Comparison of hydrogen atom abstraction rates of terminal and bridging hydrides in triosmium clusters

Absolute abstraction rate constants for benzyl radical

James A. Franz, Douglas S. Kolwaite, John Linehan, Edward Rosenberg

Research output: Contribution to journalArticle

10 Citations (Scopus)

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) (μ32-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)932-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 languageEnglish
Pages (from-to)441-445
Number of pages5
JournalOrganometallics
Volume23
Issue number3
DOIs
Publication statusPublished - Feb 2 2004

Fingerprint

Hydrides
hydrides
Carbon Monoxide
Hydrogen
Rate constants
hydrogen atoms
Atoms
Benzene
benzene
hydrogen
Osmium
Electrons
osmium
electrons
Ligands
ligands

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 journalArticle

@article{5cd8ca6f4f1a42b39f9c25bbfd9fde3a,
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(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.",
author = "Franz, {James A.} and Kolwaite, {Douglas S.} and John Linehan and Edward Rosenberg",
year = "2004",
month = "2",
day = "2",
doi = "10.1021/om0342255",
language = "English",
volume = "23",
pages = "441--445",
journal = "Organometallics",
issn = "0276-7333",
publisher = "American Chemical Society",
number = "3",

}

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.

UR - http://www.scopus.com/inward/record.url?scp=1142267470&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=1142267470&partnerID=8YFLogxK

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 -