Dehydrogenative Silylation of Alkenes
FULL PAPER
in vacuo. Yield: 17 mg, 66%. 1H NMR (500.25 MHz, [D8]toluene): d=
mixed in another Young NMR tube. Into a small vial, 4b (4.4 mg,
0.002 mmol) was dissolved in [D8]toluene (1.0 mL), which was added
equivalently into the two Young NMR tubes. The solution was heated at
1008C and the dehydrogenative silylation reaction process was monitored
3.75 (t, 2J(P,H)=32.4 Hz, 1H; Re-H), 2.73 (d, 2J(H,H)=12 Hz, 2H; h2-
ACHTUNGTRENNUNG ACHTUNGTRENNUGN
2
CHH=CHH), 2.62 (m, 6H; P-CH
h2-CHH=CHH), 1.20 (m, 18H; P-CH
(CH3)2); 13C{1H} NMR (125.8 MHz, [D8]toluene): d=34.9 (s; h2-CH2 =
CH2), 26.0 (t, (P,C)=11.9 Hz; P-CH(CH3)2), 20.4 (s; P-CH(CH3)2),
19.6 ppm (s; P-CH
(CH3)2); 31P{1H} NMR (202.5 MHz, [D8]toluene): d=
G
ACHTUNGTREN(NGNU H,H)=12 Hz, 2H;
AHCTUNGTRENNUNG
1
R
every 4 min by using H NMR spectroscopy.
J
G
G
ACHTUNGTRENNUNG
Attempt to synthesize Re–silyl species from 4b and Me2PhSiCH=CH2:
In a Young NMR tube, 1b (8.4 mg, 0.01 mmol) and Me2PhSiCH=CH2
(1.8 mL, 0.01 mmol) were mixed in toluene (0.5 mL). It immediately led
to the formation of the 18eÀ alkene adduct [ReBr(h2-CH2=
ACHTUNGTRENNUNG
15.7 ppm (s); IR (ATR): n˜ =3005 (C-H), 2970 (C-H), 2871 (C-H), 2024
(Re-H), 1665 cmÀ1 (NO); elemental analysis calcd (%) for
C20H47BrNOP2Re (645.65): C 37.20, H 7.34, N 2.17; found: C 37.10, H
7.38, N 2.06.
CHSiMe2Ph)H(NO)ACHTNURTGNEG(UN PCy3)2] at room temperature. The solution was
heated at 1008C for 30 min. 1H and 31P NMR spectra indicated the for-
mation of the ethylene-coordinated rhenium hydride 5a’ and the dehy-
drogenative silylation product Me2PhSiCH=CHSiPhMe2 (d=6.35 ppm
for SiCH=CHSi). The formation of this product could also be proven by
GC–MS (m/z 296.5 [M+]). After 4 h at 1008C, [ReBr(h2-CH2=
Synthesis of [ReBr
tube with a Young valve, [ReBrH(NO)AHCUTNGTRENNUNG
ACHTUNGTRENNUNG ACHTUNGTRENNUNG
(h2-C2H4)H(NO)
dissolved in hexane (10 mL). The nitrogen atmosphere was replaced with
ethylene gas (860 mbar) by using a freeze–pump–thaw cycle. The mixture
was stirred at room temperature for 30 min and a yellow precipitate was
formed. The supernatant solution was removed and the residue was dried
in vacuo. Yield: 68 mg, 55%. 1H NMR (500.25 MHz, [D8]toluene): d=
CHSiMe2Ph)H(NO)ACHTNUTRGENUG(N PCy3)2] had totally disappeared and the hydride 5a’
became the only remaining organometallic species in solution, along with
an increased amount of Me2PhSiCH=CHSiPhMe2.
4.11 (t, 2J
CHH=CHH), 2.60 (d, 2J
2.59 ppm (m, 66H; P
(C6H11)3); 13C{1H} NMR (125.8 MHz, [D8]toluene):
d=36.5 (t, J
(P,C)=10 Hz; P-C), 34.5, 30.7, 30.0, 28.0 (m; h2-C2H4),
A
(H,H)=9 Hz, 2H; h2-
ACHTUNGTRENNUNG
X-ray structural analyses of 4b and 5a: The single-crystal X-ray diffrac-
tion studies of 4b and 5a were carried out on an Oxford Xcalibur diffrac-
tometer (4-circle kappa platform, Ruby charge-coupled device (CCD)
detector, single-wavelength Enhance X-ray source with MoKa radiation,
l=0.71073 ꢃ) at 183(2) K.[23] The crystal structures were solved with the
Patterson method by applying the software options of the program
SHELXS-97[24] and full-matrix least-squares refinement on F2
(SHELXL-97).[24] The program PLATON[25] was used to check the result
of the X-ray analyses and the program ORTEP[26] was used to give a rep-
resentation of the structures. All software used to prepare material for
publication are included in the WINGX software.[27] For 4b, the metal
center lies on an inversion center that led to the refinement of only one
half of the molecule and caused positional disorders for the bromide, ni-
trosyl, and hydride ligands. Furthermore, the nitrosyl ligand had to be
disordered once more, because it occupied two sites near to the position
of the bromide. Consequently, the nitrogen and oxygen atoms were iso-
tropically refined. All hydrogen positions were calculated after each
cycle of refinement by using a riding model except for the hydride atom,
which was located in a Fourier map and geometrically refined. For 5b,
the positions of the hydride and the ethylenic hydrogen atoms were
found in the difference Fourier map and freely refined. All other hydro-
gen positions were calculated after each cycle of refinement by using a
riding model.
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
27.1 ppm; 31P{1H} NMR (202.5 MHz, [D8]toluene): d=4.60 ppm (s); IR
(ATR): n˜ =2928 (C-H), 2851 (C-H), 2089 (Re-H), 1668 cmÀ1 (NO); ele-
mental analysis calcd (%) for C38H71BrNOP2Re (887.04): C 51.51, H 8.08,
N 1.58; found: C 51.73, H 8.26, N 1.55.
Catalytic dehydrogenative silylation of alkenes with R’3SiH by rhenium
complexes: In a Schlenk tube with a Young valve, substrate R’3SiH
(0.25 mmol), an alkene (0.50 mmol), and an appropriate amount of rheni-
um catalyst (0.0025 or 0.01 mmol) were mixed in [D8]toluene (0.5 mL).
The mixture was kept stirring in the closed system at 100 or 1108C. After
an appropriate reaction time the yield and product distribution were de-
1
termined by H NMR spectroscopy and GC–MS analyses.
(E)-1-(p-Methoxystyryl)-2-(triphenylsilyl)ethylene: A catalytic amount of
1a (7 mg, 0.01 mmol), substrate Ph3SiH (260 mg, 1.00 mmol), and 4-me-
thoxystyrene (268 mL, 2.00 mmol) were added to a 30 mL Schlenk tube
with a Young valve. The mixture was dissolved in toluene (5 mL) and
kept stirring in the open system at 1008C for 24 h. The solvent was
evaporated in vacuo and the residue was subjected to chromatography
on a silica gel column. Pure (E)-1-(p-methoxystyryl)-2-(triphenylsilyl)-
ethylene was isolated (230 mg, 59%) as a white solid using a 1:20 Et2O/
1
pentane mixture as eluent. H NMR (300.1 MHz, [D6]benzene): d=7.20–
CCDC-681124 (4b) and CCDC-699750 (5a) contain the supplementary
crystallographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
7.74 (m, 17H; Ph), 6.90 (d, 3J
ACHTUNRGTNEUNG(H,H)trans =18.9 Hz, 2H; trans-CH=CH),
6.70 (d, 3J=8.7 Hz, 2H), 3.23 ppm (s, 3H; Ph-OCH3); 13C{1H} NMR
(75.5 MHz, C6D6): d=160.6, 149.1, 136.6, 135.3, 131.4, 129.8, 128.6, 128.3,
120.2, 114.3, 54.8 ppm; MS (ESI): m/z (%): 415.1 (100) [M+Na+].
Computational details: The geometry optimizations were performed with
the Gaussian03 program package[28] using the hybrid mPW1PW91 func-
tional, which includes the modified Perdew–Wang exchange and Perdew–
Wang 91 correlation, in conjunction with the Stuttgart/Dresden ECPs
Treatment of the catalytic system with excess of PR3: A catalytic amount
of 4b (2.3 mg, 0.0025 mmol), Et3SiH (38 mL, 0.25 mmol), 4-methoxysty-
ACHTUNGTRENNUNGrene (67 mL, 0.50 mmol), and PCy3 (7 mg, 0.025 mmol) were mixed with
[D8]toluene (0.5 mL) in a 30 mL Schlenk tube with a Young valve. The
(SDD) basis set for the Re center and the extended 6-31+GACHTUNGTRENNUNG(d,p) basis
1
mixture was kept stirring at 1008C. After 12 h, the H NMR spectrum in-
set for the remaining atoms. The nature of the optimized structures was
verified by frequency calculations at the same level of theory. The rela-
tive electronic energy includes the zero-point energies calculated by
using the nonimaginary frequencies.
dicated no reaction. However, the 31P NMR spectrum showed the forma-
tion of complex 5b.
Treatment of 1b with Ph3SiH: In a Young NMR tube, 1b (8.4 mg,
0.01 mmol) and Ph3SiH (260 mg, 1.00 mmol) were mixed in toluene
(0.5 mL). The mixture was heated at 1008C. After 12 h, the 31P NMR
spectrum indicated the formation of 4b in 76% yield.
Phosphine dissociation study of complex 5a and 5b: In a Young NMR
tube, 1b (8.4 mg, 0.01 mmol) and PiPr3 (11 mL, 0.05 mmol) were mixed in
toluene (0.5 mL). The mixture was heated at 1008C. After 1 min, the
31P NMR spectrum indicated the formation of liberated PCy3 and 5a, as
well as unidentified complexes that might be those with mixed phosphine
ligands. After 1 h at 1008C, 5b was completely transformed to 5a, which
was the only organometallic species in solution.
Acknowledgements
Support from the Swiss National Science Foundation, the European
COST program, and the Funds of the University of Zurich are gratefully
acknowledged.
KIE studies of the reaction of 4-methylstyrene with Et3SiH and Et3SiD
catalyzed by 4b: In a glove box, Et3SiH (38 mL, 0.25 mmol) and 4-meth-
ylstyrene (68 mL, 0.50 mmol) were added into one Young NMR tube, and
the same amounts of Et3SiD (38 mL) and 4-methylstyrene (69 mL) were
[1] M. A. Brook, Silicon in Organic, Organometallic and Polymer
Chemistry, Wiley, New York, 2000.
[2] a) Comprehensive Handbook on Hydrosilylation (Ed.: B. Marci-
niec), Pergamon, Oxford, 1992, Chapter 2; b) Y. Watatsuki, H. Ya-
Chem. Eur. J. 2009, 15, 2121 – 2128
ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2127