Ferrocenyloxazoline-Derived Planar Chiral Palladacycles: C-H Activation, Transmetalation, and Reversal of Diastereoselectivity

Article abstract of DOI:10.1021/acs.organomet.9b00551

Reinvestigation of the palladation of (S)-2-ferrocenyl-4-(methylethyl)oxazoline with Pd(OAc)₂ in CH₂Cl₂ was found to proceed with a dr of 3.6:1 in favor of the resulting S,S_p palladacycle. A similar 4:1 dr was o

Full text of DOI:10.1021/acs.organomet.9b00551

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Cite This: Organometallics XXXX, XXX, XXX−XXX
Ferrocenyloxazoline-Derived Planar Chiral Palladacycles: C−H
Activation, Transmetalation, and Reversal of Diastereoselectivity
Ross A. Arthurs, David L. Hughes, and Christopher J. Richards*
School of Chemistry, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, U.K.
S
* Supporting Information
ABSTRACT: Reinvestigation of the palladation of (S)-2-ferrocenyl-4-(methylethyl)-
oxazoline with Pd(OAc)2 in CH2Cl2 was found to proceed with a dr of 3.6:1 in favor of
the resulting S,Sp palladacycle. A similar 4:1 dr was obtained using Na2PdCl4 in MeOH.
As an alternative approach, highly diastereoselective lithiation (dr >100:1) and
transmetalation were investigated. Addition of PdX2(COD) (X = Cl, Br) to (S,Rp)-2-
lithio-1-(2′-(4′-methylethyl)oxazolinyl)ferrocene resulted in double halide substitution
and formation of cis-(S,S,Sp,Sp)-bis[2-(2′-(4′-methylethyl)oxazolinyl)ferrocene-1-C,3′-
N]palladium(II) (42% from X = Cl, 50% from X = Br). Selective monoprotodepalla-
dation with HCl gave an S,Sp palladacycle containing a removable ferrocenyloxazoline
ligand. Addition of PdCl2(MeCN)2 to mercuracycles in acetonitrile, themselves
generated from Li−Hg transmetalation, followed by a brine wash gave (S,Sp)-di-μ-
chlorobis[2-(2′-(4′-methylethyl)oxazolinyl)ferrocene-1-C,3′-N]dipalladium(II) as a
single diastereoisomer in high yield. The alternative S,Rp diastereoisomer was obtained
in the same way by use of a deuterium blocking group to reverse lithiation diastereoselectivity.
our hands (S,Sp)-2 was obtained in 12% yield as a single
diastereoisomer following chromatography of the initially very
dark product mixture and subsequent crystallization from
CH2Cl2/hexane. Performing the reaction at room temperature
resulted in a less dark product mixture and an increase in the
yield of the pure diastereoisomer to 36% (Scheme 1). Use of
glacial acetic acid at 95 °C with Pd(OAc)2 resulted only in
decomposition.9b The isolation of (S,Sp)-2 as a single
diastereoisomer following crystallization was supported by
formation of the hfacac complex (S,Sp)-3, which showed a
single set of signals by 19F NMR spectroscopy at −74.72 and
−75.71 ppm. Crystals of (S,Sp)-3 obtained from EtOAc/
hexane confirmed the stereochemical assignment (Figure 1).
The diastereoselectivity of the room-temperature cyclo-
palladation of (S)-1 was determined as 3.6:1 by forming the
hfacac complex from the product mixture prior to purification.
This gave an additional set of 19F signals at −74.73 and −75.68
ppm. The improved 60% yield for this reaction confirmed the
poor stability of (S,Sp)-2 toward column chromatography. This
was required to remove impurities from the initially very dark
product mixture prior to crystallization to give diastereomeri-
cally pure (S,Sp)-2.
INTRODUCTION
■
The synthesis and application of palladacycles is a significant
branch of organometallic chemistry.1 In addition to the use of
these compounds in the development of new materials,2 they
have also been employed as precatalysts3 and catalysts4 in
organic synthesis. Palladacycles have also been identified as
intermediates in many palladium-catalyzed C−H activation
reactions, resulting in new C−C5 or C−heteroatom bonds.5b,6
Similarly, C−H activation is also the principal method used for
palladacycle synthesis.7 This may be accompanied by the
generation of a new element of chirality in an enantioselective8
or diastereoselective9 process that typically, but not exclu-
sively,10 results in a planar chiral product. Ferrocenyloxazo-
lines, such as (S)-valine-derived (S)-1, are readily synthesized
precursors to planar chiral derivatives that result from the
addition of an electrophile after highly diastereoselective α-
lithiation.11 Introduction in this way of iodine, followed by
oxidative addition of Pd(0), provides access to planar chiral
palladacycles.12 Alternatively, the direct cyclopalladation of
(S)-1 is known as a route to S,Sp palladacycles, although the
diastereoselectivity of this reaction is not clear.9d In view of the
potential of palladacycles derived from (S)-1 as catalysts and
precatalysts in asymmetric synthesis, we chose to reinvestigate
this C−H activation reaction. We also explored trans-
metalation approaches to the selective generation of both
planar chiral palladacyclic diastereoisomers. The results of
these investigations are reported in this paper.
We next investigated the cyclopalladation of (S)-1 using
Na2PdCl4 in methanol at room temperature. The chloride-
bridged palladacycle (S,Sp)-4 was obtained in 42% yield as a
single diastereoisomer after chromatography. In contrast to
(S,Sp)-2, its chloride-bridged congener (S,Sp)-4 resulted in less
decomposition during column chromatography. Crystals of
RESULTS AND DISCUSSION
■
The cyclopalladation of (S)-1 with Pd(OAc)2 in CH2Cl2
heated at reflux was performed as previously reported.9d In
Received: August 14, 2019
© XXXX American Chemical Society
A
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Scheme 1. Cyclopalladation of Oxazoline (S)-1 and Subsequent Ligand Exchange
Figure 1. X-ray structure of (S,Sp)-3. Hydrogens are omitted for clarity. The structure depicted is one of four molecules contained in the unit cell.
Principal bond lengths (Å): C(1)−Pd(1) 1.955(4), N(1)−Pd(1) 2.025(3), O(1)−Pd(1) 2.099(3), O(2)−Pd(1) 2.025(3). Principal bond angles
(deg): C(1)−Pd(1)−N(1) 80.87(14), O(1)−Pd(1)−O(2) 92.40(10). Thermal ellipsoids are drawn at the 50% probability level. Flack parameter:
−0.007(5).
(S,Sp)-4 suitable for X-ray crystallography were obtained from
CH2Cl2/hexane, showing that in this phase the dimer (S,Sp)-4
is in the trans configuration (Figure 2, with trans referring to
the opposite orientation of the bidentate CN ligands about the
was determined by omitting the chromatography step prior to
reaction with Na(hfacac), and this gave a 4:1 mixture of
diastereoisomers. The chloride-bridged palladacycle (S,Sp)-4
was also obtained after room-temperature palladation with
Pd(OAc)2, acetate/chloride ligand exchange, and subsequent
column chromatography. In addition to (S,Sp)-4 (36%) and its
diastereoisomer (S,Rp)-5 (14%), this method also gave the
oxazoline-coordinated palladium chloride adduct (S,S)-6
(14%). Lower yields of (S,Sp)-4 (22%) and (S,Rp)-5 (10%)
were obtained when the initial cyclopalladation step with
Pd(OAc)2 was carried out at 40 °C, as a result of
cyclopalladation product decomposition under these con-
ditions. Analysis of (S,S)-6 by X-ray crystallography revealed
1
Pd2Cl2 core). In contrast, examination of these crystals by H
NMR spectroscopy in CDCl3 revealed a 1.7:1 ratio of isomers,
although the identity of the major dimer as cis or trans could
not be determined.
The configuration of (S,Sp)-4 was further confirmed by
generating this complex by ligand exchange from (S,Sp)-2 on
reaction with LiCl in H2O/acetone. Additionally, reaction of
Na(hfacac) with (S,Sp)-4 gave (S,Sp)-3 in a quantitative yield.
The selectivity of the cyclopalladation reaction with Na2PdCl4
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Figure 2. X-ray structure of (S,Sp)-4. Hydrogens are omitted for clarity. Principal bond lengths (Å): C(1)−Pd(1) 1.948(3), N(1)−Pd(1) 2.048(2),
Cl(1)−Pd(1) 2.4636(8), Cl(2)−Pd(1) 2.3130(7). Principal bond angles (deg): C(1)−Pd(1)−N(1) 80.27(11), Cl(1)−Pd(1)−Cl(2) 88.56(2).
Principal torsion angle (deg): C(1)−Pd(1)−Cl(2)−Pd(2) −160.20. Thermal ellipsoids are drawn at the 50% probability level. Flack parameter:
−0.005(6).
Figure 3. X-ray structures of (S,S)-6. Hydrogens are omitted for clarity. Principal torsion angles (deg): Cl(1)−Pd(1)−N(1)−C(1) −79.48, Cl(1)−
Pd(1)−N(2)−C(2) 69.43, Cl(1′)−Pd(1′)−N(1′)−C(1′) 67.55, Cl(1′)−Pd(1′)−N(2′)−C(2′) 74.22. Thermal ellipsoids are drawn at the 50%
probability level. Flack parameter: −0.003(9).
two rotameric structures in the unit cell (Figure 3), these also
being present in solution in a 1:1 ratio, as determined by H
NMR spectroscopy in MeCN-d3.
In an attempt to add selectively a single ferrocenyloxazoline
unit to palladium, zinc chloride was added to the reaction
mixture after diastereoselective lithiation to generate, by
transmetalation, the corresponding ferrocenylzinc intermedi-
ate. We reasoned that its lower reactivity would reduce the
likelihood of double addition, but instead after addition of
PdCl2(MeCN)2 only (S,S,Sp,Sp)-7 was again isolated. The
absence from these reactions of any evidence for the formation
of (S,Sp)-4 suggests that the second M to Pd (M = Li, Zn)
transmetalation reaction is faster than the first, an outcome
consistent with the high trans effect of the anionic ferrocenyl
anion ligand.14
Addition of 1 equiv of 2 M HCl in Et2O to a solution of
(S,S,Sp,Sp)-7 in dichloromethane resulted in monoprotodepal-
ladation and formation of the palladacycle (S,S,Sp)-8 (Scheme
2). Monoprotodepalladation also took place when (S,S,Sp,Sp)-7
was added to biphasic 1.6 M HClaq/dichloromethane. After
shaking, separation and evaporation gave (S,S,Sp)-8. The
identity of this complex was confirmed by the addition of 2
equiv of (S)-1 to 1 equiv of (S,Sp)-4 in an NMR tube,
confirming that oxazoline addition to the chloride-bridged
1
In light of the modest diastereoselectivity of direct
cyclopalladation and the relatively low yields obtained after
purification, we chose to explore an alternative transmetalation
approach following initial highly diastereoselective lithiation.13
This was achieved by the addition of s-BuLi to (S)-1 in diethyl
ether in the presence of TMEDA (Scheme 2).11a Subsequent
addition of a solution of PdBr2(COD) in THF at 0 °C and
warming to room temperature resulted in lithium−palladium
transmetalation occurring twice and formation of the complex
(S,S,Sp,Sp)-7 in 50% yield. The same product was obtained in
42% yield using the same procedure with PdCl2(COD).
Crystals of the complex (S,S,Sp,Sp)-7 were obtained from a
concentrated sample in chloroform, and the cis configuration
was determined by X-ray crystallography (Figure 4). The cis
configuration is, at least in part, a consequence of the S,Sp-
configured ligands, as the alternative trans arrangement would
result in an steric clash between the isopropyl and iron−
cyclopentadienyl moieties.
C
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Scheme 2. Use of Lithium−Palladium Transmetalation for the Synthesis of Palladacycles Derived from (S)-1
chiral ferrocenyloxazolines.15 One benefit of this route is that
the stable mercury species can be synthesized and, where
needed, purified to give a single diastereoisomer, leading in
turn to a single diastereoisomer of transmetalation product.
With this in mind we first attempted the synthesis of (S,Sp)-4
utilizing this methodology. Mercuracycle (S,Sp)-9 was
synthesized as reported previously with an improved yield of
73% (see the Supporting Information). This was then used in
conjunction with PdCl2(MeCN)2 under different conditions in
the attempted synthesis of (S,Sp)-4 (Table 1; see the
Supporting Information for a full list of palladium sources
and conditions investigated).
Table 1. Toward the Synthesis of (S,Sp)-4 by
a
Transmetalation with (S,Sp)-9
b
entry
solvent
temp (°C)
major product (yield (%))
c
1
2
3
4
5
6
7
CH2Cl2
acetone
MeCN
40
56
60
56
(S,S,Sp,Sp)-10
(S,Sp)-4 (48)
c
c
(S,S,Sp,Sp)-10
d
acetone
(S,S,Sp,Sp)-10
e
c f
,
acetone
room temp
room temp
room temp
(S,Sp)-11
e g
,
MeCN
MeCN
(S,Sp)-11 (95)
(S,Sp)-4 (95)
Figure 4. X-ray structure of (S,S,Sp,Sp)-7. Hydrogens are omitted for
clarity. The structure depicted is one of two molecules contained in
the unit cell. Principal bond lengths (Å): C(1)−Pd(1) 1.995(6),
N(1)−Pd(1) 2.148(4). Principal bond angles (deg): C(1)−Pd(1)−
N(1) 81.09(19), C(1)−Pd(1)−C(2) 95.8(3), N(1)−Pd(1)−N(2)
102.5(2). Thermal ellipsoids are drawn at the 50% probability level.
Flack parameter: −0.021(9).
e gh
, ,
a
All reactions were carried out with 1 equiv of PdCl2(MeCN)2 with a
b
reaction time of 16 h unless otherwise stated. Yield of (S,S,Sp,Sp)-10
not determined. Formation of Pd black observed. Addition of 10
c
d
e
f
equiv of TBAC. Reaction time reduced to 1 h. Yield not determined.
g
h
2 equiv of PdCl2(MeCN)2 used. Reaction followed immediately by
a brine wash.
dimer is essentially irreversible. The oxazoline ligand could be
removed partially by reaction with Na(hfacac) over a 48 h
period, giving a conversion of 60% and an isolated 25% yield of
(S,Sp)-3. Thus, overall, lithium−palladium transmetalation is a
viable route to planar chiral palladacycles, albeit that the
initially formed bis-palladacycle requires subsequent proto-
demetalation and ligand exchange to generate non-pallada-
cycle/ferrocenyloxazoline-based coordination sites.
An initial series of reactions with CH2Cl2, acetone, or MeCN
as solvent heated at reflux resulted in palladium black
formation (Table 1. entries 1−3). The desired palladacycle
(S,Sp)-4 was obtained as a single diastereoisomer in 48% yield
in acetone (entry 2), the other reactions resulting only in the
adduct (S,S,Sp,Sp)-10 (Scheme 3). The identity of (S,S,Sp,Sp)-
10 was revealed initially by the similarity of its H NMR
spectrum to that of (S,S)-6, in particular by both complexes
displaying signals corresponding to a 1:1 ratio of rotamers.
1
We recently reported the synthesis of planar chiral
iridacycles by transmetalation with mercury-substituted planar
D
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immediately before silica filtration gave the desired pallada-
cycle (S,Sp)-4 in 95% yield (entry 7). Heating (S,Sp)-11 in
MeCN at 60 °C overnight showed palladium black formation
and decomposition of the starting material. In contrast, heating
(S,Sp)-4 and (S,S,Sp,Sp)-10 separately in MeCN overnight
resulted in no decomposition. Silica gel chromatography of
(S,Sp)-11 also showed signs of decomposition, as when the
compound was left stationary on silica for more than 2 min the
silica turned black.
Scheme 3. Transmetalation Products Utilizing (S,Sp)-9
With a suitable method for the synthesis of diastereomeri-
cally pure palladacycle (S,Sp)-4 in hand, we turned our
attention to the synthesis of palladacycle (S,Rp)-5 (Scheme 4).
Ferrocenyloxazoline (S,Rp)-2-d-1 with 90% deuterium incor-
poration was first synthesized as previously described by highly
selective lithiation followed by a MeOH-d4 quench.17
Subsequent lithiation of (S,Rp)-2-d-1 under poorly selective
conditions17 and quenching with mercury(II) chloride gave the
mercuracycle (S,Rp)-5-d-13 as a single diastereoisomer in 59%
yield following purification. Stirring (S,Rp)-5-d-13 with 2 equiv
of Pd(MeCN)2Cl2 in MeCN at room temperature for 1 h,
followed by a brine wash and silica plug filtration, resulted in a
successful transmetalation to give the palladacycle (S,Rp)-5-d-5
in 92% yield. Its 1H NMR spectrum corresponded exactly with
that of (S,Rp)-5 obtained previously except for the absence of
cyclopentadienyl signals at 4.51 (minor) and 4.45 (major)
ppm due to deuterium incorporation (1.4:1 ratio of isomers).
Furthermore, (S,S,Sp,Sp)-10 was prepared with a yield of 44%
by addition of PdCl2 to a solution of (S,Sp)-9 in 3/2 CH2Cl2/
MeOH. Repetition of the acetone-based reaction with addition
of TBAC (tetrabutylammonium chloride) prevented palladium
black formation but only resulted in the adduct (S,S,Sp,Sp)-10
(entry 4). In contrast, performing this reaction in the absence
of TBAC at room temperature (ca. 22 °C) still resulted in
significant darkening of the reaction mixture, but a new
complex was formed as the major product. For this, a
cyclopentadienyl singlet at 4.38 ppm in the 1H NMR spectrum
and three multiplets at 4.64, 4.55, and 4.12 ppm resulting from
a doubly substituted cyclopentadienyl ring were similar to but
different from the other palladacycles described in this work.
Addition to this species of 4 equiv of PPh3 revealed only two
peaks (1:1 ratio) in the 31P NMR spectrum of the resulting
product at 38.03 and 27.69 ppm. These two signals were
identified as the phosphine complexes (S,Sp)-12 and
HgCl2(PPh3)2 by their separate preparation from palladacycle
(S,Sp)-4 and HgCl2, respectively. In light of this stoichiometry
we tentatively assigned the identity of this precursor complex
as palladacycle (S,Sp)-11 containing a bridging mercury
moiety.16
CONCLUSION
■
Cyclopalladation of (S)-1 has been determined to proceed
with an S,Sp:S,Rp diastereomeric ratio of 3.6:1 using Pd(OAc)2
in CH2Cl2 and 4:1 using Na2PdCl4 in MeOH. Palladacycles
derived from (S)-1 were also obtained by employing highly
diastereoselective lithiation followed by addition of
PdX2(COD) (X = Cl, Br) to give bis-palladacycle
(S,S,Sp,Sp)-7 incorporating two ferrocenyloxazoline units. The
same compound was obtained when lithium−zinc trans-
metalation preceded addition of PdCl2(MeCN)2. Selective
monoprotodepalladation was used to generate monopallada-
cycles from (S,S,Sp,Sp)-7. The chloride-bridged monopallada-
cycle (S,Sp)-4 was generated by transmetalation using a
mercuracyclic intermediate (itself generated by Li−Hg trans-
metalation). Key to this reaction is the use of a 2/1 Pd/Hg
stoichiometry and a brine wash prior to product isolation. In
the same way the alternative planar chiral diastereoisomer
(S,Rp)-5-d-5 was formed from the corresponding mercuracycle,
itself generated selectively by use of a deuterium blocking
group. The use of these palladacycles in catalysis is currently
under investigation and will be reported shortly.
Changing to acetonitrile as solvent at room temperature
resulted in the complete loss of mercuracycle (S,Sp)-9 and
immediate formation of (S,S,Sp,Sp)-10 and (S,Sp)-11. Increas-
ing the amount of Pd(MeCN)2Cl2 employed to 2 equiv
resulted in the sole formation of (S,Sp)-11, which was isolated
in 95% yield (Table 1, entry 6). Washing a CH2Cl2 solution of
(S,Sp)-11 with brine cleanly gave the palladacycle (S,Sp)-4.
Finally, use of the same conditions followed by a brine wash
EXPERIMENTAL SECTION
General Remarks. Caution! All organomercurials are highly toxic.
Extreme care is necessary in handling all products and their solutions.
■
Scheme 4. Synthesis of Palladacycle (S,Rp)-5-d-5 via Transmetalation
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Diethyl ether and THF were distilled over sodium and benzophenone
ketyl. Acetonitrile and dichloromethane were dried by distillation
from calcium hydride. Methanol was dried over 4 Å molecular sieves.
All cyclopalladation reactions and reactions involving the use of dry
solvents were carried out under an inert atmosphere of either nitrogen
or argon. Silica gel (60 Å pore size, 40−63 μm technical grade) and
neutral aluminum oxide (Brockmann I, 50−200 μm) were used for
chromatography.
product. Purification by column chromatography (SiO2, 15% EtOAc
in hexane) yielded an orange solid (0.06 g, 92%). Data match those
reported below for (S,Sp)-4.
Preparation of (S,Sp)-3 from (S,Sp)-4. (S,Sp)-4 (0.071 g, 0.081
mmol) and sodium hexafluoroacetylacetonate (0.052 g, 0.22 mmol)
were placed in a Schlenk tube and dissolved in a 1/1 mixture of water
and acetone (6 mL each). The resulting suspension was stirred
vigorously overnight, after which the reaction mixture was separated
between water and dichloromethane, the organic phase dried with
magnesium sulfate, and the solvent removed in vacuo. Purification by
column chromatography (SiO2, 15% EtOAc in hexane) yielded a red
solid as a single diastereoisomer (0.046, 99%). Data match those
reported above for (S,Sp)-3.
Preparation of (S,Sp)-2. (S)-111d (0.149 g, 0.50 mmol) and
palladium acetate (0.112 g, 0.50 mmol) were placed in a flame-dried
Schlenk tube and dissolved in dichloromethane (2.5 mL). After it was
stirred overnight, the reaction mixture was filtered through a short pad
of silica to remove a black residue using dichloromethane as the
eluent and the solvent removed in vacuo. The crude product was
redissolved in a minimal amount of dichloromethane and transferred
to a boiling tube, hexane was layered on top, and the mixture was
transferred to a freezer for crystals to grow. After crystal formation,
the solvent was decanted off and the crystals werewashed with ice-
cold hexane to give the product as dark red crystals (0.08 g, 36%).
20.2 °C
Preparation of (S,Sp)-4 via (S,Sp)-2. (S)-111d (0.297 g, 1.00
mmol) and palladium acetate (0.2245 g, 1.00 mmol) were placed in a
flame-dried Schlenk tube and dissolved in dichloromethane (5 mL).
After the mixture was stirred overnight at room temperature, the
solvent was removed in vacuo, the residue was redissolved in a 1/1
mixture of water and acetone (8 mL each), and lithium chloride
(0.424 g, 10.00 mmol) was added. The resulting suspension was
stirred vigorously overnight, after which the reaction mixture was
separated between water and dichloromethane, the organic phase
dried with magnesium sulfate, and the solvent removed in vacuo.
Careful purification by long-column chromatography (SiO2, 50/50
CH2Cl2/hexane) was able to separate the diastereoisomers, yielding
both as orange solids.
[α]D
= −1090 (c 0.27, CHCl3). IR (film; cm−1): 3089, 2963,
1
2930, 2870, 1609 (CN), 1577 (CO), 1507, 1411. H NMR (500
2+3
MHz, CDCl3): δ 4.30−4.26 (14H, m, CpH), 4.16 (2H, apt,
J
HH
=
3
7.2 Hz, CHH), 4.11 (2H, d, JHH = 1.6 Hz, CpH), 3.78 (2H, apt,
2+3
3
3
J
= 9.2 Hz, CHH), 3.08 (2H, dt, JHH = 12.1, JHH = 4.1 Hz,
HH
CH), 2.10−2.04 (2H, m, CH), 2.03 (6H, s, CH3), 0.93 (6H, d, 3JHH
=
6.7 Hz, CH3), 0.81 (6H, d, JHH = 7.0 Hz, CH3). 13C NMR (125
MHz, CDCl3): δ 181.1 (CH3C(O)O), 178.0 (CN), 87.0 (CpC),
72.2 (CH2), 71.2 (CpC), 71.0 (CpC), 70.3 (CpC), 66.5 (CpC), 65.9
3
First To Elute (S,Rp)-5 (0.06 g, 14%). Rf = 0.20 (50/50 CH2Cl2/
hexane). Mp: ∼150 °C dec (under argon). [α]D23.6 °C = +1215 (c 0.66,
MeCN). IR (film; cm−1): 3088, 2954, 2925, 2871, 1600 (CN), 1506.
Major isomer 1H NMR (500 MHz, MeCN-d3): δ 4.72−4.65 (6H, m,
CH2 + CpH), 4.45 (2H, d, 3JHH = 2.1 Hz, CpH), 4.30 (10H, s, CpH),
4.23 (2H, t, 3JHH = 2.3 Hz, CpH), 4.02−3.95 (2H, m, CH), 2.09−2.01
’
(CH), 63.7 (CpC), 28.9 (CH), 23.8 (CH3), 19.2 (CH3 ), 15.6 (CH3).
Data were previously reported.9d
Preparation of (S,Sp)-3 from (S,Sp)-2. (S,Sp)-2 (0.083 g, 0.09
mmol) and sodium hexafluoroacetylacetonate (0.052 g, 0.22 mmol)
were placed in a Schlenk tube and dissolved in a 1/1 mixture of water
and acetone (6 mL each). The resulting suspension was stirred
vigorously overnight, after which the reaction mixture was separated
between water and dichloromethane, the organic phase dried with
magnesium sulfate, and the solvent removed in vacuo. Purification by
column chromatography (SiO2, 15% EtOAc in hexane) yielded a red
solid as a single diastereoisomer (0.052 g, 99%). Rf = 0.24 (15%
20.7 °C
(2H, m, CH), 0.91 (6H, d, 3JHH = 7.1 Hz, CH3), 0.78 (6H, d, 3JHH
=
6.9 Hz, CH3). Minor isomer 1H NMR (500 MHz, MeCN-d3): δ
4.63−4.59 (6H, m, CH2 + CpH), 4.51 (2H, d, 3JHH = 2.2 Hz, CpH),
3
4.34 (10H, s, CpH), 4.31 (2H, t, JHH = 2.3 Hz, CpH), 4.02−3.95
3
3
(2H, m, CH), 2.53 (2H, dq, JHH = 10.0, JHH = 7.0 Hz, CH), 0.83
(6H, d, 3JHH = 7.2 Hz, CH3), 0.66 (6H, d, 3JHH = 6.9 Hz, CH3). Major
isomer 13C NMR (125 MHz, MeCN-d3): δ 180.3 (CN), 90.2
(CpC), 75.5 (CpC), 73.6 (CH2), 72.1 (CpC), 71.3 (CpC), 68.9
EtOAc in hexane). Mp: 138−140 °C (under argon). [α]D
=
’
(CpC), 67.5 (CH), 65.6 (CpC), 30.8 (CH), 18.7 (CH3 ), 14.9 (CH3).
−990 (c 0.44, CHCl3). IR (film; cm−1): 2963, 2930, 2873, 1630
Minor isomer 13C NMR (125 MHz, MeCN-d3): δ 180.5 (CN),
92.0 (CpC), 74.2 (CpC), 73.3 (CH2), 72.0 (CpC), 71.3 (CpC), 69.2
(CpC), 66.9 (CH), 65.9 (CpC), 29.7 (CH), 18.6 (CH3), 14.0 (CH3).
High-resolution MS (m/z, ASAP+): [M + H]+ = 876.8998, calcd for
C32H36Cl2Fe2N2O2Pd2 + H+ 876.9012.
1
(CN), 1604 (CO), 1510 (CO), 1477, 1261, 1208, 1148. H NMR
3
(500 MHz, CDCl3): δ 6.08 (1H, s, CH), 4.73 (1H, dd, JHH = 2.2,
2+3
4JHH = 0.5 Hz, CpH), 4.58 (2H, apd,
J
HH
= 8.2 Hz, CH2), 4.47
3
4
(1H, dd, JHH = 2.4, JHH = 0.6 Hz, CpH), 4.33 (5H, s, CpH), 4.31
(1H, t, 3JHH = 2.4 Hz, CpH), 3.97 (1H, td, 3JHH = 8.1, 3JHH = 4.1 Hz,
CH), 2.43−2.32 (1H, m, CH), 1.09 (3H, d, 3JHH = 6.9 Hz, CH3), 0.96
(3H, d, 3JHH = 7.1 Hz, CH3). 13C NMR (125 MHz, CDCl3): δ 180.6
(CN), 174.9 (2CO), 118.4 (q, 1JCF = 508 Hz, 2CF3), 90.5 (CH),
89.9 (CpC), 72.6 (CH2), 71.4 (CpC), 71.1 (CpC), 70.5 (CpC), 67.6
(CpC), 66.2 (CH), 64.7 (CpC), 28.6 (CH), 19.0 (CH3), 15.3 (CH3).
19F NMR (470 MHz, CDCl3): −74.73 (CF3), −75.71 (CF3). High-
resolution MS (m/z, ASAP+): [M + H]+ = 609.9744, calcd for
C21H19F6FeNO3Pd + H+ 609.9742.
Second To Elute (S,Sp)-4 (0.15 g, 36%). Rf = 0.17 (50/50 CH2Cl2/
20.7 °C
hexane). Mp: ∼200 °C dec (under argon). [α]D
= −1470 (c
0.27, CHCl3). IR (film; cm−1): 3096, 2960, 2926, 2870, 1600 (CN),
1
1510. Major isomer H NMR (500 MHz, MeCN-d3): δ 4.67−4.62
(4H, m, CHH + CpH), 4.59−4.51 (2H, m, CHH), 4.42 (2H, d, 3JHH
3
= 1.8 Hz, CpH), 4.27 (10H, s, CpH), 4.25 (2H, t, JHH = 2.4 Hz,
CpH), 3.95−3.88 (2H, m, CH), 2.21−2.15 (2H, m, CH), 1.09 (6H,
3
3
d, JHH = 6.9 Hz, CH3), 0.97 (6H, d, JHH = 7.1 Hz, CH3). Minor
isomer 1H NMR (500 MHz, MeCN-d3): δ 4.67−4.62 (2H, m, CpH),
Preparation of (S,Sp)-4. (S)-111d (0.149 g, 0.50 mmol), sodium
tetrachloropalladate (0.147 g, 0.50 mmol), and sodium acetate (0.045
g, 0.55 mmol) were placed in a flame-dried Schlenk tube and
dissolved in methanol (2 mL). After the mixture was stirred overnight,
the solvent was removed in vacuo and the residue filtered through
Celite using dichloromethane as the eluent, whereupon the solvent
was removed in vacuo again. Purification by column chromatography
(SiO2, 100% CH2Cl2) yielded an orange solid (0.065 g, 21%). Data
match those reported below for (S,Sp)-4.
Preparation of (S,Sp)-4 from (S,Sp)-2. (S,Sp)-2 (0.071 g, 0.08
mmol) and lithium chloride (0.033 g, 0.77 mmol) were placed in a
Schlenk tube and dissolved in a 1/1 mixture of acetone and water (5.5
mL each). After the mixture was stirred overnight at room
temperature, the resulting suspension was filtered through sintered
glass and the orange solid washed with hexane to give the crude
3
4.59−4.51 (4H, m, CH2), 4.47 (2H, d, JHH = 2.2 Hz, CpH), 4.35−
4.33 (2H, m, CpH), 4.32 (10H, s, CpH), 3.95−3.88 (2H, m, CH),
2.87−2.80 (2H, m, CH), 1.01 (6H, d, 3JHH = 6.9 Hz, CH3), 0.86 (6H,
3
d, JHH = 7.1 Hz, CH3). Major isomer 13C NMR (125 MHz, MeCN-
d3): δ 180.6 (CN), 91.9 (CpC), 74.9 (CpC), 73.4 (CH2), 72.7
(CpC), 70.9 (CpC), 68.6 (CpC), 67.6 (CH), 65.0 (CpC), 30.4 (CH),
19.2 (CH3), 15.4 (CH3). Minor isomer 13C NMR (125 MHz, MeCN-
d3): δ 180.4 (CN), 91.5 (CpC), 73.4 (CH2), 73.2 (CpC), 72.6
(CpC), 70.9 (CpC), 68.9 (CpC), 67.1 (CH), 65.2 (CpC), 29.0 (CH),
18.9 (CH3), 14.7 (CH3). High-resolution MS (m/z, ASAP+): [M +
H]+ = 876.9014, calcd for C32H36Cl2Fe2N2O2Pd2 + H+ 876.9012.
Third To Elute (S,S)-6 (0.05 g, 14%). Rf = 0.08 (50/50 CH2Cl2/
hexane). Mp: ∼225 °C dec (under argon). [α]D22.8 °C = +291 (c 0.35,
1
MeCN). IR (film; cm−1): 3095, 2958, 2929, 2874, 1633 (CN). H
F
DOI: 10.1021/acs.organomet.9b00551
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
NMR (500 MHz, MeCN-d3): δ 6.27 (2H, brs, CpH), 5.92 (2H, brs,
CpH), 5.88 (2H, brs, CpH), 5.59 (2H, brs, CpH), 4.69−4.59 (8H, m,
CpH), 4.43−4.32 (32H, m, CpH + CH2 + CH), 3.37−3.26 (2H, m,
CH), 3.06−2.97 (2H, m, CH), 1.12 (6H, d, 3JHH = 6.7 Hz, CH3), 1.08
CDCl3): δ 5.97−5.95 (1H, m, CpH), 5.55−5.52 (1H, m, CpH),
4.65−4.58 (2H, m, CH + CHH), 4.54−4.46 (3H, m, CHH + CH2),
3
4
4.44−4.42 (2H, m, CpH), 4.40 (1H, td, JHH = 2.5, JHH = 1.3 Hz,
CpH), 4.25 (5H, s, CpH), 4.22 (5H, s, CpH), 4.21−4.19 (2H, m,
3
4
(12H, d, 3JHH = 7.0 Hz, CH3), 1.03 (6H, d, 3JHH = 6.7 Hz, CH3). 13
C
CpH + CH), 4.01 (1H, dd, JHH = 2.2, JHH = 0.6 Hz, CpH), 3.19
3
NMR (125 MHz, MeCN-d3): δ 171.0 (CN), 170.8 (CN), 73.4
(CpC), 72.8 (CpC), 72.7 (4CpC), 72.6 (2CH), 72.5 (CpC), 72.1
(CpC), 71.3 (2CpC), 69.1 (CH2), 68.4 (CH2), 67.2 (CpC), 67.1
(CpC), 31.1 (CH), 30.6 (CH), 19.5 (CH3), 19.0 (CH3), 16.1 (CH3),
15.1 (CH3). High-resolution MS (m/z, ASAP+): [M-Cl]+ = 735.0367,
calcd for C32H38ClFe2N2O2Pd+ 735.0369.
(1H, m, CH), 3.05 (1H, m, CH), 1.17 (3H, d, JHH = 6.7 Hz, CH3),
1.13 (3H, d, 3JHH = 7.1 Hz, CH3), 1.06 (3H, d, 3JHH = 6.9 Hz, CH3),
0.92 (3H, d, JHH = 7.1 Hz, CH3). 13C NMR (125 MHz, CDCl3): δ
3
179.0 (CN), 170.4 (CN), 90.0 (CpC), 73.8 (CH), 72.9 (CpC),
72.1 (CH2), 72.0 (CpC), 71.8 (CpC), 71.6 (CpC), 71.4 (CpC), 71.0
(CpC), 70.2 (CpC), 69.9 (CpC), 67.8 (CH2), 67.7 (CpC), 66.8
(CpC), 66.6 (CH), 64.4 (CpC), 30.6 (CH), 28.3 (CH), 19.7 (CH3),
19.2 (CH3), 15.2 (CH3), 14.7 (CH3). High-resolution MS (m/z,
ASAP+): [M − Cl + H]+ = 699.0620, calcd for C32H36Fe2N2O2Pd +
H+ 699.0605.
Preparation of (S,S,Sp,Sp)-7. (S)-111d (0.100 g, 0.34 mmol) was
placed in a flame-dried Schlenk tube under an inert atmosphere and
dissolved in dry diethyl ether (4 mL). Tetramethylethylenediamine
(0.07 mL, 0.44 mmol) was added, and the solution was cooled to −78
°C and stirred for 5 min, after which s-butyllithium (1.4 M in
hexanes) (0.31 mL, 0.44 mmol) was slowly added and the mixture
stirred for 2 h. In a separate flame-dried Schlenk tube, a suspension of
dibromo(1,5-cyclooctadiene)palladium(II) or dichloro(1,5-
cyclooctadiene)palladium(II) (0.47 mmol) was made up in
tetrahydrofuran (5 mL). When the reaction mixture was warmed to
0 °C, the suspension was quickly added and the reaction mixture
warmed to room temperature. After 30 min, the reaction mixture was
diluted with dichloromethane (5 mL) and filtered through a pad of
Celite using dichloromethane as the eluent. The solvent was removed
in vacuo, and purification by column chromatography (SiO2, 50/50
hexane/CH2Cl2) yielded an orange solid (50% when X = Br and 42%
when X = Cl). Rf = 0.41 (10% EtOAc in hexane). Mp: ∼250 °C dec
Preparation of (S,S,Sp)-8 from (S,Sp)-4. In an NMR tube,
(S,Sp)-4 (0.0003 g, 0.001 mmol) and (S)-111d (0.001 g, 0.002 mmol)
1
were dissolved in CDCl3 (0.7 mL) and a H NMR spectrum was
1
taken straight away. H NMR data match those reported above for
(S,Sp,Sp)-8.
Preparation of (S,Sp)-3 from (S,S,Sp,Sp)-8. (S,S,Sp,Sp)-8 (0.0126
g, 0.017 mmol) was dissolved in acetone (5 mL) and water (5 mL)
and stirred vigorously in the presence of Na(hfacac) (0.0395 g, 0.171
mmol) at room temperature for 48 h. The reaction mixture was
separated with dichloromethane, the organics were dried with
magnesium sulfate, and the solvent was removed in vacuo.
Purification by column chromatography (SiO2, 15% EtOAc in
hexane) gave an orange solid (0.003 g, 25%). Data match those
reported above for (S,Sp)-3.
(under argon). [α]D25.5 °C = −2870 (c 0.15, CHCl3). IR (film; cm−1):
Preparation of (S,S,Sp,Sp)-10. (S,Sp)-915 (0.010 g, 0.019 mmol)
was placed in a flame-dried Schlenk tube along with palladium(II)
chloride (0.0034 g, 0.019 mmol). A 60/40 mixture of dichloro-
methane and methanol (1 mL) was added and the suspension stirred
at room temperature overnight. The reaction mixture was filtered
through Celite using dichloromethane as the eluent and the solvent
removed in vacuo. Purification by column chromatography (SiO2,
12% EtOAc, 20% CH2Cl2 in hexane) gave an orange solid (0.005 g,
44%). Rf = 0.40 (12% EtOAc, 20% CH2Cl2 in hexane). Mp: ∼170 °C
24.2 °C
3099, 2954, 2918, 2871, 1608 (CN). 1H NMR (500 MHz, CDCl3): δ
3
2
3
4.72 (2H, d, JHH = 1.6 Hz, CpH), 4.54 (2H, dd, JHH = 8.7, JHH
5.0 Hz, CHH), 4.49 (2H, d, 3JHH = 1.8 Hz, CpH), 4.46−4.42 (4H, m,
CpH + CHH), 4.19 (10H, s, CpH), 3.89 (2H, ddd, 3JHH = 8.9, 3JHH
=
=
3
3
4.9, JHH = 3.7 Hz, CH), 2.06 (2H, m, CH), 1.09 (6H, d, JHH = 6.8
Hz, CH3), 0.98 (6H, d, JHH = 6.8 Hz, CH3). 13C NMR (125 MHz,
3
CDCl3): δ 179.1 (CN), 89.3 (CpC), 76.3 (CpC), 75.3 (CpC), 71.1
(CH2), 70.5 (CpC), 69.6 (CpC), 68.6 (CH), 65.5 (CpC), 30.6 (CH),
19.5 (CH3), 15.3 (CH3). High-resolution MS (m/z, NSI+): [M + H]+
= 699.0590, calcd for C32H36Fe2N2O2Pd + H+ 699.0600.
dec (under argon). [α]D
= −687 (c 0.30, CHCl3). IR (film;
1
cm−1): 3094, 2958, 2930, 2872, 1628 (CN), 1603 (CN), 1509. H
Alternative Preparation of (S,S,Sp,Sp)-7. (S)-111d (0.100 g, 0.34
mmol) was placed in a flame-dried Schlenk tube under an inert
atmosphere and dissolved in dry diethyl ether (4 mL). Tetramethy-
lethylenediamine (0.07 mL, 0.44 mmol) was added, and the solution
was cooled to −78 °C and stirred for 5 min, after which s-butyllithium
(1.4 M in hexanes) (0.31 mL, 0.44 mmol) was slowly added and the
mixture stirred for 2 h. In a separate flame-dried Schlenk tube,
Pd(MeCN)2Cl2 (0.1309 g, 0.51 mmol) and tetrahydrofuran (15 mL)
were stirred vigorously until the majority of the solid had dissolved.
While still at −78 °C, a solution of zinc chloride (1.9 M in 2-
methyltetrahydrofuran) (0.27 mL, 0.51 mmol) was added and the
reaction mixture warmed to room temperature and stirred for 30 min.
Upon recooling to 0 °C the Pd(MeCN)2Cl2 suspension was quickly
added and the reaction mixture warmed to room temperature. After 1
h, the reaction mixture was diluted with dichloromethane (5 mL) and
filtered through a pad of Celite using dichloromethane as the eluent.
The solvent was removed in vacuo, and purification by column
chromatography (SiO2, 10% EtOAc in hexane) yielded an orange
solid (0.046 g, 38%). Data match those reported above for (S,S,Sp,Sp)-
7.
NMR (500 MHz, CDCl3): δ 5.11 (2H, dd, 3JHH = 2.7, 4JHH = 1.3 Hz,
3
3
3
CpH), 4.72 (2H, ddd, JHH = 9.8, JHH = 6.4, JHH = 3.1 Hz, CH),
3
4.69−4.61 (6H, m, CH + CH2), 4.61 (2H, t, JHH = 2.6 Hz, CpH),
4.48 (2H, dd, 2JHH = 8.8, 3JHH = 6.4 Hz, CHH), 4.45 (2H, dd, 3JHH
=
4
2
3
2.4, JHH = 0.6 Hz, CpH), 4.41 (2H, dd, JHH = 10.3, JHH = 8.8 Hz,
CHH), 4.39 (10H, s, CpH), 4.32 (2H, dd, 3JHH = 2.4, 4JHH = 1.4 Hz,
3
CpH), 4.23 (10H, s, CpH), 4.19 (2H, t, JHH = 2.4 Hz, CpH), 3.94
3
4
(2H, dd, JHH = 2.3, JHH = 0.7 Hz, CpH), 3.32 (2H, m, CH), 2.82
(2H, m, CH), 1.23 (6H, d, 3JHH = 6.6 Hz, CH3), 1.13 (6H, d, 3JHH
7.1 Hz, CH3), 1.07 (6H, d, 3JHH = 6.9 Hz, CH3), 0.99 (6H, d, 3JHH
=
=
6.7 Hz, CH3). 13C NMR (125 MHz, CDCl3): δ 179.0 (CN), 171.2
(CN), 91.9 (CpC), 87.4 (CpC), 79.6 (CpC), 74.9 (CH), 74.2
(CpC), 73.3 (CpC), 73.0 (CH2), 72.9 (CpC), 71.1 (CpC), 70.8
(CpC), 70.0 (CpC), 69.7 (CpC), 67.9 (CpC), 67.0 (CH2), 65.8
(CH), 64.7 (CpC), 30.5 (CH), 28.6 (CH), 20.0 (CH3), 19.3 (CH3),
15.2 (CH3), 15.1 (CH3). High-resolution MS (m/z, ASAP+): [(M −
PdCl2)/2 + H]+ = 534.0202, calcd for C16H18ClFeHgNO +
H+534.0204.
Preparation of (S,Sp)-11. (S,Sp)-915 (0.022 g, 0.04 mmol) and
bis(acetonitrile)palladium dichloride (0.021 g, 0.08 mmol) were
placed in a flame-dried Schlenk tube and dissolved in acetonitrile (2.2
mL). The reaction mixture was stirred for 1 h and then loaded onto a
plug of silica; the product was collected with 20% EtOAc in hexane
and the solvent removed in vacuo to give a dark red-brown solid (0.02
Preparation of (S,S,Sp)-8 from (S,S,Sp,Sp)-7. (S,S,Sp,Sp)-7
(0.020 g, 0.03 mmol) was placed in a flame-dried Schlenk tube and
dissolved in dichloromethane (1 mL). To this was added a solution of
hydrochloric acid (2 M, in Et2O) (14.3 μL, 0.03 mmol), and the
solution was stirred for 15 min. After complete loss of starting
material the solvent was removed in vacuo and the resulting complex
purified by column chromatography (SiO2, 20% EtOAc in hexane) to
give a dark yellow-orange solid (0.017 g, 79%). Mp: 106−108 °C.
24.2 °C
g, 95%). Mp: ∼100 °C dec (under argon). [α]D23.2 °C = −591 (c 0.30,
MeCN). IR (film; cm−1): 3094, 2958, 2925, 2868, 1599 (CN), 1509.
2
3
1H NMR (500 MHz, MeCN-d3): δ 4.69 (2H, dd, JHH = 9.1, JHH
=
= −547 (c 0.27, CHCl3). IR (film; cm−1): 3092, 2960,
5.8 Hz, CHH), 4.64 (2H, brs, CpH), 4.61 (2H, apt, 2+3JHH = 9.5 Hz,
CHH), 4.55 (2H, brs, CpH), 4.41 (2H, brs, CpH), 4.38 (10H, s,
[α]D
1
2930, 2869, 1728, 1637 (CN), 1607 (CN). H NMR (500 MHz,
G
DOI: 10.1021/acs.organomet.9b00551
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
CpH), 3.92−3.86 (2H, m, CH), 2.21−2.13 (2H, m, CH), 1.04 (6H,
d, 3JHH = 6.8 Hz, CH3)), 0.94 (6H, d, 3JHH = 7.0 Hz, CH3). 13C NMR
(125 MHz, MeCN-d3): δ 181.7 (CN), 92.0 (CpC), 74.2 (CpC),
74.1 (CH2), 72.0 (CpC), 71.6 (CpC), 69.2 (CpC), 67.1 (CH), 66.0
(CpC), 30.2 (CH), 19.0 (CH3), 15.3 (CH3). High-resolution MS (m/
z, ASAP+): [M − HgCl2 + H]+ = 876.9036, calcd for
C32H36Cl2Fe2N2O2Pd2 + H+ 876.9012.
Preparation of (S,Sp)-12. (S,Sp)-4 (0.025 g, 0.029 mmol) and
triphenylphosphine (0.015 g, 0.057 mmol) were placed in a flame-
dried Schlenk tube, dissolved in dichloromethane (1 mL), and stirred
at room temperature for 1 h. The solvent was removed in vacuo, and
purification by column chromatography (SiO2, 20% EtOAc in
hexane) yielded a deep orange solid (0.038 g, 99%). Rf = 0.21
AUTHOR INFORMATION
Corresponding Author
*E-mail for C.J.R.: Chris.Richards@uea.ac.uk.
ORCID
Christopher J. Richards: 0000-0001-7899-4082
Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS
■
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).
22.8 °C
(20% EtOAc in hexane). Mp: ∼230 °C dec (under argon). [α]D
= −825 (c 0.26, MeCN). IR (film; cm−1): 3077, 3052, 2958, 2925,
1
REFERENCES
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■
7.72, (6H, m, PhH), 7.53−7.49 (3H, m, PhH), 7.48−7.43 (6H, m,
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PhH), 4.67−4.57 (2H, m, CH2), 4.47 (1H, d, JHH = 1.9 Hz, CpH),
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3
2.87 (1H, brs, CH), 1.06 (3H, d, JHH = 6.9 Hz, CH3), 0.92 (3H, d,
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1
N), 135.6 (d, JCP = 11.7 Hz, PhC), 132.9 (d, JCP = 51.3 Hz, PhC),
3
131.6 (PhC), 129.1 (d, JCP = 10.8 Hz, PhC), 94.6 (CpC), 75.9 (d,
3JCP = 8.7 Hz, CpC), 74.2 (CpC), 73.3 (CH2), 70.9 (CpC), 69.4
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(CH3), 15.5 (CH3). 31P NMR (202 MHz, MeCN-d3): δ 37.49
(PPh3). High-resolution MS (m/z, ASAP+): [M − Cl]+ = 664.0711,
calcd for C34H33FeNOPPd+ 664.0699.
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Preparation of (S,Sp)-4 from (S,Sp)-9. (S,Sp)-915 (0.020 g, 0.04
mmol) and bis(acetonitrile)palladium dichloride (0.020 g, 0.08
mmol) were placed in a flame-dried Schlenk tube and dissolved in
acetonitrile (2 mL). The reaction mixture was stirred for 1 h and then
diluted with dichloromethane (20 mL) and washed with brine twice.
All of the organic layer was loaded onto a plug of silica, the product
collected with 30% EtOAc in hexane, and the solvent removed in
vacuo to give a deep red solid (0.016 g, 95%). Data match those
reported above for (S,Sp)-4.
(4) (a) Nomura, H.; Richards, C. J. Allylic Imidate Rearrangements
Catalyzed by Planar Chiral Palladacycles. Chem. - Asian J. 2010, 5,
1726−1740. (b) Dunina, V. V.; Gorunova, O. N.; Zykov, P. A.;
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vacuo to give a deep red solid (0.015 g, 92%). NMR data match those
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ASSOCIATED CONTENT
■
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* Supporting Information
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and X-ray crystallography details (PDF)
Accession Codes
CCDC 1938231−1938234 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
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