Synthesis, crystal structures and magnetic properties of a P-stereogenic: Ortho -(4-amino-tempo)phosphinic amide radical and its CuIIcomplex

Article abstract of DOI:10.1039/d0dt04298f

The synthesis of phosphinic amides containing one 4-amino-TEMPO substituent at the ortho position has been achieved through copper(i) catalyzed cross-coupling reactions of ortho-iodophosphinic amides with 4-amino-TEMPO. The method has been extended to the preparation of the first example of a P-stereogenic ortho-(4-amino-tempo)phosphinic amide radical 10. The reaction of 10 with Cu(hfac)2 afforded the P-stereogenic CuII complex 19. The crystal structure of both chiral compounds is reported. The molecular structure of 10 consists of a supramolecular zig-zag chain formed by intermolecular hydrogen bonds between the NH group of the phosphinic amide moiety and the nitroxide oxygen atom. In complex 19, the ligand acts as a bridge between two CuII ions coordinated to the oxygen atoms of the PO and N-O· groups leading to the formation of a polymeric helicate chain in which the metal ions exist in a distorted octahedral geometry. The magnetic behavior of ligand 10 is characterized by very weak intermolecular antiferromagnetic interactions, whereas ferro- and anti-ferromagnetic interactions are present in complex 19. This journal is

Full text of DOI:10.1039/d0dt04298f

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Synthesis, crystal structures and magnetic
properties of a P-stereogenic ortho-
(4-amino-tempo)phosphinic amide radical
and its CuII complex†
Cite this: Dalton Trans., 2021, 50,
2585
Yolanda Navarro,a Guilherme P. Guedes,b Miguel A. del Águila-Sánchez,a
a
María José Iglesias,a Francisco Lloret*c and Fernando López-Ortiz
*
The synthesis of phosphinic amides containing one 4-amino-TEMPO substituent at the ortho position has
been achieved through copper(I) catalyzed cross-coupling reactions of ortho-iodophosphinic amides with
4-amino-TEMPO. The method has been extended to the preparation of the first example of a P-stereogenic
ortho-(4-amino-tempo)phosphinic amide radical 10. The reaction of 10 with Cu(hfac)2 afforded the
P-stereogenic CuII complex 19. The crystal structure of both chiral compounds is reported. The molecular
structure of 10 consists of a supramolecular zig-zag chain formed by intermolecular hydrogen bonds
between the NH group of the phosphinic amide moiety and the nitroxide oxygen atom. In complex 19, the
ligand acts as a bridge between two CuII ions coordinated to the oxygen atoms of the PvO and N–O·
groups leading to the formation of a polymeric helicate chain in which the metal ions exist in a distorted
octahedral geometry. The magnetic behavior of ligand 10 is characterized by very weak intermolecular anti-
ferromagnetic interactions, whereas ferro- and anti-ferromagnetic interactions are present in complex 19.
Received 18th December 2020,
Accepted 12th January 2021
DOI: 10.1039/d0dt04298f
rsc.li/dalton
paramagnetic stabilized compounds whose structure can be
easily modified through organic synthesis methods, allowing
Introduction
In recent decades, remarkable attention has been paid to the introduction of new properties and different coordination
molecular magnetism due to its applications in fields such as sites for the construction of complexes with a variety of topolo-
molecular spintronics, high-density data storage and quantum gies and functionalities. Nitronyl-nitroxides and nitroxides are
computing devices.1 Thus, the design of molecular structures two of the most used organic building blocks for this purpose,
aimed at rational control of magnetic interactions between especially the TEMPO radical (2,2,6,6-tetramethylpiperidine-1-
spin carriers has become a topic of great interest. Among oxyl), from which a large number of derivatives have been syn-
them, chiral molecular magnets have been proven to be useful thesized with numerous interesting architectures and mag-
materials especially for the construction of advanced memory netic properties.4
and logic devices due to their multiferroic, magnetization-
The linkage between chirality and organic radical chemistry
induced second harmonic generation (MSHG) and magneto- has found worthwhile applications in multiple fields such as
chiral dichroism (MChD) effects2 and are also interesting due enantioselective catalysis,5 molecular magnetism,6 liquid crys-
to their potential applications in more diverse fields such as tals7 and protective agents against oxidative stress.8 Chirality
asymmetric catalysis, enantioselective separation and medi- in organic radicals may be achieved by spontaneous resolution
cine.3 Persistent organic radicals play a key role as they are from achiral molecules that give rise to a chiral structure in
the solid state,2b,9 or through the existence of atomic stereo-
genic centers, atropoisomeric conformations, helical struc-
aÁrea de Química Orgánica, Centro de Investigación CIAIMBITAL, Universidad de
tures or a combination of elements of chirality.10 The usual
Almería, Carretera de Sacramento s/n, 04120 Almería, Spain. E-mail: flortiz@ual.es
bUniversidade Federal Fluminense, Instituto de Química, Departamento de Química
approach for introducing chirality in molecular-based mag-
netic materials involves the use of enantiopure nitroxide and
nitronyl nitroxide radicals containing C-stereogenic centers
combined with coordination to paramagnetic metal ions.10,11
A wide variety of chiral nitronyl nitroxide-based radicals have
been synthesized, from which some complexes have been
reported (Fig. 1). Two isomers of a chiral nitronyl nitroxide
Inorgânica, Niterói, Rio de Janeiro, Brazil
cInstitut de Ciencia Molecular, Universitat de València, Catedràtic José Beltrán no.2,
46980 Paterna, Valencia, Spain
†Electronic supplementary information (ESI) available: NMR spectra of the com-
pounds synthesized and X-ray crystallographic data of 10 and 13. CCDC 2011812
and 2011813. For ESI and crystallographic data in CIF or other electronic format
see DOI: 10.1039/d0dt04298f
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the functionalized radical to provide discrete or extended
molecules with antiferromagnetic interactions between spin
carriers. Interestingly, light emission properties were also
observed for the terbium(III)-based complex, proving the poten-
tial of the compounds as multifunctional materials. Thus, we
thought that the introduction of chirality through the phos-
phorus atom in these systems would provide chiral ligands
that combined with paramagnetic metal ions would give rise
to advanced multifunctional materials.
The synthesis of P-stereogenic compounds can be achieved
in three different ways: nucleophilic or electrophilic attack on
the phosphorus atom, or the desymmetrization of prochiral
R2P groups.24 For the synthesis of P-stereogenic phosphinic
amides, our group has developed very efficient methodologies
based on the desymmetrization of prochiral Ph2P groups of
phosphinimidic amides25 and phosphinic amides26 through
the highly diastereoselective ortho deprotonation of derivatives
bearing C-chiral amino moieties and subsequent electrophilic
trapping. The application of this procedure to phosphinic
amide 8 provided access to a wide variety of P-stereogenic
Fig. 1 Representative examples of chiral complexes based on the
metal–radical approach.
radical have been used for the synthesis of manganese com- ortho-substituted compounds 9 in high yields and with excel-
plexes 1 and 2. Compound 1 is a polymeric 21 chain complex lent control (Scheme 1). We thought that this methodology
that acts as a ferrimagnet,12 while compound 2 shows an could be extended to the synthesis of P-stereogenic nitroxide
helical-chain structure with a very low ratio between the intra- radicals by connecting a radical moiety at the ortho position of
chain and interchain exchange parameters (J′/J = 1.5 × 10−5).13 the chiral diphenylphosphinic amide framework taking advan-
Manganese complex 3 behaves as a ferrimagnet below TC
=
tage of the substituents introduced at the ortho position.
We describe herein the amination of P-(2-iodophenyl)-P-
5.0 K, and complex 4a,14 obtained from a chiral di-tert-butyl
nitroxide radical, behaves as a metamagnet below TN = 5.4 K. phenylphosphinic amides with 4-amino-TEMPO (ATEMPO)
The same chiral radical was used for the synthesis of cobalt catalyzed by CuI salts to give ortho-alkylaminophosphinic
complex 4b,15 from which a 1D helical-chain structure with amides and the application of the method to the synthesis of
antiferromagnetic interactions between paramagnetic sites the first example of a P-stereogenic ortho-(4-amino-TEMPO)
was obtained. Complex 5 is the first example of a chiral lantha- derivative 10 and its CuII complex.
nide-radical compound combining optical chirality and mag-
netic anisotropy and shows SCM behaviour.16 Some heterome-
tallic complexes have also been described. Compound 6 is a
Results and discussion
2p–3d–4f complex showing SMM behaviour due to the CoII-
The strategies reported to introduce an ATEMPO radical to an
Rad exchange coupling interaction together with improved
single ion magnetic properties of CoII and DyIII ions.17 For
aromatic ring include reductive amination using 4-oxo-TEMPO
Mn–Cu-Rad complex 7, a strong antiferromagnetic interaction
between Mn and the organic radical was described, along with
a much weaker antiferromagnetic interaction between the Mn
(hfac)2 unit and Cu(hfac)2.18 A few examples of chiral verdazyl
radicals have also been reported.19 However, to the best of our
knowledge, there are no examples to date regarding the use of
P-stereogenic compounds in molecular magnetism.20
A number of P-containing TEMPO derivatives have been
described to date, including phosphates, phosphoramidites,
phosphazenes and phosphonates, among others.21 However,
the use of these compounds in molecular magnetism has
received little attention. Recently, our group has introduced a
new phosphinic amide-TEMPO radical, 1-piperidinyloxy-4-
[(diphenylphosphinyl)-amino]-2,2,6,6-tetramethyl
radical
(DPPNtempo), as a scaffold for the construction of achiral
magnetic systems based on the coordination of the PvO/N–O•
groups to the first row transition-metals22 such as CuII, MnII
Scheme 1 Synthesis of P-stereogenic phosphinic amides as the source
and CoII and some lanthanides,23 revealing the usefulness of of P-stereogenic TEMPO radicals and complexes.
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as a carbonyl component27 and SNAr reactions in which afforded the desired product in a conversion of 22%, together
ATEMPO acts as a nucleophile.28 Reductive amination affords with some by-products and 52% of the starting material. The
low yield and the reduction step may lead to the partial formation of 13 was established based on the analysis of the
reduction of the radical. On the other hand, SNAr reactions NMR spectra of the crude mixture and was then corroborated
require the presence of strong electron-withdrawing substitu- by the isolation of the compound through flash column
ents, such as nitro or imide, at the aromatic nucleus. For the chromatography. The key aspect was the appearance of a
1
synthesis of the radical compound 10, a method based on the highly shielded multiplet at δH 6.60 ppm in the H NMR spec-
C–N cross-coupling reaction of the P-stereogenic ortho iodo trum assigned to the ortho proton with respect to the amino
derivative 9a and the commercially available 4-amino-TEMPO group of the TEMPO moiety. This assignment was confirmed
12 was developed.
through the correlation observed in the 1H,31P HMQC spec-
Firstly, the optimized reaction conditions for the amination trum (optimized for the detection of connections via long-
of the racemic analogue ( )-11 were investigated, due to the range coupling constants) between this proton and the 31P
similarity of both the compounds and the greater simplicity of signal at δP = 29.6 ppm.
preparation. Palladium and copper are the most commonly
The increase of the reaction time to 48 h led to a decrease
used catalysts for C–N coupling reactions and some method- of the conversion to 13% (entry 2). Changing the solvent to
ologies based on Ni(II) salts have also been described for nBuOH allowed an increase in the temperature to 100 °C (entry
similar systems.29 For the reaction of ortho-iodophosphinic 3). However, the use of less hindered alcohol favoured the for-
amide 11 with 12, three different C–N coupling methodologies mation of the C–O coupling compound 14 with the solvent as
were tested using Ni(II),29a Pd(II)30 and Cu(I)31 salts as catalysts. the major product (67%). The low melting point of the TEMPO
Palladium and copper promoted the formation of the desired radical (37–39 °C) is crucial in order to overcome this issue
product, albeit in a very low yield. However, the palladium- and to improve the efficiency of the process. Thus, in the
catalyzed reaction afforded a larger number of by-products. absence of a solvent, the reaction of 11 with 10 equiv. of 12 for
For this reason, we focused on the method described by ca. 3 days afforded the desired product in a significantly
Buchwald et al.31 and made some modifications including the higher conversion of 55% (entry 4).
use of different salts, loading of catalysts, solvents, ligands,
Compounds 15, 16 and 17 were also identified as by-pro-
temperatures and reaction times in order to improve the ducts of the reaction in entry 4 (conversions of 17%, 8% and
results. The results are summarized in Table 1. The reaction of 20%, respectively). Product 15 arises from the reduction of the
11 with 1.2 equivalents of ATEMPO in the presence of 20% of starting ortho-iodophosphinic amide in the reaction media,
CuI, three equiv. of ethylene glycol, and isopropanol as the and the presence of phenol 16 can be explained by the cross-
solvent at 80 °C at a reaction time of 19 hours (entry 1) coupling of 11 with small amounts of water likely obtained
Table 1 Optimization of the coupling reaction of ortho-iodophosphinic amide 11 and ATEMPO
CuX
Mol%
Ligand (L)
Solvent
t (h)
T (°C)
Conversiona (%)
1
2
CuI
CuI
CuI
CuI
20
20
20
20
50
20
20
20
10
5
(CH2)2(OH)2
(CH2)2(OH)2
(CH2)2(OH)2
(CH2)2(OH)2
(CH2)2(OH)2
(CH2)2(OH)2
(CH2)2(OH)2
iPrOH
iPrOH
iPrOH
nBuOH
—
—
—
—
—
—
—
19
48
27
69
69
69
69
69
69
69
69
69
69
69
80
80
22
13
10
55
13
41
50
53
63
62
50
40
64
72
3
100
100
100
100
100
100
90
90
90
90
90
4b
5
CuI
6
7
8
9
10
11
12
13
14
CuBr
CuCN
CuCN
CuCN
CuCN
CuCN
CuCN
Cu2O
CuOAc
iPrOH
iPrOH
5
—
—
—
—
—
10
10
10
tBuOH
iPrOH
iPrOH
90
a Determined by integration of the 31P NMR spectrum. b For solvent-less reactions (entries 4 to 14), 10 equivalents of 12 were used.
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from slow diffusion during 3 days of the reaction. Analogously, amide (S,S)-9a (dr 94 : 6) afforded compound 10 in 50% crude
compound 17 is generated from the C–O coupling of ethylene yield (20% isolated yield).32 The decrease in the yield, com-
glycol which is used as the ligand with 11, a behaviour similar pared with that of the achiral analogue 13, can be attributed to
to that observed in the reaction in the presence of n-butanol.
the greater steric encumbrance of the (S)-(−)-3,3-dimethyl-2-
The increase of the loading of the catalyst to 50% was dis- butylamino moiety of 9a compared to the isopropyl group
advantageous (entry 5). A cleaner reaction was observed when present in compound 11, which probably hinders the
CuBr and CuCN were used as catalysts (entries 6 and 7). Under approach of 4-amino-TEMPO to the ortho position of 9a. To
CuBr catalysis, a mixture of 13, 15 and 17 was obtained in a the best of our knowledge, compound 10 is the first example
ratio of 41 : 38 : 21. However, the conversion of 13 decreased to of a P-stereogenic TEMPO-based radical. The structure of 10
41%. In contrast, the reaction catalysed by CuCN afforded was confirmed by X-ray diffraction of single crystals obtained
compound 13 in a conversion of 50%. Even though this con- from the slow evaporation of a solution of the ligand in CHCl3.
version was slightly lower than that observed in entry 4, we
The reaction of (SP,SC)-10 with an equimolar amount of Cu
decided to use this catalyst for the next optimization steps due (hfac)2 in a mixture of n-heptane/CHCl3 as the solvent afforded
to the reduced number of by-products formed. The change of after 30 days at −20 °C dark-green single crystals of 19 in a
the ligand to isopropanol resulted in the formation of only 13 yield of 20% (Scheme 2). The X-ray diffraction study of the
and 15 in a ratio 53 : 47 (entry 8). Decreasing the loading of the structure showed that the metal ion is coordinated to the
catalyst to 10 mol% provided an increase of 10% in the yield oxygen atoms of the phosphinic amide and the TEMPO moi-
(entry 9). Similar results were obtained when 5 mol% of CuCN eties. As far as we know, there are no precedents for this type
was used (entry 10). The reactions carried out in the absence of P-stereogenic complex in the literature.
of a ligand or using bulkier tert-butanol as the ligand gave
lower yields (entries 11 and 12). The performance of Cu2O as
the catalyst was similar to that of CuCN furnishing 13 in a con-
version of 64% (entry 13). Thus, the best results were achieved
using CuOAc (10 mol%) as the catalyst in the presence of
K3PO4 (3 equiv.) and isopropanol (3 equiv.) at 90 °C for ca. 3
Table S1,† while the selected bond lengths and angles are
days (entry 14, Scheme 2). In this way, the ortho-aminated
product 13 was obtained in 72% crude yield and 30% isolated
yield after the purification steps. The decrease in the yield can
Crystal structural description of 10
Compound 10 crystallizes in the orthorhombic P212121 chiral
space group and its molecular structure is shown in Fig. 2. A
summary of data collection and refinement is given in
listed in Table 2. The thermal ellipsoids are shown in
Fig. S20.†
The molecular structure of compound 10 consists of a
neutral 4-substituted amino-TEMPO radical. The N2 atom con-
be due to the two flash column chromatography eluents
needed (eluents: EtOAc : hex 1 : 1 and subsequently
nects the six-membered TEMPO ring to the chiral P-containing
CH2Cl2 : Et2O 9 : 1) in order to isolate the pure compound. As
moiety. Starting from the P-containing moiety, the PvO bond
far as we know, there are no precedents about C–N bond-
length is 1.490(1) Å, which is in the typical distance range of
forming reactions of the ATEMPO radical via cross-coupling
Ph2P(O)NHR molecules33 and is in good agreement with the lit-
processes.
erature values for similar compounds.34 The geometry around
Extension of the methodology to P-stereogenic phosphinic
amides
the phosphorus atom can be described as a distorted tetra-
hedron with bond angles ranging from 102.0(1) to 119.0(1)°.
The largest bond angle around the phosphorus atom was
observed for the O2–P1–N3 set, and this remarkable structural
difference with respect to the other bond angles involving the
P atom can be related to the steric hindrance of the 3,3-
dimethyl-2-butylamino group. Concerning the P1 and C22
chiral atoms, since the stereogenic centers of the starting
phosphinic amide 9a remained unchanged, both showed the
With the optimized reaction conditions in hand, the appli-
cation of the methodology to the P-stereogenic phosphinic
Fig. 2 Representation of the molecular unit of compound 10.
Hydrogen atoms were omitted for clarity. Color codes: Gray: carbon;
red: oxygen; orange: phosphorus and blue: nitrogen.
Scheme 2 Synthesis of 10 and complexation with Cu(hfac)2 to give 19.
2588 | Dalton Trans., 2021, 50, 2585–2595
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moiety (N3–H3 = 0.87(3) Å, H3⋯O1i = 2.12(3) Å, N3⋯O1i =
2.988(2) Å; ∠N3H3⋯O1i = 173(2)°; i = −x + 3/2, −y + 2, z + 1/2)
gives rise to a zig-zag supramolecular chain running along the
b axis, as shown in Fig. 3. Each supramolecular chain is con-
nected to the neighbouring ones through PvO⋯H–Csp2 short
contacts involving the phosphinic and amino-phenyl groups.
The intrachain distance between the paramagnetic sites is
10.423(2) Å. The closest separation among them is 8.379(2) Å,
found for the interchain N–O·····O–N distance.
Table 2 Selected bond lengths and angles for 10 and 19
Atom labels
(10)
(19)
N1–O1
P1–O2
P1–N3
P1–C15
P1–C16
N2–C5
N2–C10
1.285(2)
1.492(2)
1.649(2)
1.805(2)
1.806(2)
1.451(3)
1.375(3)
1.485(2)
—
1.292(4)
1.500(2)
1.639(3)
1.799(3)
1.808(3)
1.451(4)
1.383(4)
1.483(4)
2.569(3)
2.224(2)
1.960(2)
1.955(2)
1.952(2)
1.958(2)
123.2(3)
123.9(2)
111.0(1)
109.0(1)
118.5(1)
105.1(1)
102.7(1)
109.9(1)
150.8(1)
158.6(2)
9.3978(7)
N3–C22
Cu1–O1i
Cu1–O2
—
Structural description of copper complex (SP,SC)-19
Cu1–O3
Cu1–O4
—
—
Complex (SP,SC)-19 crystallizes in the chiral orthorhombic
P212121 space group and its crystallographic data and refine-
ment parameters are listed in Table S1.† The thermal ellip-
soids of the asymmetric unit are depicted in Fig. S21.† The
asymmetric unit consisted of one radical molecule 10 co-
ordinated to a Cu(hfac)2 moiety by a phosphinic oxygen atom,
and one toluene as the lattice solvent. Radical 10 acts as a
spacer and leads to the formation of a 1D chiral helical chain
running along the b axis (Fig. 4). The copper(II) ion shows a
tetragonally distorted octahedral geometry, coordinated to
four hfac oxygen atoms and two units of the radical ligand
through PvO and N–O• groups in a trans arrangement. The
equatorial plane is formed by four hfac oxygen atoms (O3–O6)
displaying an average Cu–O distance of 1.956(2) Å, typical of
other Cu(hfac)2 complexes reported elsewhere.35 The axial
positions are occupied by two radical molecules, with one
oxygen atom from the TEMPO moiety (O1) and the other being
the phosphinic oxygen atom (O2). Due to the Jahn–Teller
effect, the axial bond lengths are remarkably longer with Cu1–
O1i and Cu–O2 distances of 2.569(3) Å and 2.224(2) Å, respect-
ively. The bond angle involving the copper ion and the TEMPO
moiety (Cu1i–O1–N1, i = −x, 1/2 + y, 1/2 − z) is 158.6(2)°. In
addition, the bond angles between the atom from the equator-
ial plane and apical positions are in the range of 83.13(9)°
(O6–Cu1–O1) to 101.42(9)° (O2–Cu1–O5), while the largest
Cu1–O5
Cu1–O6
—
—
C5–N2–C10
P1–N3–C22
O2–P1–C15
O2–P1–C16
O2–P1–N3
N3–P1–C15
N3–P1–C16
C15–P1–C16
Cu1–O2–P1
Cu1i–O1–N1
Cu1⋯Cu1i
123.9(2)
118.0(1)
110.9(1)
110.4(1)
119.0(1)
104.1(1)
102.0(1)
109.8(1)
—
—
—
Symmetry operation: (i) = −x, 1/2 + y, 1/2 − z.
expected S configuration. The absolute crystal structure was
confirmed by the Flack parameter close to zero [0.024(9)].
In the TEMPO radical moiety, the six-membered ring is in
the chair conformation with an N–O• bond length of 1.285(2)
Å, which is similar to those observed in other TEMPO deriva-
tives.22 The plane passing by the TEMPO ring atoms (C1–C5,
N1, N2 and O1) is 59.7° displaced from the central phenyl ring
(C10–C15 atoms), while the P-phenyl ring is more parallel to
the TEMPO one, with an angle of 14.0°. This configuration
adopted by the rings is driven by the intramolecular hydrogen
bond found in the fragment PvO⋯HNTEMPO as depicted in
Fig. 3. The following geometric parameters were observed for
this intramolecular interaction: N2–H2 = 0.88(3) Å, H2⋯O2 =
1.97(3) Å, N2⋯O2 = 2.747(2) Å and ∠N2–H2⋯O2 = 147(2)°.
An intermolecular hydrogen bond involving the TEMPO
oxygen atom and α-amino group of the phosphinic amide
Fig. 3 Details of the crystal packing of 10 showing the intramolecular
PvO⋯HNTEMPO hydrogen bond, and the intermolecular interactions
that lead to the formation of a zig-zag supramolecular chain running
along the
b
axis. Only the hydrogen atoms involved are shown.
Fig. 4 Fragment of the helicate chain of (SP,SC)-19 with atom number-
ing (top). A 1D chain running parallel to the b crystallographic axis (SP,
SC)-19. Hydrogen and CF3 groups were omitted for clarity.
Symmetry operation to generate equivalent atoms: (i) = −x + 3/2, −y + 2,
z + 1/2.
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deviation from an ideal octahedral geometry is 168.05(8)°,
found for the apical positions (O1–Cu1–O2).
The best fit of the magnetic data was g = 2.00(1) and θ =
−0.290(2) K. The theoretical curve and the experimental data
The shortest intrachain distance between the copper(II) ion match quite well over the entire temperature range, as depicted
is 9.3978(7) Å (Cu1⋯Cu1i, i = −x, 1/2 + y, 1/2 − z), whereas the in Fig. 5. The X-band EPR spectrum of 10 in the solid state
shortest intermolecular one is 12.0437(7) Å (Cu1⋯Cu1ii, ii = (see the inset of Fig. 5) shows a narrow signal centered at
1 − x, −1/2 + y, 3/2 − z). Since the direct coordination among 2.005, which is characteristic of free radicals.37
copper and the nitroxide moiety of 10 was achieved, the short-
Nβ2g2
kðT ꢀ θÞ
est intramolecular distance found between the paramagnetic
χM
¼
SðS þ 1Þ:
ð1Þ
sites is indeed 2.569(2) Å, which is slightly longer than those
observed in other complexes with Cu–•ON and an octahedral
geometry around the metal described to date (in the range of
2.33–2.52 Å).36 As observed in the crystal structure of 10, an
intramolecular hydrogen bond in between the PvO⋯HNTEMPO
fragment is also present in 19, with the following geometric
parameters: N2–H2 = 0.80(4) Å, H2⋯O2 = 2.07(4) Å, N2⋯O2 =
2.785(4) Å and ∠N2–H2⋯O2 = 149(4)°. This intramolecular
interaction acts as the driving force to maintain the same
radical conformation in 19, as seen in pro-ligand 10.
The crystal packing is stabilized by a network of hydrogen
bonds involving Csp3H⋯F from hfac and methyl groups from
the TEMPO units, and Csp2H⋯F between hfac and the phenyl
ring. Moreover, weak interactions, namely Csp3H⋯Csp2 and
Magnetic properties of 19
Fig. 6 shows the thermal dependence of the χMT product for
19 (χM is the magnetic susceptibility per Cu(II) ion and per
radical). At room temperature, the χMT value is 0.79 cm3 mol−1
K as expected for two spin doublets magnetically isolated (one
Cu(II) ion and one radical). Upon cooling, the χMT values con-
tinuously increase and attain a maximum value of 0.98 cm3
mol−1 K at 5.0 K, and then decrease rapidly. In the high temp-
erature region, the shape of this curve is indicative of the
occurrence of a ferromagnetic interaction between both para-
magnetic centers (Cu-radical), while the decrease at low temp-
erature could be the result of the presence of antiferro-
magnetic interactions and/or zero-field splitting (zfs) effects.
However, due to the low anisotropy of this complex, the impor-
tant zfs effect is not expected.
Csp2H⋯Csp2, are also found among the toluene crystallization
molecules and the chain, which are responsible for the inter-
molecular stabilization between the 1D polymeric helices.
Having in mind the 1D polymeric topology of 19, where the
radical acts as a bridging ligand through its oxygen–nitroxide
and oxygen–phosphinic donor atoms, the spin magnetic coup-
ling pattern can be summarized in Scheme 3.
Magnetic properties of 10
Fig. 5 shows the thermal dependence of the χMT product for
10 (χM is the molar magnetic susceptibility). At room tempera-
ture, the χMT value is 0.377 cm3 mol−1 K as expected for a mag-
netically isolated spin doublet, S = 1/2. Upon cooling, χMT
remains basically constant until ca. 10 K, and then it decreases
to ca. 0.335 cm3 mol−1 K at 2.0 K. No maximum of the mag-
netic susceptibility is observed above 2 K. These features are
characteristic of the occurrence of very weak intermolecular
antiferromagnetic interactions. The observed data were ana-
lyzed on the basis of eqn (1), where N, β, k and g have their
usual meanings, θ is the Weiss parameter and S = 12.
Fig. 6 χMT vs. T plot of complex 19. The circles represent the experi-
mental results and the solid line represents the best-fit curve through
eqn (2).
Fig. 5 χMT vs. T plot of complex 10. The circles represent the experi-
mental results and the solid line represents the best-fit curve through
eqn (1). The inset shows the X-Band EPR spectrum of 10 at 4.3 K.
Scheme 3 Model of the magnetic interactions of 19 applied to fit the
data.
2590 | Dalton Trans., 2021, 50, 2585–2595
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Given the occurrence of both ferro- and antiferromagnetic sphinic amides via Cu(I) catalyzed cross-coupling reactions.
interactions in 19 and the presence of two different magnetic Conversions of 50 to 72% were achieved using CuOAc
exchange pathways, we analyze the magnetic data through a (10 mol%) as the catalyst (isolated yields of 20 to 30%). This
numerical expression for an alternating ferro- and antiferro- methodology was applied to the synthesis of a P-stereogenic
magnetic Heisenberg chain derived by Georges et al.38 The phosphinic amide-ortho-ATEMPO radical. Its coordination be-
corresponding Hamiltonian is defined using eqn (2), where J havior with Cu(hfac)2 provided a P-stereogenic complex with a
is the exchange coupling parameter associated with a particu- polymeric helicate chain built by the coordination of the
lar copper(II)-radical pair and αJ is the exchange constant oxygen atoms of the phosphinic amide and nitroxide donor
assigned to the adjacent unit (the alternating parameter α is sites to the Cu(II) ions. To the best of our knowledge, these are
defined as the JF/|JAF| quotient).
the first examples of Csp2–N cross-coupling reactions of
ATEMPO and of a P-stereogenic-ortho-ATEMPO radical and its
copper(II) complex. The magnetic properties of the chiral com-
pounds showed very weak intermolecular antiferromagnetic
interactions for the ligand, while ferro- and anti-ferromagnetic
interactions were observed for the copper(II) complex. The
extension of the application of the novel chiral P-stereogenic
ATEMPO-based radical in catalysis and coordination chemistry
is underway.
n=2
X
ˆ ˆ
ˆ ˆ
ˆ
H ¼ ꢀJ
ðS2iS2iꢀ1 ꢀ αS2iS2iþ1Þ:
ð2Þ
i¼1
Least-squares best-fit parameters obtained were J = 12.6(1)
cm−1, αJ = 1.11(1) cm−1, and g = 2.11(1), where g is the average
value of gCu and grad. Due to the unpaired electron of the
radical which is localized on an N-TEMPO π-orbital, the stron-
gest magnetic interaction can be attributed to the Rad-N–O–Cu
pathway, JF = +12.1 cm−1, while the weakest one must be attrib-
uted to the longest phosphinic amide magnetic pathway, JAF
=
Experimental section
Instrumentation and reagents
−1.11 cm−1. These relatively small values can be understood
by looking at the relative disposition of the magnetic orbitals
involved. In both intrachain pathways, the magnetic orbital at
each copper(II) site (that is the molecular orbital describing the
unpaired electron) is of the d(x2–y2)-type and it is mainly delo-
calized on the equatorial plane (the plane formed by the hfac
ligands) and so, the spin density at the apical position is pre-
dicted to be very small.
All reactions and manipulations were carried out under a dry
N2 gas atmosphere using standard Schlenk procedures. THF
was distilled from sodium/benzophenone immediately prior to
use. Commercial reagents were distilled prior to their use,
except for tert-butyllithium and chiral amine. TLC was per-
formed on Merck plates with aluminium backing and silica
gel 60. Purification was carried out by column chromatography
using silica gel 60 (40–63 μm) from Scharlau and different mix-
tures of ethyl acetate : hexane and methylene chloride : diethyl
ether as the eluent. NMR spectra were recorded on a Bruker
Avance 300 (1H, 300.13 MHz; 13C, 75.47 MHz; and 31P,
121.49 MHz). The spectral references used were tetramethyl-
silane as the internal standard for 1H and 13C spectroscopy,
and 85% H3PO4 as the external standard for 31P spectroscopy.
Diastereoselectivities were determined by the integration of
the 31P NMR spectra of the crude reaction mixtures. The stan-
dard Bruker software was used for acquisition and processing
methods. Infrared spectra were recorded using Bruker Alpha
FTIR equipment. High resolution mass spectra were recorded
on Agilent Technologies LC/MSD TOF and HP 1100 MSD
equipment with electrospray ionization. Melting points were
recorded using Büchi B-540 capillary melting point apparatus
and are uncorrected. Compounds 9a and 11 were prepared
according to a method described in the literature.26
The Cu(II)-d(x2–y2) magnetic-orbital and the O-(nitroxide)
π-orbital are orthogonal, leading to a ferromagnetic inter-
action.39 The small value of this ferromagnetic interaction is
due to the long bond distance Cu–O(1) (2.57 Å) as a conse-
quence of the Jahn–Teller effect. Similar ferromagnetic inter-
actions were observed in other Cu(II)-TEMPO systems.40
The magnetic interaction Cu(II)-TEMPO through the phos-
phinic amide substituent is expected to be very small, if any. So,
the calculated value JAF = −1.11 cm−1 seems to be too large and,
although the chains are quite magnetically isolated within the
crystal, some interchain antiferromagnetic interactions could be
present. In fact, the magnetic data can be reproduced by ruling
out this magnetic interaction and using the Bleaney–Bowers
equation (eqn (2)), which describes the magnetic interaction
between the two spin doublets, and introducing a Weiss para-
meter, θ, to take into account the intermolecular interactions.
The best-fit parameters obtained through eqn (2) were J = +12.6
(1) cm−1, g = 2.11(1) and θ = −0.365(3) K. In this sense, the value
of JAF = −1.11 cm−1 obtained for the magnetic interaction Cu(II)-
TEMPO through the phosphinic group would be the upper limit
for this magnetic interaction.
X-ray diffraction
Crystallographic data were collected using a Bruker APEX II
CCD area detector at 100 K, using CuKα radiation (λ =
1.54178 Å). Data collection and cell refinement were performed
with Bruker APEX241 and Bruker SAINT,42 respectively. Data
reduction was done using SAINT. Empirical multiscan absorp-
Conclusions
In summary, we have shown the feasibility of introducing a tion correction using equivalent reflections was performed
4-amino-TEMPO radical at the ortho position of ortho-iodopho- using the SADABS program.43 The structure solution and full-
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matrix least-squares refinements based on F2 were performed
The optimized conditions for the synthesis of phosphinic
using SHELXS44 and SHELXL45 programs, respectively. All amide-TEMPO ligands. To a dry Schlenk, ortho-iodophosphinic
atoms except hydrogen were refined anisotropically. The struc- amide (0.1 mmol, 1 equiv.), K3PO4 (0.3 mmol, 3 equiv.) and
tures were drawn using the Mercury program.46
CuOAc (10 mol%) were added and dried in vacuo for 15 min.
Then, 4-amino-TEMPO (10 equiv.) and isopropanol (0.3 mmol,
3 equiv.) were added under a dry atmosphere and the mixture
was warmed to 90 °C and stirred for ca. 3 days. After this time,
the reaction mixture was diluted with ethyl acetate, filtered
through Celite and poured into water. Then, the crude mixture
was extracted with EtOAc (3 × 15 mL), and dried with Na2SO4
and the solvents were removed under reduced pressure. For
the purification of the compounds, two flash column chrom-
atography eluent mixtures were needed: for the first one,
EtOAc : hex 1 : 1 was used as the eluent mixture, and
CH2Cl2 : Et2O 9 : 1 was used as the eluent mixture for the
second one.
Magnetic measurements
Variable-temperature (2–300 K) direct current (dc) magnetic
susceptibility measurements on the crushed crystals of 10 and
19 under an applied field of 0.1 T were carried out with a
Quantum Design SQUID magnetometer. The data were cor-
rected for the diamagnetism of the constituent atoms and the
sample holder. The X-band EPR spectra of the powdered
samples were recorded at 4.3 K using a Bruker ER 200 spectro-
meter equipped with a helium cryostat.
Synthesis of the compounds
N-Isopropyl-P-(2-((1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)
General procedure for the preparation of 9a and 11. amino)phenyl)-P-phenylphosphinic amide (13). Yield: 30%.
Compounds 9a and 11 were prepared according to a method Red solid. Mp: 76–77 °C. 1H NMR (CDCl3) δ 7.92 (bs, 2H), 7.55
described in the literature.26 To a solution of the corres- (bs, 5H), 7.40 (bs, 1H), 6.78 (bs, 1H), 3.54 (bs, 1H), 2.76 (bs,
ponding phosphinic amide (3.3 mmol) in 10 mL of THF, 1H), 1.35 (bs, 12H) ppm. 31P{1H} NMR (CDCl3) δ 29.6 (s) ppm.
t-BuLi (2.2 equiv. of a 1.7 M solution in pentane) was added at IR (KBr): ν 3345 (bs), 2971 (s), 2932 (s) 1596 (s), 1455 (s), 1242
−78 °C. After 1 hour of stirring, 1.2 equiv. of 1,2-diiodoethane (s), 1175 (s, PvO), 750 (m), 696 (w) cm−1. HRMS (ESI) calcd for
were added and the reaction was allowed to reach room temp- C24H36N3O2P: 429.2545, found: 429.2604. The structural
erature for an additional 15 minutes. Then, the mixture was assignment was confirmed by adding an equimolecular
poured into water, extracted with ethyl acetate (3 × 20 mL), and amount of phenyl hydrazine to the NMR sample to give
dried with anhydrous Na2SO4 and the solvents were removed N-isopropyl-P-(2-((1-hydroxy-2,2,6,6-tetramethylpiperidin-4-yl)
using a Rotavapor system. Purification: flash column chrom- amino)phenyl)-P-phenylphosphinic amide. Yield: 100%. 1H
3
3
4
atography (EtOAc : hex 4 : 1 as the eluent).
NMR (CDCl3) δ 7.87 (ddt, 2H, JPH 11.9, JHH 7.9 Hz, JHH 1.5
(S)-N-((S)-3,3-Dimethylbutan-2-yl)-P-(2-iodophenyl)-P-phenyl- Hz), 7.41–7.55 (m, 5H), 6.63 (m, 2H), 3.45 (m, 1H), 2.77 (dd,
2
3
1
3
phosphinic amide (9a). The characterization of this compound 1H, JPH 9.9, JHH 6.3 Hz), 2.09 (dt, 1H, JHH 13.0 Hz, JHH 3.5
is described.26 Yield: 80%. [α]D25 +148.1 (c 0.9, CH2Cl2). The Hz), 1.96 (dt, 1JHH 13.2 Hz, 3JHH 3.4 Hz, 1H), 1.58 (m, 1H), 1.28
NMR data obtained are in excellent agreement with those (m, 18H) ppm. 31P NMR (CDCl3) δ 29.4 (s) ppm. HRMS (ESI)
reported in the literature. 1H NMR (CDCl3) δ 8.29 (ddd, 1H, calcd for C24H37N3O2P: 430.2623, found: 430.2702.
3JPH 12.1, 3JHH 7.6, 4JHH 1.7 Hz), 7.90 (dd, 1H, 3JHH 7.9, 4JPH 3.8
(SP)-N-((SC)-3,3-Dimethylbutan-2-yl)-P-(2-((1-oxyl-2,2,6,6-tetra-
Hz), 7.64 (dd, 2H, JPH 13.1, JHH 6.9 Hz), 7.40 (m, 2H), 7.49 methylpiperidin-4-yl) amino)phenyl)-P-phenylphosphinic
3
3
(m, 2H), 7.15 (t, 1H, 3JHH 7.6 Hz), 3.41 (ddc, 1H, 3JPH 19.7, 3JHH amide (10). Yield: 20%. Red solid. Mp: 175–176 °C. [α]2D5 +395.9
3
2
3
10.1, JHH 6.6 Hz), 3.24 (dd, 1H, JPH 14.3, JHH 10.3 Hz), 1.30 (c 0.45, CH2Cl2). 1H NMR (CDCl3) δ 7.95 (bs, 2H), 7.41 (bs, 4H),
(d, 3H, JHH 6.6 Hz), 0.80 (s, 9H) ppm. 31P{1H} NMR (CDCl3) δ 7.37 (bs, 1H), 6.73 (bs, 1H), 3.00 (bs, 1H), 2.76 (bs, 1H), 2.42
3
26.6 (s) ppm.
(bs, 2H), 1.55 (bs, 4H), 1.32 (bs, 15H), 0.98 (bs, 9H) ppm. 31P
N-Isopropyl-P-(2-iodophenyl)-P-phenylphosphinamide (11). {1H} NMR (121.49 MHz, CDCl3) δ 30.0 (s) ppm. IR (KBr): ν
Yield: 72%. White solid. Mp: 108–109 °C. 1H NMR (CDCl3) δ 3256 (bs), 2961 (s), 1586 (s), 1457 (s), 1241 (s), 1172 (s, PvO),
8.29 (ddd, 1H, JPH 12.5, JHH 7.6, JHH 1.6 Hz), 7.98 (ddd, 1H, 1114 (s), 747 (m), 699 (m) cm−1. HRMS (ESI) calcd for
3
3
4
3JHH 8.0, JPH 3.9, JHH 1.3 Hz), 7.77 (ddd, 2H, JPH 12.7, JHH C27H42N3O2P: 471.3009, found: 471.3019. The structural
4
4
3
3
4
3
8.0, JHH 1.3 Hz), 7.49 (m, 2H), 7.51 (m, 2H), 7.18 (tt, 1H, JHH assignment was confirmed by adding an equimolecular
7.8, 4JHH 1.3 Hz), 3.62 (m, 1H), 3.17 (t, 1H, 2JPH = 3JHH 10.3 Hz), amount of phenyl hydrazine to the NMR sample to reduce the
1.32 (d, 3H, JHH 6.5 Hz), 1.20 (d, 3H, JHH 6.5 Hz) ppm. 13C radical. Yield: 100%. 1H NMR (CDCl3) δ 7.92 (ddd, 2H, JPH
3
3
3
{1H} NMR (CDCl3) δ 141.5 (d, JPC 9.5 Hz), 136.6 (d, JPC 125.5 11.6, JHH 7.6, JHH 1.6 Hz), 7.48 (m, 5H), 6.63 (m, 2H), 3.70
2
1
3
4
3
4
2
2
3
Hz), 136.1 (d, JPC 8.4 Hz), 132.9 (d, JPC 2.8 Hz), 132.1 (d, JPC (m, 1H), 3.00 (m, 1H), 2.76 (dd, JPH 11.1, JHH 5.3 Hz), 2.08
9.6 Hz), 132.0 (d, JPC 3.6 Hz), 131.9 (d, JPC 131.9 Hz), 128.5 (dt, 1H, 2JHH 13.0, 3JHH 3.6 Hz), 1.99 (dt, 1H, 2JHH 13.1, 3JHH 3.6
4
1
(d, JPC 13.7 Hz), 127.8 (d, JPC 10.2 Hz), 98.8 (d, JPC 7.3 Hz), Hz), 1.58 (m, 2H), 0.93 (s, 9H), 1.28 (m, 15H) ppm. 31P NMR
3
3
2
2
3
3
43.5 (d, JPC 1.4 Hz), 26.2 (d, JPC 5.4 Hz), 25.4 (d, JPC 4.9 Hz) (CDCl3) δ 30.3 (s) ppm. HRMS (ESI) calcd for C27H43N3O2P:
ppm. 31P{1H} NMR (CDCl3) δ 25.9 (s) ppm. IR (KBr): ν 3250 472.3087, found: 472.3097.
(bs), 2967 (s), 1422 (s), 1198 (s, PvO), 1114 (s), 730 (s), 690 (m)
Synthesis of the copper complex (19). 0.021 mmol of
cm−1. HRMS (ESI) calcd for C15H17NOPI: 386.0171, found: Cu(hfac)2·2H2O was added to 10 mL of boiling n-heptane. When
386.0177.
the metal complex was completely dissolved, 0.021 mmol of
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the chiral 4-amino-TEMPO ligand dissolved in CHCl3 was entry 4 (Table 1, main text) through flash column chromato-
quickly added under constant stirring. The solution was boiled graphy (EtOAc : hex 1 : 1 as the eluent mixture). Yield: 10%.
for 5 minutes and then allowed to cool. Green crystals suitable Colorless oil. 1H NMR (CDCl3) δ 7.93 (m, 2H), 7.59 (m, 1H),
3
3
for X-ray diffraction analysis were obtained after 30 days at 7.53 (m, 2H), 1.18 (d, 3H, JHH 6.4 Hz), 7.46 (dddd, 1H, JHH
3
4
5
−18 °C. Yield: 20%. Mp: 127–128 °C. [α]D25 +508.5 (c 0.2, 8.3, JHH 7.4, JHH 1.7, JPH 1.0 Hz), 7.18 (m, 1H), 7.14 (ddd,
CH2Cl2). IR (ATR, cm−1): 3319 (w, NH), 1645 (s, CO), 1259 (s, 1H, JPH 14.0, JHH 7.4, JHH 1.7 Hz), 7.00 (ddd, 2H, JHH 8.3,
3
3
4
3
CF), 1211 (s), 1149 (s, PvO), 797 (m), 679 (m). Anal. calc. for 4JPH 5.0, JHH 0.9 Hz), 6.96 (ddt, 1H, JHH 7.4, JPH 2.8, JHH 0.9
4
3
4
4
3
C37H43CuF12N3O6P: C, 46.87%; H, 4.43%; N, 4.57%. Found: C, Hz), 4.2–4.4 (m, 2H), 3.88 (m, 2H), 3.41 (sep, 1H, JHH 6.4 Hz),
46.54%; H, 4.81%; N, 4.24%. Although the crystal structure of 1.33 (d, 3H, JHH 6.4 Hz) ppm. 13C{1H} NMR (CDCl3) δ 160.8
3
2
4
2
the complex shows one toluene molecule as the lattice solvent, (d, JPC 2.0 Hz), 133.5 (d, JPC 2.1 Hz), 133.0 (d, JPC 9.8 Hz),
the elemental analysis result is more consistent with the 132.4 (d, 2JPC 9.3 Hz), 132.1 (d, 4JPC 2.8 Hz), 131.0 (d, 1JPC 133.1
3
1
toluene-free formula, suggesting the ready loss of this solvent Hz), 128.5 (d, JPC 13.1 Hz), 123.5 (d, JPC 129.3 Hz), 121.5 (d,
3
molecule during microanalysis.
3JPC 13.1 Hz), 115.0 (d, JPC 7.0 Hz), 73.3 (s), 61.1 (s), 44.0 (d,
2JPC 1.9 Hz), 26.4 (d, 3JPC 3.1 Hz), 25.8 (d, 3JPC 9.2 Hz) ppm. 31
{1H} NMR (CDCl3) δ 28.0 (s) ppm. IR (solid film): 3424 (bs),
P
By-products obtained during the optimization procedure
N-Isopropyl-P-(2-butoxiphenyl)-P-phenylphosphinic amide 2924 (m), 1591 (m), 1441 (m), 1278 (w), 1150 (bs, PvO), 1133
(14). Obtained through flash column chromatography (m), 756 (m), 696 (m) cm−1. HRMS (ESI) calcd for C17H23NO3P:
(EtOAc : hex 1 : 1 as the eluent mixture) from the reaction in 320.1416, found: 320.1417.
1
entry 3 (Table 1, main text). Yield: 40%. Colorless oil. H NMR
(S)-N-(3,3-Dimethylbutan-2-yl)-P,P-diphenylphosphinic amide
3
(CDCl3) δ 7.86 (m, 3H), 7.47 (m, 4H), 7.05 (ddt, 1H, JHH 7.4, (18). Obtained from the crude of the reaction of 9a with
4JPH 2.0, 4JHH 0.9 Hz), 6.87 (ddd, 1H, 3JHH 8.3, 4JPH 5.3, 4JHH 0.8 4-amino-TEMPO. The NMR results are in agreement with those
Hz), 4.00 (m, 2H), 3.56 (m, 1H), 3.39 (t, 1H, JHH 8.7 Hz), 1.69 reported in the literature.26 Yield: 29%. H NMR (CDCl3) δ 7.92
3
1
(m, 2H), 1.43 (m, 2H), 1.20 (d, JHH 6.3 Hz, 3H), 1.19 (dd, 3H, (m, 4H), 7.45 (m, 6H), 2.90 (ddc, 1H, 3JHH 11.1, 3JPH 8.7, 3JHH 6.7
3
3JHH 6.3 Hz, JPH 0.5 Hz), 0.96 (t, 3H, JHH, 6.3 Hz) ppm. 13C Hz), 2.68 (dd, 1H, JHH 11.1 Hz, JPH 5.2 Hz), 1.21 (d, 3H, JHH
4
3
3
2
3
{1H} NMR (CDCl3) δ 159.3 (d, JPC 3.6 Hz), 135.4 (d, JPC 131.7 6.7 Hz), 0.90 (s, 9H) ppm. 31P{1H} NMR (CDCl3) δ 22.4 (s) ppm.
2
1
2
4
2
Hz), 134.3 (d, JPC 7.5 Hz), 133.3 (d, JPC 2.5 Hz), 131.8 (d, JPC
3
4
10.6 Hz), 128.2 (d, JPC 12.2 Hz), 131.3 (d, JPC 3.5 Hz), 121.6
(d, 1JPC 124.4 Hz), 121.0 (d, 3JPC 11.6 Hz), 111.5 (d, 3JPC 7.2 Hz), Conflicts of interest
3
2
3
68.3 (d, JPC 0.3 Hz), 42.6 (d, JPC 1.5 Hz), 30.0 (s), 26.2 (d, JPC
3.4 Hz), 26.0 (d, JPC 7.0 Hz), 19.8 (s), 13.9 (s) ppm. 31P{1H}
3
There are no conflicts to declare.
NMR (CDCl3) δ 23.9 (s) ppm. IR (solid film): 3444 (bs), 2961
(m), 1590 (m), 1440 (m), 1278 (w), 1195 (bs, PvO), 1135 (w),
757 (m), 696 (m). HRMS (ESI) calcd for C19H27NO2P: 332.1779,
found: 332.1778.
Acknowledgements
Financial support from Ministerio de Economía
y
N-Isopropyl-P,P-diphenylphosphinic amide (15). Obtained
through flash column chromatography (EtOAc : hex 1 : 1 as the
eluent mixture) from the reaction in entry 4 (Table 1, main
text). Yield: 8%. White solid. The NMR data obtained for the
compound are in agreement with those reported in the litera-
ture.47 1H NMR (CDCl3) δ 7.93 (m, 4H), 7.49 (m, 6H), 3.40 (sep,
3JHH 6.6 Hz), 2.70 (t, 1H, 3JHH 7.5 Hz), 1.26 (d, 6H, 3JHH 6.6 Hz)
ppm. 31P{1H} NMR (CDCl3) δ 22.8 (s) ppm.
Competitividad (MINECO) and the FEDER program (projects
CTQ2014-57157-P, CTQ2016-75671-P, CTQ2016-75068-P, and
Excellence Unit “María de Maeztu” MDM-2015-0538) is grate-
fully acknowledged. GPG acknowledges the financial support
from Fundação Carlos Chagas de Amparo à Pesquisa do
Estado do Rio de Janeiro – FAPERJ (project number E-26/
202.720/2018). YNG thanks Ministerio de Educación, Cultura y
Deporte (MECD)40a for a PhD fellowship.
N-Isopropyl-P-(2-hydroxyphenyl)-P-phenylphosphinic amide
(16). White solid. Only traces of the compound were obtained
from the crude reaction mixture in entry 4 (Table 1, main text),
via flash column chromatography (EtOAc : hex 1 : 1 as the
eluent mixture). The assignment of the structure was carried
out based on the 1H and 31P{1H} NMR spectra and through
comparison with the corresponding spectra of a chiral ana-
logue described in the literature.26 1H NMR (CDCl3) δ 11.61 (s,
Notes and references
1 For recent reviews see: (a) C. Gong and X. Zang, Science,
2019, 363, eaav4450; (b) M. Gobbi, M. A. Novak and E. Del
Barco, J. Appl. Phys., 2019, 125, 240401; (c) L. Guo, X. Gu,
X. Zhu and X. Sun, Adv. Mater., 2019, 31, 1805355;
(d) M. Atzori and R. Sessoli, J. Am. Chem. Soc., 2019, 141,
11339–11352; (e) Z.-S. Yao, Z. Tang and J. Tao, Chem.
Commun., 2020, 56, 2071–2086.
3
3
1H), 7.94 (dd, 2H, JPH 10.7, JHH 6.8 Hz), 7.50 (m, 4H), 7.40
(m, 1H), 6.92 (m, 2H), 3.46 (m, 1H), 2.91 (m, 1H), 1.33 (d, 3H,
3
3JHH 6.5 Hz), 1.25 (d, 3H, JHH 6.5 Hz) ppm. 31P{1H} NMR
(CDCl3) δ 31.5 (s) ppm.
N-Isopropyl-P-(2-(2-hydroxyethoxy)phenyl)-P-phenylphosphi-
nic amide (17). Obtained from the crude reaction mixture in
2 (a) G. L. J. A. Rikken and E. Raupach, Nature, 1997, 390,
493–494; (b) T. Cyrille, M. Gruselle and M. Verdaguer,
Chem. Soc. Rev., 2001, 40, 3297–3312; (c) L. Bogani,
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