Synthesis, properties, and catalytic applications of caged, compact trialkylphosphine 4-phenyl-1-phospha-4-silabicyclo[2.2.2]octane

Article abstract of DOI:10.1021/om8005728

Synthesis, properties, and catalytic applications of a caged trialkylphosphine ligand with Me3P-like steric and electronic characters, 4-phenyl-1-phospha-4-silabicyclo[2.2.2]octane (Ph-SMAP), are reported. Given a phenyl group at the silicon atom, the Ph-SMAP ligand displayed nonvolatility with retention of Me₃P-like steric and electronic properties. The new ligand is air-stable, crystalline, and easy to handle. Single-crystal X-ray diffraction analyses of Ph-SMAP and its coordination compounds such as borane, rhodium(I), and Pt(II) complexes revealed a rigid, linear structural feature of the Ph-SMAP framework. DFT calculations [B3LYP/6-31G(d,p)] indicated that the electron-donating ability of Ph-SMAP is slightly stronger than that of Me ₃P and that replacement of Si atom of Ph-SMAP with a carbon atom drastically decreases the donor power. The Ph-SMAP ligand markedly accelerated the rhodium-catalyzed hydrosilylation and hydrogenation of ketones as compared with the effect of conventional phosphine ligands such as Me₃P, Bu₃P, (t-Bu)₃P, and PPh₃, when it was used in combination with [{RhCl(C₂H₄)₂}₂] and [Rh(OMe)(cod)], respectively, with P/Rh ratio of 1:1.

Full text of DOI:10.1021/om8005728

5494
Organometallics 2008, 27, 5494–5503
Synthesis, Properties, and Catalytic Applications of Caged, Compact
Trialkylphosphine 4-Phenyl-1-phospha-4-silabicyclo[2.2.2]octane
Atsuko Ochida, Go Hamasaka, Yoshihiro Yamauchi, Soichiro Kawamorita, Naoya Oshima,
Kenji Hara, Hirohisa Ohmiya, and Masaya Sawamura*
Department of Chemistry, Faculty of Science, Hokkaido UniVersity, Sapporo 060-0810, Japan
ReceiVed June 20, 2008
Synthesis, properties, and catalytic applications of a caged trialkylphosphine ligand with Me3P-like
steric and electronic characters, 4-phenyl-1-phospha-4-silabicyclo[2.2.2]octane (Ph-SMAP), are reported.
Given a phenyl group at the silicon atom, the Ph-SMAP ligand displayed nonvolatility with retention of
Me3P-like steric and electronic properties. The new ligand is air-stable, crystalline, and easy to handle.
Single-crystal X-ray diffraction analyses of Ph-SMAP and its coordination compounds such as borane,
rhodium(I), and Pt(II) complexes revealed a rigid, linear structural feature of the Ph-SMAP framework.
DFT calculations [B3LYP/6-31G(d,p)] indicated that the electron-donating ability of Ph-SMAP is slightly
stronger than that of Me3P and that replacement of Si atom of Ph-SMAP with a carbon atom drastically
decreases the donor power. The Ph-SMAP ligand markedly accelerated the rhodium-catalyzed hydrosi-
lylation and hydrogenation of ketones as compared with the effect of conventional phosphine ligands
such as Me3P, Bu3P, (t-Bu)3P, and PPh3, when it was used in combination with [{RhCl(C2H4)2}2] and
[Rh(OMe)(cod)], respectively, with P/Rh ratio of 1:1.
phosphabarrelenes (6).6 To the best of our knowledge, no
Introduction
analogous trialkylphosphine ligand exists.7
Trialkylphosphines with various structures are used in
coordination chemistry and organometallic chemistry as metal-
coordinating ligands with strong σ-donating ability. One ligand
with the extremely low steric demand is trimethylphosphine
(Me3P). We have designed and synthesized a new Me3P-like
trialkylphosphine ligand 1 (SMAP, named after silicon-
constrained monodentate alkyl phosphine) (Chart 1).1 A new
feature of this ligand is the presence of a site for functional-
ization at the backside of the P lone pair, which is not the case
for Me3P. The SMAP ligand 1 contains phosphorus and silicon
atoms at each bridgehead of the bicyclo[2.2.2]octane framework.
The molecular constraint of the bicyclic framework makes the
steric demand around the phosphorus center as small as that of
Me3P and projects the P lone pair and the Si-substituent (R) in
diametrically opposite directions on the straight line defined by
two bridgehead atoms (see Chart 1). P-donor ligands that can
be functionalized with such a directional constraint are rarely
found and are limited to phosphaalkynes (2),2 phosphabenzenes
(3),3 bicyclic phosphites (4),4 phosphatriptycenes (5),5 and
We previously reported preliminary results on the synthesis
of the first example of SMAP (1a, Ph-SMAP), which contains
a phenyl group on the Si atom that provides properties of high
crystallinity, nonvolatility, and scentlessness.1a These properties
arise from the rigidity of the bicyclic framework, which
promotes molecular assembly into a crystal phase.
Taking advantage of the ease of the silicon-centered func-
tionalization with the directional constraint, we further developed
two classes of solid-supported SMAP ligands Silica-SMAP (7)8
and [Au]-SMAP (8),9 which are shown in Chart 2. In Silica-
SMAP (7), the SMAP cages are anchored on a silica gel surface
through a disiloxane bond involving the bridgehead Si atom
and the surface Si atom. The immobilized phosphine showed
unique coordination behavior to form a 1:1 transition metal-P
complex. The heterogeneous catalyst, prepared from Silica-
SMAP and [RhCl(C2H4)2]2, showed an exceptionally high
activity for the hydrosilylation of sterically hindered ketones.8
On the other hand, [Au]-SMAP (8), in a chip form, was prepared
through the formation of self-assembled monolayer on a gold
surface with the SMAP derivative bearing an alkanethiol pendant
chain. The rhodium catalyst prepared from [Au]-SMAP (8) and
[RhCl(C2H4)2]2 was used for dehydrogenative alcohol silylation
and exhibited high activity and selectivity as well as highly
efficient reusability.9
* Corresponding author. E-mail: sawamura@sci.hokudai.ac.jp.
(1) (a) Ochida, A.; Hara, K.; Ito, H.; Sawamura, M. Org. Lett. 2003, 5,
2671–2674. (b) Ochida, A.; Ito, S.; Miyahara, T.; Ito, H.; Sawamura, M.
Chem. Lett. 2006, 35, 294–295.
(2) (a) Markovskii, L. N.; Romanenko, V. D. Tetrahedron 1989, 45,
6019. (b) Nixon, J. F. Chem. Soc. ReV. 1995, 24, 319–328.
(3) Le Floch, P.; Mathey, F. Coord. Chem. ReV. 1998, 178-180, 771–
791.
(4) Wadsworth, W. S., Jr.; Emmons, W. D. J. Am. Chem. Soc. 1962,
84, 610–617.
(6) (a) Breit, B.; Fuchs, E. Chem. Comm. 2004, 694–695. (b) Fuchs,
E.; Manfred Keller, M.; Breit, B. Chem. Eur. J. 2006, 12, 6930–6939.
(5) (a) For E ) C, see: Jongsma, C.; De Kleijn, J. P.; Bickelhaupt, F.
Tetrahedron 1974, 30, 3465–3469. (b) Kobayashi, J.; Agou, T.; Kawashima,
T. Chem. Lett. 2003, 21, 1144–1145. (c) Agou, T.; Kobayashi, J.;
Kawashima, T. Chem. Lett. 2004, 33, 1028–1029. (d) Agou, T.; Kobayashi,
J.; Kawashima, T. Heteroat. Chem. 2004, 15, 437–446. (e) For E ) Si,
see: Tsuji, H.; Inoue, T.; Kaneta, Y.; Sase, S.; Kawachi, A.; Tamao, K.
Organometallics 2006, 25, 6142-6148. (f) For E ) Ge, see: Rot, N.; De
Wijs, W.-J. A.; De Kanter, F. J. J.; Dam, M. A.; Bickelhaupt, F.; Lutz, M.;
Spek, A. L. Main Group Met. Chem. 1999, 22, 519–526.
(7) (a) For
a
diphosphine with
a
related structure, 1,4-
diphosphabicyclo[2.2.2]octane, see: Hinton, R. C.; Mann, F. G. J. Chem.
Soc. 1959, 2835. (b) See also: Thirupathi, N.; Stricklen, P. M.; Liu, X.;
Oshel, R.; Guzei, I.; Ellern, A.; Verkade, J. G. Inorg. Chem. 2007, 46,
9351–9363.
(8) Hamasaka, G.; Ochida, A.; Hara, K.; Sawamura, M. Angew. Chem.,
Int. Ed. 2007, 46, 5381–5383.
(9) Hara, K.; Akiyama, R.; Takakusagi, S.; Uosaki, K.; Yoshino, T.;
Kagi, H.; Sawamura, M. Angew. Chem., Int. Ed. 2008, 47, 5627–5630.
10.1021/om8005728 CCC: $40.75
2008 American Chemical Society
Publication on Web 10/01/2008

Caged, Compact Trialkylphosphine
Organometallics, Vol. 27, No. 21, 2008 5495
Chart 1. Structures of SMAP and Related P-Donor Ligands
Scheme 1. Synthesis of Ph-SMAP (1a)
Chart 2. Solid-Supported SMAP Ligands
13 was used without further purification for the following one-
pot reaction with LiAlH4 that completed the synthesis of Ph-
SMAP (51% after sublimation). Thus, Ph-SMAP was synthe-
sized in three steps from diethyl benzylphosphonate with 24%
overall yield.
Properties. Ph-SMAP is colorless crystalline solid with a
sharp melting point of 90.5-90.7 °C (in a sealed tube).
Purification of Ph-SMAP is easily performed upon sublimation
(40 °C/0.04 mmHg). Being odorless, Ph-SMAP does not
produce the noxious phosphine odor characteristic of volatile
phosphines.
This article reports details of our studies on the synthesis and
properties of Ph-SMAP (1), the parent compound for various
SMAP-type compounds, and some results on its applications
as a soluble ligand for homogeneous transition metal catalysis.
Solid Ph-SMAP is highly air-stable, with no detectable
oxidation observed after exposure to air for several days. To
our surprise, such stability was also observed in solution. A
solution of Ph-SMAP in C6D6 prepared without exclusion of
air underwent no oxidation detectable by 1H NMR after standing
for 3 days. Similar experiments with CD2Cl2 and acetone-d6
produced only a trace amount (<3%) of the corresponding
phosphine oxide after 1 h. This air stability is quite unusual as
a property of a trialkylphosphine. Although the reason for the
air stability is unclear, we speculate that it might arise from the
geometrical constraint around the P atom, which limits the
geometrical change that occurs in the pathway toward a
transition state for the oxidation.
Results and Discussion
Synthesis. In numerous studies pursuing the efficient syn-
thesis of Ph-SMAP, we have developed a route that uses
benzylphosphine (11) as a source of the P atom of Ph-SMAP
as shown in Scheme 1. As compared with the previously
reported synthesis,1a which used phenylphosphine, the new route
is more expeditious and features higher total yield. Thus,
phenyltrivinylsilane (9),10 which was prepared from PhSiCl3 and
vinylmagnesium bromide in 85% yield, was converted into
tribromide 10 in 88% yield (recrystallization) through anti-
Markovnikov HBr addition. On the other hand, benzylphosphine
(11)11 was prepared from diethyl benzylphosphonate (prepared
from benzyl bromide and triethyl phosphite) in 66% yield
through LiAlH4 reduction in the presence of Me3SiCl. Ben-
zylphosphine (11) was treated with BH3 · THF to convert into
a borane complex. The in-situ-prepared phosphine-borane
complex was subjected to 2-fold P-alkylation with 2 equiv of
tribromide 10 in the presence of sodium hydride to give
monocyclic phosphine-borane 12 in 71% yield based on 11
(silica gel chromatography). Unreacted tribromide 10 could
easily be recovered during the purification of 12 (42.5% based
on 10 used). Treatment of 12 with 1-octene in refluxing DME
generated a free phosphine,12 which underwent simultaneous
intramolecular P-alkylation to give bicyclic phosphonium salt
13. The phosphonium salt (13) was formed as a precipitate in
the reaction mixture. After removal of soluble materials, crude
1
NMR Spectra. In the H NMR spectrum of Ph-SMAP, the
resonances of the methylene protons on the bicyclo[2.2.2]octane
framework appeared as P-coupled multiplets with reasonable
chemical shift values, displaying an AA′MM′ pattern (Figure
1a). It indicates that the geminal protons are chemically
equivalent to each othersboth at R and ꢀ positions of the P atom.
In the 13C{1H} NMR spectrum, the signal for the ipso-carbon
of the Si-phenyl group was observed as a doublet with a 4JC-P
coupling constant of 4.5 Hz (Figure 1b). The long-range 4JC-P
couplings were also observed for other bicyclic compounds
13-15 (Chart 3).13 In contrast, no 4JC-P coupling was observed
for monocyclic compound 12. Thus, the long-range electronic
(10) Rosenberg, S. D.; Walburn, J. J.; Stankovich, T. D.; Balint, A. E.;
Ramsden, H. E. J. Org. Chem. 1957, 22, 1200–1202.
(11) Horner, L.; Hoffmann, H.; Beck, P. Chem. Ber. 1958, 91, 1583–
1588.
(12) Uziel, J.; Riege, N.; Aka, B.; Figuie`re, P.; Juge´, S. Tetrahedron
Lett. 1997, 38, 3405–3408.

5496 Organometallics, Vol. 27, No. 21, 2008
Ochida et al.
1
Figure 1. H (a) and 13C{1H} (aromatic region) (b) NMR spectra of 1a.
Table 1. Selected Angles (deg) and P · · · Si Distances (Å) of 1a and
Chart 3. Long-Range C-P Coupling in the Cyclic
14
Phosphorus Compounds
Ph-SMAP (1a)
Ph-SMAP-BH3 (14)
Angles
C(1)-P(1)-C(3)
100.42(8) C(1)-P(1)-C(3)
101.17(8) C(1)-P(1)-C(5)
101.12(8) C(3)-P(1)-C(5)
105.96(7) C(2)-Si(1)-C(4)
106.01(8) C(2)-Si(1)-C(6)
104.40(8) C(4)-Si(1)-C(6)
103.4(1)
103.9(1)
105.2(1)
104.3(1)
104.4(1)
105.2(1)
C(1)-P(1)-C(5)
C(3)-P(1)-C(5)
C(2)-Si(1)-C(4)
C(2)-Si(1)-C(6)
C(4)-Si(1)-C(6)
P(1)-C(1)-C(2)-Si(1) -15.3(2) P(1)-C(1)-C(2)-Si(1) 21.9(2)
P(1)-C(3)-C(4)-Si(1) -17.3(2) P(1)-C(3)-C(4)-Si(1) 23.6(2)
P(1)-C(5)-C(6)-Si(1) -17.3(2) P(1)-C(3)-C(4)-Si(1) 23.6(2)
Distance (Å)
P(1) · · · Si(1)
3.105
P(1) · · · Si(1)
3.031
interaction is characteristic for the cage system, suggesting
specific orbital interaction within the cage.14
for the average C-P-C and P-C-C-Si dihedral angles and
the P-Si distance are 100.9°, 15.5°, and 3.105 Å, respectively.
In BH3 complex 14, the P atom bonds to the B atom with a
distance of 1.922(2) Å.15 The average C-P-C angle is enlarged
to 104.2° (Table 1). Such a slight enlargement of the angles
around the P atom is typical for the metal coordination of a
P-donor ligand. The BH3 coordination also causes shrinkage of
the cage as indicated by enlargement of the P-C-C-Si
dihedral angles (22.3°, averaged) and shortening of the P-Si
distance (3.031 Å). Although the cage possesses some flexibility
for twisting and stretching, almost no bending of the longest
molecular axes was observed for both 1a and 14.
X-ray Crystal Structures. Single-crystal X-ray diffraction
analysis revealed a rodlike shape of Ph-SMAP 1a and Ph-
SMAP-BH3 1413 (Figure 2). Analysis also showed that the
bicyclic cage possesses some flexibility and twists toward chiral
C3-symmetric conformations. In free phosphine 1a, the values
Figure 3 represents the densely packed crystal structure of
1a and 14. The former consists of the two enantiomeric
molecules (P21/n), while only a single enantiomer is involved
in the latter (chiral space group P21). The latter is the case of
chiral crystallization of an achiral molecule with a chiral
conformation. The feature common to the crystal packing of
1a and 14 is the columnar stacking along the a-axis through
van der Waals contacts between neighboring 1-phospha-4-
silabicyclo[2.2.2]octane cages. In both cases, the one-dimen-
sional columns are further stacked along the longest molecular
axis in a head-to-tail manner to form a sheet structure on the
(13) For isolation of 14 and 15, see Supporting Information of ref
1a.
4
Figure 2. ORTEP drawings (50% probability level) for molecular
structure of 1a (a) and 14 (b).
(14) The corresponding JC-P has not been observed in 9-phospha-10-
silatriptycenes [5 (R ) Me, C12H25) and other derivatives]. See ref 5e.

Caged, Compact Trialkylphosphine
Organometallics, Vol. 27, No. 21, 2008 5497
Figure 3. Crystal packing of Ph-SMAP (1a) and its BH3 complex (14).
Table 2. Results of DFT Calculations for Various Tertiary
Phosphines
entry
phosphine
(t-Bu)3P
(i-Pr)3P
Et3P
Ph-SMAP (1a)
Me3P
Me2PhP
16
Vmin (kcal · mol-1
)
av C-P-C angle (deg)a
1b
2b
3b
4
-45.48
-44.47
-43.51
-43.14
-43.02
-40.41
-39.06
-36.76
107.5
101.6
99.5
99.7
99.4
5b
6b
6b
8b
96.2
MePh2P
a Values of optimized structures. b Data are taken from ref 16.
a,c plane. In the case of 1a, the sheets are then stacked along
the b-axis so that the cage and the aromatic rings are
alternatively arranged to allow van der Waals contacts. In
contrast, the sheet of 14 is stacked through CsH · · · π interac-
tions between neighboring aromatic rings.
Figure 4. Optimized structures for Ph-SMAP (1a) (a) and for the
carbon analogue (16) (b).
Electronic Properties. DFT calculations [B3LYP/6-31G(d,p)]
indicated that Ph-SMAP possesses an electron-donating ability
as strong as that of Me3P and that replacement of the Si atom
of Ph-SMAP with a carbon atom drastically decreases the donor
power. We optimized the geometry of Ph-SMAP and evaluated
donor ability by the value of the molecular electrostatic potential
minimum Vmin (kcal · mol-1) according to Koga’s method.16A
larger negative Vmin value corresponds to a stronger electron-
donating ability of a phosphine. For comparison, the calculations
were carried out for 4-phenyl-1-phosphabicyclo[2.2.2]octane
(16), an analogue of Ph-SMAP that has a bridgehead carbon
atom instead of the Si atom.17 As shown in Table 2, the Vmin
(-43.14 kcal/mol) of Ph-SMAP is much more negative than
the value of monoaryldialkylphosphine PhMe2P and is in the
range for trialkylphosphines, being between the values of Me3P
and Et3P.
the comparison of the C-P-C angles of the optimized structures
(Figure 4); the average angle of 16 (96.2°) is much smaller than
that of Ph-SMAP (99.7°), and the latter is almost the same as
the values of Me3P (99.4°) and Et3P (99.5°).
Transition Metal Complexes. A Vaska-type rhodium com-
plex of Ph-SMAP, trans-[RhCl(CO)(Ph-SMAP)2] (17) was
obtained by the reaction of Ph-SMAP and [{RhCl(CO)2}2] (P/
Rh ) 2.1:1) in benzene at room temperature. The 31P{1H} NMR
spectrum of 17 showed a doublet signal with a 1JP-Rh coupling
of 117.8 Hz at δ -8.8 ppm. The infrared spectrum measured
in a CHCl3 solution gave a C-O stretching band at ν ) 1965
cm-1. This C-O stretching is 2 cm-1 lower in wavenumber
than the value for the corresponding Me3P complex,18 which
was obtained by the measurement under the identical conditions.
The shift of wavenumber may be due to the increased donor
power of Ph-SMAP (1a) as compared with that of Me3P.
The molecular structure of 17 was determined by single-
crystal X-ray diffraction. An ORTEP diagram is shown in Figure
5, and selected bond distances and angles are listed in Table 3.
The structure was solved as being C2 symmetric for an axis
going through the Rh atom bearing the disordered Cl and CO
ligands. Owing to the trans geometry of Ph-SMAP with rigid
The Vmin of 16 is less negative than that of PhMe2P. The
drastic decrease in donor ability upon placement of a carbon
atom at the bridgehead is mostly due to the increase in
s-character of the P lone pair caused by the strain in the
1-phosphabicyclo[2.2.2]octane cage. The strain is evident from
(15) (a) The P-B bond length of 14 (1.922(2) Å) is apparently longer
than that of Me3P-BH3 (1.901 Å) determined by microwave spectroscopy.
See: Bryan, P. S.; Kuczkowski, R. L. Inorg. Chem. 1972, 11, 553–559. (b)
The reason of the elongation is not clear at present. Correlation between
steric/electronic properties of phosphines and P-B bond lengths are not
clear in general. For a review, see: Brunel, J. M.; Faure, B.; Maffei, M.
Coord. Chem. ReV. 1998, 178-180, 665–698.
(17) The phosphine oxide form of 1-phosphabicyclo[2.2.2]octane was
synthesized and its strain around the P atom was discussed. But it has not
been converted to the free phosphine. See: Wetzel, R. B.; Kenyon, G. L
J. Am. Chem. Soc. 1974, 96, 5189–5198.
(18) Boyd, S. E.; Field, L. D.; Hambley, T. W.; Partridge, M. G.
Organomatallics 1993, 12, 1720–1724.
(16) Suresh, C. H.; Koga, N. Inorg. Chem. 2002, 41, 1573–1578.

5498 Organometallics, Vol. 27, No. 21, 2008
Ochida et al.
Figure 5. ORTEP drawing (50% probability level) with atom-labeling scheme for the molecular structure of trans-[RhCl(CO)(Ph-SMAP)2]
(17).
Table 3. Selected Bond Lengths (Å) and Angles (deg) of 17
catalyzed hydrosilylation and hydrogenation of ketones revealed
unique properties and usefulness of Ph-SMAP as a ligand for
transition metal catalysis.
Lengths
Rh(1)-Cl(1)
Rh(1)-P(1)
2.364(4) Rh(1)-C(13)
2.316(1) C(13)-O(1)
1.75(2)
1.18(2)
1. Rh-Catalyzed Hydrosilylation of Ketones with Trior-
ganosilanes. The hydrosilylation of cyclohexanone (19) (1
mmol) with PhMe2SiH (1.2 mmol) was carried out in benzene
(1 mL) at room temperature (25 °C) in the presence of
[{RhCl(C2H4)2}2] (0.5 mol %) and a phosphine ligand (1 mol
%, Rh/P 1:1) (Scheme 2). Time-conversion curves for the
reactions with Ph-SMAP (1a) and other conventional phosphines
including Me3P, Et3P, Bu3P, (c-Hex)3P, (t-Bu)3P, and Ph3P are
given in Figure 8a. Ph-SMAP (1a) was distinguished with its
high rate-enhancement effect among the ligands tested: comple-
tion was reached within 1 h. A very interesting observation is
that Me3P (1 M toluene solution was used) was much less
efficient in the rate enhancement than 1a, while having
comparable compactness and electron-donating ability. The
lower efficiency of the Me3P might be attributable to lability
of the C-H bonds of the Me groups toward intramolecular C-H
bond actvation, albeit with no experimental proof. On the other
hand, Ph-SMAP is expected to be inert toward R C-H bond
activation because of the molecular constraint.
Angles
Cl(1)-Rh(1)-P(1)
C(13)-Rh(1)-P(1)
C(1)-P(1)-C(3)
C(1)-P(1)-C(5)
C(3)-P(1)-C(5)
C(13)-Rh(1)-P(1)
93.67(9)
89.0(5)
102.0(2)
102.3(2)
103.8(2)
89.0(5)
C(2)-Si(1)-C(4)
C(2)-Si(1)-C(6)
C(4)-Si(1)-C(6)
P(1)-C(1)-C(2)-Si(1)
P(1)-C(3)-C(4)-Si(1)
C(2)-Si(1)-C(6)
103.8(2)
103.6(2)
104.8(2)
29.1(4)
28.1(4)
103.6(2)
and linear structure features, the entire molecule displays a
rodlike structure. The C-O bond length [1.18(2) Å] of the
carbonyl ligand is significantly longer than the reported value
[1.146(4) Å] for the Me3P complex.18 This observation is
consistent with the results of the IR measurements and the DFT
calculations.
An organoplatinum(II) complex with cis-coordinated Ph-
SMAP ligands, cis-[PtMe2(Ph-SMAP)2] (18) was obtained by
the reaction of Ph-SMAP and cis-[PtMe2(η2,η2-1,5-cycloocta-
diene)] (P/Pt; 2.2:1) in benzene-d6 at room temperature. The
31P{1H} NMR spectrum showed a singlet signal at δ -21.3
accompanied by a 195Pt satellite with JP-Pt value of 1785 Hz.
Single crystals of platinum complex 18 with a composition
of PtMe2(Ph-SMAP)2 · (hexane)0.5 were obtained by recrystal-
lization from CH2Cl2/hexane. An ORTEP diagram of the
molecular structure determined by X-ray diffraction is shown
in Figure 6. Selected bond lengths and angles are listed in Table
4. The two Ph-SMAP ligands on the Pt atom adopt considerably
different conformations to each other with respect to the extent
of twisting in the bicyclic system. While one adopts a normal
twisted conformation, the bicyclic system of the other is rather
eclipsed.
Owing to the cis geometry of the rod-shaped Ph-SMAP
ligands, the platinum complex displays an L-shaped molecular
structure with the platinum atom at the corner. The crystal-
packing diagrams (Figure 7) show a supramolecular structure
with square channels filled with hexane molecules. Continuous
head-to-tail intermolecular CsH · · · π interactions between the
aromatic rings form a columnar stack of angular figures of eight
along the a axis creating a pair of square channels, which
accommodate a train of the hexane molecules with a fully
extended conformation. Although the CsH · · · π molecular
interaction is too weak for 18 to be used as functional materials
such as metal-organic framework (MOF), the novel molecular
arrangement of 18 implies that SMAP derivatives with an
appropriate functional group that allows for more strong
molecular interactions may be useful as an element of molecular
architecture toward functional materials.
The catalytic activity of [{RhCl(C2H4)2}2]/Ph-SMAP (Rh/P
1:1) system is comparable or even higher than those of the
recently reported, highly active, homogeneous Rh catalysts that
involve bulky, monocoordinating ligands such as the bowl-
shaped phosphine (BSP, 20),19 the triethynylphosphine with
bulky end caps (21),20 and the bulky terphenylisocyanide (22)
(Chart 4):21 the reactions with [{RhCl(C2H4)2}2]/20 (Rh/P 1:2),
[{RhCl(cod)}2]/21 (Rh/P 1:1) and [Rh(cod)2]BF4/22 (Rh/iso-
cyanide 1:1) required 3, 2 and 1 h for completion, respectively,
under otherwise same conditions.
When 1a was used with Rh/P ratio of 1:2, rapid reaction was
initiated after a 2 h induction period, completing within 5 h
(Figure 8b). An active species must have been formed through
the dissociation or reaction of the ethylene ligands accompanied
by metal-ligand dissproportionation. The fact that the reaction
was faster with Rh/P ratio of 1:1 than with 1:2 suggests that
(19) (a) Niyomura, O.; Tokunaga, M.; Obora, Y.; Iwasawa, T.; Tsuji,
Y. Angew Chem., Int. Ed. 2003, 42, 1287–1289. (b) Niyomura, O.; Iwasawa,
T.; Sawada, N.; Tokunaga, M.; Obora, Y.; Tsuji, Y. Organometallics 2005,
24, 3468–3475.
(20) Ochida, A.; Sawamura, M. Chem. Asian J. 2007, 2, 609–618.
(21) (a) Ito, H.; Kato, T.; Sawamura, M. Chem. Lett. 2006, 35, 1038–
1039. (b) Ito, H.; Kato, T.; Sawamura, M. Chem. Asian J. 2007, 2, 1436–
1446.
(22) The Rh-1a system showed no activity for the hydrosilylation of
dipropyl ketone (26) with PhSiH3 and (EtO)3SiH under the otherwise the
same reaction conditions, while Ph2SiH2 was more reactive than PhMe2SiH.
The reaction led to >95% conversion after 10 min with both Ph-SMAP
(1a) and Ph3P as determined by GC analysis of 4-heptanol (isolation of the
silyl ether product has not been attempted).
Applications to Transition Metal Catalysis. Our experi-
ments in the applications of Ph-SMAP (1a) to the rhodium-

Caged, Compact Trialkylphosphine
Organometallics, Vol. 27, No. 21, 2008 5499
Figure 6. ORTEP drawing (50% probability level) with atom-labeling scheme for the molecular structure of cis-[PtMe2(Ph-SMAP)2] (18).
Table 4. Selected Bond Lengths (Å), Angles (deg), and Dihedral
Angles (deg) of 18
Bond Lengths
Pt(1)-P(1)
Pt(1)-C(1)
2.286(3) Pt(2)-P(2)
2.10(1) Pt(2)-C(2)
2.293(3)
2.293(3)
Angles
P(1)-Pt(1)-P(2)
P(1)-Pt(1)-C(2)
P(2)-Pt(1)-C(1)
C(1)-Pt(1)-C(2)
C(11)-P(1)-C(13)
C(11)-P(1)-C(15)
C(13)-P(1)-C(15)
C(21)-P(2)-C(23)
97.4(1)
90.1(4)
89.2(5)
83.9(6)
97.5(7)
103.9(8)
101.2(6)
99.9(8)
C(21)-P(2)-C(25)
102.2(8)
101.7(7)
103.3(7)
106.2(6)
102.2(6)
104.0(7)
106.2(6)
105.2(6)
C(23)-P(2)-C(25)
C(12)-Si(1)-C(14)
C(12)-Si(1)-C(16)
C(14)-Si(1)-C(16)
C(22)-Si(2)-C(24)
C(22)-Si(2)-C(26)
C(24)-Si(2)-C(26)
Dihedral Angles
P(2)-C(21)-C(22)-Si(2) 9(1)
P(1)-C(11)-C(12)-Si(1) -33(1)
P(1)-C(13)-C(14)-Si(1) -25(1)
P(1)-C(15)-C(16)-Si(1) -29(1)
P(2)-C(23)-C(24)-Si(2) 10(1)
P(2)-C(25)-C(26)-Si(2) 8(1)
the active species is a Rh-1a 1:1 complex. This assumption is
consistent with the previous results with the bulky ligands such
as 20-2219-21 as well as the solid-supported SMAP derivative
Silica-SMAP (7),8 while the catalyst with the latter exhibited
exceptionally high catalytic activity (<5 min for 100% conver-
sion).
Next, we examined some other ketones (23-27) with
different steric and electronic properties for reactivity toward
the hydrosilylation wth PhMe2SiH catalyzed by the Rh-1a
system (Rh/P 1:1) under the conditions optimized for cyclo-
hexanone (19). Results are summarized in Chart 5. The reactions
of 2-methylcyclohexanone (23) and diethyl ketone (24) pro-
ceeded smoothly and completed within 2 and 5 h, respectively,
while the reactions of acetophenone (25) and di-n-propyl ketone
(26) were somewhat slower (25, 5 h, 93% conversion; 26, 8 h,
83% conversion). Although the Rh-1a catalyst showed activity
toward sterically more demanding, diisopropyl ketone (27), the
reaction was sluggish at 25 °C (72 h, 72% conversion). In sharp
contrast to the activity of the Silica-SMAP-Rh catalyst, the Rh-
1a catalyst showed very low activity toward the reaction with
Et3SiH (19, 5 h, 8% conversion; 27, 24 h, 0% conversion). No
reaction was observed for the hydrosilylation of cyclohexanone
(19) with (t-Bu)Me2SiH.
Figure 7. Crystal-packing diagrams of cis-[PtMe2(Ph-
SMAP)2] · (hexane)0.5 with a view along the c axis (side view) (a)
and with a view along the a axis (bottom view) (b).
2. Rh-Catalyzed Hydrogenation of Ketones. Hydrogena-
tion of ketones is feasible with various types of catalysts under

5500 Organometallics, Vol. 27, No. 21, 2008
Ochida et al.
Chart 4. Bulky Ligands Used for the Rh-Catalyzed
Hydrosilylation of Ketones
Figure 8. Time-conversion curves for the Rh-catalyzed hydrosi-
lylation of cyclohexanone (19) (1 mmol) with PhMe2SiH (1.2
mmol) in benzene (1 mL) at 25 °C. Yields were obtained by GC.
(a) The catalysts were prepared in situ from [{RhCl(C2H4)2}2] (0.5
mol %) and the phosphine (1 mol %, Rh/P 1:1). Results in the
absence of a phosphine ligand are also shown. (b) The catalyst
was prepared in situ from [{RhCl(C2H4)2}2] (0.5 mol %) and 1a (2
mol %, Rh/P 1:2).
Chart 5. Results (Reaction Time and Conversion) of
Hydrosilylation of Various Ketones with PhMe2SiH
Catalyzed by the Rh-1a System (Rh/P1:1)a
Scheme 2. Rh-Catalyzed Hydrosilylation of Cyclohexanone
(19) with PhMe2SiH
transfer hydrogenation conditions that employ secondary alco-
hols as a hydrogen source,23 but catalysts effective for the
hydrogenation of simple, nonchelating ketones with molecular
hydrogen are not so common.24 In particular, the hydrogenation
of hindered ketones is extremely difficult.25
The Ph-SMAP ligand showed high performance for the Rh-
catalyzed hydrogenation of ketones with molecular hydrogen,
especially toward the reaction of hindered ketones. Thus, the
hydrogenation of diisopropyl ketone (27) proceeded in the
presence of a rhodium catalyst prepared in situ from [{Rh(OMe)-
(cod)}2] (0.5 mol %) and Ph-SMAP (1a) (1 mol %, Rh/P
a
Conditions: ketone (1 mmol), PhMe2SiH (1.2 mmol), [{RhCl-
(C2H4)2}2] (0.5 mol %), 1a (1 mol %; Rh/P 1:1), benzene (1 mL), 25
°C.
1:1)with 30 atm of initial hydrogen pressure at 100 °C in THF,
showing 46% conversion to the corresponding alcohol after 20 h
(48%, 48 h) (Table 5, entry 1). Owing to the steric congestion
of the carbonyl group, diisopropyl ketone (27) is an extremely
challenging substrate for catalytic hydrogenation.25 In fact, the
hydrogenation of 27 showed only a trace of conversion when
Me3P and Bu3P were employed as a ligand (Rh/P 1:1) under
otherwise identical conditions, and did not take place at all with
(t-Bu)3P, PPh3 (Rh/P 1:1) and dppe (Rh/P 1:2) (Table 5, entries
4-8). The inferiority of Me3P as compared with Ph-SMAP is
to be noted: it may, in part, be due to its high volatility at the
high reaction temperature or to lability of the C-H bonds of
the P-Me groups as in the case of the hydrosilylation (vide info).
(23) Klomp, D.; Hanefeld, U.; Peters, J. A. In Handbook of Homoge-
neous Hydrogenation; de Vries, J. G., Elsevier, C. J., Eds.; Wiley-VCH:
Weinheim, Germany, 2007; Vol. 2, pp 585-630.
(24) Blum, Y.; Czarkle, D.; Rahamim, Y.; Shvo, Y. Organometallics
1985, 4, 1459–1461.
(25) (a) Diisopropyl ketone (27) could not be reduced with Raney nickel
or with nickel and some promoters, but was finally reduced with an equal
weight of catalyst promoted with chloroplatinic acid and sodium hydroxide.
See: Blance, R. B.; Gibson, D. T. J. Chem. Soc. 1954, 2487–2489. (b) See
also: Freiferder, M. In Catalytic Hydrogenation in Organic Synthesis.
Procedures and Commentary; Wiley: New York, 1978; Chapter 9, pp 78-
89.

Caged, Compact Trialkylphosphine
Organometallics, Vol. 27, No. 21, 2008 5501
Table 5. Ligand Effect in the Rh-Catalyzed Hydrogenation of
Various Ketonesa
silabicyclo[2.2.2]octane (Ph-SMAP), was synthesized. Although
the new phosphine is comparable to Me3P in both steric demand
and electronic property, it is air stable even in solution,
nonvolatile, and easy to handle. Furthermore, Ph-SMAP dis-
played high performance as a ligand for the Rh-catalyzed
hydrosilylation and hydrogenation of simple, nonchelating
ketones, especially for the reaction of hindered ketones.
Therefore, Ph-SMAP is not an analogue of Me3P but a new
type of phosphine ligand useful for studies in organic and
inorganic chemistry as well as transition metal catalysis.
Experimental Section
General. NMR spectra were recorded on a Varian Gemini 2000
spectrometer, operating at 300 MHz for 1H NMR, 75.4 MHz for
13C{1H} NMR, and 121.4 MHz for 31P{1H} NMR. Chemical shift
1
values for H, 13C{1H}, and 31P{1H} NMR are reference to Me4Si,
the residual solvent resonances, and external aqueous 85% H3PO4
respectively. Chemical shifts are reported in δ ppm. Mass spectra were
obtained by APCI method with a JEOL JMS-T100LC. Infrared spectra
were recorded on Perkin-Elmer Spectrum One. Only characteristic
peaks are reported in cm-1. Elemental analysis was performed at the
Center for Instrument Analysis of Hokkaido University. DFT calcula-
tions [B3LYP/6-31G(d,p)] were performed with the Gaussian 98
program at the Hokkaido University Information Initiative Center.
Anhydrous solvents were purchased from Kanto Chemical Co. and
used without further purification. [{Rh(OMe)(cod)}2] was purchased
from Sigma-Aldrich Inc. [{RhCl(CO)2}2] was purchased from Wako
Pure Chemical Industries, Ltd.
Phenyltrivinylsilane (9).10 Under an argon atmosphere, gaseous
vinyl bromide (201.3 g, 1.88 mol) was dissolved in THF (150 mL)
at -78 °C. The solution was added dropwise to Mg (45.7 g, 1.88
mol) in THF (150 mL) at room temperature over 3 h. After stirring
at room temperature for 1 h, a solution of trichlorophenylsilane
(96 mL, 0.6 mol) in THF (400 mL) was added dropwise at room
temperature over 3.5 h. After stirring at room temperature overnight,
a total of 300 mL of saturated aq NH4Cl was gradually added to
the mixture at 0 °C to cause clear phase separation (clear yellow
solution and white solid). The solid was filtrated on a pad of Celite
and was washed with diethyl ether. The solution was dried over
MgSO4 and evaporated. Distillation (66-67 °C at 280 Pa) of the
mixture gave 9 (94.3 g, 0.51 mol, 84%) as colorless oil.
Tris(2-bromoethyl)phenylsilane (10). Hydrogen bromide, which
was generated by slowly adding bromine (2.52 mol, 129 mL) to
1,2,3,4-tetrahydronaphthalene (3.47 mol, 470 mL) at room tem-
perature, was bubbled through a stirred solution of 9 (0.63 mol,
117.43 g) in toluene (1.6 L) at room temperature. After the reaction
mixture was stirred overnight, saturated aq NaHCO3 and aq Na2S2O3
were added. The resultant mixture was extracted with diethyl ether
three times. The extract was dried over MgSO4 and filtered. The
combined filtrate and washings were concentrated. Purification by
recrystallization from ethanol gave 10 as a colorless solid (232.44
g, 86%). Mp: 66.8-67.5 °C. 1H NMR (300 MHz, CDCl3): δ
1.71-1.76 (m, 6H, -SiCH2CH2Br), 3.48-3.54 (m, 6H, -Si-
CH2CH2Br), 7.43-7.47 (m, 5H, ArH). 13C NMR (75.4 MHz,
CDCl3): δ 19.0 (s, -SiCH2CH2Br), 29.0 (br s, -SiCH2CH2Br),
128.7 (s, CH), 130.6 (s, CH), 131.5 (s, C), 133.8 (s, CH). Anal.
Calcd for C12H17Br3Si: C 33.59%, H 3.99%, Br 55.87%. Found: C
33.48%, H 3.93%, Br 56.00%.
a Conditions: ketone (1 mmol), H2 (30 atm), [{Rh(OMe)(cod)}2]
(0.005 mmol), phosphine (0.01-0.02 mmol), THF (1 mL), 100 °C,
20 h. b Conversion of ketone into alcohol determined by GC. c Value in
parentheses is conversion after 48 h.
Neither phosphine-free [{Rh(OMe)(cod)}2] (Table 5, entry 3)
nor Wilkinson’s catalyst ([RhCl(PPh3)3]) were capable of
promoting the reaction.
The second equivalent of Ph-SMAP (1a) (Rh/P 1:2) com-
pletely inhibited the activity of the Rh-Ph-SMAP catalyst in
the hydrogenation of 27 (Table 5, entry 2). This result suggests
that an active catalytic species might carry only one Ph-SMAP
ligand. According to this assumption, the fact that the reaction
catalyzed by the Rh-Ph-SMAP (Rh/P 1:1) system almost ceased
to proceed at 20 h can be explained by considering the
metal-ligand disproportionation that formed inactive rhodium
species with more than two Ph-SMAP ligands and phosphine-
free rhodium species.
The superiority of Ph-SMAP over Me3P was not limited to
the hydrogenation of the bulky ketone (27), but was also
observed for the case of less hindered, more reactive ketones
such as dipropyl ketone (26), diethyl ketone (25), and cyclo-
hexanone (19). These ketones were hydrogenated with the Rh-
Ph-SMAP system with 70%, 97%, and 100% conversions,
respectively, under the conditions (Rh/P 1:1, H2 30 atm, THF,
100 °C, 20 h) that promoted the hydrogentaion of diisopropyl
ketone (27) with 46% conversion (Table 5, entries 9, 11, and
13), while the hydrogenation with Me3P resulted in <1% (trace),
3% and 54% conversions, respectively (Table 5, entries 10, 12,
and 14).
Benzylphosphine (11).11 Under an argon atmosphere, chlorot-
rimethylsilane (47.3 mL, 374 mmol) was added dropwise to a
suspension of LiAlH4 (13.7 g, 360 mmol) in THF (400 mL) at
-78 °C over 20 min. After stirring at -78 °C for 3 h,
PhCH2P(O)(OEt)2 (50 mL, 240 mmol, prepared from benzyl
bromide and triethyl phosphite) was added dropwise at -78 °C
over 3.5 h. After stirring at room temperature overnight, the mixture
was cooled to 0 °C. Degassed water (13.7 mL), 15 wt % aq NaOH
(13.7 mL), and water (41.1 mL) were successively added at 0 °C.
Conclusions
A caged trialkylphosphine with extremely small steric demand
and strong electron-donating ability, 4-phenyl-1-phospha-4-

5502 Organometallics, Vol. 27, No. 21, 2008
Ochida et al.
After stirring at room temperature for 1 h, the mixture was filtered
and washed with THF. Distillation of the solution (73-74 °C at 8
hPa) gave 11 (19.61 g, 158 mmol, 66%) as colorless oil.
solid was washed with degassed ether. The filtrate was concentrated
to leave 481 mg of white solid. The solid was treated with degassed
benzene and the mixture, which contained a considerable amount
of insoluble solid, was passed through a short-pass column of
alumina. The mixture was concentrated in a sublimation apparatus.
Purification by sublimation (60-80 °C, 20 Pa) gave 300.4 mg
(50.8%) of 1a as cubic crystals. Mp: 90.5-90.7 °C (in a sealed
tube). 1H NMR (300 MHz, C6D6): δ 0.84-0.90 (m, 6H), 1.84-1.91
(m, 6H), 7.16-7.17 (m, 3H), 7.29-7.33 (m, 2H).13C NMR (75.4
MHz, C6D6): δ 4.35 (3C), 18.0 (d, JC-P ) 16.0 Hz, 3C), 128.1
(2C), 129.7 (1C), 134.3 (2C), 136.5 (d, JC-P ) 4.5 Hz, 1C). 31P
NMR (121.4 MHz, C6D6): δ -59.2 (s). HRMS and combustion
analyses were not successful. This is probably due to oxidation
during the measurements. NMR charts are given in Supporting
Information of ref.1a
1-Boranato-4-(2-bromoethyl)-1-benzyl-4-phenyl-1-phospha-
4-silacyclohexane (12). To a BH3-THF solution (100 mL, 99
mmol, 0.99 M in THF) was added 11 (11.2 g, 90.2 mmol) at 0 °C.
The mixture was stirred at 0 °C for 19 h. The solution was
transferred over a period of 1 h through a Teflon cannula tube to
a mixture of NaH (10.8 g, 270.6 mmol, 60% in oil) and 10 (77.4
g, 180.4 mmol) in degassed THF (180 mL), which was cooled at
-78 °C. The mixture was allowed to warm to 4 °C with stirring
over a period of 20 h. Saturated aq NH4Cl (400 mL) was carefully
added, and the mixture was extracted twice with ether. The
combined extracts were dried over MgSO4 and filtered. After
concentration under reduced pressure, purification by flash chro-
matography on silica gel (silica gel; 400 g for making a column
and 100 g for charging the mixture, CH2Cl2/hexane 5:95-50:50)
gave unreacted tribromide 10 (32.89 g, 42.5% based on the amount
used) and 12 as a colorless waxy solid (25.80 g, 71%, cis/trans
mixture). 1H NMR (300 MHz, CDCl3): δ 1.12-1.93 (m, 10H),
2.95 (d, J ) 11.2 Hz, 1H), 3.11 (d, J ) 11.0, 1H), 3.38-3.45 (m,
2H), 7.07-7.47 (m, 10H). 13C NMR (75.4 MHz, CDCl3): δ 4.48
(s) and 4.82 (d, JC-P ) 1.7 Hz, 4C), 17.9 and 18.1 (d, JC-P ) 33.8
Hz, 4C), 18.8 and 20.7 (s, 2C), 29.8 and 29.9 (s, 2C), 31.8 and 32.8
(d, JC-P ) 30.3 Hz, 31.5 Hz, respectively, 2C), 127.1 and 127.3
(d, JC-P ) 2.9 Hz, 2C), 128.5 and 128.6 (s, 2C), 128.6 and 128.8
(d, JC-P ) 2.8 Hz, 2.2 Hz, respectively, 1C), 129.6 and 129.7 (d,
JC-P ) 4.0 Hz, 2C), 130.3 and 130.4 (s, 2C), 132.0 and 132.1 (d,
JC-P ) 6.9 Hz, 1C), 132.5 and 132.8 (s, 1C), 133.8 and 133.9 (s,
2C). 31P NMR (121.4 MHz, CDCl3): δ 13.0 (br s). HRMS (FAB):
Calcd for C19H27BPSiBrNa [M + Na]+ (m/z): 427.0798. Found:
427.0810.
Crystal data for 1a: monoclinic, P21/n (#14), a ) 6.3438(3) Å,
b ) 18.0866(5) Å, c ) 10.4720(6) Å, ꢀ ) 100.732(1)°, V )
1180.52(9) Å3, Z ) 4. Data collection: Rigaku RAXIS-RAPID
Imaging Plate diffractometer, T ) -153 °C. 2θmax ) 55.0°, R )
0.041, Rw ) 0.076, I > 1.5 σ(I), GOF ) 1.96.
1-Boranato-4-phenyl-1-phospha-4-silabicyclo[2.2.2]octane (14).1a
1
Mp 136 °C; H NMR (CDCl3) δ 1.23-1.32 (m, 6H), 2.16-2.24
(m, 6H), 7.36-7.45 (m, 5H); 13C NMR (CDCl3) δ 3.8 (d, JC-P
)
6.3 Hz, 3C), 18.2 (d, JC-P ) 34.3 Hz, 3C), 128.2 (2C), 130.4 (1C),
132.8 (d, JC-P ) 3.4 Hz, 1C), 133.9 (2C); 31P NMR (CDCl3) δ
-8.5 (br d JP-B ) 70.2 Hz); HRMS (APCI) calcd for C12H18PSi
(M-BH3 + H)+ m/z 221.09154. Found m/z 221.09094.
Crystal data for 14: monoclinic, P21 (#4), a ) 6.3632(3) Å, b )
7.6482(3) Å, c ) 13.6844(7) Å, ꢀ ) 97.056(2)°, V ) 660.93(5)
Å3, Z ) 2. Data collection: Rigaku RAXIS-RAPID Imaging Plate
diffractometer, T ) -153 °C. 2θmax ) 54.9°, R ) 0.028, Rw
0.037, I > 1.5 σ(I), GOF ) 1.26.
)
trans-[RhCl(CO)(Ph-SMAP)2] (17). To a solution of [{RhCl-
(CO)2}2] (58 mg, 0.15 mmol), in C6H6 (1.5 mL) was slowly added
Ph-SMAP (140 mg, 0.63 mmol) at room temperature and stirred
for 1 h. The mixture was concentrated under a reduced pressure.
The crude yellow solid was washed with degassed MeOH and
hexane. The yellow solid was dissolved in degassed CH2Cl2. The
solution was transferred to another flask through cannula tube, the
inlet of which was covered with a filter paper. Degassed EtOH
was carefully added over the CH2Cl2 solution. The solution was
kept standing at 5 °C. After large yellow crystals were grown, a
mother liquor was removed with a syringe. The crystals were dried
1-Benzyl-4-phenyl-1-phosphonia-4-silabicyclo[2.2.2]octane bro-
mide (13) (an Intermediate in the Conversion of 12 to 1a). Although
the protocol for the synthesis of Ph-SMAP (1a) does not involve
the isolation of this compound, it could alternatively be isolated
and characterized as follows. A solution of 1-octene (5.8 mL, 37
mmol) and 10 (1.5 g, 3.7 mmol) in DME (185 mL) was degassed
by three freeze-pump-thaw cycles and refluxed for a week. The
reaction mixture was cooled to room temperature. Solids in
the mixture were filtered and washed with Et2O/hexane (1:1). The
powder was dried under a reduced pressure. Purification by flash
chromatography on silica gel (MeOH/CHCl3 3:97) gave the title
compound as colorless crystals (0.955 g, 66%). Mp 225.0-226.3
°C. 1H NMR (300 MHz, CDCl3): δ 1.39-1.49 (m, 6H), 2.96-3.06
(m, 6H) 4.40 (d, J ) 16.8 Hz, 2H), 7.28-7.50 (m, 10H). 13C NMR
(75.4 MHz, CDCl3) δ 3.19 (d, JC-P ) 4.6 Hz, 3C), 14.74 (d, JC-P
1
in vacuo. Mp 183.0-184.2 °C (dec., in a sealed tube). H NMR
(300 MHz, C6D6): δ 0.77-0.83 (m, 12H), 2.44-2.52 (m, 12H),
7.12-7.15 (m, 10H). 31P NMR (121.4 MHz, C6D6): δ -8.8 (d,
JP-Rh ) 117.8 Hz). Anal. Calcd for C25H34ClOP2RhSi2: C 49.47%,
H 5.65%. Found: C 49.20%, H 5.54%. The measurement of 13C
NMR was unsuccessful because of the low solubility in C6D6 and
the reactivity in CD2Cl2 at room temperature.
) 49.8 Hz, 3C), 27.7 (d, JC-P ) 41.8 Hz, 1C), 128.2 (d, JC-P
)
9.7 Hz, 1C), 128.4 (d, JC-P ) 3.4 Hz, 1C), 128.5 (s, 2C), 129.4 (d,
JC-P ) 3.4 Hz, 2C), 129.9 (d, JC-P ) 3.3 Hz, 1C), 130.2 (d, JC-P
) 5.2 Hz), 131.1 (s, 1C), 133.8 (s, 2C). 31P NMR (121.4 MHz,
CDCl3): δ 14.3 (s). HRMS (EI): Calcd for C19H23PSi [M-HBr]+
(m/z): 310.1307. Found: 310.1308.
Crystal data for 20: monoclinic, P21/c (#14), a ) 6.914(4) Å, b
) 6.698(4) Å, c ) 28.42(2) Å, ꢀ ) 95.71(4)°, V ) 1309(1) Å3, Z
) 2. Data collection: Rigaku RAXIS-RAPID Imaging Plate
4-Phenyl-1-phospha-4-silabicyclo[2.2.2]octane (Ph-SMAP, 1a).1a
A solution of 1-octene (2.9 mL, 21.3 mmol) and 10 (1.08 g, 2.67
mmol) in DME (30 mL) was degassed by three freeze-
pump-thaw cycles and refluxed for 5 days. The reaction mixture
was cooled to room temperature. The liquid was removed with a
cannula, and the remaining solid was washed with Et2O/hexane
(1:1, 10 mL × 3). THF (30 mL) was added, and the mixture was
degassed as above. LiAlH4 (203 mg, 5.34 mmol) was added, and
the mixture was stirred at room temperature for 18 h. Degassed
water (0.2 mL) was carefully added to the ice-cooled, well-stirred
mixture. The mixture was then treated successively with 15% aq
NaOH (0.2 mL) and with water (0.6 mL) at 0 °C. After stirring
was continued for 30 min at room temperature, the mixture was
filtered through a pad of Celite on a glass filter (open air) and the
diffractometer, T ) -163 °C. 2θmax ) 55.0°, R ) 0.043, Rw
0.094, I > 1.5 σ(I), GOF ) 3.25.
)
cis-[PtMe2(Ph-SMAP)2] (18). To a C6D6 suspension of
[PtMe2(cod)]26 (2.3 mg, 0.007 mmol) in an NMR tube was added
Ph-SMAP (3 mg, 0.014 mmol). The mixture was shaken. After 30
min,18 was given. Sample for X-ray diffraction of 18 was obtained
by recrystallization from CH2Cl2/hexane. 1H NMR (300 MHz,
C6D6): δ 1.32-1.50 (dd, JH-P ) 6.6 Hz, 7.4 Hz,195Pt satellite JH-Pt
) 67.4 Hz, 6H), 2.17-2.21 (m, 12H), 7.15-7.20 (m, 6H),
7.25-7.29 (m, 4H).13C NMR (75.4 MHz, C6D6): δ 3.2 (dd, JC-P
) 10.0 Hz, 103.4 Hz, 195Pt satellite JC-Pt ) 597 Hz, 2C), 5.38-18.0
(26) Clark, H. C.; Manzer, L. E. J. Organomet. Chem. 1973, 59, 411–
428.

Caged, Compact Trialkylphosphine
Organometallics, Vol. 27, No. 21, 2008 5503
(m, 6C), 20.2-20.9 (m, 6C), 128.8 (4C), 130.6 (2C), 134.2 (4C),
135.0 (2C). 31P NMR (121.4 Hz, C6D6): δ -21.3 (s, 195Pt satellite
JP-Pt ) 1785 Hz).
Crystal data for 18: monoclinic, P21/a (#14), a ) 11.626(1) Å,
b ) 18.686(2) Å, c ) 14.094 Å, ꢀ ) 101.368(2)°, V ) 3001.9(6)
Å3, Z ) 4. Data collection: Rigaku RAXIS-RAPID Imaging Plate
was removed from the glovebox. The test tube was placed in an
autoclave whilebeing flushed with a stream of argon. The autoclave
was initially pressurized with hydrogen at 20 atm, before the
pressure was reduced to 1 atm by carefully releasing the stop valve.
This procedure was repeated three times, and then the vessel was
pressurized at 30 atm. The reaction mixture was vigorously stirring
at 100 °C. After stirring for 20 h and cooling to room temperature,
the hydrogen gas was carefully released. An internal standard
(Cl2CHCHCl2, 20 µL, 0.18 mmol) was added to the reaction
mixture. Yield of the product was determined by 1H NMR analysis.
diffractometer, T ) -150 °C. 2θmax ) 55.0°, R ) 0.074, Rw
0.104, I > 3 σ(I), GOF ) 3.31.
)
General Procedure for the Rh-Catalyzed Hydrosilylation
of Ketones. In a glovebox, a phosphine (0.01 or 0.02 mmol) and
[{RhCl(C2H4)2}2]27 (1.9 mg, 0.005 mmol), and an internal standard
(dibenzyl, 45.6 mg, 0.25 mmol) were placed in a vial tube.
Anhydrous, degassed benzene (1 mL) was added, and the mixture
was stirred at room temperature for a few minutes. Then, Me2PhSiH
(163.5 mg, 1.2 mmol) and a ketone (1.0 mmol) were added. After
being sealed with a screw cap, the vial tube was removed from the
glovebox. Conversion of the reaction was checked by GLC. After
the reaction was completed, the mixture was subjected to column
chromatography (SiO2/Et2O) and the yields of the products were
determined by GC analysis.
General Procedure for the Rh-Catalyzed Hydrogenation
of Ketones. In a glovebox, a phosphine (0.01 or 0.02 mmol) and
[Rh(OMe)(cod)]2 (2.4 mg, 0.005 mmol) were placed in a screw
test tube. A ketone (1.0 mmol) and anhydrous, degassed THF (1
mL) were added. After being sealed with a screw cap, the test tube
Acknowledgment. This work was supported by the
PRESTO program (JST) and by Grant-in-Aid for Scientific
Research (B) (No. 18350047) (JSPS). A.O. thanks JSPS for
a fellowship. G.H. was supported by MEXT program,
Initiatives for Attractive Education in Graduate Schools (T-
type Chemists with Lofty Ambition) and GCOE (Catalysis
as the Basis for Innovation in Materials Science). We thank
Professor T. Inabe (Hokkaido University) for his precious
effort in the X-ray structure analyses.
Supporting Information Available: A CIF file for 1a, 14, 17,
and 18 · (hexane)0.5 and NMR charts for 12 and 13. This material
is available free of charge via the Internet at http://pubs.acs.org.
(27) Cramer, R. Inorg. Synth. 1990, 28, 86–88.
OM8005728