Communication
Dalton Transactions
because it is less common to find any significant spin con-
tamination in DFT calculations, especially when the unrest-
ricted Kohn–Sham orbitals are utilized. All geometries were
optimized in the gas phase, with explicit solvent molecules
modeled by dimethyl ether (DME) and thermodynamic correc-
tions to the free energy were found from frequency calcu-
lations at the optimized structures. Energies in solvent were
calculated using the PBF (Poisson Boltzmann Finite element)
solvation model at the optimized gas phase geometries.20 The
final free energies were obtained by the addition of thermo-
dynamic correction (including zero point energy correction)
from the frequency calculation to the energies in solvent. The
numbers of solvents that stabilize the complex models were
suggested and each species optimized. Reaction paths were fol-
lowed by QRC in order to confirm transition states related to
corresponding minimums. Frequency calculations were
carried out to determine the thermodynamic properties of the
stationary species. For the minimum and transition state struc-
tures, real frequency values and imaginary frequency values
were accepted, respectively. In our DFT calculations, the <S2>
values were investigated after each calculation and, if the value
of <S2> differed from s(s + 1) by more than a few percent above
Notes and references
1 (a) J. Tsuji, Palladium Reagents and Catalysts, Wiley,
New York, 2nd edn, 2004; (b) Metal-Catalyzed Cross-Coup-
ling Reactions, ed. A. de Meijere and F. Diederich, Wiley-
VCH, Weinheim, 2nd edn, 2004.
2 Transition Metals for Organic Synthesis, ed. M. Beller and
C. Bolm, Wiley-VCH, Weinheim, 2nd edn, 2004.
3 (a) B. A. F. Le Bailly, M. D. Greenhalgh and S. P. Thomas,
Chem. Commun., 2012, 48, 1580; (b) E. Nakamura and
N. Yoshikai, J. Org. Chem., 2010, 75, 6061.
4 (a) B. D. Sherry and A. Fürstner, Acc. Chem. Res., 2008, 41,
1500; (b) C. Bolm, J. Legros, J. Le Paih and L. Zani, Chem.
Rev., 2004, 104, 6217.
5 (a) Y. Y. Chua and H. A. Duong, Chem. Commun., 2014, 50,
8424; (b) Iron Catalysis in Organic Chemistry, ed. B. Plietker,
Wiley-VCH, Weinheim, Germany, 2008.
6 M. Tamura and J. Kochi, J. Organomet. Chem., 1971, 31, 289.
7 M. Tamura and J. Kochi, Syntheses, 1971, 303.
8 M. Tamura and J. K. Kochi, J. Am. Chem. Soc., 1971, 93, 1487.
9 M. Tamura and J. K. Kochi, Bull. Chem. Soc. Jpn., 1971, 44,
3063.
the theoretical expectation, a restricted open shell wave func- 10 (a) C. J. Adams, R. B. Bedford, et al., J. Am. Chem. Soc.,
tion was calculated and used as an initial guess in the unrest-
ricted calculation.
2012, 134, 10333; (b) R. S. Smith and J. K. Kochi, J. Org.
Chem., 1976, 41, 502.
11 A. Fürstner, R. Martin, H. Krause, G. Seidel, R. Goddard
and C. W. Lehmann, J. Am. Chem. Soc., 2008, 130, 8773.
12 J. Kleimark, A. Hedström, P.-F. Larsson, C. Johansson and
P.-O. Norrby, ChemCatChem, 2009, 1, 152.
Conclusions
13 A. Hedström, U. Bollmann, J. Bravidor and P.-O. Norrby,
Chem. – Eur. J., 2011, 17, 11991.
In summary, the reaction paths in the iron-catalyzed cross-
coupling reaction between an alkyl halide and phenyl mag-
nesium bromide in the presence of ferric alkoxide have been
investigated by the DFT calculations and experiments. The
iron-mediated coupling of an aryl Grignard reagent with an
iron alkoxide leads to an Fe(I) oxidation state under inert con-
ditions. The resulting Fe(I) complex undergoes a reaction with
the alkyl halide leading to the cross-coupling product. This
rate-limiting step can proceed through the OA or AT pathway.
The computational studies indicate that the activation energy
for the AT pathway is lower than that for the OA pathway. The
relative energies of these pathways depend on the number of
solvent molecules included in the complex models and on the
method of cleavage of the carbon–halide bond in the AT
pathway. The lowest energy pathway was obtained when a
mono-solvated complex was formed and the atom transfer led
to Fe(I)(OCH3)S1Br. We wish to demonstrate that iron alkoxide
would be useful as an environmentally benign catalyst for C–C
cross-coupling.
14 A. Guerinot, S. Reymond and J. Cossy, Angew. Chem., 2007,
119, 6641, (Angew. Chem., Int. Ed., 2007, 46, 6521).
15 (a) J. K. Kochi, Acc. Chem. Res., 1974, 7, 351;
(b) S. M. Neumann and J. K. Kochi, J. Org. Chem., 1975, 40,
599; (c) J. K. Kochi, J. Organomet. Chem., 2002, 653, 11.
16 M. S. Kharasch and E. K. Fields, J. Am. Chem. Soc., 1941,
63, 2316.
17 Jaguar, version 8.0, Schrodinger, LLC, New York, NY, 2011.
com.
18 S. Grimme, J. Antony, S. Ehrlich and H. Krieg, J. Chem.
Phys., 2010, 132, 154104.
19 S. Arshadi, A. R. Bekhradnia and A. Ebrahimnejad, Can.
J. Chem., 2011, 89, 1403.
20 B. Marten, K. Kim, C. Cortis, R. A. Friesner, R. B. Murphy,
M. N. Ringnalda, D. Sitkoff and B. Honig, J. Phys. Chem.,
1996, 100, 11775.
Dalton Trans.
This journal is © The Royal Society of Chemistry 2015