Synthesis, characterization and reactivity of platinum-substituted ketenes [PtX{η1-C(PPh3)CO}L2]BF4, (X=Me, Cl; L2=1,5-cyclooctadiene, 1,2-bis(diphenylphosphino)ethane, cis-1,2-bis(diphenylphosphino)ethene). Steric and electronic effects of the ancillary ligands

Article abstract of DOI:10.1016/S0020-1693(01)00802-7

Ketenylidenetriphenylphosphorane, Ph₃PC=C=O, 1, has been used to synthesize platinum-substituted ketenes [PtMe{η¹-C(PPh₃)CO}L₂]BF₄, 2a, b (L₂=1,5-cyclooctadiene, cod (a), 1,2-bis(diphenylphosphino)ethane, diphos (b)). Parent compound [PtCl{η¹-C(PPh₃)CO}L₂]BF₄, 3, with L₂=cis-1,2-bis(diphenylphosphino)ethene, diphoe, was also synthesized, which is stable only at low temperature. The stability of 2 and 3 and the reactivity of the C=C=O moiety have been examined and discussed in terms of the electronic and steric characteristics of the ancillary ligands, also taking into account the reactivity of the 'PtXL₂' fragment with other carbonyl stabilized phosphorus ylides, Ph₃PCHCOR (R=Me, Ph, OMe, OEt).

Full text of DOI:10.1016/S0020-1693(01)00802-7

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Inorganica Chimica Acta 330 (2002) 213–219
Synthesis, characterization and reactivity of platinum-substituted
ketenes [PtX{h1-C(PPh3)CO}L2]BF4, (X=Me, Cl;
L2=1,5-cyclooctadiene, 1,2-bis(diphenylphosphino)ethane,
cis-1,2-bis(diphenylphosphino)ethene). Steric and electronic effects
of the ancillary ligands
Roberta Bertani a, Luciano Pandolfo b,*, Livio Zanotto c,*
a Dipartimento dei Processi Chimici di Ingegneria, Uni6ersita` di Pado6a, Via Marzolo, 9. I-35131 Pado6a, Italy
b Dipartimento di Chimica, Uni6ersita` della Basilicata, Via N. Sauro, 85. I-85100 Potenza, Italy
c CSTCMET CNR, Via Marzolo, 9. I-35131 Pado6a, Italy
Received 20 October 2001; accepted 27 November 2001
Dedicated to the memory of Professor Luigi M. Venanzi.
Abstract
Ketenylidenetriphenylphosphorane, Ph3PCꢀCꢀO, 1, has been used to synthesize platinum-substituted ketenes [PtMe{h1-
C(PPh3)CO}L2]BF4, 2a, b (L2=1,5-cyclooctadiene, cod (a), 1,2-bis(diphenylphosphino)ethane, diphos (b)). Parent compound
[PtCl{h1-C(PPh3)CO}L2]BF4, 3, with L2=cis-1,2-bis(diphenylphosphino)ethene, diphoe, was also synthesized, which is stable
only at low temperature. The stability of 2 and 3 and the reactivity of the CꢀCꢀO moiety have been examined and discussed in
terms of the electronic and steric characteristics of the ancillary ligands, also taking into account the reactivity of the ‘PtXL2’
fragment with other carbonyl stabilized phosphorus ylides, Ph3PCHCOR (R=Me, Ph, OMe, OEt). © 2002 Elsevier Science B.V.
All rights reserved.
Keywords: Platinum complexes; Ketenes; Ylides; Ketenylidenetriphenylphosphorane; Metal substituted ketenes; h1-ketenyls; Steric hindrance
1. Introduction
pounds can be also referred as mono and bis-metal
substituted ketenes in which one substituent is PPh3
and the other one is the Pt complex [3c]. We are
interested in the synthesis, characterization and study
of the reactivity of this kind of compounds [3], with the
aim, inter alia, to test the possibility to modulate the
stability and reactivity of the metal substituted ketenes
by modifying the characteristics of the metal fragment,
i.e. by changing the metal, its oxidation state and the
electronic and steric characteristics of the ancillary lig-
ands bonded to the metal.
Ketenylidenetriphenylphosphorane, Ph3PCꢀCꢀO, 1,
presents both ylide and ketene functionalities and,
thanks to these characteristics, it has been employed in
a large number of organic reactions which lead to
several interesting compounds [1], whereas only few
papers deal with its reactivity towards metal systems.
After some early works [2] 1 has been recently em-
ployed in a series of reactions with coordinatively un-
saturated Pt(II) complexes [3] yielding, through the
bonding of the ylidic carbon to the metal, stable mono
and bis-h1-ketenyl derivatives (Chart 1)1. These com-
In the course of this research project we have ob-
tained metal substituted ketenes [PtX{h1-C(PPh3)CO}-
L2]BF4, 2 and 3 (X=Me, L2=1,5-cyclooctadiene, cod,
* Corresponding authors. Tel.: +39-0971-202210/49-8275732; fax:
+39-0971-202223.
E-mail address: pandolfo@unibas.it (L. Pandolfo).
1 Some other Pd and Pt substituted mono and bisketenes resulted
stable only at low temperature (see [3a,3b]).
0020-1693/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0020-1693(01)00802-7

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R. Bertani et al. / Inorganica Chimica Acta 330 (2002) 213–219
from the solvent. This behavior, which is currently
under study, was previously observed with some other
Pt(II) h1-ketenyl derivatives obtained from 1 [3] and,
likely, is related to the interaction of free Ph3PCꢀCꢀO
with water [4]. On the other hand, decomposition pro-
cesses were also observed in chlorinated solvent,
analogously to what happens with other [LnPt{h1-
C(PPh3)CO}] derivatives [3]. Anyhow, it was possible to
obtain, for compound 2a, a solid-state CP/MAS
13C{1H} NMR determination that gave data completely
in agreement with those of other [LnPt{h1-
C(PPh3)CO}n] (n=1, 2) derivatives, both in solution [3]
and in the solid state [5]. A solid-state CP/MAS 31P{1H}
NMR determination, carried out on the same com-
pound 2a, gave a chemical shift value in very good
agreement with that found in solution. Compound 3,
instead, is unstable at room temperature and it was
characterized by IR and 31P{1H} NMR spectra at
−50 °C. The relevant spectroscopic data of com-
pounds 2 and 3 are collected in Table 1.
Chart 1.
2a, 1,2-bis(diphenylphosphino)ethane, diphos, 2b), X=
Cl, L2=cis-1,2-bis(diphenylphosphino)ethene, diphoe,
3) and here we report data on their synthesis, stability
and reactivity. Moreover, we also report the synthesis
and characterization of [PtMe{h1-CH(PPh3)C(O)-
The most evident feature observed in the IR spectra
of all derivatives is the presence of a strong, sharp signal
in the range 2071–2088 cm−1 corresponding to the
CꢀCꢀO stretching of Ph3PCꢀCꢀO bonded to the metal
through the ylidic carbon [3,6]. Also the 31P NMR data
pertaining to the Ph3PCꢀCꢀO moieties indicate the
coordination of 1 through the ylidic carbon. As a matter
of fact the chemical shifts (25–28 ppm) are in the range
of other [LnPt{h1-C(PPh3)CO}n] (n=1, 2) compounds
[3] and the values of corresponding JPPt (67–133 Hz) are
typical for a through two bonds coupling [7]. As for the
signals of coordinated diphosphines are concerned, the
assignments can be made thanks to the 195Pt coupling
constants. Particularly, 1JPPt in the range 1500–2000 Hz
is related to the phosphorus in trans position to the
methyl (P¦), whereas a value greater than 3000 Hz
indicates P%, in trans position to coordinated 1. Interest-
Me}(cod)]BF4,
4a,
[PtMe{h1-CH(PPh3)C(O)Me}-
(diphos)]BF4, 4b and its O-coordinated isomer [PtMe-
{h1-OCMeCHPPh3}(diphos)]BF4, 4b%.
2. Results and discussion
Compounds 2 were synthesized and isolated following
a standard procedure involving the formation of a
coordinative vacancy on Pt(II) followed by the addition
of Ph3PCꢀCꢀO, as sketched in Reaction 1, whereas for
compound 3 it was adopted the procedure indicated in
Reaction 2.
1
ingly, in compound 3, both the JPPt values are in the
range 3000–3500 Hz, thus reflecting, for the ligand
Ph3PCꢀCꢀO a trans influence similar to that of Cl [7].
Also 13C NMR data pertaining to the CꢀCꢀO moiety of
2a are in agreement with the corresponding data of
ketenes having organic [8] or metal [3,5,6] substituents.
Thus, even though we were unable to obtain crystals
suitable for an X-ray determination, we are completely
confident that compounds 2 and 3 are represented by
the structures sketched in Chart 2.
Some reactivity tests, performed on compound 2a,
confirm its ketene characteristics. As a matter of fact, 2a
reacts in solution with protic nucleophiles (alcohols and
amines), giving the corresponding esters and
amides according to Reaction 3, with a behavior previ-
ously observed with other h1-ketenyl derivatives
[3a,3c,6].
Reaction 1
Reaction 2
Both compounds 2a, b are stable in the solid state,
and they were isolated in almost quantitative yield and
characterized spectroscopically. The only problem en-
countered was the obtaining of the 13C{1H} NMR
spectra in solution. In fact, compounds 2, dissolved in
hexadeuteroacetone, decompose in the time with devel-
opment of CO2, likely due to interaction with adventi-
tious water which is difficult to completely eliminate
The course of the reactions was monitored by NMR
spectroscopy and reaction products were not isolated.

R. Bertani et al. / Inorganica Chimica Acta 330 (2002) 213–219
215
Table 1
Relevant IR and NMR data of compounds 2 and 3
IR
1H NMR
31P{1H) NMR
13C{1H) NMR
2a 2088 0.73 s, 2JHPt=70.8, CH3
26.05 s, 2JPPt=91.9
27.05 s, 2JPPt=114 b
−0.05 d, 1JCP=95.7, 1JCPt=766, CCO;
4.33 s, 1JCPt=603, CH3
27.55, 31.90, 34.40, CH2
2.28 m, 2.43 m, CH2
4.95 m, 5.04 m, 2JHPt=68.4, CH
100.67 s, 101.17 s, 104.38 s, 110.87 s, CH
161.03 s, CO
2b 2071 0.31 dd, 3JHP=6.9, 3JHP=4.5,
2JHPt=58.9, CH3
25.20 dd, 3JPP=9.3, 3JPP=4.2,
2JPPt=67.5, Pyl
2.42 m, CH2
47.13 d, 3JPP=9.3, 1JPPt=3526, P%
49.05 d, 3JPP=4.2, 1JPPt=1691, P¦
27.79 s, 2JPPt=133, Pyl
3 a 2079
52.98 s, 1JPPt=3515, P%
63.45 s, 1JPPt=3013, P¦
IR in Nujol (cm−1). 1H and 31P{1H) NMR in CDCl3, 13C{1H) NMR in solid, (l in ppm, J in Hz, 28 °C). 1H and 13C{1H) NMR phenyls data
are omitted.
a 1H and 31P{1H) NMR spectrum in CD2Cl2 at −50 °C.
b Solid state CP/MAS 31P{1H) NMR data.
substitution products accompanied by little quantities
of the corresponding amides, as determined by 31P{1H}
NMR spectra (Table 3). The reaction with the less basic
PhNH2 led, with long reaction times, to the formation
of little quantities of the corresponding amide, accom-
panied by several unidentified products. MeOH and
EtOH were completely unreactive even for long reac-
tion times.
Chart 2.
This loss of reactivity is quite strange for the CꢀCꢀO
moiety and it was previously observed only in the case
of bis-h1-ketenyl derivative trans-[PtCl2{h1-C(PPh3)-
CO}2], A, [3c] that reacts only with amines to give the
bis-amidic derivatives and does not react with alcohols.
This behavior was attributed to the insolubility of A in
most organic solvents and to a particularly encumbered
structure that protect the CꢀCꢀO moieties from exter-
nal attacks [3c]. Steric factors are known to be of
paramount importance in the stability and reactivity of
ketenes [8] and are to be considered also in the evalua-
tion of the different behaviors of 2a and 2b. In fact,
even in the absence of X-ray crystal structure determi-
nations for 2a and 2b, it is evident that the latter is
much more encumbered than the former and it is
Reaction 3
Most important NMR data of the amides and ester are
collected in Table 2.
Compound 2b presents a different behavior, i.e. the
CꢀCꢀO moiety is almost completely unreactive towards
the addition of protic nucleophyles. Particularly, the
reaction with Et2NH yielded only the substitution of
coordinated Ph3PCꢀCꢀO with the amine, whereas the
reactions with Me2NH and CyNH2, yielded mainly the
Table 2
Relevant NMR data on reactivity of 2a with HꢁNu
HꢁNu
1H NMR
31P{1H) NMR
Reaction time a
30 min
Me2NH
MeOH
0.46 s, 2JHPt=71.5, PtꢁCH3
2.94 s and 3.31 s, NMe2
0.45 s, 2JHPt=72.6, PtꢁCH3
3.67 s, 5JHPt=3.3, OMe
0.53 s, 2JHPt=72.5, PtꢁCH3
8.85 s, NH
27.52 s, 2JPPt=94.9
27.70 s, 2JPPt=70.1
27.62 s, 2JPPt=86.1
3 h
b
PhNH2
10 days
Reactions performed in CD2Cl2 (l in ppm, J in Hz, 28 °C). 1H NMR data pertaining to phenyls and cod are omitted.
a Time required for complete disappearance of NuꢁH.
b Little quantities of unidentified compounds were also observed.

216
R. Bertani et al. / Inorganica Chimica Acta 330 (2002) 213–219
Table 3
Relevant NMR data on reactivity of 2b with HꢁNu
1H NMR a
31P{1H) NMR
Et2NH Substitution
product
0.47 dd, 3JHP=2.9, 3JHP=6.6, 2JHPt=53.1, PtꢁCH3
3.15 m, NꢁCH2ꢁCH3
37.75 s, 1JPPt=3662, P%
50.77 s, 1JPPt=1817, P¦
1.18 m, NꢁCH2ꢁCH3
Me2NH Substitution
product
0.49 dd, 3JHP=2.9, 3JHP=6.7, 2JHPt=54.1, PtꢁCH3
38.71 s, 1JPPt=3596, P%
50.47 s, 1JPPt=1839, P¦
Addition
product
−0.02 dd, 3JHP=5.8, 3JHP=6.8, 2JHPt=58.9, PtꢁCH3 29.84 dd, 3JPP=8.6, 3JPP=2.3, 2JPPt=69.7, Pyl
45.98 d, 3JPP=8.6, 1JPPt=2994, P%
45.56 d, 3JPP=2.3, 1JPPt=1711, P¦
CyNH2 Substitution
product
0.48 dd, 3JHP=3.1, 3JHP=6.8, 2JHPt=54.8, PtꢁCH3
0.15 dd, 3JHP=5.6, 3JHP=6.9, 2JHPt=62.2, PtꢁCH3
39.59 s, 1JPPt=3753, P%
49.78 s, 1JPPt=1772, P¦
Addition
product
29.16 dd, 3JPP=6.2, 3JPP=7.7, 2JPPt=59.8, Pyl
44.74 d, 3JPP=6.2, 1JPPt=2935, P%
48.03 d, 3JPP=7.7, 1JPPt=1670, P¦
Reactions in CD2Cl2 (l in ppm, J in Hz, 28 °C).
a 1H NMR data pertaining to diphos are omitted. Only well defined and assigned signals are reported.
Moreover, the fact that the structure of compound 2b
possible that the phenyl groups of diphos contribute to
‘protect’ the CꢀCꢀO moiety from the attacks of not
very strong nucleophiles, such as alcohols and also
make difficult the attack of amines. Some evidences
support this hypothesis. Firstly, a particularly over-
crowded situation was previously observed in the crys-
tal structure of the parent compound [PtMe{h1-CH-
(PPh3)COOEt}diphos]BF4, B, which was synthesized
through the direct interaction of [PtMe(Cl)diphos] with
Ph3PCHCOOEt in the presence of AgBF4 [9]. In the
X-ray crystal structure of compound B it was possible
to observe that the fragment CHCOOEt accommo-
dates, with a full extended conformation, into a sort of
‘molecular hollow’ formed by the interactions between
the phenyl groups. It is possible that the structure of 2b
presents analogous features, (the only ‘chemical’ differ-
ence is between CHCOOEt and CCO groups) and that
also the CꢀCꢀO moiety accommodates into an
analogous hollow that shields it from external attacks.
Also different electronic effects of cod with respect to
diphos should be taken into account. In this regard, it
is worthwhile to remember that Ph3PCꢀCꢀO binds to
the metals through the nucleophilic ylidic carbon and
acts as a s-donor, without any contribution of back-
donation [2a,3c]. For this reason it is possible that the
good p-acceptor cod is able to relieve an excess of
negative charge more effectively than diphos does. This
would stabilize compound 2a with respect to 2b, but the
reactivity of the ketene moieties are expected to be
unaffected. At the most, cod would decrease, through
the metal, the negative charge on the Pt-bonded car-
bon, thus making the ketene fragment of 2a less reac-
tive than in the case of 2b, with a behavior opposite to
that observed. Thus, it seems that steric factors, rather
than electronic ones, drive the reactivity of these metal
substituted ketenes.
is particularly overcrowded is indirectly confirmed by
the instability of compound 3 that, considering only the
electronic effects, is expected to be more stable than 2b.
As a matter of fact, giving that the electronic effects of
diphos and diphoe are very similar if not identical, the
electron withdrawing Cl should stabilize 3 with respect
to 2b, in which the electron donating group Me is
present. Since it is experimentally observed an opposite
behavior it is possible to infer that the more restrictive
steric demands due to the rigid planar diphoe, with
respect to relatively deformable diphos are responsible
for the instability of 3. In other words, it is likely that
in compound 2b it has been reached a limit situation of
stability (similarly to that observed in the overcrowded
compound B), whereas in the case of compound 3 the
rigid geometrical situation of the diphoe phenyl groups
produces repulsive interactions with other ligands, and
this fact makes compound 3 unstable and let to observe
it only at low temperature.
Further support to these considerations has been
provided by the results of the interactions of the
‘PtMeL2’ fragments (L2=cod, diphos), with the car-
bonyl stabilized ylide Ph3PCHCOMe. It is known that
steric factors are of paramount importance to drive the
coordination to Pt of carbonyl stabilized ylides. Ac-
Chart 3.

R. Bertani et al. / Inorganica Chimica Acta 330 (2002) 213–219
217
(L2=cod, diphos), carried out according to the same
procedure used in the reactions with Ph3PCꢀCꢀO,
yielded solid stable compounds 4 that were isolated and
characterized through IR and NMR spectroscopies. As
indicated in Scheme 1, for L2=cod it was observed
only the formation of the C-coordinated compound, 4a,
whereas for L2=diphos it was obtained a mixture of
C-coordinated (4b) and O-coordinated (4b%) derivatives,
with a prevalence of the latter. Recrystallization yielded
4b% almost pure, while it was impossible to obtain pure
4b. To the complex 4b% it was assigned the cisoid form
2
on the basis of the high value of JHP (22.9 Hz) for the
4
methine proton and the observation of a JHP of 1.3 Hz
for the CꢁCH3 protons [11]. Relevant spectroscopic
data pertaining compounds 4 are shown in Table 4 and
complete data are reported in the Section 4.
These considerations together with the fact that the
strong nucleophilic ylide Ph3PCHCOOEt adds to the
‘PtMediphos’ fragment exclusively through the ylidic
carbon [9], confirm the particular overcrowded situa-
tion of 2b (L2=diphos) with respect to 2a (L2=cod),
that is very likely responsible for the unreactivity of the
former toward protic nucleophiles.
Scheme 1.
cording to the limit structures a and b depicted in Chart
3, these ylides can use either the ylidic carbon or the
carbonyl oxygen to bind to the metal, yielding C-coor-
dinated or O-coordinated complexes, respectively, the
latter in the cisoid or transoid form.
Particularly, it has been observed that, for R%=H
and R=Me, Ph, OMe, the relatively low sterically
demanding ‘PtCl(h3-allyl)’ allows fragment always the
coordination through the ylidic carbon, whereas, in the
cases of highly sterically demanding ‘trans-Pt(CF3)-
(PPh3)2’, only the O-coordination is possible. In the
case of ‘PtClL2’ (L2=diphos, diphoe), presenting an
intermediate degree of steric hindrance, the more steri-
cally demanding C-coordination is obtained only with a
strong nucleophilic ylide (R=OMe), whereas for the
less nucleophilic ylides (R=Me, Ph) only the less steri-
cally demanding O-coordination occurs [10].
3. Conclusions
Ph3PCꢀCꢀO has further confirmed to be a valuable
synthon to obtain, through clean and simple reactions,
h1-ketenyls that are, in effect, ketenes having as sub-
stituents the Ph3P moiety and a metal complex frag-
ment. As previously stated, it is conceivable that the
ketene stability and reactivity may be modulated to a
large extent through the modification of the electronic
and steric characteristics of the metal fragment., i.e. by
changing the metal, its oxidation state and the ancillary
ligands bonded to the metal. As for the latter point is
The reaction of Ph3PCHCOMe with [PtMe(Cl)L2]
Table 4
Relevant IR and NMR data of compounds 4
IR
1H NMR
31P{1H} NMR
13C{1H} NMR
4a
4b
4b%
1660 0.31 s, 2JHPt=71.7, PtꢁCH3
2.41 d, 4JHP=2.5, CꢁCH3
27.80 s, 2JPPt=63.1
7.79 s, 1JCPt=654, PtꢁCH3
32.79 d, 3JCP=10.7, CꢁCH3
5.56 d, 2JHP=3.8, 2JHPt=117.7, CH
38.66 d, 1JCP=44.9, 1JCPt=634, CH
204.46 d, 2JCP=7.1, 2JCPt=44.6, CO
1656 PtꢁCH3 not assigned
2.45 d, 4JHP=2.3, CꢁCH3
2.1–2.5 m, CH2
27.33 dd, 3JPP=8.9, 3JPP=5.7,
2JPPt=63.9, Pyl
42.74 d, 3JPP=8.9, 1JPPt=3153, P%
48.70 d, 3JPP=5.7, 1JPPt=1687, P¦
13.61 s, Pyl
4.96 d, 2JHP=11.8, CH
1509 0.10 dd, 3JHP=7.3, 3JHP=2.4,
2JHPt=51.6, PtꢁCH3
8.50 dd, 2JCP=90.8, 2JCP=5.8,
1JCPt=535, PtꢁCH3
34.21 s, 1JPPt=4246, P%
48.66 s, 1JPPt=1807, P¦
2.00 d, 4JHP=1.3, CꢁCH3
2.1–2.5 m, CH2
30.60 d, 3JCP=13.4, CꢁCH3
25.14 dd, 1JCP=34.8, 2JCP=5.3, CH2
30.85 dd, 1JCP=43.2, 2JCP=17.3, CH2
65.24 dd, 1JCP=105.4, 4JCP=5.4, PꢁCH
190.76 s, CO
4.23 dd, 2JHP=22.9,
5JHP=2.2, 4JHPt=15.4, CH
IR in KBr (cm−1). NMR in CDCl3 (l in ppm, J in Hz, 28 °C). 1H and 13C{1H) NMR data pertaining to phenyls and cod are omitted.

218
R. Bertani et al. / Inorganica Chimica Acta 330 (2002) 213–219
concerned, since it has been proposed [2a] and then
calculated [3c] that 1 acts exclusively as a s-donor,
without back-donation, it is expected that the nucleo-
philic attack of the ylidic carbon is favored by the
increase of the positive charge on the metal. For this
reason electron-withdrawing ancillary ligands should
favor the coordination and, likely, the stability of the
resulting metal substituted ketene. The effects of steric
parameters on the stability and reactivity are more
difficult to be evaluated. In this work it has been
observed that for the metal-fragment ‘PtXL2’ (X=Cl,
Me; L2=cod, diphos,diphoe) the addition of
Ph3PCꢀCꢀO to Pt yields a stable and reactive ketene
when L2 is the low sterically demanding cod. A stable
compound is also obtained with the more encumbered
diphos, but the ketene moiety results almost completely
unreactive, since it is in some way protected from the
external attacks by the particular geometrical situation
created by the phenyl groups of diphos and Ph3P.
Probably, this is a very unusual situation, since, with the
more sterically demanding diphoe (and Cl instead Me),
the platinum substituted ketene is unstable even if the
electronic effects of the diphosphines are very similar
and the difference between Me and Cl would, in the
case, favor the latter. Very likely, the phenyl groups of
Ph3P interact with the phenyl groups of the rigid diphoe
in some destabilizing way.
In conclusion, in this work it has been illustrated that
it is possible to tune the steric factors of the ancillary
ligands to modify the stability and reactivity of the
metal substituted ketenes that can be obtained through
the interaction of Ph3PCꢀCꢀO and coordinatively un-
saturated metal systems. Further experimental and theo-
retical work can be done to deeply examine the influence
of steric and electronic effects of other ligands on the
stability and the reactivity of these Pt-substituted kete-
nes. Moreover, the study could be extended to other
metals, with different oxidation states and coordination
geometries, with the possibility to obtain poly-metal
substituted ketenes, having stability and reactivity char-
acteristics that are difficult to predict at the present time.
removed by filtration and [{PtCl(diphoe)}2][BF4]2 was
precipitated with ethyl ether, filtered and dried under
vacuum.
IR spectra were taken on a Perkin–Elmer 983 spec-
1
trophotometer. H, 13C{1H} and 31P{1H} NMR spectra
were recorded on a Bruker AC 200 spectrometer and
chemical shifts are reported in ppm (l) relative to
tetramethylsilane (1H and 13C) and external 85% H3PO4
(31P). The solid state CP/MAS 13C{1H} and 31P{1H}
NMR spectra of compound 2a were obtained on a
Bruker AC 200 spectrometer equipped for solid state
analysis.
4.1. Synthesis of [PtMe{p1-C(PPh3)CO}(cod)]BF4, 2a
A stirred solution of [PtCl(Me)(cod)] (0.141 g, 0.40
mmol) in 20 mL of acetone was treated at 0 °C with
0.62 mL of a 0.65 M acetone solution of AgBF4. After
30 min AgCl was filtered off and the solution was cooled
at −50 °C and reacted with 0.121 g (0.40 mmol) of
Ph3PCꢀCꢀO. After 10 min a white solid appeared and
the reaction mixture was concentrated unde vacuum to
about 5 mL and ethyl ether was added to complete the
precipitation. The white solid was filtered and dried
under vacuum. Yield 0.262 g, 93%.
1
2a: IR (Nujol, cm−1) 2088, w(CCO). H NMR (l,
2
CDCl3, 28 °C), 0.73 s, JHPt=70.8 Hz, CH3, 2.28 m,
CH2, 2.43 m, CH2, 4.95 m, CH, 5.04 m, 2JHPt=68.4 Hz,
CH, 7.6–7.8 m, CHPh. 31P{1H} NMR (l, CDCl3,
28 °C), 26.05 s, 2JPPt=91.9 Hz: CP/MAS 31P{1H}
NMR (l, 28 °C), 27.05, 2JPPt=114 Hz.; CP/MAS
13C{1H} NMR (l, 28 °C),−0.05 d, 1JCP=95.7 Hz,
1JCPt=766 Hz, CCO, 4.33 s, 1JCPt=603 Hz, CH3,
27.55, 31.90, 34.40, CH2, 100.67 s, 101.17 s, 104.38 s,
110.87 s, CH, 120.93, 122,79, 125,50, 131.13, 132,77, Ph,
161.03 s, CO.
4.2. Synthesis of [PtMe{p1-C(PPh3)CO}(diphos)]BF4,
2b
Complex 2b was prepared as 2a, obtaining a yield of
93%.
1
2b: IR (Nujol, cm−1) 2071, w(CCO). H NMR (l,
3
3
CDCl3, 28 °C), 0.31 dd, JHP=6.9 Hz, JPH=4.5 Hz,
2JHPt=58.9 Hz, CH3, 2.42 m, CH2, 7.2–7.8 m, CHPh.
4. Experimental
31P{1H} NMR (l, CDCl3, 28 °C), 25.20 dd, JPP=9.3
3
3
2
3
All reactions and manipulations were carried out
under an atmosphere of dry argon with standard
Schlenk techniques. Solvents were dried by conventional
methods and distilled under argon before use. [Pt-
Cl(Me)(cod)] [12], [PtCl(Me)(diphos)] [12], Ph3PCCO
[13], Ph3PCHCOMe [14] were synthesized according to
reported methods. The dimer [{PtCl(diphoe)}2][BF4]2
was obtained in about 95% yield by stirring a
dichloromethane solution of [PtCl2(diphoe)] [15] with an
equivalent amount of AgBF4 (0.65 M in acetone) at
room temperature (r.t.) for 30 min. Resulting AgCl was
Hz, JPP=4.2 Hz, JPPt=67.5 Hz, Pyl, 47.13 d, JPP
=
9.3 Hz, 1JPPt=3526 Hz, P%, 49.05 d, 3JPP=4.2 Hz,
1JPPt=1691 Hz, P¦.
4.3. Synthesis of [PtCl{p1-C(PPh3)CO}(diphoe)]BF4 (3)
A chilled solutions (−40 °C) of 0.1 g of [{PtCl-
(diphoe)}2][BF4]2, (0.07 mmol) in 10 mL of dichloro-
methane was added to a solution of 0.043 g (0.14 mmol)
of Ph3PCCO in 10 mL of dichloromethane at the same
temperature. The resulting solution was stirred for

R. Bertani et al. / Inorganica Chimica Acta 330 (2002) 213–219
219
10 min and then taken to dryness under vacuum at
−30 °C, obtaining a solid (3) that resulted unstable in
solution at r.t.
4b%: IR (KBr, cm−1) 1509, w(CO). 1H NMR (l,
3
3
CDCl3, 28 °C), 0.10 dd, JHP=7.3 Hz, JHP=2.4 Hz,
2JHPt=51.6 Hz, PtꢁCH3, 2.00 d, 4JHP=1.3 Hz, CꢁCH3,
2.1–2.5 m, CH2, 4.23 dd, 2JHP=22.9 Hz, 5JHP=2.2 Hz,
4JHPt=15.4 Hz, CH, 7.2–7.7 m, CHPh. 31P{1H} NMR
(l, CDCl3, 28 °C), 13.61 s, Pyl, 34.21 s, 1JPPt=4246 Hz,
P%, 48.66 s, 1JPPt=1807 Hz, P¦. 13C{1H} NMR (l,
3: IR (Nujol, cm−1) 2079, w(CCO). 31P{1H} NMR
2
(l, CD2Cl2,−50 °C), 27.79 s, JPPt=133 Hz, Pyl, 52.98
1
1
s, JPPt=3515 Hz, P%, 63.45 s, JPPt=3013 Hz, P¦.
2
2
4.4. Synthesis of [PtMe{p1-CH(PPh3)-
C(O)Me}(cod)]BF4 (4a)
CDCl3, 28 °C), 8.50 dd, JCP=90.8 Hz, JCP=5.8 Hz,
1JCPt=535 Hz, PtꢁCH3, 30.60 d, 3JCP=13.4 Hz,
CꢁCH3, 25.14 dd, JCP=34.8 Hz, JCP=5.3 Hz, CH2,
30.85 dd, JCP=43.2 Hz, JCP=17.3 Hz, CH2, 65.24
dd, 1JCP=105.4 Hz, 4JCP=5.4 Hz, PtꢁCH, 124–135 m,
CPh, 190.76 s, CO.
1
2
1
2
A stirred solution of [PtCl(Me)(cod)] (0.150 g, 0.424
mmol) in 20 mL of dichloromethane was treated at 0 °C
with 0.65 mL of a 0.65 M acetone solution of AgBF4.
After 30 min AgCl was removed by filtration and the
solution was reacted with 0.135 g (0.424 mmol) of
Ph3PCHCOMe. After 10 min the reaction mixture was
concentrated under vacuum to about 5 ml and ethyl
ether was added obtaining a white solid which was
filtered and dried under vacuum. Yield 0.290 g, 94%.
4a: IR (KBr, cm−1) 1660, w(CO). 1H NMR (l,
Acknowledgements
The authors thank Dr. Alessandro Sassi (Department
of PCI, Padova) for the solid state CP/MAS 31P and 13
NMR spectra of compound 2a.
C
2
CDCl3, 28 °C), 0.31 s, JHPt=71.7 Hz, PtꢁCH3, 2.41 d,
2
2
4JHP=2.5 Hz, CꢁCH3, 5.56 d, JHP=3.8 Hz, JHPt
=
References
117.7 Hz, CHyl, 1.97–2.51 m, CH2, 4.23 m, 4.88 m, 4.99
m, 6.15 m, CH, 7.5–7.9 m, CHPh. 31P{1H} NMR (l,
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(l, CDCl3 28 °C), 7.79 s, 1JCPt=654 Hz, PtꢁCH3, 32.79
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1JCPt=123.8 Hz, 109.58 s, JCPt=38,73 Hz, 114.53 s,
1
1JCPt=36.13 Hz, CHcod, 122.43 d, 1JCP=85.3 Hz,
3JCPt=23.3 Hz, Cipso, 135.07, d, JCP=10.2 Hz, Corto
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2
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2
2
4.5. Synthesis of [PtMe{p1-CH(PPh3)C(O)Me}-
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The reaction was performed as for 4a, obtaining a
sticky solid that was recrystallized from dichloro-
methane/ethyl ether yielding a whitish solid that was
filtered and dried in vacuum, with an overall yield of
64%. IR and NMR experiments revealed the presence of
both C-coordinated (4b) and O-coordinated (4b%) iso-
mers in a 1:3 ratio. Repeated recrystallizations yielded
the O-coordinated isomer almost pure, whereas it was
impossible to isolate pure C-coordinated isomer.
4b: IR (KBr, cm−1) 1656, w(CO). 1H NMR (l,
4
CDCl3, 28 °C), 2.45 d, JHP=2.3 Hz, CꢁCH3, 2.1–2.5
2
m, CH2, 4.96 d, JHP=11.8 Hz, CH, 7.2–7.7 m, CHPh.
3
31P{1H} NMR (l, CDCl3, 28 °C), 27.33 dd, JPP=8.9
3
2
3
Hz, JPP=5.7 Hz, JPPt=63.9 Hz, Pyl, 42.74 d, JPP
=
8.9 Hz, 1JPPt=3153 Hz, P%, 48.70 d, 3JPP=5.7 Hz,
1JPPt=1687 Hz, P¦.
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