New perspectives in phosphonodithioate coordination chemistry. Synthesis and X-ray crystal structure of trans-bis-[O-ethyl-(4-methoxyphenyl)phosphonodithioato] nickel(II)

Article abstract of DOI:10.1016/S0020-1693(97)05491-1

Attempts to optimise the synthesis of a new class of nickel(II) dithiolene complexes starting from 1,3-dialkylimidazolidine-2-thione-4,5-dione (1) and Lawesson's reagent (2) have afforded a new and easy one-step synthesis of phosphonodithioate nickel(II) complexes. This consists of the direct reaction between NiCl₂ and Lawesson's reagent in the appropriate alcohol R′OH (R=Me, Et, i-Pr, Bu, Bz) as solvent, to give the bis-[O-alkyl/aryl-(4-methoxyphenyl)phosphonodithioato] nickel(II) complexes (5a-e) with high yields (64-91%). Among them, trans-bis-[O-ethyl-(4-methoxyphenyl)phosphonodithioato] nickel(II) (5b) was characterised by means of X-ray diffraction measurements on a single crystal. The compound crystallises in the triclinic, P1 space group with a=6.4840(7), b=7.6032(9), c=13.055(2) A, α=99.481(9), β=99.43(1), γ=104.487(9)° and Z=1. The compound is centrosymmetric and exhibits discrete monomeric units with the ligand acting as S,S-bidentate. To explain the reactivity of Lawesson's reagent, the formation of 4-methoxyphenyldithiophosphorane (6) as intermediate has been suggested. The reaction was also tested for Pd(II) and Pt(II), but in these cases the yields were not as satisfactory as for Ni(II).

Full text of DOI:10.1016/S0020-1693(97)05491-1

Inorganica Chimica Acta 262 (1997) 81–84
Note
New perspectives in phosphonodithioate coordination chemistry.
Synthesis and X-ray crystal structure of trans-bis-[O-ethyl-
(4-methoxyphenyl)phosphonodithioato] nickel(II)
Massimiliano Arca a, Andrea Cornia b, Francesco A. Devillanova a, Antonio C. Fabretti b,
U
Francesco Isaia a, Vito Lippolis a, Gaetano Verani a,
a Universita` di Cagliari, Dipartimento di Chimica e Tecnologie Inorganiche e Metallorganiche, via Ospedale 72, 09124 Cagliari, Italy
b Dipartimento di Chimica, via G. Campi 183, 41100 Modena, Italy
Received 24 October 1996; revised 15 November 1996; accepted 17 December 1996
Abstract
Attempts to optimise the synthesis of a new class of nickel(II) dithiolene complexes starting from 1,3-dialkylimidazolidine-2-thione-4,5-
dione (1) and Lawesson’s reagent (2) have afforded a new and easy one-step synthesis of phosphonodithioate nickel(II) complexes. This
consists of the direct reaction between NiCl2 and Lawesson’s reagent in the appropriate alcohol R9OH (RsMe, Et, i-Pr, Bu, Bz) as solvent,
to give the bis-[O-alkyl/aryl-(4-methoxyphenyl)phosphonodithioato] nickel(II) complexes (5a–e) with high yields (64–91%). Among
them, trans-bis-[O-ethyl-(4-methoxyphenyl)phosphonodithioato] nickel(II) (5b) was characterised by means of X-ray diffraction meas-
#
urements on a single crystal. The compound crystallises in the triclinic, P1 space group with as6.4840(7), bs7.6032(9), cs13.055(2)
˚
A, as99.481(9), bs99.43(1), gs104.487(9)8 and Zs1. The compound is centrosymmetric and exhibits discrete monomeric units with
the ligand acting as S,S-bidentate. To explain the reactivity of Lawesson’s reagent, the formation of 4-methoxyphenyldithiophosphorane (6)
as intermediate has been suggested. The reaction was also tested for Pd(II) and Pt(II), but in these cases the yields were not as satisfactory
as for Ni(II).
Keywords: Crystal structures; Lawesson’s reagent; Dithiolene complexes; Phosphonodithioate complexes; Nickel complexes
1. Introduction
(f10%) and this was mainly attributed to the contempora-
neous formation of the tetrathiocino derivatives (3) [6],
which are normally the only products obtained in the absence
of NiCl2, and of unidentified secondary products all having
the same chemical nature. These have now beencharacterised
as the phosphonodithioato nickel(II) complexes (5)
(Scheme 1). These findings have opened new perspectives
in phosphonodithioate coordination chemistry.
Phosphoro-, phosphono- and phosphinodithioato transi-
tion-metal complexes are well known for their important
applications in industrial and agricultural fields [1].
Although the literature is very rich in phosphoro- and phos-
phinodithioate chemistry [2], it is very poor in phosphono-
dithioate complexes because of synthetic difficulties [3] 1.
Recently a new class of nickel(II) dithiolene complexes [4]
has been prepared by direct sulfuration of 1,3-dialkylimida-
zolidine-2-thione-4,5-dione (1) with Lawesson’s reagent
[5] (2,4-bis(4-methoxyphenyl)-1,3-dithia-2,4-diphosphe-
tane-2,4-disulfide (2)) in refluxing toluene and in the pres-
ence of NiCl2. The dithiolenes (4) have been isolated by
adding methanol or ethanol to the concentrated reaction mix-
ture. The yield of the reaction was found to be very low
2. Experimental
2.1. Synthesis of the metal complexes
A typical synthesis of the phosphonodithioate Ni(II) com-
plexes (5) is as follows. Equivalent amounts of nickel(II)
chloride and of Lawesson’s reagent are suspended in the
appropriate alcohol R9OH (100 ml for 4.20 mmol of NiCl2).
The stirred reaction mixture is refluxed for 1–3 h, then filtered
and the solvent is removed under vacuum. The obtained solid
U Corresponding author. Tel.: q39 70-675 8662; fax: q39 70-675 8670.
1 The announced structure of bis-(O-ethylethylphosphonodithioato)-
nickel(II) has not been published.
0020-1693/97/$17.00 q 1997 Elsevier Science S.A. All rights reserved
PII S0020-1693(97)05491-1

82
M. Arca et al. / Inorganica Chimica Acta 262 (1997) 81–84
Scheme 1. Different pathways for the reaction of 1,3-dialkylimidazolidine-2-thione-4,5-dione (1) (RsMe, Pri, Bun) with Lawesson’s reagent (2).
Table 1
Melting points, elemental analysis and yields of phosphonodithioato nickel(II) complexes (5a–e) obtained by reacting Lawesson’s reagent with several
alchohols (R9OH). Theoretical values in parentheses
Entry
R9
M.p.
Elemental analysis (%)
Yield
(%)
C
H
S
5a
5b
5c
5d
5e
Me
Et
i-Pr
Bu
Bz
184
131
168
79
37.09
39.14
41.33
43.68
50.20
(36.59)
(39.08)
(41.32)
(43.22)
(49.65)
3.91
4.37
5.02
5.56
4.54
(3.84)
(4.37)
(4.85)
(5.61)
(4.17)
24.29
23.87
23.25
19.66
19.13
(24.42)
(23.18)
(22.06)
(20.98)
(18.93)
91
78
64
93
80
148
is dissolved in a CH2Cl2/R9OH mixture (1:1 vol./vol. ratio)
and recrystallised by slow evaporation. Purple X-ray quality
crystals of 5b were grown by slow evaporation of a diethyl
ether:ethanol solution (2:1 vol./vol. ratio). Melting points,
microanalytical data and yields are summarised in Table 1.
on an Alpha 3000/800S computer. Selected bond distances
and bond angles are given in Table 3.
3. Results and discussion
2.2. X-ray characterisation
The crystal structure of 5b consists of a discrete centro-
symmetric NiL2 (LsO-ethyl-(4-methoxyphenyl)phos-
phonodithioato) unit (Fig. 1) in which one crystallographi-
cally independent L molecule coordinates the central nickel
atom as an S,S-bidentate ligand. Thephosphorusatomsreside
in a pseudo-tetrahedral environment with the 4-methoxy-
phenyl and ethoxy groups trans disposed with respect to the
coordination plane defined by the P(1), S(1) and S(2)
atoms. The L ligand is affected by disorder which can be
essentially described as a 1808 rotation of the 4-methoxy-
phenyl group around the P(1)–C(1) bond (the two positions
have been refined with occupancy factor 0.50:0.50). The
dihedral angles between the disordered phenyl ring planes
and the coordination plane are 99.0(6) and 99.5(6)8, and the
dihedral angle between the two disordered phenyl ring planes
is 1.2(6)8. The two positions of the C(1) atom are indistin-
guishable. The crystal packing is characterised by two (C5–
C6U and C6–C6U (C6U 1yx, 1yy, 1yz)) intermolecular
The intensity data of 5b werecollectedatroomtemperature
on a Siemens P4/RA automatic diffractometer. Details on
crystal parameters, intensity data collection and refinement
are reported in Table 2. All data were corrected for Lorentz
and polarisation effects, but not for absorption. The reflec-
tions were processed by the direct methods program SIR92
[7] which provided a satisfactory set of starting parameters
for many non-hydrogen atoms. After location of the missing
non-hydrogen atoms by Fourier difference synthesis, the
atomic positions were refined by the SHELXL93 program
package [8]. Complex neutral atom scattering factors [9]
were employed throughout. Non-hydrogen atoms were
treated anisotropically, whereas the hydrogen atoms were
treated as fixed contributors at calculated positions with fixed
thermal parameters. Isotropicdisplacementparametervalues,
2
˚
1 A greater than the average of the isotropic dispacement
˚
parameters of aryl and alkyl carbon atoms, were chosen for
hydrogen atoms bonded to aryl and alkyl carbons, respec-
tively. Drawings were performed with the ORTEP plotting
program [10] (Fig. 1). Major calculations were carried out
distances less than 3.6 A. The Ni–S(1) and Ni–S(2) bond
˚
lengths are similar (2.2202(8)–2.2232(8) A), and agree
well with those previously found for chelating dithiophos-
phinate complexes [11,12]. The P–S distances (2.002(1)–

M. Arca et al. / Inorganica Chimica Acta 262 (1997) 81–84
83
Table 2
Crystal data and structure refinement for 5b
Empirical formula
Formula weight
Temperature (K)
C18H24NiO4P2S4
553.26
293(2)
˚
Radiation, l (A)
graphite monochromated
Mo Ka, 0.71069
triclinic
Crystal system
Space group
#
P1
Unit cell dimensions
˚
a (A)
6.4840(7)
7.6032(9)
13.055(2)
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
99.481(9)
99.43(1)
104.487(9)
600.31(1)
3
˚
Volume (A )
Fig. 1. ORTEP view of C18H24NiO4P2S4 trans-bis-[O-ethyl-(4-methoxy-
phenyl)phosphonodithioato] nickel(II) (5b) showing atom labelling and
thermal motion ellipsoids (60%) for the atoms. Hydrogen atoms are omitted
for clarity.
Z
1
Dc (g cmy3
)
1.530
1.311
286
m(Mo Ka) (mmy1
F(000)
)
Crystal size (mm)
u Range (8)
Index ranges
0.35=0.40=0.40
4.74–29.99
0-h-9, y10-k-10,
y18-l-18
3551
3291 (Rints0.0171)
full-matrix least-squares
on F2
3291/0/196
1.039
tively), indicating a localised P–S p bond. In the ethyl-
ammonium salt of the trans bis-[ethylphosphonodithioato]
nickel(II) [11] complex the Ni–S bonds involving the same
ligand molecule are 2.226(2), 2.212(2) and 2.221(2),
Reflections collected
Independent reflections
Refinement method
˚
2.239(2) A, respectively. However this is an anionic
nickel(II) complex with two negative charges, in contrast to
5b and trans bis-[O-isopropyl-(ethyl)-phosphonodithioato]
nickel(II), which are neutral complexes.
Data/restraints/parameters
GOF on F2
Final R indices (I)2s(I))
R indices (all data)
R1s0.0498, wR2s0.1380
R1s0.0586, wR2s0.1443
0.584, y0.545
The pathway of the competitive reaction which leads to
the phosphonodithioato nickel(II) complex 5b (Scheme 1)
can be rationalised by assuming the presence in the reaction
medium of the 4-methoxyphenyldithiophosphorane inter-
mediate (6), which derives from a breaking of 2 in toluene.
Max., min. residual electron density
y3
˚
(e A
)
2
2
2
wy1s[s2(Fo )q(0.0781P)2q0.23P], Ps1/3[Fo q2Fc ].
Table 3
˚
Selected bond distances (A) and angles (8) of 5b
Ni–S(1)
Ni–P(1)
S(1)–P(1)
C(1)–P(1)
2.2197(8)
2.8194(8)
2.002(1)
1.782(3)
Ni–S(2)
2.2225(8)
1.580(2)
1.986(1)
1.456(4)
O(1)–P(1)
S(2)–P(1)
C(8)–O(1)
Although there is no direct evidence, the presence of 6 has
also been invoked in many organic reactions when 2 is used
in toluene [14,15] 2. The addition of ethanol to lower the
solubility of the dithiolene complex 4, probably favours the
formation of 6 and consequently that of the phosphonodi-
thioato Ni(II) complex 5b. It is important to note that Law-
esson’s reagent gives oxidative addition reactions in benzene
with Pt(C2H4)(PPh3)2 [16] and in dichloromethane with
bis-phosphine-dihalide complexes of Ni(II), Pd(II) and
Pt(II) [17]. The products cis-M[S2P(S)(C6H4OMe)]-
(PPh3)2 are air stable as solids, but in solution, on the base
of IR and NMR evidence, they are oxidised to give
M[S2P(O)(C6H4OMe)](PPh3)2 (MsNi, Pd, Pt).
S(1)–Ni–S(1)1
S(1)1–Ni–S(2)
P(1)–S(2)–Ni
O(1)–P(1)–S(2)
O(1)–P(1)–S(1)
S(2)–P(1)–S(1)
C(2)–C(1)–P(1)
C(6)–C(1)–P(1)
180.0
S(1)–Ni–S(2)
P(1)–S(1)–Ni
88.14(3)
83.65(3)
99.85(13)
113.66(10)
114.23(9)
131.5(4)
112.4(4)
120.9(2)
91.86(3)
83.91(3)
114.78(12)
113.40(11)
101.57(4)
112.0(4)
129.5(5)
O(1)–P(1)–C(1)
C(1)–P(1)–S(2)
C(1)–P(1)–S(1)
C(2)–C(1)–P(1)
C(6)–C(1)–P(1)
C(8)–O(1)–P(1)
1
Symmetry transformations used to generate equivalent atoms: yx, yy,
yz.
˚
1.986(1) A) are comparable suggesting a delocalised P–S p
bond. The phosphorus–sulfur bond in fact is assumed [4] to
˚
2 A similar intermediate is probably also formed when 2,4-dimethyl-1,3-
dithia-2,4-diphosphetane-2,4-disulfide reacts with dimethylamine. In this
case the obtained dimethylammonium dimethylamidodithiomethylphos-
phonate can easily be interpreted by hypothesising the methyldithiophos-
phorane intermediate, CH3PS2, which undergoes the nucleophilic attack of
dimethylamine.
be single when higher than 2.04 A and double if lower than
˚
1.95 A. Interestinglyintransbis-[O-isopropyl-(ethyl)-phos-
phonodithioato] nickel(II) [13] the two Ni–S and the two
P–S distances were found to be distinctly different
(2.282(1), 2.118(1) and 1.901(1), 2.031(1) A, respec-
˚

84
M. Arca et al. / Inorganica Chimica Acta 262 (1997) 81–84
therein; H. So, Y.C. Lin, G.S. Huang Gibbs and S.T. Chang Terny,
Taking into account these considerations, we thought that
Wear, 166 (1993) 17; V.V. Mikhailov, Yu V. Kokhanov, K. Kazaryan,
E.N. Matreeva and A. Kozodoi, Plast. Massy, 9 (1970) 23; M. Fuller,
M. Kasrai, J.S. Sheasby, G.M. Bancroft, K. Fyfe and K.H. Tan, Tribol.
Lett., (1995) 367.
by reacting directly Lawesson’s reagent with NiCl2 and using
an alcohol as solvent, the phosphonodithioato Ni(II) com-
plex could be obtained as the main product as clearly seen in
the yields reported in the last column of Table 1.
The reaction was also carried out with PdCl2 and PtCl2; in
these cases the yields were not satisfactory and decreased
from Pd (40–60%) to Pt (5–20%) even though a longer
reflux time was used. This seems to indicate the following
reactivity order Ni4Pd)Pt.
[2] I. Haiduc, D.B. Sowerby and S.-F. Lu, Polyhedron, 14 (1995) 3389,
and Refs. therein.
[3] P.S. Shetty, P. Jose and Q. Fernando, J. Chem. Soc. Commun., (1968)
788.
[4] F. Bigoli, P. Deplano, F.A. Devillanova, V. Lippolis, P.J. Lukes, M.L.
Mercuri, M.A. Pellinghelli and E.F. Trogu, J. Chem. Soc., Chem.
Commun., (1995) 371.
[5] S. Sheibye, B.J. Pedersen and S.O. Lawesson, Bull. Soc. Chim. Belg.,
87 (1978) 229.
4. Supplementary material
[6] F. Bigoli, M.A. Pellinghelli, D. Atzei, P. Deplano and E.F. Trogu,
Phosphorus Sulphur, 37 (1987) 189.
The complete list of atomic coordinates, bond lengths and
angles, observed and calculated structure factors, and aniso-
tropic thermal parameters are available from the authors on
request.
[7] A. Altomare, G. Cascarano, C. Giacovazzo and A. Guagliardi, J. Appl.
Crystallogr., 27 (1994) 1045.
[8] G.M. Sheldrick, SHELXL93, University of Go¨ttingen, Germany; J.
Appl. Crystallogr., to be published.
[9]
[10]
[11]
[12]
[13]
[14]
D.T. Cromer and J.T. Waber, International Tables for X-ray
Crystallography, Vol. IV, Kynoch, Birmingham, UK, 1974.
C.K. Johnson, ORTEP, Rep. ORNL-3794, Oak Ridge National
Laboratory, TN, USA, 1965.
S.K. Arora, D.M. Hayes and Q. Fernando, Acta Crystallogr., Sect. B,
34 (1978) 3355.
A.G. Orpen, L. Brammer, F.H. Allen, O. Kennard, D.G. Watson and
R. Taylor, J. Chem. Soc., Dalton Trans., (1989) S1.
S.P. Bone, D.B. Sowerby, R. Constantinescu and I. Haiduc, J. Chem.
Res. S, (1979) 69; M (1979) 0933.
A.A. Fahmy, Phosphorus, Sulfur, Silicon, 63 (1991) 81; M.F. Zayed,
N. Khir-El-Din and Y.O. El-Khoshnieh, Phosphorus, Sulfur, Silicon,
63 (1991) 243; A.A. El-Barbary and S.-O. Lawesson, Tetrahedron,
38 (1982) 1163.
Acknowledgements
We are grateful to MURST (the Italian Ministry for the
University and Scientific and Technologic Research) for
grants and financial support (40%), to CICAIA of Modena
for computer facilities, and to the Centro Interdipartimentale
Grandi Strumenti of the Modena University for intensity data
collection.
References
[15]
[16]
F. Seel and G. Zindler, Chem. Ber., 113 (1980) 1837.
R. Jones, D.J. Williams, P.T. Wood and J.D. Woolins, Polyhedron, 6
(1987) 539.
[1] D. Klaman (ed.), Lubricants and Related Products, Verlag Chemie,
Weinheim, Germany, 1984; P.J. Harrison, M.J. Begley, T. Kikabhai
and F. Killer, J. Chem. Soc., Dalton Trans., (1986) 925, and Refs.
[17]
P.T. Wood and J.D. Woolins, Transition Met. Chem., 12 (1987) 403.