Kinetic evidence for π-complex formation prior to oxidative addition of propargyl halides to triphenylphosphine-platinum(O) complexes

Article abstract of DOI:10.1021/om000376l

The mechanism of oxidative addition of phenylpropargyl halides to Pt(PPh₃)₄ to give Pt-(η¹-CH₂C=CPh)(X)(PPh₃)₂ has been investigated on the basis of the kinetics of the reaction and stereomeric analysis of the products. The kinetic results of the reaction showed the contributions of two pathways involving Pt(PPh₃)₃ and Pt(PPh₃)₂ complexes as active species. The second-order rate constants for both pathways were on the order of 10³ larger than the corresponding rate constants of the oxidative addition reaction of CH₃I. Moreover, both active species and the substrate halide gave, as the kinetic product, the isomer having two PPh₃ groups located cis, which is also in sharp contrast to the case of the reaction of CH₃I. It is proposed that the rate-determining step in the reaction involving Pt(PPh₃)₂ is the coordination of the C=C bond to Pt(PPh₃)₂ to form Pt(η²-PhC=CCH₂X)(PPh₃)₂, which subsequently undergoes rapid collapse to the η₃-propargyl complex [Pt(η³-CH₂CCPh)(PPh₃)₂]X and eventually to cis-Pt(η¹-CH₂C=CPh)(X)(PPh₃)². The reaction of Pt(PPh₃)₃ may also involve a rate-determining C=C bond coordination step.

Full text of DOI:10.1021/om000376l

4488
Organometallics 2000, 19, 4488-4491
Kin etic Evid en ce for π-Com p lex F or m a tion P r ior to
Oxid a tive Ad d ition of P r op a r gyl Ha lid es to
Tr ip h en ylp h osp h in e-P la tin u m (0) Com p lexes
Takuma Nishida, Sensuke Ogoshi, Ken Tsutsumi, Yoshiaki Fukunishi, and
Hideo Kurosawa*
Department of Applied Chemistry, Faculty of Engineering, Osaka University,
Suita, Osaka 565-0871, J apan
Received May 2, 2000
The mechanism of oxidative addition of phenylpropargyl halides to Pt(PPh3)4 to give Pt-
(η1-CH2CtCPh)(X)(PPh3)2 has been investigated on the basis of the kinetics of the reaction
and stereomeric analysis of the products. The kinetic results of the reaction showed the
contributions of two pathways involving Pt(PPh3)3 and Pt(PPh3)2 complexes as active species.
The second-order rate constants for both pathways were on the order of 103 larger than the
corresponding rate constants of the oxidative addition reaction of CH3I. Moreover, both active
species and the substrate halide gave, as the kinetic product, the isomer having two PPh3
groups located cis, which is also in sharp contrast to the case of the reaction of CH3I. It is
proposed that the rate-determining step in the reaction involving Pt(PPh3)2 is the coordination
of the CtC bond to Pt(PPh3)2 to form Pt(η2-PhCtCCH2X)(PPh3)2, which subsequently
undergoes rapid collapse to the η3-propargyl complex [Pt(η3-CH2CCPh)(PPh3)2]X and
eventually to cis-Pt(η1-CH2CtCPh)(X)(PPh3)2. The reaction of Pt(PPh3)3 may also involve a
rate-determining CtC bond coordination step.
In tr od u ction
the mechanisms of the related reactions involving
palladium complexes important as intermediates in
catalysis5 or even closely related allylic substrates.
We report here intriguing kinetic behavior in the
reaction of Pt(PPh3)4 with phenylpropargyl halides, from
which a very fundamental oxidative addition mecha-
nism is offered that is consistent with the reported
formation of the cis isomer from Pt(C2H4)(PPh3)2 as the
kinetic product.
The oxidative addition reaction is one of the most
fundamental steps constituting many homogeneous
catalytic cycles. The oxidative addition of organic halides
to zerovalent group 10 metal complexes containing more
than 2 equiv of tertiary phosphine ligands gives trans
isomers of organo halo bis-phosphine complexes, except
for a limited few examples.1 These exceptions involved
the addition of sp2-carbon-halogen compounds, where
the formation of cis product is a logical outcome of the
proposed mechanistic pathway.2 In this respect it ap-
pears of special interest that Wojcicki and co-workers
reported that oxidative addition reaction of Pt(C2H4)-
(PPh3)2 with PhCtCCH2Br leads to the formation of cis-
Pt(η1-CH2CtCPh)(Br)(PPh3)2, which isomerizes further
to the more stable trans isomer.3 However, these
authors offered no mechanistic explanation for the cis
product. We took interest in elucidating the reason for
such unusual stereochemistry and, more generally, the
mechanism of the oxidative addition reaction of pro-
pargyl halides to Pt(0) complexes in view of increasing
attention paid to both inorganic and organic aspects of
propargyl and allenyl complexes.4 Moreover, there is a
possibility that studying the above-mentioned reactions
of Pt(0) complexes leads to a better understanding of
Resu lts
Ster eoch em istr y of th e Kin etic P r od u ct. We
previously reported6 that the oxidative addition product
Pt(η1-CH2CtCPh)(X)(PPh3)2 (X ) Cl, Br) from PhCt
CCH2X and Pt(PPh3)4 after recrystallization at room
temperature has two PPh3 ligands located trans to each
other. We have now confirmed by NMR examinations
that the kinetic product of the reaction of Pt(PPh3)4 with
PhCtCCH2Cl in the presence of excess PPh3 (20 equiv)
formed in toluene-d8 at temperatures from -60 to 0 °C
has the cis geometry (eq 1; L ) PPh3, n ) 2). The cis
(1) Casado, A. L.; Espinet, P. Organometallics 1998, 17, 954. Urata,
H.; Tanaka, M.; Fuchikami, T. Chem. Lett. 1987, 751. Addition of vinyl
sulfides to Pt(C2H4)(PPh3)2 also gave the cis products: Kuniyasu, H.;
Otaka, A.; Nakazono, T.; Kurosawa, H. J . Am. Chem. Soc. 2000, 122,
2375.
(2) Portnoy, M.; Milstein, D. Organometallics 1993, 12, 1665.
(3) Blosser, P. W.; Schimpff, D. G.; Gallucci, J . C.; Wojcicki, A.
Organometallics 1993, 12, 1992. Baize, M. W.; Blosser, P. W.; Plant-
evin, V.; Schimpff, D. G.; Gallucci, J . C.; Wojcicki, A. Organometallics
1996, 15, 164
complex remained stable with respect to the cis-trans
isomerization at 0 °C for 1 h, but the isomerization
(4) Doherty, S.; Corrigan, J . F.; Carty, A. J .; Sappa, E. Adv.
Organomet. Chem. 1995, 37, 39. Wojcicki, A. New J . Chem. 1994, 18,
61.
(5) Tsuji, J .; Mandai, T. Angew. Chem., Int. Ed. Engl. 1995, 34, 2587.
(6) Ogoshi, S.; Fukunishi, Y.; Tsutsumi, K.; Kurosawa, H. Inorg.
Chim. Acta 1997, 265, 9.
10.1021/om000376l CCC: $19.00 © 2000 American Chemical Society
Publication on Web 09/28/2000

Addition of Propargyl Halides to Pt(0) Complexes
Organometallics, Vol. 19, No. 22, 2000 4489
Ta ble 1. Kin etic Resu lts of th e Rea ction of
Ta ble 2. Ra te Con sta n ts for Rea ction s of P t(P P h 3)3
P t(P P h 3)4 w ith P h CtCCH2Cl
(k1) a n d P t(P P h 3)2 (k3)
kobs/[PhCtCCH2Cl]
substrate
k1 (L/(mol s))
k3 (L/(mol s))
run
[PPh3] (mol/L)
1/[PPh3] (L/mol)
(L/(mol s))
PhCtCCH2Cl
CH3I
PhCtCCH3
2.0
4.8 × 10
2.0 × 10-2
2.0 × 10
1
2
3
4
5
6
7
2.49 × 10-3
4.00 × 10-3
6.67 × 10-3
2.50 × 10-2
5.14 × 10-2
1.03 × 10-1
2.51 × 10-1
4.02 × 102
2.50 × 102
1.50 × 102
4.00 × 10
1.95 × 10
9.71
5.10
3.92
3.21
2.20
2.14
2.12
2.09
3.5 × 10-3
5.0 × 10-2
greater than 10 mol/L.7 The kinetic behavior observed
in eq 2 can be accommodated by the mechanism, which
includes the contributions of two simultaneous path-
ways to the reaction: (a) the pathway corresponding to
eq 3 and (b) the pathway described by eqs 4 and 5.
3.98
Equations 3-5 give rise to the rate law shown in eq
6.8
d[Pt(0)]
-
) kobs[Pt(0)] )
dt
F igu r e 1. 1/[PPh3] vs kobs/[PhCtCCH2Cl].
k1[PPh3] + k3K
K2 + [PPh3]
2[PhCtCCH2Cl][Pt(0)] (6)
proceeded gradually at room temperature in the toluene-
d8 solution to give 100% trans isomer after 17 h.
The kinetic product of the reaction of Pt(C2H4)(PPh3)2
with PhCtCCH2Cl was also confirmed cis-Pt(η1-CH2Ct
CPh)(Cl)(PPh3)2 in toluene-d8 at -30 °C (eq 1; L ) C2H4,
n ) 1), as reported3 in the corresponding reaction of the
bromide.
Kin etics. The rates of the reaction of Pt(PPh3)4 with
PhCtCCH2Cl were measured spectrophotometrically in
benzene at 25 °C. The measurements employed [PhCt
CCH2Cl] and [PPh3] in sufficient excess over the Pt
complex, the initial concentration ranges being 6.99 ×
10-5 mol/L for Pt(PPh3)4, 2.66 × 10-3 to 1.59 × 10-2
mol/L for PhCtCCH2Cl and 2.49 × 10-3 to 2.51 × 10-1
mol/L for PPh3. In each run the pseudo-first-order rate
constant kobs was obtained by plots of ln A (absorbance
The K2 value of eq 4 has been previously evaluated
as 1.6 × 10-4 mol/L (benzene, 25 °C) by Halpern,9 which
can be neglected relative to [PPh3] (the minimum being
2.5 × 10-3 mol/L) in the denominator of eq 6, so that eq
6 can be simplified to eq 7. This equation conforms to
the experimental rate law of eq 2.10a
kobs
1
) k1+ k3K
(7)
[PhCtCCCH2Cl]
2[PPh3]
Table 2 shows the rate constants k1 and k3, calculated
by comparing eqs 2 and 7, which represent the oxidative
addition rates of Pt(PPh3)3 and Pt(PPh3)2 species with
PhCtCCH2Cl, respectively. For comparison, Table 2
also includes the rate of the reaction of the two Pt(0)
of Pt(0) complex at 410 nm) vs time, and the kobs
/
10b,11
active species with CH3I8 and PhCtCCH3
mea-
[PhCtCCH2Cl] value at a given [PPh3] was obtained
from slopes of plots of kobs vs [PhCtCCH2Cl]. Then,
plotting kobs/[PhCtCCH2Cl] vs 1/[PPh3] gave a straight
line (Table 1 and Figure 1) from which the following
experimental kinetic equation is given:
sured under the same conditions. Interestingly, both k1
and k3 for the reaction with PhCtCCH2Cl were much
larger (by an order of 103) than the corresponding rate
constants of the oxidative addition reaction of CH3I8
(Table 2). The rates of the reaction of propargyl halides
with a range of nucleophiles other than low-valent metal
kobs
1
) 2.01 + 7.70 × 10-3
(2)
[PhCtCCH2Cl]
[PPh3]
(8) Pearson, R. G.; Rajaram, J . Inorg. Chem. 1974, 13, 246.
(9) Birk, J . P.; Halpern, J .; Pickard, A. L. Inorg. Chem. 1968, 7, 2673.
(10) (a) Another kinetic treatment of eqs 3-5 assumes steady-state
concentrations of active complexes,11 giving the rate law kobs/[PhCtCCH2-
Cl] ) k1 + k2/[(k-2/k3)[PPh3] + [PhCtCCH2Cl]], where K2 ) k2/k-2. In
the denominator of the second term [PhCtCCH2Cl] (2.66 × 10-3 to
1.59 × 10-2 mol/L) could be neglected relative to (k-2/k3)[PPh3] under
the kinetic conditions (k-2/k3 for PhCtCCH3 was observed11 as 2.5 ×
102). This gives a kinetic law consistent with eq 7. (b) The k-2 value
Discu ssion
It has been established7 that Pt(PPh3)4 dissociates to
the two active species Pt(PPh3)3 and Pt(PPh3)2 in
solution. The concentration of Pt(PPh3)4 can be ne-
glected under the kinetic conditions, since the equilib-
rium constant for the dissociation of this species is
was estimated as 5.7 × 103 L/(mol s) on the basis of the observed k2
(0.91 s-1
)
and the estimated value of K2.9 This, together with the
11
known k-2/k3, leads us to estimate k3 for the reaction of PhCtCCH3
shown in Table 2.
(11) Halpern, J .; Weil, T. A. J . Chem. Soc., Chem. Commun. 1973,
631.
(7) Tolman, C. A.; Seidel, W. C.; Gerlach, D. H. J . Am. Chem. Soc.
1972, 94, 2669.

4490 Organometallics, Vol. 19, No. 22, 2000
Nishida et al.
Sch em e 1
Sch em e 2
species are normally rather slower than those of CH3I.12
These results suggest the importance of the triple bond
coordination to Pt(0) prior to or during the oxidative
addition.
98%.13 This reaction yielded cis-Pt(η1-CH2CtCPh)(X)-
(PPh3)2 in a 1:1.2 ratio for X ) Cl vs X ) Br, suggesting
that the rate-determining step of the reaction does not
involve a carbon-halogen bond cleavage.
It is important to note that the k3 value for the
In contrast to the straightforward course of the
reaction from Pt(PPh3)2 shown in Scheme 1, it is not
certain at the moment how the proposed initial oxidative
addition product [Pt(η3-CH2CCPh)(PPh3)3]Cl from Pt-
(PPh3)3 is converted to the observable kinetic product,
cis-Pt(η1-CH2CtCPh)(Cl)(PPh3)2. The cationic 18-elec-
tron η3-propargyl complex might undergo either dis-
sociation of one PPh3 to give [Pt(η3-CH2CCPh)(PPh3)2]Cl
or η3 to η1 conversion, which gives [Pt(η1-CH2CtCPh)-
(PPh3)3]Cl. In fact, a separate treatment of [Pt(η3-CH2-
CCPh)(PPh3)2]OTf with 1 equiv of PPh3 resulted in the
observation of NMR resonances attributable to the
complex [Pt(η1-CH2CtCPh)(PPh3)3](OTf) together with
additional minor resonances possibly due to cis-
reaction of PhCtCCH2Cl was similar to the rate of
10b
coordination of PhCtCCH3 to Pt(PPh3)2
(Table 2).
This result suggests that the rate-determining step of
the oxidative addition of PhCtCCH2Cl to Pt(PPh3)2 is
the coordination of the triple bond. To gain further
support for this notion, the competition between PhCt
CCH2Cl and PhCtCCH2Br in the reaction with Pt-
(C2H4)(PPh3)2 was attempted in toluene-d8 at room
temperature. The concentrations of the two halides were
set equal to each other and were in excess relative to
the Pt(0) complex. The yields of products, cis-Pt(η1-
CH2CtCPh)(X)(PPh3)2, obtained from a mixture of the
two substrates were similar (1:1.5) for the chloride vs
bromide. If the rate-determining step of the oxidative
addition involved the C-halogen bond cleavage, the
reactivity of the bromide would have been considerably
greater than that of the chloride.
The rate-determining formation of Pt(η2-PhCtCCH2-
Cl)(PPh3)2 from Pt(PPh3)2 and PhCtCCH2Cl would be
followed by rapid collapse of this complex to the ion pair
[Pt(η3-CH2CCPh)(PPh3)2]Cl, which necessarily keeps
two PPh3 groups cis to each other (Scheme 1). It was
also confirmed that the separately isolated cationic
complex [Pt(η3-CH2CCPh)(PPh3)2](OTf) reacts readily
with Cl- to give cis-Pt(η1-CH2CtCPh)(Cl)(PPh3)2, as
also reported3 in the corresponding reaction with Br-.
With regard to the reaction of Pt(PPh3)3, it is remark-
able that the rate constant k1 for the reaction with
PhCtCCH2Cl is 40 times larger than that with PhCt
CCH3 (Table 2). In the latter case, it is possible that
the triple bond coordination to form an intermediate of
the type Pt(η2-PhCtCCH3)(PPh3)3 is not a rate-deter-
mining step. This intermediate, if formed as a discrete
species, might have to overcome a subsequent higher
barrier process, namely dissociation of PPh3. On the
other hand, in the case of the reaction of PhCtCCH2Cl
the CtC coordination complex Pt(η2-PhCtCCH2Cl)-
(PPh3)3 formed first could undergo very facile ionization
of the C-Cl bond to afford [Pt(η3-CH2CCPh)(PPh3)3]Cl
(Scheme 2). In a search for further support, the com-
petitive experiment was carried out by employing an
equimolar mixture of PhCtCCH2Cl and PhCtCCH2-
Br which are in excess relative to Pt(PPh3)4 in the
presence of a high concentration of PPh3 (1.66 × 10-1
mol/L), where the contribution of Pt(PPh3)3 species to
the overall oxidative addition is expected to exceed
{(PPh3)2Pt[CH2C(PPh3)CPh]}(OTf).14 When further
treated with Cl-, the mixture was completely converted
to cis-Pt(η1-CH2CtCPh)(Cl)(PPh3)2. It is likely that the
cationic η1-propargyl intermediate [Pt(η1-CH2CtCPh)-
(PPh3)3]Cl is formed before the observable cis product.15
Con clu sion s
The oxidative addition reaction of propargyl halides
to Pt(PPh3)4 proceeded via the two active species Pt-
(PPh3)2 and Pt(PPh3)3. The rate-determining step of the
reaction of Pt(PPh3)2 is the coordination of the triple
bond of PhCtCCH2X, which is followed by rapid col-
lapse of Pt(η2-PhCtCCH2X)(PPh3)2 to [Pt(η3-CH2CCPh)-
(PPh3)2]Cl and finally to cis-Pt(η1-CH2CtCPh)(Cl)-
(PPh3)2. The rate-determining step of the reaction of
Pt(PPh3)3 would also involve the coordination of the
triple bond to form Pt(η2-PhCtCCH2X)(PPh3)3, which
then undergoes C-Cl bond cleavage without dissocia-
tion of PPh3 ligand. These reaction profiles must be also
essential in the oxidative addition of allylic electrophiles
with zerovalent group 10 metal complexes.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All manipulations were con-
ducted under a nitrogen atmosphere using standard Schlenk
1
or drybox techniques. H and 31P nuclear magnetic resonance
(NMR) spectra were recorded on a J EOL GSX-270 spectrom-
eter. Kinetic measurements were carried out by using a
(13) The second term of eq 2 amounts to ca. 4.64 × 10-2
.
(14) Cheng, Y.-C.; Chen, Y.-K.; Huang, T.-M.; Yu, C.-I.; Lee, G.-H.;
Wang, Y.; Chen, J .-T. Organometallics 1998, 17, 2953.
(15) A similar cationic complex, [Pt(CH3)(PPh3)3]BF4, was converted
to the cis product cis-Pt(CH3)(Cl)(PPh3)2 when treated with Cl-, while
trans-Pt(CH3)(I)(PPh3)2 was the only observable product when [Pt-
(CH3)(PPh3)3]BF4 was treated with I-.16
(12) (a) Vernon, C. A. J . Chem. Soc. 1954, 4462. (b) de la More, P.
B. D. J . Chem. Soc. 1955, 3169. (c) Hughes, E. D.; Ingold. C. K.; Mackie,
J . D. H. J . Chem. Soc. 1955, 3177.
(16) Unpublished results.

Addition of Propargyl Halides to Pt(0) Complexes
Organometallics, Vol. 19, No. 22, 2000 4491
Hitachi U3500 UV-vis spectrometer. Solvents and reagents
were purchased from commercial vendors and distilled and
degassed prior to use. Benzene, tetrahydrofuran, and hexane
were purified by distillation from sodium benzophenone ketyl.
CH2Cl2 and CHCl3 were purified by distillation from CaH2.
Acetone was purified by distillation from sodium sulfate.
Literature procedures were followed to synthesize Pt(PPh3)4,
Pt(PPh3)2(C2H4), cis-Pt(CH2CtCPh)(Cl)(PPh3)2,6 and [Pt(η3-
CH2CCPh)(PPh3)2](OTf).3
(13.8 mg, 1.4 × 10-2 mmol) and PPh3 (3.7 mg, 1.4 × 10-2 mmol)
in CD2Cl2 (0.6 mL) were added in an NMR tube at room
temperature. The reaction mixture was analyzed by 1H and
31P NMR after 10 min. [Pt(η3-CH2CCPh)(PPh3)2](OTf) disap-
peared almost completely, and instead two products (3:1 ratio)
were visible. We assume the major product to be [Pt(η1-CH2Ct
CPh)(PPh3)3](OTf): 1H NMR δ 1.18 (t, J PH ) 6.5 Hz, 2H); 31P
NMR δ 23.79 (d, J PP ) 23.3 Hz, J PtP ) 2989 Hz), 16.98 (t, J PP
) 22.0 Hz, J PtP ) 2018 Hz). We assume the minor to be cis-
Rea ction of P h tCCH2Cl w ith P t(P P h 3)4 in th e P r es-
en ce of a La r ge Excess of P P h 3. To a solution of Pt(PPh3)4
(4.9 mg, 3.9 × 10-3 mmol) and PPh3 (19.1 mg, 7.3 × 10-2 mmol)
in toluene-d8 (0.6 mL) was added PhCtCCH2Cl (1.1 mg, 7.3
× 10-3 mmol) at -78 °C. The reaction mixture was analyzed
by 1H and 31P NMR at temperatures from -60 to 0 °C. The
initial product was confirmed to be formed at -40 °C, whose
31P NMR data coincided with those of cis-Pt(η1-CH2CtCPh)-
(Cl)(PPh3)2. Then the product began to isomerize to trans-Pt-
(η1-CH2CtCPh)(Cl)(PPh3)2 at about 0 °C.
Rea ction of P h CtCCH2Cl a n d P h CtCCH2Br w ith P t-
(C2H4)(P P h 3)2. To a solution of Pt(C2H4)(PPh3)2 (10.5 mg, 1.4
× 10-2 mmol) in toluene-d8 (0.6 mL) were added PhCtCCH2-
Cl (21.1 mg, 1.4 × 10-1 mmol) and PhCtCCH2Br (27.4 mg,
1.4 × 10-1 mmol) at -78 °C. The reaction mixture was
analyzed by 1H and 31P NMR at -30 °C. This reaction yielded
cis-Pt(η1-CH2CtCPh)(X)(PPh3)2 in 1:1.5 ratio for X ) Cl vs X
) Br.
Rea ction of P h CtCCH2Cl a n d P h CtCCH2Br w ith P t-
(P P h 3)4 in th e P r esen ce of a La r ge Excess of P P h 3. To a
solution of Pt(PPh3)4 (12.1 mg, 1.0 × 10-2 mmol) and PPh3 (26.6
mg, 1.0 × 10-1 mmol) in C6D6 (0.6 mL) were added PhCtCCH2-
Cl (15.0 mg, 1.0 × 10-1 mmol) and PhCtCCH2Br (20.0 mg,
1.0 × 10-1 mmol) at -20 °C. The reaction mixture was
analyzed by 1H and 31P NMR at room temperature. The
reaction yielded cis-Pt(η1-CH2CtCPh)(X)(PPh3)2 in a 1:1.2 ratio
for X ) Cl vs X ) Br after 10 min. Then the products began to
isomerize to trans isomers.
{(PPh3)2Pt[CH2C(PPh3)CPh]}(OTf): 1H NMR δ 0.7 (s, 2H); 31
NMR δ 5.20 (dd, J PP ) 37, 28 Hz), 19.5 (dd, J PP ) 33.0, 11
Hz), 20.0 (dd, J PP ) 28.1, 11 Hz). The data for the latter are
P
analogous to the spectral data of cis-{(PPh3)2Pt[CH2C(PPh3)-
CH]}(BF4).14
Then nBu4NCl (20.6 mg, 7.4 × 10-2 mmol) was added in the
tube containing the above mixture at room temperature. cis-
Pt(η1-CH2CtCPh)(Cl)(PPh3)2 was observed after 10 min in 91%
yield, which isomerized to the trans isomer after 14 h at room
temperature.
Kin etic Mea su r em en ts. The oxidative addition reactions
were followed spectrophotometrically using a U3500 recording
spectrophotometer with the cell compartment thermostated
to 25 ( 0.1 °C. The rates of the reactions were measured by
following the disappearance of the absorption due to the
reactant Pt(0) complex at 410 nm. The measurements em-
ployed [PPh3] and [PhCtCCH2Cl] in sufficient excess over [Pt-
(PPh3)4]. In each experiment, sample solutions were prepared
under an N2 atmosphere. The initial concentration ranges of
PPh3 and other species were as follows: 6.69 × 10-5 mol/L,
Pt(PPh3)4; 2.66 × 10-3 to 1.59 × 10-2 mol/L, PhCtCCH2Cl;
2.49 × 10-3 to 2.51 × 10-1 mol/L, PPh3.
Ack n ow led gm en t. Thanks are due to Professor N.
Kambe and Dr. H. Kuniyasu for advice on UV-vis
analysis and to the Analytical Center, Faculty of
Engineering, Osaka University, for NMR facilities.
Rea ction of [P t(η3-CH2CCP h )(P P h 3)2](OTf) w ith n Bu 4-
NCl. To a solution of [Pt(η3-CH2CCPh)(PPh3)2](OTf) (4.8 mg,
4.9 × 10-3 mmol) in CD2Cl2 (0.6 mL) was added nBu4NCl (2.4
mg, 8.8 × 10-3 mmol) at -78 °C. The reaction mixture was
Su p p or tin g In for m a tion Ava ila ble: Figures giving plots
of kobs vs [PhCtCCH2Cl] in each run at a given [PPh3]. This
material is available free of charge via the Internet at
http://pubs.acs.org.
1
analyzed by H and 31P NMR at -60 °C to room temperature
to show the formation of cis-Pt(η1-CH2CtCPh)(Cl)(PPh3)2.
Rea ction of [P t(η3-CH2CCP h )(P P h 3)2](OTf) w ith n Bu 4-
NCl in th e P r esen ce of P P h 3. [Pt(η3-CH2CCPh)(PPh3)2](OTf)
OM000376L