Planar chiral palladacycle precatalysts for asymmetric synthesis

Article abstract of DOI:10.1039/d0ob01331e

Chiral non-racemic palladacycles were employed as precatalysts for Pd(0) mediated asymmetric synthesis. Addition of HPAr2/base to a ferrocenyloxazoline planar chiral palladacycle resulted in ligand synthesis and palladium capture to give a bidentate Phosf

Full text of DOI:10.1039/d0ob01331e

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O rP gl ea na si ce &d Bo i on mo to al e dc juu l sa tr mC ha er mg i ins ts ry
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DOI: 10.1039/D0OB01331E
ARTICLE
Planar Chiral Palladacycle Precatalysts for Asymmetric Synthesis
Ross A. Arthurs, David L. Hughes and Christopher J. Richards*
Received 00th January 20xx,
Accepted 00th January 20xx
Chiral non-racemic palladacycles were employed as precatalysts for Pd(0) mediated asymmetric synthesis. Addition of
2
HPAr /base to a ferrocenyloxazoline planar chiral palladacycle resulted in ligand synthesis and palladium capture to give a
DOI: 10.1039/x0xx00000x
bidentate Phosferrox/Pd(0) complex. A series of these complexes were generated in situ and applied successfully as catalysts
for asymmetric allylic alkylation.
Introduction
Results and Discussion
Air-stable palladacycles containing
a bidentate carbon- Palladacycles are known to undergo ligand phosphination on
heteroatom ligated palladium(II) core have been employed reaction with MPPh
extensively in catalysis. Following the discovery that high turn- coordination to palladium followed by reductive elimination
2
(M = Li, K), where initial phosphide
1
1
5,16
over numbers may be achieved on application of the Herrmann results in C-P bond formation.
In this way a number of N-P,
2
complex to the Heck reaction, this and other palladacycles S-P and P-P bidentate ligands have been synthesised from the
have also found application in a number of cross-coupling corresponding S, N or P precursor palladacycles. Many of these
3
processes including the Suzuki-Miyaura and Buchwald-Hartwig product ligands are chiral, including planar chiral examples
4
amination reactions. In addition, related chiral non-racemic displaying stereospecific replacement of the C-Pd bond by a
1
5a,b
palladacycles have been applied successfully to the catalysis of new C-P bond.
Formation of these ligands also results in the
5
asymmetric reactions. Examples include the allylic imidate generation of Pd(0), but as far as we are aware, isolation of a
rearrangement, hydrophosphination, imine arylation, the resulting ligated Pd(0) complex in this way has not been
6
7
8
9
aza-Morita-Baylis-Hillman reaction
and Michael type reported, let alone used subsequently in catalysis.
To address this challenge we chose to start with
reactions.10 Palladium(II) mediated activation of the substrate
and retention of the palladacycle C-Pd bond in the chiral ferrocenyloxazoline (S)-1 as this may be transformed readily
1
7
1
1
7-10
18
catalyst is either demonstrated or invoked. A recent report into planar chiral palladacycles (S,S
p
)-2a/b (Scheme 1).
1
9
on palladacycle catalysed asymmetric Suzuki cross-coupling was Furthermore, the Phosferrox ligand (S,S
p
)-3 is also derived
1
2
explained by the operation of a Pd(II)/Pd(IV) catalytic cycle. In from (S)-1, this bidentate ligand having been applied
contrast, the use of chiral non-racemic palladacycles as successfully in several palladium catalysed asymmetric
2
0
precatalysts for asymmetric reactions proceeding via a reactions. It was anticipated that this would aid the
Pd(0)/Pd(II) catalytic cycle does not appear to have been identification and comparative application of a corresponding
demonstrated.13
p
palladacycle derived Pd(0) complex of (S,S )-3.
In this paper we describe the use of chiral non-racemic
palladacycles as precatalysts for the formation of Pd(0)/chiral
ligand coordinated complexes, followed by the application of
these as catalysts in asymmetric synthesis. This first report on
simultaneous bidentate ligand synthesis/palladium(0) capture
provides a new and versatile approach to the generation of
Pd/chiral ligand complexes, with potential applications across a
O
O
O
i-Pr
i-Pr
i-Pr
N
N
N
Pd
PPh2
L
Ref.
19
Ref.
Fe
Fe
Fe
1
8
2
(
S,S )-2a (L = OAc)
(S,Sp)-2b (L = Cl)
(S)-1
(S,Sp)-3
Phosferrox
p
1
4
range of palladium catalysed asymmetric transformations.
Scheme 1. Palladacycles and a chiral bidentate ligand derived from (S)-1.
School of Chemistry, University of East Anglia, Norwich Research Park, Norwich,
NR4 7TU, UK.
E-mail: Chris.Richards@uea.ac.uk
We reasoned that identification of in situ formed P-N ligated
Pd(0) would be aided by addition of a second ligand to give a
readily characterised complex. As maleic anhydride (MA) is
Electronic Supplementary Information (ESI) available: additional experimental
1
13
31
detail, copies of the H, C and P NMR spectra, HPLC traces and details of the X-
ray crystal structure determination. See DOI: 10.1039/x0xx00000x
2
1
known to result in stable low valent complexes of palladium,
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O rP gl ea na si ce &d Bo i on mo to al e dc juu l sa tr mC ha er mg i ins ts ry
Page 2 of 7
ARTICLE
Journal Name
we first used this electron deficient alkene with (S,S
Pd (dba) for the synthesis of (S,S )-4 (Scheme 2). This air-stable
Pd(0) complex was purified readily by column chromatography.
Its P NMR spectrum contained characteristic major and
minor signals at 14.39 and 15.81 ppm respectively due to the
two possible (exo/endo) orientations of the cyclic unsaturated
ligand.
p
)-3 and
View Article Online
DOI: 10.1039/D0OB01331E
2
3
p
3
1
22
8b
3
4
O
8
a
6
a
i-Pr O
7
N
Pd
61% (isolated)
Pd (dba) , MA
from (S,S )-3
2
3
P
O
p
(
S,S )-3
p
PhMe, RT, 18 h
Fe Ph Ph
3
1
O
in situ from 6a/b
Figure 1. P NMR spectra (CD
2
Cl
2 2
): (a) following the addition of PHPh (2 eq.) to
2
a, (b) ca. 10 minutes after the addition of MA (2 eq.), (c) following the addition
[
O]
2 2
of NaCH(CO Me) (10 eq.) to 6b, (d) ca. 1 h after the addition of MA (4 eq.).
(
S,S )-4
p
O
Two other major signals at 27.3 and 55.2 ppm were
observed in the 31P NMR spectra obtained before and after the
addition of MA. The first corresponds to (S,S )-7, a phosferrox
p
i-Pr
maleic anhydride
CD Cl , RT
N
2
2
P(O)Ph2
6a = no base
Fe
derived phosphine oxide for which the identity was confirmed
by independent synthesis. The second is assigned to a
6
b = base
(
S,S )-7
O
p
2
Pd(II)/PPh complex (vide infra). Formation of 4 was not
i-Pr
a (R = Ph, L = OAc, 83%)
5b (R = Ph, L = Cl, 95%)
a (R = H, L = OAc)*
N
observed when MA was added to palladacycle 2a before the
5
2
4
Pd
2
addition of PHPh due to fast competitive Michael addition.
PRPh2
L
(
S,S )-2a/b
p
Fe PRPh2
The formation of 4 and 7, as a single diastereoisomer in both
6
CH Cl , RT
2
2
1
h
6b (R = H, L = Cl, 73%)
cases, confirms that replacement of palladium by phosphorus
proceeds with no erosion of stereochemical integrity.
2
5
(
S,Sp)
(* not isolated)
N
Cl
N
L
N
N
C
HPPh2
CD2Cl2
Base
p
Scheme 2. Synthesis of Pd(0) complex (S,S )-4 by ligand exchange and ligand
synthesis/palladium capture.
2b
Pd
Pd
Pd
+
Pd0
+
C
PPh2
H
C
P
Ph2
C
PPh2
6
b
8b (L = Cl)
a (L = OAc)
(S,S )-3
p
Phosphine complexes of palladacycles (S,S
investigated using triphenylphosphine. On combination in
CH Cl at room temperature monomeric adducts 5a/b were
formed cleanly (Scheme 2). The phosphine is assigned a trans to
nitrogen orientation in the resulting complexes in accord with
the geometry of related monomeric phosphine coordinated
p
)-2a/b were first
AgOAc
8
O
i-Pr
MA
(S,S )-4
2
2
N
Pd
N
C
Base = NaCH(CO Me)
2 2
p
Fe
=
Pd
MA = maleic anhydride
palladacycles.1
ppm) and 5b (37.5 ppm), compared to PPh
used to aid the assignment of the corresponding adducts palladacycle 2b.
obtained from HPPh (-40.1 ppm). Addition of this secondary
phosphine to chloride ligated 2b gave stable and isolable adduct
b (8.4 ppm). In contrast, addition to acetate ligated 2a resulted
5b,23
The P NMR signals observed for 5a (36.5
(-5.4 ppm), were
31
22
3
p
Scheme 3. The generation of (S,S )-4. by ligand synthesis/palladium capture from
2
6
in immediate darkening to brown/black of the initially orange
solution, and after stirring for 1 hour, no phosphine adduct was
obtained.
To investigate the possibility that this colour change was
indicative of reductive elimination from an initially formed
phosphine adduct, the experiment was repeated in CD
followed by P NMR spectroscopy. Following addition of HPPh
2
Cl
2
and
3
1
2
to 2a at room temperature, a major signal observed in the 31P
NMR spectrum obtained after ca. 10 minutes (7.5 ppm) is
indicative of adduct 6a (Figure 1a). Significantly, following the
addition of MA, subsequent NMR analysis revealed the
disappearance of this complex and the formation of (S,S
p
)-4
Figure 2. A representation of the X-ray structure of 8b (hydrogen atoms omitted
for clarity). Principal bond lengths [Å] include: Pd(1)-Cl(1) = 2.4308(6), Pd(2)-Cl(1)
2.4366(6), Pd(1)-P(1) = 2.2447(6), Pd(2)-P(1) = 2.2457(6). Principal bond angles
deg] include: Pd(1)-Cl(1)-Pd(2) = 86.641(18), Pd(1)-P(1)-Pd(2) = 96.09(2). Thermal
(Figure 1b).
=
[
ellipsoids are drawn at the 50% probability level. Flack parameter = -0.002(5).
2
| J. Name., 2012, 00, 1-3
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O rP gl ea na si ce &d Bo i on mo to al e dc juu l sa tr mC ha er mg i ins ts ry
Journal Name
In contrast to 6a, the corresponding experiment with CH
ARTICLE
2
Cl
2
as solvent with THF or toluene resulted in no product
View Article Online
DOI: 10.1039/D0OB01331E
p
chloride complex 6b (formed in situ from (S,S )-2b and HPPh
2
)
formation.
required the addition of a base to promote reductive
elimination and formation of the MA adduct 4. Nitrogen bases
were employed initially, with triethylamine resulting in the
Table 1. Comparative catalysis of asymmetric allylic alkylation with preformed and
palladacycle generated Phosferrox/Pd(0) complexes.a
3
1
highest conversion (14%) as determined by
spectroscopy. With N,O-bis(trimethylsilyl)acetamide (BSA) the
P NMR
OAc
Ph
CH(CO Me)2
2
Pd source
CH Cl , RT
2
6
Ph
Ph
Ph
2
2
conversion was improved (23%), and the best result (29%) was
rac-9
(S)-10
obtained with sodium dimethyl malonate. Following addition of
this base 31P NMR spectroscopy revealed two major signals at -
Conditions A
Conditions B
3 eq. NaCH(CO Me)
Conditions C
3
3
2
eq. H C(CO Me)
10 mol% NaCH(CO Me)2
2
2
2
2
2
2
1
8.1 and 23.8 ppm (Figure 1c). The former corresponds to
Phosferrox ligand 3, and on addition of MA this signal
disappeared and was replaced predominantly by
eq. BSA
3 eq. H C(CO Me)
2
2
2
mol% KOAc
3 eq. BSA
a
Entry
Pd source
mol%)
)-3 (2.5) +
Pd(C )Cl] (1)
(S,S )-4 (1)
)-2a (1) + HPPh
Con-
ditions
A
Time Con.
(h)
<1
ee
(%)
95b
corresponding amount of 4 (Figure 1d). Following isolation of
the other complex by column chromatography it was identified
(
(%)
100
1
(S,S
p
by X-ray crystallography as Pd(II)/PPh
2
dimer 8b (Scheme 3,
[
3
H
5
2
Figure 2).27 Addition of silver acetate to 8b gave 8a ( P NMR =
31
2
3
4
5
6
7
p
A
A
A
96
96
96
96
96
3.5
6
51
77
20
0
86
85
85
94
na
88
-
55.6 ppm), revealing that this corresponding acetate-bridged
dimer is formed from the addition of HPPh to 2a (Figure 1a/b).
Addition of maleic anhydride to a solution of 8b in CD Cl did not
(S,S
p
2
(2)
(2)
(2)
2
(S,S
(S,S
p
)-2b (1) + HPPh
)-2b (1) + HPPh
2
2
2
A c,d
p
2
result in the formation of 4. Dimerisation to give 8a/b is an
alternative and apparently irreversible pathway to reductive
elimination and formation of ligand 3. It is of note that Pd(0)
does not complex with 3 to a significant extent until maleic
anhydride is added, an outcome consistent with initial and
(S,S
p
)-2a (1) or (S,S
(S,S )-3 (2.5) +
[Pd(C H )Cl] (1)
p
)-2b (1)
A
B
p
100
3
5
2
8
9
10
11
(S,S
(S,S
p
)-2b (1) + HPPh
)-2b (1) + HPPh
8b (1)
2
(2)
(2)
B
C
A
C
C
C
2.5
1
24
24
24e
24e
100
99
77
86
na
85
84
83
p
2
2
8
reversible formation of palladium nanoparticles. No oxidation
to phosphine oxide (S,S )-7 was observed, in contrast to the
0
(S,S
p
)-2b (1) + 11a (2)
)-2b (1) + 11b (2)
p
)-2b (1) + 11c (2)
18
100
100
p
1
1
2
3
(S,S
(S,S
p
appreciable formation of this compound from acetate-bridged
palladacycle 2a, revealing a significant advantage of starting
2
9
with chloride-bridged palladacycle 2b.
The successful formation of (S,S
a1 mmol rac-9 (0.6 M) unless otherwise stated. bLit. value 90% ee.20a c0.33 mmol
d
e
p
)-4 from palladacycle scale. No KOAc. Reaction essentially complete within 1 h (tlc).
precursors prompted us to investigate the use of these as
precatalysts in asymmetric synthesis. The allylic alkylation of
trans-1,3-diphenylallyl acetate 9 was chosen as an exemplar
reaction due to its experimental simplicity and the potential to
employ the basic reaction conditions for in situ ligand/Pd(0)
As sodium dimethyl malonate gave the highest and cleanest
conversion to (S,S )-4, this was employed next as both a base
and a nucleophile, and the process referenced initially by use of
S,S )-3/[Pd(C )Cl] (3 fold excess, conditions B). The lower
p
(
p
H
3 5
2
p
generation (Table 1). Furthermore, ligand (S,S )-3 is known to
product ee, compared to that obtained from the use as base of
promote high enantioselectivity in this reaction, and in our
2
0a
BSA (95% - entry 1 vs. 88% - entry 7) is consistent with the
hands repetition of conditions reported previously using BSA
3
0
superiority of the former conditions noted previously.
as base (3 eq.) gave (S)-10 in 95% ee (Conditions A, Table 1,
Significantly, addition of a three-fold excess of sodium dimethyl
malonate to rac-9 and 2 mol% of in situ generated 6b resulted
in complete conversion within 2.5 h to allylic alkylation product
entry 1). Replacing [Pd(C
3 5 2
H )Cl] with preformed Pd(0) complex
(
S,S )-4 resulted in some loss of enantioselectivity, and a very
p
significant reduction in activity due to inhibition by maleic
anhydride (entry 2). This precluded the use of this π-acidic
ligand in any subsequent runs. Instead, a catalytic asymmetric
allylic alkylation was attempted directly following the addition
(S)-10 formed in 77% ee (entry 8). Modifying these conditions
further (Conditions C) to the use sodium dimethyl malonate (10
mol%) as the base for in situ catalyst formation, and then the
addition of BSA/dimethyl malonate (3 equivalents of each)
further decreased the reaction time to 1 hour and increased the
ee of (S)-10 to 86% (entry 9). The use of Conditions C provided
an in situ generated catalyst with comparable activity and
selectivity to that obtained using a preformed ligand, and
consistent with this outcome is the absence of any catalysis with
Pd(II) complex 8b (entry 10).
2
of HPPh to 2a, and after stirring for 10 minutes, to resulting in
situ generated 6a was added sequentially rac-9, dimethyl
malonate, BSA and KOAc (entry 3). Although slow, we noted
with interest the formation of product 10, subsequently
isolated as the S enantiomer in 85% ee. Use in the same way of
chloride 2b resulted in a similar outcome (entry 4), and on
repetition in the absence of KOAc the product ee increased to
9
4% (entry 5). No product was formed in the absence of added
PHPh (entry 6). These initial results are consistent with the in
situ formation of (S,S )-3 ligated Pd(0) as the sole catalytically
2
p
active species, albeit in low concentration. Replacement of
This journal is © The Royal Society of Chemistry 20xx
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ARTICLE
Journal Name
identification of palladium based catalysts for application in
other areas of asymmetric synthesis.
O
View Article Online
DOI: 10.1039/D0OB01331E
i-Pr
Pd0
i) 2 mol% HPAr2 11a-c
N
CH2Cl2, RT, 10 min.
(
S,Sp)-2b
P
+
Catalysis
ii) 10 mol%
1
mol%
Fe Ar Ar
NaCH(CO2Me)2
RT, 5 min.
Experimental
General information
OMe
CF3
CF3
Tetrahydrofuran was distilled over sodium and benzophenone
ketyl and dichloromethane distilled over calcium hydride. All
reactions were carried out under an inert atmosphere of either
nitrogen or argon. Silica gel (60 Å pore size, 40 - 63 µm technical
grade) was used for chromatography. All starting materials not
commercially available are specifically referenced.
Ar
=
a
b
c
Scheme 4. Phosphine variation for in situ ligand synthesis/Pd(0) capture from
palladacycle (S,S )-2.
p
Finally, this led us to explore the use of asymmetric allylic
alkylation to test the viability of using electronically contrasting
diarylphosphines in the ligand synthesis/Pd(0) capture protocol
Scheme 4). For this reaction previous work with related PHOX
ligands containing PAr units with various para substituents
revealed little difference in enantioselectivity compared to the
Synthesis of (S,S
S,S
)-319 (0.087 g, 0.18 mmol), tris(dibenzylideneacetone)-
dipalladium(0) (0.076 g, 0.08 mmol) and maleic anhydride
0.024 g, 0.24 mmol) were added to a flame dried Schlenk tube
p
)-4
(
p
(
2
(
and dissolved in toluene (15 mL). The resulting deep purple
solution was stirred vigorously overnight resulting in the
formation of a dark suspension. The reaction was filtered
3
1
parent PPh
with electron-withdrawing substituents.
secondary phosphines 11a-c were added separately to
palladacycle (S,S )-2b followed by sodium dimethyl malonate,
2
containing ligand, albeit with faster conversion
3
1a
Accordingly,
TM
through Celite using toluene as the eluent and the solvent
p
removed in vacuo. Purification by column chromatography
and to the resulting solutions were added rac-9 (50 equivalents
w.r.t. Pd) and dimethyl malonate/BSA (i.e. Conditions C). Use of
electron-deficient phosphine 11a resulted in a similar level of
product enantioselectivity albeit in reduced yield (Table 1, entry
1). Further examination by P NMR spectroscopy (CD Cl ) of
2 2
the addition of 11a (-40.8 ppm) to 2b confirmed the formation
(
SiO
2
, 40 % EtOAc/hexane) yielded an orange solid (0.07 g, 61%);
+
mp decomposed ~200 °C (under argon); HRMS (AS) [M+H] anal.
calcd for C32
-
2
2
0.5°C
H
31FeNO
4
PPd 686.0389, found 686.0389; [α]
D
=
-1
538 (c = 0.46, CHCl
873, 1790, 1723, 1626; H NMR (500 MHz, CDCl
3
); νmax (film)/cm 3056, 3016, 2960, 2923,
3
1
1
1
3
) major isomer
(ratio of isomers = 1.6 : 1) δ 7.80 (2H, ddd, J = 11.6, 7.8, 1.5 Hz),
0
of the phosphine coordinated adduct (10.9 ppm), but little Pd
7
6
.56 - 7.46 (3H, m), 7.33 - 7.27 (3H, m), 7.08 (2H, ddd, J = 11.0,
.6, 3.2 Hz), 5.04 (1H, brs), 4.70 (1H, t, J = 2.6 Hz), 4.41 - 4.38
complex was observed following the addition of sodium
dimethyl malonate and MA. In this instance catalyst formation
appears to be limited by the inefficiency of reductive
elimination.32 In contrast, the catalysts derived from
phosphines 11b (entry 12) and 11c (entry 13) gave essentially
complete conversion after 1 h and ee values very similar to that
obtained from diphenylphosphine.
(1H, m), 4.35 (1H, t, J = 3.7 Hz), 4.33 - 4.21 (3H, m), 4.07 (1H, dd,
J = 10.5, 3.8 Hz), 3.96 (5H, s), 2.80 (1H, dtd, J = 13.8, 6.9, 3.3 Hz),
1
7
-
.07 (3H, d, J = 7.1 Hz), 0.99 (3H, d, J = 6.9 Hz); minor isomer
.76 - 7.68 (2H, m), 7.56 - 7.46 (3H, m), 7.33 - 7.27 (3H, m), 7.21
7.14 (2H, m), 5.04 (1H, brs), 4.72 (1H, t, J = 2.6 Hz), 4.50 - 4.46
(1H, m), 4.33 - 4.21 (3H, m), 3.86 (5H, s), 3.87 - 3.79 (2H, m),
2
.67 (1H, dtd, J = 13.7, 6.9, 3.4), 1.04 (3H, d, J = 7.0 Hz), 0.95 (3H,
1
3
d, J = 6.8 Hz); C NMR (125 MHz, CDCl
3
) major isomer δ 172.6
Conclusion
(
1
d, J = 2.0 Hz), 171.5 (d, J = 5.2 Hz), 169.1, 135.5 (d, J = 36.7 Hz),
34.9 (d, J = 16.7 Hz), 134.7 (d, J = 40.1 Hz), 131.6 (d, J = 13.3
We have established that ferrocenyloxazoline-based planar
chiral
diphenylphosphine (and for 2b a base), are viable precatalysts
for in situ catalyst generation using new ligand
palladacycles
2a/b,
on
combination
with
Hz), 131.2 (d, J = 2.0 Hz), 129.4 (d, J = 1.6 Hz), 128.6 (d, J = 10.8
Hz), 128.5 (d, J = 9.7 Hz), 75.5 (d, J = 2.6 Hz), 74.0 (d, J = 2.3 Hz),
a
7
7
1
1
4
1
2
3.5 (d, J = 46.2 Hz), 73.4 (d, J = 1.5 Hz), 73.1, 71.8 (d, J = 0.5 Hz),
1.4, 67.7, 47.4 (d, J = 31.7 Hz), 46.4 (d, J = 1.8 Hz), 29.2, 19.2,
4.7; minor isomer 172.9 (d, J = 1.5 Hz), 171.2 (d, J = 5.0 Hz),
69.1, 137.3 (d, J = 37.8 Hz), 135.1 (d, J = 16.6 Hz), 133.7 (d, J =
0.2 Hz), 131.4 (d, J = 13.1 Hz), 131.4 (d, J = 2.1 Hz), 129.1 (d, J =
.5 Hz), 128.8 (d, J = 11.2 Hz), 128.5 (d, J = 9.7 Hz), 75.9 (d, J =
.7 Hz), 75.1 (d, J = 1.8 Hz), 74.0 (d, J = 33.0 Hz), 74.0 (d, J = 2.1
synthesis/palladium(0) capture approach. This was
demonstrated by formation of a stable Phosferrox/maleic
anhydride coordinated Pd(0) complex (S,S )-4a, and by
p
application of Phosferrox/Pd(0) as a catalyst for asymmetric
allylic alkylation in the absence of maleic anhydride. The other
palladium(II) complex formed in this process is not a
competitive catalyst or catalyst precursor. Product
configuration and enantioselectivity using a palladacycle
derived catalyst are similar to that obtained using a preformed
Phosferrox ligand and a source of Pd(0). In addition to being a
precursor to an active and selective catalyst generated in one
step, palladacycle 2b may also be used for multiple catalyst
generation with other diarylphosphines. It is anticipated that
this approach will aid significantly the generation and
Hz), 73.4 (d, J = 1.3 Hz), 73.1, 71.6, 67.7, 47.8 (d, J = 1.7 Hz), 46.7
31
3
(d, J = 32.7 Hz), 29.2, 19.2, 14.9; P NMR (202 MHz, CDCl ) major
isomer δ 14.39; minor isomer 15.81.
General procedure for the synthesis of 5a, 5b and 6b.
)-2a18 or (S,S )-2b18 (0.029 mmol) and either
(S,S
p
p
triphenylphosphine or diphenylphosphine (0.057 mmol) were
2
| J. Name., 2012, 00, 1-3
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Journal Name
ARTICLE
added to a flame dried Schlenk tube and dissolved in chlorodiphenylphosphine oxide (0.076 mL, 0.4ViemwmArtoicll)e Ownlianes
dichloromethane (1 mL) and stirred at room temperature for 1 added and the reaction was allowedDOtIo: 10w.10a3rm9/D0tOoB0r1o3o3m1E
hour. The solvent was removed in vacuo yielding the product.
temperature. After an additional 15 mins, the reaction was
5
1
C
a. Obtained as a deep orange solid (0.034 g, 83%): mp 136 - diluted with diethyl ether and then quenched with saturated
+
37 °C (under argon), MS (EI) [M] anal. calcd for sodium hydrogen carbonate solution. The organics were
2
3.5°C
36
H
36FeNO
3
PPd 723.1, found 723.1; [α]
D
2 4
= -572 (c = 0.55, separated with H O, washed with brine, dried over MgSO and
-1
MeCN); νmax (film)/cm 3052, 2961, 2925, 2871, 1615, 1582, the solvent removed in vacuo giving a crude product containing
1
3
1
-
499; H NMR (500 MHz, MeCN-d ) δ 7.78 - 7.72, (6H, m), 7.52 a 2:1 mixture of diastereoisomers. The diastereoisomers were
7.48 (3H, m), 7.46 - 7.41 (6H, m), 4.63 (1H, t, J = 9.5 Hz), 4.59 - separated by column chromatography (SiO , 2 % MeOH/Et O)
2
2
4
4
.55 (1H, m), 4.45 (1H, d, J = 1.9 Hz), 4.07 (1H, ddd, J 10.0, 7.5, yielding the desired product as a yellow brown solid (0.0255 g,
.2 Hz), 4.02 (1H, t, J = 2.2 Hz), 3.90 (5H, s), 3.30 (1H, d, J = 2.2 26%): mp 197 - 198 °C; HRMS (ES) [M+H] anal. calcd for
+
1
9.4°C
Hz), 2.34 - 2.26 (1H, m), 1.25 (3H, s), 1.03 (3H, d, J = 6.9 Hz), 0.88
C
28
H
29FeNO
2
P 498.1280, found 498.1263; [α]
D
= +114 (c =
1
3
3
-1
(3H, d, J = 7.2 Hz); C NMR (125 MHz, MeCN-d ) δ 179.8, 176.3, 0.2, CHCl
3
); νmax (film)/cm 3080, 3062, 2963, 2930, 2871, 1648,
1
1
1
7
6
35.7 (d, J = 12.0 Hz), 132.1 (d, J = 50.3 Hz), 131.5 (d, J = 2.4 Hz), 1120; H NMR (500 MHz, CDCl
3
) δ 7.76 - 7.71 (2H, m), 7.69 - 7.64
29.1 (d, J = 10.7 Hz), 90.2 (d, J = 8.6 Hz), 77.3 (d, J = 9.0 Hz), (2H, m), 7.50 - 7.46 (1H, m), 7.45 - 7.36 (5H, m), 5.06 (1H, dt, J =
3.8 (d, J = 1.3 Hz), 73.1 (d, J = 3.0 Hz), 70.9, 69.7 (d, J = 2.6 Hz), 2.6, 1.4 Hz), 4.49 (5H, s), 4.45 (1H, dd, J = 4.4, 2.4 Hz), 4.22 - 4.18
3
1
8.3 (d, J = 3.3 Hz), 65.6, 29.3, 23.9, 19.3, 15.7; P NMR (202 (1H, m), 3.93 (1H, dd, J = 3.9, 2.5 Hz), 3.72 (1H, td, J = 9.3, 6.3
3
MHz, MeCN-d ) δ 36.48.
5
Hz), 3.13 (1H, t, J = 8.8 Hz), 1.53 - 1.47 (1H, m), 0.81 (3H, d, J =
6.8 Hz), 0.61 (3H, d, J = 6.8 Hz); C NMR (125 MHz, CDCl ) δ
3
1
3
b. Purified by column chromatography (SiO
2
,
20
%
EtOAc/hexane) to give the product as a deep orange solid (0.038 164.6, 134.86 (d, J = 107 Hz), 134.8 (d, J = 110.4 Hz), 131.6 (d, J
g, 95%): mp decomposed ~230 °C (under argon); HRMS (AS) [M- = 9.3 Hz), 131.4 (d, J = 9.7 Hz), 131.3 (d, J = 2.6 Hz), 131.0 (d, J =
+
Cl] anal. calcd for C34
H
33FeNOPPd 664.0699, found 664.0711; 2.9 Hz), 128.2 (d, J = 4.3 Hz), 128.1 (d, J = 4.8 Hz), 78.5 (d, J =
2
2.8°C
-1
[
α]
D
= -825 (c = 0.26, MeCN); νmax (film)/cm 3077, 3052, 14.6 Hz), 75.7 (d, J = 109.9 Hz), 74.5 (d, J = 9.1 Hz), 73.5 (d, J =
1
3
2
7
-
958, 2925, 2867, 1618, 1503; H NMR (500 MHz, MeCN-d ) δ 8.2 Hz), 72.4, 71.5 (d, J = 10.9 Hz), 71.4, 70.1, 32.3, 19.2, 18.0;
.78 - 7.72 (6H, m), 7.53 - 7.49 (3H, m), 7.48 - 7.43 (6H, m), 4.67
4.57 (2H, m), 4.47 (1H, d, J = 1.9 Hz), 4.18 (1H, ddd, J = 10.2,
3
1
3
P NMR (202 MHz, CDCl ) δ 26.40.
6
2
.3, 4.2 Hz), 4.02 (1H, t, J = 2.1 Hz), 3.97 (5H, s), 3.04 (1H, brs), Synthesis of (S,S,S
p
,S )-8b
p
1
3
.87 (1H, brs), 1.06 (3H, d, J = 6.9 Hz), 0.92 (3H, d, J = 7.2 Hz); C To a flame dried Schlenk tube (tube-1) was added sodium tert-
3
NMR (125 MHz, MeCN-d ) δ 179.9, 135.6 (d, J = 11.7 Hz), 132.9 butoxide solution (2M in THF) (0.05 mL, 0.10 mmol) followed by
(d, J = 51.3 Hz), 131.6, 129.1 (d, J = 10.8 Hz), 94.6, 75.9 (d, J = 8.7 a solution of dimethyl malonate (22.6 µl, 0.20 mmol) in THF (1
Hz), 74.2, 73.3, 70.9, 69.4, 68.0 (d, J = 3.1 Hz), 65.6, 29.4, 19.2, mL) at 0 °C. After stirring for 30 mins the solvent was removed
3
1
3
1
6
1
C
5.5 ; P NMR (202 MHz, MeCN-d ) δ 37.49.
under high vacuum to give a beige residue. In a separate flame
b. Obtained as a deep orange solid (0.025 g, 73%): mp 110 - dried Schlenk tube (tube-2), (S,S )-6b (0.0125 g, 0.020 mmol)
12 °C (under argon), MS (EI) [M] anal. calcd for was dissolved in CH Cl (1.7 mL) and then the contents of
p
+
2
2
2
2.8°C
28
H
29ClFeNOPPd 623.0, found 623.0; [α]
D
= -882 (c = 0.20, Schlenk tube (2) were transferred to Schlenk tube (1) and stirred
-1
MeCN); νmax (film)/cm 3077, 3055, 2961, 2929, 2871, 1615, at room temperature for 10 mins. The solvent was then
1
3
1
503; H NMR (500 MHz, MeCN-d ) δ 8.05 (2H, dd, J = 12.0, 7.4 removed in vacuo and the residue purified by column
Hz), 7.88 (2H, dd, J = 12.7, 7.3 Hz), 7.58 - 7.49 (4H, m), 7.47 (2H, chromatography (SiO , 10 % EtOAc/hexane) to give an orange
2
td, J = 7.3, 2.0 Hz), 6.56 (1H, d, J = 388.9 Hz), 4.64 (1H, dd, J = solid (0.007 g, 70%): mp >230 °C (under argon); HRMS (AS) [M-
+
9
(
.0, 6.2 Hz), 4.57 (1H, t, J = 9.7 Hz), 4.54 (1H, d, J = 2.2 Hz), 4.45 Cl] anal. calcd for C H Fe N O PPd 991.0103, found
4
4
46
2
2
2
2
2
0.1°C
-1
1H, brs), 4.37 (1H, t, J = 2.4 Hz), 4.17 - 4.12 (1H, m), 4.07 (5H, 991.0093; [α]D
s), 2.90 (1H, brs), 1.04 (3H, d, J = 5.9 Hz), 0.90 (3H, d, J = 7.0 Hz); 3096, 2958, 2923, 2967, 1617, 1495; H NMR (500 MHz, CDCl )
C NMR (125 MHz, MeCN-d ) δ 179.9, 135.2 (d, J = 11.1 Hz), δ 8.12 - 8.05 (4H, m), 7.38 - 7.34 (6H, m), 4.49 - 4.47 (4H, m),
= -2000 (c = 0.23, CHCl ); ν
max
(film)/cm
3
1
3
1
3
3
1
1
34.8 (d, J = 11.4 Hz), 132.2 (d, J = 2.6 Hz), 132.0 (d, J = 2.6 Hz), 4.36 (2H, d, J = 1.8 Hz), 4.08 (2H, td, J = 8.0, 4.6 Hz), 4.04 (10H,
29.9 (d, J = 10.8 Hz), 129.7 (d, J = 11.0 Hz), 129.5 (d, J = 51.2 s), 4.02 (2H, t, J = 2.3 Hz), 3.22 (2H, d, J = 1.6 Hz), 2.51 - 2.43 (2H,
1
3
Hz), 129.5 (d, J = 52.8 Hz), 91.6 (d, J = 8.0 Hz), 74.8 (d, J = 1.0 Hz), m), 1.06 (6H, d, J = 6.8 Hz), 0.97 (6H, d, J = 7.0 Hz); C NMR (125
7
6
3.8 (d, J = 15.7 Hz), 73.2 (d, J = 3.2 Hz), 70.7, 70.2 (d, J = 4.5 Hz), MHz, CDCl ) δ 177.9, 137.2 (d, J = 32.8 Hz), 135.4 (d, J = 12.7 Hz),
3
3
1
8.0 (d, J = 3.4 Hz), 66.8, 29.2, 19.1, 15.1; P NMR (202 MHz, 128.8, 127.8 (d, J = 10.5 Hz), 91.4 (d, J = 2.9 Hz), 75.1 (d, J = 8.6
3
MeCN-d ) δ 8.44.
Hz), 73.3 (d, J = 1.6 Hz), 72.2, 70.0, 69.0, 66.9, 64.5, 29.3, 19.6,
3
1
1
3
6.0; P NMR (202 MHz, CDCl ) δ 23.40.
Synthesis of (S,S
S)-117 (0.059 g, 0.2 mmol) was added to a flame dried Schlenk Synthesis of (S,S,S
tube under an atmosphere of argon and dissolved in dry THF (5 Addition of excess AgOAc to an NMR tube containing (S,S,S ,S )-
p
)-7
(
p p
,S )-8a
p
p
mL). The resulting orange solution was cooled to -78 °C and 8b showed the formation of acetate bridged palladacycle
(film)/cm- 3096, 2958, 2919, 2849, 1621,
1
stirred for 5 mins after which n-butyl lithium (2.5 M in hexanes) (S,S,S ,S )-8a; ν
(
p
p
max
1
0.11 mL, 0.28 mmol) was added slowly. After stirring for 2 1556, 1495; H NMR (500 MHz, CDCl ) δ 8.12 - 7.97 (4H, m), 7.33
3
hours the mixture was warmed to
0
°C and - 7.27 (6H, m), 4.51 - 4.46 (4H, m), 4.34 (2H, brs), 4.09 - 4.03 (2H,
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
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Page 6 of 7
ARTICLE
Journal Name
Weinheim, 2008. (c) Palladacycles: Catalysis and Beyond
m), 4.00 (10H, s), 3.97 (2H, brs), 3.00 (2H, brs), 2.70 - 2.60 (2H,
View Article Online
(
Eds.: A. R. Kapdi and D. Maiti), Elsevier, 2019.
DOI: 10.1039/D0OB01331E
m), 2.01 (3H, brs), 1.04 (6H, d, J = 6.8 Hz), 0.95 (6H, d, J = 7.1 Hz);
2
W. A. Herrmann, C. Brossmer, C.-P. Reisinger, T. H.
Riermeier, K. Ӧfele and M. Beller, Chem. Eur. J., 1997, 3,
3
1
3
P NMR (202 MHz, CDCl ) δ 55.63.
1
357.
Phosphine insertion studies
3
4
F. Bellina, A. Carpita, R. Rossi, Synthesis, 2004, 2419.
B. P. Fors and S. L. Buchwald, J. Am. Chem. Soc., 2010, 132,
1
p p
Using a glove box, 0.01 mmol of either (S,S )-2a or (S,S )-2b was
dissolved in CD Cl (0.7 mL) in an NMR tube fitted with a J.
2 2
Young valve under an inert atmosphere. After addition of the
reagents approximately 10 minutes elapsed before the first
NMR spectrum was recorded.
5914.
5
6
V. V. Dunina, O. N. Gorunova, P. A. Zykov and K. A.
Kochetkov, Russ. Chem. Rev., 2011, 80, 51.
(a) H. Nomura and C. J. Richards, Chem. Asian J., 2010, 5,
1726. (b) J. S. Cannon and L. E. Overman, Acc. Chem. Res.,
2
016, 49, 2220.
7
8
R. J. Chew and P.-H. Leung, Chem. Rec., 2016, 16, 141.
C. Schrapel and R. Peters, Angew. Chem. Int. Ed., 2015, 54,
In situ catalyst preparation and asymmetric allylic alkylation
(
conditions C).
1
0289.
To a flame dried Schlenk tube (tube-1) was added sodium tert-
butoxide solution (2M in THF) (0.05 mL, 0.10 mmol) followed by
a solution of dimethyl malonate (22.6 µl, 0.20 mmol) in THF (1
mL) at 0 °C. After stirring for 30 mins the solvent was removed
under high vacuum to give a beige residue. In a separate flame
9
1
K. Hyodo, S. Nakamura and N. Shibata, Angew. Chem. Int.
Ed., 2012, 51, 10337.
0 (a) M. Weber, S. Jautze, W. Frey and R. Peters, J. Am. Chem.
Soc., 2010, 132, 12222. (b) M. Weber and R. Peters, J. Org.
Chem., 2012, 77, 10846.
1
1
1 (a) M. P. Watson, L. E. Overman and R. G. Bergman, J. Am.
Chem. Soc., 2007, 129, 5031. (b) J. S. Cannon, S. F. Kirsch, L.
E. Overman and H. F. Sneddon, J. Am. Chem. Soc., 2010, 132,
dried Schlenk tube (tube-2), (S,S
was dissolved in CH Cl (1.7 mL) and phosphine (0.020 mmol)
was added and stirred for 10 mins. 1,3-Diphenylallyl acetate
0.252 g, 1.0 mmol) was dissolved in CH Cl (1.7 mL) and then
added to Schlenk tube (2) followed by dimethyl malonate (0.34
p
)-2b (0.0088 g, 0.010 mmol)
2
2
1
5192.
2 O. N. Gorunova, Y. K. Grishin, M. M. Ilyin (Jr.), K. A.
Kochetkov, A. V. Churakov, L. G. Kuz'mina and V. V. Dunina,
Russ. Chem. Bull., Int. Ed., 2017, 66, 282.
(
2
2
mL, 3.0 mmol). The contents of Schlenk tube (2) were 13 A number of chiral non-racemic Pd(II)-based pincer
transferred to Schlenk tube (1) and stirred for 5 mins after which
N,O-bis(trimethylsilyl)acetamide (0.74 mL, 3.0 mmol) was
added and the reaction allowed to stir at room temperature.
After completion or 24 hours (whichever came first), the
complexes have also been applied to asymmetric catalysis,
but again there appears to be no evidence that these
proceed via a Pd(0)/Pd(II) catalytic cycle. For a recent review
see: J.-K. Liu, J.-F. Gong and M.-P. Song, Org. Biomol. Chem.,
2
019, 17, 6069.
reaction was quenched with saturated ammonium chloride, 14 (a) L. F. Tietze, H. Ila and H. P. Bell, Chem. Rev., 2004, 104,
separated with diethyl ether, dried with magnesium sulphate
and the solvent removed in vacuo. A H NMR was performed at
this point to determine the conversion. Purification by column
3453. (b) Q.-A. Chen, Z.-S. Ye, Y. Duan and Y.-G. Zhou, Chem.
Soc. Rev., 2013, 42, 497.
5 (a) V. I. Sokolov, L. L. Troitskaya and O. A. Reutov, J.
Organomet. Chem., 1980, 202, C58. (b) C. Bolm, K. Wenz and
G. Raabe, J. Organomet. Chem., 2002, 662, 23. (c) V. A.
Stepanova, V. V. Dunina and I. P. Smoliakova,
1
1
chromatography (SiO
2
, 5 % EtOAc/hexane) gave the product (S)-
1
13
1
0 as a colourless oil for which the H/ C NMR spectra matched
3
3
Organometallics, 2009, 28, 6546. (d) V. A. Stepanova, V. V.
Dunina and I. P. Smoliakova, J. Organomet. Chem., 2011,
previously reported data. The enantiomeric excess was
determined by HPLC analysis using a CHIRALCEL OD-H column;
eluent = 98:2 (hexane:IPA); flow rate = 0.5 mL min ;
concentration = 0.0015 g/mL, injection volume = 5 µl,
wavelength = 254 nm. (S)-enantiomer RT = 20.5 min, (R)-
enantiomer RT = 18.9 min.
6
96, 871. (e) N. J. Korte, V. A. Stepanova and I. P.
-1
Smoliakova, J. Organomet. Chem., 2013, 745-746, 356. (f) G.
C. Dickmu, N. J. Korte, I. P. Smoliakova, J. Organomet. Chem.,
2015, 797, 13. (g) J. E. Kukowski, V. A. Stepanova and I. P.
Smoliakova, J. Organomet. Chem., 2017, 830, 155.
1
6 In addition, C-P bonds have also been formed by palladium
catalysed ortho-directed C-H activation via an intermediate
palladacycle. See L. Bonnafoux, R, Gramage-Doria, F.
Colobert and F. R. Leroux, Chem. Eur., J. 2011, 17, 11008.
Conflicts of interest
There are no conflicts to declare.
17 (a) T. Sammakia, H. A. Latham and D. R. Schaad, J. Org.
Chem., 1995, 60, 10.
1
1
2
8 (a) J.-B. Xia and S.-L. You, Organometallics, 2007, 26, 4869.
(
b) R. A. Arthurs, D. L. Hughes and C. J. Richards,
Acknowledgements
The EPSRC (EP/N019393/1) (R.A.A.) is thanked for financial
support. We also thank the EPSRC National Mass Spectrometry
Centre (University of Wales, Swansea).
Organometallics, 2019, 38, 4271.
9 (a) C. J. Richards, T. Damalidis, D. E. Hibbs and M. B.
Hursthouse, Synlett, 1995, 74. (b) Y. Nishibayashi and S.
Uemura, Synlett, 1995, 79.
0 (a) K. H. Ahn, C.-W. Cho, J. park and S. Lee, Tetrahedron:
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and P. J. Guiry, Tetrahedron Lett., 2000, 41, 2261. (c) M.
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Notes and references
1
22, 1804. (d) S.-L. You, X.-L. Hou, L.-X. Dai,. Y.-H. Yu and W.
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(a) J. Dupont, C. S. Consorti and J. Spencer, Chem. Rev., 2005,
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05, 2527. (b) Palladacycles: Synthesis Characterization and
Applications (Eds.: J. Dupont and M. Pfeffer), Wiley-VCH,
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| J. Name., 2012, 00, 1-3
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O rP gl ea na si ce &d Bo i on mo to al e dc juu l sa tr mC ha er mg i ins ts ry
Journal Name
M. Okumura, A. S. Shved and D. Sarlah, J. Am. Chem. Soc.,
ARTICLE
View Article Online
DOI: 10.1039/D0OB01331E
2
017, 139, 17787.
2
2
1 H. Minematsu, Y. Nonaka, S. Takahashi and N. Hagihara, J.
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2 3 P NMR spectral data from the use of CD
1
Cl
3
as solvent
2
2
excepting (S,S
and (S,S )-6b (MeCN-d ).
3 D. S. Black, G. B. Deacon and G. L. Edwards, Aust. J. Chem.,
994, 47, 217.
p
)-4, 8b, PPh
3
and HPPh
2
(CDCl
); (S,S
p
)-5a/b
3
p
2
2
2
1
4 J. A. Van Doorn and R. L. Wife Phosphorus Sulfur Silicon
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3
1
5 The (S,R
ppm/CDCl
9, 702.
p
) epimer of (S,S
3
p
)-7 is known ( P NMR = 36.10
). R. A. Arthurs and C. J. Richards, Org. Lett., 2017,
1
2
2
6 Full details including 31P NMR spectra are available in the
supporting information.
7 CCDC 1983850 contains the supplementary crystallographic
data for this paper. This data is provided free of charge by The
Cambridge Crystallographic Data Centre.
2
2
8 A. J. Reay and I. J. S. Fairlamb, Chem. Commun., 2015, 51,
1
6289.
9 Acetate-mediated phosphine oxidation with concomitant
Pd(II) reduction is known, but in this instance Pd(0)
formation is consistent with reductive elimination. See: C.
Amatore, A. Jutand and M. A. M’Barki, Organometallics,
1
992, 11, 3009.
3
3
0 B. M. Trost and D. L. Van Vranken, Chem, Rev., 1996, 96, 395.
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