Bromine Cation Initiated vic -Diphosphination of Styrenes with Diphosphines under Photoredox Catalysis

Article abstract of DOI:10.1055/s-0037-1609447

An N -bromosuccinimide (NBS)-initiated vic -diphosphination of styrenes with diphosphines proceeds under visible-light-promoted Ir(ppy) ₃ photoredox catalysis to deliver the corresponding 1,2-diphosphinoethane derivatives in good yields. The NBS is a bromine cation source and generates a bromophosphine, which undergoes a single-electron reduction by the excited iridium species to form phosphinyl radicals of key species in the diphoshination reaction. The newly developed photoredox catalysis demonstrates better reaction efficiency, functional group compatibility, and scalability than the previous photocatalysis using N -fluorobenzenesulfonimide (NFSI) and silylphosphine.

Full text of DOI:10.1055/s-0037-1609447

SYNTHESIS
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© Georg Thieme Verlag Stuttgart · New York
2018, 50, A–F
special topic
A
en
N. Otomura et al.
Special Topic
Synthesis
Bromine Cation Initiated vic-Diphosphination of Styrenes with
Diphosphines under Photoredox Catalysis
Nobutaka Otomura
additional example
Yuto Okugawa
N
Koji Hirano*
0
0
0
0
0-
0
0
1
9-
7
5
2
1-
9
8
5
CF3
Ir
S
Masahiro Miura*
0
0
0
0
0-
0
0
1
8-
2
8
8
6-
4
3
9
N
N
F3C
Ph2P
S
CF3
CF3
S
PPh2
Department of Applied Chemistry, Graduate School of
Engineering, Osaka University, Suita, Osaka 565-0871,
Japan
k_hirano@chem.eng.osaka-u.ac.jp
miura@chem.eng.osaka-u.ac.jp
S
P
P
(0.5 mol%)
+
NBS (20 mol%)
Ph2P PPh2
DCE, blue LEDs (2.4 W)
then S8
1.0 mmol scale, 90%
56%
Published as part of the Special Topic Photoredox
Methods and their Strategic Applications in Synthesis
Received: 19.01.2018
Accepted after revision: 13.03.2018
Published online: 04.04.2018
cation: an NBS-initiated vic-diphosphination of styrenes
with diphosphine under visible-light-promoted Ir(ppy)3
photoredox catalysis is described [Scheme 1 (c)]. The newly
developed reaction system shows better reaction efficiency
and functional group tolerance than the previous ones. We
also note that Ogawa and co-worker reported a relevant
phosphinylphosphination of aliphatic terminal alkenes
with Ph2(O)P–PPh2, but attempts to apply styrenes re-
mained unsuccessful.6
DOI: 10.1055/s-0037-1609447; Art ID: ss-2018-c0036-st
Abstract An N-bromosuccinimide (NBS)-initiated vic-diphosphination
of styrenes with diphosphines proceeds under visible-light-promoted
Ir(ppy)3 photoredox catalysis to deliver the corresponding 1,2-diphos-
phinoethane derivatives in good yields. The NBS is a bromine cation
source and generates a bromophosphine, which undergoes a single-
electron reduction by the excited iridium species to form phosphinyl
radicals of key species in the diphoshination reaction. The newly devel-
oped photoredox catalysis demonstrates better reaction efficiency,
functional group compatibility, and scalability than the previous photo-
catalysis using N-fluorobenzenesulfonimide (NFSI) and silylphosphine.
a) Cu-catalyzed conditions with silylphosphine (1st generation catalyst)
Ph2P
Ar
cat. Cu/NHC
+
Me3Si PPh2
Ar
PPh2
MnO2
Key words diphosphination, diphosphine, ligand, photocatalyst,
styrene
pyridine N-oxide
b) Photoredox catalysis with silylphosphine (2nd generation catalyst)
Bisphosphines are indispensable organophosphorus
compounds in modern synthetic organic chemistry because
they are prevalent ligands for various transition-metal
complexes and catalysts.1 Particularly, 1,2-bis(diphenyl-
phosphino)ethanes (DPPEs) are promising bidentate ligand
frameworks owing to their uniquely rigid chelating nature.
Thus, the concise preparation of DPPE-type ligands is of
great importance for the development of highly active met-
al catalysts. The direct vic-diphosphination of readily avail-
able and robust alkenes seems to be an ideal protocol, but
still remains underdeveloped.2,3 In this context, we recently
Ph2P
Ar
cat. Ir(ppy)3
+
Me3Si PPh2
PPh2
Ar
NFSI
blue LEDs
c) Photoredox catalysis with diphosphine and NBS initiator
(3rd generation catalyst: this work)
cat. Ir(ppy)3
cat. NBS
Ph2P
Ar
+
Ph2P PPh2
PPh2
Ar
blue LEDs
Scheme 1 Development of the direct vic-diphosphination of styrenes
reported
a
copper-catalyzed vic-diphosphination of
styrenes with silylphosphines and MnO2/pyridine N-oxide
combined oxidant [Scheme 1 (a)].4 Subsequently, a more ef-
ficient photoredox catalyst based reaction system with
silylphosphine and N-fluorobenzenesulfonimide (NFSI) was
developed [Scheme 1 (b)].5 However, the second generation
catalysis still suffered from narrow functional group com-
patibility associated with the strong oxidation aptitude of
NFSI. Here, we wish to report the third generation catalyst
with a combination of photoredox catalysis and bromine
In our previous work [Scheme 1 (b)], we reported a
unique reactivity of silylphosphine Me3Si–PPh2 and no re-
activity of diphosphine Ph2P–PPh2 for the vic-diphosphina-
tion of styrene (1a). However, preliminary 31P{1H} NMR
studies with Me3Si–PPh2 and Ph2P–PPh2 showed similar
spectra when they were treated with NFSI.5 Thus, we rein-
vestigated the reactivity of Ph2P–PPh2 (2a) under Ir(ppy)3
photoredox catalysis. We consequently found that the care-
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–F

B
N. Otomura et al.
Special Topic
Synthesis
F3C
F
N
N
Ru2+
N
N
N
N
N
N
N
N
F
CF3
Ir+
–
Ir
2PF6
N
F
N
N
–
PF6
F
Ir(ppy)3
[Ir{dFCF3ppy}2(bpy)]PF6
Ru(bpy)3(PF6)2
Br
O
Cl
Cl
F
N(SO2Ph)2
Cl
Cl
Br
N
COOH
Br
H
NFSI
Br
Br1
Br
Br2
O
O
Br
HO
O
O
X = Cl: NCS
X = Br: NBS
X = I: NIS
N
N
X
N
Br
Br3
Br
Br
O
Eosin Y
O
Figure 1 Structure of reagents and catalysts employed
NFSI is the representative fluorine cation source, we tested
other halogen cation donors including NCS, NBS, and NIS
(entries 4–6). Gratifyingly, NBS improved the yield to 68%
1H NMR yield (entry 5). Although some bromine cation
sources also promoted the reaction (entries 7–10), NBS was
found to be best from the viewpoints of efficiency and re-
producibility. We surveyed several metal and organic photo-
S
Ir(ppy)3 (0.5 mol%)
NBS (20 mol%)
Ph2P
S
S8
PPh2
Ar
+
Ph2P PPh2
Ar
DCE, ambient temp
blue LEDs, 4.5 h
r.t., 30 min
1
2a
3-S
R = H: 3aa-S 87% (84%), [68% (63%)]
R = Me: 3ba-S 90% (78%), [60% (48%)]
R = MeO: 3ca-S 83% (69%), [58% (44%)]
R = CF3: 3da-S 73% (60%), [73% (66%)]
R = Cl: 3ea-S 83% (73%), [54% (45%)]
R = Br: 3fa-S 75% (67%), [42% (31%)]
R = Me2N: 3ga-S 32% (25%), [0%]
S
Ph2P
S
7
sensitizers again (entries 11–13); [Ir{dFCF3ppy}2(bpy)]PF6
PPh2
showed comparable performance, but we identified
Ir(ppy)3 to be better in view of the cost. Finally, the amount
of NBS could be reduced to 20 mol%, and we obtained the
desired diphosphinated product 3aa-S in 87% 1H NMR yield
and 84% isolated yield (entry 14). Under the optimal condi-
tions, the reaction could be conducted without any special
cautions to temperature and easily scaled up to 1.0 mmol
(entry 15). Additionally, no formation of diphosphinated
product 3aa-S was observed in the absence of Ir(ppy)3 or
light (entries 16 and 17).
R
S
Ph2P
S
S
S
Ph2P
S
Ph2P
S
PPh2
PPh2
PPh2
Me
Me
3ja-S 50% (41%)
3ia-S (82%)
[58% (51%)]
3ha-S 84% (69%)
[29%]
[66% (59%)]
With the newly developed conditions using diphos-
phine, we performed the vic-diphosphination of several
styrene derivatives 1. The representative results are shown
in Scheme 2. The reaction was compatible with electron-
donating and electron-withdrawing groups at the para po-
sition, including methyl, methoxy, trifluoromethyl, chloro,
and bromo substituents to give 3aa-S–3fa-S. In the case of
3ea-S and 3fa-S, hydrodehalogenated byproducts were not
detected, which is beneficial feature of photoredox cataly-
sis, compared to the first generation copper catalyst.4 More-
over, the reaction efficiency was generally higher than that
of the previous photoredox catalysis with silylphosphine
and NFSI.6 Particularly notable is the successful diphosphi-
nation of an aniline derivative to give 3ga-S; this substrate
did not give any detectable amount of product under the
second generation catalyst system. The meta- and ortho-
methyl-substituted styrenes as well as 2-vinylnaphthalene
S
S
Ph2P
Ph2P
S
PPh2
S
PPh2
N
3ka-S 29% (26%)
3la-S 35% (34%)
[0%]
[73% (71%)]
Scheme 2 Representative diphosphinated products 3-S. Yields deter-
mined by 1H NMR of the crude mixture; isolated yields in parentheses;
yields under previous conditions5 in square brackets. Reagents and con-
ditions: 1 (0.25 mmol), Ph2P–PPh2 (2a; 0.50 mmol), NBS (0.050 mmol),
Ir(ppy)3 (0.0013 mmol), DCE (3.0 mL), r.t., blue LED irradiation (2.4 W),
4.5 h, N2 then S8 (1.3 mmol of S atom), r.t., 30 min.
ful temperature control (<30 °C) upon addition of reagents
and more than 1:1 stoichiometry of Ph2P–PPh2 and NFSI en-
abled the diphosphination of 1a (Table 1, entries 1–3). Since
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–F

C
N. Otomura et al.
Special Topic
Synthesis
Table 1 Optimization Studies for vic-Diphosphination of Styrene with
Tetraphenyldiphosphine (Ph2P–PPh2) under Visible-Light-Promoted
Photoredox Catalysisa,b
Ir(ppy)3 (0.5 mol%)
NBS (20 mol%)
S
S8
Ar2P
S
+
Ar2P PAr2
Ph
r.t.
30 min
PAr2
DCE, ambient temp
blue LEDs, 4.5 h
Ph
1a
2
S
photocatalyst (0.5 mol%)
Ph2P
S
S8
additive
Ar =
Ar =
OMe
CF3
: 3ab-S 73% (64%)
: 3ac-S 66% (56%)
+
Ph2P PPh2
Ph
PPh2
r.t.
30 min
DCE, ambient temp
blue LEDs, 4.5 h
Ph
1a
2a
3aa-S
Entry Photocatalyst
Additive
(mol%)
Temp
Yieldd (%)
of 3aa-S
Scheme 3 Diphosphination of styrene with several substituted diphos-
phines. Yields determined by 1H NMR of the crude mixture; isolated
yields in parentheses.
controlc
1e
2
3
4
5
6
7
8
9
Ir(ppy)3
Ir(ppy)3
Ir(ppy)3
Ir(ppy)3
Ir(ppy)3
Ir(ppy)3
Ir(ppy)3
Ir(ppy)3
Ir(ppy)3
Ir(ppy)3
NFSI (300)
NFSI (150)
NFSI (75)
NCS (75)
NBS (75)
NIS (75)
no
0
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
no
29
59
10
68
12
0
To gain some mechanistic insight, the following experi-
ments were implemented (Scheme 4). The vinylcyclopro-
pane derivative 1m underwent the ring-opening diphosph-
1
ination selectively to provide 3ma′-S in 87% H NMR yield
[Scheme 4 (a)]. The usual ring-remaining product 3ma-S
was not detected at all, thus suggesting radical intermedia-
cy. We next performed 31P{1H} NMR studies to uncover the
role of NBS; upon treatment of diphosphine 2a with NBS in
DCE-d4, two new signals assigned to BrPPh2 (4) and imidyl-
phosphine 5 appeared, along with some unidentified peaks
[Scheme 4 (b)].9 Thus, we independently prepared 4 and 5
and tested their performance as the additive in the di-
phosphination of styrene (1a) with Ph2P–PPh2 (2a). Where-
as the bromophosphine 4 showed comparable activity to
NBS, imidylphosphine 5 resulted in a much lower yield of
3aa-S [Scheme 4 (c)]. These findings indicate that NBS is a
bromine cation source and initiates the diphosphination by
the in situ generation of truly active bromophosphine 4
from the diphosphine 2a.
On the basis of the above observations and literature in-
formation,10 we are tempted to assume the reaction mecha-
nism of 1a with 2a as follows (Scheme 5). The diphosphine
2a partially reacts with NBS to initially form BrPPh2 (4). A
single-electron transfer from the excited Ir(III)* to the bromo-
phosphine 4 is followed by fragmentation to form the phos-
phinyl radical 6. Actually, the bromophosphine 4 efficiently
quenched the fluorescence of Ir(ppy)3 (see the Supporting
Information for details). The radical addition to styrene (1a)
and subsequent back electron transfer to the Ir(IV) species
completes the Ir catalytic cycle together with generation of
a benzylic cation 8, which is readily trapped with the di-
phosphine 2a leading to the phosphonium cation 9. There
are two plausible pathways to the product 3aa from 9. One
is direct entry into the second catalytic cycle, in which the
cation 9 undergoes single-electron transfer, giving the
phosphinyl radical 6 along with the release of 3aa (path a).
Another is the reaction with Br–, forming 3aa with concom-
itant regeneration of BrPPh2 (path b). Although we cannot
strictly distinguish two distinct pathways, the path a is
more likely because MeOTf, a representative carbon-based
electrophile and analogue to the benzylic cation 8, also effi-
ciently promoted the diphosphination of 1a with 2a.11 At
present, we cannot completely exclude the possibility of an
CBr4 (75)
Br1 (75)
Br2 (75)
Br3 (38)
54
47
67
71
0
10
11
[Ir{dFCF3ppy}2(bpy)]PF6
Ru(bpy)3(PF6)2
Eosin Y
NBS (75)
NBS (75)
NBS (75)
NBS (20)
NBS (20)
NBS (20)
NBS (20)
12
13
4
14f
15f,g
16f
17f,h
Ir(ppy)3
87 (84)
95 (90)
0
Ir(ppy)3
no
none
no
Ir(ppy)3
no
0
a Reaction conditions: 1a (0.25 mmol), Ph2P–PPh2 (2a; 0.38 mmol), additive,
photocatalyst (0.0013 mmol), DCE (3.0 mL), r.t., blue LED irradiation (2.4
W), 4.5 h, N2 then S8 (1.3 mmol of S atom), r.t., 30 min.
b The structures of the catalyst and additive are given in Figure 1.
c The reaction temperature was kept <30 °C upon addition of any reagents.
d Determined by 1H NMR of the crude mixture. Isolated yields in parentheses.
e Previous report.5
f With 2.0 equiv of Ph2P–PPh2 (2a).
g Scale: 1.0 mmol.
h In the dark.
also furnished the corresponding products 3ha-S–3ja-S in
better yields than those of previous conditions. Additional-
ly, the strongly coordinating, thus highly challenging, 4-vin-
ylpyridine also provided 3ka-S albeit in a moderate yield.
On the other hand, β-substituted indene resulted in a lower
yield of 3la-S, and attempts to apply aliphatic alkenes such
as oct-1-ene remained unsuccessful (trace, data not
shown).
The greatest advantage of the third generation catalyst
is its accommodation of substituted diphosphine deriva-
tives 2 other than the parent 2a (Scheme 3). The 4-
methoxy- and 4-trifluoromethyl-substituted diphosphines
2b and 2c could be coupled with styrene (1a) to furnish the
electronically modified DPPE-type ligands 3ab-S and 3ac-S
in 64% and 56% isolated yields, respectively.8
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–F

D
N. Otomura et al.
Special Topic
Synthesis
a) radical clock experiment
Ir(ppy)3 (0.5 mol%)
NBS (20 mol%)
+
Ph2P PPh2
Ph
DCE, ambient temp
blue LEDs, 4.5 h
1m (trans/cis > 99:1)
2a
then
S8, r.t., 30 min
S
S
Ph2P
S
Ph
Ph2P
PPh2
PPh2
Ph
3ma-S
not detected
3ma′-S 87% (1H NMR)
S
via
•
PPh2
Ph
•
PPh2
3ma′-S
Ph
b) 31P{1H} NMR studies
O
+
Ph2P PPh2
+
Br PPh2
NBS
N
PPh2
DCE-d4
r.t.
2a (0.10 mmol)
(0.10 mmol)
5
4
O
δ 74.0 ppm
δ –14.5 ppm
δ 32.2 ppm
+
unidentified signals
c) control experiments with 4 or 5
S
Ir(ppy)3 (0.5 mol%)
additive (20 mol%)
S8
Ph2P
S
+
Ph2P PPh2
Ph
1a
PPh2
r.t.
30 min
DCE, ambient temp
blue LEDs, 4.5 h
2a
Ph
3aa-S
yield of 3aa-S (1H NMR)
additive
87%
NBS
4
5
77%
9%
Scheme 4 Experiments for mechanistic investigation
energy transfer mechanism, but the performance of photo-
catalysts observed in Table 1 seems to be less dependent on
the triplet energy.12
for column chromatography. Gel permeation chromatography (GPC)
was performed by LC-20AR (pump, SHIMADZU, 3.5 or 7.5 mL/min)
and SPD-20A (UV detector, SHIMADZU, 254 nm) with two in-line GPC
H-2001 (20 × 500 mm, particle size: 15 μm) and H-2002 columns
(20 × 500 mm, particle size: 15 μm) (preparative columns, Shodex,
CHCl3 eluent) or two in-line YMC-GPC T2000 (20 × 600 mm, particle
size: 10 μm) (preparative columns, YMC, CHCl3 eluent). Blue LED irra-
diation was conducted with 300 mm blue LED tape (2.4 W, 30 mm
distance from the reaction vessel) without any special temperature
control. Unless otherwise noted, materials obtained from commercial
suppliers were used as received. Ir(ppy)3 was available from TCI. DCE
was freshly distilled from CaH2 prior to use. The vinylcyclopropane
1m was synthesized from cinnamyl alcohol.14 Diphosphines 2 were
prepared according to the literature.4,15
In conclusion, we have developed an NBS-initiated vic-
diphosphination of styrenes with diphosphines under visi-
ble-light-promoted Ir(ppy)3 photoredox catalysis. The new-
ly developed protocol is operationally simpler and more ef-
ficient than the previously reported diphosphination sys-
tems.4,5 Particularly, much better functional group
compatibility is observed. The present photoredox catalysis
allows the diphosphine to be adopted in an otherwise chal-
lenging diphosphination of alkenes, and enables ligand syn-
thesis13 from readily available and abundant hydrocarbon
materials; this could accelerate the development of newly
designed and highly efficient bisphosphine-ligated transi-
tion-metal catalysts. Further elucidation of the detailed
mechanism and related phosphination chemistry are cur-
rently underway in our laboratory.
Diphenyl(succinimido)phosphine (5)
A 20-mL microwave tube was charged with succinimide (495 mg, 5.0
mmol) and then flushed with N2. THF (5.0 mL) was added, and the
solution was cooled to 0 °C. A 1.6 M soln of BuLi in hexane (3.2 mL, 5.0
mmol) was added dropwise, and the resulting suspension was stirred
at r.t. for 2 h. A solution of ClPPh2 (1.1 g, 5.0 mmol) in THF (1.0 mL)
was then added at 0 °C, and the obtained mixture was stirred at r.t. for
an additional 20 h. The resulting mixture was filtered through a pad
of Celite under an inert atmosphere. Evaporation of volatiles from the
1H, 13C{1H}, 19F{1H}, and 31P{1H} NMR spectra were recorded at 400,
100, 376, and 162 MHz, respectively, for CDCl3 solutions. HRMS data
were obtained by APCI using TOF. Silica gel (Wakosil C-200) was used
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–F

E
N. Otomura et al.
Special Topic
Synthesis
1H NMR (400 MHz, CDCl3): δ = 2.65 (ddd, J = 1.6, 13.1, 26.1 Hz, 1 H),
2.74 (s, 6 H), 3.49–3.59 (m, 1 H), 4.97 (ddd, J = 1.2, 11.4, 23.2 Hz, 1 H),
6.08 (d, J = 8.4 Hz, 2 H), 6.86 (d, J = 7.0 Hz, 2 H), 6.99–7.05 (m, 2 H),
7.06–7.12 (m, 1 H), 7.12–7.18 (m, 2 H), 7.22–7.28 (m, 1 H), 7.31–7.45
(m, 7 H), 7.51–7.60 (m, 3 H), 7.63–7.70 (m, 2 H), 8.25–8.34 (m, 2 H).
13C{1H} NMR (100 MHz, CDCl3): δ = 32.92 (dd, J = 5.0, 53.7 Hz), 39.73
(d, J = 50.5 Hz), 40.58 (2 C), 112.00 (2 C), 119.41 (d, J = 1.9 Hz), 127.61
(d, J = 12.5 Hz, 2 C), 127.77 (d, J = 12.1 Hz, 2 C), 128.69 (d, J = 11.8 Hz, 2
C), 128.99 (d, J = 11.3 Hz, 2 C), 130.43 (d, J = 3.4 Hz), 130.52 (d, J = 9.7
Hz, 2 C), 130.78 (d, J = 73.2 Hz), 130.80 (d, J = 78.7 Hz), 130.95 (d, J =
2.9 Hz), 131.07 (d, J = 5.5 Hz, 2 C), 131.40 (d, J = 2.8 Hz), 131.40 (d, J =
10.9 Hz, 2 C), 131.45 (d, J = 9.5 Hz, 2 C), 131.74 (d, J = 78.5 Hz), 131.81
(d, J = 2.7 Hz), 132.27 (d, J = 9.1 Hz, 2 C), 134.55 (d, J = 82.4 Hz), 149.74.
NBS
Ph2P PPh2
Br PPh2
4
2a
Ir(III)*
Ir(IV)
–
[ 4 ]
•
Ph2P
Br–
Ph
1a
PPh2
Ph
• PPh2
3aa
6
4
•
•
[ 9 ]
path b
PPh2
Ph
7
Br–
Ir(IV)
path a
31P{1H} NMR (162 MHz, CDCl3): δ = 43.09 (d, J = 60.7 Hz), 52.06 (d, J =
60.7 Hz).
+
Ph2P
PPh2
+
HRMS (APCI): m/z ([M + H]+) calcd for C34H34NP2S2: 582.1602; found:
582.1614.
PPh2
Ph
PPh2
Ir(III)
Ir(III)*
Ph
8
9
1,2-Bis(diphenylthiophosphinyl)-1-(4-pyridyl)ethane (3ka-S)
visible light
Prepared according to the GP, purification by GPC (CHCl3) gave the
product (37 mg, 0.07 mmol, 26%) as a yellow solid; mp 240.6–
242.6 °C.
1H NMR (400 MHz, CDCl3): δ = 2.72 (ddd, J = 1.5, 13.9, 27.2 Hz, 1 H),
3.47–3.58 (m, 1 H), 5.02 (ddd, J = 1.4, 11.8, 23.7 Hz, 1 H), 6.88–6.92
(m, 2 H), 7.03–7.10 (m, 2 H), 7.14–7.20 (m, 2 H), 7.20–7.32 (m, 2 H),
7.36–7.48 (m, 7 H), 7.58–7.63 (m, 3 H), 7.63–7.71 (m, 2 H), 7.92 (d, J =
5.6 Hz, 2 H), 8.26–8.34 (m, 2 H).
13C{1H} NMR (100 MHz, CDCl3): δ = 32.23 (d, J = 52.4 Hz), 40.51 (d, J =
48.3 Hz), 125.27 (d, J = 5.2 Hz, 2 C), 127.95 (d, J = 12.5 Hz, 2 C), 128.11
(d, J = 12.4 Hz, 2 C), 128.88 (d, J = 12.0 Hz, 2 C), 129.25 (d, J = 11.7 Hz, 2
C), 129.59 (d, J = 78.6 Hz), 129.82 (d, J = 77.9 Hz), 130.42 (d, J = 79.5
Hz), 130.44 (d, J = 10.0 Hz, 2 C), 131.22 (d, J = 9.9 Hz, 2 C), 131.47 (d,
J = 11.0 Hz, 2 C), 131.49 (d, J = 3.0 Hz), 131.57 (d, J = 2.9 Hz), 131.76 (d,
J = 2.9 Hz), 132.21 (d, J = 9.0 Hz, 2 C), 132.31 (d, J = 2.9 Hz), 133.80 (d,
J = 83.0 Hz), 141.87 (d, J = 5.1 Hz), 148.46 (d, J = 2.1 Hz, 2 C).
2a
S
Ir(ppy)3 (0.5 mol%)
MeOTf (20 mol%)
S8
Ph2P
S
+
Ph2P PPh2
Ph
PPh2
r.t.
30 min
DCE, ambient temp
blue LEDs, 4.5 h
Ph
1a
2a
3aa-S
72% (1H NMR)
PPh2
+
Ph2P
probably via
Me
Scheme 5 Plausible mechanism and control experiment with MeOTf
filtrate under reduced pressure gave the desired imidylphosphine 5 as
an orange solid (860 mg, 85% purity, contaminated with Ph2P(O)PPh2
impurity). See the Supporting Information for NMR spectra.
31P{1H} NMR (162 MHz, CDCl3): δ = 42.16 (d, J = 55.5 Hz), 52.71 (d, J =
55.5 Hz).
NBS-Initiated vic-Diphosphination of Styrenes 1 with Diphos-
phines 2 under Visible-Light-Promoted Photoredox Catalysis; Gen-
eral Procedure (GP)
HRMS (APCI): m/z ([M + H]+) calcd for C31H28NP2S2: 540.1133; found:
540.1146.
Ir(ppy)3 (0.80 mg, 0.0013 mmol), NBS (8.9 mg, 0.050 mmol), and
Ar2P–PAr2 (2; 0.50 mmol) were placed in a 10-mL Schlenk flask,
which was filled with N2. DCE (1.5 mL) was added, and the solution
was stirred at r.t. for 10 min. A solution of styrene 1 (0.25 mmol) in
DCE (1.5 mL) was then added dropwise via a syringe, and the ob-
tained mixture was irradiated with blue LED tapes (2.4 W) at r.t. for
4.5 h. Elemental sulfur (S8; 40 mg, 1.3 mmol of S atom) was then add-
ed. The mixture was stirred for a further 30 min at r.t., and then it was
filtered through a short pad of neutral alumina and evaporated in vac-
uo. The residue was purified by column chromatography (silica gel,
hexane/EtOAc 5:1) followed by GPC (CHCl3) to afford the correspond-
ing diphosphinated product 3-S. All diphosphinated products 3-S are
known compounds, with the exception of 3ga-S, 3ka-S, 3ab-S, and
3ac-S, and spectra data is in agreement with the reported values.4,5
1,2-Bis[bis(4-methoxyphenyl)thiophosphinyl]-1-phenylethane
(3ab-S)
Prepared according to the GP, purification by GPC (CHCl3) gave the
product (104 mg, 0.16 mmol, 64%) as a white solid; mp 98.7–100.7 °C.
1H NMR (400 MHz, CDCl3): δ = 2.65 (dd, J = 13.3, 26.6 Hz, 1 H), 3.39–
3.51 (m, 1 H), 3.68 (s, 3 H), 3.69 (s, 3 H), 3.78 (s, 3 H), 3.86 (s, 3 H), 4.91
(dd, J = 10.5, 25.0 Hz, 1 H), 6.48 (dd, J = 2.2, 8.8 Hz, 2 H), 6.61 (dd, J =
2.2, 8.8 Hz, 2 H), 6.76 (t, J = 7.6 Hz, 2 H), 6.80–6.85 (m, 3 H), 7.00 (d, J =
7.3 Hz, 2 H), 7.07 (dd, J = 2.2, 8.8 Hz, 2 H), 7.16–7.30 (m, 4 H), 7.54–
7.63 (m, 2 H), 8.19–8.27 (m, 2 H).
13C{1H} NMR (100 MHz, CDCl3): δ = 33.02 (d, J = 56.2 Hz), 41.14 (d, J =
50.1 Hz), 55.22, 55.26, 55.38, 55.44, 113.23 (d, J = 13.3 Hz, 2 C), 113.28
(d, J = 13.6 Hz, 2 C), 114.22 (d, J = 13.1 Hz, 2 C), 114.52 (d, J = 12.8 Hz, 2
C), 121.19 (d, J = 82.4 Hz), 121.76 (d, J = 84.9 Hz), 123.09 (d, J = 86.8
Hz), 125.63 (d, J = 88.3 Hz), 126.91 (d, J = 3.2 Hz), 127.25 (d, J = 2.6 Hz,
2 C), 130.38 (d, J = 5.4 Hz, 2 C), 132.28 (d, J = 11.3 Hz, 2 C), 132.80 (d,
J = 4.4 Hz), 133.16 (d, J = 10.7 Hz, 2 C), 133.27 (d, J = 11.5 Hz, 2 C),
134.19 (d, J = 10.5 Hz, 2 C), 161.40 (d, J = 2.9 Hz), 161.68 (d, J = 2.9 Hz),
162.03 (d, J = 2.9 Hz), 162.44 (d, J = 2.8 Hz).
1-[4-(Dimethylamino)phenyl]-1,2-bis(diphenylthiophos-
phinyl)ethane (3ga-S)
Prepared according to the GP, purification by GPC (CHCl3) gave the
product (37 mg, 0.06 mmol, 25%) as a red-brown solid; mp 240.6–
242.6 °C.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–F

F
N. Otomura et al.
Special Topic
Synthesis
31P{1H} NMR (162 MHz, CDCl3): δ = 41.46 (d, J = 58.7 Hz), 51.80 (d, J =
58.7 Hz).
HRMS (APCI): m/z ([M + H]+) calcd for C36H37O4P2S2: 659.1603; found:
659.1619.
1973, 95, 8469. (d) Chatt, J.; Hussain, W.; Leigh, G. J.; Ali, H. M.;
Picket, C. J.; Rankin, D. A. J. Chem. Soc., Dalton Trans. 1985, 1131.
(e) Hajdók, I.; Lissner, F.; Nieger, M.; Strobel, S.; Gudat, D.
Organometallics 2009, 28, 1644.
(3) A related double hydrophosphination of alkynes to DPPE-type
ligand: (a) Kamitani, M.; Itazaki, M.; Tamiya, C.; Nakazawa, H.
J. Am. Chem. Soc. 2012, 134, 11932. (b) Di Giuseppe, A.; De Luca,
R.; Castarlenas, R.; Pérez-Torrente, J. J.; Crucianelli, M.; Oro, L. A.
Chem. Commun. 2016, 52, 5554. (c) Yuan, J.; Zhu, L.; Zhang, J.; Li,
J.; Cui, C. Organometallics 2017, 36, 455. (d) Bookham, J. L.;
Smithies, D. M.; Wright, A.; Thornton-Pett, M.; McFarlane, M.
J. Chem. Soc., Dalton Trans. 1998, 811.
(4) Okugawa, Y.; Hirano, K.; Miura, M. Angew. Chem. Int. Ed. 2016,
55, 13558.
(5) Otomura, N.; Okugawa, Y.; Hirano, K.; Miura, M. Org. Lett. 2017,
19, 4802.
1,2-Bis{bis[4-(trifluoromethyl)phenyl]thiophosphinyl}-1-pheny-
lethane (3ac-S)
Prepared according to the GP, purification by GPC (CHCl3) gave the
product (113 mg, 0.14 mmol, 56%) as a white solid; mp 207.0–
209.0 °C.
1H NMR (400 MHz, CDCl3): δ = 2.67 (dd, J = 13.2, 26.4 Hz, 1 H), 3.60–
3.72 (m, 1 H), 5.07 (dd, J = 10.4, 24.5 Hz, 1 H), 6.73 (t, J = 7.7 Hz, 2 H),
6.86 (dd, J = 6.7, 8.4 Hz, 1 H), 7.00 (d, J = 6.7 Hz, 2 H), 7.26 (dd, J = 2.2,
8.4 Hz, 2 H), 7.40 (dd, J = 2.5, 8.4 Hz, 2 H), 7.49 (dt, J = 7.4, 12.9 Hz, 4
H), 7.69 (dd, J = 2.4, 8.2 Hz, 2 H), 7.84–7.92 (m, 4 H), 8.45 (dd, J = 8.4,
11.4 Hz, 2 H).
13C{1H} NMR (100 MHz, CDCl3): δ = 32.88 (dd, J = 3.2, 53.3 Hz), 40.19
(d, J = 50.3 Hz), 123.25 (q, J = 270.9 Hz), 124.56–125.05 (m, 2 C + 2 C),
125.78–126.32 (m, 2 C + 2 C), 126.11 (q, J = 271.3 Hz), 127.87 (d, J =
2.2 Hz, 2 C), 128.17 (d, J = 3.0 Hz), 130.16 (d, J = 6.0 Hz, 2 C), 131.00 (d,
J = 10.3 Hz, 2 C), 131.22 (d, J = 4.0 Hz), 131.36 (q, J = 269.0 Hz), 131.70
(d, J = 10.2 Hz, 2 C), 131.77 (d, J = 11.5 Hz, 2 C), 132.72 (d, J = 9.8 Hz, 2
C), 132.89 (dq, J = 3.4, 32.9 Hz), 133.00 (dq, J = 3.4, 32.7 Hz), 133.88 (d,
J = 76.5 Hz), 133.98 (dq, J = 3.7, 32.2 Hz), 134.16 (d, J = 72.9 Hz),
134.29 (dq, J = 3.4, 32.7 Hz), 134.78 (d, J =79.0 Hz), 137.33 (d, J = 81.5
Hz). The carbon signal corresponding to one CF3 could not be assigned
because of complex C–F and C–P couplings.
(6) Sato, Y.; Kawaguchi, S.-i.; Nomoto, A.; Ogawa, A. Angew. Chem.
Int. Ed. 2016, 55, 9700.
(7) Hanss, D.; Freys, J. C.; Bernardinelli, G.; Wenger, O. S. Eur. J.
Inorg. Chem. 2009, 4850.
(8) Unfortunately, tetracyclohexyldiphosphine Cy2P–PCy2 did not
deliver the corresponding diphosphinated product at all.
(9) The bromophosphine BrPPh2 (4) is commercially available from
Sigma-Aldrich and showed a singlet signal at δ = 74.0 in DCE-d4
(
31P{1H} NMR, 162 MHz). The imidylphosphine 5 was prepared
from succinimide and ClPPh2. See the experimental section for
detailed procedure and the Supporting Information for NMR
spectra.
(10) Selected reviews on visible-light-promoted photoredox cataly-
sis: (a) Yoon, T. P.; Ischay, M. A.; Du, J. Nat. Chem. 2010, 2, 527.
(b) Narayanam, J. M. R.; Stephenson, C. R. J. Chem. Soc. Rev. 2011,
40, 102. (c) Prier, C. K.; Rankic, D. A.; MacMillan, D. W. C. Chem.
Rev. 2013, 113, 5322. (d) Ravelli, D.; Protti, S.; Fagnoni, M. Chem.
Rev. 2016, 116, 9850. (e) Koike, T.; Akita, M. Acc. Chem. Res.
2016, 49, 1937. Recent advances in organophosphorus chemis-
try under photoredox catalysis: (f) Luo, K.; Yang, W.-C.; Wu, L.
Asian J. Org. Chem. 2017, 6, 350.
19F{1H} NMR (376 MHz, CDCl3): δ = –63.61 (s, 3 F), –63.35 (s, 3 F),
–63.31 (s, 3 F), –63.20 (s, 3 F).
31P{1H} NMR (162 MHz, CDCl3): δ = 41.89 (d, J = 59.6 Hz), 51.39 (d, J =
59.6 Hz).
HRMS (APCI): m/z ([M + H]+) calcd for C36H25F12P2S2: 811.0676; found:
811.0667.
(11) The in situ generation of a MeOTf adduct (phosphonium cation)
Funding Information
1
can be supported by observation of a characteristic large JPP
coupling (ca. 300 Hz) in 31P{1H} NMR studies. See the Support-
ing Information for details. Also see: (a) Dahl, O. Tetrahedron
Lett. 1982, 23, 1493. (b) Unoh, Y.; Hirano, K.; Miura, M. J. Am.
Chem. Soc. 2017, 139, 6106.
This work was supported by JSPS KAKENHI Grant Nos. JP 15H05485
(Grant-in-Aid for Young Scientists (A)) to K.H. and JP 17H06092
(Grant-in-Aid for Specially Promoted Research) to M.M.
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(12) (a) Arias-Rotondo, D. M.; McCusker, J. K. Chem. Soc. Rev. 2016,
45, 5803. (b) Teegardin, K.; Day, J. I.; Chan, J.; Weaver, J. Org.
Process Res. Dev. 2016, 20, 1156.
Supporting Information
Supporting information for this article is available online at
(13) The obtained phosphine sulfides can be readily desulfidated to
the corresponding phosphines: (a) Zablocka, M.; Delest, B.; Igau,
A.; Skowronska, A.; Majoral, J.-P. Tetrahedron Lett. 1997, 38,
5997. (b) Saito, M.; Nishibayashi, Y.; Uemura, S. Organometallics
2004, 23, 4012. (c) Ref 4.
https://doi.org/10.1055/s-0037-1609447.
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References
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© Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–F