Abstract
Absolute rate constants for hydrogen atom abstraction by benzyl radical from Os3(μ-H)2 (CO)9PPh3 (1), Os3(μ-H)(H)(CO)10PPh3 (2), Os3(μ-H)(CO9) (μ3-η2-C9H6N) (3), Os3(μ-H)(CO9)- (μ-η2-C9H6N)(PPh3) (4), and Os3(μ-H)(CO10)(μ-η2- C9H6N) (5) were determined in benzene by competition of the abstraction reaction with the self-termination of benzyl radical. Thus, experimental values of kabs/kt 1/2 were combined with rate constants for self-termination of benzyl radical in benzene from the expression ln(2kt/M-1 s-1 = 27.23 - 2952.4/RT), RT in cal/mol, to give absolute rate constants for abstraction, kabs: for Os3(μ-H)2(CO)9PPh3 (1) in benzene, log(kabs/M-1 s-1) = 9.40 ± 0.30) - (8.11 ± 0.47)/θ; for Os3 (μ-H)(H)(CO)10PPh3 (2) (log(kabs/M-1 s-1) = (8.08 ± 0.33) - (4.32 ± 0.1)/θ; for Os3(μ-H)(CO)9 (μ3-η2-C9H6N) (3) log(kabs/M-1 s-1) = (10.1 ± 2) - (10.5 ± 3)/θ; and for Os3(μ-H)(CO9)(μ-η2-C9 H6N) (PPh3) (5) log(kabs/M-1 s-1) = (7.0 ± 0.27) - (4.25 ± 0.41)/θ, θ = 2.303RT kcal/mol. The terminal hydride on the Os3 cluster 2 is about 10 times more reactive than the bridging hydride in 1. The results show that while μ-H bridging retards the rate of hydrogen abstraction relative to terminal hydrogen, the bridging hydrogen remains appreciably reactive in the μ-H form. In fact, one of the fastest rates observed was for the bridging hydride in 4, Os3(μ-H)(CO10) (μ-η2-C9H6N). The 293 K rate constant for hydrogen atom abstraction from this electron-rich cluster, 5 ± 2 × 104 M-1 s-1, is almost as fast as that for the terminal hydrogen atom cluster, 2, Os3(μ-H)(H)(CO)10PPh3, kabs(298 K) = 8.2 × 104 M-1 s-1. The rate constant for hydrogen atom abstraction by benzyl radical from the Os3 clusters appears to increase with electron-rich osmium clusters and decrease with increasing steric bulk of the ligands.
| Original language | English |
|---|---|
| Pages (from-to) | 441-445 |
| Number of pages | 5 |
| Journal | Organometallics |
| Volume | 23 |
| Issue number | 3 |
| DOIs | |
| Publication status | Published - Feb 2 2004 |
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ASJC Scopus subject areas
- Inorganic Chemistry
- Organic Chemistry
Cite this
Comparison of hydrogen atom abstraction rates of terminal and bridging hydrides in triosmium clusters : Absolute abstraction rate constants for benzyl radical. / Franz, James A.; Kolwaite, Douglas S.; Linehan, John; Rosenberg, Edward.
In: Organometallics, Vol. 23, No. 3, 02.02.2004, p. 441-445.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Comparison of hydrogen atom abstraction rates of terminal and bridging hydrides in triosmium clusters
T2 - Absolute abstraction rate constants for benzyl radical
AU - Franz, James A.
AU - Kolwaite, Douglas S.
AU - Linehan, John
AU - Rosenberg, Edward
PY - 2004/2/2
Y1 - 2004/2/2
N2 - Absolute rate constants for hydrogen atom abstraction by benzyl radical from Os3(μ-H)2 (CO)9PPh3 (1), Os3(μ-H)(H)(CO)10PPh3 (2), Os3(μ-H)(CO9) (μ3-η2-C9H6N) (3), Os3(μ-H)(CO9)- (μ-η2-C9H6N)(PPh3) (4), and Os3(μ-H)(CO10)(μ-η2- C9H6N) (5) were determined in benzene by competition of the abstraction reaction with the self-termination of benzyl radical. Thus, experimental values of kabs/kt 1/2 were combined with rate constants for self-termination of benzyl radical in benzene from the expression ln(2kt/M-1 s-1 = 27.23 - 2952.4/RT), RT in cal/mol, to give absolute rate constants for abstraction, kabs: for Os3(μ-H)2(CO)9PPh3 (1) in benzene, log(kabs/M-1 s-1) = 9.40 ± 0.30) - (8.11 ± 0.47)/θ; for Os3 (μ-H)(H)(CO)10PPh3 (2) (log(kabs/M-1 s-1) = (8.08 ± 0.33) - (4.32 ± 0.1)/θ; for Os3(μ-H)(CO)9 (μ3-η2-C9H6N) (3) log(kabs/M-1 s-1) = (10.1 ± 2) - (10.5 ± 3)/θ; and for Os3(μ-H)(CO9)(μ-η2-C9 H6N) (PPh3) (5) log(kabs/M-1 s-1) = (7.0 ± 0.27) - (4.25 ± 0.41)/θ, θ = 2.303RT kcal/mol. The terminal hydride on the Os3 cluster 2 is about 10 times more reactive than the bridging hydride in 1. The results show that while μ-H bridging retards the rate of hydrogen abstraction relative to terminal hydrogen, the bridging hydrogen remains appreciably reactive in the μ-H form. In fact, one of the fastest rates observed was for the bridging hydride in 4, Os3(μ-H)(CO10) (μ-η2-C9H6N). The 293 K rate constant for hydrogen atom abstraction from this electron-rich cluster, 5 ± 2 × 104 M-1 s-1, is almost as fast as that for the terminal hydrogen atom cluster, 2, Os3(μ-H)(H)(CO)10PPh3, kabs(298 K) = 8.2 × 104 M-1 s-1. The rate constant for hydrogen atom abstraction by benzyl radical from the Os3 clusters appears to increase with electron-rich osmium clusters and decrease with increasing steric bulk of the ligands.
AB - Absolute rate constants for hydrogen atom abstraction by benzyl radical from Os3(μ-H)2 (CO)9PPh3 (1), Os3(μ-H)(H)(CO)10PPh3 (2), Os3(μ-H)(CO9) (μ3-η2-C9H6N) (3), Os3(μ-H)(CO9)- (μ-η2-C9H6N)(PPh3) (4), and Os3(μ-H)(CO10)(μ-η2- C9H6N) (5) were determined in benzene by competition of the abstraction reaction with the self-termination of benzyl radical. Thus, experimental values of kabs/kt 1/2 were combined with rate constants for self-termination of benzyl radical in benzene from the expression ln(2kt/M-1 s-1 = 27.23 - 2952.4/RT), RT in cal/mol, to give absolute rate constants for abstraction, kabs: for Os3(μ-H)2(CO)9PPh3 (1) in benzene, log(kabs/M-1 s-1) = 9.40 ± 0.30) - (8.11 ± 0.47)/θ; for Os3 (μ-H)(H)(CO)10PPh3 (2) (log(kabs/M-1 s-1) = (8.08 ± 0.33) - (4.32 ± 0.1)/θ; for Os3(μ-H)(CO)9 (μ3-η2-C9H6N) (3) log(kabs/M-1 s-1) = (10.1 ± 2) - (10.5 ± 3)/θ; and for Os3(μ-H)(CO9)(μ-η2-C9 H6N) (PPh3) (5) log(kabs/M-1 s-1) = (7.0 ± 0.27) - (4.25 ± 0.41)/θ, θ = 2.303RT kcal/mol. The terminal hydride on the Os3 cluster 2 is about 10 times more reactive than the bridging hydride in 1. The results show that while μ-H bridging retards the rate of hydrogen abstraction relative to terminal hydrogen, the bridging hydrogen remains appreciably reactive in the μ-H form. In fact, one of the fastest rates observed was for the bridging hydride in 4, Os3(μ-H)(CO10) (μ-η2-C9H6N). The 293 K rate constant for hydrogen atom abstraction from this electron-rich cluster, 5 ± 2 × 104 M-1 s-1, is almost as fast as that for the terminal hydrogen atom cluster, 2, Os3(μ-H)(H)(CO)10PPh3, kabs(298 K) = 8.2 × 104 M-1 s-1. The rate constant for hydrogen atom abstraction by benzyl radical from the Os3 clusters appears to increase with electron-rich osmium clusters and decrease with increasing steric bulk of the ligands.
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U2 - 10.1021/om0342255
DO - 10.1021/om0342255
M3 - Article
VL - 23
SP - 441
EP - 445
JO - Organometallics
JF - Organometallics
SN - 0276-7333
IS - 3
ER -