Preparation of 1,1-disubstituted silacyclopentadienes

Article abstract of DOI:10.1016/j.jorganchem.2008.01.017

Several new 1,1-disubstituted siloles containing substituents on the ring carbon atoms have been synthesized. The new siloles: 1,1-dihydrido-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (5), 1,1-dihydrido-2,5-dimethyl-3,4-diphenylsilole (6), 1,1-dimethoxy-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (7), 1,1-bis(4-methoxyphenyl)-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (8), 1,1-dipropoxy-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (9), and 1,1-dibromo-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (13) were prepared from reactions originating from the previously reported, 1,1-bis(diethylamino)-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (1) or 1,1-bis(diethylamino)-2,5-dimethyl-3,4-diphenylsilole (2). In addition, three other new organosilane byproducts were observed and isolated during the current study, bis(4-methoxyphenyl)bis(phenylethynyl)silane (11), bis(4-methoxyphenyl)di(propoxy)silane (12) and 1-bromo-4-bromodi(methoxy)silyl-1,4-bis(trimethylsilyl)-3,4-diphenyl-1,3-butadiene (14). Compounds 13 and 14 were characterized by X-ray crystallography and 14 is the first 1,1-dibromosilole whose solid state structure has been determined.

Full text of DOI:10.1016/j.jorganchem.2008.01.017

Available online at www.sciencedirect.com
Journal of Organometallic Chemistry 693 (2008) 1233–1242
www.elsevier.com/locate/jorganchem
Preparation of 1,1-disubstituted silacyclopentadienes
Janet Braddock-Wilking *, Yan Zhang, Joyce Y. Corey, Nigam P. Rath
Department of Chemistry and Biochemistry and Center for Nanoscience, University of Missouri-St. Louis, St. Louis, MO 63121, United States
Received 20 December 2007; received in revised form 10 January 2008; accepted 10 January 2008
Available online 17 January 2008
Abstract
Several new 1,1-disubstituted siloles containing substituents on the ring carbon atoms have been synthesized. The new siloles: 1,1-
dihydrido-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (5), 1,1-dihydrido-2,5-dimethyl-3,4-diphenylsilole (6), 1,1-dimethoxy-2,5-bis(trimeth-
ylsilyl)-3,4-diphenylsilole (7), 1,1-bis(4-methoxyphenyl)-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (8), 1,1-dipropoxy-2,5-bis(trimethyl-
silyl)-3,4-diphenylsilole (9), and 1,1-dibromo-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (13) were prepared from reactions originating
from the previously reported, 1,1-bis(diethylamino)-2,5-bis(trimethylsilyl)-3,4-diphenylsilole (1) or 1,1-bis(diethylamino)-2,5-dimethyl-
3,4-diphenylsilole (2). In addition, three other new organosilane byproducts were observed and isolated during the current study,
bis(4-methoxyphenyl)bis(phenylethynyl)silane (11), bis(4-methoxyphenyl)di(propoxy)silane (12) and 1-bromo-4-bromodi(methoxy)silyl-1,
4-bis(trimethylsilyl)-3,4-diphenyl-1,3-butadiene (14). Compounds 13 and 14 were characterized by X-ray crystallography and 14 is the
first 1,1-dibromosilole whose solid state structure has been determined.
Ó 2008 Elsevier B.V. All rights reserved.
Keywords: Silicon; Silole; Synthesis; Reductive cyclization
1. Introduction
The first reported syntheses of a silole by Braye and
Hubel [12] and Leavitt and coworkers [13] occurred nearly
¨
The study of silacyclopentadienes, also known as siloles,
has recently received substantial attention due to the
unique aspects of their synthesis and reaction chemistry
as well as the novel photophysical and electronic properties
exhibited by this class of compounds [1–4]. Siloles possess a
low-energy LUMO due to the r*–p* conjugation involving
the r* orbital of the exocyclic substituents on Si and the p*
orbitals of the butadiene unit in the ring that result in high
electron affinity properties for siloles [5,6]. Silole-contain-
ing p-conjugated systems generally exhibit long wavelength
absorptions in the UV–Vis region [7,8], and many have
been found to display high photoluminescent quantum effi-
ciency, especially in the solid state [9]. These novel proper-
ties make siloles ideal candidates for components in light-
emitting devices [10]. Siloles have also been recognized as
chemical sensors for nitroaromatic and other types of
explosives [11].
50 years ago. To date, several methods have been utilized
for the preparation of siloles [4] but there are two routes
that appear to be the most versatile and most widely used.
One involves the salt metathesis reaction between an active
1,4-metalla-1,3-butadiene with a dihalosilane (or related
precursor) to form two new Si–C bonds upon ring closure.
The other route involves preparation of a silane containing
two alkynyl substituents, then effecting ring closure
through formation of a new C–C bond by reductive cou-
pling. The most challenging aspect of the first method
involves construction of the required 1,4-dihalo-1,3-butadi-
ene precursor. However, a convenient one-pot synthesis of
such compounds has been reported that involves the prep-
aration of a titanocyclopentadiene intermediate as a pre-
cursor to the substituted 1,4-dihalo-1,3-butadienes via
halogenolysis [14]. The second method utilizes a reductive
cyclization reaction of bis(phenylethynyl)silanes [7] for a
multi-step preparation of 2,5-difunctionalized siloles. The
latter method has been limited primarily to phenylethynyl-
silanes but the reductive cyclization has also been success-
*
Corresponding author. Tel.: +1 314 516 6436; fax: +1 314 516 5342.
E-mail address: wilkingj@umsl.edu (J. Braddock-Wilking).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.01.017

1234
J. Braddock-Wilking et al. / Journal of Organometallic Chemistry 693 (2008) 1233–1242
ful with 4-N-indolylphenyl- and 4-N-7-azaindolylphenyle-
thynylsilanes [10b].
at room temperature [20]. Thus, the relative stability of sil-
oles is probably related to the presence of groups at the
ring carbons atoms [8,21].
The 1,1-diethylaminosilole 1 was converted to 1,1-
dimethoxysilole (7) by treatment with methanol in the
presence of AlCl3 (Eq. (1)), by analogy to the related and
previously prepared 1,1-diethoxysilole [15]. However, it
was found that an excess amount of AlCl3 and a tempera-
ture of 60 °C were required to obtain a 81% yield of 7
(see Table 1).
We report here the synthesis of six new 2,5-bis(trimethyl-
silyl)-3,4-diphenyl- and 2,5-dimethyl-3,4-diphenyl-substi-
tuted siloles in addition to other organosilyl-containing
products that have been obtained during the preparation
of synthetically useful silole compounds. The new siloles
were prepared by modifications of procedures reported
by Tamao and coworkers for the reductive cyclization
employing a bis(phenylethynyl)diethylaminosilane precur-
sor [15]. The aim of our study was to prepare new siloles
in which there were different substituents on the ring car-
bon atoms and functional groups on silicon that may be
used as precursors to build more complex silole derivatives.
Ph
Ph
Ph
Ph
AlCl3 / MeOH
60 oC
Me3Si
Me3Si
SiMe3
OMe
SiMe3
NEt2
Si
Si
MeO
Et2N
7
1
2. Results and discussion
ð1Þ
2.1. Preparation and characterization of new compounds
Treatment of 1,1-dichlorosilole 2 in diethyl ether with
(4-MeOC6H4)MgBr [22] prepared from 4-bromoanisole
afforded the 1,1-diarylsilole 8 in 82% yield (Eq. (2)). How-
ever, changing the solvent from Et2O to THF using either
an ArLi or ArMgBr
Siloles 1 and 2 have been prepared previously starting
from bis(diethylamino)-bis(phenylethynyl)silane [3,15]. Sil-
oles 1 and 2 were chosen as the starting silole reagents since
they are easily prepared and have been reported to produce
the corresponding 1,1-dichlorosiloles 3 and 4 in ca. 80%
yield upon treatment with dry HCl [15]. The latter could
then serve as convenient precursors for the preparation of
a variety of new siloles functionalized at silicon. Two of
the six new siloles, 5 and 6, reported here contain hydrogen
substituents on the silicon atom (Scheme 1). The obvious
route to 5 and 6 starting from H2Si(C ꢀ CPh)2 [16] was
unsuccessful.
Ph
Ph
Ph
Ph
2 eq 4-MeOC6H4MgBr
Et2O
Me3Si
SiMe3
Me3Si
Si
SiMe3
Si
Cl
Cl
Ar
Ar
2
8
ð2Þ
reagent did not lead to the formation of 8 but instead gave
the 1,1-dipropoxysilole 9 as illustrated in Eq. (3). The pres-
The 1,1-dihydrosiloles 5 and 6 were isolated as air and/
or moisture sensitive light yellow or white solids in yields of
50% and 80%, respectively. Exposure of hexane solutions
of either 5 or 6 resulted in the formation of an unidentified
white solid after a few minutes. Only a few 1,1-dihydrosil-
oles have been previously reported [17]. In contrast to 5
and 6, siloles that have phenyl substitutents at the 2,5-posi-
tions [18–20] are stable to air and moisture but 1-hydro-1-
methyl-2,5-diphenylsilole was found to decompose slowly
Table 1
Synthesis of 1,1-dimethoxy-2,5-bis(trimethylsilyl)-3,4-diphenylsilole 7
Reaction run
1
2
3
4
5
AlCl3 (equiv.)
Temperature (°C)
Time (h)
25
25
20
15
25
60
20
34
50
60
20
66
50
60
48
78
55
60
48
81
Yield (%)
Ph
Ph
Ph
Li
Ph
Li
Ph
Ph
a) 4Me3SiCl
4 LiNapth
or b) 4Me2SO4
a) 1:R =Me3Si
2
b) :R =Me
THF
-78 oC
to rt
Si
R
Et2N
R
NEt2
Si
Si
Si
(ref.1 5)
Et2N
NEt2
-78 oC
Et2N
NEt2
dryH Cl
Et2O, -78 oC
Ph
Ph
Ph
Ph
R
LiAlH4
Et2O
R
R
R
Si
-78 oC to rt
Cl
Cl
H
H
3:R =Me3Si
5:R =Me3Si (50% yield)
4
:R =Me
(ref.15)
6:R =Me( 80%yield)
Scheme 1.

J. Braddock-Wilking et al. / Journal of Organometallic Chemistry 693 (2008) 1233–1242
1235
ence of the propoxy groups in 9 resulting from the at-
tempted coupling reaction in THF was an unexpected re-
sult. The origin of the propoxy groups in 9 is not certain
but clearly occurs when THF is used as the solvent. It is
known that active organometallic reagents can promote
ring cleavage of THF to produce ethylene and the enolate
salt of acetaldehyde both of which are two carbon frag-
ments [23]. The enolate can be trapped, for example, with
chlorotrimethylsilane [24], however, no such related prod-
uct was identified in the reaction mixtures from 8 and
Ar–M (M = Li and MgBr) as determined by GC–MS.
Since no reaction was observed when 1,1-dichlorosilole
(2) was dissolved in pure THF after two days under an in-
ert atmosphere the organometallic reagents must be impli-
cated in this unusual result. To the best of our knowledge,
the generation of a three carbon unit from the cleavage of
THF has not been previously established. It should be
noted that the coupling of either an organolithium or Grig-
nard reagent with 1-chloro-1-phenyl-2,3,4,5-tetraphenylsil-
ole in THF was successful [9f]. As was the coupling of
2 equiv. of HC„CMgBr with 1,1-dichloro-2,3,4,5-tetra-
phenylsilole in THF [25].
In a separate attempt to prepare 1,1-diarylsiloles,
bis(phenylethynyl)bis(4-methoxyphenyl)silane (11) was
synthesized as a potential precursor for a 1,1-diaryl-substi-
tuted silole via a reductive cyclization route. Reaction of
the aryl-Grignard, 4-methoxyphenylmagnesium bromide
[22] with silicon tetrachloride produced dichloro-bis(4-
methoxyphenyl)silane [26] 10 which was then treated with
phenylethynyllithium to afford product 11 in 76% yield
(from 10). Unfortunately, the attempted reductive cycliza-
tion of 11 did not produce the desired silole 8. Instead,
bis(4-methoxyphenyl)dipropoxysilane 12 was isolated as
the major product in 42% yield (Scheme 2). As with com-
pound 9, the origin of the propoxy groups is believed to
come from THF but the mechanism by which it is incorpo-
rated into the product is not known.
Ring-functionalized 2,5-disubstituted siloles have been
prepared via halodesilylation of 2,5-disilyl-substituted
siloles. Tamao and coworkers have reported the halodesily-
lation of 1,1-dialkyl- 2,5-bis(trimethylsilyl)-3,4-diphenylsil-
oles (Me, Et, or i-Pr) with pyridinium bromide perbromide,
PyHBr3 [27]. Complex reaction mixtures were obtained
with the less bulky methyl and ethyl substitutents on silicon
(probably due to competing reactions from attack at the
ring silicon atom). But with the bulkier i-Pr groups the
halogenolysis was successful, producing the corresponding
2,5-dibromosilole in 40% yield. The authors found that
the reactivity of the siloles was dependent on the nature
of the substituents in the 3,4-positions of the silole ring
[27]. Cleaner reactions were observed with 3,4-dialkyl vs.
Ph
Ph
Ph
Ph
Me3Si
or
2 eq ArLi
2 eq ArMgBr
Me3Si
SiMe3
OPr
SiMe3
Si
Si
THF, -78 oC to rt
Ar = 4-MeOC6H4
Cl
Cl
PrO
9
2
ð3Þ
Ph
Me3Si
Ph
SiMe3
Ph
Ph
Ph
Li
Ph
Li
xs Me3SiCl
-78 oC to rt
4 LiNaph
Si
THF
Si
Si
Ar
Ar
Ar
Ar
-78 oC
Ar
Ar
8
11
MeO
Ar =
OPr
Ar
PrO
Ar
Si
12
Scheme 2.
Ph
SiMe3
Ph
PyHBr3,THF
-78 oC to rt
Me3Si
Ph
Ph
Si
PrO
Ph
OPr
Me3Si
SiMe3
NEt2
Si
9
Et2N
Br2,E t2O
Ph
-78 o C to rt
1
Me3Si
SiMe3
Si
Br Br
13
Scheme 3.

1236
J. Braddock-Wilking et al. / Journal of Organometallic Chemistry 693 (2008) 1233–1242
Ph
Ph
3,4-diphenylsiloles. A related reaction involving halodesily-
lation using Br2 with a dithienothiasiline ring system has
been reported to remove a silyl group from the thiophene
rings [28]. With molecular halogens, the most common
reaction of siloles, germoles, and stannoles appears to be
cleavage of one or both of the endocyclic Group 14 ele-
ment-carbon bonds with subsequent complicating reac-
tions [1a]. In a related study, replacement of the two
exocyclic phenyl substituents in hexaphenylstannole by
treatment with X2 (X = Br, I) while preserving the metall-
ole core was originally reported [29]. However, a later
study showed that the actual product was the ring-opened
compound, 1-bromo-4-bromodiphenylstannyl-1,2,3,4-tet-
raphenyl-1,3-butadiene [30].
The brominating reagents PyHBr3 and Br2 produced
different results. Reaction of 1,1-diethylaminosilole 1 with
PyHBr3 in THF did not result in the halodesilylation of
the SiMe3 groups by bromine. Instead, the unexpected
and previously observed product, 9 was formed in 25%
yield (Scheme 3).
Ph
SiMe3
Ph
Me3Si
MeO
Br2, Et2O
Me3Si
MeO
SiMe3
OMe
Si
Br
-78 o C to rt
Si
Br
OMe
7
14
ð4Þ
The unsymmetrical environment in 14 was confirmed by
1H and 13C NMR spectroscopy where two sets of reso-
nances were observed for the SiMe3 and OMe groups.
1
The H NMR spectrum exhibited two signals at 0.48 and
ꢁ0.07 ppm for the two distinct SiMe3 groups as well as
two separate resonances for the OMe groups at 3.71 and
3.65 ppm. The presence of two Si(OMe)2 signals can be
attributed to the two diastereotopic OMe groups.
Table 2
The reaction of 1 with Br2 in Et2O replaced the NEt2
groups instead of cleaving the trimethylsilyl groups. Color-
less crystals of 1,1-dibromosilole 13 were obtained in 52%
yield (Scheme 3). The structure of 13 was confirmed by
X-ray crystallography. However, more rigorous conditions
were used to prepare a related silole, 1,1-dibromo-2,3,4,5-
tetramethylsilole in 28% yield from the reaction of the
1,1-bis(cyclopentadienyl)-2,3,4,5-tetramethylzirconacyclo-
pentadiene with SiBr4 for two days at 150 °C [31].
In contrast when 1,1-dimethoxysilole 7 was reacted with
Br2 the ring-opened product 14 was obtained from attack
at the ring silicon atom (Eq. (4)). White crystals of 14 were
obtained in 77% yield and the structure confirmed by X-ray
crystallography
Crystal data and structure refinement details for compounds 13 and 14
13
14
Empirical formula
Mr
C22 H28 Br2 Si3
536.53
C24 H34 Br2 O2 Si3
598.60
T (K)
k (A)
100(2)
0.71073
100(2)
0.71073
˚
Crystal system
Monoclinic
C2/c
20.3293(6)
10.3868(3)
11.5102(3)
90
98.168(2)
90
2405.80(12)
4
Monoclinic
P21/c
14.4929(6)
10.8030(4)
18.5479(8)
90
109.920(2)
90
2730.24(19)
4
Space group
˚
a (A)
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
3
˚
V (A )
Z
Dc (Mg mꢁ3
)
1.481
3.525
1088
1.456
3.119
1224
l (mmꢁ1
F000
)
Crystal size (mm)
h Range (°)
0.26 ꢂ 0.21 ꢂ 0.18
2.02–33.33
ꢁ31 6 h 6 31,
ꢁ16 6 k 6 15,
ꢁ17 6 l 6 17
0.21 ꢂ 0.17 ꢂ 0.11
1.49–25.00
ꢁ16 6 h 6 17,
ꢁ12 6 k 6 12,
ꢁ22 6 l 6 22
49358
Index ranges
Number of reflections 41123
collected
Number of
4659 (0.040)
4810 (0.1042)
independent
reflections (Rint
)
Completeness to h, % 100.0 (25.00)
(°)
100 (33.33)
Numerical
Absorption
Numerical
0.608/0.471
4659/0/179
correlation
Maximum/minimum
transmission
Number of data/
restraints/
0.7663/0.6432
4810/1/316
parameters
Fig. 1. Molecular structure of 1,1-dibromo-2,5-bis(trimethylsilyl)-3,4-
diphenylsilole 13. Selected bond distances (A) and angles (°): Si(1)-Br(1),
2.2161(3); Si(1)–C(1), 1.8502(12); Si(1)–C(1)#1, 1.8501(12); Si(2)–C(1),
1.8774(12); C(1)–C(2), 1.3578(17); C(2)–C(2)#1, 1.526(2); Br(1)#1–Si(1)–
Br(1), 106.47(2); C(1)#1–Si(1)–C(1), 98.10(8); C(1)–C(2)–C(2)#1,
117.74(7); C(1)–Si(1)–Br(1), 115.69(4); C(1)–Si(1)–Br(1)#1, 110.55(4).
Goodness-of-fit on F2 1.041
1.122
0.0454
0.1022
0.701, ꢁ0.595
˚
R1 [I > 2r(I)]
wR2 (all data)
0.0238
0.0510
Maximum, minimum 0.506, ꢁ0.315
3
˚
peaks (e/A )

J. Braddock-Wilking et al. / Journal of Organometallic Chemistry 693 (2008) 1233–1242
1237
2.2. X-ray crystallographic studies
3. Conclusion
The molecular structure of 13 is shown in Fig. 1 along
with selected bond distances and angles. The crystal data
and structure refinement details for compounds 13 and
14 are listed in Table 2. The ring silicon center in 13 exhib-
its a distorted tetrahedral geometry with an endocyclic
C–Si–C angle of 98.1° due to the constraints imposed by
the 5-membered silole ring whereas the Br–Si–Br angle
was larger at 106.5°. Typical endocyclic C–Si–C angles
for siloles fall in the range of 90.5–97° [32]. Placement of
electronegative groups in the 2,5-positions of the silole ring
results in a decrease of the C–Si–C ring angle [32]. The pla-
nar silole ring exhibits endocyclic C@C double bonds and a
C–C single bond within the expected range [10c]. The Si–Br
The current study involves the preparation of several
new 1,1-disubstituted-2,5-bis(trimethylsilyl)-3,4-diphenyl-
siloles using the modified literature procedures [7,15].
Two new compounds were structurally characterized by
X-ray crystallography, 1,1-dibromosilole (13) and the
ring-opened bromosilyl-butadiene compound 14. The
results from this study have shown that the chemistry
involved in the preparation and reactivity of siloles contin-
ues to be complex and unusual. However, unexpected
results may be obtained in THF as reported in this study.
We are continuing to prepare novel silole systems with
functionality at silicon.
˚
bond distance of 2.216(3) A found in 13 is comparable to
4. Experimental
other structurally characterized four-coordinate organob-
romosilanes [33]. The structural environment in 13 is
similar to the related 1,1-dichloro-2,3,4,5-tetraphenylsilole
but with shorter distances found in the expected Si–Cl
distances but also with the Si–C bond lengths [34].
4.1. General
All reactions were performed in flame- or oven-dried
glassware under dry nitrogen or argon on a dual-manifold
Schlenk line or in an inert atmosphere box. Tetrahydrofu-
ran and diethyl ether were distilled from sodium/9-Fluore-
none under nitrogen [35]. Hexane, pentane, and methylene
chloride solvents were distilled from calcium hydride under
nitrogen. Other commercial reagents including phenylacet-
ylene and 4-bromoanisole were also dried and distilled
from calcium hydride under nitrogen. The chlorosilanes,
HSiCl3, SiCl4 and Me3SiCl were freshly distilled before
use from potassium carbonate under argon. Diethylamine
was distilled after refluxing for 3 h over barium oxide.
Methanol was dried and distilled from magnesium under
nitrogen. Naphthalene was dried in vacuo at room temper-
ature for 2 h before use. Aluminum trichloride was sub-
limed at atmospheric pressure under argon with heating.
Hydrochloric acid solutions in diethyl ether were prepared
by reaction of ammonium chloride with concentrated sul-
furic acid or purchased as a 2 N solution from Aldrich
Chemical Co. Other commercially available chemicals
were used as received. The siloles, 1,1-diethylamino-2,5-
bis(trimethylsilyl)-3,4-diphenyl-1-silacyclopentadiene (1),
1,1-dichloro-2,5-bis(trimethylsilyl)-3,4-diphenyl-1-silacy-
The molecular structure of the unsymmetrical com-
pound 14 was also confirmed by X-ray crystallography
˚
˚
(Fig. 2). The C@C (1.34–1.37 A) and C–C (1.49 A)
bond distances in the butadiene unit are within the
expected range and are similar to those found in the related
tin system, 1-bromo-4-bromodiphenylstannyl-1,2,3,4-tetra-
phenyl-1,3-butadiene [30]. Other bond distances and angles
found in 14 fall within the anticipated range.
clopentadiene
(3),
1,1-diethylamino-2,5-dimethyl-3,
4-diphenyl-1-silacyclopentadiene (2), and 1,1-dichloro-2,5-
dimethyl-3,4-diphenyl-1-silacyclopentadiene (4) were pre-
pared according to the literature procedures [3,15]. NMR
solvents were obtained from Cambridge Isotopes Inc. and
1
dried over activated molecular sieves. The H, 13C, and
29Si NMR spectra were recorded on a Bruker ARX-500
1
spectrometer at 500 MHz for H, 125 MHz for 13C, and
99 MHz for 29Si at ambient temperature. Proton chemical
shifts (d) are reported relative to residual protonated sol-
vent, CD2Cl2 (5.32 ppm) and CDCl3 (7.27 ppm). Carbon
chemical shifts (d) are reported relative to the NMR sol-
vent, CD2Cl2 (54.00 ppm) and CDCl3 (77.23 ppm). Silicon
chemical shifts (d) are reported relative to external TMS
(0 ppm). Chemical shifts are given in ppm and coupling
Fig. 2. Molecular structure of 1-bromo-4-bromodimethoxysilyl-1,4-
bis(trimethylsilyl)-3,4-diphenyl-1,3-butadiene (14). Selected bond dis-
˚
tances (A) and angles (°): Si(1)–C(1), 1.903(5); Si(2)–C(4), 1.890(5);
Si(3)–C(1), 1.850(4); C(1)–C(2), 1.375(6); C(2)–C(3), 1.494(6); C(3)–C(4),
1.343(6); C(4)–Br(1), 1.945(5); Si(3)–Br(2), 2.100(5); Si(3)–Br(3), 2.042(10);
Si(3)–Br(4), 2.2163(18); C(2)–C(1)–Si(3), 122.1(4); C(4)–C(3)–C(2),
121.0(4); C(1)–C(2)–C(3), 124.6(4); C(2)–C(1)–Si(1), 123.8(3); C(3)–C(4)–
Si(2), 134.8(4); C(3)–C(4)–Br(1), 116.6(4).

1238
J. Braddock-Wilking et al. / Journal of Organometallic Chemistry 693 (2008) 1233–1242
constants in Hz. Melting point determinations were
obtained on a Mel-Temp capillary melting point apparatus
and are uncorrected. Infrared spectra were recorded on a
Thermo-Nicolet Avatar 360 ESP FT-IR spectrometer.
Mass spectral analyses were determined on a Hewlett-
Packard GC–MS System Model 5988A (EI) or a JEOL
MStation JMS-700 mass spectrometer and peaks >15%
of the base peak are listed as well as selected smaller parent
ion peaks in some cases. The X-ray crystal structure deter-
minations were performed on a Bruker SMART 1K dif-
fractometer equipped with a CCD area detector at 100 K.
Elemental analysis determinations were obtained from
Atlantic Microlabs, Inc, Norcross, GA.
The resulting mixture was concentrated in vacuo then dry
hexane (3 ꢂ 15 mL) was added. After filtration the filtrate
was condensed under reduced pressure to give 1,1-
dichloro-2,5-dimethyl-3,4-diphenyl-1-silacyclopentadiene
(5) which was used without isolation for the preparation of
6 [15]. Dry diethyl ether (25 mL) was added to dichlorosil-
ole 4, the resulting solution cooled to ꢁ78 °C, and solid
LiAlH4 (38 mg, 1.0 mmol) was added to the solution via
a bent tube. The mixture was allowed to gradually warm
to ambient temperature and stirred for an additional
2.5 h. The ether was removed under reduced pressure and
dry hexane (3 ꢂ 15 mL) was added to the residue. After fil-
tration, the filtrate was condensed under vacuum to pro-
vide a white solid and a small amount of viscous oil. The
white solid was purified by recrystallization from pentane
at ꢁ50 °C to give 1,1-dihydrido-2,5-dimethyl-3,4-diphe-
nyl-1-silacyclopentadiene (6) in 80% yield (0.21 g, 93%
4.2. Syntheses of compounds 5–14
4.2.1. 1,1-Dihydro-2,5-bis(trimethylsilyl)-3,4-diphenyl-1-
silacyclopentadiene (5)
1
purity by GC). M.p. 103–109 °C. H NMR (CD2Cl2): d
Dry HCl gas, generated from NH4Cl (0.53 mg, 10 mmol)
and concentrated H2SO4 (0.59 mL, 11 mmol) at room tem-
perature, was bubbled through a diethyl ether solution
(30 mL) containing 1,1-bis(diethylamino)-2,5-bis(trimethyl-
silyl)-3,4-diphenyl-1-silacyclopentadiene (1) [15] (0.52 g,
1.0 mmol) at ꢁ78 °C over 1 h. The resulting mixture
was concentrated in vacuo followed by addition of dry
hexane (3 ꢂ 20 mL). After filtration under argon, the fil-
trate was concentrated under reduced pressure to obtain
1,1-dichloro-2,5-bis(trimethylsilyl)-3,4-diphenyl-1-silacy-
clopentadiene (3) which was used without isolation for the
preparation of 5 [15]. Freshly distilled diethyl ether
(30 mL) was added to dichlorosilole 3, the solution was
cooled to ꢁ78 °C, followed by addition of solid LiAlH4
(38 mg, 1.0 mmol) from a bent glass tube. The mixture
was allowed to gradually warm to ambient temperature
and stirred for 3 h. The ether was removed under reduced
pressure and dry hexane (3 ꢂ 20 mL) was added by syringe.
After filtration, the resulting filtrate was concentrated under
vacuum to give a pale yellow viscous oil (0.19 mg, 41% of 3
by GC). Recrystallization from pentane at ꢁ50 °C in an
inert atmosphere box provided pale yellow crystals of 1,1-
dihydrido-2,5-bis(trimethylsilyl)-3,4-diphenyl-1-silacyclo-
7.17–7.08 (m, 6H, ArH), 6.89–6.86 (m, 4H, ArH), 4.40 (s,
1
2 H, JSi–H = 196, SiH2), 1.90 (s, 6H, SiMe3). 13C{1H}
NMR (CD2Cl2): d 158.2, 139.4, 129.7, 129.5, 127.9,
126.7, 15.7. 29Si{1H} NMR (DEPT, CD2Cl2): d ꢁ34.4
(s). IR (solid, cmꢁ1): mSiH 2151, 2130. EI-MS: m/z (relative
abundance, %) 262 (M+, 74), 247 (56), 145 (47), 143 (23),
131 (19), 129 (21), 121 (42),115 (34), 105 (100), 77 (16),
67 (18), 53 (22).
4.2.3. 1,1-Dimethoxy-2,5-bis(trimethylsilyl)-3,4-diphenyl-1-
silacyclopentadiene (7)
Table 1 lists various reaction conditions that were exam-
ined for the formation of 7. Reaction run 5 is described in
the following experiment. 1,1-Bis(diethylamino)-2,5-bis(tri-
methylsilyl)-3,4-diphenyl-1-silacyclopentadiene (1) [15]
(0.26 g, 0.50 mmol) and AlCl3 (0.037 g, 0.28 mmol) were
placed in a two-necked round bottomed flask with a con-
denser inside the dry box then transferred to a Schlenk line
under argon. Dry methanol (15 mL) was added to the mix-
ture by syringe with vigorous stirring. The mixture was
warmed to 60 °C and kept at that temperature for 2 days
before removing the methanol under reduced pressure.
The residue was washed with hexane (3 ꢂ 15 mL) and fil-
tered through silica gel. The crude product was purified
by flash column chromatography using silica gel (ethyl ace-
tate:hexane, 3:400). The eluted product was recrystallized
from hexane at ꢁ40 °C to give colorless crystals of 1,
1-dimethoxy-2,5-bis(trimethylsilyl)-3,4-diphenyl-1-silacyclo-
pentadiene (7) in 81% yield (0.18 g). M.p. 90–92 °C.
1H NMR (CDCl3): d 7.07–7.03 (m, 6 H, ArH), 6.85–6.81
(m, 4H, ArH), 3.65 (s, 6H, OCH3), ꢁ0.11 (s, 18H, SiMe3).
13C{1H} NMR (CDCl3): d 171.0, 142.6, 134.3, 128.5, 127.3,
126.6, 50.5, 0.2. 29Si{1H} NMR (DEPT, CDCl3): d ꢁ5.8
(SiMe3), ꢁ9.6 (SiOCH3). EI-MS: m/z (relative abundance,
%) 438 (M+, 18), 423 (26), 406 (22), 391 (46), 365 (22), 319
(15), 249 (64), 219 (45), 159 (72), 145 (29), 131 (25), 129
(25), 115 (82), 105 (31), 89 (33), 73 (100), 59 (63). Anal.
Calc. for C24H34O2Si3: C, 65.69; H, 7.81. Found: C,
65.87; H, 7.75%.
1
pentadiene (5) (0.056 g, 15%). M.p. 83–87 °C. H NMR
(CD2Cl2): d 7.09–7.07 (m, 6 H, ArH), 6.91–6.89 (m, 4H,
1
ArH), 4.56 (s, 2H, JSi–H = 196, SiH2), ꢁ0.12 (s, 18 H,
SiMe3). 13C{1H} NMR (CD2Cl2): d 172.4, 143.1, 140.8,
129.2, 127.6, 126.9, ꢁ2.1. 29Si{1H} NMR: (DEPT, CDCl3):
d ꢁ7.9 (s, SiMe3), ꢁ26.9 (s, SiH2). IR (solid, cmꢁ1): mSi–H
2125. EI-MS: m/z (relative abundance, %) 378 (M+, 5),
376 (M+ꢁ2, 19), 159 (17), 145 (25), 135 (17), 73 (100).
4.2.2. 1,1-Dihydro-2,5-dimethyl-3,4-diphenyl-1-
silacyclopentadiene (6)
An HCl solution (2 N in ether, 4 mL), was added drop-
wise to a diethyl ether (30 mL) solution of 1,1-bis(diethyl-
amino)-2,5-dimethyl-3,4-diphenyl-1-silacyclopentadiene
(2) [15] (0.40 g, 1.0 mmol) at ꢁ78 °C over 50 min and the
mixture was stirred at low temperature for another 2 h.

J. Braddock-Wilking et al. / Journal of Organometallic Chemistry 693 (2008) 1233–1242
1239
4.2.4. 1,1-Bis(4-methoxyphenyl)-2,5-bis(trimethylsilyl)-3,4-
diphenyl-1-silacyclopentadiene (8)
4.2.5.3. Method C. Pyridinium tribromide, PyHBr3
(0.34 g, 1.05 mmol) was dissolved in THF (8 mL) and
added dropwise to a solution of 1 [15] (0.26 g, 0.5 mmol
in 25 mL of THF) over 5 min at ꢁ78 °C. The mixture
was stirred at low temperature for 30 min and gradually
warmed to ambient temperature over 8 h. The THF was
removed under vacuum and the residue was dissolved in
diethyl ether (30 mL), washed with water and brine
(20 mL), dried over MgSO4, filtered, and condensed. The
crude product 9 was purified as described in Method A
to give a colorless oil (0.049 g) in 25% yield.
A solution of 4-methoxyphenylmagnesium bromide [22]
was prepared by treatment of 4-bromoanisole (0.37 g,
2.0 mmol) in 35 mL diethyl ether with magnesium turnings
(0.062 g, 2.6 mmol). The Grignard reagent was filtered to
remove any unreacted Mg metal. A solution containing
1,1-dichloro-2,5-bis(trimethylsilyl)-3,4-diphenyl-1-silacy-
clopentadiene (2) [15] (0.45 g, 1.0 mmol in 20 mL of diethyl
ether) was added dropwise to the Grignard solution which
had been cooled to ꢁ78 °C. The mixture was warmed to
ambient temperature after 2 h, then stirred overnight.
The resulting reaction mixture was washed with water
(2 ꢂ 50 mL) and the organic layer was dried over anhy-
drous MgSO4 for 30 min then filtered. The filtrate was con-
centrated and the residue was purified by flash column
chromatography using silica gel (dichloromethane:hexane,
ratio = 1:7). The solid product obtained was recrystallized
from a dichloromethane–diethyl ether–pentane mixture at
2 °C to obtain colorless crystals of 1,1-bis(4-methoxy-
phenyl)-2,5-bis(trimethylsilyl)-3,4-diphenyl-1-silacyclopent-
adiene (8) in 82% yield. M.p. 204.5–206 °C.
1H NMR (CDCl3): d 7.07–7.03 (m, 6H, ArH), 6.84–6.81
(m, 4 H, ArH), 3.79 (t, J = 6.8 Hz, 4 H, CH2), 1.71 (sextet,
4H, CH2), 1.00 (t, J = 7.4 Hz, 6H, CH3), ꢁ0.11 (s, 18H,
SiMe3). 13C{1H} NMR (CDCl3): d 170.6, 142.3, 135.2,
128.6, 127.2, 126.5, 64.9, 26.1, 10.7, 0.5. 29Si{1H} NMR
(DEPT, CDCl3): d ꢁ8.7 (SiOPr), ꢁ9.9 (SiMe3). EI-MS:
m/z (relative abundance, %) 494 (M+, 3), 393 (27), 235
(23), 219 (24), 163 (17), 159 (33), 135 (21), 133 (85), 75
(15), 73 (100). Anal. Calc. for C28H42O2Si3: C, 67.95; H,
8.55. Found: C, 68.14; H, 8.76%.
1H NMR (CDCl3): d 7.75 (m, 4H, ArH), 7.09–7.04 (m,
6H, PhH), 7.00 (m, 4H, ArH), 6.95–6.92 (m, 4H, PhH),
3.88 (s, 6 H, OCH3), ꢁ0.38 (s, 18H, SiMe3). 13C{1H}
NMR (CDCl3): d 171.4, 161.2, 144.2, 142.9, 137.4, 129.0,
127.2, 126.3, 123.7, 113.9, 55.2, 1.0. 29Si{1H} NMR
(CDCl3): d 8.14 (SiAr2), ꢁ9.0 (SiMe3). HR-MS (FAB,
NBA): calcd for C36H43O2Si3, 591.2572. Found: 591.2582.
EI-MS: m/z (relative abundance,%) 482 ([MꢁC7H8O]+,
23), 467 (7), 409 (4), 343 (28), 257 (17), 207 (64), 165
(48), 159 (15), 135 (33), 73 (100), 59 (26). Anal. Calc.
for C36H42O2Si3: C, 73.16; H, 7.16. Found: C, 73.19; H,
7.09%.
4.2.6. Bis(4-methoxyphenyl)bis(phenylethynyl)silane (11)
4-Methoxyphenylmagnesium bromide was prepared by
treatment of 4-bromoanisole (3.40 g, 18.2 mmol) with mag-
nesium (0.57 g, 24 mmol) in THF (30 mL) and filtered [22].
The filtrate was added to a silicon tetrachloride (1.39 g,
8.18 mmol) solution in hexane (35 mL). The mixture was
kept at ca. 40 °C during the addition and then heated at
reflux overnight. Most of the solvent was removed under
reduced pressure and the residue was washed with hexane
(3 ꢂ 20 mL), the resulting slurry was filtered through celite.
The filtrate was concentrated and subjected to a Kugelrohr
distillation (180 °C, 0.5 mmHg) to give bis(4-methoxy-
phenyl)dichlorosilane 10 (0.85 g, 2.7 mmol) in 33% yield
as a colorless oil [26].
4.2.5. 1,1-Dipropoxy-2,5-bis(trimethylsilyl)-3,4-diphenyl-1-
silacyclopentadiene (9)
In a separate flask, phenylacetylene (0.55 g, 5.4 mmol)
was diluted with diethyl ether (10 mL) and cooled to 0 °C
followed by dropwise addition of n-BuLi (2.5 M in hexane,
2.16 mL, 5.4 mmol) with vigorous stirring. After 1 h, the
brown mixture was cooled to ꢁ78 °C and the previously
prepared diaryldichlorosilane 10 (0.85 g, 2.7 mmol) was
dissolved in diethyl ether (10 mL) and added dropwise to
the chilled solution (ꢁ78 °C) containing the phen-
ylethynyllithium. The mixture was gradually warmed to
ambient temperature and stirred overnight. The solvent
was removed under vacuum and the mixture was dissolved
in dichloromethane (50 mL) and washed with water, then
brine (35 mL). The organic layer was dried over MgSO4,
filtered, and the solvent was removed under reduced pres-
sure. The crude product was purified by silica gel column
chromatography (dichloromethane:hexane, 1:4) to afford
bis(4-methoxyphenyl)bis(phenylethynyl)silane 11 in 76%
yield (0.91 g) as a white solid. M.p. 142–143 °C, which
was recrystallized from dichloromethane–diethyl ether–
4.2.5.1. Method A. A solution of n-BuLi (2.5 M in hex-
ane, 0.4 mL, 1.0 mmol) was added to 4-bromoanisole
(0.19 g, 1.0 mmol) in THF (10 mL) at ꢁ78 °C and stirred
for an additional 1.5 h [22]. In a separate flask, the dichlo-
rosilole 2 [15] (0.45 g, 1.0 mmol) was dissolved in THF
(20 mL) and added to the cooled solution containing 4-
methoxyphenyllithium and then allowed to warm to room
temperature. The THF was removed under vacuum and
the residue was dissolved in dichloromethane (40 mL)
and washed with water (2 ꢂ 30 mL). The organic layer
was dried over MgSO4 and filtered. After removal of the
solvent the crude product 9 was purified by flash column
chromatography using silica gel (dichloromethane:hexane,
1:7) to give a colorless oil (0.47 g) in 95% yield.
4.2.5.2. Method B. 4-Methoxyphenylmagnesium bromide
(1.0 mmol) was prepared in THF (10 mL) and reacted
with the dichlorosilole 2 [15] (0.45 g, 1.0 mmol) at
ꢁ78 °C. Compound 9 was obtained in 13% yield after the
same workup procedure as described in Method A.
1
pentane. H NMR (CDCl3): d 7.83–7.80 (m, 4H, ArH),
7.62–7.59 (m, 4H, PhH), 7.39–7.33 (m, 6H, PhH), 7.01–

1240
J. Braddock-Wilking et al. / Journal of Organometallic Chemistry 693 (2008) 1233–1242
6.99 (m, 4 H, ArH), 3.85 (s, 6H, OCH3). 13C{1H} NMR
(CDCl3): d 161.6, 136.7, 132.5, 129.3, 128.5, 124.4, 122.8,
114.1, 108.5, 88.6, 55.3. 29Si{1H} NMR (CDCl3): d
ꢁ48.4. EI-MS: m/z (relative abundance, %) 444 (M+, 22),
208 (25), 207 (100), 191 (17), 129 (33), 73 (30), 59 (47).
Anal. Calc. for C30H24O2Si: C, 81.04; H, 5.44. Found: C,
80.82; H, 5.47%.
refrigerator (ꢁ40 °C) for several days. Colorless crystals
of 1,1-dibromo-2,5-bis(trimethylsilyl)-3,4-diphenyl-1-sila-
cyclopentadiene (13) were obtained in 52% yield (0.14 g).
M.p. 137–138 °C. The crystals of 13 were suitable for
X-ray crystallographic analysis. 1H NMR (CDCl3): d
7.10–7.07 (m, 6 H, ArH), 6.87–6.83 (m, 4H, ArH), ꢁ0.01
(s, 18 H, SiMe3). 13C{1H} NMR (CDCl3): d 168.6, 140.1,
137.3, 128.5, 127.5, 127.3, 0.6. 29Si{1H} NMR (CDCl3) d:
4.9 (SiBr2), ꢁ7.6 (SiMe3). EI-MS: m/z (relative abundance,
%) 523 (M+ꢁ15, 2), 521 (M+ꢁ15, 3), 519 (M+ꢁ15, 1), 456
(15), 454 (12), 441 (12), 439 (10), 245 (13), 159 (100), 129
(27), 73 (50). Anal. Calc. for C22H28Br2Si3: C, 49.25; H,
5.26. Found: C, 49.15; H, 5.36%.
4.2.7. Attempted preparation of 1,1-bis(4-methoxyphenyl)-
2,5-bis(trimethylsilyl)-3,4-diphenylsilacylopentadiene:
isolation of bis(4-methoxyphenyl)dipropoxysilane (12)
Lithium naphthalenide was prepared by stirring a mix-
ture of lithium (28 mg, 4.0 mmol) and naphthalene
(0.53 g, 4.1 mmol) in THF (8 mL) at room temperature
for 6 h. A THF solution (10 mL) of 11 (0.44 g, 1.0 mmol)
was added dropwise to the solution of lithium naphthale-
nide at ꢁ78 °C. The mixture was stirred for 1.5 h then tri-
methylchlorosilane (0.56 mL, 4.4 mmol) was added. After
stirring at ꢁ78 °C for 10 min, the mixture was allowed to
gradually warm to room temperature and stirred over-
night. The volatiles were removed under vacuum then dry
hexane (3 ꢂ 20 mL) was added to dissolve the product
and the lithium salts were removed by filtration. After
evaporation of hexane, the residue was condensed and sub-
jected to Kugelrohr distillation (70 °C/0.1 mmHg) to
remove naphthalene and other low boiling point compo-
nents. The crude yellow product was subjected to flash col-
umn chromatography column using silica gel
(dichloromethane:hexane, 1:10) to give a colorless oil of
bis(4-methoxyphenyl)dipropoxysilane (12) in 42% yield
(0.15 g). 1H NMR (CDCl3): d 7.64–7.61 (m, 4H, ArH),
6.96–6.93 (m, 4H, ArH), 3.84 (s, 6H, OCH3), 3.76 (t, 4
H, J = 6.5 Hz, OCH2), 1.65 (m, 4H, OCH2CH2), 0.96 (t,
J = 7.5 Hz, CH2CH3). 13C{1H} NMR (CDCl3): d 161.4,
136.7, 113.9, 113.7, 64.9, 55.2, 25.9, 10.5. 29Si{1H} NMR
(CDCl3): d ꢁ31.3. EI-MS: m/z (relative abundance, %)
360 (M+, 28), 301 (42), 259 (35), 253 (16), 244 (17), 243
(64), 223 (18), 211 (18), 197 (40), 195 (17), 193 (18), 169
(76), 168 (18), 153 (31), 152 (17), 149 (40), 148 (100), 139
(17), 121 (24), 108 (51), 77 (17). HR-MS (FAB, NBA+
NaI): calcd for C20H28O4Si, 360.1757. Found:
M + Na = 383.1657.
4.2.9. 1-Bromo-4-bromodimethoxysilyl-1,4-
bis(trimethylsilyl)-3,4-diphenyl-1,3-butadiene (14)
To a diethyl ether (35 mL) solution containing 1,1-dime-
thoxy-2,5-bis(trimethylsilyl)-3,4-diphenyl-1-silacyclopentadi-
ene (7) (0.44 g, 1.0 mmol) was added a diethyl ether (5 mL)
solution of bromine (51.4 lL, 1.0 mmol) at ꢁ78 °C. The
resulting solution was kept at low temperature for
10 min. Then the mixture was stirred at ambient tempera-
ture for another 30 min. The ether was removed under vac-
uum and the residue was dissolved in dry pentane
(3 ꢂ 20 mL) and the solution was filtered. The product,
bromodimethoxy[4-bromo-2,3-diphenyl-1,4-bis(trimeth-
ylsilyl)butadienyl]silane (14) was isolated after cooling the
pentane solution to ꢁ40 °C as a white crystalline solid suit-
able for X-ray crystallographic analysis in 77% yield
(0.46 g). M.p. 105–109 °C. 1H NMR (CDCl3): d 7.15–
7.12 (m, 8H, ArH), 6.98–6.96 (m, 2H, ArH), 3.71 (s, 3H,
OMe), 3.65 (s, 3H, OMe), 0.48 (s, 9H, SiMe3), ꢁ0.073 (s,
9H, SiMe3). 13C{1H} NMR (CDCl3): d 169.8, 158.8,
142.8, 141.6, 138.2, 131.7, 130.0, 129.0, 128.3, 127.9,
127.6, 127.4, 52.8, 52.1, 2.3, 1.6. 29Si{1H} NMR (DEPT,
CDCl3): d ꢁ0.4 (SiMe3), ꢁ4.3 (SiMe3), ꢁ44.7 (Si(O-
Me)2Br). HR-MS (EI): calcd for C24H3479Br2O2Si3,
596.0304. Found, 596.0240. EI-MS: m/z (relative abun-
dance, %) 600 (M+, 11), 598 (M+, 19), 596 (M+, 9), 520
(18), 519 (45), 518 (21), 517 (37), 455 (27), 446 (21), 444
(19), 431 (31), 429 (28), 367 (19), 365 (100), 351 (19), 349
(17), 335 (23), 333 (18), 319 (30), 318 (15), 317 (34), 292
(27), 291 (19), 265 (15), 262 (15), 261 (55), 245 (30), 217
(18), 202 (40), 191 (75), 179 (24), 178 (15), 175 (16), 161
(19), 159 (70), 149 (19), 115 (21), 73 (95), 69 (17). Anal.
Calc. for C24H34Br2O2Si3: C, 48.16; H, 5.73. Found: C,
48.34; H, 5.78%.
4.2.8. 1,1-Dibromo-2,5-bis(trimethylsilyl)-3,4-diphenyl-1-
silacyclopentadiene (13)
A sample of 1,1-bis(diethylamino)-2,5-bis(trimethyl-
silyl)-3,4-diphenyl-1-silacyclopentadiene (1) [15] (0.26 g,
0.50 mmol) was dissolved in 20 mL of dry diethyl ether
and cooled to ꢁ78 °C. Bromine (51.4 lL, 1.0 mmol) was
diluted with 5 mL of dry diethyl ether and added to the
silole solution dropwise over 5 min. The resulting red solu-
tion was kept at low temperature for 10 min during which
time the color of the solution became yellow and a white
solid precipitated. The mixture was stirred at ambient tem-
perature for another 30 min. The ether was removed under
vacuum and the residue was dissolved in dry pentane
(3 ꢂ 15 mL) and filtered. The solution was stored in the
4.2.10. X-ray structure determination of 13 and 14
Crystals of appropriate dimension were obtained from
pentane at ꢁ40 °C. Crystals for data collection were
mounted on glass fibers in random orientations. Prelimin-
ary examination and data collection were performed using
a Bruker Kappa Apex II Charge Coupled Device (CCD)
Detector system single crystal X-Ray diffractometer
equipped with an Oxford Cryostream LT device. All data
were collected using graphite monochromated Mo Ka radi-

J. Braddock-Wilking et al. / Journal of Organometallic Chemistry 693 (2008) 1233–1242
1241
˚
ation (k = 0.71073 A) from a fine focus sealed tube X-ray
source. Preliminary unit cell constants were determined
with a set of 36 narrow frame scans. Typical data sets con-
sist of combinations of - and / scan frames with typical
scan width of 0.5° and counting time of 15–30 seconds/
frame at a crystal to detector distance of 4.0 cm. The col-
lected frames were integrated using an orientation matrix
determined from the narrow frame scans. APEX II and SAINT
software packages (Bruker Analytical X-Ray, Madison,
WI, 2006) were used for data collection and data integra-
tion. Analysis of the integrated data did not show any
decay. Final cell constants were determined by global
refinement of xyz centroids harvested from the complete
data set. Collected data were corrected for systematic
errors using SADABS [36] based on the Laue symmetry using
equivalent reflections.
References
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Acknowledgements
We are grateful to the National Science Foundation
(CHE-0316023) and the University of Missouri Research
Board for funding of this work. We are also grateful
for funding from the National Science Foundation for
the purchase of the ApexII diffractometer (MRI, CHE-
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