James A. Franz PhD, PNNL Fellow, Pacific Northwest National Laboratory

Department of Chemistry

Visiting Speaker

James A. Franz PhD, PNNL Fellow

Pacific Northwest National Laboratory

Will present a seminar entitled:

"Persistent radicals, activated S-H and S-C Bonds, and C-S bond formation at Fe₂S₂ and Mo₂S₄ cluster catalyst centers:  kinetics, thermochemistry, and theory"

Abstract:

Iron and Molybdenum sulfide-based catalysts constitute the most important representatives of catalysts for hydrocarbon conversion and hydrodesulfurization.  Formation and cleavage of C-S and S-H bonds involving sulfur bonded to Fe₂S₂ and Mo₂S₄ core structures are key reactions in fundamental catalytic pathways.  Thus, we present the measurement of new families of homolytic and heterolytic S-H bond strengths  in (OC)₃Fe(µ-SH)(µ-SCH₃)Fe(CO)₃ and Cp*Mo(u-S)₂(u-SH)(u-SCH₃)Mo Cp*, and kinetics of reaction of benzyl radical with the activated SH groups.  We describe new kinetics of addition of one, two and three alkyl  groups to the cage structure Cp*Mo(u-S)₂(u-S₂)Mo Cp*, forming persistent radicals of the structure Cp*Mo(u-S₂)(u-S. )(µ-SR)Mo Cp*, which in turn forms a dimer possessing a very weak S-S bond in equilibrium with the radical, which displays the novel kinetic properties of a persistent radical.  The kinetics and mechanisms of radical addition and displacement at the Mo2S4 cluster are discussed.  For   the (OC)₃Fe(µ-SH)(µ-SCH₃)Fe(CO)₃ system,  the effect on S-H bond strength of replacing the Fe-Fe bond in the butterfly structure with bridging S and CO linkages is explored in DFT calculations.  The performance of DFT approaches in predicting S-H and S-C bond strengths is discussed.   The studies present a quantitative approach to understanding the catalytic transformations that may occur at FeS and Mo₂S₄ active catalyst sites.   DFT studies of the bond strengths and radical properties of the clusters will be discussed.

Friday, October 30, 2009 at 1:00 p.m.  SB 324   

Department Contact: Dr. Dennis Salahub

http://www.pnl.gov/cmsd/staff/staff_info.asp?staff_num=5592