C(sp3)-O bond-forming reductive elimination from PdIV with diverse oxygen nucleophiles

Article abstract of DOI:10.1021/ja507056u

This article describes an investigation of C(sp³)-O bond-forming reductive elimination reactions from Pd^IV complexes. Phenoxide, acetate, difluoroacetate, dimethylphosphate, tosylate, and nitrate nucleophiles are shown to participate in this reaction. In all cases, C(sp³)-O bond formation occurs with high selectivity over potentially competing C(sp²)-O coupling. Additives have a profound impact on the chemoselectivity of these reductive elimination reactions. An excess of RO^- was found to limit competing C(sp³)-C(sp²) bond-forming reductive elimination, while the presence of Lewis acidic cations was found to suppress competing C(sp³)-F coupling. Mechanistic investigations were conducted, and the available data are consistent with a sequence involving pre-equilibrium dissociation of the oxyanion ligand (RO^-) followed by nucleophilic attack of RO^- on a cationic Pd^IV-alkyl intermediate.

Full text of DOI:10.1021/ja507056u

Article
pubs.acs.org/JACS
3
IV
C(sp )−O Bond-Forming Reductive Elimination from Pd with
Diverse Oxygen Nucleophiles
́ ́
Nicole M. Camasso, Monica H. Perez-Temprano, and Melanie S. Sanford*
Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, United States
*
S Supporting Information
3
ABSTRACT: This article describes an investigation of C(sp )−O bond-
IV
forming reductive elimination reactions from Pd complexes. Phenoxide,
acetate, difluoroacetate, dimethylphosphate, tosylate, and nitrate nucleo-
3
philes are shown to participate in this reaction. In all cases, C(sp )−O bond
2
formation occurs with high selectivity over potentially competing C(sp )−
O coupling. Additives have a profound impact on the chemoselectivity of
−
these reductive elimination reactions. An excess of RO was found to limit
3
2
competing C(sp )−C(sp ) bond-forming reductive elimination, while the
3
presence of Lewis acidic cations was found to suppress competing C(sp )−
F coupling. Mechanistic investigations were conducted, and the available
data are consistent with a sequence involving pre-equilibrium dissociation
of the oxyanion ligand (RO ) followed by nucleophilic attack of RO on a cationic Pd −alkyl intermediate.
−
−
IV
3
INTRODUCTION
role in the chemoselectivity of competing C(sp )−O and
3 IV
■
IV
C(sp )−F couplings at Pd centers.
Carbon−oxygen bond-forming reductive elimination from Pd
centers is believed to serve as the product release step of
numerous important catalytic transformations, including
1
RESULTS AND DISCUSSION
■
2
3
ligand-directed C−H bond oxygenation, allylic acetoxylation,
Design of the Model System. Several considerations went
4
5,6
3
and alkene difunctionalization. Previous work by our group
into the design of a model system for studying C(sp )−O bond-
7
−10
2
IV
IV
and others
has probed the mechanism of C(sp )−O bond-
forming reductive elimination from Pd . First, a Pd −alkyl
complex that does not contain β-hydrogens was selected in
order to avoid competing β-hydride elimination. Second, a
forming reductive elimination reactions from high-valent Pd
complexes. These studies have informed the design and
2
−4
IV
development of new catalytic processes. In marked contrast,
much less is known about the corresponding C(sp )−O
coupling reactions at high-valent Pd.
investigate these transformations have been plagued by the low
stability of high-valent Pd intermediates and by side reactions
ligand environment was targeted that would render the Pd
3
intermediates isolable (or at minimum detectable) and still be
highly modular to allow for the introduction of diverse oxyanion
nucleophiles. Finally, a system that would enable the
investigation of competing C(sp )−O and C(sp )−F bond-
forming reductive eliminations was sought in order to mimic
important considerations in catalytic methodologies. For
instance, prior work by our group has shown that competing
C(sp )−O and C(sp )−F bond formation occurs during the
fluorination of 8-methylquinoline with AgF/PhI(OPiv) cata-
lyzed by high-valent Pd. Achieving the selective formation of a
single product remains a major challenge in this and related
1
1,12
Previous attempts to
1
3
3
IV
such as competing methyl group transfer from Pd
II
intermediates to Pd reactants as well as C−C coupling at
IV 13
Pd . As a result, the mechanisms of these transformations
3
3
remain opaque, and the scope of oxygen nucleophiles that can
participate in this fundamental organometallic transformation
has not been well-studied. In addition, the chemoselectivity of
C−heteroatom bond-forming reductive elimination is poorly
understood in systems where multiple competing reductive
elimination reactions could take place.
In this report, we describe the design of a model system that
has enabled the first detailed exploration of the scope,
chemoselectivity, and mechanism of C(sp )−O bond-forming
reductive elimination from Pd . We have found that these
2
15
II/IV
Pd -catalyzed methods.
IV
Previous studies by our group have demonstrated that Pd
derivatives of general structure (bpy)Pd(CH CMe -o-C H )-
2
2
6
4
16
(
F)(X) can be stable and often isolable complexes. When X =
OTf, this ligand can be readily displaced by other anions or
Lewis bases (e.g., TsNH , pyridine). Some of these complexes
have been shown to participate in selective reductive elimination
at the C(sp ) ligand. Furthermore, depending on the conditions,
competing C(sp )−X and C(sp )−F reductive eliminations can
3
−
IV
transformations can proceed even with very weak oxygen
nucleophiles such as nitrate and tosylate. To our knowledge, the
direct observation of reductive elimination reactions that form
3
3
3
3
3
C(sp )−ONO and C(sp )−OTs linkages has no precedent in
2
1
4
the literature. In addition, we demonstrate that cationic
additives (i.e., Li vs NBu ) can play a previously unappreciated
Received: July 11, 2014
+
+
4
©
XXXX American Chemical Society
A
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Journal of the American Chemical Society
Article
1
6b
be observed. Thus, this system was selected to probe the
Scheme 2. Reductive Elimination from 2a−f To Form 4a−f
3
scope, mechanism, and selectivity of C(sp )−O bond-forming
reductive elimination at Pd .
IV
Initial Studies with Phenoxide as the Nucleophile.
Phenoxide ligands are known to serve as coupling partners in a
2
number of reductive elimination reactions, including C(sp )−O
II
17
3
II 12
coupling at Pd centers, C(sp )−O coupling at Pd , and
3
IV 11b
C(sp )−O bond formation at Pt .
precedents, we targeted Pd phenoxide complex 2a for our
initial investigations. Complex 2a was obtained in 73% isolated
On the basis of these
IV
IV
yield by the treatment of Pd triflate complex 1 (which exists
predominantly as the cationic solvento complex in CH CN
3
solution) with 1 equiv of sodium phenoxide in CH CN at room
3
1
8
temperature (eq 1). Complex 2a was characterized by one-
1
13
19
and two-dimensional H, C, and F NMR spectroscopy (see
the Supporting Information for full details of the spectral
assignments).
a
b
c
d
5
0 °C, 2 h. 25 °C, 5 h. NMe DFA, 40 °C, 1 h. DMSO, 50 °C, 1 h.
4
e
NaOTs/NMe OTs, 25 °C, 12 h.
4
When 2a was heated at 50 °C for 2 h in CD CN, it underwent
3
3
Unlike the phenoxide adduct 2a, these complexes (2b−f) were
not sufficiently stable for isolation; however, they were all
C(sp )−O bond-forming reductive elimination to form 3a in
1
5
(
4% yield as determined by H NMR spectroscopic analysis
1
13
characterized in situ using one and two-dimensional H, C,
Scheme 1). The main side product in this reaction was
21
and 19F NMR spectroscopy. Notably, NMR analysis showed
IV
that the Pd complexes bearing nitrate, dimethylphosphate, and
Scheme 1. Reductive Elimination from Complex 2a
tosylate anions (2d−f) were generated as equilibrium mixtures
with the corresponding cationic species (likely the acetonitrile
+
−
adduct, [(bpy)Pd(CH CMe -o-C H )(F)(CH CN)] X ). Ob-
2
2
6
4
3
servation of the solvento complexes in these cases can be
attributed to the noncoordinating nature of the oxyanions in
2
d−f.
Warming solutions of 2b−f to between 25 and 50 °C in the
presence of 4 equiv of exogenous NaOR resulted in clean
C(sp )−O coupling, and the products 4b−e were isolated in
high yield after extraction with brine (Scheme 2).
structure of the Pd nitrate product 4d was confirmed by X-ray
crystallography, and an ORTEP of this structure is shown in
Figure 1.
3
2
2,23
The
3
2
16b
II
cyclobutane 5 derived from C(sp )−C(sp ) coupling, which
3
2
was formed in 26% yield. Importantly, no C(sp )−F or C(sp )−
heteroatom reductive elimination products were observed under
these conditions. This is in notable contrast to a recent report by
IV
Mirica, who showed that a closely related Pd (CH CMe -o-
2
2
2
C H )(OH) complex undergoes clean C(sp )−OH coupling
6
4
9
,19
upon thermolysis.
16b
On the basis of some of our prior work, we hypothesized
that the addition of exogenous PhO to reductive elimination
reactions from 2a might enhance the selectivity for C(sp )−O
coupling. Indeed, the addition of 2−4 equiv of NaOPh resulted
in the quantitative formation of 3a as determined by NMR
−
3
II
spectroscopic analysis. This Pd fluoride product was
challenging to isolate because it is highly hygroscopic. However,
Figure 1. ORTEP of reductive elimination product 4d.
extraction of CH Cl solutions of 3a with brine resulted in
2
2
substitution of the fluoride ligand with chloride to form 4a,
which was isolated in 72% yield (Scheme 2).
Scope of Oxygen Nucleophiles. We next explored the
scope of oxygen nucleophiles that participate in this trans-
formation, with a particular focus on weakly nucleophilic
oxyanions. Treatment of 1 with 1 equiv of NaOR (OR = acetate,
Influence of the Cation on the Chemoselectivity.
Selectivity for C−O versus C−F reductive elimination in
catalysis is often rationalized on the basis of the relative
−
−
nucleophilicity of F versus RO , with the more nucleophilic
24
anion dominating the reductive elimination process. There-
fore, we were intrigued by the fact that products of C−F
coupling were not observed in any of the reactions in Scheme 2,
difluoroacetate, nitrate, dimethylphosphate, and tosylate) at
IV
−
10 °C resulted in the formation of new Pd complexes, as
1
19
20
determined by H and F NMR spectroscopic analyses.
even with the very weakly nucleophilic NaNO and NaOTs.
3
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However, changing the nitrate/tosylate source from NaOR to
NBu OR under otherwise identical conditions resulted in a
4
dramatic change in the product distribution. For instance, as
shown in Scheme 3, treatment of 1 with 5 equiv of NBu NO3
4
Scheme 3. Chemoselectivity of Reductive Elimination as a
2
6,27
Function of the Cation
Figure 2. Job plot of Δδ × χ vs χ at 25 °C, where χ is the mole fraction
F
of substrate 1.
resulted in competitive formation of products derived from
Table 1. Product Distribution of C−O and C−F Reductive
3
3
a
C(sp )−O (3d, 56% yield) and C(sp )−F (6d, 44% yield)
Elimination from 1 as a Function of Cation
25
bond-forming reductive elimination. Similarly, the use of
3
NMe OTs resulted in a 42% yield of C(sp )−O-coupled
4
product 3f and a 58% yield of the corresponding alkyl fluoride
6
f. Notably, similar effects were not observed with the more
nucleophilic phenoxide, acetate, and difluoroacetate oxyanions;
in these systems, exclusive C(sp )−O coupling was observed
regardless of the cation.
3
cation (Y+)
C−O (%)
C−F (%)
We hypothesize that these counterion effects are due to
interactions between the Lewis acidic cation and the Lewis basic
Li
>98
>98
71
nd
nd
29
53
44
fluoride ligand. Consistent with this proposal, the 19F NMR
2
8
Na
K
signal for the fluoride ligand in 1 (−336 ppm in CD CN) shifts
3
Cs
47
in a concentration dependent manner upon the addition of
Lewis acidic cations. For instance, in the presence of 5 equiv of
NaOTf (0.11 M) this signal appears at −338 ppm, while with 20
equiv of NaOTf (0.44 M) the resonance appears at −341 ppm.
This effect is specific to the cation; for instance, no shift was
NBu4
56
a
1
Yields were determined by H NMR analysis of the crude reaction
mixtures. nd = not detected. Reactions were conducted under ambient
conditions with commercial solvents/reagents.
observed upon the addition of 5 equiv of NBu OTf. The
4
stoichiometry of this interaction was assessed by evaluating a
series of solutions with a constant total concentration of 1 and
NaOTf ([1] + [NaOTf] = 36 mM) but with varied mole
fraction of 1 (χ). The resulting Job plot (Figure 2) shows a
maximum at χ = 0.5, indicative of a 1:1 interaction between 1
and NaOTf.
3
these C(sp )−O bond-forming reactions. Complexes 2a−c were
selected for detailed investigation because they all undergo high-
3
yielding C(sp )−O bond formation under a standard set of
conditions, thereby enabling the direct comparison of reaction
rates and additive effects. These studies were conducted using
tetramethylammonium salts of the oxyanions in order to render
29
LiOTf, a stronger Lewis acid than NaOTf, has an even
1
9
the CH CN solutions completely homogeneous for rate
3
greater impact on the F NMR chemical shift of 1 [−343 ppm
with 5 equiv of LiOTf (0.11 M)]. In contrast, the weaker Lewis
acids KOTf and CsOTf produce negligible changes in the
chemical shift (−336 ppm). Treatment of 1 with 5 equiv of
KNO and CsNO led to 29% and 53% yields of the C−F
measurements. Under these conditions, no competing reductive
elimination processes were detected. As described in detail
below, these data are consistent with the mechanism presented
in Scheme 4. Here, pre-equilibrium dissociation of RO is
followed by rate-limiting C(sp )−O bond formation that
−
3
3
3
reductive elimination product, respectively, while the addition of
3
LiNO3 resulted in exclusive formation of the C(sp )−O
3
Scheme 4. Proposed Mechanism for C(sp )−O Bond
Formation from Complexes 2a−c
coupling product 3d (Table 1). Taken together, these data
IV
suggest that interactions between the Pd −F and the Lewis
acidic cation decrease the accessibility of C−F bond-forming
pathway(s). These results provide unprecedented new
information about the role of cations in reductive elimination
IV
reactions from Pd ; as such, they have numerous potential
applications in catalysis.
Mechanistic Investigations. A variety of experimental
studies were conducted to gain insights into the mechanism of
C
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Journal of the American Chemical Society
Article
−
proceeds via nucleophilic attack by RO on the σ-alkyl ligand.
complexes 2a−c, as such a process would be expected to display
The rate expression for the proposed pathway is shown in
Scheme 4.
We first examined the lability of the RO ligands in Pd
a first-order dependence on [NMe OR]. The zeroth-order
4
dependence on the nucleophile is fully consistent with the
proposed mechanism (see the rate expression in Scheme 4).
The values of kobs for this reaction were nearly identical for
−
IV
1
complexes 2a−c using EXSY NMR experiments. In all cases, H
19
30
and F EXSY studies showed exchange between free and bound
oxyanions at temperatures where complexes 2a−c are stable
toward reductive elimination (−10 to 15 °C). As shown in
Table 2, the minimum temperature for exchange parallels the
complexes 2a−c (Table 2). There is no correlation between
the pK of the conjugate acid of the oxyanion and the value of
a
kobs for reductive elimination over a pK range of >8. Hartwig
a
3
has reported a similar observation in studies of C(sp )−O bond-
II
12
forming reductive elimination from Pd centers. These data
are consistent with a mechanism involving two sequential steps
that have opposing electronic requirements. In our system, the
Table 2. Experimental Mechanistic Data for Reductive
Elimination from 2a−c
−
pre-equilibrium RO dissociation is accelerated with electron-
deficient oxyanions. In contrast, S 2-type attack of RO on the
−
N
IV
Pd −C bond is expected to be fastest with more electron-rich
oxyanions. In both our system and Hartwig’s, the electronic
requirements of these two steps appear to essentially cancel one
another.
−
While the electronic properties of RO had a negligible effect
on k , the addition of a large excess of water did impact the
obs
observed rate constant. For instance, in the presence of 100
equiv of water, k for reductive elimination from 2b (18 × 10−
4
obs
−1
s
at 35 °C) was approximately 2-fold faster than that under
−4
−1
31
anhydrous conditions (8.1 × 10
s
at 35 °C). Protic
additives have been reported previously to accelerate reductive
elimination reactions proceeding through ionic intermediates,
presumably by facilitating dissociation of an anionic
basicity of the oxyanion, with more basic (and therefore
presumably more coordinating) ligands requiring higher
temperatures for exchange. These results strongly support the
11b,12,32
ligand.
Consistent with this proposal, EXSY experiments
for complex 2b in the presence of 100 equiv of water showed
that exchange of free and bound acetate occurs at a lower
temperature (0 °C) than that observed under anhydrous
conditions (10 °C) (Table 2). The addition of water, therefore,
likely shifts the equilibrium proposed in Scheme 4 toward the
cationic intermediate A.
−
feasibility of rapid pre-equilibrium dissociation of RO to form a
cationic intermediate prior to C−O bond formation.
We next used rate studies to probe the kinetic order of
3
C(sp )−O bond formation from 2a−c with respect to both [Pd]
−
and [RO ]. First, reactions of 1 with 5 equiv of NMe OR (0.071
4
−
M) (RO = phenoxide, acetate, difluoroacetate) at 35 °C in
1
SUMMARY AND CONCLUSIONS
CD CN were monitored by H NMR spectroscopy. Under
■
3
In summary, this paper has described the first detailed study of
these conditions, the decays of in situ-generated 2a−c
proceeded with clean first-order kinetic behavior over 3 half-
lives, and a representative kinetics plot is shown in Figure 3. The
values of kobs for reductive elimination were determined over a
3
IV
C(sp )−O bond-forming reductive elimination from Pd
complexes. Oxyanions ranging from strongly nucleophilic
phenoxide to very weakly nucleophilic tosylate and nitrate
3
participate in this reaction. In all cases, C(sp )−O bond
range of concentrations of exogenous [NMe OR] (0.021 to 0.13
4
2
formation occurs with high selectivity over C(sp )−O coupling.
M, 1.5−9.0 equiv). In all cases, a zeroth-order dependence on
9
This is in contrast to a recent report by Mirica and may be due
[
NMe OR] was observed. These data rule out a mechanism
4
to the relative ease of oxyanion dissociation in the two systems.
Additives were found to have a profound impact on the
chemoselectivity of these reductive elimination reactions.
involving direct attack of an external oxyanion nucleophile on
−
Specifically, the addition of an excess of RO was found to
3
2
limit competing C(sp )−C(sp ) bond-forming reductive
elimination, while the presence of Lewis acidic cations was
3
found to suppress competing C(sp )−F coupling. Finally, rate
studies provide evidence consistent with a pathway involving
−
pre-equilibrium dissociation of RO to form a cationic, five-
3
coordinate intermediate followed by S 2-type C(sp )−O
N
coupling. Overall, we anticipate that the detailed studies
described herein will prove valuable in the further development,
3
optimization, and mechanistic understanding of C(sp )−O
coupling reactions catalyzed by high-valent Pd.
ASSOCIATED CONTENT
Supporting Information
■
*
S
Experimental and spectral details for all new compounds and all
reactions reported. This material is available free of charge via
the Internet at http://pubs.acs.org.
Figure 3. Reaction profile for reductive elimination from in situ-
generated 2a in the presence of 4 equiv of NMe OPh at 35 °C.
4
D
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L.; Zavalij, P. Y.; Lam, Y.-F.; Vedernikov, A. N. J. Am. Chem. Soc. 2008,
AUTHOR INFORMATION
■
1
30, 2174. (h) Vedernikov, A. N. Chem. Commun. 2009, 32, 4781.
Corresponding Author
mssanfor@umich.edu
(i) Vedernikov, A. N. Acc. Chem. Res. 2012, 45, 803. (j) Canty, A. J.;
Denney, M. C.; van Koten, G.; Skelton, B. W.; White, A. H.
Notes
Organometallics 2004, 23, 5432.
3
II
(
12) For C(sp )−O reductive elimination from Pd , see: Marquard, S.
L.; Hartwig, J. F. Angew. Chem., Int. Ed. 2011, 50, 7119.
13) (a) Canty, A. J.; Done, M. C.; Skelton, B. W.; White, A. H. Inorg.
The authors declare no competing financial interest.
(
ACKNOWLEDGMENTS
■
(
Chem. Commun. 2001, 4, 648. (b) Canty, A. J.; Denney, M. C.; Skelton,
B. W.; White, A. H. Organometallics 2004, 23, 1122.
This work was supported by the National Science Foundation
Grants CHE-111563 and CHE-1361542), and M.H.P.-T.
3
(14) For a catalytic transformation involving proposed C(sp )−
IV
OSO H bond-forming reductive elimination from Pt , see: (a) Ahli-
gratefully acknowledges support from a Foundation Ramon
́
3
quist, M.; Nielson, R. J.; Periana, R. A.; Goddard, W. A., III. J. Am.
Chem. Soc. 2009, 131, 17110. (b) Periana, R. A.; Taube, D. J.; Gamble,
S.; Taube, H.; Satoh, T.; Fujii, H. Science 1998, 280, 560.
Areces Fellowship. We acknowledge Dr. Joy Racowski for
preliminary experimental studies of these reactions. We
acknowledge Dr. Jeff Kampf for X-ray crystallographic analysis
of 4d as well as funding from NSF for X-ray instrumentation
(
15) McMurtrey, K. B.; Racowski, J. M.; Sanford, M. S. Org. Lett.
012, 14, 4094.
16) (a) Racowski, J. M.; Gary, J. B.; Sanford, M. S. Angew. Chem., Int.
Ed. 2012, 51, 3414. (b) Perez-Temprano, M. H.; Racowski, J. M.;
2
(
(
Grant CHE-0840456). Dr. Eugenio Alvarado and Dr. Ansis
Maleckis provided assistance with NMR spectroscopic analysis.
Finally, Prof. Allan Canty is gratefully acknowledged for valuable
discussions.
́
Kampf, J. W.; Sanford, M. S. J. Am. Chem. Soc. 2014, 136, 4097.
(17) Mann, G.; Shelby, Q.; Roy, A. H.; Hartwig, J. F. Organometallics
2
003, 22, 2775.
18) Unless otherwise noted, all of the PdIV complexes were formed as
a >20:1 ratio of stereoisomers.
19) In our system, treatment of 1 with NaOH or NMe OH led to the
(
REFERENCES
■
(
3
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(
4
formation of a complex mixture of products.
20) More soluble tetramethyl- or tetrabutylammonium salts were
used for low-temperature NMR characterization, except for complex
e, which was generated with sodium dimethylphosphate in DMSO.
21) See the Supporting Information for a full discussion and NMR
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22) The tosylate reductive elimination product could not be isolated
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(
(
2) For recent reviews of ligand-directed C−H functionalization, see:
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́
(
23) Reductive elimination from complex 2e proceeded cleanly only
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(
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̃
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ratios. See p S22 in the Supporting Information for complete details.
(
(
26) NMR yields are reported.
2
IV
(
5) For C(sp )−O reductive elimination from Pd , see: (a) Racowski,
27) A mixture of NMe OTs (2.5 equiv) and NaOTs (2.5 equiv) was
4
J. M.; Dick, A. R.; Sanford, M. S. J. Am. Chem. Soc. 2009, 131, 10974.
b) Dick, A. R.; Kampf, J. W.; Sanford, M. S. J. Am. Chem. Soc. 2005,
27, 12790.
used for the formation of complex 3f.
28) For an example of H-bonding between HF and a Pd fluoride,
see: Ball, N. D.; Sanford, M. S. J. Am. Chem. Soc. 2009, 131, 3796.
(
IV
(
1
(
6) Gary, J. B.; Sanford, M. S. Organometallics 2011, 30, 6143.
(
(
29) Pearson, R. G. J. Am. Chem. Soc. 1963, 85, 3533.
30) The rate constants shown in Table 2 were obtained from the
(
7) Yamamoto, Y.; Kuwabara, S.; Matsuo, S.; Ohno, T.; Nishiyama,
H.; Itoh, K. Organometallics 2004, 23, 3898.
8) (a) Oloo, W. N.; Zavalij, P. Y.; Vedernikov, A. N. Organometallics
013, 32, 5601. (b) Oloo, W. N.; Zavalij, P. Y.; Zhang, J.; Khaskin, E.;
Vedernikov, A. N. J. Am. Chem. Soc. 2010, 132, 14400.
9) Qu, F.; Khusnutdinova, J. R.; Rath, N. P.; Mirica, L. M. Chem.
Commun. 2014, 50, 3036.
average and standard deviation of three separate experiments for each
complex, with the reactions conducted under anhydrous conditions.
(
2
(31) The values of kobs for reductive elimination from complexes 2a−c
under rigorously anhydrous conditions (i.e., in an inert-atmosphere
glovebox with dried solvent and reagents) were nearly identical to those
obtained under ambient conditions (i.e., on the benchtop with
commercial solvents and reagents), where trace amounts of water are
expected. Only the addition of exogenous water (10−500 equiv added
to reactions set up under ambient conditions) impacted the reductive
elimination kinetics. See pp S30−S34 in the Supporting Information for
more details.
(
2
III
(
10) For C(sp )−O reductive elimination from Pd , see: Powers, D.
C.; Geibel, M. A. L.; Klein, J. E. M. N.; Ritter, T. J. Am. Chem. Soc. 2009,
31, 17050.
11) For C(sp )−O reductive elimination from Pt , see: (a) Williams,
B. S.; Holland, A. W.; Goldberg, K. I. J. Am. Chem. Soc. 1999, 121, 252.
1
(
3
IV
(
b) Williams, B. S.; Goldberg, K. I. J. Am. Chem. Soc. 2001, 123, 2576.
(32) Pawlikowski, A. V.; Getty, A. D.; Goldberg, K. I. J. Am. Chem. Soc.
(
c) Smythe, N. A.; Grice, K. A.; Williams, B. S.; Goldberg, K. I.
2
007, 129, 10382.
Organometallics 2009, 28, 277. (d) Luinstra, G. A.; Labinger, J. A.;
Bercaw, J. E. J. Am. Chem. Soc. 1993, 115, 3004. (e) Vedernikov, A. N.;
Binfield, S. A.; Zavalij, P. Y.; Khusnutdinova, J. R. J. Am. Chem. Soc.
2
006, 128, 82. (f) Khusnutdinova, J. R.; Zavalij, P. Y.; Vedernikov, A. N.
Organometallics 2007, 26, 3466. (g) Khusnutdinova, J. R.; Newman, L.
E
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