New synthetic approach to cyclic oxycarbene complexes from platinum(II)-alkynyl and -alkyne complexes and oxirane. X-ray crystal structure of trans-[Pt(Me){=CCH(p-tolyl)CH2CH2O}(PPh3) 2][BF4]·0.25CH<s

Article abstract of DOI:10.1021/om960274o

The cyclic five-membered platinum(II) oxycarbene complex trans-[Pt(Me){=CCH(p-tolyl)CH₂CH₂O}-(PPh₃) ₂][BF₄] (1) can be prepared in good yield under very mild conditions either by reaction of trans-[Pt

Full text of DOI:10.1021/om960274o

4096
Organometallics 1996, 15, 4096-4099
New Syn th etic Ap p r oa ch to Cyclic Oxyca r ben e
Com p lexes fr om P la tin u m (II)-Alk yn yl a n d -Alk yn e
Com p lexes a n d Oxir a n e. X-r a y Cr ysta l Str u ctu r e of
tr a n s-[P t(Me){dCCH(p-tolyl)CH2CH2O}(P P h 3)2][BF 4]‚0.25CH2Cl2
Rino A. Michelin,* Mirto Mozzon, Barbara Vialetto, and Roberta Bertani
Istituto di Chimica Industriale and Centro di Studio per la Chimica e Tecnologia dei
Composti Metallorganici degli Elementi di Transizione del CNR, Facolta` di Ingegneria,
Universita` di Padova, Via F. Marzolo 9, 35131 Padova, Italy
Franco Benetollo
Istituto di Chimica e Tecnologie Inorganiche dei Materiali Avanzati del CNR,
Corso Stati Uniti 4, 35100 Padova, Italy
Gabriella Bombieri
Istituto di Chimica Farmaceutica, Universita` di Milano, Viale Duca degli Abbruzzi,
20131 Milano, Italy
Robert J . Angelici*
Department of Chemistry, Iowa State University, Ames, Iowa 50011
Received April 9, 1996X
Summary: The cyclic five-membered platinum(II) oxy-
Recently we reported7 that, in contrast with the
above-mentioned CO and RNC reactions, no cyclic
oxycarbenes were formed from Pt(II)-alkyne or -alky-
nyl complexes and the halo alcohols HO(CH2)nCl (n )
2, 3); instead, alkyl((chloroalkyl)oxy)carbene complexes
were isolated as the only reaction products (eq 1), likely
occurring via vinylidene intermediates.8
carbene complex trans-[Pt(Me){dCCH(p-tolyl)CH2CH2O}-
(PPh3)2][BF4] (1) can be prepared in good yield under
very mild conditions either by reaction of trans-[Pt(Me)-
(CtC-p-tolyl)(PPh3)2] with oxirane in the presence of 1
equiv of HBF4 or by reaction of the cationic solvato
complex trans-[Pt(Me)(PPh3)2(solv)][BF4] with oxirane
and 1.5 equiv of p-tolylacetylene. The X-ray crystal
structure of 1 is reported.
In tr od u ction
Cyclic carbenes of transition-metal complexes are of
relevant chemical interest, owing to their increasing
importance in organic synthesis.1 Their syntheses have
been accomplished by various strategies,2 which, in our
case, involve cycloaddition reactions of the halo alcohols
HO(CH2)nX (n ) 2, 3; X ) Cl, Br) or the three-membered
In this paper we detail the first study on the reactivity
of alkynyl and alkyne complexes of platinum(II) with
oxirane, leading to the formation in good yield of cyclic
oxycarbenes and thus representing a new and straight-
forward procedure to this type of ligand.
heterocycles YCH2CH2 (Y ) O, NH, S) to unsaturated
ligands such as CO,3 CS,4 and RNC.5 This synthetic
strategy also proved effective with RCN ligands in Pt(II)
complexes to form N-heterocycles such as 2-oxazolines
and 1,3-oxazines.6
(5) (a) Michelin, R. A.; Zanotto, L.; Braga, D.; Sabatino, P.; Angelici,
R. J . Inorg. Chem. 1988, 27, 85. (b) Michelin, R. A.; Zanotto, L.; Braga,
D.; Sabatino, P.; Angelici, R. J . Inorg. Chem. 1988, 27, 93. (c) Bertani,
R.; Mozzon, M.; Michelin, R. A. Inorg. Chem. 1988, 27, 2809. (d)
Bertani, R.; Mozzon, M.; Benetollo, F.; Bombieri, G.; Michelin, R. A.
J . Chem. Soc., Dalton Trans. 1990, 1197. (e) Bertani, R.; Mozzon, M.;
Michelin, R. A.; Benetollo, F.; Bombieri, G.; Castilho, T. J .; Pombeiro,
A. J . L. Inorg. Chim. Acta 1991, 189, 175. (f) Belluco, U.; Michelin, R.
A.; Ros, R.; Bertani, R.; Facchin, G.; Mozzon, M.; Zanotto, L. Inorg.
Chim. Acta 1992, 198-200, 883 and references therein.
(6) Michelin, R. A.; Mozzon, M.; Bertani, R. Coord. Chem. Rev. 1996,
147, 299.
(7) Belluco, U.; Bertani, R.; Michelin, R. A.; Mozzon, M.; Benetollo,
F.; Bombieri, G.; Angelici, R. J . Inorg. Chim. Acta 1995, 240, 567.
(8) (a) Bruce, M. I.; Swincer, A. G. Adv. Organomet. Chem. 1983,
22, 59 and references therein. (b) Bruce, M. I. Chem. Rev. 1991, 91,
197.
X Abstract published in Advance ACS Abstracts, August 1, 1996.
(1) (a) Do¨tz, K. H.; Fischer, H.; Hofmann, P.; Kreissl, F. R.; Schubert,
U.; Weiss, K. Transition Metal Carbene Complexes; Verlag Chemie:
Weinheim, Germany, 1983. (b) Advances in Metal Carbene Chemistry;
Schubert, U., Ed., NATO ASI Series 269; Kluwer Academic: Dordrecht,
The Netherlands, 1989.
(2) (a) Ruiz, N.; Pe´ron, D.; Dixneuf, P. H. Organometallics 1995,
14, 1095 and references therein. (b) Michelin, R. A.; Facchin, G.; Braga,
D.; Sabatino, P. Organometallics 1986, 5, 2265 and references therein.
(c) Liu, C.-Y.; Chen, D.-Y.; Lee, G.-H.; Peg, S.-M.; Liu, S.-T. Organo-
metallics 1996, 15, 1055 and references therein.
(3) (a) Motschi, H.; Angelici, R. J . Organometallics 1982, 1, 343. (b)
Zanotto, L.; Bertani, R.; Michelin, R. A. Inorg. Chem. 1990, 29, 3265.
(4) Singh, M. M.; Angelici, R. J . Inorg. Chem. 1984, 23, 2691.
S0276-7333(96)00274-9 CCC: $12.00 © 1996 American Chemical Society

Notes
Organometallics, Vol. 15, No. 19, 1996 4097
Ta ble 1. Cr ysta l Da ta for Com p ou n d 1
Exp er im en ta l Section
formula
fw
cryst dimens, mm
cryst syst
a, Å
Gen er a l P r oced u r es a n d Ma ter ia ls. All reactions were
carried out under an N2 atmosphere. All the solvents were of
reagent grade and were used without further purification. IR
spectra were taken on a Perkin-Elmer 983 spectrophotometer
(abbreviations: s ) strong, m ) medium). Proton and carbon-
13 NMR spectra were obtained on a Bruker AC-200 spectrom-
eter. 1H NMR shifts were recorded relative to the residual
1H resonance in the deuterated solvent: CDCl3, δ 7.23. The
13C{1H} NMR shifts are given relative to the solvent reso-
nance: CD2Cl2, δ 53.8. The 31P{1H} NMR spectrum (CDCl3)
was run on a Varian FT 80-A spectrometer; the chemical shift
is referenced to external 85% H3PO4 with the downfield value
taken as positive. In all the NMR spectra J values are in Hz
(abbreviations used: s ) singlet, d ) doublet, t ) triplet, q )
quartet, m ) multiplet). The elemental analyses were per-
formed by the Department of Analytical, Inorganic and Or-
ganometallic Chemistry of the University of Padova. The
melting points were taken on a hot plate apparatus and are
uncorrected.
trans-[Pt(Me){dCCH(p-tolyl)CH2CH2O}-
(PPh3)2][BF4]‚0.25CH2Cl2
994.35
0.28 × 0.32 × 0.42
monoclinic
13.451(2)
12.920(3)
25.710(5)
91.42(4)
4467(2)
P21/n
1.48
4
1986
0.710 69
3.279
b, Å
c, Å
â, deg
V, Å3
space group
F(calcd), g cm-3
Z
F(000)
λ(Mo KR), Å
µ(Mo KR), mm-1
no. of rflns measd
scan method
2θmax, deg
no. of obsd rflns
(I g 2.5σ(I))
final R(F)
Rw(F2)
8353
θ/2θ
52
6690
The complexes trans-[Pt(Me)Cl(PPh3)2]9 and trans-[Pt(Me)-
(CtC-p-tolyl)(PPh3)2]7 were prepared according to literature
procedures. Oxirane (Caution! Oxirane, ethylene oxide, is
highly flammable and toxic.) and p-tolylacetylene were com-
mercially available products and used as received.
0.041
0.113
w
1/[σ2(Fo2) + 0.0000P)2 + 32.78P]a
no. of params refined 503
GOF
1.27
a
2
P ) (maxFo + 2Fc2)/3.
Syn th esis of tr a n s-[P t(Me){dCCH(p-tolyl)CH2CH2O}-
(P P h 3)2][BF 4] (1). Meth od A. To a suspension of trans-[Pt-
(Me)(CtC-p-tolyl)(PPh3)2] (200 mg, 0.235 mmol) in oxirane (20
mL) at 0 °C was added a 0.126 M ethereal solution of HBF4
(1.86 mL, 0.235 mmol) to give a clear solution, which was
stirred for an additional 2 h at 0 °C. The solution was then
taken to dryness under reduced pressure and the oily residue
was treated with benzene (20 mL) to form a white solid, which
was washed with warm benzene (2 × 10 mL) and then dried
under vacuum. Yield: 181 mg (78%). Mp: 169-170 °C dec.
Anal. Calcd for C48H45OBF4P2Pt: C, 58.73; H, 4.62. Found:
C, 59.00; H, 4.75. IR (Nujol, cm-1): ν(C-O) 1248 (s). 1H NMR
(δ, CDCl3): -0.207 [t, 3J (HP) 8.20, 2J (HPt) 46.4, 3H, CH3],
1.12 (m, 1H, CH-), 1.88 (m, 1H, CH), 2.50 [s, 3H, CH3 (p-
tolyl)], 3.63 (s, 1H, CH), 4.18 (m, 1H, OCH), 4.82 (m, 1H, OCH).
31P{1H} NMR (δ, CDCl3): 22.48 [s, 1J (PPt) 2945.3]. 13C[1H-
coupled] NMR (δ, CD2Cl2): 306.95 [t, 2J (CP) 6.2, 1J (CPt) 849.4,
measured (2θmax ) 52°). 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.11 The
structure was solved by heavy-atom methods.12 Refinement
was carried out by full-matrix least squares; the function
2
minimized was ∑w(Fo - Fc2)2, with the weighting scheme w
2
) 1/[σ2(Fo2) + (0.0182P)2 + 32.78P], where P ) max(Fo2 + 2Fc )/
3. All non-hydrogen atoms were refined with anisotropic
thermal parameters, except for the BF4 anion and for the
clathrate solvent, which were refined isotropically. The H
atoms were placed in calculated positions with fixed, isotropic
thermal parameters (1.2Uequiv of the parent carbon atom). For
2
a total of 504 parameters, Rw′ ) [∑w(Fo - Fc2)2/∑w(Fo2)2]1/2
)
0.118 (on F2), S ) 1.33, and conventional R ) 0.042, based on
F values of 6691 reflections having Fo2 g 2.5σ(Fo2). Scattering
factors were taken from ref 13. Structure refinement and final
geometric calculations were carried out with the SHELXL9314
and PAST15 programs, while drawings were obtained using
ORTEPII.16
1
3
C
carbene], 88.66 [t, J (CH) 156.9, J (CPt) 53.3, OCH2], 72.05 [d,
1J (CH) 123.11, 2J (CPt) 67.88, CH(C6H4-p-Me)], 26.47 [t, 1J (CH)
135.17, CH2], 21.38 [q, 1J (CH) 126.2, CH3], -3.32 [t, 2J (CP)
1
2.45, J (CPt) 368.5, CH3-Pt].
Meth od B. To a solution of trans-[Pt(Me)Cl(PPh3)2] (204
mg, 0.265 mmol) in CH2Cl2 (20 mL) at room temperature was
added a 0.46 M solution of AgBF4 in acetone (0.63 mL, 0.291
mmol). After it was stirred for 1 h, the suspension was filtered
off to remove AgCl, and the solution was taken to dryness
under reduced pressure to give a white solid of the solvato
complex trans-[Pt(Me)(PPh3)2(solv)][BF4] (solv ) CH2Cl2). To
this solution, at 0°C, was added oxirane (20 mL), and this
mixture was then treated with p-tolylacetylene (0.05 mL, 0.39
mmol). The reaction mixture was stirred for 3 h at 0 °C. Then
the clear, pale yellow solution was taken to dryness under
reduced pressure and the oily residue treated with benzene
(10 mL) to give a white solid of the product. It was filtered
off, washed with n-pentane (3 × 5 mL), and dried under
vacuum. Yield: 163 mg (63%).
Resu lts a n d Discu ssion
Syn th esis. The reactions leading to the synthesis
of the cyclic oxycarbene 1 are shown in Scheme 1. Route
a involves the reaction of the acetylide precursor with
oxirane in the presence of 1 equiv of HBF4 at 0 °C for 3
h, while route b involves the reaction in oxirane at 0 °C
for 3 h of the cationic solvato species trans-[Pt(Me)-
(PPh3)2(solv)][BF4], derived by treatment of trans-[Pt-
(Me)(Cl)(PPh3)2] in CH2Cl2 with 1 equiv of an acetone
solution of AgBF4, with a slight excess of p-tolylacety-
lene. The yields of 1 by the two methods were 78 and
63%, respectively. Complex 1 is a white solid, stable
Cr ysta l Str u ctu r e Deter m in a tion . Crystal data for 1 are
collected in Table 1. X-ray diffraction data were collected on
a four-circle Philips PW1100 (Febo System)10 diffractometer
in the θ/2θ scan mode with graphite-monochromated Mo KR
radiation (λ ) 0.710 69 Å). A total of 8353 reflections were
(11) North, A. T. C.; Philips, D. C.; Mathews, F. S. Acta Crystallogr.
1968, A24, 351.
(12) Sheldrick, G. M. SHELX86, Acta Crystallogr. 1990, A46, 467.
(13) International Tables for X-ray Crystallography; Kynoch Press:
Birmingham, U.K., 1974; Vol. IV, p 101.
(14) Sheldrick, G. M. SHELXL93, Program for the Refinement of
Crystal Structures from Diffraction Data; University of Go¨ttingen,
Go¨ttingen, Germany, 1993.
(15) Nardelli, M. Comput. Chem. 1983, 7, 95.
(16) J ohnson, C. K. ORTEP II; Report ORNL-5138; Oak Ridge
National Laboratory, Oak Ridge, TN, 1976.
(9) Clark, H. C.; Manzer, L. E. J . Organomet. Chem. 1973, 59, 411.
(10) Belletti, D. “FEBO”. A New Hardware and Software System
for Controlling Philips PW1100 Single Crystal Diffractometer; Internal
Report 1/93; Centro di Studio per la Strutturistica Difrattometrica del
CNR, Parma, Italy.

4098 Organometallics, Vol. 15, No. 19, 1996
Notes
Sch em e 1
in the solid state and in solution, and it was character-
ized by microanalysis, IR, and multinuclear NMR and
also by an X-ray analysis. In the IR spectrum a strong
absorption at ca. 1250 cm-1 is assigned to νstr(C-O) of
the carbene ligand, also in analogy with this type of
assignment for other alkylalkoxycarbene complexes of
Pt(II),17 while the strong band at ca. 1050 cm-1 is due
to the tetrafluoroborate anion. The 31P{1H} NMR
spectrum confirms the trans geometry (a singlet with
195Pt satellites for the phosphines). This geometry is
F igu r e 1. ORTEP drawing of trans-[Pt(Me){dCCH(p-
tolyl)CH2CH2O}(PPh3)2] (cation of 1).
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for Com p ou n d 1
Pt-P(1)
2.306(2)
2.122(9)
1.819(8)
1.820(8)
1.824(9)
1.27(1)
1.53(1)
1.50(2)
1.36(2)
1.37(2)
1.40(3)
1.38(2)
Pt-P(2)
2.314(2)
2.013(8)
1.829(9)
1.831(9)
1.833(9)
1.50(1)
1.45(2)
1.51(1)
1.39(2)
1.36(2)
1.53(2)
Pt-C(37)
Pt-C(38)
1
P(1)-C(1)
P(1)-C(7)
also supported by the H NMR spectrum, which shows
the CH3 ligand as a triplet resonance, flanked by 195Pt
satellites, due to coupling with the two magnetically
equivalent PPh3 ligands (see Experimental Section). In
P(1)-C(13)
P(2)-C(25)
O-C(38)
P(2)-C(19)
P(2)-C(31)
O-C(39)
C(38)-C(41)
C(40)-C(41)
C(42)-C(43)
C(43)-C(44)
C(45)-C(46)
C(46)-C(47)
C(39)-C(40)
C(41)-C(42)
C(42)-C(47)
C(44)-C(45)
C(45)-C(48)
1
the H NMR each proton of the -CH2- groups of the
ring appears as a distinct multiplet, due to geminal
coupling and the adjacent protons. A similar behavior
was previously observed for other cyclic carbene com-
plexes of Pt(II).5c The 13C NMR spectrum gives ad-
ditional information about the ring structure of the
carbene ligand, which can be deduced from the analysis
of the 13C-coupled spectrum. In fact, the 1J (CH) values
in saturated heterocyclic compounds are related to the
electronegativity of the heteroatom and to the influence
of ring strain on hybridation, and they provide informa-
tion about the ring size of the heterocycle.18 In the case
P(2)-Pt-C(37)
C(37)-Pt-C(38)
P(1)-Pt-C(37)
Pt-P(1)-C(13)
Pt-P(1)-C(1)
C(1)-P(1)-C(13)
Pt-P(2)-C(31)
Pt-P(2)-C(19)
C(19)-P(2)-C(31)
C(38)-O-C(39)
O-C(38)-C(41)
O-C(39)-C(40)
86.5(2) P(1)-Pt-C(38)
174.9(3) P(2)-Pt-C(38)
84.9(2) P(1)-Pt-P(2)
116.5(3) Pt-P(1)-C(7)
110.5(3) C(7)-P(1)-C(13)
106.3(4) C(1)-P(1)-C(7)
112.2(3) Pt-P(2)-C(25)
114.3(3) C(25)-P(2)-C(31)
105.7(4) C(19)-P(2)-C(25)
114.2(7) Pt-C(38)-O
95.0(2)
94.0(2)
170.43(7)
116.4(3)
100.0(4)
106.2(4)
115.0(3)
105.2(4)
103.5(4)
121.7(6)
128.8(6)
1
of 1, the J (CH) values (ca. 123-156 Hz) of the carbene
109.1(7) Pt-C(38)-C(41)
103.1(9) C(39)-C(40)-C(41) 108(1)
ligand are in agreement with those found for five-
membered O-heterocycles.18 The carbene carbon reso-
C(38)-C(41)-C(40) 103.0(8) C(40)-C(41)-C(42) 121(1)
C(38)-C(41)-C(42) 117.0(8) C(41)-C(42)-C(47) 124(1)
1
nates at 306.95 ppm with a J CPt value (849 Hz) typical
of carbene complexes.19
C(41)-C(42)-C(43) 120(1)
C(42)-C(43)-C(44) 121(1)
C(44)-C(45)-C(48) 124(1)
C(46)-C(45)-C(48) 120(1)
C(42)-C(47)-C(46) 122(1)
C(43)-C(42)-C(47) 117(1)
C(43)-C(44)-C(45) 124(1)
C(44)-C(45)-C(46) 116(2)
C(45)-C(46)-C(47) 120(1)
X-r a y Cr ysta l Str u ctu r e. Crystals of 1 suitable for
single-crystal X-ray analysis were grown by slow diffu-
sion of diethyl ether into a dichloromethane solution.
Selected bond lengths and angles are collected in Table
2, and an ORTEP plot of the molecular structure of the
cation is illustrated in Figure 1.
The complex geometry is defined by a distorted square
arrangement of the donor atoms with the two phos-
phines mutually trans. The best mean plane of the
coordinated atoms exhibits deviations of 0.008(2), 0.009-
(2), -0.171(9), and -0.137(8) Å for P(1), P(2), C(37), and
C(38), respectively, with a Pt deviation of -0.0618(4)
Å. The values of the P(1)-Pt-P(2) and C(37)-Pt-C(38)
angles are 170.43(7) and 174.9(3)°, respectively, which
further support the irregularities in the coordination
sphere. The contraction of the P(1)-Pt-P(2) angle is
likely related to the need to leave more space in order
to accommodate the carbene ligand. This latter ligand
has a half-chair conformation, and its mean plane forms
a dihedral angle of 107(4)° with that of the tolyl ligand
and of 96.3(3)° with the coordination plane (the torsion
angle C(38)-C(41)-C(42)-C(43) is 94(1)°). Two of the
three bond angles at C(38) deviate significantly from
120°, the O-C(38)-C(41) angle being 109.3(7)°, which
is comparable to the values of the corresponding angle
(17) Chisholm, M. H.; Clark, H. C.; J ohns, W. S.; Ward, J . E. H.;
Yasufuku, K. Inorg. Chem. 1975, 14, 900.
(18) Kalonowski, H. O.; Berger, S.; Braun, S. Carbon-13 NMR
Spectroscopy; Wiley: New York, 1988; p 488.
(19) Mann, B. E.; Taylor, B. F. 13C NMR Data for Organometallic
Compounds; Academic Press: New York, 1981.
(20) (a) Stepaniak, R. F.; Payne, N. C. J . Organomet. Chem. 1973,
7, 213. (b) Ibid. 1974, 72, 453.

Notes
Organometallics, Vol. 15, No. 19, 1996 4099
for similar Pt(II) alkylalkoxycarbenes,7,20 while Pt-
C(38)-C(41) is 128.8(6)°. On the other hand, the Pt-
C(38)-O bond angle is 121.7(6)° and this contraction
(compared to that observed for the symmetric Pt-
C(38)-C(41) angle) appears to be related to a Pt‚‚‚O
contact of 2.89(1) Å.
The Pt-C(38) and C(38)-O bond distances of 2.014-
(8) and 1.27(1) Å are relatively short and may be
compared with those found for cationic alkylalkoxycar-
benes of Pt(II) having a methyl group as the trans
ligand, such as trans-[Pt(Me){C(OMe)Me}(PMe2Ph)2]-
[PF6] (Pt-Ccarbene ) 2.13(1) Å, Ccarbene-O ) 1.33 Å)20a
would then be more electrophilic and susceptible to
attack by the â-carbon of the vinyl unit, resulting in the
formation of 1.
Another possible mechanism (eq 3) involves initial
protonation of the oxirane, which would then be acti-
vated to attack the weakly nucleophilic â-carbon of the
acetylide to give the reactive (hydroxyethyl)vinylidene
complex C, which would cyclize by attack of oxygen at
the vinylidene R-carbon and transfer of the OH proton
to the vinylidene â-carbon. Protonated oxirane is
and trans-[Pt(Me){COCH2CH2CH2}(PMe2Ph)2][PF6] (Pt-
Ccarbene ) 2.00(2) Å, Ccarbene-O ) 1.26(2) Å).20b
P ossible Mech a n ism s. Route a to 1 by reaction of
the acetylide complex with oxirane in the presence of
acid (Scheme 1) could proceed (eq 2) by initial protona-
tion of the acetylide ligand to give the reactive vi-
nylidene complex A; the latter undergoes attack by the
oxirane to give B, which cyclizes to the product 1. Since
known22 to undergo attack by a variety of weak nucleo-
philes. While both mechanisms (eqs 2 and 3) are
possible, it is not now possible to assign a specific
mechanism to the reaction that leads to 1 by route a.
The formation of 1 from [Pt-solv]+, HCtCR, and
oxirane by route b (Scheme 1) could occur by either of
the mechanisms in eqs 2 and 3. The acid (H+) required
in both of these mechanisms could be generated by the
reaction of [Pt-solv]+ with HCtCR to give [PtCtCR]
and H+.
While the synthesis of cyclic oxycarbene complexes
from acetylenes as shown in Scheme 1 provides a simple
route to such complexes, further studies of the mecha-
nism are required. Work is in progress to explore the
range of alkynyl and/or alkyne complexes of various
transition metals which would undergo reactions with
oxirane to form cyclic oxycarbenes as well as those using
other three-membered heterocycles such as aziridine
and thiirane.
no vinylidene complexes of Pt(II) have been detected8
upon protonation of Pt(II)-acetylide complexes, the
formation of A would presumably occur to only a small
extent. However, such protonated acetylides (A) have
been proposed as intermediates in reactions of Pt(II)
acetylides with alcohols in the presence of acid to form
Pt(II)-alkoxycarbene complexes.8a These latter species
were first synthesized by Chisholm and Clark upon
reaction of terminal alkynes in MeOH or EtOH in the
presence of trans-[Pt(CH3)Cl(PR3)2] and AgPF6.21 If A
were highly electrophilic, it could presumably react even
with the weakly nucleophilic oxirane22 to generate B.
The CH2 groups of the oxirane in this intermediate
Ack n ow led gm en t. R.A.M. thanks the MURST and
CNR for financial support. R.A.M. and R.J .A. thank
NATO for a grant (No. CRG 931224).
Su p p or tin g In for m a tion Ava ila ble: Tables giving aniso-
tropic thermal parameters, all bond lengths and angles,
fractional atomic coordinates and equivalent isotropic dis-
placement parameters, and fractional coordinates of hydrogen
atoms (7 pages). Ordering information is given on any current
masthead page.
(21) Chisholm, M. H.; Clark, H. C. Acc. Chem. Res. 1973, 6, 202
and references therein.
(22) Barton, D.; Ollis, W. D. Comprehensive Organic Chemistry;
Stoddardt, J . F., Ed.; Pergamon Press: Oxford, U.K., 1979; Vol. 1.
OM960274O