Research Synopsis: Catalysis and catalytically relevant organometallic chemistry, reactions, and mechanisms
Phone: (848) 445-5232
The research conducted in my group is focused on the reactions between transition metal complexes and simple organic molecules, particularly hydrocarbons. Our work generally involves a mechanism-based approach to the development of catalysts.
Catalytic functionalization of C-H bonds
The catalytic functionalization of alkanes and other molecules with normally inert C-H bonds is a scientifically challenging problem that presents great opportunities in terms of economics, environmental benefits, and energy self-sufficiency. Catalysts for both the dehydrogenation and the carbonylation of alkanes have been developed in our group; these were among the first efficient organometallic alkane functionalization catalysts.
Pincer catalysts for alkane dehydrogenation
We reported the first efficient solution-phase catalysts for alkane dehydrogenation that require neither the use of photochemical irradiation nor a sacrificial hydrogen acceptor. These “pincer catalysts” have also been found to catalyze reactions as industrially significant as dehydrogenation of n-alkanes, to give the important alpha-olefin products, or dehydrogenation of polymers to allow entry into a diverse manifold of functionalized polymers. Concomitantly, applications in organic synthesis are being investigated.
Alkane Metathesis and other Tandem Systems for Catalytic Hydrocarbon Transformation
Olefins are ubiquitous as intermediates in the petrochemical, commodity chemical, and pharmaceutical industries. Tandem systems that could effect dehydrogenation of alkanes or alkyl groups, followed by a useful secondary reaction of the resulting olefin, offer potentially powerful routes to various products, while avoiding undesirable secondary reactions that can occur in simple alkane dehydrogenation systems. Under the auspices of “CENTC” (see below) and in collaboration with the group of Maurice Brookhart at UNC, we have developed one such system that effects the metathesis of alkanes. A potential application of this system is in the upgrading of Fischer-Tropsch alkane product mixtures to afford greater yields of C9-C19 n-alkanes, ultimately obtained from feedstocks such as coal or biomass. Known as “FT diesel”, this comprises a transportation fuel that burns cleanly and gives ca. 35% greater mileage per ton CO2 emitted than gasoline.
Another tandem reaction discovered by our CENTC team is alkane aromatization. Remarkably this system converts n-alkanes to aromatics, under relatively mild conditions. This is the first homogeneous system reported for dehydroaromatization, and the first catalytic system of any type that converts higher n-alkanes to aromatics of the same carbon number (e.g. n-dodecane gives C12 n-alkyl aromatics).
C-H bond activation toward reactivity at sites other than the C-H bond
Oxidative addition and its reverse, reductive elimination, comprise perhaps the most important and distinctive class of reactions of transition metal based catalysts and reagents. While this class of reactions is critical for the catalytic transformations of many types of molecules, until now it appeared inaccessible with sp3-C-F and C-O bonds. Such bonds are of great interest in many contexts, ranging from pharmaceuticals to the conversion of biomass to fuels and chemicals.
Our lab has recently discovered the first example of oxidative addition of sp3-C-F bonds, an outgrowth of recent work on the novel addition of sp3-C-O bonds. Perhaps most interestingly, the reactions are found to proceed via an unprecedented pathway, in which the metal atom initially inserts into a carbon-hydrogen (C-H) bond in the molecule. This unusual pathway must also be operative for the reverse reaction, in which C-F or C-O bonds are formed.
In another surprising reaction we have found that C-H addition of an aromatic (tropone) results in nucleophilic activity at a remote site on that molecule. Oxidative addition of C-H bonds has been assumed to have great potential for the purpose of catalyzing functionalization in which there is an overall cleavage of the C-H bond. The discovery of these reactions highlights the possible applicability of C-H bond addition toward functionalization of various substrates, not necessarily at the site of the C-H bond cleavage.
Hydrocarbylation of olefins
A new target of our research is the “hydrocarbylation” of olefins. Like dehydrogenation, this reaction has a nearly unlimited number of potential applications ranging from natural gas liquefaction and petrochemical conversion to complex organic syntheses.
Computational organometallic catalysis
In addition to experimental approaches, ab initio molecular orbital calculations are conducted in collaboration with Prof. K. Krogh-Jespersen. This work has yielded new perspectives on the most fundamental aspects of organometallic chemistry such as the nature of the metal-CO bond or the process of C-H addition. We now believe that the power of computational chemistry has reached the point where the modification or even the de novo design of catalysts using MO calculations is entirely feasible; efforts in this direction are currently underway.
"Continuous Flow Alkane Dehydrogenation by Supported Pincer-Ligated Iridium Catalysts at Elevated Temperatures" B. Sheludko, M. T. Cunningham, A. S. Goldman, F. E. Celik, ACS Catal. 2018, 7828-7841 (pubs.acs)
"H2/D2 Addition to Pincer-Iridium Complexes Yielding trans-dihydride Products: Unexpected Correlations of Bond Strength with Bond Length and Vibrational Frequencies" B. S. Omar, J. Mallah, M. Ataya, B. Li, X. Zhou, S. Malakar, A. S. Goldman and F. Hasanayn Inorg. Chem. 2018, 7516-7523 (pubs.acs)
"Selective Dehydrogenative Coupling of Ethylene to Butadiene via an Iridacyclopentane Complex" Y. Gao, T. J. Emge, K. Krogh-Jespersen and A. S. Goldman J. Am. Chem. Soc. 2018, 140, 2260-2264 (pub.acs)
"PNP-Pincer Complexes of Osmium: Comparison with Isoelectronic (PCP)Ir and (PNP)Ir+ Units" N. Lease, E. M. Pelczar, T. Zhou, S. Malakar, T. J. Emge, F. Hasanayn, K. Krogh-Jespersen and A. S. Goldman Organometallics 2018, 37, 314-326 (pubs.acs)
"Dehydrogenation of Alkanes and Aliphatic Groups By PincerLigated Metal Complexes" A. Kumar, T. Bhatti, A. S. Goldman Chem. Rev. 2017, 117, 12357-12384 (pubs.acs)
"Catalytic Dehydrogenative C-C Coupling by a Pincer-Ligated Iridium Complex” M. Wilklow-Marnell, B. Li, T. Zhou, K. Krogh-Jespersen, W. W. Brennessel, T. J. Emge, A. S. Goldman, W. D. Jones J. Am. Chem. Soc. 2017, 139, 8977-8989 (pubs.acs)
"β-Hydride Elimination and C–H Activation by an Iridium Acetate Complex, Catalyzed by Lewis Acids. Alkane Dehydrogenation Cocatalyzed by Lewis Acids and (Phebox)Iridium" Gao, Y.; Guan, C.; Zhou, M.; Kumar, A.; Emge, T. J.; Wright, A. M.; Goldberg, K. I.; Krogh-Jespersen, K.; Goldman, A. S., J. Am. Chem. Soc. 2017, 139, 6338–6350 (pubs.acs)
"Large-Scale Selective Functionalization of Alkanes" K. I. Goldberg and A. S. Goldman; Acc. Chem. Res. 2017, 50, 620-626 (pubs.acs)
"Protonation and electrochemical reduction of rhodium- and iridium-dinitrogen complexes in organic solution" G. P. Connor, N. Lease, A. Casuras, A. S. Goldman, P. L. Holland and J. M. Mayer Dalton Trans. 2017, 46, 14325-14330 (rsc.org)
"High yields of piperylene in the transfer dehydrogenation of pentane catalyzed by pincer-ligated iridium complexes” A. Kumar, J. D. Hackenberg, G. Zhuo, A. M. Steffens, O. Mironov, R. J. Saxton, A. S. Goldman J. Mol. Catal. A: Chem. 2017, 426, 368-375 (sciencedirect.com)
"Alkyl-Aryl Coupling Catalyzed by Tandem Systems of Pincer-Ligated Iridium Complexes and Zeolites" Long V. Dinh, Bo Li, Akshai Kumar, William Schinski, Kathleen D. Field, Alexander Kuperman, Fuat E. Celik and Alan S. Goldman; ACS Catal. 2016, 6, 2836-2841 (pubs.acs)
"Single and Double C−H Activation of Biphenyl or Phenanthrene. An Example of C−H Addition to Ir(III) More Facile than Addition to Ir(I)"
D. A. Laviska, T. Zhou, A. Kumar, T. J. Emge, K. Krogh-Jespersen, A. S. Goldman Organometallics 2016, 35, 1613-1623 (pubs.acs)
"Electrochemical and Chemical Routes to Hydride Loss from an Iridium Dihydride" A. G. Walden, A. Kumar, N. Lease, A. S. Goldman, A. J. M. Miller Dalton Trans. 2016, 45, 9766-9769 (rsc.org)
"Catalytic alkane transfer-dehydrogenation by PSCOP iridium pincer complexes" W. Yao, X. Jia, X. Leng, A. S. Goldman, M. Brookhart, Z. Huang Polyhedron 2016, 116, 12-19 (special issue in honor of Malcolm Green) (sciencedirect.com)
"Experimental and Computational Study of Alkane Dehydrogenation Catalyzed by a Carbazolide-Based Rhodium PNP Pincer Complex" D. Bézier, C. Guan, K. Krogh-Jespersen, A. S. Goldman, M. Brookhart Chem. Sci. 2016, 7, 2579-2586 (rsc.org)
"Assessment of the Electronic Factors Determining the Thermodynamics of ‘Oxidative Addition’ of C-H and N-H Bonds to Ir(I) Complexes" D. Y. Wang, Y. Choliy, M. C. Haibach, J. F. Hartwig, K. Krogh Jespersen, A. S. Goldman J. Am. Chem. Soc. 2016, 138, 149-163 (pubs.acs)
"Recent Advances in Alkane Dehydrogenation Catalyzed by Pincer Complexes" A. Kumar and A. S. Goldman Top. Organomet. Chem. 2016, 54, 307-334 (springer.com)
"Selectivity for dimers in pentene oligomerization over acid zeolites" A. Kulkarni, A. Kumar, A. S. Goldman, F. E. Celik Catalysis Comm. 2016, 75, 98-102 (sciencedirect.com)
"Dehydrogenation of n-Alkanes by Solid-Phase Molecular Pincer-Iridium Catalysts. High Yields of α-Olefin Product" A. Kumar, T. Zhou, T. J. Emge, O. Mironov, Robert J. Saxton, K. Krogh Jespersen, A S. Goldman J. Am. Chem. Soc. 2015, 137, 9894-9911 (pubs.acs)
"Chlorination of (Phebox)Ir(mesityl)(OAc) by Thionyl Chloride" M. Zhou, A. S. Goldman, Molecules 2015, 20, 10122-10130 (mdpi.com)
"Activation and Oxidation of Mesitylene C-H Bonds by (Phebox)Ir(III) Complexes" M. Zhou, S. I. Johnson, Y. Gao, T. J. Emge, R. J. Nielsen, W. A. Goddard, A. S. Goldman, Organometallics 2015, 34, 2879–2888 (pubs.acs)
"Preface: Forum on Small Molecules Related to Carbon-Containing Fuels" E. Fujita and A. S. Goldman Inorg. Chem. 2015, 54, 5040–5042 (pubs.acs)
"Addition of C-C and C-H Bonds by Pincer-Iridium Complexes: a Combined Experimental and Computational Study" D. A. Laviska, C. Guan, T. J. Emge, M. Wilklow-Marnell, W. W. Brennessel, W. D. Jones, K. Krogh-Jespersen, A. S. Goldman Dalton Trans. 2014, 43, 16354-16365 (rsc.org)
"Catalytic Cleavage of Ether C–O Bonds by Pincer Iridium Catalysts" M. C. Haibach, N. Lease, and A. S. Goldman, Angew Chem. Int. Ed., 2014, 53, 10160–10163 (wiley.com)
"Acid-catalyzed Oxidative Addition of a C-H Bond to a Square Planar d8 Iridium Complex" J. D. Hackenberg, S. Kundu, T. J. Emge, K. Krogh-Jespersen and A. S. Goldman, J. Am. Chem. Soc. 2014, 136, 8891–8894 (pubs.acs)
"Synthesis and Characterization of Carbazolide-based Iridium PNP Pincer Complexes. Mechanistic and Computational Investigation of Alkene Hydrogenation: Evidence for an Ir(III)/Ir(V)/Ir(III) Catalytic Cycle" C. Cheng, B. G. Kim, D. Guironnet, M. Brookhart, C. Guan, D. Y. Wang, A. S. Goldman J. Am. Chem. Soc. 2014, 136, 6672−6683 (pubs.acs)
"Regeneration of an Iridium(III) Complex Active for Alkane Dehydrogenation Using Molecular Oxygen" K. E. Allen, D. M. Heinekey, A. S. Goldman and K. I. Goldberg Organometallics 2014, 33, 1337-1340 (pubs.acs)
"Activation of C-O and C-F Bonds by Pincer-Iridium Complexes" J. Hackenberg, K. Krogh-Jespersen and A. S. Goldman, in Advances in Organometallic Chemistry and Catalysis: The Silver / Gold Jubilee International Conference on Organometallic Chemistry Celebratory Book; Pombeiro, A. J. L., Ed.; John Wiley & Sons: Hoboken, NJ, 2014, 39-58.
"Rational Design of Highly Active “Hybrid” Phosphine-Phosphinite Pincer Iridium Catalysts for Alkane Metathesis" A. Nawara-Hultzsch, J. Hackenberg, B. Punji, C. Supplee, T. Emge, B. Bailey, R. R. Schrock, M. Brookhart, A. S. Goldman ACS Catalysis 2013, 3, 2505-2514 (pubs.acs)
"Olefin Hydroaryloxylation Catalyzed by Pincer-Iridium Complexes" M. C Haibach, C. Guan, D. Y. Wang, B. Li, N. Lease, A. Steffens, K Krogh-Jespersen and A S. Goldman J. Am. Chem. Soc. 2013, 135, 15062-15070 (pubs.acs)
"Catalytic Synthesis of n-Alkyl Arenes through Alkyl Group Cross Metathesis" G. E. Dobereiner. J. Yuan. R. R. Schrock. A. S. Goldman, J. D. Hackenberg J. Am. Chem. Soc. 2013, 135, 12572-12575 (pubs.acs)
"(POP)Rh pincer hydride complexes: unusual reactivity and selectivity in oxidative addition and olefin insertion reactions" M. C. Haibach, D. Y. Wang, T. J. Emge, K. Krogh-Jespersen and A. S. Goldman Chem. Sci. 2013, 4, 3683-3692 (rsc.org)
"Cleavage of Ether, Ester and Tosylate C(sp3)-O Bonds by an Iridium Complex, Initiated by Oxidative Addition of C-H Bonds. Experimental and Computational Studies" S. Kundu, J. Choi, D. Y. Wang, Y. Choliy, T. J. Emge, K. Krogh-Jespersen and A. S. Goldman J. Am. Chem. Soc. 2013, 135, 5127-5143 (pubs.acs)
"Alkane Dehydrogenation by C-H Activation at Ir(III)" K. E. Allen, D. M. Heinekey, A. S. Goldman, K I. Goldberg, Organometallics 2013, 32, 1579-1582 (pubs.acs)
"Olefin Isomerization by Iridium Pincer Catalysts. Experimental Evidence for an eta-3-Allyl Pathway and an Unconventional Mechanism Predicted by DFT Calculations" S. Biswas, Z. Huang, Y. Choliy, D. Y. Wang, M. Brookhart, K. Krogh-Jespersen, A. S. Goldman J. Am. Chem. Soc. 2012, 134, 13276-13295 (pubs.acs)
"Alkane Dehydrogenation" M. Findlater, J. Choi, A. S. Goldman, and M. Brookhart in Alkane C-H Activation by Single-Site Metal Catalysis; Pérez, P. J., Ed.; Springer: New York, 2012; Catalysis by Metal Complexes, Vol. 38, 113-141. (springer)
"Alkane Metathesis by Tandem Alkane-Dehydrogenation-Olefin-Metathesis Catalysis and Related Chemistry" M. C. Haibach, S. Kundu, M. Brookhart, A. S. Goldman, Acc. Chem. Res. 2012, 45, 947-958 (pubs.acs)
"Theoretical Structure–Reactivity Study of Ethylene Insertion into Nickel–Alkyl Bonds. A Kinetically Significant and Unanticipated Role of trans Influence in Determining Agostic Bond Strengths" F. Hasanayn, P. Achord, P. Braunstein, H. J. Magnier, K. Krogh-Jespersen, and A. S. Goldman Organometallics 2012, 31, 4680-4692 (pubs.acs)
"Preparation of Tungsten-Based Olefin Metathesis Catalysts Supported on Alumina" J. Yuan, E. M. Townsend, R. R. Schrock, A. S. Goldman, P. Müller, and M. K. Takase Adv. Synth. Catal. 2011, 353, 1985-1992 (wiley.com)
"Net Oxidative Addition of C(sp3)-F Bonds to Iridium via Initial C-H Bond Activation" J. Choi, D. Y. Wang, S. Kundu, Y. Choliy, T. J. Emge, K. Krogh-Jespersen and A. S. Goldman Science 2011, 332, 1545-1548 (sciencemag.org)
"Dehydrogenation and Related Reactions Catalyzed by Iridium Pincer Complexes" J. Choi, A. H. R. MacArthur, M. Brookhart, and A. S. Goldman Chem. Rev. 2011, 111, 1761-1779 (pubs.acs)
"Catalytic dehydroaromatization of n-alkanes by pincer-ligated iridium complexes" R. Ahuja, B. Punji, M. Findlater, C. Supplee, W. Schinski, M. Brookhart, and A. S. Goldman Nature Chem. 2011, 3, 167-171 (nature.com)
"Dehydrogenation of Ketones by Pincer-Ligated Iridium. Formation and Reactivity of Novel Enone Complexes" X. Zhang, D. Y. Wang, T. J. Emge and A. S. Goldman Inorg. Chim. Acta 2011, 369, 253-259 (special issue in honor of Robert Bergman) (sciencedirect.com)
"Ir-Catalyzed Functionalization of C–H Bonds" J. Choi and A. S. Goldman Top. Organomet. Chem. 2011, 34, 139-168 (springerlink.com)
"Reactions of phosphinites with oxide surfaces: a new method for anchoring organic and organometallic complexes" B. C. Vicente, Z. Huang, M. Brookhart, A. S. Goldman, and S. L. Scott, Dalton Trans. 2011, 40, 4268-4274. (rsc.org)
"A Highly Stable Adamantyl-Substituted Pincer-Ligated Iridium Catalyst for Alkane Dehydrogenation" B. Punji, T. J. Emge, and A. S. Goldman, Organometallics, 2010, 29, 2702-2709 (pubs.acs)
"Organometallic chemistry: Carbon–carbon bonds get a break" (News and Views) A. S. Goldman, Nature, 2010, 435-436 (nature.com)
"Dihydrogen/Dihydride or Tetrahydride? An Experimental and Computational Investigation of Pincer Iridium Polyhydrides" T. J. Hebden, K. I. Goldberg, D. M. Heinekey, X. Zhang, T. J. Emge, A. S. Goldman and K. Krogh-Jespersen Inorg. Chem. 2010, 49, 1733-1742 (pubs.acs)
"Efficient Heterogeneous Dual Catalyst Systems for Alkane Metathesis" Z. Huang, E. Rolfe, E. C. Carson, M. Brookhart, A. S. Goldman, S. H. El-Khalafy, A. H. Roy MacArthur, Adv. Synth. Catal. 2010, 352, 125-135 (wiley.com)
"Cleavage of sp3 C-O Bonds via Oxidative Addition of C-H Bonds" J. Choi, Y. Choliy, X. Zhang, T. J. Emge, K. Krogh-Jespersen and A. S. Goldman J. Am. Chem. Soc. 2009, 131, 15627-15629 (pubs.acs)
"Rational Design and Synthesis of Highly Active Pincer-Iridium Catalysts for Alkane Dehydrogenation" S. Kundu, Y. Choliy, G. Zhuo, R. Ahuja, T. J. Emge, R. Warmuth, M. Brookhart, K. Krogh-Jespersen, and A. S. Goldman, Organometallics, 2009, 28, 5432-5444 (pubs.acs)
"Highly Active and Recyclable Heterogeneous Iridium Pincer Catalysts for Transfer Dehydrogenation of Alkanes" Z. Huang, M. Brookhart, A. S. Goldman, S. Kundu, A. Ray, S. L. Scott, and B. C. Vicente, Adv. Synth. Catal. 2009, 351, 188-206 (wiley.com)
"Evaluation of Molybdenum and Tungsten Metathesis Catalysts for Homogeneous Tandem Alkane Metathesis" B. C. Bailey, R. R. Schrock, S. Kundu, A. S. Goldman, Z. Huang and M. Brookhart, Organometallics 2009, 28, 355-360 (pubs.acs)
"Combined Experimental and Computational Studies on Carbon-Carbon Reductive Elimination from Bis(hydrocarbyl) Complexes of (PCP)Ir" R. Ghosh, T. J. Emge, K. Krogh-Jespersen and A. S. Goldman, J. Am. Chem. Soc. 2008, 130, 11317–11327 (pubs.acs)
"Unusual Structural and Spectroscopic Features of Some PNP-Pincer Complexes of Iron" E. M. Pelczar, T. J. Emge, K. Krogh-Jespersen and A. S. Goldman, Organometallics 2008, 27, 5759–5767 (pubs.acs)
"Catalytic Ring Expansion, Contraction, and Metathesis-Polymerization of Cycloalkanes" R. Ahuja, S. Kundu, A. S. Goldman, M. Brookhart, B. C. Vicente, and S. L. Scott Chem. Commun. 2008, 253-255 (rsc.org)
"Dimerization of Alkynes Promoted by a Pincer-Ligated Iridium Complex. C-C Reductive Elimination Inhibited by Steric Crowding" R. Ghosh, X. Zhang, P. Achord, T. J. Emge, K. Krogh-Jespersen, and A. S. Goldman J. Am. Chem. Soc. 2007, 129, 853-866 (pubs.acs)
"Catalytic Alkane Metathesis by Tandem Alkane-Dehydrogenation–Olefin-Metathesis" A. S. Goldman, A. H. Roy, Z. Huang, R. Ahuja, W. Schinski, and M. Brookhart Science 2006, 312, 257-261 (sciencemag.org)
"Dinitrogen Complexes of Pincer-Ligated Iridium" R. Ghosh, M. Kanzelberger, T. J. Emge, G. S. Hall and A. S. Goldman Organometallics 2006, 25, 5668-5671 (pubs.acs)
"Reaction of nitromethane with an iridium pincer complex. Multiple binding modes of the nitromethanate anion" X. Zhang, T. J. Emge, R. Ghosh, K. Krogh-Jespersen and A. S. Goldman Organometallics 2006, 25, 1303-1309 (pubs.acs)
"Preparation of Olefins by Transition Metal-catalyzed Dehydrogenation" A. S. Goldman and R. Ghosh, in Handbook of C-H Transformations - Applications in Organic Synthesis, G. Dyker, Ed., Wiley-VCH, New York; 2005, pp 616-621.
"Selective Cleavage of the C-C Bonds of Aminoethyl Groups, via a Multistep Pathway, by a Pincer Iridium Complex" X. Zhang, T. J. Emge, R. Ghosh, and A. S. Goldman J. Am. Chem. Soc. 2005, 127, 8250-8251 (pubs.acs)
"Dehydrogenation of aliphatic polyolefins catalyzed by pincer-ligated iridium complexes" A. Ray, K. Zhu, Y. V. Kissin, A. E. Cherian, G. W. Coates and A. S. Goldman Chem. Commun. 2005, 3388-3390 (rsc.org)
"Oxidative Addition of Ammonia to Form a Stable Monomeric Amido Hydride Complex" J. Zhao, A. S. Goldman, J. F. Hartwig Science 2005, 307, 1080-1082 (sciencemag.org)
"Activation and Functionalization of C-H Bonds" Goldberg, K. I.; Goldman, A. S., Eds., ACS Symposium Series 885; American Chemical Society: Washington, DC, 2004, Table of Contents with links to chapters.
"C-H Bond Activation by Transition Metals: An Introduction" Goldman, A. S. and Goldberg, K. I. in Activation and Functionalization of C-H Bonds; K. I. Goldberg and A. S. Goldman, Eds. 2004;
ACS Symposium Series 885 (go to Oxford Press/ACS books); 1-44 (pdf of chapter)
"Selective Addition to Iridium of Aryl C-H Bonds Ortho to Coordinating Groups. Not Chelation-Assisted" X. Zhang, M. Kanzelberger, T. J. Emge and A. S. Goldman, J. Am. Chem. Soc. 2004, 126, 13192 -13193 (pubs.acs)
"Highly Effective Pincer-Ligated Iridium Catalysts for Alkane Dehydrogenation. DFT Calculations of Relevant Thermodynamic, Kinetic, and Spectroscopic Properties" K. Zhu, P. D. Achord, X. Zhang, K. Krogh-Jespersen and A. S. Goldman, J. Am. Chem. Soc. 2004, 126, 13044-13053 (pubs.acs)