Synthesis and reactions of cis-sily(boryl)platinum(II) complexes

Article abstract of DOI:10.1021/om020686z

Four kinds of sily(boryl)platinum(II) complexes, 2a-2d, have been prepared by oxidative addition of silylboranes to platinum(0) complexes, in situ generated from Pt(cod)₂ and 2 molar quantity of tertiary phosphine ligands (L) in Et₂O: cis-Pt(SiMe₂Ph)(BX₂)L₂ (X2 = -OCMe₂CMe₂O- (pin), L = PMe₃ (2a), PMe₂Ph (2b), PEt₃ (2c); X₂ = -NMeCH₂CH₂NMe- (dmeda), L = PMe₃ (2d)). Complexes 2a-2c undergo selective insertion of phenylacetylene into the Pt-B bond at room temperature in CD₂Cl₂, giving cis-Pt{C(Ph)=CH(Bpin)}(SiMe₂Ph)L₂ (L = PMe₃ (3a), PMe₂Ph (3c), PEt₃ (3c)), respectively, while 2d is inactive toward insertion. The X-ray structure of 3b has been determined. Kinetic study using 2a indicates the mechanism involving prior dissociation of L, followed by insertion of phenylacetylene into the Pt-B bond. The insertion complexes 3a-3c undergo C-Si reductive elimination to give (Z)-α-silyl-β-borylstyrene. The reactivity decreases in the order 3c ? 3b > 3a.

Full text of DOI:10.1021/om020686z

Organometallics 2002, 21, 5879-5886
5879
Syn th esis a n d Rea ction s of cis-Silyl(bor yl)p la tin u m (II)
Com p lexes
Takashi Sagawa, Yasuaki Asano, and Fumiyuki Ozawa*
Department of Applied Chemistry, Graduate School of Engineering, Osaka City University,
Sumiyoshi-ku, Osaka 558-8585, J apan
Received August 20, 2002
Four kinds of silyl(boryl)platinum(II) complexes, 2a -2d , have been prepared by oxidative
addition of silylboranes to platinum(0) complexes, in situ generated from Pt(cod)2 and 2 molar
quantity of tertiary phosphine ligands (L) in Et2O: cis-Pt(SiMe2Ph)(BX2)L2 (X2 ) -OCMe2-
CMe2O- (pin), L ) PMe3 (2a ), PMe2Ph (2b), PEt3 (2c); X2 ) -NMeCH2CH2NMe- (dmeda),
L ) PMe3 (2d )). Complexes 2a -2c undergo selective insertion of phenylacetylene into the
Pt-B bond at room temperature in CD2Cl2, giving cis-Pt{C(Ph)dCH(Bpin)}(SiMe2Ph)L2 (L
) PMe3 (3a ), PMe2Ph (3c), PEt3 (3c)), respectively, while 2d is inactive toward insertion.
The X-ray structure of 3b has been determined. Kinetic study using 2a indicates the
mechanism involving prior dissociation of L, followed by insertion of phenylacetylene into
the Pt-B bond. The insertion complexes 3a -3c undergo C-Si reductive elimination to give
(Z)-R-silyl-â-borylstyrene. The reactivity decreases in the order 3c . 3b > 3a .
In tr od u ction
nature of heavy elements, these complexes should be
unique in chemical properties. From this point of view,
we have already synthesized bis(silyl)-, silyl(stannyl)-,
and alkyl(silyl)platinum(II) complexes and found rather
unusual structures and reactivities.3 In this paper we
report the synthesis and reactions of silyl(boryl)plati-
num(II) complexes, which have been assumed as a key
intermediate for catalytic silylborylation of alkynes and
alkenes,2,6 but have never been observed in reality.
Scheme 1 illustrates the generally accepted catalytic
cycle for silylborylation of alkynes. The first step is the
oxidative addition of silylborane to a low-valent metal
species (step a). While the resulting silyl-boryl inter-
mediate possibly undergoes alkyne insertion into either
the M-Si or M-B bond, it has been considered that the
insertion into the M-B bond preferably takes place (step
b) and the subsequent C-Si reductive elimination
Catalytic addition of inter-element linkages1 to un-
saturated hydrocarbons has attracted a great deal of
recent interest.2 The addition of silicon-element bonds
catalyzed by platinum-group metal complexes is among
the central subjects of such reactions. We have been
interested in the reaction chemistry of platinum com-
plexes which are responsible for these catalyses.3-5
Although the catalytic mechanisms are frequently de-
scribed by a simple extension of the common organo-
metallic chemistry, the key intermediates presumed in
the catalyses are not the organometallic compounds
with metal-carbon or metal-hydrogen bonds, but a
novel class of complexes bearing the linkages between
metals and heavy elements. Reflecting the characteristic
* Corresponding author. E-mail: ozawa@a-chem.eng.osaka-cu.ac.jp.
(1) Tamao, K. J . Organomet. Chem. 2000, 611, 3.
(2) (a) Beletskaya, I.; Moberg, C. Chem. Rev. 1999, 99, 3435. (b)
Suginome, M.; Ito, Y. Chem. Rev. 2000, 100, 3221. (c) Han, L.-B.;
Tanaka, M. Chem. Commun. 1999, 395. (d) Kondo, T.; Mistudo, T.
Chem. Rev. 2000, 100, 3205.
(5) For theoretical treatment of catalytic processes, see: B-B: (a)
Cui, Q.; Musaev, D. G.; Morokuma, K. Organometallics 1997, 16, 1355.
(b) Sakaki, S.; Kikuno, K. Inorg. Chem. 1997, 36, 226. Si-Si: (c)
Sakaki, S.; Mizoe, N.; Sugimoto, M. Organometallics 1998, 17, 2510.
(d) Sakaki, S.; Ogawa, M.; Musashi, Y. J . Organomet. Chem. 1997,
535, 25. (e) Sakaki, S.; Ogawa, M.; Kinoshita, M. J . Phys. Chem. 1995,
99, 9933. (f) Sakaki, S.; Ogawa, M.; Musashi, Y.; Arai, T. J . Am. Chem.
Soc. 1994, 116, 7258. (g) Bottoni, A.; Higueruelo, A. P.; Miscione, G.
P. J . Am. Chem. Soc. 2002, 124, 5506. Si-Sn: (h) Hada, M.; Tanaka,
Y.; Ito, M.; Murakami, M.; Amii, H.; Ito, Y.; Nakatsuji, H. J . Am. Chem.
Soc. 1994, 116, 8754. B-S: (i) Cui, Q.; Musaev, D. G.; Morokuma, K.
Organometallics 1998, 17, 1383.
(6) (a) Suginome, M.; Nakamura, H.; Ito, Y. Chem. Commun. 1996,
2777. (b) Onozawa, S.-y.; Hatanaka, Y.; Tanaka, M. Chem. Commum.
1997, 1229. (c) Suginome, M.; Nakamura, H.; Ito, Y. Angew. Chem.,
Int. Ed. 1997, 36, 2516. (d) Suginome, M.; Matsuda, T.; Nakamura,
H.; Ito, Y. Tetrahedron 1999, 55, 8787. (e) Suginome, M.; Nakamura,
H.; Matsuda, T.; Ito, Y. J . Am. Chem. Soc. 1998, 120, 4248. (f)
Suginome, M.; Matsuda, T.; Ito, Y. Organometallics 1998, 17, 5233.
(g) Suginome, M.; Matsuda, T.; Yoshimoto, T.; Ito, Y. Org. Lett. 1999,
1, 1567. (h) Suginome, M.; Ohmori, Y.; Ito, Y. Synlett 1999, 10, 1567.
(i) Onozawa, S.-y.; Hatanaka, Y.; Tanaka, M. Chem. Commun. 1999,
1863. (j) Pohlman, T.; de Meijere, A. Org. Lett. 2000, 2, 3877. (k)
Suginome, M.; Ohmori, Y.; Ito, Y. J . Organomet. Chem. 2000, 611, 403.
(l) Suginome, M.; Matsuda, T.; Ito, Y. J . Am. Chem. Soc. 2000, 122,
11015. (m) Suginome, M.; Ohmori, Y.; Ito, Y. J . Am. Chem. Soc. 2001,
123, 4601. (n) Suginome, M.; Matsuda, T.; Yoshimoto, T.; Ito, Y.
Organometallics 2002, 21, 1537.
(3) (a) Ozawa, F. J . Organomet. Chem. 2000, 611, 332. (b) Ozawa,
F.; Kamite, J . Organometallics 1998, 17, 5630. (c) Ozawa, F.; Sakamoto,
Y.; Sagawa, T.; Tanaka, R.; Katayama, H. Chem. Lett. 1999, 1307. (d)
Ozawa, F.; Hikida, T. Organometallics 1996, 15, 4501. (e) Hikida, T.;
Onitsuka, K.; Sonogashira, K.; Hayashi, T.; Ozawa, F. Chem. Lett.
1995, 985. (f) Ozawa, F.; Sugawara, M.; Hayashi, T. Organometallics
1994, 13, 3237. (g) Ozawa, F.; Sugawara, M.; Hasebe, K.; Hayashi, T.
Inorg. Chim. Acta 1999, 296, 19.
(4) Related studies have been reported by several research groups.
B-B: (a) Lesley, G.; Nguyen, P.; Taylor, N. J .; Marder, T. B.
Organometallics 1996, 15, 5137. (b) Iverson, C. N.; Smith, M. R., III.
Organometallics 1996, 15, 5155. (c) Ishiyama, T.; Matsuda, N.; Murata,
M.; Ozawa, F.; Suzuki, A.; Miyaura, N. Organometallics 1996, 15, 713.
(d) Clegg, W.; Lawlor, F. J .; Lesley, G.; Marder, T. B.; Norman, N. C.;
Orpen, A. G.; Quayle, M. J .; Rice, C. R.; Scott, A. J .; Souza, F. E. S. J .
Organomet. Chem. 1998, 550, 183. Ge-Ge: (e) Mochida, K.; Wada,
T.; Suzuki, K.; Hatanaka, W.; Nishiyama, Y.; Nanjo, M.; Sekine, A.;
Ohashi, Y.; Sakamoto, M.; Yamamoto, A. Bull. Chem. Soc. J pn. 2001,
74, 123. Sn-Sn, Si-Si: (f) Obora, Y.; Tsuji, Y.; Nishiyama, K.; Ebihara,
M.; Kawamura, T. J . Am. Chem. Soc. 1996, 118, 10922. (g) Tsuji, Y.;
Nishiyama, K.; Hori, S.; Ebihara, M.; Kawamura, T. Organometallics
1998, 17, 507. Te-Si, Te-Ge, Te-Sn: (h) Han, L.-B.; Shimada, S.;
Tanaka, M. J . Am. Chem. Soc. 1997, 119, 8133.
10.1021/om020686z CCC: $22.00 © 2002 American Chemical Society
Publication on Web 11/15/2002

5880 Organometallics, Vol. 21, No. 26, 2002
Sagawa et al.
Sch em e 1
Sch em e 2
F igu r e 1. 31P{1H} NMR spectra of 2a (a) and 3a (b) in
CD2Cl2.
affords the silylborylation products (step c).6 As de-
scribed below, we have succeeded for the first time in
observing all the elementary processes assumed in this
scheme, using basic and compact tertiary phosphines
as supporting ligands (L).
Ta ble 1. 31P {1H} NMR Da ta for 2a -2d in CD2Cl2 a t
-50 °C
1
2
2
complex
δ
assignment J PtP (Hz) J SiP (Hz) J PP (Hz)
2a
-17.4 (d) trans to Si
-19.0 (br) trans to B
-5.2 (br) trans to B
-6.4 (d) trans to Si
+14.8 (br) (overlap)a
-12.6 (d) trans to Si
-14.8 (br) trans to B
1374
1375
1391
1404
1468
1465
1349
148
0
0
139
b
159
0
29
Resu lts
2b
Oxid a tive Ad d ition of Silylbor a n es. Four kinds of
silyl-boryl complexes, 2a -2d , listed in Scheme 2 were
prepared by the oxidative addition of silylboranes to Pt-
(cod)L2 complexes, which were generated in situ from
Pt(cod)2 and 2 molar quantity of phosphines in Et2O.7
The pinacol derivative of silylborane 1a rapidly reacted
with PMe3, PMe2Ph, and PEt3 complexes at room
temperature to give 2a -2c, quantitatively, as confirmed
by 31P{1H} NMR spectroscopy. On the other hand,
diaminosilylborane 1b was much less reactive, and its
reaction with Pt(cod)(PMe3)2 at room temperature took
12 h for completion.
30
24
2c
2d
a
Two phosphorus atoms exhibited the same chemical shift.
Coupling constant was obscured due to broadening of the signal.
b
satellites (2J SiP ) 148 Hz) is assignable to the phosphine
trans to the silyl ligand, whereas the broad one at δ
-19.0 arises from the phosphine trans to the boryl
ligand. The broadening phenomenon observed in the
latter signal is ascribed to the quadrupole coupling with
10B and 11B nuclei.
The reaction of 1a was examined further with other
Table 1 lists the 31P{1H} NMR data for 2a -2d . The
chemical shifts and the J PtP values for two phosphorus
phosphine ligands (PMePh2, PPh3, PPri ). In the case
3
1
of PMePh2, 31P{1H} NMR analysis of the reaction
solution strongly suggested the formation of cis-Pt-
nuclei in 2a , 2b, and 2d are comparable to one another,
showing nearly identical electronic properties of silyl
and boryl ligands. The PEt3 complex 2c exhibits only
one broad signal with 195Pt satellites even at low
temperature (-50 °C), probably due to the occurrence
of rapid dissociation of PEt3 ligands.
1
(SiMe2Ph)(Bpin)(PMePh2)2 (δ 11.8, J PtP ) 1460 Hz),
while its isolation was unsuccessful due to decomposi-
tion. The PPh3 and PPri complexes were totally unre-
3
active even under heated conditions.
Complexes 2a -2d were isolated as pale yellow solids
and characterized by NMR spectroscopy and/or elemen-
tal analysis.8 Figure 1a shows the 31P{1H} NMR spec-
trum of 2a . Two sets of signals with 195Pt satellites are
observed. The sharp doublet at δ -17.4 with 29Si
In ser tion of P h en yla cetylen e in to Silyl-Bor yl
Com p lexes. Complex 2a smoothly reacted with phe-
nylacetylene in CD2Cl2 at room temperature to give the
insertion complex 3a , quantitatively (Scheme 3). When
an excess amount of phenylacetylene (5-10 molar
quantity) was employed, the reaction was completed in
2 h. As seen from Figure 1b, the 31P{1H} NMR spectrum
(7) Complexes 2a -2d may be prepared in benzene or toluene, while
their isolation is rather difficult due to high solubility in these solvents.
Preparation in THF or CH2Cl2 was unsuccessful owing to instability
of Pt(cod)2.
(8) Analytically pure 2d could not be obtained due to contamination
of impurities.
of 3a exhibits two sets of doublets at δ -23.2 (2J PP
)
22 Hz, J PtP ) 1276 Hz) and -29.5 (2J PP ) 22 Hz, J PtP
1
1
) 1907 Hz), respectively. The former has 29Si satellites,

cis-Silyl(boryl)platinum(II) Complexes
Organometallics, Vol. 21, No. 26, 2002 5881
Sch em e 3
2
with the J SiP value (168 Hz) comparable to that of 2a
(148 Hz), showing the presence of a Pt-Si bond. On the
other hand, the signal broadening observed for 2a
bearing a Pt-B bond does not occur for 3a . Hence, the
selective insertion of phenylacetylene into the Pt-B
bond has been evidenced.
F igu r e 2. Molecular structure of 3b. Thermal ellipsoids
are drawn at the 30% probability level. Selected bond
distances (Å) and angles (deg): Pt-C(1) ) 2.062(7), C(1)-
C(2) ) 1.366(9), C(1)-C(3) ) 1.501(9), C(2)-B ) 1.54(1),
Pt-Si ) 2.371(2), Pt-P(1) ) 2.383(2), Pt-P(2) ) 2.299(2),
Pt-C(1)-C(2) ) 122.0(5), Pt-C(1)-C(3) ) 118.8(4), C(2)-
C(1)-C(3) ) 119.2(6), C(1)-C(2)-B ) 129.7(6), Si-Pt-C(1)
) 83.9(2), P(1)-Pt-C(1) ) 87.5(2), P(1)-Pt-P(2) ) 95.90-
(6), P(2)-Pt-Si ) 92.79(6).
Complex 2b exhibited reactivity comparable to 2a ,
whereas 2d was unreactive even at 60 °C. Complex 2c
was moderately reactive and gradually converted into
the insertion complex at room temperature. In this case,
the resulting 3c subsequently underwent C-Si reduc-
tive elimination to give (Z)-R-silyl-â-borylstyrene 4 (vide
infra).
In the 1H NMR spectrum of 3a , the vinylic proton
signal appeared at δ 7.00 as a doublet of doublets due
to the spin-spin coupling with the two phosphorus
other hand, the reductive elimination was effectively
retarded by free phosphines (1 molar quantity) and took
several days for completion at the same temperature.
Similar behavior has been reported for cis-alkyl(silyl)-
platinum(II) complexes, whose C-Si reductive elimina-
tion involves preliminary dissociation of phosphine
ligand.9
The PEt3-coordinated 3c was much more reactive, and
the C-Si reductive elimination giving 4 proceeded
successively after the insertion of phenylacetylene into
2c. Figure 3 shows the time course observed in CD2Cl2
at 20 °C, which adopts a typical pattern of consecutive
reactions. The amount of 3c reached a maximum after
7 h and then decreased gradually with increasing
amount of 4.
3
nuclei (4J PH ) 17.7 and 4.5 Hz, J PtH ) 122.4 Hz). The
13C{1H} NMR spectrum exhibited two sets of signals
arising from the vinylic carbons at δ 120.0 (br) and 191.9
2
(dd, J PC ) 98 and 16 Hz). The latter at the lower
magnetic field, which is assignable to the R-vinylic
2
carbon on the basis of the chemical shift and the J PC
coupling constants, disappeared in a DEPT NMR spec-
trum, whereas the former remained unchanged. Ac-
cordingly, the occurrence of regioselective insertion of
phenylacetylene, leading to the form cis-Pt{C(Ph)dCH-
(Bpin)}(SiMe2Ph)(PMe3)2, was clearly indicated. The
characteristic NMR signals were similarly observed for
3b.
Figure 2 shows the X-ray structure of 3b, which is
consistent with the NMR observations. The phenyl
group is bonded to the R-vinylic carbon of the alkenyl
ligand, and the platinum and boron atoms are situated
at mutually cis positions. The C(1)-C(2) distance (1.366-
(9) Å) is in a typical range of C-C double bonds. The
Pt-P(1) bond (2.383(2) Å) is significantly longer than
the Pt-P(2) bond (2.299(2) Å), reflecting the greater
trans influence of the silyl ligand than the alkenyl
ligand.
While the insertion complex 3c is a transient species
and could not be isolated, its formation was supported
by NMR spectroscopy. Figure 4 illustrates a part of the
1H NMR spectrum of the reaction solution of 2c with
phenylacetylene in CD2Cl2. The apparent triplet at δ
0.42 with 195Pt satellites (3J PtH ) 30.4 Hz) and the
singlet at δ 0.38 are assignable to SiMe groups of 2c
and 4, respectively. On the other hand, SiMe signals of
3c are observed as two sets of doublets with 195Pt
satellites at δ 0.20 (3J PtH ) 22.4 Hz) and 0.07 (3J PtH
)
Red u ctive Elim in a tion fr om Silyl-Alk en yl Com -
p lexes. The PMe3- and PMe2Ph-coordinated complexes
3a and 3b underwent C-Si reductive elimination under
heated conditions (Scheme 3). The reactions performed
at 60 °C in toluene-d8 were completed in 30 (3a ) and 6
h (3b), respectively, to afford (Z)-R-silyl-â-borylstyrene
4, the structure of which was identical with that
previously prepared by catalytic reactions.6b,d The re-
ductive elimination was significantly accelerated by
addition of PhCtCPh to the system. For example, in
the presence of 10 molar quantity of the acetylene, the
reaction of 3b was completed in 1 h at 60 °C. On the
23.4 Hz). The nonequivalency of two SiMe groups is
attributable to the presence of a -C(Ph)dCH(Bpin)
ligand with an unsymmetrical structure, which is
perpendicularly coordinated to the Pt(SiMe2Ph)(PEt3)2
moiety. This type of structure was confirmed for PMe2-
Ph-coordinated analogue 3b by X-ray diffraction analy-
sis (Figure 2). In the 1H NMR spectrum of 3b, SiMe
(9) (a) Hasebe, K.; Kamite, J .; Mori, T.; Katayama, H.; Ozawa, F.
Organometallics 2000, 19, 2022. (b) Ozawa, F.; Hikida, T.; Hasebe,
K.; Mori, T. Organometallics 1998, 17, 1018. (c) Ozawa, F.; Hikida,
T.; Hayashi, T. J . Am. Chem. Soc. 1994, 116, 2844. (d) Ozawa, F.;
Kitaguchi, M.; Katayama, H. Chem. Lett. 1999, 1289.

5882 Organometallics, Vol. 21, No. 26, 2002
Sagawa et al.
Ta ble 2. P seu d o-F ir st-Or d er Ra te Con sta n ts for
th e In ser tion of P h en yla cetylen e in to 2a a
run
[PhCtCH] (M)
103[PMe3] (M)
104kobsd (s-1
)
1
2
3
4
5
6
7
8
0.15
0.25
0.40
0.60
0.25
0.25
0.25
0.25
4.0
4.0
4.0
4.0
6.3
11
2.38(5)
3.8(1)
5.4(1)
6.5(3)
2.6(1)
1.49(3)
1.09(3)
0.71(4)
16
25
a
In CD2Cl2 at 20 °C. [2a ]0 ) 0.025 M.
F igu r e 3. Time course of the reaction of 2c with phenyl-
acetylene (10 molar quantity) at 20 °C in CD2Cl2. The
amount of each component at time t was determined by
1H NMR spectroscopy.
F igu r e 5. Effect of phenylacetylene concentration on the
insertion rate of phenylacetylene into 2a in CD2Cl2 in the
presence of added PMe3 at 20 °C. Initial concentration: [2a ]
) 25 mM, [PMe3] ) 4.0 mM.
F igu r e 4. 1H NMR spectrum of the reaction solution of
2c and phenylacetylene (10 molar quantity) in CD2Cl2 at
20 °C. The solution consists of a 44:28:28 ratio of 2c, 3c,
and 4. Only the SiMe proton region is shown for clarity.
groups exhibit nonequivalent signals at δ 0.22 and 0.13,
indicating restricted rotation of the -C(Ph)dCH(Bpin)
ligand around the Pt-C(1) bond. Thus, when the
rotation is a sufficiently slow process on an NMR time
scale, the two SiMe groups may be regarded as being
diastereotopic with each other to exhibit different
chemical shifts. Since the rotational barrier arises
mainly from steric repulsion between the -C(Ph)dCH-
(Bpin) and Pt(SiMe2Ph)(PMe2Ph)2 moiety in 3b , it is
reasonable to assume a similar situation for 3c, having
bulkier PEt3 ligands.
F igu r e 6. Effect of added PMe3 on the insertion rate of
phenylacetylene into 2a in CD2Cl2 at 20 °C. Initial con-
centration: [2a ] ) 25 mM, [PhCtCH] ) 0.25 M.
The 31P{1H} NMR signals of 3c appeared at δ 1.4 and
3.0 as two sets of doublets (2J PP ) 18 Hz) with small
(1251 Hz) and moderate (1965 Hz) coupling to 195Pt,
1
respectively. The J PtP values are comparable to those
amount of phenylacetylene. Table 2 lists the rate
constants (kobsd) observed at various concentration of
phenylacetylene and PMe3.
The reaction rate increased with increase in the
concentration of phenylacetylene (runs 1-4; Figure 5a).
On the other hand, the reaction progress was effectively
retarded by free PMe3 (runs 2 and 5-8; Figure 6a). The
reciprocals of kobsd values exhibited good linear correla-
of 3a and 3b and are in appropriate magnitude for the
phosphines coordinated trans to boryl and alkenyl
ligands, respectively.
Kin etic Stu d y on th e In ser tion of P h en yla cetyl-
en e. The insertion mechanism of phenylacetylene into
2a in CD2Cl2 was examined by kinetic experiments
under pseudo-first-order conditions using an excess

cis-Silyl(boryl)platinum(II) Complexes
Organometallics, Vol. 21, No. 26, 2002 5883
Sch em e 4
reciprocals of the intercepts in these figures, which
correspond to the rate constant k1 for the dissociation
of PMe3 from 2a , were in agreement with each other:
1.8(4) × 10-3 and 2.0(5) × 10-3 s-1
.
Discu ssion
We have demonstrated that all the elementary pro-
cesses presumed for catalytic silylborylation of phenyl-
acetylene with PhMe2SiBpin (1a ) can be examined
stepwise by using platinum complexes. Each of the
processes has been found to be significantly affected by
the type of tertiary phosphine ligands employed. Thus,
the oxidative addition (step a in Scheme 1) tends to
proceed preferably with compact phosphines such as
PMe3 and PMe2Ph. The subsequent insertion (step b)
also proceeds more readily with these phosphine ligands
(2a and 2b) than with the PEt3 ligand (2c). As confirmed
for 2a by kinetic experiments, the insertion rate is
controlled at two stages, i.e., dissociation of L from 2
and insertion of phenylacetylene via prior coordination
of the acetylene to 5 (Scheme 4). Since the former stage
is easier for bulkier phosphines in a general sense, it is
considered that the insertion rate is mainly dependent
on the ease of the latter stage. Although we could not
evaluate the coordination and insertion steps in the
latter stage, separately, it seems reasonable that the
bulkier phosphine inhibits the coordination of phenyl-
acetylene to cause the slower insertion rate. On the
other hand, the final process leading to C-Si reductive
elimination (step c) has been found to be easier for the
complex bearing bulkier phosphine ligands (i.e., 3c .
3b > 3c). As suggested by preliminary kinetic experi-
ments for 3b, this process involves prior phosphine
dissociation to give the [Pt{C(Ph)dCH(Bpin)}(SiMe2-
Ph)L] intermediate, which reductively eliminates (Z)-
R-silyl-â-borylstyrene 4. Accordingly, key roles of mono-
phosphine species in steps b and c in Scheme 1 (i.e., n
) 1) have been evidenced.
tion with 1/[PhCtCH] and [PMe3] values, respectively
(Figures 5b and 6b).
Scheme 4 shows our proposed mechanism. The first
step is dissociation of one of the PMe3 ligands (L) from
2a . The three-coordinate silyl-boryl intermediate 5 thus
generated successively undergoes insertion of phenyl-
acetylene into the Pt-B bond via prior coordination of
phenylacetylene to the vacant site of 5. The resulting 6
is then converted into the final product 3a by trans to
cis isomerization followed by coordination of L. This
mechanism is essentially the same as that previously
proposed for the acetylene insertion into cis-bis(silyl)-
and cis-bis(boryl)platinum(II) complexes.3b,4a,b
Steady-state approximation for the concentration of
5 leads to the following equation:
d[5]
dt
) k1[2a ] - k-1[PMe3][5] - k2[PhCtCH][5] ) 0
(1)
Thus,
k1[2a ]
[5] )
(2)
k-1[PMe3] + k2[PhCtCH]
We have also confirmed that the insertion of phenyl-
acetylene into silyl-boryl complexes 2a -2c occurs ex-
clusively at the Pt-B bond.10 This finding supports the
previously proposed mechanism for catalytic silylbory-
lation.6 Since both bis(silyl)- and bis(boryl)platinum(II)
complexes are known to undergo acetylene insertion
under similar reaction conditions,3b,4a-d the perfect
selection of the insertion site deserves a discussion.
There are two stages possibly responsible for the site
selectivity (Scheme 5). One is the phosphine dissociation
from 2. Thus, if the dissociation of the phosphine trans
to the silyl ligand is much easier than the other,
phenylacetylene may selectively insert into the Pt-B
bond via the intermediates 5 and 7. However, as judging
If the steady-state for 5 holds and the conversion of 6
to 3a is sufficiently more rapid than the acetylene
insertion into 5, the rate of formation of 3a is expressed
as follows:
d[3a ]
dt
d[2a ]
dt
) -
) k2[PhCtCH][5]
(3)
Substitution of eq 2 into eq 3 yields the final rate
expression:
k1k2[PhCtCH]
d[2a ]
dt
-
)
[2a ] (4)
k-1[PMe3] + k2[PhCtCH]
1
from the very close J PtP values of the two phosphine
Accordingly, the following relation between the kobsd
value and the concentration of phenylacetylene and
PMe3 can be obtained:
ligands observed for 2a -2c (Table 1), this possibility
seems unlikely. The other stage that we have to
examine is the insertion of phenylacetylene into the
coordinatively unsaturated species 5 and its isomer 5′.
At this stage, reflecting the bulkiness of the SiMe2Ph
ligand compared with the Bpin ligand, acetylene coor-
dination to 5 will be sterically advantageous over the
k-1[PMe3]
1
1
)
+
(5)
kobsd
k1
k1k2[PhCtCH]
Equation 5 was fully consistent with the kinetic data.
Thus, the k-1/k1k2 values, estimated from the slopes of
Figures 5b and 6b, were in good agreement with each
other: 1.35(6) × 105 and 1.36(2) × 105 s. Moreover,
(10) For insertion of acetylene into other transition metal boryl
complexes, see: Clark, G. R.; Irvine, G. J .; Roper, W. R.; Wright, L. J .
Organometallics 1997, 16, 5499. Onozawa, S.-y.; Tanaka, M. Organo-
metallics 2001, 20, 5956.

5884 Organometallics, Vol. 21, No. 26, 2002
Sagawa et al.
techniques. Nitrogen gas was dried by passing through P2O5
(Merck, SICAPENT). NMR spectra were recorded on a Varian
Mercury 300 spectrometer. Chemical shifts are reported in δ
(ppm) referred to an internal SiMe4 standard for 1H and 13C
NMR and to an external 85% H3PO4 standard for 31P NMR.
GLC analysis was performed on a Shimadzu GC-14B instru-
ment equipped with a FID detector and a CBP-1 capillary
column (25 m × 0.25 mm). Bis(1,5-cyclooctadiene)platinum-
(0)13 and silylboranes (1a , 1b)14 were prepared according to
literature procedures. THF, Et2O, pentane, and toluene were
dried over sodium benzophenone ketyl and distilled prior to
use. CH2Cl2 was dried over CaH2 and distilled prior to use.
CD2Cl2 was dried over LiAlH4, vacuum transferred, and stored
under a nitrogen atmosphere.
Sch em e 5
P r ep a r a tion of cis-P t(SiMe2P h )(Bp in )(P Me3)2 (2a ). To
a white suspension of Pt(cod)2 (226 mg, 0.55 mmol) in Et2O
(20 mL) were successively added PMe3 (84 mg, 1.1 mmol) and
PhMe2SiBpin (1a , 144 mg, 0.55 mmol) at 0 °C. The mixture
was stirred at room temperature for 1 h to give a pale yellow
homogeneous solution, which was concentrated to dryness by
pumping. The resulting oily material was cooled to -78 °C
and dissolved in Et2O (1 mL). Slow addition of pentane (3 mL)
with vigorous stirring at the same temperature led to precipi-
tation of a pale yellow solid of 2a , which was collected by
filtration, washed with pentane (3 mL × 3), and dried under
vacuum (175 mg, 51%).
coordination to 5′. Furthermore, on the subsequent
migratory insertion step, we may expect another reason
for the Bpin group migration in 7 taking place in
preference to the SiMe2Ph group migration in 7′, which
is related to orbital interaction during the migration.
Thus, the migration of sp3-hybridized ligands is known
to involve distortion energy, caused by direction change
of the sp3 orbital from metal to carbon.11 For SiH3 the
distortion energy has been estimated to be 13.8 kcal/
mol by theoretical calculation.11b On the other hand, the
Bpin ligand in 7 with sp2-hybridization may migrate
more easily to the acetylenic carbon via the participation
of the pπ orbital on B, which will reduce the energy
growth associated with the direction change of the sp2
orbital from metal to carbon.12
1
4
2a . H NMR (CD2Cl2, -50 °C): δ 0.39 (dd, J PH ) 1.5 and
3
2
1.2 Hz, J PtH ) 31.2 Hz, 6H, SiMe), 1.15 (d, J PH ) 6.9 Hz,
3J PtH ) 16.2 Hz, 9H, PMe), 1.26 (s, 12H, Bpin(Me)), 1.56 (d,
2J PH ) 7.8 Hz, J PtH ) 20.6 Hz, 9H, PMe), 7.08-7.23 (m, 3H,
3
Ph), 7.50-7.60 (m, 2H, Ph). 13C{1H} NMR (CD2Cl2, -50 °C):
3
2
1
δ 6.4 (t, J PC ) 6 Hz, J PtC ) 96 Hz, SiMe), 18.0 (m, J PC ) 24
Hz, 2J PtC ) 20 Hz, PMe), 18.6 (m, 1J PC ) 25 Hz, 2J PtC ) 31 Hz,
4
3
PMe), 26.5 (s, Bpin(Me)), 81.2 (d, J PC ) 3 Hz, J PtC ) 33 Hz,
3
Bpin), 126.3 (s, Ph), 126.7 (s, SiPh), 134.1 (s, J PtC ) 23 Hz,
SiPh), 152.9 (t, 2J PC ) 7 Hz, 2J PtC ) 29 Hz, SiPh). 31P{1H} NMR
2
1
(CD2Cl2, -50 °C): δ -17.4 (d, J PP ) 29 Hz, J PtP ) 1374 Hz,
2J SiP ) 148 Hz), -19.0 (br, J PtP ) 1375 Hz). Anal. Calcd for
1
C
20H41O2BSiP2Pt: C, 39.41; H, 6.78. Found: C, 39.67; H, 6.68.
Apart from the kinetic viewpoints, the insertion into
the Pt-B bond seems preferable in a thermodynamic
sense as well. Thus, Sakaki et al. have recently provided
the following bond energies (kcal mol-1): Pt-B(OH)2
(64.4), Pt-SiH3 (54.2), H3C-B(OH)2 (109.7), H3C-SiH3
(86.0).11c It is seen that the difference between C-B and
C-Si bonds (23.7) is significantly larger than that
between Pt-B and Pt-Si bonds (10.2). While our
consideration for the site selectivity is not conclusive,
the present findings provide an interesting opportunity
for further studies, especially for theoretical investiga-
tions.
Complexes 2b and 2c were similarly prepared in 72 and
86% yield, respectively, by using PMe2Ph and PEt3 in place of
PMe3. The synthesis of 2d followed essentially the same
procedure as 2a -2c, except for the reaction time. Thus, the
reaction of Pt(cod)2, PMe3, and PhMe2SiBdmeda (1b) in Et2O
took 12 h for completion at room temperature. Complex 2d
was obtained as a pale yellow solid in 48% yield, which was
pure by 31P NMR spectroscopy but contained a small amount
(ca. 3%) of organic impurities, as confirmed by 1H NMR
spectroscopy. Several attempts to obtain analytically pure 2d
by recrystallization were unsuccessful.
4
2b. 1H NMR (CD2Cl2, -50 °C): δ 0.37 (d, J PH ) 2.1 Hz,
3J PtH ) 32.1 Hz, 6H, SiMe), 1.04 (s, 12H, Bpin(Me)), 1.07 (d,
3
2
2J PH ) 6.9 Hz, J PtH ) 17.4 Hz, 6H, PMe), 1.45 (d, J PH ) 7.5
Hz, 3J PtH ) 21.3 Hz, 6H, PMe), 7.10-7.45 (m, 13H, Ph), 7.56-
7.64 (m, 2H, Ph). 13C{1H} NMR (CD2Cl2, -50 °C): δ 6.5 (t,
Exp er im en ta l Section
3J PC ) 5 Hz, J PtC ) 95 Hz, SiMe), 16.1 (m, J PC ) 25 Hz, J PC
Gen er a l P r oced u r es. All manipulations were carried out
under a nitrogen atmosphere using conventional Schlenk
2
1
3
2
1
3
) 5 Hz, J PtC ) 24 Hz, PMe), 16.7 (m, J PC ) 26 Hz, J PC ) 5
2
4
Hz, J PtC ) 37 Hz, PMe), 26.3 (s, Bpin(Me)), 81.2 (d, J PC ) 3
(11) (a) Sakaki, S.; Biswas, B.; Musashi, Y.; Sugimoto, M. J .
Organomet. Chem. 2000, 611, 288. (b) Biswas, B.; Sugimoto, M.;
Sakaki, S. Organometallics 1999, 18, 4015. (c) Sakaki, S.; Kai, S.;
Sugimoto, M. Organometallics 1999, 18, 4825.
Hz, 3J PtC ) 33 Hz, Bpin), 126.5 (s, SiPh), 126.8 (s, SiPh), 127.9
3
3
(d, J PC ) 6 Hz, PPh), 128.0 (d, J PC ) 5 Hz, PPh), 129.2 (s,
2
PPh), 129.3 (s, PPh), 130.7 (d, J PC ) 12 Hz, PPh), 134.4 (s,
3J PtC ) 24 Hz, SiPh), 138.6 (dd, J PC ) 40 Hz, J PC ) 3 Hz,
(12) (a) Insertion of C-C multiple bonds into a Pt-B bond of cis-
Pt{B(OH)2}(PH3)2 has been examined theoretically.5a Although no
details of orbital interaction have been described, the transition-state
structure optimized for the migratory insertion in cis-Pt{B(OH)2}2(η2-
H2CdCH2)(PH3) to give Pt{CH2CH2B(OH)2}{B(OH)2}(PH3) indicates
the participation of the pπ orbital on B. Thus, judging from the
geometry around the boron atom, the sp2 orbital is clearly oriented
toward one of the olefinic carbons to make a B-C bond (d(B-C) )
1.645 Å), while the boron still interacts with platinum to a considerable
extent (d(Pt-B) ) 2.515 Å) via the pπ orbital. (b) Importance of the
paraticipation of the boron pπ orbital has been demonstrated for
oxidative addition of (HO)2B-XH3 (X ) C, Si, Ge, Sn) to M(PH3)2 (M
) Pd, Pt).11c
1
3
1
3
PPh), 139.8 (dd, J PC ) 38 Hz, J PC ) 3 Hz, PPh), 152.5 (t,
3J PC ) 6 Hz, 2J PtC ) 35 Hz, SiPh). 31P{1H} NMR (CD2Cl2, -50
1
2
1
°C): δ -5.2 (br, J PtP ) 1391 Hz), -6.4 (d, J PP ) 30 Hz, J PtP
2
) 1404 Hz, J SiP ) 139 Hz). Anal. Calcd for C30H45O2BSiP2Pt:
C, 49.12; H, 6.18. Found: C, 49.26; H, 6.06.
(13) Crascall, L. E.; Spencer, J . L. Inorg. Synth. 1990, 28, 126.
(14) (a) Biffar, W.; No¨th, H.; Schwertho¨ffer, R. Liebigs Ann. Chem.
1981, 2067. (b) Buynak, J . D.; Geng, B. Organometallics 1995, 14, 3112.
(c) Suginome, M.; Matsuda, T.; Ito, Y. Organometallics 2000, 19, 4647.

cis-Silyl(boryl)platinum(II) Complexes
Organometallics, Vol. 21, No. 26, 2002 5885
1
3
2c. H NMR (CD2Cl2, -50 °C): δ 0.32 (s, J PtH ) 30.8 Hz,
9H, PMe), 1.26 (s, 6H, Bpin(Me)), 1.29 (d, 2J PH ) 8.4 Hz, 3J PtH
3
3
4
6H, SiMe), 0.77 (dt, J PH ) 15.3 Hz, J HH ) 7.5 Hz, 9H,
PCH2CH3), 1.00 (dt, J PH ) 15.6 Hz, J HH ) 7.5 Hz, 9H,
PCH2CH3), 1.22 (s, 12H, Bpin(Me)), 1.35 (m, 6H, PCH2CH3),
) 16.2 Hz, 9H, PMe), 1.30 (s, 6H, Bpin(Me)), 7.00 (dd, J PH
)
3
3
3
17.7 and 4.5 Hz, J PtH ) 122.4 Hz, 1H, PtCdCH), 7.0-7.9 (m,
3
10H, Ph). 13C{1H} NMR (CD2Cl2, 20 °C): δ 4.9 (dd, J PC ) 6
3
2
3
1.89 (m, 6H, PCH2CH3), 7.04-7.18 (m, 3H, Ph), 7.45 (d, J HH
and 2 Hz, J PtC ) 70 Hz, SiMe), 5.5 (dd, J PtC ) 6 and 3 Hz,
1 3
) 6.6 Hz, 2H, Ph). 13C{1H} NMR (CD2Cl2, -50 °C): δ 6.7 (t,
2J PtC ) 70 Hz, SiMe), 16.7 (dd, J PC ) 24 Hz, J PC ) 2 Hz,
2J PtC ) 21 Hz, PMe), 19.0 (dd, 1J PC ) 29 Hz, 3J PC ) 5 Hz, 2J PtC
) 29 Hz, PMe), 25.2 (s, Bpin(Me)), 25.7 (s, Bpin(Me)), 82.2 (s,
Bpin), 120.0 (br, PtC ) CH), 126.5 (s, Ph), 126.7 (s, Ph), 127.0
(s, Ph), 127.4 (s, Ph), 129.4 (d, 4J PC ) 2 Hz, 3J PtC ) 48 Hz, Ph),
3J PC ) 10 and 4 Hz, J PtC ) 97 Hz, SiMe), 8.36 (s, J PtC ) 16
2
3
Hz, PCH2CH3), 8.43 (s, J PtC ) 16 Hz, PCH2CH3), 17.4 (m,15
3
1J PC ) 26 Hz, PCH2CH3), 17.9 (m,15 J PC ) 26 Hz, PCH2CH3),
1
26.6 (s, Bpin(Me)), 81.2 (s, 3J PtC ) 33 Hz, Bpin), 125.9 (s, SiPh),
3
3
4
3
3
126.4 (s, SiPh), 133.8 (s, J PtC ) 18 Hz, SiPh), 153.0 (t, J PC
)
135.0 (d, J PC ) 2 Hz, J PtC ) 23 Hz, SiPh), 152.3 (dd, J PC )
2
2
7 Hz, J PtC ) 30 Hz, SiPh). 31P{1H} NMR (CD2Cl2, -50 °C): δ
8 and 4 Hz, SiPh), 152.9 (d, J PC ) 5 Hz, PtC(Ph)dC), 191.9
1
2
14.8 (br, J PtP ) 1468 Hz). Anal. Calcd for C26H53O2BSiP2Pt:
(dd, J PC ) 98 and 16 Hz, PtC ) CH). 31P{1H} NMR (CD2Cl2,
2
1
2
C, 45.02; H, 7.70. Found: C, 44.49; H, 7.80.
20 °C): δ -23.2 (d, J PP ) 22 Hz, J PtP ) 1276 Hz, J SiP ) 168
2 1
2d . 1H NMR (CD2Cl2, -50 °C): δ 0.16 (d, J PH ) 2.4 Hz,
4
Hz), -29.5 (d, J PP ) 22 Hz, J PtP ) 1907 Hz). Anal. Calcd for
3J PtH ) 30.6 Hz, 6H, SiMe), 1.08 (d, J PH ) 6.6 Hz, J PtH
)
2
3
C
28H47O2BSiP2Pt: C, 47.26; H, 6.66. Found: C, 46.86; H, 6.87.
2
3
3b. 1H NMR (CD2Cl2, 20 °C): δ 0.13 (d, 4J PH ) 2.4 Hz, 3J PtH
15.6 Hz, 9 H, PMe), 1.38 (d, J PH ) 7.8 Hz, J PtH ) 21.0 Hz, 9
H, PMe), 2.62 (s, 6H, NMe), 3.01 (s, 4H, NCH2), 7.06-7.20
(m, 3H, Ph), 7.48-7.56 (m, 2H, Ph). 13C{1H} NMR (CD2Cl2,
4
3
) 24.6 Hz, 3H, SiMe), 0.22 (d, J PH ) 1.8 Hz, J PtH ) 24.6 H,
2
3
3H, SiMe), 1.01 (d, J PH ) 8.4 Hz, J PtH ) 22.8 Hz, 3H, PMe),
3
2
2
3
-50 °C): δ 3.6 (t, J PC ) 11 and 5 Hz, J PtC ) 96 Hz, SiMe),
1.04 (d, J PH ) 8.1 Hz, J PtH ) 22.8 Hz, 3H, PMe), 1.05 (d,
1
3
2
2J PH ) 7.8 Hz, J PtH ) 15.6 Hz, 3H, PMe), 1.26 (d, J PH ) 8.1
3
2
15.9 (dd, J PC ) 22 Hz, J PC ) 5 Hz, J PtC ) 19 Hz, PMe), 16.3
1
3
2
Hz, 3J PtH ) 16.2 Hz, 3H, PMe), 1.38 (s, 6H, Bpin(Me)), 1.41 (s,
(dd, J PC ) 25 Hz, J PC ) 5 Hz, J Pt-C ) 32 Hz, PMe), 25.2 (s,
3
4
N(Me)C), 34.2 (s, J PtC ) 37 Hz, NMe), 123.5 (s, SiPh), 124.2
6H, Bpin(Me)), 6.92 (dd, J PH ) 17.8 and 4.9 Hz, 1H, PtCd
3
3
(s, SiPh), 131.8 (s, J PtC ) 22 Hz, SiPh), 151.6 (dd, J PC ) 7
and 5 Hz, SiPh). 31P{1H} NMR (CD2Cl2, -50 °C): δ -12.6 (d,
2J PP ) 24 Hz, 1J PtP ) 1465 Hz, 2J SiP ) 159 Hz), -14.8 (br, 1J PtP
) 1349 Hz).
CH), 7.10-7.43 (m, 16H, Ph), 7.70 (dd, 2H, Ph), 7.96 (m, 2H,
Ph). 13C{1H} NMR (CD2Cl2, 20 °C): δ 5.1 (dd, J PC ) 6 and 2
3
2
3
2
Hz, J PtC ) 70 Hz, SiMe), 5.9 (dd, J PC ) 5 and 3 Hz, J PtC
)
1
3
2
63 Hz, SiMe), 13.7 (dd, J PC ) 25 Hz, J PC ) 2 Hz, J PtC ) 24
1
3
2
Hz, PMe), 14.4 (dd, J PC ) 25 Hz, J PC ) 2 Hz, J PtC ) 23 Hz,
At t em p t a t P r ep a r a t ion of cis-P t (SiMe2P h )(Bp in )-
(P MeP h 2)2. A mixture of Pt(cod)2 (119 mg, 0.29 mmol),
PMePh2 (116 mg, 0.58 mmol), and PhMe2SiBPin (76 mg, 0.29
mmol) in Et2O (10 mL) was stirred at room temperature for 1
h. The initially white suspension gradually turned into a
reddish orange solution, whose 31P{1H} NMR spectrum ex-
hibited only a singlet signal at δ 11.8 with 195Pt satellites (1J PtP
) 1460 Hz). The solution was concentrated to dryness by
pumping to give an orange oily material, which was cooled to
-78 °C and treated with a small amount of Et2O (ca. 1 mL) to
afford an orange precipitate. The supernatant was removed
by filtration, and the precipitate was washed with pentane (2
mL × 3) and dried under vacuum (142 mg). The 31P{1H} NMR
spectrum measured in CD2Cl2 exhibited a number of unidenti-
fied peaks, together with the signal assignable to the silyl-
boryl complex (ca. 50%). The formation of a silyl-boryl complex
was strongly suggested by the appearance of a SiMe signal at
δ 0.19 in the 1H NMR spectrum, which had 195Pt satellites with
PMe), 16.6 (dd, 1J PC ) 30 Hz, 3J PC ) 5 Hz, 2J PtC ) 36 Hz, PMe),
1
3
2
17.2 (dd, J PC ) 30 Hz, J PC ) 5 Hz, J PtC ) 31 Hz, PMe), 25.2
(s, Bpin(Me)), 25.7 (s, Bpin(Me)), 82.6 (s, Bpin), 120.6 (br, PtC
) CH), 126.6 (s, Ph), 126.8 (s, Ph), 127.0 (s, Ph), 127.5 (s, Ph),
128.2 (d, 3J PC ) 4 Hz, PPh), 128.3 (d, 3J PC ) 4 Hz, PPh), 129.3
4
4
(s, Ph), 129.6 (d, J PC ) 2 Hz, PPh), 129.7 (d, J PC ) 2 Hz,
2
3
PPh), 131.1 (d, J PC ) 11 Hz, J PtC ) 9 Hz, PPh), 131.3 (d,
2J PC ) 12 Hz, J PtC ) 16 Hz, PPh), 135.1 (d, J PC ) 2 Hz, J PtC
3
4
3
1
1
) 22 Hz, SiPh), 138.8 (d, J PC ) 32 Hz, PPh), 139.4 (dd, J PC
3
3
) 42 Hz, J PC ) 5 Hz, PPh), 151.8 (dd, J PC ) 9 and 5 Hz,
2J PtC ) 59 Hz, SiPh), 152.6 (d, J PC ) 5 Hz, J PtC ) 30 Hz,
3
2
2
1
PtC(Ph)dC), 191.9 (dd, J PC ) 97 and 15 Hz, J PtC ) 783 Hz,
PtCdCH). 31P{1H} NMR (CD2Cl2, 20 °C): δ -12.3 (d, J PP
)
2
1
2
2
22 Hz, J PtP ) 1255 Hz, J SiP ) 168 Hz), -15.3 (d, J PP ) 22
1
Hz, J PtP ) 1957 Hz). Anal. Calcd for C38H51O2SiBP2Pt: C,
54.61; H, 6.15. Found: C, 54.19; H, 6.11.
X-r a y Str u ctu r a l An a lysis of 3b. A colorless prism having
approximate dimensions of 0.13 × 0.15 × 0.40 mm, which was
grown from an Et2O solution at -70 °C, was mounted on a
glass fiber. All measurements were made on a Rigaku RAXIS-
RAPID imaging plate diffractometer with graphite monochro-
mated Mo KR radiation (λ ) 0.71069 Å). Indexing was
performed from two oscillations which were exposed for 1.7
min. On the basis of the unit cell dimensions, statistical
analysis of intensity distribution, and successful solution and
refinement of the structure, the space group was determined
to be P1h(#2). The data were collected at 23 ( 1 °C to a
maximum 2θ value of 55.0°. A total of 38 images, correspond-
ing to 238.0° oscillation angles, were collected with two
different goniometer settings. Exposure time was 0.70 min per
degree. The camera radius was 127.40 mm. Readout was
performed in the 0.150 mm pixel mode. Of the 19 878 reflec-
tions collected, 8779 were unique (Rint ) 0.059); equivalent
reflections were merged. The data were corrected for Lorentz
and polarization effects and absorption (NUMABS). All cal-
culations were performed with the TEXSAN Crystal Structure
Analysis Package provided by Rigaku Corp. The structure was
solved by heavy atom Patterson methods (PATTY) and ex-
panded using Fourier techniques (DIRDIF94). All non-
hydrogen atoms were refined anisotropically. In the final cycles
of refinement, hydrogen atoms were located at idealized
positions (d(C-H) ) 0.95 Å) with isotropic temperature factors
(Biso ) 1.20Bbonded atom) and were included in calculation without
3
the J PtP value (30.0 Hz) comparable to that of 2a -2c.
P r ep a r a t ion of cis-P t {C(P h )dCH (Bp in )}(SiMe2P h )-
(P Me3)2 (3a ). To a solution of 2a (155 mg, 0.25 mmol) in
toluene (10 mL) was added phenylacetylene (127 mg, 1.24
mmol) at room temperature. The starting 2a disappeared in
2 h, as confirmed by 31P NMR spectroscopy, to be replaced by
a single product assignable to the title compound 3a . Solvent
was removed by pumping, and the pale yellow residue was
dried overnight under vacuum at room temperature. This
product was cooled to -78 °C, dissolved in a minimum amount
of Et2O (ca. 0.5 mL), and then treated with pentane (2 mL)
with vigorous stirring to afford a white precipitate of 3a , which
was collected by filtration, washed with pentane (2 mL × 2)
at -78 °C, and dried under vacuum at room temperature (96
mg, 53%). The insertion complex 3b was similarly obtained
in 58% yield.
3a . 1H NMR (CD2Cl2, 20 °C): δ -0.03 (d, J PH ) 2.1 Hz,
4
3J PtH ) 24.9 Hz, 3H, SiMe), 0.13 (d, J PH ) 2.1 Hz, J PtH
)
4
3
2
3
23.7 Hz, 3H, SiMe), 1.24 (d, J PH ) 9.0 Hz, J PtH ) 18.6 Hz,
(15) Because the two phosphorus nuclei have eventually the same
chemical shift and the J PP value for the cis-PtP2 moiety is moderate
2
(ca. 30 Hz as judging from the data for 2a and 2b), the PCH2 carbon
signal appears as a “filled-in doublet”, which has a shape intermediate
between a doublet and a virtual triplet. See: Crabtree, R. H. The
Organometallic Chemistry of the Transition Metals, 3rd ed.; Wiley:
New York, 2001; pp 260-262.

5886 Organometallics, Vol. 21, No. 26, 2002
Sagawa et al.
and examined by 1H NMR spectroscopy. The time course of
the sequence of insertion and reductive elimination processes
was followed by measuring relative peak integration of the
SiMe signals of 2c (δ 0.42), cis-Pt{C(Ph)dCH(Bpin)}(SiMe2-
Ph)(PEt3)2 (3c, δ 0.20 and 0.07), and (Z)-(PhMe2Si)CPhdCH-
(Bpin) (4, δ 0.38) (see Figure 4). Compound 4 was identified
using an authentic sample prepared independently by pal-
ladium-catalyzed silylborylation.6d
Ta ble 3. Cr ysta l Da ta a n d Deta ils of th e Str u ctu r e
Deter m in a tion for 3b
formula
C38H51O2SiBP2Pt
fw
835.75
cryst syst
triclinic
no. of reflns used for
unit cell determination (2θ range, deg)
a (Å)
b (Å)
c (Å)
9356 (3.9-54.9)
10.703(1)
11.7187(9)
17.373(1)
101.326(3)
94.811(2)
113.097(6)
1933.8(3)
P1h(#2)
3c. 1H NMR (CD2Cl2, 20 °C): δ 0.07 (d, 4J PH ) 2.1 Hz, 3J PtH
4
3
) 23.4 Hz, 3H, SiMe), 0.20 (d, J PH ) 1.8 Hz, J PtH ) 22.4 Hz,
3H, SiMe), 1.25 (s, 6H, Bpin(Me)), 1.26 (s, 6H, Bpin(Me)), 6.9-
R (deg)
â (deg)
γ (deg)
V (Å3)
space group
Z
2
8.0 (m, 5H, Ph). 31P{1H} NMR (CD2Cl2, 20 °C): δ 1.4 (d, J PP
1
2
1
) 18 Hz, J PtP ) 1251 Hz), 3.0 (d, J PP ) 18 Hz, J PtP ) 1965
Hz). The other 1H NMR signals were obscured due to overlap
with the signals of 2c and 4.
2
Dcalcd (g cm-3
)
1.435
37.57
55.0
19 878
8779 (Rint ) 0.059)
0.3986-0.7421
7551 (I g 3.0σ(I))
406
R1 ) 0.046
R ) 0.085
Rw ) 0.138
GOF ) 1.27
0.000
4. 1H NMR (CD2Cl2, 20 °C): δ 0.38 (s, 6H, SiMe), 1.09 (s,
12H, Bpin(Me)), 6.26 (s, 1H, dCH), 6.9-7.7 (m, 10H, Ph). H
µ(Mo KR) (cm-1
2θ max (deg)
)
1
NMR (toluene-d8, 20 °C): δ 0.50 (s, 6H, SiMe), 0.91 (s, 12H,
Bpin(Me)), 6.61 (s, 1H, dCH), 7.7-7.0 (m, 10H, Ph).
Red u ctive Elim in a tion fr om cis-P t{C(P h )dCH(Bp in )}-
(SiMe2P h )-(P Me2P h )2 (3b). Complex 3b (12.5 mg, 0.015
mmol) was placed in an NMR sample tube equipped with a
rubber septum cap, and the system was replaced with nitrogen
gas at room temperature. Toluene-d8 (0.6 mL) was added, and
the sample was placed in an NMR sample probe controlled at
60.0 ( 0.1 °C. The reaction progress was followed by observing
the relative peak intensity of the SiMe proton signals of 3b (δ
0.59 and 0.65) and 4 (δ 0.50).
Kin etic Stu d y of th e In ser tion of P h en yla cetylen e in to
2a . The experimental procedure for the reaction of 2a and
phenylacetylene was followed. The amounts of 2a and 3a at
time t were determined on the basis of relative peak integra-
tion of the SiMe proton signals of these complexes: 2a (δ 0.39),
3a (δ -0.03 and 0.13).
no. of reflns collected
no. of unique reflns
transmn factors
no. of obsd reflns
no. of variables
R indices (I g 2σ(I))a
max. ∆/σ in final cycle
max. and min. peak (e Å-3
)
1.56, -2.07
Function minimized ) ∑w(Fo - Fc2)2; w ) (1/[σ2(Fo2)]. R1
)
a
2
∑||Fo| - |Fc||/∑|Fo|. R ) ∑(Fo - Fc2)/Σ(Fo2). Rw ) [∑w(Fo - Fc2)2/
∑w(Fo2)2]1/2. GOF ) [∑w(|Fo| - |Fc|)2/(No - Nv)]1/2, where No and
Nv stand for the number of observations and variables, respec-
tively.
2
2
refinement of their parameters. The function minimized in
2
least-squares was ∑w(Fo2 - Fc )2 (w ) 1/[σ2(Fo2)]). Crystal data
Ack n ow led gm en t. This work was supported by a
Grant-in-Aid for Scientific Research from the Ministry
of Education, Culture, Sports, Science and Technology,
J apan.
and details of data collection and refinement are summarized
in Table 3. Additional information is available as Supporting
Information.
Rea ction of cis-P t(SiMe2P h )(Bp in )(P Et3)2 (2c) w ith
P h en yla cetylen e (F igu r e 3). Complex 2c (10.4 mg, 0.015
mmol) was placed in an NMR sample tube equipped with a
rubber septum cap, and the system was replaced with nitrogen
gas at room temperature. Phenylacetylene (15.3 mg, 0.15
mmol) was added, and then CD2Cl2 was added at 0 °C so that
total volume of the solution becomes 0.6 mL. The sample was
placed in an NMR sample probe controlled at 20.0 ( 0.1 °C
Su p p or tin g In for m a tion Ava ila ble: Details of the struc-
ture determination of 3b, including a figure giving the atomic
numbering scheme and tables of atomic coordinates, thermal
parameters, and full bond distances and angles. This material
is available free of charge via the Internet at http://pubs.acs.org.
OM020686Z