2005, 127(25), 8944-8945.
New d4 dihydrides of Ru(IV) and Os(IV) with π-donor ligands: M(H)2(chelate)(PiPr3)2 with chelate = ortho-XYC6H4 with X, Y = O, NR; R = H or CH3. Ferrando-Miguel, German; Wu, Peng; Huffman, John C.; and Caulton, Kenneth G., New Journal of Chemistry, 2005, 29(1), 193-204.
New Features of Bis(phosphinimine)-“carbene” Binding to RuII. Smurnyy, Yegor; Bibal, Christine; Pink, Maren; and Caulton, Kenneth G., Organometallics, 2005, 24(16), 3849-3855.
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