Synthesis, characterization, and reactivity of titanium(IV) complexes supported by proximally bridged p-tert-butylcalix[4]arene ligands

Article abstract of DOI:10.1016/S0022-328X(99)00279-X

Treatment of dilithium or dipotassium salt of p-tert-butylcalix[4]arene with ^tBuPCl₂ or PhPCl₂ produced 1,2-alternate phosphorus-bridged p-tert-butylcalix[4]arene derivatives (^tBuPC)H₂ (1) and (PhPC)H

Full text of DOI:10.1016/S0022-328X(99)00279-X

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 586 (1999) 223–233
Synthesis, characterization, and reactivity of titanium(IV)
complexes supported by proximally bridged
p-tert-butylcalix[4]arene ligands
Oleg V. Ozerov a, Nigam P. Rath b, Folami T. Ladipo a,*
a Department of Chemistry, Uni6ersity of Kentucky, Lexington, KY 40506-0055, USA
b Department of Chemistry, Uni6ersity of Missouri-St. Louis, 8001 Natural Bridge Road, St. Louis, MO 63121, USA
Received 23 April 1999
Abstract
Treatment of dilithium or dipotassium salt of p-tert-butylcalix[4]arene with tBuPCl2 or PhPCl2 produced 1,2-alternate
phosphorus-bridged p-tert-butylcalix[4]arene derivatives (tBuPC)H2 (1) and (PhPC)H2 (2), respectively. An X-ray diffraction study
of 2 showed that it exists in 1,2-alternate conformation. Reaction of 2 with sulfur gave (PhSPC)H2 (3), which exists in cone
conformation. Treatment of TiCl4 with 1–3 produced the corresponding dichlorides L2TiCl2 [L2=tBuPC (5); PhPC (6); and
PhSPC (7)]. Reaction of R2Mg·2THF (R=Me or CH2Ph) with (DMSC)TiCl2 (8) yielded (DMSC)TiMe2 (9) and
(DMSC)Ti(CH2Ph)2 (10), respectively. Cationic derivatives [(DMSC)Ti(NCCH3)Me2]BArF4 (11) and [(DMSC)Ti(NCCH3)
(CH2Ph)]BArF4 (12) were prepared from the respective reactions of 9 and 10 with [Ph3C]BArF4 [ArF=(CF3)2C6H3] in the presence
of CH3CN. Similarly,
9 and 10 reacted with [Ph3C]OTf (one equivalent) to yield [(DMSC)Ti(OTf)Me2] (13) and
[(DMSC)Ti(OTf)(CH2Ph)] (14), respectively. NMR data showed that the more exposed exo-alkyl was abstracted. Complexes 5–10
and 14 showed modest ethylene polymerization activities at 25°C with 500 molar equivalents of methylalumoxane (MAO) as
cocatalyst. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Aryloxide ligand; Calix[4]arene ligand; Olefin polymerization; Titanium(IV)
tion metals, tailoring of chemical reactivity remains
difficult. As part of a research program aimed at ex-
1. Introduction
ploring the influence of ancillary ligands on early tran-
Recently, there has been increased interest in the
sition metal-mediated organic transformations, we have
chemistry of homogeneous early transition metal com-
been investigating the potential of p-tert-butyl-
plexes supported by non-cyclopentadienyl ligands [1–
calix[4]arene derivatives as ancillary ligands in Group 4
19]. The expectation is that compounds with
metal chemistry [20]. Calix[4]arenes [21] usually adopt
complementary or enhanced reactivity in comparison
one of four main conformations in solution. The degree
with early transition metal metallocenes can be devel-
of steric shielding and electronic stabilization provided
oped. A number of ancillary ligand environments have
by an ancillary calix[4]arene ligand can be influenced by
been investigated in Group 4 metal chemistry including
the conformation it adopts. Recent reports by Floriani
chelating diamides [1], aryloxides [2], carboranes [3],
and co-workers described novel reactivities and bond-
amidinates [4], porphyrins [5], tetradentate Schiff bases
ing modes for a variety of organic fragments bonded to
[6], boratabenzenes [7], and calixarenes [8–19]. While
these studies have demonstrated the profound influence
of ancillary ligands on the chemical properties of transi-
Group 4–6 metal complexes of p-tert-butylcalix[4]arene
and its O-methylated derivatives in the cone conforma-
tion [8–16]. Our initial attraction to the calix[4]arene
ligand system was motivated by the possibility of ob-
taining a chelating bis(aryloxide) ligand from the 1,2-al-
ternate conformer of p-tert-butylcalix[4]arene and
* Corresponding author. Tel.: +1-606-2577084; fax: +1-606-
3231069.
E-mail address: fladipo@pop.uky.edu (F.T. Ladipo)
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00279-X

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O.V. Ozero6 et al. / Journal of Organometallic Chemistry 586 (1999) 223–233
utilizing the ligand to sterically define the reaction sites
at the metal center. When the 1,2-alternate conforma-
tion is secured by bridging proximal phenolic oxygen
atoms, a pair of bulky tBu groups and the attached pair
of phenyl rings essentially project over the two remain-
ing ‘unbridged’ phenolic oxygen atoms (Scheme 1).
Thus, when the ligand is coordinated via the two donor
oxygen atoms, it imposes this stereochemical environ-
ment at the metal center. In this paper, we report on
the synthesis of titanium(IV) complexes containing p-
tert-butylcalix[4]arene-derived chelating bis(aryloxide)
ligands. In addition, we report herein results of a
preliminary investigation of their catalytic reactivity
with alkenes.
from sodium benzophenone ketyl, methylene chloride-
d2, chloroform-d, acetonitrile-d3 from CaH2. All sol-
,
vents were stored in the glovebox over 4 A molecular
sieves that were dried in a vacuum oven at 125°C for at
least 48
h prior to use. Titanium(IV) chloride,
dichlorodimethylsilane, benzylmagnesium chloride,
methylmagnesium chloride, dimethylzinc, methyl-
lithium, triphenylmethyl chloride, silver triflate, sodium
tetrafluoroborate,
3,5-bis(trifluoromethyl)bromoben-
zene and Mg turnings were purchased from Aldrich
and were used as received. p-tert-Butylcalix[4]arene was
either purchased from Aldrich or synthesized by litera-
ture methods [22] and dried in a vacuum oven at 150°C
for 48 h. The following compounds were prepared by
literature methods: [Ph3C]OTf [23a], Na[B(3,5-(CF3)2-
C6H3)4] [23b,24,25], [Ph3C][B(3,5-(CF3)2-C6H3)4] [24],
and [(Et2O)2H][B(3,5-(CF3)2-C6H3)4] [25]. Ethylene used
in the polymerization experiments was purchased from
Aldrich (99.8% purity) and was further purified by
passage through consecutive columns packed with
nickel–copper–barium catalyst (purchased as the oxide
from BASF and reduced with H2/N2 mixture according
2. Experimental
2.1. General details
All experiments were performed under dry nitrogen
atmosphere using standard Schlenk techniques or in a
Vacuum Atmospheres glovebox. Toluene, ether, te-
trahydrofuran, and benzene were distilled twice from
sodium benzophenone ketyl. Pentane and hexane were
distilled twice from sodium benzophenone ketyl with
addition of 1 ml l−1 of tetraethyleneglycol dimethyl
ether as a solubilizing agent. Methylene chloride and
acetonitrile were distilled twice from CaH2. 1,4-Dioxane
and triethylamine were distilled from sodium. Deuter-
ated solvents were distilled as necessary; benzene-d6
,
to manufacturer’s instructions), and 4 A molecular
sieves (dried as described above). NMR spectra were
recorded on a Varian Gemini-200 or Varian VXR-400
1
spectrometer. H and 13C chemical shifts are reported
relative to residual solvent signal while the 19F-NMR
spectra were referenced externally to CFCl3. Mass spec-
tra were recorded at the mass spectroscopy center of
the University of Kentucky. Elemental analyses were
performed by E+R Microanalytical Laboratory,
Ithaca, NY.
2.2. Synthesis of calix[4]arene deri6ati6es 1–3
2.2.1. [(tBuPC)H2] (1)
A 50 ml Schlenk flask was charged with p-tert-
butylcalix[4]arene (1.948 g, 3.00 mmol), solid LDA
(0.642 g, 6.00 mmol) and toluene (30 ml) /THF (10 ml).
t
After stirring the suspension for 18 h, BuPCl2 (0.478 g,
3.00 mmol) was added and the reaction mixture was
stirred for 24 h. The mixture was filtered, the filtrate
was concentrated to dryness, and the resulting solids
were extracted with methylene chloride. After separat-
ing the extract by filtration, volatiles were removed in
vacuo. The residue was triturated with heptane and
washed with pentane (5 ml). The solid product was
dried under vacuum (0.830 g, 38%) and identified as 1
on the basis of the following data (1 was pure enough
to use for further reaction although acceptable micro-
1
analysis data could not be obtained): H-NMR (C6D6):
l 7.34 (d, 2H, J=2 Hz, arom. CH), 7.14 (d, 2H, arom.
CH), 7.11 (d, 2H, arom. CH), 6.84 (d, 2H, arom. CH),
5.97 (s, 2H, OH), 4.60 (dd, JHꢀH=13 Hz, JHꢀP=3 Hz,
1H, calixꢀCH2), 4.11 (d, J=13 Hz, 1H, calixꢀCH2),
4.08 (d, J=17 Hz, 2H, calixꢀCH2), 3.80 (d, J=17 Hz,
Scheme 1.

O.V. Ozero6 et al. / Journal of Organometallic Chemistry 586 (1999) 223–233
225
2H, calixꢀCH2), 3.22 (d, J=13 Hz, 1H, calixꢀCH2),
(C6D6): l 7.47–7.63 (m, 2H, PhP), 7.20 (br, 2H, arom.
CH), 6.67–6.80 (m, 3H, PhP), 7.11 (d, 2H, arom. CH),
6.99 (d, 2H, arom. CH), 6.66 (d, 2H, arom. CH), 6.38
(s, 2H, OH), 4.94 (d, J=14 Hz, 2H, calixꢀCH2), 4.47
(d, J=14 Hz, 1H, calixꢀCH2), 3.95 (d, J=14 Hz, 1H,
calixꢀCH2), 3.65 (d, J=14 Hz, 1H, calixꢀCH2), 3.60 (d,
J=14 Hz, 2H, calixꢀCH2), 2.91 (d, J=14 Hz, 1H,
calixꢀCH2), 1.20 (s, 18H, tBu), 1.08 (s, 18H, tBu).
13C-NMR (C6D6): l 150.75, 148.15 (d, J=6 Hz),
147.74, 143.37, 138.26, 135.48, 133.90 (d, J=2 Hz),
131.46 (br), 129.37 (br), 128.89 (d, J=1 Hz), 128.72,
128.50 (br), 126.62, 125.74, 37.53 (calixꢀCH2), 36.12
(calixꢀCH2), 33.98 (C(CH3)3), 33.94 (C(CH3)3), 33.08
(calixꢀCH2), 31.56 (C(CH3)3), 31.18 (C(CH3)3). 31P-
NMR (C6D6): l 75.2. Anal. Calc. for C50H59O4PS: C,
76.30; H, 7.56. Found: C, 76.32; H, 7.69. MS(EI): M+
(786).
t
3.18 (d, J=13 Hz, 1H, calixꢀCH2), 1.30 (s, 18H, Bu),
t
1.28 (s, 18H, Bu), 0.73 (d, J=12 Hz, 9H, PꢀC(CH3)3).
13C-NMR (C6D6): l 150.86, 150.35 (d, J=4 Hz),
147.43, 142.72, 137.29 (d, J=2 Hz), 131.47 (d, J=3
Hz), 130.86, 127.14, 126.21, 125.75, 125.19, 123.80 (d,
J=3 Hz), 37.44 (calixꢀCH2), 35.56 (d, J=17 Hz,
PꢀC(CH3)3), 34.22 (C(CH3)3), 34.11 (calixꢀCH2), 33.88
(C(CH3)3), 31.58 (C(CH3)3), 31.42 (C(CH3)3), 30.80
(calixꢀCH2), 23.86 (d, J=16 Hz, PꢀC(CH3)3). 31P-
NMR (C6D6): l 183.8. MS(EI): M+ (734).
2.2.2. [(PhPC)H2] (2)
p-tert-Butylcalix[4]arene (0.811 g, 1.25 mmol) in
toluene (40 ml) was treated with KH (0.100 g, 2.50
mmol) and the suspension was stirred for 24 h. THF (5
ml) was introduced by syringe, the mixture was stirred
for another 2 h, and PhPCl2 (0.224 g, 1.25 mmol) was
added to the mixture. After stirring for 48 h, the
mixture was filtered, and the volatiles were removed
from the filtrate under reduced pressure. The residue
was triturated with heptane and washed with pentane.
The product was dried under vacuum (0.590 g, 63%)
and identified as 2 on the basis of the following data.
1H-NMR (C6D6): l 7.39 (d, 2H, J=2 Hz, arom. CH),
6.90–7.25 (m, 9H, arom. CH), 7.11 (d, 2H, arom. CH),
6.80 (d, 2H, arom. CH), 5.73 (s, 2H, OH), 4.83 (dd,
2.3. Synthesis of titanium compounds 5–14
2.3.1. [(tBuPC)TiCl2] (5)
A solution of TiCl4 (0.214 g, 1.13 mmol) in pentane
(8 ml) was added dropwise to a suspension of 1 (0.829
g, 1.13 mmol) in ether (30 ml) at −40°C. The flask was
allowed to warm gradually up to room temperature and
left stirring for 24 h. Volatiles were removed in vacuo,
the residue was washed with pentane (3×10 ml), and
the product was dried under vacuum. The light-red
solid (0.860 g, 89%) was identified as 5 on the basis of
JHꢀH=12 Hz, JHꢀP=3 Hz, 1H, calixꢀCH2), 4.24 (d,
J=13 Hz, 1H, calixꢀCH2), 4.08 (d, J=17 Hz, 2H,
calixꢀCH2), 3.79 (d, J=17 Hz, 2H, calixꢀCH2), 3.30 (d,
J=12 Hz, 1H, calixꢀCH2), 3.27 (d, J=13 Hz, 1H,
calixꢀCH2), 1.28 (s, 18H, tBu), 1.21 (s, 18H, tBu).
13C-NMR (CDCl3): l 150.29 (d, J=4 Hz), 149.53 (d,
J=5 Hz), 147.88, 143.71, 137.02 (d, J=2 Hz), 130.82
(d, J=3 Hz), 130.32, 130.07 (br), 129.37, 128.89,
127.68 (d, J=6 Hz), 126.80, 125.75, 125.50, 125.31,
124.23 (d, J=3 Hz), 38.02 (calixꢀCH2), 34.27
(calixꢀCH2), 33.98 (C(CH3)3), 33.73 (C(CH3)3), 31.40
(C(CH3)3), 31.31 (C(CH3)3), 30.74 (calixꢀCH2). 31P-
NMR (C6D6): l 165.2. Anal. Calc. for C50H59O4P: C,
79.54; H, 7.88. Found: C, 79.67; H, 7.83. MS(EI): M+
(754).
1
the following data. H-NMR (C6D6): l 7.22 (d, 2H,
J=2 Hz, arom. CH), 7.11 (d, 2H, arom. CH), 7.01 (d,
2H, arom. CH), 6.83 (d, 2H, arom. CH), 4.69 (dd,
J=14 Hz, J=1 Hz, 1H, calixꢀCH2), 4.43 (d, J=14
Hz, 1H, calixꢀCH2), 3.76 (s, 4H, calixꢀCH2), 3.24 (d,
J=14 Hz, 1H, calixꢀCH2), 3.21 (d, J=14 Hz, 1H,
t
t
calixꢀCH2), 1.38 (s, 18H, Bu), 1.21 (s, 18H, Bu), 0.62
(d, J=11.5 Hz, 9H, PꢀC(CH3)3). 13C-NMR (C6D6=
THF): l 163.61, 149.54, 146.39, 145.28, 139.91, 137.45,
131.46, 127.22 (br), 126.13, 125.38, 125.15, 125.15,
40.58
(calixꢀCH2),
37.50
(calixꢀCH2),
34.88
(calixꢀCH2), 35.63 (d, J=18 Hz, PꢀC(CH3)3), 34.15
(C(CH3)3), 33.92 (C(CH3)3), 31.62 (C(CH3)3), 31.32
(C(CH3)3), 24.66(d, J=16 Hz, PꢀC(CH3)3). 31P-NMR
2.2.3. [(PhSPC)H2] (3)
(C6D6=THF):
l
179.4.
Anal.
Calc.
for
A 25 ml reaction vessel equipped with a Teflon
stopcock was charged with 2 (1.000 g, 1.32 mmol),
sulfur (0.047 g, 1.47 mmol), and 1,4-dioxane (15 ml).
The vessel was closed and heated at 60–70°C for 18 h.
After cooling to ambient temperature, the precipitate
was filtered off, and the filtrate was concentrated under
reduced pressure to give an oily residue. The residue
was triturated with heptane, extracted with pentane (10
ml) and quickly filtered. The pentane solution was
cooled at −30°C for 18 h; the precipitate was col-
lected, dried under vacuum (0.760 g, 73%) and iden-
C48H61Cl2O4PTi: C, 67.68; H, 7.22; Cl, 8.32. Found: C,
67.29; H, 7.14; Cl, 8.21. MS(EI): M+ (850).
2.3.2. [(PhPC)TiCl2] (6)
A solution of TiCl4 (0.128 g, 0.67 mmol) in pentane
(5 ml) was added dropwise to a suspension of 2 (0.507
g, 0.67 mmol) in ether (20 ml) at −78°C. The flask was
allowed to warm gradually up to room temperature and
left stirring for 24 h. Volatiles were removed in vacuo,
the residue was washed with pentane (3×5 ml), and
the product was dried under vacuum (0.550 g, 87%). An
analytically pure sample was obtained as a CH3CN
1
tified as 3 on the basis of the following data. H-NMR

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O.V. Ozero6 et al. / Journal of Organometallic Chemistry 586 (1999) 223–233
2.3.4. [(DMSC)TiMe2] (9)
adduct by recrystallization from CH3CN/CH2Cl2. 6 was
identified on the basis of the following data: H-NMR
1
Solid Me2Mg·2THF (0.113 g, 0.57 mmol) was added
to a suspension of (DMSC)TiCl2 (8) [20] (0.469 g,
0.57mmol) in toluene (20 ml) and 1,4-dioxane (2 ml).
After stirring for 2.5 h, the suspension was filtered
through Celite, and volatiles were removed from the
filtrate in vacuo. The solid residue was treated with
pentane (15 ml), stirred for 15 min and cooled at −20°C
for 1 h. The precipitate was collected by filtration and
washed with pentane (2×5 ml). Toluene (7 ml) and
pentane (20 ml) were introduced and the suspension was
kept at −20°C overnight. After filtration, the pale-yellow
precipitate was dried under vacuum. The product (0.330
g, 74%) was identified as 9 on the basis of the following
data. 1H-NMR (C6D6): l 7.34 (d, J=2.5 Hz, 2H, arom.
CH), 7.21 (d, J=2.5 Hz, 2H, arom. CH), 7.07 (d, 4H,
d=2.5 Hz, arom. CH), 4.44 (d, J=14.3 Hz, 1H,
calixꢀCH2), 4.32 (d, J=16.5 Hz, 2H, calixꢀCH2), 4.04 (d,
J=16.5 Hz, 2H, calixꢀCH2), 3.31 (d, J=14 Hz, 1H,
calixꢀCH2), 3.29 (d, J=14.5 Hz, 1H, calixꢀCH2), 3.20 (d,
(C6D6): l 7.86–8.00 (br m, 3H, PhꢀP), 7.24 (d, 2H, J=2
Hz, arom. CH), 7.04 (d, 2H, arom. CH), 6.99 (d, 2H,
arom. CH), 6.82–6.94 (m, 2H, PhꢀP), 6.66 (d, 2H, arom.
CH), 6.38 (d, J=13 Hz, 1H, calixꢀCH2), 5.33 (d, J=13
Hz, 2H, calixꢀCH2), 3.71 (d, J=13 Hz, 1H, calixꢀCH2),
3.56 (d, J=13 Hz, 2H, calixꢀCH2), 3.41 (d, J=13 Hz,
1H, calixꢀCH2), 2.97 (d, J=13 Hz, 1H, calixꢀCH2), 1.10
(s, 18H, Bu), 1.00 (s, 18H, Bu), 0.65 (3H, CH3CN).
13C-NMR (C6D6): l 161.69, 148.08, 146.66 (d, J=18 Hz),
145.20, 141.47, 134.76 (d, J=4 Hz), 134.33, 132.10,
131.01 (d, J=12 Hz), 128.94 (d, J=2 Hz), 128.30, 126.87,
126.38, 125.36 (br), 118.18 (CH3CN), 36.76 (calixꢀCH2),
36.00 (calixꢀCH2), 34.19 (C(CH3)3), 34.14 (C(CH3)3),
33.00 (calixꢀCH2), 31.30 (C(CH3)3), 31.25 (C(CH3)3),
0.72 (CH3CN). 31P-NMR (C6D6): l 124.0. Anal. Calc. for
(6 · CH3CN) C52H60Cl2NO4PTi: C, 68.42; H, 6.63; Cl,
7.77; N, 1.53. Found: C, 68.81; H, 7.28; Cl, 7.32; N, 1.08.
t
t
t
2.3.3. [(PhSPC)TiCl2] (7)
14 Hz, 1H, calixꢀCH2), 1.35 (s, 18H, Bu), 1.31 (s, 18H,
A solution of TiCl4 (0.170 g, 0.89 mmol) in pentane
(5 ml) was added dropwise to a suspension of 3 (0.700
g, 0.89 mmol) in ether (20 ml) at −78°C. The flask was
allowed to warm gradually up to room temperature and
left stirring for 24 h. Volatiles were removed in vacuo,
the residue was washed with pentane (3×10 ml) and the
product was dried under vacuum. The light-brown solid
(0.710 g, 88%) was identified as 7 on the basis of the
following data. NMR data established that 7 exists as a
3.5:1 mixture of 1,2-alternate:cone isomers at room
temperature: 1H-NMR (1,2-alternate, 7a) (C6D6): l 7.34–
7.48 (m, 2H, PhꢀP), 7.22 (m, 4H, arom. CH), 7.11 (d, 2H,
arom. CH), 6.91 (d, 2H, arom. CH), 6.66–6.74 (m, 3H,
PhꢀP), 4.61 (d, J=14 Hz, 1H, calixꢀCH2), 4.20 (d, J=18
Hz, 2H, calixꢀCH2), 4.09 (d, J=14 Hz, 1H, calixꢀCH2),
4.05 (d, J=18 Hz, 2H, calixꢀCH2), 3.44 (d, J=14 Hz,
1H, calixꢀCH2), 3.06 (d, J=14 Hz, 1H, calixꢀCH2), 1.32
tBu), 1.16 (s, 3H, exo-TiCH3), 0.32 (s, 3H, exo-SiCH3),
0.11 (s, 3H, endo-TiCH3), −1.45 (s, 3H, endo-SiCH3).
13C-NMR (C6D6): l 158.44, 149.49, 144.60, 144.12,
134.02, 130.38, 129.27, 128.29, 127.10, 126.32, 125.22,
64.26 (exo-TiCH3), 53.13 (endo-SiCH3), 40.58
(calixꢀCH2), 36.06 (calixꢀCH2), 35.75 (calixꢀCH2), 34.06
(C(CH3)3), 34.00 (C(CH3)3), 31.62 (C(CH3)3), 4.18 (exo-
SiCH3), −2.67 (endo-SiCH3) Anal. Calc. for
C48H64O4SiTi: C, 73.82; H, 8.26. Found: C, 73.79; H, 8.22.
2.3.5. [(DMSC)Ti(CH2Ph)2] (10)
Solid (PhCH2)2Mg·2THF (1.196 g, 3.40 mmol) was
added to a suspension of (DMSC)TiCl2 (8) [20] (2.808 g,
3.40 mmol) in ether (100 ml). After stirring for 1 h, the
suspension was filtered through Celite, and volatiles were
removed from the filtrate in vacuo. The light-orange
residue was washed with pentane (5×5ml) and dried
under vacuum. The product (2.840 g, 89%) was identified
as 10 on the basis of the following data. 1H-NMR
(CD2Cl2): l 6.85–7.30 (several multiplets, 8H, PhCH2),
7.23 (d, J=2 Hz, 2H, arom. CH), 7.14 (d, J=2 Hz,
2H, arom. CH), 7.01 (d, 2H, d=2 Hz, arom. CH),
6.96 (d, 2H, J=2 Hz, arom. CH), 6.55 (d, J=8 Hz, 2H,
o-CH of endo-PhCH2), 4.42 (d, J=14 Hz, 1H,
calixꢀCH2), 4.24 (d, J=16.5 Hz, 2H, calixꢀCH2), 3.97
(d, J=16.5 Hz, 2H, calixꢀCH2), 3.36 (d, J=14 Hz,
1H, calixꢀCH2), 3.08 (d, J=14.5 Hz, 1H, calixꢀCH2),
2.97 (d, J=14.5 Hz, 1H, calixꢀCH2), 2.11 (s, 2H,
t
t
(s, 18H, Bu), 1.25 (s, 18H, Bu). 1H-NMR (cone, 7b)
(C6D6): l 7.24–7.38 (m, 2H, PhꢀP), 7.12 (d, 2H, arom.
CH), 6.92 (d, 2H, arom. CH), 6.81 (d, 2H, arom. CH),
6.64–6.77 (m, 3H, PhꢀP), 6.52 (d, 2H, arom. CH), 5.88
(d, J=15 Hz, 1H, calixꢀCH2), 5.06 (d, J=14 Hz, 2H,
calixꢀCH2), 3.65 (d, J=16 Hz, 1H, calixꢀCH2), 3.37 (d,
J=14 Hz, 2H, calixꢀCH2), 3.33 (d, J=15 Hz, 1H,
calixꢀCH2), 2.86 (d, J=16 Hz, 1H, calixꢀCH2), 1.09 (s,
t
t
18H, Bu), 0.97 (s, 18H, Bu). 13C-NMR (C6D6, 75 °C)
(1,2-alternate, 7a): l 164.21, 148.50, 148.33, 138.15,
130.69, 130.54, 130.48, 129.41 (d), 128.33 (br), 128.28,
126.85, 126.16, 125.74, 124, 31, 39.04 (calixꢀCH2), 38.51
(calixꢀCH2), 36.43 (calixꢀCH2), 34.51 (C(CH3)3), 34.32
(C(CH3)3), 31.59 (C(CH3)3), 31.47 (C(CH3)3). 31P-NMR
(C6D6): l 69.0 (1,2-alternate, 7a); 74.2 (cone, 7b). Anal.
Calc. for C50H57Cl2O4PSTi: C, 66.44; H, 6.36; Cl, 7.84.
Found: C, 66.12; H, 6.44; Cl, 7.99. MS(EI): M+ (902).
t
t
exo-TiCH2Ph) 1.28 (s, 18H, Bu), 1.20 (s, 18H, Bu),
0.92 (s, 2H, endo-TiCH2Ph), 0.27 (s, 3H, exo-SiCH3),
−1.72 (s, 3H, endo-SiCH3). 13C-NMR (CD2Cl2): l
159.41, 149.58, 147.48, 144.95, 144.22, 142.66, 134.48,
130.30, 129.73, 129.54, 129.41, 128.39, 127.31, 126.88,
126.68, 126.55, 126.48, 125.39, 124.52, 122.74, 86.83

O.V. Ozero6 et al. / Journal of Organometallic Chemistry 586 (1999) 223–233
227
(exo-TiCH2Ph),
80.65
(endo-TiCH2Ph),
40.25
34.60 (C(CH3)3), 34.20 (C(CH3)3), 31.52 (C(CH3)3),
31.49 (C(CH3)3), 4.51 (exo-SiCH3), 3.49 (NCCH3),
−2.66 (endo-SiCH3). 19F-NMR (CDCl3): l −63.1.
Anal. Calc. for C87H80BF24NO4SiTi: C, 59.84; H, 4.62;
N, 0.80. Found: C, 59.61; H, 4.66; N, 1.02 (by NMR,
contains ca. 1.2 CH3CN per molecular unit).
(calixꢀCH2), 36.43 (calixꢀCH2), 35.15 (calixꢀCH2),
34.31 (C(CH3)3), 34.13 (C(CH3)3), 31.63 (C(CH3)3),
31.54 (C(CH3)3), 3.98 (exo-SiCH3), −2.72 (endo-
SiCH3). Anal. Calc. for C60H72O4SiTi: C, 77.22; H,
7.78. Found: C, 76.98; H, 7.78.
2.3.6. [(DMSC)Ti(Me)(NCCH3)]BArF4 (11)
2.3.8. [(DMSC)Ti(Me)(OTf)] (13)
Compound 9 (7.8 mg, 10 mmol) and [Ph3C]BAr4F
(11.1 mg, 10 mmol) were co-dissolved in CD2Cl2 in
presence of an excess of CH3CN; resulting in immediate
formation of a red solution. Numerous attempts to
isolate the product were unsuccessful due to decomposi-
tion upon crystallization and exposure to reduced pres-
sure. The product was therefore characterized in
solution in the presence of the by-product (Ph3CCH3)
as follows. 1H-NMR (CD2Cl2): l 7.72 (o-ArF), 7.56
(p-ArF), 7.00–7.30 (m, 21H, (C6H5)3C and calix. arom.
CH), 6.89 (d, J=2.5 Hz, 2H, calix. arom. CH), 4.43 (d,
J=14.5 Hz, 1H, calixꢀCH2), 4.20 (d, J=16.5 Hz, 2H,
calixꢀCH2), 3.96 (d, J=16.5 Hz, 2H, calixꢀCH2), 3.77
(d, J=13 Hz, 1H, calixꢀCH2), 3.35 (d, J=14.5 Hz,
1H, calixꢀCH2), 3.18 (d, J=13 Hz, 1H, calixꢀCH2),
2.17 (Ph3CCH3), 1.97 (s, 3H, NCCH3), 1.28 (s, 18H,
tBu), 1.22 (s, 18H, tBu), 0.35 (s, 3H, exo-SiCH3),
−0.37 (TiCH3), −1.57 (s, 3H, endo-SiCH3).
To a solution of 9 (0.391 g, 0.500 mmol) in CH2Cl2
(15 ml) was added [Ph3C][OTf] (0.196 g, 0.500 mmol).
A color change, from pale-yellow to brown, occurred
immediately. After stirring the mixture for 1 h, volatiles
were removed in vacuo. The orange–yellow solid ob-
tained was triturated with heptane (5 ml), washed on a
fritted funnel with pentane (4×5 ml) and dried in
vacuo. The product (0.370 g, 81%) was identified as 13
on the basis of the following data: 1H-NMR (CDCl3): l
7.09 (d, J=2.5 Hz, 2H, arom. CH), 6.98 (d, J=2.5 Hz,
2H, arom. CH), 6.91 (d, J=2.5 Hz, 2H, arom. CH),
6.89 (d, J=2.5 Hz, 2H, arom. CH), 4.42 (d, J=14 Hz,
1H, calixꢀCH2), 4.03 (d, AB, J=17 Hz, 2H,
calixꢀCH2), 3.97 (d, AB, J=17 Hz, 2H, calixꢀCH2),
3.37 (d, J=14 Hz, 1H, calixꢀCH2), 3.10 (d, J=14 Hz,
1H, calixꢀCH2), 2.09 (br d, J=14 Hz, 1H, calixꢀCH2),
1.25 (s, 18H, Bu), 1.17 (s, 18H, Bu), 0.37 (s, 3H,
exo-SiCH3), 0.12 (s, 3H, TiCH3), −1.61 (s, 3H, endo-
SiCH3). 13C-NMR (CDCl3+THF): l 159.84, 149.77,
145.18, 144.01, 137.02, 130.08, 130.02, 126.93, 126.58,
126.21, 125.93, 124.95, 80.34 (TiCH3), 40.71
(calixꢀCH2), 37.41 (s, calixꢀCH2), 35.90 (s, calixꢀCH2),
34.39 (C(CH3)3), 34.13 (C(CH3)3), 31.60 (C(CH3)3),
31.58 (C(CH3)3), 4.61 (exo-SiCH3), −2.68 (endo-
SiCH3). Anal. Calc. for C48H61F3O7SSiTi: C, 63.01; H,
6.72; Cl, 0.00. Found: C, 62.78; H, 7.00; Cl, 0.00.
t
t
2.3.7. [(DMSC)Ti(CH2Ph)(NCCH3)]BArF4 (12)
Compound 10 (0.117 g, 125 mmol) was treated with
CH3CN (60 mg, 1.5 mmol) in CH2Cl2 (4 ml), followed
with [Ph3C][BArF4] (0.138 g, 125 mmol). After stirring
the mixture for 10 min, most of the CH2Cl2 was re-
moved in vacuo. The dark-red oily residue was tritu-
rated with 1:1 toluene–pentane (3 ml), washed with
pentane (5×1 ml), and dried under vacuum; high
solubility of the product in pentane resulted in substan-
tial loss of product. The product (0.085g, 40%) was
identified as 12 on the basis of the following data.
1H-NMR (CD2Cl2) l: 7.77 (o-ArF), 7.60 (p-ArF), 7.30–
7.55 (m, 3H, m-,p-C6H5CH2), 7.25 (d, J=2.5 Hz, 2H,
calix. arom. CH), 7.21 (d, J=2.5 Hz, 2H, calix. arom.
CH), 7.13 (d, J=2.5 Hz, 2H, calix. arom. CH), 7.08 (d,
J=2.5 Hz, 2H, calix. arom. CH), 4.53 (d, J=14.5 Hz,
1H, calixꢀCH2), 4.22 (d, J=17 Hz, 2H, calixꢀCH2),
4.11 (d, J=17 Hz, 2H, calixꢀCH2), 3.51 (d, J=14.5
Hz, 1H, calixꢀCH2), 3.41 (d, J=14 Hz, 1H,
calixꢀCH2), 2.83 (d, J=14 Hz, 1H, calixꢀCH2), 2.24 (s,
2.3.9. Synthesis of [(DMSC)Ti(CH2Ph)(OTf)] (14)
To a solution of 10 (0.410 g, 0.440 mmol) in a 1:1
mixture of toluene/CH2Cl2 (15 ml) was added
[Ph3C][OTf] (0.167 g, 0.440 mmol). A minor amount of
insolubles was filtered off. After stirring for 1 h, the
solution was concentrated almost to dryness under
reduced pressure. The brownish solid residue was
stirred in pentane (5 ml) for 3 min, filtered, and washed
on a fritted funnel with pentane (2×5 ml). The product
(0.160 g, 37%) was dried under vacuum (while the
1
reaction is quantitative by H-NMR, 14 was isolated in
low yield because its solubility in hydrocarbon solvents
is comparable to that of the by-product, Ph3CCH2Ph).
14 was identified on the basis of the following data.
1H-NMR (CD2Cl2): l 7.0–7.25 (m, 8H), 6.82–6.92 (m,
3H), 6.75 (d, J=7.5 Hz, 2H, o-C6H5CH2), 4.41 (d,
J=15Hz, 1H, calixꢀCH2), 4.20 (d, AB, J=17 Hz, 2H,
calixꢀCH2), 3.98 (d, AB, J=17 Hz, 2H, calixꢀCH2),
3.37 (d, J=15 Hz, 1H, calixꢀCH2), 3.06 (br d, J=14
Hz, 1H, calixꢀCH2), 2.35 (br d, J=14 Hz, 1H,
t
t
3H, NCCH3), 1.32 (s, 18H, Bu), 1.21 (s, 18H, Bu),
1.18 (s, 2H, CH2Ph), 0.47 (s, 3H, exo-SiCH3), −1.50
(s, 3H, endo-SiCH3). 13C-NMR (CD2Cl2): l 162.34 (q,
J=50 Hz, ipso-ArF), 161.26, 150.00, 147.15, 144.40,
138.59, 136.70, 135.34 (br s, o-ArF), 131.32, 130.84,
130.38, 130.26, 129.76, 129.13 (br s, m-ArF), 128.08,
127.18, 127.03, 126.77, 125.57, 125.13 (q, J=272 Hz,
CF3), 118.00 (br s, p-ArF), 100.26 (PhCH2), 40.74
(calixꢀCH2), 36.54 (calixꢀCH2), 36.17 (calixꢀCH2),
t
calixꢀCH2), 1.32 (s, 18H, Bu), 1.17 (PhCH2), 1.10 (s,

228
O.V. Ozero6 et al. / Journal of Organometallic Chemistry 586 (1999) 223–233
t
18H, Bu), 0.35 (s, 3H, exo-SiCH3), −1.54 (s, 3H,
endo-SiCH3). 13C-NMR (CDCl3): l 161.10, 149.77,
145.50, 144.24, 137.82, 136.89, 132.88, 129.92, 129.26,
129.22, 127.30, 126.72, 126.49, 125.26, 103.11 (PhCH2),
40.16 (calixꢀCH2), 36.42 (br s, calixꢀCH2), 34.44
(C(CH3)3), 34.04 (C(CH3)3), 31.62 (C(CH3)3), 31.39
(C(CH3)3), 4.12 (exo-SiCH3), −2.58 (endo-SiCH3).
19F-NMR (CDCl3): l −69.3. 19F-NMR (CDCl3+ex-
data did not show any decay. Final cell constants were
determined by global refinement of xyz centroids of
8192 reflections. Structure solution and refinement were
carried out using the SHELXTL-PLUS software package
(Sheldrick, Bruker Analytical X-Ray Division,
Madison, WI, 1997). The structure was solved by direct
methods. Full matrix least-squares refinement was car-
ried out by minimizing S w(F2o−Fc2)2. The non-hydro-
gen atoms were refined anisotropically to convergence.
All hydrogen atoms were treated using appropriate
riding models (AFIX m3).
cess of CH3CN):
(14 · toluene) C61H73F3O7SSiTi: C, 67.63; H, 6.79; Cl,
0.00. Found: C, 67.45; H, 6.96; Cl, 0.00.
l
−78.8. Anal. Calc. for
2.4. Ethylene polymerization
3. Results and discussion
The catalyst precursor (20 mmol of Ti) was dissolved
in toluene (40 ml) and treated with the excess of MAO
(Al/Ti ratio 500/1). This solution was placed into a 100
ml Schlenk flask, the nitrogen atmosphere was replaced
with ethylene, and ethylene pressure of 1 atm was
maintained therefrom by slowly bubbling ethylene
through the solution, controlling the pressure with the
bubbler at the outlet. Polymerizations were quenched
with MeOH (10 ml) and then 1 M HCl (30 ml), and the
resulting suspension was vigorously stirred until both
layers were colorless and clearly separated.
Polyethylene was filtered off, washed with MeOH, 1 M
HCl, acetone–aqueous HCl mixture, distilled water and
acetone and then dried at 70°C for 48 h.
3.1. Ligand synthesis
Reaction of dilithium or dipotassium salt of p-tert-
butylcalix[4]arene (generated in situ) with BuPCl2 or
t
PhPCl2 proceeded at room temperature to yield phos-
phorus-bridged p-tert-butylcalix[4]arene compounds
(tBuPC)H2 (1) and (PhPC)H2 (2), respectively (Scheme
1). The reaction of 2 with sulfur (1.1 equivalent) in
1,4-dioxane at 60–70°C for 18 h produced PhSP-
bridged p-tert-butylcalix[4]arene (PhSPC)H2 (3) in
good yield (Scheme 1); no reaction occurred between 1
and sulfur under comparable conditions. The formula-
tions given for 1–3 were confirmed by microanalysis
and/or mass spectrometry. Their molecular structures
were established by NMR data, and X-ray crystallogra-
phy for 2. In this regard, the bridging methylenes and
2.5. Crystal data
t
(
C50H59O4P, triclinic, space group=P1, a=
the methyls from the Bu groups are useful probes for
,
,
,
13.4485(2) A, b=13.5672(2) A, c=15.1013(2) A, h=
deducing symmetry properties of p-tert-butyl-
calix[4]arenes [12,26]. Both 1 and 2 possess Cs symme-
try and adopt the 1,2-alternate conformation in
66.236° (1), i=82.248° (1), k=62.344° (1), U=2229
A , Z=2, 7845 unique data (35683 measured, 1.48°5
3
,
1
2q525.00°, Rint=0.10), 532 parameters, R1=0.0650,
wR2 (all data)=0.1899. Single crystals suitable for X-
ray diffaction were obtained by crystallization from
toluene. A crystal with the dimensions 0.31×0.20×
0.18 mm was mounted on a glass fiber in random
orientation. Preliminary examination and data collec-
tion was performed using a Bruker SMART CCD X-ray
diffractometer equipped with graphite monochromated
Mo–Ka radiation (u= 0.71073 A). Preliminary unit
cell constants were determined with a set of 45 narrow
frames (0.3° in ‚) scans. A total of 4028 frames of
intensity data were collected with a frame width of 0.3°
in ‚ and counting time of 15 s frame−1 at a crystal to
detector distance of 4.9 cm. The double-pass method of
scanning was used to exclude any noise. The collected
frames were integrated using orientation matrix deter-
mined from the narrow frame scans. The SMART soft-
ware package (Bruker Analytical X-Ray, Madison, WI,
1997) was used for data collection and the SAINT pack-
age (Bruker Analytical X-Ray, Madison, WI, 1997) was
used for frame integration. Analysis of the integrated
solution. Their H-NMR spectra show two singlets for
t
the Bu groups, and two pairs of doublets and an AB
system for the bridging methylene protons. The AB
system integrates as four protons and represents the
methylene groups not included in the mirror plane. In
their 13C-NMR spectra, three resonances are present at
l 30.80, 34.11, and 37.44 (doubly intense) (1) and l
30.74, 34.27, and 38.02 (doubly intense) (2) for the
bridging methylene carbons. These data are consistent
with 13C-NMR data for several calix[4]arenes reported
by de Mendoza and co-workers [26] which showed that

O.V. Ozero6 et al. / Journal of Organometallic Chemistry 586 (1999) 223–233
229
and the phenyl group points away from the ‘unbridged’
oxygen atoms. Thus, the lone pair on phosphorus
points toward the center of the cavity. Selected bond
distances and angles are listed in Table 1. The PꢀC and
PꢀO bond lengths are comparable to those reported for
other phosphorus-bridged calix[4]arenes [28]. The
C(ring)ꢀCH2ꢀC(ring) angles between syn- and anti-ori-
ented phenol rings (Table 1) are in line with values
expected for calix[4]arenes: the C(ring)ꢀCH2ꢀC(ring)
angle is always smaller for syn orientations (107–111°)
than for anti orientations (111–118°) [26].
1
Complex 3 is also Cs symmetric, as shown by its H-
t
and 13C-NMR spectra. Two singlets for the Bu groups
and three pairs of doublets for the methylene protons
are present in its 1H-NMR spectrum. However, the
spectrum is distinctly different from the spectra of 1, 2,
and 4. The absence of an AB system is notable, and the
JHꢀH coupling constant for the doubly intense pair of
doublets (JHꢀH=14 Hz) is smaller compared to the
corresponding coupling constant of 1, 2, or 4 [27]
(JHꢀH=16–17 Hz). In its 13C-NMR spectrum, the
bridging methylene carbons resonate at l 37.53, 36.12,
and 33.08 (doubly intense). Complex 3 evidently adopts
the cone conformation in solution. Apparently, bridg-
ing a pair of phenolic oxygens results in a downfield
shift of the resonances for the syn-connected methylene
carbon, due probably to changes in angle at the
methylene carbon [26]. These chemical shifts are com-
parable to those reported for the methylenes of doubly
bridged calix[4]arene phosphate ester derivatives in the
cone conformation (34–38 ppm) [28]. Ring-current ef-
fects from the phosphorus-bound phenyl groups could
also cause a downfield shift of the syn-connected
Fig. 1. Molecular structure of [(PhPC)H2] (2), showing the atom
labelling scheme.
Table 1
,
Selected bond distances (A) and angles (°) for 2
PꢀO(1)
PꢀO(2)
PꢀC(1)
O(1)ꢀC(7)
O(2)ꢀC(33)
O(3)ꢀC(19)
O(4)ꢀC(26)
1.662(2)
1.663(2)
1.816(3)
1.407(4)
1.409(4)
1.396(4)
1.401(4)
O(1)ꢀPꢀO(2)
O(1)ꢀPꢀC(1)
O(2)ꢀPꢀC(1)
102.85(12)
95.59(13)
95.99(13)
C(7)ꢀO(1)ꢀP
C(33)ꢀO(2)ꢀP
C(8)ꢀC(34)ꢀC(32)
C(18)ꢀC(20)ꢀC(21)
C(12)ꢀC(13)ꢀC(14)
C(28)ꢀC(27)ꢀC(25)
117.7(2)
117.1(2)
109.2(3)
110.8(3)
121.5(3)
121.6(6)
1
methylene carbons [29]. Variable-temperature H-NMR
studies show that 1–3 are conformationally stable up to
348 K.
3.2. Titanium(IV) complexes: synthesis and reacti6ity
The reactions of 1–3 with TiCl4 furnished titanium-
(IV) dichloride complexes L2TiCl2 (5–7) (L2=tBuPC,
PhPC, or PhSPC, respectively) as air- and moisture-sen-
sitive solids in moderate to excellent yield (Scheme 2).
Each compound’s proposed structure is consistent with
all of its analytical and spectroscopic data (vide infra).
The compounds are practically insoluble in aliphatic
hydrocarbon solvents. However, (PhPC)TiCl2 (6) and
(PhSPC)TiCl2 (7) are quite soluble in aromatic hydro-
carbon solvents while (tBuPC)TiCl2 (5) is only sparingly
soluble. Adding a few drops of a coordinating solvent,
such as THF or CH3CN, greatly improves the solubility
of 5 in hydrocarbon solvents. This solubilizing effect of
THF or CH3CN was utilized in obtaining NMR spec-
tra of some of the complexes (see Section 2). Dialkyl
derivatives (DMSC)TiMe2 (9) and (DMSC)Ti(CH2Ph)2
(10) were obtained in good yield from reaction of
methylene carbons of calix[4]arenes are characterized
by a resonance around l 31 when the attached phenol
rings are in a syn orientation. In contrast, a resonance
around l 37 is characteristic when the phenol rings are
anti oriented [26]. The authors attributed this difference
to the different angles imposed at the methylene carbon
1
in these two steric arrangements. Moreover, the H and
13C-NMR spectra of 1 and 2 are similar to those of
1,2-alternate dimethylsilyl-bridged p-tert-butylcalix[4]-
arene derivative (DMSC)H2 (4), recently reported by
Lattman and colleagues [27]. Single-crystal X-ray anal-
ysis of 2 confirmed the structure assigned by spec-
troscopy: the molecule exists in the 1,2-alternate
conformation. A thermal ellipsoid plot of 2 showing the
atom labelling is presented in Fig. 1. As shown in the
Figure, the geometry around phosphorus is pyramidal

230
O.V. Ozero6 et al. / Journal of Organometallic Chemistry 586 (1999) 223–233
Scheme 2.
that the displacement of a tetradentate calix[4]arene
ligand (Floriani’s case) would be less facile than the
displacement of a bidentate one. However, we cannot
rule out reduction of 8 to an unknown Ti(III) species
by alkyllithium and Grignard reagents.
Cationic metallocene alkyl complexes have been iden-
tified as the chain-propagating species in homogeneous
Ziegler–Natta a-olefin polymerization [30–33]. There-
fore, we attempted to generate the cationic derivatives
of 9 and 10 by protolysis with [(Et2O)2H]BArF4 (ArF=
(DMSC)TiCl2 (8) [20] with the appropriate dialkylmag-
nesium compound (Scheme 3). Their formulation and
structure were confirmed by microanalysis and spectro-
scopic characterization (vide infra). 5–10 are thermally
stable at 80°C in benzene, undergoing no significant
decomposition for hours. Whereas, the reaction of 8
with dibenzylmagnesium is fast and facile at ambient
temperature and relatively insensitive to the solvent
choice, a significant amount of black precipitate is
always formed in the reaction with dimethylmagnesium.
It seems likely that the decomposition of 9 by Me2Mg
occurs during its preparation. This proposal finds sup-
port in the observation that toluene solutions of pure 9
and Me2Mg turn black after a few minutes. The reac-
tion of 8 with alkylating reagents such as alkyllithium
and Grignard reagents produced complex mixtures.
This is in contrast to the report by Floriani and co-
workers [16] showing calix[4]arene-based titanium–
alkyl complexes can be prepared by alkylation of the
dichloride precursors with alkyllithium and Grignard
reagents. A potential side-reaction involves competing
displacement of the calix[4]arene ligand rather than the
chloride ligands, yielding an unstable R2TiCl2 species
which rapidly decomposes. It is reasonable to expect
Scheme 3.

O.V. Ozero6 et al. / Journal of Organometallic Chemistry 586 (1999) 223–233
231
3.3. NMR analysis
(CF3)2C6H3). Unfortunately, the reactions were compli-
cated by side-reactions that involved destruction of the
dimethylsilyl calix[4]arene (DMSC) ligand structure1.
However, alkyl abstraction with [Ph3C]BArF4 proceeded
cleanly in the presence of CH3CN in a variety of
solvents including CHCl3, CH2Cl2, and C6H6 to produce
[(DMSC)Ti(NCCH3)Me]BArF4 (11) and [(DMSC)-
Ti(NCCH3)(CH2Ph)]BArF4 (12) (Scheme 3). In solution,
11 and 12 are quite stable, undergoing no significant
decomposition at room temperature over 24 h in
methylene chloride. However, only 12 could be isolated
as a solid; it is extremely soluble in polar and aromatic
solvents and turns into an oil upon addition of any
solvent. 11 decomposes gradually as the solvent is
removed and all attempts to crystallize it at low temper-
ature have failed, as have attempts to generate cationic
complexes in the presence of other donor ligands such as
t
The methyls of the Bu groups and the bridging
methylenes are useful spectroscopic probes for charac-
terizing different symmetry properties and conforma-
tions of calix[4]arene-based metal complexes.
Compounds 5, 9–14 all exist in 1,2-alternate conforma-
1
tion and possess Cs symmetry. Their H-NMR spectra
contain two singlets for the tBu groups, and two pairs of
doublets and a broad singlet or an AB system (integrat-
ing as four protons) for the bridging methylene protons
(see Section 2). Their 13C-NMR spectra show anti-con-
nected bridging methylenes at around 40 ppm while
syn-connected bridging methylenes appear at around 36
ppm, consistent with the corresponding chemical shifts
for
1,2-alternate
doubly
dimethylsilyl-bridged
calix[4]arene (l 39.9 and 35.6) [27] and the explanation
by de Mendoza and co-workers [26]. The chemical shifts
of the Me groups of the SiMe2 unit and of the alkyl
substituents on titanium are also diagnostic of 1,2-alter-
nate conformation for the DMSC-based compounds
9–14. For example, the ‘endo’ Me group on silicon is
located inside the calixarene cavity (above the centers of
two aromatic rings), while the ‘exo’ Me group is on the
outside. Hence, endo and exo groups resonate as two
2
PMe3 or PCy3 . Alkyl abstraction did not occur cleanly
in the absence of a donor ligand in weakly coordinating
solvents, although the corresponding organic product
(Ph3CMe or Ph3CCH2Ph) was always formed quantita-
tively (by 1H-NMR). The cation, if ever formed, is
presumably unstable and rapidly decomposes to uniden-
tified products; consistent with its very low electron
count and coordinative unsaturation. Treatment of 9
and 10 with [Ph3C]OTf (OTf=CF3SO3−) in 1:1 molar
separate signals in the H- and 13C-NMR spectra (see
1
Section 2). NMR signals of the endo groups are strongly
shielded compared to corresponding signals of the exo
groups, due most likely to ring current effect [29]. This
difference between the exo- and endo-substituents is
also manifested in the reactivity of the compounds.
Thus, 11–14 are formed by abstraction of the more
exposed exo-alkyl. In other words, reaction occurs via
the less hindered face; abstraction of the second alkyl by
Ph3C+ is much slower (hours versus a few minutes for
the first abstraction) and leads to decomposition. Un-
fortunately, our attempts to obtain single crystals of
these compounds suitable for X-ray structure determi-
nations have thus far been unsuccessful.
[(PhPC)TiCl2] (6) has Cs symmetry and adopts the
cone conformation in solution. The molecular structure
of 6 was characterized as follows: Its 1H-NMR spectrum
shows two singlets for the tBu groups, and three pairs of
doublets for the bridging methylene protons. Three
resonances are present in its 13C-NMR spectrum for
the bridging methylene carbons (see Section 2), and the
resonance at l 33.00 is doubly intense. One resonance
at l 124.0 is observed in its 31P{1H}-NMR spectrum.
This represents an upfield shift from ‘free 2’ (l 165.2)
and is likely indicative of an interaction between phos-
phorus and the electrophilic titanium center. [(Ph-
SPC)TiCl2] (7) was isolated as a 3.5:1 mixture of
1,2-alternate and cone conformers. While the initial ra-
tio of the conformers varies somewhat with the isolation
procedure, solutions of 7 gradually equilibrate to this
ratio. Variable-temperature NMR analysis of 7 from
ratio
led
to
the
alkyltriflato
complexes
[(DMSC)Ti(OTf)Me] (13) and [(DMSC)Ti(OTf)(CH2-
Ph)] (14) (Scheme 3). The reaction of 14 with Na[BArF4 ]
in presence of CH3CN produced 12 (Scheme 3). Under
analogous conditions, 13 did not give 11 but instead
decomposed, reflecting the greater stability of 12 com-
pared to 11. The triflate ligand in 14 is readily dissoci-
ated in the presence of a donor ligand. Thus, when
CH3CN is added to a benzene-d6 solution of 14, the
resonance for the triflate group in the 19F-NMR spec-
trum at l −69.3 is shifted to l −78.8, which corre-
sponds to the chemical shift of the triflate anion in
[Ph3C]OTf.
1 In general, protonation of 10 led to somewhat cleaner reaction
(by NMR) but in all cases it was evident that at least partial
decomposition due to the destruction of the DMSC ligand structure
tended to occur. This is supported by the fact that when a mixture
formed by reacting 9 or 10 with [(Et2O)2H]BArF4 in CH2Cl2/pentane
was kept at −20°C for several weeks, [(calix)2Ti2] [17] precipitated
(calix=tetraanion of p-tert-butylcalix[4]arene).
2 In the presence of PMe3, alkyl abstraction proceeds over a period
of days to produce several unknown calixarene-based products. The
reaction can be monitored by appearance of Ph3CR (R=Me or
CH2Ph) in the 1H NMR spectrum. The formation of a strong
[Ph3CꢀPMe3]+ adduct which has very low degree of dissociation may
explain this sluggishness. In support of this proposal, when PCy3 is
used instead of PMe3, the reaction proceeds much faster (in minutes).
[Ph3CꢀPCy3]+ adduct, if formed, should be much less stable due to
increased steric hinderance.

232
O.V. Ozero6 et al. / Journal of Organometallic Chemistry 586 (1999) 223–233
Table 2
Ethylene polymerization at 25°C a
−1
cat
Catalyst
Catalyst (mmol)
Molar excess of MAO
Time (min)
Activity (Kg mol
h−1
)
5
6
7
8
9
0.02
0.02
0.02
0.02
0.02
0.02
0.02
500
500
500
500
500
500
500
30
30
30
30
30
30
30
9
70
15
35
15
25
24
10
14
a 1 atm C2H4 pressure bubbled through 40 ml toluene mixture of catalyst/MAO.
298 to 348 K in C6D6 showed the ratio of 1,2-alternate
to cone conformer increased reversibly from 3.5:1 to 7:1
over this temperature range.
exists in cone formation and thus has an open face for
reactivity, displayed the highest activity of the complexes
(Table 2). However, stabilization of the cationic species
by TiꢀP interaction would lead to an increased concen-
tration of the active catalyst and hence to higher activity.
A similar TiꢀS interaction has been proposed for the
increased activity of an S-bridged biphenolate titanium
(IV) dichloride complex [2d,2f,35].
3.4. Ethylene polymerization
At 25°C with 500 molar equiv of methylalumoxane
(MAO) as cocatalyst, 5–10 and 14 showed ethylene
polymerization activities (Table 2) comparable to those
reported for several noncyclopentadienyl-based Ti and Zr
systems [2d]. With the exception of 63, the compounds
were inactive towards higher a-olefins, such as propene
and 1-hexene, under comparable conditions; increasing
the temperature did not promote polymerization. The
modest ethylene polymerization activities may be due to
several factors, including a low equilibrium concentration
of the putative active cationic species. We were unable
to generate cationic complexes from 9 and 10 by alkyl
abstraction in the absence of a donor ligand (vide supra).
Moreover, we observed no poly- or oligomerization of
ethylene when either 9 or 10 was activated under an
atmosphere of ethylene with [Ph3C]BArF4 in CD2Cl2 or
C6D6. Other reasons for the modest activities observed
may be MAO interaction with the OꢀEꢀO bridge (E=P
or Si) of the calix[4]arene ligands and/or steric congestion
at titanium. Coordination of MAO to the OꢀEꢀO bridge
oxygens could disfavor formation of the cationic species
by increasing the effective positive charge on the
calix[4]arene ligand oxygens and thus the Ti center. An
analogous explanation was proposed for the lower activ-
ity of methoxy-substituted bis(indenyl)zirconium com-
plexes [34]. Alternatively, MAO interaction could disrupt
the OꢀEꢀO bridge and thereby result in a loss of
conformational rigidity4. It is interesting that 6, which
4. Conclusions
In
1,2-alternate
conformation,
p-tert-butyl-
calix[4]arene-derivedchelatingbis(aryloxide)ligandsster-
ically define reaction sites at the titanium center;
substitutionoccursatthestericallylesshinderedsite. With
MAO as co-catalyst, titanium derivatives 5–10 and 14
showed modest activities in ethylene polymerization.
Studies of organic transformations mediated by these and
related complexes are currently underway in our labora-
tory. Our results will be presented in future publications.
5. Supplementary material
Crystallographic data for the structural analysis has
been deposited with the Cambridge Crystallographic
Data Centre, CCDC No. 118419 for compound 2. Copies
of this information may be obtained free of charge from
The Director, CCDC, 12 Union Road, Cambridge, CB2
1EZ, UK (Fax: +44-1223-336-033; e-mail: deposit@-
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
3 At 25°C with 500 molar equivalent MAO as cocatalyst,
oligomerizes 1-hexene. Efforts to characterize the products and en-
hance reactivity are in progress.
6
Acknowledgements
4 Some decomposition occurs with apparent loss of DMSC ligand
structure when (DMSC)TiMe2 (9) is treated with an excess of AlCl3
in benzene-d6 under an atmosphere of ethylene. While these condi-
tions are only a crude approximation of the polymerization condi-
tions, the major product observed by 1H-NMR was 8. This suggests
that alkyl/chloride exchange between Al and Ti may be preferred over
attack on the SiꢀO bonds.
Thanks are expressed to the Kentucky National Science
Foundation EPSCoR Program (grant number EPS-
9452895) for support of this work and to the Chemistry
Department of the University of Kentucky for the award
of fellowships to O.V.O. The authors also thank Profes-
sors Jack Selegue and Mark Meier for helpful discussions.

O.V. Ozero6 et al. / Journal of Organometallic Chemistry 586 (1999) 223–233
233
C. Rizzoli, N. Re, A. Sgamellotti, J. Am. Chem. Soc. 119
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