Unusual double silylation reaction of a PtSi2P2 complex with an o-carboranyl unit

Article abstract of DOI:10.1021/om990105e

Summary: Reaction of Pt(CH₂=CH₂)(PPh₃)₂ and o-bis(dimethylsilyl)carborane provides the cyclic bis(silyl)-platinum complex 2. The complex 2 reacts with a variety of substrates such as an alkyne, dione, and nitrile, generating a new class of heteracyclic compounds incorporating an alkene, ketonate, imine, and amine.

Full text of DOI:10.1021/om990105e

1818
Organometallics 1999, 18, 1818-1820
Un u su a l Dou ble Silyla tion Rea ction of a P tSi2P 2
Com p lex w ith a n o-Ca r bor a n yl Un it
Youngjin Kang, Sang Ook Kang,* and J aejung Ko*
Department of Chemistry, Korea University, Chochiwon, Chungnam 339-700, Korea
Received February 17, 1999
Summary: Reaction of Pt(CH2dCH2)(PPh3)2 and o-bis-
(dimethylsilyl)carborane provides the cyclic bis(silyl)-
platinum complex 2. The complex 2 reacts with a variety
of substrates such as an alkyne, dione, and nitrile,
generating a new class of heterocyclic compounds incor-
porating an alkene, ketonate, imine, and amine.
complexes.4 The structure of 2 was established by a
single-crystal X-ray analysis.5
Compound 2 was found to be a good precursor for the
double-silylation reaction.6-8 Thus, thermolysis of a
toluene solution of 2 (0.153 mmol) and 1-hexyne (1.23
mmol) at 120 °C for 6 h afforded a 54% yield of 3 as a
1
colorless oil. A key feature in the H NMR spectrum of
The double silylation of unsaturated organic com-
pounds catalyzed by group 10 metals1 is a convenient
synthetic route to obtain disilacyclic compounds. Plati-
num complexes, in particular, provide excellent cata-
lysts for the transformation of disilanes. Cyclic bis(silyl)-
platinum complexes, which Eaborn et al.2 and Tanaka
et al.3 had already reported, have been implicated as
key intermediates in the platinum-catalyzed double
silylation of alkynes. However, the complexes have not
been structurally characterized. Here we report the
general synthesis of a new class of thermally stable
cyclic bis(silyl)platinum complexes with a bulky o-
carborane unit and some unusual reaction chemistry
with unsaturated organic compounds.
3 is a singlet at 6.24 ppm assigned to the vinyl proton.
A characteristic low-frequency 13C NMR resonance at
δ 138.50 provides evidence for a tethered carbon atom
of the two silicon moieties9 (Scheme 1).
Treatment of 2 with 3 equiv of 3-phenyl-2-propenal
in refluxing toluene-d8 while the reaction progress was
monitored by 1H NMR spectroscopy resulted in the dis-
appearance of the aldehyde hydrogen peak and the for-
mation of a new methine peak (δ 1.56).10 The IR spec-
trum of 4 shows a new absorption due to a νC-O stretch
at 1448 cm-1. The mass spectrum of the product showed
a molecular ion at m/z 538. To our surprise, an X-ray
study of 4 showed it to be the insertion product of two
carbonyl ligands into the C-Si bond in 2 (Figure 1).11
The reaction has the potential for developing a new
method for double C-C bond formation between the car-
boranyl unit and carbonyl compounds. Such an insertion
of the carbonyl functionality into the o-carborane has
The reaction of Pt(CH2dCH2)(PPh3)2 (0.05 mmol) and
o-bis(silyl)carborane 1 (1.4 equiv) in benzene leads to 2
in good yield (eq 1). The compound 2 is a yellow solid
stable to air and to brief heating to 120-130 °C.
(4) (a) Yamashita, H.; Tanaka, M.; Honda, K. J . Am. Chem. Soc.
1995, 117, 8873. (b) Pham, E. K.; West, R. J . Am. Chem. Soc. 1989,
111, 7667.
(5) Crystal data for 2: fw ) 1054.32, monoclinic space group C2/c, a
) 22.435(1) Å, b ) 15.855(2) Å, c ) 14.859(2) Å, R ) 90.012(8)°, â )
114.544(5)°, γ ) 89.994(6)°, V ) 4807.8(7) Å3, Z ) 4, Dcalcd ) 1.456 g
cm-3, λ(Mo KR) ) 0.7107 Å, 8219 unique data, 3210 observations with
I > 3σ(I), goodness of fit ) 1.695, R ) 0.0377, Rw ) 0.0456.
(6) (a) Tanaka, M.; Uchimaru, Y.; Lautenschlager, H.-J . Organo-
metallics 1991, 10, 16. (b) Uchimaru, Y.; Brandl, P.; Tanaka, M.; Goto,
M. J . Chem. Soc., Chem. Commun. 1993, 744.
(7) (a) Hayashi, T.; Kobayashi, T.; Kawamoto, A. M.; Yamashita,
H.; Tanaka, M. Organometallics 1990, 9, 280. (b) Tanaka, M.; Uchi-
maru, Y.; Lautenschlager, H.-J . J . Organomet. Chem. 1992, 428, 1.
(8) Reddy, N. P.; Uchimaru, Y.; Lautenschlager, H.-J .; Tanaka, M.
Chem. Lett, 1992, 45.
(9) Naka, A.; Hayashi, M.; Okazaki, S.; Kunai, A.; Ishikawa, M.
Organometallics 1996, 15, 1101.
(10) A mixture of 2 (0.2 g, 0.2 mmol) and trans-cinamaldehyde (0.21
g, 1.6 mmol) in toluene (15 mL) was heated under reflux for 16 h, and
volatiles were removed under vacuum. The resulting oil was purified
by chromatography over silica gel, with benzene and hexane as eluent
(1:1). The residue was left to crystallize at -15 °C in hexane: yield
0.06 g (56%); colorless crystals; mp 56 °C. 1H NMR (300 MHz, CDCl3):
δ 7.52-6.18 (m, 10H, Ph), 6.88 (dd, 1H, J (H,H) ) 12.3 Hz, J (H,H) )
5.8 Hz, dCH), 6.74 (dd, 1H, J (H,H) ) 12.3 Hz, J (H,H) ) 4.4 Hz, dCH),
1.56 (dd. 1H, J (H,H) ) 5.8 Hz, J (H,H) ) 4.4 Hz, CH), 0.84 (s, 12H,
Si(CH3)). 13C NMR (75.5 MHz, CDCl3): δ 137.47, 133.64, 132.15,
129.19, 128.7 (Ph), 127.60 (s, 1C, dCH), 126.43 (s, 1C, dCH), 31.59 (s,
1C, CH), 14.03 (s, 1C, Si(CH3)). 29Si NMR (50 MHz, CDCl3): δ 17.48.
MS (EI): m/z: 538. Anal. Calcd for C24H38B10O3Si2: C, 53.45; H, 7.05.
Found: C, 53.12; H, 6.88.
The 1H, 13C, 31P, and 29Si NMR data for 2 support
the proposed structure. In particular, the 29Si NMR
chemical shift of 37.17 ppm as a doublet of doublets
(J Pt-Si ) 1281.6 Hz, J Si-P(trans) ) 148.82 Hz, J Si-P(cis)
)
12.80 Hz) is close to the literature values for cis-PtSi2P2
(1) (a) Tamao, K.; Hayashi, T.; Kumada, M. J . Organomet. Chem.
1976, 114, C19. (b) Seyferth, D.; Goldman, E. W.; Escudie´, J . J .
Organomet. Chem. 1984, 271, 337. (c) Hayashi, T.; Kobayashi, T.;
Kawamoto, A. M.; Yamashita, H.; Tanaka, M. Organometallics 1990,
9, 280. (d) Ishikawa, M.; Naka, A.; Ohshita, J . Organometallics 1993,
12, 4987. (e) Ozawa, F.; Sugawara, M.; Hayashi, T. Organometallics
1994, 13, 3237.
(2) Eaborn, C.; Metham, T. N.; Pidcock, A. J . Organmet. Chem. 1973,
63, 107.
(3) (a) Tanaka, M.; Uchimaru, Y.; Lautenschlager, H.-J . Organo-
metallics 1991, 10, 16. (b) Uchimaru, Y.; Lautenschlager, H. J .; Wynd,
A. J .; Tanaka, M.; Goto, M. Organometallics 1992, 11, 2639. (c) Tanaka,
M.; Uchimaru, Y. Bull. Soc. Chim. Fr. 1992, 129, 667.
(11) Crystal data for 4: fw ) 1077.67, monoclinic, space group P21/
m, a ) 10.711(1) Å, b ) 24.060(1) Å, c ) 12.654(1) Å, R ) 89.997(8)°,
â ) 97.978(8)°, γ ) 90.001(7)°, V ) 3229.3(4) Å3, Z ) 2, Dcalcd ) 1.108
g cm-3, λ(Mo KR) ) 0.7107 Å, 6513 unique data, 2808 observations
with I > 3σ(I), R ) 0.1130, Rw ) 0.1403.
10.1021/om990105e CCC: $18.00 © 1999 American Chemical Society
Publication on Web 04/25/1999

Communications
Organometallics, Vol. 18, No. 10, 1999 1819
Sch em e 1
F igu r e 1. Crystal structure of 4. Selected bond distances
(Å): Si1-O1, 1.648(6); Si1-O2, 1.625(4); O1-C9, 1.421-
(10); C1-C9, 1.58(1); C1-C1*, 1.71(2).
F igu r e 2. Crystal structure of 5. Selected bond distances
(Å) and angles (deg): Si1′-N2, 1.749(2); Si2′-N2, 1.750-
(2); Si1′-C1′, 1.896(2); Si2′-C2′, 1.899(3); N2-C20, 1.422-
(3); N1-C20, 1.393(3); N1-C13, 1.419(3); Si2-N1, 1.764(2);
Si1-C13, 1.850(3); C13-C18, 1.363(4); C18-C19, 1.398-
(4); C19-C20, 1.370(3); Si1′-N2-Si2′, 120.5(1); N2-C20-
N1, 122.9(2); C20-N1-C13, 107.5(2); Si2-N1-C13, 118.1-
(2); N1-C13-Si1, 129.1(2).
been observed in Yamamoto’s work on the chemoselec-
tive addition of o-carborane to the aldehyde groups by
a palladium-catalyzed12 or a fluoride-promoted reac-
tion.13
(12) Nakamura, H.; Aoyagi, K.; Yamamoto, Y. J . Org. Chem. 1997,
62, 780.
(13) Cai, J .; Nemoto, H.; Nakamura, H.; Singaram, B.; Yamamoto,
Y. Chem. Lett. 1996, 792.
(14) 5 was prepared similarly, but using a 1:8 molar ratio of 2 to
fumaronitrile. The crude product was chromatographed with benzene
and hexane as eluent (1:1) and recrystallized from hexane: yield 75%;
mp 158-162 °C. 1H NMR (300 MHz, CDCl3): δ 6.51 (d, 1H, J (H,H) )
5.1 Hz, CH), 5.67 (d, 1H, J (H,H) ) 5.1 Hz, CH), 0.63 (s, 6H, Si-CH3),
0.44 (s, 6H, Si-CH3), 0.35 (s, 6H, Si-CH3), 0.29 (s, 6H, Si-CH3). 13C
NMR (75.5 MHz, CDCl3): δ 128.6, 128.2, 125.4, 124.9 (S, 1C, CN),
2.20 (s, 2C, Si-CH3), 0.93 (s, 2C, Si-CH3), 0.40 (s, 2C, Si-CH3), -0.04
(s, 2C, Si-CH3). 29Si NMR (50 MHz, CDCl3): δ 12.53, 4.36, -6.51. Anal.
Calcd for C16H46B20N2Si4: C, 32.26; H, 7.73. Found: C, 32.02; H, 7.56.
The reaction between 2 and 4 equiv of fumaronitrile
in refluxing toluene for 8 h produced 5 as colorless
crystals.14 Three singlets (δ 12.53, 4.36, -6.51) in the
29Si NMR spectrum and four singlets (δ 2.20, 0.93, 0.40,
-0.047) in the 13C NMR spectrum of 5 assigned to the
methyl groups on the silicon atom demonstrate that the
four dimethyl groups are not equivalent. The IR spec-
trum of 5 failed to show a new signal for a terminal CN.

1820 Organometallics, Vol. 18, No. 10, 1999
Communications
The ambiguous spectroscopic data led us to carry out a
single-crystal X-ray diffraction study in order to eluci-
date the structure for 5 (Figure 2).15 To our surprise,
an X-ray study revealed 5 to be a cyclization product
with two types of disilyl moieties such as the imine and
N,N-bis(silyl)amine, which are connected by a five-
membered ring. The five-membered ring (C4N) is nearly
planar, with the largest deviation of the ring atoms from
the mean plane at N(1) (0.03 Å). The C-C bond lengths
(1.363-1.398 Å) and C-N bond lengths (1.393-1.422
Å) in the ring fall between a single and double bond,16
demonstrating the delocalized ring system. Such a
transformation of nitriles to imines or N,N-bis(silyl)-
enamines has been observed during the photochemical
reaction17 or catalysis by a platinum complex.8
some credence to the notion that nucleophilic attack of
the imine is at the platinum carbene intermediate 8
formed from the migration of the silicon atom to the
nitrogen atom that leads to compound 5.18
In summary, the organometallic cyclic bis(silyl)-
platinum complex reacts with a variety of substrates
such as an alkyne, enone, and nitrile, generating a new
class of heterocyclic compounds incorporating an alkene,
ketonate, imine, and amine. In contrast to similar
PtSi2P2 compounds, 2 is relatively robust and not as
readily attacked by unsaturated organic substrates.
Studies are in progress to clarify the mechanistic details
of compounds 4 and 5.
Ack n ow led gm en t. This work was supported by a
grant from the KOSEF. J .K. thanks Professor Ishikawa
for his helpful discussions.
A reasonable mechanism for the formation of 5
involves the initial insertion of the cyano group into one
Su p p or tin g In for m a tion Ava ila ble: Text giving details
on the synthesis and characterization of compounds 2-5 and
tables giving X-ray crystallographic data for 2, 4, and 5. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OM990105E
(15) Crystal data for 5: fw ) 595.09, monoclinic, space group P21/c,
a ) 9.322(1) Å, b ) 22.191(2) Å, c ) 17.580(1) Å, R ) 90.010(6)°, â )
99.499(8)°, γ ) 90.022(8)°, V ) 3587.2(5) Å3, Z ) 4, Dcalcd ) 1.102 g
cm-3, λ(Mo KR) ) 0.7107 Å, 7270 unique data, 5056 observations with
I > 3σ(I), goodness of fit ) 2.253, R ) 0.0444, Rw ) 0.0568.
(16) Huheey, J . E. Inorganic Chemistry, 3rd ed.; Harper & Row:
New York, 1983; p 258.
(17) (a) Corriu, R. J . P.; Moreau, J . J . E.; Pataud-Sat, M. J .
Organomet. Chem. 1982, 228, 301. (b) Walter, W.; Luke, H. W. Angew.
Chem., Int. Ed. Engl. 1977, 16, 535. (c) Corriu, R. J . P.; Moreau, J . J .
E.; Pataud-Sat, M. Organometallics 1985, 4, 623.
(18) Gunnoe, T. B.; White, P. S.; Templeton, J . L.; Casarrubois, L.
J . Am. Chem. Soc. 1997, 119, 3171.
of the platinum-silicon bonds, leading to intermediate
6, followed by the cyclization to the imine 7. It lends