New: O-substituted diphenylphosphinic amide ligands: Synthesis, characterization and complexation with Zn2+, Cu2+ and Y3+

Article abstract of DOI:10.1039/c9nj02829c

Phosphinic amide derivatives have drawn significant attention in coordination chemistry and have been incorporated into the design and synthesis of new ligands. In this work, the combination of the diphenylphosphinic amide group with quinoline, pyridine a

Full text of DOI:10.1039/c9nj02829c

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New o-substituted diphenylphosphinic amide
ligands: synthesis, characterization and
Cite this:DOI: 10.1039/c9nj02829c
complexation with Zn2+, Cu2+ and Y3+†
ac
Antonia Carlene Rodrigues Furtado Medeiros,ab Marcos Martins Gouvea,
ˆ
ˆ
ac
Thaian Vieira Felipe,b Flavia Ferreira de Carvalho Marques,
´
ab
Alice Maria Rolim Bernardino,
*
Fernando Lopez Ortiz *d and
´
ab
Marcos Costa de Souza
*
Phosphinic amide derivatives have drawn significant attention in coordination chemistry and have
been incorporated into the design and synthesis of new ligands. In this work, the combination of the
diphenylphosphinic amide group with quinoline, pyridine and phosphoramidate moieties gave rise to
four new classes of ligands (6, 8, 11 and 13), in moderate to good yields. The coordination properties
were tested with Zn2+, Cu2+ and Y3+ by nuclear magnetic resonance (NMR), fluorescence and infrared
(IR) spectroscopies. The molar proportions between metal ions and ligands (M/L) were estimated from
the spectrofluorimetric titration curves and have demonstrated preponderant formation of ML2-type
complexes. From the IR spectra, the variations of wavenumber and/or intensity of the absorption bands
of ligands and complexes pointed out the participation of PQO, CQO, CQN(pyridine) and N–H functional
groups as the possible coordination sites. The results have demonstrated the capacity of some of the
synthesized substances to act as ligands, which can be useful for several applications in the field of
coordination chemistry.
Received 30th May 2019,
Accepted 4th August 2019
DOI: 10.1039/c9nj02829c
rsc.li/njc
N-Heterocyclic ligands show strong luminescence properties
as they are affected by steric, electronic and conformational
Introduction
effects.6,7 Organophosphorus compounds also present interesting
structural and photophysical characteristics.8 The combination of
both substructures into a system is a very useful strategy for the
preparation of multifunctional ligands with applications in the
design of luminescent materials.2,9–14
In this regard, phosphinic amides are attractive materials
for access to luminescent devices. The complexation ability of
the PQO linkage of phosphinic amides toward main group,
transition metal15 and lanthanide16–18 cations is well documented.
However, the luminescence properties of the –NR–PQO group19
in combination with metal ions have been little exploited.
Luminescent phosphinic amide Eu3+ complexes have been the
most studied involving mono- (I, Fig. 1)20–22 and tridentate
bis(phosphinic amide)-phosphine oxide ligands(II).23 The latter
has served as the basis for the development of highly specific
and sensitive sensors for the detection of Eu3+ in water using an
optical fiber probe24 or a membrane.25
The search for new molecular systems with optimized properties
as well as the improvement of existing systems are of increasing
interest for medical, biological, technological, environmental
and other innovative applications. Coordination compounds
play an important role in this subject since these substances
may present different characteristics when coordinated with
different metal ions.1–5
Luminescence originating from emitting molecular species,
such as complexes with transition and lanthanide metals, is
one of the desirable qualities for these systems due to the
possibility of their use as specific sensors.3,4
a
´
˜
´
´
Programa de Pos-Graduaçao em Quımica, Instituto de Quımica,
´
Universidade Federal Fluminense, Niteroi 24020-141, Brazil.
E-mail: marcoscs@id.uff.br
b
c
´
ˆ
´
Departamento de Quımica Organica, Instituto de Quımica,
´
Universidade Federal Fluminense, Niteroi 24020-141, Brazil
´
´
´
Departamento de Quımica Analıtica, Instituto de Quımica,
´
Universidade Federal Fluminense, Niteroi 24020-141, Brazil
Recently, binuclear complexes of the 1-piperidinyloxy-
4-[(diphenylphosphinyl)amino]-2,2,6,6-tetramethyl radical
(dppnTEMPO) with Gd3+, Tb3+, and Dy3+ (III) have been reported.
For the Tb3+ derivative, emission spectroscopy supported the
presence of two inequivalent metal ions.26 The dppnTEMPO
d
´
´
´
´
Area de Quımica Organica, Universidad de Almerıa, Ctra. Sacramento s/n,
´
04120 Almerıa, Spain
† Electronic supplementary information (ESI) available: Full data of 1H, 13C and
31P NMR, IR, MS and spectrofluorimetric spectra and titration curves of the
synthesized ligands with Zn2+, Cu2+ and Y3+. See DOI: 10.1039/c9nj02829c
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Fig. 1 Representative examples of luminescent (I–III) and non-luminescent (IV–VII) complexes characterized at the molecular level involving mono-,
bi- and tri-dentate ligands containing a phosphinic amide group.
ligand also acted as a mono (PQO) or bidentate (PQO, N–O) linkage with NaBH4 to give the respective ortho and ortho, ortho0
ligand towards transition metal hexafluoroacetylacetonates functionalized derivatives (Scheme 1).
([M(hfac)2], MQCu, Co, and Mn) (e.g., complex IV).
Ortho formylation of 1 was achieved via directed ortho-
Diarylphosphinic amides can be readily derivatized via ortho- lithiation with n-BuLi and TMEDA in toluene at ꢀ90 1C,
lithiation and subsequent electrophilic quenching, a process that followed by electrophilic reaction with DMF.32 Reductive ami-
makes possible the introduction of new donor groups at the ortho nation of 2 using the aminoquinolines 5 (X = Cl, Br, and F),
position. We have applied this methodology to the synthesis of ortho which were synthesized from the corresponding azidoquino-
functionalized phosphinic amides (C6H4POPhN(CH(CH3)2)2)Ph2PX, lines 4, the aminopyridines 7 (n = 1, and 2) and the aminoalk-
with X = O, S, and Se, which acted as O^X-chelating ligands towards ylphosphoramidates 9 (n = 2, 4, 5, and 6) as primary amine
ZnCl2,27 including enantiopure phosphinic amide-phosphine oxide components afforded the corresponding ortho aminomethyl
Zn2+ complexes (VI, Fig. 1).28 The mixed-donor bidentate ligands derivatives 6, 8 and 11, respectively, in good yields (59–71%).
showed outstanding catalytic performance to promote the addition
of diethylzinc to aldehydes.27
In the synthesis of phosphinic amide-phosphoramidates 11,
the intermediate imines formed by the condensation of 2
The reaction of ortho-lithiated phosphinic amides with with aminophosphoramidates 9 were isolated. The conversion
PhP(O)Cl2 as an electrophile afforded a tridentate bis(phosphinic determined by 31P NMR spectroscopy of the crude reaction
amide)-phosphine oxide PhPO(C6H4POPhN(CH(CH3)2)2)2 that mixture was higher than 82%. However, the products proved to
upon treatment with 1 and 0.5 equivalents of yttrium nitrate be very sensitive to hydrolysis and were treated with NaBH4
provided 1 : 1 (VII, Fig. 1) and 1:2 complexes of Y3+, respectively.29 without purification to afford ligands 11.
Mixed phosphinic amide-heterocyclic systems have been prepared
Compounds 6, 8 and 11 showed two characteristic doublets
by incorporating the heterocycle into the amine moiety of the in the 1H NMR spectrum due to the diastereotopic benzylic
P(O)–N group. N-(2-Pyridinyl)- and N-(2-pyrimidinyl)-P,P-diphenyl- protons. This multiplicity is a result of their proximity to a
phosphinic amides have been used as O^N-bidentate ligands chiral center generated by the diphenylphosphinic amide
1
towards Cu2+, Co2+, Ag+ 30 and Zn2+ (V).31
lithiation. Similarly, H–13C HSQC spectra showed the correla-
This work describes the synthesis and characterization of tions of the diastereotopic protons with benzylic carbons that
new diphenylphosphinic amides coupled to phosphoramidates appear as doublets due to the three-bond scalar coupling with
and heterocyclic systems (pyridine and quinoline) as well as the phosphorus atom (3JPC).
their coordination properties with Zn2+, Cu2+ and Y3+ by NMR,
Tsuji et al. have reported that ortho,ortho dilithiation of
IR and fluorescence spectroscopies. The ligands have been P,P-diphenylphosphinic amides can be achieved by treatment
designed to combine rigid and flexible frameworks containing with an excess of t-BuLi. Subsequent quenching of the dianion
different donor sites with the aim of extending the coordination with electrophiles provides an easy entry into difunctionalized
possibilities of the system.
derivatives.33 This strategy has been used to synthesize
o,o0-bisformylphosphinic amide 3 by trapping the dilithiated
species with DMF. Condensation of 3 with aminoalkylphosphor-
amidates 9 furnished the expected imines (conversion nearly
quantitative determined by 31P NMR). Similar to the analogue
monocondensation products of 2, the imines were highly prone
Results and discussion
Synthesis of ligands
The ligands used in this work (6, 8, 11 and 13) were prepared to hydrolysis. They were reduced in situ with NaBH4 to give the
through a three-step procedure: formylation (mono and double) multifunctional ligands 13 in good yields (58–69%).
at the ortho position of phosphinic amide 1; condensation with
the corresponding primary amine; and reduction of the imine in the H NMR spectra due to the symmetry of the structures.
Double ortho,ortho0 functionalization was readily identified
1
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Scheme 1 Synthetic pathways to the obtainment of ligands 6a–c, 8a, b, 11a–d and 13a–d.
In the 31P NMR spectra, two signals were obtained in different
chemical environments. At higher d, the signal corresponding
to one phosphorus atom was related to the phosphinic amide
group and, at lower d, the other signal comprising two phos-
phorous atoms was associated with the phosphoramide groups.
Complexation studies by NMR
Previous results showed that phosphinic amides and ortho
functionalized derivatives were suitable ligands for the formation
of complexes of Zn2+, Cu2+ or Y3+ (e.g., IV, VI, and VII, Fig. 1).
Based on this experience, we decided to investigate the coordi-
nation properties of the new ligands towards the same set of
metal ions.
Equimolar amounts of ligands 6a–c, 8a, b, 11a–d or 13a–d
Fig. 2 31P NMR spectra of 11b and its Zn2+ complex, highlighting the
disappearance of the PQO signal from the phosphinic amide group.
and ZnCl2, CuSO4 or Y(NO3)3 were dissolved in mixtures of
dichloromethane with acetonitrile or methanol at room
temperature, and were kept at refrigerator temperature (4 1C)
for up to 30 days. In the cases of 11a/Zn2+/Y3+, 11d/Zn2+/Y3+,
13a/Zn2+/Cu2+/Y3+ and 13c/Zn2+/Cu2+/Y3+, amorphous solids spectra from the complexation study of 11b with Zn2+.
were formed, making it unsuitable for X-ray measurements. The disappearance of the PQO signal from the phosphinic
In other cases, only yellowish oils were obtained, in addition, amide group (d E 34 ppm) was a typical phenomenon observed
attempts at recrystallization failed for several combinations of for all compounds of series 11 and 13. These results clearly
solvents. Except for the paramagnetic Cu2+ ion, all samples were support the coordination of the metal ion to the oxygen atom of
investigated by NMR spectroscopy. Fig. 2 shows the 31P NMR the N–PQO moiety.5,16,27,34
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Selective metal binding to the phosphinic amide donor site
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Compounds 11 and 13 have N–H and PQO groups somewhat
will be favoured by the rigidity provided by the aromatic rings distinguishable concerning the phosphinic amide and phosphor-
with respect to the phosphoramidate groups, linked to a amide functions. For these series, the N–H absorption bands from
flexible alkyl chain, and also by the possibility of forming a the phosphoramide and the secondary amine groups were observed
seven membered metallacycle involving N–PQO and CH2NR close to 3250 and 3400 cmꢀ1, respectively. The latter absorption
ortho substituents as in the complexes VI and VII (Fig. 1). bands, however, were not detected for 11b and 11c. Additionally,
Unfortunately, complex formation produced a large broadening the PQO bands around 1175 and 1210 cmꢀ1 were attributed to the
1
of the H NMR signals due to a very fast transversal relaxation phosphinic amide and phosphoramide functions, respectively.
or, rather, to a rapid exchange between free and coordinate These bands were not prominent in some compounds.
species (see 1H NMR spectra of 11b and 11b/ZnCl2 in the ESI†).
Titrations with zinc chloride. Spectrofluorimetric titration
This feature prevented extracting useful structural information of the phosphinic amide containing a pyridine heterocyclic
from the NMR data. Complexation with the diamagnetic Y3+ substituent (8a) showed increased fluorescence signals after the
ion produced the same effect. Prompted by these results, addition of Zn2+. The titration curve presented inflection near
we decided to use other analytical techniques to complement M/L = 0.5 (1 : 2), which indicates coordination of the metal with
the behavior investigation of the synthesized substances in the two equivalents of ligand (Fig. 3). An evident decrease of the
presence of such metal ions.
PQO absorption band was observed in the IR spectra.
The complexation study of 11c also showed a considerable
increase of fluorescence intensity after the addition of the first
aliquot of Zn2+ solution, which was stabilized up to a M/L = 1.0
(1 : 1) ratio (Fig. 3). The IR spectra showed an intense shift of
the wavenumber absorption band of the N–H bond and
approximately no change for PQO bonds. The intensity of
the PQO band from the phosphoramide group also decreased
after complexation. However, 31P NMR results for this class
suggest that the metal ion coordination with PQO probably
occurred selectively in the phosphinic amide group.
Spectrofluorimetric titrations and IR spectroscopy
All ligands from series 6, 8, 11 and 13 showed intrinsic fluores-
cence and were titrated with solutions of zinc chloride, copper
sulphate and yttrium nitrate. The stoichiometric ratios of possible
complexes were estimated by the spectrofluorimetric titration
curves. Additionally, the IR spectra of ligands and complexes were
compared in order to detect variations of wavenumber and/or
intensity of the absorption bands and, consequently, suggest the
possible coordination sites of the cations.
Titration of compounds 6a, 6b, 11a and 13b with Zn2+ showed
no appreciable variations of intensity and/or wavelength in the
fluorescence spectra. The analytical signal of the other ligands
increased after the addition of each aliquot of Zn2+ solution.
Ligand 13a also showed a great shift of maximum wavelengths of
excitation and emission.
Table 1 sums up all of the IR absorption frequencies of
ligands and their respective eventual complexes. The results
presented in the text concern mainly the ligands that showed
the best behavior, with fluorescence signals varying until a plateau.
The other fluorescence spectra and all IR spectra are available as
ESI,† (complexation data section).
Table 1 IR absorption frequencies of ligands from series 6, 8, 11 and 13 titrated with Zn2+, Cu2+ and Y3+
Zn2+ (cmꢀ1 Cu2+ (cmꢀ1
Without titration
)
)
Y3+ (cmꢀ1
CQO CQN* N–H
)
Ligand N–H
PQO
CQO CQN* N–H
PQO
CQO CQN* N–H
PQO
PQO
CQO CQN*
6a
6b
6c
8a
3378
3370
3380
3298
1167
1175
1180
1176
1687 1626 3380
1687 1628 3373
1683 1627 3356
1170
1173
1176
1167
1687 1626 3370
1687 1628 3370
1732 1627 3335
1173
1173
1150
1176
1687 1628 3379
1687 1628 3369
1731 1628 3380
1181
1174
1180
1197
1689 1625
1687 1628
1693 1619
—
—
—
—
—
—
—
—
—
—
1591 3372,
3226
1591 3360,
3178
—
—
—
—
—
—
—
—
—
—
1609 3383
—
—
—
—
—
—
—
—
—
—
1611 3360,
3219
1609 3371,
3279
—
—
—
—
—
—
—
—
—
—
1642
1646
—
8b
3298
1176
1172
1609 3320,
3179
1174
1174
11a
11b
11c
11d
13a
13b
13c
13d
3361,
3254
3340,
3227
3371,
3203
3405,
3251
3386,
3233
3409,
3265
3420,
3251
3409,
3244
1214A,
1178B
1228A,
1176B
1205A,
1177B
1205A,
1176B
1205A,
1177B
1229A,
1179B
1205A,
1177B
1205A,
1182B
—
—
—
—
—
—
—
—
3281
3295
3295
3318
3346
3338
3308
3301
1203A,
1160B
1203A,
1174B
1203A,
1172B
1203A,
1173B
1261A,
1172B
1259A,
1174B
1255A,
1175B
1254A,
1173B
—
—
—
—
—
—
—
—
3302,
3114
3397,
3267
3410,
3245
3404,
3245
3193
1203A,
1177B
1209A,
1176B
1207A,
1176B
1207A,
1174B
1278A,
1177B
1255A,
1178B
1229A,
1175B
1227A,
1174B
—
—
—
—
—
—
—
—
3345
1203A,
1174B
1203A,
1176B
1205A,
1177B
1206A,
1172B
1261A,
1177B
1295A,
1175B
1296A,
1176B
1299A,
1175B
3395,
3267
3395,
3238
3418,
3245
3247
—
—
—
—
3180
3356
—
3410,
3267
3415,
3230
3372,
3241
3372,
3238
—
—
A: phosphoramide. B: phosphinic amide. *Ring stretching.
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Fig. 3 Spectrofluorimetric spectra and titration curves of ligands 8a and 11c titrated with Zn2+
.
In the IR spectra of 6b and 6c, the N–H stretching band also intensity of N–H and PQO bands considerably decreased.
intensely decreased. Compounds from series 8 (8a, b), 11a, 11b The same phenomenon was also observed for 6b.
and 13b showed a decrease of the PQO absorption band.
A trend of complex formation with stoichiometric ratio
The absorption band of the N–H bond from compounds of M : L = 0.5 (1 : 2) was observed for 8b and 11b (Fig. 4). Shifts
series 11 and 13 was the most affected by Zn2+. A considerable in absorption bands concerning the N–H and the phosphor-
decrease was observed for 11a, b whereas a major increase was amide PQO bonds were observed for 11b and only the N–H
observed for 13a, b. For series 13, great shifts of PQO absorption bond for 8b. The band absorption intensity increased for the
bands were also observed for all compounds, especially for the N–H bond and decreased for the PQO bond in the case of 8b.
phosphoramide function.
The same behavior was also observed for the N–H bond of 8a.
Titration of 13c and 13d with Cu2+ suggested complexation
Titrations with copper sulphate. Contrary to what was
observed for Zn2+ assays, the addition of Cu2+ caused fluorescence with stoichiometric ratio M/L = 0.5 (1 : 2) (Fig. 4). The IR spectra
quenching over the titrations. Such change can be attributed to were very similar in both cases, exhibiting slight displacement
the electronic differences between diamagnetic Zn2+ (3d10) and in the position of the absorption bands of N–H and phosphor-
paramagnetic Cu2+ (3d9). In the case of Cu2+ complexes, as the amide PQO bonds. The IR spectra of ligands 11a, 13a and 13b
molecule is in the singlet excited state, the energy is emitted also showed intense increase of the N–H absorption band.
faster after the coordination of the metal with ligands, causing
signal decay.
In all cases of series 13 the addition of Cu2+ caused structural
changes on the ligands, as shown by spectrofluorimetry and IR
Titration of ligands 6a and 6c with Cu2+ suggested complex spectroscopy. Coordination with the cation occurred strongly by
formation with stoichiometric ratio M/L = 1.0 (1 : 1) (Fig. 4). N–H bonds (from amine and/or phosphoramide). Concerning
Comparison of the IR spectra showed that there were small the phosphoryl groups, considerable displacement for the
shifts of the absorption bands. However, in both cases, the phosphoramide function band and apparently little or no
Fig. 4 Spectrofluorimetric spectra and titration curves of ligands 6a, 6c, 8b, 11b, 13c and 13d titrated with Cu2+
.
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Fig. 5 Spectrofluorimetric spectra and titration curves of ligands 11b, 11c, 13a, 13c and 13d titrated with Y3+
.
participation of the phosphinic amide PQO bond were noted. to 6c (M/L = 0.25; 1 : 4 ratio) caused a major increase of the
Possibly, the chemical structures of these compounds admit fluorescence signal, which was not stabilized with successive
many spatial conformations (degrees of freedom) and, conse- additions.
quently, many forms of coordination with one or more Cu2+
Titration of 8a with Y3+ showed increasing variation of the
cations, but without the preference for a specific and stable fluorescence signals without, however, indicating a defined
coordination (similar to the studies of 11/Zn2+).
M : L ratio. In the case of 8b, fluorescence was not significantly
According to the Pearson’s principle of hard and soft acids changed by titration with Y3+. On the other hand, comparison
and bases, ligands may prefer binding metal ions of one class of the IR spectra of ligands and complexes of this series
or another, reflecting the complex stability as well. From indicates large shifts of the absorption bands due to the N–H,
Pearson’s classification, Zn2+ and Cu2+ ions do not fit into the CQN and PQO groups providing the coordination sites to
soft or hard ends, belonging to a third category, the ‘‘inter- accommodate the Y3+.
mediate’’ acids. The more defined coordination of Cu2+ ion
Within series 13, only 13d showed appreciable increasing
to the 6a, c ligands may be explained by one of the first variation of the fluorescence signals, correlated with a M/L = 0.20
Irving–Williams stability correlations which states that, for a (1: 5 ratio) complex, similar to 11c.
given ligand, the stability of the complexes with dipositive
The large coordination sphere of Y3+ is suitable to coordinate
metals follows the order Cu2+ o Zn2+. This order arises in part with binders of oxophilic nature in a possible higher M/L ratio,
due to the decrease in ionic radius within the series and in part such as M/L = 1 : 5 or 1 : 4. Great stability and selectivity are also
due to effects of the binder field. The better coordination of expected due to the strong interaction with PQO (phosphinamide)
Cu2+ is also explained by the well-known Jahn–Teller distortion, and NH (amine) groups, as reported in the literature.29,38,39
whereby some complexes tend to deviate from the octahedral
geometry and from the tetrahedral geometry, presenting tetra-
gonal distortions that facilitate coordination, which occurs
Conclusions
with Cu2+ and not with Zn2+ 35–37
.
Titrations with yttrium nitrate. The complexation study of The combination of diphenylphosphinic amide with quinoline,
11b and 11c suggested coordination with Y3+ with a tendency pyridine and phosphoramidate moieties gave rise to thirteen
to stabilize the complex in, respectively, M/L = 0.5 (1 : 2) and new ligands in moderate to good yields. The synthetic pathway
M/L = 0.2 (1 : 5) ratios (Fig. 5). The IR spectra showed consider- consisting of ortho directed lithiation of N,N-diisopropyl-P, P-
able displacements of the absorption bands of N–H bonds for diphenylphosphinic amide followed by trapping with DMF and
all compounds from series 11 indicating that the cation is subsequent reaction with different amines and reduction with
coordinated through the neighboring amine and phosphora- NaBH4 has proven to be efficient and reproducible.
mide groups. This is accompanied by the displacement of the
PQO bond band, markedly for 11a and 11b.
We have confirmed by nuclear magnetic resonance, fluores-
cence and infrared spectroscopies the ability of the phosphinic
The IR spectra of ligands from series 6 were not considerably amides to form coordination complexes with Zn2+, Cu2+
affected by the Y3+ cation. Interestingly, the spectrofluorimetric and Y3+, in agreement with our previous experience on the
titration of 6a, b showed no change of intensity with up to complexation by the group P(QO)–N. The preferred coordination
3 equivalents of Y3+. However, the first addition of Y3+ solution of the metals to the PQO bond of the phosphinic amide over the
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phosphoramide was evidenced in all compounds of series 11 and quartz cuvettes (1 cm optical path length). Fluorescence
13 by 31P NMR. We attribute this phenomenon to the rigidity spectra were acquired using the SW Eclipses Bio Pack V 1.1
provided by the aromatic rings with respect to the phosphoramidate (XP WIN2000) software, with 5, 10 and 20 nm spectral band
groups linked to a flexible alkyl chain and by the possibility of pass and 1200 nm sꢀ1 scan velocity. Fluorescence intensities of
forming a chelate with the metal via O,N-coordination involving the ligands and complexes were measured at their maximum
ortho substituent. Besides PQO, the functional groups CQO excitation and emission wavelengths.
(only from 6c), CQN (pyridine) and N–H also participate in
Characterization of the new compounds via IR, NMR
the coordination sites, as seen through the variations of the (1H, 13C, 31P) spectroscopies and mass spectrometry is described
absorption bands of ligands and complexes in the IR spectra.
The spectrofluorimetric titration curves estimated the
preponderant formation of ML2-type complexes for Cu2+ and
in the ESI.†
Materials
Zn2+. The titrations with Y3+ showed no appreciable change in The chemicals and solvents used for the synthesis of ligands
fluorescence in most cases. Exceptions were observed, however, were of reagent or analytical grade and were purchased from
with the labile ligands 11d and 13d, which were able to form Tedia (Brazil), Merck (Brazil) and Sigma-Aldrich (Brazil). All
complexes with high M/L ratio (1 :5) due to the large coordination solvents for spectrofluorimetric titrations were of analytical or
sphere of Y3+, suitable to coordinate with binders of oxophilic HPLC grade and were obtained from Vetec (Brazil) and JT Baker
nature. Among the three studied cations, a preference for coordina- (Mexico).
tion to Cu2+ was observed leading to complexes of defined stoichio-
metry, specially of ML2-type. This feature is in agreement with the
Synthesis
Irving–Williams series of relative stabilities of transition metal
General procedures. All reactions sensitive to air or moisture
complexes and can be correlated with the ability of Cu2+ to favour were carried out under N2 atmosphere in pre-dried Schlenk
distortions in the geometry of the complexes in order to adapt to tubes using distilled and dried solvents, according to known
different coordination arrangements. This behavior was evident in methodologies. Concentration of organolithium bases was
the bis-phosphoramidate series 13a–d and the pyridine series 8a, b, checked using 1H-NMR techniques.40 The reactions were
emerging as potential candidates for analytical applications.
monitored by thin layer chromatography (TLC) on aluminum
supported silica gel chromatoplates (Merck 60F-252 brand,
0.2 mm thick layer). The eluents were prepared volume-by-
volume (v/v) and visualization was performed by revelation
under ultraviolet radiation (254/366 nm) and/or iodine. The
synthesis of phosphinic amides 134 and 232 and aminoalkylphos-
Experimental
Instrumentation
Melting points, uncorrected, were determined on a Fischer phoramidates 9 41,42 has been reported in the literature.
Johns and Fisatom device (model 430 D). IR spectra were Synthesis of N,N-diisopropyl-P,P-diphenylphosphinic amide
acquired on an Alpha Bruker FTIR infrared spectrometer and (1). Compound 1 was prepared following the procedure
the absorption values were reported in wavenumbers (cmꢀ1). described in the literature.32,34 Ph2PCl (4.0 mL, 22 mmol) and
The mass spectra were acquired on an HP equipment (series iPr2NH (9.3 mL, 66 mmol) were dissolved in toluene (100.0 mL)
1100MSD) by electrospray ionization (potential: 40–260 eV). and the solution was stirred at reflux (120 1C) for 2 h under
Samples were dissolved in methanol or acetonitrile using N2 atmosphere. The solvent was evaporated under reduced
ammonium formate buffer (pH 3.5) and formic acid. Detection pressure and the residue was dissolved in THF (60.0 mL).
was accomplished in positive mode and the addition of sodium The solution was cooled down to ꢀ10 1C and H2O2 solution
chloride led, in some cases, to the observation of mass peaks (3.06 mL, 30% v/v) was added dropwise. These conditions were
corresponding to the molecular ion captured with sodium.
maintained for 15 min and the solvent was evaporated under
NMR spectra were obtained on a Varian Unity Plus/Bruker reduced pressure. Chloroform (40.0 mL) was added and the
Advance DPX spectrometer (300 or 500 MHz): 1H: 299.95/ organic layer was washed three times with H2O (50.0 mL) and
300.13 MHz or 499.84/500.13 MHz; 13C: 75.43/75.47 MHz or dried over anhydrous Na2SO4. After evaporation, diethyl ether
125.69/125.76 MHz; and 31P: 121.42/121.49 MHz or 202.34/ (80.0 mL) was added to the oily residue to precipitate the white
202.46 MHz. Samples were dissolved in the specified solvent, product, which was purified by column chromatography using
CDCl3 or DMSO-d6, and chemical shifts were expressed in d ethyl acetate (EtOAc) as solvent. Solvent evaporation afforded 1
1
(ppm) for the following references: tetramethylsilane (internal) in a yield of 80%. H and 31P NMR spectra were in agreement
for 1H and 13C; and 85% phosphoric acid (external) for 31P. with the reported data.34,43
Coupling constants ( J) were expressed in Hertz (Hz) and the
Synthesis of P,P-bis-(2-formylphenyl)-N,N-diisopropylphosphinic
areas of the signals were obtained by electronic integration. amide (3). t-BuLi (7.8 mL, 1.7 mol Lꢀ1 in hexane, 13.3 mmol) was
Multiplicity of signals was noted as: s-singlet, d-doublet, added to a solution containing phosphinic amide 1 (1.00 g,
t-triplet, q-quartet, quint-quintet, m-multiplet, dd-doublet of 3.3 mmol) in toluene (50.0 mL) and the mixture was stirred under
doublets, dt-doublet of triplets, and dhep-double heptet.
N2 atmosphere for 90 min at 0 1C. The temperature was cooled
Fluorescence measurements were performed on a Varian down to ꢀ90 1C and DMF (10 equivalents) was added. Stirring was
luminescence spectrophotometer (Cary Eclipse model) using kept for up to 2 h and the reaction was quenched with a drop of
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methanol. Chloroform (20.0 mL) was added to the mixture and the Anhydrous Na2SO4 was added and the reaction mixture was
organic layer was washed three times with H2O (20.0 mL), dried refluxed for 1 h. Na2SO4 was filtered off and the organic phase
over anhydrous Na2SO4 and evaporated under reduced pressure. was evaporated under reduced pressure, yielding the respective
Purification by column chromatography (EtOAc : hexane 1 : 1) led to crude products as yellow oils 10a–d, which were reduced
the yellow product 3 (65%). Warning! t-BuLi is a pyrophoric subsequently to the corresponding amines (11).
chemical. It should be handled with extreme care, under anhydrous
atmosphere and solvents in a well-ventilated fume hood.
Synthesis of diisopropyl(n-((2-((diisopropylamino)(phenyl)-
phosphoryl)benzyl)amino)alkyl)phosphoramidate (11). NaBH4
Synthesis of 4-amino-3-carboethoxy-8-haloquinolines (5). (0.19 g, 5.0 mmol) was added to solutions of the imines
Aminoquinolines 5a–c have been prepared from azidoquino- (2.0 mmol) 10a (1.07 g), 10b (1.12 g), 10c (1.15 g) and 10d
lines 4a–c following a modified procedure described in the (1.18 g) in methanol (20.0 mL) and the reaction mixture was
literature.44,45 Solutions containing 4-azido-3-carboethoxy-8- magnetically stirred for 1 h at room temperature. Chloroform
chloroquinoline (4a) (303.00 mg, 1.00 mmol) or 4-azido-3- (20.0 mL) was added and the organic layer was washed three
carboethoxy-8-bromoquinoline (4b) (157.00 mg, 0.49 mmol) or times with H2O (30.0 mL), dried over anhydrous Na2SO4 and
4-azido-3-carboethoxy-8-fluoroquinoline (4c) (146.00 mg, evaporated under reduced pressure. The obtained solids were
0.56 mmol) were prepared in methanol (20.0 mL) and an purified by column chromatography (EtOAc : hexane 1 : 1) to
equimolar amount of sodium dithionite was added: 174.00 mg give the respective alkyl substituted products: 11a (68%), 11b
for 4a, 56.00 mg for 4b and 97.00 mg for 4c. The reaction was (65%), 11c (68%) and 11d (69%).
stirred under reflux for 24 h, poured into ice and filtered. The
Synthesis of tetraisopropyl(((1E,10E)-((((diisopropylamino)-
precipitates were purified by column chromatography (toluene: phosphoryl)bis(2,1-phenylene))bis(methanylylidene))bis(azanyl-
EtOAc 8 : 2), giving the respective amino-substituted products: ylidene))bis(alkane-n,1-diyl))diphosphoramidate (12). o,o-Diformyl-
5a (65%), 5b (62%) and 5c (70%).
phosphinic amide 3 (0.07 g, 0.20 mmol) was dissolved in methanol
Synthesis of 3-carbethoxy-8-halo-4-((2-((diisopropylamino)- (20.0 mL) and the desired diisopropylaminoalkylphosphoramidate
(phenyl)phosphoryl)benzyl)amino)quinolines (6). o-Formyl- (0.60 mmol) was added: ethyl (9a) (0.13 g), butyl (9b) (0.15 g), pentyl
phosphinic amide 2 (134.00 mg, 0.40 mmol; or 56.00 mg, (9c) (0.16 g) and hexyl (9d) (0.17 g). Anhydrous Na2SO4 was added
0.17 mmol; or 94.00 mg, 0.28 mmol) and anhydrous Na2SO4 and the reaction mixture was refluxed for 1 h. Na2SO4 was filtered
were added to solutions containing methanol (25.0 mL) and 5a off and the organic phase was evaporated under reduced pressure,
(102.00 mg, 0.40 mmol) or 5b (50.00 mg, 0.17 mmol) or 5c yielding the respective crude products as yellow oils 12a–d, which
(67.00 mg, 0.28 mmol), respectively. The reaction was stirred were reduced subsequently to the corresponding amines (13).
under reflux for 4 h and then cooled down to room tempera-
Synthesis of tetraisopropyl((((((diisopropylamino)phosphoryl)-
ture. NaBH4 (2.5 equiv.) was added and the mixture was stirred bis(2,1-phenylene))bis(methylene))bis(azanediyl))bis(alkane-n,1-
for 1 h. Na2SO4 was filtered off, chloroform (20.0 mL) was diyl))diphosphoramidate (13). NaBH4 (0.19 g, 5.0 mmol) was
added and the organic layer was washed three times with H2O, added to solutions of the imines (2.0 mmol) 12a (1.54 g), 12b
dried over anhydrous Na2SO4 and evaporated under reduced (1.65 g), 12c (1.70 g) and 12d (1.76 g) in methanol (20.0 mL) and
pressure. The obtained solids were recrystallized from ethanol/ the reaction mixture was magnetically stirred for 1 h at room
water to give the respective purified halo-substituted products: temperature. Chloroform (20.0 mL) was added and the organic
6a (62%), 6b (59%) and 6c (69%).
layer was washed three times with H2O (30.0 mL), dried over
Synthesis of N,N-diisopropyl-P-phenyl-P-(2-(((pyridin-2-yl)alkyl- anhydrous Na2SO4 and evaporated under reduced pressure.
amino)methyl)phenyl)phosphinic amide (8). o-Formylphosphinic The obtained solids were purified by column chromatography
amide 2 (170.00 mg, 0.50 mmol) was dissolved in methanol (EtOAc : hexane 2 : 1) to give the respective alkyl-substituted
(25.0 mL). Anhydrous Na2SO4 and commercial aminopyridines products: 13a (68%), 13b (58%), 13c (62%) and 13d (69%).
2-pyridylmethylamine (7a) (0.05 mL, 0.50 mmol) or 2-(2-pyridyl)-
Spectrofluorimetric titrations
ethylamine (7b) (0.06 mL, 0.50 mmol) were added and stirred
under reflux for 3 h. The mixture was cooled down to room
Solutions. Standard stock solutions of ligands (0.001, 0.10 or
temperature, then NaBH4 (2.5 equivalents) was added and stirring 1.00 mmol Lꢀ1) were prepared in dichloromethane or DMSO by
was maintained for 1 h. Na2SO4 was filtered off, chloroform precisely weighing an appropriate mass in an analytical balance
(20.0 mL) was added and the organic layer was washed three (GR-202, AND, Japan). Similarly, standard stock solutions of
times with H2O, dried over anhydrous Na2SO4 and evaporated zinc chloride (0.10 or 0.20 mol Lꢀ1), copper sulphate (0.04, 0.08
under reduced pressure. The obtained solids were purified by or 0.12 mol Lꢀ1) and yttrium nitrate (0.01, 0.02, 0.06 or 0.12 mol Lꢀ1
column chromatography (EtOAc : hexane 3 : 1) to give the respec- were prepared in methanol.
)
tive alkyl substituted products: 8a (71%) and 8b (69%).
Complexation studies. The synthesized ligands (6a–c; 8a, b;
Synthesis of (E)-diisopropyl(n-((2-((diisopropylamino)(phenyl)- 11a–d; 13a–d) were added to cuvettes (2.5 mL) and aliquots
phosphoryl)benzylidene)amino)alkyl)phosphoramidate
(10). (5 mL) of the metal ion solutions (Zn2+; Cu2+; Y3+) were
o-Formylphosphinic amide 2 (1.00 g, 3.0 mmol) was dissolved subsequently added in order to increase the molar proportions
in methanol (20.0 mL) and the desired diisopropylamino- in 0.25 for Zn2+ and Cu2+ and 0.05 for Y3+. The fluorescence
alkylphosphoramidate (3.0 mmol) was added: ethyl (9a) (0.68 g), spectra were acquired in the absence of metal ions and after
butyl (9b) (0.76 g), pentyl (9c) (0.80 g) and hexyl (9d) (0.92 g). each added aliquot to obtain the spectrofluorimetric titration
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Paper
15 M. W. G. de Bolster and W. L. Groeneveld, Z. Naturforsch., B:
Anorg. Chem., Org. Chem., Biochem., Biophys., Biol., 1972, 27, 759.
curves. Graphics were plotted correlating the fluorescence
intensity (in arbitrary units) and the molar proportion between
metal ions and ligands (M/L). After each titration, the solvent
was carefully removed under reduced pressure and the residue
was subjected to qualitative analysis by IR spectroscopy.
´
´
16 S. G. Reis, M. A. Aguila-Sanchez, G. P. Guedes, G. F. Braga,
´
M. A. Novak, N. L. Speziali, F. Lopez-Ortiz and M. G. F. Vaz,
Dalton Trans., 2014, 43, 14889.
17 L. B. Zinner and G. Vicentini, Inorg. Chim. Acta, 1975, 15, 235.
18 J. R. Matos, L. B. Zinner, K. Zinner, G. Vicentini and P. O.
Dunstan, Thermochim. Acta, 1993, 219, 173.
19 A. Wada, T. Yasuda, Q. Zhang, Y. S. Yang, I. Takasu,
S. Enomoto and C. Adachi, J. Mater. Chem. C, 2013, 1, 2404.
20 S. Ram and S. K. Sinha, J. Solid State Chem., 1987, 66, 225.
21 A. B. Nascimento, G. Vicentini, L. B. Zinner and H. F. Brito,
Lanthanide Actinide Res., 1988, 2, 253.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
22 H. Xu, K. Yin and W. Huang, ChemPhysChem, 2008, 9, 1752.
˜
The authors thank the Fundaçao Carlos Chagas Filho de Amparo
`
´
23 F. J. Sainz-Gonzalo, M. Casimiro, C. Popovici, A. Rodrıguez-
a Pesquisa do Estado do Rio de Janeiro (FAPERJ) (process
number E 26/202.808/2015), Coordenaçao de Aperfeiçoamento
de Pessoal de Nıvel Superior (CAPES) (project number CAPES/
DGU 268/12) and the MINECO and FEDER program (project
CTQ2014-57157-P) for financial support.
´
´
´
´
´
Dieguez, J. F. Fernandez-Sanchez, I. Fernandez, F. Lopez-
˜
´
´
Ortiz and A. Fernandez-Gutierrez, Dalton Trans., 2012, 41, 6735.
´
´
´
24 F. J. Sainz-Gonzalo, C. Elosua, J. F. Fernandez-Sanchez,
´
´
C. Popovici, I. Fernandez, F. Lopez-Ortiz, F. J. Arregui,
´
´
I. R. Matias and A. Fernandez-Gutierrez, Sens. Actuators, B,
2012, 173, 254.
´
25 F. J. Sainz-Gonzalo, C. Popovici, M. Casimiro, A. Raya-Baron,
Notes and references
´
´
´
´
F. Lopez-Ortiz, I. Fernandez, J. F. Fernandez-Sanchez and
´
´
A. Fernandez-Gutierrez, Analyst, 2013, 138, 6134.
1 E. H. Faria, E. J. Nassar, K. J. Ciuffi, M. A. Vicente,
R. Trujillano, V. Rives and P. S. Calefi, ACS Appl. Mater.
Interfaces, 2011, 3, 1311.
26 S. G. Reis, M. Briganti, S. Soriano, G. P. Guedes, S. Calancea,
´
´
C. Tiseanu, M. A. Novak, M. A. del Aguila-Sanchez, F. Totti,
´
F. Lopez-Ortiz, M. Andruh and M. G. F. Vaz, Inorg. Chem.,
2 H. Dai, Y. Tang, C. Wang, S. Chen, Y. Tong and Z. Zhang,
J. Solid State Chem., 2017, 256, 130.
2016, 55, 11676.
´
´
´
27 M. A. Aguila-Sanchez, N. M. Santos-Bastos, M. C. Ramalho-
3 Y. Wu, J. Wu, B. Xie, L. Zou, Y. Li, Y. Han and X. Wu,
J. Lumin., 2017, 192, 775.
Freitas, J. G. Lopez, M. C. Souza, J. A. L. Camargos-Resende,
M. Casimiro, G. Alves-Romeiro, M. J. Iglesias and F. L. Ortiz,
Dalton Trans., 2014, 43, 14079.
4 J. Sun, P. Zhang, H. Qi, J. Jia, X. Chen, S. Jing, L. Wang and
Y. Fan, Inorg. Chim. Acta, 2018, 469, 298–305.
´
´
´
´
28 M. A. del Aguila-Sanchez, Y. Navarro, J. Garcıa-Lopez, G. P.
5 N. Liu, H. Liu, J. Lu, Z. He, Z. Wang, S. Wang, Y. Li and
Y. Huang, Inorg. Chim. Acta, 2018, 469, 515.
´
Guedes and F. LopezOrtiz, Dalton Trans., 2016, 45, 2008.
´
˜
´
29 C. Popovici, I. Fernandez, P. Ona-Burgos, L. Roces, S. Garcıa-
6 T. Gneuß, M. J. Leitl, L. H. Finger, N. Rau, H. Yersin and
J. Sundermeyer, Dalton Trans., 2015, 44, 8506.
7 F. Zhang, Y. Guan, X. Chen, S. Wang, D. Liang, Y. Feng,
S. Chen, S. Li, Z. Li, F. Zhang, C. Lu, G. Cao and B. Zhai,
Inorg. Chem., 2017, 56, 3742.
´
Granda and F. LopezOrtiz, Dalton Trans., 2011, 40, 6691.
30 C.-W. Yeh, K.-H. Chang, C.-Y. Hu, W. Hsu and J.-D. Chen,
Polyhedron, 2012, 31, 657.
31 C.-W. Yeh and J.-D. Chen, Inorg. Chem. Commun., 2011,
14, 1212.
8 R. Reau Baumgartner, Chem. Rev., 2006, 106, 4681.
˜ ´ ´
32 C. Popovici, P. Ona-Burgos, I. Fernandez, L. Roces, S. Garcıa-
`
9 L. J. Charbonniere, R. Ziessel, M. Montalti, L. Prodi,
´
N. Zaccheroni, C. Boehme and G. Wipff, J. Am. Chem. Soc.,
2002, 124, 7779.
Granda, M. J. Iglesias and F. Lopez-Ortiz, Org. Lett., 2010, 12, 428.
33 H. Tsuji, S. Komatsu, Y. Kanda, T. Umehara, T. Saeki and
10 R. Shritz, R. Shapira, E. Borzin, B. Tumanskii, W. Reichstein,
K. Tamao, Chem. Lett., 2006, 35, 758.
´
´
´
C. Meichner, F. Schwaiger, P. M. Reichstein, J. Kreyenschmidt, 34 I. Fernandez, P. O. Burgos, G. R. Gomez, C. Bled, S. Garcıa-
´
D. Haarer, L. Kador and Y. Eichen, Chem. – Eur. J., 2015,
21, 11531.
Granda and F. Lopez-Ortiz, Synlett, 2007, 611.
35 R. G. Pearson, J. Chem. Educ., 1968, 45, 581.
11 S. K. Gibbons, R. P. Hughes, D. S. Glueck, A. T. Royappa, 36 H. Mayr, M. Breugst and A. R. Ofial, Angew. Chem., Int. Ed.,
A. L. Rheingold, R. B. Arthur, A. D. Nicholas and H. H.
Patterson, Inorg. Chem., 2017, 56, 12809.
12 S. Shuvaev, M. Starck and D. Parker, Responsive, Chem. –
Eur. J., 2017, 23, 9974.
2011, 50, 6470.
37 M. A. Hitchman, Y. V. Yablokov, V. E. Petrashen, M. A.
Augustyniak-Jabłokov, H. Stratemeier, M. J. Riley, K. Lukaszewicz,
P. E. Tomaszewski and A. Pietraszko, Inorg. Chem., 2002, 41, 229.
13 Y. Hirai, T. Nakanishi and Y. Hasegawa, J. Lumin., 2016, 38 R. H. Platel, A. J. P. White and C. K. Williams, Inorg. Chem.,
170, 801. 2011, 50, 7718.
14 M. Wallesch, D. Volz, D. M. Zink, U. Schepers, M. Nieger, 39 P. E. Sues, A. J. Lough and R. H. Morris, Inorg. Chem., 2012,
T. Baumann and S. Braese, Chem. – Eur. J., 2014, 20, 6578. 51, 9322.
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New J. Chem.

View Article Online
Paper
NJC
40 T. R. Hoye, B. M. Eklov and M. Voloshin, Org. Lett., 2004, 43 D. B. G. Williams, S. J. Evans, H. de Bod, M. S.
6, 2567. Mokhadinyana and T. Hughes, Synthesis, 2009, 3106.
41 M. C. Souza, W. P. Macedo, T. S. Torres, L. F. Pedrosa and 44 J. C. Borges, C. D. Oliveira, L. C. S. Pinheiro, R. K. F. Marra,
H. G. Alt, Phosphorus, Sulfur Silicon Relat. Elem., 2006, 181, 1885.
M. A. Khan, J. L. Wardell, S. M. S. V. Wardell and A. M. R.
42 L. F. Pedrosa, M. S. C. de Souza, M. A. F. Faustino,
Bernardino, J. Braz. Chem. Soc., 2007, 18, 1571.
´
M. G. P. M. S. Neves, A. M. S. Silva, A. C. Tome, V. F. Ferreira 45 B. K. Ghotekar, M. G. Ghagare, R. B. Toche and M. N.
and J. A. S. Cavaleiro, Aust. J. Chem., 2011, 64, 939. Jachak, Monatsh. Chem., 2010, 141, 169.
New J. Chem.
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