Tris(triorganosilyl)phosphites-New ligands controlling catalytic activity of Pt(0) complex in curing of silicone rubber

Article abstract of DOI:10.1016/j.apcata.2010.03.041

Applying novel and efficient method, new tris(triorganosilyl)phosphites were synthesized and further used for the preparation of new well-defined platinum complexes [Pt(DVTMDS)(P(OSiR₃)₃ )3}] (DVTMDS-(H₂C-CHSiMe₂)₂O, R₃-Si ₇O₉(¹OCt)₇, ¹Pr ₃, MePh₂, Ph₃, (O^tBu)₃, (OSiMe₃)₃) which were well characterized by spectroscopic methods. Structures of two platinum(O) complexes, [Pt{T|⁴(H ₂C=CHSiMe₂)₂o}{P(OSiPh₃) ₃}] (10) and [Pt(η-(H₂C=CHSiMe₂) ₂O}{P(OSi(O^tBu₃)₃}] (11) were determined by X-ray analysis. The new complexes proved to be very effective catalysts of a crosslinking of silicones via hydrosilylation at elevated temperature with relatively short cure time and the enthalpy of network formation similar to that of Pt-Karstedt's/DAM (DAM - diallyl maleate) catalytic system. Additionally, the catalyzed silicone formulation had sufficiently long pot-life at room temperature.

Full text of DOI:10.1016/j.apcata.2010.03.041

Applied Catalysis A: General 380 (2010) 105–112
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Tris(triorganosilyl)phosphites—New ligands controlling catalytic activity
of Pt(0) complex in curing of silicone rubber
Ireneusz Kownackia, Bogdan Marcinieca,∗, Karol Szuberta, Maciej Kubickia,
Magdalena Jankowskaa, Helmut Steinbergerb, Sławomir Rubinsztajnc
a Adam Mickiewicz University, Faculty of Chemistry, Grunwaldzka 6, 60-780 Poznan, Poland
b Momentive Performance Materials, D-51368 Leverkusen, Germany
c GE Global Research Center, 1 Research Circle, Schenectady, NY 12309, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Applying novel and efficient method, new tris(triorganosilyl)phosphites were synthesized and fur-
ther used for the preparation of new well-defined platinum complexes [Pt(DVTMDS){P(OSiR3)3}]
(DVTMDS = (H2C CHSiMe2)2O, R3 = Si7O9(iOct)7, iPr3, MePh2, Ph3, (OtBu)3, (OSiMe3)3) which were
well characterized by spectroscopic methods. Structures of two platinum(0) complexes, [Pt{␩4-
(H2C CHSiMe2)2O}{P(OSiPh3)3}] (10) and [Pt{␩4-(H2C CHSiMe2)2O}{P(OSi(OtBu3)3}] (11) were
determined by X-ray analysis. The new complexes proved to be very effective catalysts of a cross-
linking of silicones via hydrosilylation at elevated temperature with relatively short cure time and the
enthalpy of network formation similar to that of Pt-Karstedt’s/DAM (DAM = diallyl maleate) catalytic sys-
tem. Additionally, the catalyzed silicone formulation had sufficiently long pot-life at room temperature.
Received 11 January 2010
Received in revised form 15 March 2010
Accepted 18 March 2010
Available online 25 March 2010
Keywords:
Hydrosilylation
Karstedt’s catalyst
Platinum complexes
Silylphosphites
Curing
© 2010 Elsevier B.V. All rights reserved.
Silicones
1. Introduction
diorganophosphines by potassium silanolate was also described
[6].
Derivatives of phosphorus acids having at least one acidic hydro-
gen atom replaced by organosilyl group belong to the class of
compounds called silyl esters of phosphorus acid. Synthetic meth-
ods and application of various silyl esters of phosphorus acid have
been widely reviewed by Chojnowski [1].
Silyl esters of phosphorus acid found a wide range of
applications in the areas of organic, inorganic and bioorganic
chemistry [7–19]. Trimethylsilyl derivatives were used as efficient
reagents in synthesis of various organophosphorus compounds,
e.g. using Arbuzov reaction [7–10] or the Perkow reaction
[11].
We are interested in phosphorus derivatives containing three
organosilicon groups bonded to phosphorus atom via three
oxygen atoms. Such compounds can be obtained by silyla-
tion of phosphorus acid with different silylation agents, e.g.
tris(trimethylsilyl)phosphite produced in the reaction of phospho-
rus acid H3PO3 with chlorotrimethylsilane (TMSCl). Introduction
of two silyl groups occurs easily without any HCl acceptor.
However, incorporation of the third group requires an use
of amine or another reagent, which transforms the diester
into P(III) tautomeric form [2–4]. Reaction of trialkyl phos-
phites with three equivalents of chlorotriorganosilane was
reported as an efficient synthetic method for the preparation of
tris(triorganosilyl)phosphites [5]. Preparation of monosilyl esters
of P(III) via replacement of the chlorine substituent in chloro-
A
complex of platinum(0) with 1,3-divinyltetramethyl-
disiloxane, so-called Karstedt’s catalyst, is commercially available,
high activity catalyst for vulcanization of silicone elastomers
via hydrosilylation. Majority of commercial applications require
an addition of inhibitors, which temporarily diminish high cat-
alytic activity of the Karstedt’s catalyst. The unsaturated diesters,
e.g. maleates and fumarates, are the most important and com-
monly used class of the platinum inhibitors. Their inhibition
properties were described in many papers and patents [20–23].
Triorganophosphites were also reported as efficient inhibitors of
Pt-catalyzed hydrosilylation process [24]. Well-defined platinum
complexes with triorganophosphites were also employed as silicon
fluids vulcanization catalysts [24f–h, 25] and appeared to be very
efficient for this such purpose.
Many Pt(0) complexes prepared by treatment of the Karstedt’s
catalyst with various phosphines [26] have been isolated and used
as catalysts of the hydrosilylation process. Other Pt(0, +2) com-
∗
Corresponding author. Tel.: +48 061 8291366; fax: +48 061 8291508.
E-mail address: bogdan.marciniec@amu.edu.pl (B. Marciniec).
0926-860X/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2010.03.041

106
I. Kownacki et al. / Applied Catalysis A: General 380 (2010) 105–112
Table 1
plexes with phosphirane [27,28] chelating ligands also appeared
selective and efficient in the hydrosilylation reaction.
Crystal data, data collection and structure refinement.
Our previous studies on the synthesis, properties and appli-
cation of various triorganophosphites as inhibitors that control
the catalytic activity of platinum Karstedt’s complex in the cross-
linking of silicone fluids as well as useful starting phosphorus
based ligands for the preparation of platinum(0) complexes,
new efficient catalysts of curing process [24f–h], encouraged
us to develop the new type of phosphorus ligands containing
organometalloid substituents. Therefore, the aim of this work
was to prepare several novel tris(triorganosilyl)phosphites of
the general formula P(OSiR3)3 and platinum(0) complexes with
these silylphosphite ligands [Pt(DVTMDS){P(OSiR3)3}] as well as
to study their efficiency in catalysis of cross-linking process of
the vinyl-terminated polydimethylsiloxane with polyhydrosilox-
ane.
Compound
Formula
Formula weight
Crystal system
Space group
a (Å)
10
11
C62H63O4PPtSi5
1238.63
Monoclinic
P21/c
15.4224(5)
13.0054(4)
28.5569(9)
96.002(3)
5696.4(3)
4
C44H99O13PPtSi5
1202.74
Monoclinic
P2/c
19.782(2)
13.4645(14)
23.0571(18)
98.248(7)
6077.8(10)
4
b (Å)
c (Å)
ˇ (◦)
V (Å3)
Z
Dx (g cm−3
F (0 0 0)
)
1.444
2520
2.643
1.314
2520
2.484
ꢂ (mm−1
)
Crystal size (mm)
T (K)
0.3 × 0.2 × 0.15
0.15 × 0.1 × 0.1
100(1)
100(1)
ꢃ range (◦)
hkl range
2.42–29.81
−21 ≤ h ≤ 16
−17 ≤ k ≤ 16
−39 ≤ l ≤ 37
2.66–25.00
−23 ≤ h ≤ 19
−15 ≤ k ≤ 14
−27 ≤ l ≤ 27
2. Experimental
Reflections:
Collected
Unique (Rint
All syntheses and manipulations were carried out under argon
using standard Schlenk’s and vacuum techniques. 1H, 13C, 31P, and
29Si NMR spectra were recorded on a Varian Gemini 300 VT and
Varian Mercury 300 VT spectrometers in benzene-d6.
56426
14924 (0.041)
10883
26371
10226 (0.088)
5176
)
With I > 2ꢄ(I)
Number of parameters
R(F) [I > 2ꢄ(I)]
662
629
The chemicals were obtained from the following sources:
chlorosilanes, PCl3, NaH and benzene-d6 from Aldrich, Karstedt’s
catalyst from Aldrich and GE Silicones, polyhydromethylsilox-
ane (1.0 wt% of SiH), vinyl-terminated polydimethylsiloxane
(0.0248 wt% of –CH CH2) from GE Silicones, solvents from POCH
Gliwice (Poland). The curing process was studied in a system
consisting of vinyl-terminated polydimethylsiloxane and polyhy-
dromethylsiloxane as a cross-linker. The standard formulation had
([ SiH]/[ SiCH CH2] = 1.93 and the platinum concentration was
0.0332
0.0690
0.0589
0.0738
1.013
0.041
0.047
0.101
0.051
0.72
wR(F2) [I > 2ꢄ(I)]
R(F) [all data]
wR(F2) [all data]
Goodness of fit
max/min ꢀꢅ (e Å−3
)
1.78/−0.86
0.88/−0.74
CCDC deposition number
CCDC-664896
CCDC-664897
(11). Copies of this information may be obtained free of charge
from: The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK.
Fax: +44(1223)336-033, e-mail:deposit@ccdc.cam.ac.uk, or www:
www.ccdc.cam.ac.uk.
[
SiH]:[Pt] = 1:10−5. The progress of the curing process was moni-
tored by Differential Scanning Calorimetry (DSC) test method. DSC
measurements were made using a DSC 204 NETCH. The instru-
ment was calibrated with indium (ꢀH = 28.4 J/g). Analysis conditions
(DSC): Hold for 5.0 min at 30 ◦C, heat from 20 to 220 ◦C at 10 ◦C/min,
cool from 250 to 30 ◦C at 20 ◦C/min. DSC experiments were made
in triplicate for each test.
2.2. Descriptions of syntheses
2.2.1. Procedures for syntheses of silanols
2.2.1.1. Synthesis of tri-iso-propylsilanol (A). A solution of 5.76 g
(0.057 mol) of triethylamine in 150 mL of water and 300 mL of
diethyl ether were placed in a 750 mL two-neck, round-bottomed
flask, equipped with a magnetic stirrer and a thermometer. The
reaction flask was cooled by an ice bath. 10 g (0.052 mol) of tri-
iso-propylchlorosilane was added dropwise to a vigorously stirred
reaction mixture at 0 ◦C. After 1 h, the reaction mixture was trans-
ferred into the 1L separatory-funnel and the water layer was
removed. The organic layer was washed twice with DI water. The
ether solution was finally dried over 30 g of anhydrous magne-
sium sulfate. Solvent was evaporated under reduced pressure and
the product obtained was used toward the synthesis of tris(tri-iso-
propylsilyl)phosphite without additional purification. Yield 8.23 g
(91%).
2.1. X-ray structure determination
Colourless single crystals of the compounds 10 and 11 were
grown by crystallization in low temperature, where toluene for
10 and pentane 11 were used. Diffraction data were collected at
100 K by the ␻-scan on a KUMA KM4CCD diffractometer [29] with
graphite-monochromatized MoK␣ radiation (ꢁ = 0.71073 Å). The
data were corrected for Lorentz-polarization effects as well as for
absorption [30]. Accurate unit-cell parameters were determined by
the least-squares fit of 30553 (10) and 5563 (11) reflections of high-
est intensity, chosen from the whole experiment. The structures
were solved with SHELXS97 [31] and refined with the full-matrix
least-squares procedure on F2 by SHELXL97 [32]. Scattering fac-
tors incorporated in SHELXL97 were used. All non-hydrogen atoms
were refined anisotropically, hydrogen atoms were placed geomet-
rically, in idealized positions, and refined as rigid groups, Uiso of
hydrogen atoms were set as 1.2 (1.3 for methyl groups) times Ueq of
the appropriate carrier atom. In 11, one of the t-Bu groups is disor-
dered; the site occupation factors of these groups refined at 0.55(1)
and 0.45(1). Relevant crystal data are listed in Table 1, together with
refinement details.
2.2.1.2. Synthesis of methyldiphenylsilanol (B). This compound was
prepared in analogous way as tri-iso-propylsilanol, starting from
4.76 g (47 mmol) of NEt3, 10 g (43 mmol) of chloromethyldiphenyl-
silane (SiClMe2Ph). The product obtained was purified by
distillation under vacuum using the trap-to-trap technique. Yield
5.36 g (82%).
2.1.1. Supplementary material
2.2.1.3. Synthesis of tris(trimethylsiloxy)silanol (C). This com-
pound was prepared analogously as described for the silanol
A, starting from 3.36 g (33 mmol) of NEt3, 10 g (30 mmol)
of chlorotris(trimethylsiloxy)silane (SiCl(OSiMe3)3). The product
Crystallographic data (excluding structure factors) for the
structural analyses have been deposited with the Cambridge Crys-
tallographic DataCentre, Nos. CCDC-664896(10)andCCDC-664897

I. Kownacki et al. / Applied Catalysis A: General 380 (2010) 105–112
107
obtained was used for the next step without additional purification.
Yield 8.92 g (95%).
2.2.5. Synthesis of tris(triphenylsilyl)phosphite P(OSiPh3)3 (4)
The solution of triphenylsilanol (5 g, 18 mmol) in 50 mL of dried
and deoxidized THF was added dropwise to a vigorously mix
suspension of NaH (0.8 g, 36 mmol) in 20 mL of THF at room tem-
perature under dry argon atmosphere over 20 min. The reaction
was conducted for 2 h at 50 ◦C. After this time the mixture was
filtered off by a cannula system. PCl3 (0.745 g, 5.42 mmol) was
added to the solution of sodium triphenylsilanolate and the mix-
ture was stirred for 12 h at 60 ◦C. At the next step the content
was cooled to room temperature, THF was removed under reduced
pressure, and benzene was added. The suspension obtained was
warmed up to 65 ◦C and filtered off by cannula system, and
solvent was evaporated under reduced pressure. Subsequently,
Tris(triphenylsilyl)phosphite was washed twice with hexane and
dried under vacuum. Yield 4.37 g (94%).
Anal. calc. for C54H45O3PSi3 C 75.67; H 5.29; found C 75.72;
H 5.40. 1H NMR (300 MHz, C6D6, 300 K) ı (ppm) = 7.60 (d), 7.18
(m), 7.06 (t), (45H, o,m,p-Ph). 13C NMR (75.42 MHz, C6D6, 300 K) ı
(ppm) = 136.03; 136.01; 134.74; 130.19; 130.88; 128.12. 31P NMR
(121.47 MHz, C6D6, 300 K) ı (ppm) = 112.49. 29Si NMR (59.59 MHz,
C6D6, 300 K) ı (ppm) = 13.28 (d, JSi–P = 10 Hz).
2.2.2. Procedures for syntheses of tris(triorganosilyl)phosphites
(compounds 1–6)
2.2.2.1. Synthesis of phosphorussilsesquioxane (1). The solution of
Si7O9(OH)3(iOct)7 (POSS-iso-Octyl, POSS® = Polyhedral Oligomeric
Silsesquioxane) (5 g, 4.22 mmol) in 30 mL of dried and deoxidized
THF was added dropwise to a vigorously mix suspension of NaH
(0.608 g, 25.3 mmol) in 10 mL of THF at room temperature under
dry argon atmosphere over 20 min. The reaction was carry on for
24 h at room temperature. After this time the solution of sodium
POSS-iso-Oct-trisilanolate was filtered off by a cannula system.
PCl3 (0.562 g, 4.09 mmol) was added to the solution of sodium
POSS-iso-Oct-trisilanolate and the mixture was stirred for 24 h at
room temperature, and subsequently stirred for 2 h at 50 ◦C. At
the next step the reaction mixture was cooled to room temper-
ature, solvent was removed under reduced pressure, and hexane
was added. The suspension obtained was filtered off by a cannula
system and the solvent was evaporated under reduced pres-
sure. Phosphorussilsequioxane was obtained with a yield of 94%
(4.66 g).
2.2.6. Synthesis of tris(tri-tert-butoxysilyl)phosphite
Anal. calc. for C56H119O12PSi7 C 55.49; H 9.90; found C 58.58;
H 10.05. 1H NMR (300 MHz, C6D6, 300 K) ı (ppm) = 2.24 (bm, 7H,
–CH–); 1.8–0.8 (bm, 112H, H–). 13C NMR (75.42 MHz, C6D6, 300 K) ı
(ppm) = 54.79, 54.39, 53.91; 31.03, 30.08, 29.28; 25.47, 25.18, 24.85,
23.94. 31P NMR (121.47 MHz, C6D6, 300 K) ı (ppm) = 84.64.
P(OSi(OtBu)3)3 (5)
This compound was prepared in analogous way as com-
pound 2, starting from 5 g (19 mmol) of tri-tert-butoxysilanol
(Si(OH)(OtBu)3), 0.91 g (38 mmol) of NaH and 0.83 g (6.02 mmol)
of PCl3. After addition of PCl3 the mixture was stirred for 24 h at
55 ◦C. The suspension obtained was filtered off by a cannula system,
and then solvent was evaporated under reduced pressure giving
tris(tri-tert-butoxysilyl)phosphite as white solid. Yield 4.55 g (92%).
Anal. calc. for C36H81O12PSi3 C 52.65; H 9.94; found C 52.70; H
10.06. 1H NMR (300 MHz, C6D6, 300 K) ı (ppm) = 1.52 (81H, OtBu).
13C NMR (75.42 MHz, C6D6, 300 K) ı (ppm) = 74.89; 74.41; 74.16;
73.01; 72.86 (–O–CMe3); 31.2; 31.30; 31.32; 31.39; 31.67 (–Me).
31P NMR (121.47 MHz, C6D6, 300 K) ı (ppm) = 109.62.
2.2.3. Synthesis of tris(tri-iso-propylsilyl)phosphite P(OSiiPr3)3
(2)
The tri-iso-propylsilanol (A) (5 g, 28.7 mmol) was added drop-
wise to a vigorously mix suspension of NaH (1.00 g, 42 mmol) in
50 mL of THF at room temperature under dry argon atmosphere
over 20 min. The reaction was conducted for 24 h at room tem-
perature. Subsequently, the reaction mixture was filtered off by a
cannula system. PCl3 (1.24 g, 9.08 mmol) was added to the solu-
tion of sodium tri-iso-propylsilanolate and the mixture was stirred
for 24 h at 60 ◦C. At the next step, the content was cooled to room
temperature and the solvent was removed under reduced pressure,
then the pentane was added. The suspension obtained was filtered
off by a cannula system, and solvent was evaporated under reduced
pressure giving tris(tri-iso-propylsilyl)phosphite as colorless oil.
Yield 4.70 g (94%).
Anal. calc. for C27H63O3PSi3 C 58.85; H 11.52; found C 58.91;
H 11.61. 1H NMR (300 MHz, C6D6, 300 K) ı (ppm) = 1.21 (d, 54H,
–Me); 1.11, 1.04 (m, 9H, SiCHMe2). 13C NMR (75.42 MHz, C6D6,
300 K) ı (ppm) = 18.48, 18.45 (–Me), 13.88 (SiCHMe2). 31P NMR
(121.47 MHz, C6D6, 300 K) ı (ppm) = 110.18, 29Si NMR (59.59 MHz,
C6D6, 300 K) ı (ppm) = 15.23 (JSi–P = 14.66 Hz).
2.2.7. Synthesis of tri(tris(trimethylosiloxy)silyl)phosphite
P(OSi(OSiMe3)3)3 (6)
This compound was prepared analogously as described for
2, starting from 5 g (16 mmol) of Si(OH)(OSiMe3)3 (C), 0.57 g
(24 mmol) of NaH and 0.68 g (5.0 mmol) of PCl3. After addition
of PCl3 mixture was stirred for 24 h at 60 ◦C. The suspen-
sion obtained was filtered off by a cannula system, and then
the solvent was evaporated under reduced pressure giving
tri(tris(trimethylsiloxy)silylphosphite as colourless oil. Yield 4.59 g
(95%).
Anal. calc. for C27H81O12PSi12 C 33.57; H 8.45; found C 33.63; H
8.54. 1H NMR (300 MHz, C6D6, 300 K) ı (ppm) = 0.32 (s, 81H, –Me).
13C NMR (75.42 MHz, C6D6, 300 K) ı (ppm) = 2.36 (–Me). 31P NMR
(121.47 MHz, C6D6, 300 K) ı (ppm) = 111.73. 29Si NMR (59.59 MHz,
C6D6, 300 K, INEPT) ı (ppm) = 11.89 (JSi–P = 60.27 Hz).
2.2.4. Synthesis of tris(methyldiphenylsilyl)phosphite
P(OSiMePh2)3 (3)
This compound was prepared in analogous way as compound
2, starting from 3 g (14 mmol) of methyldiphenylsilanol (B), 0.67 g
(28 mmol) of NaH and 0.6 g (4.37 mmol) of PCl3. After addition of
PCl3 mixture was stirred for 24 h at 55 ◦C. The suspension obtained
was filtered off by a cannula system, and solvent was evaporated
under reduced pressure giving tris(methyldiphenylsilyl)phosphite
as white solid. Yield 2.67 g (91%).
Anal. calc. for C39H39O3PSi3 C 69.81; H 5.86; found C 69.88;
H 5.95. 1H NMR (300 MHz, C6D6, 300 K) ı (ppm) = 7.54 (m), 7.36
(m) (30H, o,m,p-Ph); 0.61 (s, 9H, SiMePh2). 13C NMR (75.42 MHz,
C6D6, 300 K) ı (ppm) = 137.44; 133.87; 129.46; 127.62 (–Ph); −0.44
(–Me). 31P NMR (121.47 MHz, C6D6, 300 K) ı (ppm) = −13.61. 29Si
NMR (59.59 MHz, C6D6, 300 K, INEPT) ı (ppm) = −7.10.
2.2.8. General procedure for synthesis of complexes (7–12)
Complexes 7–12 were synthesized under inert atmosphere by
reacting the calculated amounts of Karstedt’s catalysts and corre-
sponding silylphosphite 1–6 in molar ratio [Pt]:[P(OSi )3] = 1:1.02.
Reactions were conducted for 24 h at room temperature for com-
plexes 7–9, 11 and 12. After this time the mixtures were filtered off
by a cannula system and solvent was evaporated under vacuum for
24 h at 50 ◦C. Solid products were three times washed with pentane
by decantation at −70 ◦C.
2.2.9. Analytical data of platinum(0) complexes
2.2.9.1. Complex [Pt{ꢆ4-(H2C CHSiMe2)2O}{P(Si7O12(iOct)7}] (7).
Yield 1.21 g (98%). Anal. calc. for C66H143O13PPtSi9 C 48.82; H

108
I. Kownacki et al. / Applied Catalysis A: General 380 (2010) 105–112
Fig. 1. Anisotropic ellipsoid representation of complex 10. The ellipsoids are drawn
at 50% probability level, hydrogen atoms are omitted for clarity.
Fig. 2. Anisotropic ellipsoid representation of complex 11. The ellipsoids are drawn
at 50% probability level, hydrogen atoms are omitted for clarity.
8.88; found C 48.90; H 9.03. 1H NMR (300 MHz, C6D6, 300 K) ı
(ppm) = 2.43 (m), 3.4–2.8 (m) (6H, –CH CH2); 2.2 (bm, 7H, –CH–);
1.7–0.83 (bm, 112H, H-aliphatic); 0.53 (s), 0.516 (s) (6H, –Me);
−0.13(m), −0.25(m) (6H, –Me). 13C NMR (75.42 MHz, C6D6, 300 K)
ı (ppm) = 57.55, 57.25, 56.47, 55.84 (–CH CH2); 54.34, 53.90;
31.08, 30.08, 29.28; 25.46, 23.94; 1.44, −2.19, −2.04. 31P NMR
(121.47 MHz, C6D6, 300 K) ı (ppm) = 83.12 (JP–Pt = 6687.6 Hz).
−0.23, −0.35 (6H, –Me). 31P NMR (121.47 MHz, C6D6, 300 K) ı
(ppm) = 97.04 (JP–Pt = 6332.6 Hz).
2.2.9.4. Synthesis
of
complex
[Pt{ꢆ4-(H2C CHSiMe2)2O}
{P(OSiPh3)3}] (10). 15 mL of benzene was added to a Schlenk’s tube
containing 1.0 g (1.17 mmol) of compound 4. The resulting mixture
was warmed up to 50 ◦C to dissolve the phosphite. Subsequently,
7.48 g (1.15 mmol of Pt) solution of Karstedt’s catalyst (3% of Pt in
xylene) was added dropwise to the reaction mixture. The reaction
was conducted for 24 h at 50 ◦C on stirring the reaction mixture
with a magnetic stirrer. After this time solvent was evaporated
and the solid obtained was dried under vacuum. Crude complex
was washed three times with 5 mL of pentane and dried under
vacuum. Yield 1.35 g (95%).
2.2.9.2. Complex
[Pt{ꢆ4-(H2C CHSiMe2)2O}{P(OSiiPr3)3}]
(8).
Yield 1.63 g (98%). Anal. calc. for C35H81O4PPtSi5 C 45.08; H
8.76; found C 45.13; H 8.83. 1H NMR (300 MHz, C6D6, 300 K) ı
(ppm) = 3.13 (m), 2.61 (m) 2.40 (m) (6H, –CH CH2); 1.38(m),
1.20(s), 1.18(s) (63H, iso-Pr); 0.62 (s, 6H, SiMe2); 0.02 (s, 6H,
SiMe2). 13C NMR (75.42 MHz, C6D6, 300 K) ı (ppm) = 49.24 (s)
(d, JC–Pt = 168.13 Hz) 49.14 (d, JC–Pt = 168.13 Hz); 44.39 (s) (d,
JC–Pt = 107.08 Hz); 44.16 (s) (d, JC–Pt = 107.38 Hz) 18.68 (–Me); 14.57
(–CH(Me)2); 2.15, −1.41 (SiMe2). 31P NMR (121.47 MHz, C6D6,
300 K) ı (ppm) = 86.40 (JP–Pt = 6379.05 Hz).
Anal. calc. for C62H63O4PPtSi5 C 60.12; H 5.13; found C 60.17;
H 5.18. 1H NMR (300 MHz, C6D6, 300 K) ı (ppm) = 7.60 (d), 7.18
(t), 7.06 (t) (45H, o,m,p-Ph); 2.43 (m), 2.25(m) (6H, –CH CH2);
0.473 (s), 0.471 (s) (6H, –Me); −0.09 (6H, –Me). 13C NMR
(75.42 MHz, C6D6, 300 K) ı (ppm) = 136.18; 133.93; 130.45; 130.88;
128.13; 50.60 (d, JC–Pt = 6.6 Hz); 46.14 (d, JC–Pt = 17.58 Hz); 1.99,
1.95, −0.83. 31P NMR (121.47 MHz, C6D6, 300 K) ı (ppm) = 94.25
(JP–Pt = 6454.55 Hz).
2.2.9.3. Complex [Pt{ꢆ4-(H2C CHSiMe2)2O}{P(OSiMePh2)3}] (9).
Yield 0.75 g (98%). Anal. calc. for C47H57O4PPtSi5 C 53.64; H
5.46; found C 53.70; H 5.72. 1H NMR (300 MHz, C6D6, 300 K) ı
(ppm) = 7.58 (m), 7.37 (m) (30H, o,m,p-Ph); 2.80–3.80 (m) (6H,
–CH CH2); 0.62 (s, 9H, –SiPh2Me); 0.43, 0.42 (s) (6H, –Me);
2.2.9.5. Complex [Pt{ꢆ4-(H2C CHSiMe2)2O}{P(OSi(OtBu3)3}] (11).
Crude complex was washed three times with 3 mL of pentane at
minus 70 ◦C, and dried under vacuum. Yield 1.40 g (97%). Anal.
calc. for C44H99O13PPtSi5 C 43.94; H 8.30; found C 43.99; H 8.36.
1H NMR (300 MHz, C6D6, 300 K) ı (ppm) = 3.26 (m), 2.64 (m), 1.89
(m) (6H, –CH CH2); 1.35 (s), 1.34 (s), 1.32 (s), 1.31 (s), 1.28 (s),
1.27 (s) (81H, –OtBu); 0.313 (s), 0.310 (s) (6H, –Me); −0.26 (6H,
–Me). 13C NMR (75.42 MHz, C6D6, 300 K) ı (ppm) = 73.72; 48.62
(td, J = 73.0 Hz, J = 6.2 Hz); 42.98; (td, J = 56.2 Hz, J = 17.6 Hz); 31.85;
31.33; 1.76; 1.74; −1.05. 31P NMR (121.47 MHz, C6D6, 300 K) ı
(ppm) = 81.74 (JP–Pt = 6521.42 Hz).
Table 2
Selected geometrical parameters (distances in Å and angles in◦). X describes the
middlepoint of the double bond.
10
11
Pt–P
Pt–X
2.2.2405(8)
2.034(3)
2.043(3)
1.581(2)
1.584(2)
1.585(2)
1.655(2)
1.656(2)
1.660(2)
2.2444(13)
2.033(4)
2.040(3)
1.564(3)
1.583(3)
1.592(3)
1.632(3)
1.607(3)
1.633(3)
1.604(9)
P–O
O–Si
2.2.9.6. Complex
[Pt{ꢆ4-(H2C CHSiMe2)2O}{P(OSi(OSiMe3)3)3}]
ꢀSi–O(tBu)ꢁ
ꢀSi–C(ar)ꢁ
X–Pt–X
(12). Yield 1.34 g (98%). Anal. calc. for C35H99O13PPtSi14 C 31.20;
H 7.41; found C 31.27; H 7.46. 1H NMR (300 MHz, C6D6, 300 K)
ı (ppm) = 3.33 (m), 2.84 (m), 2.54 (m) (6H, –CH CH2); 0.62 (s,
6H, SiMe2), 0.31 (s, 81H, –SiMe3); 0.14 (s, 6H, SiMe2). 13C NMR
1.865(5)
133.01(13)
113.54(10)
113.45(9)
131.4(2)
114.21(12) 114.28(16)
X–Pt–P

I. Kownacki et al. / Applied Catalysis A: General 380 (2010) 105–112
109
Table 3
Catalytic properties of the new platinum(0) complexes in cross-linking of the model mixture of vinyl-terminated polydimethylsiloxane and polyhydromethylsiloxane in the
presence of [Pt] = 10−5 mol.
Catalysts
Pt/DAM
Pot-life at 25 ◦
C
Curing time at 120 ◦
C
DSC analysis
Average peak
Average enthalpy
of reaction (J/g)
temperature (◦C)
111.7
−20.35
7
12 h
1 min 30 s
96.6
−8.89
8
9
30 days (no curing)
3 min
164.5
105.6
−21.93
−5.16
30 min
Not measured
10
40 days (no curing)
2 min
124.4
−22.50
−20.58
11
30 days (no curing)
2 min
133.65
12
30 days (no curing)
5 min
105.2
−21.48
Reaction conditions (DSC): [HSi]:[Pt] = 1:10−5, temperature rate—10 ◦C/min, helium.
(75.42 MHz, C6D6, 300 K) ı (ppm) = 48.67 (s) (d, JC–Pt = 168.43 Hz),
48.58(s) (d, JC–Pt = 168.38 Hz); 44.72 (s) (d, JC–Pt = 111.30 Hz);
44.49 (d, JC–Pt = 110.85 Hz); 2.70 (–SiMe3); 2.07, 2.00; 1.67, 1.63
(SiMe2). 31P NMR (121.47 MHz, C6D6, 300 K) ı (ppm) = 87.21
(JP–Pt = 6415.73 Hz).
reaction mixture on the hot plate until getting the dry cured mate-
rial.
The pot-life time was measured from the moment of Pt-catalyst
addition to mixture of mentioned above polysiloxanes up to the
total curing of the initial mixture at room temperature. Typically,
the pot-life is defined as the time when a viscosity of the catalyzed
mixture is doubled.
2.3. General procedure of curing time and pot-life determination
The calculated amounts a well-defined Pt complex were added
to 4.00 g mixture of vinyl-terminated polydimethylsiloxane and
polyhydromethylsiloxane. The catalyzed mixture was stirred for
30 min. The curing process of the polysiloxanes mixture was per-
formed in an aluminum vessel (15 mm × 20 mm × 7 mm) using a
hot plate heated up to 120 ◦C. The curing time was measured
from the moment of placing the aluminum vessel with liquid
3. Results and discussion
As we discussed previously [24f–h], the key step of Karst-
edt’s catalyst inhibition process is the Pt–P bond formation by
coordination of phosphites ligand, which leads to the forma-
tion of a new complex. The complex formed is responsible for
a change of Pt catalytic activity in cross-linking of polysiloxane

110
I. Kownacki et al. / Applied Catalysis A: General 380 (2010) 105–112
Fig. 4. DSC curve of the curing process performed in the presence of 10 ppm of
complex 11.
depends on the electronic properties as well as on the steric hin-
drance of coordinated ligands. The hindrance effect is produced
by the size of substituents bonded to the donating atom, but ␴-
donation properties as well as back-bonding interaction of this
atom depend strongly on electronic properties of the substituents.
The influence of electronic properties of phosphorus ligands on
the metal centre was widely discussed in textbooks [33]. We
have chosen the values of chemical shift in 31P NMR spectra as
benchmark measure of the phosphite electronic properties. The
data collected for organosubstitued phosphites show that the 31P
NMR chemical shifts are in the range of 127–148 ppm for aryl
derivatives and 137–145 ppm for aliphatic derivatives [24h]. The
phosphites studied, whose chemical shifts were nearly 130 ppm for
arylphosphites and 140 ppm for alkylphosphites, appeared conve-
nient ligands controlling platinum catalytic activity in the curing
process. The analysis of NMR data encouraged us to look for other
phosphites with bulky substituents and having low values of 31P
NMR chemical shift. Reported by Feher phosphorosilsesquioxanes
[34] well satisfy the above requirements (31P NMR chemical shift
of the phosphorus nuclei at 86.12 ppm, sufficiently large Tolman’s
cone angle of 167◦, which is similar to PPh3). Phosphorus-iso-
octylsilsesquioxane (1) was synthesized according to the method
proposed in [24f–h]. We have looked also for other silicon con-
taining phosphites, cheapest and easier to produce, which could
be used as efficient inhibitors of Karstedt’s catalyst or ligands of
new Pt complexes. Previously reported method for the synthesis of
tris(triorganosilyl)phosphites involve use of triorganochlorosilane
as a substrate, which leads to formation of undesirable and diffi-
cult to remove by-products. To eliminate this problem, we have
used for the first time sodium silanolates for the preparation of
various tris(triorganosilyl)phosphites. Proceeding according to the
new method presented in [24f–h] and using simple silanols instead
of POSS-iso-octylsilsesquioxanes, new silylphosphites (2–6) were
synthesized, and well characterized by NMR method [35]. We
affirmed that 31P NMR chemical shifts values for phosphorus atom
surrounded by organosilicon substituents were in the expected
range of 109–112.5 ppm for compounds 2, 4–6. Interestingly, the
31P NMR chemical shift for compound 3 had exceptionally low
value of −13.61 ppm. In the next step all the compounds obtained
were employed for the preparation of new Karstedt’s based plat-
inum complexes (7–12) [35], according to the procedures described
previously [24f–h]. The new platinum compounds obtained were
fully characterized by NMR technique as well as structures of 10
and 11 were determined by X-ray analysis.
Fig. 3. DSC curves of the curing process: (a) catalyzed by 10 ppm of the complex 10;
(b) catalyzed by 10 ppm of the complex 10—after 10 days of storage; (c) catalyzed
by Karstedt’s/DAM catalytic system (curves [1]—100 ppm of Pt, [2]—70 ppm of Pt,
[3]—50 ppm of Pt, [4]—25 ppm of Pt)
fluids by hydrosilylation. We also concluded that separately syn-
thesized, well-defined complexes of Pt with organophosphites
might be employed as effective catalysts of the cross-linking pro-
cess, since their catalytic activity at room temperature is very
low; consequently we developed the one-part polysiloxane com-
pound with relatively long storage time. Results presented in the
above-mentioned publication showed that it is possible to adjust
catalytic activity of platinum centre in hydrosilylation reaction
by controlling bulkiness and electronic properties of the sub-
stituents at phosphorous center [24h]. Unexpected result obtained
for P(OC6F5)3 encouraged us to look for an explanation of such phe-
nomenon. It is commonly known that reactivity of a metal centre
Figs. 1 and 2 show the perspective views of complexes 10 and
11; Table 2 presents some selected geometrical parameters. The

I. Kownacki et al. / Applied Catalysis A: General 380 (2010) 105–112
111
coordination of Pt is triangular; the Pt atom is displaced from the
plane made by three points: P1 atom and the middlepoints of the
double bonds (X1 and X2) only by 0.002(1) Å in 10. However, for
11 this displacement is more significant, 0.054(3) Å. The distances
Pt–X and Pt–P take typical mean values of 2.040 and 2.242 Å, respec-
tively. The conformation of six-membered organometallic ring
Pt–X–Si–O–Si–X might be described as flattened, distorted chair.
In both complexes, the 1,3-divinyltetramethyldisiloxane fragment
has approximate Cs symmetry, with the mirror plane passing
through the oxygen atom. The four carbon atom of two vinyl groups
are in a good approximation planar, and the platinum atom in both
cases lies almost exactly in the plane which makes small dihedral
angle of 2–3◦ with the coordination plane. It might be noted that
(P)–O–Si distances in 10, where Si is further connected with phenyl
rings are significantly longer than in 11, where there are tert-butoxy
groups. The largest flexibility is observed in P–O–Si angles (changes
as large as 30◦). The crystal packing is determined mainly by close
packing requirement and van der Waals interactions.
Scheme 1.
On the other hand, relatively short pot-life observed for the sil-
icone formulations catalyzed by complexes 7 and 9 as well as low
enthalpy of the curing process might be explained, by not enough
bulky ligands coordinated to the platinum centre leading in conse-
quence to hydrosilylation reaction at room temperature.
4. Conclusions
Various tris(triorganosilyl)phosphites with bulky silyl sub-
stituents were synthesized and used as efficient ligands coordi-
nated to the platinum centre. New, well-defined Pt(0)-(DVTMDS)-
tris(triorganosilyl)phosphites complexes (7–12) were synthesized
and characterized by NMR spectroscopy (X-ray structure of com-
plexes 10 and 11 were also solved). The curing studies of the model
polysiloxane formulation proved that new platinum(0) complexes
(8, 10–12) showed a very low catalytic activity at room tempera-
ture giving sufficiently long pot-life for the catalyzed silicone (up
to 40 days) and efficiently catalyze silicone cross-linking process at
elevated temperature. The high catalytic activity of the now com-
plexes was confirmed by the model system curing studies and DSC
method. The selected complexes are promising candidates as novel
Pt(0) catalysts for commercial one-part silicone formulations.
The catalytic properties of the new platinum complexes were
examined in a cross-linking of the model mixture of vinyl-
terminated polydimethylsiloxane and polyhydromethylsiloxane.
Results, which include a pot-life at 25 ◦C, curing time at 120 ◦C as
well as DSC analysis, are compiled in Table 3.
The complexes obtained appear efficient and very promising
catalysts for vinyl-terminated polydimethylsiloxane cross-linking
process. Particularly exciting results were obtained for complexes
8, 10–12. These complexes showed very low catalytic activity at
room temperature (the catalyzed polysiloxane formulation did not
show any symptoms of cure for at least 40 days), provided relatively
short curing time at 120 ◦C, as well as average value of enthalpy (J/g)
and average peak temperature were approximately similar to those
obtained for the commercial Pt/DAM catalytic system (Table 3).
Exemplary DSC curves (Figs. 3a and 4) recorded for the curing
process performed in the presence of 10 ppm catalysts 10 and 11
show that the cross-linking process occurs at lower temperature
than the reaction catalyzed by 25 ppm of Pt(0) as Karstedt’s catalyst
with DAM as inhibitor (Fig. 3c). The DSC curves of the cross-linking
process in the presence of the new complexes 10 and 11 showed
sharper exothermal cure peaks, than that one recorded for the
process catalyzed by 25 ppm of Pt(0)-Karstedt’s/DAM. These peaks
were comparable to the cure peak recorded at 100 ppm of Pt(0)-
Karstedt’s/DAM (Fig. 3c).; therefore the new complexes appeared
more efficient then the commercially used Karstedt’s/DAM cat-
alytic system. It is also essential that the new complexes are stable
as formulated into the polysiloxane mixture and their catalytic
activity is not affected by a long storage time. Curing tests showed
that the activity of complex 10 added to polysiloxanes mixture does
not change after 10 days of storage time. This result was addition-
ally confirmed by DSC measurement (Fig. 3a and b), which showed
that average peak temperature as well as the average enthalpy of
cross-linking process for polysiloxane system catalyzed by 10 did
not change after 10 days of storage.
The above results suggest that introduction of phosphites
with bulky organosilicon substituents into platinum coordination
sphere makes the metal centre less accessible to organosil-
icon polymeric reactants at room temperature. Additionally,
more electron-donating character of the triorganosilicon phos-
phites ligands in comparison with that of organosubstituted
phosphites might stabilize a six-membered organometallic ring
Pt–X–Si–O–Si–X (Scheme 1) by increasing of back-bonding
interaction between the platinum centre and vinyl groups of
1,3-divinyltetramethyldisiloxane ligand. As a consequence, the
equilibrium between both forms of the complex can be shifted to
the left side of the equation; therefore the new complexes are inac-
tive at storage conditions and provide a long pot-life for catalyzed
silicone.
Acknowledgment
The financial support from Momentive Performance Materials
(formerly GE Silicones) is gratefully acknowledged.
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