Organometallics
Communication
Present Address
These calculations suggest that the anionic nitrogen ligand has
a significant effect on whether dissociation of the ether occurs
in concert with (TS1) or prior to (TS2 or TS3) reductive
elimination.
§D.M.P.: University of California, San Francisco, California
94158, United States.
Notes
A comparison of these computational results to those from
our prior work reveals that, although the geometries of
transition state structures are similar, the identity of the alkyl
ligand has a significant effect on the relative energies for
competing mechanisms of reductive elimination. Calculations
predict that reductive elimination from (L2)Pd(neopentyl)-
(NHAr) (2b) occurs after dissociation of the ether, rather than
occurring in concert with dissociation of the ether. In contrast,
the computed barriers of the two pathways for reductive
elimination from (L2)Pd(3-CH3norborn-2-yl)(NHAr) are
nearly equal.17
In summary, the bidentate ligands Ad2(2-OCH3-5-(CF3)-
C6H3)P (L1) and Ad2PCH2CH2OCH3 (L2) enabled the
synthesis of monomeric neopentylpalladium(II) anilido and
methyleneamido complexes that are sufficiently stable to be
isolated and characterized. However, the weak coordination by
the oxygen atom allows these complexes to reductively
eliminate N-neopentyl amine and imine products at moderate
temperatures. These P,O ligand structures should enable the
synthesis of stable four-coordinate analogues of other reactive
three-coordinate palladium(II) intermediates without signifi-
cantly altering the reactivity of those complexes. Future studies
will assess this hypothesis.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors gratefully acknowledge funding from the National
Science Foundation Center for Enabling New Technologies
through Catalysis (Grant CHE-1205189). X-ray diffraction
crystallography, including solution, was performed by Nicholas
Settineri at the UC Berkeley CheXRay facility (NIH S10-
RR027172). We thank Dr. Hasan Celik and Dr. Nanette
Jarenwattananon at the UC Berkeley NMR Facility for their
assistance with DOSY experiments. T.R.C. and Q.J. acknowl-
edge the National Science Foundation for support (CHE-
1531468).
REFERENCES
■
(1) Hartwig, J. F. Organotransition Metal Chemisty From Bonding to
Catalysis, 1st ed.; University Science Books: Mill Valley, CA, 2010.
(2) Hili, R.; Yudin, A. K. Nat. Chem. Biol. 2006, 2, 284.
(3) Boyd, G. V., Advances in the Chemistry of Amino and Nitro
Compounds. In Patai’s Chemistry of Functional Groups; Wiley: 2009.
(4) Carey, J. S.; Laffan, D.; Thomson, C.; Williams, M. T. Org.
Biomol. Chem. 2006, 4 (12), 2337−2347.
(5) Roughley, S. D.; Jordan, A. M. J. Med. Chem. 2011, 54 (10),
3451−3479.
DFT calculations suggest that the reductive elimination
resembles a migration of the alkyl ligand to nitrogen and that
the degree of dissociation of the weakly bound O-donor group
depends on the alkyl and nitrogen-based ligands. The similarity
in mechanisms for reactions of complexes containing either
primary or secondary alkyl groups and either anilido or
methyleneamido ligands supports our proposal that concerted
reductive elimination from Pd(II) complexes may be applied as
a general strategy to form various C(sp3)−N bonds.
(6) Dugger, R. W.; Ragan, J. A.; Ripin, D. H. B. Org. Process Res. Dev.
2005, 9 (3), 253−258.
(7) Pawlikowski, A. V.; Getty, A. D.; Goldberg, K. I. J. Am. Chem.
Soc. 2007, 129 (34), 10382−10393.
(8) Marquard, S. L.; Rosenfeld, D. C.; Hartwig, J. F. Angew. Chem.,
Int. Ed. 2010, 49 (4), 793−796.
(9) Marquard, S. L. Reductive elimination of alkylamines and ethers:
reactions of bisphosphine-ligated palladium(II) complexes. Dissertation,
University of Illinois at Urbana-Champaign, 2012.
(10) Koo, K.; Hillhouse, G. L. Organometallics 1995, 14 (9), 4421−
4423.
(11) Koo, K.; Hillhouse, G. L. Organometallics 1996, 15 (12), 2669−
2671.
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
(12) Lin, B. L.; Clough, C. R.; Hillhouse, G. L. J. Am. Chem. Soc.
2002, 124 (12), 2890−2891.
́
(13) Perez-Temprano, M. H.; Racowski, J. M.; Kampf, J. W.;
Sanford, M. S. J. Am. Chem. Soc. 2014, 136 (11), 4097−4100.
Experimental procedures, characterization data, kinetic
data, computational methods, and crystallographic
́
(14) Pendleton, I. M.; Perez-Temprano, M. H.; Sanford, M. S.;
Zimmerman, P. M. J. Am. Chem. Soc. 2016, 138 (18), 6049−6060.
(15) Camasso, N. M.; Canty, A. J.; Ariafard, A.; Sanford, M. S.
Organometallics 2017, 36 (22), 4382−4393.
Optimized coordinates for calculated structures (XYZ)
(16) Hanley, P. S.; Marquard, S. L.; Cundari, T. R.; Hartwig, J. F. J.
Am. Chem. Soc. 2012, 134 (37), 15281−15284.
Accession Codes
(17) Peacock, D. M.; Jiang, Q.; Hanley, P. S.; Cundari, T. R.;
Hartwig, J. F. J. Am. Chem. Soc. 2018, 140 (14), 4893−4904.
(18) Pan, J.; Su, M.; Buchwald, S. L. Angew. Chem., Int. Ed. 2011, 50
(37), 8647−8651.
tallographic data for this paper. These data can be obtained
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
(19) Esposito, O.; Lewis, A. K. de K.; Hitchcock, P. B.; Caddick, S.;
Cloke, F. G. N. Chem. Commun. 2007, 1157−1159.
(20) Esposito, O.; Gois, P. M. P.; Lewis, A. K. de K.; Caddick, S.;
Cloke, F. G. N.; Hitchcock, P. B. Organometallics 2008, 27 (24),
6411−6418.
(21) The adamantyl groups in L1 (replacing the tert-butyl groups in
our prior work) were introduced to facilitate isolation of the metal
complexes.
(22) For applications of structurally similar P,N ancillary ligands to
Pd-catalyzed cross-coupling reactions, see: Stradiotto, M. In New
Trends in Cross-Coupling: Theory and Applications; The Royal Society
of Chemistry: 2015; pp 228−253.
AUTHOR INFORMATION
■
Corresponding Authors
ORCID
D
Organometallics XXXX, XXX, XXX−XXX