A silyliumylidene cation stabilized by an amidinate ligand and 4-dimethylaminopyridine

Article abstract of DOI:10.1002/chem.201300255

The synthesis and reactivity of a silyliumylidene cation stabilized by an amidinate ligand and 4-dimethylaminopyridine (DMAP) are described. The reaction of the amidinate silicon(I) dimer [LSi:]₂ (1; L=PhC(NtBu) ₂) with one equivalent of N-trimethylsilyl-4-dimethylaminopyridinium triflate [4-NMe₂C₅H₄NSiMe₃]OTf and two equivalents of DMAP in THF afforded [LSi(DMAP)]OTf (2). The ambiphilic character of 2 is demonstrated from its reactivity. Treatment of 2 with 1 in THF afforded the disilylenylsilylium triflate [L′₂(L)Si]OTf (3; L′=LSi:) with the displacement of DMAP. The reaction of 2 with [K{HB(iBu)₃}] and elemental sulfur in THF afforded the silylsilylene [LSiSi(H){(NtBu)₂C(H)Ph}] (4) and the base-stabilized silanethionium triflate [LSi(S)DMAP]OTf (5), respectively. Compounds 2, 3, and 5 have been characterized by X-ray crystallography. 1 becomes 2: The singlet silyliumylidene cation 2, which is stabilized by both an amidinate ligand and 4-dimethylaminopyridine (DMAP), can be synthesized by the reaction of the amidinate Si^I dimer 1 with N-trimethylsilyl-4-dimethylaminopyridinium triflate and DMAP (see scheme). The ambiphilic character of 2 can be demonstrated by its reactivity. Copyright

Full text of DOI:10.1002/chem.201300255

DOI: 10.1002/chem.201300255
A Silyliumylidene Cation Stabilized by an Amidinate Ligand and
4-Dimethylaminopyridine
Hui-Xian Yeong,[a] Hong-Wei Xi,[b] Yongxin Li,[a] Kok Hwa Lim,[b] and Cheuk-Wai So*[a]
Abstract: The synthesis and reactivity
of a silyliumylidene cation stabilized by
an amidinate ligand and 4-dimethyla-
minopyridine (DMAP) are described.
The reaction of the amidinate silicon(I)
G
placement of DMAP. The reaction of 2
with [K{HB(iBu)3}] and elemental
sulfur in THF afforded the silylsilylene
[LSiSi(H){(NtBu)2C(H)Ph}] (4) and the
base-stabilized silanethionium triflate
[LSi(S)DMAP]OTf (5), respectively.
Compounds 2, 3, and 5 have been char-
acterized by X-ray crystallography.
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
dimer [LSiD]2 (1; L=PhCACTHUNGRTNE(NUG NtBu)2) with
one equivalent of N-trimethylsilyl-4-di-
methylaminopyridinium triflate [4-
NMe2C5H4NSiMe3]OTf and two equiv-
alents of DMAP in THF afforded [LSi-
Introduction
Recently, the ability of amidinate ligands to stabilize a
wide variety of low-valent silicon compounds has been dem-
onstrated.[4] They can also stabilize silylium moieties in
small ring compounds. Examples include a zwitterionic 2,4-
disila-1,3-diphosphacyclobutadiene,[5] a germatrisilacyclobu-
tadiene,[6] a five-membered cationic CSi3P ring,[7] and a tet-
rasilacyclobutadiene dication.[8] On the basis of these results,
it seems that amidinate ligands can stabilize a low-valent sil-
icon cation. However, in a recent communication on the
synthesis of the base-stabilized tetrasilacyclobutadiene dica-
tion,[8] Driess et al. suggest that the amidinate silyliumyli-
The silyliumylidene cation with the composition HSiD+ is the
simplest form of polyatomic low-valent silicon moiety. Since
it consists of two vacant orbitals and a lone pair of electrons
on the low-valent silicon cation, it is Lewis ambiphilic and
can possess both electrophilic and nucleophilic characters.
By virtue of its diverse electronic structure, the silyliumyli-
dene cation can serve as a useful building block for the syn-
thesis of novel silicon compounds. However, it is highly re-
active and can only be observed in the gas phase under
mass spectrometric and astrophysical conditions.[1] Since the
discovery of an N-heterocyclic silylene by West et al.,[2] the
concepts of thermodynamic and/or kinetic stabilization have
been applied successfully in the isolation of stable low-
valent silicon compounds. Accordingly, stable derivatives of
the silyliumylidene cation, which contain sterically hindered
substituents with electron-donor moieties, were synthe-
sized.[3] However, the high synthetic potential of these cati-
ons is hampered by the particular stabilization effects of the
substituents. In this context, the quest for isolating other
types of stable silyliumylidene cation is still very demanding.
dene cation [LSiD]+ (L=PhC
ACTHNUTRGNEN(UG NtBu)2) is highly electrophilic.
Moreover, the electron-deficient silicon atom cannot be
shielded from coordination to reactive nucleophilic inter-
mediates. As a result, it undergoes a disproportionation to
form the base-stabilized tetrasilacyclobutadiene dication.
The results show that the isolation of an amidinate silyliu-
mylidene cation is a formidable challenge.
We anticipate that an amidinate silyliumylidene cation
should be a resonance hybrid of the canonical formulas I
and II (Scheme 1). The electronic-deficient low-valent sili-
con atoms could be stabilized by coordination to a Lewis
base. Herein, we report the synthesis of the singlet silyliu-
mylidene cation [LSiACHTNUGRTENUNG(DMAP)]OTf (2), which is stabilized
by both an amidinate ligand and 4-dimethylaminopyridine
(DMAP). Additionally, its theoretical and reactivity studies
are described.
[a] H.-X. Yeong, Dr. Y. Li, Dr. C.-W. So
Division of Chemistry and Biological Chemistry
Nanyang Technological University
21 Nanyang Link, Singapore 637371
Fax : (+65)6791-1961
E-mail: CWSo@ntu.edu.sg
[b] Dr. H.-W. Xi, Prof. Dr. K. H. Lim
Division of Chemical and Biomolecular Engineering
Nanyang Technological University
62 Nanyang Drive, Singapore 637459
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201300255.
Scheme 1. Canonical forms of an amidinate silyliumylidene cation.
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Chem. Eur. J. 2013, 19, 11786 – 11790

FULL PAPER
Results and Discussion
The reaction of the amidinate SiI dimer [LSiD]2 (1)[9] with
one equivalent of N-trimethylsilyl-4-dimethylaminopyridini-
um triflate, [4-NMe2C5H4NSiMe3]OTf,[10] and two equiva-
lents of DMAP in THF at room temperature afforded [LSi-
ACHTUNGTRENNUNG(DMAP)]OTf (2) in 54% yield (Scheme 2). The byproduct
À
is Me3Si SiMe3, the structure of which was confirmed by
29Si and 1H NMR spectroscopy and mass spectrometry.[11]
The reaction appears to proceed through the oxidation of 1
SiI
radical
[LSi ]
with
[4-
C
or
the
transient
À
NMe2C5H4NSiMe3]OTf to form 2 and Me3Si SiMe3.
Compound 2 is soluble in THF, CH2Cl2, and CHCl3. It is
stable in the solid state at room temperature under an inert
atmosphere. Compound 2 has been characterized by NMR
Figure 1. ORTEP drawing of compound 2 (50% thermal ellipsoids). The
hydrogen atoms and disorder in the triflate moiety are omitted for clarity.
À
À
Selected bond lengths [ꢁ] and angles [8]: Si1 N1 1.8514(18), Si1 N2
1
spectroscopy. The H and 13C NMR spectra of 2 display res-
À
À
À
1.8625(18), Si1 N3 1.8777(18), C5 N1 1.342(3), C5 N2 1.340(3); N1-Si1-
N2 69.91(8), N1-Si1-N3 98.20(8), N2-Si1-N3 97.95(8).
onances due to the amidinate and DMAP ligands. The
19F NMR spectrum of 2 shows a singlet at d=À78.9 ppm for
it is almost nonhybridized and
possesses lone-pair electrons
with high
s character. The
shortest Si1···F (3.59 ꢁ) dis-
tance is longer than the sum of
van der Waals radii (3.57 ꢁ),
which suggests that the Si1
cation does not have any inter-
À
action with the CF3SO3 coun-
À
teranion.
(1.8514(18),
The
Si Namidinate
1.8625(18) ꢁ)
bond lengths are comparable
with those in [LSiNMe2]
(1.893(1), 1.905(1) ꢁ).[12b] The
Scheme 2. Synthesis of compound 2.
À
Si1 N3 bond (1.8775(18) ꢁ) is
longer than the Si Namide bond in [LSiNMe2]
À
the CF3SO3 anion. The 29Si NMR spectrum of 2 exhibits a
À
singlet at d=À82.3 ppm, which shows an upfield shift rela-
tive to that of the three-coordinate amidinate-stabilized sily-
lenes [LSiX] (X=Cl: d=14.6 ppm; X=NMe2: d=
À2.62 ppm).[12] This can be explained by the strong donor–
acceptor interaction between the nitrogen atom of DMAP
and the low-valent silicon cation, thus reducing the Lewis
acidity of the latter. Interestingly, the reactivity studies show
that DMAP can be released, hence 2 shows an ambiphilic
character (see below). In addition, the 29Si NMR spectro-
scopic signal is significantly shifted upfield relative to that of
the three-coordinate bis(iminophosphorane) chelate ligand-
stabilized [SiCl]+ (d=À3.3 ppm),[3c] in which an extensive
electronic delocalization is observed. It is also intermediate
(1.724(2) ꢁ).[12b] It is comparable with that in the DMAP-
stabilized
(CMeNAr)}Si
To understand the bonding nature of 2, DFT calculations
of [LSi
(DMAP)]+ (2+; Figure S1 in the Supporting Informa-
tion) without a counteranion were performed (M06-2X/6-
311+G(2d) for Si and 6-311+G
(d,p) for H, C, and N).[14]
silanone
ACHTUNGTRENNUNG
derivative
[{HC(CACTHGNUTERNU{NG =CH2}NAr)-
G
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
The calculated structural parameters are in good agreement
with the crystallographic data of 2. The lone-pair orbital at
the Si1 atom can be illustrated in the HOMO (Figure S2a in
the Supporting Information). Accordingly, the natural bond
orbital (NBO)[15] analysis (Table S1 in the Supporting Infor-
mation) shows that the lone-pair orbital is high in s charac-
ter (sp0.37, electron occupancy: 1.94 e). Moreover, the natural
population analysis (NPA) charges indicate that the silicon
atom has a positive charge (+1.16).
The ambiphilic character of 2 can be demonstrated by its
reactivity. The reaction of 2 with 1 in THF formed the disily-
lenylsilylium triflate [L’2(L)Si]OTf (3, L’=LSiD, 23.3% yield)
with the displacement of DMAP (Scheme 3). The reaction
appears to proceed through the oxidative addition of 2 with
between that of [HC
d=69.3 ppm) and
ACHTUNGTRENNUNG
À400.2 ppm).[3a,b] The results indicate that the nature of the
silicon(II) cation is strongly influenced by the kinetic and
electronic stabilization of the ligand.
Compound 2 has been characterized by X-ray crystallog-
raphy (Figure 1). The SiNCN four-membered ring is puck-
ered. The Si1 cation adopts a distorted trigonal-pyramidal
geometry (sum of bond angles: 266.18), which indicates that
I
I
À
the Si Si bond in 1. Another possible mechanism is that
Chem. Eur. J. 2013, 19, 11786 – 11790
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www.chemeurj.org
11787

C.-W. So et al.
Figure 2. ORTEP drawing of compound 3 (50% thermal ellipsoids). The
hydrogen atoms and disorder in the triflate moiety are omitted for clarity.
À
À
Selected bond lengths [ꢁ] and angles [8]: Si1 Si2 2.441(3), Si2 Si3
À
À
À
À
2.451(3), Si1 N1 1.852(6), Si1 N2 1.864(6), Si2 N3 1.843(6), Si2 N4
À
À
1.819(6), Si3 N5 1.865(6), Si3 N6 1.877(6); N1-Si1-N2 69.8(3), N1-Si1-
Si2 105.6(2), N2-Si1-Si2 106.5(2), Si1-Si2-Si3 120.41(10), N3-Si2-N4
71.2(2), N5-Si3-N6 69.9(3), N5-Si3-Si2 107.2(2), N6-Si3-Si2 104.1(2).
Scheme 3. Synthesis of compounds 3–5.
to afford the silylsilylene [LSiSi(H)ACTHNUTRGNEUNG
{(NtBu)2C(H)Ph}] (4)[17]
one of the SiI atoms in 1 acts as a Lewis base to form an
adduct with 2. Compound 3 is the first example of a stable
silylium cation that comprises low-valent silicon substituents,
although the chemistry of stable silylium cations has been
studied in recent decades.[16]
in 13.4% yield with the displacement of DMAP (Scheme 3).
The reaction appears to proceed through the formation of
the hydrosilylene intermediate [LSiH], which then reacts
with the amidinate ligand of another [LSiH] molecule to
form 4. We have also reported the synthesis of compound 4
by the reduction of [LSiHCl2] with 4 equivalents of KC8.[17]
The existence of the lone-pair electrons in compound 2
can be illustrated by the reaction of 2 with elemental sulfur
in THF to form the base-stabilized silanethionium triflate
Compound 3 is soluble in THF, DME, and pyridine. It is
stable in the solid state at room temperature under an inert
atmosphere. Compound 3 has been characterized by NMR
1
spectroscopy. The H and 13C NMR spectra of 3 display res-
onances due to the amidinate ligands. The 29Si NMR spec-
trum of 3 exhibits two singlets at d=2.96 and À0.53 ppm for
the silylium cation and low-valent silicon atoms, respectively.
The 29Si NMR spectroscopic signals are intermediate be-
tween the silicon cations (d=53.4 ppm) and the three-coor-
dinate low-valent silicon atoms (d=À128.7 ppm) in the
base-stabilized tetrasilacyclobutadiene dication.[8]
Compound 3 was characterized by X-ray crystallography
(Figure 2). The Si1 and Si3 atoms adopt a distorted trigonal-
pyramidal geometry (sum of bond angles of Si1: 281.98; Si3:
281.28), which indicates that they are almost nonhybridized
and possess lone-pair electrons with high s character. The
lone-pair electrons on these Si atoms have a gauche-bent
[LSi(S)ACTHNGUTRENNU(G DMAP)]OTf (5) in 30.9% yield (Scheme 3). A simi-
lar compound supported by the bis(iminophosphorane) che-
late ligand has been reported by Driess et al. very recen-
tly.[3c] Compound 5 is soluble in THF, CH2Cl2, and CHCl3. It
is stable in the solid state at room temperature under an
inert atmosphere. Compound 5 has been characterized by
NMR spectroscopy. The 29Si NMR spectrum of 5 exhibits
one singlet at d=À14.09 ppm, which shows a downfield
shift relative to that of 2. The 29Si NMR spectroscopic signal
of 5 is intermediate between the four-coordinate amidinate
silanethione complexes [LSi(S)Cl] (d=À17.5 ppm) and
[LSi(S)StBu] (d=1.57 ppm).[18a,b] It shows a downfield shift
relative to that of the five-coordinate amidinate silanethione
complex [L2SiS] (d=À70.7 ppm).[18c]
À
conformation. The Si Si bonds (2.441(3), 2.451(3) ꢁ) are
I
I
[9]
À
comparable to the Si Si bond (2.413(2) ꢁ) in 1. They are
longer than those in the base-stabilized tetrasilacyclobuta-
diene dication (2.321(2), 2.331(2) ꢁ).[8] The results indicate
Compound 5 has been characterized by X-ray crystallog-
raphy (Figure 3). The Si1 cation adopts a tetrahedral geome-
À
try. The Si1 S1 bond (1.969(10) ꢁ) is comparable with that
À
that the Si Si bonds in 3 do not have any multiple-bond
in the amidinate–silanethione complexes such as [LSi(S)St-
Bu] (1.984(8) ꢁ), [LSi(S)Cl] (2.079(6) ꢁ), and [L2SiS]
(2.0193(9) ꢁ).[18] It is also comparable with those in base-sta-
bilized silanethione complexes (2.006(1)–2013(3) ꢁ).[19] The
À
character. The Si2 N bonds (1.819(6), 1.843(6) ꢁ) are short-
ened relative to those in 2 because the oxidation state of the
silicon cation increases from +II to +IV.
À
In principle, compound 2 is highly electrophilic and can
react with a wide range of nucleophilic reagents. As such,
results indicate that the Si1 S1 bond could have double-
À
bond character or zwitterionic Si+
S
bonding character.
À
À
the reaction of 2 with [K{HB
N
The Si Namidinate (1.800(2), 1.801(2) ꢁ) bond lengths are
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Chem. Eur. J. 2013, 19, 11786 – 11790

Silyliumylidene Cation
FULL PAPER
(400.2 MHz, [D8]THF, 24.88C): d=1.07 (s, 18H; tBu), 3.22 (s, 6H;
NMe2), 7.12–7.55 (m, 7H; Ph and DMAP), 8.37 ppm (d, 3J
ACHTUNGTRENNUNG(H,H)=
6.44 Hz, 2H; DMAP); 13C NMR (100.6 MHz, [D8]THF, 24.78C): d=
31.16 (CMe3), 39.61 (NMe2), 54.64 (CMe3), 108.84 (Ph), 121.72 (q, 1J-
AHCTUNGTREG(NUNN C,F)=321.7 Hz; CF3), 126.16, 128.14, 128.71 (Ph), 128.95 (br; meta-
CDMAP), 129.48, 131.22, 132.46 (CNMe2 and Ph), 146.02 (br; ortho-
CDMAP), 171.63 ppm (NCN); 29Si{1H} NMR (78.65 MHz, [D8]THF,
22.78C): d=À82.27 ppm; 19F{1H} NMR (375.94 MHz, [D8]THF, 23.28C):
d=À78.90 ppm; elemental analysis calcd (%) for C23H33F3N4O3SSi: C
52.06, H 6.27, N 10.56; found: C 51.73, H 6.15, N 10.16.
Crystal data for 2: [C23H33F3N4O3SSi]; Mr =530.68; monoclinic; space
group Cc; a=14.0577(6), b=10.8815(4), c=18.3062(8) ꢁ; b=
102.662(2)8; V=2732.18(19) ꢁ3; Z=4; 1calcd =1.290 mgmÀ3; 18381 meas-
ured reflections; 7566 independent reflections; 391 refined parameters;
R1 =0.0443, wR2 =0.0919 (I>2s(I)).
Synthesis of 3: A solution of 2 (0.107 g, 0.201 mmol) in THF (13.4 mL)
was added dropwise to a stirring solution of 1 (0.104 g, 0.201 mmol) in
THF (5 mL) at ambient temperature. The resulting dark red solution was
stirred for 2 h. Volatiles were removed under vacuum, and the residue
was extracted with DME. After filtration and concentration of the fil-
trate, 3 was obtained as yellow crystals (0.028 g, 22.6%). M.p. 270.18C
(decomp); 1H NMR (399.5 MHz, [D5]Pyr, 23.68C): d=1.20 (s, 36H;
tBu), 1.32 (s, 18H; tBu), 7.35–7.70 ppm (m, 15H; Ph); 13C NMR
(100.5 MHz, [D5]Pyr, 24.18C): d=31.41 (CMe3), 31.73 (CMe3), 53.59
(CMe3), 55.91 (CMe3), 128.21, 128.30, 128.78, 128.92, 129.20, 129.64,
Figure 3. ORTEP drawing of compound 5 (50% thermal ellipsoids). Hy-
drogen atoms are omitted for clarity. Selected bond lengths [ꢁ] and
À
À
À
À
angles [8]: Si1 S1 1.9686(10), Si1 N1 1.801(2), Si1 N2 1.800(2), Si1 N3
1.794(2); N1-Si1-N2 73.03(11), N1-Si1-N3 104.46(11), N2-Si1-N3
106.30(11), N1-Si1-S1 124.65(9), N2-Si1-S1 124.91(9), N3-Si1-S1
115.49(8).
130.85 (Ph), 132.09 (q, 1J
ACHTNUTRGNEU(GN C,F)=301.0 Hz; CF3) 133.11 (Ph), 165.76,
182.92 ppm (NCN); 29Si{1H} NMR (78.65 MHz, DME, 23.48C): d=
À0.534 (LSiD), 2.96 ppm (Si+); 19F{1H} NMR (375.94 MHz, [D5]Pyr,
23.78C): d=À77.09 ppm; elemental analysis calcd (%) for
C46H69F3N6O3SSi3: C 59.58, H 7.51, N 9.07; found: C 59.31, H 7.24, N
8.75.
shorter than those in 2 because the oxidation state of the sil-
icon cation increases from +II to +IV.
Crystal data for 3: [C46H69F3N6O3SSi3]; Mr =927.40; monoclinic; space
group P21/n; a=16.0420(13), b=17.2604(16), c=18.4942(15) ꢁ; b=
90.112(6)8; V=5120.9(8) ꢁ3; Z=4; 1calcd =1.203 mgmÀ3; 40958 measured
reflections; 8788 independent reflections; 651 refined parameters; R1 =
0.0819, wR2 =0.1866 (I>2s(I)).
Conclusion
The silyliumylidene cation [LSiACTHUNTGRNEUNG(DMAP)]OTf (2), which is
Synthesis of 4: [K{HBACTHNUTRGNEUNG(iBu)3}] (0.22 mL, 1m in THF) was added dropwise
stabilized by both an amidinate ligand and DMAP, can be
synthesized by a simple procedure. Its reactivity toward the
amidinate silicon(I) dimer, [K{HBACTHNUTRGNENUG(iBu)3}], and sulfur dem-
onstrates that it has both electrophilic and nucleophilic char-
acters. Further reactivities of 2 are currently under investiga-
tion.
to a stirring solution of 2 (0.107 g, 0.201 mmol) in THF (13.4 mL) at
À788C. The resulting orange solution was warmed to ambient tempera-
ture and stirred for an additional 2 h. Volatiles were removed under
vacuum, and the residue was extracted with a mixture of toluene and
THF. After filtration and concentration of the filtrate, 4 was obtained as
colorless crystals (0.0071 g, 13.4%). For spectroscopic data of 4, see the
literature.[17]
Synthesis of 5: A solution of sulfur (0.0079 g, 0.246 mmol) in THF
(1 mL) was added to a stirring solution of 2 (0.111 g, 0.208 mmol) in THF
(13.8 mL) at À788C. The reaction mixture was warmed to ambient tem-
perature and stirred for an additional 3 h. The insoluble precipitate was
removed by filtration, and the filtrate was concentrated to obtain 5 as
colorless crystals (0.036 g, 30.9%). M.p. 281.48C (decomp); 1H NMR
Experimental Section
General procedure: All manipulations were carried out under an inert at-
mosphere of argon gas using standard Schlenk techniques. THF, DME,
and toluene were dried and distilled over Na/K alloy prior to use.
(399.5 MHz, [D1]chloroform, 23.28C): d=1.13 (s, 18H; tBu), 3.02 (s, 6H;
3
NMe2), 6.52 (d, J
N
A
ACHTUNGTREN(NUGN H,H)=7.79 Hz, 2H;
[D8]THF was dried and distilled over
K metal prior to use.
AHCTUNGTRENNUNG
[D1]Chloroform and [D5]Pyr were dried and distilled over CaH2 prior to
use. Compound 1 and [4-NMe2C5H4NSiMe3]OTf were prepared as descri-
bed in the literature.[9,10] The 1H, 13C, 19F, and 29Si NMR spectra were re-
corded using a JEOL ECA 400 spectrometer. The chemical shifts (d) are
AHCTUNGTREG(NNUN H,H)=5.95 Hz, 1H; ortho-CH of DMAP), 8.68 ppm (br, 2H; meta-CH
of DMAP); 13C NMR (100.6 MHz, [D1]chloroform, 24.28C): d=30.99
(CMe3), 39.34 (NMe2), 57.06 (CMe3), 106.83, 115.84 (Ph and DMAP),
120.60 (q, 1J
ACHTNUTRGNE(NUG C,F)=319.14 Hz; CF3), 127.08, 128.62, 129.74, 132.64,
1
relative to SiMe4 for H, 13C, and 29Si; and CFCl3 for 19F. Elemental anal-
149.19, 154.71 (Ph and DMAP), 166.83 ppm (NCN); 29Si{1H} NMR
(79.49 MHz, [D1]chloroform, 23.68C): d=À14.09 ppm; 19F{1H} NMR
(372.5 MHz, [D1]chloroform, 23.48C): d=À79.16 ppm; elemental analy-
sis calcd (%) for C23H33F3N4O3S2Si: C 49.10, H 5.92, N 9.96; found: C
48.87, H 5.63, N 9.74.
yses were performed by the Division of Chemistry and Biological Chem-
istry, Nanyang Technological University. Melting points were measured
in sealed glass tubes and were not corrected.
Synthesis of 2:
A solution of [4-NMe2C5H4NSiMe3]OTf (0.0735 g,
0.213 mmol) in THF (1 mL) was added to a stirring solution of 1 (0.108 g,
0.208 mmol) and DMAP (0.0518 g, 0.424 mmol) in THF (15 mL) at ambi-
ent temperature. The resulting dark red solution was stirred for 2 h. Vola-
tiles were removed under vacuum, and the residue was extracted with
toluene. After filtration and concentration of the filtrate, 2 was obtained
as colorless crystals (0.060 g, 54.3%). M.p. 169.78C (decomp); 1H NMR
Crystal data for 5: [C23H33F3N4O3S2Si]; Mr =562.74; triclinic; space group
¯
P1; a=8.7357(12), b=10.7468(12), c=15.909(2) ꢁ; a=103.952(3), b=
97.110(3), g=100.141(6)8; V=1405.0(3) ꢁ3; Z=2; 1calcd =1.330 mgmÀ3
;
22636 measured reflections; 7624 independent reflections; 333 refined
parameters; R1 =0.0652, wR2 =0.1647 (I>2s(I)).
Chem. Eur. J. 2013, 19, 11786 – 11790
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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C.-W. So et al.
X-ray data collection and structural refinement: Intensity data for com-
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the disordering in the triflate moieties in compounds 2 and 3 are descri-
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Received: January 23, 2013
Revised: May 28, 2013
Published online: July 12, 2013
11790
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