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Title: Ultrafast studies of organometallic photochemistry: The mechanism of carbon-hydrogen bond activation in solution

Abstract

When certain organometallic compounds are photoexcited in room temperature alkane solution, they are able to break or activate the C-H bonds of the solvent. Understanding this potentially practical reaction requires a detailed knowledge of the entire reaction mechanism. Because of the dynamic nature of chemical reactions, time-resolved spectroscopy is commonly employed to follow the important events that take place as reactants are converted to products. For the organometallic reactions examined here, the electronic/structural characteristics of the chemical systems along with the time scales for the key steps in the reaction make ultrafast UV/Vis and IR spectroscopy along with nanosecond Step-Scan FTIR spectroscopy the ideal techniques to use for this study. An initial study of the photophysics of (non-activating) model metal carbonyls centering on the photodissociation of M(CO){sub 6} (M = Cr, W, Mo) was carried out in alkane solutions using ultrafast IR spectroscopy. Next, picosecond UV/vis studies of the C-H bond activation reaction of Cp{sup *}M(CO){sub 2} (M = Rh, Ir), conducted in room temperature alkane solution, are described in an effort to investigate the origin of the low quantum yield for bond cleavage ({approximately}1%). To monitor the chemistry that takes place in the reaction after CO is lost, amore » system with higher quantum yield is required. The reaction of Tp{sup *}Rh(CO){sub 2} (Tp{sup *} = HB-Pz{sub 3}{sup *}, Pz{sup *} = 3,5-dimethylpyrazolyl) in alkanes has a quantum yield of {approximately}30%, making time resolved spectroscopic measurements possible. From ultrafast IR experiments, two subsequently formed intermediates were observed. The nature of these intermediates are discussed and the first comprehensive reaction mechanism for a photochemical C-H activating organometallic complex is presented.« less

Authors:
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Energy Research, Washington, DC (United States)
OSTI Identifier:
290873
Report Number(s):
LBNL-41643
ON: DE98054177; TRN: AHC29901%%78
DOE Contract Number:  
AC03-76SF00098
Resource Type:
Technical Report
Resource Relation:
Other Information: TH: Thesis (Ph.D.); PBD: May 1998
Country of Publication:
United States
Language:
English
Subject:
40 CHEMISTRY; ORGANOMETALLIC COMPOUNDS; ALKANES; CHEMICAL ACTIVATION; PHOTOLYSIS; CHROMIUM COMPOUNDS; TUNGSTEN COMPOUNDS; MOLYBDENUM COMPOUNDS; CARBONYLS; RHODIUM COMPOUNDS; IRIDIUM COMPOUNDS; CHEMICAL REACTION KINETICS; EXPERIMENTAL DATA

Citation Formats

Bromberg, S E. Ultrafast studies of organometallic photochemistry: The mechanism of carbon-hydrogen bond activation in solution. United States: N. p., 1998. Web. doi:10.2172/290873.
Bromberg, S E. Ultrafast studies of organometallic photochemistry: The mechanism of carbon-hydrogen bond activation in solution. United States. https://doi.org/10.2172/290873
Bromberg, S E. 1998. "Ultrafast studies of organometallic photochemistry: The mechanism of carbon-hydrogen bond activation in solution". United States. https://doi.org/10.2172/290873. https://www.osti.gov/servlets/purl/290873.
@article{osti_290873,
title = {Ultrafast studies of organometallic photochemistry: The mechanism of carbon-hydrogen bond activation in solution},
author = {Bromberg, S E},
abstractNote = {When certain organometallic compounds are photoexcited in room temperature alkane solution, they are able to break or activate the C-H bonds of the solvent. Understanding this potentially practical reaction requires a detailed knowledge of the entire reaction mechanism. Because of the dynamic nature of chemical reactions, time-resolved spectroscopy is commonly employed to follow the important events that take place as reactants are converted to products. For the organometallic reactions examined here, the electronic/structural characteristics of the chemical systems along with the time scales for the key steps in the reaction make ultrafast UV/Vis and IR spectroscopy along with nanosecond Step-Scan FTIR spectroscopy the ideal techniques to use for this study. An initial study of the photophysics of (non-activating) model metal carbonyls centering on the photodissociation of M(CO){sub 6} (M = Cr, W, Mo) was carried out in alkane solutions using ultrafast IR spectroscopy. Next, picosecond UV/vis studies of the C-H bond activation reaction of Cp{sup *}M(CO){sub 2} (M = Rh, Ir), conducted in room temperature alkane solution, are described in an effort to investigate the origin of the low quantum yield for bond cleavage ({approximately}1%). To monitor the chemistry that takes place in the reaction after CO is lost, a system with higher quantum yield is required. The reaction of Tp{sup *}Rh(CO){sub 2} (Tp{sup *} = HB-Pz{sub 3}{sup *}, Pz{sup *} = 3,5-dimethylpyrazolyl) in alkanes has a quantum yield of {approximately}30%, making time resolved spectroscopic measurements possible. From ultrafast IR experiments, two subsequently formed intermediates were observed. The nature of these intermediates are discussed and the first comprehensive reaction mechanism for a photochemical C-H activating organometallic complex is presented.},
doi = {10.2172/290873},
url = {https://www.osti.gov/biblio/290873}, journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri May 01 00:00:00 EDT 1998},
month = {Fri May 01 00:00:00 EDT 1998}
}