Electrocatalytic alcohol oxidation with ruthenium transfer hydrogenation catalysts

Article abstract of DOI:10.1021/jacs.6b09705

Octahedral ruthenium complexes [RuX-(CNN)(dppb)] (1, X = CI; 2, X = H; CNN = 2-aminomethyl-6-tolylpyridine, dppb = 1, 4-bis-(diphenylphosphino)butane) are highly active for the transfer hydrogenation of ketones with isopropanol under ambient conditions. Turnover frequencies of 0.88 and 0.89 s^-I are achieved at 25 °C using 0.1 mol % of 1 or 2, respectively, in the presence of 20 equiv of potassium t-butoxide relative to ' catalyst. Electrochemical studies reveal that the Ru-hydride 2 is oxidized at low potential (-0.80 V versus ferrocene/, ferrocenium, Fc^0/+) via a chemically irreversible process with concomitant formation of dihydrogen. Complexes 1 and 2 are active for the electrooxidation of isopropanol in the presence of strong base (potassium r-butoxide) with an onset potential near -IV versus Fc. By cyclic voltammetry, fast turnover frequencies of 3.2 and 4.8 s^-I for isopropanol oxidation are achieved with 1 and 2, respectively. Controlled potential electrolysis studies confirm that the product of isopropanol electrooxidation is acetone, generated with a Faradaic efficiency of 94 ± 5%.

Full text of DOI:10.1021/jacs.6b09705

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Article
Electrocatalytic Alcohol Oxidation with
Ruthenium Transfer Hydrogenation Catalysts
Kate M. Waldie, Kristen R. Flajslik, Elizabeth McLoughlin,
Christopher E. D. Chidsey, and Robert M. Waymouth
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.6b09705 • Publication Date (Web): 20 Dec 2016
Downloaded from http://pubs.acs.org on December 20, 2016
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Electrocatalytic Alcohol Oxidation with Ruthenium Transfer Hydrogenation
Catalysts
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Kate M. Waldie, Kristen R. Flajslik, Elizabeth McLoughlin, Christopher E. D. Chidsey,
Robert M. Waymouth*
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Department of Chemistry, Stanford University, Stanford, CA, 94305
*waymouth@stanford.edu
ABSTRACT
Octahedral ruthenium complexes [RuX(CNN)(dppb)] (1, X = Cl; 2, X = H; CNN = 2ꢀ
aminomethylꢀ6ꢀtolylpyridine, dppb = 1,4ꢀbis(diphenylphosphino)butane) are highly active for
the transfer hydrogenation of ketones with isopropanol under ambient conditions. Turnover
frequencies of 0.88 and 0.89 sꢀ1 are achieved at 25°C using 0.1 mol% of 1 or 2, respectively, in
the presence of 20 equivalents of potassium tꢀbutoxide relative to catalyst. Electrochemical
studies reveal that the Ruꢀhydride 2 is oxidized at low potential (ꢀ0.80 V versus
ferrocene/ferrocenium, Fc0/+) via a chemically irreversible process with concomitant formation
of dihydrogen. Complexes 1 and 2 are active for the electrooxidation of isopropanol in the
presence of strong base (potassium tꢀbutoxide) with an onset potential near ꢀ1 V versus Fc0/+. By
cyclic voltammetry, fast turnover frequencies of 3.2 and 4.8 sꢀ1 for isopropanol oxidation are
achieved with 1 and 2, respectively. Controlled potential electrolysis studies confirm that the
product of isopropanol electrooxidation is acetone, generated with a Faradaic efficiency of 94 ±
5 %.
INTRODUCTION
The transition to a renewable energy economy will require the storage of energy from
renewable energy resources such as solar and wind power in chemical fuels, and the efficient
extraction of useable energy from these fuels on demand. Carbonꢀbased fuels are well suited to
function as largeꢀscale energy carriers because of their high energy densities. In particular, liquid
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fuels such as alcohols offer obvious safety and handling advantages and can be stored and
delivered using established infrastructure.1ꢀ4
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The production of liquid fuels using renewable energy via reduction of carbon dioxide
has been proposed as a means to address the first half of this energy cycle, i.e. fuel generation.5ꢀ9
To this end, chemical10ꢀ24 and electrocatalytic25ꢀ26 hydrogenation of CO2 to liquid products with
homogeneous transition metal complexes has been the focus of much recent research. For the
second half of the cycle, combustion remains the primary method for harvesting energy from
carbon fuels on a global scale, particularly in the transportation sector.27 However, combustion
engines are thermodynamically wasteful, with most of the generated energy being lost as heat.
Fuel cells are a promising alterative to combustion engines due to their significantly higher
theoretical efficiencies. Vehicles powered by hydrogen fuel cells are now being offered in select
regions,28 although hydrogen gas presents many difficulties as a chemical fuel.4 Direct alcohol
fuel cells are also being explored, but their efficiency is severely limited by the high
overpotentials required to generate reasonable currents even with the most optimized
heterogeneous electroꢀoxidation catalysts.3,29
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The electrochemical oxidation of alcohols using molecular Ru polyꢀpyridyl catalysts has
been extensively explored,30ꢀ32 but high overpotentials are required in order to generate the key
Ruꢀoxo active catalyst. Transfer hydrogenation33ꢀ34 of carbonyl substrates with alcohol hydrogen
donors using metalꢀhydride catalysts represents a promising strategy for the discovery of systems
capable of energyꢀefficient electrocatalytic alcohol oxidation.35ꢀ38 The rapid formation of a
metalꢀhydride from the alcohol donor during transfer hydrogenation implies that the metalꢀ
hydride bond is readily generated near the reversible thermodynamic potential for alcohol
oxidation. The conversion of a chemical transfer hydrogenation cycle into an electrocatalytic
scheme for alcohol oxidation requires replacement of the ketone substrate with an electrode as
the terminal oxidant (Figure 1).
We previously reported on a class of RuII transfer hydrogenation catalysts33ꢀ34 that are
active for electrocatalytic alcohol oxidation in aqueous solution (pH 11.5) when physisorbed
onto edgeꢀplane graphite electrodes.36 Electrocatalytic conversion of methanol to formate was
observed at a rate of 1.35 Mꢀ1 sꢀ1, but at very positive potentials (ca. 0.6 V versus NHE, pH 11.5).
Mechanistic studies implicated a Ruꢀoxo species32 as the active catalyst instead of the targeted
Ruꢀhydride cycle.
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Herein, we examine the electrocatalytic oxidation of isopropanol with Ruꢀchloride 1 and
Ruꢀhydride 2, one of the most efficient systems reported for ketone transfer hydrogenation in
refluxing isopropanol (Figure 1).39ꢀ40 We demonstrate that these complexes maintain their high
activity for transfer hydrogenation under ambient conditions. Detailed kinetic studies suggest a
complicated rate law in which reversible substrate inhibition occurs with enolizable ketones. The
Ruꢀhydride 2 exhibits a lowꢀpotential, chemically irreversible oxidation by cyclic voltammetry,
which changes from a oneꢀelectron to a twoꢀelectron process upon the addition of potassium tꢀ
butoxide. In the presence of isopropanol under strongly basic conditions, complexes 1 and 2
exhibit rapid turnover frequencies for the twoꢀelectron electrocatalytic oxidation of isopropanol
to acetone with a maximum current enhancement at approx. ꢀ0.5 V versus ferrocene/ferrocenium
(Fc0/+) in tetrahydrofuran.
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Transfer Hydrogenation
Alcohol Electrooxidation
O
O
[Ru] H
O
[Ru] H
R
R'
Ph2
P
P
Ph2
[Ru]
OH
O
[Ru] O
N Ru
X
NH2
[Ru]
O
R
[Ru]
S
R'
R
R'
OH
OH
1, X = Cl
2, X = H
Net reaction:
Net reaction:
[Ru] H
O
[Ru] H
OH
O
O
OH
R'
OH
2e- 2H+
R
R'
R
Figure 1. Left: Ruthenium Complexes 1 and 2. Center: Transfer hydrogenation of ketones with Ruꢀhydride catalyst
2. Right: Proposed electrocatalytic alcohol oxidation using the Ruꢀhydride catalyst 2.
RESULTS AND DISCUSSION
Synthesis and Characterization. The Ruꢀchloride 139,41 and Ruꢀhydride 235,38 were
synthesized as previously described. The Ruꢀphenoxide 3 was prepared as an isolable analogue
of the Ruꢀisopropoxide species. Treatment of 1 with phenol in the presence of potassium tꢀ
butoxide in tetrahydrofuran yields the Ruꢀphenoxide 3, which is isolated as an orange powder.
The 31P NMR of 3 displays two sets of doublet at δP 61.2 and 39.4 ppm with 2J(PP) = 35.1 Hz,
comparable to the coupling constants observed for other RuꢀOR complexes in this family.41ꢀ42
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Crystals of 3 suitable for Xꢀray diffraction were obtained by slow evaporation of a
saturated pꢀxylene solution. The ruthenium center in 3 is in a distorted octahedral geometry with
the tridentate CNN ligand and bidentate phosphine ligand (Figure 2), similar to the solidꢀstate
structures of 139 and other closely related complexes.42ꢀ43 The RuꢀO bond length of 2.165 Å for 3
is comparable to that of the Ruꢀformate and Ruꢀacetate complexes.42
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Figure 2. Structure of 3, 50 % probability ellipsoids. Hydrogen atoms are omitted for clarity. Selected bond
distances (Å) and angles (°): Ru1ꢀC1 2.052(4), Ru1ꢀN1 2.060(3), Ru1ꢀN2 2.224(4), Ru1ꢀP1 2.233(1), Ru1ꢀP2
2.295(1), Ru1ꢀO1 2.165(3); N1ꢀRu1ꢀC1 80.2(1), N1ꢀRu1ꢀN2 76.9(1), N1ꢀRu1ꢀP1 92.61(9), N1ꢀRu1ꢀP2 172.6(1),
N2ꢀRu1ꢀC1 155.1(2), N2ꢀRu1ꢀP1 103.3(1), N2ꢀRu1ꢀP2 99.1(1), C1ꢀRu1ꢀP1 87.0(1), C1ꢀRu1ꢀP2 102.6(1), P1ꢀRu1ꢀ
P2 94.40(4), P1ꢀRu1ꢀO1 176.14(9).
Catalytic Transfer Hydrogenation. The transfer hydrogenation of acetophenone with 1
and 2 in isopropanol was investigated under identical conditions (Scheme 1). Turnover
frequencies (TOF) calculated from the initial rates are presented in Table 1, entries 1 and 2.
Reactions were performed at 25 °C in order to mimic our electrochemical conditions (vide infra).
Using 0.1 mol% of 1 or 2, ca. 80 % conversion of acetophenone is observed by 1H NMR within
15 minutes in tetrahydrofuranꢀd8 with 25 equivalent of potassium tꢀbutoxide relative to catalyst.
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OH
O
[Ru catalyst]
O
OH
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tetrahydrofuran-d8
25°C
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Scheme 1. Transfer hydrogenation of acetophenone with isopropanol using 1 or 2.
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Table 1. Initial turnover frequencies for acetophenone transfer hydrogenation. a
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TOF (s-1) b
0.88
Entry
Catalyst
[KOtBu] (M)
1
2
3
0.01
0.01
ꢀ
1
2
2
0.89
0.89
a Conditions: 0.1 mol% [Ru], 0.5 M acetophenone, 3.0 M isopropanol in tetrahydrofuranꢀd8 with 0.5 M pꢀxylene as
an internal standard. b TOF = (mmol acetophenone consumed)/(mmol catalyst × time), measured at 900 s.
The presence of strong base and alcohol is required to activate the Ruꢀchloride preꢀ
catalyst 1,41 while the Ruꢀhydride 2 is active in the absence of base. Comparable rates for
transfer hydrogenation are observed with 1 plus base and 2 without base (Table 1, entries 1 and
3). Furthermore, the addition of potassium tꢀbutoxide to the Ruꢀhydride 2 does not lead to a rate
enhancement for ketone transfer hydrogenation at room temperature, contrary to the observations
from Baratta and coꢀworkers44 that the catalytic rate is increased with 2 in the presence of added
base at elevated temperatures.
Kinetic Studies. Investigations into the behavior of 1 and 2 under stoichiometric and
catalytic conditions at elevated temperatures have been reported by Baratta.41,43ꢀ45 Detailed
studies into the full kinetic profile for transfer hydrogenation at room temperature were
undertaken in order to gain a better understanding of the key chemical steps in the catalytic
mechanism under conditions relevant to electrochemical studies.
Organic acids such as acetic acid rapidly protonate the Ruꢀhydride 2 to generate H2 and
the corresponding Ruꢀalkoxide.41 The analogous reaction with unactivated aliphatic alcohols
such as isopropanol would provide a scheme for alcohol oxidation in the absence of ketones via
acceptorless dehydrogenation.46 We find that 2 reacts slowly with isopropanol at ambient
temperature, yielding a single ruthenium species after four hours. This product is assigned as the
[Ruꢀisopropoxide][isopropanol] adduct based on reported 31P NMR data for this species.45 The
formation of H2 is also confirmed by 1H NMR, which appears as a singlet at δH 4.53 ppm.
In light of these results, acceptorless dehydrogenation was examined as a potential
competitive pathway under transfer hydrogenation conditions. Beller and coꢀworkers47 reported
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acceptorless isopropanol dehydrogenation with 1 in the presence of 2000 equivalents of sodium
isopropoxide at reflux. Similar results were also obtained with tetrahydroꢀ1ꢀnapthol in the
presence of potassium tꢀbutoxide (50 equivalents) in tꢀbutanol at 130 °C.48 However, our transfer
hydrogenation conditions were carried out at lower temperatures. The transfer hydrogenation of
acetophenone with isopropanol using the Ruꢀchloride 1 (1 mM) and potassium tꢀbutoxide (25
mM) was monitored by 1H NMR at 25 °C, and the concentration of each species was determined
(Figure S3). At each time point, the reactant consumption is exactly matched by product
formation within experimental error, indicating that acetone production via acceptorless
dehydrogenation is negligible under these conditions. Furthermore, no acetone is generated over
24 hours in the absence of acetophenone under otherwise identical conditions.
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With acceptorless alcohol dehydrogenation eliminated as a relevant competitive reaction,
the kinetic profile of transfer hydrogenation was investigated. The transfer hydrogenation of 2ꢀ
heptanone with isopropanolꢀd8 using 2 was selected as a model system for these studies (Scheme
2). The choice of using the Ruꢀhydride 2 instead of the Ruꢀchloride 1 removes the need for the
addition of alkoxide base, and prevents preꢀcatalyst activation from complicating the kinetic
analysis. A series of 1H NMR experiments were performed in tetrahydrofuranꢀd8 at 25 °C in
which the standard conditions (1.3 mM 2, 0.32 M 2ꢀheptanone, 3.2 M isopropanolꢀd8) were
varied by changing the concentration of each species individually. Plots of 2ꢀheptanone
conversion over time for each run are presented in the Supporting Information: a representative
plot for Table 2, entry 2 is shown in Figure 3a. In each case, conversion of 2ꢀheptanone follows a
single exponential decay, and the observed rate constants kobs are summarized in Table 2.
D
D
D
D
O
O
[Ru-hydride 2]
O
O
D3C
CD3
D3C
CD3
tetrahydrofuran-d8
Scheme 2. Transfer hydrogenation of 2ꢀheptanone with isopropanolꢀd8 using 2.
Under these conditions, there is a clear firstꢀorder dependence of kobs on the catalyst
concentration (Figure 3b). This result is in agreement with previous studies, where the transfer
hydrogenation of acetophenone was found to be first order in [1] at high base concentration.44
The observed reaction rate is zeroꢀorder in isopropanolꢀd8 (Figure S22), which is present in tenꢀ
fold excess relative to substrate. Negative order dependences on both of the products, acetone
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and 2ꢀheptanol, (Figures S23 and S24) are consistent with this being an equilibrium reaction, and
may suggest a more complicated rate law in which product terms are present in the
denominator.49 Unexpectedly, the plot of kobs versus [2ꢀheptanone] is not linear and does not pass
through the origin (Figure 3c). A faster reaction rate is achieved with lower substrate
concentrations, indicative of reversible substrate inhibition.
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Table 2. Kinetic data for the transfer hydrogenation of 2ꢀheptanone with isopropanolꢀd8 using 2.a
[2]
(mM)
[2-Heptanone]
(M)
[Isopropanol-d8] [2-Heptanol]
[Acetone]
(M)
kobs
Entry
(M)
(M)
(10-3 s-1) b
1
2
0.63
1.26
2.53
3.67
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1.26
1.26
1.26
1.26
1.26
1.26
1.26
1.26
1.26
1.26
1.26
1.26
1.26
0.32
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0.32
0.32
0.16
0.24
0.32
0.63
0.78
0.95
0.32
0.32
0.32
0.32
0.32
0.32
0.32
0.32
3.16
ꢀ
ꢀ
0.68±0.07
1.26±0.13
2.26±0.14
3.46±0.20
3.29±0.33
1.63±0.16
1.15±0.11
0.63±0.10
0.70±011
0.56±0.08
1.20±0.07
1.28±0.08
1.08±0.09
0.89±0.07
0.81±0.06
0.98±0.08
0.80±0.06
0.60±0.05
3.16
3.16
3.16
9.28
9.28
9.28
9.28
9.28
9.28
4.68
6.22
3.16
3.16
3.16
3.16
3.16
3.16
ꢀ
ꢀ
3
ꢀ
ꢀ
4
ꢀ
ꢀ
5
ꢀ
ꢀ
6
ꢀ
ꢀ
7
ꢀ
ꢀ
8
ꢀ
ꢀ
9
ꢀ
ꢀ
10
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ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
0.10
0.20
0.32
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
0.11
0.21
0.31
ꢀ
ꢀ
a Conditions: Reactions performed in tetrahydrofuranꢀd8 at 25 °C with 0.32 M pꢀxylene as an internal standard. b
Observed rate constant kobs is obtained from the firstꢀorder exponential decay fit of [2ꢀheptanone] versus time plots.
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Figure 3. (a) Conversion of 2ꢀheptanone over time for Table 2, entry 2: single exponential decay fit (red). (b)
Dependence of kobs on the concentration of the Ruꢀhydride 2. (c) Dependence of kobs on the concentration of 2ꢀ
heptanone.
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Substrate inhibition has been reported with other bifunctional catalysts for H250ꢀ51 and
transfer52 hydrogenation. For these systems, it was posited that a metalꢀamide intermediate
reversibly forms an adduct with the ketone substrate, from which deprotonation of the ketone by
the basic amide ligand site may occur to generate an enolate complex. This reversible reaction is
fast relative to product formation, resulting in an offꢀpath equilibrium that depends on the
substrate concentration.
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Evidence of enolate formation with the Ruꢀhydride 2 is revealed by incorporation of
deuterium into the ketone substrate under catalytic conditions. In isopropanolꢀd8, 53 % and 47 %
deuterium is observed at the βꢀmethyl and methylene positions of 2ꢀheptanone, respectively,
after six minutes, while only 35 % conversion to the product 2ꢀheptanol has occurred by this
point (Scheme 3). This rapid deuteration of the substrate suggests that fast and reversible
formation of the 2ꢀheptanone enolate occurs during transfer hydrogenation. Similar results are
obtained when the Ruꢀphenoxide 3 is treated with 2ꢀheptanone in the presence of isopropanolꢀd8.
In both cases, deuteration of the substrate suggests that the catalyst is operating under basic
conditions, despite the absence of added base. This behavior may be attributed to ionization of
the Ruꢀisopropoxide or Ruꢀphenoxide bond, providing a strong alkoxide base capable of
substrate deprotonation in situ. Deuteration of secondary alcohols has been reported by Baratta
and coꢀworkers53 for a series of related ruthenium and osmium complexes, although these
experiments were performed in the presence of excess alkoxide base.
[Ru-hydride 2]
isopropanol-d8
O
O
D3C
tetrahydrofuran-d8
D D
53 % D and 47 % D
after 6 minutes
Scheme 3. Deuteration of 2ꢀheptanone during transfer hydrogenation with 2. Conditions: 1.26 mM 2, 0.32 M 2ꢀ
heptanone, 3.16 M isopropanolꢀd8 in tetrahydrofuranꢀd8.
The transfer hydrogenation of benzophenone, a nonꢀenolizable substrate, in isopropanolꢀ
d8 was also examined to further probe the possible involvement of an enolate complex during
transfer hydrogenation with 2. Under the same standard conditions as described above, the
concentration of benzophenone was varied from 0.15 – 0.37 M. The reaction progress again
follows a single exponential decay (Figure S25 – S27); however, the rates do not exhibit
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substrate inhibition and the observed rate constants kobs are approximately independent of
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benzophenone concentration within experimental error (Figure S28).
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Proposed Mechanism. On the basis of the experimental data on the transfer
hydrogenation of ketones with 2, a threeꢀstep mechanism for product formation is proposed with
an additional offꢀpath equilibrium, as shown in Scheme 4. The Ruꢀhydride 2 reacts with the
ketone substrate38 to generate a Ruꢀalkoxide intermediate (Step A). Alkoxide exchange to form
the Ruꢀisopropoxide complex and release the product alcohol is driven by the presence of a large
excess of isopropanol solvent (Step B). Regeneration of 2 occurs by elimination of acetone from
the Ruꢀisopropoxide (Step C). We recently reported an experimental and theoretical study of the
energetics and mechanism for the reaction of ketones with 2, which established that the Ruꢀ
hydride 2 reacts rapidly and reversibly with acetone to generate the Ruꢀisopropoxide (Steps A
and C) in a nearꢀergoneutral equilibrium process.38
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The reversible formation of a Ruꢀenolate complex (Step D) is proposed as an offꢀpath
equilibrium process responsible for the observed decrease in the rate of transfer hydrogenation
with increasing 2ꢀheptanone concentration. Previous studies have established the Ruꢀ
isopropoxide as the catalyst resting state in Scheme 4 when isopropanol is present in large
excess.44ꢀ45 Partial or full ionization of this RuꢀO bond44 would generate the isopropoxide anion
that can deprotonate the ketone substrate to form the corresponding enolate, which may be
stabilized via coordination to ruthenium.
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Ph2
P
P
Ph2
O
O
R1
R2
N Ru
H
NH2
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2
C
A
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O
OH
R1
R2
Ph2
P
P
Ph2
P
P
Ph2
P
P
N Ru
O
N Ru
O
N Ru
O
Ph2
Ph2
Ph2
B
R1
R1
R2
NH2
NH2
NH2
D
R2
H
H
OH
R2
OH
R1
Scheme 4. Proposed mechanism for ketone transfer hydrogenation with isopropanol using the Ruꢀhydride 2.
The mechanism of transfer hydrogenation starting from the Ruꢀchloride preꢀcatalyst 1 is
similar; however, an initial activation step with strong base is required to generate the active Ruꢀ
OR species.41 Baratta and coꢀworkers observed an increase in the rate of transfer hydrogenation
with increasing sodium isopropoxide concentration up to 100 equivalents relative to 1 in
refluxing isopropanol,44 although in our hands, the rate enhancement beyond 20 equivalents of
base is negligible at 25 °C. Notably, there is no rate improvement with the addition of base when
using the Ruꢀhydride 2 as the preꢀformed active catalyst (vide supra); therefore, the reversible
formation of a cationic isopropanol complex suggested by Baratta is not included here.44
Electrochemical Studies. Characterization. The electrochemical properties of 1 – 3 are
summarized in Table 3. All measurements were performed in tetrahydrofuran with tetraꢀnꢀ
butylammonium hexafluorophosphate as supporting electrolyte, unless otherwise noted. The Ruꢀ
chloride 1 exhibits a reversible oneꢀelectron oxidation at ꢀ0.20 V versus ferrocene/ferrocenium
(Fc0/+), which is assigned to the RuII/RuIII couple (Figure 4a). The Ruꢀphenoxide 3 also displays
a reversible RuII/RuIII couple at a slightly more negative potential than 1. (Figure 4b). The large
peakꢀtoꢀpeak separation for both features is attributed to uncompensated solution resistance in
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tetrahydrofuran (ε = 7.58 at 25 °C), as ferrocene displays a similarly large ∆Ep at the same scan
rate (Figure S29).
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Table 3. Cyclic voltammetry data of 1 – 3.a
e
Complex
E1/2 (V) b
ꢀ0.20
∆Ep (mV) d
ia/ic
1.01
ꢀ
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ꢀ
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ꢀ0.80c
ꢀ0.35
1.08
a Conditions: 1 mM Ru in 0.1 M Bu4NPF6 in tetrahydrofuran, glassy carbon working electrode, Pt auxiliary
electrode, Ag/AgNO3 reference electrode, 100mV/s. b E1/2 = 0.5(Epa + Epc), where Epa and Epc are anodic and
cathodic peak potentials, respectively. Potentials reported versus Fc0/+. c Oxidation potential of chemically
irreversible feature. d ∆Ep = Epa ꢀ Epc. e ia = andodic peak current, ic = cathodic peak current.
The Ruꢀhydride 2 is oxidized at ꢀ0.80 V versus Fc0/+ at 100 mV/s (Figure 4c), and the
anodic peak current ia shows a linear dependence on the concentration of 2 (Figure 4c, inset).
This oxidation potential is significantly lower than the RuII/RuIII couple of the chloride or
phenoxide complexes 1 and 3. The ordering of oxidation potentials in this series (i.e. 2 < 3 < 1)
scales with the basicity of the anionic ligand. Furthermore, this potential is lower than observed
for the oxidation of other neutral Ruꢀhydride complexes such as [Cp*RuH(PPh3)2]54 likely as a
consequence of the strongly donating, anionic CNN ligand. The oxidation of 2 is chemically
irreversible, and no discernable reduction feature is observed up to 2 V/s (Figure S29). This
behavior is consistent with a fast chemical step occurring after initial oxidation of the RuIIꢀ
hydride. In the presence of an equimolar solution of ferrocene, integration of the voltammagram
reveals that the area of the Ruꢀhydride oxidation wave is approximately equal to that of the
ferrocene oxidation wave (Figure S29), establishing this as a oneꢀelectron per ruthenium
oxidation. Furthermore, the charge passed during a controlledꢀpotential electrolysis of 2 at ꢀ0.60
V versus Fc0/+ is 91 % of the theoretical value for a oneꢀelectron process (Figure S43).
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Figure 4. Cyclic voltammograms of (a) Ruꢀchloride 1, (b) Ruꢀphenoxide 3, and (c) Ruꢀhydride 2 (1 mM Ru in 0.1
M Bu4NPF6) in tetrahydrofuran. Scan rate 100 mV/s. Inset: Dependence of the oxidative peak current ia on [2].
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The oxidation of d6 metalꢀhydrides is often followed by further complex reactions.55ꢀ58 To
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determine the nature of the oxidation product, the Ruꢀhydride 2 was treated with ferrocenium
ꢀ
tetrafluoroborate (Fc+BF4 ) as a oneꢀelectron chemical oxidant. The addition of one equivalent of
ꢀ
Fc+BF4 to a solution of 2 in tetrahydrofuranꢀd8 resulted in complete conversion to a single Ru
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species, as observed by 1H and 31P NMR. Unexpectedly, the 1H and 31P NMR spectra of this
product are identical to those of Ruꢀchloride 1 (Figure S37 and S38). Oxidation using perchlorate
salts of silver(I) or ferrocenium also yielded similar NMR spectra. We tentatively assign this
ꢀ
ꢀ
species as the sixꢀcoordinate complex [RuX(dppb)(CNN)] (X = ClO4 or BF4 ), where either the
perchlorate or tetrafluoroborate anions are bound to the ruthenium center. The ability of these
typically nonꢀcoordinating anions to function as ligands in transition metal complexes has been
previously reported.59ꢀ65 On the other hand, chemical oxidation of 2 with ferrocenium or silver(I)
in acetonitrile leads to rapid formation of the cationic acetonitrile complex
[Ru(CH3CN)(dppb)(CNN)]+ 4 as the major product based on 1H and 31P NMR analysis.42
Formation of the [Ruꢀsolvato] cation in acetonitrile versus the [RuꢀX] complex in
tetrahydrofuran is in line with the stronger ligating ability of acetonitrile. Furthermore, the
formation of dihydrogen is observed by 1H NMR analysis of the reaction (Figure S39),
demonstrating that oneꢀelectron oxidation of 2 results in H2 evolution.
Two reasonable mechanisms for the oxidation of the Ruꢀhydride 2 are depicted in
Scheme 5: (a) oneꢀelectron oxidation to the RuIIIꢀhydride cation followed by deprotonation by
another equivalent of RuIIꢀhydride and rapid reꢀoxidation of the transient RuI species (ErCiEr’);
or (b) oneꢀelectron oxidation to the RuIIIꢀhydride cation followed by bimolecular elimination of
hydrogen (ErErCi). The overall stoichiometry for either mechanism is oneꢀelectron per ruthenium
with the concomitant formation of dihydrogen, consistent with the results of our chemical
oxidation experiments. While the data to date do not allow us to distinguish between the
mechanisms in Scheme 5a and 5b for the oxidation of 2 in the absence of base, deprotonation of
the RuIIIꢀhydride by solvent or electrolyte can be ruled out (Scheme 5c), as this would require an
overall stoichiometry of twoꢀelectrons per ruthenium and would not produce H2.
RuII
RuII
H
H
RuIII
RuI
H
(a)
e
RuII Xn+
e
RuIII
H
H2
RuI
RuII Xn+
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RuII
RuIII
H
RuIII
RuII Xn+
H
(b)
(c)
e
H
H2
2
2
RuII
RuIII
H
RuIII
RuI
H
e
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H
H+
RuII Xn+
RuI
e
Scheme 5. Possible mechanisms for the electrochemical oxidation of the Ruꢀhydride 2, where X = solvent (n = 1) or
electrolyte anion (n = 0).
Treatment with Base. Treatment of the RuꢀCl 1 with alkoxides in the presence of excess
alcohol generates the Ru alkoxides.41 We note that it is critical that the alkoxide base be added to
a solution of 1 only after the addition of alcohol – in the absence of isopropanol or other alcohol,
treatment of 1 with alkoxide base (tꢀbutoxide or isopropoxide) causes the solution color to
immediately change from yellow to dark brown with the accompanying formation of an
unidentified black precipitate. Cyclic voltammetry of the dark solution yields no discernable
features within a potential window of ꢀ1 to +0.5 V versus Fc0/+, indicating decomposition has
occurred. In contrast, the Ruꢀhydride 2 is stable in the presence of potassium tꢀbutoxide, even in
the absence of alcohol: neither decomposition nor deprotonation of 2 occurs based on 1H NMR
(Figure S40). By cyclic voltammetry, the addition of excess potassium tꢀbutoxide (20 mM) to a
solution of 2 (1 mM) results in a marked increase in the current of the oneꢀelectron oxidation at ꢀ
0.80 V (Figure 5). Integration of the voltammogram before and after addition of base reveals that
the area of the wave is doubled in the presence of potassium tꢀbutoxide. Furthermore, controlledꢀ
potential electrolysis of 2 in the presence of 35 equivalent of potassium tꢀbutoxide is consistent
with an overall twoꢀelectron oxidation (Figure S44). These results imply that rapid deprotonation
of the RuIIIꢀhydride cation by alkoxide base occurs after oneꢀelectron oxidation of 2, generating a
transient RuI species that would be rapidly oxidized by the electrode at these potentials (Scheme
5c).66 Therefore, the oxidation of 2 in the presence of potassium tꢀbutoxide is an overall twoꢀ
electronꢀoneꢀproton process according to mechanism (c) shown in Scheme 5. Amines such as
1,4ꢀdiazabicyclo[2.2.2]octane (DABCO) and 1,5,7ꢀtriazabicyclo[4.4.0]decꢀ5ꢀene (TBD) do not
affect the electrochemical behavior of 2, indicating that these bases are not sufficiently strong to
change the mechanism of Ruꢀhydride oxidation from a oneꢀelectron to twoꢀelectron per
ruthenium process.
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Figure 5. Cyclic voltammograms of the Ruꢀhydride 2 (1 mM Ru in 0.1 M Bu4NPF6) in tetrahydrofuran without base
(black), and with 20 mM potassium tꢀbutoxide (blue). Scan rate 25 mV/s.
Electrocatalytic Alcohol Oxidation. The twoꢀelectronꢀoneꢀproton oxidation of the Ruꢀ
hydride 2 in the presence of potassium tꢀbutoxide represents the key electrochemical step for the
electrocatalytic oxidation of alcohols, as proposed in Figure 1. Following twoꢀelectronꢀoneꢀ
proton oxidation of 2, formation of a cationic Ruꢀisopropanol intermediate is expected to proceed
rapidly in alcohol solution, and deprotonation to the Ruꢀisopropoxide complex should occur
under sufficiently basic conditions.45 Regeneration of 2 from the Ruꢀisopropoxide would close
the electrocatalytic cycle (Scheme 6). In fact, an increase in current of the lowꢀpotential
oxidation for 2 in the presence of isopropanol (Figure S33) suggests that such an electrocatalytic
cycle for isopropanol oxidation may be operative even in the absence of base.67
Further studies into the electrocatalytic oxidation of isopropanol were performed using
the Ruꢀchloride preꢀcatalyst 1. We note that potassium tꢀbutoxide was added to electrochemical
solutions of 1 only following the addition of isopropanol in order to avoid decomposition of the
complex. At low concentrations of potassium tꢀbutoxide with a large excess of isopropanol (0.5
M), the conversion of 1 into the Ruꢀhydride and Ruꢀisopropoxide complexes is evident by cyclic
voltammetry (Figure 6). The oxidation feature at ꢀ0.4 V versus Fc0/+ is assigned to oxidation of
the Ruꢀisopropoxide complex based on comparison to the redox potential of the Ruꢀphenoxide 3.
This behavior mirrors the results from chemical transfer hydrogenation studies where treatment
of the Ruꢀchloride 1 with base and alcohol yields a mixture of the hydride and alkoxide species
under ambient conditions. Further addition of potassium tꢀbutoxide results in a significant
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increase in current at an onset potential near that of the Ruꢀhydride oxidation and reaching a
maximum current at ca. ꢀ0.5 V versus Fc0/+ (Figure 7a).
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Figure 6. Cyclic voltammograms of the Ruꢀchloride 1 (1 mM Ru) in tetrahydrofuran with 0.5 M isopropanol
(black), followed by addition of 1 mM (blue) and 2 mM (red) potassium tꢀbutoxide. Scan rate 100 mV/s.
Figure 7. (a) Cyclic voltammograms of the Ruꢀchloride 1 (0.5 mM Ru) with isopropanol (0.5 M) and potassium tꢀ
butoxide (23 mM) in tetrahydrofuran (black, solid), followed by further addition of 1. Cyclic voltammogram
isopropanol (0.5 M) and potassium tꢀbutoxide (23 mM) in the absence of 1 shown by black dashed trace. Scan rate
100 mV/s. (b) [1] dependence on the maximum catalytic current icat.
In order to determine the origin of the electrocatalytic current, controlled potential
electrolysis of 1 in the presence of isopropanol and potassium tꢀbutoxide was performed at ꢀ0.6
V versus Fc0/+ (Figure S45). A higher electrolyte concentration (0.2 M) in 1:1
tetrahydrofuran/1,2ꢀdifluorobenzene was used here in order to decrease the resistivity of the
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solution. Analysis of the working electrode compartment solution postꢀelectrolysis by gas
chromatography reveals acetone to be the twoꢀelectron oxidation product, generated with a
Faradaic efficiency of 94 ± 5 %. No acetone is produced in the absence of applied potential.
Furthermore, for the controlled potential electrolysis in the absence of 1 under otherwise
identical conditions, the current decays to background levels rapidly (Figure S46), indicating that
oxidation of isopropanol at the carbon working electrode is negligible at this potential.
The catalytic turnover frequency (TOF) for the electrocatalytic oxidation of isopropanol
can be roughly estimated from the catalytic current enhancement icat/ip, the ratio of the maximum
catalytic current icat to the peak current ip in the absence of substrate. Using equations (1) and (2)
for icat and ip, respectively, equation (3) for icat/ip is derived,68ꢀ71 where ncat = number of electrons
consumed in the catalytic reaction, np = number of electrons transferred in the absence of
substrate, F = Faraday’s constant, A = electrode area, D = diffusion coefficient, R = universal gas
constant, T = temperature, v = scan rate (V/s), and kobs = pseudo first order rate constant:
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(1)
(2)
(3)
ꢀꢁꢂꢃ = ꢄꢁꢂꢃFA[catalyst] Dꢆ
ꢅ
ꢇꢈꢉ
ꢎ/ꢏ
Fꢌ
ꢎ/ꢏ
[
]
ꢀꢊ = 0.4463 ꢋ
ꢍ
ꢄꢊꢌ/ꢏADꢎ/ꢏ catalyst ꢐ
RT
ꢀꢁꢂꢃ
ꢄꢁꢂꢃ
RTꢆꢇꢈꢉ
=
ꢒ
ꢌ
ꢀꢑ
0.4463 Fꢐꢄꢊ
For a plateauꢀshaped wave under substrate saturation conditions, the TOF is related to the pseudo
first order rate constant kobs. Using equation (3), the turnover frequency for the twoꢀelectron
oxidation of isopropanol to acetone with 1 is thus estimated to be 3.2 sꢀ1. While this method of
determining the rate constant is approximate72, the calculated kobs value is in reasonable
agreement with the TOF observed for the chemical transfer hydrogenation of acetophenone with
1 in isopropanol at 25 °C (ca. 1 sꢀ1). Electrocatalytic current is also observed starting with the
Ruꢀhydride 2 under the same conditions (Figure S36). Unexpectedly, a higher TOF (4.8 sꢀ1) for
isopropoxide oxidation is estimated for the Ruꢀhydride 2 compared to the Ruꢀchloride 1. The
origin of this rate difference is not clear, though may be attributed to incomplete activation of the
Ruꢀchloride preꢀcatalyst.
There are limited examples of transition metal complexes beyond the Ru polyꢀpyridyl
oxo systems30ꢀ32 that are capable of electrocatalytic alcohol oxidation. Oxidation of 4ꢀ
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methoxybenzyl alcohol to the corresponding aldehyde with Irꢀdiaminoꢀdiolefin catalysts in the
presence of sodium 4ꢀnonylphenolate occurs at ꢀ0.06 V versus Fc0/+ in orthoꢀdichlorobenzene,73
or using ferrocenium as a chemical oxidant.74 An “organometallic fuel cell” for the
electrocatalytic oxidation of ethanol to acetate was constructed using a Rhꢀhydride catalyst in
aqueous KOH solution.75ꢀ76 Appel and coꢀworkers70 reported the oxidation of isopropanol using
a Ni phosphine catalyst bearing pendant amines at ꢀ0.4 V versus Fc0/+ in acetonitrile with
triethylamine as the base. Recently, the electrocatalytic oxidation of a series of alcohols at ꢀ0.14
V versus Fc0/+ was achieved using a CuI/nitroxyl radical coꢀcatalyst with triethylamine in
acetonitrile.77 The TOF for isopropanol oxidation with this CuI/nitroxyl system is ca. 3 sꢀ1,
comparable to that exhibited by ruthenium complexes 1 and 2, while the TOF of the Ni catalyst70
is approximately 7 times lower. Direct comparison of the catalytic activity and overpotentials of
these catalyst systems is complicated due to the use of different solvents and illꢀdefined pH in
nonꢀaqueous solution; however, we note that the overpotential for electrocatalysis with 1 and 2 is
likely considerably larger than that of the Ni and Cu systems due to the difference in the strength
of the base required for electrocatalysis. There is an ca. 21 unit difference between the pKa’s of
triethylammonium and isopropanol, which correlates to a significant (1.2 V) difference in the
equilibrium potential E0 for the isopropanol/acetone couple.
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The effects of the base, alcohol, and catalyst on the electrocatalytic behavior of 1 were
examined by varying the concentration of each component individually. As seen in Figure 7b,
the catalytic current icat shows a linear correlation to the concentration of the Ruꢀchloride 1
between 0.5 – 1.8 mM, indicating a first order dependence on [1] according to equation (1). The
TOF increases linearly with isopropanol concentration up to 0.5 M (Figure S34), after which
point the current becomes independent of alcohol, indicative of saturation behavior. There is a
second order dependence of the catalytic current on the concentration of potassium tꢀbutoxide up
to 6 – 8 mM, and no further rate increase is observed at higher base concentrations (Figure S35).
This behavior is attributed to activation of the Ruꢀchloride 1, which is known from transfer
hydrogenation studies to be slow in the absence of a large excess of alkoxide (vide supra).
A proposed mechanism for the electrocatalytic oxidation of isopropanol is depicted in
Scheme 6. In the presence of excess isopropanol and isopropoxide base, the Ruꢀchloride preꢀ
catalyst 1 is activated via elimination of potassium chloride and formation of the Ruꢀ
isopropoxide complex (Step A). It is well established from the known transfer hydrogenation and
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chemical reactivity studies with this system that the reversible interconversion between the Ruꢀ
isopropoxide complex and the Ruꢀhydride 2 is rapid and near ergoneutral under ambient
conditions.38 Thus, generation of Ruꢀhydride 2 with concomitant release of acetone in Step B is
facile. Electrochemical oxidation of 2 at ca. ꢀ0.8 V versus Fc0/+ occurs via an overall twoꢀ
electron oneꢀproton process under basic conditions, generating a RuII cationic complex that may
be stabilized by an electrolyte anion or solvent at the sixth coordination site (Step C). With a
large excess of isopropanol in solution, the cationic Ruꢀisopropanol complex will readily form
via coordination of isopropanol (Step D). The rapid coordination of alcohols to complexes of this
type has been previously demonstrated.45 Finally, the Ruꢀisopropoxide complex is regenerated
by deprotonation of the Ruꢀisopropanol species in the presence of sufficiently strong base (Step
E).45
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Ph2
P
N
Ru
P
Ph2
Cl
NH2
1
+ KOtBu, iPrOH
- KCl
A
Ph2
P
P
E
ROH
B
N
O
Ru
O
Ph2
RO
NH2
H
+
Ph2
P
Ph2
P
N
Ru
P
N
Ru
P
Ph2
Ph2
O
H
H
NH2
NH2
2
H
+
OR
Ph2
P
P
D
OH
-
C
2e , HOR
N
S
Ru
Ph2
NH2
S = solvent, HOR
Scheme 6. Proposed mechanism for the electrocatalytic oxidation of isopropanol in tetrahydrofuran.
CONCLUSIONS
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The octahedral Ruꢀchloride and hydride complexes 1 and 2 are highly active for ketone
transfer hydrogenation under ambient conditions, displaying TOFs of ca. 1 sꢀ1 when isopropanol
is used as the hydrogen donor. Kinetic studies probing the mechanism of acetophenone transfer
hydrogenation with 2 are indicative of substrate inhibition at higher ketone concentrations.
Under electrochemical conditions in the absence of ketone substrate, 1 and 2 are both active for
electrocatalytic isopropanol oxidation in the presence of alkoxide base. The Ruꢀchloride 1
exhibits a rate of 3.2 sꢀ1 for isopropanol electrooxidation at ca. ꢀ0.6 V versus Fc0/+, while a
turnover frequency of 4.8 sꢀ1 is achieved using the Ruꢀhydride 2. The onset potential for
electrooxidation occurs near that of the oxidation of 2, suggesting that the twoꢀelectron, oneꢀ
proton oxidation of the Ruꢀhydride complex is a critical step in the electrocatalytic mechanism.
Controlled potential electrolysis establishes acetone as the product of the twoꢀelectron oxidation
of isopropanol. This work demonstrates the promising utility of transfer hydrogenation catalysts
for the discovery of new alcohol electroꢀoxidation systems based on reactive metal hydrides.
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EXPERIMENTAL SECTION
Materials. All manipulations were carried out under an inert atmosphere of nitrogen or
argon with the use of standard vacuum line, Schlenk, and glove box techniques. Solvents were
dried by standard methods and degassed via three freezeꢀpumpꢀthaw cycles. Deuterated solvents
for NMR were purchased from Cambridge Isotope Laboratories. All reagents were used as
received unless otherwise described. The synthesis of the Ruꢀchloride 139 and Ruꢀhydride 238
were described previously. Benzophenone (SigmaꢀAldrich) was purified by sublimation prior to
use. Tetrabutylammonium hexafluorophosphate (SigmaꢀAldrich) was recrystallized from
ethanol, dried under reduced pressure, and stored in an inert atmosphere glove box. Ferrocene
(SigmaꢀAldrich) was sublimed under vacuum, and stored in an inert atmosphere glove box.
Instrumentation. NMR spectra were recorded on Varian 300, 500, or 600 MHz
spectrometers. All NMR spectra were taken at room temperature unless stated otherwise.
Residual solvent proton and carbon peaks were used as reference. Chemical shifts are reported in
parts per million (δ). Highꢀresolution mass spectra were obtained by LC/ESIꢀMS on a Waters
Acquity UPLC and Thermo Fisher Exactive Orbitrap mass spectrometer. CHN elemental
analysis was performed by Robertson Microlit Laboratories, New Jersey, USA.
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Single crystals for Xꢀray analysis were mounted on a Kapton loop using Paratone N
hydrocarbon oil. Measurements were made on a Bruker Kappa X8ꢀAPEX II diffractometer with
graphite monochromated MoꢀKα radiation (λ = 0.71073 Å). Frames corresponding to an
arbitrary sphere of data were collected using a combination of ωꢀ and φꢀscans of 0.5°. Data were
corrected for absorption and polarization effects, and analyzed for space group determination.
Structures were solved by direct methods,78 expanded routinely, and refined by fullꢀmatrix leastꢀ
squares procedures based on F2.79 Hydrogen atoms were included in ideal positions and refined
isotropically in riding model with Uiso = 1.5Ueq(X) for methyl groups and Uiso = 1.2Ueq(X) for
other atoms, where Ueq(X) are thermal parameters of parent atoms. Nonꢀhydrogen atoms were
refined anisotropically. Crystallographic data for 3 is presented in the Supporting Information.
Cyclic voltammetry experiments were performed using a WaveNow USB Potentiostat
(Pine Research Instrumentation) at ambient temperature in an inert atmosphere glove box. A
typical electrochemical cell consisted of a threeꢀelectrode setup using a glassy carbon working
electrode (3 mm diameter, Bioanalytical Systems, Inc.), platinum wire auxiliary electrode, and
Ag/AgNO3 nonꢀaqueous reference electrode (Bioanalytical Systems, Inc.). All electrochemical
experiments were performed with 0.1 M tetrabutylammonium hexafluorophosphate supporting
electrolyte in tetrahydrofuran, unless stated otherwise. No compensation for the solution
resistance was applied in any cyclic voltammetry experiments. The glassy carbon working
electrode was polished between each scan. Potentials are referenced to the Fc0/+ couple (0.0 V)
using cobaltocenium hexafluorophosphate (ꢀ1.3 V) as an internal reference.
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Controlled potential electrolysis was performed using a standard twoꢀcompartment Hꢀ
cell, or custom gasꢀtight cell (see Supporting Information) with a Teflon cap having openings
customized to accept each electrode or cell component: glassy carbon disk (3 mm diameter,
Bioanalytical Systems) for cyclic voltammetry, carbon cloth (Fuel Cell Store) for electrolysis,
and Ag/AgNO3 nonꢀaqueous reference electrode (Bioanalytical Systems, Inc.) isolated from the
solution by a Vycor frit. A platinum coil was used as the auxiliary electrode, which was
separated from the cell solution in a 12 mm diameter glass tube terminating with a 20 mm
diameter fine glass frit. Acetone was quantified using a Shimadzu GCꢀ2014 gas chromatograph
equipped with a thermal conductivity detector, a CarbonPLOT column, and nitrogen carrier gas.
Faradaic efficiency is given by comparing the total product formation to the theoretical amount
based on the charge passed during electrolysis.
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Synthesis. [Ru(OC6H5)(CNN)(dppb)] 3. Potassium tꢀbutoxide (0.023 g, 0.20 mmol) was
added to a solution of the Ruꢀchloride 1 (0.15 g, 0.20 mmol) and phenol (0.024 g, 0.25 mmol) in
tetrahydrofuran (20 mL). The solution was stirred at room temperature for 4.5 hours, and then
filtered through a celite plug. The resulting filtrate was evaporated in vacuo to yield 3 as an
orange powder. Yield 85% (0.14 g). Xꢀray quality crystals were obtained by slow evaporation of
a solution of 3 in pꢀxylene. 1H NMR (500 MHz, C6D6) δ 8.57 (t, J = 8.5 Hz, 2H), 8.02 (t, J = 7.6
Hz, 2H), 7.82 (s, 1H), 7.38 (br s, 2H), 7.29ꢀ7.25 (m, 3H), 7.20 (d, J = 7.2 Hz, 2H), 7.16ꢀ7.08 (m,
5H), 7.01 (dd, J = 7.7, 0.9 Hz, 1H), 6.96 (dd, J = 8.4, 7.2 Hz, 2H), 6.63 (t, J = 7.3 Hz, 1H), 6.53
(t, J = 7.8 Hz, 2H), 6.47 (br m, 2H), 6.42 (t, J = 7.8 Hz, 1H), 6.23 (d, J = 7.5 Hz, 2H), 6.08 (br m,
2H), 5.81 (d, J = 7.4 Hz, 1H), 4.55 (br m, 1H), 3.28 (dd, J = 15.3, 4.1 Hz, 1H), 3.17ꢀ3.12 (m,
1H), 3.06 (q, J = 12.8 Hz, 1H), 3.00 (t, J = 13.2 Hz, 1H), 2.31 (s, 3H), 2.12 (dd, J = 14.6, 9.2 Hz,
1H), 2.03 (t, J = 14.4 Hz, 1H), 1.91ꢀ1.66 (m, 4H), 0.96ꢀ0.93 (m, 1H). 13C NMR (125 MHz,
C6D6) δ 184.8, 168.5, 163.9, 156.3, 148.9 (d, J = 2.6 Hz), 148.3 (d, J = 1.1 Hz), 144.3 (d, J =
30.0 Hz), 140.8 (d, J = 30.0 Hz), 138.1 (d, J = 29.2 Hz), 136.1, 135.6 (d, J = 10.8 Hz), 135.4 (d,
J = 29.5 Hz), 134.3, 133.8, 131.3 (d, J = 7.1 Hz), 130.0 (d, J = 7.8 Hz), 129.4 (d, J = 25.9 Hz),
126.8, 126.3 (d, J = 7.8 Hz), 123.0, 121.6, 121.1, 115.3, 114.9, 112.8, 51.9, 31.1 (d, J = 27.9 Hz),
30.6 (d, J = 25.2 Hz), 26.8, 22.1, 22.0. 31P NMR (162 MHz, C6D6) δ 61.2 (d, J = 35.1 Hz), 39.4
(d, J = 35.1 Hz). Elemental Anal. Calcd for C54H54N2OP2Ru [M + C7H8]: C, 71.27%; H, 5.98%;
N, 3.08%. Found: C, 71.23%; H, 5.64%; N, 3.45%. HRMS. Calcd for C41H41N2P2Ru [(M –
OC6H5)+]: m/z 725.1788. Found: m/z 725.1789.
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Chemical Studies. Representative Procedure for Turnover Frequency Measurement. A
stock solution of 1 (0.019 M) was prepared in tetrahydrofuranꢀd8, and a 25 ꢁL aliquot was added
to a sealable NMR tube in an inert atmosphere glove box. A stock solution of acetophenone
(1.26 M), isopropanol (7.51 M), and the internal standard pꢀxylene (1.26 M) was prepared in
tetrahydrofuranꢀd8, and a 0.4 mL aliquot was added via syringe to the NMR tube. A stock
solution of potassium tꢀbutoxide (0.067 M) in tetrahydrofuranꢀd8 was prepared, and a 0.175 mL
aliquot was added to the NMR tube via syringe to initiate the reaction. The initial turnover
frequency was determined by 1H NMR from the conversion of acetophenone after 15 minutes
according to the following equation:
mmol acetophenone consumed
TOF =
(mmol catalyst)(time)
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Representative Procedure for Transfer Hydrogenation Kinetics. In a typical experiment,
Ruꢀhydride 2 (1.0 mg, 0.0014 mmol) was weighed into a sealable NMR tube in an inert
atmosphere glove box. A solution of 2ꢀheptanone (48 ꢁL, 0.34 mmol), isopropanolꢀd8 (262 ꢁL,
3.42 mmol), and the internal standard pꢀxylene (39 ꢁL, 0.32 mmol) was prepared in
tetrahydrofuranꢀd8 (0.74 mL), and was added via syringe to the NMR tube. The reaction progress
was monitored by 1H NMR and pseudoꢀfirst order rate constants kobs were obtained by fitting [2ꢀ
heptanone] versus time to a single exponential decay, with R2 > 0.99. Plots showing ketone
conversion over time and pseudoꢀfirst order fits are given in the Supporting Information.
Representative Procedure for Chemical Oxidation of Ru Complexes. Ruꢀhydride 2 (2.9
mg, 0.004 mmol) was weighed into a sealable NMR tube and dissolved in tetrahydrofuranꢀd8
(0.6 mL) in an inert atmosphere glove box. Ferrocenium tetrafluoroborate (1.1 mg, 0.004 mmol)
was added, and the resulting mixture was analyzed by 1H and 31P NMR to establish the identity
of the oxidation products.
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ASSOCIATED CONTENT
Supporting Information. Crystallographic data files (CIF format), tabulated Xꢀray data,
and molecular structures obtained from single crystal Xꢀray diffraction. 1H NMR spectrum of 3.
Conversion versus time plots for transfer hydrogenation kinetic studies. Additional cyclic
voltammograms, chemical oxidation studies, and controlled potential electrolysis plots. This
material is available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author:
waymouth@stanford.edu
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENT
This material is based on work supported by the Global Climate and Energy Program at
Stanford, and the National Science Foundation (CHEꢀ1213403). K.M.W. and K.R.F. are grateful
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for Center for Molecular Analysis and Design (CMAD) Fellowships. K.M.W. is also grateful for
a Gabilan Stanford Graduate Fellowship and a National Science and Engineering Research
Council of Canada (NSERC) Postgraduate Scholarship.
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REFERENCES
(1)
Gurau, B.; Viswanathan, R.; Liu, R.; Lafrenz, T. J.; Ley, K. L.; Smotkin, E. S.;
Reddington, E.; Sapienza, A.; Chan, B. C.; Mallouk, T. E.; Sarangapani, S. J. Phys. Chem. B
1998, 102, 9997ꢀ10003.
(2)
Liu, H.; Song, C.; Zhang, L.; Zhang, J.; Wang, H.; Wilkinson, D. P. J. Power Sources
2006, 155, 95ꢀ110.
(3)
(4)
(5)
(6)
99.
(7)
(8)
Bianchini, C.; Shen, P. K. Chem. Rev. 2009, 109, 4183ꢀ4206.
Olah, G. A. Angew. Chem. Int. Ed. 2005, 44, 2636ꢀ2639.
Joó, F. ChemSusChem 2008, 1, 805ꢀ808.
Benson, E. E.; Kubiak, C. P.; Sathrum, A. J.; Smieja, J. M. Chem. Soc. Rev. 2009, 38, 89ꢀ
DuBois, M. R.; DuBois, D. L. Acc. Chem. Res. 2009, 42, 1974ꢀ1982.
Appel, A. M.; Bercaw, J. E.; Bocarsly, A. B.; Dobbek, H.; DuBois, D. L.; Dupuis, M.;
Ferry, J. G.; Fujita, E.; Hille, R.; Kenis, P. J. A.; Kerfeld, C. A.; Morris, R. H.; Peden, C. H. F.;
Portis, A. R.; Ragsdale, S. W.; Rauchfuss, T. B.; Reek, J. N. H.; Seefeldt, L. C.; Thauer, R. K.;
Waldrop, G. L. Chem. Rev. 2013, 113, 6621ꢀ6658.
(9)
Costentin, C.; Robert, M.; Savéant, J.ꢀM. Chem. Soc. Rev. 2013, 42, 2423ꢀ2436.
(10) Darensbourg, D. J.; Rokicki, A.; Darensbourg, M. Y. J. Am. Chem. Soc. 1981, 103, 3223ꢀ
3224.
(11) DuBois, D. L.; Berning, D. E. Appl. Organomet. Chem. 2000, 14, 860ꢀ862.
(12) Hayashi, H.; Ogo, S.; Abura, T.; Fukuzumi, S. J. Am. Chem. Soc. 2003, 125, 14266ꢀ
14267.
(13) Jessop, P. G.; Joó, F.; Tai, C.ꢀC. Coord. Chem. Rev. 2004, 248, 2425ꢀ2442.
(14) Creutz, C.; Chou, M. H. J. Am. Chem. Soc. 2007, 129, 10108ꢀ10109.
(15) Tanaka, R.; Yamashita, M.; Nozaki, K. J. Am. Chem. Soc. 2009, 131, 14168ꢀ14169.
(16) Federsel, C.; Boddien, A.; Jackstell, R.; Jennerjahn, R.; Dyson, P. J.; Scopelliti, R.;
Laurenczy, G.; Beller, M. Angew. Chem. Int. Ed. 2010, 49, 9777ꢀ9780.
(17) Chakraborty, S.; Zhang, J.; Krause, J. A.; Guan, H. J. Am. Chem. Soc. 2010, 132, 8872ꢀ
8873.
(18) Rankin, M. A.; Cummins, C. C. J. Am. Chem. Soc. 2010, 132, 10021ꢀ10023.
(19) Langer, R.; DiskinꢀPosner, Y.; Leitus, G.; Shimon, L. J. W.; BenꢀDavid, Y.; Milstein, D.
Angew. Chem. Int. Ed. 2011, 50, 9948ꢀ9952.
(20) Huff, C. A.; Sanford, M. S. J. Am. Chem. Soc. 2011, 133, 18122ꢀ18125.
(21) Tanaka, R.; Yamashita, M.; Chung, L. W.; Morokuma, K.; Nozaki, K. Organometallics
2011, 30, 6742ꢀ6750.
(22) Schmeier, T. J.; Dobereiner, G. E.; Crabtree, R. H.; Hazari, N. J. Am. Chem. Soc. 2011,
133, 9274ꢀ9277.
(23) Huff, C. A.; Sanford, M. S. ACS Catal. 2013, 3, 2412ꢀ2416.
(24) Zhang, Y.; MacIntosh, A. D.; Wong, J. L.; Bielinski, E. A.; Williard, P. G.; Mercado, B.
Q.; Hazari, N.; Bernskoetter, W. H. Chem. Sci. 2015, 6, 4291ꢀ4299.
25
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Page 26 of 29
1
2
3
4
5
6
(25) Pugh, J. R.; Bruce, M. R. M.; Sullivan, B. P.; Meyer, T. J. Inorg. Chem. 1991, 30, 86ꢀ91.
(26) Kang, P.; Cheng, C.; Chen, Z.; Schauer, C. K.; Meyer, T. J.; Brookhart, M. J. Am. Chem.
Soc. 2012, 134, 5500ꢀ5503.
7
8
9
(27) U.S. Energy Information Administration Consumption & Efficiency. Monthly Energy
Review, December 2015. Published Online: 2015. http://www.eia.gov/consumption/.
(28) U.S. Department of Energy, Energy Efficiency & Renewable Energy. Alternative Fuels
Data Center - Hydrogen. Published Online: 2014.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
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40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
http://www.afdc.energy.gov/fuels/hydrogen.html.
(29) Kakati, N.; Maiti, J.; Lee, S. H.; Jee, S. H.; Viswanathan, B.; Yoon, Y. S. Chem. Rev.
2014, 114, 12397ꢀ12429.
(30) Meyer, T. J.; Huynh, M. H. V. Inorg. Chem. 2003, 42, 8140ꢀ8160.
(31) Cheung, K.ꢀC.; Wong, W.ꢀL.; Ma, D.ꢀL.; Lai, T.ꢀS.; Wong, K.ꢀY. Coord. Chem. Rev.
2007, 251, 2367ꢀ2385.
(32) Paul, A.; Hull, J. F.; Norris, M. R.; Chen, Z.; Ess, D. H.; Concepcion, J. J.; Meyer, T. J.
Inorg. Chem. 2011, 50, 1167ꢀ1169.
(33) Ikariya, T.; Blacker, A. J. Acc. Chem. Res. 2007, 40, 1300ꢀ1308.
(34) Palmer, M.; Walsgrove, T.; Wills, M. J. Org. Chem. 1997, 62, 5226ꢀ5228.
(35) Brownell, K. R. Ph.D. Thesis, Stanford University, 2012.
(36) Brownell, K. R.; McCrory, C. C. L.; Chidsey, C. E. D.; Perry, R. H.; Zare, R. N.;
Waymouth, R. M. J. Am. Chem. Soc. 2013, 135, 14299ꢀ14305.
(37) Buonaiuto, M.; De Crisci, A. G.; Jaramillo, T. F.; Waymouth, R. M. ACS Catal. 2015, 5,
7343ꢀ7349.
(38) Ramakrishnan, S.; Waldie, K. M.; Warnke, I.; De Crisci, A. G.; Batista, V. S.;
Waymouth, R. M.; Chidsey, C. E. D. Inorg. Chem. 2016, 55, 1623ꢀ1632.
(39) Baratta, W.; Chelucci, G.; Gladiali, S.; Siega, K.; Toniutti, M.; Zanette, M.; Zangrando,
E.; Rigo, P. Angew. Chem. Int. Ed. 2005, 44, 6214ꢀ6219.
(40) Chelucci, G.; Baldino, S.; Baratta, W. Coord. Chem. Rev. 2015, 300, 29ꢀ85.
(41) Baratta, W.; Bosco, M.; Chelucci, G.; Zotto, A. D.; Siega, K.; Toniutti, M.; Zangrando,
E.; Rigo, P. Organometallics 2006, 25, 4611ꢀ4620.
(42) Baratta, W.; Ballico, M.; Del Zotto, A.; Herdtweck, E.; Magnolia, S.; Peloso, R.; Siega,
K.; Toniutti, M.; Zangrando, E.; Rigo, P. Organometallics 2009, 28, 4421ꢀ4430.
(43) Baratta, W.; Baldino, S.; Calhorda, M. J.; Costa, P. J.; Esposito, G.; Herdtweck, E.;
Magnolia, S.; Mealli, C.; Messaoudi, A.; Mason, S. A.; Veiros, L. F. Chem. Eur. J. 2014, 20,
13603ꢀ13617.
(44) Baratta, W.; Siega, K.; Rigo, P. Chem. Eur. J. 2007, 13, 7479ꢀ7486.
(45) Baratta, W.; Ballico, M.; Esposito, G.; Rigo, P. Chem. Eur. J. 2008, 14, 5588ꢀ5595.
(46) Friedrich, A.; Schneider, S. ChemCatChem 2009, 1, 72ꢀ73.
(47) Nielsen, M.; Kammer, A.; Cozzula, D.; Junge, H.; Gladiali, S.; Beller, M. Angew. Chem.
Int. Ed. Engl. 2011, 50, 9593ꢀ9597.
(48) Baratta, W.; Bossi, G.; Putignano, E.; Rigo, P. Chem. Eur. J. 2011, 17, 3474ꢀ3481.
(49) Wisman, R. V.; de Vries, J. G.; Deelman, B.ꢀJ.; Heeres, H. J. Org. Process Res. Dev.
2006, 10, 423ꢀ429.
(50) Rautenstrauch, V.; HoangꢀCong, X.; Churlaud, R.; AbdurꢀRashid, K.; Morris, R. H.
Chem. Eur. J. 2003, 9, 4954ꢀ4967.
(51) Wylie, W. N. O.; Lough, A. J.; Morris, R. H. Organometallics 2011, 30, 1236ꢀ1252.
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4
5
(52) Mikhailine, A. A.; Maishan, M. I.; Lough, A. J.; Morris, R. H. J. Am. Chem. Soc. 2012,
134, 12266ꢀ12280.
(53) Bossi, G.; Putignano, E.; Rigo, P.; Baratta, W. Dalton Trans. 2011, 40, 8986ꢀ8995.
(54) Romming, C.; Smith, K.ꢀT.; Tilset, M. Inorg. Chim. Acta 1997, 259, 281ꢀ290.
(55) Smith, K.ꢀT.; Ramming, C.; Tilset, M. J. Am. Chem. Soc. 1993, 115, 8681ꢀ8689.
(56) Bianchini, C.; Peruzzini, M.; Ceccanti, A.; Laschi, F.; Zanello, P. Inorg. Chim. Acta
1997, 259, 61ꢀ70.
(57) Ramakrishnan, S.; Chakraborty, S.; Brennessel, W. W.; Chidsey, C. E. D.; Jones, W. D.
Chem. Sci. 2015, 7, 117ꢀ127.
(58) Bourrez, M.; Steinmetz, R.; Ott, S.; Gloaguen, F.; Hammarstrom, L. Nat. Chem. 2015, 7,
140ꢀ145.
(59) Sunkel, K.; Urban, G.; Beck, W. J. Organomet. Chem. 1983, 252, 187ꢀ194.
(60) Cutler, A. R.; Todaro, A. B. Organometallics 1988, 8, 1782ꢀ1787.
(61) Uddin, M.; LaliaꢀKantouri, M.; Hadjikostas, C. C.; Voutsas, G. Z. Anorg. Allg. Chem.
1998, 624, 750ꢀ753.
(62) Amani Komaei, S.; van Albada, G. A.; Haasnoot, J. G.; Kooijman, H.; Spek, A. L.;
Reedijk, J. Inorg. Chim. Acta 1999, 286, 24ꢀ29.
(63) Esteban, D.; Banobre, D.; Bastida, R.; de Blas, A.; Macias, A.; Rodriguez, A.;
RodriguezꢀBlas, T.; Fenton, D. E.; Adams, H.; Mahia, J. Inorg. Chem. 1999, 38, 1937ꢀ1944.
(64) Hamstra, B. J.; Cheng, B.; Ellison, M. K.; Scheidt, W. R. Inorg. Chem. 1999, 38, 3554ꢀ
3561.
(65) Cimadevilla, F.; Garcia, M. E.; GarciaꢀVivo, D.; Ruiz, M. A.; Graiff, C.; Tiripicchio, A.
Inorg. Chem. 2012, 51, 7284ꢀ7295.
(66) The reduction of complexes 1ꢀ4 is not observed by cyclic voltammetry within the solvent
window, indicating that the Ru(I/II) couple is at potentials much more negative than ꢀ0.8 V
versus Fc0/+.
(67) While protonation of the Ruꢀhydride with isopropanol to generate the Ruꢀisopropoxide
and dihydrogen has been established from chemical reactivity studies, this reaction is too slow at
room temperature to be responsible for this second feature on the CV time scale.
(68) Nicholson, R. S.; Shain, I. Anal. Chem. 1964, 36, 706ꢀ723.
(69) Saveant, J. M.; Vianello, E. Electrochim. Acta 1965, 10, 905ꢀ920.
(70) Weiss, C. J.; Wiedner, E. S.; Roberts, J. A. S.; Appel, A. M. Chem. Commun. 2015, 51,
6172ꢀ6174.
(71) Helm, M. L.; Stewart, M. P.; Bullock, R. M.; DuBois, M. R.; DuBois, D. L. Science
2011, 333, 863ꢀ866.
(72) Sun, C.; Prosperini, S.; Quagliotto, P.; Viscardi, G.; Yoon, S. S.; Gobetto, R.; Nervi, C.
Dalton Trans. 2016, 45, 14678ꢀ14688.
(73) Bonitatibus, P. J.; Rainka, M. P.; Peters, A. J.; Simone, D. L.; Doherty, M. D. Chem.
Commun. 2013, 49, 10581ꢀ10583.
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14
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16
17
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20
21
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42
43
44
45
46
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48
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50
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52
53
54
55
56
57
58
59
60
(74) Bonitatibus, P. J.; Chakraborty, S.; Doherty, M. D.; Siclovan, O.; Jones, W. D.;
Soloveichik, G. L. Proc. Natl. Acad. Sci. U.S.A. 2015, 112, 1687ꢀ1692.
(75) Annen, S. P.; Bambagioni, V.; Bevilacqua, M.; Filippi, J.; Marchionni, A.; Oberhauser,
W.; Schönberg, H.; Vizza, F.; Bianchini, C.; Grützmacher, H. Angew. Chem. Int. Ed. 2010, 49,
7229ꢀ7233.
(76) Bellini, M.; Bevilacqua, M.; Filippi, J.; Lavacchi, A.; Marchionni, A.; Miller, H. A.;
Oberhauser, W.; Vizza, F.; Annen, S. P.; Grützmacher, H. ChemSusChem 2014, 7, 2432ꢀ2435.
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(77) Badalyan, A.; Stahl, S. S. Nature 2016, 535, 406ꢀ406.
(78) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112ꢀ122.
(79) XL: Program for the Refinement of Xꢀray Crystal Structure, Part of the SHELXTL
Crystal Structure Determination Package, Bruker Analytical Xꢀray Systems Inc., Madison, WI,
1995ꢀ99.
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