Bis(tetramethylselenophosphoramidoyl) methylamine complexes of Cd(Ii) and Zn(Ii): Synthesis and multinuclear (31P, 77Se, and 113Cd) Nmr Characterization in solution

Article abstract of DOI:10.1080/10426507.2012.690120

Five new complexes ZnL2(ClO4)2 (1), CdL2(ClO4)2 (2), CdL2(BF4)2 (3), CdLCl2 (4), and CdL(NO3)2 (5) [L = ((Me2N)2PSe)2NMe] have been synthesized and characterized by elemental analysis, infrared (IR) and multinuclear ( ³¹P, ⁷⁷Se, and ¹¹³Cd), and nuclear magnetic resonance (NMR) spectroscopy. The ³¹P and ⁷⁷Se NMR data showed that the title ligand is coordinated in a bidentate fashion to the metal center via its both P=Se groups. The solution structure of the cadmium complexes was further confirmed by its ¹¹³Cd NMR spectra, which displayed a quintuplet for the perchlorate complex and a triplet for each of the nitrate and chloride complexes, respectively due to coupling with four (two ligands) and two (one ligand) equivalent phosphorus nuclei, consistent with a four-coordinate tetrahedral geometry for the cadmium center. The results are discussed and compared with the corresponding oxo and thio analogues.

Full text of DOI:10.1080/10426507.2012.690120

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Phosphorus, Sulfur, and Silicon and the
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Bis(Tetramethylselenophosphoramidoyl)
Methylamine Complexes of Cd(Ii) and
Zn(Ii): Synthesis and Multinuclear (31P,
77Se, and 113Cd) Nmr Characterization in
Solution
Meriem Bennis a & Khaled Alouani a
a Laboratoire de Synthèse Organique par Voies Organométalliques,
Faculté des Sciences de Tunis, El Mana I, Tunis, Tunisia
Accepted author version posted online: 11 May 2012.Version of
record first published: 10 Sep 2012.
To cite this article: Meriem Bennis & Khaled Alouani (2012): Bis(Tetramethylselenophosphoramidoyl)
Methylamine Complexes of Cd(Ii) and Zn(Ii): Synthesis and Multinuclear (31P, 77Se, and 113Cd) Nmr
Characterization in Solution, Phosphorus, Sulfur, and Silicon and the Related Elements, 187:12,
1490-1497
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Phosphorus, Sulfur, and Silicon, 187:1490–1497, 2012
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2012.690120
BIS(TETRAMETHYLSELENOPHOSPHORAMIDOYL)
METHYLAMINE COMPLEXES OF Cd(II) AND Zn(II):
SYNTHESIS AND MULTINUCLEAR (31P, 77Se,
AND 113Cd) NMR CHARACTERIZATION IN SOLUTION
Meriem Bennis and Khaled Alouani
Laboratoire de Synthe`se Organique par Voies Organome´talliques, Faculte´ des
Sciences de Tunis, El Mana I, Tunis, Tunisia
GRAPHICAL ABSTRACT
Abstract Five new complexes ZnL2(ClO4)2 (1), CdL2(ClO4)2 (2), CdL2(BF4)2 (3), CdLCl2
(4), and CdL(NO3)2 (5) [L = ((Me2N)2PSe)2NMe] have been synthesized and characterized by
elemental analysis, infrared (IR) and multinuclear (31P, 77Se, and 113Cd), and nuclear magnetic
resonance (NMR) spectroscopy. The 31P and 77Se NMR data showed that the title ligand is
coordinated in a bidentate fashion to the metal center via its both P=Se groups. The solution
structure of the cadmium complexes was further confirmed by its 113Cd NMR spectra, which dis-
played a quintuplet for the perchlorate complex and a triplet for each of the nitrate and chloride
complexes, respectively due to coupling with four (two ligands) and two (one ligand) equivalent
phosphorus nuclei, consistent with a four-coordinate tetrahedral geometry for the cadmium
center. The results are discussed and compared with the corresponding oxo and thio analogues.
Keywords Cadmium complex; zinc complex; Bis(N,N,Nꢀ,Nꢀ-tetramethylselenophosphorami-
doyl)methylamine; 31P, 77Se, and 113Cd NMR
Received 1 April 2012; accepted 28 April 2012.
The authors would like to thank Dr. M. A. Sanhoury, MRSC, of the Department of Chemistry, Faculty of
Sciences of Tunis, for helpful discussion and assistance.
Address correspondence to Meriem Bennis, Laboratoire de Synthe`se Organique par Voies
Organome´talliques, Faculte´ des Sciences de Tunis, Campus Universitaire, 2092, El Mana I, Tunis, Tunisia.
E-mail: beni.meri@yahoo.fr
1490

BIS(TETRAMETHYLSELENOPHOSPHORAMIDOYL) METHYLAMINE
1491
INTRODUCTION
The coordination chemistry of bidentate phosphine chalcogenide ligands of the type
HN[P(E)R2]2 (E = O, S, and Se) has been extensively investigated.1–3 This has become an
active area of research due to the convenient synthetic routes to HN[P(E)R2]2 and related
compounds developed by Woollins et al.4 These ligands are of interest owing to their use
as lanthanide nuclear magnetic resonance (NMR) shift reagents5 and catalysts.6 There are,
however, relatively few studies on their analogs of the type RN[P(E)R2]2 (R = alkyl).7–9 For
instance, the nonamethylimidodiphosphoramide, MeN[P(O)(NMe2)2]2 (NIPA), has been
shown to be an excellent extracting ligand of metal ions and the corresponding complexes
with Al, Be, and Cd have been prepared.8 In a previous work, we reported the preparation
and kinetic studies of Cd and Zn complexes with the thio analog, MeN[P(S)(NMe2)2]2
(SNIPA).9 This work is now being extended to the investigation of the diselenide analog,
MeN[P(Se)(NMe2)2]2 (SeNIPA), and we report here on the synthesis and spectroscopic
characterization of new Cd(II) and Zn(II) complexes with this diselenide ligand. The new
compounds were characterized by elemental analysis, infrared (IR), and comparison of
their NMR data with those related to the free ligand.
RESULTS AND DISCUSSION
Synthesis
The synthesis of MeN[P(Se)(NMe2)2]2 was performed using a method previously
reported for related systems.10 The reaction scheme for the ligand preparation is shown in
Scheme 1.
Me
N
Me
N
NMe2
NMe2
Me2N
Me2N
1- HNMe2/Et3N, 4-DMAP
CH3-NH2,HCl
2 PCl3
Et2O anhyd.
2- 2 Se
Heptane/ pyridine
Cl2P
PCl2
P
P
Se
Se
Scheme 1
The IR spectrum shows PSe, PNP, and NMe peaks in the expected region (see
Experimental section). We have recently reported the X-ray structure of the ligand and
showed that it adopts the anticonformation with the P Se groups rotated with respect to
the P–N–P plane.11
Treatment of the metal salts in an ethanol solution with the ligand produces complexes
1–5. The new compounds are white solid powders, quite stable and soluble in nitromethane,
dichloromethane, and moderately soluble in chloroform. The conductivity measurements
show the adducts 4 and 5 to be essentially nonelectrolytes.
The IR spectrum of the ligand shows a strong band at 541 cm−1 attributed to νP=Se
.
The latter is shifted by ∼13 cm−1 toward lower wave numbers on coordination to the metal
ion. The coordination shift is attributed to a lowering of the P Se bond order in the complex.
This small shift compared with that of P O and P S absorptions12 in the corresponding
complexes is reasonable since the vibrations involving the relatively heavy selenium atom
would be less sensitive to coordination than those with the lighter phosphorus, oxygen, or
sulfur atoms.

1492
M. BENNIS AND K. ALOUANI
Table 1 NMR data (δ (ppm) and J (Hz)) for complexes 1–5 and their ligand (L) in CD2Cl2
31P
77Se
113Cd
ꢀδ31P
ꢀδ77Se
1J31
1J31
1J113
77
13
77
P− Se
P− Cd
Cd− Se
L
75.6
63.5
64.3
64.2
68.4
66.8
−239.6
−119.2
−152.0
−150.6
−161.6
−160.6
–
–
–
–
823.5
–
–
41.3
46.6
35.9
–
–
–
(1)
(2)
(3)
(4)
(5)
12.1
11.3
11.4
7.2
120.4
87.6
89.0
78.0
79.1
645.1
659.9
659.9
673.1
560.1
614.3
622.1
532.4
604.1
322.8
297.6
–
–
8.7
NMR Studies
The multinuclear NMR data (Table 1) indicate the formation of complexes 1–5. For
instance, the 31P NMR resonances of bound ligand are shifted to lower frequency compared
with those of the free ligand, whereas the 77Se NMR resonances show a higher frequency
shift on complexation. The difference in the 77Se chemical shift between free and bound
ligands is more important than that observed in 31P NMR spectra. Furthermore, the coupling
1
constant JP
of the free ligand is larger than that of the bound one. Such changes are
Se
attributed to a weakening of the P=Se bond upon coordination to the metal atom through
selenium.13
Although the two-bond P–Cd and the one-bond Se–Cd couplings were observed at
ambient temperatures in the 31P and 77Se spectra, the 113Cd showed broad features and
1
the samples were cooled to 188 K to improve resolution. The 31P{ H} NMR spectra show
singlet resonances for each complex (∼75% of the total intensity) flanked by two satellites of
equal intensities (∼12,5% each) arising from the two-bond cadmium–phosphorus coupling,
2J(113/111Cd–31P), with weak selenium satellites (Figure 1). In addition, the 77Se NMR
Figure 1 31P{1H} NMR spectrum of complex 2 in CDCl3 at 298 K (+ and ∗: signals related to Se and Cd
satellites, respectively).

BIS(TETRAMETHYLSELENOPHOSPHORAMIDOYL) METHYLAMINE
1493
Figure 2 77Se NMR spectrum of complex 3 in CD2Cl2 at 298 K (+: Cd satellites).
spectrum shows for the complex a doublet due to coupling with the phosphorus atom.
Each signal of the doublet is flanked by cadmium satellites (see Figure 2). In order to
better confirm the structure of these complexes in solution, 113Cd NMR spectroscopy was
used.
Figure 3 113Cd NMR spectrum of complex 3 in dichloromethane at 188 K.

1494
M. BENNIS AND K. ALOUANI
Figure 4 113Cd NMR spectrum of complex 4 in dichloromethane at 188 K.
The 113Cd NMR spectrum at 188 K (Figure 3) displays a quintuplet for each of the
complexes 2 and 3 due to coupling with four magnetically equivalent phosphorus atoms
with two-bond 113Cd–31P coupling of ∼50 Hz, showing a stoichiometry of CdL2(ClO4)2 and
CdL2(BF4)2. This value compares well with that observed for related cadmium complexes
using the monodentate analog (Me2N)3P(Se)14 or Ph3PSe15 as ligands. Interestingly, the
113Cd NMR spectra show a triplet for each of the complexes 4 and 5 owing to coupling
with two phosphorus atoms, consistent with the formula CdLX2 (X = Cl or NO3) (see
Figure 4). Further evidence in support of this assignment is obtained from conductivity
measurements, which showed that compounds 4 and 5 are nonelectrolytes in acetonitrile
and suggest that both complexes are adducts containing coordinated chlorides and nitrates,
whereas complexes 2 and 3 behave as 1:2 electrolytes. This is also confirmed in the IR
spectra of 5, which exhibit strong stretches at 1421, 1390, and 1378 cm−1, in agreement
with coordinated O–NO216–18 and those of 2 which show the v(ClO4) to appear as a sharp
single stretch at ca. 1091 and a weak stretch at 620 cm−1. It is worth noting that, when
comparing complexes 2–5, the chemical shifts and coupling constants listed in Table 1
suggest that the SeNIPA ligand binds more strongly to the cadmium center than in its
corresponding monodentate complex,14 showing the effect of chelate ring coordination.
2
The J(113Cd–31P) coupling constant for complex 2 is considerably larger than the
value measured for the disulfide (SNIPA) analog (∼50 vs. 30 Hz).9 Such a difference in the
metal–phosphorus coupling constant is probably due to the fact that both Se and Cd are big
in size whereas there is considerable size difference between S and Cd atoms. This may
account for a more important increase in the valence s electron density at the metal nucleus,
2
which would increase the observed J(113Cd–31P) value for the SeNIPA complex (2) as
compared with the SNIPA species. This is also in good agreement with the results obtained

BIS(TETRAMETHYLSELENOPHOSPHORAMIDOYL) METHYLAMINE
1495
for related complexes which showed that the more bulky the ligand the more important the
2J(113Cd–31P) value.19,20
CONCLUSION
We have shown that the ligand SeNIPA forms stable chelate complexes with zinc and
cadmium ions. The results show that the combination of 31P, 77Se, and 113Cd NMR data in
the study of such species is very informative of changes related to complex formation as
well as in the elucidation of the structure and composition of metal–ligand coordination
compounds. We have also shown that the stability of the selenophosphoryl complexes is
comparable to that obtained for sulfur analogs.
EXPERIMENTAL
Materials
All preparations were carried out under a nitrogen atmosphere in solvents dried by
standard techniques21 and stored over molecular sieves.
Zn(ClO4)2·4H2O (Aldrich) and cadmium salts: perchlorate hydrate (Ventron, 99.9%),
Cd(BF4)2·4H2O (Aldrich, Steinhem, Germany), nitrate tetrahydrate (Fluka, Germany,
99%), and chloride anhydrous (Merck, Darmstardt, Germany, 99%) were used as received.
Measurements
The NMR spectra were recorded on Brucker AC-300 instrument, equipped with a
variable temperature unit B-VT-2000 and two probes, CD2Cl2 were used as solvent; 31P
at 121 MHz (85% H3PO4–D2O), 77Se at 57.2 MHz (Me2Se), and 113Cd at 66.5 MHz (aq.
Cd(NO3)2, 2 M).
The IR spectra were recorded on a Brucker ISS 66 v/S spectrometer. The conduc-
tivity measurements were carried out for 10−3 M solutions of the complexes dissolved in
acetonitrile (dried on molecular sieves).
Preparation of the Ligand11
To a stirred mixture of Me2NH (14.4 g, 0.32 mol), Et3N (32.67 g, 0.32 mol) and
4-DMAP (1.58 g, 0.013 mol) in anhydrous diethyl ether (250 mL) cooled at −10 ◦C was
added dropwise (Cl2P)2NMe22–24 (19 g, 0.08 mol) in the same solvent (10 mL). The reaction
was kept at −10 ◦C for 10 h then left overnight at room temperature. After removal of the
ammonium salt and evaporation of solvent, the oil obtained was dissolved in acetonitrile
and cooled to 0 ◦C, and then selenium (12.8 g, 0.16 mol) was added. The reaction mixture
was stirred for 1 h at room temperature and filtered to remove excess Se. The solvent was
evaporated to give the product [(Me2N)2PSe]2NMe as an oil, which solidified on cooling.
This was found to be pure as shown by its 31P and 77Se NMR spectra. Yield 62%, IR (KBr):
νP = Se (541 cm−1).

1496
M. BENNIS AND K. ALOUANI
Preparation of Complexes
Zn(Se-NIPA)2(ClO4)2 (1). The complex was prepared in the solid state from the
hydrated zinc perchlorate and the ligand in the presence of triethylorthoformate following
a method first described by Van Leeuwen and Groeneveld.25 The hydrated zinc perchlorate
(0.30 g, 1.25 mmol) was dissolved in ethanol (30 mL) and an appropriate quantity of
triethylorthoformate. After 2 h, a stoichiometric amount of the ligand (1.06 g, 2.50 mmol)
was added. The white solid obtained was washed with diethyl ether and dried in vacuo.
Melting points (168.8–170 ◦C) Anal. calcd. for C18H54ZnCl2N10O8P2Se2: C, 19.38;
H, 4.84; N, 12.56. Found: C, 19.11; H, 4.93; N, 12.72. IR (KBr): νP=Se (528 cm−1). ꢁM
=
290 cm2 ꢂ−1 mol−1
.
Cd(Se-NIPA)2(ClO4)2 (2). Note: Caution: cadmium perchlorate is potentially ex-
plosive and should be handled in small quantities with extreme care!
This complex was prepared and purified in the same manner as complex (1) from
the cadmium salt Cd(ClO4)2·4H2O and the title ligand. Melting points (210.0–210.2 ◦C).
Anal. calcd. for C18H54CdCl2N10O8P2Se2: C, 18.59; H, 4.64; N, 12.05. Found: C, 18.41;
H, 4.33; N, 12.32. IR (KBr): νP=Se (529 cm−1), νSe–Cd (321 cm−1). ꢁM = 310 cm2 ꢂ−1
mol−1 in CH3CN.
Cd(Se-NIPA)2(BF4)2 (3). Complex 3 was prepared and purified in the same manner
as complex (1) from the cadmium salt Cd(BF4)2·4H2O and the title ligand. The complex
was recrystallized from dichloromethane to obtain a white crystalline solid. Yield 60%.
◦
Melting points (144.0–144.2 C) Anal. calcd. for C18H54CdN10P4Se4B2F8: C, 19.01; H,
4.75; N, 12.32. Found: C, 18.95; H, 4.61; N 12.11. IR (KBr): νP=Se (528 cm−1); νCd–Se
(323 cm−1). ꢁM = 270 cm2 ꢂ−1 mol−1 in CH3CN.
Cd(Se-NIPA)Cl2 (4). To a stirred solution of cadmium chloride (0.40 g, 2.20 mmol)
in ethanol (30 mL), a solution of Se-NIPA (0.93 g, 2.20 mmol) was added dropwise. The
reaction mixture was stirred for 3 h. The white solid obtained was washed with diethyl ether
and dried in vacuo. Yield 1.21 g (82%). Melting points (189.0–189.1 ◦C). Anal. calcd. for
C9H27CdCl2N5P2Se2: C, 17.75; H 4.43; N, 11.50. Found: C, 17.82; H, 4.38; N 11.42. IR
(KBr): νP=Se (524 cm−1); νCd–Se (321 cm−1). ꢁM = 35 cm2 ꢂ−1 mol−1 in CH3CN.
Cd(Se-NIPA)(NO3)2 (5). This complex was prepared and purified in the same
◦
manner as for complex 4; yield 67%. Melting points (191.7–191.9 C) Anal. calcd. for
C9H27CdN7P2Se2O6: C, 16.32; H, 4.08; N, 14.81. Found: C, 16.45; H, 4.31; N 15.02. IR
(KBr): νP=Se (527 cm−1); νCd–Se (322 cm−1). ꢁM = 64 cm2 ꢂ−1 mol−1 in CH3CN.
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