TY - JOUR
T1 - Ditantalum dinitrogen complex
T2 - Reaction of H 2 molecule with "end-on-Bridged" [Ta IV] 2(μ-η 1: η 1-N 2) and bis(μ-nitrido) [Ta V] 2(μ-N) 2 complexes
AU - Zhang, Wenchao
AU - Tang, Yanhui
AU - Lei, Ming
AU - Morokuma, Keiji
AU - Musaev, Djamaladdin G.
PY - 2011/10/3
Y1 - 2011/10/3
N2 - To elucidate (i) the physicochemical properties of the {(η 5- C 5Me 5)[Ta IV](i-Pr)C(Me)N(i-Pr)} 2(μ- η 1:η 1-N 2), I, [Ta IV] 2(μ- η 1:η 1-N 2), and {(η 5-C 5Me 5)[Ta V](i-Pr)C(Me)N(i-Pr)} 2(μ-N) 2, II, [Ta V] 2(μ-N) 2, complexes; (ii) the mechanism of the I → II isomerization; and (iii) the reaction mechanism of these complexes with an H 2 molecule, we launched density functional (B3LYP) studies of model systems 1, 2, and 3 where the C 5Me 5 and (i-Pr)C(Me)N(i-Pr) ligands of I (or II) were replaced by C 5H 5 and HC(NCH 3) 2, respectively. These calculations show that the lower-lying electronic states of 1, [Ta IV] 2(μ- η 1:η 1-N 2), are nearly degenerate open-shell singlet and triplet states with two unpaired electrons located on the Ta centers. This finding is in reasonable agreement with experiments [J. Am Chem. Soc.2007, 129, 9284-9285] showing easy accessibility of paramagnetic and diamagnetic states of I. The ground electronic state of the bis(μ-nitrido) complex 2, [Ta V] 2(μ-N) 2, is a closed-shell singlet state in agreement with the experimentally reported diamagnetic feature of II. The 1-to-2 rearrangement is a multistep and highly exothermic process. It occurs with a maximum of 28.7 kcal/mol free energy barrier required for the (μ- η 1: η 1-N 2) → (μ- η 2: η 2-N 2) transformation step. Reaction of 1 with H 2 leading to the 1,4-addition product 3 proceeds with a maximum of 24.2 kcal/mol free energy barrier associated by the (μ- η 1: η 1-N 2) → (μ- η 2: η 1-N 2) isomerization step. The overall reaction 1 + H 2 → 3 is exothermic by 20.0 kcal/mol. Thus, the addition of H 2 to 1 is kinetically and thermodynamically feasible and proceeds via the rate-determining (μ- η 1:η 1-N 2) → (μ- η 2:η 1-N 2) isomerization step. The bis(μ-nitrido) complex 2, [Ta V] 2(μ-N) 2, does not react with H 2 because of the large energy barrier (49.5 kcal/mol) and high endothermicity of the reaction. This conclusion is also in excellent agreement with the experimental observation [J. Am Chem. Soc.2007, 129, 9284-9285].
AB - To elucidate (i) the physicochemical properties of the {(η 5- C 5Me 5)[Ta IV](i-Pr)C(Me)N(i-Pr)} 2(μ- η 1:η 1-N 2), I, [Ta IV] 2(μ- η 1:η 1-N 2), and {(η 5-C 5Me 5)[Ta V](i-Pr)C(Me)N(i-Pr)} 2(μ-N) 2, II, [Ta V] 2(μ-N) 2, complexes; (ii) the mechanism of the I → II isomerization; and (iii) the reaction mechanism of these complexes with an H 2 molecule, we launched density functional (B3LYP) studies of model systems 1, 2, and 3 where the C 5Me 5 and (i-Pr)C(Me)N(i-Pr) ligands of I (or II) were replaced by C 5H 5 and HC(NCH 3) 2, respectively. These calculations show that the lower-lying electronic states of 1, [Ta IV] 2(μ- η 1:η 1-N 2), are nearly degenerate open-shell singlet and triplet states with two unpaired electrons located on the Ta centers. This finding is in reasonable agreement with experiments [J. Am Chem. Soc.2007, 129, 9284-9285] showing easy accessibility of paramagnetic and diamagnetic states of I. The ground electronic state of the bis(μ-nitrido) complex 2, [Ta V] 2(μ-N) 2, is a closed-shell singlet state in agreement with the experimentally reported diamagnetic feature of II. The 1-to-2 rearrangement is a multistep and highly exothermic process. It occurs with a maximum of 28.7 kcal/mol free energy barrier required for the (μ- η 1: η 1-N 2) → (μ- η 2: η 2-N 2) transformation step. Reaction of 1 with H 2 leading to the 1,4-addition product 3 proceeds with a maximum of 24.2 kcal/mol free energy barrier associated by the (μ- η 1: η 1-N 2) → (μ- η 2: η 1-N 2) isomerization step. The overall reaction 1 + H 2 → 3 is exothermic by 20.0 kcal/mol. Thus, the addition of H 2 to 1 is kinetically and thermodynamically feasible and proceeds via the rate-determining (μ- η 1:η 1-N 2) → (μ- η 2:η 1-N 2) isomerization step. The bis(μ-nitrido) complex 2, [Ta V] 2(μ-N) 2, does not react with H 2 because of the large energy barrier (49.5 kcal/mol) and high endothermicity of the reaction. This conclusion is also in excellent agreement with the experimental observation [J. Am Chem. Soc.2007, 129, 9284-9285].
UR - http://www.scopus.com/inward/record.url?scp=80053295192&partnerID=8YFLogxK
U2 - 10.1021/ic201159z
DO - 10.1021/ic201159z
M3 - Article
C2 - 21894917
AN - SCOPUS:80053295192
SN - 0020-1669
VL - 50
SP - 9481
EP - 9490
JO - Inorganic Chemistry
JF - Inorganic Chemistry
IS - 19
ER -