of 84
1
Supporting Information
Photogenerated Ni(I)
Bipyridine Halide Complexes: Structure
-
Function
Relationships for Competitive C(sp
2
)
Cl Oxidative Addition
and
Dimerization
Reactivity Pathways
David A. Cagan
, Daniel Bím
, Brendon J. McNicholas, Nathanael P. Kazmierczak,
Paul H. Oyala, and Ryan G. Hadt*
Division of Chemistry and Chemical Engineering, Arthur Amos Noyes Laboratory of Chemical Physics, California
Institute of Technology, Pasadena, California 91125,
United States
*Corresponding Author:
rghadt@caltech.edu
2
Table of Contents
S1. Experimental Section.
................................
................................
................................
.............
4
S1.1. General Considerations.
................................
................................
................................
......
4
S1.2. Photochemical Setup.
................................
................................
................................
.........
5
S1.3. Synthetic Details.
................................
................................
................................
................
5
Preparation of parent Ni(II)
bpy aryl halide complexes.
................................
.......................
5
Preparation of the dimeric [Ni(I)(
t
-
Bu
bpy)Cl]
2
complex.
................................
..........................
6
Preparation of Ni(I)
bpy halide complexes.
................................
................................
............
7
S1.4. Steady
-
State UV
-
vis Spectroscopy.
................................
................................
..................
10
S1.5. Experimental Photolysis Kinetics, Quantum Yields,
and Global Kinetic Modeling.
......
12
Experimental Photolysis Kinetics.
................................
................................
.........................
12
Experimental Quantum Yield Determination.
................................
................................
........
13
Global Kinetic Modeling.
................................
................................
................................
.......
15
S1.6. Electrochemical Studies.
................................
................................
................................
...
19
Cyclic Voltammetry.
................................
................................
................................
...............
19
Spectroelectrochemistry Analysis.
................................
................................
.........................
19
S1.7. Oxidative Addition Experiments.
................................
................................
.....................
21
Steady
-
state Ni(I)
bpy halide reactivity by UV
-
vis.
................................
..............................
21
Steady
-
state Ni(I)
bpy halide reactivity by NMR.
................................
................................
.
23
Time
-
resolved Ni(I)
bpy halide reactivity kine
tics with 2
-
chloro
-
toluene by UV
-
vis.
..........
26
Time
-
resolved Ni(I)
bpy halide reactivity kinetics with
4
-
R
-
chlorobenzene by UV
-
vis and
associated Hammett analysis.
................................
................................
................................
28
S1.8. Thermal Decomposition Experiments and Eyring Analysis.
................................
...........
30
Thermodynamics Experiments and Eyring Analysis.
................................
.............................
30
Identification of the Thermal Decomposition Product(s).
................................
.....................
31
S1.9. Temperature and Concentration Depe
ndent Speciation by EPR and UV
-
vis.
.................
34
Variable Temperature and Concentration EPR Analysis.
................................
.....................
34
Variable Temperature UV
-
vis Analysis.
................................
................................
................
38
Summary of Speciation Experiments.
................................
................................
....................
41
S2. Computational Section.
................................
................................
................................
........
42
S2.1. General Computational Details.
................................
................................
........................
42
S2.2. Sample ORCA inputs
................................
................................
................................
.......
43
S2.3. Intrinsic bond orbital analysis.
................................
................................
..........................
45
S2.4. Molecular Orbital Diagrams, Energetics, and Correlations
................................
..............
47
S2.5. TDDFT Spectra and Tabulated Transitions
................................
................................
......
54
S2.6. DFT Reactivity
Investigations
Oxidative Addition and Dimerization
..........................
69
S2.7. Additional Analysis of EPR Spectra
................................
................................
.................
75
S3. Additional NMR Data.
................................
................................
................................
..........
77
S4. References.
................................
................................
................................
.............................
80
3
4
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 4,4′
-
di
-
tert
-
butyl
-
2,2′
-
bipyridine
(
t
-
Bu
bpy), 2,2′
-
bipyridine (bpy), and
dimethyl
-
2,2′
-
bipyridine
-
4,4′
-
dicarboxylate (
MeOOC
bpy)
were
purchased from Sigma
-
Aldrich. Aryl halide compounds, 2
-
chloro
-
toluene, 2
-
bromo
-
toluene
,
2
-
iodo
-
toluene
,
2
-
chloro
-
α,α,α
-
trifluorotoluene
,
4
-
chloro
-
anisole,
4
-
chloro
-
toluene,
chloro
-
benzene,
4
-
chloro
-
benzamide,
and
4′
-
chloro
-
acetophenone
were also obtained from Sigma
-
Aldrich. Solids were dried under vacuum and brought into a nitrogen
-
atmosphere glove box;
liquids 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 the solvent
purification system (SPS), then stored in the glove box over 3 Å molecular sieves. Tetrahydrofuran
(THF)
,
2
-
methyl tetrahydrofuran (
2
-
MeTHF), and
d
8
-
t
etrahydrofuran
(
d
8
-
THF)
w
ere
inhibitor
-
free. 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 see
n even in the solid state if left exposed for extended time.
Room temperature
UV
-
vis spectra of the complexes were obtained on a Varian Cary 500
spectrophotometer
or
a StellarNet Inc. Black Comet UV
-
vis spectrophotometer
.
Variable
temperature
(heating)
decomposition
kinetics were acquired on a UV
-
vis HP Agilent 8453
spectrophotometer coupled to an HP 89090A Peltier temperature controller with a cell holder.
Variable temperature
(cooling)
UV
-
vis spectra were acquired using a Varian Cary 50
spect
rophotometer equipped with a USP
-
203 series cryostat (UNISOKU Co.) and a liquid nitrogen
dewar. Samples were equilibrated at each temperature for five minutes prior to acquisition.
All
spectra were baselined in THF at the appropriate temperature.
Starna Ce
lls 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
On
eProbe.
13
C NMR spectra were collected on a Bruker AV
-
III HD 400 MHz spectrometer
and
were
1
H
decoupled.
19
F
NMR were externally referenced to neat fluorobenzene (δ =
-
113.15 ppm).
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 (
d
8
-
THF
= 3.58 ppm).
Deuterated solvents
were dried and stored over activated 3 Å molecular sieves in a nitrogen
-
filled glove box
for at least
three days before use
.
Fourier transform infrared (FTIR) spectra were collected using a Thermo
Scientific Nicolet iS5 FTIR spectrometer with an iD5 diamond ATR accessory in an inert
-
atmosphere glove box.
Electron paramagnetic resonance (EPR)
spectroscopy was performed using
a
Bruker EMX X
-
band CW
-
EPR Spectrometer
equipped with a ER4119HS high sensitivity
resonator or ER4116DM dual mode resonator for room temperature and cryogenic experiments,
respectively. Room temperature spectra in 2
-
MeTHF w
ere collected in a 1.5 mm I.D. quartz
capillary tube inside an air
-
free standard 4 mm O.D. quartz X
-
band EPR tube. Spectra at cryogenic
temperatures were performed using an
Oxford ESR 900 liquid helium/nitrogen flow
-
through
cryostat
after freezing samples
in l
iquid nitrogen
.
The recorded spectra were simulated in EasySpin
for M
atlab
.
Room temperature cyclic voltammetry was performed in a nitrogen
-
filled glove box
with a Gamry Reference 600 or Biologic SP
-
200 potentiostat using a three
-
electrode cell.
Spectr
oelectrochemistry was performed in a nitrogen
-
filled glove box with a Gamry Reference
600 or Biologic SP
-
200 potentiostat.
5
S1.2. Photochemical Setup.
Photochemical stocks were prepared in a nitrogen
-
filled glove box and distributed into separate
spectroscopic cuvettes (Starna Cells,
2
-
or 10
-
mm
path length) with air
-
tight seals. Each cuvette
cell had volume of
3.0
mL as determined by syringe and were pl
aced 5 cm away from a Kessil
PR160L LED (λ
max
= 3
7
0 nm
unless otherwise stated
,
P
LED
=
7
0
mW cm
-
2
at 5 cm distance
) on
highest setting. A cooling fan was used to maintain room temperature irradiation during the
experiment. Sample positions were rotated periodically to ensure even irradiation throughout the
entire duration of the experiment.
S1.3. Synthetic Details
.
Preparation of
p
arent Ni(II)
bpy
aryl halide complexes.
The p
arent four
-
coordinate
complexes, Ni(II)(
t
-
Bu
bpy)(
o
-
tolyl)Cl, Ni(II)(
t
-
Bu
bpy)(
o
-
tolyl)Br,
Ni(II)(bpy)(
o
-
tolyl)Cl, and Ni(II)(
t
-
Bu
bpy)(CF
3
Ph)Cl
were
synthesized according to
previous
reports.
1,2
Their spectroscopic properties were identical to those described prior.
1,2
The parent
complexes Ni(II)(
t
-
Bu
bpy)(
o
-
tolyl)I and Ni(II)(
MeOOC
bpy)(
o
-
tolyl)Cl were
prepared follow
ing a
modified literature procedure
(see below).
Ni(
tBu
bpy)(
o
-
tolyl)I
.
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.
195
g,
0.709
mmol, 1 eq
.
), and 4,4′
-
tert
-
butyl
-
2
-
2′
-
bipyridine (0.2
10
g,
0.782
mmol, 1.
1
eq
.
). To this vial, 3.0 mL THF was added, and
the mixture was stirred for one hour affording a deep purple solution. Subsequently,
0
.
3
mL of 2
-
iodo
-
toluene (excess) was added
dropwise, while stirring. A
red
solid
precipitated. Mixture was
left stirring for 15
minutes longer, then transferred to aa 75 mL amber jar.
Pentanes (
4
0 mL)
wer
e
added, and the mixture was left to stir for 45 minutes
. The
jar
was placed in the freezer (
-
35
C)
overnight
to complete
the
precipitation. The solid was
then
collected by filtration, washed with
pentanes
(3x
10
mL
or until filtrate is clear
), then dried under vacuum (0.3
56
g, 9
2
% yield). UV
-
vis
(THF): λ
MLCT
=
488
nm
,
ε
488 nm
= 2200 M
-
1
cm
-
1
.
1
H
NMR (400 MHz, CD
2
Cl
2
): δ 9.
56
(d,
J
=
6
.
0
Hz, 1H), 7.8
3
(d,
J
=
14
.0 Hz,
2
H), 7.
58
(d,
J
=
7
.
4
Hz, 1H), 7.
46
(d,
J
=
6
.
0
Hz,
1
H), 7.1
7
(d,
J
=
6.2, 2.1 Hz, 1H), 6.8
7
6.
8
0 (m,
2
H),
6
.
77
(
t
,
J
= 7.3 Hz,
1
H),
6
.
7
0
(
t
,
J
= 7.
2
Hz, 1
H),
2.96
(
s
,
3
H),
1.4
0
(s, 9H), 1.34 (s, 9H).
13
C{
1
H}NMR (100 MHz, CD
2
Cl
2
) δ
163.44, 162.93, 155.88,
153.80, 153.24, 149.50, 147.92, 143.19, 137.82, 127.50, 123.81, 123.26, 122.29, 117.78, 117.37,
35.56, 30.27, 30.09, 26.76.
FT
-
IR (ATR, cm
-
1
):
600, 734, 840, 858,
1015, 1250, 1407, 1544, 1616,
2862, 2896, 2961, 3052
.
6
Ni(
CH
3
OOC
bpy)(
o
-
tolyl
)Cl
.
In a nitrogen filled glove box, a 25
0
mL Schlenk flask was charged
with a Teflon coated stir bar and
crystalline
Ni(TMEDA)(
o
-
tolyl)Cl
(
red crystals
grown from slow
evaporation in hexanes/THF
,
2.25
g, 0.
746
mmol, 1 eq.). To this vial, dimethyl
-
2,2′
-
bipyridine
-
4,4′
-
dicarboxylate (
2.23
g, 0.
8
19
mmol, 1
.1
eq.) was added along with
128
mL of heptane and
22
mL toluene (6:1 heptane/toluene).
Note that it was
important to carefully wash the solid down the
sides of the Schlenk flask
, as separation of unreacted starting Ni(TMEDA)(o
-
tolyl)Cl
is
challenging during the work
-
up phase
; excess bpy is used to aid in consumption of all
Ni(TMEDA)(o
-
tolyl)Cl
.
Upon removal
from the glove box, the flask was sonicated
for 10 minutes
to promote solubilization of the reagents.
The flask was attached to the nitrogen Schlenk line,
covered in aluminum foil (
product is light sensitive),
and stirred at 60
C
for 18 hours
affording
a
deep purple solution.
The temperature was then increased to 65
C
for an additional 8 hours.
After
allowing
the Schlenk flask
to cool, it
was brought back into the glove box
where it had
precipita
ted
a purple solid. This solid was
collected by vacuum filtration, washed
copiously with
pentanes and
hexanes, then was dried under vacuum (
3.1
g,
91
% yield).
Spectroscopic properties were identical
to those
reported previously
.
1,2
Preparation of the dimeric [Ni(I)(
t
-
Bu
bpy)Cl]
2
complex.
[Ni(I)(
t
-
Bu
bpy)Cl]
2
.
The title complex was prepared according to literature precedent,
2
save that
the washing step was done with toluene and 2
-
methyl THF instead of benzene and THF owing to
decreased solubility of the complex in the former solvents.
When fully dry, the solid is a gray
powder; when
wet or in solution, it
is black
-
brown.
1
H NMR (400 MHz,
d
8
-
THF
)
:
δ
130 (broad s,
1.3H), 56
58 (broad d, 3.0H), 36
41 (broad d, 2.7H), 1.29 (s, 35.0 H).
EPR analysis gave no
resolvable signals
as demonstrated previously
(
T =
5 K,
9.63
8 GHz, 8 G modulation amplitude,
2.184
mW
power).
7
Preparation of Ni(I)
bpy halide complexes.
Ni(I)(
R
bpy)X compounds were
accessed directly from
their parent Ni(II)
bpy ar
yl halide
precursors
by air
-
and moisture
-
free irradiation at 370 nm using Kessil PR160L purple LEDs
and
were characterized by UV
-
vis
and EPR spectroscopies.
Typical irradiation times were ~30
-
60
minutes, but these varied with each complex and were dependent on the individual compound’s
rate of Ni(I)
photochemical
formation and decay,
initially
described in our earlier work by
k
p
and
k
d
,
respectively
(Table S
1
)
.
1
These irradiation times,
t
,
were chosen to maximize the concentration
of Ni(I) in solution and minimize the amount
of decomposition product
(
s
)
by observing the
following kinetic analysis.
Scheme S
1
.
Photochemical r
eaction pathway
initially
modeled
in reference
1
using global
analysis.
In this model,
k
p
is the
first
-
order
rate
constant f
or the photolysis step and
k
d
is the
bimolecular
rate constant
for the decay step.
For an initial
approximation, we can
model the process given in
Scheme
S
1
as a
sequential
first
-
order
reaction involving the conversion of
A
to
C
via an intermediate species,
B
,
i.e.
,
[
A
B
,
B
C
]
,
where the initial concentrations of the
intermed
i
ate and product
species are zero,
i.e.,
[
B
]
o
= [
C
]
o
= 0,
[
A
]
o
> 0,
the concentration of
B
can be given by
eq
uation
S1, and the change
in its concetration by eq
uation
S2.
[
]
=
!
'
"
!
)
'
#
$
!
%
#
$
"
%
)
[
]
&
(eq. S1)
[
]
훿푡
=
!
'
"
!
)
'
!
#
$
!
%
+
"
#
$
"
%
)
[
]
&
(eq. S
2
)
Solving for the maximum concentration of
B
, we set eq
uation
S2 to zero and find eq
uation
s
S3
-
S5
.
!
#
$
!
%
=
"
#
$
"
%
(eq. S
3
)
ln
'
!
)
!
=
ln
(
"
)
"
(eq. S
4
)
ln
'
!
)
ln
(
"
)
=
'
!
"
)
(eq. S
5
)
Therefore, the
irradiation
time,
t
,
which maximizes the concentration of the Ni(I)
bpy halide
species is given by equation S6.
=
ln
'
!
)
ln
(
"
)
'
!
"
)
(eq. S
6
)
8
These irradiation times were used for the preparation of the Ni(I)
bpy halide complexes
as reported
below.
More detailed modelling of the
photogeneration of the Ni(I) complexes
using 370 nm
incident light
is provided
in Section S1.5.
Table S
1
.
Summary of
the optimized
first
-
order rate constants for the
[
A
B
,
B
C
] reaction model
described previously
1
and the irradiation time
to maximize the Ni(I) concentration.
Parent Ni(II) Complex
Ni(I) Complex
k
p
(x10
-
2
min
-
1
)
k
d
(x10
-
2
min
-
1
)
t
(min)
Ni(II)(
t
-
Bu
bpy)(
o
-
tolyl)Cl
1
-
Cl
4.1
± 0.4
0.70
± 0.03
52
Ni(II)(
t
-
Bu
bpy)(
o
-
tolyl)Br
1
-
Br
8.1
± 0.8
0.26
± 0.09
44
Ni(II)(
t
-
Bu
bpy)(
o
-
tolyl)I
1
-
I
7
.
7
± 0.
3
0.
08
± 0.0
1
60
Ni(II)(bpy)(
o
-
tolyl)Cl
2
-
Cl
3.3
± 0.5
0.5
b
67
Ni(II)(
MeOOC
bpy)(
o
-
tolyl)Cl
3
-
Cl
15.0
± 0.8
0.27
± 0.06
27
a
Data
for
1
-
I
are
given in Supporting Information Section S
1.
5
.
b
No value for
k
d
was found for
2
-
Cl
, so w
e
have approximated it as
0.5 x10
-
2
M
-
1
min
-
1
,
i.e.,
an intermediate
value
between
1
-
Cl
and
3
-
Cl
.
Ni(I)(
t
-
Bu
bpy)Cl,
1
-
Cl
.
Air
-
and moisture
-
free
i
rradiation of
the
parent Ni(II) compound,
Ni(II)(
t
-
Bu
bpy)(
o
-
tolyl)Cl
, for
t
=
~
50 minutes
afforded
the title compound
.
UV
-
vis (THF): λ
1
=
660
nm
(
15,152 cm
-
1
)
, λ
2
=
422
nm, (
23,
7
00 cm
-
1
).
EPR
(2
-
MeTHF
,
T = 5 K,
frequency = 9.637
GHz, power = 2.2 mW, modulation amplitude = 8 G
):
g
z
=
2.248, g
x
= 2.050, g
y
= 2.070, g
iso
=
2.123.
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
t
=
~
45 minutes,
afforded the title compound.
UV
-
vis (THF):
λ
1
=
6
53
nm (
15
,
314
cm
-
1
), λ
2
=
386
nm, (
2
5
,
906
cm
-
1
).
EPR (2
-
MeTHF,
T = 5 K, frequency = 9.637
GHz, power = 2.2 mW, modulation amplitude = 8 G
):
g
z
=
2.255
, g
x
=
2.042
, g
y
= 2.07
9
, g
iso
=
2.12
5
.