Insertion of an overcrowded silylene into hydro- and haloboranes: A novel synthesis of silylborane derivatives and their properties

Article abstract of DOI:10.1021/om049558w

Reactions of stable silylene-isocyanide complexes Tbt(Mes)SiCNAr (3a, Ar = Mes*; 3b, Ar = Tbt; 3c, Ar = Tip; Tbt = 2,4,6-tris[bis(trimethylsilyl) methyl]phenyl, Mes = mesityl, Mes* = 2,4,6-tri-tert-butylphenyl, Tip = 2,4,6-triisopropylphenyl) with boron compounds were investigated. Reactions of 3a,b with BH₃·THF afforded the first stable silylborane-isocyanide complexes, Tbt(Mes)SiHBH₂·CNAr (4a,b). Silylene complex 3a reacted with BH₃·PPh₃ as well to give the corresponding silylborane-phosphine complex Tbt(Mes)SiHBH ₂·PPh₃ (12). In addition, silylene 2 thermally generated from the corresponding disilene, Tbt(Mes)Si= Si(Mes)Tbt (1), gave 12 when reacted with BH₃·PPh₃. These results strongly suggested that the reactions of 3 with BH₃·THF and BH ₃·PPh₃ proceeded via insertion of a silylene, Tbt-(Mes)Si: (2), into the B-H bond rather than the nucleophilic attack of the silicon atom of 3 toward the boron atom. Thermal dissociation of 4 and 12 into a base-free silylborane, Tbt(Mes)SiHBH₂ (9), was evidenced by the base-exchange reactions. Furthermore, silylene 2 was found to insert into boron-halogen bonds as well as boron-hydrogen bonds. The novel reactivity of silylene 2 was applied to the syntheses of a variety of silylborane derivatives such as base-free silylboranes, silylborane-isocyanide complexes, and silylborates.

Full text of DOI:10.1021/om049558w

Organometallics 2004, 23, 4723-4734
4723
In ser tion of a n Over cr ow d ed Silylen e in to Hyd r o- a n d
Ha lobor a n es: A Novel Syn th esis of Silylbor a n e
Der iva tives a n d Th eir P r op er ties
Takashi Kajiwara, Nobuhiro Takeda, Takahiro Sasamori, and Norihiro Tokitoh*
Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, J apan
Received J une 16, 2004
Reactions of stable silylene-isocyanide complexes Tbt(Mes)SiCNAr (3a , Ar ) Mes*; 3b,
Ar ) Tbt; 3c, Ar ) Tip; Tbt ) 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, Mes ) mesityl,
Mes* ) 2,4,6-tri-tert-butylphenyl, Tip ) 2,4,6-triisopropylphenyl) with boron compounds were
investigated. Reactions of 3a ,b with BH3‚THF afforded the first stable silylborane-isocyanide
complexes, Tbt(Mes)SiHBH2‚CNAr (4a ,b). Silylene complex 3a reacted with BH3‚PPh3 as
well to give the corresponding silylborane-phosphine complex Tbt(Mes)SiHBH2‚PPh3 (12).
In addition, silylene 2 thermally generated from the corresponding disilene, Tbt(Mes)Sid
Si(Mes)Tbt (1), gave 12 when reacted with BH3‚PPh3. These results strongly suggested that
the reactions of 3 with BH3‚THF and BH3‚PPh3 proceeded via insertion of a silylene, Tbt-
(Mes)Si: (2), into the B-H bond rather than the nucleophilic attack of the silicon atom of
3 toward the boron atom. Thermal dissociation of 4 and 12 into a base-free silylborane,
Tbt(Mes)SiHBH2 (9), was evidenced by the base-exchange reactions. Furthermore, silylene
2 was found to insert into boron-halogen bonds as well as boron-hydrogen bonds. The novel
reactivity of silylene 2 was applied to the syntheses of a variety of silylborane derivatives
such as base-free silylboranes, silylborane-isocyanide complexes, and silylborates.
In tr od u ction
thermal dissociation of 1 into the corresponding silylene
2,6,7 which can be applied to the syntheses of various
organosilicon compounds.6a,8 Furthermore, we have
reported the synthesis and reactions of the first stable
silylene-isocyanide complexes, 3a -c,8c,9,10 which are also
important as the first stable Lewis base complexes of a
silylene.11
In recent years, silylboranes and their derivatives
have attracted much attention from the standpoints of
both fundamental and applied chemistry. Transition
metal-catalyzed additions of silylboranes to unsaturated
organic molecules (silaboration reactions) have been
actively investigated.1 Generation of silyl anions2 and
silyl radicals3 from silylboranes has also been reported,
showing their potential in the syntheses of organosilicon
compounds. Furthermore, (triarylsilyl)dimesitylboranes
have been reported to exhibit absorption in the visible
region due to their Si-B moiety.4 Despite these inter-
esting properties and the relatively long history of
silylboranes, their chemistry has not been fully disclosed
yet mainly due to the limited synthetic methods for
them.
Silylboranes are most commonly prepared by the
reaction of silyllithium with halo-, hydro-, or alkoxy-
boranes.5 However, due to the high reactivity of silyl-
boranes and the difficulty in the preparation of precur-
sors, only a few examples are known to date. In this
context, development of a novel synthetic method of
silylboranes has long been desired.
Although silylene complexes with Lewis bases have
been extensively studied,11 there has been much less
(5) For example, see: (a) No¨th, H.; Ho¨llerer, G. Angew. Chem., Int.
Ed. Engl. 1962, 1, 551-552. (b) No¨th, H.; Ho¨llerer, G. Chem. Ber. 1966,
99, 2197-2205. (c) Biffar, W.; No¨th, H.; Pommerening, H. Angew.
Chem., Int. Ed. Engl. 1980, 19, 56-57. (d) Biffar, W.; No¨th, H.;
Schwertho¨ffer, R. Liebigs Ann. Chem. 1981, 2067-2080. (e) Buynak,
J . D.; Geng, B. Organometallics 1995, 14, 3112-3115. (f) Bonnefon,
E.; Birot, M.; Dunogue`s, J .; Pillot, J .-P.; Courseille, C.; Taulelle, F. Main
Group Metal Chem. 1996, 19, 761-767. (g) Suginome, M.; Matsuda,
T.; Ito, Y. Organometallics 2000, 19, 4647-4649.
(6) (a) Tokitoh, N.; Suzuki, H.; Okazaki, R.; Ogawa, K. J . Am. Chem.
Soc. 1993, 115, 10428-10429. (b) Suzuki, H.; Tokitoh, N.; Okazaki,
R.; Harada, J .; Ogawa, K.; Tomoda, S.; Goto, M. Organometallics 1995,
14, 1016-1022.
On the other hand, we have reported the synthesis
of an extremely hindered disilene 1 and found the
* Corresponding author. E-mail: tokitoh@boc.kuicr.kyoto-u.ac.jp.
(1) For recent reviews, see: (a) Suginome, M.; Ito, Y. Chem. Rev.
2000, 100, 3221-3256. (b) Suginome, M.; Ito, Y. J . Organomet. Chem.
2003, 680, 43-50.
(2) Kawachi, A.; Minamimoto, T.; Tamao, K. Chem. Lett. 2001,
1216-1217.
(3) Matsumoto, A.; Ito, Y. J . Org. Chem. 2000, 65, 5707-5711.
(4) Pillot, J .-P.; Birot, M.; Bonnefon, E.; Dunogue`s, J .; Rayez, J .-C.;
Rayez, M.-T.; Liotard, D.; Desvergne, J .-P. Chem. Commun. 1997,
1535-1536.
(7) For a review on silylenes, see: Gaspar, P. P.; West, R. In The
Chemistry of Organic Silicon Compounds; Rappoport, Z., Apeloig, Y.,
Eds.; J ohn Wiley & Sons: New York; 1998; Vol. 2; Part 3; pp 2463-
2568.
10.1021/om049558w CCC: $27.50 © 2004 American Chemical Society
Publication on Web 08/27/2004

4724 Organometallics, Vol. 23, No. 20, 2004
Kajiwara et al.
Sch em e 1. Rea ction of 3 w ith BH3‚THF
focus on the reactions of silylenes with Lewis acids.12-16
Theoretical calculations by Bharatam et al. have re-
vealed that nucleophilicity of a silylene can be shown
only after its electrophilicity gets satisfied, though a
silylene itself usually shows electrophilicity.14 Indeed,
a recently reported silylene-borane adduct A, which is
slowly converted into silylborane B, has been obtained
from the corresponding silylene having a delocalized 6
π-electron system, where the π-electrons are delocalized
on the vacant p orbitals of the silicon atom.15-17
Sch em e 2. P ossible Mech a n ism s for th e
F or m a tion of 4
During the course of our studies on the properties of
silylene-isocyanide complexes 3a -c,8c,9,10 we have found
that they show not only reactivity as a silylene equiva-
lent but also high reactivity toward electrophilic
reagents.9b This finding has prompted us to investigate
the reactions of silylene-isocyanide complexes 3 with
boron compounds, and we have succeeded in the syn-
thesis of the first stable silylborane-isocyanide com-
plexes by the reaction of 3a ,b with BH3‚THF.18 Here,
we describe the reactions of 3 (or disilene 1) with various
kinds of hydro- and haloboranes giving base-free si-
lylboranes or silylborane-Lewis base complexes, de-
pending on the substituents at the boron atom. The
formation mechanism of the silylboranes is discussed
in detail, and the thermal reaction of resulting silyl-
borane-isocyanide complexes is also described.
respectively, together with hydrosilanes 5 and 6 (Scheme
1). By contrast, no silylborane complex 4c was obtained
in the reaction of 3c, although the formation of 5 and 6
was confirmed (Scheme 1). In these reactions, the yields
of the products were affected by the amount of BH3‚
THF used. Thus, the reaction of 3a with an excess
amount (5.5 molar equiv) of BH3‚THF gave hydrosilane
5 as a main product (59%) along with 4a (4%) and 6
(15%) (Scheme 1).
The formation of 4a ,b can be explained by two
possible mechanisms. One involves the initial dissocia-
tion of silylene-isocyanide complexes 3 into the corre-
sponding silylene 2 and isocyanides 7. Silylene 2 thus
generated inserts into the B-H bond of BH3. The
coordination of the isocyanide to the boron atom of the
resultant base-free silylborane leads to the final product
4 (Scheme 2). The other involves the initial electrophilic
attack of BH3 at the lone pair of the silicon atom of 3 to
afford the Lewis acid-silylene-Lewis base adduct,14
followed by the consecutive migration giving 4 (Scheme
2). At this stage, we can rule out neither mechanism,
and the studies on the reaction mechanism will be
discussed later.
Resu lts a n d Discu ssion
Rea ction of 3 w ith BH3‚THF . Reaction of silylene-
isocyanide complexes 3a and 3b with BH3‚THF afforded
the corresponding silylborane-isocyanide complexes 4a
and 4b as air-stable compounds in 33 and 35% yields,
(8) (a) Suzuki, H.; Tokitoh, N.; Okazaki, R. J . Am. Chem. Soc. 1994,
116, 11572-11573. (b) Suzuki, H.; Tokitoh, N.; Okazaki, R. Bull. Chem.
Soc. J pn. 1995, 68, 2471-2481. (c) Tokitoh, N.; Suzuki, H.; Takeda,
N.; Kajiwara, T.; Sasamori, T.; Okazaki, R. Silicon Chem. 2002, 1, 313-
319.
(9) (a) Takeda, N.; Suzuki, H.; Tokitoh, N.; Okazaki, R.; Nagase, S.
J . Am. Chem. Soc. 1997, 119, 1456-1457. (b) Takeda, N.; Kajiwara,
T.; Suzuki, H.; Okazaki, R.; Tokitoh, N. Chem. Eur. J . 2003, 9, 3530-
3543.
(10) (a) Takeda, N.; Tokitoh, N.; Okazaki, R. Chem. Lett. 2000, 244-
245. (b) Takeda, N.; Tokitoh, N.; Okazaki, R. Chem. Lett. 2000, 622-
623.
(11) For a review on silylene-Lewis base complexes, see: Belzner,
J .; Ihmels, H. Adv. Organomet. Chem. 1999, 43, 1-42.
(12) (a) Timms, P. L.; Ehlert, T. C.; Margrave, J . L.; Brinckman, F.
E.; Farrar, T. C.; Coyle, T. D. J . Am. Chem. Soc. 1965, 87, 3819-3823.
(b) Kirk, R. W.; Smith, D. L.; Airey, W.; Timms, P. L. J . Chem. Soc.,
Dalton Trans. 1972, 1392-1396.
(13) Bock, C. W.; Trachtman, M.; Mains, G. J . J . Phys. Chem. 1988,
92, 294-299, and references therein.
(14) (a) Prasad, B. V.; Kaur, D.; Uppal, P. Indian J . Chem. A 1997,
36, 1013-1017. (b) Bharatam, P. V.; Moudgil, R.; Kaur, D. Organo-
metallics 2002, 21, 3683-3690. (c) Bharatam, P. V.; Moudgil, R.; Kaur,
D. Inorg. Chem. 2003, 42, 4743-4749.
(15) Metzler, N.; Denk, M. Chem. Commun. 1996, 2657-2658.
(16) Reactions of decamethylsilicocene Cp*2Si with boron halides
leading to Si-B systems via intermediary silylene-borane adducts have
been reported. Holtmann, U.; J utzi, P.; Ku¨hler, T.; Neumann, B.;
Stammler, H.-G. Organometallics 1999, 18, 5531-5538.
(17) Borane adducts of intramolecularly base-stabilized germylene
and stannylene have also been reported. Drost, C.; Hitchcock, P. B.;
Lappert, M. F. Organometallics 1998, 17, 3838-3840.
(18) Takeda, N.; Kajiwara, T.; Tokitoh, N. Chem. Lett. 2001, 1076-
1077.
Very recently, silylborane-isocyanide complexes have
been postulated as reactive intermediates in the inser-
tion reactions of isocyanides into the silicon-boron bond
of silylboranes, giving the corresponding (boryl)(silyl)-
iminomethanes,19 although no spectral evidence for the
intermediates has been observed. Compounds 4a ,b are
the first examples of isolation of silylborane-isocyanide
complexes, and therefore, it is very attractive to inves-
tigate their structure and properties.
Sp ectr a l P r op er ties of Silylbor a n e-Isocya n id e
Com p lexes 4. The 29Si NMR spectra of 4a ,b showed
very broad and weak signals at -43.3 ppm for 4a and
-39.9 ppm for 4b, respectively. This severe broadening
of the signals is attributed to the fast quadrupole-
induced relaxation of the boron atom and the scalar
coupling with 10B and 11B, strongly suggesting the
existence of B-Si bonds. Although the resonances for
the protons assignable to the BH2 group for 4a ,b and
the signal of the isocyanide carbon for 4b were not
1
observed in the H and 13C NMR spectra probably due
(19) Suginome, M.; Fukuda, T.; Nakamura, H.; Ito, Y. Organome-
tallics 2000, 19, 719-721.

Insertion of Silylene into Hydro- and Haloboranes
Organometallics, Vol. 23, No. 20, 2004 4725
(Mes*NC)4] (1.14-1.20 Å),28 and the Tbt-substituted
free isocyanide 7b (1.156(7) Å).9b
Th eor etica l Ca lcu la tion s for Silylbor a n e-Isocya -
n id e Com p lex. Spectral data and structural param-
eters for 4a ,b thus obtained were compared with
theoretical values29 for Ph2SiHBH2‚CNPh, the model
compound of 4a ,b with phenyl groups. The structure
optimized at the B3LYP/6-31G(d) level was similar to
that analyzed by X-ray crystallography except for the
bond angles around the silicon atom (Figure 2). The
observed C2-Si1-B1 bond angle (121.81(16)°) is slightly
larger than the calculated ones (110.6° and 112.0°),
while the C29-Si1-B1 bond angle (104.43(16)°) is
smaller. These differences are probably due to the steric
congestion caused by the extremely bulky Tbt group.
Vibrational frequencies of B-H, CtN, and Si-H,
calculated at the B3LYP/6-31G(d) level and scaled by
0.9613,30 were in good agreement with those experi-
mentally observed (Table 1). Calculations of NMR
chemical shifts at the GIAO-B3LYP/6-311+G(2d,p) level
also gave values similar to the experimental ones, except
the 29Si NMR chemical shifts (Table 1). This difference
is probably caused by the above-mentioned structural
difference around the silicon atom, since calculations
for a bulkier model compound, Mes(Ph)SiHBH2‚CNPh,
gave the geometry around the silicon atom (118.1° for
CMes-Si-B and 110.7° for CPh-Si-B) similar to that
analyzed and the 29Si NMR chemical shift (-20.49 ppm)
was also comparable to the observed one (Figure 2 and
Table 1).31
F igu r e 1. ORTEP drawing of 4a with thermal ellipsoid
plots (50% probability).
to the same reason (a broad signal assigned to the
isocyanide carbon was observed at 151.2 ppm in the 13C
NMR of 4a ), the absorptions assignable to the B-H
(2400 and 2369 cm-1 for 4a and 2400 and 2365 cm-1
for 4b) and CtN (2213 cm-1 for 4a and 2207 cm-1 for
4b) stretchings were observed along with the Si-H
stretchings (2139 cm-1 for 4a and 2126 cm-1 for 4b) in
the IR spectra. The 11B NMR spectra showed signals in
the region of tetracoordinated borons (-42.6 ppm for
4a and -43.0 ppm for 4b) to support the existence of
BH2 moieties.
X-r a y Str u ctu r a l An a lysis of Silylbor a n e-Isocya -
n id e Com p lex 4a . Single crystals of 4a suitable for
X-ray crystallographic analysis were obtained by re-
crystallization from benzene. The ORTEP drawing of
4a (Figure 1) shows the tetrahedral geometry of the
silicon atom and the almost linear B1-C1-N1-C38
structure. The Si1-B1-C1 angle (105.9(3)°) suggests
that the boron atom has a tetrahedral geometry. The
Si1-B1 bond length (2.052(4) Å) of 4a is slightly longer
than those of the previously reported silylborane-
phosphine complex Me3SiBH2‚P(C6H12)3 (2.007(4) Å)20,21
and lithium silylborates (RPh2SiBH3)Li (R ) Ph, t-Bu)
(1.984-1.993 Å)22 and is close to those of tri- and
tetrasilylborates [(Me3Si)3BR]Li (R ) Me, SiMe3) (2.017-
2.034 Å),21 silylborohydride complexes of tantalum
(2.02-2.030 Å),23 and dimesityl(triphenylsilyl)borane
(2.106(4) Å).5f The B1-C1 bond length (1.538(6) Å) of
4a is shorter than that of o-Me3SiO-C6H4NC‚BPh3
(1.616(2) Å)24 and almost equal to those of polyhedral
heteroborane-isocyanide adducts (1.537-1.560 Å).25 The
C-N bond length of 4a (1.154(4) Å)26 is almost the same
as those of the rhodium complex [RhCl(Mes*NC)3]
(1.142-1.175 Å),27 the platinum complex [Pt2(µ-S)-
(26) Some of the structural parameters for 4a reported in the
preliminary communication18 have been revised in this paper by
reanalyzing with the newer version of the crystal structure analysis
package.43 The results for crystallographic analysis for 4a described
in this paper are identical with those submitted to the CCDC.
(27) Yamamoto, Y.; Aoki, K.; Yamazaki, H. Inorg. Chem. 1979, 18,
1681-1687.
(28) Yamamoto, Y.; Yamazaki, H. J . Chem. Soc., Dalton Trans. 1986,
677-680.
(29) All calculations were carried out using Gaussian 98W or
Gaussian 03W programs. (a) Frisch, M. J .; Trucks, G. W.; Schlegel, H.
B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J . R.; Zakrzewski, V. G.;
Montgomery, J . A., J r.; Stratmann, R. E.; Burant, J . C.; Dapprich, S.;
Millam, J . M.; Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.;
Tomasi, J .; Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli,
C.; Adamo, C.; Clifford, S.; Ochterski, J .; Petersson, G. A.; Ayala, P.
Y.; Cui, Q.; Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari,
K.; Foresman, J . B.; Cioslowski, J .; Ortiz, J . V.; Baboul, A. G.; Stefanov,
B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.;
Martin, R. L.; Fox, D. J .; Keith, T.; Al-Laham, M. A.; Peng, C. Y.;
Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; J ohnson, B.; Chen,
W.; Wong, M. W.; Andres, J . L.; Gonzalez, C.; Head-Gordon, M.;
Replogle, E. S.; Pople, J . A. Gaussian 98, Revision A.9; Gaussian,
Inc.: Pittsburgh, PA, 1998. (b) Frisch, M. J .; Trucks, G. W.; Schlegel,
H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J . R.; Montgomery, J .
A., J r.; Vreven, T.; Kudin, K. N.; Burant, J . C.; Millam, J . M.; Iyengar,
S. S.; Tomasi, J .; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.;
Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota,
K.; Fukuda, R.; Hasegawa, J .; Ishida, M.; Nakajima, T.; Honda, Y.;
Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J . E.; Hratchian, H. P.;
Cross, J . B.; Adamo, C.; J aramillo, J .; Gomperts, R.; Stratmann, R.
E.; Yazyev, O.; Austin, A. J .; Cammi, R.; Pomelli, C.; Ochterski, J . W.;
Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J .
J .; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.;
Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman,
J . B.; Ortiz, J . V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J .;
Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
Martin, R. L.; Fox, D. J .; Keith, T.; Al-Laham, M. A.; Peng, C. Y.;
Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; J ohnson, B.; Chen,
W.; Wong, M. W.; Gonzalez, C.; Pople, J . A. Gaussian 03, Revision B.05;
Gaussian, Inc.: Pittsburgh, PA, 2003.
(20) Blumenthal, A.; Bissinger, P.; Schmidbaur, H. J . Organomet.
Chem. 1993, 462, 107-110.
(21) Imamoto et al. have also reported the same compound, although
structural analysis has not been reported. Imamoto, T.; Hikosaka, T.
J . Org. Chem. 1994, 59, 6753-6759.
(22) Lippert, W.; No¨th, H.; Ponikwar, W.; Seifert, T. Eur. J . Inorg.
Chem. 1999, 817-823.
(23) J iang, Q.; Carroll, P. J .; Berry, D. H. Organometallics 1993,
12, 177-183.
(24) Tamm, M.; Lu¨gger, T.; Hahn, F. E. Organometallics 1996, 15,
1251-1256.
(30) For the scaling factor of 0.9613, see: Wong, M. W. Chem. Phys.
Lett. 1996, 256, 391-399.
(25) Sˇt´ıbr, B.; Holub, J .; J el´ınek, T.; Fontaine, X. L. R.; Fusek, J .;
Kennedy, J . D.; Thornton-Pett, M. J . Chem. Soc., Dalton Trans. 1996,
1741-1751.
(31) The 29Si NMR chemical shift (-23.19 ppm) calculated for Ph2-
SiHBH2‚CNPh, the structure of which was fixed to the geometry
determined by X-ray analysis, was comparable to the observed value.

4726 Organometallics, Vol. 23, No. 20, 2004
Kajiwara et al.
F igu r e 2. Structural parameters of 4a (observed)26 and Ph2SiHBH2‚CNPh and Mes(Ph)SiHBH2‚CNPh (calculated).
Ta ble 1. Sp ectr a l Da ta for 4a ,b (obser ved ) a n d P h 2SiHBH2‚CNP h a n d Mes(P h )SiHBH2‚CNP h (ca lcu la ted )
4a
4b
Ph2SiHBH2‚CNPh
Mes(Ph)SiHBH2‚CNPh
δH(Si-H)
δB(Si-B)
δSi(Si-B)
δC(N-C)
ν(B-H)
5.21
5.14
-43.0
-39.9
not observed
2400, 2365
2207
5.53a
5.60a
-42.6
-43.3
151.2
2400, 2369
2213
-52.54a
-6.42a
160.74a
2445, 2393b
2201b
-49.33a
-20.49a
160.75a
2452, 2406b
2198b
ν(CtΝ)
ν(Si-H)
2139
2126
2092b
2094b
a
b
Calculated at the GIAO-B3LYP/6-311+G(2d,p) level. Calculated at the B3LYP/6-31G(d) level and scaled by 0.9613.
Sch em e 3. Th er m olysis of 4
Interestingly, thermolysis of the isolated 8a at 120
°C resulted in the regeneration of the original silyl-
borane-isocyanide complex 4a to give a 1:5 mixture of
4a and 8a (Scheme 4). This product ratio was the same
as that observed in the case of thermolysis of 4a . This
result strongly suggests the existence of an equilibrium
between 4a and 8a .
Mech a n ism of th e Migr a tion Rea ction of 4 a n d
8. Thermal reaction of silylborane-isocyanide complex
4a in the presence of isocyanide 7b proceeded at 120
°C to give not only the migration product but also the
silylborane complexes with the Tbt-substituted iso-
cyanide 7b. Thus, a mixture of four compounds, i.e., the
original complex 4a (trace), migration product 8a (mi-
nor), base-exchanged product 4b (trace), and migration
and base-exchanged product 8b (major), was obtained
as judged by the 1H NMR spectra, where 8a and 8b
were observed with the ratio of 1:4 (Scheme 5).
The mechanism of the isocyanide-exchange reaction
is reasonably interpreted in terms of the initial dis-
sociation of silylborane complex 4a into the correspond-
ing base-free silylborane 9 and isocyanide 7a , followed
by the complexation of 9 with 7b to give 4b. Since the
migration reaction and the isocyanide-exchange reaction
occur at the same temperature, the migration reaction
is also suggested to proceed via the initial dissociation
into the free silylborane. Although the detailed mech-
anism of the migration reaction is not clear at present,
the bridged structure 11 might be a possible intermedi-
ate (Scheme 6). There have been no reports on the
doubly bridged silylborane such as 11, but theoretical14c
and experimental32 evidence have been reported for
several compounds having an Si-H-B bridge.33
Th er m olysis of Silylb or a n e-Isocya n id e Com -
p lexes 4. When complex 4a was heated at 120 °C in
C6D6, a 1:5 mixture of 4a and the corresponding mesityl-
migrated product 8a was obtained (Scheme 3). In
contrast to the case of previously reported intermediary
silylborane-isocyanide complexes,19 (boryl)(silyl)imi-
nomethane (silyl-migrated product) was not formed in
this reaction. Thermolysis of 4b at 120 °C in C6D6 also
gave a mixture of 4b and 8b with the ratio of 1:10
(Scheme 3).
1
The structures of 8a ,b were determined by H, 13C,
and 11B NMR spectra, difference NOE experiments, and
1
IR spectra. The BH proton was not observed in the H
NMR spectra, as in the case of 4, but 11B NMR spectra
showed signals in the region of tetracoordinated borons
(-37.0 ppm for 8a and -36.5 ppm for 8b), suggesting
the existence of a BH part. In the IR spectra were
observed the absorptions assignable to the B-H stretch-
ings (2348 cm-1 for 8a and 2362 cm-1 for 8b) as well as
the CtN (2199 cm-1 for 8a and 2197 cm-1 for 8b) and
Si-H (2110 cm-1 for 8a and 2084 cm-1 for 8b) stretch-
ings. The difference NOE experiments on 8a showed the
NOEs of the SiH protons only with the o-methine
protons of the Tbt group, while both peaks for the
o-methine protons of the Tbt group and the o-methyl
protons of the mesityl group were enhanced by the
irradiation of the SiH proton in the case of 4a (Figure
3). These observations indicate the absence of not the
Tbt group but the mesityl group on the silicon atom in
8a . Observed spectral data were in good agreement with
those calculated for PhSiH2BH(Ph)‚CNPh (Table 2).29
(32) Wrackmeyer, B.; Milius, W.; Tok, O. L. Chem. Eur. J . 2003, 9,
4732-4738.
(33) A similar type of double migration ([1,2]2-dyotropic rearrange-
ment) has been postulated in the reactions of Cp*2Si with Cp*BCl2;
see ref 16.

Insertion of Silylene into Hydro- and Haloboranes
Organometallics, Vol. 23, No. 20, 2004 4727
F igu r e 3. Observed NOEs for 4a and 8a .
Ta ble 2. Sp ectr a l Da ta for 8a ,b (obser ved ) a n d
Sch em e 6. P la u sible Mech a n ism for th e Rea ction
of 4a w ith 7b
P h SiH2BH(P h )‚CNP h (ca lcu la ted )
8a
8b
PhSiH2BH(Ph)‚CNPh
δH(Si-H)
δB(Si-B)
ν(B-H)
ν(CtΝ)
4.54-4.56
-37.0
2348
2199
2110
4.38, 4.69
-36.5
2362
2197
2084
4.91a
-37.75a
2396b
2192b
ν(Si-H)
2122, 2101b
a
b
Calculated at the GIAO-B3LYP/6-311+G(2d,p) level. Calcu-
lated at the B3LYP/6-31G(d) level and scaled by 0.9613.
Sch em e 4. Th er m olysis of 8a
Sch em e 5. Th er m olysis of 4a in th e P r esen ce of
Isocya n id e 7b
Sch em e 7. Rea ction of 3a or 1 w ith BH3‚P P h 3
2 rather than the electrophilic attack of the boron
reagent to the silicon atom of 3. Indeed, silylborane-
phosphine complex 12 was also obtained by the reaction
of BH3‚PPh3 with disilene 1, which gives the corre-
sponding base-free silylene 2 upon heating (Scheme 7).
Sp ect r a l a n d St r u ct u r a l P r op er t ies of Silyl-
bor a n e-P h osp h in e Com p lex 12. The structure of 12
From the ratio of the two major compounds (8a :8b )
1:4), it is supposed that the less hindered isocyanide 7b
coordinates more strongly to silylborane 10 than the
more hindered 7a does. This trend is the same as that
in silylene-isocyanide complexes 3.9b
1
Rea ction of 3 w ith BH3‚P P h 3. To elucidate the
mechanism of the reaction of silylene-isocyanide com-
plexes 3 with BH3, the reaction of 3 with BH3‚PPh3 was
examined. When a THF solution of silylene-isocyanide
complex 3a and BH3‚PPh3 was heated at 60 °C in a
sealed tube, the deep blue color of 3a gradually disap-
peared. After the workup and separation with HPLC,
silylborane-phosphine complex 12 was obtained as a
stable compound along with the silylborane-isocyanide
complexes 4a and 8a (Scheme 7). Since the electrophi-
licity at the boron atom of BH3‚PPh3 is suppressed by
the coordination of triphenylphosphine, the formation
of silylborane-phosphine complex 12 strongly suggests
that this reaction proceeds via the insertion of silylene
was determined by H, 13C, 11B, and 31P NMR and IR
spectra. Although the BH2 protons were not observed
1
in the H NMR spectrum, the evidence for their exist-
ence was obtained by 11B NMR (-36.5 ppm) and IR
(B-H stretches: 2396 and 2360 cm-1) spectra, as in the
case of silylborane-isocyanide complexes 4. The observa-
tion of an absorption assignable to the B-P stretching
(1437 cm-1) in the IR spectrum clearly indicates the
coordination of the phosphine to the boron atom. The
molecular structure of 12 was determined by X-ray
crystallographic analysis (Figure 4). The structural
parameters for the Si-B-P moiety of 12 were similar
to those of a previously reported silylborane-phosphine
complex, Me3SiBH2‚P(C6H12)3 (C) (Figure 5).20

4728 Organometallics, Vol. 23, No. 20, 2004
Kajiwara et al.
Sch em e 9. Ba se Exch a n ge Rea ction of 12
Sch em e 10. Rea ction of 4a w ith BH3‚THF
F igu r e 4. ORTEP drawing of 12 with thermal ellipsoid
plots (50% probability).
migration of the mesityl group in 9 followed by the
coordination with isocyanide 7a gives 8a .
According to the mechanism shown in Scheme 8,
thermal dissociation of silylborane-phosphine complex
12 may occur at 60 °C (or below), which is much lower
than the dissociation temperature of silylborane-iso-
cyanide complexes 4 and 8 (120 °C). To confirm the
thermal dissociation of 12, the base-exchange reaction
of the isolated 12 was examined.
F igu r e 5. Structural parameters of 12 and Me3SiBH2‚
P(C6H12)3.
When a C6D6 solution of compound 12 and Mes*NC
(7a ) was heated at 60 °C for 6 h, no change was
observed. The base-exchange reaction started to occur
at 80 °C, although the major compound was still 12.
Heating at 80 °C for 4 h gave a mixture of 12, 4a , and
8a with the ratio of 20:1:5 (Scheme 9). This difference
in the ratio of products between the reaction of 3a with
BH3‚PPh3 and the reaction of 12 with 7a may be
attributed to the difference in the concentration of the
reaction mixture or that in the ratio of 12 to 7a . In both
cases, mesityl-migrated silylborane-phosphine complex
13 was not obtained probably due to the severe steric
repulsion.
Sch em e 8. Mech a n ism for th e F or m a tion of 12
Since silylborane-phosphine complex C has not been
reported to liberate the base-free silylborane,34 it is very
interesting that dissociation of 12 (and also that of
silylborane-isocyanide complexes 4 and 8) proceeds upon
heating. We believe that the introduction of the ex-
tremely bulky substituents to the silicon atom (and also
to the isocyanides or the phosphine) facilitates the
dissociation.
Mech a n ism of th e Rea ction of 3 w ith BH3‚THF .
The formation of silylborane complexes 4 in the reaction
of silylene-isocyanide complexes 3 with hydroboranes
is reasonably interpreted in terms of the insertion of a
base-free silylene 2 into the B-H bond rather than the
electrophilic attack of hydroboranes to the silicon atom
(vide supra). To elucidate the formation mechanism of
the hydrosilane byproducts 5 and 6, the reaction of 4
with BH3‚THF was examined.
Although 4a did not react with BH3‚THF at room
temperature, the reaction at 120 °C afforded a mixture
including hydrosilanes 5 and 6 (5:6 ) 1:4) (Scheme 10).
Since 4 dissociates into the base-free silylborane 9 and
isocyanides 7 at this temperature, it is strongly sug-
Mech a n ism of th e Rea ction of 3a w ith BH3‚P P h 3.
As described above, the formation of 12 strongly sug-
gests the silylene-insertion mechanism for the reaction
of silylene-isocyanide complexes 3 with boranes. In
addition, this insertion mechanism is supported by the
thermal reaction of disilene 1 with BH3‚PPh3 giving the
same product 12. A plausible mechanism for the reac-
tion of 3a (or 1) with BH3‚PPh3 is shown in Scheme 8:
(1) silylene 2 generated from silylene-isocyanide complex
3a or disilene 1 inserts into the B-H bond of BH3‚PPh3,
(2) the resulting silylborane-phosphine complex 12
dissociates into the corresponding base-free silylborane
9, and then (3) the coordination of isocyanide 7a ,
generated from 3a , to 9 affords 4a , while (4) the
(34) See ref 5e, although details of reaction conditions have not been
described.

Insertion of Silylene into Hydro- and Haloboranes
Organometallics, Vol. 23, No. 20, 2004 4729
Sch em e 11. Mech a n ism for th e Rea ction of 3 w ith
Sch em e 12. Rea ction of 2 w ith Na BH4
BH3‚THF
Sch em e 13. Rea ction of 2 w ith P in a colbor a n e
gested that hydrosilanes 5 and 6 might be derived from
9 and 10, respectively. Thus, the following mechanism
(Scheme 11) for the reaction of silylene-isocyanide
complexes 3 with BH3‚THF is proposed: (1) B-H
insertion of silylene 2 generated from 3 leads to the
base-free silylborane 9, (2) the coordination of isocyanide
7 once dissociated from 3 affords a silylborane-iso-
cyanide complex 4, while the reaction of 9 with an
additional BH3 gives dihydrosilane 5, (3) the migration
of a mesityl group of 9 before the reaction with 7 or BH3
resulted in the generation of 10, and the subsequent
reaction of 10 with 7 or BH3 gives silylborane-isocyanide
complex 8 or trihydrosilane 6, respectively. Although
8a could not be isolated in the reaction of 3a with BH3‚
THF, the careful search on the 1H NMR spectrum of
the crude mixture resulted in the detection of a small
amount of 8a . It is considered that the migration
reaction of silylborane 9 followed by the coordination
of 7a actually took place at 0 °C, but the resulting 8a
slowly decomposed during separation.
This mechanism is supported by the fact that the
reaction of 3 with excess BH3 resulted in the increase
of the yield of hydrosilanes 5 and 6 and the decrease of
that of 4. No production of silylborane complex 4c in
the case of 3c is also explained by this mechanism. In
silylene complexes 3, as reported previously,9b coordina-
tion of isocyanide 7c is much stronger than that of 7a
and 7b. Therefore, the concentration of silylene 2
generated in situ is much lower in this case, and there
is an excess amount of BH3 relative to 9 generated by
the reaction of 2 with BH3 in the reaction mixture.
Reaction of 9 (and 10) with an additional BH3 prefer-
entially occurred to give hydrosilanes 5 (and 6), as in
the case of the reaction of 3a with excess BH3‚THF.
Rea ction of Silylen e 2 w ith Na BH 4. Treatment of
silylene-isocyanide complex 3a with NaBH4 led to the
gradual disappearance of the deep blue color of 3a . The
1H NMR spectrum of the reaction mixture showed a
signal assignable to the SiH proton at 5.23 ppm, and
the 11B NMR spectrum showed a quartet at -38.8 ppm
(J ) 81 Hz). Similar chemical shifts and coupling
constants of the quartets have been reported for lithium
silylborates (RPh2SiBH3)Li (R ) Ph, -42.6 ppm, 78 Hz;
R ) t-Bu, -43.8 ppm, 78 Hz),22 strongly suggesting the
formation of sodium (silyl)trihydroborate 14. The ther-
mal reaction of disilene 1 with NaBH4 also afforded 14
via silylene 2 (Scheme 12). In both cases, unfortunately,
silylborate 14 could not be isolated due to its decomposi-
tion during purification.
Rea ction of Silylen e 2 w ith P in a colbor a n e. The
reaction of silylene-isocyanide complex 3a with pina-
colborane proceeded in a few minutes to give the
corresponding silyl(pinacol)borane 15 in 58% yield
(Scheme 13). Silylborane-isocyanide complex 16 was not
obtained in this case probably due to the decrease of
the electrophilicity at the boron atom, which is caused
by the delocalization of the lone pairs at the oxygen
atoms adjacent to the vacant p orbital of the boron atom.
By contrast, the reaction of 3c with pinacolborane
proceeded very slowly, and only 9% of 15 was obtained
even after the reaction for several days (Scheme 13).
This difference in the reactivity agrees with the previous
results that isocyanide 7c coordinates more strongly to
silylene 2 than 7a does,9b and these results also support
the silylene-insertion mechanism. Indeed, the reaction
of disilene 1 with pinacolborane also gave 15 in 74%
yield (Scheme 13).
In reactions of silyllithiums with boron compounds,
the formation of silylboranes is severely limited by their
high propensity to react with an additional silyllithium
giving silylborates.5e,35 It is interesting that we suc-
ceeded in the synthesis of silylboranes and silylborates
by the reactions of silylene 2 with hydroboranes and
hydroborates, respectively.
Although insertion reactions of isocyanides into the
Si-B bond of silylboranes have been reported,19 silyl-
borane 15 did not react with Mes*NC (7a ) even at 80
°C (Scheme 14). This difference may be explained by
the difference in the reaction conditions (solvent and/
or concentration) or, probably more significantly, by the
(35) For examples of the syntheses of silylborates, see: (a) Seyferth,
D.; Raab, G.; Grim, S. O. J . Org. Chem. 1961, 26, 3034-3035. (b) Biffar,
W.; No¨th, H. Angew. Chem., Int. Ed. Engl. 1980, 19, 58-65. (c) Biffar,
W.; No¨th, H. Chem. Ber. 1982, 115, 934-945. (d) Ref 22.

4730 Organometallics, Vol. 23, No. 20, 2004
Kajiwara et al.
Sch em e 14. Rea ction of 15 w ith Isocya n id e 7a
Sch em e 15. Rea ction of 3a w ith BF 3‚OEt2
F igu r e 6. ORTEP drawing of 20 with thermal ellipsoid
plots (30% probability).
Sch em e 16. Rea ction of 2 w ith Ch lor obor a n es
the direct synthesis of silylcatecholboranes from silyl-
lithiums has not been successful and only a multistep
synthesis has been reported,5e,g our method has the
great advantage of preparing a silylcatecholborane
directly from a silylene.
Con clu sion s
Reactions of the stable silylene-isocyanide complexes
3 with hydroboranes gave the corresponding (hydro-
silyl)boranes or their complexes. The reaction mecha-
nism can be reasonably interpreted in terms of the
insertion of a base-free silylene 2 into the B-H bond of
hydroboranes. Although silylene 2 was inactive to B-C,
B-O, and B-N bonds, 2 was found to undergo insertion
into a B-halogen bond to give the corresponding
(halosilyl)boranes.
Since silylboranes are generally not very stable and
their synthetic method is limited, there have been only
a few examples to date. Although hydrogenated or
halogenated silylboranes may be versatile precursors for
various kinds of functionalized silylboranes, they have
been difficult to synthesize by the conventional synthetic
methods. By contrast, our synthetic approach was found
to give useful and versatile routes to these compounds.
Further investigations on the reactivity of the (hydro-
silyl)- or (halosilyl)boranes and the derivation to func-
tionalized silylboranes are attractive.
steric congestion of the extremely hindered substituents
(Tbt, Mes, and Mes* groups).
Rea ction of Silylen e 2 w ith Bor on Ha lid es. We
further investigated the reactions of 1 or 3 with various
kinds of boron compounds. Although reactions of 3a
with BPh3, B(OMe)3, or B(NMe2)3 did not proceed at all,
the reaction of 3a with BF3‚OEt2 gave fluorosilane 17
after workup (Scheme 15). The formation of 17 can be
explained by the hydrolysis of an intermediary silylbo-
1
rane, 18, during separation. The H NMR spectrum of
the reaction mixture showed only signals corresponding
to a free isocyanide 7a in this region, strongly suggest-
ing the formation of not silylborane-isocyanide complex
19 but base-free silylborane 18. This result indicates
that silylene 2 inserts into the B-F bond as well as B-H
bonds.
Reaction of disilene 1 with B-chloropinacolborane
proceeded smoothly to afford the corresponding B-Cl
insertion product, (chlorosilyl)pinacolborane 20 (Scheme
16). X-ray crystallographic analysis of 20 showed that
the anticipated structure was correct (Figure 6), al-
though the refinement was not sufficient to provide
accurate bond lengths and angles because of the poor-
ness of the crystal. Similarly, the reaction of 1 or 3a
with B-chlorocatecholborane gave (chlorosilyl)catechol-
borane 21 (Scheme 16). Although the isolation of 21
failed due to its air-sensitivity in the case of 3a , the
recrystallization from hexane resulted in the successful
isolation of pure 21 in the case of 1 (Scheme 16). Since
Exp er im en ta l Section
Gen er a l Rem a r k s. All experiments were performed under
anhydrous conditions with an argon atmosphere unless oth-
erwise noted. 1H NMR (300 MHz), 13C NMR (75 MHz), 11B
NMR (96 MHz), 29Si NMR (59 MHz), and 31P NMR (121 MHz)
spectra were recorded on a J EOL J NM AL-300 spectrometer.
1H NMR (400 MHz), 13C NMR (100 MHz), and 19F NMR (372
MHz) spectra were recorded on a J EOL J NM AL-400 spec-
1
trometer. The H NMR chemical shifts were reported in ppm
downfield from tetramethylsilane (δ scale) and referenced to
the internal residual CHCl3 (7.25 ppm) or C6D5H (7.15 ppm).
The 13C NMR chemical shifts were reported in ppm downfield
from tetramethylsilane (δ scale) and referenced to the carbon-
13 signals of CDCl3 (77.0 ppm) or C6D6 (128.0 ppm). Multiplic-
ity of signals in 13C NMR spectra was determined by DEPT
techniques. The 11B, 29Si, 31P, and 19F NMR chemical shifts
were referenced to the external standards BF3‚OEt2 (0 ppm),
tetramethylsilane (0 ppm), 85% phosphoric acid in water (0

Insertion of Silylene into Hydro- and Haloboranes
Organometallics, Vol. 23, No. 20, 2004 4731
ppm), and CFCl3 (0 ppm), respectively. IR spectra were
recorded on a J ASCO FT/IR-5300 or a J ASCO FT/IR-460 Plus
spectrometer. Mass spectra were recorded on a J EOL J MS-
700 spectrometer. Melting points were determined on a Yanaco
micro melting point apparatus and are uncorrected. Elemental
analyses were carried out at the Microanalytical Laboratory
of the Institute for Chemical Research, Kyoto University. GPC-
HPLC was performed on an LC-918 or an LC-908 (J apan
Analytical Industry Co., Ltd.) equipped with J AIGEL 1H and
2H columns using chloroform or toluene as an eluent. PTLC
CDCl3): δ -0.14 (s, 9H), -0.08 (s, 9H), -0.01 (s, 36H), 0.02
(s, 36H), 0.03 (s, 18H), 1.25 (s, 1H), 1.37 (s, 1H), 1.63 (s, 2H),
2.13 (s, 3H), 2.38 (s, 6H), 2.46 (s, 1H), 2.59 (s, 1H), 5.14 (d,
1H, J ) 6.9 Hz), 6.18 (s, 1H), 6.33 (s, 1+1H), 6.44 (s, 1H), 6.63
(s, 2H), the signals of BH2 were not observed. 13C NMR (75
MHz, CDCl3): δ 0.2 (q), 0.5 (q), 0.7 (q), 0.8 (q), 0.9 (q), 1.0 (q),
1.3 (q), 1.6 (q), 21.0 (q), 25.1 (d × 2), 25.6 (q), 26.9 (d), 27.1 (d),
30.0 (d), 31.4 (d), 119.8 (s), 121.5 (d), 122.3 (d), 126.1 (d), 127.4
(d), 128.7 (d), 129.6 (s), 136.6 (s), 137.1 (s), 142.1 (s), 142.2 (s
× 2), 143.1 (s), 145.7 (s), 151.7 (s), 151.8 (s), the signal of NC
was not observed. 11B NMR (CDCl3): δ -43.0. 29Si NMR
(CDCl3): δ -39.9, 1.4, 1.9, 2.1, 2.3. IR (KBr): 2400 [ν(B-H)],
2365 [ν(B-H)], 2207 [ν(CtN)], 2126 [ν(Si-H)] cm-1. LRMS
(FAB): m/z 1289 [(M - H)+], 1275 [(M - Me)+], 1217 [(M -
was performed with Merck Kieselgel 60 PF254
.
Ma ter ia ls. All reaction solvents were dried and distilled
from CaH2, stored over 4 Å molecular sieves, and then freshly
distilled from Na/benzophenone ketyl under argon prior to use.
C6D6 used as a reaction solvent was dried over Na and then K
mirror. Disilene 1,6 isocyanides 7a ,27 7b,9 and 7c,36 silylene-
isocyanide complexes 3a -c,9 and B-chloropinacolborane37 were
prepared according to the procedures reported in the literature.
TMS)+], 1172 [(M - Mes + H)+]. Anal. Calcd for C64H132
-
BNSi13: C, 59.51; H, 10.30; N, 1.08. Found: C, 59.54; H, 10.49;
N, 1.08.
Rea ction of Silylen e-Isocya n id e Com p lex 3c w ith BH3‚
THF . Silylene-isocyanide complex 3c, prepared from disilene
1 (74.5 mg, 53.2 µmol) and isocyanide 7c (24.7 mg, 108 µmol)
in THF (1.2 mL), was dissolved in THF (1.3 mL) and cooled to
0 °C. A 1.0 M solution of BH3‚THF in THF (90 µL, 90 µmol)
was added, and the mixture was stirred for 15 h, during which
time it was warmed to room temperature. The resulting yellow
solution was evaporated, and hexane was added to the residue.
After the filtration through Celite, the solvent was removed
and the mixture was separated with HPLC (LC-918, CHCl3)
and PTLC (SiO2/hexane). Tbt(Mes)SiH2 (5) was obtained as
the main product (29.0 mg, 41.3 µmol, 39%) together with
TbtSiH3 (6) (5.1 mg, 8.7 µmol, 8%).
Syn th esis of Silylbor a n e-Isocya n id e Com p lex Tbt-
(Mes)SiHBH2‚CNMes* (4a ). Silylene-isocyanide complex 3a ,
prepared from disilene 1 (84.1 mg, 60.1 µmol) and isocyanide
7a (32.8 mg, 121 µmol) in THF (1.2 mL), was dissolved in THF
(1.4 mL) and cooled to 0 °C. A 1.0 M solution of BH3‚THF in
THF (120 µL, 120 µmol) was added, and the mixture was
stirred at 0 °C for 1 h, during which time the deep blue solution
turned pale yellow. After further stirring for 11 h at room
temperature, the solvent was removed. The crude products
were dissolved in hexane, and insoluble materials were
removed by filtration through Celite. After removal of the
solvent, the residue was separated with HPLC (LC-918,
CHCl3) to afford silylborane-isocyanide complex 4a (38.6 mg,
39.2 µmol, 33%) together with Tbt(Mes)SiH2 (5)6b (18.9 mg,
26.9 µmol, 22%) and TbtSiH3 (6)6b (5.6 mg, 9.6 µmol, 8%). 4a :
colorless crystals. Mp: 173-174 °C (dec). 1H NMR (300 MHz,
CDCl3): δ -0.14 (s, 9H), -0.08 (s, 9H), 0.02 (s, 18H), 0.04 (s,
18H), 1.26 (s, 1H), 1.29 (s, 18H), 1.30 (s, 9H), 2.14 (s, 3H), 2.37
(s, 6H), 2.49 (s, 1H), 2.61 (s, 1H), 5.21 (d, 1H, J ) 7.0 Hz),
6.19 (s, 1H), 6.33 (s, 1H), 6.61 (s, 2H), 7.31 (s, 2H), the signals
of BH2 were not observed. 13C NMR (75 MHz, CDCl3): δ 0.6
(q), 0.8 (q), 0.90 (q), 0.94 (q), 1.2 (q), 1.5 (q), 20.9 (q), 25.3 (q),
26.8 (d), 27.0 (d), 29.7 (q), 30.0 (d), 31.2 (q), 35.4 (s), 35.5 (s),
120.3 (s), 122.1 (d), 122.4 (d), 127.5 (d), 128.5 (d), 129.3 (s),
136.8 (s), 137.2 (s), 142.2 (s), 143.4 (s), 147.5 (s), 151.2 (s), 151.7
(s), 151.8 (s), 152.3 (s). 11B NMR (CDCl3): δ -42.6. 29Si NMR
(CDCl3): δ -43.3, 1.5, 1.8, 2.0, 2.3. IR (KBr): 2400 [ν(B-H)],
2369 [ν(B-H)], 2213 [ν(CtN)], 2139 [ν(Si-H)] cm-1. LRMS
(FAB): m/z 1006 [(M + Na)+], 983 [M+], 968 [(M - Me)+], 864
Rea ction of Silylen e-Isocya n id e Com p lex 3a w ith
Excess BH3‚THF . Silylene-isocyanide complex 3a , prepared
from disilene 1 (25.2 mg, 18.0 µmol) and isocyanide 7a (10.0
mg, 36.8 µmol) in THF (0.5 mL), was dissolved in THF (0.8
mL) and cooled to 0 °C. A 1.0 M solution of BH3‚THF in THF
(200 µL, 200 µmol, 5.5 equiv) was added, and the deep blue
color immediately disappeared. The mixture was warmed to
room temperature, and the solvent was removed. The crude
products were dissolved in hexane, and insoluble materials
were removed by filtration through Celite. After removal of
the solvent, the residue was separated with HPLC (LC-918,
CHCl3) and further purified with PTLC (SiO2/hexane) to afford
Tbt(Mes)SiH2 (5) as the main product (14.9 mg, 21.2 µmol,
59%) together with TbtSiH3 (6) (3.1 mg, 5.3 µmol, 15%) and
silylborane-isocyanide complex 4a (1.5 mg, 1.5 µmol, 4%).
Th er m olysis of Silylbor a n e-Isocya n id e Com p lex Tbt-
(Mes)SiHBH2‚CNMes* (4a ). In a 5 mm i.d. NMR tube was
placed a solution of silylborane-isocyanide complex 4a (10.3
mg, 10.5 µmol) in C6D6 (0.6 mL). After five freeze-pump-thaw
cycles, the tube was evacuated and sealed. The solution was
heated at 120 °C in the dark for 6 h and then cooled to room
temperature. The 1H NMR spectrum of this solution showed
the formation of a migration product, TbtSiH2BH(Mes)‚
CNMes* (8a ). A mixture of 4a and 8a was obtained with the
ratio of 1:5, and any other products were not observed. Further
heating at 120 °C for 12 h did not change this ratio. The tube
was opened, and the mixture was separated carefully with
PTLC (SiO2/hexane). The product slowly decomposed on silica
gel during separation. Isolated yield: 4a , 14% (1.5 mg, 1.5
µmol); 8a , 69% (7.1 mg, 7.2 µmol). 8a : colorless crystals. Mp:
94-96 °C (dec). 1H NMR (300 MHz, CDCl3): δ -0.18 (s, 18H),
0.01 (s, 18H), 0.02 (s, 18H), 1.25 (s, 1H), 1.31 (s, 9H), 1.41 (s,
18H), 1.92 (br, s, 2H), 2.17 (s, 3H), 2.42 (s, 6H), 4.54-4.56 (br,
m, 2H), 6.18 (s, 1H), 6.30 (s, 1H), 6.68 (s, 2H), 7.36 (s, 2H),
the signal of BH was not observed. 13C NMR (75 MHz, C6D6):
δ 0.9 (q), 1.0 (q), 1.1 (q), 1.3 (q), 1.5 (q), 1.7 (q), 21.1 (q), 26.0
(d × 2), 30.0 (q), 30.6 (d), 31.0 (q), 31.8 (q), 35.4 (s), 35.8 (s),
120.9 (s), 121.7 (d), 122.5 (d), 126.4 (d), 128.7 (s), 128.9 (d),
129.1 (s), 134.7 (s), 142.9 (s), 143.2 (s), 149.0 (s), 152.0 (s), 152.1
(s), 153.2 (s), the signal of NC was not observed. 11B NMR
(CDCl3): δ -37.0. IR (KBr): 2348 [ν(B-H)], 2199 [ν(CtN)],
[(M - Mes)+], 699 [Tbt(Mes)SiH+]. Anal. Calcd for C55H102
-
BNSi7: C, 67.08; H, 10.44; N, 1.42. Found: C, 66.94; H, 10.69;
N, 1.50.
Syn th esis of Silylbor a n e-Isocya n id e Com p lex Tbt-
(Mes)SiHBH2‚CNTbt (4b). Silylene-isocyanide complex 3b,
prepared from disilene 1 (84.0 mg, 60.0 µmol) and isocyanide
7b (69.2 mg, 120 µmol) in THF (1.4 mL), was dissolved in THF
(1.4 mL) and cooled to 0 °C. To this solution was added a 1.0
M solution of BH3‚THF in THF (120 µL, 120 µmol), and the
mixture was stirred at 0 °C for 1 h, during which time the
greenish blue solution turned pale yellow. After further
stirring for 16 h at room temperature, the solvent was
removed. The crude products were dissolved in hexane, and
insoluble materials were removed by filtration through Celite.
After the removal of the solvent, the residue was separated
with HPLC (LC-918, CHCl3) and further purified with PTLC
(SiO2/hexane) to afford silylborane-isocyanide complex 4b (54.7
mg, 42.3 µmol, 35%) together with Tbt(Mes)SiH2 (5) (13.6 mg,
19.4 µmol, 16%) and TbtSiH3 (6) (1.8 mg, 3.1 µmol, 3%). 4b:
colorless crystals. Mp: 153-155 °C (dec). 1H NMR (300 MHz,
(36) Obrecht, R.; Herrmann, R.; Ugi, I. Synthesis 1985, 400-402.
(37) Mendoza, A.; Matteson, D. S. J . Organomet. Chem. 1978, 156,
149-157.

4732 Organometallics, Vol. 23, No. 20, 2004
Kajiwara et al.
2110 [ν(Si-H)] cm-1. LRMS (FAB): m/z 983 [M+], 968 [(M -
Me)+], 864 [(M - Mes)+], 581 [(TbtSiH2)+]. HRMS (FAB): m/z
983.6493, calcd for C55H102BNSi7, 983.6490. Anal. Calcd for
afforded a mixture of silylborane-isocyanide complexes 4a and
8a (29.4 mg, 29.9 µmol, 46%; the ratio of 4a :8a was 20:1 as
judged by 1H NMR) together with silylborane-phosphine
complex 12 (3.8 mg, 3.9 µmol, 6%). 12: colorless crystals. Mp:
160-162 °C (dec). 1H NMR (300 MHz, CDCl3): δ -0.26 (s, 9H),
-0.18 (s, 9H), 0.02 (s, 18H), 0.07 (s, 9H), 0.09 (s, 9H), 1.24 (s,
1H), 1.69 (s, 3H), 2.15 (s, 3H), 2.25 (s, 3H), 2.81 (s, 1H), 3.05
(s, 1H), 5.10 (d, 1H, J ) 7.1 Hz), 6.16 (s, 1H), 6.26 (s, 1H),
6.32 (s, 1H), 6.54 (s, 1H), 7.21-7.42 (m, 15H), the signals of
BH2 were not observed. 13C {1H} NMR (75 MHz, CDCl3): δ
0.5 (CH3), 0.8 (CH3), 0.9 (CH3), 1.4 (CH3), 1.8 (CH3), 20.9 (CH3),
23.6 (CH3), 25.3 (CH3), 26.3 (CH), 26.6 (CH), 29.8 (CH), 122.6
C
55H102BNSi7: C, 67.08; H, 10.44; N, 1.42. Found: C, 66.45;
H, 10.47; N, 1.42.
Th er m olysis of Silylbor a n e-Isocya n id e Com p lex Tbt-
(Mes)SiHBH 2‚CNTbt (4b). In a 5 mm i.d. NMR tube was
placed a solution of silylborane-isocyanide complex 4b (15.2
mg, 11.8 µmol) in C6D6 (0.6 mL). After five freeze-pump-thaw
cycles, the tube was evacuated and sealed. The solution was
heated at 120 °C in the dark for 9 h and then cooled to room
temperature. The 1H NMR spectrum of this solution showed
the formation of a migration product, TbtSiH2BH(Mes)‚CNTbt
(8b). A mixture of 4b and 8b was obtained with the ratio of
1:10, and any other products were not observed. 8b: colorless
2
(CH), 127.8 (CH), 127.9 (CH), 128.3 (d, J PC ) 9.9 Hz, CH),
128.9 (CH), 129.8 (d, 1J PC ) 58 Hz, C), 130.6 (d, 4J PC ) 2.5 Hz,
3
3
CH), 130.8 (d, J PC ) 9.2 Hz, C), 133.2 (d, J PC ) 9.2 Hz, CH),
136.2 (C), 137.6 (C), 141.6 (C), 141.9 (C), 144.9 (C), 151.7 (C),
151.9 (C). 11B NMR (CDCl3): δ -36.5. 31P NMR (CDCl3): δ
19.5. IR (KBr): 2396 [ν(B-H)], 2360 [ν(B-H)], 2117 [ν(Si-
H)], 1437 [ν(B-P)] cm-1. LRMS (FAB): m/z 997 [(M + Na)+],
974 [M+], 959 [(M - Me)+], 901 [(M - TMS)+], 855 [(M -
Mes)+], 699 [Tbt(Mes)SiH+]. Anal. Calcd for C54H88BPSi7: C,
66.48; H, 9.09. Found: C, 66.12; H, 9.18.
1
crystals. Mp: 122-126 °C (dec). H NMR (300 MHz, CDCl3):
δ -0.19 (s, 18H), -0.06 (s, 18H), 0.00 (s, 18H), 0.03 (s,
18+36H), 1.24 (s, 1H), 1.41 (s, 1H), 1.85 (br s, 2H), 1.98 (br s,
2H), 2.12 (s, 3H), 2.43 (s, 6H), 4.38 (s, 1H), 4.69 (d, 1H, J )
5.1 Hz), 6.18 (s, 1H), 6.29 (s, 1H), 6.36 (s, 1H), 6.47 (s, 1H),
6.65 (s, 2H), the signal of BH was not observed. 13C NMR (75
MHz, C6D6): δ 0.4 (q), 0.5 (q), 0.6 (q), 0.9 (q), 1.0 (q), 1.37 (q),
1.44 (q), 1.6 (q), 21.0 (q), 25.9 (d × 2), 30.2 (d × 2), 30.4 (q),
30.6 (d), 31.8 (d), 120.1 (s), 121.6 (d), 121.8 (d), 126.3 (d), 128.5
(d), 128.9 (s), 129.1 (d), 129.4 (s), 134.5 (s), 142.4 (s), 143.46
(s), 143.50 (s × 2), 146.8 (s), 152.1 (s), 152.2 (s), the signal of
NC was not observed. 11B NMR (CDCl3): δ -36.5. IR (KBr):
2362 [ν(B-H)], 2197 [ν(CtN)], 2084 [ν(Si-H)] cm-1. LRMS
(FAB): m/z 1290 [M+], 1275 [(M - Me)+], 1171 [(M - Mes)+].
Rea ction of Disilen e 1 w ith BH3‚P P h 3. In a 10 mm i.d.
Pyrex glass tube was placed a THF solution (0.9 mL) of a
mixture of disilene 1 (46.0 mg, 32.9 µmol) and BH3‚PPh3 (21.4
mg, 77.5 µmol). After three freeze-pump-thaw cycles, the
tube was evacuated and sealed. The solution was heated at
60 °C for 18 h, during which time the original orange color
disappeared. The tube was opened, and the solvent was
removed. Separation by HPLC (LC-918, CHCl3) afforded
silylborane-phosphine complex 12 (27.7 mg, 28.4 µmol, 43%).
Reaction of Silylbor an e-P h osph in e Com plex Tbt(Mes)-
SiHBH2‚P P h 3 (12) w ith Mes*NC (7a ). In a 5 mm i.d. NMR
tube was placed a C6D6 solution (0.5 mL) of silylborane-
phosphine complex 12 (7.2 mg, 7.4 µmol) and Mes*NC (7a )
(2.2 mg, 8.1 µmol). After three freeze-pump-thaw cycles, the
tube was evacuated and sealed. The solution was heated at
80 °C for 4 h and cooled to room temperature. The 1H NMR
spectrum of this solution showed the formation of a mixture
of the original phosphine complex 12 and isocyanide complexes
4a and 8a with the ratio of 20:1:5.
HRMS (FAB): m/z 1289.7439, calcd for
C64H132BNSi13,
1289.7453. Anal. Calcd for C64H132BNSi13: C, 59.51; H, 10.30;
N, 1.08. Found: C, 59.38; H, 10.48; N, 1.21.
Th er m olysis of Silylbor an e-Isocyan ide Com plex TbtSi-
H2BH(Mes)‚CNMes* (8a ). In a 5 mm i.d. NMR tube was
placed a solution of 8a (5.3 mg, 5.4 µmol) in C6D6 (0.6 mL).
After five freeze-pump-thaw cycles, the tube was evacuated
and sealed. The solution was heated at 120 °C in the dark for
1
10 h and cooled to room temperature. The H NMR spectrum
of this solution showed the formation of 4a . A mixture of 4a
and 8a was obtained with the ratio of 1:5, and any other
products were not observed.
Reaction of Silylbor an e-Isocyan ide Com plex Tbt(Mes)-
SiHBH2‚CNMes* (4a ) w ith TbtNC (7b) a t Room Tem p er -
a tu r e. Silylborane-isocyanide complex 4a (11.0 mg, 11.2 µmol)
and TbtNC (7b) (19.1 mg, 33.0 µmol) were dissolved in THF
(1.0 mL). The solution was stirred for 107 h at room temper-
ature. After removal of the solvent, the residue was separated
by HPLC (LC-918). Starting materials were recovered quan-
titatively.
Reaction of Silylbor an e-Isocyan ide Com plex Tbt(Mes)-
SiHBH2‚CNMes* (4a ) w ith BH3‚THF a t Room Tem p er a -
tu r e. Silylborane-isocyanide complex 4a (9.9 mg, 10 µmol) was
dissolved in THF (1.0 mL), and the solution was cooled to 0
°C. A 1.0 M solution of BH3‚THF in THF (20 µL, 20 µmol) was
added, and the mixture was stirred at 0 °C for 1 h. After
further stirring for 107 h at room temperature, the solvent
was removed. Usual workup resulted in the quantitative
recovery of 4a .
Reaction of Silylbor an e-Isocyan ide Com plex Tbt(Mes)-
SiHBH2‚CNMes* (4a ) w ith TbtNC (7b) a t High Tem p er -
a tu r e. A C6D6 solution (0.6 mL) of silylborane-isocyanide
complex 4a (5.4 mg, 5.5 µmol) was added to TbtNC (7b) (4.3
mg, 7.4 µmol) placed in a 5 mm i.d. NMR tube at room
temperature. After five freeze-pump-thaw cycles, the tube
was evacuated and sealed. The solution was heated at 120 °C
in the dark for 6 h and then cooled to room temperature. The
1H NMR spectrum of this solution showed the formation of a
mixture of 4a (trace), 8a (minor), 4b (trace), and 8b (major),
where 8a and 8b were obtained with the ratio of 1:4. Further
heating at 120 °C for 6.5 h did not change this ratio.
Rea ction of Silylen e-Isocya n id e Com p lex 3a w ith BH3‚
P P h 3. A THF (0.9 mL) solution of silylene-isocyanide complex
3a , prepared from disilene 1 (45.4 mg, 32.4 µmol) and Mes*NC
(7a ) (18.4 mg, 67.8 µmol) in C6D6 (0.5 mL), was added to BH3‚
PPh3 (19.5 mg, 70.6 µmol) placed in a 10 mm i.d. Pyrex glass
tube at room temperature. After three freeze-pump-thaw
cycles, the tube was evacuated and sealed. The solution was
heated at 60 °C for 8.5 h, during which time the original deep
blue color turned pale yellow. The tube was opened, and
solvent was removed. Separation by HPLC (LC-918, CHCl3)
Reaction of Silylbor an e-Isocyan ide Com plex Tbt(Mes)-
SiHBH2‚CNMes* (4a ) w ith BH3‚THF a t High Tem p er a -
tu r e. In a 5 mm i.d. NMR tube was placed a solution of
silylborane-isocyanide complex 4a (9.8 mg, 10.0 µmol) in C6D6
(0.6 mL). A 1.0 M solution of BH3‚THF in THF (20 µL, 20 µmol)
was added at room temperature. After five freeze-pump-thaw
cycles, the tube was evacuated and sealed. The solution was
heated at 120 °C for 3.5 h and then cooled to room tempera-
ture. The 1H NMR spectrum of this solution showed the
disappearance of the starting material. Hydrosilanes 5 and 6
1
were observed with the ratio of 1:4 as judged by H NMR.
R ea ct ion of Silylen e-Isocya n id e Com p lex 3a w it h
Na BH4. A THF (0.8 mL) solution of silylene-isocyanide
complex 3a , prepared from disilene 1 (42.5 mg, 30.4 µmol) and
isocyanide 7a (16.5 mg, 60.8 µmol) in THF (0.8 mL), was added
to NaBH4 (3.6 mg, 95 µmol) at room temperature. The mixture
was stirred for 10 min at room temperature, during which time
the deep blue solution turned yellow. After further stirring
overnight at room temperature the solvent was removed. The
crude products were dissolved in hexane, and insoluble
materials were removed by filtration through Celite. After

Insertion of Silylene into Hydro- and Haloboranes
Organometallics, Vol. 23, No. 20, 2004 4733
removal of the solvent, the 1H and 11B NMR spectra were
measured for the residue to observe a free isocyanide, 7a ,
together with the signal assignable to silylborate [Tbt(Mes)-
SiHBH3]Na (14). Silylborate 14, however, could not be isolated
due to its decomposition during purification. The yield of 14
was ca. 40% from the ratio of the integrated intensity of the
1H NMR signals. 14: colorless crystals. 1H NMR (300 MHz,
C6D6): δ 5.23 (br, s, 1H), other peaks could not be assigned.
silylborane 15 (17.5 mg, 21.1 µmol) and Mes*NC 7a (5.5 mg,
20 µmol). After three freeze-pump-thaw cycles, the tube was
evacuated and sealed. The solution was heated at 80 °C for
28 h and then cooled to room temperature. No change was
observed in the 1H NMR spectrum.
Rea ction of Silylen e-Isocya n id e Com p lex 3a w ith BF3‚
OEt2. To a THF (0.9 mL) solution of silylene-isocyanide
complex 3a , prepared from disilene 1 (60.2 mg, 43.0 µmol) and
isocyanide 7a (23.4 mg, 86.2 µmol) in THF (0.9 mL), was added
BF3‚OEt2 (11 µL, 87 µmol) at room temperature. The mixture
was stirred at room temperature for 1 h, during which time
the deep blue solution turned pale yellow. After further stirring
overnight the solvent was removed. The crude products were
dissolved in hexane, and insoluble materials were removed by
filtration through Celite. After removal of the solvent, the
residue was separated with HPLC (LC-918, CHCl3) and
further purified with PTLC (hexane) to afford fluoro(hydro)-
silane 17 as a main product (29.3 mg, 40.7 µmol, 47%). 17:
colorless crystals. Mp: 153.5-155.2 °C. 1H NMR (400 MHz,
CDCl3): δ -0.08 (s, 9H), -0.05 (s, 9+9H), -0.01 (s, 9H), 0.04
(s, 18H), 1.32 (s, 1H), 2.08 (s, 1H), 2.25 (s, 3+1H), 2.41 (d, 6H,
1
11B NMR (C6D6): δ -38.8 (q, J HB ) 81 Hz).
Rea ction of Disilen e 1 w ith Na BH4. In a 10 mm i.d.
Pyrex glass tube was placed a THF solution (0.9 mL) of a
mixture of disilene 1 (49.2 mg, 35.2 µmol) and NaBH4 (4.3 mg,
110 µmol). After three freeze-pump-thaw cycles, the tube was
evacuated and sealed. The solution was heated at 60 °C for
16 h, during which time the original orange color disappeared.
The sealed tube was opened in a glovebox filled with argon,
and the solvent was evaporated. The 1H and 11B NMR spectra
were measured for the residue to confirm the formation of 14.
Silylborate 14, however, could not be isolated due to its
decomposition during purification.
R ea ct ion of Silylen e-Isocya n id e Com p lex 3a w it h
P in a colbor a n e. In a 5 mm i.d. NMR tube was placed a C6D6
solution (0.6 mL) of silylene-isocyanide complex 3a , prepared
from disilene 1 (52.3 mg, 37.4 µmol) and isocyanide 7a (20.9
mg, 77.0 µmol) in THF (0.8 mL). When pinacolborane (11 µL,
76 µmol) was added to this solution at 0 °C, the original deep
blue color faded in a few minutes. After three freeze-pump-
2
1
5J FH ) 1.9 Hz), 5.99 (d, 1H, J FH ) 52.4 Hz, J SiH ) 224 Hz),
6.25 (s, 1H), 6.39 (s, 1H), 6.80 (s, 2H). 13C{1H} NMR (100 MHz,
CDCl3): δ 0.7 (CH3), 0.8 (CH3), 1.0 (CH3), 21.1 (CH3), 23.5 (d,
4J FC ) 2.5 Hz, CH3), 27.3 (CH), 27.4 (CH), 30.8 (CH), 122.6
2
(CH), 124.3 (d, J FC ) 13.2 Hz, C), 127.4 (CH), 129.1 (CH),
2
129.6 (d, J FC ) 14.8 Hz, C), 140.4 (C), 144.0 (C), 145.9 (C),
1
151.9 (C), 152.1 (C). 29Si NMR (CDCl3): δ -11.4 (d, J FSi
)
1
thaw cycles, the tube was evacuated and sealed. The H NMR
290 Hz), 1.8, 2.2, 2.5, 2.6, 2.7. 19F NMR (CDCl3): δ -163.9 (d,
spectrum of this solution showed the formation of silylborane
15. The tube was opened, and the solvent was removed.
Separation by HPLC (LC-918, CHCL3) gave silylborane 15 as
the main product (36.2 mg, 43.7 µmol, 58%). 15: colorless
2J HF ) 52.4 Hz, 1J SiF ) 290 Hz). IR (KBr): 2182 [ν(SiH)] cm-1
.
LRMS (FAB): m/z 718 [M+], 703 [(M - Me)+], 645 [(M -
TMS)+], 626 [(M - TMS - F)+]. HRMS (FAB): m/z 718.3955,
calcd for C36H71FSi7: 718.3925. Anal. Calcd for C36H71FSi7: C,
60.09; H, 9.95. Found: C, 59.43; H, 9.86.
1
crystals. Mp: 162-164 °C (dec). H NMR (300 MHz, CDCl3):
δ -0.19 (s, 9H), -0.15 (s, 9H), 0.03 (s, 18H), 0.08 (s, 18H),
1.03 (s, 6H), 1.11 (s, 6H), 1.28 (s, 1H), 2.18 (s, 3H), 2.36 (br s,
Rea ction of Disilen e 1 w ith B-Ch lor op in a colbor a n e.
In a 10 mm i.d. Pyrex glass tube was placed a THF solution
(2.4 mL) of a mixture of disilene 1 (150 mg, 107 µmol) and
B-chloropinacolborane (35.6 mg, 219 µmol). After three freeze-
pump-thaw cycles, the tube was evacuated and sealed. The
solution was heated at 60 °C for 17 h, during which time the
original orange color disappeared. The tube was opened, and
the solvent was removed. Purification by silica gel chroma-
tography (n-hexane/CHCl3, 3:2) afforded silylborane 20 as the
main product (157 mg, 182 µmol, 85%). 20: colorless crystals.
1
6H), 2.38 (br, 2H), 4.96 (s, 1H, J SiH ) 185 Hz), 6.23 (s, 1H),
6.38 (s, 1H), 6.69 (s, 2H). 13C NMR (75 MHz, CDCl3): δ 0.4
(q), 0.6 (q), 0.9 (q), 1.2 (q), 1.4 (q), 21.1 (q), 24.0 (q), 24.7 (q),
25.0 (q), 28.1 (d), 28.4 (d), 30.3 (d), 83.8 (s), 122.5 (d), 125.9
(s), 127.5 (d), 128.2 (d), 131.4 (s), 137.7 (s), 143.4 (s), 144.2 (s),
151.4 (s × 2). 11B NMR (CDCl3): δ 35.4. 29Si NMR (CDCl3): δ
-62.7, 2.1, 2.3, 2.6. IR (KBr) 2151 [ν(SiH)] cm-1. LRMS
(FAB): m/z 849 [(M + Na)+], 826 [M+], 742 [(M - C6H12)+],
711 [(M - C6H12O2 + H)+]. Anal. Calcd for C42H83BO2Si7: C,
60.96; H, 10.11. Found: C, 60.49; H, 10.37.
1
Mp: 212-215 °C (dec). H NMR (300 MHz, CDCl3): δ -0.13
R ea ct ion of Silylen e-Isocya n id e Com p lex 3c w it h
P in a colbor a n e. In a 5 mm i.d. NMR tube was placed a C6D6
solution (0.5 mL) of silylene-isocyanide complex 3c, prepared
from disilene 1 (37.0 mg, 26.4 µmol) and isocyanide 7c (11.7
mg, 51.0 µmol) in THF (0.8 mL). To this solution was added
pinacolborane (10 µL, 69 µmol) at 0 °C. After three freeze-
pump-thaw cycles, the tube was evacuated and sealed. The
1H NMR spectrum of this solution showed that the reaction
was very slow. After further standing for two weeks at room
temperature, the tube was opened and the solvent was
removed. Separation by HPLC (LC-918, CHCl3) afforded
silylborane 15 in 9% yield (3.9 mg, 4.7 µmol).
Rea ction of Disilen e 1 w ith P in a colbor a n e. In a 10 mm
i.d. Pyrex glass tube was placed a THF solution (2.0 mL) of a
mixture of disilene 1 (153 mg, 109 µmol) and pinacolborane
(58.9 mg, 460 µmol). After three freeze-pump-thaw cycles,
the tube was evacuated and sealed. The solution was heated
at 60 °C for 16.5 h, during which time the original orange color
disappeared. The tube was opened, and solvent was removed.
The crude products were dissolved in hexane, and insoluble
materials were removed by filtration through Celite. After
removal of the solvent, the mixture was separated by HPLC
(LC-918, CHCl3) to give silylborane 15 as a main product (133
mg, 161 µmol, 74%).
(br s, 18H), 0.04 (s, 18H), 0.07 (s, 9H), 0.09 (s, 9H), 1.09 (s,
6H), 1.13 (s, 6H), 1.30 (s, 1H), 2.19 (s, 3H), 2.45 (br, 6+2H),
6.26 (s, 1H), 6.39 (s, 1H), 6.68 (s, 2H). 13C NMR (75 MHz,
CDCl3): δ 0.80 (q), 0.84 (q), 1.0 (q), 1.1 (q), 1.7 (q), 1.9 (q), 20.9
(q), 24.1 (q), 24.7 (q), 25.1 (q), 27.7 (d), 28.0 (d), 30.5 (d), 84.4
(s), 122.9 (d), 127.7 (s), 128.0 (d), 129.6 (d), 130.8 (s), 138.7 (s),
143.7 (s), 144.6 (s), 151.5 (s × 2). 11B NMR (CDCl3): δ 33.1.
29Si NMR (CDCl3): δ -15.0, 1.8, 1.9, 2.7, 2.8, 3.0. LRMS
(FAB): m/z 861 [(M + H)+]. Anal. Calcd for C42H82BClO2Si7:
C, 58.52; H, 9.59. Found: C, 58.29; H, 9.72.
Rea ction of Disilen e 1 w ith B-Ch lor oca tech olbor a n e.
In a 5 mm i.d. NMR tube was placed a C6D6 solution (0.6 mL)
of a mixture of disilene 1 (26.4 mg, 18.9 µmol) and B-
chlorocatecholborane (6.4 mg, 41 µmol). After three freeze-
pump-thaw cycles, the tube was evacuated and sealed. The
solution was heated at 60 °C for 14 h, during which time the
original orange color disappeared. The 1H NMR spectrum of
this solution showed the formation of silylborane 21. The tube
was opened in a glovebox filled with argon, and solvent was
removed. Recrystallization from n-hexane at -40 °C gave pure
(chlorosilyl)catecholborane 21 (20.1 mg, 23.5 µmol, 62%). 21:
colorless crystals. Mp: 229-233 °C (dec). 1H NMR (300 MHz,
CDCl3): δ -0.19 (s, 18H), 0.02 (s, 9H), 0.05 (s, 9+18H), 1.33
(s, 1H), 2.10 (s, 1H), 2.19 (s, 1H), 2.22 (s, 3H), 2.59 (s, 6H),
6.27 (s, 1H), 6.41 (s, 1H), 6.78 (s, 2H), 7.05-7.12 (m, 2H), 7.21-
7.28 (m, 2H). 13C NMR (75 MHz, CDCl3): δ 0.6 (q), 0.8 (q), 1.0
Rea ction of Silylbor a n e 15 w ith Mes*NC (7a ). In a 5
mm i.d. NMR tube was placed a C6D6 solution (0.6 mL) of

4734 Organometallics, Vol. 23, No. 20, 2004
Kajiwara et al.
(q), 1.6 (q), 1.8 (q), 20.9 (q), 25.4 (q), 29.3 (d), 29.6 (d), 30.7 (d),
113.0 (d), 122.8 (d), 123.0 (d), 127.0 (s), 127.9 (d), 128.6 (s),
130.3 (d), 139.7 (s), 144.3 (s), 145.5 (s), 148.1 (s), 151.5 (s), 151.8
(s). 11B NMR (CDCl3): δ 34.6. 29Si NMR (C6D6): δ 2.1, 2.2,
3.3, 3.5, the signal of BSi was not observed. HRMS (EI): m/z
852.3820 and 854.3786, calcd for C42H74B35ClO2Si7 852.3855
and C42H74B37ClO2Si7 854.3826. Anal. Calcd for C42H74BClO2-
Si7: C, 59.08; H, 8.73. Found: C, 59.23; H, 9.06.
atoms of 4a were located in difference Fourier syntheses and
included in the refinement, but all other hydrogen atoms were
placed in calculated positions. Calculations for 4a were
performed using the CrystalStructure41,43 crystallographic
software package. Crystal data for 4a : formula C55H102BNSi7,
formula weight 984.83, colorless, block, crystal dimensions
(mm) 0.30 × 0.30 × 0.10, T ) 93(2) K, triclinic, P1h (#2), a )
9.709(5) Å, b ) 16.612(7) Å, c ) 20.306(10) Å, R ) 83.42(1)°, â
R ea ct ion of Silylen e-Isocya n id e Com p lex 3a w it h
B-Ch lor oca tech olbor a n e. A C6D6 (0.5 mL) solution of si-
lylene-isocyanide complex 3a , prepared from disilene 1 (50.0
mg, 35.7 µmol) and isocyanide 7a (22.5 mg, 82.9 µmol) in THF
(0.8 mL), was added to B-chlorocatecholborane (11.5 mg, 74.5
µmol) at room temperature, and the original deep blue color
faded in a few minutes. After three freeze-pump-thaw cycles,
) 89.18(2)°, γ ) 78.73(1)°, V ) 3190.8(24) Å3, Z ) 2, Dcalc
)
1.025 g/cm3, µ ) 1.81 cm-1, 2θmax ) 55.0°, independent
reflections/parameters 14 013/589, R1(I > 2σ(I)) ) 0.0670, wR2-
(all data) ) 0.1550, GOF ) 1.064, CCDC-183015.26 Crystal
data for 12: formula C54H88BPSi7, formula weight 975.65,
colorless, platelet, crystal dimensions (mm) 0.40 × 0.18 × 0.08,
T ) 93(2) K, triclinic, P1h (#2), a ) 12.2961(5) Å, b )
12.9373(4) Å, c ) 20.9079(2) Å, R ) 73.508(13)°, â )
73.145(13)°, γ ) 82.555(15)°, V ) 3048.12(16) Å3, Z ) 2, Dcalc
) 1.063 g/cm3, µ ) 2.14 cm-1, 2θmax ) 50.0°, independent
1
the tube was evacuated and sealed. The H NMR spectrum of
this solution showed the formation of (chlorosilyl)catechol-
borane 21. Silylborane 21, however, could not be isolated due
to its decomposition during purification. The yield of 21 was
ca. 60%, as estimated from the 1H NMR spectrum.
reflections/parameters 10 523/589, R1(I>2σ(I))
) 0.0801,
wR2(all data) ) 0.1331, GOF ) 1.166. Crystal data for 20:
formula C42H82BClO2Si7, formula weight 861.97, colorless,
prism, crystal dimensions (mm) 0.35 × 0.20 × 0.10, T ) 103-
(2) K, triclinic, P1h (#2), a ) 9.199(7) Å, b ) 12.808(10) Å, c )
Th eor etica l Ca lcu la tion s. All theoretical calculations
were carried out using the Gaussian 98W or Gaussian 03W
programs29 with density functional theory at the B3LYP
level.38 The structural optimization was performed at the
B3LYP/6-31G(d) level. The vibrational frequency was calcu-
lated at the B3LYP/6-31G(d) level and scaled by 0.9613.30 The
NMR chemical shifts were calculated at the GIAO-B3LYP/6-
311+G(2d,p) level. Reference molecules for the chemical shifts
were also calculated at the same level: Si(CH3)4 for H, C, and
Si (0 ppm), B2H6 for B (16.6 ppm).39
X-r a y Cr ysta llogr a p h ic An a lysis. Single crystals of 4a ,
12, and 20 suitable for X-ray analysis were obtained by
recrystallization from benzene at room temperature (for 4a ),
from hexane in a refrigerator (for 12), and from dichlo-
romethane/methanol at room temperature (for 20), respec-
tively. A colorless crystal was mounted on a glass fiber (for
4a and 12) or a loop (for 20). The intensity data were collected
on a Rigaku/MSC Mercury CCD diffractometer with graphite-
monochromated Mo KR radiation (λ ) 0.71070 Å). The
structures were solved by a direct method (SIR-97)40 and
refined by full-matrix least-squares procedures on F2 for all
reflections (CRYSTALS41 for 4a and SHELXL-9742 for 12 and
20). All non-hydrogen atoms were refined with anisotropic
thermal parameters. Hydrogen atoms on the silicon and boron
23.663(17) Å,
R ) 99.905(12)°, â ) 92.269(11)°, γ )
108.236(13)°, V ) 2595(3) Å3, Z ) 2, Dcalc ) 1.103 g/cm3, µ )
2.66 cm-1, 2θmax ) 50.0°, independent reflections/parameters
8929/503, R1(I > 2σ(I)) ) 0.1139, wR2(all data) ) 0.2959, GOF
) 1.116.
Ack n ow led gm en t. This work was partially sup-
ported by Grants-in-Aid for COE Research on Elements
Science (No. 12CE2005), Scientific Research on Priority
Area (No. 14078213), and the 21st Century COE Pro-
gram on Kyoto University Alliance for Chemistry from
the Ministry of Education, Culture, Sports, Science and
Technology, J apan. We thank Central Glass Co., Ltd.
for the generous gift of tetrafluorosilane.
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
coordinates, bond distances, angles, and anisotropic displace-
ment parameters for Tbt(Mes)SiHBH2‚CNMes* (4a ), Tbt(Mes)-
SiHBH2‚PPh3 (12), and Tbt(Mes)Si(Cl)B(pin) (20); X-ray data
in CIF format are also available. This material is available
free of charge via the Internet at http://pubs.acs.org.
(38) Becke, A. D. J . Chem. Phys. 1993, 98, 5648-5652.
(39) Onak, T. P.; Landesman, H.; Williams, R. E.; Shapiro, I. J . Phys.
Chem. 1959, 63, 1533-1535.
OM049558W
(40) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. J . Appl. Crystallogr. 1999, 32, 115-119.
(42) Sheldrick, G. M. SHELX-97, Program for the Refinement of
Crystal Structures; University of Go¨ttingen: Go¨ttingen, Germany,
1997.
(43) CrystalStructure 2.00, Crystal Structure Analysis Package;
Rigaku and MSC, 2001.
(41) Watkin, D. J .; Prout, C. K.; Carruthers, J . R.; Betteridge, P.
W. CRYSTALS Issue 10; Chemical Crystallography Laboratory:
Oxford, UK, 1999.