Platina-β-diketones as catalysts for hydrosilylation and their reactivity towards hydrosilanes

Article abstract of DOI:10.1016/j.jorganchem.2009.07.020

The platina-β-diketones [Pt₂{(COMe)₂H}₂(μ-Cl)₂] (1), [PPh₄][Pt{(COMe)₂H}Cl₂] (2) and [Pt{(COMe)₂H}-(acac)] (3) were found to catalyze the hydrosilylation of alkynes (h

Full text of DOI:10.1016/j.jorganchem.2009.07.020

Journal of Organometallic Chemistry 694 (2009) 3548–3558
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Platina-b-diketones as catalysts for hydrosilylation and their reactivity
towards hydrosilanes
*
Sebastian Schwieger, Renate Herzog, Christoph Wagner, Dirk Steinborn
Institut für Chemie, Martin-Luther-Universität Halle-Wittenberg, Kurt-Mothes-Str. 2, 06120 Halle (Saale), Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
The platina-b-diketones [Pt2{(COMe)2H}2(l-Cl)2] (1), [PPh4][Pt{(COMe)2H}Cl2] (2) and [Pt{(COMe)2H}-
(acac)] (3) were found to catalyze the hydrosilylation of alkynes (hex-1-yne, hex-2-yne, hex-3-yne)
Received 19 May 2009
Accepted 7 July 2009
Available online 14 July 2009
and alkenes (hex-1-ene, styrene, trimethylvinylsilane) with methyldiphenylsilane (nsilane:nsubstrate
:
nPt = 3000:3000:1, T = 27 °C, in C6D6). The comparison with the well-established catalysts from Speier
(4) and Karstedt (5) exhibited up to twice as high activities for catalyst 1 and comparable regioselectiv-
ities. To get insight into the mechanism of the hydrosilylation, Si–H oxidative addition reactions towards
the dinuclear platina-b-diketone 1 have been explored. Reactions of 1 with 2-picolyl substituted hydro-
silanes of the type N SiMe2H and N SiMeH N resulted in decomposition with the formation of plati-
num black, only. On the other hand, the analogous reaction with the 8-quinolyl substituted silane of
the type N SiMeH N was found to proceed under loss of H2 with the formation of a diacetyl(silyl)plat-
inum(IV) complex [Pt(COMe)2Cl(N SiMe N-j2N,N0,jSi)] (23). DFT calculations gave insight into the rea-
son for this different reactivity and into the course of reaction. For comparison, the reaction of 1 with
bis(2-picolyl)amine was performed resulting under proton shift in the sense of an oxidative addition
Keywords:
Hydrosilylation
Platina-b-diketones
Silyl platinum(IV) complexes
Acetyl platinum(IV) complexes
Chelate assisted oxidative addition
DFT calculations
reaction in the formation of the diacetyl(hydrido)platinum(IV) complex [Pt(COMe)2Cl(N NH N-j
3N,
N0,N00)] (25). The complexes 23 and 25 were fully characterized spectroscopically (1H, 13C, 195Pt, 29Si
NMR, IR) and by single-crystal X-ray structure determinations.
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
intramolecular hydrogen bond (1–3, Scheme 1). Because these type
of complexes can be formally derived from organic b-diketones in
For decades catalytic hydrosilylation reactions have played an
important role in synthetic organic chemistry by facilitating the
introduction of silicon functionalities to a broad variety of unsatu-
rated compounds [1]. In polymer chemistry hydrosilylations are
broadly used, above all, for cross coupling reactions of silicones
[1a,2]. With the help of a wide range of catalytic systems it is pos-
sible to perform these reactions under mild reaction conditions.
Most widely used are homogeneous platinum containing catalytic
systems such as Speier’s catalyst (hexachloroplatinic acid in iso-
propanol, 4) [3] and Karstedt’s catalyst ([Pt2{(CH2@CHSiMe2)2O}3],
5) [4]. Furthermore, a wide range of other platinum complexes in
all typical oxidation states (0, II, IV) can be used as precatalysts.
Catalytic intermediates in most cases are organometallic Pt(0)/
Pt(II) complexes, whereas in selected cases the catalytic cycle has
been described via Pt(II)/Pt(IV) intermediates [5]. Although con-
vincing, no direct proof of the Pt(IV) intermediates has been
provided.
their enolic form by replacing the central methine moiety with a
metal fragment, they are called metalla-b-diketones [6]. Among
the metalla-b-diketones known, the platina-b-diketones in Scheme
1 possess unique properties. Due to their 16 valence electrons, they
easily undergo oxidative addition and reductive elimination reac-
tions [7]. Because of this, it can be expected that these complexes
are capable of catalyzing hydrosilylation reactions. Here we report
on the catalytic potential of the platina-b-diketones shown in
Scheme 1 in hydrosilylations of non-activated alkynes and alkenes.
Furthermore, we have investigated the reactivity of the platina-b-
diketone 1 towards hydrosilanes as the oxidative addition of
hydrosilanes to the platinum center is expected to be the first step
in the catalytic cycle [8].
2. Experimental
2.1. General procedure
We have previously prepared platinum(II) complexes that con-
tain hydroxycarbene and acetyl ligands, stabilized through an
All reactions and manipulations were carried out under an ar-
gon atmosphere using standard Schlenk techniques. Benzene,
hexadeuterobenzene, toluene, n-pentane and thf were dried over
Na/benzophenone, dichloromethane was dried over CaH2,
* Corresponding author. Tel.: +49 345 55 25620; fax: +49 345 55 27028.
E-mail address: steinborn@chemie.uni-halle.de (D. Steinborn).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.07.020

S. Schwieger et al. / Journal of Organometallic Chemistry 694 (2009) 3548–3558
3549
2JSi,H = 8.1 Hz, 2H, SiCH2), 6.94 (t, JH,H = 6.3 Hz, 2H, 3,5-py), 7.47
3
O
3
4
3
Cl
Cl
O
O
O
O
O
Cl
Pt Pt
Cl
O
O
(td, JH,H = 7.6 Hz, JH,H = 1.9 Hz, 1H, 4-py), 8.40 (d, JH,H = 4.8 Hz,
[PPh4]
H
H
Pt
H
Pt
H
1
1H, 6-py). 13C NMR (50 MHz CDCl3): d ꢀ2.0 (s + d, JSi,C = 51.6 Hz,
O
O
1
SiCH3), 30.0 (s + d, JSi,C = 44.0 Hz, SiCH2), 118.8 (s, 5-py), 121.8 (s,
3-py), 135.4 (s, 4-py), 148.7 (s, 6-py), 161.0 (s, 2-py). 29Si NMR
(99 MHz, CDCl3): d 2.3 (s). GC–MS: m/z 165, 150, 120, 106, 93,
73, 65, 43, 29, 15.
1
2
3
Reference catalysts:
Me2 Me2
Si
Si
2.2.4. Bis(2-picolyl)methylsilane (20)
O
Yield: 5.1 g (30%). Kp.: 110–114 °C (0.08 Torr). 1H NMR
Pt
SiMe2
Pt
Me2Si
H2[PtCl6]/i-PrOH
3
(500 MHz, CDCl3): d 0.04 (d, JH,H = 3.66 Hz, 3H, CH3), 2.42 (m,
Me2Si
SiMe2
O
O
4H, CH2), 4.09 (m, 1H, SiH), 6.95 (m, 2H, 5-py), 6.97 (m, 2H, 3-
py), 7.46 (m, 2H, 4-py), 8.41 (m, 2H, 6-py). 13C NMR (125 MHz,
CDCl3): d ꢀ6.4 (s, CH3), 25.8 (s, CH2), 119.6 (s, 5-py), 122.5 (s, 3-
py), 136.0 (s, 4-py), 149.2 (s, 6-py), 160.3 (s, 2-py). 29Si NMR
(99 MHz, CDCl3): d ꢀ8.4 (s).
4
5
(Speier's catalyst)
(Karstedt's catalyst)
Scheme 1.
2.2.5. Bis(2-picolyl)dimethylsilane (21)
Yield: 4.7 g (38%). Kp.: 85–88 °C (0.04 Torr). 1H NMR (400 MHz,
CDCl3): d ꢀ0.07 (s, 6H, SiCH3), 2.32 (s, 4H, CH2), 6.87–6.91 (m, 4H,
3,5-py), 7.38–7.41 (m, 2H, 4-py), 8.35–8.36 (m, 2H, 6-py). 13C NMR
(125 MHz, CDCl3): d ꢀ3.5 (s, CH3), 28.4 (s, CH2), 119.2 (s, 5-py),
122.3 (3-py), 135.7 (s, 4-py), 148.9 (s, 6-py), 160.6 (s, 2-py). 29Si
NMR (99 MHz, CDCl3): d 3.5 (s).
isopropanol with Na, and all solvents were freshly distilled prior
use. Hexachloroplatinic acid was available from m&k GmbH
(47.4% Pt). The platina-b-diketones [Pt2{(COMe)2H}2(l-Cl)2] (1)
[9], [PPh4][Pt{(COMe)2H}Cl2] (2) and [Pt{(COMe)2}(acac)] (3) [10]
as well as 8-bromoquinoline [11] and bis(8-quinolyl)methylsilane
(22) [12] were prepared according to known procedures. All other
substrates were commercially available and used as received. 1H,
13C, 29Si and 195Pt NMR spectra were recorded on Varian Gemini
200 and Unity 500 spectrometers. Chemical shifts are relative to
solvent signals (CDCl3, dH 7.24, dC 77.0; CD2Cl2, dH 5.32, dC 53.8;
C6D6, dH 7.15, dC 128.0) as internal references; d(29Si) and d(195Pt)
are relative to external SiMe4 (dSi 0.0) and H2[PtCl6] in D2O (dPt
0.0), respectively. Assignments of NMR signals, if necessary, were
revealed by means of NMR correlation experiments. Microanalyses
were performed in the Microanalytical Laboratory of the University
of Halle using a CHNS-932 (LECO) as well as a VARIO EL (Elemen-
taranalysensysteme) elemental analyzer. IR spectra were recorded
on a Mattson 5000 Galaxy FT-IR spectrometer using CsBr or KBr
pellets and a Tensor 27 FT-IR spectrometer using an ATR sampler,
respectively.
2.2.6. [Pt(COMe)2Cl{(C9H6N)2SiMe-j2N,N0,jSi}] (23)
At ꢀ60 °C a solution of bis(8-quinolyl)methylsilane (22, 98 mg,
0.33 mmol) in thf (5 ml) was added dropwise to a solution of
the platina-b-diketone [Pt2{(COMe)2H}2(l-Cl)2] (1, 108 mg, 0.17
mmol) in thf (5 ml). The solution was warmed to room tempera-
ture with stirring within 30 min and stirred at that temperature
for further 30 min. Then the volume of the resulting reaction mix-
ture was reduced in vacuo (1 ml) and diethyl ether (16 ml) was
added. The precipitate was filtered, washed with diethyl ether
(3 ꢁ 5 ml) and dried in vacuo. Yield: 80 mg (40%). Tdec: 107–
108 °C. Anal. Calc. for C23H21ClN2O2PtSi (616.04): C, 44.84; H,
3.44. Found: C, 44.86; H, 3.78%. 1H NMR (500 MHz, CD2Cl2): d
3
1.14 (s + d, JPt,H = 22.7 Hz, 3H, SiCH3), 2.25 (s (br), 6H, COCH3),
3
3
7.49 (dd, JH,H = 5.1 Hz, JH,H = 8.1 Hz, 2H, 3-QuinH), 7.55 (dd,
3JH,H = 7.4 Hz, JH,H = 7.4 Hz, 2H, 6-QuinH), 7.75 (d, JH,H = 8.0 Hz,
3
3
2.2. Preparations
3
2H, 5-QuinH), 8.11 (d, JH,H = 6.7 Hz, 2H, 4-QuinH), 8.21 (d,
3JH,H = 8.0 Hz, 2H, 7-QuinH), 10.33 (d (br), JH,H = 3.8 Hz, 2H, 2-
3
2.2.1. General procedure for the synthesis of 2-picolyl silanes
The synthesis was adapted from previously published proce-
dures [13]. At ꢀ78 °C n-butyllithium in n-hexane (1.6 M, 64 ml,
102 mmol) was added dropwise to 2-picoline (10 ml, 102 mmol)
in thf (200 ml). The resulting red suspension was stirred at room
temperature for 1 h. Afterwards, the corresponding chlorosilanes
(102 mmol) and dichlorosilanes (51 mmol), respectively, in thf
(50 ml) were added dropwise within 2 h. The volumes of the
resulting reaction mixtures were reduced in vacuo (20 ml) and tol-
uene (20 ml) was added. Then, the lithium chloride was filtered
and washed with toluene (3 ꢁ 5 ml). From the combined solutions
the solvents were evaporated under reduced pressure and the res-
idue was distilled in vacuo.
QuinH). 13C NMR (125 MHz, CD2Cl2): d ꢀ7.8 (s, SiCH3), 41.0 (s + d,
2JPt,C = 194.9 Hz, COCH3), 122.7 (s, 3-QuinC), 128.0 (s, 6-QuinC),
129.7 (s, 4a-QuinC), 129.9 (s, 4-QuinC), 136.6 (s + d, JPt,C = 24.2 Hz,
2
7-QuinC), 140.0 (s, 5-QuinC), 142.0 (s + d, JPt,C = 43.5 Hz, 8a-
QuinC), 151.5 (s + d, JPt,C = 33.3 Hz, 8-QuinC), 152.7 (s, 2-QuinC)
1
200.9 (s + d, JPt,C = 991.8 Hz, PtC). 29Si NMR (99 MHz, CD2Cl2): d
1
13.7 (s + d, JPt,Si = 1233 Hz). 195Pt NMR (107 MHz, CD2Cl2): d
1
ꢀ2078 (s + d, JPt,Si = 1245 Hz). IR (ATR):
m 3049 (w), 2960 (w),
2905 (w), 2055 (w), 1643 (s), 1588 (m), 1567 (m), 1495 (m),
1416 (m), 1373 (m), 1333 (m), 1301 (m), 1244 (m), 1229 (m),
1103 (s), 1082 (s), 1024 (m), 996 (m), 931 (m), 844 (s), 787 (s),
766 (s), 730 (s), 589 (s), 550 (m), 446 (s), 414 (s), 388 (s), 227 (s),
208 (s) cmꢀ1
.
2.2.2. (2-Picolyl)dimethylsilane (18)
Yield: 3.5 g (23%). Kp.: 47–50 °C (6 Torr). 1H NMR (200 MHz,
2.2.7. Reaction of [Pt2{(COMe)2H}2(
C5H4N)CH2]2NH
l-Cl)2] (1) with [(2-
3
3
CDCl3): d 0.05 (d, JH,H = 3.6 Hz, 6H, CH3), 2.37 (d, JH,H = 3.3 Hz,
2H, CH2), 3.98 (m, 1H, SiH), 6.94 (m, 2H, 3,5-pyH), 7.31–7.60 (m,
1H, 4-pyH), 8.40 (m, 1H, 6-pyH). 13C NMR (50 MHz, CDCl3): d
ꢀ4.5 (s, CH3), 27.5 (s, CH2), 119.3 (s, 5-pyC), 122.2 (s, 3-pyC),
135.9 (s, 4-pyC), 149.1 (s, 6-pyC), 160.8 (s, 2-pyC).
At ꢀ75 °C bis(2-picolyl)amine (139 mg, 0.700 mmol) was added
by means of a syringe to a solution of the platina-b-diketone 1
(222 mg, 0.350 mmol) in dichloromethane (2 ml). Then the reac-
tion mixture is warmed to room temperature within 30 min while
stirring. Afterwards, n-pentane (10 ml) is carefully added on top of
the reaction mixture by condensation. Colorless crystals could be
obtained from this mixture at ꢀ40 °C after 12 h that were filtered
and washed with n-pentane (2 ꢁ 10 ml) and dried in vacuo. The
2.2.3. (2-Picolyl)trimethylsilane (19)
Yield: 4.2 g (25%). Kp.: 41–44 °C (5 Torr). 1H NMR (200 MHz,
2
CDCl3):
d
0.00 (s + d, JSi,H = 6.5 Hz, 9H, SiCH3), 2.32 (s + d,

3550
S. Schwieger et al. / Journal of Organometallic Chemistry 694 (2009) 3548–3558
product was recrystallized from dichloromethane/n-pentane
(2 ml/10 ml). Yield: 265 mg (73%). Two products with an approx.
ratio of 9:1 are formed. Main product: 1H NMR (500 MHz, CDCl3):
were refined isotropically and their positions were included in
the models in calculated positions using the riding model.
d
ꢀ17.74 (s + d, 1JPt,H = 1579.3 Hz, 1H, PtH), 2.62 (s + d,
2.4. Computational details
3JPt,H = 33.4 Hz, 3H, COCH3 trans to NHR2), 3.07 (s + d,
3JPt,H = 26.8 Hz, 3H, COCH3 trans to py), 4.44 (d, JH,H = 17.9 Hz,
DFT calculations of compounds were carried out by the GAUSSIAN
03 program package [15] using the hybrid functional B3LYP [16].
The 6-311G(d,p) basis sets as implemented in GAUSSIAN 03 were em-
ployed for main group atoms. The valence shell of platinum has
been approximated by a split valence basis set too; for its core
orbitals an effective core potential in combination with consider-
ation of relativistic effects has been used [17]. The appropriateness
of the functional in combination with the basis sets and effective
core potential used for reliable interpretation of structural and
energetic aspects of related platinum complexes has been demon-
strated [18,19]. All systems were fully optimized without any sym-
metry restrictions if not stated otherwise explicitly. The resulting
geometries were characterized as equilibrium structures by the
analysis of the force constants of normal vibrations. Solvent effects
were considered according to the polarized continuum model as
implemented in GAUSSIAN 03 [20]. The AIM analyses were performed
using the program package AIMPAC as provided by Bader et al. [21].
1
1
1H, CHHendo), 4.74 (d, JH,H = 17.3 Hz, 1H, C0HHendo), 4.94 (dd,
1JH,H = 17.9 Hz, JH,H = 7.3 Hz, 1H, CHHexo), 5.13 (dd, JH.,H = 17.3 Hz,
3
1
3JH,H = 6.3 Hz, 1H, C0HHexo), 7.24–7.26 (m, 1H, 50-pyH), 7.35–7.38
3
3
(m, 1H, 5-pyH), 7.47 (d, JH,H = 7.8 Hz, 3-pyH), 7.62 (d, JH,H = 30-
3
pyH), 7.76–7.81 (m, 2H, 4-pyH/40-pyH), 8.46 (d, JH,H = 5.2 Hz, 1H,
3
3
60-pyH), 8.62 (dd, JH,H = 7.3 Hz, JH,H = 6.3 Hz, 1H, NH), 8.99 (d,
3JH,H = 5.5 Hz, 1H, 6-pyH). 13C NMR (50 MHz, CDCl3): d 46.6 (s + d,
2JPt,C = 250.9 Hz, COCH3 trans to NHR2), 47.1 (s + d, 2JPt,C = 249.1 Hz,
COCH3 trans to py), 59.8 (s, CH2), 61.2 (s, C0H2), 122.8 (s, 3-pyC),
123.7 (s, 30-pyC), 124.3/124.4 (s/s, 5-pyC/50-pyC), 139.4/139.6 (s/
s, 4-pyC/40-pyC), 148.3/148.6 (s/s, 6-pyC/60-pyC), 160.4/160.6 (s/s,
1
2-pyC/20-pyC), 193.5 (s + d, JPt,C = 836.1 Hz, COMe), 200.9 (s + d,
1JPt,C = 840.5 Hz, COMe). Side product: 1H NMR (200 MHz, CDCl3):
1
3
d ꢀ19.28 (s + d, JPt,H = 1529.6 Hz, 1H), 2.17 (s + d, JPt,H = 31.3 Hz,
3
3H, COCH3), 2.87 (s + d, JPt,H = 26.9 Hz, 3H, COCH3). 2-Picolyl
groups trans to the acetyl ligand are marked by a dash.
2.5. Catalytic experiments
2.3. X-ray crystal structure determinations
All hydrosilylation reactions were carried out in C6D6 under ar-
gon atmosphere in NMR tubes that were sealed by melting. At
ꢀ78 °C the NMR tube was loaded by means of syringes with the
Suitable crystals for X-ray diffraction analyses of complexes
23ꢂCH2Cl2 and 25ꢂCH2Cl2 have been obtained from dichlorometh-
ane solutions after addition of diethyl ether. Intensity data were
collected on a STOE-IPDS diffractometer using graphite-monochro-
solvent (C6D6, 250 ll), the two substrates (methyldiphenylsilane
and alkyne/olefin), the catalyst solution and, finally, an additional
matized Mo Ka radiation (k = 0.71073 Å) at 220(2) K. A summary
amount of the solvent (250 l). If the catalyst was added in the so-
l
of the crystallographic data, the data collection parameters and
the refinement parameters is given in Table 1. Absorption correc-
tions were applied semiempirically (Tmin./Tmax.: 0.23/0.48, 23;
0.13/0.40, 25). The structures were solved by direct methods with
SHELXS-97 and refined using full-matrix least-squares routines
against F2 with SHELXL-97. [14] All non-hydrogen atoms were re-
fined with anisotropic displacement parameters. Hydrogen atoms
lid state, it was added to the NMR tube first, followed by the addi-
tion of all solutions. The course of the reactions was monitored by
1H NMR spectroscopic measurements at 15 min intervals during
the first 4 h and every 60 min for the following 6 h. Additional
measurements have been undertaken if the reaction was not com-
plete after this time. The product signals were assigned using 1H,
13C and correlated NMR spectroscopic methods. For kinetic analy-
ses, the sum of the integrals over all aromatic 1H NMR signals were
used as internal standard.
Table 1
Crystallographic and data collection parameters for complexes 23 and 25.
Stock solutions of the catalysts were prepared under an argon
atmosphere and stored at ꢀ40 °C. The dinuclear platina-b-diketone
23ꢂCH2Cl2
25ꢂCH2Cl2
[Pt2{(COMe)2H}2(
l
-Cl)2] (1, 1.7 ꢁ 10ꢀ5 mol, 11 mg) was dissolved
Empirical formula
Mr
Crystal system
Space group
a (Å)
C23H21ClN2O2PtSiꢂCH2Cl2 C16H19ClN3O2PtꢂCH2Cl2
in C6D6 (500
l
l). Speier’s catalyst (4) was prepared by dissolving
700.97
Orthorhombic
P212121
11.1963(9)
10.4562(7)
22.353(2)
90
90
90
2616.9(4)
4
600.81
hexachloroplatinic acid (50.7 ꢁ 10ꢀ5 mol, 217 mg) in isopropanol
Triclinic
P1
ꢀ
(4 ml). Karstedt’s catalyst (5) was obtained from Aldrich as a solu-
8.4675(8)
10.1020(9)
14.270(1)
107.38(1)
94.06(1)
110.24(1)
1072.1(2)
2
tion
of
platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane
b (Å)
c (Å)
complex in xylene (Pt 2%). The monomeric platina-b-diketones
[PPh4][Pt{(COMe)2H}] (2) and [Pt{(COMe)2H}(acac)] (3) have been
added as solids due to low solubility in common solvents and/or
decomposition reactions in suitable solvents.
In a typical experiment a molar ratio of unsaturated sub-
strate:methyldiphenylsilane:platinum of 3000:3000:1 has been
employed using 0.88 mmol of hexynes and 0.81 mmol of olefins,
respectively, and the requisite amounts of methyldiphenylsilane
and catalyst.
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (g cmꢀ1
)
1.779
1.861
l
(Mo K
F(0 0 0)
h range (°)
a
) (mmꢀ1
)
5.738
6.933
1360
578
2.03–25.98
17 708
5065 (0.054)
2.27–25.00
7616
3464 (0.069)
No. of reflections collected
No. of independent
2.6. NMR data of products
reflections (Rint
No. of reflections observed
[I > 2 (I)]
)
4788
3074
r
2.6.1. (E)-1-(Methyldiphenylsilyl)hex-1-ene (6)
No. of data/restraints/
parameters
5065/0/298
3464/2/247
1H NMR (500 MHz, C6D6): d 0.56 (s, 3H, SiCH3), 0.79 (t,
3JH,H = 7.3 Hz, 3H, CH2CH3), 1.17–1.26 (m, 4H, CH2CH2CH3), 2.05
(m, 2H, @CCH2), 5.98 (dt, 3JH,H = 18.5 Hz, 4JH,H = 1.5 Hz, 1H, @CHSi),
6.17 (dt, 3JH,H = 18.5 Hz, 3JH,H = 6.2 Hz, 1H, @CHCH2), 7.14–7.17 (m,
6H, CHAr), 7.55–7.57 (m, 4H, CHAr). 13C NMR (125 MHz, C6D6): d
ꢀ3.3 (s, SiCH3), 14.2 (s, CH2CH3), 22.6 (s, CH2CH3), 31.0 (s,
Goodness-of-fit (GOF) F2
1.013
1.028
R1/wR2 (I > 2
r
(I))
0.0226, 0.0493
0.0249, 0.0502
ꢀ1.153 and 0.672
0.0294, 0.0652
0.0366, 0.0678
ꢀ2.002 and 1.422
P
R1/wR2
(
)
Largest difference peak and
hole (e Åꢀ3
)

S. Schwieger et al. / Journal of Organometallic Chemistry 694 (2009) 3548–3558
3551
CH2CH2CH3), 37.0 (s, @CHCH2), 125.9 (s, @CHSi), 128.1/129.4/135.2
7.45–7.48 (m/m/m, 1H/8H/6H, CHAr). 13C NMR (125 MHz, C6D6):
d ꢀ4.3 (s, SiCH3), 16.7 (s, SiCH2), 30.3 (s, SiCH2CH2), 125.9/128.2/
128.6/129.5/134.8/135.2/137.2/145.0 (s/s/s/s/s/s/s/s, CAr). 29Si
NMR (99 MHz, C6D6): d ꢀ7.4 (s).
(s/s/s, CAr), 151.7 (s, @CHCH2). 29Si NMR (99 MHz, C6D6): d ꢀ15.3
(s).
2.6.2. 2-(Methyldiphenylsilyl)hex-1-ene (7)
1H NMR (500 MHz, C6D6): d 0.59 (s, 3H, SiCH3), 0.73 (t,
3JH,H = 7.3 Hz, 3H, CH2CH3), 1.27–1.33 (m, 4H, CH2CH2CH3), 2.17–
2.20 (m, 2H, @CCH2), 5.48–5.49/5.82 (m/m, 1H/1H, @CHH/@CHH),
7.14–7.17 (m, 6H, CHAr), 7.55–7.57 (m, 4H, CHAr). 13C NMR
(125 MHz, C6D6): d ꢀ3.6 (s, SiCH3), 14.1 (s, CH2CH3), 23.3 (s,
CH2CH3), 31.4 (s, CH2CH2CH3), 36.2 (s, @CHCH2), 128.6 (s, @CH2),
128.1/129.4/135.2 (s/s/s, CAr), 148.8 (s, @CSi).
2.6.9. Dimethyl(phenyl)[2-(trimethylsilyl)ethyl]silane (17)
1H NMR (500 MHz, C6D6): d ꢀ0.06 (s + d, 9H, Si(CH3)3), 0.48 (s,
3H SiPh2CH3), 0.47–0.51 (m, 2H, CH2SiMe3), 0.96–0.99 (m, 2H,
CH2SiMePh2), 7.14–7.18/7.49–7.51 (m/m, 6H/4H, CHAr). 13C NMR
(125 MHz, C6D6): d ꢀ4.7 (s, SiPh2CH3), ꢀ2.1 (s, Si(CH3)3,), 6.8 (s,
CH2SiPh2Me), 9.1 (s, CH2SiMe3), 128.2/134.9 (s/s, Co/Cm), 129.4 (s,
Cp), 137.5 (s, i-C).
2.6.3. (E)-1-(Methyldiphenylsilyl)hex-2-ene (8)
1H NMR (500 MHz, C6D6): d 0.47 (s, 3H, SiCH3), 0.77 (t,
3. Results and discussion
3JH,H = 7.3 Hz, 3H, CH2CH3), 1.10–1.14 (m, 2H, CH2CH3), 1.85 (m,
3
4
2H, @CHCH2CH2), 1.94 (dq, JH,H = 7.7 Hz, JH,H = 1.0 Hz, 2H,
3.1. Catalysis
3
@CCH2Si), 5.24–5.30 (m, JH,H = 15.1 Hz [22], 1H, @CHCH2CH2),
3
5.38–5.45 (m, JH,H = 15.1 Hz [22], 1H, @CHCH2Si), 7.14–7.17 (m,
3.1.1. Hydrosilylation of Hexynes
6H, CHAr), 7.55–7.57 (m, 4H, CHAr). 13C NMR (125 MHz, C6D6): d
ꢀ4.7 (s, SiCH3), 13.8 (s, CH2CH3), 22.8 (s, CH2CH3,), 20.6 (s, CH2Si),
35.3 (s, @CHCH2CH2), 125.4 (s, @CHCH2Si), 128.1/129.4/135.2 (s/
s/s, CAr), 130.6 (s, @CHCH2CH2).
The hydrosilylation reactions were carried out at 27 °C with a
molar ratio of nalkyne/olefin:nsilane:nPt = 3000:3000:1. Because of the
dinuclear structure of the platina-b-diketone 1 (Scheme 1) the
resulting molar ratio was nsilane:n1 = 6000:1. Methyldiphenylsilane
was chosen as the hydrosilane because the 1H NMR signal of the
methyl group was well separated from other signals and thus the
course of reaction could be followed easily using 1H NMR
spectroscopy.
Reactions of hex-1-yne with equimolar amounts of methyldi-
phenylsilane in the presence of 0.33 mol% Pt catalyst (1, 4 and 5)
yielded the hydrosilylation product (E)-1-(methyldiphenylsi-
lyl)hex-1-ene (6) together with smaller amounts of 2-(methyldi-
phenylsilyl)hex-1-ene (7) and (E)-1-(methyldiphenylsilyl)hex-2-
ene (8) (Scheme 2). Most likely, compound 8 was formed from 6
by double bond isomerization. The Markovnikov product 7 is only
obtained to the extent of 10–15 mol%. The exclusive formation of
the (E) isomers was proved by the magnitude of the vicinal H,H
2.6.4. (E)-2-(Methyldiphenylsilyl)hex-2-ene (9)
1H NMR (500 MHz, C6D6): d 0.58 (s, 3H, SiCH3), 0.80 (t,
3JH,H = 7.4 Hz, 3H, CH2CH3), 1.20–1.30 (m, 2H, CH2CH2CH3), 1.71–
3
1.72 (m, 3H, CH3C@), 2.03 (q, JH,H = 7.1 Hz, 2H, @CCH2), 5.93 (qt,
3
4JH,H = 1.7 Hz, JH,H = 6.9 Hz, 1H, @CH), 7.15–7.17/7.53–7.56 (m/m,
6H/4H, CHAr). 13C NMR (125 MHz, C6D6): d ꢀ4.0 (s, SiCH3), 14.1
(s, CH2CH3), 15.5 (s, CH3C@), 22.2 (s, CH2CH3), 31.0 (s, @CCH2),
128.1/129.4/135.5 (s/s/s, CAr), 136.7 (s, Ci), 137.2 (s, @CSi), 144.8
(s, @CH). 13C NMR (gated decoupling, 125 MHz, C6D6): d 15.5 (qd,
3
1JC,H = 126 Hz, JC,H = 11 Hz, CH3C@).
2.6.5. (E)-3-(Methyldiphenylsilyl)hex-2-ene (10)
1H NMR (500 MHz, C6D6): d 0.59 (s, 3H, SiCH3), 0.73 (t,
coupling constants (3JH,H = 18.5 Hz, 6; JH,H = 15.1 Hz, 8). This is,
as expected, in accord with a syn addition of the hydrosilane to
the triple bond [23].
The periods after which the hydrosilane was consumed by 50%
(t50) and 95% (t95) are given in Table 2 showing the following order
of activity: platina-b-diketone (1) > Speier’s catalyst (4) > Kar-
stedt’s catalyst (5). The formation of the main product 6 for the
three different catalysts used versus the reaction time is shown
in Fig. 1. The decrease in the yield of product 6 at longer reaction
times using the catalysts 1 and 5 is in accord with an increase in
the yield of the double bond isomer 8.
3
3JH,H = 7.3 Hz, 3H, CH2CH3), 1.20–1.30 (m, 2H, CH2CH2CH3), 1.57
3
(d, JH,H = 6.63, 3H, CH3C@), 2.19 (m, 2H, @CCH2), 5.99 (q,
3JH,H = 6.6 Hz, 1H, @CH), 7.15–7.17/7.53–7.56 (m/m, 6H/4H, CHAr.).
13C NMR (125 MHz, C6D6): d ꢀ3.3 (s, SiCH3), 14.6 (s, CH2CH3), 14.7
(s, CH3C@), 23.4 (s, CH2CH3), 32.4 (s, @CCH2), 128.1/129.4/135.5 (s/
s/s, CAr), 132.8 (s, Ci), 138.7 (s, @CSi), 139.7 (s, @CH).
2.6.6. (E)-3-(Methyldiphenylsilyl)hex-3-ene (11)
1H NMR (500 MHz, C6D6): d 0.60 (s, 3H, SiCH3), 0.82 (t,
3
3JH,H = 7.6 Hz, 3H, @CSiCH2CH3), 0.83 (t, JH,H = 7.5 Hz, 3H,
3
@CHCH2CH3), 2.04 (m, 2H, @CHCH2), 2.91 (q, JH,H = 7.6 Hz, 2H,
The hydrosilylation of hex-2-yne with methyldiphenylsilane
was investigated with the dinuclear (1) and the mononuclear pla-
tina-b-diketones (2, 3) and with Speier’s (4) and Karstedt’s cata-
lysts (5) for comparison (Table 2). In the hydrosilylation
reactions the two regioisomers 9 and 10 were formed. In the main
product (9) the silicon group is attached to the carbon atom pos-
sessing the sterically less demanding group (Me versus n-Pr)
(Scheme 2). The highest regioselectivity (n9:n10 = 80:20) was
achieved with complex 2. The 3JC,H coupling constant of 11 Hz indi-
cated the formation of the (E) isomer of 9 being in accord with a
syn addition to the triple bond. The hydrosilylation reactions with
the platina-b-diketones 1 and 3 proceeded noticeably faster than
those with the reference catalysts 4 and 5. Due to its symmetry,
the hydrosilylation of hex-3-yne yielded one main product only
3
@CSiCH2), 5.89 (t, JH,H = 7.0 Hz, 1H, @CH), 7.14–7.17/7.54–7.57
(m/m, 6H/4H, CHAr). 13C NMR (125 MHz, C6D6): d ꢀ3.3 (s, SiCH3),
14.2 (s, @CHCH2CH3), 15.2 (s, @CSiCH2CH3), 22.2 (s, @CHCH2), 23.3
(s, @CSiCH2), 128.1/129.4/135.6 (s/s/s, CAr), 137.2 (s, Ci), 138.4 (s,
@CSi), 146.9 (s, @CH). 29Si NMR (99 MHz, C6D6): d ꢀ10.3 (s).
2.6.7. Hexyl(methyl)diphenylsilane (12)
1H NMR (500 MHz, C6D6): d 0.46 (s, 3H, SiCH3), 0.82 (t,
3JH,H = 7 Hz, 3H, CH2CH3), 0.99–1.02 (m, 2H, SiCH2), 1.12–1.29 (m,
6H, CH2CH2 CH2CH3) 1.33–1.39 (m, 2H, SiCH2CH2), 7.09–7.16/
7.44–7.48 (m/m, 6H/4H, CHAr). 13C NMR (125 MHz, C6D6): d ꢀ4.2
(s, SiCH3), 14.3 (s, CH2CH3), 14.6 (s, SiCH2), 23.0 (s, CH2), 24.2 (s,
SiCH2CH2), 31.4 (s, CH2), 33.7 (s, CH2), 128.1/129.4/134.8 (s/s/s,
CAr), 137.7 (s, Ci). 29Si NMR (99 MHz, C6D6): d ꢀ7.4 (s).
3
(11, Scheme 2). The JC,H coupling constant of 10.5 Hz gave proof
for the formation of the (E) isomer manifesting a syn addition of
the hydrosilane. In all these reactions the platina-b-diketone 1
showed a substantially higher activity compared to the reference
catalysts (Table 2). Even using half the catalyst concentration of
2.6.8. Methyl(diphenyl)(2-phenylethyl)silane (15)
1H NMR (500 MHz, C6D6): d 0.45 (s, 3H, SiCH3), 1.34–1.38 (m,
2H, SiCH2), 2.62–2.66 (m, 2H, SiCH2CH2), 7.07–7.12/7.15–7.16/

3552
S. Schwieger et al. / Journal of Organometallic Chemistry 694 (2009) 3548–3558
SiMePh2
MePh2SiH
MePh2Si
8 (< 5 mol-%)
MePh2Si
6 (65−75 mol-%)
...
cat.
7 (10−15 mol-%)
MePh2Si
SiMePh2
MePh2SiH
cat.
...
9 (55−80 mol-%)
10 (20−35 mol-%)
MePh2Si
MePh2SiH
cat.
...
11 (ca. 95 mol-%)
Scheme 2.
Table 2
hexyl(methyl)diphenylsilane (12) could be identified as the main
product, but in all cases considerable amounts of double bond
isomerization products (13a, 13b and 14) were also formed. All
platinum complexes exhibited roughly the same initial activity
(see Supporting Information). Karstedt’s catalyst (5) showed the
lowest productivity, a degree of conversion of hex-1-ene of only
about 50% was reached after 1 h. The anionic complex 2 showed
a very low activity, after 6 h the degree of conversion amounted
to 15% only.
Under the same reaction conditions, treatment of hexenes with
internal double bonds (cis- and trans-hex-2-ene, cis- and trans-hex-
3-ene) with methyldiphenylsilane mainly resulted in double bond
isomerizations (see Scheme 3 for trans-hex-2-ene and the Support-
ing Information for the others). The only hydrosilylation product
found (12) is identical with that of hex-1-ene, but it is only formed
to an extent of <5 mol%. Thus, prior to the hydrosilylation a double
bond shift into the terminal position took place.
Times at 50/95% degree of conversion of methyldiphenylsilane (t50/t95 in min) in
hydrosilylation reactions of hexynes using the platina-b-diketone [Pt2{(COMe)2H}2(
Cl)2] (1) as well as Speier’s (4) and Karstedt’s (5) catalysts (nalkyne:nPt = 3000:1, in
C6D6, 27 °C). Additionally, in the case of hex-2-yne [PPh4][Pt{(COMe)2H}Cl2] (2) and
[Pt{(COMe)2H}(acac)] (3) have been used as catalysts.
l
-
Catalyst
Hex-1-yne
Hex-2-yne
Hex-3-yne
t50
t95
t50
t95
t50
t95
1
5–10
40–45
90
45–50
470–510
530–660
475–510
700–930
15–30
55–70
50–70
1a
2
200b
130–180
125–130
65–70
110–115
115–120
170–200
3
4
5
15–20
25–30
120–130
250c
1070–1300
100–110
100–105
420–570
430–510
1050–1400c
a
nalkyne:nPt = 6000:1.
b
c
t85.
.
t90
The hydrosilylation of styrene with methyldiphenylsilane pro-
ceeded comparatively slow with a yield of approximately 80% after
five days at room temperature (catalysts 1 and 5). Catalyst 4
showed the lowest productivity giving a yield of only 40% after four
days. The reactions proved to be highly regioselective, only the
anti-Markovnikov product 15 was found (Scheme 4 and Table 4).
Additionally, minor amounts (<5 mol%) of ethylbenzene (16) were
formed, possibly as the product of a dehydrogenative silylation
[24]. Trimethylvinylsilane reacted with methyldiphenylsilane in
the presence of platinum complexes as catalysts giving the ex-
pected hydrosilylation product 17 (Scheme 4). The reaction was
relatively fast with t50 values ranging from 5 to 40 min (Table 4).
Minor amounts of side products were obtained (<10 mol%), but
not identified.
80
70
60
50
40
30
20
10
catalysts:
1
1 (nalkyne : nPt = 6000 : 1)
Speier's catalyst (4)
Karstedt's catalyst (5)
3.2. Reactions of the platina-b-diketone 1 with hydrosilanes
0
100
200
300
400
500
600
700
time/min
Reactions of the dinuclear platina-b-diketone 1 with simple
hydrosilanes (Et2MeSiH, Et3SiH, MePh2SiH) resulted in all cases
in decomposition of the platinum species yielding platinum black,
only. Subsequently, we applied the concept of the chelate-assisted
hydrosilylation [25] to our reaction system in order to facilitate the
oxidative addition reaction on the one hand and to reduce the pos-
sibility of subsequent Si–X reductive eliminations (X = Cl, Me,
COMe, etc.) on the other hand. For this purpose 2-picolyl substi-
tuted hydrosilanes of the type N SiMe2H (18) and N SiMeH N
(20) (Scheme 5) have been prepared by deprotonation of the
methyl group of 2-picoline with n-BuLi followed by treatment with
the corresponding chlorosilanes (see Section 2). Additionally, the
Fig. 1. Degree of formation of (E)-1-(methyldiphenylsilyl)hex-1-ene (6) vs. time for
the catalysts 1, 4 and 5.
1 resulted in lower reaction times compared to the reference
catalysts.
3.1.2. Hydrosilylation of olefins
The results of the reactions of hex-1-ene with methyldiphenyl-
silane in the presence of the platinum catalysts 1, 3, 4 and 5 are
shown in Scheme 3 and Table 3. The hydrosilylation product

S. Schwieger et al. / Journal of Organometallic Chemistry 694 (2009) 3548–3558
3553
MePh2SiH
MePh2Si
...
cat.
13a
14
12
13b
MePh2SiH
cat.
MePh2Si
12 (< 5 mol-%)
13b (5−10 mol-%)
14 (ca. 15 mol-%)
Scheme 3.
Table 3
Table 4
Times at 50/80% degree of conversion of hex-1-ene (t50/t80 in min) and product ratios
at t80 (in mol%) in the hydrosilylation reaction of hex-1-ene with methyldiphenyl-
silane (nalkene:nPt = 3000:1, in C6D6, 27 °C).
Times at 50% degree of conversion of methyldiphenylsilane (t50 in min) in the
hydrosilylation reaction of methyldiphenylsilane with styrene and trimethylvinylsi-
lane (nalkene:nPt = 3000:1, in C6D6, 27 °C).
Catalyst
t50
t80
x(12)
x(13a)
x(R
(14 + 13b + SP))a
Catalyst
Styrene
Trimethylvinylsilane
t50
t50
1
3
4
5
15–20
45–55
15–20
110–150
110–135
140–180
–
55
55
60
50b
15
15
10
<5b
5–10
10
1
4
5
525–560
550–750a
875–1010
5–10
35–40
10–15
<5
150–270
<5b
a
a
SP – unidentified side products.
t35.
b
Ratio at t50
.
21 (Scheme 5) prompted us to investigate the analogous reaction
using the bis(2-picolyl)amine N NH N (24, Scheme 7). The reac-
tion resulted in facial coordination of the tridentate ligand and a
proton shift from the O–Hꢂ ꢂ ꢂO bridge of the platina-b-diketone to
the metal center in the sense of an oxidative addition reaction
forming the octahedral hydridoplatin(IV) complex 25 as the main
product. This complex could be fully characterized by NMR spec-
troscopy and an X-ray crystal structure determination. Further-
more, the formation of a side product (ca. 10%) was detected
NMR spectroscopically. Although its constitution could not be fully
revealed, it was made clear that it is a platinum(IV) complex bear-
ing a hydrido ligand and two chemically nonequivalent acetyl
ligands.
analogous methyl derivatives N SiMe3 (19) and N SiMe2 N (21)
have also been prepared in order to test the general reactivity of
silylated pyridines towards the platina-b-diketone 1. But all these
reactions resulted also in its decomposition forming platinum
black, only. Several attempts have been made to isolate products
even at temperatures as low as ꢀ78 °C but due to the high instabil-
ity of the products formed, this was also not successful. Interest-
ingly,
a
decomposition took place regardless of which
hydrosilanes (18/20) or their methylated congeners (19/21) were
used as substrates. Thus, these results must not be interpreted in
terms of the instability of a hydrido–silyl–platinum(IV) intermedi-
ate complex, which might be formed by an oxidative addition
starting from 18/20 and 1.
A quinoline based bidentate (being potentially tridentate after
deprotonation) N SiMeH N hydrosilane (22, Scheme 6) that is
very similar to the silane 20 has been successfully used by Tilley
and co-workers in oxidative addition reactions to Rh(I), Ir(I) and
Pt(II) [12,26]. The reaction of this hydrosilane with the platina-b-
diketone 1 resulted in the Pt(IV) complex 23 bearing the tridentate
[N SiMe N]ꢀ ligand, two acetyl groups and a chloro ligand
(Scheme 6). The constitution of complex 23 could be unambigu-
ously proved by NMR spectroscopy and an X-ray crystal structure
determination (Fig. 2). The release of dihydrogen during the reac-
tion was proved by GC–MS. The bonding of Si to Pt(IV) gives rise
to a large Pt–Si coupling constant (1JPt,Si = 1239 Hz) that was ob-
served both in 195Pt and 29Si NMR spectra. The existence of only
one set of the acetyl and quinolyl signals in 1H and 13C NMR spectra
clearly indicates the equivalence of these ligands thus proving the
OC-6-24 configuration.
3.2.1. Structures of complexes 23 and 25
Crystals of the NSiN-coordinated complex 23 could be obtained
from dichloromethane solutions by adding a layer of diethyl ether.
The complex crystallized as a dichloromethane adduct 23ꢂCH2Cl2
in the chiral space group P212121. The molecular structure of com-
plex 23 is shown in Fig. 2, selected geometrical parameters are gi-
ven in the figure caption. The platinum atom is coordinated in an
octahedral geometry by the facial binding NSiN ligand, two acetyl
groups and one chloro ligand in trans position to the Si atom. The
N–Pt–Si (83.61(9)/83.63(9)°) angles are clearly below 90° due to
the rigidity of the NSiN ligand. The Pt–Cl1 bond is remarkably long
(2.536(1) Å) in comparison with known Pt(IV)–Cl bonds (median:
2.318 Å, lower/upper quartile: 2.308/2.330 Å, number of observa-
tions n = 1232), obviously due to the high trans influence of the si-
lyl ligand and the hydrogen bonds in which the chloro ligand is
involved (see below). Interestingly, the Pt–X (X = Cl1, Si, N1/N2)
bonds in the octahedral Pt(IV) complex 23 are longer than the cor-
The immediate formation of platinum black in reactions of the
platina-b-diketone 1 with pyridine functionalized silanes 20 and
SiMePh2
SiMePh2
MePh2SiH
MePh2SiH
...
Si
Si
cat.
cat.
...
17 (ca. 90 mol-%)
15 (40 − 80 mol-%)
16 (<5mol-%)
Scheme 4.

3554
S. Schwieger et al. / Journal of Organometallic Chemistry 694 (2009) 3548–3558
Si
Si
H
SiMe3
SiMe2H
N
N
N
N
N
N
19
21
18
20
Scheme 5.
Crystals of the bis(2-picolyl)amine-coordinated complex 25
could be obtained by crystallisation from dichloromethane/diethyl
Si
H
ether as a dichloromethane solvate (25ꢂCH2Cl2). The complex crys-
N
N
ꢀ
tallizes in the space group P1. In the crystals there were found
22
O
O
O
Cl
Cl
Si
complex cations, chloride anions and solvate molecules that are
connected through a network of hydrogen bonds, see the asym-
metric unit shown in Fig. 3. Selected bond lengths and angles are
given in the figure caption. As observed elsewhere [28], the hydr-
ido ligand was not found in the electron density map but its exis-
tence was unambiguously proved by 1H NMR spectroscopy. The
atoms of one of the two acetyl ligands were found to be disordered
over two positions (67/33%).
1
/
2
H
Pt
Pt
H
N
N
Pt
− H2
O
MeOC
COMe
Cl
23
1
Scheme 6.
In the complex cation the platinum atom is coordinated in an
octahedral fashion by the facially binding bis(2-picolyl)amine,
two acetyl ligands and the hydrido ligand. Due to the rigid back-
bone of the tridentate NNN-ligand the angles around the complex
center are substantially different from 90° ranging from 77.8(2)°
(N2–Pt–N1) to 102(1)° (N1–Pt–C3b). The Pt–N bond lengths
(2.176(4)–2.205(4) Å) are noticeably longer than other typical
Pt(IV)–N bond lengths (median: 2.064 Å, upper/lower quartile:
2.148/2.033 Å, n = 2465 [29]), most likely due to the high trans
influences of the ligands in trans position (acetyl and hydrido li-
gands). In the cations of complex 25 were found C–Hꢂ ꢂ ꢂO hydrogen
bonds where the O atom of an acetyl ligand acts as a hydrogen
acceptor (C9–Hꢂ ꢂ ꢂO2b, C15–Hꢂ ꢂ ꢂO2b, C15–Hꢂ ꢂ ꢂO2a, see Table 5).
Furthermore, the chloride anions act as hydrogen acceptors both
for the N–H group (N–Hꢂ ꢂ ꢂCl1) and for a C–H group of the dichlo-
romethane molecule (C17–Hꢂ ꢂ ꢂCl1), see Fig. 3 and Table 5.
C23
C5
Si
O2
N1
C8
C9
C3
O1
Pt
N2
C17
C1
Cl1
3.3. Quantum chemical calculations
Fig. 2. Structure of the octahedral complex 23 in crystals of 23ꢂCH2Cl2. Thermal
ellipsoids are shown at the 30% probability level. H atoms are omitted for clarity
except those involved in hydrogen bonds. Selected bond lengths (Å) and angles (°):
Pt–C1 2.032(5), Pt–C2 2.031(3), Pt–N1 2.216(4), Pt–N2 2.217(3), Pt–Si 2.294(1), Pt–
Cl1 2.536(1); N1–Pt–N2 87.6(1), N1–Pt–C3 89.5(2), Si–Pt–Cl1 175.18(4), Si–Pt–N1
83.6(1), Si–Pt–N2 83.63(9), N1–Pt–C1 174.0(2), N2–Pt–C3 174.8(2).
To get insight into the different reactivities of the N SiMeH N
hydrosilanes having quinoline (22) and pyridine (20) backbones,
respectively, quantum chemical calculations on the DFT level of
theory using the hybrid functional B3LYP and high-quality 6-
311G(d,p) basis sets for all main group atoms as well as a dou-
ble-f basis set for Pt along with a pseudopotential considering rel-
ativistic effects for its core electrons (see Section 2) were
performed.
The calculations exhibited that the diacetylchloroplatinum(IV)
complexes bearing the quinoline and the pyridine based anionic
N SiMe N-j2N,N0,jSi ligands (23calc versus 26), respectively, are
very similar in their structures, see Fig. 4 and Table 6. Furthermore,
the calculated structure 23calc, representing the structure in the gas
phase, was found to be very close to the experimentally observed
structure in crystals of 23ꢂCH2Cl2.
responding bonds in the square planar Pt(II) complex [Pt(NSiN)Cl]
(X = Cl: 2.536(1) versus 2.528(2) Å; X = Si: 2.294(1) versus
2.225(2) Å, X = N: 2.216(4)/2.217(3) versus 2.031(5)/2.040(5) Å)
[26a,27]).
In crystals of 23ꢂCH2Cl2 several hydrogen bonds were found (Ta-
ble 5). On the one hand, the chloro ligand acts as hydrogen accep-
tor in intramolecular C–Hꢂ ꢂ ꢂCl1 hydrogen bonds (Fig. 2). On the
other hand intermolecular hydrogen bonds between 23 and the
solvate molecule (C24–Hꢂ ꢂ ꢂCl10, C24–Hꢂ ꢂ ꢂO1) and between two
neighboured molecules 23 (C9–Hꢂ ꢂ ꢂCl100, C23–Hꢂ ꢂ ꢂO20) were found.
H
N
H
N
N
N
O
O
O
O
Cl
Cl
24
N
H
N
H
Pt
Pt
H
Cl
Pt
, ...
COMe
COMe
1
25
Scheme 7.

S. Schwieger et al. / Journal of Organometallic Chemistry 694 (2009) 3548–3558
3555
Table 5
Table 6
Selected parameters (distances in Å, angles in °) of hydrogen bonds in the crystals
23ꢂCH2Cl2 and 25ꢂCH2Cl2.
Calculated structural parameters (lengths in Å, angles in °) of [Pt(COMe)2Cl{SiMe-
(quin)2-j2N,N0,jSi}] (23calc and [Pt(COMe)2Cl{SiMe(CH2py)2-j2N,N0,jSi}] (26). For
comparison the requisite values in crystals of 23ꢂCH2Cl2 are given.
)
23ꢂCH2Cl2
D–Hꢂ ꢂ ꢂA
25ꢂCH2Cl2
D–Hꢂ ꢂ ꢂA
23calc
23
26
d(D. . .A)/\(D–Hꢂ ꢂ ꢂA)
d(Dꢂ ꢂ ꢂA)/\(D–Hꢂ ꢂ ꢂA)
Pt–C
Pt–N
Pt–Si
2.059/2.062
2.316/2.350
2.331
2.031(3)/2.032(5)
2.216(4)/2.217(3)
2.294(1)
2.054/2.057
2.329/2.366
2.338
Intramolecular
C8–Hꢂ ꢂ ꢂCl1
3.385(5)/131
3.371(5)/131
C15–H. . .O2a
C15–H. . .O2b
C9–Hꢂ ꢂ ꢂO2b
3.15(3)/133
3.04(2)/137
3.09(4)/136
C17–Hꢂ ꢂ ꢂCl1
Pt–Cl
2.574
2.536(1)
2.575
Si–Pt–Cl
Si–Pt–N
Pt–Si–CMe
169.6
80.7/81.9
123.9
175.18(4)
83.6(1)/83.63(9)
123.2(2)
170.3
80.8/81.4
122.4
Intermolecular
C24–Hꢂ ꢂ ꢂO1a
C24–Hꢂ ꢂ ꢂCl10
C9–Hꢂ ꢂ ꢂCl100
C23–Hꢂ ꢂ ꢂO20
3.220(8)/164
3.666(7)/162
3.575(5)/157
3.402(6)/162
N2–Hꢂ ꢂ ꢂCl1
C17–Hꢂ ꢂ ꢂCl1
C17–Hꢂ ꢂ ꢂCl10
C90–Hꢂ ꢂ ꢂO2b
C14–Hꢂ ꢂ ꢂO10
3.14(1)/157
3.592(7)/155
3.602(8)/170
3.11(3)/147
3.259(9)/131
(Scheme 8). These complexes have been calculated both with the
quinoline and the pyridine based ligands whereas two isomers
have been considered each, namely those having the Si–H group
directed towards the platinum (27a/28a) and those having the
Si–Me group directed towards the platinum (27b/28b). The struc-
tures are shown in Fig. 5, selected structural parameters and the
relative energies are given in Table 7.
Comparison of the Si–H distances (27a versus 27b and 28a ver-
sus 28b) shows that the complexes in which the Si–H group is di-
rected towards the Pt do not have prolonged Si–H bonds, although
the Ptꢂ ꢂ ꢂH distance of 2.410 Å in 27a and, likely also of 2.939 Å in
28a, points to a Ptꢂ ꢂ ꢂH interaction via the doubly occupied 6dz2
orbital of Pt. This is also supported by the existence of bond critical
a
C24 is the C atom of the solvate molecule (CH2Cl2).
C13
C14
Cl3
Cl2
C15
N3
C17
N2
C1
C9
N1
points (qbcp) within the framework of the AIM theory [31], see Sup-
plemental material. Thus, the Si–Hꢂ ꢂ ꢂPt interactions can be under-
stood in terms of 3-center–4-electron bonds [32]. Compared with
the non-coordinated ligands, the Si–C8-quin–C8a-quin (27a/27b) and
Si–CH2–C2-py (28a/28b) angles are widened up by 7/11° (27a/
27b) and 12/3° (28a/28b), respectively, exhibiting (apart from
28b) a remarkable coordination induced angle strain.
O2
C3
O1
Cl1
Pt
C2
C4
Remarkably, in the case of the quinoline based ligand, the com-
plex with the Si–H group directed towards platinum (27a) is more
stable by 3.24 kcal/mol than 27b, whereas in the case of the pyri-
dine based ligand the complex with the Si–Me group directed to-
wards platinum (28b) is by 8.57 kcal/mol more stable than 28a.
As clearly seen in the side view pictures of the complexes (Fig. 5)
this is due to the flexibility of the Si–CH2–py units allowing that
the whole SiMeH group is bent away from platinum. It should be
mentioned that we failed to localize other equilibrium structures
(analogous 28a and 28b but with exchanged H and Me groups
each) on the energy hypersurface.
Fig. 3. Solid-state structure of the octahedral complex 25ꢂCH2Cl2. Thermal ellip-
soids are shown at the 30% probability level. The sixth ‘‘free” coordination site is
occupied by an hydrido ligand that could not be located in the electron density map.
The atoms of the acetyl group C3/C4/O2 are disordered over two positions (67:33),
only the major occupied positions are shown. H atoms are omitted for clarity except
those involved in hydrogen bonds. Selected bond lengths (Å) and angles (°): Pt–C1
2.037(5), Pt–C3 2.02(1)/2.02(2) (the values for the major occupied positions are
given first), Pt–N1 2.176(4), Pt–N2 2.182(5), Pt–N3 2.205(4); N1–Pt–N2 77.8(2),
N2–Pt–N3 78.2(2), N1–Pt–N3 84.5(2), N3–Pt–C3 101.1(5)/102(1), N1–Pt–C1
176.6(2), N2–Pt–C3 178.0(3)/167.0(8).
In all four complexes, the platina-b-diketone units show the ex-
pected features [19]. The O–Hꢂ ꢂ ꢂO hydrogen bonds are unsymmet-
rical. This gives rise to shorter Pt–C and longer C–O bonds in the
hydroxycarbene-like moieties compared with the requisite values
Furthermore, analogous to reactions with other bidentate che-
late ligands (NN, PP, NO, NS donors) [7,30], the first step of the
reaction of 1 with 22/20 can be assumed to be the cleavage of
the Pt–Cl–Pt bridges forming mononuclear cationic platina-b-dike-
tones having bidentately N,N0 coordinated hydrosilane ligands
in the acetyl-like moieties
(D(Pt–C) = 0.021–0.024 Å, D(C–
O) = 0.024–0.028 Å). The Oꢂ ꢂ ꢂO distances indicate very strong
Fig. 4. Calculated structures of [Pt(COMe)2Cl{SiMe(quin)2-j2N,N0,jSi}] (23calc, left) and [Pt(COMe)2Cl{SiMe(CH2py)2-j2N,N0,jSi}] (26, right).

3556
S. Schwieger et al. / Journal of Organometallic Chemistry 694 (2009) 3548–3558
Fig. 5. Calculated structures of [Pt{(COMe)2H}{SiMeH(quin)2-j2N,N0}]+ (27a/27b) and [Pt{(COMe)2H}{SiMeH(CH2py)2-j2N,N0}]+ (28a/28b) and the side views as wire models
(lower row).
H3C
H
Si
+
+
H3C
H
H
CH3
Pt
+
N
Si
N
Si
N
O
O
Cl
Cl
O
O
N
− Cl−
1
/
H
Pt
Pt
H
Pt
2
H
H
O
O
N
N
O
O
1
27a/28a
27b/28b
28a/b
27a/b
H3C
H
Si
H
Si
N
Si
H
N
N
N
N
N
20
22
Scheme 8.
Table 7
Calculated structural parameters (lengths in Å, angles in °) and relative energies (in kcal/mol) of cationic platina-b-diketones [Pt{(COMe)2H}{SiMe(quin)2-j2N,N0}]+ (27a/27b) and
[Pt{(COMe)2H}{SiMe(CH2py)2-j2N,N0}]+ (28a/28b).
27a (Si–H towards Pt)
27b (Si–Me towards Pt)
28a (Si–H towards Pt)
28b (Si–Me towards Pt)
Pt–Ccarb/Pt–Cacyl
C–Ocarb/C–Oacyl
Oꢂ ꢂ ꢂO
1.994/2.017
1.264/1.237
2.398
1.486
127.2/128.0
2.410
1.999/2.023
1.265/1.237
2.403
1.486
130.5/131.3
1.997/2.018
1.261/1.237
2.394
1.483
124.9/126.0
2.939
3.294
0
0
1.994/2.017
1.263/1.238
2.396
1.487
116.9/117.0
Si–H
Si–C–Ca
Ptꢂ ꢂ ꢂH
Ptꢂ ꢂ ꢂSi
3.142
0
3.216
4.042
Relative energy
+3.24
ꢀ8.57
(+3.42/+1.96)b
(ꢀ6.56/ꢀ6.02)b
a
27a/27b: Si–C8-quin–C8a-quin. 28a/28b: Si–CH2–C2-py. In the non-coordinated ligands these angles were calculated to be 119.7/120.9° and 113.6/114.2°, respectively.
In parentheses Gibbs free enthalpy at 298 K for the reaction in the gas phase and in the solvent thf, respectively, is given.
b
hydrogen bonds. On the basis of the linear relationship between
seems to be feasible which could be obtained by an oxidative
addition either of the Si–H group (29) or by a shift of the O–
Hꢂ ꢂ ꢂO proton of the platina-b-diketone unit (30), Scheme 9. The
calculated molecular structures of complexes 29 and 30 are given
in Supplemental material. They are only higher in energy by
the Oꢂ ꢂ ꢂO distances and the strength of the hydrogen bonds found
in a series of metalla-b-diketones [10,19] a strength of the hydro-
gen bonds in 27/28 of about 27 kcal/mol can be estimated.
If we assume that complex 27a is an intermediate in the reac-
tion of 1 with 22 yielding the diacetylchloroplatinum(IV) complex
23 having the quinoline based ligand tridentately coordinated
(N SiMe N-j2N,N0,jSi), there can only be speculated on the pre-
cursor complex for the dihydrogen elimination. Among others,
the formation of a hydridoplatinum(IV) intermediate complex
6.51 kcal/mol (29,
DG = 8.08 kcal/mol, D
Gthf = 8.80 kcal/mol)1 and
1
Gibbs free enthalpy at 298 K for the reaction in the gas phase and in the solvent
thf, respectively.

S. Schwieger et al. / Journal of Organometallic Chemistry 694 (2009) 3548–3558
3557
+
Si
H
N
Pt
N
+
H
Si
O
Si
N
+ Cl−
− H2
O
29
N
O
O
O
H
Pt
Cl
Pt
H
N
O
+
N
H
Si
H
27a
N
23
Pt
N
O
30
O
Scheme 9.
1100
1000
900
800
700
600
500
400
300
200
100
0
tion of hexynes is superior to Speier’s and Karstedt’s catalysts. In
the case of the alkenes (hex-1-ene, styrene, trimethylvinylsilane)
complex 1 and Speier’s catalyst exhibited comparable activities.
On the other hand, there are no remarkable differences in the
regioselectivities in the investigated hydrosilylation reactions be-
tween the platina-b-diketones 1–3 and the reference catalysts 4
and 5.
A solution of hexachloroplatinic acid (H2PtCl6ꢂ6H2O) in isopro-
anol (Speier’s catalyst 4) undergoes a reduction of Pt(IV) at ele-
vated temperatures (or after adequate time even at room
platina-β-diketone 1
Speier's catalyst (4)
Karstedt's catalyst (5)
temperature) yielding
H[PtCl3(
2-C3H6)] (Scheme 10, reaction a, R1 = iPr, R2 = Me) [33]
analogous to Zeise’s acid (H[PtCl3(
2-C2H4)]) that is obtained in
a
p-propene platinum(II) complex
g
g
the requisite reaction with ethanol [34]. The subsequent reaction
with Me3SiC„CH was found to result under cleavage of the Si–C
bond in the formation of the carbene platinum(II) complex cis-
[PtCl2{C(OiPr)Me}2] (Scheme 10, reaction b) [35]. Analogously,
the platina-b-diketone 1 is formed in the reaction of hexachloro-
platinic acid in n-butanol with silylated alkynes (preferably
trimethyl-
vinylsilane
hex-1-yne
hex-2-yne
hex-3-yne
hex-1-ene styrene
Fig. 6. Times at 50% degree of conversion of methyldiphenylsilane in the hydro-
silylation reactions reported in this paper for the catalysts used. In the case of hex-
1-ene the t50 values are based on the conversion of hex-1-ene instead of the silane.
Me3SiC„CSiMe3) again with cleavage of the Si–C bond via a
p-
butene platinum(II) complex as intermediate (Scheme 10, reac-
tion a/c, R1 = nBu, R2 = Et). Interestingly, also good catalytic activ-
ity of the carbene platinum(II) complex cis-[PtCl2{C(OiPr)Me}2]
for hydrosilylation of alkynes has been acknowledged without
giving any further details [35].
by 5.80 kcal/mol (30,
DG = 4.51 kcal/mol, DGthf = 6.48 kcal/mol),
respectively, than complex 27a. Thus, from the thermodynamic
point of view, either of these two complexes could be an intermedi-
ate in the reaction 27a ? 23.
It has been shown, that reactions of the platina-b-diketone 1
with hydrosilanes, even with hydrosilanes containing N-donor
sites in the molecule, do not lead to stable hydridosilylplati-
num(IV) complexes. In most cases, reduction to platinum black oc-
curred. Only in one case – using a hydrosilane with a very rigid
quinoline based backbone – a silylplatinum(IV) complex (23) could
be isolated. From the quantum chemical calculations there is no
obvious reason why reactions of the platina-b-diketone 1 with 22
and 20 result in the formation of the stable complex 23 (see
4. Conclusions
In this work, catalytic properties of the platina-b-diketones 1–
3 (Scheme 1) in the hydrosilylation of non-activated alkynes and
alkenes have been investigated and compared with the well-
established hydrosilylation catalysts from Speier (4) and Karstedt
(5). The results are summarized in Fig. 6 and show that the
activity of the dinuclear platina-b-diketone 1 in the hydrosilyla-
OR1
Cl
Cl
HC CSiMe3
b
R1 = iPr
Pt
OR1
R2
Cl
R1OH
a
Cl
Cl
Pt
H
H2PtCl6 H2O
O
O
Cl
Cl
O
O
Me3SiC CSiMe3
c
H
H
Pt
Pt
1
Scheme 10.

3558
S. Schwieger et al. / Journal of Organometallic Chemistry 694 (2009) 3548–3558
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Acknowledgment
The authors gratefully acknowledge the Deutsche Forschungs-
gemeinschaft for financial support and Merck (Darmstadt) for gifts
of chemicals.
Appendix A. Supplementary material
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CCDC 721482 and 721483 contains the supplementary crystal-
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tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary
data associated with this article can be found, in the online version,
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