Evidence for platinum(II)-vinylidene complexes and their reactions with water to give hydrocarbons and olefins

Article abstract of DOI:10.1016/S0022-328X(99)00119-9

Treatment of the alkynyl complexes trans-[Pt(Me)(CCR)(PPh₃)₂] (R=p-tolyl (1a), Ph (1b)) at low temperature in a CD₂Cl₂ solution with stoichiometric amounts of the acids HBF₄·Et₂O or CF₃SO₃H affords the corresponding vinylidene derivatives trans-[Pt(Me){=C=C(H)R}(PPh₃)₂]X (R=p-tolyl, X=BF₄ (2aBF₄); R=p-tolyl, X=CF₃SO₃ (2aCF₃SO₃); R=Ph, X=BF₄ (2bBF₄)) on the basis of ¹H- and ³¹P{¹H}-NMR data. The reactions of the in situ generated complexes 2 with water, which were followed by ¹H- and ³¹P{¹H}-NMR, lead to the formation of a mixture of the carbonyl complex [Pt(Me)(CO)(PPh₃)₂]X (3) and the hydroxo-bridged dinuclear compound [Pt(μ-OH)(PPh₃)₂]₂X₂ (4) in a ca. 1:2 ratio. The formation of 3 and 4 is accompanied with the liberation of hydrocarbons R-CH₃ and olefins CH₃CH=CHR (R=p-tolyl, Ph), respectively, which arise from the vinylidene ligand likely via an hydroxycarbene intermediate.

Full text of DOI:10.1016/S0022-328X(99)00119-9

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 583 (1999) 131–135
Evidence for platinum(II)–vinylidene complexes and their reactions
with water to give hydrocarbons and olefinsꢀ
Umberto Belluco, Roberta Bertani, Fiorella Meneghetti, Rino A. Michelin *,
Mirto Mozzon
Dipartimento di Processi Chimici dell’Ingegneria and Centro di Chimica e Tecnologia dei Composti Metallorganici degli Elementi di Transizione,
C.N.R., Uni6ersita` di Pado6a, Via Marzolo 9, 35131 Pado6a, Italy
Received 5 August 1998; received in revised form 4 December 1998
Abstract
Treatment of the alkynyl complexes trans-[Pt(Me)(CꢀCR)(PPh3)2] (R=p-tolyl (1a), Ph (1b)) at low temperature in a CD2Cl2
solution with stoichiometric amounts of the acids HBF4·Et2O or CF3SO3H affords the corresponding vinylidene derivatives
trans-[Pt(Me){ꢁCꢁC(H)R}(PPh3)2]X (R=p-tolyl, X=BF4 (2aBF4); R=p-tolyl, X=CF3SO3 (2aCF3SO3); R=Ph, X=BF4
1
(2bBF4)) on the basis of H- and 31P{1H}-NMR data. The reactions of the in situ generated complexes 2 with water, which were
1
followed by H- and 31P{1H}-NMR, lead to the formation of a mixture of the carbonyl complex [Pt(Me)(CO)(PPh3)2]X (3) and
the hydroxo-bridged dinuclear compound [Pt(m-OH)(PPh3)2]2X2 (4) in a ca. 1:2 ratio. The formation of 3 and 4 is accompanied
with the liberation of hydrocarbons R–CH3 and olefins CH3CHꢁCHR (R=p-tolyl, Ph), respectively, which arise from the
vinylidene ligand likely via an hydroxycarbene intermediate. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Alkynyl; Hydrocarbons; Olefins; Platinum(II) complexes; Vinylidene
alcohols R%OH to afford alkyl(alkoxy)carbene deriva-
tives Pt{ꢁC(OR%)CH2R}.
Following our research project on transition metal
1. Introduction
The chemistry of transition metal vinylidene com-
plexes, LnMꢁCꢁC(H)R, has developed rapidly in the
last 20 years. Several methods have been employed for
promoted cyclization reactions of unsaturated ligands
such as isocyanides, R–NꢀC, [3] carbonyl, CꢀO, [4] and
nitriles, R–CꢀN, [5] by the haloalcohols HO–(CH2)n–
the preparation of mononuclear vinylidene complexes,
¸¹¹¹º
X (X=Cl, Br; n=2, 3) and oxirane, OCH2CH2, we
have recently extended this reaction chemistry to
Pt(II)–alkyne and –alkynyl complexes to give carbene
[6] or vinyl ether [7] derivatives. The formation of the
carbene derivatives has been suggested to proceed via
intermediate Pt(II)–vinylidene species, which were not
so far detected, but whose implication has been pro-
posed by analogy with the known reactions of vinyli-
dene complexes with nucleophiles to give carbene
derivatives [1]. We now report the reactions of the
acetylide complexes trans-[Pt(Me)(CꢀCR)(PPh3)2] (R=
p-tolyl, Ph) with protic acids to give Pt(II)–vinylidene
derivatives, which have been characterized by NMR
spectroscopy. The reactivity of the in situ prepared
Pt(II)–vinylidene species with water is also described.
This latter process proceeds with the formation of
in particular from 1-alkynes via a formal 1,2-hydrogen
shift or by addition of electrophiles such as protic acids
to metal alkynyl complexes [1]. Early studies on these
reactions with platinum(II)–terminal alkyne and
–alkynyl complexes have been made by Clark and
Chisholm, who suggested the formation from these
+
species of a vinyl carbocation intermediate, Pt– C
ꢁC(H)R [2], which would explain the reactions with
ꢀ Dedicated to our dear friend and colleague, Professor Alberto
Ceccon, on the occasion of his 65th birthday.
* Corresponding author. Tel.: +39-49-8275522; fax: +39-49-
8275525.
E-mail address: michelin@ux1.unipad.it (R.A. Michelin)
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00119-9

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U. Belluco et al. / Journal of Organometallic Chemistry 583 (1999) 131–135
hydrocarbons and olefins likely arising from the
organic vinylidene group.
nances that could be assigned to the carbonyl trans-
[Pt(Me)(CO)(PPh3)2][BF4] (3BF4) [6c, 8] and the
hydroxo-bridged [Pt(m-OH)(PPh3)2]2[BF4]2 (4BF4) [9]
complexes together with other minor unidentified prod-
ucts. Integration of the PPh3 resonances in the 31P{1H}-
NMR spectra showed that 3BF4 and 4BF4 were formed
in a ca. 1:2 ratio. GC/MS analysis of the reaction
mixture after 8 h at room temperature revealed the
presence of p-xylene (m/z 106; r.t. 7.8 min) and
CH3C(H)ꢁC(H)C6H4-p-CH3 (m/z 132, r.t. 9.2 min) in a
ca. 1:2 ratio.
2. Experimental
2.1. General procedures and materials
Tetrahydrofuran (THF) and diethyl ether were
purified by distillation over sodium/benzophenone un-
der a dinitrogen atmosphere, while dichloromethane
under dinitrogen over calcium hydride. All other chem-
icals were of reagent grade and used as received. All
reactions and manipulations were performed under a
dry nitrogen atmosphere by using standard Schlenck
techniques. The complexes trans-[Pt(Me)(CꢀC–
R)(PPh3)2] (R=p-tolyl, 1a; Ph, 1b) were prepared as
described in the literature [6a]. CD2Cl2 for NMR exper-
After 24 h the reaction was stopped and the
dichloromethane-d2 solution was worked up as follows.
The pale yellow crystals which were formed inside the
NMR tube were filtered off and analyzed by IR (Nujol
mull: w(OH) 3550 cm−1) and 31P{1H}-NMR: l 7.81 (s,
1
PPh3, JPPt 3744 Hz) [9]. These data agree with those
previously reported for 4BF4 [9]. The CD2Cl2 solution
1
iments was dried over molecular sieves. H-, 13C{1H}-
was then treated with Et2O to give a brownish precipi-
and 31P{1H}-NMR spectra were recorded on a Bruker
200 AC instrument operating at 200.13, 50.32 and 81.01
MHz, respectively. Peak positions are relative to te-
tramethylsilane and were calibrated against the residual
solvent resonance (1H) or the deuterated solvent multi-
plet (13C). 31P chemical shifts were measured relative to
external 85% H3PO4 with downfield values taken as
positive. Infrared spectra were recorded as Nujol mulls
on a Perkin Elmer 983 spectrophotometer. GC/MS
determinations have been performed on a QMD 1000
instrument: column, PS264, 30 m; from 100 to 280°C,
10° min−1; 1 ml min−1, He flow.
tate which was characterized by IR, H- and 31P{1H}-
1
NMR as 3BF4. IR (Nujol mull): w(CO) 2097 cm−1
.
3
1H-NMR (CD2Cl2): l 0.47 (t, CH3, 3H, JHP 7.99 Hz,
2JHPt 60.9 Hz). 31P{1H}-NMR (CD2Cl2): l 21.70 (s,
1
PPh3, JPPt 2624 Hz) [6c,8].
2.3. Reaction of trans-[Pt(Me)(CꢀC-p-tolyl)(PPh3)2]
(1a) with CF3SO3H and with water in a screw cap
with PTFE/silicone septum NMR tube
CD2Cl2 (0.8 ml) was transferred under nitrogen in a
5-mm NMR tube containing 1a (103 mg, 0.12 mmol).
Addition at −40°C of CF3SO3H (10.6 ml, 0.12 mmol)
dissolved complex 1a giving a deep red solution. The
tube was introduced into the NMR probe precooled at
−20°C. The reaction progress was monitored by vari-
2.2. Reaction of trans-[Pt(Me)(CꢀC-p-tolyl)(PPh3)2]
(1a) with HBF4·Et2O and with water in a screw cap
with PTFE/silicone septum NMR tube
1
able temperature H- and 31P{1H}-NMR spectroscopy.
1
CD2Cl2 (0.8 ml) was transferred under nitrogen in a
5-mm NMR tube containing 1a (103 mg, 0.12 mmol).
Addition at −40°C of 20 ml of a 54% ethereal solution
(0.14 mmol) of HBF4·OEt2 completely dissolved com-
plex 1a giving a deep red solution. The tube was
introduced into a NMR probe precooled at −20°C.
The reaction progress was monitored by variable tem-
The H- and 31P{1H}-NMR spectra showed the imme-
diate appearance of signals attributed to the formation
of the vinylidene complex trans-[Pt(Me){ꢁCꢁC(H)(p-
tolyl)}(PPh3)2][CF3SO3] (2aCF3SO3). NMR data for
2aCF3SO3. 1H-NMR (CD2Cl2, −20°C): l 0.76 (t, CH3,
3
2
3
3H, JHP 6.1, JHPt 74.1 Hz); l 3.72 (s, ꢁCH, 1H, JHPt
43.6 Hz). 31P{1H}-NMR (CD2Cl2, −20°C): l 30.63 (s,
PPh3, JPPt 2808 Hz).
1
1
1
perature H- and 31P{1H}-NMR spectroscopy. The H-
and 31P{1H}-NMR spectra showed the immediate ap-
pearance of signals attributed to the formation of the
On warming to 0°C no spectral changes were ob-
served and then H2O (0.27 mmol, 5 ml) was added. On
warming the NMR tube to room temperature and
during a period of time (ca. 8 h) the 31P-NMR spectra
of the reaction mixture showed resonances which could
be attributed to the formation of the carbonyl complex
trans-[Pt(Me)(PPh3)2(CO)][CF3SO3] (3CF3SO3) and
[Pt(m-OH)(PPh3)2]2[CF3SO3]2 (4CF3SO3) together with
other minor unidentified products. GC/MS analysis of
the reaction mixture after 8 h at room temperature
showed the formation of p-xylene (m/z 106; r.t. 7.8 min)
and CH3C(H)ꢁC(H)C6H4-p-CH3 (m/z 132, r.t. 9.2 min).
vinylidene
complex
trans-[Pt(Me){ꢁCꢁC(H)(p-
1
tolyl)}(PPh3)2][BF4] (2aBF4). NMR data for 2aBF4. H-
3
NMR (CD2Cl2, −20°C): l 0.77 (t, CH3, 3H, JHP 6.2,
2JHPt 74.1 Hz); l 3.92 (s, ꢁCH, 1H, JHPt 44.5 Hz).
3
31P{1H}-NMR (CD2Cl2, −20°C): l 30.8 (s, PPh3, JPPt
1
2807 Hz). On warming to 0°C the NMR tube no
spectral changes were observed and then H2O (0.27
mmol, 5 ml) was added. The reaction mixture was
1
allowed to reach room temperature and the H- and
31P{1H}-NMR analyses showed the presence of reso-

U. Belluco et al. / Journal of Organometallic Chemistry 583 (1999) 131–135
133
During this time pale yellow crystals formed in the
NMR tube, which were filtered off. IR (Nujol mull):
w(OH) 3550 cm−1 31P{1H}-NMR: l 7.90 (s, PPh3,
.
1JPPt 3765 Hz). The compound was identified as
4CF3SO3 by comparison with the data reported for
4BF4. The CD2Cl2 solution was then treated with di-
ethyl ether to give a brownish precipitate which was
1
(1)
characterized as 3CF3SO3. H-NMR (CD2Cl2): l 0.47
3
2
(t, CH3, 3H, JHP 8.10, JHPt 61.2 Hz). 31P{1H}-NMR:
1
The H-NMR spectra at low temperature (−20°C)
of complexes 2 show the methyl resonance at 0.76–0.77
ppm (ca. 1 ppm downfield compared to that found for
the alkynyl species 1 [6a]), which shows up as a triplet
due to coupling with the two magnetically equivalent
phosphorous atoms and flanked by 195Pt satellites (2JHPt
ca. 72–74 Hz). This latter coupling constant value is
significantly higher than that found for the acetylide
complexes 1 (2JHPt ca. 53 Hz [6a]) and also higher than
those found in the carbene trans-[Pt(Me){ꢁC-
(OCH2CH2X)CH2R}(PPh3)2][BF4] (X=Cl [6a]; Br, I,
OH [6c]; 2JHPt ca. 45 Hz), carbonyl trans-
[Pt(Me)(CO)(PPh3)2][BF4] (2JHPt ca. 61 Hz [6c]) and
chloro derivative trans-[Pt(Me)(Cl)(PPh3)2] (2JHPt 43.5
1
l 22.16 (s, PPh3, JPPt 2609 Hz).
2.4. Reaction of trans-[Pt(Me)(CꢀC-Ph)(PPh3)2] (1b)
with HBF4·Et2O and with water in a screw cap with
PTFE/silicone septum NMR tube
CD2Cl2 (0.8 ml) was transferred under nitrogen in a
5-mm NMR tube containing 1b (106 mg, 0.13 mmol).
Addition at −40°C of 20 ml of ethereal solution 54%
(0.14 mmol) of HBF4·OEt2 completely dissolved com-
plex 1b giving a deep red solution. The tube was
introduced into a NMR probe precooled at −20°C.
The reaction progress was monitored by variable tem-
1
1
perature H- and 31P{1H}-NMR spectroscopy. The H-
and 31P{1H}-NMR spectra showed the immediate ap-
pearance of signals attributed to the formation of the
2
Hz [10]). The JHPt values of the Me-resonance of 2
may also be compared with those found in the iso-
cyanide complex trans-[Pt(Me)(CNC6H4-p-OMe)(P-
MePh2)2][BF4] (2JHPt 61.2 Hz [11]) and the vinyl com-
vinylidene
complex
trans-[Pt(Me){ꢁCꢁC(H)(Ph)}-
1
(PPh3)2][BF4] (2bBF4). NMR data for 2bBF4. H-NMR
pound
trans-[Pt(Me){C(OCH2CH2Cl)ꢁCH(p-tolyl)}-
3
2
(PPh3)2] (2JHPt 46.9 Hz [6c]). On the other hand the
2JHPt values of 2 fit well with those found for the nitrile
complexes trans-[Pt(Me)(NCR)(PPh3)2][BF4] (R=Me,
(CD2Cl2, −20°C): l 0.76 (t, CH3, 3H, JHP 6.4, JHPt
72.1 Hz); l 3.95 (s, ꢁCH, 1H, JHPt 41.8 Hz). 31P{1H}-
3
1
NMR (CD2Cl2, −20°C): l 30.7 (s, PPh3, JPPt 2799
2JHPt 78.1 Hz; R=Ph, JHPt 77.7 Hz, [13]). Thus, based
2
Hz).
2
On warming the NMR tube to 0°C no spectral
changes were observed. At 0°C H2O (0.27 mmol, 5 ml)
was added. On warming to room temperature and
within a period of time (ca. 8 h), the 31P-NMR spectra
showed the formation of 3BF4 and 4BF4 together with
other minor unidentified products. GC/MS analysis of
the reaction mixture after 8 h at room temperature
showed the formation of CH3C(H)ꢁC(H)C6H5 (m/z
118, r.t. 6.2 min, identified by comparison with an
authentic sample) and toluene (m/z 92, r.t. 2.8 min).
on JHPt values of the methyl resonance in platinum(II)
complexes, the following order of NMR trans influence
[12] is found: R–CꢀN (R=Me, Ph):ꢁCꢁC(H)R (R=
p-tolyl, Ph)BCO:CꢀN–C6H4 - p-OMeB −CꢀC–R
(R=p-tolyl, Ph)B −C(OCH2CH2Cl)ꢁCH(p-tolyl):
ꢁC(OCH2CH2X)CH2R (X=Cl, Br, I, OH). The pres-
1
ence of vinylidene ligands in 2 is shown by H-NMR
resonances at ca. 3.7–3.9 ppm due to the vinylidene
hydrogen [14] which appear as singlets flanked by 195Pt
satellites (3JHPt 41.8–44.5 Hz).
The 31P{1H}-NMR spectra run at −20°C of 2 show
a single resonance at ca. 30 ppm flanked by 195Pt
satellites (1JPPt ca. 2800 Hz) due to the two magnetically
equivalent trans-PPh3 ligands. No other signals were
present. The 13C{1H}-NMR spectrum of 2aBF4
recorded at −40°C does not show the resonance due to
the a-carbon atom of the vinylidene group, while that
due to the b-carbon is clearly evident at 71.9 ppm (2JCPt
3. Results and discussion
Treatment of the acetylide complexes trans-
[Pt(Me)(CꢀCR)(PPh3)2] (R=p-tolyl, Ph) (1) with stoi-
chiometric amounts of the protic acids HX
(HX=HBF4·OEt2, CF3SO3H) at low temperature
(range from −40 to −20°C) immediately gives rise to
deep red solutions. Monitoring the reactions in a screw
cap NMR tube (CD2Cl2) by spectroscopy (1H- and
31P{1H}-NMR) shows the quantitative formation of
new species, which can be described as the vinylidene
derivatives trans-[Pt(Me){ꢁCꢁC(H)R}(PPh3)2]X (2)
(Eq. 1).
2
28.3 Hz). The resonance at 5.42 ppm (t, JCP 4.4 Hz,
1JCPt 619 Hz) is attributed to the carbon atom of the
methyl group bound to Pt and the singlet at 21.57 ppm
to the CH3–Ph carbon. The IR spectrum of the CD2Cl2
solution of 2aBF4 shows a medium-intensity absorption
at 1620 cm−1 attributable to the vinylidene CꢁC bond
[14].

134
U. Belluco et al. / Journal of Organometallic Chemistry 583 (1999) 131–135
It is interesting to note that resonances analogous to
1
those of 2aBF4 are observed in the H-NMR spectra of
the reaction mixtures between the solvento cationic
complex trans-[Pt(Me)(PPh3)2(solv)][BF4], which is pre-
pared from the corresponding chloro derivative by
treatment with AgBF4, and the terminal alkyne H–
CꢀC-p-tolyl (Eq. 2).
(3)
A proposed mechanism for the reaction products
observed in Eq. 3 is given in Scheme 1. This entails
initial formation of the unstable hydroxycarbene species
A derived by nucleophilic attack of H2O on the vinyli-
1
(2)
dene group. The H-NMR spectra of the 1:1 reaction
mixtures of 2aBF4, 2aCF3SO3 or 2bBF4 and H2O show
The mechanism of the 1-alkyne to vinylidene conver-
sion at a Pt(II) center is not known, although it most
likely proceeds by initial formation of the h2-alkyne
intermediate
H)][BF4] which was not clearly detected by low temper-
1H-NMR
ature spectroscopy and eventually
3
new resonances at ca. 0.33–0.34 ppm (t, JHP ca. 6.7–
2
6.4 Hz, JHPt ca. 86–89 Hz), respectively, which were
tentatively assigned to the CH3–Pt group of species A.
The hydroxycarbene OH resonance could not be lo-
cated. The corresponding 31P-NMR spectra showed
singlets at 24.8 ppm (1JPPt 3268 Hz for R=p-tolyl) and
24.9 ppm (1JPPt 3256 Hz for R=Ph). These latter
signals slowly decrease in intensity and after 8 h two
main resonances are detected in the spectrum: a singlet
at 7.8 ppm (1JPPt 3744) and a singlet at 21.7 ppm (1JPPt
2624 Hz) attributed to the dinuclear hydroxo-bridged
species [Pt(PPh3)2(m-OH)]22+ (4) [9] and the carbonyl
complex trans-[Pt(Me)(CO)](PPh3)2]+ (3) [6c,8],
respectively.
The formation of the carbonyl complex trans-
[Pt(Me)(CO)](PPh3)2]+ and p-xylene or toluene (route i
of Scheme 1) parallels the behaviour reported for the
Ru- and Re-assisted CꢀC bond cleavage of terminal
alkynes by water, which has been shown to proceed via
hydroxycarbene intermediates to give the metal car-
bonyl and hydrocarbons [14,17]. The formation of the
carbonyl ligand as a result of the nucleophilic attack by
water on the vinylidene a-carbon atom and subsequent
carbon–carbon cleavage has been confirmed by reac-
tion of 2aBF4 with H128O. In this case the reaction leads
trans-[Pt(Me)(PPh3)2(h2-R–CꢀC–
tautomerizes to the vinylidene group possibly via a
1,2-hydrogen shift as proposed, on the basis of EHMO
calculations, by Silvestre and Hoffmann [15a] and re-
cently supported by ab initio studies on the conversion
of [RuCl2(PH3)2(HCꢀCH)] to [RuCl2(PH3)2(ꢁCꢁCH2)]
[15b]. The Re-assisted h2-alkyne to vinylidene isomer-
ization via the 1,2-H shift mechanism has been sug-
gested by Bianchini et al. who characterized the
p-alkyne
complex
[(triphos)Re(CO)2(h2-H–CꢀC–
H)][BF4] which spontaneously transforms into the
vinylidene complex [(triphos)Re(CO)2(ꢁCꢁCH2)][BF4]
[14b]. In conclusion, we suggest that as for
[(triphos)Re(CO)2]+,
also
for
the
trans-
[Pt(Me)(PPh3)2]+ fragment the alternative 1,3-hydro-
gen shift mechanism [16] to vinylidene via oxidative
addition of the alkyne C–H bond is hardly accessible
due to its low electron-richness.
The reactions of the in situ prepared vinylidene spe-
cies 2 in CD2Cl2 with stoichiometric amounts of water
were followed by 1H- and 31P{1H}-NMR initially at
0°C and then at room temperature for an additional 8
h. The NMR data revealed the formation from the
reaction mixture of mainly two species, i.e. the carbonyl
complex 3 and the hydroxo-bridged dinuclear com-
pound 4 (Eq. 3) accompanied with the parallel forma-
tion of hydrocarbons RCH3 (i.e. p-xylene from 2aBF4
and 2aCF3SO3 and toluene from 2bBF4) and olefins of
the type CH3CHꢁCHR (R=p-tolyl, Ph)1 in a ca. 1:2
ratio, which were identified by GC/MS analysis (see
Experimental).
1 Both olefins are formed as cis and trans stereoisomers in about a
2:10 ratio. CH3–CHꢁCH–C6H5 has been identified on the basis of a
comparison with an authentic sample, and its mass spectrum recog-
’
nized in the NBS data base [M+ ], m/z 118. CH3–CHꢁCH–C6H5-p-
CH3 has been identified on the basis of its mass spectrum recognized
’
in the NBS data base [M+ ], m/z 132.
Scheme 1.

U. Belluco et al. / Journal of Organometallic Chemistry 583 (1999) 131–135
135
to the formation of trans-[Pt(Me)(PPh3)2(C18O)][BF4] as
shown by the red-field shift exhibited by the stretching
vibration of the carbonyl group [w1(OC8)=2054 cm−1]. The
frequency change Dw(CO)=w1(OC6)−w(1OC8)=2098−2054
cm−1=44 cm−1 is in good agreement with the value
that may be calculated from the change in reduced
mass (Dw(CO)=47 cm−1) [18].
Angelici, Inorg. Chem. 27 (1988) 85. (b) R.A. Michelin, L.
Zanotto, D. Braga, P. Sabatino, R.J. Angelici, Inorg. Chem. 27
(1988) 93. (c) R. Bertani, M. Mozzon, R.A. Michelin, Inorg.
Chem. 27 (1988) 2809. (d) R. Bertani, M. Mozzon, F. Benetollo,
G. Bombieri, R.A. Michelin, J. Chem. Soc. Dalton Trans. (1990)
1197. (e) R. Bertani, M. Mozzon, R.A. Michelin, F. Benetollo,
G. Bombieri, T.J. Castilho, A.J.L. Pombeiro, Inorg. Chim. Acta
189 (1991) 175. (f) U. Belluco, R.A. Michelin, R. Ros, R.
Bertani, G. Facchin, M. Mozzon, L. Zanotto, Inorg. Chim. Acta
198–200 (1992) 883 and references therein.
The formation of 4 and the olefins of the type
CH3CHꢁCHR (route ii of Scheme 1) can be explained
by a migratory process of the methyl group on the
carbene carbon of the hydroxycarbene complex pro-
moted by water whose coordinating ability leads to the
formation of the required cis-hydrido-carbene interme-
diate, possibly a pentacoordinate species of the type B.
This latter rearranges to the unstable species C, which
eventually decomposes to afford 4 and the olefin. Al-
though we have no spectroscopic evidence for B and C,
such a mechanism agrees well with previous studies
reported on the hydride to carbene migration catalyzed
by acetonitrile¸f¹or¹¹th¹e¹hºydrido-dithiocarbene complex
trans-[Pt(H)(ꢁCSCH2CH2S)(PPh3)2][BF4]. This latter
[4] (a) H. Motschi, R.J. Angelici, Organometallics 1 (1982) 343. (b)
L. Zanotto, R. Bertani, R.A. Michelin, Inorg. Chem. 29 (1990)
3265.
[5] R.A. Michelin, M. Mozzon, R. Bertani, Coord. Chem. Rev. 147
(1996) 299.
[6] (a) U. Belluco, R. Bertani, R.A. Michelin, M. Mozzon, F.
Benetollo, G. Bombieri, R.J. Angelici, Inorg. Chim. Acta 240
(1995) 567. (b) R.A. Michelin, M. Mozzon, B. Vialetto, R.
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affords
the
migratory-insertion
product
cis-
¸¹¹¹¹¹¹¹º
[Pt{C(H)SCH2CH2S}(PPh3)2][BF4], which was isolated
a»nd¹¹st¹ru¹c¹tu¹ra¹l¹ly¹c¹ha¼racterized [19] showing a metallacy-
clopropane structure of the Pt–C–S moiety, via the
[10] H.C. Clark, L.E. Manzer, J. Organomet. Chem. 59 (1973) 411.
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Inorg. Chem. 27 (1988) 85.
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G. Bombieri, R.J. Angelici, Organometallics 13 (1994) 1341.
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Zanobini, Organometallics 15 (1996) 272. (b) C. Bianchini, A.
Marchi, L. Marvelli, M. Peruzzini, A. Romerosa, R. Rossi,
Organometallics 15 (1996) 3804 and references therein.
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(b) Y. Wakatsuki, N. Koga, H. Yamazaki, K. Morokuma, J.
Am. Chem. Soc. 116 (1994) 8105.
¸¹¹¹¹¹º
pentacoordinate intermediate [Pt(H)(ꢁCSCH2CH2S)-
(PPh3)2(MeCN)][BF4], which could be detected by a
FAB/MS study [20]. Migration of an alkyl ligand to a
transition metal coordinated carbene is a known pro-
cess and it has been recently demonstrated to be the
basis for the catalytic formation of tetrahydrofuranyli-
dene esters via alkyl migration in Pt(II)–carbene com-
plexes [21].
Acknowledgements
[16] I. de los Rios, M. Jimenez-Tenorio, M.C. Puerta, P. Valerga, J.
Chem. Soc. Chem. Commun. (1995) 1757.
[17] C. Bianchini, J.A. Casares, M. Peruzzini, A. Romerosa, F.
Zanobini, J. Am. Chem. Soc. 118 (1996) 4586.
R.A.M. thanks MURST and C.N.R. for financial
support.
[18] D.M.P. Mingos, in: E.W. Abel, F.G.A. Stone, G. Wilkinson
(Eds.), Comprehensive Organometallic Chemistry, vol. 3, Perga-
mon Press, Oxford, 1982, p. 1.
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