Synthesis, first structures, and catalytic activity of the monomeric rhodium(I)-siloxide phosphine complexes

Article abstract of DOI:10.1139/v03-145

Four new square-plane rhodium siloxide complexes of the general formula [Rh(cod)(PR₃′)(OSiR₃)] (where R = Me, i-Pr, O-t-Bu, R′ = Cy, Ph) were synthesized and the structures of three of them were resolved by the X-ray method. [Rh(cod)(PCy₃)(OSiMe₃)] (1) appeared to be a very efficient catalyst for hydrosilylation of allyl glycidyl ether to yield, selectively, 3-glycidoxypropyltriethoxysilane, a commercially important silane coupling agent. Catalytic measurements and stoichiometric experiments of 1 with triethoxysilane suggest a mechanism where an unsaturated Rh-H species is responsible for the catalysis.

Full text of DOI:10.1139/v03-145

1292
Synthesis, first structures, and catalytic activity of
the monomeric rhodium(I)-siloxide phosphine
complexes1
Bogdan Marciniec, Paulina B»aóejewska-Chadyniak, and Maciej Kubicki
Abstract: Four new square-plane rhodium siloxide complexes of the general formula [Rh(cod)(PR3′)(OSiR3)] (where
R = Me, i-Pr, O-t-Bu, R′ = Cy, Ph) were synthesized and the structures of three of them were resolved by the X-ray
method. [Rh(cod)(PCy3)(OSiMe3)] (1) appeared to be a very efficient catalyst for hydrosilylation of allyl glycidyl ether
to yield, selectively, 3-glycidoxypropyltriethoxysilane, a commercially important silane coupling agent. Catalytic mea-
surements and stoichiometric experiments of 1 with triethoxysilane suggest a mechanism where an unsaturated Rh-H
species is responsible for the catalysis.
Key words: rhodium (phosphine) siloxides, hydrosilylation, catalysis.
Résumé : On a synthétisé quatre nouveaux complexes siloxyde de rhodium de géométrie plan carré et de formule
générale [Rd(cod)(PR3′)(OSiR3)] (dans lesquels R = Me, i-Pr, O-t-Bu; R′ = Cy; Ph) et on a déterminé les structures
de trois d’entre eux par diffraction des rayons X. Il semble que le [Rh(cod)(PCy3)(OSiMe3)] (1) est un catalyseur
très efficace pour l’hydrosilylation de l’oxyde d’allyle et de glycidyle conduisant à la formation sélective du 3-
glycidoxypropyltriéthoxysilane, un silane commercialement important comme agent de couplage. Des mesures catalyti-
ques et des expériences stoechiométriques du composé 1 avec le triéthoxysilane suggèrent un mécanisme dans lequel
l’espèce Rh-H insaturée est responsable de la catalyse.
Mots clés : rhodium(phosphine)siloxydes, hydrosilylation, catalyse.
[Traduit par la Rédaction] Marciniec et al. 1298
Introduction
Catalytic activity of [Rh(cod)(µ-OSiMe3)]2 has been illus-
trated in some reactions, i.e., in the hydrosilylation of
alkenes (12) and allyl alkyl ethers (13, 14) and in the silyl-
ative coupling of vinylsilanes with alkenes (15).
The aim of this work was to prepare monomeric rhodium-
siloxide complexes, to determine their structures by X-ray
methods, and to assess their catalytic activity in the hydro-
silylation process.
Siloxides similar to alkoxides have been employed as an-
cillary ligands of transition metal (TM) complexes, markedly
influencing the reactivity of a metal center by electronic and
steric effects of the substituents at silicon. They can be re-
garded as very good molecular models of metal complexes
supported on silica and silicate surfaces, which are known to
catalyze a variety of organic and organometallic transforma-
tions particularly by early transition metal complexes (1).
Unlike the early TM-siloxides the information on the late
TM-siloxides is scarce. Only exceptional siloxy derivatives
of Fe (2), Co (3), Ni (4), Ru (5), Rh (6–9), Pt (10), Os (11),
and Ir (10c) have been synthesized and characterized spec-
troscopically, and the structures of all of them have been a
subject of recent interest. The dimeric complexes included
[Rh(CO)2(µ-OSiR3)]2, where R = Me (8), Ph (6b), and
[Rh(cod)(µ-OSiPh3)]2 (6b), [Rh(diene)(µ-OSiMe3)]2, where
diene = cod (7a, 7b), nbd (7c).
Experimental section
General methods and chemicals
All syntheses and operations were carried out using stan-
dard Schlenk techniques under a carefully deoxygenated and
1
dried argon. H, 13C, 31P, and 29Si NMR spectra were re-
corded on Varian Mercury and Varian Gemini 300 VT spec-
trometers. The reagents were obtained from the following
sources: C6H6 from OBR PR Plock (Poland), PPh3 from
Fluka, sodium trimethylsilanolate from Aldrich, THF and
Received 11 April 2003. Published on the NRC Research Press Web site at http://canjchem.nrc.ca on 21 October 2003.
Dedicated to celebrate Professor John Harrod’s productive career and in recognition of his great contribution to organosilicon
chemistry and catalysis.
B. Marciniec,2 P. B»aóejewska-Chadyniak, and M. Kubicki. Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6,
60-780 Pozna½, Poland.
1This article is part of a Special Issue dedicated to Professor John Harrod.
2Corresponding author (e-mail: marcinb@main.amu.edu.pl).
Can. J. Chem. 81: 1292–1298 (2003)
doi: 10.1139/V03-145
© 2003 NRC Canada

Marciniec et al.
1293
C5H12 from POCh Gliwice (Poland), HOSi(O-t-Bu)3 and i-
Pr3SiCl from ABCR Co. All solvents were distilled in an in-
ert atmosphere prior to use. [{Rh(cod)(µ-Cl)}2] (16, 17),
[{Rh(cod)(µ-OSiMe3)}2] (5) (7a) were prepared according
to the previously reported procedures.
(C6D6) δ: 1.02 (m, 3H, -CH=), 1.20 (d, 18H, -CH3). Anal.
calcd. for NaOSiC9H21: C 55.06, H 10.78; found: C 54.82, H
11.11.
Synthesis of the complex [Rh(Cl)(cod)(PCy3)]
Portions of 0.22 g (0.8 mmol) of PCy3 and 0.21 g
(0.4 mmol) of [{Rh(cod)(µ-Cl)}2] were placed in a Schlenk
flask in an Ar atmosphere. Then 5 mL of dried and deoxy-
genated C6H6 was added and the mixture was stirred with a
magnetic stirrer. After 2 h, C6H6 was evaporated and 5 mL
of dried and deoxygenated C5H12 was added. The precipitate
was decanted three times by C5H12. The complex was dried
in vacuum for about 3 h. It was obtained with a yield of
Synthesis of the complex [Rh(cod)(PCy3)(OSiMe3)] (1)
Portions of 0.1 g [{Rh(cod)(µ-OSiMe3)}2] (0.33 mmol)
and 0.2 g (0.71 mmol) PCy3 were placed in a Schlenk flask
under Ar. Then 6 mL of dried and deoxygenated C6H6 was
added. The reaction was carried out for 4 h at room tempera-
ture (r.t.). After this time, C6H6 was evaporated and 5 mL of
dried and deoxygenated C5H12 was added. The precipitate
was decanted three times by C5H12. The complex was dried
in vacuum for about 3 h. It was obtained with a yield of
1
95%. H NMR (C6D6) δ: 1.20–2.19 (m, 33H, -Cy), 2.32 (m,
4H, -CH2-), 3.60 (m, 4H, -CH2-), 5.72 (m, 4H, =CH-).
31P NMR (C6D6) δ: 27.33 (d, JRh-P = 350.7 Hz). Anal. calcd.
for RhPClC26H45: C 59.26, H 8.61; found: C 59.82, H 8.84.
1
75%. H NMR (C6D6) δ: 0.46 (s, 9H, -CH3), 1.20–2.02 (m,
33H, -Cy), 2.35 (m, 4H, -CH2-), 3.26 (m, 4H, -CH2-), 5.41
(m, 4H, =CH-). 13C NMR (C6D6) δ: 6.0 (-OSiMe3, -CH3),
27.21, 28.28, 28.40, 29.07, 30.80, 31.80, 31.97, 32.50,
32.71, 34.07 (-Cy, -CH2-), 62.83, 63.01 (cod, -CH2-), 99.15,
99.26, 99.32, 99.42 (cod, =CH-). 31P NMR (C6D6) δ: 25.28
(d, JRh-P= 151 Hz). 29Si NMR δ: –3.35. Anal. calcd. for
RhPSiOC29H54: C 59.98, H 9.37; found: C 60.22, H 9.44.
Synthesis of 3
Portions of 0.2 g (0.38 mmol) [Rh(cod)(PCy3)(Cl)] and
0.08 g (0.42 mmol) NaOSi-i-Pr3 were placed in a Schlenk
flask in an Ar atmosphere. Then 5 mL of dried and deoxy-
genated C6H6 was added. The reaction was conducted for
24 h at r.t. After this time, C6H6 was evaporated and 8 mL of
dried and deoxygenated C5H12 was added. The entire mix-
ture was filtered off by a cannula system. The solvent was
evaporated from the obtained filtrate leaving a yellow solid.
Synthesis of the complex [Rh(cod)(PPh3)(OSiMe3)] (2)
Complex 2 was prepared in a similar way to complex 1,
except for the fact that PPh3 (0.09 g, 0.34 mmol) was used
instead of PCy3. The yellow complex was obtained with the
1
The complex was isolated with a yield of 85%. H NMR
1
yield of 70%. H NMR (C6D6) δ: 0.30 (s, 9H, -CH3), 1.68
(C6D6) δ: 1.22 (m, 3H, -CH=), 1.48 (d, 18H, -CH3), 1.57–
2.28 (m, 33H, -Cy), 2.30 (m, 4H, -CH2-), 3.47 (m, 4H,
-CH2-), 5.28 (m, 4h, =CH-). 13C NMR (C6D6) δ: 16.99–
20.32, 26.49–34.04 (m, -OSi-i-Pr3 + -Cy), 61.75, 61.93 (cod,
-CH2-), 97.92, 98.03, 98.09, 98.19 (cod, =CH-). 31P NMR
(C6D6) δ: 27.40 (d, JRh-P = 149 Hz). 29Si NMR (C6D6)
δ: –21.51. Anal. calcd. for RhPSiOC35H66: C 63.23, H
10.01; found: C 62.91, H 10.11.
(m, 4H, -CH2-), 2.18 (m, 4H, -CH2-), 2.88 (m, 2H, -CH=),
5.62 (m, 2H, -CH=), 7.07 (m, 9H, -Ph), 7.75 (m, 6H, -Ph).
13C NMR (C6D6) δ: 5.06 (-OSiMe3, -CH3), 29.02, 33.67
(cod, -CH2-), 64.60, 64.78 (cod, -CH=), 103.18 (bs, cod,
=CH-), 130.10, 131.57, 132.38, 135.23 (-Ph). 31P NMR
(C6D6) δ: 25.21. 29Si NMR (C6D6) δ: 21.55. Anal. calcd.
RhPSiOC29H36 for: C 61.92, H 6.45; found: C 62.18, H
6.37.
Synthesis of the complex [Rh(cod)(PCy3){OSi(O-t-Bu)3}]
(4)
Synthesis of the complex [Rh(cod)(PCy3)(OSi-i-Pr3)] (3)
Preparation of HOSi-i-Pr3
Preparation of NaOSi(O-t-Bu)3
i-Pr3SiCl (10 mL) was added to a water–ether mixture
(H2O (300 mL), ether (150 mL)) that was stirred with a
magnetic stirrer for 24 h at r.t. Then the aqueous phase was
removed and the ether solution was dried by addition of
CaCl2. After 24 h it was filtered off by a cannula system and
the solvent was evaporated to dryness. The product was ob-
tained with a yield of 87%.
Fifty mL portions of anhydrous and deoxygenated THF
and 0.35 g (15 mmol) of metallic Na were placed into a
100 mL double-necked round-bottomed flask equipped with
a reflux condenser and an attachment for gas supply. Then
4 g of HOSi(O-t-Bu)3 (15 mmol) was added and the mixture
was heated at a boiling point for 4 h. After the reaction, the
contents of the flask were filtered off hot by a cannula to a
Schlenk flask. Having cooled the contents, the solvent was
evaporated and the white solid was washed with diethyl
Preparation of NaOSi-i-Pr3
Thirty mL portions of anhydrous and deoxygenated THF
and 1.20 g (53 mmol) of metallic Na were placed into a
50 mL double-necked round-bottomed flask equipped with a
reflux condenser and an attachment for gas supply. Then
7.8 g of HOSiO-i-Pr3 (45 mmol) was added over 30 min
with constant stirring by a magnetic stirrer. After this time,
the mixture was heated at a boiling point for 6 h. After the
reaction, the contents of the flask were filtered off hot by a
cannula to a Schlenk flask. Having cooled the contents, the
solvent was evaporated and the product was dried in vacuum
ether (3 × 5 mL). The product was obtained with a 90%
1
yield. H NMR (C D ) : 1.57 (s, 27H, -CH ).
δ
6
6
3
Preparation of 4
Complex 4 was prepared in a similar way to complex 3,
except for the fact that NaOSi(O-t-Bu)3 (0.12 g, 0.42 mmol)
was used instead of NaOSi-i-Pr3. The yellow complex was
1
obtained with the yield of 90%. H NMR (C6D6) δ: 1.56 (s,
27H, -CH3), 1.81 (m, 33H,-CH2-), 2.50 (m, 4H, -CH2-), 3.25
(m, 4H, -CH2-), 5.05 (m, 4H, =CH-). 13C NMR (C6D6) δ:
26.91, 27.83, 27.96, 28.78, 30.87, 31.68, 32.62, 33.58, 33.80,
1
for about 3 h. It was obtained with a 90% yield. H NMR
© 2003 NRC Canada

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Can. J. Chem. Vol. 81, 2003
Table 1. Crystal data.
Compound
Formula
1
3
4
RhPSiOC29H54
RhPSiOC35H66
RhPSiO4C38H72C0.5(C5H12)
Formula weight
Colour, shape
T (K)
580.69
Yellow, block
293(2)
664.85
Pale-yellow, plate
293(2)
791.00
110(1)
Crystal system
Space group
Triclinic
P-1
Triclinic
P-1
Monoclinic
P21/c
a (Å)
b (Å)
c (Å)
α (°)
10.3468(5)
10.6222(5)
16.5714(7)
94.299(4)
93.677(3)
110.484(4)
1693.35(13)
2
10.814(2)
11.696(2)
15.956(3)
80.06(3)
75.94(3)
68.51(3)
1813.7(6)
2
9.9104(7)
22.3863(13)
19.2440(12)
90
96.002(5)
90
4246.0(5)
4
1.237
β (°)
γ (°)
V (Å3)
Z
dx (Mg m–3)
1.139
1.217
µ (mm–1)
0.604
0.572
0.504
F(000)
620
716
1708
Crystal size (mm)
θ Range for data collection (°)
Reflections collected
Independent reflections
[Rint]
0.2 × 0.3 × 0.3
3.4–27
14221
7260
[0.028]
0.1 × 0.15 × 0.3
3.1–24
13858
6343
[0.040]
0.2 × 0.2 × 0.3
3.03–27
36670
9248
[0.085]
R (I > 2σ(I))
wR2 (I > 2σ(I))
R (all data)
wR2 (all data)
S
∆ρmax/∆ρmin (e Å–3)
0.0405
0.1040
0.0479
0.1093
1.07
0.0468
0.0772
0.0870
0.0854
0.97
0.0587
0.1184
0.0975
0.1322
0.98
0.90/–0.51
0.73/–0.49
1.53/–0.97
33.94 (-Cy, -CH2-), 33.43 (-OSi(O-t-Bu3)3, -CH3), 61.33, 61.51
(cod, -CH2-), 72.56 (-OSi(O-t-Bu3)3, -OC(CH3)3), 100.27,
100.37, 100.42, 100.53 (cod, =CH-). 31P NMR (C6D6) δ:
27.03 (d, JRh-P = 143 Hz). 29Si NMR (C6D6) δ: –21.53. Anal.
calcd. for RhPSiO4C38H72: C 60.46, H 9.61; found: C 60.72,
H 9.08.
from the whole experiment. Lorentz and polarization effects
were accounted for (19), and then data were corrected for
absorption and merged with SORTAV (20). The structures
were solved by direct methods with the SHELXS-97 pro-
gram (21), and refined with full-matrix least-squares by
SHELXL-97 (22). All non-hydrogen atoms, including those
from the disordered solvent–pentane molecule in 3, were re-
fined anisotropically. The positions of hydrogen atoms were
generated geometrically and they were refined as a “riding
model”. The Uiso parameters of hydrogen atoms were set at
1.2 times Ueq of the appropriate carrier atom.
Crystallization of the complexes
A portion of about 0.05 g of the complex and an amount
of dry and deoxygenated C5H12 sufficient to obtain a clear
solution were placed in a Schlenk flask. Crystallization was
conducted for 10–14 days at –15 °C. A few crystals selected
under a microscope were placed in glass capillary tubes of
0.3 mm in diameter and subjected to X-ray diffraction study.
A summary of crystal data, data collection and refinement
is given in Table 1.
X-ray crystallography
Results and discussion
X-ray diffraction data was collected, from the crystals
sealed in glass capillaries, on a KUMA KM4CCD diffracto-
meter (18) using graphite-monochromated MoKα radiation
(λ = 0.71073 Å). Data collections were performed in
six separate runs (a total of 782 frames for 1 and 4, and
588 frames for 3) to cover an appropriate part of the reflec-
tion sphere. The ω-scan was used, two reference frames
were measured after every 50 frames, and they did not show
any systematical changes neither in the peak position nor in
their intensities. The unit-cell parameters were determined
by least-squares treatment of the setting angles of 9625 (1),
5103 (3), and 5665 (4) highest-intensity reflections, chosen
Two types of reactions were used for the synthesis of the
rhodium-siloxide complexes:
C6 H6 , 2 h
[Rh(cod)(µ-OSiMe3)]2 + 2PR3′
→
room temp.
2[Rh(cod)(PR3′)(OSiMe3)]
where R′ = Cy, Ph and
[Rh(cod)(PCy3)(CI)] + NaOSiR3
C6 H6 , 24 h
→
room temp.
[Rh(cod)(PCy3)(OSiR3)] + NaCI
© 2003 NRC Canada

Marciniec et al.
1295
Fig. 2. Anisotropic displacement representation of complex 3
showing the labelling scheme. Displacement ellipsoids are shown
at the 33% probability level and hydrogen atoms are omitted for
clarity.
Fig. 1. Anisotropic displacement representation of complex 1
showing the labelling scheme. Displacement ellipsoids are shown
at the 33% probability level and hydrogen atoms are omitted for
clarity.
where R = i-Pr, O-t-Bu. All the rhodium-siloxide products
1
were characterized by H, 13C, 31P, and 29Si NMR spectros-
copy.
triethoxysilane leading to glycidoxypropyltriethoxysilane,
which is a commercially important silane coupling agent.
The reaction gives the hydrosilylation product (A) with
very high yield accompanied by products of the dehydro-
genative silylation (B + C) according to the following
scheme:
The molecular structures of complexes [Rh(cod)-
(PCy3)(OSiMe3)] (1), [Rh(cod)(PCy)3(OSi-i-Pr3)] (3), and
[Rh(cod)(PCy)3(OSi(O-t-Bu)3)] (4) with the atom-
numbering scheme are depicted in Figs. 1, 2, and 3, respec-
tively. Selected geometrical parameters are listed in Table 2.
In all three complexes the coordination of rhodium is
square planar, providing that the middle points of the
cyclooctadiene double bonds are regarded as the coordina-
tion sites X1 and X2. This is confirmed by the values of
bond angles at rhodium (cf. Table 2) as well as by the least-
squares calculation of the mean plane through five points:
Rh, X1, X2, O, and P. Maximum deviation from this plane is
0.017(2) Å in 1, 0.059(5) Å in 3, and 0.005(2) Å in 4. The
cyclooctadiene double bonds are approximately perpendicu-
lar to the central coordination plane.
The bond lengths and angles are quite typical. All cyclo-
hexyl rings are slightly distorted chairs, and the conforma-
tions of cyclooctadiene rings are close to a C2 – twist-boat,
the minimum energy conformation (23, 24). Despite these
similarities there are some quite interesting differences in
the overall conformation between alkyl-substituted siloxide
complexes 1 and 3 and, on the other side, the alkoxy-
substituted siloxide complex 4. For example, the disposition
of the substituents at the Si atom with respect to the O—Si
bond can be described as +sc,–sc, ap (Rh-O-Si-C torsion an-
gles approximately +60°, –60°, 180°) in 1 and 3, while in 4
it is +ac,–ac, sp (Rh-O-Si-O values are close to +120°,
–120°, 0°).
The effect of the catalyst 1–4 concentrations as well as
other conditions (temperature and time of the reaction) on
the yield of the main product and by-products is compiled in
Table 3. Dimeric [Rh(cod)(µ-OSiMe3)]2 (5), whose structure
(7b) and catalytic activity in this reaction (13, 14) was re-
ported previously, is used for comparison.
The order of the activity is as follows:
[Rh(cod)(µ-OSiMe3)]2 ≈ [Rh(cod)(PCy3)(OSiMe3)] ≥
5
1
[Rh(cod)(PPh3)(OSiMe3)] ≈ [Rh(cod)(PCy3)(OSi-i-Pr3)] >>
2
3
[Rh(cod)(PCy3)(OSi(O-t-Bu)3)] and can be explained by
4
increasing steric effects of the siloxy group influencing di-
rectly the rate of the hydrosilylation process as well as by a
complex stereoelectronic effect of the trisubstituted phos-
phine (1 ≥ 2). The latter effect is a result of facile oxygena-
tion and dissociation of PCy3 vs. PPh3 caused mainly by an
All the monomeric rhodium-siloxide complexes 1–4 were
tested in the hydrosilylation of allyl glycidyl ether by
© 2003 NRC Canada

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Can. J. Chem. Vol. 81, 2003
Fig. 3. Anisotropic displacement representation of complex 4 showing the labelling scheme. Displacement ellipsoids are shown at the
50% probability level and hydrogen atoms are omitted for clarity.
Table 3. The hydrosilylation of allyl glycidyl ether by
triethoxysilane catalyzed by rhodium siloxide(I) complexes (1–5).
Table 2. Selected bond lengths (Å) and bond angles (°) (X1, X2
denote the middle points of the cyclooctadiene double bonds)
with esds in parentheses.
Yield (%)
Compound
1
3
4
Catalyst
A
B + C
Conditions: 25 °C, [Rh] = 5 × 10–3 mol L–1, 15 min
Bond lengths (Å)
Rh1—X1
Rh1—X2
Rh1—P1
RH1O2
<P—C>
2.086(3)
1.995(3)
2.3411(7)
2.030(2)
1.860(6)
1.577(2)
2.007(5)
2.110(6)
2.3444(15)
2.064(3)
1.854(11)
1.593(4)
2.083(5)
2.002(4)
2.3609(12)
2.065(3)
1.859(3)
1.561(3)
1
2
3
4
96
70
99
40
90
4
2
—
2
5*
10
O2—Si2
Conditions: 25 °C, [Rh] = 10–3 mol L–1, 4 h
Bond angles (°)
X1-Rh1-X2
X1-Rh1-P1
X1-Rh1-O2
X2-Rh1-P1
X2-Rh1-O2
P1-Rh1-O2
Rh1-O2-Si2
1
2
3
4
99
100
68
35
98
1
—
1
—
2
86.53(15)
176.53(11)
90.84(11)
96.87(12)
177.15(13)
85.77(6)
85.6(3)
178.5(2)
92.0(2)
95.08(16)
174.9(2)
87.48(10)
147.4(2)
86.3(2)
175.46(13)
90.91(16)
98.19(14)
177.2(2)
84.57(10)
143.6(2)
5*
Conditions: 40 °C, [Rh] = 10–4 mol L–1, 24 h
1
2, (2*)
5*
98
99 (98)
99
2
152.70(13)
1 (2)
1
Conditions: 60 °C, [Rh] = 5 × 10–5 mol L–1, 1 h
increase in electron-donor properties of the former phos-
phine.
1, (1)
2, (2)
5
98 (50)
41 (4)
98
1 (–)
Traces
—
Similarly to the hydrosilylation by dimeric rhodium
siloxide 5 (25), monomeric phosphine rhodium siloxides (1–4)
undergo an oxidative addition with triethoxysilane followed
by elimination of disiloxane according to the mechanistic
pathways proposed in Scheme 1.
Note: All reactions carried out under the following conditions (except
for those designated by *): [HSi(OEt)3]:[ether] = 1:1.5, glass ampoules, air
(* indicates reactions carried out in an argon atmosphere).
Preliminary 1H NMR study on the stoichiometric reactions
of (1) with triethoxysilane performed in C6D6 in room tem-
perature and in air, right away after mixing of the substrate,
revealed the presence of several doublets at δ ~ –13.35 and
JRh-H ~ 43 in the spectra to be formed in the mixture of the
penta-coordinate complexes similarly to the spectra ob-
served previously in the system – dimeric complex 5
© 2003 NRC Canada

Marciniec et al.
1297
Scheme 1. Catalysis of hydrosilylation by monomeric rhodium-
siloxide phosphine complexes.
of dehydrogenative silylation observed (1% to 2%), is omit-
ted from the scheme for clarity.
Conclusions
Four new monomeric, square-planar rhodium siloxide
complexes of the general formula [Rh(cod)(PR3′)(OSiR3)]
where R′ = Cy, Ph, R = Me, i-Pr, O-t-Bu were synthesized
and three of them were structurally characterized.3
The complex (1) ([Rh(cod)(PCy)3(OSiMe3)]) appeared to
be a very efficient catalyst for hydrosilylation of allyl
glycidyl ether occurring in air. All catalytic data and
stoichiometric reactivities of (1) with triethoxysilane are
consistent with a mechanism involving a generation of tetra-
coordinated Rh-H species (responsible for catalysis).
Acknowledgement
The work was supported by State Committee for Scien-
tific Research, Project Nos. K026/T09/2001 and 7 T09B
004 20.
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Canada, Ottawa, ON K1A 0S2, Canada (http://www.nrc.ca/cisti/irm/unpub_e.shtml for information on ordering electronically). CCDC
205459 (1), 205460 (3), and 205461 (4) contain the crystallographic data for this manuscript. These data can be obtained, free of charge, via
www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
U.K.; fax +44 1223 336033; or deposit@ccdc.cam.ac.uk).
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