B.S. 1994 Saint Mary's University Ph.D. 1998 University of Missouri-Columbia NSERC of Canada Postdoctoral Fellow, Dept. of Chemical Engineering and Materials Science, 1999-2001, University of Minnesota
NSF CAREER Award (2004)
Organic Chemistry; Organic Chemistry Laboratory I; Advanced General Chemistry; Intro to Research Experimentation, X-Ray Crystallography, Special Topics in Organic Chemistry
Research in the Holman lab generally lies at the intersection of organic, organometallic, and solid-state chemistry. Broadly, we are interested in molecular recognition and supramolecular chemistry ― the organization of molecules into multi-component entities through non-covalent forces. With respect to solution phase chemistry, our interests lead us to the design of molecules capable of selectively binding and/or sensing appropriate substrates, those capable of spontaneously organizing into interesting and complex structures, or those that might influence the organization of other molecules, perhaps for purposes of reaction (e.g., supramolecular organocatalysis). Applied to the solid-state, we use supramolecular principals to attempt to empirically design crystalline structure (e.g., crystal engineering), thereby being able to impart selected properties to materials. Research projects are inherently multidisciplinary, allowing students to develop expertise in synthetic organic and/or organometallic chemistry, physical organic chemistry, solid-state organic chemistry, powder and single crystal X-ray diffraction, various spectroscopic techniques (NMR, neutron scattering), thermal analysis, etc. Current projects involve:
1. Molecular Encapsulation
A principal area of research in our group involves the synthesis and study of so-called container molecules. As the name suggests, container molecules possess the unique and remarkable ability to completely encapsulate smaller, molecule-sized substrates. This feature provides several attractive avenues for chemistry. To name but a few, container molecules have been used for (enantio)selective recognition and sensing, for stabilizing and characterizing highly reactive chemical species, as micro-reaction chambers, and to demonstrate new forms of stereo- and “social” isomerism. Our work in this area falls into a few categories:
Supramolecular Organocatalysis – We are pursuing the chemical functionalization of the cavity interiors so as to use molecular containers as catalysts in which to perform chemical reactions. The cavities ought to be selective with respect to the size, shape, and chemical nature of potential reagents which might react within their interiors. Moreover, chiral molecular containers may function as effective asymmetric catalysts via their ability to organize the spatial arrangements of reactants.
Storage Materials – The closed-surface nature of certain molecular containers provides large steric barriers to the ingress and egress of guests. The resulting complexes experience a corresponding enhancement in their kinetic stabilities. This feature augurs well for gas separation or storage applications . We have initiated a program aimed at tuning the kinetic stabilities of materials generally derived from container molecules, one future goal of which is the synthesis of microporous materials with novel gas storage or separation capabilities. Relative to traditional clathrates and solid-state inclusion compounds, we have shown that materials constructed from container-like molecules exhibit appreciable stability with respect to the thermal loss of encapsulated guests.
Anion Binding – Modification of the cavity exteriors with transition metal moieties converts ostensibly electron rich, cation-binding molecular containers, into ones which are pi-acidic and capable of selectively binding anions. These molecules are among the first that are specifically designed to exploit the anion-pi interaction as a motif for selective anion recognition.
2. Metal-Organic and Metal-Organometallic Materials
The past fifteen years have witnessed the burgeoning of a powerful new approach in synthetic solid-state chemistry based upon the premise that simple organic ligands can be judiciously combined with simple transition metal ions to give new and important materials with controllable architectures and useful properties (e.g., porosity, low density, high surface area). Our own work in the field involves the exploratory synthesis of new metal-organic framework (MOF) materials derived from designer-ligands which are expected to impart unique properties. These ligands might be:
container molecules, providing molecular recognition and storage features
homochiral, yielding homochiral, porous MOFs
organometallic compounds, providing metal-derivatized frameworks with varied properties, or
known organocatalysts, providing opportunities for heterogenous catalysis
3. Metal-Arene Chemistry
Appendage of electron withdrawing transition metal moieties to arenes dramatically affects their reactivity and supramolecular chemistry. With respect to chemical reactivity, we are further exploring the well-known ability of transition metals to activate arenes toward nucleophilic attack. For instance, we have achieved, for the first time, the regiospecific syntheses of various arylsulfonates by sulfodehalogenation of a series of metal-activated aryl chlorides. We are also exploring the anion-pi interactions of pi-acidic, metalated arenes.
Ugono, O.; Holman, K. T. "An achiral form of the hexameric resorcinarene capsule sustained by hydrogen bonding with alcohols," Chem. Commun.2006, 2144-2146.
Fairchild, R. M.; Holman, K. T. “Selective anion encapsulation by a metalated cryptophane with a pi-acidic interior,” J. Am. Chem. Soc. 2005, 127,16364-16365.
Mough, S. T.; Goeltz, J. C.; Holman, K. T. “Isolation and Structure of an ‘Imploded’ Cryptophane” Angew. Chem. Int. Ed. 2004, 43, 5631-5635.
Holman, K. T. “Cryptophanes: Molecular Containers” In Encyclopedia of Supramolecular Chemistry; J. A. Atwood, J. W. Steed, Eds., Marcel Dekker: New York, NY 2004; pp. 340-348.
Holman, K. T.; Hammud, H. H.; Isber S.; Tabbal, M. “One-dimensional coordination polymer [Co(H2O)4(pyz)](NO3)2·2H2O (pyz = pyrazine) with intra- and inter-chain H-bonds: structure, electronic spectral studies and magnetic properties” Polyhedron, 2005, 221-228.