Nickel dithiolene complexes as a source of a new family of S,S-dinegative chiral ligands R4btimdt = 5,5′-bis(1,3-dialkyl-4-imidazolidine-2-thione-4-thiolate)

Article abstract of DOI:10.1039/b108471b

The reaction of the complex [Ni(Bu₂timdt)₂] (Bu₂timdt= -1 charged 1,3-dibutylimidazolidine-2,4,5-trithione) with polyfunctional phosphines: tp [tp = bis(2-diphenylphosphinophenyl)phenylphosphine] and qp [qp = tris(2-diphen

Full text of DOI:10.1039/b108471b

View Article Online / Journal Homepage / Table of Contents for this issue
Nickel dithiolene complexes as a source of a new family of
S,S-dinegative chiral ligands R4btimdt ؍ 5,5Ј-bis(1,3-dialkyl-
4-imidazolidine-2-thione-4-thiolate)
Francesco Bigoli,a Simona Curreli,b Paola Deplano,*b Laura Leoni,b Maria Laura Mercuri,b
Maria Angela Pellinghelli,a Angela Serpeb and Emanuele F. Trogub
a Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica,
Viale delle Scienze 78, I-43100 Parma, Italy
b Dipartimento di Chimica Inorganica ed Analitica, Università di Cagliari,
Cittadella di Monserrato, I-09042 Monserrato, Cagliari, Italy.
E-mail: deplano@vaxca1.unica.it
Received 20th September 2001, Accepted 25th February 2002
First published as an Advance Article on the web 10th April 2002
The reaction of the complex [Ni(Bu2timdt)2] (Bu2timdt = Ϫ1 charged 1,3-dibutylimidazolidine-2,4,5-trithione)
with polyfunctional phosphines: tp [tp = bis(2-diphenylphosphinophenyl)phenylphosphine] and qp [qp = tris(2-
diphenylphosphinophenyl)phosphine] produces [Ni(tp)(Bu4btimdt)] (1) and [Ni(qp)(Bu4btimdt)] (2), respectively.
X-Ray crystallographic studies show that in both complexes, the nickel ion is coordinated in a trigonal bipyramidal
geometry with three P-atoms of the tp and of qp (one of the ‘arms’ of qp is non-coordinating) ligands occupying
three facial sites and with two sulfur atoms of Bu4btimdt [5,5Ј-bis(1,3-dibutyl-4-imidazolidine-2-thione-4-thiolate)].
This new S,S dinegative chelating ligand is generated in situ by desulfurisation of one of the two vicinal sulfur atoms
on each ligand in [Ni(Bu2timdt)2] and C–C coupling between the two imidazole rings. The Bu4btimdt anion is chiral,
as free rotation about the C–C bond between the two imidazole rings is hindered by high energy barriers. No
desulfurisation is observed when reacting Bu4N[Ni(dmit)2] with tp, and the obtained product is [Ni(tp)(dmit)] (3),
a nickel complex where the metal is still coordinated with a trigonal bipyramidal geometry (three P-atoms of the
tp ligand and two sulfur atoms of the dmit ligand).
groups instead of sulfur atoms in the penta-atomic ring
Introduction
adjacent to the dithiolene core. These complexes can also
The importance of metal-dithiolene complexes has increased in
provide a convenient route for synthesising new sulfur-based
recent years due to their applications in the field of new molec-
heterocyclic molecules which are difficult to obtain or are
ular materials. Solids that exhibit electrical1 and magnetic
unobtainable by conventional methods. The reaction of [Ni(R2-
properties,2 near-infrared dyes,3 and non-linear optical
timdt)2]9 with dibromine at 0 ЊC produces a dimer (R2timdt)2
10
materials4 based on metal-dithiolenes have been reported.
similar to (dmit)2, as shown in Scheme 1.
Interest is also devoted to their reactions which produce sulfur-
based heterocyclic systems.5 Molecules derived from C3S5
2Ϫ
(dmit) have received extra attention due to their relevance
for the synthesis of new electronic and photonic materials.6
Rauchfuss et al. have shown that the treatment of an
acetonitrile solution of a salt of [Zn(dmit)2]2Ϫ with sulfuryl
chloride at Ϫ40 ЊC gives rise to a (dmit)2 dimer, formed by two
planar C3S5 units interconnected by persulfide bridges, and a
(dmit)n polymeric compound.7 The redox properties of dmit
and related molecules have recently been deeply investigated.8
We are extensively investigating the properties of a class
of nickel dithiolenes [Ni(R2timdt)2], (R2timdt = Ϫ1 charged 1,3-
dialkylimidazolidine-2,4,5-trithione) synthesised in our labor-
atory. The R2timdt ligand, where N-electron donor atoms
of the imidazoline ring are forced into co-planarity with the
dithiolene ring, was revealed to be valuable in shifting the low
energy transition typical of this class of complexes within a
region of interest for near-infrared (NIR) dyes, while stability
was maintained.9 † [Ni(R2timdt)2] differs from the structural
Scheme 1
analog [Ni(dmit)2] in the presence of the better donor NR
(R2timdt)2 is a stable molecule that can be stored and used as
a very convenient source of the ligand to prepare metal-
† The neutral complexes absorb very strongly at approximately
1000 nm, a region of special interest for NIR-dyes for their use in
dithiolene complexes since the reductive cleavage of the S–S
Q-switching neodymium lasers. Moreover these complexes work as
bonds easily occurs without alteration of the molecule. In this
case this is particularly relevant due to the fact that R2timdt
switchable NIR-dyes, since the absorption is shifted to approximately
1400 nm on reversible reduction.
DOI: 10.1039/b108471b
J. Chem. Soc., Dalton Trans., 2002, 1985–1991
This journal is © The Royal Society of Chemistry 2002
1985

View Article Online
ligands cannot be isolated when non-coordinated. For this
reason, the nickel-complexes are prepared by the in situ
sulfurisation reaction of the 1,3-dialkylimidazolidine-2-thione-
4,5-dione in the presence of the metal. The sulfurisation of this
vicinal dione, in the absence of nickel, following a procedure
which works well to prepare six- and seven-membered cyclic
dithiooxamides, does not produce the foreseen 1,3-dialkyl-
imidazolidine-2,4,5-trithione, but 4,5,6,7-tetrathiocino[1,2-b:
3,4-bЈ]diimidazolyl-1,3,8,10-tetraalkyl-2,9-dithione (R4todit,
shown in Scheme 2).11
Results and discussion
The reaction of [Ni(Bu2timdt)2] with mono-(Ph3P) or bi-
functional (dppe) phosphines leaves the reagents unchanged
(see details in Experimental section). Unexpectedly the same
reaction with polyfunctional phosphines [tp = bis(2-diphenyl-
phosphinophenyl)phenylphosphine], and qp [qp
= tris(2-
diphenylphosphinophenyl)phosphine] produces [Ni(tp)(Bu4-
btimdt)] (1) and [Ni(qp)(Bu4btimdt)] (2), respectively, according
to Scheme 3.
The molecular structures of 1 and of 2, which lack butyl and
non-bridging phenyl groups for clarity, are reported in Fig. 1
and 2, respectively, with the corresponding atom-labelling
scheme and selected bond lengths and angles collected in Tables
1 and 2. A brief description of 1 has been reported previously.13
In both complexes, the nickel ion is coordinated with a trigonal
bipyramidal geometry with three fac P atoms of the tp or qp
ligands and with two S atoms of the Bu4btimdt ligand. The
chelation of tp and qp results in the formation of two penta-
atomic rings showing an ‘envelope’ conformation. Both tp and
qp behave as tripodal ligands, since one of the ‘arms’ of qp is
not coordinating. This behaviour can be explained considering
that in five-coordinated nickel() complexes an 18eϪ configur-
ation is reached, and that Bu4btimdt is unsuitable as a mono-
coordinated ligand. An ‘arm off’ coordination by polypodal
phosphines has been observed in the case where an 18eϪ
trigonal bipyramidal species goes to a 16eϪ square one.14
Fluxionality and arm-off reactions of octahedral rhodium()
Scheme 2 R4todit.
A C–C coupling between two imidazole rings and the form-
ation of an octa-atomic ring containing four sulfur atoms
connected through persulfide bonds is achieved. This molecule,
which has relevant properties as an anticancer agent,12 is, in
contrast to (R2timdt)2, unsuitable as a source of ligands in the
preparation of metal-dithiolenes.
R4todit are electro-active heterocycles and undergo reduction
and elimination of two sulfur atoms by reacting with an
alcoholate and new anions R4btimdt [5,5Ј-bis(1,3-dialkyl-4-
imidazolidine-2-thione-4-thiolate] are obtained. These anions
have been trapped in the complex [Ni(dppe)(R4btimdt)] if [Ni-
(dppe)Cl2] [dppe = 1,2-bis(diphenylphosphino)ethane] is added
to the above mentioned reaction mixture, buffered with
ammonium acetate. R4btimdt is oxygen sensitive and from
its solution left open to the air, a trimer, where persulfide
bridges connect three R4btimdt units, has been isolated as
oxidation product.13 R4btimdt is also unexpectedly obtained
from [Ni(R2timdt)2]9 when reacting these complexes with
polyfunctional phosphines as described here.
complexes with tripodal phosphines have been reported.15
A
facile oxidation of the uncoordinated P-atom is predicted.16
The Ni–Papical distances are shorter than Ni–Pequatorial ones, in
contrast with a possible elongation of the apical distances due
to the trans effect of the sulfur atoms of the Bu4btimdt ligand.
A similar shortening of the Ni–Papical distance of the central
phosphorus of tricoordinated ligands has been previously
observed in the complex [NiI2(eptp)] (eptp = PhP(CH2)2-
PPh(CH2)2PPh2) and ascribed to the “double chelate effect” of
the central phosphorus which is simultaneously part of two
five-membered rings.17 However, since the Ni–S distances
also differ, the shorter being that involving the sulfur at the apex
Scheme 3 i = tp excess, THF, reflux under N2, 24 h.
1986
J. Chem. Soc., Dalton Trans., 2002, 1985–1991

View Article Online
Table 1 Selected bond lengths [Å] and angles [deg] for [Ni(tp)-
(Bu4btimdt)] (1)
Ni–P(1)
Ni–P(2)
Ni–P(3)
Ni–S(21)
2.297(3)
2.174(3)
2.204(3)
2.270(3)
2.341(3)
1.693(8)
1.716(8)
1.701(9)
1.746(8)
1.838(9)
1.837(8)
1.820(8)
1.823(8)
1.825(9)
1.805(9)
1.825(9)
1.813(8)
P(3)–C(1G)
N(11)–C(11)
N(11)–C(31)
N(11)–C(41)
N(21)–C(11)
N(21)–C(21)
N(21)–C(81)
N(12)–C(12)
N(12)–C(32)
N(12)–C(42)
N(22)–C(12)
N(22)–C(82)
N(22)–C(22)
C(21)–C(31)
C(31)–C(32)
C(22)–C(32)
1.810(10)
1.359(11)
1.391(10)
1.462(12)
1.350(11)
1.401(9)
1.461(11)
1.380(11)
1.407(10)
1.441(12)
1.340(11)
1.456(12)
1.392(9)
Ni–S(22)
S(11)–C(11)
S(21)–C(21)
S(12)–C(12)
S(22)–C(22)
P(1)–C(1C)
P(1)–C(1A)
P(1)–C(1B)
P(2)–C(6C)
P(2)–C(6E)
P(2)–C(1D)
P(3)–C(1E)
P(3)–C(1F)
1.371(11)
1.446(11)
1.350(11)
P(2)–Ni–P(1)
P(3)–Ni–P(1)
P(2)–Ni–P(3)
P(2)–Ni–S(21)
P(3)–Ni–S(21)
S(21)–Ni–P(1)
P(2)–Ni–S(22)
P(3)–Ni–S(22)
84.74(9)
118.37(9)
84.33(9)
169.94(10)
85.95(10)
97.65(9)
88.36(9)
136.46(10)
100.50(9)
103.51(9)
111.8(3)
106.6(3)
102.7(4)
103.1(4)
103.5(4)
106.2(2)
122.7(3)
116.2(3)
104.9(4)
106.2(4)
104.4(4)
109.5(2)
106.0(3)
124.2(3)
105.0(4)
103.8(4)
103.8(4)
106.2(3)
115.6(3)
120.9(3)
C(11)–N(11)–C(31)
C(11)–N(11)–C(41)
C(31)–N(11)–C(41)
C(11)–N(21)–C(21)
C(11)–N(21)–C(81)
C(21)–N(21)–C(81)
C(12)–N(12)–C(32)
C(12)–N(12)–C(42)
C(32)–N(12)–C(42)
C(12)–N(22)–C(82)
C(12)–N(22)–C(22)
C(82)–N(22)–C(22)
N(21)–C(11)–N(11)
N(21)–C(11)–S(11)
N(11)–C(11)–S(11)
C(31)–C(21)–N(21)
C(31)–C(21)–S(21)
N(21)–C(21)–S(21)
C(21)–C(31)–N(11)
C(21)–C(31)–C(32)
N(11)–C(31)–C(32)
N(22)–C(12)–N(12)
N(22)–C(12)–S(12)
N(12)–C(12)–S(12)
C(32)–C(22)–N(22)
C(32)–C(22)–S(22)
N(22)–C(22)–S(22)
C(22)–C(32)–N(12)
C(22)–C(32)–C(31)
N(12)–C(32)–C(31)
110.1(7)
125.8(8)
124.1(8)
111.4(7)
122.9(7)
125.7(7)
107.9(7)
123.9(8)
127.4(8)
125.1(8)
110.5(7)
124.4(8)
105.7(7)
127.6(7)
126.8(7)
105.1(7)
130.4(6)
124.4(6)
107.6(7)
124.8(7)
127.0(8)
106.9(7)
127.5(7)
125.6(7)
106.9(7)
127.4(6)
125.7(7)
107.8(7)
127.2(8)
125.0(8)
Fig. 1 Projection of [Ni(tp)(Bu4btimdt)] (1) along a. Phenyl rings and
butyl chains are omitted for clarity.
S(21)–Ni–S(22)
P(1)–Ni–S(22)
C(21)–S(21)–Ni
C(22)–S(22)–Ni
C(1C)–P(1)–C(1A)
C(1C)–P(1)–C(1B)
C(1A)–P(1)–C(1B)
C(1C)–P(1)–Ni
C(1A)–P(1)–Ni
C(1B)–P(1)–Ni
C(6C)–P(2)–C(6E)
C(6C)–P(2)–C(1D)
C(6E)–P(2)–C(1D)
C(6C)–P(2)–Ni
C(6E)–P(2)–Ni
C(1D)–P(2)–Ni
C(1E)–P(3)–C(1F)
C(1E)–P(3)–C(1G)
C(1F)–P(3)–C(1G)
C(1E)–P(3)–Ni
C(1F)–P(3)–Ni
C(1G)–P(3)–Ni
Fig. 2 Molecular structure of [Ni(qp)(Bu4btimdt)] (2). Phenyl rings
and butyl chains are omitted for clarity.
of the bipyramid, it seems preferable to explain the longer
equatorial and shorter bond lengths by using an over-simplified
crystal field model which has been proposed for similar
complexes.18 Accordingly, since in a trigonal bipyramidal d8
is chiral, the free rotation about C(31)–C(32) being hindered
by high energy barriers,19 which result from contacts
S ؒ ؒ ؒ Cbutyl, Cbutyl ؒ ؒ ؒ Cbutyl. The value of the torsion angle
C(21)–C(31)–C(32)–C(22) observed for the chelating ligand
[ 58(1) and 57(1)Њ for 1 and 2, respectively] is exactly the same
as calculated for the free ligand at the minimum of energy
[ 57(1)Њ]. These values also indicate that the enantiomers of the
free ligand can be isolated. Therefore 1 and 2 are chiral, but
both enantiomers are present in the crystals.
The 1,3-dithiole ring based counterpart of the R4btimdt
dianion: C6S82Ϫ, has been prepared via the reactions shown in
Scheme 4 and used to prepare Ni() complexes.20
In order to check whether or not the desulfurisation reaction
induced by tp also works with dmit-based nickel-dithiolenes to
form C6S82Ϫ, we have allowed (Bu4N)[Ni(dmit)2] to react with tp
according to Scheme 5.
In the obtained product [Ni(tp)(dmit)] (3) the dmit ligand is
recovered unchanged. The nickel ion is coordinated similarly as
in 1 and 2 with a trigonal bipyramidal geometry with three fac P
atoms of the tp ligand and with two S atoms of the dmit ligand
(see Fig. 3, selected bond lengths and angles are in Table 3). The
coordination to the metal through the two thiolato sulfur atoms
of the dmit ligand produces a penta-atomic ring (including the
metal) showing an envelope conformation. The dmit anion is
2
configuration, the dz is unoccupied being destabilised com-
pared with other orbitals, shorter axial and longer equatorial
bond lengths will produce an increase in the energy of the
2
unoccupied dz orbital and a stabilisation of the occupied
orbitals. As cited above, the Bu4btimdt dianion acts as a bi-
dentate ligand being coordinated to the metal through the two
thiolato sulfur atoms, in such a way that a hepta-atomic ring
showing a pseudo two fold-axis (including the metal) results.
This ligand is generated in situ for elimination of one of the two
vicinal sulfur atoms on each R2timdt coordinated to the metal
in the nickel complex with a coupling of two imidazole rings
through the formation of a C–C single bond similarly to what
happens in the sulfurisation reaction of the 1,3-dialkylimid-
azolidine-2-thione-4,5-dione to produce R4todit.
The structural parameters of the Bu4timdt anion in com-
pounds 1 and 2 are in good agreement. The two imidazoline
rings are planar and their orientation, determined by the
mutually opposite disposition of the butyl groups, is indicated
by the torsion angle N(11)–C(31)–C(32)–N(12) [Ϫ72(1) and
Ϫ65(2)Њ for 1 and 2, respectively]. Of all the butyl groups
in compounds 1 and 2 only one, the C(42)–C(5)–C(6)–C(7)
group of 2 (the fragment C(5)–C(6)–C(7) is not reported in
Fig. 2 for clarity), results in the extended shape. The Bu4btimdt
J. Chem. Soc., Dalton Trans., 2002, 1985–1991
1987

View Article Online
Table 2 Selected bond lengths [Å] and angles [deg] for [Ni(qp)-
(Bu4btimdt)] (2)
Table 3 Selected bond lengths [Å] and angles [deg] for [Ni(tp)-
(dmit)] (3)
Ni–P(1)
Ni–P(2)
Ni–P(3)
Ni–S(21)
2.246(3)
2.188(2)
2.199(3)
2.291(2)
2.344(3)
1.813(6)
1.806(5)
1.822(6)
1.819(4)
1.842(4)
1.840(5)
1.819(5)
1.813(6)
1.850(5)
1.842(5)
1.849(5)
1.864(5)
1.686(11)
S(21)–C(21)
S(12)–C(12)
S(22)–C(22)
N(11)–C(11)
N(11)–C(31)
N(11)–C(41)
N(21)–C(11)
N(21)–C(81)
N(21)–C(21)
N(12)–C(12)
N(12)–C(32)
N(12)–C(42)
N(22)–C(12)
N(22)–C(22)
N(22)–C(82)
C(21)–C(31)
C(31)–C(32)
C(22)–C(32)
1.757(10)
1.693(10)
1.734(9)
Ni–P(1)
Ni–P(2)
Ni–P(3)
Ni–S(1)
Ni–S(2)
S(1)–C(2)
S(2)–C(1)
2.241(2)
2.146(1)
2.216(1)
2.240(1)
2.347(1)
1.747(4)
1.738(4)
S(3)–C(1)
S(3)–C(3)
S(4)–C(2)
S(4)–C(3)
S(5)–C(3)
C(1)–C(2)
1.747(4)
1.729(5)
1.748(4)
1.721(5)
1.653(4)
1.340(6)
1.343(12)
1.425(12)
1.431(13)
1.381(14)
1.434(13)
1.431(12)
1.365(12)
1.392(10)
1.414(12)
1.358(12)
1.407(10)
1.442(12)
1.312(12)
1.421(12)
1.365(12)
Ni–S(22)
P(1)–C(1B)
P(1)–C(1C)
P(1)–C(1A)
P(2)–C(1D)
P(2)–C(1G)
P(2)–C(2C)
P(3)–C(1E)
P(3)–C(1F)
P(3)–C(2D)
P(4)–C(1H)
P(4)–C(1I)
P(4)–C(2G)
S(11)–C(11)
P(1)–Ni–P(2)
P(1)–Ni–P(3)
P(1)–Ni–S(1)
P(1)–Ni–S(2)
P(2)–Ni–P(3)
P(2)–Ni–S(1)
P(2)–Ni–S(2)
P(3)–Ni–S(1)
P(3)–Ni–S(2)
S(1)–Ni–S(2)
Ni–S(1)–C(2)
Ni–S(2)–C(1)
86.72(4)
129.47(4)
90.21(5)
107.74(5)
86.38(4)
174.93(5)
93.07(4)
92.48(5)
122.58(5)
91.71(4)
99.12(14)
96.69(13)
C(1)–S(3)–C(3)
C(2)–S(4)–C(3)
S(2)–C(1)–S(3)
S(2)–C(1)–C(2)
S(3)–C(1)–C(2)
S(1)–C(2)–S(4)
S(1)–C(2)–C(1)
S(4)–C(2)–C(1)
S(3)–C(3)–S(4)
S(3)–C(3)–S(5)
S(4)–C(3)–S(5)
98.4(2)
98.1(2)
120.1(2)
124.7(3)
115.2(3)
120.2(2)
123.4(3)
116.3(3)
111.9(2)
124.2(3)
123.9(3)
P(2)–Ni–P(1)
85.68(9)
123.21(10)
85.70(9)
168.03(10)
90.24(10)
87.15(10)
91.43(8)
117.24(10)
119.00(10)
100.43(9)
103.7(3)
104.1(4)
103.7(3)
120.1(3)
105.3(2)
117.9(2)
108.8(3)
102.4(3)
105.3(3)
111.31(19)
119.9(2)
107.49(19)
107.3(3)
99.9(3)
C(22)–S(22)–Ni
109.5(3)
109.4(8)
124.0(9)
126.6(8)
124.0(9)
107.8(7)
127.7(10)
109.6(7)
124.2(8)
125.5(8)
110.3(7)
123.8(8)
125.9(8)
107.0(8)
126.2(9)
126.7(8)
108.0(9)
130.2(8)
121.8(7)
107.8(8)
128.5(9)
123.2(8)
106.2(8)
126.0(8)
127.7(8)
105.9(7)
130.1(7)
123.9(6)
107.7(7)
126.1(7)
126.2(7)
P(3)–Ni–P(1)
P(2)–Ni–P(3)
P(2)–Ni–S(21)
P(3)–Ni–S(21)
P(1)–Ni–S(21)
P(2)–Ni–S(22)
P(3)–Ni–S(22)
P(1)–Ni–S(22)
C(11)–N(11)–C(31)
C(11)–N(11)–C(41)
C(31)–N(11)–C(41)
C(11)–N(21)–C(81)
C(11)–N(21)–C(21)
C(81)–N(21)–C(21)
C(12)–N(12)–C(32)
C(12)–N(12)–C(42)
C(32)–N(12)–C(42)
C(12)–N(22)–C(22)
C(12)–N(22)–C(82)
C(22)–N(22)–C(82)
N(11)–C(11)–N(21)
N(11)–C(11)–S(11)
N(21)–C(11)–S(11)
C(31)–C(21)–N(21)
C(31)–C(21)–S(21)
N(21)–C(21)–S(21)
C(21)–C(31)–N(11)
C(21)–C(31)–C(32)
N(11)–C(31)–C(32)
N(12)–C(12)–N(22)
N(12)–C(12)–S(12)
N(22)–C(12)–S(12)
C(32)–C(22)–N(22)
C(32)–C(22)–S(22)
N(22)–C(22)–S(22)
C(22)–C(32)–N(12)
C(22)–C(32)–C(31)
N(12)–C(32)–C(31)
S(21)–Ni–S(22)
C(1B)–P(1)–C(1C)
C(1B)–P(1)–C(1A)
C(1C)–P(1)–C(1A)
C(1B)–P(1)–Ni
C(1C)–P(1)–Ni
C(1A)–P(1)–Ni
C(1D)–P(2)–C(1G)
C(1D)–P(2)–C(2C)
C(1G)–P(2)–C(2C)
C(1D)–P(2)–Ni
C(1G)–P(2)–Ni
C(2C)–P(2)–Ni
C(1E)–P(3)–C(1F)
C(1E)–P(3)–C(2D)
C(1F)–P(3)–C(2D)
C(1E)–P(3)–Ni
C(1F)–P(3)–Ni
C(2D)–P(3)–Ni
C(1H)–P(4)–C(1I)
C(1H)–P(4)–C(2G)
C(1I)–P(4)–C(2G)
C(21)–S(21)–Ni
Scheme 5 i = tp excess, THF, reflux under N2, 24 h.
104.1(3)
115.1(3)
117.9(2)
110.43(19)
100.4(3)
106.1(3)
100.0(3)
112.4(3)
Fig. 3 Molecular structure of [Ni(tp)(dmit)] (3). Phenyl rings are
omitted for clarity. The unlabelled carbon atom connected to P(1)
belongs to the phenyl ring A, which is disordered.
Scheme 4
nearly planar (dev. max = 0.027(2) Å). As observed in 1 and 2,
the apical Ni–P and Ni–S distances are shorter than the
equatorial ones. While metal complexes containing phosphorus
and dithiolene ligands have been known for a long time,21–23
structurally characterised examples are uncommon and among
and the six coordinate [W(CO)2(dmit)L2]25 (L2 = (PR3)2 and
dppe) have been reported. Bond distances of dmit fragments in
these complexes are in accordance with those in 3 where dmit
works similarly as a dianion. Raman scattering has been shown
them the square-planar [M(dppe)(dmit)]24 (M᎐Ni, Pd and Pt)
to be highly suitable to correlate the C᎐C frequency and the
᎐
᎐
1988
J. Chem. Soc., Dalton Trans., 2002, 1985–1991

View Article Online
charge for the [M(dmit)2]nϪ (n = 0, 0.29, 0.5, 1, 2; M = Ni, Pd)
case,26 and [Ni(Pri2timdt)(dmit)]nϪ compounds (Pri = iso-propyl,
(27200), 352 sh (∼16200), 3]. These spectra are similar to those
of trigonal bipyramidal complexes of nickel() coordinated
with polypodal phosphorus ligands, and the assignments of the
electronic spectra of trigonal-pyramidal Ni-complexes have
been established for a long time.28 ‡ Following these assignments,
the bands found at lower frequencies should be mainly due to
n = 0; n = 1).27 A Raman peak which can be assigned to the C᎐C
᎐
stretching vibration for 3 has been observed at 1450 cmϪ1 and is
reported in Fig. 4. The position of this band, very close to the
frequency of the C᎐C peak for [Ni(dmit) ]Ϫ2, Fig. 5, suggests a
᎐
2
2
2
the dx y , dxy
dz2 and to dxz, dyz
dz2 transitions, while
Ϫ
the strong bands in the 280–350 nm region may be assigned to
Ni and S Ni CTLM transitions. As previously observed
P
in Ni() trigonal bipyramidal complexes with polyfunctional
phosphines, these peaks show unusually high intensity for d–d
transitions. Their intensity has been explained taking into
account a large mixture of higher configurations by odd
crystal-field components.28b
In summary, by reacting nickel dithiolenes belonging to the
class of [Ni(R2timdt)2] complexes with the polyfunctional
phosphines tp and qp a novel desulfurisation reaction with
concomitant C–C coupling between two imidazoline rings and
production of a new class of dithiolate ligands (R4btimdt) has
been achieved. No dmit based counterpart of the R4btimdt
ligand is formed by this route, and this could be ascribed to the
different capability of the two rings adjacent to the dithiolene-
core to give C–C coupling. Imidazole rings have been shown to
be able to undergo C–C coupling easily, as reported above, in
ref. 11 by us and as observed by Rauchfuss et al. when reacting
1-methylimidazole (MeIm) to produce a methylimidazolium
Fig. 4 The Raman spectrum of a single crystal of 3.
salt of the anion C6H2N4S4Me2Ϫ 29
Further experimental and
.
theoretical work is required to explain this behaviour. The
potential of metal-dithiolene complexes to work as precursors
of sulfur-rich donors seems high in order to provide alternative
routes for synthesising new ligands, which are not easily
attained or are unobtainable by conventional routes, and
have potential interest in several fields of chemistry (material,
medicinal and coordination chemistry).
Experimental
Reagents and solvents of reagent grade quality were used
as supplied by Aldrich. The polyphosphines tp and qp were
prepared according to reference 30.
Fig. 5 Linear correlation of the totally symmetric C᎐C stretching
᎐
vibration against the charge (nϪ) for [Ni(dmit)2nϪ] (᭹), [Ni(Pri2-
timdt)(dmit)nϪ] (᭜). The peak at 1450 cmϪ1 assigned to the C᎐C
᎐
Reaction with PPh3
stretching vibration for 1 is reported in this correlation (᭿).
[Ni(Bu2timdt)2] (0.06 g; 0.1 mmol) and PPh3 (0.06 g; 0.12 mmol)
(1 : 1 molar ratio) were mixed and refluxed in THF (100 mL)
under N2 for 24 h. The colour of the reaction mixture remained
unchanged. After one day the refluxing was stopped, and, on
cooling, the reagents precipitated from the reaction mixture.
Further amounts of reagents to an almost quantitative recovery
were obtained from the filtrate by rotary-evaporation. No
reaction was also observed with other [Ni(R2timdt)2] complexes
on varying the R groups.
double negative charged dithiolene ligand is in accordance with
structural results. 1, 2 and 3 (Fig. 6) show similar electronic
spectra characterised in the visible region by the presence of
one well resolved peak (in parenthesis: ε = dm3 molϪ1 cmϪ1
,
compound) at 568 (8400, 1), 578 (8000, 2) and 557 nm (6900, 3)
and shoulders (sh) or peak at 430 (1), 416–500 (2) (sh) and 492
nm (5900, 3). In the UV-region an intense peak with a shoulder
or a broad band are observed in the 280–350 nm region
[280 (sh, ε ∼29200), 325 sh (∼25500), 1; 280 (41600), 2; 299
Reaction with dppe
[Ni(Bu2timdt)2] (0.06 g; 0.1 mmol) and dppe (0.16 g; 0.4 mmol)
(1 : 4 molar ratio) were mixed and refluxed in THF (100 mL)
under N2 for 24 h. Following the same procedure described
above, the reagents were recovered unchanged.
Synthesis of 1
[Ni(Bu2timdt)2] (0.05 g; 0.08 mmol) and an excess of tp (0.20 g;
0.3 mmol) (1 : 4 molar ratio) were mixed and refluxed in THF
‡ One low energy band derived from the transition 1EЈ
1A1 [dx
,
2
2
Ϫ y
Fig. 6 Absorption spectra of 1.0 × 10Ϫ4 mol dmϪ3 CH2Cl2 solutions of
1, 2, 3; silica cell 0.5 cm in the 230–400 nm range (suffix b) and 1.0 cm in
the 400–700 nm range (suffix a). The absorbance scale refers to 3, while
it is translated by 0.2 and 0.4 units for spectra of 2 and 3, respectively, to
avoid overlapping spectra.
dxy (eЈ)
dz2(a1Ј)] in D3h symmetry is expected. A second band
1A1 [dxz, dyz (eЉ) dz2(a1Ј)], electronically forbidden in D3h,
1EЉ
becomes allowed in C3v symmetry. These peaks are expected to be split
on going to low symmetry. In the 200–400 nm region charge-transfer
ligand-to-metal transitions are expected.
J. Chem. Soc., Dalton Trans., 2002, 1985–1991
1989

View Article Online
Table 4 Crystallographic data of compounds 1–3
[Ni(tp)(Bu4btimdt)]
(1)
[Ni(qp)(Bu4btimdt)]
(2)
[Ni(tp)(dmit)]
(3)
Compound
Chemical formula
M
Crystal system
Space group
a/Å
b/Å
c/Å
C64H69N4NiP3S4
1174.09
C76H78N4NiP4S4
1358.25
Orthorhombic
Pca21 (No. 29)
16.689(5)
23.461(5)
18.253(5)
C45H33NiP3S5
885.63
Monoclinic
P21/n (No. 14)
9.541(6)
21.873(5)
19.730(5)
Triclinic
¯
P1 (No. 2)
11.057(4)
12.973(6)
23.023(9)
78.69(2)
75.88(2)
69.89(2)
2985(2)
2
α/deg
β/deg
99.97(2)
γ/deg
V/Å3
7147(3)
4
4055(3)
4
Z
Wavelength, λ/Å
T /K
Cu-Kα(1.541838)
293(2)
28.66
Cu-Kα(1.541838)
293(2)
26.72
Cu-Kα(1.541838)
293(2)
44.70
µ/cmϪ1
Reflns collected
Ind. reflns
R[I > 2σ(I )]
wR2(all data)
11289
11289
0.0867
0.3316
7015
7015
0.0666
0.1925
7886
7665
0.0584
0.1842
(50 mL), under N2 for 24 h. The solution turned from olive-
green to purple. The solvent was removed in vacuo and by
repeated recrystallization of the crude product from CH3CN–
Et2O a complete separation of 1 from the excess of the less
soluble tp was achieved. Well-shaped shiny red–brown crystals
(0.07 g; 72% yield) of 1, suitable for X-ray studies, were
obtained. Anal. Found: C, 65.72; H 6.53; N 4.66; S 10.22; Calc.
for C64H69N4NiP3S4: C, 65.47; H 5.92; N 4.77; S 10.92%; IR
(cmϪ1): 3050w, 2960mw, 2940mw, 2860w, 1480mw, 1430m,
1405s, 1385ms, 1355mw, 1300w, 1260w, 1220m, 1115m, 1100m,
1070w, 1030w, 1000w, 940w, 770w, 740s, 695s, 680w, 670w,
620w, 545s, 530s, 510ms, 480w, 470w; Raman (cmϪ1): 1615 ms,
1575w, 1525m, 1401ms, 1420sh, 1285w, 1256w, 1100w, 1000w,
750w, 720w, 675vw, 525w, 575w, 420s, 310m; UV-Vis. [λ/nm
(ε/dm3 molϪ1 cmϪ1)]: 280 sh (∼29200), 325 sh (∼25500), 430 sh,
490sh, 568 (8400), 744 (1400), 875 (1400).
3, suitable for X-ray studies, were obtained. Anal. Found: C,
60.18; H, 3.83; N, 0.60; S, 17.97; Calc. for C45H33NiP3S5ؒ1/2
CH3CN: C, 60.97; H, 3.84; N, 0.77; S, 17.69%; IR (cmϪ1):
3051m, 2995ms, 2930ms, 2867m, 1737w, 1620w, 1479w, 1432m,
1401s, 1383ms, 1351mw, 1293w, 1253w; Raman (cmϪ1): 1453ms,
1055w, 1025w, 1000w, 901mw, 891mw, 551mw, 514s, 467w,
446w, 304w; UV-Vis. [λ/nm (ε/dm3 molϪ1 cmϪ1)]: 299 (27200),
352sh (∼16200), 492 (5900), 557 (6900).
Raman spectra
Raman spectra were carried out at room temperature on single
crystals using a LABRAM Jobin-Yvon spectrometer equipped
with an integrated microscope (BX 40, Olimpus) for micro
Raman measurements. The excitation wavelength was a He–Ne
(632.8 nm, 20 mW) laser, the laser power being reduced by
a factor 100 in order to avoid sample damage and degradation.
A 100x Objective has been used for the injection of laser line
and collection of Raman signal in back scattering configur-
ation. The laser line is removed by an holographic super notch
filter and the Raman signal is dispersed by a stigmatic 300 mm
focal length spectrometer equipped with two exchangeable
gratings. A 1800 l/mm grating was used for obtaining the
maximum in term of spectral resolution. The signal is finally
detected by a CCD 1024 × 256 pixels cooled by a TE Peltier.
The scattering peaks were calibrated against a Si standard (ν =
520 cmϪ1). No sample decomposition was observed during the
experiments.
Synthesis of 2
[Ni(Bu2timdt)2] (0.1 g; 0.5 mmol) and an excess of qp (0.536 g;
2 mmol) (1 : 4 molar ratio) were mixed and refluxed in THF
(100 mL), under Ar for 24 h. The solution turned from olive-
green to dark blue: after filtration to remove at first the excess
of qp the solvent was evaporated in vacuo and the crude prod-
uct recrystallized once from CH3CN–Et2O in freezer and twice
from CH3CN–THF at room temperature in order to achieve a
complete separation of 2 from the excess of the less soluble qp.
Well-shaped shiny dark blue crystals (0.114 g, 13% yield) of 2,
suitable for X-ray studies, were obtained. Anal. Found: C,
67.64; H, 6.32; N, 4.10; S, 8.38; Calc. for C76H78N4NiP4S4: C,
67.19; H, 5.79; N, 4.13; S, 9.45%. IR (cmϪ1) 3051m, 2995ms,
2930ms, 2867m, 1737w, 1620w, 1479w, 1432m, 1401s, 1383ms,
1351mw, 1293w, 1253w, 1213m, 1185w, 1113m, 1095m, 1048w,
1027w, 935w, 843vw, 742s, 694s, 673mw, 652vw, 544s, 526s,
509s; Raman (cmϪ1): 1623mw, 1538mw, 1405mw, 1384mw,
546w, 488w, 419s, 313m, 292mw, 244m, 238m, 159s; UV-Vis.
[λ/nm (ε/dm3 molϪ1 cmϪ1)]: 280 (41600), 416 sh, 502 sh, 578
(8000), 799 (2100).
IR spectra
IR spectra (4000–200 cmϪ1) were recorded on KBr pellets with
a Perkin Elmer mod. 983 spectrometer.
Electronic spectra
Electronic spectra were recorded at room temperature in
CH2Cl2 solutions (c = 1.0 × 10Ϫ4 mol dmϪ3) in the 200–1000 nm
range, in 0.5 and 1.0 cm silica cells with a Cary 5 Spectro-
photometer.
Synthesis of 3
Crystal structure determination
Bu4N[Ni(dmit)2]6 (0.1 g; 0.5 mmol) and an excess of tp (0.364 g;
2 mmol) (1 : 4 molar ratio) were mixed and refluxed in THF
(100 mL), under Ar for 24 h. The solution turned from olive-
green to purple: after filtration to remove at first the excess of tp
the solvent was evaporated and the crude product recrystallized
from CH3CN–THF at room temperature by standing. After 4
days well-shaped shiny dark red crystals (0.091 g, 71% yield) of
Crystal data and the most relevant parameters adopted in the
X-ray data collections and refinements are reported in Table 4.
Diffraction data were collected at room temperature on a
Enraf-Nonius CAD4 and on a Siemens AED diffractometer for
1 and 2–3 compounds, respectively. The lattice parameters were
obtained by least-squares analysis of the setting angle of 29, 30,
1990
J. Chem. Soc., Dalton Trans., 2002, 1985–1991

View Article Online
7 X. Yang, T. B. Rauchfuss and S. Wilson, J. Chem. Soc., Chem.
Commun., 1990, 34.
8 J. G. Breitzer, A. I. Smirnov, L. F. Szczepura, S. R. Wilson and
T. B. Rauchfuss, Inorg. Chem., 2001, 40, 1421.
and 32 carefully centered reflections choosed from diverse
regions of reciprocal spaces in the ranges 18–30, 19–38, and
18–40 Њ for 1–3, respectively. The check of the standard
reflections showed no significant decrease. The space groups
were choosed on the basis of the systematic extinction and of
intensity statistics. The intensities recorded by the θ–2θ scan
technique, were corrected for Lorentz and polarization factors.
An absorption correction was applied after the last isotropic
refinement cycle following the empirical method by Walker and
Stuart,31 for 3 (maximum and minimum values for the trans-
mission factors: 1.000 and 0.697); the corresponding attempts
for 1 and 2 were unsuccessful. The structures were solved using
direct methods (Sir9232) and refined by the full-matrix least-
squares on F 2 with SHELXL-97,33 first with isotropic thermal
parameters and then with anisotropic thermal parameters for
non-hydrogen atoms, excluding the carbon atoms of the butyl
groups of 1 and 2 and those of the disordered phenyl ring A of
3. The butyl groups have a large thermal motion, indicating the
presence of severe disorder. Attempts to split the carbon atoms
in “partial” atoms were unsuccessful. Rigid-body constraints
were introduced for these groups, for the phenyl rings of 2, and
for the two images of the phenyl ring A of 3 (occupancy factor:
0.6 and 0.4, respectively). All the hydrogen atoms were intro-
duced from geometrical calculations and refined using a riding
model. Compound 2 crystallizes in the space group Pca21,
however a Flack34 parameter of Ϫ0.05(3) confirms the absolute
structure.
9 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; F. Bigoli, P. Deplano, F. A. Devillanova,
J. R. Ferraro, V. Lippolis, P. J. Lukes, M. L. Mercuri, M. A.
Pellinghelli, E. F. Trogu and J. M. Williams, Inorg. Chem., 1997, 36,
1218; F. Bigoli, P. Deplano, M. L. Mercuri, M. A. Pellinghelli,
G. Pintus, E. F. Trogu, G. Zonnedda, H. H. Wang and J. M.
Williams, Inorg. Chim. Acta, 1998, 273, 175.
10 P. Deplano, M. L. Mercuri, G. Pintus and E. F. Trogu, Comments
Inorg. Chem. (A), 2001, 22, 353.
11 D. Atzei, F. Bigoli, P. Deplano, M. A. Pellinghelli and E. F. Trogu,
Phosphorus Sulfur, 1988, 37, 189.
12 A. Pani, E. Pinna, F. Scintu, G. Perra, S. Corrias, E. Trogu,
P. Deplano and P. La Colla, Anticancer Res., 1998, 18, 4429.
13 F. Bigoli, P. Deplano, M. L. Mercuri, M. A. Pellinghelli, G. Pintus
and E. F. Trogu, Chem. Commun., 1999, 2093.
14 D. J. Rauscher, E. G. Thaler, J. C. Huffmann and K. G. Caulton,
Organometallics, 1991, 10, 2209; E. G. Thaler, K. Folting and
K. G. Caulton, J. Am. Chem. Soc., 1990, 112, 2664.
15 K. Brandt and W. S. Sheldrick, Chem. Ber., 1996, 129, 1199.
16 C. Bianchini, C. Mealli, A. Meli and M. Sabat, Inorg. Chem., 1984,
23, 2731; C. Bianchini, C. A. Gilardi, A. Meli and A. Orlandini,
J. Organomet. Chem., 1985, 286, 259.
17 G. Dyer and J. Roscoe, Inorg. Chem., 1996, 35, 4098.
18 T. L. Blundell and H. M. Powell, Acta Crystallogr., Sect. B, 1971, 27,
2304.
19 M. Nardelli,
A Fortran Routine for Calculating Non-Bonded
Potential Energy, University of Parma, 1996.
The not so satisfactory values for 1 and 2 result from the bad
quality of the crystals (most of them were twinned), as well as
from the above mentioned disorder. Atomic scattering factors
and the anomalous scattering coefficients were taken from
International Tables for X-ray Crystallography35 The final
geometries were analysed by the program PARST9736 and the
drawings were made with ZORTEP.37 All calculations were
carried out on the ENCORE 91 and DIGITAL AlphaStation
255 computers of the CSSD of the C. N. R. Parma. Selected
bond lengths and angles are reported in Tables 2,3, and 4 for
1–3, respectively.
20 J.-H. Chou, T. B. Rauchfuss and L. F. Szczepura, J. Am. Chem. Soc.,
1998, 120, 1805.
21 W. P. Mayweg and G. N. Schrauzer, Chem. Commun., 1966,
640.
22 Z.-Q. Tian, J. P. Donahue and R. H. Holm, Inorg. Chem., 1995, 34,
5568; G. A. Bowmaker, P. D. W. Boyd and G. K. Campbell, Inorg.
Chem., 1983, 22, 1208; J. M. Bevilacqua, J. A. Zuleta and
R. Eisenberg, Inorg. Chem., 1994, 33, 258.
23 G. A. Bowmaker, P. D. W. Boyd and G. K. Campbell, Inorg. Chem.,
1982, 21, 2403.
24 R. Vicente, J. Ribas, X. Solans, M. Font-Altaba, A. Mari, P. De Loth
and P. Cassoux, Inorg. Chim. Acta, 1987, 132, 229.
25 P. K. Baker, M. G. B. Drew, E. E. Parker, N. Robertson and A. E.
Underhill, J. Chem. Soc., Dalton Trans., 1997, 1429.
26 K. I. Pokhodnya, C. Faulmann, I. Malfant, R. Andreu-Solano,
P. Cassoux, A. Mlayah, D. Smirnov and J. Leotin, Synth. Met., 1999,
103, 2016.
CCDC reference numbers 102390, 171252 and 171253.
See http://www.rsc.org/suppdata/dt/b1/b108471b/ for crystal-
lographic data in CIF or other electronic format.
27 F. Bigoli, P. Cassoux, P. Deplano, M. L. Mercuri, M. A. Pellinghelli,
G. Pintus, A. Serpe and E. F. Trogu, J. Chem. Soc., Dalton. Trans.,
2000, 4639.
28 (a) J. W. Dawson, T. J. McLennan, W. Robinson, A. Merle,
M. Dartiguenave, Y. Dartiguenave and H. B. Gray, J. Am. Chem.
Soc., 1974, 96, 4428; (b) M. J. Norgett, J. H. Thornley and L. M.
Venanzi, J. Chem. Soc. A, 1967, 540; (c) A. B. P. Lever, Inorganic
Electronic Spectroscopy, Elsevier Publishing Company, Amsterdam,
1968, pp. 347–349.
29 S. Al-Ahmad, B. Boje, J. Magull, T. B. Rauchfuss and Y. Zheng,
J. Am. Chem. Soc., 1995, 117, 1145.
30 B. Chiswell and L. M. Venanzi, J. Chem. Soc. A, 1966, 417 and
references therein.
Acknowledgements
The University of Cagliari is acknowledged for financial
support to this research. Thanks are due to Dr. M. Placidi,
Jobin Yvon S.r.l., for running Raman spectra and Prof. Gladiali,
University of Sassari, for helpful discussion on chirality.
References
1 P. Cassoux and L. Valade, Inorganic Materials, ed. D. W. Bruce
and D. O’Hare, John Wiley & Sons, Chichester, 1996, 2nd edn.;
H. Tanaka, Y. Okano, H. Kobayashi, W. Suzuki and A. Kobayashi,
Science, 2001, 291, 285.
2 A. T. Coomber, D. Beljonne, R. H. Friend, J. K. Brédas,
A. Charlton, N. Robertson, A. E. Underhill, M. Kurmoo and
P. Day, Nature, 1996, 380, 144.
3 U. T. Mueller-Westerhoff, B. Vance and D. I. Yoon, Tetrahedron,
1991, 47, 909.
4 C. S. Winter, C. A. S. Hill and A. E. Underhill, Appl. Phys. Lett.,
1991, 58, 107.
31 N. Walker and D. Stuart, Acta Crystallogr., Sect. A, 1983, 39, 58;
F. Ugozzoli, Comput. Chem., 1987, 11, 109.
32 A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, M. C.
Burla, G. Polidori and M. Camalli, J. Appl. Crystallogr., 1994, 27,
435.
33 G. M. Sheldrick, SHELXL-97, Program for Crystal Structure
Refinement, University of Göttingen, Göttingen, Germany,
1997.
5 N. Svenstrup and J. Becker, Synthesis, 1995, 215; P. J. Nigrey, Synth.
React. Met.-Org. Chem., 1986, 16, 1351.
6 P. Cassoux, L. Valade, H. Kobayashi, A. Kobayashi, R. H. Clark
and A. E. Underhill, Coord. Chem. Rev., 1991, 110, 115; I. Malfant,
N. Cordente, P. G. Lacroix and C. Lepetit, Chem. Mater., 1991, 10,
4079.
34 H. D. Flack, Acta Crystallogr., Sect. A, 1983, 39, 876.
35 International Tables for X-ray Crystallography, Kynoch Press,
Birmingham, England, 1974, vol. IV, pp. 99–102, 149.
36 M. Nardelli, J. Appl. Crystallogr., 1995, 28, 659.
37 L. Zsolnai and H. Pritzkow, ZORTEP, ORTEP Original Program
Modified for PC, University of Heidelberg, Germany, 1994.
J. Chem. Soc., Dalton Trans., 2002, 1985–1991
1991