Intramolecularly base-coordinated silylenes that behave as sila-ylides

Article abstract of DOI:10.1080/10426500212275

Divalent silicon species bearing an 8-amino- or 8-phosphino-1-naphthyl group have been shown to behave as nucleophilic sila-ylides in the presence of diphenylacetylene to afford zwitterionic intermediates containing alkenyl anion and ammonium or phosphoni

Full text of DOI:10.1080/10426500212275

This article was downloaded by: [University of Waterloo]
On: 04 November 2014, At: 12:00
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,
37-41 Mortimer Street, London W1T 3JH, UK
Phosphorus, Sulfur, and Silicon and the Related
Elements
Publication details, including instructions for authors and subscription information:
http://www.tandfonline.com/loi/gpss20
Intramolecularly Base-Coordinated Silylenes That
Behave as Sila-Ylides
Akio Toshimitsu a , Tomoyuki Saeki a & Kohei Tamao a
a Institute for Chemical Research , Kyoto University , Kyoto, Japan
Published online: 27 Oct 2010.
To cite this article: Akio Toshimitsu , Tomoyuki Saeki & Kohei Tamao (2002) Intramolecularly Base-Coordinated
Silylenes That Behave as Sila-Ylides, Phosphorus, Sulfur, and Silicon and the Related Elements, 177:6-7, 1409-1412, DOI:
10.1080/10426500212275
To link to this article: http://dx.doi.org/10.1080/10426500212275
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained
in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no
representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the
Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and
are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and
should be independently verified with primary sources of information. Taylor and Francis shall not be liable for
any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever
or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of
the Content.
This article may be used for research, teaching, and private study purposes. Any substantial or systematic
reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any
form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://
www.tandfonline.com/page/terms-and-conditions

Phosphorus, Sulfur and Silicon, 2002, Vol. 177:1409–1412
C
Copyright 2002 Taylor & Francis
1042-6507/02 $12.00 + .00
DOI: 10.1080/10426500290092811
INTRAMOLECULARLY BASE-COORDINATED
SILYLENES THAT BEHAVE AS SILA-YLIDES
Akio Toshimitsu, Tomoyuki Saeki, and Kohei Tamao
Institute for Chemical Research, Kyoto University, Kyoto, Japan
(Received July 29, 2001; accepted December 25, 2001)
Divalent silicon species bearing an 8-amino- or 8-phosphino-1-
naphthyl group have been shown to behave as nucleophilic sila-ylides
in the presence of diphenylacetylene to afford zwitterionic intermediates
containing alkenyl anion and ammonium or phosphonium cation moi-
eties. The reaction pathways of these zeitterionic intermediates have
been clarified to be highly dependent on the character of the cationic
center such as N and P.
Keywords: Base-coordinated silylene; ligand coupling; pentacoordinate
silicon; phosphonium ylide; sila-ylide; thermolysis
It is well known that the ground state of a divalent silicon species, sily-
lene, is a singlet with an electron pair in orbital and a vacant orbital
of symmetry. A priori, silylenes can behave as ambiphiles because
both the electron pair and the vacant orbital can take part in the reac-
tions. In the reported examples, however, the first step has been shown
to have an electrophilic character; that is, the reaction proceed through
the vacant orbital. By the coordination of Lewis base to this vacant or-
bital, the electrophilic character is expected to be reduced. In the case
where the coordination be strong enough as to make a bond, such a sili-
con center would no longer show the electrophilic character but behave
as nucleophile; some examples that strongly suggest the nucleophilic
6
character of base-coordinated silylenes have been reported.1 We re-
port herein that (1) the silylenes bearing an 8-amino- or 8-phosphino-
1-naphthyl group behave as nucleophilic sila-ylides during the reaction
with diphenylacetylene and (2) the reaction pathways of the interme-
diates produced by this reaction are highly dependent on the character
of the coordinating element, nitrogen or phosphorus.
Address correspondence to Akio Toshimitsu, Institute for Chemical Research, Kyoto
University, Uji Kyoto 611-0011, Japan.
1409

1410
A. Toshimitsu et al.
RESULTS AND DISCUSSIONS
The pentacoordinate fluorodisilanes 1a–1c bearing an 8-amino- or
8-phosphino-1-naphthyl group, the precursors of the ammonium or
phosphonium sila-ylide, were prepared by the reaction of 8-amino-
or 8-phosphino-1-naphthyllithium with 1,1-difluoro-1,2-dimethyl-2,2-
diphenyldisilane. The coordination of the nitrogen or phosphorus atom
to the silicon atom has been shown in the solid state and in solution by
X-ray crystallographic analysis and by NMR spectroscopy, respectively.
Thermal degradation of 1a–1c was completed at 110–140 C† to af-
ford the -elimination product, fluoromethyldiphenylsilane, in almost
quantitative yield. The other products, base-coordinated silylenes 2,
were trapped with diphenylacetylene to afford various types of cyclized
products 4–6 shown in Figure 1.
In the case of 1a containing the dimethylamino group, the
1-silaphenalene skeleton was formed through the incorporation of
diphenylethenyl group between the silicon atom and naphthyl carbon
accompanied by the migration of the amino group to the silicon atom to
afford 4.
In the case of 1b containing the diethylphosphino group, the products
were the mixture of stereoisomers (ca. 2:1) of the six-membered cyclic
compound 5, which contained an ethylydene bridge between the silicon
atom and the phosphorus atom and a (Z)-diphenylethenyl group on the
silicon atom, indicative of hydrogen migration from the methylene in
the diethylphosphino group to the alkenyl carbon atom.
In the case of 1c containing the diphenylphosphino group, the
product was a seven-membered cyclic compound 6, in which the
diphenylethenyl group was incorporated between the silicon atom and
the phosphorus atom and one phenyl group migrated from the phospho-
rus to silicon. The P to Si phenyl migration was confirmed by a similar
experiment using the di(4-fluorophenyl)phosphino analogue, in which
the 4-fluorophenyl group migrated to afford 60.
All of the cyclization reactions just described are best understood by
assuming that the silicon center in 2 nucleophilically adds to dipheny-
lacetylene to afford the zwitterionic intermediates 3, which contain
Coordination of phosphorus to silicon in 1c has been shown to be similar to that of
nitrogen to silicon in 1a0 (SiPh3 instead of SiMePh2 in 1a) in the following parameters.
%TBPe: 1c, 76%; 1a0, 80%: X Si–F angle: 1c (X = P), 175.89(8) ; 1a0 (X = N), 166.10(9) :
X
Si distance/van der Waals radii: 1c (X = P), 77%; 1a0 (X = N), 78%.
†Temperatures required for the thermal degradation of 1a (140 C), 1b (110 C), and
1c (140 C) indicate that the formation of phosphine-coordinated silylenes 2b and 2c is
not less favorable than that of nitrogen-coordinated silylene 2a.

Base-Coordinated Silylenes
1411
FIGURE 1
alkenyl anion and ammonium or phosphonium cation moeities. For the
diethylphosphino derivative 3b, the alkenyl anion abstracts a proton
from the methylene of the diethylphosphino group to form the phospho-
nium ylide 7. The formed ylide carbanion nucleophilically attacks the
silicon atom, causing silicon phosphorus bond fission, resulting in the
formation of the six-membered cyclic product 5. The reaction course

1412
A. Toshimitsu et al.
of the nitrogen analogue 3a is different from that of 3b, presumably
because the proton abstraction from the dimethylamino group in 3a is
not possible due to the lower ability of nitrogen to stabilize the ylide.
Thus, the alkenyl anion nucleophilically attacks the naphthyl carbon,
accompanied by carbon nitrogen bond fission, which is equivalent to
the migration of the amino group from carbon to silicon. For the di-
arylphosphino derivative 3c where the proton abstraction is also not
possible from the diarylphosphino group, the reaction course is still dif-
ferent from that of 3a. As also shown in Figure 1, the alkenyl anion in
3c nucleophilically attacks the phosphorus atom to form a pentavalent
phosphorane intermediate 8 (or a transition structure), which under-
10
goes ligand coupling7
of the aryl group and the silicon atom on the
phosphorus center, resulting in the formation of the seven-membered
cyclic product 6 or 60. This route seems to have emerged due to the
intrinsic ability of phosphorus to form pentavalent species.
The reaction course of the sila-ylide with acetylenes clearly reflect
the character of the cationic center. Further studies on the reaction
pathways of sila-ylide bearing other cationic moieties should contribute
to clarifying the character of the element.
REFERENCES
[1] D. Seyferth and T. F. O. Lim, J. Am. Chem. Soc., 100, 7074 (1978).
[2] R. J. P. Corriu, G. Lanneau, C. Priou, F. Soulairol, N. Auner, R. Probst, R. Conlin,
and C. Tan, J. Organomet. Chem., 466, 55 (1994).
[3] N. Takeda, H. Suzuki, N. Tokitoh, and R. Okazaki, J. Am. Chem. Soc., 119, 1456
(1997).
[4] J. Belzner, U. Dehnert, H. Ihmels, M. Hu¨bner, P. Mu¨ller, and I. Uso´n, Chem. Eur. J.,
4, 852 (1998).
[5] J. Belzner, In Organosilicon Chemistry III. From Molecules to Materials, eds. N.
Auner and J. Weis (VCH, Weinheim, 1998), p. 58.
[6] K. Tamao, M. Asahara, T. Saeki, S.-G. Fen, and A. Toshimitsu, Chem. Lett., 660
(2000).
[7] G. Wittig and A. Maercker, Chem. Ber., 97, 747 (1964).
[8] D. Seyferth, J. Fogel, and J. K. Heeren, J. Am. Chem. Soc., 88, 2207 (1966).
[9] G. R. Newkome and D. C. Hager, J. Am. Chem. Soc., 100, 5567 (1978).
[10] S. Oae and Y. Uchida, Acc. Chem. Res., 24, 202 (1991).