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

AN - SCOPUS:1142267470

VL - 23

SP - 441

EP - 445

JO - Organometallics

JF - Organometallics

SN - 0276-7333

IS - 3

ER -