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

Abstract

Thermodynamic, kinetic, and computational studies are reported for oxygen atom transfer (OAT) to the complex V(N[t-Bu]Ar)3 (Ar = 3,5-C6H3Me2, 1) from compounds containing N-O bonds with a range of BDEs spanning nearly 100 kcal mol(-1): PhNO (108) > SIPr/MesCNO (75) > PyO (63) > IPr/N2O (62) > MesCNO (53) > N2O (40) > dbabhNO (10) (Mes = mesityl; SIPr = 1,3-bis(diisopropyl)phenylimidazolin-2-ylidene; Py = pyridine; IPr = 1,3-bis(diisopropyl)phenylimidazol-2-ylidene; dbabh = 2,3:5,6-dibenzo-7-azabicyclo[2.2.1]hepta-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 (N2O); (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/N2O); (IV) steady-state kinetics in which no detectable intermediates are observed (dbabhNO and MesCNO). Thermochemical studies of OAT to 1 show that the V-O bond in O≡V(N[t-Bu]Ar)3 is strong (BDE = 154 ± 3 kcal mol(-1)) 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(-1)) and that dissociation of dbabhNO to anthracene, N2, and a (3)O atom is thermodynamically favorable at room temperature. Comparison of the OAT of adducts of N2O and MesCNO to the bulky complex 1 show a faster rate than in the case of free N2O or MesCNO despite increased steric hindrance of the adducts.

Rhodium(I) Pincer Complexes of Nitrous Oxide

“…5 [10,12] By drawing parallels with the reaction of aneutral rhodium PNP analogue with N 2 O, where formation of ad iscrete adduct is inferred but not experimentally corroborated, we suggest 2 decomposes by abimetallic oxygen atom transfer mechanism that is initiated by dissociation of N 2 Oa nd proceeds via {(pincer)Rh II -N = N-O-Rh II (pincer)} 2+ . [9,13] Consistent with this assertion, enhanced solution stability was observed under aN 2 Oa tmosphere (2 %/30 %d ecomposition of 2a/b after 24 h).…”

Synthetic chemistry with nitrous oxide

“…34 Oxygen atom transfer was also demonstrated for cyclopentadienyl complexes of vanadium, 35 tantalum, 36 zirconium, 37 and hafnium. 44 At low temperature, however, an overall second order was observed. The Mindiola group has shown that vanadium 39 and titanium 40 alkyl complexes can be oxidized with N 2 O to give complexes with terminal oxo ligands.…”

Terminal Molybdenum Phosphides with d Electrons: Radical Character Promotes Coupling Chemistry

“…Elimination of arenes resulting in group transfer has been employed to deliver a variety of moieties, including N − ,,, NH, CH, NCN,, O, PCH, and P 2 ,. Recently, ClPA was employed to transfer P + to an anionic vanadium nitride to generate the pnictogen–pnictogen linkage in a transient P−N complex .…”

“…Monometallic four‐electron oxidative addition is known, but is limited to the insertion of metal fragments into unsaturated C=O, C=S, C=N,, and N=N bonds. Group transfer through the elimination of a single arene equivalent more typically results in two‐electron processes,,,,, although four‐electron reactivity has been demonstrated when employing two metal centers as group or atom acceptors . The hapticity change of the metal–arene interaction from η 6 ( 1 ) to η 2 ( 2 ) facilitates this multi‐electron transformation; the d orbitals engaging in Mo−arene π bonding in the low‐valent starting material are liberated to form the Mo−P bonds in the product.…”