Theoretical DFT studies of chromium tricarbonyl complexes with polycyclic aromatic ligandsстатья
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Дата последнего поиска статьи во внешних источниках: 18 июля 2013 г.
Аннотация:This paper presents a theoretical analysis of the structures of tricarbonyl chromium complexes of carboand
heterocyclic polyaromatic ligands (PAL) and the mechanisms of interring haptotropic rearrangement
in such complexes performed by using density functional theory (DFT) with the nonempirically constructed
PBE functional and extended split basis sets. The reaction paths were calculated for interring
haptotropic rearrangements and rotations of the metalcarbonyl fragment in the regioisomeric complexes.
The structures and energy characteristics of stationary points of the systems were determined. The
migration of the Cr(CO)3 group was shown to occur at the periphery of the ligand via transition states
with the structure of g3-allylic or g4-trimethylmethane complexes. Calculated geometries of the complexes
and the activation barriers were in a close agreement with the experimental data.
The reaction of g6-tricarbonylchromium complexes of PAL with n-BuLi (lithiation) was also studied by
the DFT. The kinetic and thermodynamic factors that control the direction and selectivity of metallation
were calculated for the model g6-biphenylenetricarbonylchromium complex. Both approaches indicate
that lithiation occurs exclusively at the aromatic ring bonded to the transition metal, which agrees with
the experimental data. The selectivity inside this ring is governed by a thermodynamic factor. The solvation
effects were simulated for the lithium salt of the model g6-naphthalenechromium tricarbonyl complex
in which lithium is localized at the a(1)-position of coordinated ring. The simulation showed the
most stable coordination of the lithium atom with two THF molecules. Addition of extra THF molecules
is thermodynamically unfavorable. The tricarbonylchromium complexes of naphthalene, biphenyl,
biphenylene and dibenzothiophene calculated relative energies for all solvated by two THF molecules
lithium salts indicate that the difference in energies DE 6 1 kcal mol1 corresponds to the experimentally
observed absence of selectivity, while the difference more than 2.5 kcal mol1 corresponds to the selectivity
of the reaction. No additional coordination of lithium to heteroatom was observed for the sulfurcontaining
dibenzothiophene complex. Similar calculation shows that double metallation in the dibenzothiophene
complex occurs at positions 1 and 4. The developed approach enables one to predict the direction
and selectivity of metallation reactions of transition metal complexes with different arenes and thus
to synthesize labeled complexes for the investigation of degenerate IRHR.