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Title: Comparison of Hydrogen Atom Abstraction Rates of Terminal and Bridging Hydrides in Triosmium Clusters: Absolute Abstraction Rate Constants for Benzyl Radical

Abstract

Absolute rate constants for hydrogen atom abstraction by benzyl radical from Os3(m-H)2 (CO)9PPh3(1), Os3 (m-H)(H)(CO)10PPh3(2), Os3(m-H)(CO)9(m3-h2-C9H6N)(3), Os3(m-H)(CO)9(m-h2-C9H6N)PPh3 (5) and Os3(m-H)(CO)10(m-h2-C9H6N) (4) were determined in benzene by competition of the abstraction reaction with the self termination of benzyl radical. Thus, experimental values of kabs/kt1/2 were combined with rate constants for self-termination of benzyl radical in benzene from the expression ln(2kt/M-1s-1= 27.23 - 2952.4/RT), RT in cal/mol, to give absolute rate constants for abstraction, kabs: for Os3(m-H)2 (CO)9PPh3(1) in benzene, log (kabs/M-1s-1)= (8.86 .20) - (6.90 .31)/q; for Os3 (m-H)(H)(CO)(10PPh3) (2) log (kabs/M-1s-1)= (8.15 .49) - (4.41 .72)/q; for Os3(m-H)(CO)9(m3-h2-C9H6N) (3) log (kabs/M-1s-1)= (8.9 2) (8.8 3)/q; value for 4 and for Os3(m-H)(CO9)(m-h2-C9H6N)(PPh3) (5) log (kabs/M-1s-1)= (7.0 .38) - (4.15 .56)/q, q= 2.303RT kcal/mol. The terminal hydride on the Os3 c luster 2 is about 10 times more reactive than bridging hydride in 1. The results show that while m-H bridging retards the rate of hydrogen abstraction relative to terminal hydrogen, the bridging hydrogen remains appreciably reactive in the m-H form. In fact, the highest rate observed was for the bridging hydride in 4, Os3(m-H)(CO)10(m-h2-C9H6N). Temperature dependent kinetics for compound 4 were not determined because of significant CO loss above room temperature.more » However at 293 K the rate constant of hydrogen atom abstraction from this electron-rich cluster, 5 2 x 104 M-1s-1, is at least twice as fast as that for the terminal hydrogen atom cluster, 2, Os3 (m-H)(H)(CO)10PPh3, kabs (298 K)= 1.8 x 104 M-1s-1. The rate constants for hydrogen atom abstraction by benzyl radical from these osmium clusters increase with increasing electron density on the osmium cluster and decrease with increasing steric bulk of the ligands.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
15007483
Report Number(s):
PNNL-SA-38160
KC0302010
DOE Contract Number:  
AC06-76RL01830
Resource Type:
Journal Article
Journal Name:
Organometallics, 23(3):441-445
Additional Journal Information:
Journal Name: Organometallics, 23(3):441-445
Country of Publication:
United States
Language:
English
Subject:
08 HYDROGEN

Citation Formats

Franz, James A, Kolwaite, Douglas S, Linehan, John C, and Rosenberg, Edward. Comparison of Hydrogen Atom Abstraction Rates of Terminal and Bridging Hydrides in Triosmium Clusters: Absolute Abstraction Rate Constants for Benzyl Radical. United States: N. p., 2004. Web. doi:10.1021/om0342255.
Franz, James A, Kolwaite, Douglas S, Linehan, John C, & Rosenberg, Edward. Comparison of Hydrogen Atom Abstraction Rates of Terminal and Bridging Hydrides in Triosmium Clusters: Absolute Abstraction Rate Constants for Benzyl Radical. United States. https://doi.org/10.1021/om0342255
Franz, James A, Kolwaite, Douglas S, Linehan, John C, and Rosenberg, Edward. 2004. "Comparison of Hydrogen Atom Abstraction Rates of Terminal and Bridging Hydrides in Triosmium Clusters: Absolute Abstraction Rate Constants for Benzyl Radical". United States. https://doi.org/10.1021/om0342255.
@article{osti_15007483,
title = {Comparison of Hydrogen Atom Abstraction Rates of Terminal and Bridging Hydrides in Triosmium Clusters: Absolute Abstraction Rate Constants for Benzyl Radical},
author = {Franz, James A and Kolwaite, Douglas S and Linehan, John C and Rosenberg, Edward},
abstractNote = {Absolute rate constants for hydrogen atom abstraction by benzyl radical from Os3(m-H)2 (CO)9PPh3(1), Os3 (m-H)(H)(CO)10PPh3(2), Os3(m-H)(CO)9(m3-h2-C9H6N)(3), Os3(m-H)(CO)9(m-h2-C9H6N)PPh3 (5) and Os3(m-H)(CO)10(m-h2-C9H6N) (4) were determined in benzene by competition of the abstraction reaction with the self termination of benzyl radical. Thus, experimental values of kabs/kt1/2 were combined with rate constants for self-termination of benzyl radical in benzene from the expression ln(2kt/M-1s-1= 27.23 - 2952.4/RT), RT in cal/mol, to give absolute rate constants for abstraction, kabs: for Os3(m-H)2 (CO)9PPh3(1) in benzene, log (kabs/M-1s-1)= (8.86 .20) - (6.90 .31)/q; for Os3 (m-H)(H)(CO)(10PPh3) (2) log (kabs/M-1s-1)= (8.15 .49) - (4.41 .72)/q; for Os3(m-H)(CO)9(m3-h2-C9H6N) (3) log (kabs/M-1s-1)= (8.9 2) (8.8 3)/q; value for 4 and for Os3(m-H)(CO9)(m-h2-C9H6N)(PPh3) (5) log (kabs/M-1s-1)= (7.0 .38) - (4.15 .56)/q, q= 2.303RT kcal/mol. The terminal hydride on the Os3 c luster 2 is about 10 times more reactive than bridging hydride in 1. The results show that while m-H bridging retards the rate of hydrogen abstraction relative to terminal hydrogen, the bridging hydrogen remains appreciably reactive in the m-H form. In fact, the highest rate observed was for the bridging hydride in 4, Os3(m-H)(CO)10(m-h2-C9H6N). Temperature dependent kinetics for compound 4 were not determined because of significant CO loss above room temperature. However at 293 K the rate constant of hydrogen atom abstraction from this electron-rich cluster, 5 2 x 104 M-1s-1, is at least twice as fast as that for the terminal hydrogen atom cluster, 2, Os3 (m-H)(H)(CO)10PPh3, kabs (298 K)= 1.8 x 104 M-1s-1. The rate constants for hydrogen atom abstraction by benzyl radical from these osmium clusters increase with increasing electron density on the osmium cluster and decrease with increasing steric bulk of the ligands.},
doi = {10.1021/om0342255},
url = {https://www.osti.gov/biblio/15007483}, journal = {Organometallics, 23(3):441-445},
number = ,
volume = ,
place = {United States},
year = {Mon Feb 02 00:00:00 EST 2004},
month = {Mon Feb 02 00:00:00 EST 2004}
}