************第５１回尾張コンプレックスセミナー*************
　　　　
題  　目：
Title   ： 　Cleavage of RnE-CN bonds (E = C, N, O, and F) in the Presence
of Iron and
         　　Molybdenum Silyl Complexes. DFT Theoretical Studies.

発 表 者：　 アブデルラハマン A. ダヒー
Speaker ：　 AbdelRahman A. Dahy

所　  属：   アシュート大学
Affiliation：Assiut University, Egypt

日  　時：　 １０月１日（月）午後１時００分〜（約１時間）
Date    ：　 Mon. Oct. 1st, 13:00 pm (Almost one hour)

場　  所：　情報科学研究科４階セミナー室
Place   :   4F Seminar Room, Graduate School of Information Science

内　  容：
Abstract：

Using hybrid density functional theory calculations with the 
B3LYP functional, the reaction mechanisms for cleavage of 
RnE-CN bonds (RnE=H3C, H2N, Me2N, MeO, and F) in the presence 
of unsaturated iron silyl complex and/or molybdenum silyl 
catalyst, Cp(CO)2MSiMe3 (M=Fe or (CO)Mo), were studied. 
While there is one stage for the cleavage of RnE-CN bonds 
in presence of iron silyl complex, there are two stages 
in the case of molybdenum siyl catalyst. The stage (1) is 
the cleavage of RnE-CN bond and it is similar in the 
presence of iron and molybdenum silyl complexes. 
The favorable sequence of reactions for this stage are 
as following; (i) coordination of a nitrile through the 
lone pair of electrons on the nitrile nitrogen (N_CN) atom 
to give an end-on complex; (ii) isomerization of the end-on 
complex to a side-on complex; (iii) migration of the silyl 
group to the NCN to form a stable M-C-N_CN three-membered 
ring intermediate with an M-N_CN dative bond; (iv) 
dissociation of the N_CN atom from M and coordination of 
an E (E_ERn) atom to M leading to an M-C-(E_ERn) 
three-membered ring intermediate; and (v) cleavage of 
the RnE-C bond to form a silylisocyanide complex. Stage 
(2) is the regeneration of the active catalyst through 
two σ-metathesis steps; in the first σ-metathesis 
Cp(CO)2MoERn reacts with HSiMe3 to give Cp(CO)2MoH and 
RnESiMe3, and the second σ-metathesis of Cp(CO)2MoH 
with HSiMe3 regenerates Cp(CO)2MoSiMe3.
Step (iv) in the first stage possesses the largest 
activation energy, the rate-determining step in cases 
of the two complexes. The activation energies for this 
step were calculated to be 28.9, 29.9, 28.0, 19.1, and 
15.9 kcal/mol for RnE=H3C, H2N, Me2N, MeO, and F in cases 
of iron silyl complexes and  36.4, 38.3, and 26.6 kcal/mol 
for for RnE=H2N, Me2N, and MeO in the cases of molybdenum 
silyl catalyst, respectively, based on potential energies 
with zero-point energy correction. After dissociation of 
silylisocyanide ligand from silylisocyanide complex, it 
will be isomerized to silylcyanide. There are other paths 
for the cleavage of RnE-CN, oxidative addition and 
σ-metathesis, but they excluded because they require 
high activation energies. The hypervalent character 
of Si atom and its electrostatic interaction with NCN 
atom facilitate the cleavage of RnE-CN bonds. The 
effect of the group or atom (RnE) attached to CN group 
on the reaction mechanism will be discussed as well as 
the comparison between cleavage of RnE-CN bonds in the 
presence of iron silyl complex and molybdenum silyl 
catalyst will be discussed.

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