Synthesis, characterization and crystal structure of [Pt(Me)(dppe){η1-CH(PPh3)(COOEt)}]BF4. An example of overcrowded molecule and correlated properties

Article abstract of DOI:10.1016/S0022-328X(01)00864-6

The complex [Pt(Me)(dppe){η¹-CH(PPh₃)(COOEt)}]BF₄ has been synthesized and characterized spectroscopically and structurally. It crystallizes in the space group P2₁/n, with lattice constants a=14.525(3) A?, b=14.931(3) A?, c=21.921(4) A?, β=103.47(3)°. The X-ray analysis revealed a particularly overcrowded molecular structure containing high stereochemical constraints. The structural features account for specific chemical and physical properties of this compound, thus representing an interesting example of applied crystallography.

Full text of DOI:10.1016/S0022-328X(01)00864-6

Journal of Organometallic Chemistry 629 (2001) 201–207
www.elsevier.com/locate/jorganchem
Synthesis, characterization and crystal structure of
[Pt(Me)(dppe){h1-CH(PPh3)(COOEt)}]BF4. An example of
overcrowded molecule and correlated properties
F. Benetollo a, R. Bertani b, P. Ganis c,*, L. Pandolfo d,*, L. Zanotto e
a ICTIMA CNR, I-35100 Padua, Italy
b Dipartimento di Processi Chimici di Ingegneria, Uni6ersita` di Pado6a, I-35131 Padua, Italy
c Dipartimento di Chimica Fisica, Uni6ersita` di Pado6a, I-35131 Padua, Italy
d Dipartimento di Chimica, Uni6ersita` della Basilicata, I-85100 Potenza, Italy
e CSTCMET CNR, I-35131 Padua, Italy
Received 27 February 2001; accepted 2 May 2001
Abstract
The complex [Pt(Me)(dppe){h1-CH(PPh3)(COOEt)}]BF4 has been synthesized and characterized spectroscopically and struc-
,
,
,
turally. It crystallizes in the space group P21/n, with lattice constants a=14.525(3) A, b=14.931(3) A, c=21.921(4) A,
i=103.47(3)°. The X-ray analysis revealed a particularly overcrowded molecular structure containing high stereochemical
constraints. The structural features account for specific chemical and physical properties of this compound, thus representing an
interesting example of applied crystallography. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Crystal structures; Platinum; Metal complexes; Phosphorus ylides
1. Introduction
As a part of this ongoing research we have synthe-
sized complexes [Pt(Me)(LꢀL){h1-C(PPh3)CO}]BF4, 1a,
1b [LꢀL=1,2-bis(diphenylphosphino)ethane (dppe) (a),
1,5-cyclooctadiene (cod) (b)], according to Reaction 1.
Both of the compounds 1a and 1b have been charac-
terized and the corresponding results will be reported
elsewhere. For a deeper investigation into the molecular
structure of 1a, an X-ray analysis was attempted on
single crystals, which accidentally formed in the mother
liquors of the synthesis reaction consisting of an ace-
tone–ethyl ether mixture.
Complexes of transition metals with phosphorus
ylides [1] play an important role in organometallic
chemistry [2]. Of particular interest is the organometal-
lic chemistry of carbonyl-stabilized phoshorus ylides,
which can be used in the air and give rise to
metalꢀC(ylide) or metalꢀO(ylide) coordination [2d] or
chelating systems that, in some cases, have been re-
vealed to be important olefin oligomerization catalysts
[3].
The structural data showed, to our disappointment,
that the complex had a quite different chemical compo-
sition [Pt(Me)(dppe){h1-CH(PPh3)(COOEt)}]BF4, 2,
(Chart 2). This complex could only form from the
reaction of 1a with ethanol, which was most likely
present as an impurity in the solvents we have used.
Continuing our studies on Pt(II) and Pd(II) com-
plexes with carbonyl-stabilized phosphorus ylides [4],
we have recently taken into consideration the
organometallic chemistry of a particular stabilized
ylide, ketenylidenetriphenylphosphorane, Ph3PCꢁCꢁO,
a cumulene ylide that has shown to be an easy-to-use
synthon in the attainment of metal-substituted ketenes
of the type LnM(PPh3)CꢁCꢁO (Chart 1) [5].
* Corresponding authors.
E-mail addresses: bertani@ux1.unipd.it (R. Bertani), pan-
dolfo@unibas.it (L. Pandolfo).
Chart 1.
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)00864-6

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F. Benetollo et al. / Journal of Organometallic Chemistry 629 (2001) 201–207
(1)
31P{1H}-NMR data, confirmed the coordination of the
carboethoxymethylenetriphenylphosphorane to Pt(II)
through the ylidic carbon, on the basis of the phospho-
nium chemical shift at 27.44 ppm, which is about 9
ppm downfield from that observed for the free ylide,
and from the phosphorus–platinum coupling constant
value (71.5 Hz) [4]. In the 1H-NMR spectrum the
methyne proton generated a doublet of doublet of
doublets at 4.61 ppm, flanked by 195Pt satellites
(2JPtH=90.8 Hz), due to the coupling with phospho-
nium and with both the cis and trans inequivalent
phosphorus atoms of the diphosphine ligand. The pres-
ence of a platinum-bonded methyl group was indicated
by a doublet of doublets at 0.18 ppm, flanked by 195Pt
satellites, whereas the ethyl CH3 gave rise to a triplet at
1.06 ppm. The signal of ꢀOꢀCH2ꢀ showed a complex
pattern corresponding to an AB system, confirmed
through a simulation experiment (Fig. 1), indicating the
inequivalence of the two methylene protons. The sig-
nals resulting from ꢀCH2ꢀCH2ꢀ spanned quite a wide
range, consisting of two complex systems centered at
2.8 and 1.6 ppm, respectively.
Chart 2.
However, compound 2, in spite of its apparent irrele-
vance in relation to our aims, was revealed to exhibit
rather interesting properties from a crystallochemical
point of view, which prompted us to prepare it pur-
posely for a thorough characterization. Here we report
the synthesis, physico-chemical characterization and
crystal structure of 2.
2. Results and discussion
13C{1H}-NMR spectrum was in agreement with the
suggested coordination mode through the ylidic carbon.
Signals attributable to CO (172.57 ppm), CH (27.60
ppm), PtꢀCH3 (1.62 ppm), ꢀOꢀCH2ꢀ (61.07 ppm) and
ꢀOꢀCH2ꢀCH3 (15.04 ppm) were observed, along with
the complex pattern arising from the phenyl groups.
We first attempted to obtain compound 2 by treating
complex 1a with ethanol, without success [6]. Instead,
we succeeded in the synthesis of 2 by direct reaction of
[Pt(Cl)Me(dppe)] with carboethoxymethylenetriphenyl-
phosphorane, Ph3PCHCOOEt, according to Reaction
2.
(2)
Compound 2 thus obtained has been fully character-
Signals due to ꢀCH2ꢀCH2ꢀ were present as two distinct
doublets of doublets at 28.23 and 20.20 ppm, mirroring
the quite large difference between these two methylene
groups observed in the H-NMR spectrum.
Positive-ion ESI mass spectrum of 2 in CH3CN
1
ized by elemental analysis, IR and H-, 31P- and 13C-
NMR spectroscopy and ESI mass spectrum.
1
The IR spectrum showed a strong CꢁO band at 1695
cm−1 in agreement with the literature IR data for the
carbonyl stretching of MꢀC(ylide) complexes [7]. The
showed several fragments including that corresponding

F. Benetollo et al. / Journal of Organometallic Chemistry 629 (2001) 201–207
203
nals were observed at m/z 626 [Pt(Me)(dppe)+H2O]+,
649 [Pt(Me)(dppe)+CH3CN]+ and 911 [M−
CH3CH2OH]+.
An ms/ms experiment performed on the [M]+ ions
yielded the same isotopic clusters as those present in the
main spectrum. These features are particularly interest-
ing, since ESI is a ‘soft’ ionization method that usually
allows observation of the molecular ions with little or
no fragmentation. The fact that the most intense signal
in the spectrum corresponded to a fragment resulting
from the loss of the s-bonded ylide could be an indica-
tion that this ligand is weakly bonded and that M+ is
relatively unstable.
All these data confirmed the chemical structure of 2
and excluded any isomeric constitution, for example,
the coordination of the ylide to Pt through oxygen.
However we were unable to obtain crystals of 2
prepared in this manner for a further confirmation
through an X-ray analysis. This circumstance, together
with the apparent impossibility of obtaining 2 through
direct treatment of 1a with ethanol and the ESI MS
results appeared to be ascribable to the molecular and
crystal structure itself of the complex 2.
Fig. 1. Experimental (a) and simulated (b) 1H-NMR spectrum rela-
tive to the ꢀOꢀCHAHBꢀ fragment.
to the molecular ion [Pt(Me)(dppe){h1-CH(PPh3)-
(COOEt)}], [M]+, centered at m/z 957. The higher
isotopic cluster in the spectrum was that centered at
m/z 608, corresponding to [Pt(Me)(dppe)]+ and arising
from [M]+ through the loss of Ph3PCHCOOEt. A
signal at m/z 349, corresponding to the protonated
ylide, [Ph3PCH2COOEt]+ was also present. Other sig-
Our belief was supported by the results of the X-ray
analysis of the crystals of 2 accidentally formed during
,
Fig. 2. ORTEP view of 2 (thermal ellipsoids at 50% probability level). Selected geometrical parameters are: bond distances (A): PtꢀC(27) 2.162(7),
PtꢀC(49) 2.103(7), PtꢀP(1) 2.307(2), PtꢀP(2) 2.226(2); bond angles (°): C(27)ꢀPtꢀC(49) 91.3(3), C(27)ꢀPtꢀP(1) 93.8(2), P(1)ꢀPtꢀP(2) 86.1(1),
P(2)ꢀPtꢀC(49) 90.5(2); torsion angles (°): C(33)ꢀC(28)ꢀP(3)ꢀC(27) 35.0(7), C(35)ꢀC(34)ꢀP(3)ꢀC(27) 66.0(7), C(45)ꢀC(40)ꢀP(3)ꢀC(27) 64.3(7),
,
C(27)ꢀC(46)ꢀO(2)ꢀC(47) −170.6(7), C(46)ꢀO(2)ꢀC(47)ꢀC(48) −163.1(7), P(2)ꢀC(1)ꢀC(2)ꢀP(1) 46.3(6); non-bonded distances (A) between atoms
of the phenyl rings C(40)“C(45) and C(9)“C(14): C(10)···C(45) 3.65(1), C(10)···C(44) 3.42(1), C(12)···C(42) 3.81(2), C(11)···C(42) 3.52(1),
C(11)···C(43) 3.462(1), C(12)···C(42) 3.81(2).

204
F. Benetollo et al. / Journal of Organometallic Chemistry 629 (2001) 201–207
Table 1
trolled by attractive dispersion forces. However the
most important feature of the structure is the presence
of a number of intramolecular contact distances which
could give rise either to weak bonding interactions or to
repulsive van der Waals interactions.
Some relevant short intramolecular contact distances and angles
present in 1
,
,
X···HꢀC (X=O, C)
X···C (A)
X···H (A)
X···HꢀC (°)
O(1)···H(35)ꢀC(35)
3.20(1)
3.28(1)
3.98(1)
3.84(1)
3.50(1)
3.88(2)
3.44(1)
3.52(1)
3.27(1)
3.39(1)
3.39(1)
3.96(1)
3.79(1)
2.51(1)
2.65(1)
3.12(1)
3.00(1)
3.04(1)
3.09(1)
2.74(1)
2.73(1)
2.66(1)
2.88(1)
3.04(1)
3.31(1)
2.96(1)
132
141
155
150
111
144
132
140
121
114
103
127
146
Most of these distances are reported in Table 1, and
will be discussed separately.
O(1)···H(49C)ꢀC(49)
C(16)···H(45)ꢀC(45)
C(15)···H(45)ꢀC(45)
C(16)···H(49B)ꢀC(49)
C(19)···H(44)ꢀC(44)
C(21)···H(49A)ꢀC(49)
C(22)···H(49A)ꢀC(49)
C(34)···H(49B)ꢀC(49)
C(35)···H(49B)ꢀC(49)
C(35)···H(49C)ꢀC(49)
C(36)···H(49B)ꢀC(49)
C(1)···H(49B)ꢀC(49)
,
The distances O(1)···H(35) 2.51(1) A, O(1)···H(49C)
,
,
2.48(1) A, or O(1)···C(35) 3.20(1) A, O(1)···C(49)
,
3.28(1) A, fall unequivocally in the range of the now
generally accepted classical hydrogen bonding of the
type CꢀH···X (X acceptor=O, N) [10], even though
only the angle O(1)···H(49C)ꢀC(49) 141(1)° fits for this
assumption [11]. Thus we can attribute to these dis-
tances a significant role in the stabilization of the
molecular conformation of the cation.
The distances between the hydrogen atoms of the
platinum bonded methyl group and atoms of the
phenyl rings deserve special comments, in particular
Table 2
,
A few crucial contact distances (A) involving the C(49)’s methyl
protons in the assumed conformation (a) and in the alternative limit
orientation as obtained by a rotation of 60° (b)
,
,
H(49B)···C(35) 2.89(1) A, H(49B)···C(34) 2.67(1) A,
,
,
H(49B)···C(39) 2.96(1) A, H(49A)···C(21) 2.74(1) A,
,
,
H(49A)···C(22) 2.73(1) A and H(49B)···C(21) 3.06(1) A.
The methyl protons have been localized at idealized
positions assuming CꢀH distances of 0.96 A, sp ge-
Atom···atom
a
b
3
,
H(49A)···C(16)
H(49B)···C(34)
H(49B)···C(35)
H(49B)···C(36)
H(49A)···H(16)
H(49B)···C(39)
O(1)···H(49C)
3.46
2.67
2.88
3.31
2.72
2.96
2.48
2.76
2.46
2.43
3.10
1.98
3.16
3.19
ometry and the orientation of the methyl group as
suggested by electron density residuals in the difference
Fourier syntheses. The intramolecular non-bonded dis-
tances arising from different orientations of the methyl
protons would be expected to be almost unchanged or
much shorter, as has been tested by suitable calcula-
tions (see for example Table 2). Thus we ascribe to the
assumed hydrogen coordinates
confidence.
a high degree of
-mthe synthesis of 1a (vide supra) that are reported and
discussed here [8].
The molecular structure of [Pt(Me)(dppe){h1-
CH(PPh3)(COOEt)}]BF4 is shown in Fig. 2, with atom
labeling. Some geometrical parameters are also
reported.
A few of these non-bonded distances could be con-
sidered as possible p-hydrogen bonding of the type
CꢀH···C(p) [12]. Actually CꢀH units in analogous situa-
tions have been proved to operate as hydrogen-bond
donors [13]. The most severe criticism of this bonding
interaction concerns the geometrical features present in
these structures. This kind of bonding is directional in
nature and aims for linearity, and the involved hydro-
gen atoms should be nearly equidistant from all the
atoms belonging to the p-system, in the present case the
phenyl groups [12]. In this structure the first require-
The main features of this molecule are normal: the
coordination about Pt is square planar without any
appreciable deviation from a regular geometry; the
PPh3 group shows the usual propeller conformation [9];
the ester group assumes the most stable full extended
conformation; the phenyl groups C(40)“C(45) and
C(9)“C(14) face each other at graphite distances con-
Table 3
Possible CH···F hydrogen bonds
,
,
CH in xyz
C···F (A)
H···F (A)
CꢀH···F (°)
Equivalent position of F
C(2)H(2A)
C(10)H(10)
C(20)H(20)
C(18)H(18)
C(23)H(23)
C(37)H(37)
C(31)H(31)
C(2)···F(2) 3.31(2)
C(10)···F(3) 3.50(2)
C(20)···F(2) 3.72(2)
C(18)···F(1) 3.35(2)
C(23)···F(3) 3.52
H(2A)···F(2) 2.59(1)
H(10)···F(3) 2.72(1)
H(20)···F(2) 2.57(1)
H(18)···F(1) 2.48(1)
H(23)···F(3) 2.62(1)
H(37)···F(1) 2.57(1)
H(37)···F(1) 2.71(1)
C(2)H(2A)···F(2) 131(1)
C(10)H(10)···F(3) 143 (1)
C(20)H(20)···F(2) 152 (1)
C(18)H(18)···F(1) 156(1)
C(23)H(23)···F(3) 159(1)
C(37)H(37)···F(1) 150(1)
C(37)H(37)···F(1) 173(1)
x, y, z
x, y, z
x, y, z
−0.5−x, −0.5+y, −0.5−z
0.5−x, −0.5+y, −0.5−z
x, 1−y, z
C(37)···F(1) 3.40(1)
C(31)···F(1) 3.64(1)
0.5+x, 0.5−y, 0.5+z

F. Benetollo et al. / Journal of Organometallic Chemistry 629 (2001) 201–207
205
ment is not always satisfied whilst the second is abso-
4. Experimental
lutely absent in spite of the quite short distances ob-
served between methyl protons and some phenyl
carbon atoms (Table 3).
Thus, we consider the contact distances reported in
Table 2 as repulsive ones [14].
All reactions and manipulations were carried out
under an atmosphere of dry Ar using standard Schlenk
techniques. Solvents were dried by conventional meth-
ods and distilled under Ar before use. [Pt(Me)Cl(dppe)]
[17] and Ph3PCHCOOEt [18] were synthesized accord-
ing to literature methods. IR spectra were recorded on
The above-mentioned observations furnish a picture
of a quite overcrowded molecule, probably lacking any
degree of conformational freedom, which is likely to
exhibit the same structure both in the solid state and in
solution.
Under the assumption that complex 1a has almost
the same molecular structure as 2, a noticeable stereo-
chemical hindrance can be imagined for an attack of
ethanol at the ketenyl group, which is tightly enclosed
and screened in a sort of molecular hollow, thus pre-
venting the direct formation of 2 from 1a. As noted
earlier 2 was formed from 1a just serendipitously,
maybe in the presence of some impurity which acted as
a catalyst.
1
a Perkin–Elmer 983 spectrophotometer. H-, 13C- and
31P-NMR spectra were recorded at 298 K on a Bruker
AC 200 spectrometer. Chemical shifts are reported in
ppm (l) relative to Me4Si (1H and 13C) and external
85% H3PO4 (31P). Electrospray Ionization (ESI) mass
spectra of 2 were recorded on a LCQ (Finnigan MAT)
instrument. Elemental analyses were provided by the
Microanalysis Laboratory of the Chimica Inorganica,
Metallorganica e Analitica (CIMA) department, Uni-
versity of Padua.
4.1. Synthesis of compound 2
Moreover, a similar problem also seems to be present
in the crystallization process of the whole complex. An
inspection of the packing features reveals the presence
of weak forces involved in the lattice stabilization of
this ionic complex. The Coulomb energy which falls off
with the ionic separation [15], is here certainly very
poor on account of the centre-to-centre distances be-
A 0.65 M acetone solution of AgBF4 (0.55 ml, 0.36
mmol) was added dropwise to a stirred solution of
[Pt(Me)Cl(dppe)] (0.212 g, 0.33 mmol) in CH2Cl2 (30
ml). After 1 h the reaction mixture was filtered to
remove solid AgCl and the obtained solution was
treated with Ph3PCHCOOEt (0.115 g, 0.33 mmol) in
CH2Cl2 (10 ml). After 2 h the solution was concen-
trated to a small volume (5 ml) and on addition of Et2O
a white solid precipitated. This solid was filtered off,
washed with Et2O and dried under vacuum. Yield:
0.282 g (82%).
,
tween anions and cations in the range of 6.3–6.8 A. In
fact, the lattice stabilization seems to be mainly due to
the weak hydrogen bonds BF···HC between units at x,
y, z; x, 1−y, z; −0.5−x, −0.5+y, −0.5−z; 0.5−
x, −0.5+y, −0.5−z (see Table 3) which are charac-
2: m.p. 187–189°C (dec.). Anal. Found: C, 55.79, H,
4.56. Calc. for C49H48O2BF4P3Pt: C, 56.39; H, 4.64%.
,
terized by reliable H···F distances of ca. 2.4–2.7 A and
CꢀH···F angles of ca. 130–160°, producing a self-as-
1
IR (Nujol, cm−1) 1695. H-NMR (CDCl3, 200 MHz,
sembled three-dimensional molecular network [16].
TMS): l=7.90–7.05 (m, 35H, Ph), 4.61 (ddd, 2JP(y)H
=
10.14, 3JPH=8.30, 3JPH=7.77, 2JPtH=90.8 Hz, 1H,
CH), 4.13 (m, 2JHH=10.78, 3JHH=7.10, 1H,
OꢀCHAHB), 3.94 (m, 2JHH=10.78, 3JHH=7.10, 1H,
OꢀCHAHB), 3.2–2.4, 1.8–1.4 (m, 4H, CH2CH2), 1.06
(t, 3JHH=7.10 Hz, 3H, CH3), 0.18 (dd, 3JPH=6.98,
3JPH=5.03, 2JPtH=62.1 Hz, 3H, PtꢀCH3). 31P{1H}-
NMR (CDCl3, 80 MHz, 85% H3PO4): l=49.24 (d,
2JPP=8.18, 1JPtP=1705 Hz), 42.22 (d, 2JPP=7.77,
1JPtP=3097 Hz), 27.44 (dd, 2JPP=8.18, 2JPP=7.77,
2JPtP=71.5 Hz). 13C{1H}-NMR (CDCl3, 50 MHz,
3. Conclusions
In this work we have reported the synthesis and
characterization
of
[Pt(Me)(dppe){h1-CH(PPh3)-
(COOEt)}]BF4. Spectroscopic data are in agreement
with a square planar coordination around Pt atom and
the ESI mass spectrum of this complex suggests a
relative instability of the cation [Pt(Me)(dppe){h1-
CH(PPh3)(COOEt)}]+. The X-ray structural analysis of
serendipitously obtained crystals of 2 indicates the pres-
ence of several molecular constraints due mainly to van
der Waals repulsive interactions which are only weakly
counterbalanced by intramolecular hydrogen bonds
and London dispersion forces. No stabilizing p-hydro-
gen bonds can be surmised as the complex lacks the
usual geometrical requirements. The overcrowding of
the cationic moiety accounts for the relatively weak
bonding of the ylide fragment to Pt.
2
2
TMS): l=172.57 (d, JPC=4.97, JPtC=42.7 Hz, CO),
135.7–121.6 (m, Ph), 61.07 (s, OꢀCH2), 28.23 (dd,
1JPC=33.13, 2JPC=7.80 Hz, CH2CH2), 20.60 (dd,
1JPC=73.29, 2JPC=49.92 Hz, CH2CH2), 27.60 (dd,
1JPC=38.06, 2JPC=15,77 Hz, CH), 15.04 (s, CH3), 1.62
(d, 2JPC=82.71, 1JPtC=534.7 Hz, PtꢀCH3). ESI MS
(CH3CN): 957 [Pt(Me)(dppe)(Ph3PCHCOOEt)]+, [M]+,
911
[M−CH3CH2OH]+,
649
[Pt(Me)(dppe)+
CH3CN]+, 626 [Pt(Me)(dppe)+H2O]+, 608 [Pt(Me)-
(dppe)]+, 349 [Ph3PCH2COOEt]+.

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F. Benetollo et al. / Journal of Organometallic Chemistry 629 (2001) 201–207
References
4.2. Crystal structure determination
[1] A.W. Johnson, Ylides and Imines of Phosphorus, Wiley, New
York, 1993.
Crystal data for C49H48O2BF4P3Pt, 2: MW=
1043.68 monoclinic, space group P21/n, a=14.525(3),
[2] (a) H. Schmidbaur, Acc. Chem. Res. 8 (1975) 62;
(b) H. Schmidbaur, Angew. Chem. Int. Ed. Engl. 22 (1983) 907;
(c) W.C. Kaska, Coord. Chem. Rev. 48 (1983) 1;
(d) U. Belluco, R.A. Michelin, M. Mozzon, R. Bertani, G.
Facchin, L. Zanotto, L. Pandolfo, J. Organomet. Chem. 557
(1998) 37.
,
b=14.931(3), c=21.921(4) A, i=103.47(3)°; V=
3
4623(2) A ; Z=4, Dcalc=1.50 g cm−3; F(000)=2088;
,
u(Mo–Ka)=0.71073 A; v=31.93 cm−1, T=293(2)
,
K. A prismatic colorless crystal of dimensions 0.24×
0.30×0.32 mm was centered on a four-circle Philips
PW1100 (Febo System) [19] diffractometer operating
in q–2q scan mode with graphite-monochromated
Mo–Ka, following standard procedures. There were
no significant fluctuations of intensities other than
those expected from Poisson statistics. The intensity
data were corrected for Lorentz–polarization effects
and for absorption, as described by North et al. [20].
The structure was solved by heavy atoms methods
[21]. Refinement was carried out by full-matrix least-
squares; the function minimized was ꢀw(F2o−Fc2)2,
with weighting scheme w=1/[s2(Fo2)+23.17P], where
P=max(F2o+2F2c)/3. All non-hydrogen atoms were
refined with anisotropic thermal parameters. The H-
atoms were placed in calculated positions with fixed,
isotropic thermal parameters (1.2Ueq of the parent
carbon atom). For a total of 543 parameters, wR%=
[ꢀw(F2o−F2c)2ꢀw(F2o)2]1/2=0.121, S=1.34, and con-
ventional R=0.057, based on the F values of 9853
reflections having F2o=2|(Fo2).
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Structure refinement and final geometrical calcula-
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the crystals of 2 used in the determination of X-ray crystal
structure. It presented all main features observed in the spectrum
of compound 2 obtained from Reaction 2.
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5. Supplementary material
Crystallographic data for the structural analysis
have been deposited with the Cambridge Crystallo-
graphic Data Centre, CCDC no. 15688 for compound
2. Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (Fax: +44-1223-336033;
e-mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
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Acknowledgements
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This work was supported by the CNR/RAS joint
project. The authors are grateful to Dr Donata Fa-
vretto (CSTCMET CNR, Padua, Italy) for the execu-
tion and discussion of ESI mass spectra of 2.
(b) A. Ceccon, A. Gambaro, F. Manoli, A. Venzo, D. Kuck,
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