of 54
Supporting Information
for
Light Enhanced
Fe
-
M
ediated
Nitrogen Fixation:
Mechanistic
I
nsights
R
egarding
H
2
Elimination
,
HER
,
and
NH
3
G
eneration
Dirk J. Schild and Jonas C. Peters*
Division of Chemistry and Chemical Engineering,
California Institute of Tec
hnology (Caltech), Pasadena, California
91125, United States
Corresponding Author
*
jpeters@caltech.edu
.
S
1
T
able of Contents:
Experimental Section
................................
................................
................................
..............
S
2
NMR Spectra
................................
................................
................................
............................
S
9
IR Spectra
................................
................................
................................
...............................
S
23
Cyclic Voltammog
rams
................................
................................
................................
.........
S
26
EPR Spectra
................................
................................
................................
...........................
S
28
Mӧssbauer Spectr
a
................................
................................
................................
................
S
31
UV
-
vis Spectra
................................
................................
................................
.......................
S
32
Catalytic experiments
................................
................................
................................
............
S
35
Crystallographic Details and Tables
................................
................................
....................
S
43
DFT Calculations
................................
................................
................................
...................
S
51
Supplementary References
................................
................................
................................
...
S
53
S
2
Exp
erimental Section
General considerations.
All manipulations were carried out using standard Schlenk or glovebox
techniques under an N
2
atmosphere. Unless otherwise noted, solvents were deoxygenated and dried
by thoroughly sparging with
a
r
gon
gas followed by p
assage through an activated alumina
column
in the
solvent
purification system by SG Water, USA LLC. 2
-
MeTHF was degassed by three
free
ze
-
pump
-
thaw
cycles, followed by drying over NaK to remove traces of water.
Deuterated
solvents were purchased from Cambri
dge Isotope Laboratories, Inc., degassed, filtered through an
alumina plug, and dried over 3Å molecular sieves prior to use.
All reage
nts were purchased from
commercial vendors and used without further purification unless stated otherwise.
P
2
P
Ph
FeBr
2
(
3
)
a
nd P
2
P
Ph57
FeCl
2
,
1
[H(OEt
2
)
2
][BAr
F
4
] (BAr
F
4
= tetrakis(3,5‐bis(trifluoromethyl)phenyl)borate),
2
Cp*
2
Co,
3
and KC
8
4
were synthesized following literature procedures.
Physical Methods.
NMR
spectra were recorded at room temperature unless
otherwise noted.
1
H
,
13
C
and
29
Si
chemical
shifts are reported in ppm
relative t
o
tetramethylsilane
, using residual solvent proton and
13
C
resonances as internal standards.
29
Si NMR chemical shifts were determined from 29Si
-
HMBC
two
-
dimensional spectra
15
N and
31
P
and chemical shifts are reported
relative to
CH
3
NO
2
and
85
%
aqueous H
3
PO
4
respectively
.
Solution phase magnetic measurement were performed by the
method of Evans.
5
IR
spectra were
obtained using a Bruker Alpha Platinum ATR spectrometer with OPUS software
in a glovebox under an N
2
atmosphere.
UV
-
Vis
measure
ments were collected using a Cary 50 instrument with Cary WinUV software.
X
-
band EPR
spectra were obtained on a Bruker EMX spectrometer
on 2
-
5 mM solutions prepared
as frozen glasses in 2
-
MeTHF. Samples were collected at powers ranging from 20 μW to
2
mW
a
nd modulation amplitudes of 1
5 Gauss
. Spectra were simulated
using
the
Easyspin
suite of
programs with Matlab 2018
.
Mössbauer
spectra
were recorded
on a spectrometer from SEE Co.
operating in the constant
acceleration mode in a tran
smission geometry. Spectra were recorded with the temperature of the
sample maintained at 80 K. The sample was kept in an SVT
-
400 Dewar from Janis. The quoted
isomer shifts are
relative to
the centroid o
f the spectrum of a metallic foil of α
-
Fe at room
tem
perature. Data analysis was performed using the program
WMOSS
(www.wmoss.org) and
quadrupole doublets were fit to Lorentzian lineshapes.
Cyclic voltammetry
measurements were carried out in a glovebox un
der an N
2
atmosphere in a one
-
compartment cell using a CH Instruments 600B electrochemical analyzer. A glassy carbon
electrode was used as the working electrode and a carbon rod was used as the auxiliary electrode.
The reference electrode was AgOTf/Ag in T
HF isolated by a CoralPor™ frit (obtained from BASi).
The ferrocenium/ferrocene couple (Fc
+
/Fc) was used as an external reference. THF solutions of
electrolyte (0.1 M [NBu
4
][PF
6
]) and analyte were also prepared under an inert atmosphere
.
Hydrogen Analysis
.
The headspace of reaction flasks was analyzed by gas chromatography to
quantify H
2
evolution with an Agilent 7890A gas chromatograph (HPPLOT U, 30 m, 0.32 mm i.d.,
30
°
C isothermal, 1 mL/min flow rate, N
2
carrier gas) using a thermal conductivity detector
.
S
3
X
-
Ray Crystallography.
X
-
ray diffraction studies were carried out at the Caltech Division of
Chemistry and Chemical Engineering X
-
ray Crystallography Facility on a Bruker three
-
circle
SMART diffractometer
with a SMART 1K CCD detector, APEX CCD detector, or Bruker D8
VENTURE Kappa
Duo PHOTON 100 CMOS detector. Data were collected at 100 K using Mo
Kα radiation (λ = 0.71073 Å) or Cu Kα radiation (λ = 1.54178 Å). Structures
were solved
by
direct
or
Patterson m
ethods using SHELXS and refined against F2 on all data by
full
-
matrix
least s
quares
with SHELXL
-
97.68 All non
-
hydrogen atoms were refined anisotropically. All hydrogen atoms
were placed
at
geometrically calculated positions and refined using a riding model. T
he isotropic
displacement parameters of all hydrogen atoms were fixed at 1.2
(1.5 for methyl groups) times the
Ueq of the atoms to which they
are bonded
.
See below for any special refinement details for
individual data sets.
Combustion analysis
measurements were collected using a PerkinElmer 2400 Series II CHN
Elemental Analyzer
.
C
omputational methods
Geometry optimizations were performed using the Gaussian
09
package
all optimizations.
6
The
TPSS
functional
7
was employed
in combination
with
def2
-
TZVP
8
basis set
on transition metals and a def2
-
SVP
8
basis set
fo
r
all
remaining atoms in
frequency calculations
and
geometry
optimizations.
Experimental
P
2
P
Ph
:
A
1.6 M
n
-
BuLi
solution (
6.5 mL,
10.4 mmol) was added
dropwise
to
a stirring solution of
(2
-
bromophenyl)diisopropylphosphine
(2.83 g, 10.3 mmol) in 40 mL diethyl
ether at
-
78 °C.
Following the addition,
t
he
light
-
yellow
reaction mixture was stirred for 90 minutes at
-
78 °C
.
P,P
-
dichl
or
ophenyl
phosphine (0.924 g, 5.1 mmol) in 6 mL diethyl ether
was
added
over 30 minutes,
resulting
in a color chan
ge to red. The
yellow
suspension
obtained
after
warm
ing
to room
temperature overnight
,
wa
s brought into the glovebox
an
d
filtered
over
celite
.
The
flask
w
a
s rinsed
four times with 8 mL diethyl ether
and the
resulting solutionswere
subsequently passed over
celite
and combined with the filtrate
. The solvent of the combined filtrates
wa
s removed
in vacuo
,
yielding
a
pale
yellow
powder. The po
wder
wa
s washed with pentane (3 x 5 mL) and dried under
vacuum to give P
2
P
Ph
(
1
)
as a white solid
(1.23 g,
2.5 mmol, 47 %)
evident by
comparing
spectroscopic properties with previously reported spectra.
1
1
H NMR (
Benzene
-
d
6
, 400 MHz) δ ppm
7.49
7.40
(m, 2
H), 7.39
7.31 (m, 2H), 7.08
(t, J = 6.7 Hz, 7H), 6.97 (t, J = 7.5 Hz, 2H), 2.11
(td, J = 7.0, 2.6 Hz, 2H), 1.98 (hept, J = 7.1
Hz, 2H), 1.18 (td, J = 13.8, 7.0 Hz, 12H), 0.92
(ddd, J
= 32.8, 11.5, 7.0 Hz, 12H).
13
C NMR (C
6
D
6
, 101 MHz) δ ppm 148.42 (
m), 1
42.42 (m), 139.73 (dt),
135.64 (d), 134.88 (m), 132.44 (m), 128.91 (s), 128.45 (d), 24.94 (m), 20.56 (m), 19.88 (m).
31
P{1H} (C
6
D
6
, 162 MHz) δ ppm
-
2.17 (dd,
3
J
PP
= 158.7,
3
J
PP
= 147.0 Hz, 2P, P
-
Ar),
-
14.26 (dt,
3
J
PP
= 158.7,
3
J
PP
= 147.0 Hz, 1P, P
-
Ph).
(
P
2
P
Ph
)
FeBr
(
4
)
:
A dark purple solution of
3
(173.0 mg, 243 μmol)
dissolved in 8 mL THF
was
stirred
over sodium amalgam (5.8 mg, 252
μ
mol
)
for 2
h
at room
temperature
during which
the
color changed to
dark
red. The red solution was filtered over celite and d
ried
in vacuo
. The
resulting
red
solid wa
s extracted with
4 mL
Et
2
O and filtered over celite.
Washing the red solid
4
times
with
1.5 mL pentane
yield
e
d
P
2
P
Ph
FeBr as a red solid (
99.8 mg, 158 μmol 65%
).
Crystals suitable for
XRD were obtained by vapor diffus
ion of pentane into a benzene solution of P
2
P
Ph
FeBr.
1
H NMR
(400 MHz, Benzene
-
d
6
) δ 124.74 (2H), 104.79 (2H), 17.85 (2H), 7.96 (6H), 6.46,4.89
, 3.84
(2H),
2.41 (2H), 1.02 (2H),
-
2.64 (6H),
-
7.19 (6H),
-
17.74 (2H),
-
20.57 (
1H).
UV
-
Vis (Benzene, nm {cm
-
S
4
1
M
-
1
}):
320 {6950}, 375 {5225}, 433 {4785}, 830 {1315}.
μ
eff
(C
6
D
6
, Evans Method, 25 °C):
4.11 μ
B
. Anal: calculated for C
30
H
41
BrFeP
3
: C 57.17, H 6.56 fo
und:
C 56.83, H 6.58
[
(
P
2
P
Ph
)
Fe
(
H
)
]
2
N
2
)
(
1
)
:
A 20 mL vial containing
4
(97.4 mg, 154.5 μmol) in 10 mL to
luene
wa
s cooled down to
78 °C. 6.1 mL of an 0.25 M NaHBEt
3
solution
in toluene
was
added after
which the mixture
was
stirred at
-
78 °C for 30 minutes
followed by 2 h at room
temperature
. Upon
warming to room temperature
the color
change
d
from dark red to forest green. The s
olvent was
removed
in vacuo,
after which the residue was extracted with
6
mL pentane.
Reducing the solvent
to 3 mL and
storing at −35 °C
yielded
1
as green crystals
(
50.1 μmol,
61 %)
, as was evident by
comparing the spectroscopic properties with
previously
reported spectra.
1
1H NMR (THF
-
d
8
, 500
MHz) δ ppm 8.15 (d, J = 7.5 Hz, 2H), 7.52 (d, J = 7.5 Hz, 2
H), 7.43 (t, J = 7.3 Hz, 2H), 7.26 (t, J
= 7.3 Hz, 2H), 7.14 (t, J = 7.3 Hz, 2H
), 6.63 (d, J = 7.4 Hz, 2H), 6.12 (t,
J = 7.5 Hz, 1H), 2.99
(broad s, 2H), 2.59 (broad s, 2H), 0.
72 (m, 6H),
0.42 (m, 6H).
(
P
2
P
Ph
)
Fe(N
2
)
2
(5)
from 3
:
50 mL of a
THF
solution of
3
(555.8 mg, 782 μmol) was stirred over
sodium
mercury
amalgam (36.
7 mg, 1.596 μmol
, 9.6 g Hg) for
16
h at room temperature during
which the color changed to
wine r
ed
. The THF solution was filtered over celite, and the solvent
was subsequently removed
in vacuo
. The
material was
extracted with pentane
40
mL and filtered
ov
e
r celite. Cooli
ng down the filtrate down to
35
°C yields crystalline P
2
P
Ph
Fe(N
2
)
2
(
205.2
mg,
33
9
μ
mol
43
%). Additional product can be obtained by cooling down the concentrated mother
liquor.
No satisfactory elemental analysis could be obtained, with C an
d H
percentages slightly
higher
than expected
. The nitrogen content
wa
s consistently low, which i
s likely due to the loss of
an N
2
ligand.
The
equilibrium discussed in the main text
also hampers obtaining quantitative
integrals in certain regions.
1
H NMR (
400 MHz, Benzene
-
d
6
) δ 7.63 (t, J = 6.3 Hz, 2H), 7.50 (dd,
J = 6.0, 3.9 Hz, 2H), 7.12
6.75 (m,
9H), 2.86
2.53 (m, 4H), 1.57
1.40 (m, 6H), 1.35
0.96
(m, 18H),
13
C NMR (101 MHz, THF) δ 147.69, 131.47, 130.21, 129.07, 128.66, 127.29, 32.49,
27.
99, 19.
29, 18.84
,
31
P NMR (162 MHz,
Benzene
-
d
6
) δ 122.76 (
t, J = 63.0 Hz
, 1H
), 100.26 (d, J
= 63.0 Hz
2P
).
IR (ATR, THF C
6
D
6
film):
ν
N
2
= 2065 cm
1
, 2005 cm
1
.
UV
-
Vis (Et
2
O, nm {cm
-
1
M
-
1
}): 251 {25000}
,
322 {8816}, 405 {5480}, 490 {3820}, 830
(P
2
P
Ph
)
Fe(N
2
)
2
(5) f
rom 4
: A 7 mL THF solution of
4
(81.0 mg, 128 μmol)
was stirred over sodium
mercury amalgam
(3.6
mg, 156 μmol)
for 1 hour and subsequently filtered over celite. THF was
remove
in vacuo
and the residue was extracted with 6 mL pentane and filtered over celit
e. Cooling
the solution to −35 °C yields P
2
P
Ph
Fe(N
2
)
2
as a crystalline solid (37.8 mg, 62 μmol,
48%).
Additional product can be obtained by cooling down the concentrated mother liquor.
(
P
2
P
Ph
)
57
Fe(N
2
)
2
(
57
5)
: Complex
57
5
was prepared using the synthetic p
rocedure for
5
with
P
2
P
Ph57
FeCl
2
instead. The
1
H NMR spectrum matched that of
5
, while additional
coupling with
57
Fe
was
present
in the
31
P NMR spectrum.
31
P NMR (162 MHz, Benzene
-
d
6
) δ 122.76 (
dt,
2
J
PP
= 64.5
Hz,
1
J
FeP
= 46.2 Hz
, 1P
), 100.26 (
t
, J = 63.0
Hz
, 2P
).
[
(
P
2
P
Ph
)
Fe]
2
μ
N
2
(6)
: An NMR tube containing
5
(20.5 mg, 33.8 μmol) in 0.6 mL toluene
-
d
8
was
freeze
-
pump thawed three times, stored for 4 hours and freeze
-
pump thawed three
additional times.
A
31
P NMR spectrum was recorded to ensure full conversio
n to
6
.
During the cycles, th
e color
changes from maroon to a dark purple.
If
5
was still present, addition
al
freeze
-
pump thaw cycles
were performed
until the signal corresponding to
5
was
negligible
.
Attempts to isolate the product
as a
crystal
li
ne
solid were unsucce
ssful.
1
H NMR (500 MHz,
Toluene
-
d
8
) δ 7.97 (d, J = 7.4 Hz,
2H), 7.44 (d, J = 7.3 Hz, 2H), 7.31 (
dd
, J = 7.3 Hz,
J = 7.3 Hz,
2H), 6.94 (
dd
, J = 7.4 Hz,
J = 7.3
Hz,
2H), 6.87
(dd
, J = 7.3 Hz,
J = 7.3 Hz,
2H), 6.46 (s, 2H), 5.79 (s, 1H), 5.35 (s, 2H), 5.07
(s,
S
5
2H), 1.61 (s, 6H),
1
.05 (s, 6H
), 1.01 (s, 6H)
0.43 (s, 6H).
31
P NMR (202 MHz, Toluene
-
d
8
, 298 K)
δ 184.84
.
31
P NMR (202 MHz, Toluene
-
d
8
,
203 K
) δ 130.42, 123.63
Small amounts of an unknown
species are present at 98.05 and 92.51 ppm, but they account fo
r less than 5%
(
P
2
P
Ph
)
Fe(N
2
)(H)
2
(
2)
: A Schlenk tube containing
5
(60.9 mg, 100 μmol) in THF (6 mL) was
freeze
-
pump
-
thawed
3
times
and exposed to 1
atmosphere of H
2
. The reaction was stirred
vigorously at room temperature for 24 hours before it was freez
e‐pump‐thawed
2
times
, re‐expose
d
to 1 atmos
phere of N
2
, and stirred for another 24 hours, during which the
solution
turned yellow.
The solvent was
removed
in vacuo
, yielding
2
quantitatively
(58.0 mg, 100 μmol, 100%)
. The
nature of the solid was determi
ned by comparing its NMR and IR fe
atures with those reported.
1
1
H
NMR (THF
-
d
8
, 500 MHz) δ ppm 8.09 (t, J = 6.4 Hz, 2H), 7.77 (d, J = 7.2 Hz, 2H), 7.40 (p, J = 7.2
Hz, 4H), 7.22
7
.15 (m, 5H), 2.67 (h, J = 6.8 Hz,
2H), 2.56
2.50 (m, 2H), 1.43 (q, J = 7.0 Hz, 6
H),
1.15
1.19 (m, 12H), 0.46 (q, J = 6.9, 6H)
,
-
9.43 (td, J = 38.2 , 15.7 H
z, 1H),
-
20.71 (td, J = 43.2 ,
15.6 Hz, 1H),
31
P NMR (162 MHz, Benzene
-
d
6
) δ ppm 119.2 (2P), 110.2 (1P).
IR (ATR, THF
C
6
D
6
film): 2071 cm
-
1
(
ν
N
2
), 1796 cm
-
1
(
ν
Fe
H).
[
(
P
2
P
Ph
)
Fe(N
2
)
2
(H)][BAr
F
4
]
(
7
):
A 20 mL vial containing
1
(16.4 mg, 14.5 μmol) in 1.5 mL
diethyl
ether
was
cooled down to
78 °C. A cooled solution of FcBAr
F
4
(32.8 mg, 31.2 μmol) in 1.5 mL
diethyl ether
was
added dropwise during which the color changes from green to orange. The
solution
was
stirred at
78 °C for 1 hour and
warmed to room tem
perature. The mixture
was
subsequently filtered over celite. The filtrate
was
layered with 10 mL pentane and stored at
35 °C
overnight
, which resulted
in the formation of
orange crystals (
41.0 mg, 27.8 μmol 96 %). The
obtained crystalline material was sui
table for X
-
ray diffraction.
1
H NMR (THF
-
d
8
, 400 MHz) δ
ppm 8.22
8.10 (m), 7.85
7.69 (m), 7.59
7.50 (m), 7.36 (t, J =
7.9, 1H), 7.30
7.27 (m), 7.27
7.21
(m), 6.60 (t, J = 9.3 Hz, 2H), 3.14
2.92 (m, 4H), 1.56
1.41 (m), 1.35
1.14 (m),
-
16.85 (dt (q), J =
54
.9, 1H).
11
B NMR (
THF
-
d
8
, 128 MHz) δ ppm
-
4.68 (s).
19
F NMR (THF
-
d
8
, 376 MHz) δ ppm
-
61.51 (s).
31
P{
1
H}
(THF
-
d
8
, 162 MHz) δ ppm 113.41 (overlapping dt, J = 34.6, 25.0 Hz, 103 1P,
PPh), 95.75 (dd, J = 29.5, 7.5 Hz, 2P, P
i
Pr
2
). IR (thin film from evaporation
of THF
-
d
8
; cm
-
1
): 2193
(
ν
N
N), 2162 (
ν
N
N), 2069 (
ν
Fe
H).
UV
-
Vis (Et
2
O, nm {cm
-
1
M
-
1
}):
367{2200}
Anal: calculated
for C
62
H
54
BF
24
FeN
4
P
3
: C 50.64, H 3.70 N 3.81, found: C 50.23, H 4.00, N 3.17
[
(
P
2
P
Ph
)
Fe(N
2
)(H)]
[K(18
-
crown
-
6
]
(
8
)
:
A
4 mL vial containing
1
(28.4 mg, 25 μmol) in THF
was
cooled down to −78 °C. Simultaneously, a 20 mL vial containing KC
8
(7.0 mg (51 μmol) and a stir
bar
was
cooled down. After
20
minutes, the THF solution containing
1
was
rapidly added to the
vial containing KC
8
. The mixture i
s stirred for 45
minutes at −78, after which 18
-
crown
-
6 (20.4
mg, 77 μmol) was added. The solution was stirred an additional 45 minutes at room temperature,
layered with 6 mL pentane and stored at −35 °C. Over four days black crystals formed
suitable for
X
RD
,
(35.4 mg, 40
μmol, 90%)
.
1
H NMR (400 MHz, THF
-
d
8
) δ 7.75 (q,
J
= 4.2 Hz, 2H), 7.43 (t,
J
= 4.2 Hz, 2H), 7.24 (t,
J
= 7.6 Hz, 2H), 7.04
6.88 (m, 6H), 6.83 (t,
J
= 7.2 Hz, 1H), 2.53 (d,
J
=
9.2 Hz, 2H), 2.42
2.26 (m, 2H), 1.24 (ddt,
J
= 21.2, 13.8, 6
.6 Hz, 6H), 0.88 (q,
J
= 6.8 Hz, 12H),
0.29 (q,
J
= 6.6 Hz, 6H),
-
9.69 (td,
J
= 68.8, 67.9, 27.3 Hz, 1H
).
31
P NMR (162 MHz, THF
-
d
8
) δ
ppm 120.62 (m, 1P) 119.89
118.98 (m. 2P).
IR
(
thin
film from evaporation of THF
-
d
8
; cm
-
1
):
1924
(
ν
N
N),
1733
(
ν
Fe
H)
Anal
: calculated for C
62
H
54
BF
24
FeN
4
P
3
: C 5
7
.
86
, H
7.
81
N
2.93
,
found: C 5
7
.23, H
7.34
, N
1.89
S
6
[
(P
2
P
Ph
)
Fe(N
2
)][K(18
-
crown
-
6]
(
9
):
A 20 mL vial containing
5
(20.6 mg, 34 μmol
) in 1.5 Ml THF
was
cooled down to −78 °C and 340 μL of a 100 μM potassium naphthalide
solution (34 μmol)
was
added after which the species
was
stirred. After one hour of stirring, an excess 18
-
crown
-
6
was added (18 mg, 68 μmol). The solution was stirred f
or an hour at room temperature and
subsequently layered with 6 mL pentane. Storing the
solution in the freezer for 24 h resulted in the
formation of dark crystals suitable for XRD (20.9 mg, 23.8 μmol 70%).
1
H NMR (400 MHz, THF
-
d
8
) δ
63.91
26.76, 20.51, 18.
28, 13.61
.
9.85
,
6.27
,
5.22, 1.04
,
-
2.15,
-
7.78
,
-
27.16 ppm.
IR (ATR,
THF C
6
D
6
film):
1872
cm
-
1
(
ν
N
2
),
Anal: calculated for C
62
H
5
3
BF
24
FeN
4
P
3
: C 5
7
.
64
, H
7.61
N
2.93
, found: C 5
7
.23, H
7.34
, N
1.89
[
(
P
2
P
Ph
)
Fe(N
2
)]
[
K
2
(THF)
3
]
(
10
):
A 20 mL vial
containing
5
(120.1 mg, 198 μmol) dissolved in
5
mL
NaK dried THF
was
cooled down to
78 °C. Simu
ltaneously, a 20 mL vial containing KC
8
(80
.2
mg
, 600 μmol)
and a stir bar was
cooled down to −78 °C. The cooled solution
containing
5
was added to the vial containing KC
8
after which the vial was rinsed with
0.5 mL THF
which was
subsequently added.
The so
lution was stirred for 15 minutes
. and
filtered
over celite
.
To assure the
frit
and celite are sufficiently dry,
3 mL
NaK
dried
THF was passed through the frit four times
before the reaction mixture
wa
s passed over celite
.
The
reaction
vial was rinsed
with
1 mL THF
,
and the wash was passed over celite.
The filt
rate
was
divided in
to
two
20 mL vials and each vial
was layered w
ith 15 mL pentane. Crystals
of
10
suitable
for XRD formed over a period of a week.
(110.1 mg, 126 μmol,
63%).
1
H NMR (400 MHz, THF
-
d
8
)
δ 7.87 (
m
, 2H), 7.51
7.34 (m, 2H),
6.89 (
m
, 8H), 6.71 (t, J = 7.2 Hz,
1H), 2.90
2.58 (m, 2H), 2.58
2.38 (m, 2H), 1.29 (
m
, J = 1
2
H),
0.81 (q, J = 5.8 Hz, 6H), 0.23 (q, J = 5.9 Hz, 6H).
13
C NMR (101 MHz, THF
-
d
8
) δ 157.27, 154.67,
153.04, 131.46, 129.79
, 128.62, 128.05
122.99 (m), 35.82, 29.2
3, 24.12
19.34 (m).
15
N NMR
(41 MHz, THF
-
d
8
) δ 2.36,
-
25.91.
31
P NMR (162 MHz, THF
-
d
8
) δ 113.13 (d, J = 33.8 Hz), 95.15
(t, J = 33.8 Hz)
.
No satisfactory combustion analysis could be obtained.
[
(
P
2
P
Ph
)
Fe
(
NNSiMe
3
)]K
(11
-
NNSiMe
3
)K
:
A 20 mL vial containing
5
(
55.9
mg,
92
μmol,
in
5
mL NaK dried THF was cooled down to
-
78 °C in a glovebox
Coldwell
after wh
ich it was added
to a vial
containing KC
8
(
37.4
mg,
276 μ
mol 3 equiv.) at
-
7
8 °C,
Stirring the solution for 30 minutes
resulted in a color
change to dark purple
. The cold suspension was filtered over celite, and
subsequently cooled down to
-
78 °C
followed by the addition of
TMSCl
(11.6 μL, 92 μmol)
which
resulted in an
immediate
col
or change to brown
. The mixture was sub
sequently stirred at
78 °C
for 30 minutes,
followed by
30 minutes
at room temperature
. Volatiles were removed
in vacuo
and
the residue was dissolved in benzene and filtered over celite. Benzene was removed
in vacuo
,
and
the
solid
washed
with pentane (3
x
2
mL) and filtered over
a
celite
plug
. The remaining
solids were
dissolved in diethyl ether and passed over the
same
celit
e plug
. Removal of diethyl ether
in vacuo
yields [P
2
P
Ph
Fe(NNTMS)]K (
35
mg,
54
μ
mol
, 58%
)
. Crystals suitable for XRD coul
d be grown
by layerin
g a concentrated benzene solution with pentane.
1
H NMR (C
6
D
6
, 400 MHz): δ 7.84 (m,
2H), 7.68 (d,
3
J
HH
= 6.69 Hz, 2H), 7.10
-
6.96 (m, 6H), 6.66
-
6.42 (m, 3H), 2.99
-
2.76 (m, 2H), 2.31
-
2.17 (m, 2H), 1.59
-
1.40 (m, 6H), 1.33
-
0.89 (m, 18H), 0.
38 (s, 9H, Si(CH
3
)
3
)
;
29
Si NMR (
7
9 MHz,
C
6
D
6
,
HMBC) δ:
4
.
72
(s, N
-
SiCH3).
13
C NMR (101 MHz,
C
6
D
6
) δ 130.65 (d,
J
= 10.4 Hz), 127.98,
127.54 (d,
J
= 6.0 Hz), 126.48
125.86 (m), 125.54 (d,
J
= 11.5 Hz), 32.72 (t,
J
= 9.4 Hz), 28.26
(d,
J
= 8.4 Hz), 21.36
19.79 (m), 0.
98,
-
1.11.
31
P NMR (162 MHz, C
6
D
6
) δ 117.48 (d,
J
= 16.7
Hz, 2P, PAr), 109.12 (t,
J
= 16.6 Hz, 1P, PPh).
Anal: calculated for C
33
H
56
FeKN
2
P
3
Si
: C 5
7
.
38
, H
7.81
N
4.06
, found: C 5
7
.
17
, H
7.
07
, N
3.61
S
7
[
(P
2
P
Ph
)
Fe
(
NNSi
i
Pr
3
)]K
(1
1
-
NNSi
i
Pr
3
)
: P
2
P
Ph
Fe(N
2
)
2
(
50
.
1
m
g,
83
μmol
)
in
2
.5
mL NaK dried
THF was cooled down to
78 °C in a glovebox
coldwell and passed over a pipette with a thin layer
of KC
8
(4 mm)
.
The mixture was passed over the pipette three times during which the color changed
to dark purple.
T
iPSOTf
(
20 μ
L, 7
4 μmol
was added upon which an immediate color change to
orange
brown was observed. The mixture was subsequently stirred at
78 °C for 30
minutes, after
which it was taken out of the coldwell and stirred at room temperature for 30 minutes. Volatiles
we
re removed
in vacuo
and the residue was dissolved in benzene and filtered over celite. Benzene
was removed
in vacuo
and
the remaining residue washed with
HMDSO
(
5
x
1.5
mL) and filtered
over celite. The remaining brown residue in the vial an
d
on the celite
was dissolved in diethyl ether.
Removal of diethyl ether
in vacuo
yields [P
2
P
Ph
Fe(
NNT
i
P
S
)]K in
75
%
yield
(
43.0
mg
, 55
μmol
).
1
H NMR (300 MHz, Benzene
-
d
6
) δ 7.89 (s, 3H), 7.69 (d,
J
= 6.7 Hz, 2H), 7.09, (s, 6H), 6.62 (s,
3H), 3.55 (s
, 3H)
2.88 (s, 2H), 2.62 (s, 2H), 1.50 (td,
J
= 14.5, 13.7, 6.4 Hz, 1
2
H), 1.38
1.14 (m,
35H), 0.97
0.81 (m, 1
2
H).
31
P NMR (121 MHz,
Benzene
-
d
6
) δ 118.22 (d,
J
= 17.9 Hz), 1
11.69
(
t
,
J
= 17.9 Hz)
.
IR (ATR, C
6
D
6
film):
1469
cm
-
1
(
ν
N
2
),
S
tochiometric reactivity
Addition of H
2
to 5 at
-
78 °C
. The headspace of a J
-
Young NMR tube containing
5
(5.9 mg,
9.7μmol)
was
degasse
d
once
by a freeze
-
pump
-
th
aw cycle
. The tube
wa
s warmed
transferred
into
a dry ice
acetone
bath
and one atmosphere of
H
2
was
added. The
cold
tube
was
rapidly shaken for
5 seconds and inserted into the precooled NMR spectrometer.
Addition of H
2
to 6 at
-
78 °C
. To a J
-
Young NRM tube containing
6
, generated
in situ
according
to the preparation described above,
was
added on
e atmosphere of H
2
.
The
cold
tube
was
rapidly
shaken for 5 seconds and inserted into the precooled NMR spectrometer.
General procedure for the synthesis of [
(
P
2
P
Ph
)
Fe(N
2
)
2
(H)][BAr
F
4
] (7) from 1, 2 or 5 with
HBAr
F
4
:
A
20 mL vial containing
1
,
2
, or
5
(9.4 μmol for
1
, 18.8 μmol for
2
and
5
) in diethyl ether
(1 mL) was chilled to
78 °C in the glovebox coldwell. In a separate 4 mL vial, a diethyl ether
solution of HBAr
F
4
(0.019 g, 18.4 μmol, 250 μL diethyl ether) was chi
lled to
78 °C. Both solutions
were allowed to cool for 20 min before th
e HBAr
F
4
solution was added to the vial containing
1
,
2
or
5
at
-
78 °C in one shot. The vial containing HBAr
F
4
was subsequently rinsed with 250 μL of
pre
-
chilled diethyl ether and the
rinsing w
as
added to the vial containing. The reaction mixture was
stirred at
78 °C for 1 hour and 15 minutes before it was warmed to warm to room temperature.
Analysis by NMR and I
R spectroscopy confirms the nature of the product
as
7
.
NMR analysis of a
ddition of HBAr
F
4
to 5 at
-
78 °C
:
5
(5.9 mg, 9.7μmol)
was
dissolved in 0.4
mL THF
-
d
8
and added to a J
-
Young NMR tube at
78 °C. HBAr
F
4
(10.3 mg, 10.7 μmol)
was
cooled to
78 °C
and added to the NMR tube. The
col
d
tube
was
rapidly shaken for 5 seconds
,
taken out of the glovebox
and inserted
into the precooled NMR spectrometer at
78 °C.
Oxidation of [
(
P
2
P
Ph
)
Fe(
NNSiMe
3
)]K a
t room temperature.
To a stirring solution of
[P
2
P
Ph
Fe(NNTMS)]K (13.0 mg, 17 μmol) in 3 mL THF was added [Cp*
2
Co][PF
6
] (8.2 mg, 17 17
μmol) suspended in 1 mL THF. The mixture was stirred for 24 hours, followed by removal of the
solvent
in vacuo
.
Extracting
the solid twice with 5 mL pentane results in an off
-
white residue. The
pentane extracts were combined and removal of the solvents
in vacuo
gives a brow solid (10 mg).
Analysis of the solid by NMR spectroscopy reveals the presence of
5
and cobaltocene.
S
8
Oxi
dation of [(P
2
P
Ph
)Fe(
NNSiMe
3
)]K
(11
-
NNSiMe
3
)
at −78 °C.
To a cooled stirring solution of
[
(
P
2
P
Ph
)
Fe(N
N
TMS
)]K (4 μmol) in 1 mL 2
-
MeTHF at −78 °C was added [Cp*
2
Co][PF
6
] (8.2 mg,
17 μmol) suspended in 0.5 mL 2
-
MeTHF. The solution was stirred for 5 minutes
a
t −78 °C after
which the sample was frozen. The frozen solution was briefly thawed and a 300 μL aliquot was
transferred to a precooled EPR tube which was subsequently frozen.
Add
itional
EPR spectra were
recorded for the frozen samples stored at −78 °C for
24 hours.
(P
2
P
Ph
)Fe(
NN
i
Pr
3
) (12
-
NN
i
Pr
3
)
:
A
cooled stirring solution
of
[
(
P
2
P
Ph
)
Fe(NN
TiPS
)]K
(
15
.0 mg,
19 μmol) in 1 mL was added to
[Cp*
2
Co][PF
6
]
(9.1 mg, 19 μmol) at −78 °C. The solution
was
stirred at −78 for 10 minutes followed by 10 minutes at room te
mperature. The solvent
was
removed
in vacuo
and the residue extracted with pentane. Filtering over celite and removal of the
solvent in vacuo gives a product characterized as
12
TiPS
.
1
H NMR (300 MHz, Benzene
-
d
6
)
δ
1
H
NMR (400 MHz, THF
-
d
8
) δ 12.22 9.31 7.2
4 5.90
,
4.92
,
3.39
,
2.36
1.
63
0.48
.
IR (ATR, THF
film):
1659
cm
-
1
(
ν
N
2
),
S
9
NMR Spectra
Figure S
1
1
H NMR spectrum of
(
P
2
P
Ph
)
FeBr (
4
) in C
6
D
6
at room temperature
Figure
S
2
1
H NMR spectrum of
(
P
2
P
Ph
)
Fe(N
2
)
2
(
5
) in C
6
D
6
at room
temperature
. Additional broad peaks corresponding to
6
are present due to the equilibrium as described in the main text.
Figure
S
3
13
C NMR spectrum of
(
P
2
P
Ph
)
Fe(N
2
)
2
(
5
) in
THF
at room temperatur
e