Effect of free and chelating phosphine coordination environments on the NiS2P2 chromophore: Synthesis, NMR and other spectral studies. Crystal and molecular structures of (N,N-dipropyldithiocarbamato) di(triphenylphosphine)nickel(II)

Article abstract of DOI:10.1016/j.poly.2003.09.013

Planar [Ni(dnpdtc)(PPh₃)₂] ClO ₄·PPh₃ (1) and [Ni(dnpdtc)(dppe)]BPh ₄·H₂O (2) (dnpdtc=N,N-dipropyldithiocarbamate, dppe=1,2-bis(diphenylphosphino)ethane) complexes were prepared and charact

Full text of DOI:10.1016/j.poly.2003.09.013

Polyhedron 23 (2004) 77–82
www.elsevier.com/locate/poly
Effect of free and chelating phosphine coordination
environments on the NiS2P2 chromophore: synthesis, NMR
and other spectral studies. Crystal and molecular structures of
(N,N-dipropyldithiocarbamato)di(triphenylphosphine)nickel(II)
perchlorate and (N,N-dipropyldithiocarbamato)1,2-
bis((diphenylphosphino)ethane)nickel(II) tetraphenylborate
a
a,
a
B. Arul Prakasam , Kuppukkannu Ramalingam *, M. Saravanan ,
b
Gabriele Bocelli , Andrea Cantoni
b
a
Department of Chemistry, Annamalai University, Annamalainagar 608 002, India
b
IMEM, CNR, Parma, Italy
Received 26 July 2003; accepted 9 September 2003
Abstract
Planar [Ni(dnpdtc)(PPh3)2] ClO4 Æ PPh3 (1) and [Ni(dnpdtc)(dppe)]BPh4 Æ H2O (2) (dnpdtc ¼ N,N-dipropyldithiocarbamate,
dppe ¼ 1,2-bis(diphenylphosphino)ethane) complexes were prepared and characterized by elemental analysis, electronic, IR and
NMR spectra and their structures were determined by single crystal X-ray crystallography. Both the complexes were diamagnetic. IR
spectra of the two compounds show isobidentate coordination of the dithiocarbamate moiety. The important stretching mode
characteristic of the thioureide bond occurs at 1536 and 1526 cmꢀ1 for 1 and 2, respectively. The BVS data support the highly covalent
nature of the Ni–S interaction. NMR spectra of the complexes show very large (ꢁ20 ppm) 31P chemical shifts in both compounds. The
most important N13CS2 chemical shifts appear at 199.17 and 201.88 ppm for 1 and 2, respectively. Structural implications are very
large for 2 compared to 1 when free phosphines are replaced by chelating dppe with the P–Ni–P angle shrinking to approximately 12°.
Ó 2003 Elsevier Ltd. All rights reserved.
Keywords: Nickel; Dithiocarbamate; PPh3; Dppe; X-ray crystal structure; NMR
1. Introduction
complexes with a NiS2P2 chromophore which are again
planar and diamagnetic in nature [5–7]. Synthetic and
structural studies on [Ni(dtc)Cl(PPh3)] and [Ni(dtc)
(PPh3)2]ClO4 complexes, where dtc ¼ S2CN(C2H5)2,
S2CNH(C2H4OH), S2CN(C2H4OH)2, S2CN(C4H8O),
S2CN(C5H10) have been reported from our laboratory [8].
The effect of alkyl substitutents in the metal dithiocar-
bamates have been investigated earlier [9]. In order to
understand the influence of free and chelating phosphines
on the NiS2P2 chromophore and on the thioureide C–N
bond, in this paper, we report the synthesis, spectral and
structural characterization of two new complexes,
[Ni(dnpdtc)(PPh3)2]ClO4 Æ PPh3 (1), and [Ni(dnpdtc)
(dppe)]BPh4 (2) where, dnpdtc ¼ N,N-dipropyldithioc-
arbamate.
Divalent nickel complexes of dithiocarbamates with
different substituents contain planar diamagnetic MS4
chromophores. Ni(II)dithiocarbamates are borderline
acceptors and they prefer to react with soft Lewis bases
such as phosphines and hard bases such as nitrogenous
ligands [1,2]. The symbiotically induced softness and the
electronic effects of the substitutents on the dithiocarba-
mate ligands were found to be important in deciding the
reactivity [3,4]. On reaction with phosphines, they form
* Corresponding author. Tel.: +91-413-2202-834; fax: +91-414-422-
265.
E-mail addresses: krauchem@yahoo.com, krchem@rediffmail.com
(K. Ramalingam).
0277-5387/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2003.09.013

78
B. Arul Prakasam et al. / Polyhedron 23 (2004) 77–82
2. Experimental
Calc. for C61H59ClNNiO4P3S2: C, 65.34; H, 5.30; N, 1.25.
Found: C, 65.12; H, 5.14; N, 1.17%.
All the reagents and solvents employed were com-
mercially available analytical grade materials and were
used as supplied, without further purification. IR spec-
tra were recorded on an ABB Bomem MB 104 spec-
trophotometer (range 4000–400 cmꢀ1) as KBr pellets.
The UV–vis spectra were recorded in CH2Cl2 on a U-
2001 spectrophotometer. NMR spectra were recorded
on a Bruker AMX 400 spectrometer at room tempera-
ture, using CDCl3 as solvent.
2.1.2. 1,2-Bis((diphenylphosphino)ethane)(N,N-dip-
ropyldithiocarbamato)nickel(II) tetraphenylborate
2.1.2.1. [Ni(dnpdtc)(dppe)]BPh4 ꢂ H2O (2). A mixture
of Ni(dnpdtc)2 (420 mg, 1 mmol), dppe (790 mg, 2 mmol),
NiCl2 Æ 6H2O (240 mg, 1 mmol) and NaBPh4 (680 mg, 2
mmol) was refluxed for about 3 h in methanol–dichlo-
romethane solvent mixture (50:50, 50 cm3). The solution
was then concentrated to ca. 25 cm3. The purple-red so-
lution obtained was filtered and was kept for evaporation.
After 2 days a purple-red coloured solid separated out and
was recrystallized from methanol–dichloromethane
mixture. Single crystals suitable for X-ray structural
analysis were obtained by repeated recrystallization from
the same solvent mixture (yield 65%, 1.2 g, dec. 182 °C).
Anal. Calc. for C57H58BNNiOP2S2: C, 70.67; H, 6.03; N,
1.44. Found: C, 70.12; H, 5.97; N, 1.32%.
2.1. Preparation of complexes
2.1.1. Bis(triphenylphosphine)(N,N-dipropyldithiocarb-
amato)nickel(II) perchlorate
2.1.1.1. [Ni(dnpdtc)(PPh3)2]ClO4 (1). A mixture of
Ni(dnpdtc)2 (210 mg, 0.5 mmo1), PPh3(520 mg, 2 mmol),
NiCl2 Æ 6H2O (120 mg, 0.5 mmol) and NH4ClO4 (115 mg,
1 mmol) was refluxed for about 2 h in methanol–dichlo-
romethane solvent mixture (50:50, 50 cm3), and was then
concentrated to ca. 25 cm3. The purple-red solution ob-
tained was filtered and was left for evaporation. The fine
single crystals suitable for X-ray structural analysis were
obtained by repeated recrystallization from the same
solvent mixture (yield 60%, 520 mg, dec. 178 °C). Anal.
2.2. X-ray crystallography
Details of the crystal data, data collection and re-
finement parameters for 1 and 2 are summarized in
Table 1. Intensity data were collected at ambient tem-
perature (295 K) on Philips PW 100 (for 1) and SMART
Table 1
Crystal data, data collection and refinement parameters for [Ni(dnpdtc)(PPh3)2]ClO4 and [Ni(dnpdtc)(dppe)]BPh4
Compound
[Ni(dnpdtc)(PPh3)2]ClO4 ꢂ PPh3 (1)
61H59ClNNiO4P3S2
1121.3
[Ni(dnpdtc)(dppe)]BPh4 ꢂ H2O (2)
C57H58BNNiOP2S2
Empirical formula
Formula weight
Colour
C
968.6
purple-red
purple-red
needle
Habit
column, irregular
0.17 ꢃ 0.24 ꢃ 0.29
triclinic
Crystal dimensions (mm)
Crystal system
Space group
0.20 ꢃ 0.29 ꢃ 0.36
triclinic
ꢀ
ꢀ
P1
13.787 (2)
P1
9.460 (2)
ꢁ
a (A)
ꢁ
b (A)
17.625 (2)
12.350 (3)
14.526 (2)
21.083 (2)
ꢁ
c (A)
a (°)
b (°)
c (°)
99.88 (3)
99.09 (3)
108.360 (2)
101.370 (3)
74.57 (2)
2829.9 (9)
90.400 (3)
2688.3 (7)
3
ꢁ
U (A )
Z
2
1.316
2
1.197
Dc (g cmꢀ3
l cmꢀ1 (L)
F ð000Þ
)
5.96
1172
5.36
1020
ꢁ
k (A)
Mo Ka (0.71069)
3.03–30.02
Mo Ka (0.71069)
1.04–30.47
h range (°)
Scan type
Index ranges
x-2h
x-2h
ꢀ19 6 h 6 19, ꢀ24 6 k 6 24, 0 6 l 6 15
ꢀ12 6 h 6 13, ꢀ20 6 k 6 14, ꢀ29 6 l 6 28
Reflections collected
Observed reflections Fo > 4rðFoÞ
Weighting scheme
16 150
6791
12 357
7900
2
2
W ¼ 1=½r2ðFo2Þ þ ð0:0447PÞ þ 0:00Pꢄ, where
W ¼ 1=½r2=ðFo2Þ þ ð0:0968PÞ þ 0:00Pꢄ, where
P ¼ ðFo2 þ 2Fc2Þ=3
894
P ¼ ðFo2 þ 2Fc2Þ=3
836
Number of parameters refined
Final R, Rw (observed, data)
GOOF
0.0414, 0.0890
0.816
0.0510, 0.1409
0.904

B. Arul Prakasam et al. / Polyhedron 23 (2004) 77–82
79
Table 2
Bond distances (A) and angles (°) for [Ni(dnpdtc)(PPh3)2]ClO4 and [Ni(dnpdtc)(dppe)]BPh4
ꢁ
[Ni(dnpdtc)(PPh3)2]ClO4 (1)
[Ni(dnpdtc)(dppe)]BPh4 ꢂ H2O (2)
Bond distances
Ni(1)–P(31)
Ni(1)–S(3)
Ni(1)–S(2)
Ni(1)–P(12)
S(2)–C(4)
2.1919(10)
2.2094(9)
2.2120(10)
2.2253(10)
1.722(3)
Ni(1)–P(12)
Ni(1)–P(15)
Ni(1)–S(2)
Ni(1)–S(3)
S(2)–C(4)
S(3)–C(4)
C(4)–N(5)
N(5)–C(6)
N(5)–C(9)
2.1607(9)
2.1715(7)
2.1931(8)
2.2108(9)
1.718(3)
1.715(3)
1.314(4)
1.477(4)
1.492(5)
S(3)–C(4)
1.727(3)
1.304(3)
C(4)–N(5)
N(5)–C(9)
N(5)–C(6)
1.464(4)
1.478(3)
Bond angles
P(31)–Ni(1)–S(3)
P(31)–Ni(1)–S(2)
S(3)–Ni(1)–S(2)
P(31)–Ni(1)–P(12)
S(3)–Ni(1)–P(12)
S(2)–Ni(1)–P(12)
C(4)–S(2)–Ni(1)
C(4)–S(3)–Ni(1)
N(5)–C(4)–S(2)
N(5)–C(4)–S(3)
S(2)–C(4)–S(3)
C(4)–N(5)–C(9)
C(4)–N(5)–C(6)
C(9)–N(5)–C(6)
N(5)–C(6)–C(7)
93.56(4)
171.99(3)
78.61(4)
98.41(4)
167.99(3)
89.45(4)
85.65(9)
85.60(9)
124.8(2)
126.6(2)
108.60(14)
120.7(2)
121.9(3)
117.3(2)
111.7(3)
P(12)–Ni(1)–P(15)
P(12)–Ni(1)–S(2)
P(15)–Ni(1)–S(2)
P(12)–Ni(1)–S(3)
P(15)–Ni(1)–S(3)
S(2)–Ni(1)–S(3)
C(4)–S(2)–Ni(1)
C(4)–S(3)–Ni(1)
N(5)–C(4)–S(3)
N(5)–C(4)–S(2)
S(3)–C(4)–S(2)
C(4)–N(5)–C(6)
C(4)–N(5)–C(9)
C(6)–N(5)–C(9)
N(5)–C(6)–C(7)
86.50(3)
94.72(3)
167.70(4)
172.06(3)
100.32(3)
79.49(3)
85.25(10)
84.74(10)
125.3(2)
124.4(2)
110.21(16)
122.7(3)
120.9(3)
116.1(3)
111.8(3)
AXS (for 2) diffractometers using graphite monochro-
ꢁ
moiety towards the metal centre increases the contri-
bution of the polar thioureide form in both the cases.
This is reflected in the shift in mC–N values to higher wave
numbers compared with that observed in the parent
complex at 1508 cmꢀ1. The mC–S band appears at 1091
cmꢀ1 for 1 and 999 cmꢀ1 for 2 without any splitting,
supporting the bidentate coordination of the dithiocar-
bamate moiety [12].
mated Mo Ka radiation (k ¼ 0:71069 A). Lorentz and
polarization corrections were applied. The structures
were solved by direct methods using SHELXS-97 [10] and
were refined by SHELXL-97 [11]. All the non-hydrogen
atoms were refined anisotropically and all the hydrogen
atoms were refined isotropically. Selected bond lengths
and bond angles are given in Table 2.
3.2. NMR spectral studies
3. Results and discussion
NMR spectra were recorded at room temperature
using TMS as an internal reference. For all the com-
pounds CDCl3 was used as solvent. The 13C NMR
spectra were recorded in the proton decoupled mode.
The 1H, 13C and 31P NMR chemical shift values are
given in Table 3 with splitting patterns.
3.1. IR spectral studies
The IR spectrum of 1 shows the thioureide mC–N band
at 1536 cmꢀ1 and that of compound 2 at 1526 cmꢀ1. The
mesomeric shift of electrons from the dithiocarbamate
Table 3
NMR spectral data (chemical shift values in ppm)
Compound
NMR
PPhx
BPh4
CH3
b-CH2
a-CH2
–PCH2CH2P–
S123CN
199.17
1
1H
13C
31P
7.20–7.60(m)
128–137
31.0
0.81(t)
11.06
1.61(m)
20.70
3.50(t)
51.13
2
1H
13C
31P
7.10–7.60(m)
121–136
6.7–6.9
163–165
0.88(t)
11.12
1.62(m)
20.71
3.49(t)
51.27
1.91(t)
25.80
60.80
201.88
Where x ¼ 3 for compound 1 and 2 for compound 2.

80
B. Arul Prakasam et al. / Polyhedron 23 (2004) 77–82
1
3.2.1. H NMR
3.4. Structural analysis
For compound 1, the methyl group protons resonate
at 0.81 ppm as a triplet. The methylene protons were
observed at 1.61 and 3.50 ppm. Of these two signals, the
triplet at 3.50 ppm was assigned to a-CH2 protons and
the multiplet at 1.61 ppm was assigned to b-CH2 pro-
tons. A multiplet in the region of 7.20–7.60 ppm was due
to aromatic protons. For compound 2, apart from the
propyl group signals (the splitting pattern was the same
as observed for compound 1), a triplet in the upfield
region of 1.91 ppm was assigned to methylene protons
present in the chelating phosphine. In the downfield
region, two sets of signals were obtained for aromatic
protons of PPh3 and BPh4.
The ORTEP diagram of 1 is shown in Fig. 1. Two units
of [Ni(dnpdtc)(PPh3)2]ClO4 Æ PPh3 are present in the unit
cell. It is interesting to note that a free triphenylphosphine
molecule is also present along with the complex in the unit
cell. The NiS2P2 chromophore is not of perfect square
planar geometry because of the small bite angle associated
with the dithiocarbamate moiety [78.61(4)°]. The Ni–P
ꢁ
distances [2.1919(10) and 2.2253(10) A] show asymmetry,
as reported earlier for similar compounds [8]. The pla-
narity of the molecule is in keeping with the observed
diamagnetism of the complex. The asymmetry in the Ni–P
distances and the observed large P–Ni–P bond angle is
due to the bulkiness of the PPh3 group. The C–S bond
ꢁ
3.2.2. 13C NMR
lengths are 1.722(3) and 1.727(4) A, which are shorter
ꢁ
than the single bond length of 1.81 A and higher than the
C@S distance of 1.69 A. The observed intermediate value
between the single and double bond distances indicates a
The chemical shifts of thioureide carbon (N–13CS2)
were observed at 199.17 and 201.88 ppm for complexes 1
and 2, respectively. The slight upfield shift from the
normal chemical shift values of Ni(dtc)2 complexes
(206–210 ppm) [13] is supported by the higher mC–N
values observed for complexes 1 and 2 in the present
study. This was due to the mesomeric shift of electron
density from the dithiocarbamate moiety towards the
metal centre. This supports the bidentate coordination
of the dithiocarbamate and the strong back bonding in
both the compounds. For compound 2, the low intensity
signals in the region of 163–165 ppm were due to BPh4
aromatic carbons.
ꢁ
partial double bond character. The short thioureide C–N
ꢁ
distance, 1.304(3) A, indicates that the p electron density
is delocalized over the S2CN moiety and that this bond
has a strong double bond character. This is also confirmed
by the fact that the two S–C–N angles are much greater
than that of the S–C–S (108.60(14)°) angle.
There is a shortening of the Ni–P distances for the
ꢁ
N,N-dipropyl analogue [2.1919(10) and 2.2253(10) A]
compared to its N,N-diisopropyl analogue [2.215(2) and
ꢁ
2.224(3) A] [19]. Also, the S–Ni–S angle decreases in the
ꢁ
N,N-diisopropyl compound [77.7(1) A] compared to
that in the N,N-dipropyldithiocarbamate analogue
ꢁ
[78.61(4) A] indicating a reduced steric requirement of
the isopropyl compound. In [Ni(dnpdtc)(PPh3)2]ClO4
3.2.3. 31P NMR
31P NMR for compound 1 shows a signal at 31 ppm
and is assigned to coordinated phosphorus. The free
PPh3 phosphorus resonates at the more upfield region of
)5.8 ppm. For compound 2, the signal at 60.8 ppm is
assigned to the phosphorus of the chelating phosphine
[14]. The very high deshielding for the coordinated
phosphorus in both the cases compared with the free
phosphines indicates the drift of electron density from
the phosphorus towards the metal centre. The shift is
phenomenal with the free dppe chemical shift being
observed at 40 ppm [15].
3.3. BVS calculations
For the two complexes, BVS values were calculated
by two procedures [16,17]. The values are 3.0646 (B/
OK), 2.9338 (OK/B); 3.2629 (B/OK), 3.1602 (OK/B)
for the two complexes 1 and 2, respectively. In both the
complexes, the values are higher than the expected
formal oxidation state of +2. The higher value ob-
served in the present set of compounds supports the
fact that the Ni–S, Ni–P bonds are more covalent and
the back bonding effects are very highly pronounced
[18].
Fig. 1. ORTEP diagram for compound 1 (PPh3 is omitted for clarity).

B. Arul Prakasam et al. / Polyhedron 23 (2004) 77–82
81
ꢁ
(1) the thioureide C–N distance is 1.304(3) A and in
ꢁ
[Ni(dipdtc)(PPh3)2]ClO4 it is 1.321(11) A, the observed
is smaller than that in the diisopropyl analogue:
87.3(1)°.
reduction of the thioureide distance in 1 shows the ef-
fective p back bonding of the phosphines in 1. The Cl–O
Comparison of 1 and 2 shows that S–Ni–S bite
angles [78.61(4)° versus 79.49(3)°] and the Ni–S–C
angles [85.625° versus 84.995°] are very similar. On the
other hand, a significant difference is observed in the
P–Ni–P angles that are subtended by dppe, a bidentate
ligand, being about 12° smaller than that found in 1,
where the PPh3 groups exert higher steric hindrance.
Thus, the P–Ni–P angles show a large change and are
influenced by the bulkiness of the nature of the phos-
phines. The thioureide C–N bond is 1 is shorter than
the bond in 2. The significant shortening is a clear
manifestation of mesomeric shift of electron density
towards nickel through the thioureide C–N bond in 1
compared to 2. Though the Ni–P bonds in 2 are rela-
tively shorter than those in 1, the back bonding effects
are felt more pronounced in 1 and hence the corre-
sponding thioureide bond shows a shortening of its
length. As a result of the reduced P–Ni–P chelated
angle in 2, the S–Ni–S angle increases by 0.49° com-
pared to 1. Hence, both electronic and steric influences
of dppe over PPh3 are exemplified by compound 2 with
respect to the compound 1.
ꢁ
distances vary from 1.340 to 1.421 A and the O–Cl–O
angles vary from 107.8° to 112.5° in 1 indicating the
distortion from tetrahedral geometry. The phenyl rings
show normal bond parameters. The P–C bond distances
ꢁ
are also normal with an average value of 1.8286 A. The
C–P–C angles deviate appreciably from the ideal tetra-
hedral angle of 109.5° and the resultant crowding of the
phenyl rings causes the P–C–C angles to be asymmetric.
[Ni(dnpdtc)(dppe)]BPh4 (2) is monomeric with two
molecules per unit cell. The ORTEP diagram of the
molecule is shown in Fig. 2. The molecule is approxi-
mately planar, in keeping with the observed diamagne-
ꢁ
tism. The Ni–S [2.1931(8) and 2.2108(9) A] and C–S
ꢁ
[1.718(3) and 1.715(3) A] bonds are symmetric, showing
that the negative charge on the dithiocarbamate ligand
is equally distributed all over the two donor atoms as
found in 1. One molecule of water is found in the unit
ꢁ
cell. The short thioureide C–N distance of 1.314(4) A
indicates that the electron density is delocalized over the
S2CN moiety and this bond has partial double bond
character. The bond lengths and bond angles of
[Ni(dipdtc)(dppe)]þ reported from our laboratory [19]
show a similarity in thioureide C–N distance [(1.314(4)
4. Supplementary data
þ
ꢁ
ꢁ
A] in 2, and 1.316(8) A in [Ni(dipdtc)(dppe)] ). The
N,N-dipropyl complexes (1) and (2) exhibit a relatively
larger steric influence compared to the diisopropyl
analogue. In 2, the P–Ni–P angle is 86.50(3)° which
Supplementary data are available from The Director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax:
+44-1223-336033; E-mail: deposit@ccdc.cam.ac.uk or
www:http://www.ccdc.cam.ac.uk) on request, quoting
the deposition number(s) CCDC 211258 and CCDC
211259.
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