Synthesis, characterization, and alkyne cyclotrimerization chemistry of titanium complexes supported by calixarene-derived bis(aryloxide) ligation

Article abstract of DOI:10.1016/j.jorganchem.2003.10.039

Proximally bridged calix[4]arene compounds (DESC)H₂ (3), (DMSHC)H₂ (4), (DMSMC)H₂ (5), and (DPSC)H₂ (6), in which one R₂Si group (R=alkyl or aryl) bridges adjacent oxygens, were synthesized via reaction between dialkyl- or diaryldichlorosilane and the corresponding calix[4]arene. Treatment of p- tert -butylcalix[4]arene with Ph₂SiCl₂ at room temperature or (o-MeC₆ H₄)₂SiCl₂ at 80 °C gave (ClPh₂SiCl)₂Calix-H₂ (7) and (o-Tol₂SiCl)₂Calix-H₂ (8), respectively. Titanium dichloride complexes 9-12 (L₂ TiCl₂, where L₂=DESC, DMSHC, DMSMC, or DPSC) were prepared in high yield from reaction of 3-6 with TiCl₄. The molecular structures of 7 and 12 were established by single-crystal X-ray diffraction studies. Reduction of 9, 11, and 12 with activated magnesium (Mg*) in the presence of an excess of Me₃SiC≡CH produced titananorbornadiene complexes L₂Ti{η⁶-1,2,4-C₆H₃ (SiMe₃)₃} (13-15, L₂=DESC, DMSMC, or DPSC), which were characterized in solution. Catalytic cyclotrimerization of both terminal and internal alkynes was achieved using catalyst systems derived from L₂TiCl₂ complexes 9-12 and Mg*. For unsymmetrically substituted internal alkynes, preference for 1,2,4-substitution decreased as the size difference of the substituent groups decreased. The cyclotrimerization of PhC≡CMe was more facile when the calixarene-derived bis(aryloxide) ligand was DPSC versus DMSMC, suggesting that the DPSC ligand may provide a less crowded titanium center and exert greater kinetic control over the course of the cyclotrimerization.

Full text of DOI:10.1016/j.jorganchem.2003.10.039

Journal of Organometallic Chemistry 689 (2004) 502–514
www.elsevier.com/locate/jorganchem
Synthesis, characterization, and alkyne cyclotrimerization chemistry
of titanium complexes supported by calixarene-derived
bis(aryloxide) ligation q
a,
a
Folami T. Ladipo *, Vallipuram Sarveswaran a,1, Jesudoss V. Kingston ,
Rebecca A. Huyck a,2, Sergei Y. Bylikin a,3, Shana D. Carr , Randy Watts , Sean Parkin
a
a
a
a
Department of Chemistry, University of Kentucky, Lexington, KY 40506-0055, USA
Received 18 July 2003; accepted 31 October 2003
Abstract
Proximally bridged calix[4]arene compounds (DESC)H2 (3), (DMSHC)H2 (4), (DMSMC)H2 (5), and (DPSC)H2 (6), in which
one R2Si group (R ¼ alkyl or aryl) bridges adjacent oxygens, were synthesized via reaction between dialkyl- or diaryldichlorosilane
and the corresponding calix[4]arene. Treatment of p-tert-butylcalix[4]arene with Ph2SiCl2 at room temperature or (o-
MeC6H4)2SiCl2 at 80 °C gave (ClPh2SiCl)2Calix-H2 (7) and (o-Tol2SiCl)2Calix-H2 (8), respectively. Titanium dichloride complexes
9–12 (L2TiCl2, where L2 ¼ DESC, DMSHC, DMSMC, or DPSC) were prepared in high yield from reaction of 3–6 with TiCl4. The
molecular structures of 7 and 12 were established by single-crystal X-ray diffraction studies. Reduction of 9, 11, and 12 with ac-
tivated magnesium (Mg*) in the presence of an excess of Me3SiCBCH produced titananorbornadiene complexes L2Ti{g6-1,2,4-
C6H3(SiMe3)3} (13–15, L2 ¼ DESC, DMSMC, or DPSC), which were characterized in solution. Catalytic cyclotrimerization of both
terminal and internal alkynes was achieved using catalyst systems derived from L2TiCl2 complexes 9–12 and Mg*. For unsym-
metrically substituted internal alkynes, preference for 1,2,4-substitution decreased as the size difference of the substituent groups
decreased. The cyclotrimerization of PhCBCMe was more facile when the calixarene-derived bis(aryloxide) ligand was DPSC versus
DMSMC, suggesting that the DPSC ligand may provide a less crowded titanium center and exert greater kinetic control over the
course of the cyclotrimerization.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Calixarene compounds; Alkyne cyclotrimerization; Titanium(IV); Reduced titanium
1. Introduction
4 metal complexes containing non-cyclopentadienyl
ligand arrays, such as aryloxides [2], chelating diamides
[3], porphyrins [4], amine-bis(phenolate)s [5], bis(sali-
cylaldiminate)s [6], carboranes [7], amidinates [8], bo-
ratabenzenes [9], Schiff bases [10], and calixarenes
[11,12], have increasingly been investigated. While pre-
cise control of chemical reactivity is difficult, the ex-
pectation is that compounds with comparable or
superior reactivity to group 4 metal metallocenes can be
developed since steric and electronic properties of an-
cillary ligands profoundly influence the reactivity of
transition metals.
Metallocene complexes of the group 4 metals have
been the focus of intense study, mainly because of their
usefulness in organic and polymer chemistry [1]. Group
q Supplementary data associated with this article can be found, in the
online version, at doi:10.1016/j.jorganchem.2003.10.039.
* Corresponding author. Tel.: +1-859-257-7084; fax: +1-859-323-
1069.
E-mail address: fladip0@uky.edu (F.T. Ladipo).
Present address: Department of Chemistry and Biochemistry,
1
University of Notre Dame, Notre Dame, IN 46556, USA.
2
We have been exploring the chemistry of titanium
complexes supported by dianionic, proximally bridged
p-t-butylcalix[4]arene ligands [12]. Previously, we re-
ported the synthesis of conformationally stable Ti(IV)
Present address: Chemistry Department, Transylvania University,
Lexington, KY 40508, USA.
3
Present address: Department of Chemistry, Russian State Medical
University, 1 Ostrovityanov St., Moscow 117869, Russia.
0022-328X/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2003.10.039

F.T. Ladipo et al. / Journal of Organometallic Chemistry 689 (2004) 502–514
503
dichlorides that contain calixarene-derived bis(arylox-
ide) ligands in 1,2-alternate conformation, (DMSC)-
TiCl2 (1a) [12b] and (t-BuPC)TiCl2 (1b) [12a] (Fig. 1). In
this conformation, a pair of bulky tert-butylated phenyl
rings essentially define a cavity into which a coordina-
tion site at titanium must project. We found that 1a
catalyzes cyclotrimerization of terminal alkynes at 80 °C
and in the presence of excess Na (with respect to Ti) to
give high yields of 1,2,4-substituted benzenes with ex-
cellent regioselectivity [12b]. The reaction of 1a with
activated magnesium (Mg*) in the presence of an excess
of Me3SiC B CH produced (DMSC)Ti{g6-1,2,4-
C6H3(SiMe3)3} (2a, Fig. 1), which is an efficient catalyst
for regioselective cyclotrimerization of terminal alkynes
to 1,2,4-substituted benzenes at room temperature [12c].
The steric bulk of the alkyne affects both the rate and
regioselectivity of the cyclotrimerization reaction. Bulky
terminal alkynes, such as Pri3SiC B CH, and most in-
ternal alkynes react very sluggishly with 2a, and are
rarely cyclotrimerized even at elevated temperatures.
Our mechanistic investigations revealed that dis-
placement of 1,2,4-C6H3(SiMe3)3 from 2a by alkyne is
rate-limiting. Furthermore, the observed 1,2,4-regiose-
lectivity is best explained by the directing influence (ki-
netic control) of the DMSC ligand [12b,12c]. That is, the
size of the cavity defined by the DMSC ligand sterically
governs the preferred orientation of a coordinated al-
kyne molecule by influencing placement of its sub-
stituent group inside or outside of the cavity.
Accordingly, whether a larger cavity size will permit
efficient cyclotrimerization of internal alkynes is of in-
terest. A careful analysis of the molecular structures of
DMSC-based titanium complexes revealed that the
bridging SiMe2 group can adopt different orientations,
and thereby permit some degree of flexibility in the
calixarene ligand. Herein, we describe results from a
study aimed at elucidating the effect of the steric prop-
erties of the SiR2 bridging group of calixarene-derived
bis(aryloxide) ligands on reactivity of titanium
complexes.
2. Results and discussion
2.1. Calix[4]arene derivatives
The synthesis of proximally bridged calix[4]arene
compounds 3–6 is summarized in Scheme 1. The method
reported by Lattman and colleagues [13] for the syn-
thesis of (DMSC)H2 was adapted to prepare 3–5. At
room temperature, reaction between Me2SiCl2 or
Et2SiCl2 and the appropriate calix[4]arene derivative in
the presence of 2 equiv of Et3N for 24–48 h gave 3–5 in
high yield after work-up. No reaction was observed
between p-tert-butylcalix[4]arene and Pri2SiCl2 or
But2SiCl2 under identical conditions while reaction with
Ph2SiCl2 mainly produced (ClPh2Si)2Calix-H2 (7,
Scheme 1), along with minor amounts of (DPSC)H2 (6).
It is likely that formation of 7 occurs by sequential
substitution of p-tert-butylcalix[4]arene with ClPh2Si
groups. This suggests that at room temperature inter-
molecular reaction of the presumed mono-substituted
intermediate (ClPh2Si)Calix-H3 with Ph2SiCl2 to give 7
proceeds at a faster rate than intramolecular chloride
substitution to produce (DPSC)H2 (6). Reasoning that
both initial substitution of p-tert-butylcalix[4]arene to
give (ClPh2Si)Calix-H3 and ‘‘HCl’’ elimination from
(ClPh2Si)Calix-H3 should be more facile at higher tem-
peratures, we conducted the reaction at 80 °C and iso-
lated (DPSC)H2 (6) in 78% yield. In contrast, reaction
between p-tert-butylcalix[4]arene and more bulky (o-
MeC6H4)2SiCl2 at 80 °C gave (o-Tol2SiCl)2Calix-H2 (8)
in excellent yield (Scheme 1). Compounds 3–8 are air-
stable, hygroscopic white solids. While 3 and 5–8 are
fairly soluble in aromatic hydrocarbon solvents, such as
benzene and toluene, and in polar hydrocarbon solvents,
such as ether, THF, chloroform, and dichloromethane
(DMSHC)H2 (4) is only sparingly soluble in these sol-
vents. All of the compounds are considerably less solu-
ble in aliphatic hydrocarbon solvents.
Mass spectral and solution NMR data of 3–8 are
consistent with their proposed formulation and struc-
ture. The NMR data for 3–5 demonstrate that they
possess Cs symmetry and adopt 1,2-alternate confor-
mation in solution. 1H and 13C NMR resonances for the
endo-SiR group (located inside the calixarene cavity) of
1,2-alternate R2Si-bridged calix[4]arene compounds are
always strongly shielded compared to signals for the
exo-SiR group (located outside the calixarene cavity)
[12,13], due probably to ring current effect [14]. For
1
example, H NMR resonances for the endo-SiCH2CH3
group of (DESC)H2 (3) show as a triplet at d 0.65
Fig. 1.

504
F.T. Ladipo et al. / Journal of Organometallic Chemistry 689 (2004) 502–514
Scheme 1.
(SiCH2CH3) and a quartet at d )0.63 (SiCH2CH3) while
the exo-SiCH2CH3 group is observed as a multiplet at d
0.86–0.96. Similarly, in the 13C NMR spectrum of 3, two
resonances at d 7.2 (SiCH2CH3) and d 4.9 (SiCH2CH3)
are observed for the endo-SiCH2CH3 group while reso-
nances for the exo-SiCH2CH3 group are observed at d
8.2 (SiCH2CH3) and 7.4 (SiCH2CH3). 1H NMR spectra
of 3–5 also show two pairs of doublets and an AB sys-
tem for the bridging CH2 protons. The AB system in-
tegrates as four protons and represents CH2 groups not
included in the mirror plane. Furthermore, coupling
constants (JH–H ꢀ16 Hz) for the AB system are typical
of 1,2-alternate conformation (16–17 Hz) [12a,12b].
The poor solubility of (DMSHC)H2 (4) prevented
that methylene carbons of calix[4]arenes are character-
ized by a resonance around d 31 ppm when the attached
phenol rings are oriented syn. Whereas, a resonance
around d 37 ppm is characteristic when the phenol rings
adopt anti orientation (Fig. 2). NMR data for
(DPSC)H2 (6) confirm its Cs symmetry in solution and
show that it adopts the cone conformation. Hence two
singlets and three pairs of doublets are observed in its
R
R
R
OH
acquisition of its solution 13C NMR data. However, 13
C
OH
NMR spectra of 3 and 5 showed three resonances for
the bridging methylene carbons at d 32.8, 36.2, and 37.4
(doubly intense) (3) and d 31.9, 35.2, and 36.1 (doubly
intense) (5). These data parallel 13C NMR data reported
for several calix[4]arene derivatives [13,15], which show
OH
OH
R
syn
anti
Fig. 2.

F.T. Ladipo et al. / Journal of Organometallic Chemistry 689 (2004) 502–514
505
1H NMR spectrum for But groups and methylene pro-
tons, respectively. The spectrum is distinct from the
spectra of 3–5 in that an AB system is absent and the
coupling constant (JH–H) for the doubly intense pair of
doublets is ꢀ14 Hz while the corresponding JH–H for 3–5
is ꢀ16 Hz. In its 13C NMR spectrum, the bridging
methylene carbons resonate at d 38.0, 33.8 (overlapped
with C(CH3)3 resonance), and 32.8 (doubly intense).
The resonance at 38.0 belongs to CH2 carbon connect-
ing syn-oriented Ph2Si-bridged phenol rings. Similar
data have previously been reported for proximally
bridged calixarenes in cone conformation [12a,16].
1H and 13C NMR data for (ClPh2Si)2Calix-H2 (7)
and (o-Tol2SiCl)2Calix-H2 (8) indicate that they are C2v
symmetric in solution. Their 1H NMR spectra show two
equally intense doublets for the calixarene CH2 groups
at d 4.64 and 3.10 for 7 and at d 4.57 and 3.10 for 8.
Their JH–H coupling constants of ꢀ14 Hz and the pres-
ence of a single resonance for calixarene CH2 carbons in
their 13C NMR spectrum at d 33.1 for 7 and d 33.2 for 8
reveal that the compounds exist in cone conformation.
The structure assigned for 7 by spectroscopy was con-
firmed by single-crystal X-ray crystallographic analysis:
the molecule adopts cone conformation with the
ClPh2Si groups substituted symmetrically. The molecu-
lar structure of 7 is shown in Fig. 3 and its crystallo-
graphic data and selected metrical parameters are
presented in Tables 1 and 2. Metrical parameters for 7
are within the range observed for related calixarene
compounds [12a,13,16].
2.2. Synthesis and reactivity of titanium complexes
Reaction between TiCl4 and 3–6 produced L2TiCl2
complexes 9–12 (L2 ¼ DESC, DMSHC, DMSMC, or
DPSC) in high yield Eq. (1), as air- and moisture-
sensitive orange or orange-brown solids. Both micro-
analysis and NMR data strongly support the proposed
formulation and structure of each compound. Com-
pounds 9, 11 and 12 are quite soluble in aromatic- and
chlorinated hydrocarbon solvents while (DMSHC)TiCl2
(10) is only sparingly soluble. All of the compounds are
practically insoluble in aliphatic hydrocarbon solvents.
1H and 13C NMR data show that 9–12 exist in 1,2-
9; L2 ¼ DESC;87%
L2H2
ƒƒƒƒƒƒƒƒƒƒƒ!
10; L2 ¼ DMSHC;84%
TiCl4
L TiCl
2 2
11; L2 ¼ DMSMC;95%
ꢁ40–25 °C pentane=ether
12; L2 ¼ DPSC;82%
Fig. 3. An ORTEP diagram of the molecular structure of 7 showing
50% thermal ellipsoid probabilities.
ð1Þ
Table 1
Crystallographic data for 7, 12, and 16 ꢂ 1.5(C5H12
)
7
12
16 ꢂ 1.5(C5H12
C85:50H104O5SiTi
)
Formula
Formula wt.
T (K)
C68H74Cl2O4Si2
1082.35
144(1)
C56H62Cl2O4SiTi
945.97
173(1)
1287.69
173(1)
Crystal system
Space group
Z
Triclinic
ꢀ
Triclinic
ꢀ
Monoclinic
P21=n
4
P1
P1
2
2
ꢁ
a (A)
11.093(2)
14.490(2)
20.103(2)
87.288(10)
77.736(10)
76.081(10)
3064.8(8)
1.173
9.392(3)
15.463(6)
19.154
11.0560(10)
30.443(3)
22.699(2)
90
ꢁ
b (A)
ꢁ
c (A)
a (°)
b (°)
c (°)
102.67(2)
91.60(2)
99.34(2)
2672.2(17)
1.213
100.649(10)
90
3
ꢁ
V (A )
7508.4(12)
1.141
dcalc (g/cm3)
Final R indices [I > 2rðIÞ]: R1, wR2
0.0657, 0.0919
0.1097, 0.1015
0.0534, 0.1138
0.0855, 0.1267
0.0818, 0.2188
0.1067, 0.2328
wR2, R1 (all data)

506
F.T. Ladipo et al. / Journal of Organometallic Chemistry 689 (2004) 502–514
Table 2
Table 3
ꢁ
ꢁ
Selected bond distances (A) and angles (°) for 7
Selected bond distances (A) and angles (°) for 12
Si(1)–O(2)
Si(1)–C(45)
Si(1)–C(51)
Si(1)–Cl(1)
Si(2)–O(4)
Si(2)–C(57)
Si(2)–C(63)
Si(2)–Cl(2)
O(1)–C(25)
O(2)–C(26)
O(3)–C(27)
O(4)–C(28)
1.650(2)
1.833(3)
1.841(3)
2.0522(13)
1.643(2)
1.837(3)
1.841(3)
2.0517(12)
1.384(3)
1.405(3)
1.385(3)
1.404(3)
Ti–O(1)
Ti–O(2)
Ti–Cl(1)
Ti–Cl(2)
Si–O(4)
Si–O(3)
Si–C(45)
Si–C(51)
1.766(2)
1.769(2)
2.1980(14)
2.2332(14)
1.631(2)
1.642(2)
1.840(3)
1.867(4)
O(1)–Ti–O(2)
O(1)–Ti–Cl(1)
O(2)–Ti–Cl(1)
O(1)–Ti–Cl(2)
O(2)–Ti–Cl(2)
Cl(1)–Ti–Cl(2)
103.56(10)
110.06(8)
117.51(8)
108.90(9)
111.73(9)
104.95(5)
C(26)–O(2)–Si(1)
C(28)–O(4)–Si(2)
125.67(17)
125.07(17)
alternate conformation and possess Cs symmetry. Thus,
a change in conformation of (DPSC)H2 occurs when it
reacts with TiCl4 to form (DPSC)TiCl2 (12) [17]. 1H
NMR spectra of 9–12 contain two pairs of doublets and
an AB system (integrating as four protons) for the
bridging CH2 protons. Also, we could identify endo- and
exo-SiR (R ¼ Me or Et) resonances for 9–11 (see Section
3). 13C NMR spectra of 9, 11 and 12 showed methylenes
bridging anti-oriented phenolic rings at around d 40
ppm while methylenes bridging syn-oriented phenolic
rings generally appeared at around d 36 ppm, consistent
with previously reported data for related 1,2-alternate
calix[4]arene derivatives [12a,13,15]. A single-crystal
X-ray crystallographic study of 12 established that the
DPSC ligand adopts 1,2-alternate conformation and
that the geometry about Ti is tetrahedral (Fig. 4). Sim-
ilar to the DMSC ligand [12b], DPSC imposes distinct
stereochemical environments about the titanium-bound
chlorides. Thus, access to the endo chloride Cl(2) is more
hindered relative to the exo chloride Cl(1). Bond dis-
tances and angles for 12 (Table 3) are within the ex-
pected ranges [18].
Though the synthesis and chemistry of titananor-
bornadienes remain largely undeveloped [19], we
have demonstrated that titananorbornadienes (DMSC)
Ti{g6-1,2,4-C6H3(SiMe3)3} (2a) and (DMSC)Ti(g6-1,
3,5-C6H3But3) (2b) are excellent Ti(II) synthons [12b,
12c,12d]. Therefore, we saw benefit in extending the
series of titananorbornadiene compounds and explor-
ing their reactivity. Since 2a was isolated from the
black mixture that resulted upon reaction of
(DMSC)TiCl2 (1a) with an excess of Me3SiCBCH and
Mg* (generated by degradation of C14H10Mg(THF)3
[20]) in toluene containing ꢀ1–2% by volume of THF,
we examined the reduction of L2TiCl2 complexes 9–12
with Mg* in the presence of 10 equivalents of
Me3SiCBCH in C6D6 containing ꢀ1–2% by volume
of THF. 1H NMR analysis of the resulting black
mixtures
revealed
that
cyclotrimerization
of
Me3SiCBCH occurred in all cases to give mixtures of
1,2,4- and 1,3,5-C6H3(SiMe3)3 (see Section 3). More-
over, titananorbornadiene complexes L2Ti{g6-1,2,4-
C6H3(SiMe3)3} (13–15) were observed in solution
when L2 ¼ DESC, DMSMC, or DPSC Eq. (2). Efforts
to prepare and cleanly isolate 13–15 via a variety of
approaches have so far been unsuccessful because of
low conversion of the L2TiCl2 precursors into a ti-
tananorbornadiene (vide infra). Therefore, the com-
pounds were characterized only in solution by 1H
NMR data.
ðiÞ Mgꢃ
ðiiÞ Me3SiC ꢄ CH; ðxsÞ
L2TiCl2
L2Tifg6-1; 2; 4-C6H3ðSiMe3Þ g
ƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒƒ!
C6D6=THf
3
black solution
9; L2 ¼ DESC
13; L2 ¼ DESC
14; L2 ¼ DMSMC
15; L2 ¼ DPSC
11; L2 ¼ DMSMC
12; L2 ¼ DPSC
ð2Þ
The 1H NMR data for 13–15 clearly demonstrate
that they are C1-symmetric in solution although some
Fig. 4. An ORTEP diagram of the molecular structure of 12 showing
50% thermal ellipsoid probabilities.

F.T. Ladipo et al. / Journal of Organometallic Chemistry 689 (2004) 502–514
507
resonances were obstructed by signals due to other
products and THF (see Section 3). For instance, three
singlets are observed in their H NMR spectra for the
Cl
Mg
Mg
Mg
Mg
THF
THF
TiCl3
+
xs Mg
THF
1
THF
Cl
Cl
Ti
Ti
inequivalent g6-arene SiMe3 groups. Furthermore, 13
and 15 each show four singlets between d 1.2 and 1.6
ppm for But groups while the calixarene methyls of 14
show as four singlets between d 2.0 and 2.4 ppm. That
the calixarene ligand of 14 and 15 exists in 1,2-alternate
conformation was deduced from the upfield shift of the
endo-SiMe resonance (at d )0.65 ppm for 14) and/or
from the magnitude of the coupling constants for the
calixarene methylene protons (JH–H typically equal 16-
17 Hz for CH2 groups bridging anti-oriented phenolic
units, vide supra). Resonances for six of the eight
calixarene methylene protons of 13 could be identified,
four of which have coupling constants (JH–H ꢀ16 Hz)
typical of CH2 groups bridging anti-oriented phenolic
rings. However, a complex multiplet between d 0.82–
0.92 ppm was observed for SiEt2 protons and an up-
field resonance typical of an endo-SiR group was not
observed. Unambiguous assignment of the conforma-
tion of the calixarene ligand of 13 must therefore await
further data.
THF
Mg
Cl
TiMgCl2(THF)x + 0.5 MgCl2(THF)2
+
0.5 MgCl2(THF)2
ð3Þ
solutions, it is likely that the solutions also contained
paramagnetic species similar to those proposed by
Bogdanovic and colleagues. We presume that titana-
norbornadiene and paramagnetic calixarene-containing
species are produced via competing pathways since
black solutions result immediately upon addition of
THF to a suspension of L2TiCl2 (9–12), Mg* and
Me3SiCBCH in toluene or C6D6. In contrast, very
sluggish reaction of (DMSMC)TiCl2 (11) or
(DPSC)TiCl2 (12) with Mg* and Me3SiCBCH (10
equiv) occurred in toluene (in the absence of THF). The
orange suspensions did not change color for 1.5 h
and 1H NMR revealed plenty of unreacted titanium
dichloride.
The reduction of L2TiCl2 complexes 9, 11, and 12 in
the presence of alkyne (P10 equiv) was studied at dif-
ferent temperatures in a variety of solvents, including
toluene, THF, and 1,4-dioxane. The reaction was in-
vestigated for a range of reducing agents (such as acti-
vated Zn [21], Na, activated Ca [22], Mg*, and C8K [23])
and alkynes (such as Me3SiCBCH, p-MeC6H4CBCH,
ButCBCH, MeCBCMe, and PhCBCMe). Titananor-
bornadiene complexes were formed in significant
amount only when the reductant was Mg*, the alkyne
was Me3SiCBCH, and the reaction was conducted at
room temperature in toluene containing 1–2% (by vol-
ume) of THF. Although catalytic cyclotrimerization
of the alkynes occurred using other reducing agents,
harsher conditions were generally required and reduc-
tion of L2TiCl2 proceeded at a slower rate than alkyne
cyclotrimerization. High conversion of L2TiCl2 com-
plexes 9, 11, and 12 into corresponding titananorbor-
nadienes (13–15) requires complete reduction of the
L2TiCl2 precursor prior to catalytic Me3SiCBCH cy-
clotrimerization. Otherwise, reduced titanium species
formed in the initial stages of L2TiCl2 reduction will
consume all of the alkyne before the reduction was
complete (since alkyne cyclotrimerization is catalytic).
Bogdanovic and colleagues [24] have reported that
reduction of TiClx (x ¼ 3 or 4) with Mg in THF pro-
duced black solutions containing paramagnetic Ti–Mg
species TiMgCl2(THF)x and [Ti(MgCl)2(THF)x]y (the
local structure about Ti in the latter species was char-
acterized by EXAFS, Eq. (3)). Since reactions of
L2TiCl2 complexes 9–12 with Mg* and Me3SiCBCH (10
equiv) in toluene or C6D6 containing 1–2% of THF
proceed immediately to form black
We reasoned that increased MgCl2 precipitation from
reactions of L2TiCl2 complexes 9–12 with Mg* and
Me3SiCBCH should favor titananorbornadiene forma-
tion. Therefore, we explored reactions of (DESC)TiCl2
(9) with Mg* and Me3SiCBCH (P10 equiv) in toluene/
THF containing different amounts of 1,4-dioxane. While
precipitation of MgCl2(dioxane)n did improve conversion
to(DESC)Ti{g6-1,2,4-C6H3(Si Me3)3} (13), the experi-
mental results were irreproducible and depended on the
mixing rate, the reaction scale, and solvent ratios. Finally,
we explored reactions of various alkynes with L2Ti(g2-
alkene) or L2Ti(g2-alkyne) species (prepared in situ via
modifications of the Neghishi [25], Eisch [26], or Sato [27]
protocols). Titananorbornadiene formation was very
seldom observed and in very small amount.
In an effort to examine the effect of calixarene-derived
bis(aryloxide) ligands on reactivity of titanium, we de-
cided to examine the scope of alkynes that can be
cyclotrimerized using L2TiCl2 complexes 9–12 in the
presence of Mg* as catalyst (see Section 3). Table 4 out-
lines results from our preliminary investigations and show
that both terminal and internal alkynes can be cyclotri-
merized. Terminal alkynes are cyclotrimerized with high
regioselectivity (Table 4, entries 1 and 2) while steric
properties of the substituent groups of internal alkynes
greatly influence both efficacy and regioselectivity of the
reaction. Thus, an ethyl or phenyl unit is about the limit of
a substituent that may be placed inside the calixarene
cavity and still observe catalytic cyclotrimerization under
our conditions (Table 4, entries 3–15). In the case of un-
symmetrically substituted internal alkynes, preference for
1,2,4-substitution decreased as the size difference of the

508
F.T. Ladipo et al. / Journal of Organometallic Chemistry 689 (2004) 502–514
Table 4
Catalytic alkyne cyclotrimerization
R
R
R
R'
R'
R'
R
R'
R'
R
L2TiCl2/ Mg*
+
R C C R'
(10 equiv)
toluene/THF
²
R
R'
No.
Alkyne
L2TiCl2
% Isomerc
C6R6
Rxn. timee
1,2,4-
1,3,5-
1
2
p-MeC6H4C B CHa
PhC B CHa
12
12
92
8
ꢀ2 h at 75 °C
>92
72
<8d
28
ꢀ2 h at 75 °C
3
PhC B CMea
PhC B CMeb
PhC B CEta
11
12
ꢀ24 h at 70 °C
ꢀ1 h at 70 °C
4
90
69
10
31
5
11
12
ꢀ24 h at 70 °C
ꢀ24 h at 70 °C
ꢀ18 h at 70 °C
ꢀ2 h at 75 °C
6
PhC B CEt
68
32
7
MeC B CMea
MeC B CMea
MeC B CEtb
MeC B CEta
EtC B CEta
11
12
100
100
8
9
12
11
ꢀ75
ꢀ25
ꢀ2 h at 75 °C
10
11
12
13
14
15
75
25
ꢀ20 h at 70 °C
ꢀ48 h at 70 °C
ꢀ48 h at 70 °C
5 days at 70–100 °C
5 days at 70–100 °C
5 days at 70–100 °C
11
12
100
100
EtC B CEtb
Me2NCH2C B CEta
9–12
9–12
9–12
–
–
–
–
Me3SiC B CMea
Me3SiC B CSiMe3
a
–
a A screw-capped NMR tube was charged with C14H10Mg(THF)3 along with all other reactants and C6D6 in a glovebox. The NMR tube was then
heated at 70–75 °C. See Section 3 (method 1) for full details.
b C14H10Mg(THF)3 was first decomposed in C6D6 at 80 °C to Mg* and anthracene. All other reactants were added after cooling to ambient
temperature. See Section 3 (method 2) for full details.
c Isomer ratios were determined from GC-MS and 1H NMR data. For unsymmetrical alkynes RC B CR0, 1,2,4-substitution refers to substitution
of R at 1-, 2-, and 4-positions of the benzene ring.
d The yield of 1,3,5-Ph3C6H3 was estimated based on the result obtained for p-tolylacetylene. 12C NMR data confirmed the major product as 1,2,4-
substituted isomer and GC-MS showed only one peak. 1H NMR data could not be used to characterize the 1,3,5-substituted isomer, presumably
because of extensive peak overlap.
e For 100% conversion.
substituent groups decreased (Table 4, entries 2, 4, and 6).
Nonetheless, 1,2,4-substitution was favored over 1,3,5-
substitution in all cases by about 3:1.
It is noteworthy that cyclotrimerization of 1-phenyl-
1-propyne was more facile when the calixarene-derived
bis(aryloxide) ligand was DPSC versus DMSMC (Table
4, entries 3 and 4). This result suggests that the DPSC
ligand may provide a less crowded titanium center and
thereby reduce steric inhibition of alkyne coordination.
Thus, the DPSC ligand may exert greater kinetic control
over the course of cyclotrimerization and thereby ex-
plain the high regioselectivity [28]. When the reaction of
(DPSC)TiCl2 (12) with Mg* and PhC B CMe (3 equiv)
was conducted on a preparative scale in toluene/THF,
we isolated a small amount of a titanacyclopent-2-ene
derivative 16 [29]. The molecular structure of 16 (Fig. 5)
was characterized by X-ray diffraction study and its
crystallographic data are listed in Table 1. The poor
crystal quality could be due to a small amount of
unresolved twinning, and limits the accuracy of geo-
metrical parameters. Nevertheless, connectivity is
unambiguous and bond lengths and angles (Table 5) are
within expected ranges [2h,2k,30]. Remarkably, the
molecular structure of 16 revealed that the DPSC ligand
has undergone activation of one of its methylene C-H
bonds and that the methylene carbon is bonded to the a-
sp3-carbon of the titanacyclopent-2-ene. The calixarene
Fig. 5. An ORTEP diagram of the molecular structure of 16 showing
50% thermal ellipsoid probabilities.

F.T. Ladipo et al. / Journal of Organometallic Chemistry 689 (2004) 502–514
509
Table 5
Selected bond distances (A) and angles (°) for 16 ꢂ 1.5(C5H12
use. Calix[4]arene [34], p-methylcalix[4]arene [35], C14
H10Mg(THF)3 [20], and (o-MeC6H4)2SiCl2 [36] were
prepared by literature methods. All other chemicals
were purchased from Aldrich Chemical Co. and used
without further purification (unless otherwise stated).
The calix[4]arene starting materials were dried in a
ꢁ
)
O(1)–Ti
O(2)–Ti
1.817(3)
1.853(3)
2.105(3)
2.143(5)
2.177(4)
1.534(6)
1.528(6)
1.536(6)
1.528(6)
1.552(6)
1.520(6)
1.337(7)
1.497(6)
104.68(14)
130.88(13)
84.67(13)
O(1)–Ti–C(57)
O(2)–Ti–C(57)
O(1T)–Ti–C(57)
O(1)–Ti–C(62)
O(2)–Ti–C(62)
O(1T)–Ti–C(62)
C(57)–Ti–C(62)
C(1)–C(2)–C(57)
C(1)–C(2)–C(3)
C(57)–C(2)–C(3)
C(58)–C(57)–C(2)
90.54(15)
85.94(15)
138.55(15)
110.31(16)
141.03(16)
85.23(16)
77.27(17)
114.3(3)
Ti–O(1T)
Ti–C(57)
Ti–C(62)
1
vacuum oven at 150 °C for 48 h prior to use. H and
C(2)–C(57)
C(1)–C(2)
C(2)–C(3)
12C NMR spectra were recorded on a Varian Gemini-
200 spectrometer or a Varian VXR-400 spectrometer at
ca. 22 °C. 1H and 12C chemical shifts were referenced to
residual solvent peaks. GC-MS analyses were per-
formed on a Hewlett Packard 5890 series II gas chro-
matograph with a Hewlett Packard 5972 series mass
selective detector at an ionizing potential of 70 eV.
Other mass spectral data were obtained from the Uni-
versity of Kentucky Mass Spectrometry Center on a
Thermo Finnigan (San Jose, CA) Polaris Q (quadruple
ion trap) spectrometer. Elemental analyses were per-
formed by Complete Analysis Laboratories, Inc., Par-
sippany, NJ.
C(57)–C(58)
C(57)–C(59)
C(59)–C(60)
C(60)–C(62)
C(60)–C(61)
O(1)–Ti–O(2)
O(1)–Ti–O(1T)
O(2)–Ti–O(1T)
109.8(3)
114.9(4)
111.1(4)
C(58)–C(57)–C(59) 113.5(4)
C(2)–C(57)–C(59)
C(58)–C(57)–Ti
C(2)–C(57)–Ti
C(59)–C(57)–Ti
112.2(4)
109.1(3)
105.6(3)
104.9(3)
ligand exists in 1,2-alternate conformation and the ge-
ometry about Ti can be described as distorted square
pyramidal, with the basal plane defined by C57, C62,
O2, and O1(T). Equally surprising, a phenyl substituent
is positioned at the a-position of the titanacycle on the
same side as a THF molecule coordinated on the endo-
face of titanium (directed toward the calixarene cavity)
[31]. We propose that orientation of one of the phenyl
units of the SiPh2 bridging group such that it can fit
between two phenolic units of the calixarene ligand
(Fig. 5) allows the DPSC ligand to open up its cavity
and accommodate more bulky substituents than the
DMSC or DMSMC ligands.
In summary, it seems likely that the size of the cavity
provided by proximally bridged calixarene ligands may
be tuned through proper choice of bridging group. The
observed regioselectivity for alkyne cyclotrimerization in
the present study probably represent the lower-limit
since paramagnetic calixarene-containing species that
catalyze alkyne cyclotrimerization (with modest regi-
oselectivity) are also generated under our reaction
conditions. Efforts to isolate titananorbornadiene com-
plexes and investigate their chemistry are continuing in
our laboratory.
3.2. Synthesis of calix[4]arene derivatives 3–8
3.2.1. (DESC)H2 (3)
6.58 g (10.1 mmol) of p-t-Bu-calix[4]arene was
charged into a 250 mL Schlenk flask followed by toluene
(120 mL) and then 1.52 mL (10.1 mmol) of Et2SiCl2 in
toluene (6 mL). Next, a solution of Et3N (2.82 mL, 10.3
mmol) in toluene (10 mL) was added dropwise to the
suspension over a 20 min period. After stirring for 48 h,
the reaction mixture was filtered and Et3NHCl was
extracted with additional toluene (10 mL) and pentane
(20 mL). The filtrate and extracts were combined and
stripped to dryness under reduced pressure. The result-
ing white solid was washed with pentane (3 ꢅ 10 mL)
1
and dried under vacuum. Yield: 6.51 g, 88%. H NMR
(C6D6) d: 7.24 (d, J ¼ 2:6 Hz, 2H, arom CH), 7.17 (d,
2H, J ¼ 2:6 Hz, arom CH), 7.11 (d, J ¼ 2:6 Hz, 2H,
arom CH), 6.98 (d, 2H, J ¼ 2:6 Hz, arom CH), 6.15 (s,
2H, OH), 4.38 (d, J ¼ 14 Hz, 1H, calix-CH2), 4.27 (d,
J ¼ 16:2 Hz, 2H, calix-CH2), 4.08 (d, J ¼ 13:6 Hz, 1H,
calix-CH2), 3.82 (d, J ¼ 16:2 Hz, 2H, calix-CH2), 3.44
(d, J ¼ 14 Hz, 1H, calix-CH2), 3.41 (d, J ¼ 14:8 Hz, 1H,
calix-CH2), 1.29 (s, 18H, t-Bu), 1.24 (s, 18H, t-Bu), 0.86–
0.96 (m, 5H, exo-SiCH2CH3), 0.65 (t, 3H, endo-
SiCH2CH3), )0.63 (q, 2H, endo-SiCH2CH3). 13C NMR
(C6D6): 150.6, 150.5, 145.0, 143.4, 130.1, 130.0, 128.8,
127.5, 126.9, 126.2, 126.1, 125.8, 37.4 (calix-CH2),
36.2 (calix-CH2), 34.5 (C(CH3)3), 34.4 (C(CH3)3, 32.8
(calix-CH2), 32.1 (C(CH3)3), 31.9 (C(CH3)3), 8.2
(exo-SiCH2CH3), 7.4 (exo-SiCH2CH3), 7.2 (endo-
SiCH2CH3), 4.9 (endo-SiCH2CH3). MS(EI): Mþ (732).
3. Experimental
3.1. General
All experiments were performed under dry nitrogen
atmosphere using standard Schlenk techniques or in a
MBraun glovebox. All of the solvents were dried and
distilled by standard methods [33] then stored in the
glovebox over 4A molecular sieves, which had been
dried under vacuum at 150 °C for at least 48 h prior to
use. Alkynes were purchased from Aldrich or GFS
Chemicals, Inc. and were distilled from CaH2 prior to
3.2.2. (DMSHC)H2 (4)
2.37 g (5.58 mmol) of calix[4]arene was charged into a
250 mL Schlenk flask followed by toluene (60 mL) and

510
F.T. Ladipo et al. / Journal of Organometallic Chemistry 689 (2004) 502–514
then 0.710 mL (5.86 mmol) of Me2SiCl2 in toluene (5
mL). Next, a solution of Et3N (1.87 mL, 13.4 mmol) in
toluene (10 mL) was added dropwise to the suspension
over a 20 min period. After stirring for 48 h, the reaction
mixture was filtered and the filtrate was stripped to
dryness under reduced pressure. The resulting white
solid was washed with pentane (3 ꢅ 15 mL) and dried
8.23 (m, 2H, arom CH), 7.80 (m, 2H, arom CH), 7.52 (s,
2H, OH), 7.20-7.30 (m, 4H, arom CH), 6.80–7.10 (m,
10H, J ¼ 2:6 Hz, arom CH), 5.02 (d, J ¼ 14 Hz, 1H,
calix-CH2), 4.94 (d, J ¼ 13:6 Hz, 2H, calix-CH2), 3.93
(d, J ¼ 14:4 Hz, 1H, calix-CH2), 3.59 (d, J ¼ 13:6 Hz,
2H, calix-CH2), 3.26 (d, J ¼ 14 Hz, 1H, calix-CH2), 3.15
(d, J ¼ 15:4 Hz, 1H, calix-CH2), 1.14 (s, 18H, t-Bu),
1.10 (s, 18H, t-Bu). 13C NMR (C6D6): 148.9, 145.1,
142.9, 138.6, 134.7, 134.5, 132.5, 131.7, 130.6, 130.3,
129.3, 128.9, 128.2, 127.7, 127.1, 126.7, 125.6, 125.5,
38.0 (calix-CH2), 33.8 {C(CH3)3 and calix-CH2}, 32.8
(calix-CH2), 31.4 (C(CH3)3), 31.2 (C(CH3)3). MS(EI):
Mþ (828).
1
under vacuum. Yield: 2.38 g, 89%. H NMR (C6D6) d:
6.78–6.96 (m, 8H, arom CH), 6.62–6.74 (m, 4H, arom
CH), 6.10 (s, 2H, OH), 4.24 (d, J ¼ 14:4 Hz, 1H, calix-
CH2), 4.18 (d, J ¼ 15:8 Hz, 2H, calix-CH2), 3.90 (d,
J ¼ 14:4 Hz, 1H, calix-CH2), 3.64 (d, J ¼ 15:8 Hz, 2H,
calix-CH2), 3.43 (d, J ¼ 14:4 Hz, 1H, calix-CH2), 3.23
(d, J ¼ 14:4 Hz, 1H, calix-CH2), 0.27 (s, 3H, exo-SiMe),
)0.69 (s, 3H, endo-SiMe). MS(EI): Mþ (480).
3.2.5. (Ph2SiCl)2Calix-H2 (7)
5.00 g (7.70 mmol) of p-t-Bu-calix[4]arene was
charged into a 250 mL Schlenk flask followed by toluene
(100 mL) and then 1.62 mL (7.70 mmol) of Ph2SiCl2 in
toluene (6 mL). Next, a solution of Et3N (2.15 mL, 15.4
mmol) in toluene (10 mL) was added dropwise into the
suspension over a 20 min period. After stirring for 48 h,
the reaction mixture was filtered and the filtrate was
stripped to dryness under reduced pressure. The result-
ing white solid was washed with pentane (3 ꢅ 15 mL),
dried under vacuum, and identified as (Ph2SiCl)2Calix-
H2 (7) on the basis of NMR, MS, and X-ray diffraction
data. Yield: 1.58 g (1.46 mmol), 38% on the basis of the
maximum yield possible under these conditions (3.85
mmol). 1H NMR (C6D6) d: 7.98–8.10 (m, 8H, arom
CH), 7.06–7.14 (m, 12H, arom CH), 7.03 (s, 4H, arom
CH), 6.87 (s, 2H, OH), 6.78 (s, 4H, arom CH), 4.64 (d,
J ¼ 13:4 Hz, 4H, calix-CH2), 3.10 (d, J ¼ 13:6 Hz, 4H,
calix-CH2), 1.32 (s, 18H, t-Bu), 0.84 (s, 18H, t-Bu). 13C
NMR (C6D6): 151.2, 146.1, 144.8, 142.1, 135.4, 131.8,
131.6, 130.9, 128.9, 128.5, 126.0, 125.6, 33.8 (C(CH3)3),
33.7 (C(CH3)3, 33.1 (calix-CH2), 31.8 (C(CH3)3), 30.9
(C(CH3)3). MS(EI): Mþ (1082).
3.2.3. (DMSMC)H2 (5)
A toluene (90 mL) solution of Et3N (1.07 mL, 7.68
mmol) and Me2SiCl2 (0.460 mL, 3.79 mmol) was added
very slowly into a 500 mL toluene solution of p-methyl-
calix[4]arene (1.84 g, 3.83 mmol) at room temperature
with vigorous stirring. After 24 h, the reaction mixture
was filtered and the filtrate was stripped to dryness un-
der reduced pressure. The residue was washed with cold
pentane (3 ꢅ 10 mL) and dried under vacuum to give a
1
pure white powder (1.83 g, 90%). H NMR (CDCl3) d:
6.97 (br s, 4H, arom CH), 6.84 (br d, 2H, arom CH),
6.72 (br d, arom CH), 5.96 (s, 2H, OH), 4.25 (d,
J ¼ 14:8 Hz, 1H, calix-CH2), 4.12 (d, J ¼ 16 Hz, 2H,
calix-CH2), 3.90 (d, J ¼ 14 Hz, 1H, calix-CH2), 3.80 (d,
J ¼ 16 Hz, 2H, calix-CH2), 3.43 (d, J ¼ 14 Hz, 1H,
calix-CH2), 3.42 (d, J ¼ 14:8 Hz, 1H, calix-CH2), 2.26
(s, 6H, Me), 2.22 (s, 6H, Me), 0.42 (s, 3H, exo-SiMe),
)0.97 (s, 3H, endo-SiMe). 13C NMR (CDCl3): 149.6,
131.4, 130.4, 130.3, 129.8, 129.6, 129.5, 129.3, 128.8,
128.5, 126.2, 36.1 (calix-CH2), 35.2 (calix-CH2), 31.9
(calix-CH2), 20.8 (calix-Me), 20.7 (calix-Me), 2.8 (exo-
SiCH2CH3), )2.06 (endo-SiCH2CH3). MS(EI): Mþ
(536).
The pentane washings were combined, concentrated
under vacuum to ꢀ5 mL, and then cooled at )78 °C for
30 min. The resulting solids were collected by filtration,
dried under vacuum, and identified as (DPSC)H2 (6).
Yield of 0.68 g (0.82 mmol), 11% on the basis of the
maximum yield possible (7.70 mmol).
3.2.4. (DPSC)H2 (6)
A toluene (30 mL) solution of Et3N (6.45 mL, 46.2
mmol) and Ph2SiCl2 (4.86 mL, 23.1 mmol) was charged
into an addition funnel. The addition funnel was con-
nected via a reflux condenser to a 250 mL Schlenk flask
containing a toluene (120 mL) solution of p-t-Bu-
calix[4]arene (15.0 g, 23.1 mmol), which was heated at
80 °C. The Et3N/Ph2SiCl2 solution was added dropwise
into the p-t-Bu-calix[4]arene solution (over a 30 min
period) and the resulting mixture was stirred at 80 °C for
another 4h. After cooling to room temperature, the re-
action mixture was filtered and the filtrate was stripped
to dryness under reduced pressure. The resulting white
solid was washed with pentane (3 ꢅ 15 mL) and dried
3.2.6. (o-Tol2SiCl)2calix-H2 (8)
A toluene (30 mL) solution of Et3N (2.00 mL, 14.3
mmol) and o-Tol2SiCl2 (2.00 g, 7.11 mmol) was charged
into an addition funnel. The addition funnel was con-
nected via a reflux condenser to a 250 mL Schlenk flask
containing a toluene (120 mL) solution of p-t-Bu-ca-
lix[4]arene (4.61 g, 7.11 mmol), which was heated at 80
°C. The Et3N/o-Tol2SiCl2 solution was added dropwise
into the p-t-Bu-calix[4]arene solution (over a 30 min
period) and the resulting mixture was stirred at 80 °C
for another 3h. After cooling to room temperature, the
1
under vacuum. Yield: 15.0 g, 78%. H NMR (C6D6) d:

F.T. Ladipo et al. / Journal of Organometallic Chemistry 689 (2004) 502–514
511
reaction mixture was filtered and the filtrate was strip-
ped to dryness under reduced pressure. The resulting
white solid was washed with pentane (5 ꢅ 10 mL) and
toluene (5 mL) then dried under vacuum. Yield: 4.00 g
(3.51 mmol), 98% on the basis of the maximum yield
J ¼ 14:2 Hz, 1H, calix-CH2), 4.11 (d, AB, J ¼ 17:6 Hz,
2H, calix-CH2), 3.97 (d, AB, J ¼ 17:6 Hz, 2H, calix-
CH2), 3.66 (d, J ¼ 14:2 Hz, 1H, calix-CH2), 3.51 (d,
J ¼ 14:2 Hz, 1H, calix-CH2), 0.38 (s, 3H, exo-SiCH3),
)1.60 (s, 3H, endo-SiCH3). Anal. Calcd. for C30H26
O4SiTiCl2: C, 60.32; H, 4.39. Found: C, 59.97; H, 4.33.
1
possible under these conditions (3.56 mmol). H NMR
(C6D6) d: 8.61 (m, 4H, arom CH), 7.10–7.20 (m, 8H,
arom CH), 6.99 (s, 4H arom CH ), 6.92 (m, 4H, arom
CH), 6.79 (s, 4H arom CH ), 6.22 (s, 2H, OH), 4.57 (d,
J ¼ 14 Hz, 4H, calix-CH2), 3.10 (d, J ¼ 14 Hz, 1H,
calix-CH2), 2.39 (s, 12H, o-Me C6H4), 1.28 (s, 18H, t-
Bu), 0.93 (s, 18H, t-Bu). 13C NMR (C6D6): 151.4, 146.4,
145.6, 144.6, 142.7, 136.8, 132.5, 132.1, 131.6, 131.3,
129.7, 126.7, 126.4, 125.9, 34.3 (C(CH3)3), 33.2 (calix-
CH2), 33.1 (C(CH3)3), 32.2 (C(CH3)3), 31.5 (C(CH3)3).
MS(EI): Mþ (1138).
3.3.3. (DMSMC)TiCl2 (11)
A pentane (5.0 mL) solution of TiCl4 (0.208 g, 1.09
mmol) was added dropwise into a stirred suspension of
(DMSMC)H2 (0.536 g, 1.00 mmol) in ether (30 mL) at
)40 °C. The mixture turned orange-brown and was
warmed slowly to room temperature and let stir for 12 h.
Volatiles were then removed under vacuum, the residue
was washed with pentane (3 ꢅ 10 mL), and the orange
product was dried in vacuo. Yield: 0.62 g, 95%. 1H
NMR (C6D6) d: 6.88 (d, J ¼ 2 Hz, 2H, arom CH), 6.77
(d, J ¼ 2 Hz, 2H, arom CH), 6.73 (d, J ¼ 2 Hz, 2H,
arom CH), 6.55 (d, J ¼ 2 Hz, 2H, arom CH), 4.54 (d,
J ¼ 14:4 Hz, 1H, calix-CH2), 4.39 (d, J ¼ 14:8 Hz, 1H,
calix-CH2), 3.86 (d, AB, J ¼ 16:8 Hz, 2H, calix-CH2),
3.76 (d, AB, J ¼ 17:6 Hz, 2H, calix-CH2), 3.33 (d,
J ¼ 14:8 Hz, 1H, calix-CH2), 3.24 (d, J ¼ 14:4 Hz, 1H,
calix-CH2), 2.21 (s, 3H, p-Me-calix), 2.00 (s, 3H, p-Me-
calix), 0.29 (s, 3H, exo-SiCH3), -1.38 (s, 3H, endo-
SiCH3). 12C NMR (CDCl3): 163.3, 149.7, 138.4, 134.8,
132.1, 131.3, 131.2, 130.7, 129.7, 129.1, 128.8. 127.0,
39.3 (calix-CH2), 36.2 (calix-CH2), 35.8 (calix-CH2),
21.0 (p-Me-calix), 4.0 (exo-SiCH3), -2.6 (endo-SiCH3).
Anal. Calcd. for C34H34O4SiTiCl2: C, 62.49; H, 5.24.
Found: C, 62.30; H, 5.36.
3.3. Synthesis of titanium complexes 9–12
3.3.1. (DESC)TiCl2 (9)
A pentane (10 mL) solution of TiCl4 (0.544 g, 2.86
mmol) was added dropwise into a stirred suspension of
(DESC)H2 (2.00 g, 2.73 mmol) in ether (50 mL) at )40
°C. The mixture turned orange-brown and was warmed
gradually to room temperature and let stir for 24 h.
Volatiles were then removed under vacuum, the residue
was washed with pentane (3 ꢅ 10 mL), and the orange
product was dried in vacuo. Yield: 2.01 g, 87%. 1H NMR
(CDCl3) d: 7.23 (s, 2H, arom CH), 7.12 (s, 2H, arom
CH), 7.10 (s, 2H, arom CH), 7.04 (s, 2H, arom CH), 4.40
(d, J ¼ 14 Hz, 1H, calix-CH2), 4.38 (d, J ¼ 14:2 Hz, 1H,
calix-CH2), 4.02 (d, AB, J ¼ 16 Hz, 2H, calix-CH2), 3.96
(d, AB, J ¼ 16 Hz, 2H, calix-CH2), 3.60 (d, J ¼ 14:2 Hz,
1H, calix-CH2), 3.47 (d, J ¼ 14 Hz, 1H, calix-CH2), 1.32
(s, 18H, t-Bu), 1.31 (s, 18H, t-Bu), 0.88 (br m, 5H, exo-
SiCH2CH3), 0.29 (t, 3H, endo-SiCH2CH3), -1.40 (q, 2H,
endo-SiCH2CH3). 13C NMR (CDCl3): 162.2, 149.1,
147.9, 144.5, 137.5, 128.6, 128.5, 127.2, 126.9, 126.4,
125.6, 124.9, 39.9 (calix-CH2), 36.6 (calix-CH2), 35.9
(calix-CH2), 34.6 (C(CH3)3), 34.2 (C(CH3)3, 31.7
(C(CH3)3), 31.6 (C(CH3)3), 8.9 (exo-SiCH2CH3), 7.6
(exo-SiCH2CH3), 6.9 (endo-SiCH2CH3), 3.8 (endo-
SiCH2CH3). Anal. Calcd. for C48H62O4SiTiCl2: C,
67.84; H, 7.35. Found: C, 67.64; H, 7.42.
3.3.4. (DPSC)TiCl2 (12)
A pentane (10 mL) solution of TiCl4 (0.458 g, 2.41
mmol) was added dropwise into a stirred suspension of
(DPSC)H2 (2.00 g, 2.41 mmol) in ether (50 mL) at )40
°C. The mixture turned orange-brown and was warmed
slowly to room temperature and let stir for 12 h. Vola-
tiles were then removed under vacuum, the residue was
washed with pentane (3 ꢅ 5 mL), and the orange prod-
1
uct was dried in vacuo. Yield: 1.88 g, 82%. H NMR
(C6D6) d: 7.65 (m, 2H, arom CH), 7.24 (br d, 2H, arom
CH), 6.99-7.13 (m, 8H, arom CH), 6.82 (br d, 2H, arom
CH), 6.66 (br t, 2H, arom CH), 6.27 (d, J ¼ 7 Hz, 2H,
arom CH), 5.16 (d, J ¼ 15:4 Hz, 1H, calix-CH2), 4.93
(d, J ¼ 14:2 Hz, 1H, calix-CH2), 4.17 (d, AB, J ¼ 17:2
Hz, 2H, calix-CH2), 3.81 (d, AB, J ¼ 17:2 Hz, 2H, calix-
CH2), 3.38 (d, J ¼ 15:4 Hz, 1H, calix-CH2), 3.12 (d,
J ¼ 15:0 Hz, 1H, calix-CH2), 1.40 (s, 18H, t-Bu), 1.16 (s,
18H, t-Bu). 12C NMR (C6D6): 163.3, 150.4, 147.2, 145.3,
138.9, 138.4, 135.4, 133.6, 133.5, 130.6, 130.5, 129.4,
129.3, 129.1. 128.2, 125.6, 125.2, 40.1 (calix-CH2), 38.7
(calix-CH2), 38.4 (calix-CH2), 34.5 (C(CH3)3), 34.4
(C(CH3)3), 32.0 (s, C(CH3)3), 31.6 (s, C(CH3)3). Anal.
Calcd. for C56H62O4SiTiCl2: C, 71.10; H, 6.60. Found:
C, 70.98; H, 6.41.
3.3.2. (DMSHC)TiCl2 (10)
A pentane (8.0 mL) solution of TiCl4 (0.379 g, 2.00
mmol) was added dropwise into a stirred suspension of
(DMSHC)H2 (0.805 g, 1.67 mmol) in ether (50 mL) at
)50 °C. The mixture turned orange-brown and was
warmed gradually to room temperature and let stir for
24 h. The precipitate was filtered, washed with pentane
(3 ꢅ 7 mL), and the orange product was dried in vacuo.
Yield: 0.838 g, 84% based on the amount of
1
(DMSHC)H2. H NMR (CDCl3) d: 6.84-7.24 (m, 12H,
arom CH), 4.40 (d, J ¼ 14:8 Hz, 1H, calix-CH2), 4.34 (d,

512
F.T. Ladipo et al. / Journal of Organometallic Chemistry 689 (2004) 502–514
3.4. Reactivity studies
CH), 6.72 (br d, 1H, arom CH), 6.60 (br d, 1H, arom
CH), 5.37 (br d, 1H, C6H3{SiMe3}3), 5.26 (d, 1H, calix-
CH2), 5.03 (br d, 1H, C6H3{SiMe3}3), 4.99 (d, J ¼ 16:4
Hz, 1H, calix-CH2), 4.71 (br s, 1H, C6H3{SiMe3}3), 4.43
(d, J ¼ 17:2 Hz, 1H, calix-CH2), 4.20 (d, J ¼ 17:6 Hz,
1H, calix-CH2), 4.04 (d, 1H, calix-CH2), 4.03 (d, 1H,
calix-CH2), 3.15 (d, J ¼ 16:4 Hz, 1H, calix-CH2), 1.40
(s, 9H, t-Bu), 1.37 (s, 9H, t-Bu), 1.31 (s, 9H, t-Bu), 1.22
(s, 9H, t-Bu), )0.09 (s, 9H, C6H3{SiMe3}3), )0.30 (s,
9H, C6H3{SiMe3}3), )0.34 (s, 9H, C6H3{SiMe3}3).
After complete consumption of Me3SiC B CH, 1H
NMR revealed ꢀ3:1 ratio of 1,2,4-C6H3(SiMe3)3 and
1,3,5-C6H3(SiMe3)3, along with minor amounts un-
identified Ti(IV) species.
3.4.1. In situ formation of titananorbornadienes L2Ti
{g6-1,2,4-C6H3(SiMe3)3} (L2 ¼ DESC, DMSMC or
DPSC)
12.6 lmol of C14H10Mg(THF)3 was charged into a
screw-capped 5-mm NMR tube along with 0.8 mL of
C6D6. The mixture was heated at 80 °C for 5 min to
produce Mg* and release anthracene. The tube was
transferred into a glovebox after cooling to room tem-
perature. 106 lmol of Me3SiC B CH was introduced
followed by 10.6 lmol of the L2TiCl2 complex. The
NMR tube was vigorously shaken and the reaction
mixture turned dark brown-black. The reaction was
1
monitored at room temperature by H NMR spectros-
copy until all of the Me3SiC B CH was completely
consumed. The formation of a titananorbornadiene
3.4.2. Typical alkyne cyclotrimerization procedure using
[L2TiCl2]/Mg* (L2 ¼ DESC, DPSC, DMSMC or
DMSHC) as catalyst
1
complex was confirmed by the observed H NMR data
and by comparison of the data with that previously re-
ported for structurally characterized (DMSC)Ti{g6-
C6H3(SiMe3)3} (2a) [12c].
Method 1: 10.6 lmol of (DPSC)TiCl2 (12), 12.6 lmol
of C14H10Mg(THF)3, and 106 lmol of 2-pentyne were
charged into a screw-capped 5-mm NMR tube along
with 0.8 mL of C6D6. The reaction mixture was heated
at 75 °C and the course of the reaction was monitored
by 1H NMR until the alkyne was completely consumed.
At this point, the C6D6 solution was poured into pen-
tane (15 mL) and treated with MeOH (0.5 mL). This
solution was allowed to stand for 20 min in the air and
was then passed through a plug of silica gel. An ap-
propriate aliquot of the solution was subjected to GC-
MS analysis.
1
(DESC)Ti{g6-1,2,4-C6H3(SiMe3)3} (13). H NMR
(unobstructed resonances, C6D6): d 6.80 (br s, 1H, arom
CH), 6.57 (br s, 1H, arom CH), 5.77 (d, J ¼ 12:8 Hz,
1H, calix-CH2), 5.40 (br d, 1H, C6H3{SiMe3}3), 5.06 (br
d, 1H, C6H3{SiMe3}3), 4.68 (br s, 1H, C6H3{SiMe3}3),
4.48 (d, J ¼ 15:6 Hz, 1H, calix-CH2), 4.18 (br d,
J ¼ 16:4 Hz, 1H, calix-CH2), 4.08 (d, J ¼ 12:8 Hz, 1H,
calix-CH2), 3.86 (d, 1H, J ¼ 16:4 Hz, calix-CH2), 3.20
(d, J ¼ 15:6 Hz, 1H, calix-CH2), 1.52 (s, 9H, t-Bu), 1.48
(s, 9H, t-Bu), 1.35 (s, 9H, t-Bu), 1.25 (s, 9H, t-Bu), 0.82–
0.92 (m, 10H, SiEt2), )0.05 (s, 9H, C6H3{SiMe3}3),
)0.29 (s, 9H, C6H3{SiMe3}3), )0.35 (s, 9H,
C6H3{SiMe3}3). After complete consumption of
Method 2: 12.6 lmol of C14H10Mg(THF)3 was de-
composed into Mg* and anthracene in C6D6 (0.8 mL) in
a screw-capped 5-mm NMR tube at 80 °C. After cooling
to ambient temperature, 10.6 lmol of L2TiCl2 and 106
lmol of alkyne were then charged into the NMR tube.
1
Me3SiC B CH, H NMR revealed ꢀ3:1 ratio of 1,2,4-
1
C6H3(SiMe3)3 and 1,3,5-C6H3(SiMe3)3, along with mi-
nor amounts unidentified Ti(IV) species.
The reaction was monitored by H NMR and worked-
up as described in method 1.
(DMSMC)Ti{g6-C6H3(SiMe3)3} (14). 1H NMR
(unobstructed resonances, C6D6): 6.56 (br s, 1H, arom
CH), 6.39 (br s, 1H, arom CH), 6.16 (br s, 1H, arom
CH), 5.78 (d, J ¼ 12:8 Hz, 1H, calix-CH2), 5.48 (br d,
1H, C6H3{SiMe3}3), 5.21 (br d, 1H, C6H3{SiMe3}3),
4.71 (br s, 1H, C6H3{SiMe3}3), 4.31 (d, J ¼ 15:2 Hz,
1H, calix-CH2), 4.11 (d, J ¼ 16:8 Hz 1H, calix-CH2),
3.93 (d, J ¼ 12:8 Hz, 1H, calix-CH2), 3.69 (m, 2H,
calix-CH2) 3.48 (d, 1H, J ¼ 16 Hz, calix-CH2), 3.14
(d, J ¼ 16 Hz, 1H, calix-CH2), 2.34 (s, 3H, calix-Me),
2.30 (s, 3H, calix-Me), 2.14 (s, 3H, calix-Me), 2.08 (s,
3H, calix-Me), )0.02 (s, 9H, C6H3{SiMe3}3), )0.23 (s,
9H, C6H3{SiMe3}3), )0.34 (s, 9H, C6H3{SiMe3}3),
)0.65 (s, endo-SiMe). After complete consumption of
The substituted benzene products were characterized
1
by H NMR and MS data, as well as by comparison to
literature data (see Supplementary Material).
3.5. Crystallographic study
The crystal data for (ClPh2Si)2Calix-H2 (7),
(DPSC)TiCl2 (12), and the titanacyclopentene derivative
16 ꢂ 1.5(C5H12) are collected in Table 1. Further details
of the crystallographic study are given in the supple-
mentary material.
1
Me3SiC B CH, H NMR revealed ꢀ2:1 ratio of 1,2,4-
4. Supplementary material
C6H3(SiMe3)3 and 1,3,5-C6H3(SiMe3)3, along with
minor amounts of an unidentified Ti(IV) species.
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC Nos. 215560–215562 for 7, 12, and
1
(DPSC)Ti{g6-C6H3(SiMe3)3} (15). H NMR (un-
obstructed resonances, C6D6): d 6.86 (br d, 1H, arom

F.T. Ladipo et al. / Journal of Organometallic Chemistry 689 (2004) 502–514
513
(i) H. Mack, M.S. Eisen, J. Organomet. Chem. 525 (1996) 81;
16 ꢂ 1.5(C5H12), respectively. Copies of the information
may be obtained free of charge from The Director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (Fax:
+44-1223-336033; e-mail: deposit@ccdc.cam.ac.uk or
http://www.Ccdc.cam.ac.uk).
(j) V.C. Gibson, B.S. Kimberley, A.J.P. White, D.J. Williams, P.
Howard, J. Chem. Soc., Chem. Commun. (1998) 313;
(k) Y.-M. Jeon, S.J. Park, J. Heo, K. Kim, Organometallics 17
(1998) 3161.
[4] (a) G. Du, L.K. Woo, Organometallics 22 (2003) 450;
(b) J.L. Thorman, L.K. Woo, Inorg. Chem. 39 (2000) 1301;
(c) H.-J. Kim, S. Jung, Y.-M. Jeon, D. Whang, K. Kim, Chem.
Commun. (1999) 1033;
Acknowledgements
(d) S.D. Gray, J.L. Thorman, V.A. Adamian, K.M. Kadish, K.L.
Woo, Inorg. Chem. 37 (1998) 1;
Thanks are expressed to the US National Science
Foundation (Grant No. CHE-9984776) for financial
support of this work. NMR instruments utilized in this
research were funded in part by the CRIF program of
the US National Science Foundation (Grant No. CHE-
9974810). Thanks are expressed to Professor Carl
Hertzel (Transylvania University) for recruitment of
R.A. Huyck, and to Mr. Marc Maynor for his help with
mass spectral data.
(e) X. Wang, S.D. Gray, J. Chen, K.L. Woo, Inorg. Chem. 37
(1998) 5.
[5] E.Y. Tshuva, I. Goldberg, M. Kol, H. Weitman, H.Z. Goldsch-
midt, Chem. Commun. (2000) 379.
[6] (a) Y. Yoshida, S. Matsui, Y. Takagi, M. Mitani, T. Nakano, H.
Tanaka, N. Kashiwa, T. Fujita, Organometallics 20 (2001) 4793;
(b) S.-i. Ishii, J. Saito, M. Mitani, J.-i. Mohri, N. Matsukawa, Y.
Tohi, S. Matsui, N. Kashiwa, T. Fujita, J. Mol. Catal. A 179
(2002) 11;
(c) J. Tian, P.D. Hustad, G.W. Coates, J. Am. Chem. Soc. 123
(2001) 5134;
(d) P.D. Hustad, J. Tian, G.W. Coates, J. Am. Chem. Soc. 124
(2002) 3614.
References
[7] (a) E. Hong, Y. Han, M.H. Lee, H. Jang, Y. Do, Spec. Publ.,
Royal Soc. Chem. 253 (2000) 20;
(b) D.J. Crowther, N.C. Baenziger, R.F. Jordan, J. Am. Chem.
Soc. 113 (1991) 1455.
[1] (a) See for example: A. Togni, R.L. Halterman (Eds.), Metall-
cocenes: Synthesis, Reactivity, and Applications, vols. 1 and 2,
Wiley-VCH, Weinheim, 1998;
[8] (a) Y. Zhang, D.A. Kissounko, J.C. Fettinger, L.R. Sita,
Organometallics 22 (2003) 21;
(b) I. Marek (Ed.), Titanium and Zirconium in Organic Synthesis,
Wiley-VCH, Weinheim, 2002.
(b) J.A.R. Schmidt, J. Arnold, J. Chem. Soc., Dalton Trans (2002)
3454;
[2] (a) See for example: R.A. Himes, P.E. Fanwick, I.P. Rothwell,
Chem. Commun. (2003) 18;
(c) J.R. Hagadorn, J. Arnold, Organometallics 17 (1998) 1355;
(d) J.R. Hagadorn, J. Arnold, J. Chem. Soc., Dalton Trans. (1997)
3087;
(b) T. Hanazawa, K. Sasaki, Y. Takayama, F. Sato, J. Org. Chem.
68 (2003) 4980;
(e) J.C. Flores, J.C.W. Chien, M.D. Rausch, Organometallics 14
(1995) 1827.
(c) M.C.W. Chan, K.-H. Tam, Y.-L. Pui, N. Zhu, J. Chem. Soc.,
Dalton Trans. 16 (2002) 3085;
[9] (a) A.J. Ashe III, J.W. Kampf, M.W. Schiesher, Organometallics
22 (2003) 203;
(d) L.G. Quan, J.K. Cha, Tetrahedron Lett. 42 (2001) 8567;
(e) M.G. Thorn, J.S. Vilardo, P.E. Fanwick, I.P. Rothwell, J.
Chem. Soc., Chem. Commun. (1998) 2127;
(b) A.J. Ashe III, S. Al-Ahmad, J.W. Kampf, Organometallics 18
(1999) 4234;
(f) H. Mack, M.S. Eisen, J. Chem. Soc., Dalton Trans. (1998) 917;
(g) E.S. Johnson, G.J. Balaich, P.E. Fanwick, I.P. Rothwell, J.
Am. Chem. Soc. 119 (1997) 11086;
(c) Z.J.A. Komon, G.C. Bazan, Spec. Publ., Royal Soc. Chem.
253 (2000) 3;
(d) G.C. Bazan, G. Rodriguez, A.J. Ashe III, S. Al-Ahmad, C.
Muller, J. Am. Chem. Soc. 118 (1996) 2291.
[10] (a) D. Owiny, S. Parkin, F.T. Ladipo, J. Organomet. Chem.
(2003) 678, 134;
(h) A. van der Linden, C.J. Schaverien, N. Meijboom, C. Ganter,
A.G. Orpen, J. Am. Chem. Soc. 117 (1995) 3008;
(i) G.J. Balaich, J.E. Hill, S.A. Waratuke, P.E. Fanwick, I.P.
Rothwell, Organometallics 14 (1995) 656;
(b) E.B. Tjaden, D.C. Sewnson, R.F. Jordan, J.L. Petersen,
Organometallics 14 (1995) 371;
(j) S. Fokken, T.P. Spaniol, H.-C. Kang, W. Massa, J. Okuda,
Organometallics 15 (1996) 5069;
(c) E. Solari, C. Floriani, A. Chiesi-Villa, C. Rizzoli, J. Chem.
Soc., Dalton Trans. (1992) 367.
(k) G. Balaich, P.E. Fanwick, I.P. Rothwell, Organometallics 13
(1994) 4117.
[11] (a) See for example: S. Fantacci, F. De Angelis, A. Sgamellotti, N.
Re, Organometallics 20 (2001) 4031;
[3] (a) See for example: A. Shafir, M.P. Power, G.D. Whitener, J.
Arnold, Organometallics 20 (2001) 1365;
(b) D.R. Evans, M. Huang, J.C. Fettinger, T.L. Williams, Inorg.
Chem. 41 (2002) 5986;
(b) C. Lorber, B. Donnadieu, R. Choukroun, Organometallics 19
(2000) 1963;
(c) F.A. Cotton, E.V. Dikarev, C.A. Murillo, M.A. Petrukhina,
Inorg. Chim. Acta 332 (2002) 41;
(c) R. Baumann, R. Stumpf, W.M. Davis, L.-C. Liang, R.R.
Schrock, J. Am. Chem. Soc. 121 (1999) 7822;
(d) B. Tsuie, D.C. Swenson, R.F. Jordan, Organometallics 16
(1997) 1392;
(d) F. Corazza, C. Floriani, W. Lesueur, A. Chiesi-Villa, C.
Guastini, J. Chem. Soc., Chem. Commun. (1990) 1083;
(e) F. Corazza, C. Floriani, A. Chiesi-Villa, C. Guastini, J. Chem.
Soc., Chem. Commun. (1990) 640;
(e) T.H. Warren, R.R. Schrock, W.M. Davis, Organometallics 17
(1998) 308;
(f) B. Castellano, A. Zanotti-Gerosa, E. Solari, C. Floriani,
Organometallics 15 (1996) 4894;
(f) F. Guerin, D.H. McConville, N.C. Payne, Organometallics 15
(1996) 5085;
(g) L. Giannini, A. Caselli, E. Solari, C. Floriani, A. Chiesi-Villa,
C. Rizzoli, N. Re, A. Sgamellotti, J. Am. Chem. Soc. 119 (1997)
9198;
(g) A.D. Horton, J. de With, A.J. van der Linden, H. van de Weg,
Organometallics 15 (1996) 2672;
(h) J.D. Scollard, D.H. McConville, N.C. Payne, J.J. Vittal,
Macromolecules 29 (1996) 5241;
(h) L. Giannini, A. Caselli, E. Solari, C. Floriani, A. Chiesi-Villa,

514
F.T. Ladipo et al. / Journal of Organometallic Chemistry 689 (2004) 502–514
C. Rizzoli, N. Re, A. Sgamellotti, J. Am. Chem. Soc. 119 (1997)
9709;
(c) R.D. Rieke, T.P. Burns, R.M. Wehmeyer, B.E. Kahn, in:
High-Energy Processes in Organometallic Chemistry, ACS Symp.
Ser., vol. 333, American Chemical Society, Washington, DC,
1987, p. 223.
(i) L. Giannini, E. Solari, A. Zanotti-Gerosa, C. Floriani, A.
Chiesi-Villa, C. Rizzoli, Angew. Chem. Int. Ed. Engl. 36 (1996)
85;
[22] M.J. McCormick, K.B. Moon, S.R. Jones, T.P. Hanusa, J. Chem.
Soc., Chem. Commun. (1990) 778.
(j) A. Zanotti-Gerosa, E. Solari, C. Floriani, A. Chiesi-Villa, C.
Rizzoli, J. Chem. Soc., Chem. Commun. (1997) 183;
(k) A. Caselli, L. Giannini, E. Solari, C. Floriani, N. Re, A.
Chiesi-Villa, C. Rizzoli, Organometallics 16 (1997) 5457;
(l) A. Zanotti-Gerosa, E. Solari, L. Giannini, C. Floriani, N. Re,
A. Chiesi-Villa, C. Rizzoli, Inorg. Chim. Acta 270 (1998) 298;
(m) M.M. Olmstead, G. Sigel, H. Hope, X. Xu, P.P. Power, J.
Am. Chem. Soc. 107 (1985) 8087;
[23] A. Furstner, H. Weidmann, J. Organomet. Chem. 354 (1988) 15.
[24] L.E. Aleandri, B. Bogdanovic, A. Gaidies, D.J. Jones, S. Liao, A.
Michalowicz, J. Roziere, A. Schott, J. Organomet. Chem. 459
(1993) 87.
[25] E. Neghishi, T. Takahashi, Bull. Chem. Soc. Jpn. 71 (1998)
755.
[26] J.J. Eisch, J.N. Gitua, P.O. Otieno, X. Shi, J. Organomet. Chem.
624 (2001) 229.
(n) X. Delaigue, M.W. Hosseini, E. Leize, S. Kieffer, A. van
Doersselaer, Tetrahedron Lett. 34 (1993) 7561;
(o) J.A. Acho, S.J. Lippard, Inorg. Chim. Acta 229 (1995) 5.
[27] F. Sato, H. Urabe, in: I. Marek (Ed.), Titanium and Zirconium in
Organic Synthesis, Wiley-VCH, Weinheim, 2002, p. 319.
[28] A reaction proceeding via a statistical distribution of the four
possible titanacyclopentadiene intermediates (A–D, below) with
identical rates would yield a 3:1 ratio of 1,2,4- and 1,3,5-
substitutional isomers. For relevant mechanistic discussion, see
Ref. [12b] and J.E. Hill, G. Balaich, P.E. Fanwick, I.P. Rothwell,
Organometallics 12 (1993) 2911.
[12] (a) O.V. Ozerov, F.T. Ladipo, N.P. Rath, J. Organomet. Chem.
586 (1999) 223;
(b) O.V. Ozerov, B.O. Patrick, F.T. Ladipo, J. Am. Chem. Soc.
121 (1999) 7941;
(c) O.V. Ozerov, B.O. Patrick, F.T. Ladipo, J. Am. Chem. Soc.
122 (2000) 6423;
(d) O.V. Ozerov, S. Parkin, C.P. Brock, F.T. Ladipo, Organo-
metallics 19 (2000) 4187;
(e) O.V. Ozerov, C.P. Brock, S. Carr, S. Parkin, F.T. Ladipo,
Organometallics 19 (2000) 5016;
exo-
face
endo-
face
endo-
face
exo-
face
Me
β
α
Ph
endo-
face
Me
exo-
face
exo-
face
endo-
face
Ph
β
α
Me
Me
β'
Ph
β
α
Me
Ph
β'
Me
β
α
Ph
Ph
β'
(f) J.V. Kingston, O.V. Ozerov, S. Parkin, C.P. Brock, F.T.
Ladipo, J. Am. Chem. Soc. 124 (2002) 12217;
β'
α'
Ph
α'
Ph
α'
Me
α'
Me
(g) J.V. Kingston, V. Sarveswaran, S. Parkin, F.T. Ladipo,
Organometallics 22 (2003) 136.
Ti
Ti
Ti
Ti
L2
L2
L2
L2
[13] M. Fan, H. Zhang, M. Lattman, Organometallics 15 (1996) 5216.
[14] H. Gunther, NMR Spectroscopy: An Introduction, Wiley, New
York, 1980, pp.77–86.
(a)
(b)
(c)
(d)
[29] The black mixture obtained on reaction of 1.20 g (1.27 mmol) of
(DPSC)TiCl2 (12) with 0.950 mg (2.26 mmol) of Mg* and 0.646
mL (5.16 mmol) of PhC B CMe in toluene/THF at room
temperature was concentrated to dryness and then the volatiles
were removed in vacuo. The remaining solids were triturated with
heptane, extracted with pentane until the washings were colorless
and then filtered. The pentane extract was concentrated and
the residue was treated with ꢀ5 mL of ether. Crystals of the
titanacyclopent-2-ene derivative 16 were obtained from the
resulting solution at )15 °C..
[15] C. Jaime, J. de Mendoza, P. Prados, P.M. Nieto, C. Sanchez, J.
Org. Chem. 56 (1991) 3372.
[16] O. Aleksiuk, F. Grynszpan, S.E. Biali, J. Incl. Phenom. 19 (1994)
237.
[17] We have previously observed changes in conformation for
proximally bridged calixarene compounds upon reaction with
TiCl4. For example, crystallographically-characterized (PhPC)H2
[12a] exists in the 1,2-alternate conformation but forms cone-
(PhPC)TiCl2 upon reaction with TiCl4. See Ref. [12a] for more
details as well as other examples..
[30] D.B. Millward, A.P. Cole, R.M. Waymouth, Organometallics 19
[18] (a) See for example: S.A. Waratuke, M.G. Thorn, P.E. Fanwick,
A.P. Rothwell, I.P. Rothwell, J. Am. Chem. Soc. 121 (1999) 9111;
(b) N. Kanehisa, Y. Kai, N. Kasai, H. Yasuda, Y. Nakayama, K.
Takei, A. Nakamura, Chem. Lett. (1990) 2167.
[19] (a) J.R. Hagadorn, J. Arnold, Angew. Chem. Int. Ed. Engl. 37
(1998) 1729;
(2000) 1870.
[31] Placement of the more bulky phenyl group at the a-position of
the titanacycle on the same side of the calixarene and of a
THF molecule oriented toward the calixarene cavity is unexpected
since unfavorable steric interactions with nearby aromatic
rings and the attached But groups should decrease the thermo-
dynamic stability and kinetic accessibility of 16. For example, in a
related tantalacyclopentadiene system, the thermodynamic stabil-
ity and kinetic accessibility of the a,a0 (or 2,5)-substituted
regioisomer is lost as steric congestion at the metal center
increases [32].
(b) F. Calderazzo, I. Ferri, G. Pampaloni, U. Englert, M.L.H.
Green, Organometallics 16 (1997) 3100;
(c) S. Troyanov, J. Organomet. Chem. 475 (1994) 139;
(d) S. Troyanov, J. Polacek, H. Antropiusova, K. Mach, J.
Organomet. Chem. 431 (1992) 317;
(e) U. Thewalt, F. Stollmaier, J. Organomet. Chem. 228 (1982)
149;
[32] D.P. Smith, J.R. Strickler, S.D. Gray, M.A. Bruck, R.S. Holmes,
D.E. Wigley, Organometallics 11 (1992) 1275.
(f) U. Thewalt, F. Osterle, J. Organomet. Chem. 172 (1979) 317;
(g) E.O. Fischer, F. Rohrschied, J. Organomet. Chem. 6 (1966) 53;
(h) F. Martin, F. Vohwinkel, Chem. Ber. 94 (1961) 2416.
[20] (a) B. Bogdanovic, S. Liao, M. Schwickardi, P. Sikorsky, B.
Spliethoff, Angew. Chem., Int. Ed. Engl. 19 (1980) 818;
(b) B. Bogdanovic, Acc. Chem. Res. 21 (1988) 261;
(c) W.M. Brooks, C.L. Raston, R.E. Sue, F.J. Lincoln, J.J.
McGinnity, Organometallics 10 (1991) 2098.
[33] D.D. Perrin, W.L.F. Armarego, Purification of Laboratory
Chemicals, Butterworth-Heinemann, Oxford, 1988.
[34] (a) C.D. Gutsche, L.-G. Lin, Tetrahedron 42 (1986) 1633;
(b) C.D. Gutsche, J.A. Levine, P.K. Sujeeth, J. Org. Chem. 50
(1985) 5802.
[35] (a) F. Hajek, E. Graf, M.W. Hosseini, Tetrahedron Lett. 37 (1996)
1409;
(b) M. Almi, A. Arduini, A. Casnati, A. Pochini, R. Ungaro,
Tetrahedron 45 (1989) 2177.
[36] H. Gilman, G.N.R. Smart, J. Org. Chem. 15 (1950) 720.
[21] (a) X. Wu, R.D. Rieke, J. Org. Chem. 60 (1995) 6658;
(b) M.V. Hanson, J.D. Brown, R.D. Rieke, Q.J. Niu, Tetrahedron
Lett. 35 (1994) 7205;