Synthesis and characterisation of thiolato Schiff base nickel(n) complexes. X-Ray structures of Ni(η5-C5H5)(PPh3)(SC 6H4N=CHC6-H4Br-4′) and Ni(η5-C5</s

Article abstract of DOI:10.1039/a906949f

A series of complexes of formula Ni(η⁵-C₅H₅)(PR₃)(SC ₆H₄N=CHC₆H₄X-4′) (R = Ph, Bu; X = F, Cl, Br, CH₃, OH, H) has been isolated from the reactions of Ni(η

Full text of DOI:10.1039/a906949f

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Synthesis and characterisation of thiolato Schiff base nickel(II)
complexes. X-Ray structures of Ni(ꢀ5-C H )(PPh )(SC H N᎐CHC -
᎐
5
5
3
6
4
6
H Br-4Ј) and Ni(ꢀ5-C H )(PBu )(SC H N᎐CHC H CH -4Ј)‡
᎐
4
5
5
3
6
4
6
4
3
Funzani A. Nevondo, Andrew M. Crouch† and James Darkwa*
Department of Chemistry, University of the Western Cape, Private Bag X17, Bellville 7535,
South Africa. E-mail: jdarkwa@uwc.ac.za
Received 27th August 1999, Accepted 4th November 1999
A series of complexes of formula Ni(η5-C H )(PR )(SC H N᎐CHC H X-4Ј) (R = Ph, Bu; X = F, Cl, Br, CH , OH, H)
᎐
5
5
3
6
4
6
4
3
has been isolated from the reactions of Ni(η5-C5H5)(PPh3)Cl or the bromo derivative, the thiol Schiff base ligands,
4-HSC H N᎐CHC H X-4Ј, and triethylamine. Preliminary thermal analysis data indicate that the PBu complexes
᎐
6
4
6
4
3
could exhibit liquid crystalline behaviour. Electrochemistry of the PPh3 compounds gave irreversible redox couples,
in contrast to the quasi-reversibility of the PBu3 compounds.
Introduction
Early investigations of Schiff bases that contain imine nitrogen
and anionic sulfur ligands centred on their use as biological
models.1 These were usually metal complexes of the ligands,
formed in situ from the condensation of 2-mercaptoaniline and
a carbonyl compound in the presence of a metal ion.2 The lig-
ands bind in a bidentate fashion through the nitrogen and the
sulfur atoms. Without this in situ approach, the condensation
products of the 2-mercaptoaniline and the carbonyl compound
result in an undesirable cyclization to form heterocyclic com-
pounds;3 though the cyclized products exist in equilibrium with
a small amount of a non-cyclized thiol compound.4 Some of
the recent work on Schiff base ligands has however concen-
trated on their potential use in materials science; specifically
liquid crystals5 and non-linear optical materials.6 In such appli-
cations, it is anticipated that the presence of a metal in a com-
plex that contains a Schiff base would modify the properties
of the complex. In particular, Schiff base ligands that can
bind two metal centers as bridging ligands and posses delocal-
ised π-electrons could function as conducting materials.
Our interest in the synthesis and charaterization of nickel()
thiolato complexes7 has been extended to thiolato Schiff base
ligands. We expect, in this approach, to use these Schiff base
Chart 1
ligand complexes as building blocks for preparing compounds
that could be used as liquid crystals and conducting materials.
base ligands to form metallomesogens with that of the thiolate
Schiff base complexes that behave as metallomesogens are of
two types. The first type are complexes where the Schiff base is
bound to a metal.8 This includes a number of tetradentate
nickel Schiff base compounds9 (Chart 1). The second type are
complexes where the Schiff base ligand is attached to a ligand
bound to a metal via atoms other than the imine unit. These
latter compounds are substituted ferrocenes, with one of the
cyclopentadienyl ligands carrying the Schiff base6,10 (Chart 1).
Apart from nickel Schiff base metallomesogens, nickel thio-
lates11,12 and dithiolene13 compounds also show a range of
liquid crystalline behaviour. The dinuclear complexes, Ni2-
(S2CR)4 (R = CnH2n ϩ 1), exhibit monotropic lamellar meso-
phases when n = 4 or 8.12
ligands to synthesize nickel thiolato Schiff base complexes. The
result is the synthesis of a new class of nickel thiolato Schiff
base compounds with potential mesogenic behaviour.
Experimental
Materials and instrumentation
All solvents were dried by procedures described as previously
reported.7c All the commercially available chemicals were used
as received. The nickel starting materials, Ni(η5-C5H5)(PPh3)-
Cl,14 Ni(η5-C5H5)(PPh3)Br14 and Ni(η5-C5H5)(PBu3)Cl,15 were
prepared by the literature procedures. Infrared spectra were
recorded on a Perkin-Elmer Paragon 1000PC FT spectrometer
as Nujol mulls. The 1H, 13C and 31P NMR spectra were recorded
on a Varian Gemini 2000 and referenced to residual CHCl3 for
1H (δ 7.26), 13C (δ 77.0) and to PPh3 (δ Ϫ5.00) for 31P. Mass
spectra of ligands were recorded on a Finnigan MAT GCQ
GC/MS. The mass spectra of the metal complexes were
In this project we have combined the potential of Schiff
† Present address: Department of Chemistry, University of Stellen-
bosch, Private Bag X1, Matieland 7602, South Africa.
‡ Supplementary data available: rotatable 3-D crystal structure diagram
in CHIME format. See http://www.rsc.org/suppdata/dt/a9/a906949f/
J. Chem. Soc., Dalton Trans., 2000, 43–50
This journal is © The Royal Society of Chemistry 2000
43

View Article Online
recorded on a JEOL JMS-HX100 EBE in the FAB mode, using
nitrobenzyl alcohol as the matrix as described previously.16
Thermal analyses were performed on a Perkin-Elmer TGA-7
and a Perkin-Elmer DSC-7 at a heating rate of 10 ЊC minϪ1
under nitrogen. Elemental analyses were performed in-house
with a CARLO ERBA NA analyzer.
CHC6H5); 3.49 (s, 1H, SH). IR (Nujol mull, cmϪ1): ν(C᎐N) 1597.
᎐
MS (EI): m/z = 213 (Mϩ, 100%).
Reaction of Ni(ꢀ5-C H )(PPh )Br with 4-HSC H N᎐CHC H -
᎐
5
5
3
6
4
6
4
X-4Ј: formation of Ni(ꢀ5-C H )(PPh )(SC H N᎐CHC H X-4Ј)
᎐
5
5
3
6
4
6
4
(X ؍ F 1b, Cl 2b, Br 3b, CH3 4b, OH 5b, H 6b)
In a typical reaction a mixture of Ni(η5-C5H5)(PPh3)Br (0.63 g,
1.29 mmol) and 1a ( 0.30 g, 1.28 mmol) was degassed. Addition
of degassed toluene (75 mL), followed by Et3N (0.5 mL)
immediately changed the solution from purple to brownish-
green. After stirring for 4 h the mixture was filtered to remove
solid Et3NHBr by-product. The filtrate was concentrated to
about 20 mL; an equal volume of hexane was added and the
solution cooled at Ϫ15 ЊC to precipitate the product. Recrystal-
lization from CH2Cl2–hexane gave dark green crystalline 1b.
Yield 62%. Anal. Calc. for C36H29FNPSNi: C, 70.15; H, 4.74;
N, 2.27. Found: C, 70.08; H, 4.61; N, 2.35%. 1H NMR (CDCl3):
Electrochemical measurements
Cyclic voltammetric measurements were performed on a BAS-
C50W electrochemical analyzer at room temperature, using
sample concentrations of 10Ϫ3 M. Tetra-n-butylammonium
tetrafluoroborate was used as supporting electrolyte. A three-
electrode configuration, consisting of a platinum working
electrode a platinum wire as auxiliary electrode and Ag/AgCl
reference electrode was employed. The ferrocene/ferrocenium
couple (ϩ0.46 V vs. Ag/AgCl in CH2Cl2) was used as an
internal standard. High purity and dry dichloromethane was
used as the solvent and experiments were performed under dry
nitrogen.
δ 8.43 (s, 1H, N᎐CH); 7.86 (dd, JHH = 8.40 Hz, JHF = 5.80 Hz,
᎐
2H, SC H N᎐CHC H F-4Ј), 7.69 (m, 6H, PPh ); 7.39 (m, 11H,
᎐
6
4
6
4
PPh , SC H N᎐CHC H F-4Ј); 7.13 (t, JHH/JHF3 = 8.20 Hz, 2H,
᎐
3
6
4
6
4
SC H N᎐CHC H F-4Ј); 6.87 (d, J = 8.40 Hz, 2H, SC H N᎐
᎐
᎐
6
4
6
4
HH
6
4
CHC6H4F-4Ј); 5.14 (s, 5H, C5H5). 13C{1H} NMR (CDCl3):
Syntheses
δ 154.1 (s, N᎐CH); 144.2 (s); 132.2 (s); 131.7 (d, JCP = 42.0 Hz);
᎐
Schiff base ligands. The thioimines, 4-HSC H N᎐CHC H -
᎐
6
4
6
4
131.4 (s); 130.5 (s); 128.6 (s); 128.4 (s); 128.2 (d, JCP = 10.6 Hz);
126.4 (d, JCP = 41.0 Hz); 118.2 (s); 114.1 (s); 113.7 (s); 92.1 (s).
31P{1H} NMR (CDCl3): δ 35.38 (s, PPh3). IR (Nujol mull, cmϪ1):
X-4Ј (X = F 1a, Cl 2a, Br 3a, CH3 4a, OH 5a, H 6a), were
prepared by the following general procedure. To a solution of
4-aminothiophenol in ethanol (50 mL) was added the appropri-
ate para-substituted benzaldehyde in a 1:1 mole ratio and the
solution stirred at room temperature for 6–24 h. The initial
yellow solutions gave precipitates within 30 min, except for the
hydroxy derivative, 5a. The precipitates were isolated by suction
filtration and recrystallized from CH2Cl2–hexane. In isolating
5a, the clear solution was first evaporated to dryness and the
residue recrystallized from CH2Cl2–hexane. The yields were
generally moderate to high, 60–86%.
ν(C᎐N) 1597. MS (FAB): m/z = 615 (Mϩ, 8%).
᎐
All the PPh3 complexes were prepared and worked up in a
similar manner as described above. Their analytical data were
as reported below.
Complex 2b. Yield 66%. Anal. Calc. for C36H29ClNPSNi: C,
68.33; H, 6.20; N, 2.21. Found: C, 67.41; H, 4.48; N, 2.21%. 1H
NMR (CDCl ): δ 8.43 (s, 1H, N᎐CH); 7.81 (d, JHH = 8.40 Hz,
᎐
3
2H, SC H N᎐CHC H Cl-4Ј), 7.69 (m, 6H, PPh ); 7.38 (m, 13H,
᎐
6
4
6
4
3
Complex 1a. Yield: 63%. Anal. Calc. for C13H10FNS: C,
67.51; H, 4.36; N, 6.06. Found: C, 66.96; H, 4,41; N, 5.86%. 1H
PPh , SC H N᎐CHC H Cl-4Ј); 6.87 (d, JHH = 8.40 Hz, 2H,
᎐
3
6
4
6
4
SC H N᎐CHC H Cl-4Ј); 5.14 (s, 5H, C H ). 13C{1H} NMR
᎐
6
4
6
4
5
5
NMR (CDCl ): δ 8.41 (s, 1H, N᎐CH); 7.33 (m, 6H, SC H N᎐
᎐
᎐
3
6
4
(CDCl ): δ 156.6 (s, N᎐CH); 146.6 (s); 145.2 (s); 137.4 (s); 135.9
᎐
3
CHC6H4F-4Ј); 6.59 (d, 2H, JHH = 8.80 Hz, SC H N᎐CHC H -
᎐
6
4
6
4
F-4Ј); 3.49 (s, 1H, SH). IR (Nujol mull, cmϪ1): ν(C᎐N) 1591. MS
(s); 134.8 (s); 134.4 (d, JCP = 42.0 Hz); 134.0 (s); 133.1 (s); 130.9
(d, JCP = 9.2 Hz); 129.7 (s); 129.0 (d, JCP = 41.0 Hz); 120.9 (s);
94.7 (s). 31P{1H} NMR (CDCl3): δ 35.37 (s, PPh3). IR (Nujol
᎐
(EI): m/z = 231 (Mϩ, 100%).
Complex 2a. Yield: 71%. Anal. Calc. for C13H10ClNS: C,
mull, cmϪ1): ν(C᎐N) 1590. MS (FAB): m/z = 631 (Mϩ, 3%).
63.03; H, 4.04; N, 5.65. Found: C, 63.19; H, 3.98; N, 5.63%. 1H
᎐
NMR (CDCl ): δ 8.41 (s, 1H, N᎐CH); 7.42 (m, 6H, SC -
᎐
3
6
Complex 3b. Yield 70%. Anal. Calc. for C36H29BrNPSNi: C,
H N᎐CHC H Cl-4Ј); 6.59 (d, J = 8.80 Hz, 2H, SC H N᎐
᎐
᎐
4
6
4
HH
6
4
63.79; H, 4.31; N, 2.06. Found: C, 64.01; H, 4.27; N, 1.99%. 1H
CHC6H4Cl-4Ј); 3.49 (s, 1H, SH). IR (Nujol mull, cmϪ1): ν(C᎐N)
᎐
1591. MS (EI): m/z = 247 (Mϩ, 100%).
NMR (CDCl ): δ 8.41 (s, 1H, N᎐CH); 7.71 (m, 8H, PPh ,
᎐
3
3
SC H N᎐CHC H Br-4Ј); 7.58 (d, J = 8.40 Hz, 2H, SC H N᎐
᎐
᎐
6
4
6
4
HH
6
4
Complex 3a. Yield: 74%. Anal. Calc. for C13H10BrNS: C,
53.44; H, 3.42; N, 4.79. Found: C, 53.23; H, 3.49; N, 4.68%. 1H
CHC H Br-4Ј); 7.38 (m, 11H, PPh , SC H N᎐CHC H Cl-4Ј);
᎐
6
4
3
6
4
6
4
6.87 (d, JHH = 8.40 Hz, 2H, SC H N᎐CHC H Br-4Ј); 5.14 (s,
᎐
6
4
6
4
NMR (CDCl ): δ 8.39 (s, 1H, N᎐CH); 7.32 (m, 8H, SC H N᎐
᎐
᎐
3
6
4
5H, C5H5). 13C{1H} NMR (CDCl ): δ 156.6 (s, N᎐CH); 146.5
CHC6H4Br-4Ј); 3.49 (s, 1H, SH). IR (Nujol mull, cmϪ1): ν(C᎐N)
᎐
(s); 136.3 (s); 134.8 (s); 134.4 (d, JCP3= 42.00 Hz); 134.0 (s); 133.1
(s); 132.7 (s); 130.9 (d, JCP = 9.00 Hz); 130.6 (s); 129.0 (d,
JCP = 40.80 Hz); 125.9 (s); 120.9 (s); 94.7 (s). 31P{1H} NMR
᎐
1590. MS (EI): m/z = 293 (Mϩ, 100%).
Complex 4a. Yield: 86%. Anal. Calc. for C14H13NS: C, 74.00;
H, 5.72; N, 6.16. Found: C, 74.02; H, 6.12; N, 5.90%. 1H NMR
(CDCl3): δ 35.37 (s, PPh3). IR (Nujol mull, cmϪ1): ν(C᎐N) 1587.
᎐
(CDCl ): δ 8.39 (s, 1H, N᎐CH); 7.78 (d, JHH = 8.00 Hz, 2H,
᎐
3
SC H N᎐CHC H CH -4Ј); 7.25 (m, 4H, SC H N᎐CHC H -
᎐
᎐
6
4
6
4
6
4
6
4
CH3-4Ј); 6.58 (d, JHH3= 8.80 Hz, 2H, SC H N᎐CHC H CH -
Complex 4b. Yield 67%. Anal. Calc. for C37H32NPSNi: C,
᎐
6
4
6
4
3
72.65; H, 5.27; N, 2.28. Found: C, 73.16; H, 5.39; N, 2.25%. 1H
4Ј); 3.47 (s, 1H, SH); 2.09 (s, 3H, SC H N᎐CHC H CH -4Ј).
᎐
6
4
6
3
IR (Nujol mull, cmϪ1): ν(C᎐N) 1602. MS (EI): m/z = 4227 (Mϩ,
NMR (CDCl ): δ 8.43 (s, 1H, N᎐CH); 7.70 (m, 8H, PPh ,
᎐
3
3
᎐
SC H N᎐CHC H CH -4Ј);7.38(m,11H,PPh ,SC H N᎐CHC -
100%).
᎐
᎐
6
4
6
4
3
3
6
4
6
H4CH3-4Ј); 7.25 (d, JHH = 8.40 Hz, 2H, SC H N᎐CHC H CH -
Complex 5a. Yield: 70%. Anal. Calc. for C13H11NOS: C,
68.12; H, 4.80; N, 6.11. Found: C, 66.91; H, 5.15; N, 6.14%. 1H
NMR (d6-DMSO): δ 8.40 (s, 1H, N᎐CH); 7.50 (m, 8H, SC -
᎐
6
4
6
4
3
4Ј); 6.87 (d, JHH = 8.40 Hz, 2H, SC H N᎐CHC H CH -4Ј); 5.14
᎐
6
4
6
4
3
(s, 5H, C H ); 2.39 (s, 3H, SC H N᎐CHC H CH -4Ј). 13C{1H}
᎐
5
5
6
4
6
4
3
᎐
6
H N᎐CHC H OH-4Ј); 3.50 (s, 1H, SH). IR (Nujol mull, cmϪ1):
NMR (CDCl ): δ 157.7 (s, N᎐CH); 143.4 (s); 134.2 (s); 133.7 (d,
᎐
3
᎐
4
6
4
ν(C᎐N) 1600. MS (EI): m/z = 229 (Mϩ, 100%).
JCP = 42.40 Hz); 132.4 (s); 130.2 (d, JCP = 10.60 Hz); 129.5 (s);
128.5 (s); 128.3 (d, JCP = 40.80 Hz); 120.2 (s); 94.0 (s); 21.5 (s).
31P{1H} NMR (CDCl3): δ 35.41 (s, PPh3). IR (Nujol mull, cmϪ1):
᎐
Complex 6a. Yield: 75%. Anal. Calc. for C13H11NS: C, 73.23;
H, 5.16; N, 6.57. Found: C, 73.13; H, 5.90; N, 6.57%. 1H NMR
(CDCl ): δ 8.44 (s, 1H, N᎐CH); 7.88 (m, 2H, SC H N᎐
ν(C᎐N) 1602. MS (FAB): m/z = 611 (Mϩ, 15%).
᎐
᎐
᎐
3
6
4
CHC H ); 7.48 (m, 3H, SC H N᎐CHC H ); 7.32 (d, JHH = 8.40
᎐
6
5
6
4
6
Hz, 2H, SC H N᎐CHC H ); 7.12 (d, J 5= 8.60 Hz, SC H N᎐
Complex 5b. Yield 67%. Anal. Calc. for C36H30NOPSNi: C,
᎐
᎐
6
4
6
5
HH
6
4
44
J. Chem. Soc., Dalton Trans., 2000, 43–50

View Article Online
70.38; H, 4.92; N, 2.28. Found: C, 68.71; H, 4.68; N, 2.41%. 1H
NMR (CDCl ): δ 8.37 (s, 1H, N᎐CH); 7.69 (m, 8H, PPh ,
Table 1 Crystal data for 3b and 4c
᎐
3
3
3b
4c
SC H N᎐CHC H OH-4Ј); 7.35 (m, 11H, PPh , SC H N᎐CHC -
᎐
᎐
6
4
6
4
3
6
4
6
H4OH-4Ј); 7.25 (d, JHH = 8.40 Hz, 2H, SC H N᎐CHC H -
᎐
6
4
6
4
Formula
FW
T/K
λ/Å
Crystal system
Space group
a/Å
b/Å
C36H29BrNPSNi
677.25
296(2)
0.71073
Monoclinic
P21/n
10.833(5)
14.848(5)
19.742(9)
C31H47NPSNi
552.41
293(2)
OH-4Ј); 6.86 (dd, JHH = 8.60 Hz, JHH = 4.00 Hz, 4H, SC H N᎐
᎐
6
4
CHC6H4OH-4Ј); 5.13 (s, 5H, C5H5). 13C{1H} NMR (CDCl3):
δ 154.2 (s, N᎐CH); 136.1 (s); 136.0 (s); 132.3 (s); 131.7 (d,
᎐
0.71070
JCP = 42.40 Hz); 130.0 (s); 128.6 (s); 128.2 (s); 126.4 (d,
Triclinic
JCP = 40.80 Hz); 118.1 (s); 113.8 (s); 92.1 (s). 31P{1H} NMR
¯
P1
(CDCl3): δ 35.43 (s, PPh3). IR (Nujol mull, cmϪ1): ν(C᎐N) 1604.
10.809(1)
10.916(1)
14.430(1)
80.813(2)
73.796(2)
68.446(2)
1517.5(1)
4
1.209
0.780
592
0.21 × 0.35 × 0.28
13355/6780
᎐
MS (FAB): m/z = 613 (Mϩ, 50%).
c/Å
α/Њ
β/Њ
Complex 6b. Yield: 73%. Anal. Calc. for C36H30NPSNi: C,
72.26; H, 5.05; N, 2.34. Found: C, 72.10; H, 5.10; N, 2.35%.
1H NMR (CDCl ): δ 8.47 (s, 1H, N᎐CH); 7.83 (m, 2H,
102.899(10)
γ/Њ
V/Å3
3095.0(2)
4
1.4531
2.063
1384
0.80 × 0.54 × 0.06
17906/6929
᎐
3
Z
SC H N᎐CHC H ); 7.69 (m, 6H, PPh ); 7.39 (m, 14H, PPh ,
᎐
6
4
6
5
3
3
Dcalc/Mg mϪ3
SC H N᎐CHC H ); 6.83 (d, J = 8.40 Hz, 2H, SC H N᎐
᎐
᎐
6
4
6
5
HH
6
4
µ/mmϪ1
CHC6H5); 5.14 (s, 5H, C5H5). 13C{1H} NMR (CDCl3): δ 157.6
F(000)
(s, N᎐CH); 146.4 (s); 134.2 (s); 133.7 (d, JCP = 42.66 Hz);
᎐
Crystal size/mm
No. of reflections
collected/unique
R(int.)
Data/restraints/parameters
Final R indices [I > 2σ(I)]
133.4 (s); 132.5 (s); 132.2 (s); 130.2 (d, JCP = 10.60 Hz); 128.6
(d, JCP = 36.40 Hz); 128.3 (d, JCP = 40.00 Hz); 120 (s); 92.1 (s).
31P{1H} NMR (CDCl3): δ 35.36 (s, PPh3). IR (Nujol mull, cmϪ1):
0.045
0.044
6929/0/486
R1 = 0.0525,
wR2 = 0.1363
R1 = 0.0847,
wR2 = 0.1568
0.584, Ϫ0.462
8801/0/305
R1 = 0.0651,
wR2 = 0.1605
R1 = 0.0794,
wR2 = 0.1704
3.0, Ϫ3.1
ν(C᎐N) 1581.
᎐
Reaction of Ni(ꢀ5-C H )(PBu )Cl with 4-HSC H N᎐CHC H -
᎐
5
5
3
6
4
6
4
R indices (all data)
X-4Ј: formation of Ni(ꢀ5-C H )(PBu )(SC H N᎐CHC H X-4Ј)
᎐
5
5
3
6
4
6
4
Largest difference peak
and hole/e ÅϪ3
(X ؍ F 1c, Cl 2c, Br 3c, CH3 4c, H 6c)
To a solution of 4-HSC H N᎐CHC H F-4Ј 1a (0.35 g, 1.38
᎐
6
4
6
4
mmol) in toluene (25 mL) was added a solution of Ni(η5-
C5H5)(PBu3)Cl (0.53 g, 1.38 mmol) in toluene (25 mL) via a
pressure equalizing dropping funnel. Addition of excess Et3N
(1.0 mL) gradually changed the purple solution to brown. After
stirring the reaction mixture for 18 h, it was filtered to remove
Et3NHCl as a by-product. The solvent was removed under
reduced pressure and the residue recrystallized from CH2Cl2–
hexane and isolated as dark brown crystalline 1c. Yield 69%.
Anal. Calc. for C30H44FNPSNi: C, 64.79; H, 7.37; N, 2.52.
H4Br-4Ј); 5.27 (s, 5H, C5H5); 1.49 (m, 18H, PBu3); 0.93 (t,
JHH = 7.00 Hz, 9H, PBu3). 13C{1H} NMR (CDCl3): δ 153.8 (s,
N᎐CH); 143.7 (s); 143.2 (s); 134.7 (s); 133.3 (s); 131.7 (s); 127.7
᎐
(s); 127.3 (s); 118.3 (s); 89.9 (s); 24.3 (s); 22.5 (d, JCP = 110.60
Hz); 22.2 (d, JCP = 53.20 Hz); 11.7 (s). 31P{1H} NMR (CDCl3):
δ 22.45 (s, PBu3). IR (Nujol mull, cmϪ1): ν(C᎐N) 1592.
᎐
Complex 4c. Yield 73%. Anal. Calc. for C31H47NPSNi: C,
67.03; H, 8.53; N, 2.53. Found: C, 67.23; H, 8.60; N, 2.64%. 1H
1
Found: C, 64.02; H, 7.81; N, 2.57%. H NMR (CDCl3): δ 8.44
NMR (CDCl ): δ 8.43 (s, 1H, N᎐CH); 7.76 (d, JHH = 8.40 Hz,
᎐
3
(s, 1H, N᎐CH); 7.88 (dd, JHH = 8.80 Hz, JHF = 5.60 Hz, 2H,
᎐
2H, SC H N᎐CHC H CH -4Ј); 7.61 (d, JHH = 8.60 Hz, 2H,
᎐
6
4
6
4
3
SC H N᎐CHC H F-4Ј); 7.63 (d, J = 8.20 Hz, 2H, SC H N᎐
᎐
᎐
6
4
6
4
HH
6
4
SC H N᎐CHC H CH -4Ј);7.25(d,J = 8.00Hz,2H,SC H N᎐
᎐
᎐
6
4
6
4
3
HH
6
4
CHC6H4F-4Ј); 7.13 (t, JHF = 8.60, 2H, SC H N᎐CHC H F-4Ј);
᎐
6
4
6
4
CHC6H4CH3-4Ј); 6.95 (d, JHH = 8.40 Hz, 2H, SC H N᎐CHC -
᎐
6
4
6
6.95 (d, JHH = 8.40 Hz, 2H, SC H N᎐CHC H F-4Ј); 5.27 (s, 5H,
᎐
6
4
4
C5H5); 1.43 (m, 18H, PBu3); 0.92 (t, JHH =67.00 Hz, 9H, PBu3).
H CH -4Ј); 5.26 (s, 5H, C H ); 2.40 (s, 3H, SC H N᎐CHC -
᎐
4
3
5
5
6
4
6
13C{1H} NMR (CDCl ): δ 155.9 (s, N᎐CH), 145.9 (s); 144.7 (s);
H4CH3-4Ј); 1.47 (m, 18H, PBu3); 0.92 (t, JHH = 7.00 Hz, 9H,
᎐
3
PBu3). 13C{1H} NMR (CDCl ): δ 155.6 (s, N᎐CH); 144.5 (s);
᎐
3
133.7 (s); 133.0 (s); 130.4 (d, JCF = 86.60 Hz); 120.0 (s); 115.8 (d,
JCF = 86.60 Hz); 91.8 (s); 26.3 (s); 24.5 (d, JCP = 112.00 Hz); 21.1
(d, JCP = 53.20 Hz); 13.7 (s). 31P{1H} NMR (CDCl3): δ 22.41 (s,
142.0 (s); 139.3 (s); 132.2 (s); 131.7 (s); 127.5(s); 126.6 (s); 118.3
(s); 89.9 (s); 24.3 (s); 24.3 (s); 22.5 (d, JCP = 28.22 Hz); 22.2
(d, JCP = 13.38 Hz); 19.5 (s); 11.7 (s). 31P{1H} NMR (CDCl3):
PBu3). IR (Nujol mull, cmϪ1): ν(C᎐N) 1601.
᎐
δ 22.45 (s, PBu3). IR (Nujol mull, cmϪ1): ν(C᎐N) 1607.
᎐
Complex 2c. Yield 66%. Anal. Calc. for C30H44ClNPSNi:
C, 62.94; H, 7.16; N, 2.45. Found: C, 62.63; H, 7.51; N, 2.38%.
1H NMR (CDCl ): δ 8.44 (s, 1H, N᎐CH); 7.81 (d, JHH = 8.60
Complex 6c. Yield 70%. Anal. Calc. for C30H45NPSNi: C,
66.93; H, 7.81; N, 2.60. Found: C, 66.80; H, 8.06; N, 2.52%. 1H
᎐
3
NMR (CDCl ): δ 8.48 (s, 1H, N᎐CH); 7.86 (d, JHH = 8.40 Hz,
᎐
3
Hz, 2H, SC H N᎐CHC H Cl-4Ј); 7.63 (d, JHH = 8.40 Hz, 2H,
᎐
6
4
6
4
2H, SC H N᎐CHC H ); 7.62 (d, J = 8.60 Hz, 2H, SC H N᎐
᎐
᎐
6
4
6
HH
6
4
CHC6H5); 7.45 (t, JHH5= 7.40 Hz, 3H, SC H N᎐CHC H ); 6.96
SC H N᎐CHC H Cl-4Ј); 7.41 (d, J = 8.60 Hz, 2H, SC H N᎐
᎐
᎐
6
4
6
4
HH
6
4
᎐
6
4
6
5
CHC6H4Cl-4Ј); 6.96 (d, JHH = 8.40 Hz, 2H, SC H N᎐CHC -
᎐
6
4
6
(d, JHH = 8.60 Hz, 2H, SC H N᎐CHC H ); 5.27 (s, 5H, C H );
᎐
6
4
6
5
5
5
H4Cl-4Ј); 5.27 (s, 5H, C5H5); 1.48 (m, 18H, PBu3); 0.92 (t,
1.54 (m, 18H, PBu3); 0.92 (t, JHH = 7.20 Hz, 9H, PBu3). 31P{1H}
JHH = 7.00 Hz, 9H, PBu3). 13C{1H} NMR (CDCl3): δ 155.7 (s,
NMR (CDCl3): δ 22.41 (s, PBu3). IR (Nujol mull, cmϪ1): ν(C᎐N)
᎐
N᎐CH); 145.2 (s); 136.7 (s); 135.3 (s); 133.7 (s); 129.0 (s); 128.9
᎐
1615.
(s); 120.3 (s); 91.9 (s); 26.3 (d, JCP = 4.60 Hz); 24.2 (d,
JCP = 53.20 Hz); 22.5 (d, JCP = 110.60 Hz); 13.6 (s). 31P{1H}
Crystal structure determination of 3b
NMR (CDCl3): δ 22.43 (s, PBu3). IR (Nujol mull, cmϪ1): ν(C᎐N)
᎐
1589.
The structures of 3b and 4c were determined using a Siemens
SMART and Enraf-Nonius Kappa diffractometers respectively,
with graphite-monochromated Mo-Kα radiation (λ = 0.71073
Å). The crystal data, a summary of data collection and struc-
ture refinement are given in Table 1. The structures were solved
by the Patterson method for primary atom sites and by differ-
ence map for atoms in secondary sites.17 All non-hydrogen
atoms were refined anisotropically and hydrogen atoms were
Complex 3c. Yield 64%. Anal. Calc. for C30H44BrNPSNi:
C, 58.40; H, 6.65; N, 2.27. Found: C, 58.80; H, 6.80; N, 2.63%.
1H NMR (CDCl ): δ 8.44 (s, 1H, N᎐CH); 7.81 (d, JHH = 8.60
᎐
3
Hz, 2H, SC H N᎐CHC H Br-4Ј); 7.62 (d, JHH = 8.60 Hz, 2H,
᎐
6
4
6
4
SC H N᎐CHC H Br-4Ј); 7.42 (d, J = 8.40 Hz, 2H, SC H N᎐
᎐
᎐
6
4
6
4
HH
6
4
CHC6H4Br-4Ј); 6.96 (d, JHH = 8.40 Hz, 2H, SC H N᎐CHC -
᎐
6
4
6
J. Chem. Soc., Dalton Trans., 2000, 43–50
45

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Fig. 1 1H NMR spectra of 1c (insert) and 2c.
refined without restraints. The structures were refined by full-
matrix least-squares on F 2 and calculations by either SHELX-
TL 9517 or SHELXL 97.18 In the refinement of 4c, the scale
factor was allowed to vary by not setting a scale factor restraint.
Absorption corrections were either fitted empirically by spheri-
cal harmonic functions19 or with the SORTAV20 programme.
CCDC reference number 186/1731.
See http://www.rsc.org/suppdata/dt/a9/a906949f/ for crys-
tallographic files in .cif format.
Results and discussion
Synthesis of complexes
Scheme 2
studies of Ni(η5-C H )(PPh )(SC H N᎐CHC H Br-4Ј) con-
The condensation of 4-aminothiophenol and different para-
substituted benzaldehydes resulted in formation of thiol imines
(L) (Scheme 1), capable of functioning as monodentate ligands
via the sulfur atom.
᎐
5
5
3
6
4
6
4
firmed the products as formulated in Scheme 2.
The 1H NMR spectra of complexes where X is a halide
showed no significant chemical shift for the N᎐CH proton in
᎐
the free ligand and when complexed. A similar observation was
made by Silver et al. for the iminyl protons of Fe(η5-C5H5)-
(η5-C H CH᎐NC H Y-4Ј) and p-Me NC H CH᎐NC H Y-4Ј
᎐
᎐
5
4
6
4
2
6
4
6
4
(Y = F, Cl, Br21), where the iminyl protons have chemical shifts
ranging from 8.38–8.43 ppm. This peak was also indifferent to
the phosphine used. The observed peak values for both phos-
phine ligands were 8.43 ppm (PPh3) and 8.44 ppm (PBu3). The
1
major differences in the H NMR spectra were found for the
C5H5 ring chemical shifts. All the PPh3 compounds had essen-
tially the same chemical shift of 5.14 ppm, whilst the PBu3
compounds had chemical shifts of 5.27 ppm. We reported a
similar trend for 4-chlorothiophenolate complexes, Ni(η5-
C5H5)(PR3)(SC6H4Cl-4Ј), with the same set of phosphines.7c
This suggests that back-bonding from the Ni to PBu3 is more
extensive than to PPh3. The back-bonding reduces the electron
density on the nickel, which in turn draws electron density from
the C5H5 ring and thus de-shields its protons. Further evidence
of this is provided by the 31P NMR spectra, where the PBu3
peaks are more upfield than those of PPh3 despite the former
being a better σ-donor. The chemical shift values of ca. 35.4
ppm and ca. 22.4 ppm for all the PPh3 and PBu3 complexes
respectively point to the lack of any effect of the para-
substituents of the thiolate ligand on the 31P NMR chemical
shifts.
Scheme 1
These thiol imines had characteristic νCN stretching frequen-
cies in their infrared spectra. The nature of X, where X is a
halide, affects the stretching frequency the most when the halide
is fluorine. The more electronegative fluorine is expected to
decrease the N᎐CH double bond electron density, which should
᎐
result in a lower νCN frequency. Hence it is not clear why the
observed νCN for the fluoro compound is the highest. The
1
chemical shifts observed in the H NMR spectra appear to be
invariant for the compounds 1a–6a and show no effect of the
substituents on the ligands. However, variation of X has some
electronic influence on the electron density as shown by the
electrochemical data (Table 2), discussed later.
Each of the two phenyl groups in the thiolato ligands of the
1
The reactions of L with Ni(η5-C5H5)(PR3)Br (R = Ph, Bu),
when the ligand was deprotonated by Et3N, at room temper-
ature produced the thiolato complexes, Ni(η5-C5H5)(PR3)-
complexes exhibit a classical AAЈBBЈ spin system22 in the H
NMR spectra and the spectrum of 2c depicts this clearly
(Fig. 1). The 1H NMR spectral assignments for the C6-ring were
made by reference to the para-fluoro derivative. This is facili-
tated by the hydrogen–fluorine coupling, affording an easy way
to assign the ring protons based on the labeling in structure C.
Protons Hd and HdЈ appear as a doublet of doublets, as a result
(SC H N᎐CHC H X-4Ј) (Scheme 2). All the nickel complexes
᎐
6
4
6
4
isolated, 1a–6b, were dark-brown to dark green crystalline
solids. Spectroscopic characterization, elemental analyses, mass
spectrometry and subsequent single crystal X-ray diffraction
46
J. Chem. Soc., Dalton Trans., 2000, 43–50

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Fig. 2 (a) Crystal structure of 3b. Selected bond distances (Å) and angles (Њ) are: Ni–S(1) 2.1834(10), Ni–P 2.1447(10), Cp–Ni 1.743, C(11)–S(1)
1.766(4), C(7)–N(1) 1.261(5), C(1)–Br(1); P(1)–Ni–S(1) 91.18(4), Ni–S(1)–C(11) 112.04(13). (b) Packing diagram of 3b.
spectrometer. From thermal gravimetric analysis (TGA) (vide
infra), it could be established that 3b readily decomposed at
180 ЊC whereas the rest of the complexes decompose above this
temperature. It is therefore likely that the inability of 3b to give
a molecular ion, even in the FAB mode, could be due to thermal
decomposition.
Molecular structures of 3b and 4c
of coupling of these protons with Hc and HcЈ and with the
fluorine. Similarly, Hc and HcЈ are observed as a pseudo triplet
from the same set of coupling. Thus for all complexes the most
downfield doublets, doublet of doublets for the fluoro deriv-
atives, are peaks of the Hd and HdЈ protons whilst Hc and HcЈ are
the second most downfield peaks. By a similar argument the
upfield doublets belong to Ha and HaЈ.
When the mass spectra of compounds 1b–5b were run using
the soft FAB ionisation technique, all the compounds except 3b
showed molecular ions. However, even with the soft FAB ion-
ization technique there was considerable fragmentation. All
the compounds had fragments of m/z values of 385 and 647 as
the dominant peaks in the spectra. These were identified as
[(η5-C5H5)Ni(PPh3)]ϩ and [(η5-C5H5)Ni(PPh3)2]ϩ respectively.
The latter ion is a product of a re-arrangement in the mass
The proposed structures from the analytical data were con-
firmed by single crystal X-ray diffraction studies of 3b and 4c.
The structures are depicted in Fig. 2 and 3, with selected bond
distances and angles. Of particular note in the structure of 4c is
a high residual electron density, about 0.3 Å from the nickel.
This high residual electron density normally arises from
inadequate treatment of data for absorption. But considering
the absorption treatment applied to 4c, the high residual
electron density may be due to the quality of the crystal. The
structures are typical of the structural motifs found for Ni(η5-
C5H5)(PR3)(EC6H4Cl-4) (R = Ph, Bu; E = S, Se; X = H, Cl).7a–c
They include similarities in Cp–Ni, Ni–P and Ni–S bond dis-
tances. Comparison of the C᎐N distances of the Schiff base
᎐
ligands in 3b and 4c with the free thio Schiff base ligand, N,NЈ-
bis(4-chlorobenzylidene)-2,2Ј-diaminodiphenyldisulfide23 simi-
J. Chem. Soc., Dalton Trans., 2000, 43–50
47

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Fig. 3 (a) Crystal structure of 4c. Selected bond distances (Å) and angles (Њ) are: Ni–S(1) 2.1483(12), Ni–P 2.1351(10), Cp–Ni 1.764, C(6)–S
1.752(5), C(12)–N 1.262(7), C(16)–C(19); P–Ni–S 92.32(5), Cp–Ni–P 132.8, Cp–Ni–S 134.8, Ni–S–C(6) 110.48(17). (b) Packing diagram of 4c.
Table 2 Electrochemical data for PPh3 and PBu3 complexes
larly reveals no significant effect of the bonding interactions
with the nickel. The C᎐N bond distances in the free disulfide
᎐
ligand are 1.261(5) and 1.258(5) Å respectively,23 whilst the C᎐N
Reduction
potential/V
Oxidation
potential/V
᎐
Complex
∆E/V
distances in 3b and 4c are 1.261(5) and 1.262(7) Å respectively.
The most striking features of the structures are found in the
molecular packing [Fig. 2(b) and 3(b)]. Both have pair-wise
association of molecules in a donor (D)–π-acceptor (A) DAAD
type packing, with the cyclopentadienylnickel phosphino end
of the molecule as donor and the Schiff base ligand as the
acceptor. This DAAD type of packing is best depicted by 3b
when the packing is viewed along the a-axis [Fig. 2(b)]. From
this view the C6-ring arrangement of the thio ligand from each
molecule are 4.5–5.2 Å apart.24 In both molecules the two C6-
rings are in different planes, at right angles to each other.
Another interesting feature of the packing is the orientation of
the cyclopentadienyl rings. Again, in both molecules the cyclo-
pentadienyl rings are oriented in different directions away from
the pair-wise array of the rings. This allows the thio ligands
to pack in an almost DAAD fashion in 3b, but in 4c the
ring with the methyl substitution is bent away from the rest of
the molecule to avoid steric crowding. The DAAD structural
motif is similar to that observed in the ferrocenyl Schiff base
1b
2b
3b
4b
5b
1c
2c
3c
4c
0.197
0.208
—
0.202
0.210
0.299
0.312
0.324
0.301
0.509
0.460
0.439
0.456
0.476
0.420
0.418
0.405
0.394
0.312
0.252
—
0.254
0.266
0.121
0.106
0.081
0.093
tances of 3.478 Å. However, the inter-ring distances in 3b imply
there is no such π–π interaction.
Electrochemical studies
Cyclic voltammograms of 1b–5b and 1c–4c were measured in
CH2Cl2, with two representative voltammograms shown in Fig.
4. The results of the electrochemistry of the complexes are
summarized in Table 2. Complexes 1b–5b showed irreversible
redox behaviour, whereas 1c–4c were quasi-reversible. The
triphenylphosphine complexes had ill-defined reduction
compounds Fe(η5-C H )(η5-C H CH᎐NC H NO -4Ј).21 This
᎐
5
5
5
4
6
4
2
type of stacking normally gives rise to C6-ring π–π interactions,
which exists in the ferrocenyl compound above with ring dis-
48
J. Chem. Soc., Dalton Trans., 2000, 43–50

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Table 3 Thermal analysis of selected complexes
Weight
Temperature
Peak
valueb/ЊC kJ molϪ1
∆Hb/
Compounds
lossa (%)
rangeb/ЊC
3b
1c
2c
3c
4c
4.80, 20.78
41.18 (43.58)
11.78 (11.95)
19.31, 16.71
43.49 (43.15)
138.1–151.9
102.2–114.9
82.0–94.1
78.5–93.6
77.4–90.1
145.2
109.6
89.4
88.4
84.5
2.67
46.22
41.04
28.16
41.92
a Data from TGA (calculated weight loss in brackets). b Data from
DSC.
Fig. 5 Thermal analysis of 4c: (a) TGA and (b) DSC.
Fig. 4 Cyclic voltammograms of (a) 4b and (b) 4c.
these complexes depends on two factors. First the PPh3 com-
plex 3b had a higher onset temperature, accompanied by a low
∆H (Table 3). For the PBu3 complexes (1c–4c) the onset of
the endothermic peak was at much lower temperatures and
decreased with the electronegativity of the para-substituent.
The lowest temperature was observed for the CH3 analogue
(4c). This appears to indicate that the nickel end of the mole-
cule needs electron density on the metal, whereas the other end
is less electron rich. The high values of the endothermic peaks
could be due to heat associated with mesophase changes.25 We
are currently performing experiments to establish whether these
complexes are indeed liquid crystalline.
peaks, whereas the tributylphosphine compounds exhibited
well-defined reduction and oxidation peaks. The effect of the
phosphine ligands on the electrochemical behaviour of the
compounds was evident when triphenylphosphine was replaced
with tributylphosphine (Fig. 4). Apart from 1c–4c being easier
to oxidize, the quasi-reversibility of these compounds could be
attributed to stabilization of the electroactive species by the
more basic PBu3 as compared to PPh3. The voltammograms
also indicate that a faster transfer kinetics is operational in
complexes with the tributylphosphine ligand. The trend in the
peak potentials of the halide derivatives (Table 2) was similar
regardless of the phosphine. It appears the more electronegative
halide derivatives were more difficult to oxidize, but it is difficult
to see how these substituents could influence the ease of elec-
tron removal from the nickel centre. This trend, though, and
the rest of the redox properties are similar to that found for
Ni(η5-C5H5)(PR3)(SC6H4X-4Ј) (R = Ph, Bu; X = Cl, Br).7c
Conclusions
Schiff base nickel complexes that have the ligands bound to
the metal via a sulfur atom are readily prepared. The PBu3
complexes show the onset of endothermic peaks in their DSC
at temperatures ranging from 77.4 to 102.2 ЊC. Lower onset
temperatures are associated with complexes containing less
electron withdrawing groups in the 4Ј-position of the Schiff
base ligand. The effect of the substituent can also be seen in
the case of oxidation of the nickel centre as established
from cyclic voltammetric studies. In this regard, the compounds
with electron withdrawing substituents are more difficult to
oxidise.
Thermal properties of 1c–4c and 3b
The thermal properties of selected complexes were investigated
by thermogravimetric analysis (TGA) and by differential scan-
ning calorimetry (DSC). Their thermal behaviour is typified by
4c (Fig. 5). Table 3 shows the rest of the thermal analysis data.
All the complexes decomposed above 180 ЊC, except 3b, which
decomposed at 180 ЊC. In the TGA, decomposition was gener-
ally via the loss of the thioimine ligand (L), except for 2c and
3b. The chloro derivative, 2c, showed loss of the cyclopentadi-
enyl ligand; whereas 3b showed two successive losses of 4.80%
and 20.78% that could not be attributed to any logical fragmen-
tation sequence. The DSC data was obtained by two heating
and cooling cycles to confirm the authenticity of the data. All
complexes investigated gave endothermic peaks with ∆H values
ranging from a low of 2.67 kJ molϪ1 for 3b to a high of 46.22 kJ
molϪ1 for 1c (Table 3). The onset of the endothermic peaks in
Acknowledgements
Financial support from the National Research Foundation
(NRF), South Africa, is gratefully acknowledged. One of us
(F. A. N.) thanks the NRF and ESKOM, South Africa for
bursary support. We are grateful to Ms. Leanne Cook,
University of the Witwatersrand, South Africa and Dr John
Bacsa, University of Cape Town, South Africa, who deter-
mined the structures as a service. Finally we wish to thank Ms.
J. Chem. Soc., Dalton Trans., 2000, 43–50
49

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12 K. Ohta, H. Ema, Y. Morizumi, T. Watanabe, T. Fujimoto and
Ayesha Jacobs, University of Cape Town for the thermal anal-
ysis and Mr Tim Lesch, University of the Western Cape, for the
elemental analysis.
I. Yamamoto, Liq. Cryst., 1990, 3, 311.
13 (a) A.-M. Giroud and U. T. Müller-Westerhoff, Mol. Cryst. Liq.
Cryst., 1977, 41, 11; (b) A.-M. Giroud, Ann. Phys. (Paris), 1978,
3, 47; (c) A.-M. Giroud, A. Nazzal and U. T. Müller-Westerhoff,
Mol. Cryst. Liq. Cryst., 1980, 56, 225; (d) U. T. Müller-Westerhoff,
A. Nazzal, R. J. Cox and A.-M. Giroud, Mol. Cryst. Liq. Cryst.,
1980, 56, 249; (e) M. Cortrait, J. Gaultier, C. Polycarpe, A.-M.
Giroud and U. T. Müller-Westerhoff, Acta Crystallogr., Sect. C,
1983, 39, 833.
References
1 (a) Y. Sugiura and Y. Hirayama, Inorg. Chem., 1976, 15, 679;
(b) L. Casella, Inorg. Chem., 1984, 23, 679.
2 Y. Elerman and I. Svoboda, Acta Crystallogr., Sect. C, 1996, 52,
2705.
3 (a) R. G. Charles and H. Freiser, J. Org. Chem., 1953, 18, 422; (b)
H. Jadamus, Q. Fernando and H. Freiser, J. Am. Chem. Soc., 1964,
86, 3056; (c) Y. Sugiura, Y. Hirayama, T. Tanaka and K. Ishizu,
J. Am. Chem. Soc., 1975, 97, 5577; (d) S. Ide, S. G. Öztas, N. Ancin
and M. Tüzün, Cryst. Res. Technol., 1996, 31, 427.
4 L. F. Lindoy and S. E. Livingstone, Inorg. Chem., 1968, 7, 1149.
5 D. E. Wheeler, S. T. Hill, S. Milos, J. D. Williams and J. D. Johnson,
J. Organomet. Chem., 1997, 530, 83 and references therein.
6 W. E. Lindsell and L. Xinxin, J. Chem. Res. (S), 1998, 62 and
references therein.
14 K. W. Barnett, J. Chem. Educ., 1974, 51, 422.
15 J. Darkwa, Organometallics, 1994, 13, 4734.
16 M. S. Thomas, J. Darkwa, E. Y. Osei-Twum and L. A. Latorja, Jr.,
Polyhedron, 1999, 18, 2803.
17 G. M. Sheldrick, SHELXTL 95, Program for the Refinement of
Crystal Structures, University of Göttingen, Germany, 1995.
18 G. M. Sheldrick, SHELXTL 97, Program for the Refinement of
Crystal Structures, University of Göttingen, Germany, 1997.
19 G. M. Sheldrick, SADABS, An Empirical Absorption Correction,
private communication to subscribers of the Siemens CCD e-mail
list.
7 (a) J. Darkwa, F. Bothata and L. M. Koczon, J. Organomet. Chem.,
1993, 455, 235; (b) J. Darkwa and W. Milius, Acta Crystallogr., Sect.
C, 1996, 52, 2159; (c) J. Darkwa, R. M. Moutloali and T. Nyokong,
J. Organomet. Chem., 1998, 564, 37.
8 (a) P. Espinet, M. A. Esteruelas, L. A. Oro, J. L. Serrano and
E. Sola, Coord. Chem. Rev., 1992, 117, 215; (b) S. A. Hudson and
P. M. Maitlis, Chem. Rev., 1993, 93, 861; (c) M. Ghedini, D. Pucci,
A. Crispini and G. Baberio, Organometallics, 1999, 18, 2116;
(d) M. Lee, Y.-S. Yoo and M.-G. Choi, Macromolecules, 1999, 32,
2777.
9 R. Pache, H. Zaschke, A. Madicke. J. R. Chipperfield, A. B. Blake,
P. G. Nelson and G. W. Gray, Mol. Liq. Cryst. Lett., 1988, 6, 81.
10 J. Malthête and J. Billard, Mol. Liq. Cryst. Lett., 1976, 34, 117.
11 K. Ohta, H. Ema, I. Yamamoto and K. Matsuzaki, Liq. Cryst.,
1988, 3, 1671.
20 R. H. Blessing, J. Appl. Crystallogr., 1997, 30, 421.
21 A. Houlton, N. Jasim, R. M. G. Roberts, J. Silver, D. Cunningham,
P. McArdle and T. Higgins, J. Chem. Soc., Dalton Trans., 1992, 2235.
22 H. Freibolin, Basic one- and two-dimensional NMR spectroscopy,
VCH, New York, 2nd edn., 1993, p. 121.
23 S. Ide, S. G. Öztas, N. Ancin and M. Tüzün, Acta Crystallogr.,
Sect. C, 1997, 53, 376.
24 Inter-ring distances were determined with the program PLATON;
A. L. Spek, University of Utrecht, The Netherlands, 1995.
25 M. E. Brown, Introduction to Thermal Analysis, Techniques and
Applications, Chapman and Hall, London, 1988, p. 43.
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