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Organometallics
Article
Notes
ether to 15 as determined by using 0.1 equiv of HMDSO as an
internal standard, indicating that an excess of vinyl ether is not
necessary for decomposition. This result is consistent with our
predicted metathesis-dependent decomposition pathway as
long as catalyst initiation to 9 is slower than Fischer carbene
exchange from 9 to 18. Wang et al. previously computed
initiation of 3 with styrene. The rate-limiting step of the
initiation is retro-[2 + 2] to form the free 2-isopropoxystyr-
ene.25 The computed barrier for this step in the reaction of 3
with phenyl vinyl ether is 23.4 kcal/mol.27 Therefore, initiation
is significantly slower than carbene exchange. During the
decomposition process, only a small portion of the catalyst will
be initiated to 9 and then the remaining vinyl ether will react
rapidly with 9, epimerizing the complex to 18 (leading to
hydride 15). This final step regenerates 1 equiv of vinyl ether,
leading to net consumption of 1 equiv of vinyl ether per
equivalent of catalyst in the decomposition process. The rapid
epimerization of 9 to 18 also explains why we do not observe
two Fischer carbene isomers experimentally. While 9 and 18
are in rapid equilibrium, 18 is predicted to be heavily favored
(>98% at room temperature).21
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The research described was financially supported by the NSF
(CHE-1502616), NIH (GM031332), and ONR
(N000141310895 and N00014-14-1-0650). Calculations
were performed using the NSF funded (OCI-1053575)
Extreme Science and Engineering Discovery Environment
(XSEDE), the UCLA IDRE Hoffman2 Cluster, and the ONR
supported Copper Cluster. T.S.A. is grateful for support from
the National Science Foundation through a Graduate Research
Fellowship. D. VanderVelde is acknowledged for his assistance
with NMR experiments. B. L. Quigley is thanked for helpful
discussions. Materia, Inc. is thanked for generous donations of
catalysts 3 and 4.
REFERENCES
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In conclusion, we have demonstrated that Fischer carbenes
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Z-selective ruthenium metathesis catalysts. These Fischer
carbenes degrade to ruthenium hydrides rapidly under the
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(8) Vorfalt, T.; Wannowius, K.-J.; Plenio, H. Angew. Chem., Int. Ed.
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(10) Takahira, Y.; Morizawa, Y. J. Am. Chem. Soc. 2015, 137, 7031−
7034.
(11) Endo, K.; Grubbs, R. H. J. Am. Chem. Soc. 2011, 133, 8525−
8527.
1
reaction conditions, as identified by H NMR experiments.
Using DFT, we have also shown that Fischer carbenes such as
9 and 18 are not metathesis inactive if carbenes of similar
stability result. These results have an important effect for the
future use of vinyl ethers to quench reactions involving
cyclometalated Z-selective catalysts. When vinyl ethers are
used to quench a metathesis reaction, ruthenium hydrides can
form rapidly in the reaction mixture if the Fischer carbene is
not separated promptly. The presence of hydrides can
potentially lead to degradation of the Z-olefin content or
olefin walking. Experiments to determine how these hydrides
affect internal olefins are currently underway.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
met.8b00150.
(12) Keitz, B. K.; Endo, K.; Patel, P. R.; Herbert, M. B.; Grubbs, R.
H. J. Am. Chem. Soc. 2012, 134, 693−699.
Experimental procedures, detailed NMR studies, com-
putational details, and energies of computed structures
(PDF)
Coordinates of all computed species (optimized at the
B3LYP level) (XYZ)
(13) Rosebrugh, L. E.; Herbert, M. B.; Marx, V. M.; Keitz, B. K.;
Grubbs, R. H. J. Am. Chem. Soc. 2013, 135, 1276−1279.
(14) Liu, P.; Xu, X.; Dong, X.; Keitz, B. K.; Herbert, M. B.; Grubbs,
R. H.; Houk, K. N. J. Am. Chem. Soc. 2012, 134, 1464−1467.
(15) Herbert, M. B.; Lan, Y.; Keitz, B. K.; Liu, P.; Endo, K.; Day, M.
W.; Houk, K. N.; Grubbs, R. H. J. Am. Chem. Soc. 2012, 134, 7861−
7866.
AUTHOR INFORMATION
■
(16) See the Supporting Information of this reference for a recent
example: Hartung, J.; Dornan, P. K.; Grubbs, R. H. J. Am. Chem. Soc.
2014, 136, 13029−13037.
Corresponding Authors
(17) (a) Courchay, F. C.; Sworen, J. C.; Ghiviriga, I.; Abboud, K. A.;
Wagener, K. B. Organometallics 2006, 25, 6074−6086. (b) Rowley, C.
N.; Foucault, H. M.; Woo, T. K.; Fogg, D. E. Organometallics 2008,
27, 1661−1663. (c) Ashworth, I. W.; Hillier, I. H.; Nelson, D. J.;
Percy, J. M.; Vincent, M. A. Eur. J. Org. Chem. 2012, 2012, 5673−
5677. (d) Clark, J. R.; Griffiths, J. R.; Diver, S. T. J. Am. Chem. Soc.
2013, 135, 3327−3330.
ORCID
Jessica M. Grandner: 0000-0001-5068-8665
K. N. Houk: 0000-0002-8387-5261
Robert H. Grubbs: 0000-0002-0057-7817
Author Contributions
§T.S.A. and J.M.G. contributed equally to this work. Ahmed
performed the majority of experiments and Grandner
performed all computations.
(18) This observation is consistent with studies of previously
reported Fischer carbenes.9
(19) Shifts are consistent with those of other Ru−H complexes.15
D
DOI: 10.1021/acs.organomet.8b00150
Organometallics XXXX, XXX, XXX−XXX