of 88
1
Supporting
Information
Ultrafast Photophysics of Ni(I
)
bipyridine Halide Complexes: Spanning the
Marcus Normal and Inverted Regimes
Erica Sutcliffe
, David A. Cagan
, Ryan G. Hadt*
a
Division
of Chemistry and Chemical Engineering, Arthur Amos Noyes Laboratory of Chemical
Physics, California Institute of Technology, Pasadena, California 91125, United States
Authors contributed equally
*Corresponding Author:
rghadt@caltech.edu
2
Table of Contents
S1. Experimental Section.
................................
................................
................................
................................
.......
3
S1.1. General Considerations.
................................
................................
................................
.....
3
S1.2. Synthetic Details.
................................
................................
................................
...............
6
Preparation of Parent Ni(II)
bpy Aryl Halide Complexes.
................................
.....................
6
Photochemical Preparation of Ni(I)
bpy Halide Complexes.
................................
.................
9
Isolation of a Ni(I)
bpy Halide Complex.
................................
................................
.............
12
S1.3. X
-
ray Crystallography.
................................
................................
................................
....
15
S1.4. Steady
-
State UV
-
vis
-
NIR Spectroscopy.
................................
................................
.........
17
Steady
-
State Spectra
................................
................................
................................
..............
17
Fitting of Steady
-
State Spectra
................................
................................
..............................
19
S1.5 Time
-
Resolved Spectroscopy
................................
................................
...........................
21
Transient Absorption Spectra
................................
................................
................................
21
Discussion of Anomalous Long
-
lived Feature
................................
................................
......
43
S1.6 Fits to Alternative Relaxation Models
................................
................................
..............
46
S2. Computational Section.
................................
................................
................................
................................
..
51
S2.1. General Computational Details.
................................
................................
.......................
51
S2.2. Sample ORCA Inputs.
................................
................................
................................
.....
52
S2.3. DFT Molecular Orbital Diagrams and Vibrational Energies
................................
...........
53
S2.4. TDDFT Spectra and Tabulated Transitions
................................
................................
.....
63
S2.5 Limitations of DFT/TD
-
DFT
................................
................................
............................
73
S3. NMR and IR Spectra.
................................
................................
................................
................................
....
74
S4. Appendix.
................................
................................
................................
................................
..........................
81
S5.
References
................................
................................
................................
................................
.........................
85
3
S1. Experimental Section.
S1.1. General Considerations.
All purchased compounds were used as
received unless otherwise noted. Bis
-
(1,5
-
cyclooctadiene)
nickel(0) was purchased from Strem Chemicals. Ligands
N,N,N′,N′
-
tetramethyl ethylenediamine
(TMEDA),
4,4′
-
di
-
tert
-
butyl
-
2,2′
-
bipyridine (
t
-
Bu
bpy), 4,4′
-
dimethyl
-
2,2′
-
bipyridine (
Me
bpy), 2,2′
-
bipyridine (bpy),
4,4'
-
diphenyl
-
2,2'
-
bipyridine (
Ph
bpy),
and dimethyl
-
2,2′
-
bipyridine
-
4,4′
-
dicarboxylate (
MeO2C
bpy) were purchased from
Sigma
-
Aldrich
. Aryl halide compounds, 2
-
chloro
-
toluene, 2
-
bromo
-
toluene, 2
-
iodo
-
toluene, and
2
-
bromo
-
α,α,α
-
trifluorotoluene
were also obtained
from Sigma
-
Aldrich. Solids were dried under vacuum and brought into a nitrogen
-
atmosphere
glove box; liquids
(including aryl halides)
were sparged (N
2
) and degassed via freeze
-
pump
-
thaw
techniques, brought into the glove box, and stored over 3 Å molecular sieves. All solvents were
air
-
free and collected from
a
solvent purification system (SPS), then stored in the glove box over
3 Å molecular sieves
in amber jars
. Tetrahydrofuran (THF), 2
-
methyl tetrahydrofuran (2
-
M
eTHF),
and
d
8
-
tetrahydrofuran (
d
8
-
THF) were inhibitor
-
free.
All deuterated solvents were
purchased from
Cambridge Isotope Laboratories, Inc. and
also dried and stored over activated 3 Å molecular sieves
in a nitrogen
-
filled glove box for at least three days before use.
All synthesized compounds were
made using air
-
free Schlenk techniques or made in the glove box. All synthesized complexes are
considered air and moisture sensitive. Light sensitivity was also seen even in the solid state if left
exposed for e
xtended time.
UV
-
vis spectra of the complexes were obtained on a Varian Cary 500 spectrophotometer or
a
StellarNet Inc. Black Comet UV
-
vis spectrophotometer.
Starna Cells 6
-
Q 2
-
or 10
-
mm path length
cuvettes fitted with air
-
tight seals were used. Proton nuclear magnetic resonance (
1
H NMR) and
fluorine nuclear magnetic resonance (
19
F NMR) spectra were recorded on a 400 MHz Varian
Spectrometer with broadband auto
-
tune OneProbe.
19
F
NMR were externally referenced to neat
fluorobenzene (
δ =
-
113.15
ppm).
13
C NMR spectra were collected on a Bruker AV
-
III HD 400
MHz spectrometer and were
1
H
decoupled. Chemical shifts are reported in parts per million (
δ
in
ppm, s: singlet, d: doublet, t: triplet, m: multiplet) and are referenced to residual solvent signal
(THF
-
d
8
= 3.58 ppm).
NMR samples were prepared in the glove box into Norell J
-
Young tubes.
IR measurements were performed on a Bruker Alpha Platinum ATR spectrometer
.
S
amples were
analyzed
with
h
igh resolution m
ass
s
pectrometry
(HRMS)
by
Field Desorption ionization using a
JEOL AccuTOF GC
-
Alpha (JMS
-
T2000GC) mass spectrometer interfaced with an Agilent 8890
GC system.
Electron paramagnetic resonance (EPR) spectroscopy was collected on a Bruker EMX
X
-
band CW
-
EPR Spectrometer using either an Oxford ESR 900 liquid helium/nitrogen flow
-
through cryostat or a liquid nitrogen immersion dewar for experiments at a fixed temperat
ure of
77 K.
The recorded spectra were simulated in EasySpin for Matlab.
1
EPR samples were prepared
in the glove box into Wilmad quartz low pressure/vacuum EPR tubes fitted with a with air
-
tight
PTFE piston.
Ultrafast laser pulses used for the
transient absorption (TA) measurements
originate from a
Coherent Astrella Ti:Sapphire amplifier system, which generates 5
m
J, 40 fs pulses centered on
800 nm at a 1 kHz repetition rate. These pulses were passed into an Ultrafast Systems Helios
spectrometer system to carry out the transient absorption spectroscopy measurements. Pulses from
the Astrella were attenuated and then
delayed by the Helios’ built
-
in 7 ns delay stage before
undergoing supercontinuum generation to generate a white
-
light probe. Three different non
-
linear
optical media were
used to generate white light across the UV to the NIR as needed: CaF
2
(330
4
650 nm), Sapphire (470
750 nm), YAG (850
1600 nm). The majority of the beam was focused
onto the sample and then subsequently into a fiber spectrometer, while the remaining portion of
the beam bypassed the sample and was focused into a second fiber spe
ctrometer to act as a
reference.
Pump pulses were generated through various means using a stronger portion of the Astrella output
than that of the probe. To generate 560, 700 and 1200 nm pump pulses, a Coherent OPerA optical
parametric amplifier was used in various configurations. For pum
ping at 800nm, the fundamental
output of the Astrella was used and for 400 nm the fundamental was frequency doubled in a
β
-
barium borate (BBO) crystal (EKSMA Optics, 10 mm x
10 mm x 0.2 mm,
θ = 29.2
º,
ɸ
= 90º,
P/P@400
-
800 nm)
crystal. After wavelength mani
pulation, the pump was chopped, attenuated
with a
variable neutral density
filter, focused onto the sample, and subsequently blocked.
TA
samples were prepared in a nitrogen
-
filled glovebox using 2 mm quartz cuvettes fitted with
air
-
tight PTFE piston seals (Schlenk cuvettes).
Concentration varied between measurements but
was chosen to maximize absorbance while minimizing the dimerization
occurring
at high
concentrations. Thus, typical absorbances at the pumped wavelength were around 0.1
0.3 OD.
Some compounds were especially prone to dimerization and the resultant precipitate caused
significant scattered pump light in the results.
This
was minimized through the use of spectral
filters (
ThorLabs
FELH0450, FESH0650, FESH0750
)
to block the pump wavelengths, but these
also blocked
wavelengths shorter than 400 nm so were only used when necessary.
A
magnetic
stirrer was
also
used to stir the sample over the course of the measurement.
Data
were
acquired using the Helios control software and subsequently exported to a custom
MATLAB script for processing. Each datapoint was averaged for 2 s (1000 total pump
-
probe
cycles) and an exponentially
-
spaced time
-
array was used to capture the decay of the s
ignal. Each
s
can
was repeated five times. Background points collected before time
-
zero where no signal was
present were subtracted from the remaining data to remove pump scatter and other unwanted
effects. Following this, the chirp in the data was
corrected by tracking the position of the center of
the cross
-
phase modulation (XPM) feature across the first picosecond of the spectrum and
resampling the data with the original time array to remove the chirp. The data were then globally
fit through nonl
inear least
-
squares to a series of exponentials convoluted with a gaussian
instrument response function
.
Since
the true pulse length at the sample is unknown
,
the width o
f
the response function
was set to 70 fs to best fit the data
. In most cases, the XPM
was many times
larger than the actual signal and so greatly biased the fit. In this work our interest lies with the
dynamics after the first picosecond so the signal between
-
0.3 and 0.3 ps (0.5 ps for toluene due to
a wider XPM) was excluded from the fit.
The fitting procedure yields several fitted time constants
alongside the decay
-
associated spectrum (DAS) corresponding to each exponential decay. For
some cases, the least
-
squared algorithm
w
ould not converge so coarse manual tuning of the
parameters was
necessary to provide a good fit. Further processing can convert the DAS into
evolution
-
or species
-
associated spectra but the presence of significant vibrational cooling violates
the assumption of bilinearity required by the global fitting procedure making
subsequent
postprocessing of the spectrum questionable. However, the time constants are still valid and the
DAS can still be used to understand the origin of each component.
Errors on the fitted parameters can be estimated through the residuals and numerical Jacobian
matrix outputted by the fitting algorithm. The errors on the time constants calculated this way
ranged from around 0.1 to 1%. However, errors calculated this way
notoriously underestimate the
5
true uncertainty and more accurate errors can only be garnered from more complex statistical
methods such as
bootstrapping.
2,3
Therefore, we adopt a compromise here. Across all compounds,
1
and
5
were studied most thoroughly so the standard deviation o
f
3
across many different samples
and measurements was taken as the error and found to be 5 and 4%, respectively. Such a large
number of individual measurements were not possible for all compounds, so instead several
permutations of repeats of the noisiest,
4
, were fitted and their standard deviation found to also be
around 5%. Therefore, we approximate the error on
3
to be 5% fo
r all compounds. The shorter
time constants typically correspond to a much smaller change in the signal and so have larger
uncertainty. However, these components are of less relevance to the study as a whole and thus a
detail consideration of their corresp
onding errors is considered beyond the scope of this work.
6
S1.
2
. Synthetic Details.
The parent four
-
coordinate complexes, Ni(II)(
t
-
Bu
bpy)(
o
-
tolyl)Cl, Ni(II)(
t
-
Bu
bpy)(
o
-
tolyl)Br,
Ni(II)(
t
-
Bu
bpy)(
o
-
tolyl)I,
Ni(II)(bpy)(
o
-
tolyl)Cl, and
Ni(II)(
MeO
2
C
bpy)(
o
-
tolyl)Cl,
were synthesized
according to
previous reports.
4
6
Their spectroscopic properties were identical to those described
prior. The
precatalyst, Ni(II)TMEDA(
o
-
tolyl)Br
, and the
parent complexes
,
Ni(II)(
Me
bpy)(
o
-
tolyl)
Cl, Ni(II)(
Ph
bpy)(
o
-
tolyl)Cl,
and Ni(II)(
MeO
2
C
bpy)(
o
-
tolyl)
Br
were prepared
as given b
elow.
Preparation of
P
arent Ni(II)
bpy
A
ryl
H
alide
C
omplexes.
Ni(
Me
bpy)(
o
-
tolyl)
Cl
. In a nitrogen filled glove box, a 20 mL scintillation vial was charged with a
Teflon coated stir bar, bis
-
(1,5
-
cyclooctadiene) nickel(0) (0.
240
g, 0.
870
mmol, 1
.00
eq
.
), and 4,4′
-
dimethyl
-
2
-
2′
-
bipyridine (0.
165
g, 0.
896
mmol, 1
.03
eq
.
). To this vial,
5
.0 mL THF was added,
and the mixture was stirred for
90 minutes
affording a deep purple solution. Subsequently,
1
.
5
mL
of 2
-
chloro
-
toluene (excess) was added dropwise, while stirring. A
n
orange
solid precipitated
after
3.5 hours
alongside a gray
-
black solid
.
P
entane (
1
0 mL) were added
to the mixture to complete
precipitation.
The
crude
solid
mixture
was then collected by filtration, washed with pentane
and
heptane
(3x
5
mL
each
)
,
and the filtrate discarded. Into a second, clean filter flask, the solid mixture
was rinsed with diethyl ether
,
affording a
red/orange filtrate; the insoluble solids were discarded.
To this filtrate, pentane
was
added to precipitate an orange solid. This solid was collected by
filtration, washed again with pentane and heptane (3x5 mL each)
then dried under vacuu
m (0.
075
g,
23
% yield).
Note:
T
he solid product is prone to decomposition over the course of days/weeks,
even in the glove box, becoming an orange/brown solid. Sample should be stored at low
temperature, if possible. Solutions decompose at room temperature over the course of
several
hours
to
days. Solutions should be used immediately to avoid insoluble decomposition products.
UV
-
vis (THF):
λ
MLCT
=
477
nm
/
20
,
964 cm
-
1
(
ε
MLCT
=
4530 cm
-
1
M
-
1
)
.
1
H
NMR (400 MHz,
CD
2
Cl
2
):
δ
8.97 (
d,
J
= 6.0 Hz, 1H), 7.71 (d,
J
= 1.6 Hz, 1H), 7.67 (d,
J
= 1.5 Hz, 1H), 7.54
7.48
(m, 1H), 7.35 (dd,
J
= 5.2, 1.6 Hz, 1H), 7.10 (d,
J
= 5.7 Hz, 1H), 6.91 (dd,
J
= 5.5, 1.9 Hz, 1H),
6.83
6.74 (m, 3H), 3.04 (s, 3H), 2.49 (s, 3H), 2.37 (s, 3H).
13
C{
1
H}NMR (100 MHz, CD
2
Cl
2
)
δ
156.
1
, 151.
3
, 150.
5
, 149.2, 142.7, 135.8, 127.5, 127.
2
, 123.
3
, 123.2, 122.8, 121.8, 121.0, 25.
2
,
21.
7
, 21.5.
FT
-
IR (ATR, cm
-
1
):
3036,
2977, 1615, 1556,
1478, 1445, 1418,
1024, 1018, 921, 846,
827, 7
33, 650, 556, 515
.
HRMS (FD
-
MS):
calculated for [C
1
9
H
19
N
2
Ni
Cl
]
+
:
368.0590
found:
368.05
84
.
7
Ni(
Ph
bpy)(
o
-
tolyl)Cl
.
Synthetic procedure was adapted from
a literature method
.
5
In a nitrogen
filled glove box, a
4 mL vial with
air
-
tight septa cap
was charged with a Teflon coated stir bar and
Ni(TMEDA)(
o
-
tolyl)Cl (
0.024
g, 0.
0
80
mmol, 1
.00
eq.). To this
vial
,
4,4′
-
di
phenyl
-
2,2′
-
bipyridine
(
0.02
6
g, 0.
08
5
mmol, 1.
06
eq.) was added along with
1.6
mL of
benzene
.
The vial was
capped
and sealed
with three turns of electrical tape,
removed from the glove box,
and stirred at
4
5
C for
4
hours affording a d
ark
red
solution
with precipitate
. After allowing the
vial
to cool, it was brought
back into the glove box where
the
red
solid was collected by vacuum filtration, washed with
benzene (
2
x
2
mL)
,
diethyl ether (2x
2
mL), and
pentane
(
4
x
2
mL)
,
then was dried under vacuum
(
0.02
8
g,
73
% yield). Spectroscopic properties were identical to those reported previously.
UV
-
vis (THF):
λ
MLCT
=
500
nm /
20,000
cm
-
1
(
ε
MLCT
=
5300
).
1
H
NMR (400 MHz, CD
2
Cl
2
):
δ
9.25
(d,
J
= 5.7 Hz, 1H), 8.
20
(
s
, 1H), 8.15 (s, 1H), 7.83
7.76 (m, 3H), 7.73
7.68 (m, 2H), 7.63
7.49 (m, 7H), 7.36 (d,
J
= 3.0 Hz, 2H), 6.89
6.78 (m, 3H), 3.09 (s, 3H).
HRMS (FD
-
MS):
calculated for [C
2
9
H
23
N
2
Ni
Cl
]
+
:
492.09
0
3
found:
492.09
2
3
.
Ni(TMEDA)(
o
-
tolyl)Br
.
In a nitrogen filled glove box, a 20 mL scintillation vial was charged
with a Teflon coated stir bar and bis
-
(1,5
-
cyclooctadiene) nickel(0)
(0.250 g, 0.
909
mmol, 1 eq.).
Via micro syringe,
0.175
mL (1.
182
mmol
,
1.3 eq.
) of N,N,N′,N′
-
tetramethyl ethylenediamine was
added along with 3.
2
5 mL of 2
-
bromo
-
toluene
(excess).
A red
/
orange
solid began precipitating in
the vial.
After 5 hours stirring at room
temperature,
h
exanes was added (10 mL) to
further
precipitate the solid
;
the mixture was left overnight. The red
/orange
solid was collected by vacuum
filtration where it was rinsed
thoroughly with
hexane
and
pentane,
and dried (
290
mg,
92
% yield)
.
1
H
NMR (400 MHz, CD
2
Cl
2
):
δ
7.38 (
dd,
J
= 7.3, 1.4 Hz, 1H), 6.70
6.62 (m, 2H), 6.61
6.53
(m, 1H), 3.41 (s, 4H), 2.79
2.31 (m,
12
H), 2.17 (d,
J
= 10.4 Hz, 2H), 1.78 (s,
2
H).
13
C{
1
H}NMR
(100 MHz, CD
2
Cl
2
)
δ
144.8, 143.7, 136.2, 126.
5
, 122.5, 121.9,
61.
4
, 57.
3
, 50.
1
, 49.
1
, 47.7, 47.0,
26.
7
.
FT
-
IR (ATR, cm
-
1
):
3037, 2971, 2893,
2840, 2784, 1558,
1456, 1277, 1123,
1047, 1018,
1010, 953, 806, 772,
749, 648, 605
.
HRMS (FD
-
MS): calculated for [C
13
H
23
N
2
NiBr]
+
: 344.03
98
found: 344.03
96
.
8
Ni(
Me
O
2
C
bpy)(
o
-
tolyl)
Br
. In a nitrogen filled glove box, a
10
0
mL Schlenk flask was charged with
a Teflon coated stir bar
and
Ni(TMEDA)(
o
-
tolyl)
Br
(
0.250
g, 0.7
23
mmol, 1
.00
eq.). To this vial,
dimethyl
-
2,2′
-
bipyridine
-
4,4′
-
dicarboxylate (
0.240
g, 0.8
8
1
mmol, 1.
22
eq.) was added along with
2
4
mL of heptane and
4
mL toluene (
7
:1 heptane/toluene). Upon removal from the glove box, the
flask was sonicated to promote
solubilization of the reagents. The flask was attached to the nitrogen
Schlenk line, covered in aluminum foil, and stirred at 60
C for
24
hours affording a deep purple
solution
with purple precipitate.
O
range starting material was still seen in the flask
after inspection
,
so
t
he temperature was then increased to 65
C
and the reaction continued
for an additional
48
hours. After allowing the Schlenk flask to cool, it was brought back into the glove box
.
A
purple
solid
had precipitated; it
was collected by v
acuum filtration, washed copiously with
heptane
,
diethyl ether (3x2 mL), and excess
pentane, then was dried under vacuum (
0.25
5
g,
70
% yield).
UV
-
vis (THF):
λ
MLCT
= 5
38
nm /
18
,
587
cm
-
1
(
ε
MLCT
=
5100 M
-
1
cm
-
1
).
1
H
NMR (400 MHz,
CD
2
Cl
2
):
δ
9.73 (
d,
J
= 5.0 Hz, 1H), 8.58 (d,
J
= 2.5 Hz, 1H), 8.51 (d,
J
= 1.4 Hz, 1H), 8.11 (dd,
J
= 5.7, 1.7 Hz, 1H), 7.71 (dd,
J
= 6.0, 1.8 Hz, 1H), 7.48 (dd,
J
= 6.9, 1.8 Hz, 1H), 7.43 (d,
J
= 6.1
Hz, 1H), 6.88
6.76 (m, 3H), 4.03 (s, 3H), 3.97 (s, 3H), 2.96 (s, 3H).
13
C{
1
H}NMR (100 MHz,
CD
2
Cl
2
)
δ
164.
1
, 163.9, 155.8, 15
3
.
0
, 152.2, 151.6, 147.4, 142.1, 139.7, 138.3, 135.6, 127.8, 126.3,
125.
8
, 123.
5
, 122.9, 120.
8
, 120.1, 25.1.
FT
-
IR (ATR, cm
-
1
):
3028, 2950,
1725, 1556, 1433, 1398,
1322,
1250, 1232, 1121, 1012, 962,
884, 841, 840, 766, 737, 715,
649
.
HRMS (FD
-
MS): calculated
for [C
21
H
19
N
2
O
4
NiBr]
+
:
499.98
82
found:
499.98
99
.
Ni(
MeO
2
C
bpy)(
o
-
CF
3
Ph
)Br
.
In a nitrogen filled
glove box, a 20 mL scintillation vial was charged
with a Teflon coated stir bar, bis
-
(1,5
-
cyclooctadiene) nickel(0) (0.2
20
g, 0.8
00
mmol, 1.00 eq
.
),
and
dimethyl
-
2,2′
-
bipyridine
-
4,4′
-
dicarboxylate
(0.
225
g, 0.8
26
mmol, 1.03 eq
.
). To this vial, 5.0
mL THF was added, and the mixture was stirred for 90 minutes affording a deep purple solution.
Subsequently,
2.0
mL of
2
-
bromobenzotrifluoride
(excess) was added while stirring.
The product
solid precipitated after
4
hours.
Hexane
(10 mL) w
as
added to the mixture to complete
precipitation
, and
the mixture was placed in the glovebox freezer (
-
35 °C) for 60 hours
. Th
e
solid
was
finally
collected by filtration, washed
thoroughly
with
he
xane
, diethyl ether (3x2 mL), and
excess pentane
,
then dried under vacuum (0.
405
g,
91
% yield).
UV
-
vis (THF):
λ
MLCT
=
49
9
nm /
20,0
4
0
cm
-
1
(
ε
MLCT
=
43
70
M
-
1
cm
-
1
).
1
H
NMR (400 MHz,
d
8
-
toluene
):
δ
9.74 (
d,
J
= 5.7 Hz, 1H), 7.96
7.92 (m, 1H), 7.91 (s, 1H), 7.74 (s, 1H), 7.65 (s, 1H),
7.37 (d,
J
= 8.3 Hz, 2H), 7.22 (t,
J
= 5.2 Hz, 2H), 6.55 (d,
J
= 5.4 Hz, 1H), 3.40 (s, 3H), 3.36 (s,
3H)
.
19
F NMR (400 MHz, CD
2
Cl
2
)
δ
58.6
ppm
;
(400 MHz,
d
8
-
THF
)
δ
58.
4
ppm
.
13
C{
1
H}NMR
(100 MHz, CD
2
Cl
2
)
δ
163.
8
, 155.8, 152.
8
, 152.
1
, 146.
1
, 137.9, 137.
1
, 128.3, 126.0, 125.
7
, 123.0,
9
120.8, 120.3, 120.2.
Low signal to noise precluded the resolution of the
J
C
F
coupling values for
the trifluorotoluene peak.
FT
-
IR (ATR, cm
-
1
):
3061, 2960, 1723,
1558, 1435, 1398, 1311, 1232,
1148,
1092, 1020, 967, 883,
842, 764, 735, 702, 6
75, 638
.
HRMS (FD
-
MS): calculated for
[C
21
H
1
6
N
2
O
4
F
3
NiBr]
+
:
553.95
99
found:
553.959
4
.
P
hotochemical P
reparation of Ni(I)
bpy
H
alide
C
omplexes.
Following our previous report,
6
the
Ni(I)(
R
bpy)X
(
R =
t
-
Bu, Me, Ph, H, MeO
2
C; X = Cl, Br, I)
compounds
studied herein
were
accessed directly from
their parent Ni(II)
bpy aryl halide
precursors
by air
-
and moisture
-
free irradiation
(
370 nm
or 390 nm)
.
Stock solutions of p
arent Ni(II)
bpy aryl
halide complexes
(0.5
1 mM)
were prepared in a
nitrogen
-
filled glove box and distributed into separate spectroscopic cuvettes (Starna Cells, 2
-
or
10
-
mm path length) fitted with air
-
tight PTFE piston seals (Schlenk cuvettes).
Solutions were
prepared fresh daily for analysis.
Each cuvette was placed 5 cm away from either a Gen 2 Kessil
PR160L 370 nm LED or Kessil PR160L 390 nm LED on highest setting. A cooling fan was used
to maintain room temperature irradiation during the experiment
.
Note:
Kessil LEDs
ma
y
auto
-
shut
off if left on for extended periods without the external fan due to overheating.
Typical irradiation
times
,
t
,
were ~60 minutes, but these varied with each complex and are
listed
below.
Ni(I)(
t
-
Bu
bpy)Cl,
1
.
Air
-
and moisture
-
free irradiation of the parent Ni(II) compound,
Ni(II)(
t
-
Bu
bpy)(
o
-
tolyl)Cl, for
6
0 minutes
using
a Gen 2 Kessil PR160L 370 nm LED
afforded the
title compound. UV
-
vis (THF):
λ
1
= 660
nm (15,152 cm
-
1
),
λ
2
= 422
nm, (23,700 cm
-
1
).
Spectroscopic properties were identical to those reported previously.
Ni(I)(
t
-
Bu
bpy)
Br
,
1
-
Br
.
Air
-
and moisture
-
free irradiation of the parent Ni(II) compound,
Ni(II)(
t
-
Bu
bpy)(
o
-
tolyl)
Br
, for
45
minutes
using a
Kessil PR160L 390 nm LED
afforded the title
compound. UV
-
vis (THF):
λ
1
=
653
nm (15,314 cm
-
1
),
λ
2
= 386
nm, (25,906 cm
-
1
)
. Spectroscopic
properties were identical to those reported previously.
10
Ni(I)(
t
-
Bu
bpy)
I
,
1
-
I
.
Air
-
and moisture
-
free irradiation of the parent Ni(II) compound,
Ni(II)(
t
-
Bu
bpy)(
o
-
tolyl)
I
, for 60 minutes
using a
Kessil PR160L 390 nm LED
afforded the title
compound. UV
-
vis (THF):
λ
1
=
640
nm (15,625
cm
-
1
),
λ
2
=
382
nm, (26,178
cm
-
1
).
Spectroscopic
properties were identical to those reported previously.
Ni(I)(
Me
bpy)Cl,
2
.
Air
-
and moisture
-
free irradiation of the parent Ni(II) compound,
Ni(II)(
Me
bpy)(
o
-
tolyl)Cl, for 60 minutes
using a
Kessil PR160L 390 nm LED
afforded the title
compound. UV
-
vis (THF):
λ
1
= 660
nm (15,152 cm
-
1
),
λ
2
=
440
nm, (
22,727
cm
-
1
).
Ni(I)(
H
bpy)Cl,
3
.
Air
-
and moisture
-
free irradiation of the parent Ni(II) compound,
Ni(II)(
H
bpy)(
o
-
tolyl)Cl, for
75
minutes using a Kessil PR160L 390 nm LED afforded the title
compound
.
Precipitation can occur after extended irradiation
;
it
can be
filtered off in a glove
box
to
yield
a homogenous
filtrate
solution of the Ni(I) complex.
UV
-
vis (THF):
λ
1
=
673
nm
(15,625
cm
-
1
),
λ
2
=
431
nm, (23,200
cm
-
1
).
Spectroscopic properties were identical to those
reported previously.
Ni(I)(
Ph
bpy)Cl,
4
.
Air
-
and moisture
-
free irradiation of the parent Ni(II) compound,
Ni(II)(
Ph
bpy)(
o
-
tolyl)Cl, for
75
minutes
using
a Gen 2 Kessil PR160L 370 nm LED
afforded the
title compound. UV
-
vis (THF):
λ
1
=
1
175
nm (
8,
510
cm
-
1
),
λ
2
=
915
nm, (
10,92
9
cm
-
1
)
,
λ
3
=
690
nm, (
14,493
cm
-
1
)
,
λ
4
=
485
nm, (
20,619
cm
-
1
)
.
11
Ni(I)(
MeO
2
C
bpy)Cl,
5
.
Air
-
and moisture
-
free irradiation of the parent Ni(II) compound,
Ni(II)(
MeO
2
C
bpy)(
o
-
tolyl)Cl, for
4
5 minutes using a Gen 2 Kessil PR160L 370 nm LED afforded
the title compound. UV
-
vis (THF):
λ
1
=
1178
nm (
8
,
490
cm
-
1
)
,
λ
2
=
805
nm (12,422
cm
-
1
),
λ
3
=
523 nm (19,120
cm
-
1
).
Spectroscopic properties were identical to those reported previously.
Ni(I)(
MeO
2
C
bpy)
Br
,
5
-
Br
.
Air
-
and moisture
-
free irradiation of the parent Ni(II) compound,
Ni(II)(
MeO
2
C
bpy)(
o
-
tolyl)
Br
, for
4
5 minutes using a Gen 2 Kessil PR160L 370 nm LED afforded
the title compound. UV
-
vis (THF):
λ
1
=
11
67
nm (
8,
570
cm
-
1
)
,
λ
2
=
785
nm (12,
739
cm
-
1
),
λ
3
=
52
0
nm (19,
231
cm
-
1
).
Table S1.
Summary of the
photochemical parameters used to generate the Ni(I)
bpy halide
complexes
from their Ni(II)
bpy
aryl halide parents (Ar =
o
-
tolyl) a
longside their
photochemical
properties
.
MLCT peak
positions and molar extinction
coefficients
are given for the lowest energy
MLCT transition seen in the UV
-
vis
-
NIR data.
Solvent = THF
;
t
= irradiation time.
Parent Ni(II) Complex
Ni(I
I
)
MLCT
(nm / cm
-
1
)
Ni(II)
ε
MLCT
(M
-
1
cm
-
1
)
LED
(nm)
t
(min)
Ni(I)
Complex
Ni(I)
MLCT
(nm / cm
-
1
)
Ni(I)
ε
MLCT
(M
-
1
cm
-
1
)
a
Ni
(II)
(
t
-
Bu
bpy)(
Ar
)Cl
475 / 21
053
4970
3
70
60
1
660 / 15
150
2000
Ni
(II)
(
t
-
Bu
bpy)(
Ar
)Br
479 / 20
877
3100
390
45
1
-
Br
653 / 15
310
2100
Ni
(II)
(
t
-
Bu
bpy)(
Ar
)I
488 /
20
492
2200
390
60
1
-
I
640 / 15
625
1000
Ni
(II)
(
Me
bpy)(
Ar
)Cl
46
5
/
21
5
05
4540
390
60
2
660 / 15
150
1900
Ni
(II)
(
H
bpy)(
Ar
)Cl
483 /
20
704
4070
390
75
3
673 / 14
860
2100
Ni
(II)
(
Ph
bpy)(
Ar
)Cl
50
1
/
19
960
5400
b
3
70
75
4
1
175
c
/
851
0
800
Ni
(II)
(
MeO
2
C
bpy)(
Ar
)Cl
532 / 18
797
6
100
370
4
5
5
1178 / 8490
5500
Ni
(II)
(
MeO
2
C
bpy)(
Ar
)Br
538 / 18
587
5100
370
45
5
-
Br
1167 / 8570
2500
a
Values obtained
following complete photoly
sis of parent Ni(II) complexes
and may be underestimated.
b
Reference
value
5
.
c
Identified
by
using both
the
UV
-
vis
-
NIR
absorption
peak
and the ground state bleach
feature
in the transient
absorption spectrum
(Figure S3
1
)
.
12
Isolation of
a
Ni(I)
bpy
H
alide
C
omplex
.
Ni(I)(
MeO
2
C
bpy)Cl
,
5′
.
In a nitrogen filled glove box
Ni(II)(
MeO
2
C
bpy)(
o
-
tolyl)Cl
6
(
0.
160
g
,
0.
350
mmol)
was dissolved in
175
.0
mL of diethyl ether
.
This
purple
solution was filtered to ensure
homogeneity
and transferred t
o
a
35
0
mL Schlenk flask
with a Teflon coated stir bar
. The flask
was sealed and removed from the glovebox.
The flask was attached to a nitrogen Schlenk line
and
allowed to stir. Two
Gen 2 Kessil PR160L 370 nm LED
s were p
ointed at the flask (one on either
side)
; a fan was pointed at the entire setup to ensure room temperature irradiation. The LEDs were
allowed to irradiate the solution on their maximum setting for 48 hours.
During the course of the
irradiation, a dark precipitate could be seen evolving from the solution.
The
flask was then returned
to the glovebox, and the solid collected by
vacuum filtration
(fraction 1)
.
The
purple
filtrate was
transfer
red
back in
to the Schlenk flask, removed from the glovebox, and
reattached to the nitrogen
line. Irradiation of the solution was continued in the same manner
as before
for
an additional
24
hours, affording more
precipitated
solid.
The flask was
again
returned to the glovebox, and the
new
solid collected by vacuum filtration (fraction
2
)
; the filtrate was
discarded
.
The
collected
navy
blue solid was
washed with excess diethyl ether
,
2
-
methyl tetrahydrofuran
(
5x1 mL)
, hexane (
3
x2
mL),
and pentane (3x
2
mL)
, then dried under reduced pressure (
fraction 1:
0.0
7
2
g
,
fraction 2
:
0.029
g
,
co
mbined
fractions
:
0.101 g
,
81
%
yield
).
Note:
The title compound is
highly
air
and moisture
sensitive
. It is
insoluble
in pentane, hexane,
heptane,
and
ether
. It
is sparingly soluble in 2
-
MeTHF
and is
soluble in benzene, toluene, and THF.
The compound reacts readily with
dichloromethane (affording a red solution) and decomposes in
acetonitrile (becoming a black solution).
The compound readily reacts with aryl bromides.
P
owder sample
X
-
band CW
-
EPR
(
T
= 5 K; frequency = 9.638 GHz; power = 2.2 mW; modulation
amplitude = 8 G)
:
g
avg
= 2.146 (
g
x
= 2.053,
g
y
= 2.123,
g
z
= 2.262
;
g
(strain)
x
= 0.025,
g
(strain)
y
=
0.035,
g
(strain)
z
= 0.033
.
FT
-
IR
solid sample
(ATR, cm
-
1
):
3073, 2957, 1716, 1567,
1511,
1435,
1398,
1316,
1277,
1224,
1102,
1014,
992, 885, 836, 751,
726,
698, 542.
Frozen solution
(
toluene
)
X
-
band CW
-
EPR
(
T
= 5 K; frequency = 9.63
9
GHz; power = 2.2 mW;
modulation amplitude = 8 G):
g
iso
=
2.2011
;
g
(strain) = 0.
5.
Frozen solution
(
THF
)
X
-
band CW
-
EPR
(
T
= 5 K; frequency = 9.639 GHz; power = 2.2 mW; modulation amplitude = 8 G):
g
1,
iso
=
2.2011;
g
1
(strain) = 0.5
;
g
2
,iso
=
2.1870
;
g
2
(strain)
= 0.0902
.
UV
-
vis (THF):
λ
1
=
1178
nm (8,490
cm
-
1
)
,
λ
2
=
805
nm (12,422
cm
-
1
),
λ
3
=
523
nm (19,120
cm
-
1
)
.
UV
-
vis (
Benzene
):
λ
2
=
11
81
nm
(8,490
cm
-
1
)
,
λ
2
=
8
20
nm (12,422
cm
-
1
),
λ
3
=
52
6
nm (19,120
cm
-
1
).
Paramagnetic
1
H
NMR (400
MHz,
d
8
THF
):
δ
10.51
(
br s, 1H), 8.31 (br s,
2
H),
3.81 (
br
s,
3
H).
Effective magnetic moment
(Evans method, 29
8
K, C
6
D
6
): 1.
9
μB
.
13
Figure S
1
.
Frozen solution (toluene) X
-
band CW
-
EPR
spectrum and
fit
(blue and orange lines,
respectively)
of
5′
(
T
= 5 K; frequency = 9.639 GHz; power = 2.2 mW; modulation amplitude = 8
G
)
. Anisotropy
in
the signal could not be resolved due to line broadening
, likely arriving
from
suspended particles of the complex which precipitated upon freezing or were not fully solvated
.
Simulation values:
g
iso
= 2.201;
g
(strain) = 0.5.
Figure S
2
.
Frozen
solution (
THF
) X
-
band CW
-
EPR
spectrum and fit
(blue and orange lines,
respectively)
of
5′
(
T
= 5 K; frequency = 9.639 GHz; power = 2.2 mW; modulation amplitude = 8
G
)
.
(
Left
)
Full spectrum
plotted showing two species; a
nisotropy in the signal could not
be resolved
due to line broadening, likely ar
is
ing from suspended particles of the complex which precipitated
upon freezing or were not fully solvated.
The second feature in the spectrum (labeled as
g
2
) is
attribut
ed
to
a small fraction of the species coordinating to THF
, which may occur during freezing
of the sample
.
Dual spin
s
imulation values:
g
1,iso
= 2.201;
g
1
(strain) = 0.5;
g
2,iso
= 2.187;
g
2
(strain)
= 0.090.
(
Right
) Spectrum after subtraction of the broad signal corresponding to
g
1
.
S
imulation
values:
g
z
= 2.2
30
,
g
x
= 2.
180
,
g
y
= 2.1
4
6
,
g
avg
= 2.1
85
;
g
z
(strain)
=
0.0
43
,
g
x
(strain)
=
0.043
,
g
y
(strain)
= 0.065.
14
Figure S
3
.
UV
-
vis
-
NIR spectra of
5′
pre
-
and post
-
addition
(blue and orange lines, respectively)
of
10
0
μ
L of
2
-
bromobenzotrifluoride
.
Figure S
4
.
Aryl bromide r
eactivity analysis of
5′
by
19
F NMR
(
d
8
-
THF
)
.
(A) Reaction
scheme
for
the oxidative addition of
the
aryl bromide by
Ni(I)
, forming
Ni
(II)
(
MeO
2
C
bpy)(
o
-
CF
3
Ph
)Br
and
paramagnetic
Ni
(II)
(
MeO
2
C
bpy)
Cl
2
.
6,7
(B)
19
F
NMR spectrum of i
ndependently synthesized
Ni(
MeO
2
C
bpy)(
o
-
CF
3
Ph
)Br
. (C)
19
F NMR spectrum
of
5′
post
-
addition of 100
μ
L of
2
-
bromobenzotrifluoride
.
15
S1.
3
.
X
-
ray Crystallography
.
Collection and
Re
finement
D
etails for
Ni
(II)
(
MeO
2
C
bpy)(
o
-
tolyl
)
Cl
.
Ni
(II)
(
MeO
2
C
bpy)(
o
-
tolyl
)
Cl
was crystallized by slow evaporation
in
diethyl ether.
Low
-
temperature diffraction data (
-
and
-
scans) were collected on a Bruker AXS D8 VENTURE
KAPPA diffractometer coupled to a PHOTON
II CPAD
detector with Mo
K
radiation (
=
0.71073 Å) from an I
μ
S micro
-
source for the structure of compound
V23337
. The structure was
solved by direct methods using SHELXS
8
and refined against
F
2
on all data by full
-
matrix least
squares with SHELXL
-
201
9
9
using established refinement techniques
.
10
All non
-
hydrogen atoms
were refined anisotropically. All hydrogen atoms were included into the model at geometrically
calculated positions and refined using a riding model. The isotropic displacement parameters of
all hydrogen atoms were fixed to 1.2 times
the
U
value of the atoms they are linked to (1.5 times
for methyl groups).
All disordered atoms were refined with the help of similarity restraints on the
1,2
-
and 1,3
-
distances and displacement parameters as well as
enhanced
rigid bond restraints for
an
isotropic displacement parameters.
Ni
(II)
(
MeO
2
C
bpy)(
o
-
tolyl
)
Cl
crystallizes
in the monoclinic
space group
P
2
1
/
n
with one molecule in the asymmetric unit.
The
o
-
tolyl group was modeled as a
two
-
component
disorder.
These data are provided free of charge from The Cambridge
Crystallographic Data Centre by The Cambridge
Crystallographic Data Centre.
top view
side view
Figure S
5
. Top down and side views of the refined crystal structure of
Ni
(II)
(
MeO
2
C
bpy)(
o
-
tolyl
)
Cl
.
The
o
-
tolyl group was modeled as a two
-
component disorder
, with one conformer pointing up and
the other pointing down
.