Organometallic Chemistry of Ph3PC=C=O. Synthesis, Characterization, X-ray Structure Determination, and Density Functional Study of the First Stable Bis-η1-ketenyl Complex, trans-[PtCl2{η1-C(PPh3)CO}2]

Article abstract of DOI:10.1021/om990826d

Mono- and bis-η¹-ketenyl Pt(II) complexes have been synthesized by reacting Zeise's salt or the related dimeric compound, [{PtCl₂(C₂H₄)}₂], with the oxocumulenic ylide ketenyliden-etriphenylphosphorane, Ph₃PC=C=O, 1, in suitable ratios. In particular, the η¹-ketenyl derivative, trans-[PtCl₂(C₂H₄){η¹-C(PPh ₃)CO}], 2, has been isolated and characterized. The reaction of 2 with one more equivalent of 1 displaces the coordinated ethylene giving the first stable bis-η¹-ketenyl derivative, trans-[PtCl₂{η¹-C(PPh₃)CO}₂], 6. The X-ray crystal structure of 6 shows a trans centrosymmetric geometry around Pt, with the PCCO moiety and the metal lying in a plane that forms an angle of ～65° with the Pt(II) coordination plane. Density functional calculations indicate that steric effects play a leading role in determining such an arrangement. Data on the reactivity of 2 and 6 are also reported. ? Dipartimento Processi Chimici di Ingegneria, Universita? di Padova. ? Dipartimento di Chimica Inorganica, Metallorganica ed Analitica, Universita? di Padova.

Full text of DOI:10.1021/om990826d

Organometallics 2000, 19, 1373-1383
1373
Or ga n om eta llic Ch em istr y of P h 3P CdCdO. Syn th esis,
Ch a r a cter iza tion , X-r a y Str u ctu r e Deter m in a tion , a n d
Den sity F u n ction a l Stu d y of th e F ir st Sta ble
Bis-η1-k eten yl Com p lex, tr a n s-[P tCl2{η1-C(P P h 3)CO}2]
Roberta Bertani,*,† Maurizio Casarin,*,‡ Paolo Ganis,§ Chiara Maccato,‡
Luciano Pandolfo,*,| Alfonso Venzo, Andrea Vittadini,# and Livio Zanottof
Dipartimento Processi Chimici di Ingegneria, Universita` di Padova, Via Marzolo 9,
I-35131 Padova, Italy, Dipartimento di Chimica Inorganica, Metallorganica ed Analitica,
Universita` di Padova, Via Marzolo 1, I-35131 Padova, Italy, Dipartimento di Chimica Fisica,
Universita` di Padova, Via Loredan 2, I-35131 Padova, Italy, Dipartimento di Chimica,
Universita` della Basilicata, Via N. Sauro 85, I-85100 Potenza, Italy, CSSMRE CNR,
Via Loredan 2, I-35131 Padova, Italy, CSSRCC CNR, Via Marzolo 1,
I-35131 Padova. Italy, and CSCTCMET CNR, Via Marzolo 9, I-35131 Padova, Italy
Received October 18, 1999
Mono- and bis-η1-ketenyl Pt(II) complexes have been synthesized by reacting Zeise’s salt
or the related dimeric compound, [{PtCl2(C2H4)}2], with the oxocumulenic ylide ketenyliden-
etriphenylphosphorane, Ph3PCdCdO, 1, in suitable ratios. In particular, the η1-ketenyl
derivative, trans-[PtCl2(C2H4){η1-C(PPh3)CO}], 2, has been isolated and characterized. The
reaction of 2 with one more equivalent of 1 displaces the coordinated ethylene giving the
first stable bis-η1-ketenyl derivative, trans-[PtCl2{η1-C(PPh3)CO}2], 6. The X-ray crystal
structure of 6 shows a trans centrosymmetric geometry around Pt, with the PCCO moiety
and the metal lying in a plane that forms an angle of ∼65° with the Pt(II) coordination
plane. Density functional calculations indicate that steric effects play a leading role in
determining such an arrangement. Data on the reactivity of 2 and 6 are also reported.
Ch a r t 1
In tr od u ction
At the beginning of this century Staudinger synthe-
sized and characterized Ph2CdCdO, the first reported
ketene.1 Since Staudinger’s discovery, ketenes have
been the subject of theoretical and experimental inves-
tigations, and comprehensive reports on these molecules
have been published.2 The electronic structure, the
stability, and the reactivity of ketenes (RR′)CdCdO
have been examined as a function of the steric and
electronic characteristics of R and R′, usually organic
fragments or silyl groups.2c,3
When the ketene moiety bears as substituent(s) one
or two metal centers, in particular transition metals,
the corresponding compounds are considered as metal
complexes σ-coordinating a CdCdO fragment and are,
thereafter, named η1-ketenyl (a ) and µ2-ketenylidene (b)
complexes respectively (Chart 1).4,5
Reports on η1-ketenyl and µ2-ketenylidene complexes
are relatively scanty, likely due to difficulties encoun-
tered in the syntheses of these peculiar ketenes, with
respect to those bearing organic and/or silyl substitu-
ents, for which a large variety of synthetic procedures
are available.6 To our knowledge, only one procedure
has been so far reported for the synthesis of crystallo-
graphically established Zr(II) and Hf(II) µ2-ketenylidene
derivatives.5,7 Moreover, general synthetic procedures
for η1-ketenyl derivatives are not yet available. In this
regard, some Mo and W η1-ketenyl derivatives have
been synthesized by the Kreissl group through ligand-
induced CO migration to a carbyne ligand,8 while
unstable compounds, which are at the same time η1-
ketenyl and η2-(C,C) ketene derivatives, have been
obtained by coordination of the bisketene carbon sub-
oxide (OdCdCdCdO) to Pt(0) and Ni(0) complexes.9
† Dipartimento Processi Chimici di Ingegneria, Universita` di Padova.
‡ Dipartimento di Chimica Inorganica, Metallorganica ed Analitica,
Universita` di Padova.
§ Dipartimento di Chimica Fisica, Universita` di Padova.
| Dipartimento di Chimica, Universita` della Basilicata.
CSSMRE CNR.
#
CSSRCC CNR.
f CSCTCMET CNR.
(1) Staudinger, H. Chem. Ber. 1905, 38, 1735.
(2) (a) Staudinger, H. Die Ketene; Verlag Enke: Stuttgart, 1912. (b)-
The Chemistry of Ketenes, Allenes, and Related Compounds; Patai, S.,
Ed.; Wiley: New York, 1980. (c) Tidwell, T. T. Ketenes; Wiley: New
York, 1995.
(3) Gong, L.; McAllister, M. A.; Tidwell, T. T. J . Am. Chem. Soc.
1991, 113, 6021, and references therein.
(5) Calderazzo, F.; Englert, U.; Guarini, A.; Marchetti, F.; Pampa-
loni, G.; Segre, A.; Tripepi, G. Chem. Eur. J . 1996, 2, 412.
(6) (a) Hanford, W. E.; Sauer, J . C. Org. React. 1946, 3, 108. (b)
Ward, R. S. In The Chemistry of Ketenes, Allenes, and Related
Compounds; Patai, S., Ed.; Wiley: New York, 1980; pp 223-277. (c)
Schaumann, E.; Scheiblich, S. Methoden der Organischen Chemie;
Theime Verlag: Stuttgart, 1993; Vol. E15, pp 2353-2530, 2818-2881,
2933-2957. (d) Tidwell, T. T. Ketenes; Wiley: New York, 1995; pp 52-
149.
(4) Geoffroy, G. L.; Bassner, S. L. Adv. Organomet. Chem. 1988, 28,
1.
10.1021/om990826d CCC: $19.00 © 2000 American Chemical Society
Publication on Web 03/10/2000

1374 Organometallics, Vol. 19, No. 7, 2000
Bertani et al.
C3O2 also gives monoinsertion reactions into a Pt-
oxygen bond10 and some metal-hydride bonds as well,11
yielding compounds where an η1-ketenyl fragment
and a carbonylic functionality are present. Further-
more, it was observed that the oxocumulenic ylide
Ph3PCdCdO, 1,12 is able to displace a weakly bonded
ligand (CO or acetonitrile) from some low-valence
complexes of early and medium transition metals,
giving, by coordination through the ylidic carbon, η1-
ketenyl derivatives in which PPh3 is the second ketene
substituent.13 Incidentally, η1-ketenyl derivatives can
be considered as a peculiar kind of ketenes, bearing two
different substituents, an organic moiety and a metal
center. This is supported by IR CO stretching values
and 13C NMR chemical shifts of the CdCdO moieties
of η1-ketenyl derivatives, falling in the same ranges
reported for ketenes,2,4 and this is particularly impor-
tant in the case of η1-ketenyls obtained through the use
of Ph3PCdCdO. As a matter of fact, although its
structure is ketene-like, 1 is not a “true” ketene (for
instance it does not dimerize), its π-electron system
being different from that of ketenes.12b However, 1
assumesa ketenecharacter byprotonation or alkylation,12b,14
i.e., by the attack of an electrophile, as it can be
considered a metal center, to the ylidic carbon.
over, it also could be possible to address the reactivity
of the bonded ketene fragment toward other ligands
coordinated in suitable arrangements, and finally, tak-
ing advantage of the relatively high coordination num-
ber of transition metals, more than one CdCdO group
could coordinate to the same metal center, obtaining 1,3-
bis, tris, and so on, η1-ketenyls.
Preliminary results indicated that 1 reacts with
suitable Pt(II) and Pd(II) complexes yielding η1-ketenyl
derivatives.15 Particularly, we obtained the first X-ray
crystal structure determination of an η1-ketenyl complex
with a CdCdO moiety involved in an ylide grouping15a
as well as IR and multinuclear NMR evidence of the
existence, at low-temperature (-50 °C), of a cis-bis-η1-
ketenyl derivative (two CdCdO moieties bonded to the
same Pt(II) center).15b
Here we report the synthesis of an η1-ketenyl deriva-
tive, trans-[PtCl2(C2H4){η1-C(PPh3)CO}], 2, containing
the CdCdO moiety and ethylene bonded to the
same Pt atom, obtained by reacting Zeise’s salt with
Ph3PCdCdO, and the study of its reactivity. The
synthesis, the X-ray structure determination, and pre-
liminary data on the reactivity of the first, stable, bis-
η1-ketenyl derivative, trans-[PtCl2{η1-C(PPh3)CO}2], 6,
are also reported. Finally, the electronic structure of 6
has been investigated by means of density functional
calculations.
As a part of ongoing research dealing with the
synthesis and characterization of metal-ketene deriva-
tives, we are exploring the use of Ph3PCdCdO as a
valuable synthon for η1-ketenyl transition metal com-
plexes where one of the CdCdO substituents is triph-
enylphosphine and the other one is a metal center. The
electronic structure and the steric hindrance of the
latter may be changed, in principle, to a large extent,
thus influencing ketene stability and reactivity. More-
Exp er im en ta l Section
Gen er a l Com m en t s. All reactions and manipulations
were carried out under an atmosphere of dry argon with
standard Schlenk techniques. All solvents were dried by con-
ventional methods and distilled under argon prior to use.
Ph3PCdCdO, 1,12c Zeise’s salt,16 [{PtCl2(C2H4)}2],17 and
Ph3PCHCOR (R ) Me, Ph)18 were synthesized according to
literature methods. IR spectra were taken on a Perkin-Elmer
983 spectrophotometer. 1H, 13C, and 31P NMR spectra of
compounds 2 and 6 were recorded at 298 K on a Bruker
Avance-600 instrument equipped with a 5 mm TXI 1H-1
reverse probe. Other 1H and 31P NMR spectra were recorded
on a Bruker 200 AC instrument. Chemical shifts are given
in ppm (δ) relative to tetramethylsilane (1H and 13C) and
external 85% H3PO4 (31P). The 13C resonances were assigned
through a 2D 1H/13C correlation via heteronuclear zero and
double quantum coherence (HMQC) using a BIRD sequence
with decoupling during acquisition.19 Quadrature detection
along F1 was achieved using the TPPI method.20 Due to
its low solubility (compound 6) and occurrence of parasite
reaction(s) in chlorinated solvents (compound 2), it was im-
possible to observe any 1D detection of the ketenyl 13C
resonances, which instead were observed through a 2D 1H/
13C correlation via heteronuclear zero and double quantum
coherence optimized on long-range couplings with low-pass
J -filter to suppress one-bond correlations (HMBC); no decou-
pling during acquisition was performed.21 The electrospray
ionization (ESI) mass spectrum of 6 was recorded on a LCQ
(Finnigan MAT) instrument. The Microanalysis Laboratory of
(7) (a) Compounds formulated as M2CdCdO (M ) Ag, Cu, Au) and
named “ketenides” have been reported (Blues, E. T.; Bryce-Smith, D.;
Hirsh`ıch, H.; Simons, M. J . Chem. Commun. 1970, 699. Blues, E. T.;
Bryce-Smith, D.; Kettlewell, B.; Roy, M. J . Chem. Soc., Chem. Commun.
1973, 921. Blues, E. T.; Bryce-Smith, D.; Lawston, I. W.; Wall, G. D.
J . Chem. Soc., Chem Commun. 1974, 513), but poor crystallinity and
low solubility hampered their complete characterization, as well as
for Rh µ2-ketenylidene compounds (Paiaro, G.; Pandolfo, L. Angew.
Chem., Int. Ed. Engl. 1980, 20, 289. Pandolfo, L.; Paiaro, G. Gazz.
Chim. Ital. 1985, 115, 561). (b) In the literature (see ref 4) are even
reported µ3-ketenylidene derivatives, in which the CdCdO fragment
interacts with three metal centers of some carbonylic clusters.
(8) (a) Kreissl, F. R.; Frank, A.; Shubert, U.; Lindner, T. L.; Huttner,
G. Angew. Chem., Int. Ed. Engl. 1976, 15, 632. (b) Kreissl, F. R.; Eberl,
I.; Uedelhoven, W. Chem. Ber. 1977, 110, 3782. (c) Kreissl, F. R.;
Friedrich, P.; Huttner, G. Angew. Chem., Int. Ed. Engl. 1977, 16, 102.
(d) Kreissl, F. R.; Uedelhoven, W.; Eberl, I. Angew. Chem., Int. Ed.
Engl. 1978, 17, 859. (e) Kreissl, F. R.; Eberl, I.; Uedelhoven, W. Angew.
Chem., Int. Ed. Engl. 1978, 17, 860. (f) Uedelhoven, W.; Eberl, I.;
Kreissl, F. R. Chem. Ber. 1979, 112, 3376. (g) Eberl, I.; Uedelhoven,
W.; Karsch, H.; Kreissl, F. R. Chem. Ber. 1980, 113, 3377. (h) Kreissl,
F. R.; Reber, G.; Mu¨ller, G. Angew. Chem., Int. Ed. Engl. 1986, 25,
643.
(9) (a) Paiaro, G.; Pandolfo, L. Angew. Chem., Int. Ed. Engl. 1980,
20, 288. (b) Pandolfo, L.; Morandini, F.; Paiaro, G. Gazz. Chim. Ital.
1985, 115, 711. (c) List, A. K.; Smith, M. R., II; Hillhouse, G. L.
Organometallics 1991, 10, 361.
(10) Pandolfo, L.; Paiaro, G.; Valle, G.; Ganis, P. Gazz. Chim. Ital.
1985, 115, 59.
(11) (a) Hillhouse, G. L. J . Am. Chem. Soc. 1985, 107, 7772. (b)
Pandolfo L.; Paiaro, G. Gazz. Chim. Ital. 1990, 120, 531. (c) Ganis, P.;
Paiaro, G.; Pandolfo, L.; Valle, G. Gazz. Chim. Ital. 1990, 120, 541.
(12) (a) Mattews, C. N.; Birum, G. H. Tetrahedron Lett. 1966, 46,
5707. (b) Bestmann, H. J . Angew. Chem., Int. Ed. Engl. 1977, 16, 349.
(c) Bestmann, H. J .; Sandmeier, D. Chem. Ber. 1980, 113, 274.
(13) (a) Berke, H.; Lindner, E. Angew. Chem., Int. Ed. Engl. 1973,
12, 667. (b) Lindenberger, H.; Birk, R.; Orama, O.; Huttner, G.; Berke,
H. Z. Naturforsch. 1988, 43b, 749.
(15) (a) Pandolfo, L.; Paiaro, G.; Dragani, L. K.; Maccato, C.; Bertani,
R.; Facchin, G.; Zanotto, L.; Ganis, P.; Valle, G. Organometallics 1996,
15, 3250. (b) Bertani, R.; Meneghetti, F.; Pandolfo, L.; Scarmagnan,
A.; Zanotto, L. J . Organomet. Chem. 1999, 583, 146.
(16) Chock, F. B.; Halpern, J .; Paulik, F. E. Inorg. Synth. 1973, 15,
90.
(17) Hartley, F. R. Organomet. Chem. Rev. A 1970, 6, 119.
(18) Ramirez, F.; Dershowitz, S. J . Org. Chem. 1957, 22, 41.
(19) Bax, A.; Subramanian, S. J . Magn. Reson. 1986, 67, 565.
(20) (a) Otting, C.; Wu¨thrich, K. J . Magn. Reson. 1988, 76, 569. (b)
Drobny, G.; Pines, A.; Sinton, S.; Weitekamp, D.; Wemmer, D. Faraday
Symp. Chem. Soc. 1979, 13, 49.
(14) (a) Bestmann, H. J .; Schmid, G.; Sandmeier, D.; Kisielowski,
L. Angew. Chem., Int. Ed. Engl. 1977, 16, 268. (b) Bestmann, H. J .;
Geismann, C.; Zimmermann, R. Chem. Ber. 1994, 127, 1501.
(21) Bax, A.; Summers, M. S. J . Am. Chem. Soc. 1986, 108, 2093.

Organometallic Chemistry of Ph3PCdCdO
Organometallics, Vol. 19, No. 7, 2000 1375
Ta ble 1. Su m m a r y of th e Cr ysta l Da ta a n d
In ten sity Collection for Com p ou n d 6
the Inorganic Chemistry Department of the University of
Padova provided elemental analyses.
Syn th esis of tr a n s-[P tCl2(C2H4){η1-C(P P h 3)CO}], 2. (a)
To a solution of 0.980 g of K[PtCl3(C2H4)]‚H2O (2.53 mmol) in
40 mL of THF was added 0.780 g of 1 (2.58 mmol). The course
of the reaction was monitored by IR spectroscopy, observing
the rapid disappearance of the free ligand signal and the
formation of a sharp ketenyl peak at 2085 cm-1. After 10 min
the resulting suspension was quickly concentrated under
vacuum and KCl filtered off. Addition of n-pentane to the
solution produced the precipitation of a yellow solid, which was
filtered, washed with ethyl ether, and dried under vacuum.
Yield: 1.20 g (79%).
formula
PtCl2C40H30P2O2
M
870.62
space group
a/Å
P1h
10.004(2)
b/Å
c/Å
9.973(2)
9.395(2)
R/deg
â/deg
90.6(1)
112.9(1)
γ/deg
83.2(1)
856.7
V/Å3
Z
2
cryst dimens/mm
DC/gcm-3
µ/cm-1
T/K
0.20 × 0.25 × 0.25
(b) The synthesis of 2 was also performed by using
anhydrous [{PtCl2(C2H4)}2]. To a solution of 0.340 g of
[{PtCl2(C2H4)}2] (0.58 mmol) in 50 mL of THF was added 0.350
g of 1 (1.16 mmol). The solution was stirred for 10 min and
then concentrated under vacuum. Addition, under vigorous
stirring, of n-pentane caused the precipitation of a yellow solid,
which was filtered, washed with ethyl ether, and dried under
vacuum. Yield: 0.650 g (94%).
1.69
41.83
298
radiation
graphite-monochromated Mo KR
(λ ) 0.7107 Å)
take-off angle/deg
scan speed/deg min-1
2θ range/deg
3
2.0 in the 2θ scan mode
3.0 e 2θ e 45
2747
obsd reflns [Fo g 3σ (Fo2)]
2
2: mp 140-142 °C (dec). Anal. Found: C 44.18; H 3.15.
R (on Fo)
0.067
Calcd for C22H19Cl2OPPt: C 44.31; H 3.21. IR (Nujol, cm-1):
Rw
0.070
1
νCO 2078, (2085 in THF) νPtCl 303 and 330. H NMR (CDCl3):
GOF
1.0
0.80
Hortho 7.83 (m), Hmeta 7.57 (m), Hpara 7.67 (m), C2H4 4.64 (s)
(2J HPt 54.1 Hz). 31P{1H} NMR (CDCl3): 26.14 (2J PPt 96.6 Hz).
13C{1H} NMR (CDCl3): Cortho 134.0 (2J CP 10.7 Hz), Cmeta 129.4
(3J CP 13.4 Hz), Cpara 133.8 (4J CP 3.2 Hz), Cipso 130.9 (1J CP 12.9
Hz), C2H4 80.3 (s) (1J CPt 133.8 Hz), Pt-C 0.7, CO 190.1.
Syn th esis of tr a n s-[P tCl2{η1-C(P P h 3)CO}2], 6. (a) To a
solution of 0.480 g of compound 2 (0.805 mmol) in 40 mL of
THF was added 0.245 g of 1 (0.81 mmol). The solution was
stirred for 24 h at room temperature (alternatively for 3 h at
50 °C), obtaining the formation of a light yellow solid, which
was filtered off, washed with THF and ethyl ether, and dried
under vacuum. Yield: 0.528 g (75%).
highest map res./e Å-3
were treated by the frozen core approximation. Moreover, the
binding energy (BE) was computed by employing the local
density approximation (Vosko-Wilk-Nusair formula)24 and
including the quasi-relativistic scalar correction.25 The BE has
been then analyzed in terms of atomic orbitals by applying
the Ziegler’s generalized transition state method:26
BE ) -[∆Ees + ∆EPauli + ∆Eint
]
(1)
(b) To a solution of [{PtCl2(C2H4)}2] (0.160 g, 0.27 mmol) in
30 mL of THF was added 0.333 g of 1 (1.1 mmol). After 10
min a light yellow solid began to precipitate, and the suspen-
sion was stirred at room temperature for 24 h. The solid was
filtered off, washed with THF and ethyl ether, and dried under
vacuum. Yield: 0.285 g (59%).
6: mp 230-232 °C (dec). Anal. Found: C 54.53; H 3.38.
Calcd for C40H30Cl2O2P2Pt: C 55.18; H 3.47. IR (Nujol, cm-1):
νCO 2062, νPtCl 325. 1H NMR (CDCl3): Hortho 7.87 (m), Hmeta
7.51 (m), Hpara 7.64 (m). 31P{1H} NMR (CDCl3): 21.98 (2J PPt
99.2 Hz). 13C{1H} NMR (CD2Cl2): Cortho 134.5 (2J CP 11.6 Hz),
Cmeta 125.1 (3J CP 13.8 Hz), Cpara 133.2 (4J CP 2.8 Hz), Cipso
130.7 (1J CP 13.8 Hz), Pt-C 1.4, CO 191.4. ESI MS (saturated
CH2Cl2 solution): m/z 870 [M]+, 893 [M + Na]+, 1741 [2M]+,
1764 [2M + Na]+.
where ∆Ees, ∆EPauli, and ∆Eint represent contributions due to
the pure electrostatic interaction, the Pauli repulsion (here-
after ∆Ees + ∆EPauli ) ∆Esr, steric repulsion), and ∆Eint, the
orbital interaction, respectively.
X-r a y Cr ysta l Str u ctu r e Deter m in a tion . X-ray-quality
crystals of 6 were obtained by evaporation from a dilute
CH2Cl2 solution. Single crystals were mounted on a Philips
PW-100 computer-controlled four-circle diffractometer with
graphite monochromator. Standard centering and autoindex-
ing procedures indicated a triclinic lattice. The space group
P1h was assigned and confirmed by well-behaved refinement
processes. The orientation matrix and accurate unit cell
dimensions were determined from angular settings of 25 high-
angle reflections. The data were corrected for Lorentz and
polarization effects; an empirical correction was also applied
(Ψ scan). Crystallographic data are collected in Table 1. All
the atoms, excluding the hydrogens, were located from suc-
cessive Fourier maps (Pt is centered in 000). The hydrogen
atoms were located at calculated positions and refined with
fixed geometry with respect to the carrier atoms (C-H 1.08
Å). The non-hydrogen atoms were refined with anisotropic
thermal parameters. Blocked-cascade least-squares refine-
ments were used. They converged to the conventional R index
reported in Table 1. Scattering factors for the atoms were
taken from Cromer and Waber.27,28 All the computations
concerning the crystal structure determination were carried
out on a Cyber 76 computer using the SHELX-76 program.29
The reactivity of compounds 2 and 6 was studied by
monitoring the course of some reactions through IR and
multinuclear NMR spectroscopies and will be discussed further
1
on. Reaction products were not isolated or purified. H NMR
spectra of corresponding reaction mixtures are available as
Supporting Information.
Com p u ta tion a l Deta ils. Calculations have been performed
by running the ADF package22 based on the density functional
(DF) theory and developed by Baerends and co-workers.23
A
triple-ú Slater-type basis set with a single polarization function
was used for all atoms. The inner cores of platinum (1s-5p),
phosphorus and chlorine (1s-2p), and oxygen and carbon (1s)
(22) ADF 2.3.0, Department of Theoretical Chemistry, Vrije Uni-
versiteit, Amsterdam, 1997.
(24) Vosko, S. J .; Wilk, M.; Nusair, M. Can. J . Phys. 1980, 58, 1200.
(25) (a) Snijdeders, J . G.; Baerends, E. J . Mol. Phys. 1978, 36, 1789.
(b) Snijdeders, J . G.; Baerends, E. J .; Ros, P. Mol. Phys. 1979, 38, 1909.
(c) Ziegler, T.; Tschinke, V.; Baerends, E. J .; Snijdeders, J . G.; Ravenek,
W. J . Phys. Chem. 1989, 93, 3050.
(26) Ziegler, T.; Rauk. A. Theor. Chim. Acta 1977, 46, 1.
(27) Cromer, D. T.; Waber, J . T. Acta Crystallogr. 1965, 18, 104.
(28) Cromer, D. T. Acta Crystallogr. 1965, 18, 17.
(23) (a) Post, D.; Baerends, E. J . J . Chem. Phys. 1983, 78, 5663. (b)
Baerends, E. J .; Ellis, D. E.; Ros, P. Chem. Phys. 1988, 2, 41. (c)
Boerrigter, P. M.; te Velde, G.; Baerends, E. J . Int. J . Quantum Chem.
1988, 33, 87. (d) van der Hoek, P. J .; Klein, A. W.; Baerends, E. J .
Commun. At. Mol. Phys. 1989, 23, 93. (e) te Velde, G.; Baerends, E. J .
J . Comput. Chem. 1992, 99, 84.

1376 Organometallics, Vol. 19, No. 7, 2000
Bertani et al.
Resu lts
the appearance in the IR spectrum of a signal at 2338
cm-1, whose intensity increases as the η1-ketenyl signal
decreases. The reaction of 2 with water has not been
further investigated; nevertheless, it has to be pointed
out that the synthesis of 2, performed by using mono-
hydrated Zeise’s salt gave a lower yield with respect to
that in which anhydrous [{PtCl2(C2H4)}2] was used (see
Experimental Section), likely due to water-promoted
decomposition of the ketenyl derivative.
Syn t h eses a n d Ch a r a ct er iza t ion s. By react-
ing Zeise’s salt or [{PtCl2(C2H4)}2] with 1 equiv
of
1
(reaction I) the η1-ketenyl derivative
The reactivity of 2 with protic nucleophiles has been
further tested with dimethylamine, methanol, and etha-
nol, observing the expected formation of amide and ester
derivatives, as evidenced by IR as well as H and 31P
1
(I)
NMR spectra of the reaction mixtures. Specifically,
CH2Cl2 solutions of 2 were treated, separately, with
equimolecular amounts of NMe2H, MeOH, and EtOH,
observing, in the corresponding IR spectra, the disap-
pearance of the η1-ketenyl signal and the formation of
signals in the carbonylic region [νCO 1624, 1699, 1696
[PtCl2(C2H4){η1-C(PPh3)CO}], 2, has been isolated in
good yields and characterized by elemental analysis, IR,
1
and H, 13C, and 31P NMR spectroscopies.
1
cm-1, respectively]. Data obtained from H and 31P NMR
In the 31P NMR spectrum of 2 only one singlet,
flanked by 195Pt satellites, is present. The chemical shift
and the 195Pt coupling constant are both in good agree-
ment with the data previously reported for other η1-
ketenyl ylidic complexes [Pt(η3-C3H5)(PPh3){η1-C(PPh3)-
CO}]BF4 (A)15a and [Pt(η3-C3H5)Cl{η1-C(PPh3)CO}] (B).15b
Particularly, the value of the 195Pt coupling constant
spectra of the reaction mixtures in CD2Cl2 (Table 2)
agree with IR data and are consistent with the forma-
tion of the carbonylic derivatives, 3a -c, according to
reaction II.
2
30
(96.6 Hz) is consistent with a J PPt
.
The presence of
(II)
coordinated ethylene is indicated by the singlets at 4.64
and 80.52 ppm in the 1H and 13C NMR spectra,
2
respectively, both flanked by 195Pt satellites. The J HPt
1
and J CPt values (54.1 and 133.8 Hz, respectively) lie in
Before going on, it has to be pointed out that the
reaction of 2 with NMe2H, carried out at -10 °C,
produced the immediate formation of the amide deriva-
tive in more than 60% yield, together with some other
products. In contrast to that, reactions of 2 with alcohols
required, even at room temperature, longer times and
some starting materials remained unchanged.
the ranges found for trans-[PtCl2(C2H4){η1-CH(PPh3)-
COR}] (R ) Me, Ph, OMe).31a Since for this class of
2
1
compounds J HPt and J CPt values are related to the
trans influence of the ligand bonded to Pt in trans
position to the olefin,32 it can be inferred that
Ph3PCdCdO, σ bonded to Pt through the ylidic carbon,
displays a trans influence quite similar to that of
carbonyl-stabilized phosphonium ylides and greater
Compound 2 has been also reacted with carbonyl-
stabilized ylides, observing the occurrence of two simul-
1
than that of chlorine (2J HPt 64 Hz and J CPt 195 Hz).31
1
taneous processes. The H NMR spectrum of the reac-
13C NMR signals at 0.7 and 190.1 ppm correspond to
the η1-coordinated ylidic and carbonylic carbon atoms,
respectively. It was impossible to detect any 195Pt
satellites for both signals. Finally, the IR spectrum of 2
shows a sharp signal at 2078 cm-1, typical for the CO
stretching of η1-ketenyl complexes,4,15 and signals in the
νPtCl region, consistent with a trans geometry.33 These
data converge to indicate for 2 the trans-η1-ketenyl
structure sketched in reaction I.
tion mixture of 2 with an equimolecular amount of
Ph3PCHCOMe indicated a partial release of ethylene,
displaced by the stabilized ylide, according to route a
in reaction III, with formation of the trans-bisylidic
derivative 4.
Compound 2 reacts with protic nucleophiles. If water
is added to a THF solution of 2, a complex reaction takes
place, leading to the formation of CO2, as evidenced by
(29) Sheldrix, G. M. SHELX-76, Program for Crystal Structure
Determination; Cambridge University, 1976.
(30) Pregosin, P. S.; Kunz, R. W. In NMR. Basic Principles and
Progress; Vol. 16, Springer-Verlag: Berlin, 1979.
(III)
(31) (a) Facchin, G.; Zanotto, L.; Bertani, R.; Nardin, G. Inorg. Chim.
Acta 1996, 245, 157. (b) Hall, P. W.; Puddephat, R. J .; Tipper, C. F. H.
J . Organomet. Chem. 1974, 71, 145. (c) Plutino, M. R.; Otto, S.; Roodt,
A.; Elding, L. J . Inorg. Chem. 1999, 38, 1233.
(32) (a) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem.
Rev. 1973, 10, 335. (b) Meester, M. A. M.; Stufkens, D. J .; Vrieze, K.
Inorg. Chim. Acta 1976, 16, 191. (c) Meester, M. A. M.; Stufkens, D.
J .; Vrieze, K. Inorg. Chim. Acta 1977, 21, 25. (d) Pregosin, P. S.; Sze,
S. N.; Salvadori, P.; Lazzaroni, R. Helv. Chim. Acta 1977, 60, 2514.
(33) Fracarollo, D.; Bertani, R.; Mozzon, M.; Belluco, U.; Michelin,
R. A. Inorg. Chim. Acta 1992, 201, 15.
At the same time, 1H and 31P NMR spectra evidenced
also the occurrence of a parallel reaction (route b ),

Organometallic Chemistry of Ph3PCdCdO
Organometallics, Vol. 19, No. 7, 2000 1377
Ta ble 2. 1H a n d 31P {1H} NMR Da ta of
[P tCl2(C2H4){η1-CH(P P h 3)CONu }] (Nu ) NMe2 (3a ),
OMe (3b), OEt (3c))a
1H
31P{1H}
C2H4
CH3
CH2
CH
P
3a 4.61(s)
2J HPt 48.5
3.50(s)
5.51(d)
28.48(s)
2J HP 8.6
2J HPt 113.5
5.45(d)
2J PPt 79.3
3b 4.60(s)
2J HPt 49.9
3.60(s)
1.07(t)
27.24(s)
2J HP 7.2
2J PPt 79.2
2J HPt 113.5
3c 4.59(s)
4.05(qd) 5.42(d)
27.20(s)
2J HPt 50.1 3J HH 7.1 3J HH 7.1 2J HP 7.1
5J HP 2.9 2J HPt 112.3
2J PPt 75.9
a
28 °C, CD2Cl2, chemical shifts in ppm, J in Hz. Signals due to
phenyl hydrogens are not reported.
Ta ble 3. 1H a n d 31P {1H} NMR Da ta of
[P tCl2{η1-C(P P h 3)CO}{η1-CH(P P h 3)COMe}], 4, a n d
[P tCl2(C2H4){η1-CH(P P h 3)COMe}], 5a
1H
31P{1H}
F igu r e 1. Molecular structure of 6 with atom labeling.
C2H4
CH3
CH
PCdC
PCH
4
5
2.61(d)
4.77(d)
25.92(s)
25.40(s)
route b), is very scarcely soluble in most organic
solvents, and it has been isolated, with good yields, by
filtration.
4J HP 2.2 2J HP 2.7
2J PPt 83.9 2J PPt 139.8
2J HPt 14.1
6.11(d)
4.70(s)
2.49(d)
27.83(s)
2J HPt 50.6 4J HP 2.5 2J HP 4.3
2J PPt 65.1
Compound 6 has been characterized by elemental
2J HPt 113.9
1
analysis, IR, and H, 31P, and 13C NMR spectroscopies
a
28 °C, CDCl3, chemical shifts in ppm, J in Hz. Signals due to
and ESI mass spectrometry. Its low solubility prevented
a molecular weight determination and did not allow any
1D detection of the ketenyl 13C resonances, which
instead were observed through a 2D 1H-13C correlation
via heteronuclear zero and double quantum coherence
(see Experimental Section). Once again, it was impos-
sible to detect any 195Pt satellites. The ESI mass
spectrum showed the occurrence of signals at 870 and
893 m/z, corresponding to the molecular ([M]+) and the
[M + Na]+ ions, respectively. Signals at 1741 ([2M]+)
and 1763 ([2M + Na]+) are likely due to association
phenomena, a feature often observed under ESI condi-
tions.
phenyl hydrogens are not reported.
where the coordinated heterocumulenic ylide 1 is dis-
placed by Ph3PCHCOMe, thus yielding the known
Zeise’s salt derivative, 5.31a 1H and 31P NMR data of
compounds 4 and 5 are reported in Table 3.
During the reaction of 2 with Ph3PCHCOMe, decom-
position reactions took place, evidencing, in the time,
the formation of the Zeise’s salt anion [PtCl3(C2H4)]-,
with a behavior similar to that previously observed in
the case of trans-[PtCl2(C2H4){(η1-CH(PPh3)COR}].31a
Attempts to react 2 with a less nucleophilic ylide, such
as Ph3PCHCOPh, had the only result of drastically
decreasing the reaction rates for both routes a and b,
thus making more evident the above-mentioned decom-
position reactions.
The stoichiometry of the synthesis reaction with
evolution of ethylene, ESI MS data, a single IR signal
at 2062 cm-1 (νCO), a singlet in the 31P NMR spectrum
at 21.98 ppm (2J PPt ) 99.2 Hz), and the signals at 1.4
and 191.4 ppm, in the 13C NMR spectrum, correspond-
ing to η1-coordinated ylidic and carbonylic carbon atoms,
respectively, strongly suggest for compound 6 the trans-
bis-η1-ketenyl structure sketched in reaction IV.
This structural hypothesis has been confirmed by an
X-ray single-crystal structure determination. The mo-
lecular structure of compound 6 is shown in Figure 1,
and selected molecular parameters are reported in Table
4.
Particularly interesting was the result obtained by
reacting compound 2 with one further equivalent of
Ph3PCdCdO. In THF solution, ethylene was completely
displaced by 1, thus obtaining complex 6 (reaction IV,
route a ). This compound, afterward obtained also by
Pt is located on an inversion center; thus the molecule
is structurally centrosymmetrical; the coordination
about Pt is almost exactly square-planar (C(1)-Pt-Cl
) 91.2°, C(1)-Pt-Cl′ ) 88.8°). The CdCdO grouping
bonded to Pt is also involved in a potential ylide moiety,
analogously to what is observed, for the first time, in
the complex [Pt(η3-C3H5)(PPh3){η1-C(PPh3)CO}]BF4
(A),15a whose most significant geometrical parameters
are also reported for comparison (Table 4). In 6 the
P-C(1) bond length (1.76(1) Å) is in the norm for an
ylidic nature and exhibits a partial double-bond char-
(IV)
direct reaction of [{PtCl2(C2H4)}2] with 1 (reaction IV,

1378 Organometallics, Vol. 19, No. 7, 2000
Bertani et al.
Ta ble 5. Op tim ized Ca lcu la ted Geom etr ica l
Ta ble 4. Selected Geom etr ica l P a r a m eter s of
Com p ou n d s 6 a n d A15a (in squ a r e br a ck ets)
P a r a m eter s for P h 3P CdCdO (1) a n d H3P CdCdO
(1a )a
Bond Lengths (Å)
Pt-Cl
2.300(6)
2.171(4)
1.76(1)
1.80(1)
1.79(1)
1.79(2)
1.26(2)
1.16(2)
Pt-C(1)
P-C(1)
[2.120(7)]
[1.75(1)]
P-C(2)
P-C(8)
P-C(14)
C(1)-C(20)
C(20)-O
[1.798(7)]
[1.786(9)]
[1.786(7)]
[1.280(8)]
[1.160(8)]
H3PCCO (1a ) Ph3PCCO (1)calc Ph3PCCO (1)exp
P-C1
1.648
1.281
1.178
134.6
1.657
1.273
1.183
142.4
[1.648]
[1.210]
[1.185]
[145.5]
C1-C2
C2-O
P-C1-C2
Bond Angles (deg)
91.2(2)
a
Experimental values for 139 in square brakets. Bond lengths
C(1)-Pt-Cl
and bond angles in Å and deg, respectively.
Pt-C(1)-P
121.7(2)
123.3(2)
179.6(9)
114.3(2)
106.5(2)
119.3(5)
108.0(4)
88.8(2)
[124.0(7)]
[118(1)]
[175(1)]
[118(1)]
Pt-C(1)-C(20)
C(1)-C(20)-O
P-C(1)-C(20)
C(1)-P-C(2)
C(1)-P-C(8)
C(1)-P-C(14)
C(1)-Pt-Cl′
When dealing with molecular systems carrying bulky
phenyl groups, they are usually theoretically modeled
with H atoms in order to save computational time.
Nevertheless, some of us recently demonstrated that
this practice is not always successful.37 For this reason,
before tackling the study of 6, we decided to carry out a
series of preliminary total energy calculations on the
actual ligand (Ph3PCdCdO) as well as on the model
compound H3PCdCdO. The geometry optimization has
been extended to the whole H3PCdCdO, while it has
been limited to the ketenyl moiety (CdCdO) in
Ph3PCdCdO.38 Optimized bond lengths and bond angles
are reported in Table 5.
At variance with theoretical results reported by
Albright et al.,40 but in agreement with X-ray data,39
also included for comparison in Table 5, our calculations
point out that the ylide inorganic skeleton (P-C-C-
O) is not linear, the P-C-C bond angle being 142° and
135° in Ph3PCdCdO and H3PCdCdO, respectively. As
far as bond lengths are concerned, the agreement with
literature crystallographic data39 is also satisfactory.
In a hypothetical ylide with a linear P-C-C-O
skeleton, the π atomic orbitals (AOs) localized on C and
O atoms (six orbitals for a total of eight electrons) would
originate three double degenerate π molecular orbitals
(MOs): π1, π2, and π3. π1 is totally bonding (no node
along the skeleton) and mainly localized on the O atom,
π2 is C1-C2 (C2-O) bonding (antibonding) (one node
along the skeleton) and highly concentrated on C1, while
π3 is C1-C2 and C2-O antibonding (two nodes along the
skeleton) with a strong participation of C2 AOs. Among
these three orbitals, π1 and π2 are occupied, while π3 is
empty.
Torsion Angles (deg)
Cl-Pt-C(1)-P
Cl-C(1)-P-C(20)
Pt-C(1)-P-C(14)
105
-162
80
Cl-Pt-C(1)-C(20)
Pt-C(1)-P-C(8)
-66
-42
acter;34 C(1)-C(20) (1.26(2) Å) and C(20)-O (1.16(2) Å)
seem still to indicate both a partial triple-bond charac-
ter. These values are in the range of those reported for
several η1-ketenyl derivatives8h,11c,15a and can be ex-
plained in terms of mesomeric effects,4,15a excluding any
multiple character of the Pt-C(1) bond. Accordingly, the
Pt-C(1) bond length (2.171(1) Å) is even longer than
that observed in the case of A (2.120(7) Å, see Table 4).
Furthermore, it is worth noting that for an angle
P-C(1)-C(20) of 114.3° we would expect, as it has been
previously described,35 a longer C(1)-C(20) distance (in
the range of 1.30-1.32 Å).4,8h,35 The value of 1.26 Å
found here seems to reveal, as in the case of A, a
through-bond inductive effect of the metal center on the
charge distribution in the ketenyl grouping.
The two ketenyl moieties of the molecule and the
metal lie in a plane forming a dihedral angle of ∼65°
with the coordination plane of Pt. As a result, the
CdCdO groups are almost oriented as far as possible
from the chlorine atoms: they are also in eclipsed
conformation with respect to one phenyl ring of the PPh3
moiety, thus allowing the largest contact distances
between Pt and the phenyl groups.
Electr on ic Str u ctu r e a n d Rea ctivity of 6. To get
further insight into the mechanism governing the at-
tainment of the actual molecular geometry of compound
6, the first stable, crystallographically established bis-
η1-ketenyl derivative, a series of numerical experiments,
within the DF theory, have been carried out on it, as
well as on the model complex trans-[PtCl2{η1-C(PH3)-
CO}2], 6a . It is in fact widely accepted that first-
principle DF calculations can be used as a practical tool
to get information about the molecular and electronic
structure of complex molecules.36 Incidentally, our
calculations can take advantage of a complete set of
structural data.
Despite the nonlinearity of the inorganic skeleton, DF
calculations point out that the two outermost occupied
MOs of Ph3PCdCdO and H3PCdCdO are substantially
degenerate, mainly localized on C1 and accounting for
a π interaction, C1-C2 (C2-O) bonding (antibonding),
parallel (π2|), and perpendicular (π2 ) to the P-C-C-O
plane. Incidentally, the π2| MO is the one responsible
for the Ph3PCdCdO σ donor properties. Atomic charges
of the inorganic skeleton, computed through the Hir-
shfeld scheme,42 are reported in Figure 2 for the actual
(37) Bertoncello, R.; Bettinelli, M.; Casarin, M.; Maccato, C.; Pan-
dolfo, L.; Vittadini, A. Inorg. Chem. 1997, 36, 4707.
(38) The bond angles and bond lengths involving phenyl moieties
have been kept fixed to the experimental values39 during the geometry
optimization.
(39) Daly. J . J .; Wheatley, P. J . J . Chem Soc. (A) 1966, 1703.
(40) Albright and co-workers41 computed, by means of ab initio
calculations, a P-C-C bond angle of 180° for H3PCdCdO.
(41) Albright, T. A.; Hofmann, P.; Rossi, A. R. Z. Naturforsch. 1980,
35b, 343.
(34) J ohnson, A. W. Ylides and Imines of Phosphorus; Wiley: New
York, 1993, and references therein.
(35) (a) Gil, J . M.; Howard, J . A. K.; Navarro, R.; Stone, F. G. A. J .
Chem. Soc., Chem. Commun. 1979, 1168. (b) Casey, C. P.; Fagan, P.
J . J . Am. Chem. Soc. 1982, 104, 7360.
(36) Ziegler, T. Chem. Rev. 1991, 91, 651.

Organometallic Chemistry of Ph3PCdCdO
Organometallics, Vol. 19, No. 7, 2000 1379
F igu r e 2. Hirshfeld atomic charges localized on the P-C-
C-O skeleton of H3PCCO and (in parentheses) Ph3PCCO.
and model ligand. Minor differences are found in the
two cases, confirming that the electronic properties of
Ph3PCdCdO are reasonably mimicked by the model
H3PCdCdO.
Before entering into details of theoretical results
pertaining to 6, we wish to provide a qualitative
description of the bonding scheme of the model complex
6a mainly based on symmetry arguments and overlap
considerations.
The Pt 5d orbitals can be divided into two sets
according to the nature (σ or π) of their interactions with
ligand-based MOs. In the adopted framework dxz, dyz,
2
and dxy AOs constitute the 5dπ set, while the dz and
2
2
dx -y orbitals belong to the σ one. The former is
completely occupied, while the latter includes an empty
2
2
AO, the 5dx -y orbital.
In Figure 3 we have reported a sketch of the bonding
combinations between the occupied 5dπ Pt orbitals and
the symmetric combinations of Cl 3pπ and C1 π2 levels
for θ ) 0° and 90° (θ is the angle between π2 and the
Pt(II) coordination plane, i.e., θ ) 0° corresponds to the
CdCdO moiety perpendicular to the Pt(II) coordination
plane, while θ ) 90° is representative of the ketene
fragments coplanar to the same plane).43 Since both the
metal-based and the ligand-based orbitals reported in
Figure 3 are fulfilled, both bonding and antibonding
combinations are completely occupied and the overall
interaction is, as a whole, destabilizing.
Interestingly, the Pt 5d orbitals differently interact
with the ligand-based MOs for different θ values. For θ
) 0°, the 5dxy AO participates in a multicentered
interaction, delocalized over the whole coordination
plane; the 5dyz AO can interact only with the symmetric
combination of the Cl 3pz AOs, while the 5dxz behaves
as a pure nonbonding orbital. For θ ) 90°, the interac-
tion of the Pt 5dyz with the Cl 3pz AOs is unchanged,
while the multicentered bonding in the coordination
plane cannot take place any more. In detail, the 5dxy
and 5dxz AOs limit their interaction to the gerade Cl
3px and C1 π2 combination, respectively.
On qualitative grounds, the overlap between the Pt
5d AOs and the ligand-based MOs is substantially the
same for θ ) 0° and 90°. This does not hold when we
consider the interligand repulsion. Actually, the mul-
ticentered, delocalized interaction taking place when θ
) 0° has an overall destabilizing effect because, as
already mentioned, it involves occupied orbitals. On this
basis, it can be foreseen that, from a purely electronic
F igu r e 3. Qualitative representation of the bonding
interactions between Pt 5d AOs and C1 π2 /Cl 3pπ orbitals
for θ ) 0° and 90° in 6a .
point of view, the θ ) 0° configuration should be less
stable than the θ ) 90° one.
In Figure 4 the values of BE, ∆Esr, and ∆Eint (see eq
1 in the Experimental Section), pertaining to the model
compound 6a , as a function of θ (0° e θ e 90°) are
reported.44
According to the qualitative bonding scheme we have
proposed, ∆Eint is a decreasing function of θ. In contrast
to that, ∆Esr shows the opposite behavior, despite the
presence of the PH3 moieties, which should minimize
the ligand steric hindrance. The energy range spanned
by ∆Esr is close to that of ∆Eint, and the pattern of the
BE curve has a minimum for θ ) 70° and a maximum
for θ ) 30° (corresponding to an angle of 20° and 60°,
respectively, between the Pt(II) coordination plane and
the plane determined by the O-C-C-Pt-C-C-O
skeleton). Furthermore, according to the qualitative
bonding scheme, BE(θ ) 0°) ) BE(θ ) 90°).
(42) (a) Hirshfeld, F. L. Theor. Chim. Acta 1977, 44, 1703. (b)
Wiberg, K. B.; Rablen, P. R. J . Comput. Chem. 1993, 14, 1504.
2-y2
(43) The σ bonding between the Pt 5dx
and suitable linear
combinations of Cl 3pσ and π1 levels is not displayed in the figure
because it is negligibly affected by θ.
These results stress the leading role played by
steric effects in determining the molecular conforma-

1380 Organometallics, Vol. 19, No. 7, 2000
Bertani et al.
Among the remaining four 5d AOs, two of them (the
2
dxz and the dz ) have an atom-like character (see Figure
5), while the 5dxy and the 5dyz AOs strongly interact with
symmetric combinations of Cl 3p and C1 π2 orbitals.
In Figure 7 (8) the 49ag and 60ag (52ag and 61ag) MOs
are reported. The former pair accounts for the bonding
and antibonding components of the multicentered, de-
localized interaction above-described and involving the
5dxy Pt AO, while the latter pair represents the bonding
and antibonding partners of the interaction between the
Pt 5dyz and Cl 3pz orbitals.
Hirshfeld atomic charges of 6 are reported in Figure
9. Their values are consistent with a bonding scheme
dominated by a ligand-to-metal σ donation without any
metal-to-ligand π back-donation and agree with the
rather large Pt-C(1) bond length (see Table 4). More-
over, they indicate that the negative charge σ donated
by the ylidic carbon to the metal is easily shared through
inductive effects involving the electron-withdrawing Cl
ligands. Finally, the calculated charge distribution on
the CdCdO moieties is quite normal for a ketene
grouping.2b,c
The reactivity of 6 with protic nucleophiles has been
examined. In particular, we have treated the bis-η1-
ketenyl complex, suspended in CH2Cl2, with t-BuNH2
1
(molar ratio 1:2), observing, through IR and H and 31P
NMR spectroscopies, the formation of diastereomeric
diamide species (reaction V).
(V)
In about 30 min the suspension changed to a clear
yellow solution, and its IR spectrum showed the com-
plete disappearance of the η1-ketenyl signal and the
formation of a broad amide CO signal at 1624 cm-1. The
solution was taken to dryness under vacuum, and the
1H NMR spectrum in CDCl3 of the obtained sticky solid
showed (Figure 10) two doublets with 195Pt satellites,
F igu r e 4. BE, ∆Esr, and ∆Eint vs θ for 6a .
tion, and it sounds reasonable that their influence
is much more important in determining the arrange-
ment of 6, where the bulkier phenyl groups are
present.
2
at 4.83 ppm (2J HP and J HPt are 9.3 and 133 Hz,
respectively) and 4.75 ppm (2J HP 9.4 Hz, 2J HPt masked),
due to the CH of diastereomeric diamide species. These
signals are in ca. 2:1 ratio, and the same integration
ratio is presented by two singlets at 1.21 and 1.19 ppm
(C(CH3)3) and two broad signals at 6.56 and 6.65 ppm,
attributable to amide NH. The corresponding 31P{1H}
NMR spectrum showed two singlets, once again in
about 2:1 ratio, at 27.97 ppm (2J HPt 67.5 Hz) and 28.49
ppm (2J HPt 72.7 Hz), in a range formerly observed for
trans-[PtCl2{η1-CH(PR3)C(O)R′}2].31a
Analogously to compound 2, we attempted to react 6
with alcohols and with water, but rather surprisingly,
no reaction was observed even when THF suspensions
of 6, containing a 5-fold excess of water or MeOH, were
refluxed for a week.
Theoretical calculations for 6 have been run by
idealizing its structure and assuming an angle of 90°
rather than the experimental one of 65° between the
Pt(II) coordination plane and the plane determined by
the O-C-C-Pt-C-C-O skeleton. In this way the
symmetry properties of 6 are described by the C2h
symmetry point group. In Figure 5 the gross partial
density of states (hereafter GPDOS) of the Pt 5d AOs,
together with those of C1 and Cl atoms are reported.
According to the well-established bonding scheme of
Pt(II) square planar complexes,45 the Pt 5d AO mainly
contributing to the metal-ligand interaction is the
2
2
5dx -y (see Figures 5 and 6), the only one having an
empty antibonding component.
Discu ssion
(44) The geometry of 6a for θ ) 0° has been optimized. Calculations
for θ > 0° have been carried out without any optimization by simply
rotating the H3PCdCdO groups around the x axis.
(45) (a) Purcell, K. F.; Kotz, J . C. Inorganic Chemistry; Hot-Saunders
International Edition, J apan, 1985. (b) Cotton, F. A.; Wilkinson, G.
Advances in Inorganic Chemistry, 5th ed.; Wiley-Interscience: New
York, 1988.
As previously pointed out, η1-ketenyl derivatives can
be considered a particular kind of ketenes, bearing two
different substituents, an organic fragment and a metal
center. In this regard, it is worthwhile to note that

Organometallic Chemistry of Ph3PCdCdO
Organometallics, Vol. 19, No. 7, 2000 1381
F igu r e 5. Partial density of states (PDOS) of Pt 5d, Cl, and C1 in 6. The zero corresponds to the HOMO energy.
F igu r e 7. Contour plots of the 49ag and 60ag MOs of 6.
Contour parameters are the same of Figure 6.
are typical for single Pt-C bonds with no multiple
F igu r e 6. Contour plots of the 42ag MO of 6. Contour
values are (0.40, (0.20, (0, 10, ..., Å1/2/e3/2, with negative
values in dashed lines.
character, as already stressed by theoretical results
pertaining to 6. It is also of relevance to point out that
experimental (A15a and 6) and calculated (6a ) CdC and
CdO bond lengths as well as the CdCdO electron
charge distribution (6) are consistent with a ketene
character.2b,c Incidentally, such a behavior seems to be
insensitive to the formal charge localized on the elec-
trophilic “metal” center (in A it is an ionic species,
whereas it is neutral in 6).
Bestmann and co-workers12b,14 observed that, despite
the presence of the ketene-like structure in the
CdCdO fragment, the π system and the reactivity of
Ph3PCdCdO differ from those of ketenes. Instead, the
oxocumulenic ylide is transformed into a highly reactive
“true” ketene by attack of an electrophile, as H+ or Me+,
to the nucleophilic ylidic C1 atom. Exactly the same
holds for η1-ketenyl derivatives obtained by reacting
Ph3PCdCdO with suitable metal systems. Accordingly,
X-ray data available for η1-ketenyl compounds derived
from Ph3PCCO (A15a and 6) indicate that the Pt-C1
distances (2.120 and 2.171 Å in A and 6, respectively)
As a whole 6 is not only the first stable bis-η1-ketenyl
but also the first stable 1,3-bisketene structurally
established. As far as this last point is concerned, it is
noteworthy that 6 is one of the few 1,3-bisketenes
quoted in the literature. As a matter of fact, after the
synthesis of the first bisketene (the 1,1-bisketene carbon

1382 Organometallics, Vol. 19, No. 7, 2000
Bertani et al.
Ch a r t 2
bisketenes,2c and they seem to be particularly important
even in the case of compound 6, whose ketene moieties
have sterically demanding substituents. Theoretical
outcomes and X-ray data are in tune with this assump-
tion and indicate that the coordination geometry of the
two Ph3PCCO moieties allows the largest possible
contact distances between the CdCdO groups, as well
as between Pt and the phenyl groups of PPh3, and
maintains the ketenyl groups as far as possible from
the chlorine atoms.54 Despite the lack of the molecular
structure of Me2Si(CHdCdO)2, it is noteworthy that
even for this compound a slightly distorted anti confor-
mation has been calculated to be more stable than the
syn one.52 The different stabilities of 6 (stable even at
F igu r e 8. Contour plots of the 52ag and 61ag MOs of 6.
Contour parameters are the same as Figure 6.
F igu r e 9. Hirshfeld atomic charges of 6.
relatively high temperature) and [Pt(η3-C3H5){η1-C(PPh3)-
15b
CO}2]BF4
(it exists in solution only at low tempera-
ture) further support the above considerations.
As far as the reactivity of compounds 2 and 6 is
concerned, we observed that the mono-η1-ketenyl 2
reacts with protic nucleophiles (alcohols and amines)
analogously to other known η1-ketenyls,4,15 yielding the
expected amide or ester derivatives. At variance to that,
compound 6 reacts, relatively slowly, only with the
strong nucleophile t-BuNH2, lacking the reactions with
alcohols and water. Certainly, the insolubility of com-
pound 6 contributes to its inertness, but it is very likely
that even other factors are not to be disregarded.
F igu r e 10. 1H NMR spectrum of the diastereomeric
diamides mixture resulting from the reaction of 6 with
t-BuNH2. Signals due to Me and Ph are not reported.
Addition of water and amines is a prototypical reac-
tion of ketenes, and these reactions have been deeply
studied. Particularly neutral hydration2c,55 and am-
mination56 have been proved to occur with quite com-
plex mechanisms, providing an initial nucleophilic
attack to the carbonylic carbon atom. In neutral hydra-
tion it has been found that there is a significant effect
of the structure on reactivity, crowded ketenes being
quite unreactive, as indicated by the relative values
of hydration rate constants (kH2O) for CH2CdCdO,
t-BuCHdCdO, and (t-Bu)2CdCdO, which are 1, 0.4,
and 4 × 10-6, respectively.57
suboxide46), a large number of 1,2- and 1,4-bisketenes
have been prepared47 (mainly due to the stabilizing
effect afforded by silyl substituents on these com-
pounds),3,48 while reports on 1,3-bisketenes are scanty.
If we exclude the rather unstable 1,5-pentatetraendione,
C5O2,49 compounds a and b (Chart 2) postulated as
reactive intermediates but never characterized,50 and
the dication c, whose existence has been claimed on the
1
basis of the H NMR spectrum of a reaction mixture,51
only Me2Si(CHdCdO)252 has been recently synthesized
and spectroscopically characterized.53
Further, it is noteworthy that Me2Si(CHdCdO)2 is
characterized by an unexpected high reactivity toward
water, giving the relatively unstable acidic derivative
Me2Si(CH2COOH)2,52 while the slightly more encum-
Steric factors are known to be of paramount impor-
tance in determining the stability of ketenes and
(46) Diels, O.; Wolf, B. Chem. Ber. 1906, 39, 689.
(47) (a) Tidwell, T. T. Ketenes; Wiley: New York, 1995; pp 405-
428. (b) Allen, A. D.; Ma, J .; McAllister, M. A.; Tidwell, T. T.; Zhao,
D.-c. Acc. Chem. Res. 1995, 28, 265.
(48) (a) Zhao, D.; Tidwell, T. T. J . Am. Chem. Soc. 1992, 114, 10980.
(b) Zhao, D.; Allen, A. D.; Tidwell, T. T. J . Am. Chem. Soc. 1993, 115,
10097. (c) McAllister, M. A., Tidwell, T. T. J . Org. Chem. 1994, 59,
4506.
(49) (a) Meier, G.; Reisenauer, H. P.; Sha¨fer, U.; Balli, H. Angew.
Chem., Int. Ed. Engl. 1988, 27, 566. (b) Meier, G.; Reisenauer, H. P.;
Ulrich, A. Tetrahedron Lett. 1991, 32, 4469.
(50) (a) Beringer, F. M.; Winter R. E. K.; Castellano, J . A. Tetrahe-
dron Lett. 1968, 6183. (b) Vierling, R. A. Ph.D. Thesis, Cornell
University, 1962; Chem. Abstr. 1963, 58, 7838a.
(52) Sung, K.; Tidwell, T. T. J . Am. Chem. Soc. 1996, 118, 2768.
(53) Recently we succeeded in obtaining a cis-bis-η1-ketenyl deriva-
tive, [Pt(η3-C3H5){η1-C(PPh3)CO}2]BF4 (ref 15b), which, although stable
only at low temperature, is another example of a 1,3-bisketene.
(54) The trans geometry of 6 contributes to stabilize it because it is
known that the interaction between two ketenyl groups in bisketenes
is, as indicated by ab initio calculations, destabilizing (ref 3). In the
1,2-bisketene (HCdCdO)2 the transoid form is 1.6 kcal/mol more stable
than the cisoid form.
(55) Tidwell, T. T. Acc. Chem. Res. 1990, 23, 273.
(56) (a) Sung, K.; Tidwell, T. T. J . Am. Chem. Soc. 1998, 120, 3034.
(b) Allen, A. D.; Tidwell, T. T. J . Org. Chem. 1999, 64, 266.
(57) Tidwell, T. T. Ketenes; Wiley: New York, 1995; p 581.
(51) McDonald, R. N.; Morris, D. L.; Petty, H. E.; Hoskins, T. L.
Chem. Commun. 1971, 743.

Organometallic Chemistry of Ph3PCdCdO
Organometallics, Vol. 19, No. 7, 2000 1383
bered 1,2-bisketene (Me3SiCdCdO)2 does not react with
moist CHCl3 without photolysis or acid catalysis.58
Even reactions of amines with ketenes, to give cor-
responding amides, are sensitive to steric factors, but
ammination rates are largely greater than hydration
rates (103 to 1013 times).56b
Without entering in the wide, and largely studied,
field of addition reactions to ketenes,2c it is very likely
that steric factors are important in the lack of reactivity
of 6 toward water and alcohols, and only strong nucleo-
philes, as primary aliphatic amines, can add, in a
reasonable time, to this particularly encumbered 1,3-
bisketene.
organometallic ketenes (and 1,3-bisketenes) are not
easily predictable, but they appear to be very stable and,
in some cases, poorly reactive.
As a whole, the present study is encouraging to
further investigate the interaction of Ph3PCdCdO with
other metal substrates for at least two reasons: (i) to
synthesize more complex ketenes and bis- and tris-
ketenes as well, whose reactivity can be modulated by
changing the characteristics of the “metal” fragments,
and (ii) to study the interaction of the CdCdO moieties
bonded to metals, from the small molecules’ metal
activation (or deactivation) point of view.
Ack n ow led gm en t. This work was supported by the
Italian Ministero dell’Universita` e della Ricerca Scien-
tifica e Tecnologica (MURST Rome) and by the Consiglio
Nazionale delle Ricerche (CNR Rome). The authors wish
to thank Dr. D. Favretto (CSCTCMET CNR, Padova.
Italy) for the ESI MS spectrum of compound 6.
Con clu sion s
In this paper we have reported the syntheses and the
study of a mono-η1-ketenyl derivative (compound 2)
containing an ethylene molecule coordinated to Pt and
of the first stable and crystallographically established
bis-η1-ketenyl compound (compound 6), both simply
obtained from Ph3PCdCdO. The electronic structure of
6 is typical of 1,3-bisketenes, and, from this point of
view, it is the second isolated 1,3-bisketene and the first
structurally established. The characteristics of these
Su p p or tin g In for m a tion Ava ila ble: A listing of bond
lengths and angles, the final values of all refined atomic
coordinates, fractional atomic coordinates of H atoms, and
anisotropic thermal parameters (Uij) of 6 and 1H NMR
spectra of the reactions of 2 with NMe2H, MeOH, EtOH, and
Ph3PCHCOMe, yielding 3a -c, 4, and 5, are available free of
charge via the Internet at http://pubs.acs.org.
(58) Allen, A. D.; Ma, J .; McAllister, M. A.; Tidwell, T. T.; Zhao, D.-
c. J . Chem. Soc., Perkin Trans. 2 1995, 847.
OM990826D