H. Boegel et S. Tobisch, DFT CALCULATIONS OF ALTERNATIVE STRUCTURES IN THE ALLYL-NICKEL CATALYZED POLYMERIZATION OF BUTADIENE, International journal of quantum chemistry, 60(7), 1996, pp. 197-205
The pi-allyl insertion mechanism of the 1,4-cis polymerization of buta
diene by means of allyl-nickel catalysts has been studied theoreticall
y by density functional theory (DFT) for the ligand free cationic bute
nyl nickel(II) complexes [Ni(C3H5)(C4H6)](+), I, [Ni(C3H5)(C4H6)(C2H4)
](+), II, and [Ni(C7H11)(C4H6,)](+), III DFT energy profiles have been
determined for the insertion of s-cis-butadiene into the anti-eta(3)-
butenyl nickel(II) bond in the supine and prone orientation of the rea
cting ligands. One of the objectives of the study was to support the p
roposed pi-allyl insertion mechanism. With increasing size of the mode
l compound there is better agreement between the calculated reaction a
nd activation energies in relation to the known experimental behavior.
Among the different arrangements (anti- or syn-butenyl) of the allyli
c end of the growing polymer chain and the relative orientation (supin
e or prone) of cisoid butadiene at the catalytic site, the anti-buteny
l/prone reacts in compound III with a small activation barrier (8.2 kc
al/mol) to the product (-5.7 kcal/mol). The stabilizing effect of the
coordination of an additional double bond of the growing polymer chain
for the correct description of the geometrical and energetical aspect
s of the insertion reaction was demonstrated by II. The results suppor
t the s-cis-butadiene insertion into the anti-eta(3)-butenyl nickel(II
) bond according to the proposed pi-allyl mechanism. (C) 1996 John Wil
ey & Sons, Inc.