P-Chirogenic Triazole-Based Phosphine: Synthesis, Coordination Chemistry, and Asymmetric Catalysis

Article abstract of DOI:10.1002/ejoc.202000723

Herein we report the synthesis of a new P-chirogenic triazole-based phosphine according to the ephedrine methodology. Upon reaction with late transition-metal derivatives, Rh^I and Pd^II, phosphine-triazole forms complexes with bidenta

Full text of DOI:10.1002/ejoc.202000723

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Stereoselective Synthesis
P-Chirogenic Triazole-Based Phosphine: Synthesis, Coordination
Chemistry, and Asymmetric Catalysis
Jérôme Bayardon,*[a] Benjamin Rousselle,[a] Yoann Rousselin,[a] Quentin Bonnin,[a] and
Raluca Malacea-Kabbara*[a]
Abstract: Herein we report the synthesis of a new P-chirogenic P,N coordination, as demonstrated by spectroscopic and X-ray
triazole-based phosphine according to the ephedrine method- crystallographic analyses. First experiments in asymmetric catal-
ology. Upon reaction with late transition-metal derivatives, RhI ysis showed the catalytic potential of this new chiral P,N-type
and PdII, phosphine-triazole forms complexes with bidentate ligand.
Introduction
phosphino group on the aromatic ring linked to the triazole
backbone were also synthesized by Balakrishna[8] for their stud-
ies in coordination chemistry with various transition metals.
1,2,3-Triazole-based phosphines are new class of compounds
which have found many applications, especially in coordination
chemistry as well as in catalysis.[1] The phosphine moiety can
be incorporated either directly on the triazole ring such as in
compounds 1–3 (Figure 1) or into the fragments attached to
the nitrogen ring as for 4–7 (Figure 1). As examples in the first
case, Zhang developed ca. 10 phosphine ligands 1 named
“Clickphos” on a 1,2,3-triazole backbone for Pd-catalyzed amin-
ation or Suzuki–Miyaura coupling reaction.[2] In parallel, exten-
sions of their synthesis and luminescent properties were stud-
ied by Bräse and co-workers.[3] Diphosphines supported by
bis(triazole) backbone 2 were recently synthesized by Manoury
and Virieux in order to study their coordination chemistry to-
ward transition metals.[4] Chiral planar triazolylphosphines were
also synthesized using click-chemistry such as Clickferrophos 3
which was able to induce high enantioselectivities in asymmet-
ric rhodium- and ruthenium-catalyzed hydrogenation of alk-
enes or ketones as well as in copper-catalyzed synthesis of pyr-
rolidines.[5] In the second case, different linkers were used to
attach phosphine moiety to the triazole unit. Alkyl ligating
groups such as methylene or ethylene were employed, respec-
tively for the synthesis of bis-phosphinotriazoles 4 used in the
preparation of PCP pincer complexes, and for the modular syn-
thesis of more than twenty P-chirogenic BH3-protected mono-
phosphines 5, as described by Gandelman[6] and Kann.[7] On
the other hand, mono- and diphosphines such as 6–7 bearing
Figure 1. Examples of 1,2,3-triazole-based phosphines.
The triazole itself has already shown its good metal-coordi-
nation properties[9] but surprisingly, the use of triazoles as nitro-
gen donors in P,N ligands has been only few described to
date.[1g,1n,1o,8] Moreover, chiral P,N ligands containing a triazole
backbone and their coordination chemistry have, as far as we
know, not been reported yet.[10]
As a part of our ongoing research concerned with the stereo-
selective synthesis of P-chirogenic ortho-functionalized aryl-
phosphine and their application in asymmetric catalysis,[11] we
will report herein the preparation of a P-chirogenic 1,2,3-tri-
azole-based phosphine, in which the nitrogen ring is located in
ortho-position of the phosphorus center (Figure 2), its coordina-
[a] Dr. J. Bayardon, B. Rousselle, Y. Rousselin, Q. Bonnin,
Dr. R. Malacea-Kabbara
Institut de Chimie Moléculaire de l'Université de Bourgogne-Franche-Comté,
ICMUB-OCS (UMR-CNRS 6302),
19 avenue A. Savary BP 47870, 21078 Dijon CEDEX, France
E-mail: jerome.bayardon@u-bourgogne.fr
raluca.malacea@u-bourgogne.fr
http://www.icmub.com/fr/membres/bayardon-jerome.html
http://www.icmub.com/fr/membres/malacea-kabbara-raluca.html
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under https://doi.org/10.1002/ejoc.202000723.
Figure 2. P-chirogenic phosphine 8.
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tion chemistry toward transition metal, RhI and PdII, and some
preliminary results in Rh- and Pd-catalyzed asymmetric reac-
tions.
Results and Discussion
The new P-chirogenic 1,2,3-triazole-based phosphine 8 has
been synthesized according to ephedrine methodology starting
from (+)-oxazaphospholidine borane complex 9, prepared from
(–)-ephedrine,[12] as illustrated in Scheme 1.
Figure 3. View of phosphine-triazole 8. Thermal ellipsoids are drawn at 50 %
probability plot. Hydrogen atoms were omitted for clarity.
With new triazole-phosphine-containing P,N ligand in hands,
we examined the complexation with PdII and RhI salts
(Scheme 2). Phosphine 8 reacted with half equivalent of
[Pd(η3-C3H5)Cl]2 and AgPF6 in CH2Cl2/MeOH at room tempera-
ture to give the corresponding cationic palladium-allylic com-
plex 16 in 68 % yield. Spectroscopic and X-ray crystallographic
analyses (vide infra) have elucidated that the phosphine-triazole
subunit in 16 coordinates to the palladium(II) center as the
P,N-bidentate ligand.
Scheme 1. Synthetic route to P-chirogenic phosphine-triazole 8.
The reaction of the complex (+)-9 with o-anisyllithium[13]
stereospecifically affords the aminophosphine-borane 10 in
90 % yield, by a ring opening reaction upon P–O bond cleav-
age. After acidolysis of the aminophosphine-borane 10 with dry
HCl,[14] the resulting chlorophosphine-borane 11 reacted with
2-[2-(trimethylsilyl)ethynyl]phenyllithium[15] to provide the cor-
responding P-chirogenic phosphine-borane 12 in moderate
yield because of the partial decomplexation of the borane due
to the high steric hindrance around the phosphorus center.[16]
To prevent this, the phosphine borane 12 is immediately trans-
formed to phosphine-sulfide 13 by a tandem decomplexation-
sulfidation reaction in presence of DABCO and elementary
sulfur. The phosphine-sulfide 13 is obtained in 80 % overall
yield from 10 and its analysis by HPLC on chiral column (99 %
ee), proves that the two-step reaction sequence proceeds with-
out racemization at the P-center. The desilylation of 13 was
readily achieved at room temperature using K2CO3 in methanol/
THF. The resulting terminal alkyne 14 was isolated in 97 % yield
after silica gel chromatography. It was then subjected to the
CuI-catalyzed cycloaddition with phenyl azide under classical
Click reaction conditions [CuSO4·5H2O (10 mol-%)/sodium
ascorbate (20 mol-%) in tBuOH-H2O (1:1)][17] to form the corre-
sponding triazolylphosphine-sulfide 15 in 62 % yield. Finally,
desulfidation of 15 was performed by reaction with Si2Cl6[18] in
toluene at 80 °C during one hour to give, after recrystallization,
P-chirogenic phosphine 8 in 83 % yield (Scheme 1). The enan-
tiomeric excess of phosphine-triazole 8 was determined by
HPLC on a chiral column with 99 % ee. Moreover, crystals of 8
suitable for X-ray analysis have been obtained and the X-ray
structure is depicted in Figure 3. The compound 8 crystallizes in
P212121 chiral space group and the Flack parameter refinement
allows the unambiguous determination of the R-absolute con-
figuration at the phosphorus atom.[19]
Scheme 2. Synthesis of PdII and RhI complexes with P-chirogenic phosphine-
triazole 8.
In {1H}31P NMR spectroscopy, a clear shift of the phosphine
signal with respect to the free ligand was observed (from
1
–22.4 ppm for 8 to 11.4 ppm for 16). The H NMR signal of the
triazole proton is shifted 0.63 ppm to lower field (from 8.19 to
8.82 ppm).[20] In addition, 15N NMR spectroscopy of phosphine-
triazole 8 and PdII complex 16 was recorded using 1H-15N HMBC
correlation experiment (Table 1). For the phosphine-triazole 8,
the 15N NMR chemical shifts are –25 and –126 ppm for N-1 and
N-3 atom respectively[21] (entry 1). In the case of the PdII com-
Table 1. 15N NMR chemical shift in ppm[a] for the compound 8, 16 and 17.[b,c]
Entry
Compound
δN-1
δN-2
δN-3
[d]
1
2
3
8
16
17
–25
–102
–106
–
–
–
–126
–122
–123
[d]
[d]
[a] Referenced to neat CH3NO2. [b] N-1, N-2 and N-3 for compounds 8, 16
and 17represented above. [c] In CD2Cl2. [d] Not determined.
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plex 16, a large upfield shift (–77 ppm) of N-1 atom was ob-
The coordination geometry is pseudo square-planar. The four
served (entry 2), attesting the binding of the triazole ring to the coordination sites are occupied by the P- and N-atom of the
metal center.[22]
phosphine-triazole ligand and the allylic termini. Bond lengths
and bond angles are within the expected range for [Pd(η3-allyl)]
complexes with a soft and a hard donor atom.[24]
Single crystals of PdII complex 16 suitable for X-ray diffrac-
tion analysis were obtained by recrystallization in CH2Cl2/
MeOH. The structure of the complex 16 is shown in Figure 4.
Rhodium complex 17 was also synthesized in 81 % yield by
mixing phosphine-triazole 8 and [Rh(COD)2]BF4 in CH2Cl2 at
room temperature (Scheme 2). Analysis of this complex by
{1H}31P- NMR spectroscopy shows the presence of a doublet at
δ = 23.4 ppm (1JRh-P 148.7 Hz).[25] As previously observed for Pd
1
complex 16, the H NMR peak of the triazole proton is clearly
shifted (from 8.19 ppm for 8 to 8.69 ppm for 17) and 15N NMR
indicates also a shift of ca. –81 ppm toward lower frequency
for N-1 atom (from –25 ppm for 8 to –106 ppm for 17; Table 1,
entries 1 and 3). These data all point to the formation of a
rhodium complex in which the phosphine-triazole 8 shows bi-
dentate P,N coordination.
In the next step, we evaluated the catalytic performance of
the new P-chirogenic phosphine-triazole 8 as chiral ligand in
asymmetric catalysis. The Rh-catalyzed asymmetric hydrogen-
ation of methyl α-acetamidocinnamate 18 and Pd-catalyzed
asymmetric allylic alkylation of (E)-1,3-diphenylprop-2-en-1-yl
acetate 20 served as test reactions[26] (Scheme 3).
Figure 4. View of complex 16. Thermal ellipsoids are drawn at 50 % probabil-
ity plot. Hydrogen atoms, disordered part and other complex present in
asymmetric unit are omitted for clarity.
The compound 16 crystallizes with two complexes in asym-
metric unit. “endo/exo” isomers of 16 can be defined when the
central C-atom of the allyl group points in opposite direction
or toward the o-anisyl substituent. In one of them, the allyl
ligand was found to be disordered and was refined with the
central C-atom in two positions. Refining the occupancy factors
afforded an “endo/exo” ratio of 50 %. The other complex is the
“endo” form as depicted in Figure 4.
This structure confirms that ligand 8 binds palladium
through phosphorus and nitrogen atoms to form a six-mem-
bered ring chelate. The conformations of the six-membered
rings of the bound ligand were assessed by ring-puckering
analysis[23] (Q = 0.407, Θ = 120° Φ = 215° for Pd1 complex,
Q = 0.589, Θ = 66.8° Φ = 49° for Pd1A complex), and reveal a
half-boat conformation where the phosphorus atom is farthest
from the mean plane of six-membered ring (P1 = 0.257 Å from
Pd1, N1, C23, C22, C17, P1 mean plane and P1A = 0.378 Å from
Pd1A, N1A, C23A,C22A,C17A, P1A mean plane). Both complexes
have a sinister conformation of phosphorus atom but differ by
the different orientation of the o-anisyl group as shown the
superposition in Figure 5.
Scheme 3. Asymmetric transition-metal-catalyzed reactions studied using
P-chirogenic phosphine-triazole 8.
Hydrogenation of methyl α-acetamidocinnamate 18 was car-
ried out using 1 mol-% of [Rh(COD)8]BF4 in methanol at room
temperature during 18 hours under hydrogen (10 bar). In these
conditions, hydrogenated product 19 was obtained in full con-
version and with low enantioselectivity (18 % ee) (Scheme 3a).
Pd-catalyzed asymmetric allylic alkylation of (E)-1,3-diphenyl-
prop-2-en-1-yl acetate 20 was carried out at room temperature
for 5 h in toluene using 2 mol-% of [Pd(η3-C3H5)Cl]2 and 4 mol-
% of ligand 8 in the presence of N,O-bis(trimethylsilyl)acet-
amide (BSA) and a catalytic amount of potassium acetate as
bases. The complex with 8 gave the product 21 in full conver-
sion with 84 % ee (Scheme 3b).
Conclusions
New P-chirogenic triazole-based phosphine could be stereo-
selectively synthesized by using ephedrine methodology and
Click-type chemistry. The ability of this phosphine to coordinate
with metal centers was also studied and a RhI complex and
a PdII complex could be synthesized. Spectroscopic and X-ray
crystallographic analyses have elucidated the structures of both
Figure 5. Superposition of both Pd coordination complex present in asym-
metric unit.
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phine-borane 10 (0.786 g, 2 mmol) and the reaction was stirred
under argon at room temperature during two hours. The ephedrine
hydrochloride was filtered off using a Millipore 4 μm filter. The re-
sulting solution of o-anisyl-chloro-phenylphosphine-borane 11 was
collected and cooled to –78 °C. Under argon, 2-[2-(trimethyl-
silyl)ethynyl]phenyllithium (4 mmol), previously prepared by reac-
tion between 2-[2-(trimethylsilyl)ethynyl]-bromobenzene (1.01 g,
complexes in which phosphine-triazole shows bidentate P,N co-
ordination. Preliminary studies in asymmetric catalysis have
demonstrated the usefulness of this ligand, especially in Pd-
catalyzed asymmetric allylic alkylation for which ee up to 84 %
was achieved. The synthesis of further P-chirogenic phosphine-
triazoles such as 8 and their application as ligand in different
asymmetric transformations is under investigation.
4 mmol) and nBuLi (2.5
M in hexane) (1.8 mL, 4.4 mmol) in THF
(5 mL) at –78 °C during one hour, was added and the resulting
mixture was stirred until room temperature during 5 hours. After
hydrolysis with water (20 mL), the mixture was extracted with di-
chloromethane (3 × 20 mL) and the combined organic phases were
dried with MgSO4. The solvent was removed under vacuum and the
resulting crude product was purified by column chromatography
on silica gel using petroleum ether/ethyl acetate (3:1) as eluent. The
corresponding phosphine borane 12, obtained partially decom-
plexed was dissolved under argon in dry toluene (10 mL) and
DABCO (0.450 g, 4 mmol) and sulfur (0.128 g, 4 mmol) were succes-
sively added. The reaction mixture was stirred at 50 °C during 3
hours and the solvent was evaporated. The crude product was puri-
fied by column chromatography on silica gel using petroleum
ether/ethyl acetate (3:1) as eluent to give compound 13 as a white
solid (0.673 g, 80 %). Rf 0.44 (petroleum ether/ethyl acetate, 3:1);
m.p. 50–52 °C (dec.); Enantiomeric excess: 99 % by HPLC analysis
[Chiralpak IA, 1 mL min–1, hexane/2-propanol 90:10, tR (R) 6.9 min,
tR (S) 9.4 min]; [α]D = –48.3 (c = 0.5, CHCl3). 1H NMR (600 MHz,
CD2Cl2): δ = 0.01 (s, 9H), 3.52 (s, 3H), 6.95 (dd, J = 5.3, 8.0 Hz, 1H),
7.16–7.19 (m, 1H), 7.35–7.38 (m, 1H), 7.44–7.61 (m, 7H), 8.02–8.05
(m, 2H), 8.17 (ddd, J = 2.0, 8.0, 16.7 Hz, 1H); {1H}13C NMR (151 MHz,
CD2Cl2): δ = –0.9, 55.2, 102.7 (d, JC-P = 6.4 Hz), 103.5, 111.5
(d, JC-P = 5.1 Hz), 120.5 (d, JC-P = 85.7 Hz), 121.1 (d, JC-P = 13.7 Hz),
Experimental Section
General: All reactions were carried out using standard Schlenk
techniques under an inert gas. Solvents were dried using a MBRAUN
SPS 800. Methylene chloride, diethyl ether, ethyl acetate, pentane,
petroleum ether, tetrahydrofuran (THF), toluene and methanol were
purchased in anhydrous form. Hexane and 2-propanol for HPLC
were of chromatographic grade and used without purification. The
reagents 2-[2-(trimethylsilyl)ethynyl]-bromobenzene, nBuLi (2.5
M in
hexane), DABCO, sulfur, potassium carbonate, tert-butanol, sodium
ascorbate, copper sulfate pentahydrate, hexachlorodisilane, allyl-
palladium(II) chloride dimer and bis(1,5-cyclooctadiene)rhodium(I)
tetrafluoroborate were purchased from commercial suppliers.
(2R,4S,5R)-(+)-2,4-dimethyl-2,5-diphenyl-1,3,2-oxazaphospholidine-
2-borane 9 and (Sp)-(–)-N-methyl-N-[(1R,2S)(1-hydroxy-2-methyl-1-
phenyl-2-propyl)]amino-o-anisylphenyl-phosphine-borane 10 were
prepared according to published procedure.[14,27] Phenyl azide was
prepared from aniline according to procedure described by Mangi-
one et al.[28] Flash chromatography was carried out with the indi-
1
cated solvents using silica gel 60 (60AAC, 35–70 μm; SDS). H (and
1H decoupled), 13C, 31P and 15N NMR spectra were recorded with
Bruker 600 Avance III-HD or Bruker 500 Avance III spectrometers at
25 °C, using tetramethylsilane as internal reference for 1H and 13C
spectra, 85 % phosphoric acid as external reference for 31P NMR
and a neat solution of nitromethane as external reference for 15N
NMR. Sweep width for spectra recorded at 600 MHz were 20,240,
396 and 13–400 ppm for 1H, 13C, 31P and 15N NMR respectively and
125.2 (d, JC-P = 6.9 Hz), 127.7 (d, JC-P = 13.7 Hz), 128.0 (d, JC-P
13.7 Hz), 130.3 (d, JC-P = 2.1 Hz), 131.0 (d, JC-P = 3.0 Hz), 131.8 (d,
C-P = 12.0 Hz), 132.5 (d, JC-P = 10.3 Hz), 133.2, 134.0 (d, JC-P = 1.9 Hz),
134.8 (d, JC-P = 6.9 Hz), 135.4 (d, JC-P = 10.3 Hz), 136.0, 160.3; {1H}31
=
J
P
NMR (243 MHz, CD2Cl2): δ = 40.5 (s). HRMS calcd. for C24H26OPSSi
[M + H]+ m/z 421.12058; found m/z 421.11908. Anal. Calcd for
C24H25OPSSi: C, 68.54; H, 5.99; found C, 68.40; H, 6.32.
for spectra recorded at 500 MHz 20, 237 and 405 ppm for H, 13C,
1
31P NMR respectively. The signals of 13C NMR spectra were allocated
by the J-mod technology. Data are reported in ppm as follows:
multiplicity (s = singlet, d = doublet, t = triplet, q = quartet, m =
multiplet, br.s = broad signal), coupling constant(s), integration.
HPLC analyses were performed on a Shimadzu chromatograph
equipped with a UV detector at λ = 210 and 254 nm. Mass spec-
trometry and accurate mass measurements (HRMS) were recorded
on a Thermo LTQ Orbitrap XL ESI-MS (ElectroSpray Ionization Mass
Spectrometry). Melting points were measured with a Kofler melting
points apparatus and are uncorrected. Optical rotation values were
measured at 20 °C with a Perkin-Elmer 241 polarimeter at 589 nm
(sodium lamp). Elemental analyses were measured with a precision
superior to 0.4 % on a CHNS/–O Thermo Electron Flash EA 1112
Series instrument apparatus.
(Sp)-o-Anisyl-[2-(ethynyl)phenyl]-phenylphosphine-sulfide (14):
To a solution of compound 13 (0.430 g, 1.02 mmol) in a mixture of
MeOH/THF (2:1) (7.5 mL) was added K2CO3 (0.141 g, 1.02 mmol).
The mixture was stirred at room temperature during two hours and
the solvent was evaporated. Water (5 mL) and CH2Cl2 (15 mL) were
added and organic phase was separated then washed with water
(5 mL) and finally dried with MgSO4. After filtration and evaporation
of the solvent, the crude product was purified by column chroma-
tography on silica gel using petroleum ether/ethyl acetate (3:1) as
eluent to give compound 14 as a white solid (0.345 g, 97 %). Rf 0.39
(petroleum ether/ethyl acetate, 3:1); m.p. < 50 °C; [α]D = +2.5 (c =
0.3, CHCl3). 1H NMR (600 MHz, CD2Cl2): δ = 2.95 (s, 1H), 3.53 (s, 3H),
6.95 (dd, J = 5.5, 7.7 Hz, 1H), 7.16–7.18 (m, 1H), 7.38–7.41 (m, 1H),
7.46–7.62 (m, 7H), 8.03–8.07 (m, 2H), 8.19 (ddd, J = 1.7, 7.7, 17.1 Hz,
1H); {1H}13C NMR (151 MHz, CD2Cl2): δ = 55.2, 81.3 (d, JC-P = 6.6 Hz),
85.0, 111.3 (d, JC-P = 5.6 Hz), 120.3 (d, JC-P = 85.4 Hz), 121.0 (d, JC-
X-ray Experimental Procedure: All experimental data procedure
and refinement are detailed in Supporting Information.
Deposition Numbers 1953272 and 1953273 contain the supplemen-
tary crystallographic data for this paper. These data are provided
free of charge by the joint Cambridge Crystallographic Data Centre
and Fachinformationszentrum Karlsruhe Access Structures service
www.ccdc.cam.ac.uk/structures.
= 14.0 Hz), 123.8 (d, JC-P = 5.6 Hz), 127.8 (d, JC-P = 12.9 Hz), 128.5
P
(d, JC-P = 11.8 Hz), 130.3 (d, JC-P = 2.4 Hz), 131.2 (d, JC-P = 3.5 Hz),
131.6 (d, JC-P = 11.8 Hz), 132.5 (d, JC-P = 89.4 Hz), 132.7 (d, JC-P
=
11.8 Hz), 134.1 (d, JC-P = 2.4 Hz), 135.0 (d, JC-P = 9.4 Hz), 135.5 (d,
(Sp)-o-Anisyl-phenyl-{2-[2-(trimethylsilyl)ethynyl]phenyl}phos- JC-P = 10.6 Hz), 136.7 (d, JC-P = 88.2 Hz), 160.4; {1H}31P NMR
phine-sulfide (13): A freshly titrated toluene solution of dry HCl
(40 mL, 12 mmol) was added to (Sp)-(–)-N-methyl-N-[(1R,2S)-
(1-hydroxy-2-methyl-1-phenyl-2-propyl)]amino-o-anisylphenylphos-
(243 MHz, CD2Cl2): δ = 40.6 (s). HRMS calcd. for C21H18OPS [M + H]+
m/z 349.08105, found m/z 349.08151. Anal. Calcd for C21H17OPS:
C, 72.40; H, 4.92; found C, 72.08; H, 5.07.
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(Sp)-4-[2-(o-Anisylphenylthiophosphinyl)phenyl]-1-phenyl-1H-
1,2,3-triazole (15): To a solution of phosphine-alkyne 14 (0.399 g,
tion of diethyl ether to the filtrate induced the formation of a pow-
der which was filtered and washed with diethyl ether. Crystallization
1.15 mmol) in tBuOH (2 mL) were successively added phenyl azide in CH2Cl2/MeOH gave the palladium complex 16 as a white crystal-
(0.136 g, 1.15 mmol) then a solution of CuSO4·5H2O (5.5 mg, line solid (0.051 g, 68 %). M.p. 202–204 °C; [α]D = –27.8 (c = 0.3,
0.034 mmol) and sodium ascorbate (13.6 mg, 0.068 mmol) in water
(2 mL). The resulting mixture was stirred at 40 °C during 16 hours.
After cooling to room temperature, a solution of NH4OH (30 % in
water) (2 mL) was added followed by 5 mL of water. The mixture
was extracted with dichloromethane (3 × 10 mL) and the combined
CHCl3). 1H NMR (600 MHz, CD2Cl2): δ = 3.05 (br.s, 1H), 3.28 (br.s, 1H),
3.65 (s, 3H), 3.89–3.92 (m, 1H), 4.95 (br.s, 1H), 5.79 (t, J = 8.2 Hz, 1H),
6.61–6.64 (m, 1H), 6.86–6.89 (m, 1H), 6.95–6.98 (m, 1H), 7.04–7.07
(m, 1H), 7.28–7.54 (m, 10H), 7.62–7.64 (m, 1H), 7.79–7.80 (m, 2H),
7.94–7.96 (m, 1H), 8.82 (s, 1H); {1H}13C NMR (151 MHz, CD2Cl2): δ =
organic phases were dried with MgSO4. After filtration and evapora- 55.8, 57.0, 79.5 (d, JC-P = 29.4 Hz), 111.5 (d, JC-P = 3.9 Hz), 116.5 (d,
tion of the solvent, the crude product was purified by column chro-
matography on silica gel using petroleum ether/ethyl acetate (1:1)
as eluent to give the titled compound 15 as a pale yellow solid
J
C-P = 48.6 Hz), 120.8, 121.5 (d, JC-P = 7.8 Hz), 121.9 (d, JC-P = 5.8 Hz),
122.5, 123.3 (d, JC-P = 40.8 Hz), 128.1 (d, JC-P = 48.8 Hz), 129.3 (d,
JC-P = 10.9 Hz), 130.1, 130.3 (d, JC-P = 6.5 Hz), 130.5, 130.8 (d, JC-P
=
(0.333 g, 62 %). Rf 0.40 (petroleum ether/ethyl acetate, 1:1); m.p. 8.7 Hz), 131.7 (d, JC-P = 2.2 Hz), 131.9 (d, JC-P = 16.3 Hz), 132.5, 133.4
1
88–90 °C; [α]D = –32.0 (c = 0.4, CHCl3). H NMR (600 MHz, CD2Cl2):
δ = 3.54 (s, 3H), 6.76 (br. t, J = 7.1 Hz, 1H), 6.98 (br. t, J = 7.1 Hz,
1H), 7.35–7.55 (m, 11H), 7.64 (t, J = 7.1 Hz, 1H), 7.87–7.89 (m, 1H),
8.06 (dd, J = 8.0, 14.2 Hz, 2H), 8.37 (dd, J = 7.6, 17.0 Hz, 1H), 8.92
(d, JC-P = 4.3 Hz), 133.9 (d, JC-P = 8.7 Hz), 134.0, 135.7, 146.3
(d, JC-P = 5.3 Hz), 160.3 (d, JC-P = 7.0 Hz), one C missing; {1H}31P NMR
(243 MHz, CD2Cl2): δ = 11.4 (s), –144.4 (hept, JF-P = 710.5 Hz). HRMS
calcd. for C30H27N3OPPd [M – PF6]+ m/z 582.09211, found m/z
582.09182.
(s, 1H); {1H}13C NMR (151 MHz, CD2Cl2): δ = 55.0, 111.2 (d, JC-P
=
6.3 Hz), 119.3 (d, JC-P = 83.5 Hz), 120.5, 120.7 (d, JC-P = 12.7 Hz),
124.3, 127.7 (d, JC-P = 13.0 Hz), 127.9 (d, JC-P = 13.0 Hz), 128.4, 129.5,
130.8 (d, JC-P = 2.0 Hz), 131.2, 131.2 (d, JC-P = 15.0 Hz), 131.5 (d,
Rhodium Complex (17): A solution of phosphine-triazole 8
(0.050 g, 0.115 mmol) in dichloromethane (3.5 mL) was slowly
added to a suspension of [Rh(COD)2]BF4 (0.045 g, 0.110 mmol) in
dichloromethane (2.5 mL). The resulting mixture was stirred at room
temperature during one hour then half of the solvent was removed
under vacuum. Addition of diethyl ether induced the formation of
an orange powder which was filtered, washed with diethyl ether
and dried under vacuum. The rhodium complex was obtained as
an orange solid (0.069 g, 81 %). M.p. 214–216 °C (dec.). 1H NMR
(500 MHz, CD2Cl2): δ = 2.9–2.30 (m, 2H), 2.39–2.42 (m, 3H), 2.52–
2.69 (m, 3H), 3.62 (br. s, 1H), 3.76 (br. s, 1H), 3.78 (s, 3H), 5.77–5.80
(m, 1H), 6.18–6.20 (m, 1H), 7.01–7.10 (m, 3H), 7.42–7.53 (m, 5H),
7.60–7.78 (m, 7H), 7.84–7.86 (m, 2H), 7.92–7.93 (m, 1H), 8.69 (s, 1H);
{1H}13C NMR (126 MHz, CD2Cl2): δ = 28.1, 29.1, 31.4, 33.3, 55.4, 79.5
(d, J = 11.9 Hz), 80.4 (d, J = 11.9 Hz), 105.4 (dd, J = 6.3, 10.0 Hz),
J
C-P = 9.0 Hz), 132.1 (d, JC-P = 86.8 Hz), 132.5 (d, JC-P = 12.0 Hz), 133.1
(d, JC-P = 8.0 Hz), 133.4, 133.9 (d, JC-P = 2.0 Hz), 135.2 (d, JC-P
=
9.0 Hz), 136.8, 145.1 (d, JC-P = 4.6 Hz), 159.4; {1H}31P NMR (243 MHz,
CD2Cl2): δ = 41.1 (s). HRMS calcd. for C27H22N3OPSNa [M + Na]+ m/z
490.11134, found m/z 490.11154. Anal. Calcd for C27H22N3OPS:
C, 69.36; H, 4.74; found C, 69.02; H, 4.87.
(Rp)-4-[2-(o-Anisylphenylphosphinyl)phenyl]-1-phenyl-1H-1,2,3-
triazole (8): To a solution of compound 15 (0.31 g, 0.663 mmol) in
toluene (14 mL) was added Si2Cl6 (0.23 mL, 1. 326 mmol). The result-
ing mixture was stirred under argon at 80 °C during one hour. After
cooling to 0 °C, a solution of NaOH (30 % in water) (20 mL) was
added dropwise followed by water (10 mL) and dichloromethane
(20 mL). The two phases were separated then aqueous phase was
extracted with dichloromethane (2 × 20 mL). The combined organic
phases were dried with MgSO4, filtered and the solvent was evapo-
rated. The crude product was purified by column chromatography
on silica gel using petroleum ether/ethyl acetate (1:1) as eluent and
recrystallization in hexane/CH2Cl2 to give the phosphine-triazole 8
as a white crystalline solid (0.24 g, 83 %). Rf 0.65 (petroleum ether/
ethyl acetate, 1:1); m.p. 134–136 °C; Enantiomeric excess: 99 % by
HPLC analysis [Chiralpak IA, 1.0 mL min–1, hexane/2-propanol 90:10,
tR (R) 32.6 min, tR (S) 35.2 min]; [α]D = +49.0 (c = 0.3, CHCl3). 1H
NMR (600 MHz, CD2Cl2): δ = 3.76 (s, 3H), 6.78–6.80 (m, 1H), 6.92 (t,
J = 7.2 Hz, 1H), 6.98 (dd, J = 4.6, 7.9 Hz, 1H), 7.07–7.09 (m, 1H),
7.31–7.58 (m, 11H), 7.69 (d, J = 7.9 Hz, 2H), 8.05–8.07 (m, 1H), 8.19
(s, 1H); {1H}13C NMR (151 MHz, CD2Cl2): δ = 55.7, 110.5, 120.3, 121.2,
121.6 (d, JC-P = 17.8 Hz), 125.1 (d, JC-P = 11.5 Hz), 128.2, 128.5, 128.7
(d, JC-P = 7.6 Hz), 128.8, 128.9, 129.6 (d, JC-P = 5.1 Hz), 129.7, 130.6,
134.0, 134.1, 134.2 (d, JC-P = 2.6 Hz), 135.2 (d, JC-P = 17.4 Hz), 135.5
107.2 (dd, J = 6.9, 9.0 Hz), 111.6 (d, JC-P = 3.5 Hz), 114.0 (d, JC-P
48.3 Hz), 120.6, 121.4 (d, JC-P = 9.4 Hz), 122.6, 123.4 (d, JC-P
=
=
43.5 Hz), 128.6 (d, JC-P = 47.5 Hz), 129.1 (d, JC-P = 11.1 Hz), 129.6 (d,
JC-P = 7.1 Hz), 130.0, 130.1, 130.5, 130.9 (d, JC-P = 16.6 Hz), 131.5 (d,
JC-P = 2.4 Hz), 131.8, 132.4, 134.0, 131.9 (d, JC-P = 12.7 Hz), 135.6 (d,
JC-P = 8.7 Hz), 135.7, 160.3, two C missing; {1H}31P NMR (203 MHz,
CD2Cl2): δ = 23.4 (d, JRh-P = 148.7 Hz). HRMS calcd. for C35H34N3OPRh
[M – BF4]+ m/z 646.14890, found m/z 646.14781.
Procedure for Asymmetric Hydrogenation: A solution of
[Rh(COD)8]BF4 (3.7 mg, 0.005 mmol, 1 mol-%) and methyl α-acet-
amidocinnamate 18 (109.5 mg, 0.5 mmol) in dry methanol (7.5 mL)
was introduced in a stainless steel autoclave. The autoclave was
closed, purged with hydrogen and then pressurized with 10 bar of
hydrogen. After 16 h of stirring at room temperature, the pressure
was released to atmospheric pressure and the solution was trans-
ferred to a round-bottomed flask. The solvent was removed to give
a residue, which was purified by column chromatography on silica
gel to afford the hydrogenated product 19. Enantiomeric excess
was determined by HPLC analysis [Chiralcel OD-H, 1 mL min–1, hex-
ane/2-propanol 95:5, tR (R) 21.4 min, tR (S) 34.7 min]. 1H NMR
(500 MHz, CDCl3): δ = 1.97 (s, 3H), 3.06–3.07 (m, 2H), 3.64 (s, 3H),
4.85–4.87 (m, 1H), 6.11 (br. s, 1H), 7.18–7.20 (m, 5H).
(d, JC-P = 27.6 Hz), 136.4 (d, JC-P = 11.6 Hz), 137.1, 146.7 (d, JC-P
=
4.9 Hz), 161.2 (d, JC-P = 14.1 Hz); {1H}31P NMR (243 MHz, CD2Cl2):
δ = –22.4 (s). HRMS calcd. for C27H22N3OPNa [M + Na]+ m/z
458.13927, found m/z 458.13979. Anal. Calcd for C27H22N3OP:
C, 74.47; H, 5.09; found C, 74.57; H, 4.99.
Palladium Complex (16): To a solution of phosphine-triazole 8
(0.050 g, 0.115 mmol) and [Pd(η3-C3H5)Cl]2 (0.019 g, 0.052 mmol) in
dichloromethane (1 mL) was added a solution of AgPF6 (0.026 g, 0.
104 mmol) in methanol (0.3 mL). The mixture was stirred at room
temperature in the dark during one hour and the finely divided
precipitate was filtered off using a Millipore 4 μm filter. Slow addi-
Procedure for Asymmetric Allylic Alkylation: A solution of
[Pd(η3-C3H5)Cl]2 (3.6 mg, 0.010 mmol), phosphine-triazole 8 (8.8 mg,
0.020 mmol) and (E)-1,3-diphenylprop-2-en-1-yl acetate 20 (126 mg,
0.5 mmol) in 2 mL of toluene was stirred one hour at room tempera-
ture. Dimethylmalonate (0.12 mL, 1.0 mmol) was added followed
by BSA (0.24 mL, 1.0 mmol) and KOAc (5.0 mg, 0.05 mmol). The
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1750; c) H. Oki, I. Oura, T. Nakamura, K. Ogata, S.-i. Fukuzawa, Tetrahe-
dron: Asymmetry 2009, 20, 2185–2191.
reaction was stirred at room temperature during 5 hours (full con-
version). The reaction mixture was diluted with Et2O and saturated
aqueous NH4Cl solution was added. The mixture was extracted with
Et2O, and the organic phases were dried with MgSO4. After filtra-
tion, the solvent was removed to give a residue, which was purified
by column chromatography on silica gel to afford the product 21.
Enantiomeric excess was determined by HPLC analysis [Chiralpak
IA, 1 mL min–1, hexane/2-propanol 90:10, tR (R) 8.5 min, tR (S)
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Acknowledgments
The authors are grateful for the financial support provided by
the CNRS, Ministère de l'Education Nationale et de la Recherche,
Université de Bourgogne, Conseil Régional de Bourgo-
gne through the Plan d′Actions Régional pour l′Innova-
tion (PARI) and the Fonds Européen de Développement Ré-
gional (FEDER) programs. It is also a pleasure to thank M. J.
Penouilh and M. Picquet at the Sayens/Pôle Chimie Moléculaire
for the NMR and mass spectrometry analyses, and M. J. Eymin
for her skilled technical assistance.
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Keywords: P-Chirogenic phosphine · Stereoselective
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Asymmetric catalysis
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Received: May 22, 2020
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Stereoselective Synthesis
The stereoselective synthesis of a
novel P-chirogenic triazole-based
phosphine was achieved. Its coordina-
tion to transition-metals was explored,
and a P,N-chelation mode was demon-
strated. Application to this chiral phos-
phine as ligand in asymmetric catalysis
is also reported.
J. Bayardon,* B. Rousselle,
Y. Rousselin, Q. Bonnin,
R. Malacea-Kabbara* ........................ 1–8
P-Chirogenic Triazole-Based Phos-
phine:
Synthesis,
Coordination
Chemistry, and Asymmetric Cataly-
sis
doi.org/10.1002/ejoc.202000723
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