PC Chemistry | Chemistry Faculty

 

Christopher M. Laperle, Ph.D.

Assistant Professor of Chemistry **

** Beginning July 1^st 2008

Department of Chemistry and Biochemistry, Providence College, Providence RI

Contact:

Email: claperle@providence.edu

phone: 401-863-3207

 

Education and Appointments:

2006-2008   National Institutes of Health Ruth L. Kirschtein Research Fellow
                Warren Alpert Medical School of Brown University (J. R. Wands)

2005-2006   Postdoc, Brown University (C. Rose-Petruck)

2004 Ph.D.   University of California, San Diego (R. E. Continetti)

1999 B.S.    University of Massachusetts, Amherst (R. B. Metz)

Research Interests:

The interaction between solvent and solute molecules plays a significant role in determining chemical reactivity of solvated species in solution. It is well known that the selection of a proper solvent medium is vital for predicting desired synthetic and catalytic chemical reaction outcomes. In spite of this, many of the physical mechanisms that underlie solvation dynamics and chemical reactivity trends for important chemical reactions are not well established. My research focuses on the experimental investigation of solvent-induced equilibrium electronic and geometric structures of organometallic compounds that are important in synthetic, catalytic and biological chemistry. More specifically I am interested in characterizing the site specific solvation dynamics of the pentacoordinated transition metal carbonyls Ru(CO)₅ and Os(CO)₅ using Fourier Transform Infrared (FTIR) spectroscopy and density functional theory (DFT) calculations.

In the gas-phase, these systems have trigonal bipyramidal geometry with D_3h molecular symmetry (see inserted picture).

Calculated structure of Fe(CO)5 solvated with a single ethanol molecule Image courtesy of Lessing et al. J. Phys. Chem. A.; 2008; 112(11); 2282-2292.

Typically molecules are stabilized in solution through a number of non-specific weak interactions with several solvent molecules. However, recent studies have shown that iron pentacarbonyl, Fe(CO)₅, solvated in alcohol- or arene-based solutions, exhibits a significantly strong interaction with a single solvent molecule that induces a structural and/or electronic deformation. As a result the symmetric CO stretch vibrational mode, which is only Raman active in the D_3h species, becomes IR-active. Relative populations of the solvent-complexed Fe(CO)₅ have been determined by measuring the spectral intensity of these solvent-induced IR vibrational frequencies with FTIR spectroscopy. The data allows for a thorough thermodynamic characterization of these solvated complexes. My research focuses on the measurement of complimentary comparative FTIR absorption data of solvated Ru(CO)₅ and Os(CO)₅ which, coupled with corresponding DFT calculations, will provide insight on the periodic trends associated with the solvation of the Group VIII transition metal carbonyls.

The site-specific solvation, although weak, provides a ‘pre-assembly’ between the solute and solvent. As a result, photo-induced bimolecular reactions between them may occur on the timescale of molecular vibration (~10^-15 seconds). In the absence of this ‘pre-assembly’ the timescale for reaction is diffusion limited and on the order of ~10^-12 seconds. The large difference in reaction timescale of these important systems necessitates the study of the equilibrium structures in solution, both for applied chemistry and interpretation of ultrafast chemical dynamics data.

The overarching focus of this research is to produce a more comprehensive picture of solution-phase chemical structure and its impact on the reactivity of organometallic compounds. The information will aid the future development and discovery of optimal solvent composition in synthetic and catalytic processes involving the pentacoordinated Group VIII transition metal carbonyls.

The research can be divided into two distinct programs: experimental FTIR measurements of solvated Ru(CO)₅ and Os(CO)₅ and corresponding DFT calculations of equilibrium structures and energetics. Undergraduates in my group will have an opportunity to explore both the experimental and theoretical intricacies of these important physical chemistry problems.