Solid state and solution structures of the nickel(II) complex NiL 2 of the ambidentate (S,S)- or (P,S)-chelating ligand 3-diphenylphosphane-carbothioyl-1,1-dimethyl-thiourea (HL)

Article abstract of DOI:10.1016/j.inoche.2003.09.021

The ambidentate (S,S)- or (P,S)-bidentate ligand, 3-diphenylphosphane-carbothioyl-1,1-dimethyl-thiourea (HL), has been prepared, and the solid state and solution structures of its nickel(II) complex, NiL ₂, investigated. In the solid state the nickel(II) centre is square-planar and the ligand is coordinated in the (S,S)-bidentate mode, whereas in chloroform solution an equilibrium mixture of three isomers is rapidly formed, in which a (P,S)-bidentate species is the major component.

Full text of DOI:10.1016/j.inoche.2003.09.021

Inorganic Chemistry Communications 7 (2004) 38–41
www.elsevier.com/locate/inoche
Solid state and solution structures of the nickel(II) complex NiL2
of the ambidentate (S,S)- or (P,S)-chelating ligand
3-diphenylphosphane-carbothioyl-1,1-dimethyl-thiourea (HL)
*
Jonathan D. Crane , Andrew Herod
Department of Chemistry, University of Hull, Cottingham Road, Kingston-upon-Hull HU6 7RX, UK
Received 18 August 2003; accepted 2 September 2003
Published online: 31 October 2003
Abstract
The ambidentate (S,S)- or (P,S)-bidentate ligand, 3-diphenylphosphane-carbothioyl-1,1-dimethyl-thiourea (HL), has been pre-
pared, and the solid state and solution structures of its nickel(II) complex, NiL2, investigated. In the solid state the nickel(II) centre
is square-planar and the ligand is coordinated in the (S,S)-bidentate mode, whereas in chloroform solution an equilibrium mixture of
three isomers is rapidly formed, in which a (P,S)-bidentate species is the major component.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Nickel(II); Ambidentate ligands; Dithiobiuret; Phosphines
1. Introduction
into the adjacent thiocarbonyl group and thus reduce
the latterꢀs donor ability as a ligand. However, the cor-
ollary of this is that the R2P group is available to co-
ordinate to the metal centre instead of the thiocarbonyl
group; i.e., the system may act as a (P,S)-bidentate li-
gand. The coordinating behaviour of these potentially
ambidentate ligands will necessarily depend upon a
subtle balance of steric and electronic factors, as well as
the nature of the metal ion. We herein report the syn-
thesis of such a R2P-containing dithiobiuret analogue,
3-diphenylphosphane-carbothioyl-1,1-dimethyl-thiourea
(HL), and the solid state and solution structures of its
homoleptic nickel(II) complex, NiL2.
The dithiobiurets are amongst the simplest, and least
odoriferous, (S,S)-bidentate ligands available to coor-
dination chemistry, and a wide range of derivatives are
easy to prepare by straightforward methods [1–4]. De-
spite being thioamides, dithiobiurets are good ligands
for transition metal ions for two simple reasons: the
central NH group is acidic and readily deprotonates to
give a delocalised anionic ligand (cf. acetylacetonate),
and the lone pairs of the two terminal R2N groups are
delocalised into the thiocarbonyl groups. As a conse-
quence there are several resonance structures for the
dithiobiuret anion in which the sulphur atoms are for-
mally anionic.
Surprisingly, the replacement of one (or both) of the
terminal R2N groups in dithiobiuret-type ligands with
R2P groups has not been reported. The phosphorus lone
pair would be expected to be very much less delocalised
* Corresponding author. Tel.: +44-1482-465457; fax: +44-4182-
466410.
E-mail address: j.d.crane@hull.ac.uk (J.D. Crane).
1387-7003/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2003.09.021

J.D. Crane, A. Herod / Inorganic Chemistry Communications 7 (2004) 38–41
39
2. Experimental
2.1. Synthesis of NiL2ꢀCH2Cl2
Under an atmosphere of dinitrogen, dimethylthio-
carbamoyl chloride (1.24 g, 10 mmol) was added drop-
wise (5 min) with stirring to a solution of potassium
thiocyanate (0.98 g, 10 mmol) in dry acetonitrile
(40 cm3). During the addition a fine white precipitate of
potassium chloride was formed. After 30 min diphe-
nylphosphine (1.87 g, 10 mmol) was added and the so-
lution stirred for a further 15 min, then nickel(II) acetate
tetrahydrate (1.25 g, 5 mmol) added and the reaction
mixture instantly became dark brown. The crude prod-
uct was precipitated with water (200 cm3), isolated by
filtration, dried in air and recrystallised from dichlo-
romethane/ethanol as brown crystals of NiL2 Æ CH2Cl2;
yield 1.45 g (36%). The compound slowly loses the di-
chloromethane of crystallisation upon standing. Anal.
Calc. for C33H34Cl2N4NiP2S4 (MW ¼ 806.44): C, 49.15;
H, 4.12; N, 6.95; S, 15.90%. Found: C, 48.84; H, 4.20; N,
Fig. 1. ORTEP view of the molecular structure of NiL2 with thermal
ꢀ
ellipsoids shown at 50% [7]. Selected bond lengths (A) and angles (°):
Ni(1)–S(1), 2.1548(6); Ni(1)–S(2), 2.1668(6); S(1)–C(1), 1.704(2); S(2)–
C(2), 1.725(2); P(1)–C(1), 1.858(2); P(1)–C(5), 1.826(2); P(1)–C(11),
1.831(2); N(1)–C(2), 1.333(3); N(1)–C(3), 1.460(3); N(1)–C(4), 1.471(3);
N(2)–C(1), 1.298(3); N(2)–C(2), 1.358(3); S(1)–Ni(1)–S(2), 97.04(2);
Ni(1)–S(1)–C(1), 115.73(8); Ni(1)–S(2)–C(2), 116.90(8); S(1)–C(1)–
N(2), 133.34(18);S(2)–C(2)–N(2), 129.07(17); C(1)–N(2)–C(2), 126.6(2).
1
6.88; S, 15.65%. H NMR (400 MHz, CDCl3): d 7.95
(III, 4H, m, ArH), 7.79 (IV, 4H, m, ArH), 7.57–7.27 (m,
ArH), 3.38 (IV, 3H, s, CH3), 3.35 (III, 3H, s, CH3), 3.31
(IV, 3H, s, CH3), 3.26 (I/II, 3H, br s, CH3), 3.22 (III,
3H, s, CH3), 2.83 (IV, 3H, s, CH3), 2.79 (III, 3H, s,
CH3), 2.72 (III, 3H, s, CH3), 2.69 (IV, 3H, s, CH3), 2.64
(I/II, 3H, br s, CH3). 31P NMR (162.07 MHz, CDCl3): d
spectroscopy showed that it exists as an equilibrium
mixture of three species in chloroform solution at room
temperature (vide supra); the same equilibrium mixture
in solution was also obtained after repeated recrystalli-
sation of the compound, and by dissolving large, X-ray
quality, single crystals.
4
24.72 (III, d, JPPðtransÞ ¼ 14 Hz), 21.95 (I/II or IV, s),
4
20.48 (I/II or IV, s), )20.74 (III, d, JPPðtransÞ ¼ 14 Hz),
1
The X-ray structure of NiL2 (Fig. 1) shows that it
)21.63 (IV, s). mmax (cmꢁ1): 1470(s) 1433(m), 1382(s),
1278(m), 1185(w), 1125(m), 1025(w), 998(w), 920(w),
897(m), 738(m), 691(m), 568(w), 497(w), 477(w), 440(w).
crystallises as a single isomer (isomer I) from dichlo-
romethane/ethanol, presumably because this isomer has
the lowest solubility under these conditions. The nick-
el(II) centre has a square-planar geometry with a trans
arrangement of the two ligands and the phosphorus at-
oms are not coordinated to the metal centre. The two Ni–
3. Results and discussion
ꢀ
S bond lengths, 2.1548(6) and 2.1668(6) A, are very
similar, as are the corresponding S–C distances, 1.704(2)
The ligand, 3-diphenylphosphanecarbothioyl-1,1-di-
methyl-thiourea (HL), was readily prepared in situ by the
reaction of dimethylthiocarbamoyl isothiocyanate with
diphenylphosphine in acetonitrile (Scheme 1). The free
ligand was not isolated, but was complexed immediately
with nickel(II). The brown nickel(II) complex, NiL2,
crystallises as a single isomer, but 1H and 31P NMR
ꢀ
and 1.725(2) A, and the ligand bite-angle is 97.04(2)°. The
structure shows that the phosphorus atom is pyramidal
[C–P–C angles: 100.44(10), 104.07(11) and 104.34(11)°]
and that the phosphorus lone-pair is almost ideally
1
Crystal data: NiL2ꢀCH2Cl2: C33H34Cl2N4NiP2S4, Mr ¼ 806.43,
monoclinic, space group C2/c, a ¼ 13:9946ð18Þ, b ¼ 9:0639ð7Þ,
3
ꢀ
ꢀ
c ¼ 29:079ð3Þ A, b ¼ 97:666ð10Þ°, U ¼ 3655:5ð7Þ A , Z ¼ 4,
Dc ¼ 1:465 g cmꢁ3, l ¼ 1:023 mmꢁ1, F ð000Þ ¼ 1664. Crystal dimen-
sions 0.20 ꢂ 0.15 ꢂ 0.10 mm3. Data for NiL2ꢀCH2Cl2 were collected at
ꢀ
150(2) K employing a wavelength of 0.71073 A, on a Stoe IPDS II
image plate diffractometer with hmin ¼ 2:68° and hmax ¼ 34:81° (index
ranges ꢁ21 6 h 6 22, ꢁ14 6 k 6 14, ꢁ45 6 l 6 46). A solution was
provided via direct methods and refined by full-matrix least-squares on
F 2 using SHELXL-97 [6]. 23,334 reflections were measured, producing
7861 unique data [I > 2rðIÞ] with Rint ¼ 0:0740. 213 parameters with
no restraints refined to R1 ¼ 0:0492 and wR2 ¼ 0:1150 [I > 2rðIÞ] with
S ¼ 0:857 and residual electron density extremes of 0.938 and )1.149e
ꢁ3. See also supplementary material.
ꢀ
Scheme 1. Synthesis of HL and NiL2.
A

40
J.D. Crane, A. Herod / Inorganic Chemistry Communications 7 (2004) 38–41
Table 1
Summary of characteristic 1H and 31P NMR data for isomers I (and/or II), III and IV in CDCl3 solution
Isomer I (and/or II)
26%
Isomer III
13%
Isomer IV
61%
Ratio
1H NMR
Methyl
d 3.26 (br s)
d 2.64 (br s)
–
d 3.35 (s)
d 3.22 (s)
d 2.79 (s)
d 2.72 (s)
d 7.95 (m)
d 3.38(s)
d 3.31 (s)
d 2.83 (s)
d 2.69 (s)
d 7.79 (m)
ortho-CH
(Bound P)
31P NMR
4
(Bound P)
(Unbound P)
–
d )20.74 (d, JPPðtransÞ ¼ 14 Hz)
d )21.63 (s)
d 20.48 (s) or 21.95 (s)
4
d 20.48 (s) or 21.95 (s)
d 24.72 (d, JPPðtransÞ ¼ 14 Hz)
orientated to conjugate into the ligand backbone. How-
ever, the relative weakness of this interaction (compared
with the dimethylamino group) is demonstrated by the
perfect planarity of N(1) [sum of angles ¼ 360.0(2)°] and
the clear short-long-short alternation of bond distances
for the chain of atoms N(1)–C(2)–N(2)–C(1): 1.333(3),
ꢀ
1.358(3) and 1.298(3) A respectively. Moreover, the P(1)–
ꢀ
C(1) bond, 1.858(2) A, is significantly longer than the
ꢀ
P(1)–C(phenyl) bonds, 1.826(2) and 1.831(2) A.
In chloroform solution NiL2 exists as an equilibrium
mixture of three detectable components I (and/or II), III
1
and IV in the approximate ratio 2:1:5 by H and 31P
NMR spectroscopy (Table 1). These isomers arise due to
the ambidentate nature of the ligand, i.e., it may bind as
either an (S,S)- or (P,S)-chelate, which combined with
cis and trans isomerisation, results in the possibility of
six plausible mononuclear structures (Fig. 2). Two of the
solution species are readily identified as III and IV as
they have C1 symmetry, as evinced by the observation of
Fig. 2. The relevant possible isomers for NiL2.
observed for the mutually trans disposition of the
phosphines in III (4JPPðtransÞ ¼ 14 Hz). In the third ob-
served isomer of NiL2 the two ligands are equivalent
and there is no NMR evidence for the phosphorus at-
oms being coordinated to the nickel(II) centre, hence
this should correspond to the structurally characterised
isomer (isomer I). However, the broadness of the two
2
four methyl signals in the 1H NMR spectrum for each ,
and the relative integrations of these two sets of signals
show they exist in the approximate ratio 1:5. Further-
1
more, for each of these isomers the H NMR signal for
the ortho-CH proton of the single phosphine group
3
bound to the nickel(II) centre is shifted to higher d ,
1
methyl signals in the H NMR spectrum (of which the
4
clear of the overlapped multiplet in the range d 7.28–
7.58 for all the other aryl-CH protons, and these have
the correct relative integrations (and are in the ratio 1:5)
for the assignment as III and IV. The 31P NMR spec-
trum is also consistent with these assignments, but ad-
ditionally allows III to be identified as the minor
component due to the presence of 31P–31P coupling,
which would only be expected to be large enough to be
high d signal is broader) may indicate that both the
trans (I) and cis (II) isomers are present, but interconvert
sufficiently quickly on the NMR timescale to appear as a
single species. The absence of significant amounts of
isomers V and VI may be simply rationalised by the
greater trans-influence of phosphine ligands favouring
III over V, and steric hindrance favouring IV over VI.
In conclusion, the phosphine-containing dithiobiuret
analogue 3-diphenylphosphane-carbothioyl-1,1-dimeth-
2
There is substantial N–C double bond character in the thioamide
group and the energy barrier to rotation is slightly higher (DGz ꢃ 100
kJ molꢁ1) than for the corresponding amides [5], hence inequivalent
methyl groups.
4
The two broad signals are not coalescing with one another, hence
the broadness is probably produced by interconversion of I and II on
the NMR timescale. The methyl signals with d > 3:2 are tentatively
assigned to be proximal to sulphur, and those with d < 2:9 proximal to
nitrogen, and this is consistent with the greater broadness of the signal
at d 3.26 being caused by isomer interconversion.
3
The assignment of these two high d signals as ortho-protons on the
phenyl rings was confirmed by successful computer simulation with
2
3
reasonable values for the coupling constants: JPH ¼ 11:8, JHH ¼ 8:2,
4JHH ꢃ 1 Hz.

J.D. Crane, A. Herod / Inorganic Chemistry Communications 7 (2004) 38–41
41
yl-thiourea (HL) has been successfully prepared, and
References
isolated as the nickel(II) complex NiL2. Although in the
solid state the ligand is coordinated to the nickel(II) ion
in a traditional dithiobiuret manner, in solution the
ambidentate nature of the ligand becomes apparent. In
chloroform the complex exists as a mixture of three
isomers, with the major isomer having one phosphine
group bound to the nickel centre.
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[2] J.E. McGrady, D.M.P. Mingos, J. Chem. Soc., Perkin Trans. 2
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[5] M. Oki (Ed.), Applications of Dynamic NMR Spectroscopy to
Organic Chemistry, VCH, 1985.
Supplementary material
[6] G.M. Sheldrick, SHELXL-97 – a program for crystal structure
refinement, release 97-2, University of Germany, Germany,
1997.
Supplementary data for is available from the CCDC,
12 Union Road, Cambridge, CB2 1EZ, UK, quoting the
deposition number: CCDC 217270.
[7] L.J. Farrugia, ORTEP-3 for Windows, J. Appl. Crystallogr. 30
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