Supporting Information
Electronically Modified Cobalt Aminopyridine Complexes
Reveal an Orthogonal Axis for Catalytic Optimization for CO
2
Reduction
Alon
Chapovetsky,
†
Jeffrey J. Liu,
†
Matt
hew
Welborn,
‡
John M. Luna,
†
Thomas Do,
†
Ralf Haiges,
†
Thomas F. Miller III
,
*
,
‡
and Smaranda C. Marinescu
*
,
†
†
Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States
‡
Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United
States
*Corresponding Authors: Smaranda C. Marinescu (
smarines@usc.edu
)
and Thomas F. Miller III
(
tfm@caltech.edu
)
S
1
Contents
Page
General Considerations
S
2
Calculation
of Binding Constant from Cyclic Voltammetry
S
3
Calculations of the Hammett Parameters for 1
-
4
S
3
Crystallographic Data
S
4
–
S
6
Electrochemical
Experiments and Analyses
S
7
-
S1
4
Hammett Analysis
S1
5
Density Functional Theory Calculation Details
S1
6
Synthetic
Schemes and
Procedures
S
1
6
-
S
2
6
NMR Spectra
S
2
7
-
S4
0
Evans Method Experiments
S4
1
-
S4
3
High Scan Rate C
yclic Voltammetry Scans for
Complex 2
S4
4
Supplementary
C
yclic Voltammetry Titration Data
S4
5
–
S
4
7
Supplementary
CPE Data
S
4
8
Faradic Efficiency Corrected
(
i
cat
/i
p
)
2
Plots
S
49
1
H NMR of Complex 4 with DCM
S5
0
TFE Titration of Complex 1
S5
1
Calculation of Diffusion
Coefficients for Complexes 2
–
4
S5
1
-
S52
Coordinates of Intermediates Examined in Density Functional Theory Studies
S
5
3
-
S
6
0
References
S
6
1
-
S6
2
S
2
General
All manipulations of air and moisture sensitive materials were conducted under a nitrogen
atmosphere in a Vacuum Atmospheres drybox or on a dual manifold Schlenk line. The glassware
was oven
-
dried prior to use. All solvents were degassed with nitrogen and
passed through activated
alumina columns and stored over 4Å Linde
-
type molecular sieves. Deuterated solvents were dried
over 4Å Linde
-
type molecular sieves prior to use. Proton NMR spectra were acquired at room
temperature using Varian (Mercury 400 2
-
Chann
el, VNMRS
-
500 2
-
Channel, VNMRS
-
600 3
-
Channel, and 400
-
MR 2
-
Channel) spectrometers and referenced to the residual
1
H resonances of
the deuterated solvent (
1
H: CDCl
3
, δ 7.26; C
6
D
6
, δ 7.16; CD
2
Cl
2
, δ 5.32; CD
3
CN, δ
1
.94) and are
reported as parts per
million relative to tetramethylsilane. Elemental analyses were performed
using Thermo Scientific™ FLASH 2000 CHNS/O Analyzers. All the chemical reagents were
purchased from commercial vendors and used without further purification.
Cyclic Voltammetry (CV)
Electrochemistry experiments were carried out using a Pine potentiostat. The experiments
were performed in a single compartment electrochemical cell under nitrogen or CO
2
atmosphere
using a 3 mm diameter glassy carbon electrode as the working electrode, a
platinum wire as
auxiliary electrode and a silver wire as the reference electrode.
Ohmic drop was compensated using
the positive feedback compensation implemented in the instrument.
All
reported potentials are
referenced relative to ferrocene (Fc) with the
Fe
3+/2+
couple at 0.0 V. Alternatively, in cases when
the redox couple of ferrocene overlapped with other redox waves of interested,
decamethylferrocene (Fc*) was as an internal standard with the Fe*
3+/2+
couple at
–
0.48 V.
All
electrochemical experiments
were performed with 0.1 M tetrabutylammonium
hexafluorophosphate as supporting electrolyte.
The
concentrations
of the cobalt complexes
1
–
4
were generally at 0.5 mM and experiments with CO
2
were performed at gas saturation
or varying
amounts of CO
2
in dimethylformamide (DMF)
.
Controlled
-
potential electrolysis (CPE)
CPE measurements were conducted in a two
-
chambered H cell. The first chamber held the
working and reference electrodes in 50
mL of 0.1 M tetrabutylammonium hexafluorophosphate
and
1.3
M
trifluoroethanol
in DMF. The second chamber held the auxiliary electrode in 25 mL of
0.1 M tetrabutylammonium hexafluorophosphate in DMF. The two chambers were separated by a
fine porosity glass
frit. The reference electrode was placed in a separate compartment and
connected by a Vycor tip. Glassy carbon plate electrodes (6 cm × 1 cm × 0.3 cm; Tokai Carbon
USA) were used as the working and auxiliary electrodes. Using a gas
-
tight syringe, 10 mL of
gas
were withdrawn from the headspace of the H cell and injected into a gas chromatography
instrument (Shimadzu GC
-
2010
-
Plus) equipped with a BID detector and a Restek ShinCarbon ST
Micropacked column.
Faradaic efficiencies were determined by diving the me
asured CO produced
by the amount of CO expected based on the charge passed during the bulk electrolysis experiment.
For each species the
controlled
-
potential electrolysis measurements were performed at least twice,
leading to similar behavior. The
reported Faradaic efficiencies and mmol of CO produced are
average values.
S
3
X
-
ray Diffraction Data Collection and Processing
The X
-
ray intensity data were collected on a Bruker APEX DUO 3
-
circle platform diffractometer
with the
χ
-
axis fixed at 50.74°, and using Mo
K
a
radiation (
λ = 0.71073
Å
) from a fine
-
focus tube
monochromatized by a TRIUMPH curved
-
crystal monochromator.
1
The diffractometer was
equipped with an APEX II CCD detector and an Oxford Cryosystems Cryostream 700 apparatus
for low
-
temperature data collection adjusted to 173(2) K. The crystal was mounted in a Cryo
-
Loop
using Paratone oil. A
complete hemisphere of data was scanned on omega (0.5°) at a detector
distance of 50 mm and a resolution of 512 x 512 pixels. The frames were integrated using the
SAINT algorithm
2
to give the hkl files corrected for Lp/decay.
Data were corrected for
absorption
effects using the multi
-
scan method (SADABS).
3
The structure
s
w
ere
solved
by intrinsic phasing
and refined
with
the Bruker SHELXTL Software Package
.
4
–
7
Calculation
of Binding Constant from Cyclic Voltammetry
8
The CV’s for complex
4
under N
2
and CO
2
are indicative
of CO
2
binding to the m
etal center which
can be approximated using
the following equation
∆
퐸
=
%
!"
#$
&
푙푛
)
1
+
[
퐶푂
%
]
퐾
&
1
(6)
In Eq (
6
), ΔE corresponds to the change in potential (59 mV) for the Co
I/0
couple when the
atmosphere is changed from N
2
to CO
2
. R is the universal gas constant (8.314 J K
-
1
mol
-
1
), T is the
temperature Kelvin (298.15 K), F is faraday’s constant (96,485 C mol
-
1
), n is the number of
electrons involve in the reduction from Co
I
to
Co
0
(1 electron), [CO
2
] is the concentration of CO
2
in DMF (0.2 M) and K
Q
is the binding constant between CO
2
and the cobalt catalyst.
Calculations of the Hammett Parameters for 1
-
4
The cumulative Hammett Parameters for
1
-
4
were calculated by the summat
ion of the individual
Hammet
t
constants for each substituent. The literature
9
values used were:
σ
p,H
= 0
σ
p,CF
3
= 0.54
σ
p,NMe
2
=
–
0.83
For
complex
1
, 0 × 4
=
0
For
complex
2
, 0.54 × 4
=
2.16
For
complex
3
, 2 × 0 + 2 × (
−
0.83) =
−
1.66
For
complex
4
, 2 × 0.54 + 2 × (
−
0.83) =
−
0.58
S
4
Crystallographic data
Figure
S
1
.
(
A
) Thermal ellipsoid drawing of
complex
4
displayed at 50% probability level
.
Hydrogen atoms and BF
4
–
counteranions
are
omitted for
clarity.
(
B
)
Overlay of wireframe
representations of complexes
2
(
blue
)
and the unsubstituted cobalt aminopyridine
1
(black).
(
C
)
Overlay of wireframe representations of complexes
4
(blue) and the unsubstituted cobalt
aminopyridine
1
(black).
S
5
Table S1. Sample and crystal data for 2.
Chemical formula
C
112
H
72
B
8
Co
4
F
80
N
40
Formula weight
3820.29 g/mol
Temperature
100(2) K
Wavelength
0.71073 Å
Crystal size
0.207
́
0.210
́
0.390 mm
Crystal habit
clear orange
-
red prism
Crystal system
monoclinic
Space group
P
1
21/c
1
Unit cell dimensions
a
= 19.663(4) Å
α = 90.00(3)°
b
= 10.366(2) Å
β = 115.34(3)°
c
= 19.730(4) Å
γ = 90.00(3)°
Volume
3634.6(15) Å
3
Z
1
Density (calculated)
1.745 g/cm
3
Absorption
coefficient
0.614 mm
–
1
F(000)
1892
Diffractometer
Bruker APEX DUO
Radiation source
fine
-
focus tube, MoKα
Theta range for data collection
1.15 to 30.66°
Index ranges
–
28
≤
h
≤
28,
–
14
≤
k
≤
14,
–
28
≤
l
≤
28
Reflections collected
87008
Independent reflections
11058 [R(int) = 0.0356]
Coverage of independent reflections
98.4%
Absorption correction
multi
-
scan
Max. and min. transmission
0.8830 and 0.7960
Structure solution technique
direct methods
Structure solution program
SHELXTL XT 2
014/5 (Bruker AXS, 2014)
Refinement method
Full
-
matrix least
-
squares on
F
2
Refinement program
SHELXTL XL 2014/7 (Bruker AXS, 2014)
Function minimized
Σ w(
F
o
2
–
F
c
2
)
2
Data / restraints / parameters
11058 / 29 / 607
Goodness
-
of
-
fit on F
2
1.027
Δ/σ
max
0.002
Final R indices
8892 data; I>2σ(I)
R
1
= 0.0485,
wR
2
= 0.1221
all data
R
1
= 0.0635,
wR
2
= 0.1371
Weighting scheme
w
=
1/[σ
2
(
F
o
2
)+(0.0618P)
2
+5.1672P]
where P
=
(
F
o
2
+2
F
c
2
)/3
Largest diff. peak and hole
0.921 and
–
0.658 eÅ
–
3
R.M.S.
deviation from mean
0.084 eÅ
–
3