3 research outputs found
Thermodynamic and Kinetic Study of Cleavage of the N–O Bond of N‑Oxides by a Vanadium(III) Complex: Enhanced Oxygen Atom Transfer Reaction Rates for Adducts of Nitrous Oxide and Mesityl Nitrile Oxide
Thermodynamic,
kinetic, and computational studies are reported for oxygen atom transfer
(OAT) to the complex VÂ(NÂ[<i>t</i>-Bu]ÂAr)<sub>3</sub> (Ar
= 3,5-C<sub>6</sub>H<sub>3</sub>Me<sub>2</sub>, <b>1</b>) from
compounds containing N–O bonds with a range of BDEs spanning
nearly 100 kcal mol<sup>–1</sup>: PhNO (108) > SIPr/MesCNO
(75) > PyO (63) > IPr/N<sub>2</sub>O (62) > MesCNO (53) >
N<sub>2</sub>O (40) > dbabhNO (10) (Mes = mesityl; SIPr = 1,3-bisÂ(diisopropyl)Âphenylimidazolin-2-ylidene;
Py = pyridine; IPr = 1,3-bisÂ(diisopropyl)Âphenylimidazol-2-ylidene;
dbabh = 2,3:5,6-dibenzo-7-azabicyclo[2.2.1]Âhepta-2,5-diene). Stopped
flow kinetic studies of the OAT reactions show a range of kinetic
behavior influenced by both the mode and strength of coordination
of the O donor and its ease of atom transfer. Four categories of kinetic
behavior are observed depending upon the magnitudes of the rate constants
involved: (I) dinuclear OAT following an overall third order rate
law (N<sub>2</sub>O); (II) formation of stable oxidant-bound complexes
followed by OAT in a separate step (PyO and PhNO); (III) transient
formation and decay of metastable oxidant-bound intermediates on the
same time scale as OAT (SIPr/MesCNO and IPr/N<sub>2</sub>O); (IV)
steady-state kinetics in which no detectable intermediates are observed
(dbabhNO and MesCNO). Thermochemical studies of OAT to <b>1</b> show that the V–O bond in Oî—ĽVÂ(NÂ[<i>t</i>-Bu]ÂAr)<sub>3</sub> is strong (BDE = 154 ± 3 kcal mol<sup>–1</sup>) compared with all the N–O bonds cleaved. In contrast, measurement
of the N–O bond in dbabhNO show it to be especially weak (BDE
= 10 ± 3 kcal mol<sup>–1</sup>) and that dissociation
of dbabhNO to anthracene, N<sub>2</sub>, and a <sup>3</sup>O atom
is thermodynamically favorable at room temperature. Comparison of
the OAT of adducts of N<sub>2</sub>O and MesCNO to the bulky complex <b>1</b> show a faster rate than in the case of free N<sub>2</sub>O or MesCNO despite increased steric hindrance of the adducts
Thermodynamic and Kinetic Study of Cleavage of the N–O Bond of N‑Oxides by a Vanadium(III) Complex: Enhanced Oxygen Atom Transfer Reaction Rates for Adducts of Nitrous Oxide and Mesityl Nitrile Oxide
Thermodynamic,
kinetic, and computational studies are reported for oxygen atom transfer
(OAT) to the complex VÂ(NÂ[<i>t</i>-Bu]ÂAr)<sub>3</sub> (Ar
= 3,5-C<sub>6</sub>H<sub>3</sub>Me<sub>2</sub>, <b>1</b>) from
compounds containing N–O bonds with a range of BDEs spanning
nearly 100 kcal mol<sup>–1</sup>: PhNO (108) > SIPr/MesCNO
(75) > PyO (63) > IPr/N<sub>2</sub>O (62) > MesCNO (53) >
N<sub>2</sub>O (40) > dbabhNO (10) (Mes = mesityl; SIPr = 1,3-bisÂ(diisopropyl)Âphenylimidazolin-2-ylidene;
Py = pyridine; IPr = 1,3-bisÂ(diisopropyl)Âphenylimidazol-2-ylidene;
dbabh = 2,3:5,6-dibenzo-7-azabicyclo[2.2.1]Âhepta-2,5-diene). Stopped
flow kinetic studies of the OAT reactions show a range of kinetic
behavior influenced by both the mode and strength of coordination
of the O donor and its ease of atom transfer. Four categories of kinetic
behavior are observed depending upon the magnitudes of the rate constants
involved: (I) dinuclear OAT following an overall third order rate
law (N<sub>2</sub>O); (II) formation of stable oxidant-bound complexes
followed by OAT in a separate step (PyO and PhNO); (III) transient
formation and decay of metastable oxidant-bound intermediates on the
same time scale as OAT (SIPr/MesCNO and IPr/N<sub>2</sub>O); (IV)
steady-state kinetics in which no detectable intermediates are observed
(dbabhNO and MesCNO). Thermochemical studies of OAT to <b>1</b> show that the V–O bond in Oî—ĽVÂ(NÂ[<i>t</i>-Bu]ÂAr)<sub>3</sub> is strong (BDE = 154 ± 3 kcal mol<sup>–1</sup>) compared with all the N–O bonds cleaved. In contrast, measurement
of the N–O bond in dbabhNO show it to be especially weak (BDE
= 10 ± 3 kcal mol<sup>–1</sup>) and that dissociation
of dbabhNO to anthracene, N<sub>2</sub>, and a <sup>3</sup>O atom
is thermodynamically favorable at room temperature. Comparison of
the OAT of adducts of N<sub>2</sub>O and MesCNO to the bulky complex <b>1</b> show a faster rate than in the case of free N<sub>2</sub>O or MesCNO despite increased steric hindrance of the adducts
Thermodynamic and Kinetic Study of Cleavage of the N–O Bond of N‑Oxides by a Vanadium(III) Complex: Enhanced Oxygen Atom Transfer Reaction Rates for Adducts of Nitrous Oxide and Mesityl Nitrile Oxide
Thermodynamic,
kinetic, and computational studies are reported for oxygen atom transfer
(OAT) to the complex VÂ(NÂ[<i>t</i>-Bu]ÂAr)<sub>3</sub> (Ar
= 3,5-C<sub>6</sub>H<sub>3</sub>Me<sub>2</sub>, <b>1</b>) from
compounds containing N–O bonds with a range of BDEs spanning
nearly 100 kcal mol<sup>–1</sup>: PhNO (108) > SIPr/MesCNO
(75) > PyO (63) > IPr/N<sub>2</sub>O (62) > MesCNO (53) >
N<sub>2</sub>O (40) > dbabhNO (10) (Mes = mesityl; SIPr = 1,3-bisÂ(diisopropyl)Âphenylimidazolin-2-ylidene;
Py = pyridine; IPr = 1,3-bisÂ(diisopropyl)Âphenylimidazol-2-ylidene;
dbabh = 2,3:5,6-dibenzo-7-azabicyclo[2.2.1]Âhepta-2,5-diene). Stopped
flow kinetic studies of the OAT reactions show a range of kinetic
behavior influenced by both the mode and strength of coordination
of the O donor and its ease of atom transfer. Four categories of kinetic
behavior are observed depending upon the magnitudes of the rate constants
involved: (I) dinuclear OAT following an overall third order rate
law (N<sub>2</sub>O); (II) formation of stable oxidant-bound complexes
followed by OAT in a separate step (PyO and PhNO); (III) transient
formation and decay of metastable oxidant-bound intermediates on the
same time scale as OAT (SIPr/MesCNO and IPr/N<sub>2</sub>O); (IV)
steady-state kinetics in which no detectable intermediates are observed
(dbabhNO and MesCNO). Thermochemical studies of OAT to <b>1</b> show that the V–O bond in Oî—ĽVÂ(NÂ[<i>t</i>-Bu]ÂAr)<sub>3</sub> is strong (BDE = 154 ± 3 kcal mol<sup>–1</sup>) compared with all the N–O bonds cleaved. In contrast, measurement
of the N–O bond in dbabhNO show it to be especially weak (BDE
= 10 ± 3 kcal mol<sup>–1</sup>) and that dissociation
of dbabhNO to anthracene, N<sub>2</sub>, and a <sup>3</sup>O atom
is thermodynamically favorable at room temperature. Comparison of
the OAT of adducts of N<sub>2</sub>O and MesCNO to the bulky complex <b>1</b> show a faster rate than in the case of free N<sub>2</sub>O or MesCNO despite increased steric hindrance of the adducts