Unprecedented reactivity of 1-alkynes with 2-chloroethanol promoted by cationic solvento(trifluoromethyl)platinum(II) complexes. Synthesis of β-alkoxyalkenyl derivatives and X-ray structure of trans-[Pt{C(H)=C(Ph)OCH2CH2Cl}(CO)(PPh3) 2][BF4]·Et2O

Article abstract of DOI:10.1021/om970467r

Reactions at ambient temperature of the solvento cationic trifluoromethyl complex trans-[Pt(CF₃)(PPh₃)₂(solv)][BF₄] with 1.5 equiv of 1-alkynes RC≡CH (R = Ph, p-tolyl) and 2-chloroethanol afford in high yield the β-alkoxyalkenyl complexes trans-[Pt{C(H)=C(R)-OCH₂CH₂Cl}(CO)(PPh₃) ₂][BF₄] (R = Ph (1), p-tolyl (2)). In these reactions the CF₃ group is also converted to a CO ligand. Complexes 1 and 2 were characterized by spectroscopic techniques and 1 also by an X-ray diffraction analysis. Reaction of the alkynyl complex trans-[Pt(CF₃)(C≡C-p-tolyl)(PPh₃)₂] with 2-chloroethanol and 1 equiv of HBF₄ gives the acetylide-carbonyl derivative trans-[Pt(C≡C-p-tolyl)(CO)(PPh₃)₂][BF₄] (3), which was also formed by reaction of trans-[Pt(CF₃)(C≡C-p-tolyl)(PPh₃)₂] with aqueous HBF₄. Possible mechanisms of these reactions are discussed. ? Dedicated to Professor Warren R. Roper on the occasion of his 60th birthday.

Full text of DOI:10.1021/om970467r

1220
Organometallics 1998, 17, 1220-1226
Un p r eced en ted Rea ctivity of 1-Alk yn es w ith
2-Ch lor oeth a n ol P r om oted by Ca tion ic
Solven to(tr iflu or om eth yl)p la tin u m (II) Com p lexes.
Syn th esis of â-Alk oxya lk en yl Der iva tives a n d X-r a y
Str u ctu r e of
tr a n s-[P t{C(H)dC(P h )OCH2CH2Cl}(CO)(P P h 3)2][BF 4]‚Et2O†
Rino A. Michelin,* Mirto Mozzon, Barbara Vialetto, and Roberta Bertani
Dipartimento di Processi Chimici dell’Ingegneria and Centro di Studio per la Chimica e
Tecnologia dei Composti Metallorganici degli Elementi di Transizione del CNR,
Universita` di Padova, Via F. Marzolo 9, 35131 Padova, Italy
Giuliano Bandoli
Dipartimento di Scienze Farmaceutiche, Universita` di Padova, Via F. Marzolo 5,
35131 Padova, Italy
Robert J . Angelici
Department of Chemistry, Iowa State University, Ames, Iowa 50011
Received J une 5, 1997
Reactions at ambient temperature of the solvento cationic trifluoromethyl complex trans-
[Pt(CF3)(PPh3)2(solv)][BF4] with 1.5 equiv of 1-alkynes RCtCH (R ) Ph, p-tolyl) and
2-chloroethanol afford in high yield the â-alkoxyalkenyl complexes trans-[Pt{C(H)dC(R)-
OCH2CH2Cl}(CO)(PPh3)2][BF4] (R ) Ph (1), p-tolyl (2)). In these reactions the CF3 group is
also converted to a CO ligand. Complexes 1 and 2 were characterized by spectroscopic
techniques and 1 also by an X-ray diffraction analysis. Reaction of the alkynyl complex
trans-[Pt(CF3)(CtC-p-tolyl)(PPh3)2] with 2-chloroethanol and 1 equiv of HBF4 gives the
acetylide-carbonyl derivative trans-[Pt(CtC-p-tolyl)(CO)(PPh3)2][BF4] (3), which was also
formed by reaction of trans-[Pt(CF3)(CtC-p-tolyl)(PPh3)2] with aqueous HBF4. Possible
mechanisms of these reactions are discussed.
In tr od u ction
We have previously reported that unsaturated ligands
such as CO,1 RNC,2 and RCN3 in carbonyl, isocyanide,
and nitrile complexes of various transition metals
undergo cyclization reactions with 2-chloroethanol or
oxirane to form five-membered dioxy-, aminooxy-, and
N-coordinated 2-oxazoline derivatives, respectively. Re-
cently, this reaction chemistry has been extended to
PtII-alkyne and -alkynyl complexes. Thus, it has been
shown for instance that the reaction of PhCtCH in
2-chloroethanol with the solvento cationic complex
trans-[Pt(Me)(PPh3)2(solv)][BF4] (eq 1) or the reactions
of the halo alcohols HO(CH2)nCl (n ) 2,3) in the
presence of 1 equiv of HBF4 with the acetylides trans-
[Pt(CH3)(CtCR)(PPh3)2] (R ) Ph, p-tolyl) (eq 2) afforded
† Dedicated to Professor Warren R. Roper on the occasion of his 60th
birthday.
(1) (a) Motschi, H.; Angelici, R. J . Organometallics 1982, 1, 343. (b)
Zanotto, L.; Bertani, R.; Michelin, R. A. Inorg. Chem. 1990, 29, 3265.
(2) (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.
(3) Michelin, R. A.; Mozzon, M.; Bertani, R. Coord. Chem. Rev. 1996,
147, 299.
alkylalkoxycarbene complexes, formally originating from
the addition of the halo alcohol at the R-carbon atom of
the alkyne or the alkynyl, with no evidence of cyclization
reaction products as found for other C- or N-unsaturated
S0276-7333(97)00467-6 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 02/26/1998

Cationic Pt(II) Solvento Trifluoromethyl Complexes
Organometallics, Vol. 17, No. 6, 1998 1221
ligands.4 In this respect the reactions of halo alcohols
with PtII-alkynyl and -alkyne complexes parallel those
reported in the literature with MeOH.5 On the other
hand, similar reactions with oxirane gave cyclic oxy-
carbene complexes, as illustrated in eq 3.6
solution of AgBF4 (1.56 mL, 0.348 mmol) in acetone. The
reaction mixture was stirred for 1 h; then the precipitate of
AgCl was filtered off and the solution was treated with NEt3
(73 µL, 0.522 mmol) and p-tolylacetylene (132 µL, 1.044 mmol).
The reaction mixture was stirred overnight to give a brown
precipitate. After filtration, the solid residue was treated with
CH2Cl2 (25 mL) and the resulting filtered solution was reduced
to a small volume under reduced pressure. Addition of
n-pentane (15 mL) gave a white solid, which was filtered,
washed with n-pentane (3 × 5 mL), and dried under vacuum.
Yield: 110 mg (35%). Mp: 209-211 °C dec. Anal. Calcd for
C
46H37F3P2Pt‚CH2Cl2: C, 57.09; H, 3.98. Found: C, 58.06; H,
4.00. IR (Nujol, cm-1): ν(CtC) 2113 (s). 1H NMR: 2.11 [s,
3H, CH3]. 19F NMR: -16.33 [t, 2J (FPt) 469, 3J (FP) 14.6, CF3].
1
3
31P{1H} NMR: 21.80 [q, J (PPt) 2898, J (PF) 14.62].
The same complex can also be prepared using n-BuLi
instead of NEt3. The cationic solvento complex trans-[Pt(CF3)-
(PPh3)2(solv)][BF4], obtained from trans-[Pt(CF3)Cl(PPh3)2]7
(750 mg, 0.91 mmol) and a 0.46 M solution of AgBF4 (2 mL,
0.91 mmol) in acetone (40 mL), was dissolved in 30 mL of THF,
and the suspension was treated with n-BuLi (0.85 mL, 1.365
mmol) and p-tolylacetylene (0.346 mL, 2.73 mmol). The
solution became pale yellow and was stirred for 2 h at room
temperature. During this time a precipitate formed. After
filtration, the solid residue was treated with CH2Cl2 (20 mL)
and the resulting filtered solution was reduced to a small
volume under reduced pressure. Addition of n-pentane (20
mL) gave a white solid, which was filtered, washed with
n-pentane (3 × 5 mL), and dried under vacuum. Yield: 0.386
g (47%).
During these investigations, we found that the reac-
tions of unsaturated cationic trifluoromethyl complexes
of Pt(II) of the type trans-[Pt(CF3)(PPh3)2(solv)][BF4]
with 1-alkynes (RCtCH, R ) Ph, p-tolyl) and 2-chloro-
ethanol proceed differently from those of the parent CH3
derivatives (eq 1), since Pt(II) complexes containing a
â-alkoxyalkenyl (or vinyl ether) ligand, -C(H)dC(OCH2-
CH2Cl)R, formally originating from the addition of the
halo alcohol at the â-carbon atom of the alkyne ligand,
are formed. Also, the reaction of the acetylide complex
trans-[Pt(CF3)(CtC-R)(PPh3)2] (R ) p-tolyl) with 2-
chloroethanol in the presence of HBF4 proceeds differ-
ently from that of the parent CH3 derivative (eq 2). The
results of this study are reported herein.
Syn th esis of tr a n s-[P t{C(H)dC(P h )OCH2CH2Cl}(CO)-
(P P h 3)2][BF 4] (1). A 0.95 M acetone solution of AgBF4 (0.363
mL, 0.345 mmol) was added to a suspension of trans-
[Pt(CF3)Br(PPh3)2] (300 mg, 0.345 mmol) in 50 mL of CH2Cl2.
The reaction mixture was stirred for 40 min at room temper-
ature; then the precipitate of AgBr was filtered off and the
yellow solution was concentrated under reduced pressure to
ca. 15 mL. Diethyl ether (100 mL) was added, and the
resulting white precipitate of the cationic complex trans-
[Pt(CF3)(PPh3)2(solv)][BF4] was collected by filtration and dried
under vacuum. The cationic solvento complex was dissolved
in 30 mL of THF, and the solution was treated with 2-chloro-
ethanol (2 mL) and phenylacetylene (57 µL, 0.518 mmol). The
reaction mixture was stirred for 1 h at room temperature and
then taken to dryness. The solid residue was dissolved in
CH2Cl2 (5 mL), and upon addition of diethyl ether (15 mL)
and n-hexane (15 mL) a white solid precipitated which was
filtered, washed with n-hexane (3 × 5 mL), and dried under
vacuum. Yield: 0.251 g (80.5%). Mp: 170-172 °C dec. Anal.
Calcd for C47H40O2ClBF4P2Pt: C, 55.56; H, 3.97. Found: C,
55.05; H, 4.05. IR (Nujol, cm-1): ν(CO) 2103 (s); ν(CdC) 1590
Exp er im en ta l Section
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. 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 residual 1H
resonance in the deuterated solvent: CDCl3, δ 7.23. The
13C{1H} NMR shifts are given relative to the solvent reso-
nance: CDCl3, δ 77.0. The 31P{1H} NMR spectra (CDCl3) were
run on a Varian FT 80-A spectrometer; the chemical shift is
referenced to external 85% H3PO4 with the downfield value
taken as positive. The 19F NMR spectrum (CDCl3) was run
on a Varian FT 80-A spectrometer, with CFCl3 as internal
reference. In all the NMR spectra chemical shifts are in ppm
and J values are in Hz (abbreviations used: s ) singlet, t )
triplet, q ) quartet). The elemental analyses were performed
by the Department of Analytical, Inorganic and Organo-
metallic Chemistry of the University of Padova. The melting
points were taken on a hot plate apparatus and are uncor-
rected. Phenylacetylene and p-tolylacetylene were commer-
cially available products and were used as received.
3
2
cm-1 (m-w). 1H NMR: 4.88 [t, J (HP) 4.98, J (HPt) 37.2, 1H,
3
3
CHd], 3.42 [t, J (HH) 5.41, 2H, OCH2], 2.99 [t, J (HH) 5.41,
2H, CH2Cl]. 31P{1H} NMR: 14.4 [s, J (PPt) 2553].
1
Syn th esis of tr a n s-[P t{C(H)dC(p-tolyl)OCH2CH2Cl}-
(CO)(P P h 3)2][BF 4] (2). This compound was prepared by
treating trans-[Pt(CF3)Br(PPh3)2] (212 mg, 0.244 mmol) in 20
mL of CH2Cl2 at room temperature with a 0.46 M acetone
solution of AgBF4 (0.53 mL, 0.244 mmol). After the solid AgBr
was removed, the solution was taken to dryness and the
cationic solvento complex was dissolved in 20 mL of 2-chloro-
ethanol and then p-tolylacetylene (46 µL, 0.366 mmol) was
added. The colorless solution became immediately dark red.
The reaction mixture was stirred for 1.5 h at room temperature
and then taken to dryness. The solid residue was dissolved
in acetone (5 mL), and upon addition of diethyl ether (20 mL)
a white solid precipitated which was filtered, washed with
diethyl ether (3 × 5 mL), and dried under vacuum. Yield:
182.2 mg (72.5%). Mp: 134-136 °C dec. Anal. Calcd for
The complex trans-[Pt(CF3)Br(PPh3)2]7 was prepared ac-
cording to the literature procedure, while trans-[Pt(CF3)-
(CtC-p-tolyl)(PPh3)2] was prepared as follows. A suspension
of trans-[Pt(CF3)Br(PPh3)2] (302 mg, 0.348 mmol) in acetone
(50 mL) at room temperature was treated with a 0.244 M
(4) Belluco, U.; Bertani, R.; Michelin, R. A.; Mozzon, M.; Benetollo,
F.; Bombieri, G.; Angelici, R. J . Inorg. Chim. Acta 1995, 240, 567.
(5) Chisholm, M. H.; Clark, H. C. Acc. Chem. Res. 1973, 6, 202.
(6) Michelin, R. A.; Mozzon, M.; Vialetto, B.; Bertani, R.; Benetollo,
F.; Bombieri, G.; Angelici, R. J . Organometallics 1996, 15, 4096.
(7) Michelin, R. A.; Napoli, M.; Ros, R. J . Organomet. Chem. 1979,
175, 239.
C
48H42O2ClBF4P2Pt: C, 55.97; H, 4.11. Found: C, 55.57; H,
3.97. IR (Nujol, cm-1): ν(CO) 2099 (s); ν(CdC) 1588 cm-1 (m-

1222 Organometallics, Vol. 17, No. 6, 1998
Michelin et al.
Ta ble 1. Cr ysta l Da ta for Com p ou n d 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
formula
[C47H40ClO2P2Pt][BF4]‚(C2H5)2O
fw
1090.1
0.10 × 0.15 × 0.25
orthorhombic
19.141(3)
20.113(3)
23.768(4)
9150(2)
Pbca
Pt-P(1)
Pt-P(2)
Pt-C(1)
Pt-C(5)
C(5)-O(2)
2.353(4)
2.345(4)
2.02(2)
1.91(2)
1.14(2)
C(1)-C(2)
C(2)-O(1)
C(3)-O(1)
C(3)-C(4)
Cl-C(4)
1.31(2)
1.46(2)
1.41(2)
1.46(2)
1.76(2)
cryst dimens, mm
cryst syst
a, Å
b, Å
c, Å
V, Å3
P(1)-Pt-P(2)
P(1)-Pt-C(1)
P(1)-Pt-C(5)
P(2)-Pt-C(1)
P(2)-Pt-C(5)
C(1)-Pt-C(5)
174.1(1)
88.3(4)
91.5(4)
87.9(4)
92.3(4)
179.3(6)
Pt-C(5)-O(2)
Pt-C(1)-C(2)
C(1)-C(2)-O(1)
C(2)-O(1)-C(3)
Cl-C(4)-C(3)
177(1)
131(2)
120(2)
121(2)
107(2)
space group
F(calcd), g cm-3
Z
1.583
8
F(000)
4368
λ(Mo KR), Å
µ(Mo KR), cm-1
no. of rflns measd
scan method
2θmax, deg
no. of obsd rflns [I > 2σ(I)]
final R(F)a
Rw(F2)b
0.710 73
32
5979
ω-2θ
45
4251
0.069
0.187
from electron density calculations and introduced in a se-
quence of cycles where occupancies and isotropic thermal
coefficients were refined alternatively. They were maintained
constant during the rest of the structure refinement; neverthe-
less, such a treatment of the disorder led to unreasonable bond
distances and no other attempt was made to solve this
disorder. The largest shift/error ratio in the final cycle was
0.05 in the cation and, although a difference peak with a
magnitude of about 1 e Å-3 was seen at about 1 Å from the Pt
atom, no significant electron density was observed at chemi-
cally reasonable distances from the other atoms. Selected bond
distances and angles are given in Table 2. Structure deter-
mination and refinement were performed with the SHELXTL/
PC and SHELXTL-93 program packages.8
no. of params refined
286
GOFc
1.43
a
b
2
2
R(F) ) ||Fo| - |Fc||/∑|Fo|. Rw(F2) ) [∑(w(|Fo| - |Fc| )2)/
∑w(|Fo| )]1/2
.
c GOF ) [∑(w(|Fo| - |Fc| )2)/(n - p)]1/2
.
2
2
2
w). 1H NMR: 4.80 [t, 3J (HP) 4.84, 2J (HPt) 35.07, 1H, CH],
2.98 [t, 3J (HH) 5.47, 2H, CH2Cl], 3.45 [t, 3J (HH) 5.47, 2H,
OCH2], 2.28 [s, 3H, CH3-p-C6H4]. 31P{1H} NMR: 15.36 [s,
1J (PPt) 2557]. 13C{1H} NMR: 175.74 (s, CO), 154.01 [t, 2J (CP)
25.0, 195Pt satellites too weak to be observed, CH], 104.04 [t,
2J (CPt) 213.62, 3J (CP) 10.77, C-C6H4-p-Me], 66.43 [s, OCH2],
42.80 [s, CH2Cl], 21.11 [CH3].
Resu lts
Syn th esis of â-Alk oxya lk en yl Com p lexes. The
reactions leading to 1 and 2 are summarized in eq 4.
Syn th esis of tr a n s-[P t(CtC-p-tolyl)(CO)(P P h 3)2][BF 4]
(3). To a solution of trans-[Pt(CF3)(CtC-p-tolyl)(PPh3)2] (151
mg, 0.167 mmol) in benzene (30 mL) at 0 °C was added a 54%
solution of HBF4 in Et2O (13 µL, 0.184 mmol) and ClCH2CH2-
OH (0.2 mL, 2.98 mmol). After the ice-water bath was
removed, the reaction mixture was stirred for a few hours at
room temperature. The pale yellow solution was then con-
centrated under reduced pressure to ca. 5 mL, and upon
addition of diethyl ether (10 mL) a white solid precipitated.
After filtration the solid obtained was washed with n-pentane
(3 × 5 mL), and dried under vacuum. Yield: 70 mg (44%).
Mp: 286-288 °C dec. Anal. Calcd for C46H37BF4OP2Pt: C,
58.18; H, 3.93. Found: C, 58.08; H, 3.80. IR (Nujol, cm-1):
ν(CO) and ν(CtC) 2129 cm-1 (s) partially overlapped. 1H
NMR: 2.12 [s, 3H, CH3]. 31P{1H} NMR: 16.01 [s, 1J (PPt)
2161]. Complex 3 was also obtained by reaction of trans-
[Pt(CF3)(CtC-p-tolyl)(PPh3)2] (115 mg, 0.123 mmol) with a
48% aqueous solution of HBF4 (3 drops). The suspension was
stirred for 24 h at room temperature. Then the solid was
filtered, washed with n-pentane (3 × 5 mL), and dried under
vacuum. Yield: 0.053 g (45%).
Cr ysta l Str u ctu r e Deter m in a tion . Crystal data and
summary of data collection and structure refinement details
for 1 are collected in Table 1. Crystals were grown by slow
diffusion of Et2O into a CH2Cl2 solution of 1. A yellow crystal
was mounted on a glass fiber with epoxy, and all measure-
ments were made on a Nicolet Siemens R3m/V four-circle
diffractometer. Cell constants were obtained from a least-
squares refinement, using the setting angles of 50 reflections
with 2θ > 20°. Three reflections were measured every 200
reflections as orientation and intensity control, and significant
intensity decay (up to 15%) was observed. Decay, Lorentz, and
polarization, but no absorption, corrections were made. The
structure was solved by standard Patterson and Fourier
methods and refined by full-matrix least squares against F2
with application of anisotropy only to Pt, P, and Cl atoms.
Difference maps showed that the ether molecule was disor-
Treatment in CH2Cl2 of trans-[Pt(CF3)(Br)(PPh3)2] with
1 equiv of an acetone solution of AgBF4 at ambient
temperature affords, after filtration of AgBr, in almost
quantitative yield the cationic solvento complex trans-
[Pt(CF3)(PPh3)2(solv)][BF4], which can be isolated as a
white crystalline product upon addition of Et2O to the
dichloromethane solution.9 This latter complex was
then dissolved in 2-chloroethanol and treated with ca.
1.5 equiv of the terminal acetylene to give a dark red
solution, which was stirred for ca. 1-1.5 h at room
temperature. After this time, workup of the reaction
mixture afforded 1 and 2 in ca. 80 and 72% yield,
respectively, as the only isolated reaction products.
(8) (a) Sheldrick, G. M. SHELXTL/PC, Version 5.03; Siemens
Analytical X-ray Instruments Inc., Madison, WI, 1994. (b) Sheldrick,
G. M. SHELXL-93, Program for the Refinement of Crystal Structures;
University of Go¨ttingen, Go¨ttingen, Germany, 1993.
-
dered into, at least, two positions and in addition the BF4
anion showed signs of the usual rotational disorder. Occupan-
cies of the disordered Et2O solvate molecule were estimated

Cationic Pt(II) Solvento Trifluoromethyl Complexes
Organometallics, Vol. 17, No. 6, 1998 1223
F igu r e 1. (a, left) ORTEP drawing of trans-[Pt{C(H)dC(Ph)OCH2CH2Cl}(CO)(PPh3)2]+ (cation of 1). Thermal ellipsoids
-
for Pt, P, and Cl atoms are shown at 40% probability. The solvate molecule and the BF4 anion have been omitted for
clarity. (b, right) Drawing of the cation viewed down the P(1)‚‚‚P(2) axis, showing the phenyl ring arrangement. The atoms
are shown as arbitrarily sized uniform circles.
The structures of 1 and 2 were assigned on the basis
of microanalytical, IR, and multinuclear (1H, 31P, 13C)
NMR data and also by an X-ray structural determina-
tion carried out for 1 (see below). The IR spectra (Nujol
mulls) show a strong absorption at ca. 2100 cm-1 due
to the carbonyl ligand and also a weak-medium band
at ca. 1600 cm-1, which can be assigned to the CdC
stretching of the vinyl group. The strong absorption at
tures. In the cation the Pt atom has C2P2 roughly
square planar (within 0.05(2) Å) coordination (Figure
1a) and deviates by 0.04 Å from the mean plane of the
four donors. There is some deformation from the ideal
square with the internal angles in the range 87.9-92.3°
and P(1)-Pt-P(2) and C(1)-Pt-C(5) angles of 174.1
and 179.3°, respectively. The phenyl ring of the organic
ligand is virtually perpendicular to the platinum coor-
dination plane, the dihedral angle being 87.6°, while the
C(1)dC(2)-O(1) portion makes a dihedral angle of 85.1°
with the same plane. The P(1)‚‚‚P(2) axis is perpen-
dicular to the C(1)‚‚‚C(5) (angle of 90.6°) and to the
C(1A)‚‚‚C(4A) line (angle of 88.9°). The phenyl rings
C(1B)/C(1F), C(1C)/C(1E), and C(1D)/C(1G) are inclined
to one another by 35.2, 21.0, and 38.7°, respectively
(Figure 1b). Comparison of the bond distances with the
data reported in a survey,10 covering inter alia the
mononuclear Pt(II) complexes, and completed by the
recent entries from the Cambridge Structural Database
(CSD), shows a somewhat lengthened Pt-PPh3 bond
(mean 2.349 Å compared to a reference value of 2.30
Å), accompanied by a shortening of the Pt-CO bond
(1.91 vs 2.04 Å), while the Pt-C(1) bond length com-
pares well with those found for similar complexes (2.02
vs 2.05 Å). The relatively short O(2)‚‚‚O(2) (at 1 - x,
-y, -z) contact of 2.93 Å represents the only separation
at van der Waals contact distances.
ca. 1050 cm-1 is due to the BF4 ion.
-
The trans geometry of 1 and 2 is clearly determined
by the 31P{1H} NMR spectra, which show a singlet for
the magnetically equivalent trans PPh3 ligands, ac-
companied by 195Pt satellites (see Experimental Section).
1
The H NMR spectra of 1 and 2 show, in particular, the
vinyl proton (δ 4.74-4.98) as a triplet due to coupling
with the two P atoms (3J HP ca. 4.9), flanked by 195Pt
satellites (2J HPt ca. 35-37). Two triplets at ca. δ 3.4
and 2.9 are also observed, which have been assigned to
the -OCH2- and -CH2Cl methylene protons, respec-
tively, of the alkoxy substituent (3J HH ca. 5.4). The
13C{1H} NMR spectrum carried out for 2 shows the
R-vinyl carbon at δ 154.0 as a triplet due to coupling
with the two cis P atoms (2J CP 25.0), while the 195Pt
satellites were too weak to be observed. The carbonyl
carbon resonance appears as a singlet at δ 175.7.
X-r a y Cr ysta l Str u ctu r e of 1. Figure 1 illustrates
the molecular geometry of the cation complex. As can
be seen from the esd’s, the structure is not a particularly
accurate one (see Experimental Section), but it does
answer a chemical question and the model provides an
adequate conclusion about binding/stereochemistry fea-
Discu ssion
Formation of â-alkoxyalkenyl complexes by nucleo-
philic attack of alcohols on alkynes activated by coor-
dination to an electron-withdrawing transition-metal
center has been reported for internal alkynes, RCtCR,5
(9) The cationic solvento complex trans-[Pt(CF3)(PPh3)2(solv)][BF4]
so prepared appears, on the basis of NMR data, to be a mixture of two
species, likely due to two different coordinated solvent molecules, e.g.
Et2O and CH2Cl2, while the presence of coordinated acetone can be
ruled out on the basis of IR data. 31P{1H} NMR (CDCl3): δ 26.11 (q,
(10) (a) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.;
Watson, D. G.; Taylor, R. J . Chem. Soc., Dalton Trans. 1989, S1-S83.
(b) Allen, F. H.; Davies, J . E.; J ohnson, O.; Kennard, O.; Macrae, C.
F.; Mitchell, E. M.; Mitchell, G. F.; Smith, J . M.; Watson, D. G. J . Chem.
Inf. Comput. Sci. 1991, 31, 187.
3
1
3
1J PPt 3040, J PF 20.2), 26.52 (q, J PPt 3050, J PF 20.9). 19F NMR
2
3
2
3
(CDCl3): -9.18 (t, J PtF 768, J PF 20.2 Hz), -8.91 (t, J PtF 802, J PF
20.9). In CD3COCD3 the 31P NMR spectrum shows the presence of only
1
3
one species at δ 32.08 (q, J PPt 3094, J PF 20.0).

1224 Organometallics, Vol. 17, No. 6, 1998
Michelin et al.
Sch em e 1
while similar reactions with terminal alkynes, RCtCH,
lead to the formation of alkylalkoxycarbene deriva-
tives.5,11 Thus, for instance, reactions in methanol of
trans-[Pt(Me)(Cl)L2] (L ) PMe2Ph, AsMe2Ph) complexes
with the acetylenes RCtCR (R ) CO2Me, CH2OH,
CO2H) in the presence of a silver salt gave cationic
â-alkoxyalkenyl derivatives of the type trans-[Pt{C(R)dC-
(OMe)R}L2]+,5 which did not show the presence of the
methyl group, being eliminated as methane according
to the eq 5.
by alcohols at the electrophilic R-carbon atom, as found
for several other transition-metal vinylidene com-
plexes.11a,b
The unexpected formation of â-alkoxyalkenyl deriva-
tives (eq 4) from terminal alkynes and 2-chloroethanol
when the trifluoromethyl cationic complex trans-[Pt(CF3)-
(PPh3)2(solv)]+ is the starting material must be related
to a different role of the CF3 ligand compared to CH3.
The electronic and chemical properties of the tri-
fluoromethyl group in transition-metal complexes have
been extensively investigated.13 Late-transition-metal
trifluoromethylated compounds are found to be signifi-
cantly more thermally and oxidatively stable and also
to have shorter M-C bond distances than the analogous
methylated species. As a consequence, the M-CF3
metal-carbon bond is less reactive and is stronger than
the M-CH3 metal-carbon bond.13 This finding has
been rationalized by invoking back-bonding from the
filled metal d orbitals to the nominally unoccupied C-F
antibonding orbitals, a type of bonding that is not
available to M-CH3 derivatives. This would explain, for
instance, the shortening of the Pt-Cl bond length in
the perfluoroalkyl complexes trans-[Pt(RF)Cl(PMePh2)2]
(RF ) CF3, C2F5) compared to that found in the methyl
derivative trans-[Pt(CH3)Cl(PMePh2)2].13b
Similarly, the cationic 2-butyne complex [Fe(η5-C5H5)-
(CO)(MeCtCMe)(PPh3)][BF4] reacts with a variety of
nucleophiles (H-, SBu-, SPh-, OEt-, CN-, CtCH-,
Ph-, Me-), giving the corresponding η1-vinyl complexes
formed by trans addition of the nucleophile with respect
to the metal.12 The observed reactivity was explained
with the formation of intermediate η2-alkyne species,
which could be also isolated for the Fe(II) complexes and
also in some cases for the Pt(II) derivatives.
The higher electron-withdrawing properties of the
CF3 group compared to CH3 would make the cationic
complex [Pt(CF3)(PPh3)2(solv)]+ more electrophilic, and
this feature may reasonably explain a greater stabiliza-
tion of the π-alkyne A compared to the vinylidene B
intermediate (Scheme 1).
Nucleophilic attack of 2-chloroethanol at the electro-
philic â-carbon atom of the π-alkyne A would lead to
the trifluoromethyl-â-alkoxyalkenyl intermediate C
with liberation of H+ and then to the final carbonyl-
â-alkoxyalkenyl complexes 1 and 2. The presence of B
as an intermediate is therefore ruled out because it
would be expected to lead to the formation of alkyl-
alkoxycarbene derivatives of type D, as otherwise found
for similar reactions of Pt(II) complexes with 1-alkynes
and alcohols.4,11a,b On the other hand, the intermediacy
of the η2-alkyne A appears to be supported by spectro-
scopic data, which have been obtained upon following
Conversely, as mentioned earlier, nucleophilic attack
by alcohols on terminal alkynes coordinated to Pt(II)
leads to alkylalkoxycarbene derivatives, as specifically
reported for the reactions of a number of cationic species
of the type trans-[Pt(CH3)(RCtCH)L2]+ (R ) aryl, L )
tertiary phosphine or arsine) with R′OH to give trans-
[Pt(CH3){dC(CH2R)OR′}L2}+ (R′ ) CH3,5 CH2CH2Cl4).
The same products are also formed by reaction of
platinum acetylides of the type trans-[Pt(CH3)(CtCR)-
L2] with R′OH in the presence of a strong acid (HBF4,
HPF6).4,5 In both cases, the formation of alkoxyalkyl-
carbene complexes may be reasonably explained by the
intermediacy of a PtII-vinylidene species4,11a,b (although
never isolated or characterized for Pt(II) systems),
PtdCdC(H)R, which then undergoes nucleophilic attack
(11) (a) Bruce, M. I.; Swincer, A. G. Adv. Organomet. Chem. 1983,
22, 59. (b) Bruce, M. I., Chem. Rev. 1991, 91, 197. (c) Bell, R. A.;
Chisholm, M. H.; Couch, D. A.; Rankel, L. A., Inorg. Chem. 1977, 16,
677.
(12) (a) Reger, D. L.; McElligott, P. J . J . Am. Chem. Soc. 1980, 102,
5924. (b) Reger, D. L.; Coleman, C. J .; McElligott, P. J . J . Organomet.
Chem. 1979, 171, 73.
(13) (a) Morrison, J . A. Adv. Organomet. Chem. 1993, 35, 211. (b)
Bennett, M. A.; Chee, H. K.; Robertson, G. B. Inorg. Chem. 1979, 18,
1061.

Cationic Pt(II) Solvento Trifluoromethyl Complexes
Organometallics, Vol. 17, No. 6, 1998 1225
Sch em e 2
reaction 4, but without any 2-chloroethanol added, by
19F and 31P NMR spectroscopy (eq 6).
(PPh3)2]. For instance, the reaction with an ethereal
solution of HBF4 affords the highly reactive difluoro-
carbene intermediate trans-[Pt(H)(dCF2)(PPh3)2][BF4],
which then converts to the hydrido-carbonyl derivative
trans-[Pt(H)(CO)(PPh3)2][BF4] in the presence of adven-
titious water in the reaction mixture. The rapid hy-
drolysis of metal-bound CF2 groups to CO has been
reported to occur also in certain complexes of Ru and
Fe.15
Rea ction of tr a n s-[P t(CF 3)(CtC-p-tolyl)(P P h 3)2]
w ith 2-Ch lor oeth a n ol a n d HBF 4. The reaction of the
alkynyl complex trans-[Pt(CF3)(CtC-p-tolyl)(PPh3)2],
HBF4 (1 equiv), and 2-chloroethanol (Scheme 2, route
a), yields trans-[Pt(CtC-p-tolyl)(CO)(PPh3)2][BF4] (3),
with no evidence of formation of â-alkoxyalkenyl (eq 4)
or carbene complexes (eq 2). Complex 3 was also
obtained by reaction of the acetylide with an aqueous
solution of HBF4 (route b).
To the initial solvento complex trans-[Pt(CF3)(PPh3)2-
(solv)][BF4] was added in CDCl3 1.5 equiv of p-toly-
lacetylene at room temperature. The 31P NMR spec-
trum of the reaction mixture shows after 30 min the
presence of a singlet at 16.04 ppm (1J PPt 2156), which
is assigned to trans-[Pt(CtC-p-tolyl)(CO)(PPh3)2][BF4]
(complex 3, see below) and a quartet at 14.91 ppm (3J FP
Complex 3 was characterized by microanalysis and
multinuclear (1H, 31P) NMR spectroscopy (see Experi-
mental Section). As also discussed earlier, the forma-
tion of 3 may be explained by an initial electrophilic
attack of HBF4 on a fluorine atom of the CF3 group to
give the difluorocarbene intermediate [Pt(dCF2)(CtC-
p-tolyl)(PPh3)2][BF4], which then rapidly reacts with
adventious H2O to afford the carbonyl derivative. Reac-
tion a of Scheme 2 was followed by 19F and 31P NMR at
the probe temperature. To an initial solution of trans-
[Pt(CF3)(CtC-p-tolyl)(PPh3)2] in CDCl3 was added 1
equiv of ethereal HBF4: 31P NMR shows the immediate
formation of 3 as the major product, together with two
small quartets, flanked by 195Pt satellites, which were
assigned on the basis of 19F NMR data to the solvento
species trans-[Pt(CF3)(PPh3)2(solv)][BF4] and the π-alkyne
complex trans-[Pt(CF3)(PPh3)2{η2-C(H)tC(p-tolyl)}][BF4],
respectively. It is also observed in the 19F NMR
spectrum that the resonance corresponding to the cat-
ionic solvento species slowly converts to that attributed
to the π-alkyne complex, which then converts to 3 and
eventually disappears upon addition of 2-chloroethanol.
1
18.6, J PPt 2447), which is attributed to the η2-alkyne
complex trans-[Pt(CF3)(PPh3)2{η2-C(H)tC(p-tolyl)}][BF4].
The assignment of this latter species appears to be
supported by 19F NMR data. In fact, the same reaction
mixture shows in the 19F NMR spectrum a new triplet,
2
flanked by 195Pt satellites, at -20.89 ppm with J FPt 618
3
and J FP 18.6; no other resonances were observed.
These data may be compared with those obtained in a
similar reaction of trans-[Pt(CF3)(PPh3)2(solv)][BF4] with
1 equiv of CH3CtCCH3, which would likely give trans-
[Pt(CF3)(PPh3)2{η2-C(CH3)tC(CH3)}][BF4] (δ(CF3) -20.62
3
(t), J FP 22.6). This latter complex is formed in a very
low concentration, and the 19F-195Pt coupling could not
be safely assigned; addition of more 2-butyne leads to
the formation of a white precipitate likely due to a poly-
merization process of the alkyne, as previously observed
by Chisholm and Clark.5
In the reactions reported in Scheme 1, a CF3 ligand
is converted to CO, as shown in the final complexes 1
and 2. The mechanism of this conversion is currently
not known. However, it is likely that this reaction
would initially proceed by electrophilic attack of H+ on
CF3 to give an intermediate difluorocarbene species. The
susceptibility of the C-F bonds in (trifluoromethyl)-
platinum(II) complexes to undergo electrophilic attack
by proton or Lewis acids was previously reported14 for
the trifluoromethyl-hydrido species trans-[Pt(CF3)(H)-
Thus, this reaction chemistry indicates that the
preferential sites of attack by H+ are the fluorine atoms
of the CF3 group rather than the â-carbon atom of the
acetylide, which would give a vinylidene intermediate,
as proposed for the other PtII-alkynyl reactions.4,11
(14) Michelin, R. A.; Ros, R.; Guadalupi, G.; Bombieri, G.; Benetollo,
F.; Chapuis, G. Inorg. Chem. 1989, 28, 840.
(15) Clark, G. R.; Hoskins, S. V.; Roper, W. R. J . Organomet. Chem.
1982, 234, C9. Richmond, T. G.; Crespi, A. M.; Shriver, D. F.
Organometallics 1984, 3, 314.

1226 Organometallics, Vol. 17, No. 6, 1998
Michelin et al.
Con clu d in g Rem a r k s
This study has shown that the reactions of terminal
alkynes with halo alcohols, and specifically 2-chloro-
ethanol, promoted by cationic Pt(II) solvento complexes
of the type trans-[Pt(R′)(PPh3)2(solv)]+ appear to be
influenced by the electronic properties of the alkyl
ligand R′. When R′ ) CH3, a strong σ-electron donor,
the reactions lead to the formation of acyclic oxycarbene
derivatives of type I, while with R′ ) CF3, a good
electron-withdrawing group, these lead to â-alkoxy-
alkenyl derivatives of type II.
The formation of the two different reaction products
has been suggested to occur through different reaction
intermediates i.e., a Pt(II) vinylidene, PtdCdC(H)R, in
the case of I and a π-alkyne, Pt(η2-RCtCH), in the case
of II.
Ack n ow led gm en t. R.A.M. thanks MURST and the
CNR for financial support. R.A.M. and R.J .A. thank
NATO for a grant (CRG 931224).
Su p p or tin g In for m a tion Ava ila ble: Tables giving crys-
tal data and refinement details, positional and thermal
parameters, and bond distances and angles for 1 (7 pages).
Ordering information is given on any current masthead page.
OM970467R