Unusual Pt-catalyzed stereo and regioselective intramolecular hydrosilylation of propargyl alcohols to (E,E)-1,6-dioxa-2,7-disila-3,8-ecidienes

Article abstract of DOI:10.1016/S0022-328X(98)00638-X

Stereo- and regioselective functionalization of propargyl alcohols have been achieved via intramolecular hydrosilylation reaction promoted by solvated Pt-atoms.

Full text of DOI:10.1016/S0022-328X(98)00638-X

Journal of Organometallic Chemistry 564 (1998) 57–59
Unusual Pt-catalyzed stereo and regioselective intramolecular
hydrosilylation of propargyl alcohols to
(E,E)-1,6-dioxa-2,7-disila-3,8-ecidienes
Anna Maria Caporusso *, Silvia Barontini, Paolo Pertici, Giovanni Vitulli, Piero Salvadori
Centro di Studio del CNR per le Macromolecole Stereordinate ed Otticamente Atti6e,
Dipartimento di Chimica e Chimica Industriale dell’Uni6ersita` di Pisa, Via Risorgimento 35, 56126 Pisa, Italy
Received 23 January 1998
Abstract
Stereo- and regioselective functionalization of propargyl alcohols have been achieved via intramolecular hydrosilylation reaction
promoted by solvated Pt-atoms. © 1998 Elsevier Science S.A. All rights reserved.
Keywords: Silicon; Intramolecular hydrosilylation; Propargyl alcohols; Platinum atoms; Catalysis
1
There is a great deal of attention in catalytic in-
tramolecular hydrosilylation reactions as new powerful
approach to regiocontrolled syntheses [1,2].
Hydrodimethylsilylethers derived from homopropar-
gyl alcohols have been reported to rapidly undergo
chloroplatinic acid catalyzed cis-intramolecular hydrosi-
lylation to penta-cyclovinyl silanes, while propargyl
alcohol silyl ether derivatives gave only polymeric mate-
rials under similar reaction conditions [2].
We found that mesitylene solvated platinum atoms,
already reported [3] as remarkable catalysts for the
hydrosilylation of dienes and acetylenes, are able to
promote the intramolecular hydrosilylation of hy-
drodimethylsilylethers of propargyl alcohols to ten mem-
bered rings as illustrated in Scheme 1.
Propargyl alcohols 1, quantitatively converted to hy-
drodimethylsilylethers 2 by reaction with tetramethyldis-
ilazane at r.t., rapidly undergoes, in the presence of
mesitylene solvated Pt atoms (3–5×10−3 g atom%
based on the hydrosilyl ether 2), a selective cyclodimer-
ization to (E,E)-5,10-dialkyl-2,2,7,7-tetramethyl-1,6-
dioxa-2,7-disila-3,8-ecidienes, 3. Compounds 3 have been
fully characterised by MS, H- and 13C-NMR; the trans
configuration of the double bonds has been also confi-
rmed by a bromine cleavage of the silicon–carbon bonds
of 3a, which proceeds with complete inversion of stere-
ochemistry [4], achieving the cis bromide 4a (Scheme 1).
It is worth noting that, using H2PtCl6 as catalytic
precursor, we found that compounds 3 are formed only
in traces; in this reaction polymeric materials are the
main reaction product, as observed with other propargyl
alcohol silyl ether derivatives [2]. The different behaviour
found using solvated Pt-atoms and H2PtCl6 as catalysts
could be rationalized considering that in the platinum
catalyzed hydrosilylation the true catalytic species are
likely to be Pt colloids [5]; their formation from H2PtCl6
will require an induction period which could overtake,
for some substrates, by reactions, such as polymerization;
on the contrary solvated Pt-atoms can be regarded as
already reactive ‘naked’ Pt clusters, able to rapidly
promote hydrosilylation reactions [3].
* Corresponding author. Fax: +39 50 918260.
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00638-X

58
A.M. Caporusso et al. / Journal of Organometallic Chemistry 564 (1998) 57–59
Scheme 1.
The reaction pathway to 3 is probably complicated; a
mg atom of platinum [3], were added to the crude oil
obtained. The mixture was stirred at 25°C for 1 h. The
mesitylene was removed in vacuo and the crude
product was dissolved in diethyl ether and filtered on
celite. Pure ecidiene 3 was isolated as an oil by simple
solvent evaporation.
likely first step of the reaction could be the formation
of a six membered intermediate 5 deriving from a
6-endo-dig ring clousure involving the Pt atom. It will
then appear that a further reductive elimination should
afford a strained pentacyclo product, making more
favoured a dimerization process, as also observed in the
cyclohydrosilylation of allyl alcohols [6].
Although the mechanistic problems require further
investigations, the reported results indicate that the
MVS catalytic precursor [3] provides an efficient and
general way for the functionalization of acetylenic
carbinols with high stereo- and regioselectivity.
Actually, mesitylene solvated Pt-atoms are extremely
effective also in promoting the intramolecular hydrosi-
lylation of homopropargyl hydrodimethylsilyl ethers
affording a practical tool for the selective preparation
of a wide range of polyfunctionalized intermediates
such as compounds 7 (Scheme 2).
1.1.1. (E,E)-5,10-di(tertbutyl)-2,2,7,7-tetra-
methyl-1,6-dioxa-2,7-disila-3,8-ecidiene (3a)
1H-NMR (CDCl3, l ppm): 0.06 (6H, s, CH3Si), 0.11
(6H, s, CH3Si), 0.82 (18H, s, CH3), 3.68 (2H, d, J=6.2
Hz, CH–O), 5.70 (2H, d, J=18.9 Hz, ꢀCH–Si), 6.11
(2H, dd, J=18.9 and 6.2 Hz, ꢀCH). 13C-NMR (CDCl3,
l ppm): −0.98, −0.51, 25.9, 29.7, 83.5, 129.0, 148.4.
MS m/z: 340 (M+), 57 (100%). Anal. Found: C, 63.34;
H, 10.64. C18H36O2Si2 Calc.: C, 63.49; H, 10.66
1.1.2. (E,E)-5,10-diphenyl-2,2,7,7-tetramethyl-
1,6-dioxa-2,7-disila-3,8-ecidiene (3b)
1H-NMR (CDCl3, l ppm): 0.10 (6H, s, CH3Si), 0.13
(6H, s, CH3Si), 5.06 (2H, d, J=5.0 Hz, CH–O), 5.78
(2H, dd, J=18.7 Hz, ꢀCH–Si), 6.15 (2H, dd, J=18.7
and 5.0 Hz, ꢀCH), 7.23 (10H, m, PhH). 13C-NMR
(CDCl3, l ppm): −1.16, −1.01, 77.2, 125.7, 126.4,
127.1, 142.7, 150.5. MS m/z: 380 (M+), 77 (100%).
Anal. Found: C, 69.30; H, 7.39. C22H28O2Si2 Calc.: C,
69.44; H, 7.42.
1. Experimental details
All experiments were carried out under exclusion of
air and moisture.-NMR spectra were determined with a
1
Varian Gemini 200 instrument (200 MHz for H, 50.3
MHz for 13C); mass spectra were obtained at 70 eV on
a VG Analitical 7070 mass spectrometer.
1.1. General procedure for the synthesis of 3a,b
1.2. Preparation of (Z)-1-bromo-4,4-dimethyl-
1-penten-3-ol (4a)
Typically, in a 25 ml Pyrex Carius tube, 5 mmol of
the propargyl carbinol 1 were treated with 1,1,3,3-te-
tramethyldisilazane (1.07 g, 8.0 mmol) and anhydrous
NH4Cl (ca. 5 mg). After stirring at r.t. for 15 h, the
excess of tetramethyldisilazane was removed in vacuo
and 3 ml of a Pt/Mesitylene solution, containing 0.015
In a dry 25 ml round-bottomed flask, bromine (0.192
g, 62 ml, 1.2 mmol) was added dropwise with a microsy-
ringe to a solution of the ecidiene 3a (200 mg, 0.6
mmol) in CCl4 (5 ml) at 0°C. The mixture was stirred at
0°C for 4 h. Then, KHF2 (280 mg, 3.6 mmol) and

A.M. Caporusso et al. / Journal of Organometallic Chemistry 564 (1998) 57–59
59
Scheme 2.
MeOH (5 ml) were added; the resulting mixture was
stirred at r.t. for 12 h and filtered. The filtrate was
treated with diluted aq.Na2S2O3 and extracted with
ether. The organic layer was washed with water, 6 N
aq. HCl, and diluted aq.NaHCO3, dried (Na2SO4) and
concentrated in vacuo to give the crude product 4a
which was purified by bulb-to-bulb distillation (yield:
192 mg, 83%).
(1H, ddd, J=1.1, 4.8 and 14.5 Hz, CHCꢀ), 2.84 (1H,
ddd, J=0.8, 8.4 and 14.5 Hz, CHCꢀ), 5.02 (1H, dd,
J=4.8 and 8.4 Hz, CH–O), 5.52 (1H, m, ꢀCH2), 5.66
(1H, m, ꢀCH2), 7.30 (5H, m, PhH). 13C-NMR (CDCl3,
l ppm): 51.3, 71.6, 120.0, 125.8, 127.9, 128.5, 130.1,
142.8. MS m/z: 129 (M+-Br, -H2O, 2%), 107 (100).
1.6. (E)-2-bromo-1-trimethylsilyl-1-penten-4-ol (7b)
1H-NMR (CDCl3, l ppm): 1.01 (9H, s CH3), 2.27
(1H, s, OH), 3.65 (1H, dd, J=7.2 and 1.4 Hz, CH–O),
6.18 (1H, dd, J=8.6 and 7.2 Hz, ꢀCH), 6.34 (1H, dd,
J=8.6 and 1.4 Hz, ꢀCHBr). MS m/z: 194 (M+for
81Br), 192 (M+for 79Br), 57 (100%).
1H-NMR (CDCl3, l ppm): 0.17 (9H, s, CH3Si), 1.20
(3H, d, 6.2 Hz, CH3), 1.77 (1H, s, OH), 2.58 (2H, d,
J=6.6 Hz, CH2), 4.00–4.21 (1H, m, CH–O), 6.08 (1H,
s, ꢀCH). 13C-NMR (CDCl3, l ppm): −0.97, 22.2, 55.5,
65.5, 132.7, 138.8. MS m/z: 223 (M+-15, for 81Br, 2%),
221 (M+-15, for 79Br, 2%), 73 (98), 45 (100). The (E)
configuration of the double bond was determined by
1H-NMR NOE experiments.
Compounds 7a and 7b were prepared by the above
methods, with total yields noted in Scheme 2.
1.3. 2,2-Dimethyl-3-methylene-5-phenyl-
1-oxa-2-silacyclopentane (6a)
1H-NMR (CDCl3, l ppm): 0.29 (6H, s, CH3Si), 2.49
(1H, dd, J=9.5 and 14 Hz, CHCꢀ), 2.68 (1H, dd,
J=4.0 and 14. Hz, CHCꢀ), 4.84 (1H, m, CH–O), 5.64
(1H, d, J=2.0 Hz, ꢀCH2), 5.77 (1H, m, ꢀCH2), 7.37
(5H, m, PhH). 13C-NMR (CDCl3, l ppm): 0.5, 46.3,
72.7, 125.8, 127.3, 128.3, 129.1, 144.3, 148.3. MS m/z:
204 (M+, 96%), 77 (100). Anal. Found: C, 70.37; H,
7.89. C12H16OSi Calc.: C, 70.55; H, 7.90.
Acknowledgements
We gratefully acknowledge support by ‘Progetto
Strategico del CNR per le Tecnologie Chimiche Inno-
vative’.
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