From platina-β-diketones to diacetylplatinum(II) complexes - Synthesis, characterization and structural features

Article abstract of DOI:10.1016/j.jorganchem.2008.04.016

The reaction of the electronically unsaturated platina-β-diketone [Pt₂{(COMe)₂H}₂(μ-Cl)₂] (1a) with N^{frown}N donors led to the formation of diacetyl(hydrido)platinum(IV) complexes [Pt(COMe)₂

Full text of DOI:10.1016/j.jorganchem.2008.04.016

Journal of Organometallic Chemistry 693 (2008) 2369–2376
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
From platina-b-diketones to diacetylplatinum(II) complexes – Synthesis,
characterization and structural features
Michael Werner a, Clemens Bruhn b, Dirk Steinborn a,
*
a Institut für Chemie – Anorganische Chemie, Martin-Luther-Universität Halle-Wittenberg Kurt-Mothes-Str. 2, D-06120 Halle, Germany
b Fachbereich 18, Naturwissenschaften, Abt. Metallorganische Chemie, Universität Kassel, Heinrich-Plett-Strasse 40, D-34132 Kassel, Germany
a r t i c l e i n f o
a b s t r a c t
The reaction of the electronically unsaturated platina-b-diketone [Pt2{(COMe)2H}2(l-Cl)2] (1a) with N_
N
Article history:
donors led to the formation of diacetyl(hydrido)platinum(IV) complexes [Pt(COMe)2Cl(H)(N_N)] (2). By
the reaction of these complexes with NaOH in a two-phase system (H2O/CH2Cl2) diacetylplatinum(II)
complexes [Pt(COMe)2(N_N)] (N_N = bpy, 4a; 4,40-Me2-bpy, 4b; 4,40-t-Bu2-bpy, 4c; 4,40-Ph2-bpy, 4d;
4,40-t-Bu2-6-n-Bu-bpy, 4e; bpym, 4f; bpyr, 4g; phen, 4h; 4-Me-phen, 4i; 5-Me-phen, 4j) were obtained.
All complexes were characterized by microanalysis, IR and 1H and 13C NMR spectroscopy. Additionally,
complexes 4a, 4c, 4d and 4e were characterized by single-crystal X-ray diffraction analysis. The observed
variety of packing patterns resulting from p–p stacking and hydrogen bonding is discussed.
Ó 2008 Elsevier B.V. All rights reserved.
Received 15 February 2008
Received in revised form 1 April 2008
Accepted 11 April 2008
Available online 16 April 2008
Keywords:
Platinum complexes
Metalla-b-diketones
Acyl complexes
X-ray diffraction analysis
p–p Stacking
Hydrogen bonding
1. Introduction
4,40-Me2-bpy; 4,40-t-Bu2-bpy) decomposed rapidly at 0 °C with
reductive elimination of methane [4].
Metalla-b-diketones are hydroxycarbene complexes being
stabilized by an intramolecular O–Hꢀ ꢀ ꢀO hydrogen bond to a neigh-
boured acyl ligand. Dinuclear platina-b-diketones [Pt2{(COR)2H}2-
(l-Cl)2] (1), synthesized from hexachloroplatinic acid and trimeth-
ylsilyl substituted alkynes, exhibit a unique reactivity due to their
electronic unsaturation and their kinetically labile ligand sphere
[1]. Thus, the platina-b-diketone 1a was found to react with a wide
variety of bidentate N_N, P_P, S_S, and N_O donors in the follow-
ing reaction sequence (Scheme 1): (i) cleavage of the Pt–Cl–Pt
bridges yielding mononuclear platina-b-diketones, (ii) oxidative
addition yielding diacetyl(hydrido)platinum(IV) complexes 2 and
(iii) reductive C–H elimination yielding acetyl(chloro)platinum(II)
complexes 3 and acetaldehyde. The course of the reactions proved
While the reductive C–H elimination of type 2 complexes
(Scheme 1, iii) is well documented, only a few type 2 complexes
were found to reductive eliminate HCl yielding diacetylplati-
num(II) complexes (Scheme 1, iv). Thus, the platina-b-diketone
1a reacted with 1,4-di-n-propyl-1,4-diazabutadiene and syn-2-
pyridinaldoxime under the formation of the requisite diacetylplat-
inum(II) complexes as the main and side product, respectively
[5,6]. Furthermore, diacetylplatinum(II) complexes with mono- or
bidentate P ligands were accessible directly from the platina-b-
diketone 1a by its reaction with NaOMe in the presence of the cor-
responding phosphine (Scheme 2) [7].
Another way to synthesize diacetylplatinum(II) complexes
was described by Klinger et al. [8]: The treatment of
to be strongly dependent on the nature of the L_L ligand. With P_
P
with CO led to the formation of [Pt(COn-
[Pt{C(O)CH2CH2CH2}(bpy)]
ligands for instance, 1a was found to react yielding complexes 3
even at temperatures <0 °C whereas with N_N ligands thermally
extraordinarily stable diacetyl(chloro)hydridoplatinum(IV) com-
plexes of type 2 were obtained [2,3]. With bipyridine and phenan-
throline ligands the reductive elimination reaction (iii) did not
proceed until 150 °C in the solid-state [2,3]. In sharp contrast, the
analogous dimethyl complexes [PtCl(H)Me2(N_N)] (N_N = bpy;
Pr)2(bpy)] in a yield of approximately 15% and a polymeric dicar-
bonyl(bipyridine)platinum(II) species (Scheme 3).
Dimethylplatinum(II) complexes bearing N_
N ligands like
bipyridine were extensively studied in their reactivity towards
oxidative addition reactions [9]. The requisite diacetyl platinum(II)
complexes let expect a different stability and reactivity because the
acetyl ligand is a much weaker r-donor than the methyl ligand and
may also act as a weak p-acceptor. Here we report on straightfor-
ward syntheses and characterization of diacetylplatinum(II) com-
plexes having bipyridine and phenanthroline coligands starting
from the platina-b-diketone 1a via diacetyl(hydrido)platinum(IV)
* Corresponding author. Tel.: +49 345 5525620; fax: +49 345 5527028.
E-mail address: dirk.steinborn@chemie.uni-halle.de (D. Steinborn).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.04.016

2370
M. Werner et al. / Journal of Organometallic Chemistry 693 (2008) 2369–2376
iii
)
L
L
COMe
Cl
Pt
− MeCHO
i)
Me
Pt
Me
Me
Pt
Me
Me
Pt
Me
COMe
3
O
O
Cl
Cl
O
O
L
L
O
O
L
L
COMe
ii)
L
L
Cl
1/2
H
H
H
Pt
Cl
H
L
L
COMe
COMe
iv
− HCl
)
1a
2
Pt
4
Scheme 1. Reactivity of the platina-b-diketone 1a towards bidentate ligands.
smoothly a reductive HCl elimination yielding diacetylplatinum(II)
complexes 4 (Scheme 4). The immediate change of colour from yel-
low to red when adding an aqueous solution of NaOH to solutions
of complexes 2 in CH2Cl2 exhibited that the reactions proceeded
within seconds at room temperature. Complexes 4a–j have been
isolated after recrystallizing from CH2Cl2/n-pentane in moderate
to good yields (60–85%). The intensive red (4a, 4d, 4e, 4f, 4g) and
orange coloured (4b, 4c, 4h, 4i, 4j) powdery complexes proved to
be air and moisture stable. To remove traces of water in the result-
ing products, the complexes 4 were dried in vacuum over P4O10 for
several days. Their identities were unambiguously confirmed by
microanalysis, NMR (1H, 13C) and IR spectroscopy. Additionally,
crystals suitable for X-ray diffraction analysis were obtained for
complexes 4a, 4c, 4d and 4e.
Me
Pt
Me
Pt
O
O
Cl
O
L
L
COMe
COMe
2 NaOMe
2 L2
2
H
H
Pt
Cl
O
Me
Me
L2 = 2 PPh3, 2 PMePh2, dppe, dppp, ...
1a
Scheme 2. Synthesis of [Pt(COMe)2L2].
O
O
n
-Pr
-Pr
N
N
N
N
CO
+ [{Pt(bpy)(CO)2}x]
Pt
Pt
CH3CN
n
O
2.2. Spectroscopic characterization
Scheme 3. Synthesis of [Pt(COPr)2(bpy)].
1H and 13C NMR spectra of complexes 4a–j are fully consistent
with the constitution of the complexes given in Scheme 4. Selected
NMR spectroscopic data are shown in Table 1. As comparison of the
NMR parameters of the diacetylplatinum(II) complexes having
substituted bipyridine ligands (4a–d) revealed, the different 4/40
substitution (H, Me, t-Bu, Ph) do not have any significant influence
on NMR parameters of the acetyl ligands. In complexes with asym-
metrically substituted N_N ligands (4e, 4i, 4j) the two acetyl
ligands are chemically inequivalent. The 6-n-butyl substituent in
4e gives rise to two sets of signals for the two acetyl signals both
in the 1H and 13C NMR spectrum. In the case of the 4- and 5-methyl
substituted phenantrolines (4i, 4j) only the chemical shifts of the
directly to platinum-bound carbon atoms differ slightly. The sig-
nals of the methyl groups (COCH3) are isochronous.
intermediate complexes (1a ? 2 ? 4; L_L = bpy, phen and deriva-
tives; Scheme 1). Depending on the coligand and cocrystallizing
solvate molecules different patterns of p–p stacking as well as dif-
ferent types of hydrogen bonds in crystals of these complexes have
been found.
2. Results and discussion
2.1. Synthesis
The dinuclear platina-b-diketone 1a was found to react with
2,20-bipyridines (bpy), 1,10-phenanthrolines (phen), 2,20-bipyrimi-
dine (bpym) and 2,20-bipyrazine (bpyr) yielding diace-
tyl(chloro)hydridoplatinum(IV) complexes 2 in good yields of
75–90% [3,10]. When reacting with NaOH in a two-phase mixture
(methylene chloride/water), complexes 2 were found to undergo
Overall, in all complexes the H and C chemical shifts of the acet-
yl ligands are in a narrow range. Even the chemical shifts of the di-
rectly platinum-bound carbon atoms differ by 6.5 ppm only. The
magnitude of 1JPt,C coupling constants of the non-substituted ‘‘par-
COMe
N
N
COMe
N
N
COMe
COMe
CH2Cl2 / NaOH (H2O)
Pt
Cl
2
Pt
− HCl
H
4a−j
R4
N
R1
R1
R3
N
N
N
N
N
N
N =
N
N
N
N
N
N
R2
4a 4b 4c
4d 4e
-Bu Ph -Bu
-Bu
4f
(bpym)
4g
(bpyr)
4h 4i 4j
R1
R2
H
H
Me
H
t
t
R3
R4
H
H
Me
H
H
H
H
n
Me
Scheme 4. Synthesis of diacetylplatinum(II) complexes 4.

M. Werner et al. / Journal of Organometallic Chemistry 693 (2008) 2369–2376
2371
Table 1
Selected NMR spectroscopic parameters of [Pt(COCH3)2(N_N)] (4a–j) (d in ppm, J in
Hz)
N_
N
CH3
Pt–C
dH (3JPt,H
)
dC (2JPt,C
)
dC (1JPt,C
)
4a
4b
4c
4d
4e
bpy
2.34 (22.7)
2.21 (23.7)
2.26 (24.3)
2.28 (23.8)
2.17 (24.4)
2.27 (20.5)
2.32 (28.0)
2.33 (27.8)
2.40 (21.2)
2.32 (25.1)
44.4 (371)
44.4 (370)
44.4 (374)
44.4 (370)
42.2 (378)
44.7 (358)
44.2 (386)
44.0 (385)
44.6 (385)
44.5 (386)
230.1 (1269)
230.6 (1265)
231.3 (1263)
230.4 (1262)
225.8 (1250)
232.8 (1244)
226.6 (1244)
226.3 (1296)
230.1 (1274)
227.7
4,40-Me2-bpy
4,40-t-Bu2-bpy
4,40-Ph2-bpy
4,40-t-Bu2-6-n-Bu-bpy
4f
bpym
bpyr
phen
4-Me-phen
4g
4h
4i
Fig. 1. Asymmetric unit of the crystal structure of [Pt(COMe)2(bpy)] ꢀ H2O
(4a ꢀ H2O). The thermal ellipsoids are drawn at a 30% probability level.
227.8
4j
5-Me-phen
2.32 (25.3)
44.5 (387)
227.2
227.8
ent” ligands was found to increase roughly parallel with the
squared LUMO coefficient at the N-atoms of the N_N ligands
[11]: 4f (N_N = bpym, 1244 Hz) <4a (N_N = bpy, 1269 Hz) ꢁ 4g
(N_N = bpyr, 1296 Hz).
According to the greater trans influence of P ligands compared
to N ligands [12] the resonances of the platinum-bound carbon
atoms of 4 are high-field shifted and the values of coupling con-
1
stants JPt,C are increased compared to diacetylplatinum(II) com-
plexes with
P
ligands (e.g. cis-[Pt(COMe)2(PPh3)2], dC (1JPt,C):
246.0 ppm (1037 Hz)) [7]. Comparison of the spectroscopic param-
eters of 4 with those of [Pt(COMe)(Cl)(N_N)] (3) showed that the
chemical shifts in 1H NMR and 13C NMR spectra are in the same
range but the coupling constants are different. Thus, the 1JPt,C cou-
pling constant in the acetyl chloro complex [Pt(COMe)Cl(bpy)]
(989 Hz) is approximately 300 Hz lower than those in complex
4a [3].
Fig. 2. Molecular structure of [Pt(COMe)2(4,40-t-Bu2-bpy)] (4c). The thermal ellip-
soids are drawn at a 30% probability level.
2.3. Structural characterization
2.3.1. General
Slow diffusion of diethyl ether into the reactions mixtures 4a,
4c and 4e led to the formation of crystals 4a ꢀ H2O, 4c and 4e ꢀ H2O
suitable for X-ray diffraction analyses. Furthermore, diffusion of
diethyl ether into a CHCl3 solution of 4d resulted in the formation
of single crystals of 4d ꢀ 1/2CHCl3. In crystals of 4a ꢀ H2O and
4d ꢀ 1/2CHCl3 two symmetry independent molecules were found.
Whereas both molecules 4d in crystals of 4d ꢀ 1/2CHCl3 exhibited
a very similar geometry, the geometric parameters for the symme-
try independent molecules 4a in crystals of 4a ꢀ H2O were found to
differ more strongly. In Fig. 1 the asymmetric unit in crystals of
4a ꢀ H2O is shown. The molecular structures of 4c, 4d ꢀ 1/2CHCl3
and 4e ꢀ H2O are shown in Figs. 2–4. Selected bond lengths and an-
gles are collected in Table 2.
Fig. 3. Molecular structure of [Pt(COMe)2(4,40-Ph2-bpy)] (4d) in crystals of 4d ꢀ 1/2
CHCl3. The thermal ellipsoids are drawn at a 30% probability level.
In all four complexes the platinum atoms showed a square-pla-
nar geometry having coordinated the chelating N_N ligand and
two acetyl ligands. Inspection of the angles between the mean
planes of the two halfs of the bipyridine ligands exhibited a
remarkable twist of the bpy ligands in complexes 4c (10.5(3)°)
and 4e ꢀ H2O (12.3(4)°). Furthermore, only in complex 4d ꢀ 1/2
CHCl3 was found a coplanarity in good approximation between
the mean bipyridine plane and the mean complex plane (interpla-
nar angle: 2.1(5)/2.9(5)°). The acetyl ligands form angles with the
complex planes between 32(1) and 87(1)°. Noteworthy, there were
found two different arrangements: While in the complexes 4a and
4c the carbonyl oxygen atoms of the two acetyl ligands are orien-
tated on the same side of the complex plane (‘‘cisoid” conforma-
tion), they are on different sides of the complex plane in
complexes 4d and 4e (‘‘transoid” conformation).
While the Pt–C-bond lengths (1.986(9)–2.040(6) Å) are in the
range of other structurally characterized acylplatinum(II) com-
plexes (median: 2.023 Å; lower/upper quartile 1.990/2.052 Å;
number of observations n = 72 [13]) the C@O bond lengths
(1.169(8)–1.26(1) Å) show a higher diversity (median: 1.220 Å;
lower/upper quartile 1.193/1.235 Å; n = 72 [13]). All C@O bonds
in 4a (1.21(1)–1.23(1) Å) fall in this range whereas in the other
complexes rather short (1.169(8) Å) and long (1.26(1) Å) C@O
bonds were also found.

2372
M. Werner et al. / Journal of Organometallic Chemistry 693 (2008) 2369–2376
Table 3
Distances of the planes a (in Å), Cgꢀ ꢀ ꢀCg distances b (in Å), interplanar angles c (in °)
and angles between Cg–Cg vector and plane normal a (in °; see Fig. 5) for the p–p
stackings in the structures of complexes 4
a
b
a
c
[Pt(COMe)2(bpy)] ꢀ H2O (4a ꢀ H2O)a
A
B
C
3.40/3.40
3.37
3.72/3.69
3.65
24.1/22.7
22.4
15.6
5.2/2.2
1.8
2.2
3.47
3.60
[Pt(COMe)2(4,40-t-Bu2-bpy)] (4c)
3.38
3.79
28.3
10.5
3.6/5.4
[Pt(COMe)2(4,40-Ph2-bpy)] ꢀ 1/2CHCl3 (4d ꢀ 1/2CHCl3)
3.38/3.39
3.78/3.81
26.9/27.3
a
Due to symmetry, types B and C stacking result in just one set of parameters
Fig. 4. Molecular structure of [Pt(COMe)2(4,40-t-Bu2-6-n-Bu-bpy)] (4e) in crystals of
4e ꢀ H2O. The thermal ellipsoids are drawn at a 30% probability level.
whereas in type A stacking two sets were found.
Table 2
Selected bond length (in Å), bond angles (in °) and interplanar angles c (in °)
4a ꢀ H2Oa
4c
4d ꢀ 1/2CHCl3
4e ꢀ H2O
a
Pt1–C1
Pt1–C2
C1–O1
C2–O2
C1–Pt1–C2
C2–Pt1–N1
N1–Pt1–N2
N2–Pt1–C1
c(coord/MeC1@O1)
c(coord/MeC2@O2)
1.99(1)/1.986(9)
1.991(8)/2.011(9)
1.22(1)/1.21(1)
1.22(1)/1.23(1)
91.7(4)/88.2(4)
95.6(3)/97.8(3)
76.9(3)/77.0(3)
95.9(4)/96.7(3)
54.3(9)/84(0)
1.998(6)
2.040(6)
1.187(9)
1.169(8)
88.8(2)
97.2(2)
76.2(2)
98.1(2)
55.5(8)
83.9(7)
2.04(1)/2.09(1)
1.99(1)/1.99(1)
1.19(1)/1.17(1)
1.26(1)/1.24(1)
89.5(4)/89.6(4)
95.4(4)/96.1(4)
76.6(3)/76.5(3)
98.6(3)/98.0(3)
38(1)/32(1)
1.99(1)
1.95(1)
1.23(1)
1.26(1)
82.2(4)
93.6(3)
76.5(3)
107.5(3)
79.3(9)
87(1)
78.2(9)/74(1)
88(1)/86(1)
a
Values for the two symmetry independent molecules are separated by a slash.
Fig. 6. Packing mode of [Pt(COMe)2(bpy)] (4a) in crystals of 4a ꢀ H2O. Hydrogen
atoms are omitted for clarity.
interplanar angle c. These four parameters are listed in Table 3
for the relevant p–p interactions in the structures of 4a ꢀ H2O, 4c
and 4d ꢀ 1/2CHCl3.
Fig. 5. Characteristic parameters of p–p stacking.
2.3.2. p–p stacking
In crystals of 4a ꢀ H2O three different types of p–p stacking were
found (Fig. 6, Table 3): Type A (see also Fig. 1) between two sym-
metry independent molecules, type B between two identical mol-
ecules that are not involved in hydrogen bonds and type C
between two identical molecules that are involved in hydrogen
bonds. Thus, the stacking mode can be described as ABACABAC. . .
The parameters of the p–p stacking modes A, B and C in 4a ꢀ H2O
are in the usual range of p–p stacking.
In all four structures the packing of molecules in crystals can be
rationalized in terms of p–p stacking and/or of the formation of
hydrogen bonds. To describe p–p stacking in accord to Ref. [14]
the following parameters have to be considered: the length of
the ring normal of one ring to the plane formed by the other ring
(a, Fig. 5), the centroid–centroid-distance (b), the angle between
the ring normal and the centroid–centroid-vector (a), and the
Fig. 7. Asymmetric units of the crystal structures of 4c (A) and 4d ꢀ 1/2CHCl3 (B).

M. Werner et al. / Journal of Organometallic Chemistry 693 (2008) 2369–2376
2373
Table 4
in water (e.g. H2O: Oꢀ ꢀ ꢀO 2.75–2.92 Å [15]) and between water and
ketones (Oꢀ ꢀ ꢀO 2.823(2) Å, [16]), respectively.
Characteristic parameters of the C–Hꢀ ꢀ ꢀO und O–Hꢀ ꢀ ꢀO hydrogen bonds (distances in
Å; angles in °) in the structures of complexes 4
In the crystals of 4d ꢀ 1/2CHCl3 the solvate molecules act as H
donors and the acetyl ligands as H acceptors in C–Hꢀ ꢀ ꢀO hydrogen
bonds (Fig. 7, B, Table 4). The Cꢀ ꢀ ꢀO distance (3.17(1) Å) is charac-
teristic for analogous hydrogen bonds formed between ketones
and chloroform (mean Cꢀ ꢀ ꢀO distance 3.18 [16]).
[Pt(COMe)2(bpy)] ꢀ H2O (4a ꢀ H2O)
C–Hꢀ ꢀ ꢀO:
O–Hꢀ ꢀ ꢀO:
C3ꢀ ꢀ ꢀO1
3.137(9)
2.789(9)
2.743(9)
2.77(1)
O1ꢀ ꢀ ꢀH
2.39
2.43
C3–Hꢀ ꢀ ꢀO1
C3–Hꢀ ꢀ ꢀO1
135
136
a
O1ꢀ ꢀ ꢀO5 (D)
O2ꢀ ꢀ ꢀO6 (D)
O5ꢀ ꢀ ꢀO60 (E)
a
a
In crystals of [Pt(COMe)2(4,40-t-Bu2-6-n-Bu-bpy)] ꢀ H2O (4e ꢀ
H2O) the water molecules act as H donors and acetyl O atoms as
H acceptors (C1@O1ꢀ ꢀ ꢀH–O3–Hꢀ ꢀ ꢀO20@C20) thus connecting two
neighboured molecules 4e (Fig. 4, Table 4). The Oꢀ ꢀ ꢀO distances
(2.81(1)/2.83(1) Å) are in the expected range for hydrogen bonds
between water and ketones (Oꢀ ꢀ ꢀO 2.823(2) Å, [16]). 4e ꢀ H2O crys-
tallizes in the chiral space group P62. Thus, along the crystallo-
graphic c-axis a helical structure results in which the molecules
of 4e are connected through these hydrogen bonds (Fig. 8).
Furthermore, additionally to all these hydrogen bonds in which
solvate molecules are involved, intramolecular C–Hꢀ ꢀ ꢀO hydrogen
bonds having aromatic C–H groups as donors and acetyl O atoms
as acceptors were found. Most likely, these hydrogen bonds
(C3–Hꢀ ꢀ ꢀO1) in the structures of 4a ꢀ H2O, 4c and 4d ꢀ 1/2CHCl3
(Figs. 1–3) give rise to a decrease of the interplanar angle between
the acetyl ligand involved (MeC1@O1) and the complex plane by
20–50°. The geometrical parameters of these C3–Hꢀ ꢀ ꢀO1 hydrogen
bonds are in the expected range [16,17].
[Pt(COMe)2(4,40-t-Bu2-bpy)] (4c)
C–Hꢀ ꢀ ꢀO: C3ꢀ ꢀ ꢀO1 3.180(9)
O1ꢀ ꢀ ꢀH
[Pt(COMe)2(4,40-Ph2-bpy)] ꢀ 1/2CHCl3 (4d ꢀ 1/2CHCl3)
C–Hꢀ ꢀ ꢀO:
C3ꢀ ꢀ ꢀO1
C8ꢀ ꢀ ꢀO3
C13ꢀ ꢀ ꢀO4
3.06(1)
3.02(1)
3.17(1)
O1ꢀ ꢀ ꢀH
O3ꢀ ꢀ ꢀH
O4ꢀ ꢀ ꢀH
2.34
2.29
2.20
C3–Hꢀ ꢀ ꢀO1
C8–Hꢀ ꢀ ꢀO3
C13–Hꢀ ꢀ ꢀO4
133
133
163
[Pt(COMe)2(4,40-t-Bu2-6-n-Bu-bpy)] ꢀ H2O (4e ꢀ H2O)
O–Hꢀ ꢀ ꢀO:
O1ꢀ ꢀ ꢀO30
O2ꢀ ꢀ ꢀO3
2.81(1)
2.83(1)
a
The hydrogen atoms of the water molecules were not included in the solution of
the crystal structure.
Complexes 4c and 4d ꢀ 1/2CHCl3 are packed pairwise via p–p
stacking (Fig. 7). Inspection of the angles a (Table 3) reveals a rel-
atively strong shift (26.9–28.3°) likely due to the bulky tert-butyl
substituents in 4c and the phenyl groups in 4d ꢀ 1/2CHCl3,
respectively.
Further p–p interactions in 4d ꢀ 1/2CHCl3 with centroid–plane
distances of 3.69–3.78 Å, centroid–centroid distances of
4.08–4.45 Å and interplanar angles of 5.8–17.5° are found leading
to a complex packing. In crystals of 4e p–p stacking is not observed
at all.
2.4. Conclusion
Reactions of the dinuclear platina-b-diketone 1 with chelating
N_N donors resulting in an oxidative C–H addition followed by a
reductive H–Cl elimination induced by OHꢂ proved to be a
straightforward synthesis for diacetylplatinum(II) complexes hav-
ing N_N coligands in a wide variety (4a–4j). As the ‘‘parent”
methyl complexes of this type, [PtMe2(N_N)] (5), complexes 4
proved to be thermally stable and air-stable. Due to the higher
electron density on platinum centre, complexes 5 were found to
undergo oxidative addition reactions more readily than complexes
4 [18].
2.3.3. Hydrogen bonds
Complexes 4a, 4d and 4e were found to crystallize with solvent
molecules (H2O, CHCl3) giving rise to the formation of O–Hꢀ ꢀ ꢀO and
C–Hꢀ ꢀ ꢀO hydrogen bonds, respectively (Table 4). In complex
4a ꢀ H2O two water molecules are connected through a hydrogen
bond (Fig. 6, E; Oꢀ ꢀ ꢀO 2.77(1) Å) and each of them acts as a hydro-
gen donor to an O atom of an acetyl ligand (Fig. 6, D; Oꢀ ꢀ ꢀO
2.743(9)/2.789(9) Å). These hydrogen bonds link the columns
formed by p–p stacking (Fig. 6). The Oꢀ ꢀ ꢀO distances of type D
and E hydrogen bonds are typically for analogous hydrogen bonds
In the crystal structures of type 5 complexes, [PtMe2(N_N)], the
packing of the molecules is mainly dominated by p–p stacking of
Fig. 8. (A) One strand of the double helix in the crystals of [Pt(COMe)2(4,40-t-Bu2-6-n-Bu-bpy)] ꢀ H2O (4e ꢀ H2O). The hydrogen atoms are omitted for clarity. (B) View along
the crystallographic c-axis.

2374
M. Werner et al. / Journal of Organometallic Chemistry 693 (2008) 2369–2376
the aromatic ring systems [19]. Additionally to p–p stacking in type
4 complexes the formation of hydrogen bonds was found to be a
structure giving motif. This might be caused by the ability of the
oxygen atoms of the acetyl ligands to act as hydrogen bond
acceptors.
3.3.2. [Pt(COMe)2(4,40-Me2-bpy)] (4b)
Yield: 165 mg (80%). Anal. Calc. for C16H18N2O2Pt (465.4 g/mol):
C, 41.29; H, 3.90; N, 6.02. Found: C, 41.15; H, 4.05; N, 6.06%. 1H
3
NMR (CDCl3, 400 MHz) d 2.21 (s + d, JPt,H = 23.7 Hz, 6H, COCH3),
2.39 (s, 6H, bpy-CH3), 7.15 (m, 2H, H5,50 of bpy), 7.79 (m, 2H,
H3,30 of bpy), 8.83 (m, 2H, H6,60 of bpy). 13C NMR (CDCl3,
2
400 MHz) d 21.6 (s, bpy-CH3), 44.4 (s + d, JPt,C = 370 Hz, COCH3),
122.9 (s, C3,30 of bpy), 127.1 (s, C5,50 of bpy), 150.0 (s, C4,40 of
bpy), 150.7 (s, C6,60 of bpy), 154.6 (s, C2,20 of bpy), 230.6 (s + d,
3JPt,C = 1265 Hz, Pt–C). IR: m (cmꢂ1) 3066(w), 2962(w), 2886(w),
1614(s), 1590(s), 1485(w), 1442(m), 1413(m), 1334(w), 1243(w),
1107(m), 1088(m), 1024(w), 924(w), 831(m), 606(w).
3. Experimental
3.1. General comments
All reactions were performed under an argon atmosphere using
the standard Schlenk techniques. Solvents were dried (Et2O over
Na/benzophenone, CH2Cl2 over CaH2) and distilled prior to use.
NMR spectra were recorded on Varian spectrometers Gemini 200,
VXR 400 and Unity 500 operating at 200, 400 and 500 MHz for
1H, respectively. Solvent signals (1H, 13C) were used as internal ref-
erences. When necessary, assignments were revealed by running
1H–1H and 1H–13C COSY NMR experiments. IR spectra were re-
corded on a Galaxy Mattson 5000 FT-IR spectrometer using KBr
pellets. Microanalyses were performed by the University of Halle
microanalytical laboratory using CHNS-932 (LECO) and Vario EL
(Elementaranalysensysteme) elemental analysers. The complex
[Pt2{(COMe)2H}2(l-Cl)2] (1a) was prepared according to a pub-
lished method [2].
3.3.3. [Pt(COMe)2(4,40-t-Bu2-bpy)] (4c)
Yield: 180 mg (70%). Anal. Calc. for C22H30N2O2Pt (549.6 g/mol):
C, 48.08; H, 5.50; N, 5.10. Found: C, 48.51; H, 5.83; N, 5.19%. 1H
NMR (400 MHz, CDCl3) d 1.34 (s, 18H, C(CH3)3), 2.26 (s + d,
3JPt,H = 24.3 Hz, 6H, COCH3), 7.43 (m, 2H, H5,50 of bpy), 7.89 (m,
2H, H3,30 of bpy), 8.62 (m, 2H, H6,60 of bpy). 13C NMR (100 MHz,
CDCl3)
d 30.1 (s, C(CH3)3), 35.4 (s, C(CH3)3), 44.4 (s + d,
2JPt,C = 374 Hz, COCH3), 118.5 (s, C3,30 of bpy), 123.8 (s, C5,50 of
bpy), 150.5 (s, C6,60 of bpy), 155.1 (s, C2,20 of bpy), 163.5 (s, C4,40
of bpy), 231.3 (s + d, JPt,C = 1263 Hz, Pt–C). IR: m (cmꢂ1) 3074(w),
3
2962(m), 2906(m), 2870(w), 1618(s), 1591(s), 1481(m), 1465(m),
1411(m), 1365(w), 1324(w), 1252(w), 1103(m), 1020(w), 928(w),
900(w), 876(w), 841(w), 605(w).
3.2. Synthesis of [Pt(COMe)2Cl(H)(N_N)] (2a–j)
3.3.4. [Pt(COMe)2(4,40-Ph2-bpy)] (4d)
According to Ref. [3], complexes 2a–j were prepared by the
addition of the corresponding N_N ligand (0.32 mmol) to a solu-
tion of 1a (100 mg, 0.16 mmol) in CH2Cl2 (10 ml) at ꢂ78 °C. After
stirring for 30 min at this temperature, the solution was warmed
to 0 °C and stirred for additional 30 min. Then, the solvent was
removed under reduced pressure. The residue was dissolved in
CH2Cl2 (ca. 2 ml) and Et2O (ca. 5 ml) was added. The precipitate
formed was filtered, washed with Et2O (2 ꢃ 2 ml) and dried in
vacuum.
Yield: 240 mg (85%). Anal. Calc. for C26H22N2O2Pt (589.5 g/mol):
C, 52.87; H, 3.76; N, 4.75. Found: C, 52.45; H, 3.62; N, 4.82%. 1H
3
NMR (400 MHz, CDCl3) d 2.28 (s + d, JPt,H = 23.8 Hz, 6H, COCH3),
7.52 (m, 6H, p-Ph, o-Ph), 7.60 (m, 2H, H5,50 of bpy), 7.70 (m, 4H,
m-Ph), 8.28 (m, 2H, H3,30 of bpy), 8.74 (m, 2H, H6,60 of bpy). 13C
2
NMR (100 MHz, CDCl3) d 44.4 (s + d, JPt,C = 370 Hz, COCH3), 120.0
(s, C3,30 of bpy), 124.4 (s, C5,50 of bpy), 127.1 (s, m-Ph), 129.6 (s,
o-Ph), 130.5 (s, p-Ph), 136.3 (s, C4,40 of bpy), 151.2 (s, i-Ph), 151.4
(s, C6,60 of bpy), 155.5 (s, C2,20 of bpy), 230.4 (s + d, 3JPt,C = 1262 Hz,
Pt–C). IR: m (cmꢂ1) 3055(w), 2975(w), 1662(w), 1610(s), 1581(s),
1544(w), 1475(w), 1408(m), 1331(w), 1100(m), 1089(m),
1016(w), 926(w), 849(w), 761(m), 695(m), 627(w), 592(w).
Yield: 70–90%. The identities of the products were confirmed by
comparison with 1H NMR data given in Ref. [3].
3.3. Synthesis of [Pt(COMe)2(N_N)] (4a–j)
3.3.5. [Pt(COMe)2(4,40-t-Bu2-6-n-Bu-bpy)] (4e)
To a solution of [Pt(COMe)2Cl(H)(N_N)] (2) (0.1 mmol) in
CH2Cl2 (20 ml) an aqueous solution of NaOH (20 mg in 10 ml)
was added. After vigorously stirring for approximately 30 min
the colour of the organic layer became red. The phases were sep-
arated and the aqueous phase was extracted with CH2Cl2
(2 ꢃ 10 ml). The combined organic extracts were dried with
NaSO4, filtered and the solvent was removed under reduced
pressure. The residue was dissolved in CH2Cl2 (ca. 2 ml) and n-pen-
tane (ca. 5 ml) was added. The precipitate obtained was filtered,
washed with n-pentane (2 ꢃ 2 ml) and dried in vacuum over
Yield: 175 mg (60%). Anal. Calc. for C26H38N2O2Pt (605.7 g/
mol): C, 51.56; H, 6.32; N, 4.63. Found: C, 50.98; H, 6.09; N,
4.91%. 1H NMR (200 MHz, CDCl3) d 0.81 (t, 3H, CH2CH3), 1.23
(m, 2H, CH2CH3),1.28 (s, 18H, C(CH3)3), 1.54 (m, 2H, CH2CH2CH3),
3
3
2.17 (s + d, JPt,H = 24.4 Hz, 3H, COCH3), 2.27 (s + d, JPt,H = 20.5 Hz,
3H, COCH3), 2,74 (m, 2H, bpy-CH2), 7.27 (m, 2H, H5,50 of bpy),
7.71 + 7.79 (m, 2H, H3,30 of bpy), 8.46 (m, 1H, H60 of bpy). 13C
NMR (125 MHz, CDCl3) d 13.8 (s, CH2CH3), 22.0 (s, CH2CH3),
30.1 (s, C(CH3)3), 31.9 (s, CH2CH2CH3), 35.1 + 35.4 (s, C(CH3)3),
2
39.9 (s, bpy-CH2), 42.2 (s + d, JPt,C = 378 Hz, COCH3), 44.7 (s + d,
2JPt,C = 358 Hz, COCH3), 116.5 + 119.3 (s, C3,30 of bpy),
122.7 + 123.2 (s, C5,50 of bpy), 149.5 (s, C60 of bpy),
155.5 + 156.3 (s, C2,20 of bpy), 163.1 + 163.2 (s, C4,40 of bpy),
P4O10
.
3.3.1. [Pt(COMe)2(bpy)] (4a)
3
Yield: 175 mg (85%). Anal. Calc. for C14H14N2O2Pt (437.4 g/mol):
C, 38.44; H, 3.23; N, 6.41. Found: C, 38.20; H, 3.01; N, 6.32%. 1H NMR
(CDCl3, 400 MHz): d 2.34 (s + d, 3JPt,H = 22.7 Hz, 6H, COCH3), 7.54 (m,
2H, H5/50 of bpy), 8.04 (m, 4H, H3/30, H4,40 of bpy), 8.86 (m, 2H, H6/
165.9 (s, C6 of bpy), 225.8 (s + d, JPt,C = 1250 Hz, Pt–C), 232.8
3
(s + d, JPt,C = 1244 Hz, Pt–C). IR:
m ) 3081(w), 2960(s),
(cmꢂ1
2870(m), 1616(s), 1547(m), 1460(m), 1423(m), 1363(m),
1309(m), 1257(w), 1105(m), 1016(w), 925(w), 906(w), 734(w),
692(w), 598(w).
2
60 of bpy). 13C NMR (CDCl3, 125 MHz): d 44.4 (s + d, JPt,C = 371 Hz,
COCH3), 121.9 (s, C3/30 of bpy), 126.8 (s, C5/50 of bpy), 138.7 (s,
C4/40 of bpy), 151.2 (s, C2/20 of bpy), 155.1 (s, C6/60 of bpy), 230.1
3.3.6. [Pt(COMe)2(bpym)] (4f)
1
(s + d, JPt,C = 1269 Hz, Pt–C). IR: m (cmꢂ1) 3060(w), 2970(w),
Yield: 165 mg (80%). Anal. Calc. for C12H12N4O2Pt (439.3 g/mol):
C, 32.81; H, 2.75; N, 12.75. Found: C, 32.46; H, 2.88; N, 12.38%. 1H
2898(w), 1606(s), 1581(s), 1558(m), 1473(m), 1446(m), 1413(m),
1334(m), 1319(m), 1166(w), 1110(m), 1090(m), 1016(w), 930(w),
762(s), 727(m), 601(w).
3
NMR (CDCl3, 200 MHz) d 2.32 (s + d, JPt,H = 28.0 Hz, 6H, COCH3),
7,69 (m, 2H, H5,50 of bpym), 9.20 (m, 4H, H4,40 + H6,60 of bpym).

M. Werner et al. / Journal of Organometallic Chemistry 693 (2008) 2369–2376
2375
2
13C NMR (CDCl3, 100 MHz) d 44.2 (s + d, JPt,C = 386 Hz, COCH3),
124.1 + 127.2 (s, C3 + C8 of phen) 125.4. + 126.3 (s, C10a + C10b
of phen), 130.8 (s, C7 of phen), 138.1 (s, C5 + C6 of phen),
146.3 + 146.8 (s, C4a + C6a of phen), 148.4 (s, C4 of phen),
150.8 + 151.5 (s, C2 + C9 of phen), 227.7 + 227.8 (s, Pt–C). IR: m
(cmꢂ1) 3078(w), 2966(w), 2897(w), 1589(s), 1516(m), 1423(m),
1325(w), 1227(w), 1103(m), 916(w), 835(w), 721(w), 604(w).
123.7 (s, C5,50 of bpym), 157.7 + 159.1 (s, C4,40 + C6,60 of bpym),
3
161.6 (s, C2,20 of bpym), 226.6 (s + d, JPt,C = 1244 Hz, Pt–C). IR: m
(cmꢂ1) 3074(m), 2964(w), 1620(s), 1581(s), 1409(s), 1330(m),
1260(w), 1105(m), 1012(w), 943(w), 920(w), 820(w), 752(m),
661(m), 606(w).
3.3.7. [Pt(COMe)2(bpyr)] (4g)
3.3.10. [Pt(COMe)2(5-Me-phen)] (4j)
Yield: 160 mg (75%). Anal. Calc. for C12H12N4O2Pt (439.3 g/mol):
Yield: 175 mg (75%). Anal. Calc. for C17H16N2O2Pt (475.4 g/mol):
C, 32.81; H, 2.75; N, 12.75. Found: C, 32.54; H, 2.81; N, 12.67%. 1H
C, 42.95; H, 3.39; N, 5.89. Found: C, 42.82; H, 3.29; N, 6.01%. 1H
3
3
NMR (CDCl3, 400 MHz) d 2.33 (s + d, JPt,H = 27.8 Hz, 6H, COCH3),
NMR (400 MHz, CDCl3) d 2.32 (s + d, JPt,H = 25.3 Hz, 6H, COCH3),
8.98 (m, 4H, H3,30 + H5,50 of bpyr), 9.52 (m, 2H, H6,60 of bpyr).
5.32 (s, 3H, phen-CH3), 7.71 (m, 1H, H6 of phen), 7.80 + 7.86 (m,
2H, H3 + H8 of phen), 8.42 + 8.63 (m, 2H, H4 + H7 of phen),
8.99 + 9.07 (m, 2H, H2 + H9 of phen). 13C NMR d (100 MHz, CDCl3)
18.7 (s, phen-CH3), 44.5 (s + d, 2JPt,C = 387 Hz, COCH3),
124.9 + 125.2 (s, C3 + C8 of phen) 126.1 (s, C6 of phen),
129.7 + 130.2 (s, C10a + C10b of phen), 134.7 + 137.0 (s, C4 + C7 of
phen), 135.0 (s, C5 of phen), 145.6 + 146.5 (s, C4a + C6a of phen),
150.2 + 150.7 (s, C2 + C9 of phen), 227.2 + 227.8 (s, Pt–C). IR: m
(cmꢂ1) 3072(w), 2974(w), 2899(w), 1616(m), 1589(s), 1518(w),
1423(m), 1328(w), 1219(w), 1107(m), 931(w), 871(w), 798(w),
724(w), 602(w).
2
13C-NMR (CDCl3, 100 MHz) d 44.0 (s + d, JPt,C = 385 Hz, COCH3),
143.6 (s, C3,30 of bpyr) 144.5 (s, C5,50 of bpyr), 147.9 (s, C2,20 of bpy-
raz), 149.0 (s, C6,60 of bpyr), 226.3 (s + d, 3JPt,C = 1296 Hz, Pt–C). IR:
m (cmꢂ1) 3053(w), 3032(w), 2972(w), 2897(w), 1731(w), 1587(s),
1471(w), 1410(m), 1333(w), 1155(m), 1111(m), 1041(m), 928(w),
849(w), 605(w), 474(w), 453(w).
3.3.8. [Pt(COMe)2(phen)] (4h)
Yield: 175 mg (80%). Anal. Calc. for C16H14N2O2Pt (461.4 g/
mol): C, 41.65; H, 3.06; N, 6.07. Found: C, 41.98; H, 3.19; N,
3
5.91%. 1H NMR (400 MHz, CDCl3) d 2.40 (s + d, JPt,H = 21.2 Hz,
6H, CH3), 7,82 (m, 2H, H3 + H8 of phen), 8,04 (m, 2H, H5 + H6 of
phen), 8,50 (m, 2H, H4 + H7 of phen), 9.11 (m, 2H, H2 + H9 of
3.4. X-ray crystallography
2
phen). 13C NMR (100 MHz, CDCl3) d 44.6 (s + d, JPt,C = 385 Hz,
Single crystals suitable for X-ray diffraction measurements
were obtained by recrystallisation from methylene chloride/
diethyl ether (1:2) (4a ꢀ H2O, 4c, 4e ꢀ H2O) and by recrystallisation
from chloroform/pentane (1:1) (4d ꢀ 1/2CHCl3), respectively. Inten-
sity data were collected on a STOE IPDS 2 at 153(2) K (4a ꢀ H2O, 4c,
4e ꢀ H2O) and 133(2) K (4d ꢀ 1/2CHCl3), respectively, with Mo Ka
radiation (k = 0.71073 Å, plane graphite monochromator). Absorp-
tion corrections were applied numerically (Tmin/Tmax 0.075/0.232,
4a ꢀ H2O; Tmin/Tmax 0.221/0.480, 4c; Tmin/Tmax 0.191/0.794, 4d ꢀ
1/2CHCl3; Tmin/Tmax 0.214/0.725, 4e ꢀ H2O). The crystallographic
data and structure refinement parameters are listed in Table 5.
All structures were solved by direct methods with SHELXS-97 and
refined using full-matrix least-square routines against F2 with
SHELXL-97 [20]. Non-hydrogen atoms were refined with anisotropic
and hydrogen atoms with isotropic displacement parameters.
Hydrogen atoms were refined according the ‘‘riding model”.
CH3), 125.3 (s, C3 + C8 of phen) 127.3 (s, C5 + C6 of phen), 129.9
(s, C10a + C10b of phen), 137.9 (s, C4 + C7 of phen), 146.3 (s,
C4a + C6a of phen), 151.3 (s, C2 + C9 of phen), 230.1 (s + d,
3JPt,C = 1274 Hz, Pt–C). IR: m (cmꢂ1) 3079(w), 2979(w), 2898(w),
1610(s), 1583(s), 1512(m), 1429(m), 1329(m), 1109(m), 928(w),
843(m), 717(m), 607(w).
3.3.9. [Pt(COMe)2(4-Me-phen)] (4i)
Yield: 170 mg (75%). Anal. Calc. for C17H16N2O2Pt (475.4 g/mol):
C, 42.95; H, 3.39; N, 5.89. Found: C, 42.45; H, 3.21; N, 5.93%. 1H
3
NMR (400 MHz, CDCl3) d 2.32 (s + d, JPt,H = 25.1 Hz, 6H, COCH3),
5.31 (s, 3H, phen-CH3), 7.60 + 7.80 (m, 2H, H3 + H8 of phen),
7.92 + 8.06 (m, 2H, H5 + H6 of phen), 8.50 (m, 1H, H7 of phen),
8.85 + 9.04 (m, 2H, H2 + H9 of phen). 13C NMR (100 MHz, CDCl3)
2
d
19.6 (s, phen-CH3), 44.5 (s + d, JPt,C = 386 Hz, COCH3),
Table 5
Crystallographic and data collection parameters for compounds 4a ꢀ H2O, 4c, 4d ꢀ 1/2CHCl3 and 4e ꢀ H2O
4a ꢀ H2O
28H32N4O6Pt2
4c
4d ꢀ 1/2CHCl3
C53H45Cl3N4O4Pt2
1298.5
4e ꢀ H2O
C26H40N2O3Pt
623.7
Empirical formula
Mr
C
C22H30N2O2Pt
549.6
910.8
Crystal system
Space group
a (Å)
b (Å)
c (Å)
a (°)
b (°)
Triclinic
P1
Monoclinic
P21/n
11.192(1)
12.932(1)
14.933(1)
90
96.048(7)
90
2149.3(3)
4
1.698
6.546
2.09–25.50
14314
3615
Orthorhombic
P212121
14.273(1)
11.8988(5)
28.273(1)
90
90
90
4801.6(5)
4
1.796
6.038
1.44–25.00
31241
3798
4711
Hexagonal
P62
20.575(1)
20.575(1)
11.6908(6)
90
90
120
4286.0(4)
6
1.450
4.936
1.98–25.49
17001
4209
4736
ꢀ
10.054(2)
11.012(3)
13.841(3)
110.89(2)
92.46(2)
103.19(2)
1380.9(5)
2
2.190
10.169
1.59–25.00
9018
4102
c (°)
V (Å3)
Z
Dcalc (g cmꢂ1
)
l (Mo Ka) (mmꢂ1
h Range (°)
)
Number of reflections collected
Number of reflections observed [I > 2r(I)]
Number of independent reflections
Number of data/restraints/parameters
Goodness-of-fit on F2
4578
4578/0/365
1.065
4001
4001/0/253
1.157
4711/0/600
0.939
4736/1/302
1.017
R1, wR2 [I > 2r(I)]
0.0493, 0.1222
0.0529, 0.1244
4.441/ꢂ5.132
0.0297, 0.0731
0.0342, 0.0744
1.078/ꢂ1.165
0.0278, 0.0602
0.0405/0.0627
1.163/ꢂ1.676
0.0421, 0.0895
0.0361, 0.0879
0.669/ꢂ0.528
R1, wR2 (all data)
Largest difference peak and hole (e Åꢂ3
)

2376
M. Werner et al. / Journal of Organometallic Chemistry 693 (2008) 2369–2376
[5] A. Vyater, C. Wagner, K. Merzweiler, D. Steinborn, Organometallics 21 (2002)
Acknowledgement
4369.
[6] T. Gosavi, E. Rusanov, H. Schmidt, D. Steinborn, Inorg. Chim. Acta 357 (2004)
1781.
We gratefully acknowledge support by the Deutsche Fors-
chungsgemeinschaft. We also thank Merck (Darmstadt) for gifts
of chemicals.
[7] C. Albrecht, Ph.D. Thesis, Martin-Luther-Universität Halle-Wittenberg, 2006.
[8] R.J. Klingler, J.C. Huffman, J.K. Kochi, J. Am. Chem. Soc. 104 (1982) 2147.
[9] L.M. Redina, R.J. Puddephatt, Chem. Rev. 97 (1997) 1735.
[10] D. Steinborn, A. Vyater, C. Bruhn, M. Gerisch, H. Schmidt, J. Organomet. Chem.
597 (2000) 10.
Appendix A. Supplementary material
[11] V. Barone, C. Cauletti, M.N. Piancastelli, M. Ghedini, M. Toscano, J. Phys. Chem.
95 (1991) 7217.
CCDC 677227, 677228, 677229 and 677230 contain the supple-
mentary crystallographic data for 4a ꢀ H2O, 4c, 4d ꢀ 1/2CHCl3 and
4e ꢀ H2O. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/da-
ta_request/cif. Supplementary data associated with this article
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