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Title: Absolute rate expressions for hydrogen atom abstraction from molybdenum hydrides by carbon-centered radicals

Abstract

A new family of basis rate expressions for hydrogen atom abstraction by primary, secondary, and tertiary alkyl radicals in dodecane and benzyl radical in benzene from the molybdenum hydride Cp*Mo-(CO){sub 3}H and for reactions of a primary alkyl radical with CpMo(CO){sub 3}H in dodecane are reported (Cp* = {eta}{sup 5}-pentamethylcyclopentadienyl, Cp = {eta}{sup 5}-cyclopentadienyl). Rate expressions for reaction of primary, secondary, and tertiary radical clocks with Cp*Mo(CO){sub 3}H were as follows: for hex-5-enyl, log(k/M{sup {minus}1} s{sup {minus}1}) = (9.27 {+-} 0.13) {minus} (1.36 {+-} 0.22)/{theta}, {theta} = 2.303RT kcal/mol; for hept-6-en-2-yl, log(k/M{sup {minus}1} s{sup {minus}1}) = (9.12 {+-} 0.42) {minus} (1.91 {+-} 0.74)/{theta}; and for 2-methylhept-6-en-2-yl, log(k/M{sup {minus}1} s{sup {minus}1}) = (9.36 {+-} 0.18) {minus} (3.19 {+-} 0.30)/{theta} (errors are 2{sigma}). Hydrogen atom abstraction from CpMo(CO){sub 3}H by hex-5-enyl is described by log(k/M{sup {minus}1} s{sup {minus}1}) = (9.53 {+-} 0.34) {minus} (1.24 {+-} 0.62)/{theta}. Relative rate constants for 1{degree}:2{degree}:3{degree} alkyl radicals were found to be 26:7:1 at 298 K. Benzyl radical was found to react 1.4 times faster than tertiary alkyl radical. The much higher selectivities for CP*Mo(CO){sub 3}H than those observed for main group hydrides (Bu{sub 3}SnH, PhSeH, PhSH) with alkyl radicals, together with the very fast benzyl hydrogen-transfermore » rate, suggest the relative unimportance of simple enthalpic effects and the dominance of steric effects for the early transition-state hydrogen transfers. Hydrogen abstraction from Cp*Mo(CO){sub 3}H by benzyl radicals is described by log(k/M{sup {minus}1} s{sup {minus}1}) = (8.89 {+-} 0.22) {minus} (2.31 {+-} 0.33)/{theta}.« less

Authors:
; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab., Richland, WA (US)
Sponsoring Org.:
USDOE
OSTI Identifier:
20013675
DOE Contract Number:  
AC06-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of the American Chemical Society; Journal Volume: 121; Journal Issue: 42; Other Information: PBD: 27 Oct 1999
Country of Publication:
United States
Language:
English
Subject:
40 CHEMISTRY; MOLYBDENUM HYDRIDES; HYDROGEN; KINETICS; ALKYL RADICALS; BENZYL RADICALS; HYDROGENATION; HYDROGEN TRANSFER

Citation Formats

Franz, J.A., Linehan, J.C., Birnbaum, J.C., Hicks, K.W., and Alnajjar, M.S.. Absolute rate expressions for hydrogen atom abstraction from molybdenum hydrides by carbon-centered radicals. United States: N. p., 1999. Web. doi:10.1021/ja991412e.
Franz, J.A., Linehan, J.C., Birnbaum, J.C., Hicks, K.W., & Alnajjar, M.S.. Absolute rate expressions for hydrogen atom abstraction from molybdenum hydrides by carbon-centered radicals. United States. doi:10.1021/ja991412e.
Franz, J.A., Linehan, J.C., Birnbaum, J.C., Hicks, K.W., and Alnajjar, M.S.. Wed . "Absolute rate expressions for hydrogen atom abstraction from molybdenum hydrides by carbon-centered radicals". United States. doi:10.1021/ja991412e.
@article{osti_20013675,
title = {Absolute rate expressions for hydrogen atom abstraction from molybdenum hydrides by carbon-centered radicals},
author = {Franz, J.A. and Linehan, J.C. and Birnbaum, J.C. and Hicks, K.W. and Alnajjar, M.S.},
abstractNote = {A new family of basis rate expressions for hydrogen atom abstraction by primary, secondary, and tertiary alkyl radicals in dodecane and benzyl radical in benzene from the molybdenum hydride Cp*Mo-(CO){sub 3}H and for reactions of a primary alkyl radical with CpMo(CO){sub 3}H in dodecane are reported (Cp* = {eta}{sup 5}-pentamethylcyclopentadienyl, Cp = {eta}{sup 5}-cyclopentadienyl). Rate expressions for reaction of primary, secondary, and tertiary radical clocks with Cp*Mo(CO){sub 3}H were as follows: for hex-5-enyl, log(k/M{sup {minus}1} s{sup {minus}1}) = (9.27 {+-} 0.13) {minus} (1.36 {+-} 0.22)/{theta}, {theta} = 2.303RT kcal/mol; for hept-6-en-2-yl, log(k/M{sup {minus}1} s{sup {minus}1}) = (9.12 {+-} 0.42) {minus} (1.91 {+-} 0.74)/{theta}; and for 2-methylhept-6-en-2-yl, log(k/M{sup {minus}1} s{sup {minus}1}) = (9.36 {+-} 0.18) {minus} (3.19 {+-} 0.30)/{theta} (errors are 2{sigma}). Hydrogen atom abstraction from CpMo(CO){sub 3}H by hex-5-enyl is described by log(k/M{sup {minus}1} s{sup {minus}1}) = (9.53 {+-} 0.34) {minus} (1.24 {+-} 0.62)/{theta}. Relative rate constants for 1{degree}:2{degree}:3{degree} alkyl radicals were found to be 26:7:1 at 298 K. Benzyl radical was found to react 1.4 times faster than tertiary alkyl radical. The much higher selectivities for CP*Mo(CO){sub 3}H than those observed for main group hydrides (Bu{sub 3}SnH, PhSeH, PhSH) with alkyl radicals, together with the very fast benzyl hydrogen-transfer rate, suggest the relative unimportance of simple enthalpic effects and the dominance of steric effects for the early transition-state hydrogen transfers. Hydrogen abstraction from Cp*Mo(CO){sub 3}H by benzyl radicals is described by log(k/M{sup {minus}1} s{sup {minus}1}) = (8.89 {+-} 0.22) {minus} (2.31 {+-} 0.33)/{theta}.},
doi = {10.1021/ja991412e},
journal = {Journal of the American Chemical Society},
number = 42,
volume = 121,
place = {United States},
year = {Wed Oct 27 00:00:00 EDT 1999},
month = {Wed Oct 27 00:00:00 EDT 1999}
}