Journal of the American Chemical Society
Article
Notes
computed, rather than complexes of the full DTBM−
SEGPHOS ligand. Although the energies of these computed
compounds will differ from those of the experimental system
because the DTBM−SEGPHOS is more hindered and more
electron-donating, the computations provided insight into the
stability of intermediates and rates of the elementary steps of
the cycle.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the Director, Office of Science, of
the U.S. Department of Energy under Contract No. DE-AC02-
05CH11231. We thank Johnson-Matthey for gifts of IrCl3 and
[Ir(cod)Cl]2 and Takasago for a gift of (S)-DTBM−
SEGPHOS. C.S.S. thanks the NSF for a graduate research
fellowship.
The calculations were conducted with the Gaussian 09
package. Geometry optimization was conducted with the M06
functionals with the lanl2dz basis set and ECP for iridium and
the 6-31g(d,p) basis set for all other atoms at 298 K. Frequency
analysis was conducted at the same level of theory to verify the
stationary points to be minima or saddle points and to obtain
the thermodynamic energy corrections. Single-point energies
were calculated with the M06 functionals with the lanl2tz(f)
basis set and ECP for iridium and the 6-311++g** basis set for
all other atoms. Solvation was modeled with the IEFPCM.
The computed barriers and Gibbs free energies of
intermediates are provided in Figure 4. These computed
energies are consistent with reaction by pathway B. The barrier
for oxidative addition of furan directly to complex 3 to form 7
in pathway A was computed to be 39.4 kcal/mol at 298 K. The
energy of this transition state is higher than the experimental
value from the kinetic measurements and is much higher than
those for each of the steps computed for reaction by pathway B.
Consequently, we conclude that the furan adds to 3 by the
multistep sequence in pathway B of Figure 4 to form 8, not by
the direct addition in pathway A of Figure 4.
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CONCLUSIONS
■
In conclusion, we have reported a rare example of the oxidative
olefination of furans with unactivated alkenes to form branched
vinylfurans in high yields and with high selectivities.
Mechanistic studies, including the observation of faster product
formation at lower temperatures, led to the development of
new ligands that form complexes capable of catalyzing
olefination of a wide range of furans under mild conditions.
Efforts to extend the scope of this process to arenes are
ongoing.
ASSOCIATED CONTENT
* Supporting Information
Experimental procedures and characterization of all new
compounds including NMR spectroscopy data, kinetic studies,
and optimization data. This material is available free of charge
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AUTHOR INFORMATION
Corresponding Author
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dx.doi.org/10.1021/ja504414c | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX