Assiut university researches
Density Functional Theory Study of N−CN and
O−CN Bond Cleavage by an Iron Silyl
Complex
AbdelRahman A. Dahy, Nobuaki Koga, and Hiroshi Nakazawa
Abstract:
Using hybrid density functional theory calculations with the
B3LYP functional, the reaction mechanisms for cleavage of
an unsaturated iron(II) silyl complex, CpFe(CO)SiMe3, were
studied. The following sequence of reactions was shown to
be favorable: (i) coordination of a nitrile through the lone pair
of electrons on the nitrile N atom (NCN) to form an end-on
complex, (ii) isomerization of the endon complex to a side-on
complex, (iii) migration of the silyl group to NCN facilitated by
the hypervalent character of the Si atom and its electrostatic
attraction with NCN to form a stable Fe−C−NCN threemembered-ring intermediate with an Fe−NCN dative bond,
(iv) dissociation of the NCN atom from Fe and coordination of
an amino N atom (NNR2) or methoxy O atom to Fe leading to
an Fe−C−NNR2 or Fe−C−O three-membered-ring
intermediate, and (v) cleavage of the R2N−C or MeO−C bond
to form a silyl isocyanide ligand. Step iv possesses the
largest activation energy in the sequence of reactions. The
activation energies for the reactions of H2NCN, Me2NCN,
and MeOCN were calculated to be 29.9, 28.0, and 19.1
kcal/mol, respectively, on the basis of potential energies with
zero-point energy correction. This accounts for the
experimental observation that the intermediates formed by
silyl group migration can be isolated. The effects of the amino
and methoxy groups are discussed by comparing their
reaction profiles with that for the reaction of acetonitrile.
Localized orbital analysis showed that in the threemembered-ring intermediates formed in step iv, the R2N−C
and MeO−C bonds are activated by ring strain, whereas the
Me−CN bond is activated by interaction of the Me−C bond
with the vacant coordination site that is produced in the
dissociation of NCN.
Published in:
Organometallics ,Vol.31,PP.3995−4005