TY - JOUR
T1 - Stepwise reduction of dinitrogen occurring on a divanadium model compound
T2 - A synthetic, structural, magnetic, electrochemical, and theoretical investigation on the [V=N=N=N](n+) [n = 4-6] based complexes
AU - Ferguson, Richard
AU - Solari, Euro
AU - Floriani, Carlo
AU - Osella, Domenico
AU - Ravera, Mauro
AU - Re, Nazzareno
AU - Chiesi-Villa, Angiola
AU - Rizzoli, Corrado
PY - 1997
Y1 - 1997
N2 - This report details an extensive investigation on vanadium-dinitrogen complexes containing the [V(μ-N2)V](n+) skeleton with a variable oxidation state of the metal and reduction degree of dinitrogen, n varying from 6 → 5 → 4. This skeleton can be associated to alkali cations in ion-separated or ion-pair tight forms. The reaction of [(Mes)3V(thf)], 1 [Mes = 2,4,6-Me3C6H2], with Lewis acids [AlPh3, B(C6F5)3] removed the THF molecule leading under nitrogen to the formation of the diamagnetic complex [(Mes)3 V (μ-N2) V (Mes)3], 4. The reaction of 1 with N2 also occurs under reducing conditions using Na or K metals. As supported by the electrochemical study, the preliminary stages is in both cases the formation of the vanadium(II) desolvated form [V(mes)3]-, 5. The reaction of 5 with N2 in the case of potassium and in the presence of 1 leads to the compound {[(mes)3V(μ-N2)V(Mes)3]-[K(digly)3]+}, 11, which, depending on the reaction conditions, undergoes a further reduction to [{K(digly)3(μ-Mes)2(Mes)V}2(μ-N2)], 12 [digly = diethylene glycol dimethyl ether]. Similarly, the reduction of 1 with sodium gave, depending on the workup model, {[(Mes)3V(μ-N2)V(Mes)3]2-[Na(digly)2]+2}, 13 or {[(Mes)3V(μ-N2)(μ-N2(μ-Na)V(Mes)3]-[Na(digly)2]+}, 14, both containing the dianion [(Mes)3V(μ-N2)V(Mes)3]2-, 8. Complex 4 release upon protonation exclusively N2, while complexes 11-14 release N2, N2H4, and NH3 in amounts depending on the degree of reduction of the dinitrogen and the structure of the complex. The electrochemical reduction of 1 shed light on the intermediate formation of 5 and its conversion to 8, which was oxidized to the monoanion [(Mes)3V(μ-N2)V(Mes)3]-, 7 (which is the precursor of 8 in the chemical reduction). The magnetic studies coupled with the theoretical interpretation are in agreement with the presence of d2-d2 couple in 4, a d1-d1 in 12-14, and a d1-d0 in 11. This, along with the structural studies on 11-14, suggest a cumulenic structure [V=N=N=V](+n) [n = 5, 4] for 11-14.
AB - This report details an extensive investigation on vanadium-dinitrogen complexes containing the [V(μ-N2)V](n+) skeleton with a variable oxidation state of the metal and reduction degree of dinitrogen, n varying from 6 → 5 → 4. This skeleton can be associated to alkali cations in ion-separated or ion-pair tight forms. The reaction of [(Mes)3V(thf)], 1 [Mes = 2,4,6-Me3C6H2], with Lewis acids [AlPh3, B(C6F5)3] removed the THF molecule leading under nitrogen to the formation of the diamagnetic complex [(Mes)3 V (μ-N2) V (Mes)3], 4. The reaction of 1 with N2 also occurs under reducing conditions using Na or K metals. As supported by the electrochemical study, the preliminary stages is in both cases the formation of the vanadium(II) desolvated form [V(mes)3]-, 5. The reaction of 5 with N2 in the case of potassium and in the presence of 1 leads to the compound {[(mes)3V(μ-N2)V(Mes)3]-[K(digly)3]+}, 11, which, depending on the reaction conditions, undergoes a further reduction to [{K(digly)3(μ-Mes)2(Mes)V}2(μ-N2)], 12 [digly = diethylene glycol dimethyl ether]. Similarly, the reduction of 1 with sodium gave, depending on the workup model, {[(Mes)3V(μ-N2)V(Mes)3]2-[Na(digly)2]+2}, 13 or {[(Mes)3V(μ-N2)(μ-N2(μ-Na)V(Mes)3]-[Na(digly)2]+}, 14, both containing the dianion [(Mes)3V(μ-N2)V(Mes)3]2-, 8. Complex 4 release upon protonation exclusively N2, while complexes 11-14 release N2, N2H4, and NH3 in amounts depending on the degree of reduction of the dinitrogen and the structure of the complex. The electrochemical reduction of 1 shed light on the intermediate formation of 5 and its conversion to 8, which was oxidized to the monoanion [(Mes)3V(μ-N2)V(Mes)3]-, 7 (which is the precursor of 8 in the chemical reduction). The magnetic studies coupled with the theoretical interpretation are in agreement with the presence of d2-d2 couple in 4, a d1-d1 in 12-14, and a d1-d0 in 11. This, along with the structural studies on 11-14, suggest a cumulenic structure [V=N=N=V](+n) [n = 5, 4] for 11-14.
UR - http://www.scopus.com/inward/record.url?scp=0030662509&partnerID=8YFLogxK
U2 - 10.1021/ja971229q
DO - 10.1021/ja971229q
M3 - Article
SN - 0002-7863
VL - 119
SP - 10104
EP - 10115
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 42
ER -