Synthesis and structural characterization of [(C5H4)SiMe2(N-t-Bu)]Ti[(o-C6H4)C(Ph){double bond, long}C(Ph)], generated via an alkyne-Ti benzyne coupling reaction

Article abstract of DOI:10.1016/j.jorganchem.2007.06.019

The thermolysis of [(C₅H₄)SiMe₂(N-t-Bu)]TiPh₂ in the presence of diphenylacetylene proceeds at 80 °C in cyclohexane solution with the sole formation of the titanacyclic complex [(C₅H₄)SiMe₂(N-t-Bu)]Ti[(o-C₆H₄)C(Ph){double bond, long}C(Ph)], which has been characterized by solution NMR measurements and X-ray crystallographic analysis. This reaction is accompanied by the elimination of benzene and presumably occurs via coupling of a titanium benzyne intermediate with diphenylacetylene. The two chemically inequivalent Ti-C bonds of 2.081(7) and 2.103(6) A? in [(C₅H₄)SiMe₂(N-t-Bu)]Ti[(o-C₆H₄)C(Ph){double bond, long}C(Ph)] reflect the increased electrophilicity of the d⁰ Ti(IV) center arising from the presence of the bifunctional ansa-cyclopentadienyldimethylsilylamido ligand.

Full text of DOI:10.1016/j.jorganchem.2007.06.019

Journal of Organometallic Chemistry 692 (2007) 4654–4660
www.elsevier.com/locate/jorganchem
Synthesis and structural characterization of
[(C5H4)SiMe2(N-t-Bu)]Ti[(o-C6H4)C(Ph)@C(Ph)], generated via
an alkyne-Ti benzyne coupling reaction
*
Shawn M. Nettles, Jeffrey L. Petersen
C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, WV 26505-6045, United States
Received 30 March 2007; received in revised form 9 June 2007; accepted 9 June 2007
Available online 23 June 2007
Dedicated to Professor Gerhard Erker on the occasion of his 60th birthday.
Abstract
The thermolysis of [(C5H4)SiMe2(N-t-Bu)]TiPh2 in the presence of diphenylacetylene proceeds at 80 ꢀC in cyclohexane solution with
the sole formation of the titanacyclic complex [(C5H4)SiMe2(N-t-Bu)]Ti[(o-C6H4)C(Ph)@C(Ph)], which has been characterized by solution
NMR measurements and X-ray crystallographic analysis. This reaction is accompanied by the elimination of benzene and presumably
occurs via coupling of a titanium benzyne intermediate with diphenylacetylene. The two chemically inequivalent Ti–C bonds of
0
˚
2.081(7) and 2.103(6) A in [(C5H4)SiMe2(N-t-Bu)]Ti[(o-C6H4)C(Ph)@C(Ph)] reflect the increased electrophilicity of the d Ti(IV) center
arising from the presence of the bifunctional ansa-cyclopentadienyldimethylsilylamido ligand.
ꢁ 2007 Elsevier B.V. All rights reserved.
Keywords: Ti-benzyne intermediate; Coupling reaction; Titanacyclic complex
1. Introduction
Δ
Transition metals have the ability to stabilize highly
reactive organic fragments, such as benzyne [1]. The heat-
ing of a reaction mixture of diphenyltitanocene and diphe-
nylacetylene leads to the elimination of benzene and
concomitant formation of a titanacyclic species (Eq. (1))
[2]. Vol’pin and his co-workers [3] subsequently observed
that the thermolysis of diphenyltitanocene in the presence
of CO2 produced a five-membered oxatitanacyclic complex
(Eq. (2)). Both of these reactions presumably involve the
participation of a titanium-benzyne intermediate.
ð1Þ
ð2Þ
Cp2TiPh2
+
+
PhC CPh
Cp2Ti
- C6H6
Ph
Ph
Δ
Cp2TiPh2
Cp2Ti
CO2
- C6H6
O
O
In the late 1970s, Erker [4] investigated the thermal stabil-
ity of diphenyl- and ditolyl-zirconocene complexes and dem-
onstrated the intermediacy of a benzyne complex. His classic
study involved the thermolysis of various diarylzirconocenes
in aromatic hydrocarbon solvents and then analyzing the
biphenyls produced upon photodegradation. Thermolysis
*
Corresponding author.
E-mail address: jpeterse@wvu.edu (J.L. Petersen).
0022-328X/$ - see front matter ꢁ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.06.019

S.M. Nettles, J.L. Petersen / Journal of Organometallic Chemistry 692 (2007) 4654–4660
4655
of di-p-tolylzirconocene and di-m-tolylzirconocene in ben-
zene produced mixed tolyl-phenyl Zr complexes with the
eventual observation of diphenylzirconocene. Alternatively,
thermolysis of diphenylzirconocene in toluene occurs with
replacement of the phenyl ligands by tolyl groups and the
concerted elimination of benzene. Erker proposed the inter-
mediacy of a Zr-aryne species, which is formed by the
abstraction of an ortho proton from a r-bonded aryl ligand
by the other aryl ligand. Subsequent reactivity studies
revealed that this Zr-aryne intermediate is capable of reduc-
tive coupling with olefins to form zirconaindan derivatives
(Eq. (3)) [5] and reacting with W(CO)6 to afford a Fischer-
type zirconaoxycarbene complex (Eq. (4)) [6]
bifunctional chelating ligand [(C5Me4)SiMe2(N-t-Bu)]2ꢀ
provides an effective means to enhance the Lewis acidity
of an electrophilic metal center. The weaker p-donating
character and lower steric requirement of the amido func-
tionality increases the metal’s Lewis acidity by the simulta-
neous reduction of the formal electron count and the steric
congestion at the metal center. The incorporation of bifunc-
tional monocyclopentadienylamido ligands on group 4 met-
als may be accomplished by conventional metathesis routes
[10,11] or by the thermally-induced amine elimination reac-
tion of M(NMe2)4 with (C5R4H)L(NHR0), where L is either
a silyl or hydrocarbon linkage [12]. The conversion
of [(C5R4)SiMe2(NR0)]M(NMe2)2 to the corresponding
dichloride derivatives may in some cases be accomplished
by treatment with excess SiMe3Cl [12d,12e].
In this paper, we wish to report the synthesis and
structural characterization of [(C5H4)SiMe2(N-t-Bu)]Ti[(o-
C6H4)C(Ph)@C(Ph)], which was prepared by the thermoly-
sis of [(C5H4)SiMe2(N-t-Bu)]TiPh2 in the presence of
diphenylacetylene. The formation of this titancyclic com-
plex presumably occurs via the coupling of the alkyne with
a titanium-benzyne intermediate, reminiscent of the related
zirconocene benzyne chemistry initially examined by Ger-
hard Erker and co-workers 30 years ago.
Δ
ð3Þ
R
Cp2ZrPh2
+
Cp2Zr
- C6H6
R
Δ
ð4Þ
Cp2ZrPh2
+
Cp2Zr
W(CO)6
- C6H6
O
W(CO)5
Buchwald and his co-workers [7] extended Erker’s semi-
nal contribution by coupling an assortment of nitriles with
the Zr-benzyne generated from diphenylzirconocene. More
significantly, they successfully isolated the trimethylphos-
phine adduct of the zirconocene-benzyne intermediate and
determined its molecular structure [8]. The structural data
revealed that the g2-benzyne moiety experiences little strain,
with the ‘‘triple bond’’ length and angles at the two
Zr-bound carbon atoms varying only slightly from those in
benzene. In contrast to the in situ generated Zr-benzyne
intermediate, its PMe3 adduct reacts cleanly with ketones
and nitriles to produce oxazirconacyclopentenes (Eq. (5a))
and azazirconacyclopentadienes (Eq. (5b)) [7,9], respectively
2. Experimental
2.1. General considerations
Reagent grade hydrocarbon and etheral solvents were
purified using standard methods [13] and distilled under
nitrogen. These solvents were then transferred to storage
flasks containing either [(C5H5)2Ti(l-Cl)2]2Zn [14] or
potassium benzophenone ketyl. Hexamethyldisiloxane
was dried over (C5H5)2ZrMe2. The deuterated solvents,
C6D6 (Cambridge Isotopes, 99.5%) and CDCl3 (Aldrich,
99.8%), were dried over activated 4A molecular sieves prior
to use, as was NH2-t-Bu (Acros).
Starting materials such as Ti(NMe2)4, (C5H5)Si-
Me2(N(H)-t-Bu), and [(C5H4)SiMe2(N-t-Bu)]TiCl2 were
prepared by literature procedures [12d]. Other starting
materials such as TiCl4 (Aldrich), LiNMe2 (Aldrich 95%),
Na (Aldrich), dicyclopentadiene (Kodak), and phen-
ylmagnesiumbromide (Aldrich) were used without further
purification, whereas diphenylacetylene (Kodak) was puri-
fied by sublimation. SiMe2Cl2 (Acros) and SiMe3Cl
(Acros) were vacuum distilled prior to use.
O
R
R
5a
5b
Cp2Zr
R
O
R
Cp2Zr
N
CR
PMe3
The 1H and 13C NMR spectra were measured with either
a JEOL GX-270 or a JEOL Eclipse 270 NMR spectrometer
operating in the FT mode at 270 MHz (1H) or 67.5 MHz
(13C). The 1H chemical shifts are referenced to the residual
proton peaks of benzene-d6 at d 7.15 (vs. TMS) or chloro-
form-d1 at d 7.24 (vs. TMS). The 13C resonances are refer-
enced to the central peak of benzene-d6 at d 128.0
(vs. TMS) or chloroform-d1 at d 77.0 (vs. TMS).
Cp2Zr
N
R
Although the reactivity of group 4 metallocene benzynes
has been extensively examined, far less is known about the
influence of the electrophilicity of the metal center on the
stability and reactivity of the metal-stabilized benzyne. Ber-
caw and co-workers [10] demonstrated that the replacement
of a pair of cyclopentadienyl rings with the dianionic
To minimize exposure to air and moisture, all manipula-
tions and reactions were carried out on a high-vacuum line

4656
S.M. Nettles, J.L. Petersen / Journal of Organometallic Chemistry 692 (2007) 4654–4660
or in a Vacuum Atmosphere glovebox equipped with a HE-
493 Dri-Train. Reactions were typically carried out in
pressure equalizing filter-frits equipped with high vacuum
Teflon stopcocks. All glassware was oven-dried or flame-
dried under vacuum prior to use. NMR sample tubes were
sealed normally under 400–500 Torr of nitrogen pressure.
Nitrogen was purified by passage over reduced BTS
catalysts and activated 4A molecular sieves. Elemental
analyses were performed by E&R Microanalytical Labs,
Parsippany, NJ 07054.
6.38; N, 2.72%. 1H NMR (CDCl3): d 7.18, 7.13, 7.05,
6.83, 6.75, 6.70 (10 H, C6H5), 7.00, 6.96, 6.83, 6.50 (4H,
o-C6H4), 7.47, 7.03, 6.20, 5.55 (4H, C5H4), 1.58 (9H,
NCMe3), 0.59, 0.49 (6H, SiMe2). 13C{1H} NMR (CDCl3):
d 206.1, 193.7 (Ti–C), 147.9, 145.8 (Ti–C@C), 144.4, 138.9
(ipso-C(Ph)), 131.05, 129.8, 127.8, 126.2, 125.7, 123.7
(C6H5), 128.2, 127.4, 126.5, 124.7 (o-C6H4), 126.4, 126.0,
122.05, 121.8 (C5H4), 107.9 (bridgehead C), 60.1 (NCMe3),
34.0 (NCMe3), 1.01, 0.75 (SiMe2). 2D HETCOR (CDCl3):
d 131.05/6.70, 129.8/7.05, 127.8/7.18, 126.2/7.13, 125.7/
6.75, 123.7/6.83 (C6H5), 128.2/6.96, 127.4/7.00, 126.5/6.50,
124.7/6.83 (o-C6H4), 126.4/6.20, 126.0/5.55, 122.05/7.47,
121.8/7.03 (C5H4), 34.0/1.58 (NCMe3), 1.01/0.59, 0.75/
0.49 (SiMe3).
2.2. Synthesis of [(C5H4)SiMe2(N-t-Bu)]TiPh2
A 1.50-g sample (4.8 mmol) of [(C5H4)SiMe2(N-t-
Bu)]TiCl2 was placed in a two-neck 100-mL pear-shaped
flask equipped with Solv-seal joints. One neck was capped
with a Suba-seal septum and the other was attached to a
filter frit assembly. Diethyl ether (ca. 30 mL) was added
by vacuum distillation. The reaction mixture was then
cooled in a liquid N2/2-propanol bath. While stirring the
reaction mixture under a N2 flush, 3.20-mL of a 3.0 M
solution of PhMgBr in Et2O was added dropwise via syr-
inge over a 45 min period. The solution was slowly warmed
to room temperature and stirred overnight. The solvent
was transferred under reduced pressure into a liquid N2
cooled trap and the product was washed initially with cold
pentane to remove soluble impurities and then extracted
with pentane to give 1.08 g of a reddish orange crude prod-
uct, which upon recrystallization gave 0.98 g (51.4% yield)
of [(C5H4)SiMe2(N-t-Bu)]TiPh2 as a yellow semi-crystalline
solid. Anal. Calc. for C23H29SiNTi (395.45): C, 69.85; H,
7.39; N, 3.54. Found: C, 69.71; H, 7.21; N, 3.63%. 1H
2.4. X-ray structural analysis of [(C5H4)SiMe2
(N-t-Bu)]Ti(o-C6H4)C(Ph)@C(Ph)]
A crystal of [(C5H4)SiMe2(N-t-Bu)]Ti[(o-C6H4)C(Ph)@
C(Ph)] was sealed in a glass capillary tube under a N2
atmosphere and then optically aligned on the goniostat
of a Siemens P4 X-ray diffractometer. The reflections that
were used for the unit cell determination were located
and indexed by the automatic peak search routine provided
with XSCANS [15]. A body-centered monoclinic cell was used
for data collection and then converted to the conventional
C-centered monoclinic cell prior to performing the struc-
tural analysis. The lattice parameters and other pertinent
crystallographic information are summarized in Table 1.
Intensity data were measured with graphite-monochro-
˚
matic Mo Ka radiation (k = 0.71073 A) and variable x
scans (2–10ꢀ/min). Background counts were measured at
the beginning and at the end of each scan with the crystal
and counter kept stationary. The intensities of three stan-
dard reflections showed no indication of crystal decompo-
sition or sample movement. The raw data were corrected
for Lorentz-polarization effects.
3
NMR (C6D6, JHH in Hz): d 8.14, 7.12, 7.09 (C6H5, m),
6.56, 5.27 (C5H4, t, 2.1), 0.90 (NCMe3, s), 0.61 (SiMe2,
1
s). Gated nondecoupled 13C NMR (C6D6, JCH in Hz): d
188.4 (ipso-carbon of C6H5, s), 133.7, 128.7, 126.7 (C6H5,
d, 169), 118.5, 118.0 (proximal and distal carbons of
C5H4, d, 169), 110.5 (bridgehead carbon, s), 60.5 (NCMe3,
s), 33.8 (NCMe3, q, 124), 1.51 (SiMe2, q, 118).
Initial coordinates for the non-hydrogen atoms were
determined by a combination of direct methods and differ-
ence Fourier calculations. The hydrogen atom positions
were idealized with isotropic temperature factors set at
1.2 times that of the adjacent carbon. The positions of
the methyl hydrogens were optimized by a rigid rotating
group refinement with idealized tetrahedral angles. Full-
matrix least-squares refinement with SHELXL-93 [16], based
2.3. Preparation of [(C5H4)SiMe2(N-t-Bu)]
Ti[(o-C6H4)C(Ph)@C(Ph)]
A 0.492-g sample (1.24 mmol) of [(C5H4)SiMe2(N-t-Bu)]-
TiPh2 was combined with 0.222 g (1.24 mmol) of diphenyl-
acetylene in a 100 mL pear-shaped flask, which was
attached via a Solv-seal joint to a filter-frit assembly.
Cyclohexane (ca. 20 mL) was added via vacuum transfer
and the reaction mixture was stirred at 80 ꢀC overnight.
The solvent was removed under reduced pressure and the
red product residue was washed with hexamethyldisiloxane
and then dried under vacuo to afford 0.330 g (53.5% yield).
Recrystallization by slow removal of pentane from a con-
centrated solution yielded reddish-orange crystals of
[(C5H4)SiMe2(N-t-Bu)]Ti[(o-C6H4)C(Ph)@C(Ph)] suitable
for crystallographic analysis. Anal. Calc. for C31H33NSiTi
(495.58): C, 75.12; H, 6.71; N, 2.82. Found: C, 75.69; H,
P
2
upon the minimization of
wijF 2o ꢀ F 2cj with weighting
2
given by the expression wꢀi 1 ¼ ½r2ðF 2oÞ þ ð0:0586PÞ ꢁ where
P ¼ ðMaxðF 2o; 0Þ þ 2F 2cÞ=3, converged to give the values of
the final discrepancy indices [17] provided in Table 1.
3. Results and discussion
The stoichiometric reaction of [(C5H4)SiMe2(N-t-
Bu)]TiCl2 with two equivalents of PhMgBr was carried
out in ether at ꢀ40 ꢀC, affording [(C5H4)SiMe2(N-t-
Bu)]TiPh2 as a semi-crystalline yellow solid. Its identity
1
was verified by solution H and 13C NMR measurements,

S.M. Nettles, J.L. Petersen / Journal of Organometallic Chemistry 692 (2007) 4654–4660
4657
Table 1
inequivalent protons on the two independent phenyl sub-
stituents of the titanacyclopentadiene ring. The four proton
resonances of the o-C6H4 moiety are centered at d 7.00,
6.96, 6.83, and 6.50, with the four chemically inequivalent
protons of the cyclopentadienyl group appearing as pseudo
triplets at d 7.47, 7.03, 6.20, and 5.55. The singlet at d 1.58
represents the nine methyl protons of the t-butyl group and
the two singlets at d 0.59 and d 0.49 correspond to the two
inequivalent methyl groups of the SiMe2 bridge.
X-ray data for [(C5H4)SiMe2(N-t-Bu)]Ti[(o-C6H4)C(Ph)@C(Ph)]
A. Crystal data
Empirical formula
Color
Crystal dimensions (mm)
Crystal system
Space group
C31H33NSiTi
Red orange
0.15 · 0.34 · 0.36
Monoclinic
C2/c
30.993(3)
11.418(2)
16.616(2)
109.55(1)
5541.1(11)
8
˚
a (A)
˚
b (A)
˚
c (A)
1
The H NMR resonances for the cyclopentadienyl and
b (ꢀ)
Volume (A )
Z
3
˚
o-C6H4 fragments were further distinguished by an exami-
nation of the 2D COSY NMR spectrum. The proton reso-
nance at d 6.50 has three off-diagonal peaks at d 6.83, 6.96,
and 7.00 due to coupling with three nearby protons. The
remaining three proton resonances of the o-C6H4 function-
ality exhibit three off-diagonal peaks consistent with their
assignment to the o-C6H4 unit. In the case of the cyclopen-
tadienyl group, the distal and proximal protons are diaste-
reotopic and each exhibit the expected set of three off-
diagonal peaks.
Formula weight (amu)
Calculated density (g/cm3)
l (cmꢀ1
F(000)
495.57
1.188
3.71
2096
)
Temperature (ꢀC)
22
B. Data collection and structural analyses
Scan type
Scan rate (ꢀ/min
x, variable
2.0–10.0
3.0–40.0
2h Range (ꢀ)
The corresponding 13C{1H} NMR spectrum exhibits 25
carbon resonances. Due to a significant number of overlap-
ping resonances, a 2D HETCOR NMR spectrum was
recorded to assist with the assignment of the carbon reso-
nances for the carbons bearing one or more hydrogen
atoms. The two methyl carbons of the SiMe2 bridge appear
at d 0.75 and d 1.01. The three methyl carbons and the qua-
ternary carbon of the amido functionality appear at d 34.0
and d 60.1, respectively. The cyclopentadienyl group exhib-
its five resonances with the signal at d 107.9 representing
the bridgehead carbon and the four resonances at d
121.8, 122.05, 126.0, and 126.4 corresponding to the four
remaining carbon atoms of the cyclopentadienyl ring.
There are six carbon resonances for the o-C6H4 moiety,
with the signals at d 124.7, 126.5, 127.4, and 128.2 corre-
sponding to the four carbons bearing hydrogens and the
two peaks at d 145.8 and d 193.7 representing the two qua-
ternary carbons within the titanacyclopentadiene ring. The
two phenyl substituents exhibit the expected eight carbon
resonances, with the signals at d 123.7, 125.7, 126.2,
127.8, 129.8, and 131.05 representing the ortho-, meta-,
2h Range, centered reflections
Reflections sampled
10–25
h (ꢀ18 6 h 6 33),
k (ꢀ12 6 k 6 1),
l (ꢀ17 6 l 6 17)
4287
3558 (Rint = 0.0473)
1769
R1 = 0.0636, wR2 = 0.1206
R1 = 0.1627, wR2 = 0.1896
1.020
Number of reflections collected
Number of unique data
Number of data, I > 2r(I)
R indices, I > 2r(I)
R indices, all data
r1, GOF
Number of variables
Maximum difference in peak and hole
312
0.208, ꢀ0.221
which indicated the presence of mirror symmetry in solu-
tion. The thermally-induced reaction of diphenylacetylene
with [(C5H4)SiMe2(N-t-Bu)]TiPh2 proceeds in cyclohexane
with the sole formation of [(C5H4)SiMe2(N-t-Bu)]Ti[(o-
C6H4)C(Ph)@C(Ph)]. This coupling reaction occurs with
the intramolecular elimination of benzene to produce a
benzyne intermediate. Following metal complexation of
diphenylacetylene, intramolecular C–C bond formation
affords the titanacyclopentadiene product (Eq. (6)).
Ph
- C6H6
80 C
PhC
CPh
Ph
Ph
Ph
Ti
Ti
Ti
Me2Si
Me2Si
Me2Si
ð6Þ
N
N
N
The identity of [(C5H4)SiMe2(N-t-Bu)]Ti[(o-C6H4)C-
and para-carbons and the two resonances at d 138.9 and
d 144.4 assigned to the two ipso-quaternary carbons. The
two resonances at d 147.9 and d 206.1 correspond to
the two remaining carbons of the titanacyclopentadiene
ring.
1
(Ph)@C(Ph)] was initially established by solution H and
13C NMR measurements, including 2D HETCOR and
COSY experiments. The 1H NMR spectrum contains
peaks at d 7.18, 7.13, 7.05, 6.83, 6.75, and 6.70 for the six

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S.M. Nettles, J.L. Petersen / Journal of Organometallic Chemistry 692 (2007) 4654–4660
Table 2
3.1. Molecular structure of [(C5H4)SiMe2(N-t-Bu)]Ti
[(o-C6H4)C(Ph)@C(Ph)]
˚
Interatomic distances (A) and bond angles (ꢀ) for [(C5H4)SiMe2-
(N-t-Bu)]Ti[(o-C6H4)C(Ph)@C(Ph)]a
A. Interatomic distances
Ti–N
Ti–C(12)
Ti–C(1)
Ti–C(3)
Ti–C(5)
The molecular structure of [(C5H4)SiMe2(N-t-Bu)]Ti-
[(o-C6H4)C(Ph)@C(Ph)] was confirmed by an X-ray crys-
tallographic analysis. A perspective view of its molecular
structure is shown in Fig. 1 with the atom numbering
scheme. Pertinent bond distances and angles are provided
in Table 2. The molecular structure is well-behaved with
no evidence of a structural disorder or excessive thermal
motion.
1.915(5)
2.081(7)
2.299(6)
2.379(7)
2.332(7)
1.744(5)
1.850(8)
1.416(9)
1.383(10)
1.411(9)
1.530(9)
1.404(8)
1.355(8)
1.381(8)
1.469(8)
1.363(8)
Ti–Cp(c)
Ti–C(15)
Ti–C(2)
Ti–C(4)
N–C(8)
Si–C(1)
Si–C(7)
C(2)–C(3)
C(4)–C(5)
C(8)–C(9)
C(8)–C(11)
C(13)–C(14)
C(12)–C(16)
C(14)–C(20)
C(16)–C(17)
C(18)–C(19)
2.025
2.103(6)
2.332(2)
2.410(7)
1.489(7)
1.855(8)
1.845(7)
1.380(9)
1.391(9)
1.516(8)
1.548(8)
1.511(8)
1.390(8)
1.511(8)
1.381(8)
1.386(9)
Si–N
Si–C(6)
C(1)–C(2)
C(3)–C(4)
C(5)–C(1)
C(8)–C(10)
C(12)–C(13)
C(14)–C(15)
C(13)–C(19)
C(15)–C(26)
C(17)–C(18)
The most prominent feature in this structure is the
titanacyclopentadiene ring constructed from the direct
C–C coupling of a Ti-coordinated benzyne fragment with
diphenylacetylene. This titanacyclic ring is essentially pla-
nar with the mean deviation for the Ti and four carbon
˚
atoms being 0.035 A. The three independent C–C distances
˚
of 1.404(8), 1.511(8) and 1.355(8) A are consistent with
B. Bond angles
Cp(c)–Ti–N
alternating localized C@C double bonds around the ring
with the longer C@C bond being associated with the
o-C6H4 fragment. The titanacyclopentadiene and o-C6H4
rings are essentially coplanar, with the acute dihedral angle
between their respective planes being only 3.5ꢀ. To mini-
mize interring repulsions, the two phenyl substituents con-
taining carbon atoms C(20)–C(25) and C(26)–C(31) are
rotated by 76.8ꢀ and 41.3ꢀ, respectively, out of the plane
of the titanacyclopentadiene ring.
108.4
Cp(c)–Ti–C(12)
N–Ti–C(12)
C(12)–Ti–C(15)
C(15)–Ti–Si
N–Si–C(7)
C(1)–Si–C(6)
C(6)–Si–C(7)
C(8)–N–Si
C(2)–C(1)–C(5)
C(5)–C(1)–Si
C(2)–C(3)–C(4)
C(4)–C(5)–C(1)
C(16)–C(12)–Ti
C(12)–C(13)–C(14)
C(14)–C(13)–C(19)
C(13)–C(14)–C(20)
C(14)–C(15)–C(26)
C(26)–C(15)–Ti
115.3
110.8(2)
85.1(3)
Cp(c)–Ti–C(15)
N–Ti–C(15)
C(12)–Ti–Si
118.2
117.5(2)
129.8(2)
93.4(3)
137.8(2)
116.0(3)
110.1(4)
111.0(4)
126.4(4)
104.2(6)
121.5(6)
109.2(8)
110.7(8)
133.2(5)
118.1(6)
121.7(6)
116.2(5)
124.9(6)
125.9(5)
N–Si–C(1)
N–Si–C(6)
C(1)–N–C(7)
Si–N–Ti
113.4(3)
111.8(4)
103.4(2)
129.7(4)
121.8(6)
109.4(7)
106.5(8)
108.4(5)
118.2(6)
120.3(6)
119.0(6)
124.9(6)
109.0(5)
C(8)–N–Ti
C(2)–C(1)–Si
C(1)–C(2)–C(3)
C(3)–C(4)–C(5)
C(13)–C(12)–Ti
C(13)–C(12)–C(16)
C(12)–C(13)–C(19)
C(13)–C(14)–C(15)
C(15)–C(14)–C(20)
C(14)–C(15)–Ti
a
The asymmetric pseudo-tetrahedral Ti coordination
sphere consists of the p-bonded cyclopentadienyl ring and
its appended amido functionality and two chemically
˚
inequivalent Ti–C bonds of 2.081(7) and 2.103(6) A. These
two distances are considerably shorter than the two inde-
˚
pendent Ti–C bonds of 2.172(5) and 2.141(5) A reported
by Atwood and co-workers [18] for the related planar
titanacyclopentadiene ring of (C5H5)2Ti(C4Ph4), which
was prepared by the photolysis of (C5H5)2TiMe2 in the
Cp(c) corresponds to the centroid of the five-membered cyclopenta-
dienyl ring.
Fig. 1. The molecular structure of [(C5H4)SiMe2(N-t-Bu)]Ti[(o-C6H4)C(Ph)@C(Ph)] with the atom labeling scheme. The thermal ellipsoids are scaled to
enclose 30% probability.

S.M. Nettles, J.L. Petersen / Journal of Organometallic Chemistry 692 (2007) 4654–4660
4659
presence of diphenylacetylene. Comparable Ti–C distances
ranging from 2.14 to 2.18 A have been reported for several
fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.
ac.uk. Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/
j.jorganchem.2007.06.019.
˚
titanacyclopentadiene complexes, including (C5H5)2Ti-
[C(SiMe3)C(Ph)C(Ph)C(SiMe3)], [SiMe2(C5H4)2]Ti(C4Ph4),
and (C5H5)Ti(N@P(t-Bu)3](C4Ph4) [19]. The substantial
decrease observed for the two Ti–C bond distances in
[(C5H4)SiMe2(N-t-Bu)]Ti[(o-C6H4)C(Ph)@C(Ph)] reflects
the increased electrophilicity of the electron deficient d0
Ti(IV) center arising from the presence of the bifunctio-
nal ansa-cyclopentadienyldimethysilylamido ligand. The
C(12)–Ti–C(15) bond angle of 85.1(3)ꢀ within the titanacy-
clopentadiene ring of [(C5H4)SiMe2(N-t-Bu)]Ti[(o-C6H4)-
C(Ph)@C(Ph)] is ca. 5ꢀ larger than the corresponding
C–Ti–C angle in (C5H5)2Ti(C4Ph4). This increase is accom-
panied by a ca. 3ꢀ decrease in the Ti–Ca–Cb bond angles.
The presence of the SiMe2 linkage between the cyclopen-
tadienyl and amido functionalities of [(C5H4)SiMe2(N-
t-Bu)]Ti[(o-C6H4)C(Ph)@C(Ph)] produces a Cp(c)–Ti–N
angle of 108.4ꢀ, which is only modestly larger than its cor-
responding value of 107.0ꢀ in [(C5H4)SiMe2(N-t-Bu)]TiCl2
[12d]. The similarity of the respective Ti–N(amido)
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[16] SHELXL-93 is a FORTRAN-77 program (Professor G. Sheldrick, Institute
CCDC 642293 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retriev-
ing.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fur Anorganische Chemie, University of Go¨ttingen, D-37077, Go¨t-
¨
tingen, Germany) for single crystal X-ray structural analyses.

4660
S.M. Nettles, J.L. Petersen / Journal of Organometallic Chemistry 692 (2007) 4654–4660
[17] The discrepancy indices were calculated from the expressions R1 ¼
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P
P
P
P
2
2 1=2
kF oj ꢀ jF ck= jF oj and wR2 ¼ ½ ½wiðF 2o ꢀ F c2Þ Þꢁ=½ ½wiF o2ꢁ ꢁ
and the standard deviation of an observation of unit weight (GOF) is
P
2
equal to ½ ðwiðF 2o ꢀ F c2Þ Þ=ðn ꢀ pÞꢁ1=2, where n is the number of
reflections and p is the number of parameters varied during the last
refinement cycle.
(c) T.W. Graham, J. Kickham, S. Courtenay, P. Wei, D.W. Stephan,
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