Platina- and palladalactam complexes derived from 2-benzoylacetanilide; Syntheses and X-ray structure of [Pd{NPhC(O)CHC(O)Ph}(bipy)]·CH2Cl2

Article abstract of DOI:10.1016/S0020-1693(99)00190-5

Reactions of the complexes [PtCl₂(cod)] (cod=cyclo-octa-1,5-diene), cis-[PtCl₂(PPh₃)₂], and [PdCl₂(bipy)] (bipy=2,2′-bipyridine) with 2-benzoylacetanilide and excess silver(I) oxide gives metallalacta

Full text of DOI:10.1016/S0020-1693(99)00190-5

www.elsevier.nl/locate/ica
Inorganica Chimica Acta 292 (1999) 260–265
Note
Platina- and palladalactam complexes derived from
2-benzoylacetanilide; syntheses and X-ray structure of
[Pd{NPhC(O)CHC(O)Ph}(bipy)]·CH2Cl2
W. Henderson a,*, A.G. Oliver a,b, C.E.F. Rickard b, L.J. Baker b
a Department of Chemistry, Uni6ersity of Waikato, Pri6ate Bag 3105, Hamilton, New Zealand
b Department of Chemistry, Uni6ersity of Auckland, Pri6ate Bag 92019, Auckland, New Zealand
Received 27 October 1998; accepted 13 April 1999
Abstract
Reactions of the complexes [PtCl2(cod)] (cod=cyclo-octa-1,5-diene), cis-[PtCl2(PPh3)2], and [PdCl2(bipy)] (bipy=2,2%-
bipyridine) with 2-benzoylacetanilide and excess silver(I) oxide gives metallalactam complexes [M{PhNC(O)CH(COPh)}L2] in
good yields. The complexes have been characterised by NMR and IR spectroscopies, elemental analysis, and electrospray mass
spectrometry (ESMS). A single-crystal X-ray structure of the bipy palladium complex reveals the expected four-membered ring
system, which is almost planar. No evidence was observed for platinumꢀoxygen bonded products, which were a possibility based
on the result of the related system involving PhC(O)CH2C(O)CH2C(O)Ph reported in the literature, which yielded a six-membered
dienediolate platinacycle. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Crystal structures; Platinum complexes; Palladium complexes; Lactam complexes; Metallacyclic complexes
1. Introduction
metal dihalide complex with either N-cyanoacetyl-
urethane [1,2] or acetoacetanilide [3] mediated by sil-
ver(I) oxide, giving complexes 1 and 2, respectively.
Other metallacyclic systems including platinalactone 3
[4], platinaureylene 4 [5], and platinacyclobutan-3-one
We recently reported on the synthesis of a range of
metallalactam complexes of platinum(II) and palla-
dium(II) formed by the reaction of the appropriate
(h3-oxodimethylenemethane) 5 [6] complexes have also
been prepared using the same methodology. These syn-
theses are successful providing that the organic precur-
* Corresponding author. Tel.: +64-7-856 2889; fax: +64-7-838
4219.
E-mail address: w.henderson@waikato.ac.nz (W. Henderson)
0020-1693/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(99)00190-5

W. Henderson et al. / Inorganica Chimica Acta 292 (1999) 260–265
261
sor contains sufficiently acidic NH and/or CH groups,
2. Results and discussion
which can be deprotonated by silver(I) oxide, which acts
as a halide abstracting reagent and a strong base.
Following on from our studies on acetoacetanilide [3],
in this paper we report on our investigations into the
reactions of 2-benzoylacetanilide, PhC(O)CH2C-
(O)NHPh, with various platinum(II) and palladium(II)
dihalide complexes. It has previously been observed that
the reactions of MeO2CCH2C(O)CH2CO2Me (dimethyl
acetone-1,3-dicarboxylate) [6] or MeC(O)CH2C(O)CH2-
C(O)Me (heptane-2,4,6-trione) [7] with a number of
platinum(II) and platinum(0) complexes lead to platin-
um(II) oxodimethylenemethane (platinacyclobutan-3-
one) complexes of the type 5.
2.1. Syntheses and structural characterisation
The reactions of the complexes [PtCl2(cod)] (cod=cy-
clo-octa-1,5-diene), cis-[PtCl2(PPh3)2], and [PdCl2(bipy)]
(bipy=2,2%-bipyridine) with one mole equivalent of
2-benzoylacetanilide and excess silver(I) oxide in reflux-
ing dichloromethane give, after workup, the metallalac-
tam complexes 9a–c.
The complexes are isolated as white to pale yellow
(platinum) or orange (palladium) air-stable solids which
are soluble in dichloromethane and chloroform. Ligand
displacement of the cod ligand of 9a with phosphines
also provides a useful route for the syntheses of 9b and
9d, and potentially a range of other derivatives. In all
cases, the isolated products were of high purity, and
there was no indication of any isomeric products con-
taining platinumꢀoxygen bonds.
An X-ray diffraction study of the bipy palladium
complex 9c was undertaken in order to compare the
structural features with those of other metallalactam
complexes, in particular the related acetoacetanilide
palladium complex 2a. Details of the X-ray structure
determination are given in Table 1, and in Section 3.
Selected bond lengths and angles are given in Table 2.
The complex crystallises with one molecule of
dichloromethane per molecule of complex. However,
elemental microanalysis on a vacuum-dried sample
yielded results which better fit 0.5CH2Cl2 molecules of
crystallisation per molecule of complex (see Section 3).
The structure confirms the expected approximately
square-planar palladium(II) centre which is part of a
slightly puckered four-membered ring, and the struc-
tural features are similar overall to those of 1a and the
related acetoacetanilide complex 2a reported previously.
The fold angle between the N(1)ꢀPdꢀC(2) and
N(1)ꢀC(1)ꢀC(2) planes is 5.2°. The metallacycle is there-
fore comparable, but somewhat more planar than that
of complex 2a, which has a fold angle of 17.5°. The
plane of the bipy ligand is twisted slightly, by 2.60(5)°,
relative to the plane of the palladacycle.
In marked contrast, reaction with the phenyl analogue
of the above triones, PhC(O)CH2C(O)CH2C(O)Ph, does
not lead to oxodimethylenemethane complexes, but in-
stead to the six-membered ring, platinumꢀoxygen
bonded dienediolate complex 6 [7]. The phenyl groups
presumably stabilise the extensively p-delocalised sys-
tem. It was therefore of interest to examine whether
metallalactam or six-membered ring analogues would be
formed with the phenyl-rich 2-benzoylacetanilide sys-
tem; possible complexes derived from 2-benzoylac-
etanilide containing PtꢀO bonds are 7 and 8.
As expected from trans-influence considerations, the
,
PdꢀN(3) bond length (2.104(7) A) is noticeably longer

262
W. Henderson et al. / Inorganica Chimica Acta 292 (1999) 260–265
Table 1
,
than PdꢀN(2) (2.042(5) A), with N(2) being trans to a
relatively low trans-influence nitrogen, and N(3) trans
to carbon. Similar bond lengths were observed for the
acetoacetanilide complex 2a. The phenyl substituent
on N(1) is bent away from the bipy ligand, as shown
by bond angles PdꢀN(1)ꢀC(21) and C(1)ꢀN(1)ꢀC(21)
(138.3(4) and 122.9(5)°, respectively). The benzoyl
substituent on C(2) does not show this behaviour
(bond angles PdꢀC(2)ꢀC(3) 112.7(4); C(1)ꢀC(2)ꢀC(3)
121.1(5)°), presumably because the steric bulk of the
benzoyl substituent is further removed from the pal-
ladacycle, with the additional CꢀC bond. The benzoyl
and phenyl substituents lie rotated out of the palla-
dium coordination plane, presumably for steric rea-
sons.
X-ray crystallographic data for [Pd{NPhC(O)CHC(O)Ph}(bipy)]-
(9c·CH2Cl2)
Crystal data
Empirical formula
Formula weight
Crystal system
Space group
C25H19N3O2Pd·CH2Cl2
584.76
monoclinic
P21/c
10.688(3)
12.074(7)
18.480(4)
101.81(2)
2334(2)
,
a (A)
,
b (A)
,
c (A)
i (°)
3
,
V (A )
Z
4
Dc (g cm−3
)
1.644
Data collection
Diffractometer
Radiation
Wavelength (A)
Temperature (K)
Nonius CAD4
Mo Ka
0.71073
2.2. NMR spectroscopy
,
193(2)
Crystal size (mm)
0.25×0.33×0.33
ꢀ-scans
The NMR spectroscopic features are generally simi-
lar to those of other platina- and palladalactam com-
plexes reported previously [1–3]. The cod complex 9a
shows, as a result of the asymmetry of the metallacy-
cle, four inequivalent cod CH groups, and four in-
equivalent cod CH2 groups, in both the 1H and
13C{1H} NMR spectra. In the 13C{1H} spectrum, two
resonances at l 106.6 and 105.8 both show 1J(PtC)
coupling constants of 62 Hz and are assigned to CH
groups trans to the platinacyclic CH(COPh) group.
Data collection mode
q Ranges for data collection (°)
Index ranges
1.95–24.95
−125h50
05k513
−215l521
4291
4062 [R(int)=0.0299]
1.054
1176
Reflections collected
Independent reflections
Absorption coefficient (mm−1
)
F(000)
Structural analysis and refinement
Solution by
Method of refinement
direct methods
1
Resonances at l 87.9 and 86.1 show J(PtC) values of
full-matrix least-squares
based on F2
167 and 157 Hz, respectively, and are assigned to the
cod CH groups trans to NPh, based on trans-influence
considerations. Similar results were observed for the
cod platinum cyanoacetylurethane and acetoacetanilide
complexes 1a [2] and 2b [3], respectively. No conclu-
sions regarding the differing trans influences of the
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I\2|(I)]
R indices (all data)
4062/0/307
1.041
R1=0.0562, wR2=0.1420
R1=0.0850, wR2=0.1626
w=[|2(Fo2)+(0.1041P)2
+3.1952P]−1 where
P=(Fo2+2Fc2)/3
1.945, −1.620
1
NR groups could be made based on the J(PtC) val-
Largest difference peak, hole
ues.
−3
,
(e A
)
Programs used
SHELXS-86 [15] and
SHELXL-93 [16]
2.3. Electrospray mass spectrometry (ESMS)
ESMS is a relatively new, powerful technique for the
characterisation of inorganic and organometallic com-
plexes [8]. For complexes which contain basic oxygen
or nitrogen atoms, strong [M+H]+ (or [M+NH4]+)
ions are observed when low cone voltages are em-
ployed. At the low cone voltage of 20 V all metallalac-
tam complexes give strong pseudo-molecular ion peaks
[M+H]+. Excellent agreement between observed and
calculated isotope distribution patterns was observed
for all major ions. Aggregate ions of the type [2M+
H]+, [2M+NH4]+, [3M+NH4]+ etc. were also typi-
cally observed, although to variable extents. The source
of the ammonium cations is undoubtedly the acetoni-
trile mobile phase used. The aggregates for the plat-
inum-cod 9a and palladium-bipy 9c complexes were
more intense than those for the complexes containing
Table 2
,
Selected bond lengths (A) and angles (°) for [Pd{NPhC(O)CHC(O)-
Ph}(bipy)](9c·CH2Cl2) with e.s.d.s in parentheses
Bond lengths
Pd–N(1)
Pd–C(2)
N(1)–C(1)
C(1)–C(2)
2.021(5)
2.054(6)
1.324(8)
1.521(8)
Pd–N(2)
Pd–N(3)
C(1)–O(1)
C(3)–O(2)
2.042(5)
2.104(5)
1.239(8)
1.249(8)
Bond angles
N(1)–Pd–C(2)
N(1)–Pd–N(3)
C(1)–N(1)–Pd
C(21)–N(1)–Pd
67.1(2)
110.7(2)
98.0(4)
N(2)–Pd–C(2)
N(2)–Pd–N(3)
C(1)–N(1)–C(21)
N(1)–C(1)–C(2)
103.0(2)
79.2(2)
122.9(5)
104.3(5)
138.3(4)

W. Henderson et al. / Inorganica Chimica Acta 292 (1999) 260–265
263
phosphine ligands, presumably because the reduced
steric bulk of the bipy and cod ligands allows a closer
association of the metallacycles around an ammonium
ion.
10H, Ph], 5.15–5.35 [m, 2H, cod CH, J(PtH) not
2
discernible], 4.90–4.84 [m, 1H, cod CH, J(PtH) 62.5],
2
4.16–4.09 [m, 1H, cod CH, J(PtH) 59.5], 3.87 [s, 1H,
2
ring CH, J(PtH) 100], 2.70–1.90 [m, 8H, cod CH2].
2
13C{1H} NMR: l 197.3 [s, COPh, J(PtC) 51], 173.9 [s,
2
ring CO, J(PtC) 162], 144.5–124.1 [m, Ph], 106.6 [s,
1
1
3. Experimental
cod CH, J(PtC) 62], 105.8 [s, cod CH, J(PtC) 62],
1
1
87.9 [s, cod CH, J(PtC) 167], 86.1 [s, cod CH, J(PtC)
157], 40.5 [s, ring CH, J(PtC) 435], 32.3 [s, cod CH2],
1
3.1. General
30.5 [s, cod CH2], 29.3 [s, cod CH2], 28.1 [s, cod CH2].
Electrospray mass spectra were recorded in positive-
ion mode on a VG Platform II instrument using
CH3CN/H2O (1:1 v/v) as the mobile phase. Sample
delivery was by means of a SpectraSystem P1000 HPLC
pump, operating at a flow rate of 0.01 ml min−1. The
sample was introduced by means of a Rheodyne injec-
tor valve fitted with a 10 ml sample loop. Spectra were
typically an average of ten scans. Spectra were recorded
using cone voltages of 20 V while the capillary voltage
was kept constant at 3.5 kV. Identification of all major
ions was assisted by comparison of experimental and
calculated isotope distribution patterns, the latter being
obtained by use of the isotope simulation program [9].
1H and 13C{1H} NMR data were recorded in CDCl3
solution on a Bruker AC300P NMR spectrometer at
300.13 and 75.47 MHz, respectively. 31P{1H} NMR
spectra were recorded on a JEOL FX90Q NMR spec-
trometer at 36.23 MHz; samples were referenced to
external 85% H3PO4 and were recorded in CH2Cl2 with
a D2O insert for lock. IR spectra were recorded as KBr
discs on a BIO-RAD FTS-40 spectrometer. All melting
points were recorded on a Reichert Thermopan appara-
tus in air, and are uncorrected. Elemental microanaly-
ses were carried out at the University of Otago
Microanalytical Unit.
3.3. Synthesis of [Pt{PhNC(O)CHC(O)Ph}(PPh3)] (9b)
from 9a by ligand displacement
The complex [Pt{PhNC(O)CHC(O)Ph}(cod)] (9a)
(0.038 g, 0.071 mmol) and triphenylphosphine (0.039 g,
0.148 mmol) were dissolved in dichloromethane (0.5
cm3). The complex was precipitated by the addition of
light petroleum (5 cm3) and filtered yielding the product
as a light yellow solid after drying under vacuum (yield
0.066 g, 97%). M.p. 173–174°C (decomp.). IR: w(CO)
1636 cm−1 (br, s). Found: C, 64.0; H, 4.2; N, 1.5.
C51H41NO2P2Pt requires: C, 64.1; H, 4.3; N, 1.5%.
ESMS: [M+H]+ (m/z 957, 100%), [2M+H]+ (m/z
1
1914, 5%), [2M+NH4]+ (m/z 1931, 3%). H NMR: l
7.80–6.50 (m, 40H, Ph), 3.53–3.36 [dd, ring CH,
3
3
2J(PtH) 41.2, J(PH) 4.9, J(PH) 4.0]. 13C{1H} NMR:
2
3
l 201.2 [s, COPh, J(PtC) 32, J(PC) 4], 174.1 [s, ring
2
3
CO, J(PtC) 75, J(PC) 7], 144.0–123.1 (m, Ph), 45.9
2
1
[d, ring CH, J(PC) 64 J(PtC) 390]. 31P{1H} NMR:
AB spin system l 16.33 [P trans C, 1J(PtP) 2351, 2J(PP)
1
2
17], 10.00 [P trans N, J(PtP) 3733, J(PP) 17].
3.4. Preparation of [Pt{PhNC(O)CHC(O)Ph}(PPh3)2]
(9b) from cis-[PtCl2(PPh3)2]
The compounds [PtCl2(cod)] [10], [PdCl2(cod)] [11],
[PdCl2(bipy)] [12], 1,2-bis(diphenylphosphino)ethane
[13] and silver(I) oxide [14] were prepared by literature
methods. 2-Benzoylacetanilide (Aldrich) and triphenyl-
phosphine (Pressure Chemical Co.) were used as re-
ceived.
The complex cis-[PtCl2(PPh3)2] was prepared in situ
from [PtCl2(cod)] (0.065 g, 0.171 mmol) and
triphenylphosphine (0.097 g, 0.370 mmol) in
dichloromethane (10 cm3). 2-Benzoylacetanilide (0.044
g, 0.186 mmol) and silver(I) oxide (0.289 g, excess) were
added to this stirred solution with additional dichlo-
romethane (10 cm3) and the mixture refluxed for 24 h.
The mixture was filtered, the volume of the filtrate
reduced and addition of light petroleum gave a light tan
powder. This was filtered off and dried under vacuum
to give the product 9b (yield 0.118 g, 72%). The product
was identified by ESMS and 31P{1H} NMR.
3.2. Synthesis of [Pt{PhNC(O)CHC(O)Ph}(cod)] (9a)
A mixture of [PtCl2(cod)] (0.140 g, 0.375 mmol),
2-benzoylacetanilide (0.092 g, 0.385 mmol) and Ag2O
(0.266 g, excess) was refluxed in dichloromethane (20
cm3) for 18 h. The silver salts were removed by filtra-
tion, giving a light yellow solution, which was concen-
trated under reduced pressure. The pale yellow product
was precipitated by the addition of light petroleum,
filtered off and dried (yield 0.139 g, 69%). M.p. 163–
165°C (decomp.). IR: w(CO) 1663 cm−1 (vs). Found: C,
51.2; H, 4.2; N, 2.6. C23H24NO2Pt requires: C, 51.1; H,
4.5; N, 2.6%. ESMS: [M+H]+ (m/z 541, 100%),
3.5. Preparation of [Pd{NPhC(O)CHC(O)Ph}(bipy)]
(9c)
The complex [PdCl2(bipy)] (0.177 g, 0.531 mmol),
2-benzoylacetanilide (0.128 g, 0.536 mmol) and silver(I)
oxide (0.412 g, excess) in dichloromethane (20 cm3)
were refluxed for 24 h. Filtration of the silver salts
1
[2M+H]+ (m/z 1081, 16%). H NMR: l 8.1–6.9 [m,

264
W. Henderson et al. / Inorganica Chimica Acta 292 (1999) 260–265
of light petroleum (5 cm3) precipitated the product as a
tan solid, which was filtered off and dried under vac-
uum, (0.042 g, 89%). M.p. 131–133°C (decomp.). IR:
w(CO) 1632 cm−1 (br, s). Found: C, 59.4; H, 4.4; N,
1.7. C41H40NO2P2Pt requires: C, 59.4; H, 4.3; N, 1.7%.
ESMS: [M+H]+ (m/z 831, 100%), [2M+H]+ (m/z
1
1662, 24%), [2M+NH4]+ (m/z 1679, 3%). H NMR: l
8.34 (m, 30H, Ph), 3.81–3.77 [dd, 1H, ring CH, 2J(PtH)
3
3
72.0, J(PH)trans 9.1, J(PH)cis 1.9], and 2.4–1.8 (m, br,
4H, CH2, dppe). 13C{1H} NMR: l 199.3 [d, COPh,
3J(PC) 3], 174.5 [d, ring CO, J(PtC) 142, J(PC) 8],
2
3
1
146.4–123.0 (m, Ph), 44.3 [d, ring CH, J(PtC) 323,
2J(PC) 61], 31.7–28.2 (m, dppe CH2). 31P{1H} NMR:
1
AB spin system l 44.3 [P trans C, J(PtP) 2607], 35.9 [P
trans N, J(PtP) 3234].
1
3.7. X-ray diffraction study of
[Pd{PhNC(O)CHC(O)Ph}(bipy)](9c·CH2Cl2)
X-ray crystallographic data for complex 9c and the
details of the solution and refinement are summarised
in Table 1, and in the supplementary data. Preliminary
studies were performed by X-ray precession photogra-
phy, giving approximate cell dimensions and the space
group.
Fig. 1. ZORTEP diagram of the complex [Pd{NPhC(O)CHC(O)Ph}-
(bipy)](9c·CH2Cl2), showing the atom numbering scheme. Ellipsoids
are shown at the 50% probability level, the dichloromethane of
crystallisation, and all hydrogen atoms have been omitted. The inset
shows a side view of the molecule showing the slight puckering of the
palladalactam ring.
Thecomplexcrystallised withonemoleculeofdichloro-
methane in the lattice, and there appears to be
a
hydrogen-bonded network of symmetry-related
,
dichloromethane molecules [Cl(2)ꢀH(10B%) 2.829 A]. The
closest intermolecular contacts of the dichloro-
methane to the palladalactam complex are C(101)···C(12)
afforded a bright orange solution, which yielded a pale
orange microcrystalline powder upon removal of the
solvent. The product was recrystallised by liquid–liquid
diffusion of a dichloromethane/methanol (0.5:0.1 cm3)
solution layered with light petroleum (5 cm3) to give
0.210 g (78%) of 9c·CH2Cl2. Orange crystals of X-ray
crystallographic quality were thus obtained. M.p. 167–
168°C (decomp.). IR: w(CO) 1603 cm−1 (br, s). A
sample for elemental analysis was recrystallised from
dichloromethane-light petroleum and dried under
vacuum. Found: C, 56.1; H, 3.7; N, 7.8.
C25H19N3O2Pd·0.5CH2Cl2 requires: C, 56.5; H, 3.7; N,
7.8%. ESMS: [M+H]+ (m/z 500, 100%), [2M+H]+
(m/z 1001, 46%), [3M+H]+ (m/z 1500, 3%). 1H NMR:
l 9.1–7.0 (m, 18H, Ar), 5.29 (s, CH2Cl2 of crystallisa-
tion), 3.58 (s, 1H, ring CH). 13C{1H} NMR: l 201.2 (s,
COPh), 171.7 (s, ring CO), 154.8–121.9 (m, Ar), 35.9
(s, ring CH).
,
3.856, Cl(1)···O(2) 3.114 and Cl(2)···N(2) 3.175 A, none
of which represent a hydrogen bond (Fig. 1).
4. Supplementary material
Full tables of atomic coordinates, bond lengths and
angles, and thermal parameters have been deposited
with the Cambridge Crystallographic Data Centre, and
can be obtained from author W.H. on request.
Acknowledgements
We thank the Universities of Waikato and Auckland,
and the New Zealand Lottery Grants Board for finan-
cial support. We also thank Johnson Matthey plc for a
generous loan of platinum, Wendy Jackson (University
of Waikato) for technical assistance, together with
Assoc. Professor Gary Willett and Dr Keith Fisher
(University of New South Wales) for mass spectra.
A.G.O. thanks the University of Waikato for a scholar-
ship.
3.6. Preparation of [Pt{PhNC(O)CHC(O)Ph}(dppe)]
(9d) by ligand displacement from 9a
The complex [Pt{PhNC(O)CHC(O)Ph}(cod)] (9a)
(0.034 g, 0.064 mmol) and dppe (0.026 g, 0.066 mmol)
were dissolved in dichloromethane (0.5 cm3). Addition

W. Henderson et al. / Inorganica Chimica Acta 292 (1999) 260–265
265
Russell, L.J.S. Sherry, J. Chem. Soc., Dalton Trans. (1985) 549.
References
[8] (a) R. Colton, A. D’Agostino, J.C. Traeger, Mass Spectrom.
Rev. 14 (1995) 79. (b) W. Henderson, B.K. Nicholson, L.J.
McCaffrey, Polyhedron 17 (1998) 4291.
[9] L.J. Arnold, J. Chem. Educ. 69 (1992) 811.
[10] J.X. McDermott, J.F. White, G.M. Whitesides, J. Am. Chem. Soc.
98 (1976) 6521.
[11] D. Drew, J.R. Doyle, Inorg. Synth. 13 (1972) 52.
[12] B.J. McCormick, E.N. Jaynes Jr., R.I. Kaplan, Inorg. Synth. 13
(1972) 216.
[13] J. Chatt, F.A. Hart, J. Chem. Soc. (1960) 1378.
[14] H.L. Riley, H.B. Baker, J. Chem. Soc. (1926) 2510.
[15] G.M. Sheldrick, SHELXS-86, Program for solving crystal
structures, University of Go¨ttingen, Germany, 1986.
[16] G.M. Sheldrick, SHELXL-93, Program for refining crystal
structures, University of Go¨ttingen, Germany, 1993.
[1] W. Henderson, B.K. Nicholson, A.G. Oliver, Polyhedron 13 (1994)
3099.
[2] W. Henderson, B.K. Nicholson, A.G. Oliver, J. Chem. Soc., Dalton
Trans. (1994) 1831.
[3] W.Henderson,J.Fawcett,R.D.W.Kemmitt,C.Proctor,D.R.Rus-
sell, J. Chem. Soc., Dalton Trans. (1994) 3085.
[4] W. Henderson, R.D.W. Kemmitt, A.L. Davis, J. 12 Chem. Soc.,
Dalton Trans. (1993) 2247.
[5] M.B. Dinger, W. Henderson, B.K. Nicholson, A.L. Wilkins, J.
Organomet. Chem. 526 (1996) 303.
[6] R.D.W. Kemmitt, M.A. Mazid, P. McKenna, D.R. Russell, L.J.S.
Sherry, J. Chem. Soc., Dalton Trans. (1984) 1993.
[7] A. Imran, R.D.W. Kemmitt, A.J.W. Markwick, P. McKenna, D.R.
.