science
.sciencemag.org/content/
369/6505/850
/suppl/DC1
Supp
lementary
Material
s
for
A molecular mediator for reductive concerted proton
-
electron transfers
via electrocatalysis
Matthew J.
Chalkley
*
,
Pablo
Garrido
-
Barros
*
,
Jonas C.
Peters
†
*These authors contributed equally to this work.
†
Correspond
ing author. Email
: jpeters@caltech.edu
Published
14 August
20
20
,
Science
369
,
850
(20
20
)
DOI:
10.1126/science.
abc1607
This PDF file
includes:
Materials and Methods
Supplementary
Text
Figs. S1 to S
94
Tables S1 to S
44
Reference
s
S
1
Table of Contents:
S2
-S5
S1. Experimental
Details
S6-S7
S2. Synthetic Details
S8-S1
2
S3. NMR Spectroscopy
S1
3
-S1
4
S4. UV
-Vis Spectroscopy
S1
5
-S1
6
S5.
EPR Spectroscopy
S1
7
S6. IR
Spectroscopy
S18
S7. X
-ray Crystallography
S19
-S2
3
S8. Kinetic Analysis
S24
-S40
S9
. Cyclic
Voltammetry
S41
-S50
S10
. p
K
a
Determination
S51
-S52
S1
1
. Experimental
Thermochemistry
S53
-S55
S1
2
. Computational Thermochemistry
S5
6
-S59
S1
3. GC
Calibration
Curves
S60
-S68
S1
4. Controlled Potential
Coulometry
S6
9-S74
S1
5. Discussion of Hammett
Correlations
S75
-S84
S1
6. DFT Coordinates
S
2
S1. Experimental Details
:
S1.1. General Considerations:
All manipulations were carried out using
standard Schlenk or glovebox techniques under
an N
2
atmosphere. Solvents were deoxygenated and dried by thoroughly sparging with N
2
followed
by passage through an activated alumina column in a solvent purification system by SG Water,
USA LLC. Non
-
halogenat
ed solvents were tested with sodium benzophenone ketyl in
tetrahydrofuran (THF) in order to confirm the absence of oxygen and water. Deuterated solvents
were purchased from Cambridge Isotope Laboratories, Inc., degassed, and dried over activated 3
-
Å molecu
lar sieves prior to use.
Cobaltocenium hexafluorophosphate
([Cp
2
Co][PF
6
])
, trifluoromethanesulfonimide,
triflic
acid
,
ferrocene,
acetophenone
(PhC(O)Me)
,
2
-
pentanone
(C
3
H
7
C(O)Me)
4
-
methoxyacetophenone,
4
-
methylacetophenone,
4
-
chloroacetophenone,
4
-
trifluoromethylacetophenone,
2,3
-
diphenyl
-
2,3
-
butanediol, dodecane, 4
-
cyanoaniline (
4
-
CN
PhNH
3
),
2
-
chloroaniline
(
2
-
Cl
PhNH
2
)
,
4
-
chloroaniline
(
4
-
Cl
PhNH
2
)
,
samarium diiodide (
SmI
2
)
,
and tetrabutylammonium hexafluorophosphate
([TBA][PF
6
])
were all used as purchased.
Ferrocenium triflate
,
(
33
)
4
-
lithiodimethylaniline
,
(
34
)
anilinium triflate acids,
(
17
)
deutero
-
substituted 4
-
cyanoaniline (
4
-
CN
PhND
2
)
,
(
35
)
and [D(OEt
2
)
2
][BAr
F
4
] ([BAr
F
4
]
−
= tetra(2,6
-
trifluoromethylphenyl)borate)
(
36
)
were
synthesized as described previously.
S1.2 Computational Details
:
All calculations were performed using the ORCA 4.0 program.
(
37
,
38
)
In cases where
crystal structures were available these coordinates wer
e used as the input. The calculations were
performed using the TPSS (meta
-
GGA)
(
39
)
functional with def2
-
TZVPP
(
40
,
41
)
on all atoms,
Grimme
-
d3 dispersion correction
,
(
42
)
and SMD
(
43
)
solvation
modelling acetonitrile.
That
optimized structures represented true stationary points was checked by doing a single
-
point
frequency calculations on the optimized structure and ensuring that there were no
significant
negative frequencies (
i.e.
, all frequencies are ≥
−
50 cm
−
1
).
Re
duction potentials were determined via
calculated
exchange reactions with
ferrocene/ferrocenium. The p
K
a
values were
likewise
determined via exchange reactions with 2
-
chloroanilinium/2
-
chloroaniline.
(
23
)
The hydricity values were determined via exchange re
actions
with CO
2
/
[
HCO
2
]
−
(formate).
(
44
)
The bond dissociation free energies (BDFEs) were calculated
directly using the free energy of
H∙.
S1.3 EPR Spectroscopy:
X
-
band (9.4 GHz)
continuous wave (CW) electron paramagnetic resonance (EPR)
spectra
were acquired using a Bruker EMX spectrometer equipped with a Super High
-
Q (SHQE) resonator
using Bruker Win
-
EPR software (ver. 3.0). Spectra were acquired at 77 K using a vacuum
-
insulated
quartz liquid nitrogen immersion dewar inserted into the EPR resonator.
S
3
S1.4 X
-
Ray Crystallography:
X
-
ray diffraction (XRD)
studies were carried out at the Beckman Institute Crystallography
Facility on a Bruker Kappa Apex II diffractometer (Mo K
α
radia
tion). Structures were solved using
SHELXS or SHELXT and refined against F
2
on all data by full
-
matrix least squares with
SHELXL.
(
45
)
All of the solutions were performed in the Olex2 program.
(
46
)
The crystals were
mounted on a glass fiber under Paratone N
oil.
S1.5 Electrochemistry:
A CHI instruments 600B electrochemical analyzer was used for
all electrochemical
data
collection.
Cyclic
v
oltammetry (CV),
linear sweep v
oltammetry (LSV) and
d
ifferential
p
ulse
v
oltammetry (DPV) experiments were carried out
i
n
a one
-
compartment three
-
electrode cell
using
a
g
lassy
c
arbon (GC) disk
or a boron doped diamond (BDD) disk
as the working electrode
(3 mm
diameter)
, a
Pt wire as
the
counter electrode,
and
a Ag/AgOTf
(5 mM) reference electrode.
Details
for the
CVs and LSVs
are noted as they appear.
DPV
s
were obtained with the following
parameters: amplitude= 50 mV, step height=4 mV, pulse width= 0.05 s, pulse period= 0.5 s and
sampling width= 0.0167 s.
E
1/2
values for
the reversible waves were obtained from the half
potential between the oxidative and reductive peaks and for irreversible processes are estimated
according to the potential at the I
max
in DPV measurements.
For all
measurement
s
were IR
compensation
was app
lied accounting for
85%
of the total resistance
.
All
of
the re
p
orted potentials
are referenced to the ferrocenium/ferrocene couple (Fc
+/0
)
used as internal standard.
Controlled potential
coulometry
(CP
C
)
experiments
were carried out in a gas
-
tight single
c
ompartment cell using a BDD plate (dimensions 1x2 cm)
working elec
t
rode, a Ag/AgOTf (5 mM)
reference electrode, and a GC plate (dimensions 1x5 cm)
counter elecrode. The solution was stirred
throughout the CPE.
In a typical experiment, 7 ml of
DME
of
0.2 M
[
TBA
][
PF
6
]
was
added to the
electrochemical cell.
Then
,
120.5
mg of toluenesulfonic acid
(100 mM)
and
40
μ
L
of acetophenone
(50 mM)
were added
.
In
experiments using cobaltocene as catalyst,
either
3.2 mg of
[
(C
p)
Co
(Cp
N
)
][OTf]
(1 mM)
or
2.3
mg of
[Cp
2
Co][PF
6
]
(1 mM)
were
then
added.
GC electrodes
were pretreated by
polishing with 1, 0.3 and 0.05 μm alumina paste followed
by rinsing with water and aceton
e
.
T
he BDD electrodes were pre
-
treated according to
literature
procedures.
(
47
)
S1.
7
Products quantification
:
Upon completion
of CPE
s
, the headspace
is
analyzed for H
2
via gas chromatography with
a thermal conductivity detector (GC
-
TCD). A 100
μ
L
Hamilton syringe was used to sample the
headspace and to inject into the GC
-
TCD.
GC
-
TCD was performed in the Environmental Analysis
Center (Caltech) using a HP 5890 Series II i
nstrument
with N
2
as
the
carrier gas.
A c
alibration
curve was
determined
by direct injection of
known volumes of
H
2
.