Methods for the synthesis of the diels-alder catalysts (ArO)2TiX2 (X = Cl, Br, I; Ar = 2-tert-butyl-6-methylphenyl)

Article abstract of DOI:10.1021/om9808099

A procedure for converting titanium diethylamidos to the corresponding dihalides (Cl, Br, I) and a complementary method for converting titanium dichlorides into dibromides and diiodides are reported. These methods were utilized to synthesize a family of homogeneous and polymer-supported Diels-Alder catalysts with the general formula (ArO)₂TiX₂ (X = Cl, Br, I; Ar = 2-tert-butyl-6-methylphenyl).

Full text of DOI:10.1021/om9808099

Organometallics 1999, 18, 2557-2560
2557
Meth od s for th e Syn th esis of th e Diels-Ald er Ca ta lysts
(Ar O)2TiX2 (X ) Cl, Br , I; Ar )
2-ter t-Bu tyl-6-m eth ylp h en yl)
Brian P. Santora, Peter S. White, and Michel R. Gagne´*
Department of Chemistry CB#3290, University of North Carolina,
Chapel Hill, North Carolina 27599-3290
Received September 28, 1998
Summary: A procedure for converting titanium diethy-
lamidos to the corresponding dihalides (Cl, Br, I) and a
complementary method for converting titanium dichlo-
rides into dibromides and diiodides are reported. These
methods were utilized to synthesize a family of homo-
geneous and polymer-supported Diels-Alder catalysts
with the general formula (ArO)2TiX2 (X ) Cl, Br, I; Ar
) 2-tert-butyl-6-methylphenyl).
2c (>95% pure by 1H NMR).3 Removal of the boron-
containing byproducts in vacuo followed by recrystalli-
zation gave the dibromide and diiodide with yields
improved over the SiX4 route. We favor the BX3 route
for scale-up for reasons of yield and ease of preparing
2a (see Experimental Section, method 1). The former
method, however, has several advantages for the syn-
thesis of polymer-immobilized catalysts (vide infra).
The 1H NMR spectra of the series of dihalide com-
pounds show some interesting features. On going from
chloride to bromide to iodide, an upfield shift is seen in
the methyl resonances (Cl ) 2.15, Br ) 2.10, I ) 2.0
ppm), while the tert-butyl resonances shift downfield (Cl
) 1.55, Br ) 1.60, I ) 1.70 ppm). A similar trend has
been observed in the series Ti(ebmp)X2 (ebmp ) 2,2′-
ethylenebis(6-tert-butyl-4-methylphenyl); X ) Cl, Br, I).4
Red crystals of 2a suitable for X-ray crystallography
were grown from a saturated toluene solution layered
with pentane at -35 °C (Figure 1). The pseudo-C2-
symmetric structure is monomeric with a tetrahedral
coordination geometry around titanium. The relatively
short titanium-oxygen bond lengths (1.753(4) and
1.752(5) Å) as well as the large angles at oxygen (162.2-
(4)° and 163.4(4)°) suggest substantial pπ-dπ donation
from oxygen to the formally eight-electron titanium
center.5 The metrical parameters for 2a are nearly
identical to the crystal structure of Ti(ebmp)Br2, sug-
gesting that the chelating ligand in the latter is virtually
free of torsional strain.2b
In the context of a broader program aimed at develop-
ing transition metal catalysts whose selectivity has an
outer-sphere component, our lab has recently become
interested in the chemical manipulation of titanium
aryloxide complexes.1 As part of these efforts, we wish
to report methods for synthesizing and interconverting
(ArO)2TiX2 complexes (good Diels-Alder catalysts) that
are amenable to polymer-bound analogues (X ) Cl, Br,
I; Ar ) 2-tert-butyl-6-methylphenyl).
Treatment of the bisamido compound 1a with excess
SiX4 (X ) Cl, Br) in toluene at 23 °C results in rapid
conversion to the dihalides 2a and 2b, respectively
1
(>95% pure by H NMR; eq 1).2 The silicon-containing
byproducts were removed in vacuo, and 2a /2b were
purified in modest yield by recrystallization from toluene/
hexanes (-35 °C). The synthesis of the diiodide 2c
required more forcing conditions, as the reaction of 1a
with SiI4 at room temperature stopped at the pale
yellow (ArO)2Ti(NEt2)I. Warming to 60 °C, however,
cleanly converted this material to the diiodide 2c, which
was purified by first subliming away the silicon-contain-
ing byproducts and then recrystallizing from pentane
(-35 °C). The poor yields for these complexes reflect
their high solubility.
Another synthetic route into the dihalide compounds
2b and 2c is shown in eq 2. Treatment of 2a with BX3
(X ) Br, I) resulted in immediate conversion to 2b and
(1) Santora, B. P.; Larsen, A. O.; Gagne´, M. R. Organometallics 1998,
17, 3138-3140.
We recently reported the use of polymer immobilized
(2) (a) For the cleavage of Ti-OiPr with SiCl4, see: Corey, E. J .;
Matsumura, Y. Tetrahedron Lett. 1991, 32, 6289-6292. (b) For the
cleavage of Ti-OiPr with Me3SiX (X ) Br, I), see: Fokken, S.; Spaniol,
T. P.; Okuda, J .; Sernetz, F. G.; Mulhaupt, R. Organometallics 1997,
16, 4240-4242. (c) For the cleavage of M-NMe2 (M ) Ti, Zr) with
Me3SiCl, see: J ones, R. A.; Hefner, J . G.; Wright, T. C. Polyhedron
1984, 3, 1121-1124. (d) For the cleavage of Ti-NMe2 with MeI, see:
J ohnson, A. R.; Wanandi, P. W.; Cummins, C. C.; Davis, W. M.
Organometallics 1994, 13, 2907-2909. (e) For the cleavage M-NMe2
(M ) Ti, Zr) with HCl or NMe3‚HCl see: Carpenetti, D. W.; Kloppen-
burg, L.; Kupec, J . T.; Petersen, J . L. Organometallics 1996, 15, 1572-
1581. (f) For the cleavage of Zr-NMe2 with Me2NH‚HCl see: Scollard,
J . D.; McConville, D. H.; Vittal, J . L. Organometallics 1995, 14, 5478-
5480. (g) For the cleavage of Ti-CH2Ph with I2, see: Tsuie, B.;
Swenson, D. C.; J ordan, R. F.; Petersen, J . L. Organometallics 1997,
16, 1392-1400.
(ArO)2TiCl2 as a catalyst for the Diels-Alder reaction.1
(3) For the conversion of Cp2MCl2 to Cp2MX2 with BX3 (M ) Ti, Zr,
Hf; X ) Br, I), see: Druce, P. M.; Kingston, B. M.; Lappert, M. F.;
Spalding, T. R.; Srivastava, R. C. J . Chem. Soc. (A) 1969, 2106-2110.
(4) Footnote 2b and: Fokken, S. Ph.D. Dissertation, University of
Mainz, 1997.
(5) For the effect of pπ-dπ bonding in Ti-aryloxide complexes, see:
(a) Latesky, S. L.; Keddington, J .; McMullen, A. K.; Rothwell, I. P.
Inorg. Chem. 1985, 24, 995-1001. (b) Durfee, L. D.; Latesky, S. L.;
Rothwell, I. P.; Huffmann, J . C.; Folting, K. Inorg. Chem. 1985, 24,
4569-4573. (c) For
a discussion of the problems associated with
utilizing the C-O-M bond angle in early transition metal aryloxide
complexes as a probe for the magnitude of pπ-dπ bonding, see: Steffey,
B. D.; Fanwick, P. E.; Rothwell, I. P. Polyhedron 1990, 9, 963-968.
10.1021/om9808099 CCC: $18.00 © 1999 American Chemical Society
Publication on Web 05/27/1999

2558 Organometallics, Vol. 18, No. 13, 1999
Notes
F igu r e 1. ORTEP drawing of (ArO)2TiCl2 (2a ) with
ellipsoids at the 50% probability level. Selected bond
lengths (Å) and angles (deg): Ti-O1, 1.753 (4); Ti-O2,
1.752(5); Ti-Cl1, 2.217(3); Ti-Cl2, 2.207(3); O1-Ti-O2,
112.63(22); Cl1-Ti-Cl2, 110.33 (11); C-O1-Ti, 162.2(4);
C-O2-Ti, 163.4(4).
Sch em e 1
F igu r e 2. Plots of ln[dienophile] vs time (pseudo-first-
order in diene, 33 °C) for the catalysts 1a (1), P 1 (×), 2a
(2), P 2Cl ([), 2b (9), and P 2Br (b).
phile by GC yielded the plots highlighted in Figure 2.
As expected, the π-basic bisamido ligand set of 1a and
P 1 showed negligible activity.6 As previously reported,
P 2Cl (kobs ) 3.4 × 10-3 s-1) is roughly 3 times slower
than its solution analogue 2a (kobs ) 12 × 10-3 s-1).1
Intriguingly, the polymer-bound catalyst P 2Br (kobs
)
4.5 × 10-3 s-1) is slightly faster than P 2Cl, while its
solution analogue 2b (kobs ) 7.5 × 10-3 s-1) is slower
than the dichloride solution catalyst. Poorly behaved
kinetics consistent with strong product inhibition or
catalyst death were observed with the diiodide catalysts
2c and P 2I (not shown). The diiodide-based catalysts
were initially competitive, but after 3 or 4 turnovers
their activity dropped dramatically and was accompa-
nied (in solution) by an off-white precipitate. Dichloride
and dibromide reaction rates (polymer and solution)
were reproducible within 5-10%, represent averages of
two runs, and were accompanied by only slight clouding
of the homogeneous reaction solutions. Control experi-
ments further indicate that SiX4 (X) Cl, Br, and I) are
not Diels-Alder catalysts and that polymer removal
midway through catalysis runs halts the conversion to
product. The latter controls are consistent with catalysis
occurring in the polymer matrix, not from leached
complex. All catalysts gave a product endo:exo diaste-
reoselectivity of 98:2, with the solution catalyst 2a and
polymer-bound catalyst P 2Cl giving the Diels-Alder
product in 68% and 75% isolated yields, respectively.
In summary, we have developed two complementary
methods for synthesizing the Diels-Alder catalysts
(ArO)2TiX2 (X ) Cl, Br, I) and their polymer-im-
mobilized analogues. We hope that the synthetic meth-
To extend this chemistry, we have used the reactions
described above to prepare homogeneous and polymer-
immobilized dibromide and diiodide catalysts as well.
To synthesize the polymer-immobilized catalysts, the
strategy in Scheme 1 was employed wherein metal-
lomonomer 1b was incorporated into a highly cross-
linked, yet porous polymer matrix. In analogy with the
solution chemistry, treatment of the yellow-orange
insoluble polymer P 1 with SiX4 changes its color to the
dark reds characteristic of the dihalide catalysts. Even
with large lumps of polymer (∼0.5 cm3), the color
changed throughout the polymer. Removal of the silicon
byproducts reveals the red, insoluble polymers we
formulate as P 2X (X ) Cl, Br, I). Surface area analysis
(BET) of these polymers indicates very high surface
areas (∼500-600 m2/g polymer), suggestive of a stable
porous organic network.
The compounds (ArO)2TiX2 and the polymers P 2X
were evaluated as catalysts for the Diels-Alder reaction
between 3-acryloyloxazolidinone and 1,3-cyclohexadiene
(eq 3). Monitoring the rate of disappearance of dieno-
(6) Hillhouse, G. L.; Bulls, A. R.; Santarsiero, B. D.; Bercaw, J . E.
Organometallics 1988, 7, 1309-1312.

Notes
Organometallics, Vol. 18, No. 13, 1999 2559
red solution was stirred for 12 h at room temperature. The
solvent was removed in vacuo to give 2a in >95% purity as a
red powder. The product was purified by recrystallization from
toluene/pentane at -35 °C (6.08 g, 93% yield).
odologies highlighted herein will be useful in synthe-
sizing dihalide complexes from both dialkylamido and
dichloride complexes of titanium.
Meth od 2. SiCl4 (0.33 mL, 2.8 mmol) was added to (ArO)2Ti-
(NEt2)2 (148 mg, 0.28 mmol) (1a ) dissolved in 10 mL of toluene
at room temperature. The reaction mixture was stirred for 3
h at 23 °C and then concentrated in vacuo to give 2a . The
product was purified by recrystallization from toluene/hexanes
at -35 °C (63 mg, 42%). 1H NMR (250 MHz, C6D6): δ 7.05 (m,
2H), 6.70 (m, 4H), 2.15 (s, 6H), 1.50 ppm (s, 18H). 13C{1H}
NMR (50.28 MHz, CD2Cl2): δ 18.7, 30.5, 35.3, 125.0, 125.1,
129.5, 131.5, 138.0, 168.9 ppm. Anal. Calcd for C22H30Cl2O2-
Ti: C, 59.34; H, 6.79. Found: C, 59.19; H, 7.03.
Exp er im en ta l Section
All reactions were carried out under an atmosphere of dry
argon or nitrogen using standard Schlenck techniques or in a
MBraun Lab-Master 100 glovebox. All solvents were dried by
passing through a column of activated alumina7 and stored
under argon prior to use. C6D6 was vacuum transferred from
sodium/benzophenone-ketyl, and CD2Cl2 was distilled from
CaH2. Both protiated and deuterated solvents were freeze-
pump-thaw degassed before use. 3-Acryloyloxazolidin-2-one
was prepared according to literature procedures.8 All reagents
were obtained from Aldrich and stored under a nitrogen
atmosphere. TiCl4, SiCl4, and BI3 were used as received. 2-tert-
Butyl-6-methylphenol (ArOH) was dried over activated mo-
lecular sieves prior to use. SiBr4 was heated under reflux and
vacuum transferred. BBr3 was shaken with mercury, heated
under reflux, and distilled.3 SiI4 was sublimed under vacuum
prior to use. Styrene and technical grade divinylbenzene were
distilled from CaH2 and freeze-pump-thaw degassed before
use. 2,2′-Azobisisobutyronitrile (AIBN) was recrystallized from
MeOH and dried under vacuum. Cyclohexadiene was distilled
from NaBH4. Gas chromatography was performed on an HP-5
column (30 m × 0.32 mm). NMR spectra were recorded on
Bruker WM250 and Bruker AC200 spectrometers for 1H and
13C, respectively, and referenced to internal solvent signals.
Surface area analyses (nitrogen BET) were performed at
DuPont CR&D. Elemental analyses of the solution catalysts
were performed by E&R Microanalytical Laboratory, Inc.,
Parsippany, NJ . The polymer catalysts were analyzed by
neutron activation at the North Carolina State University
nuclear science center, Raleigh, NC.
(Ar O)2Ti(NEt2)2 (1a ). A 25 mL solution of ArOH (2-tert-
butyl-6-methylphenol, 3.175 g, 19.36 mmol) in toluene was
added to a 100 mL solution of Ti(NEt2)4 (3.257 g, 9.73 mmol)
in toluene (23 °C). The orange solution was stirred for 12 h at
room temperature, followed by solvent removal in vacuo to
yield 1a as a yellow solid. The product was purified by
recrystallization from Et2O/pentane at -35 °C (4.52 g, 90%
yield). 1H NMR (250 MHz, C6D6): δ 7.27 (m, 2H), 7.05 (m, 2H),
6.82 (m, 2H), 3.70 (q, J ) 7.0 Hz, 8H), 2.34 (s, 6H), 1.58 (s,
18H), 0.81 (t, J ) 7.0 Hz, 12H). 13C{1H} NMR (50.28 MHz,
CD2Cl2): δ 13.8, 18.6, 30.5, 35.2, 46.2, 119.9, 124.6, 128.8,
129.2, 137.6, 163.0. Anal. Calcd for C30H50N2O2Ti: C, 69.48;
H, 9.72; N, 5.40. Found: C, 69.76; H, 10.00; N, 5.23.
(Ar O)2TiBr 2 (2b). Meth od 1. SiBr4 (1.0 g, 2.8 mmol) was
added to (ArO)2Ti(NEt2)2 (148 mg, 0.28 mmol) (1a ) dissolved
in 10 mL of toluene at room temperature. The dark red
solution was stirred for 2.5 h at 23 °C and then concentrated
in vacuo to give the dark red solid 2b. The product was purified
by recrystallization from toluene/hexanes at -35 °C (64.0 mg,
42% yield).
Meth od 2. BBr3 (119 mg, 0.47 mmol) was added to
(ArO)2TiCl2 (192 mg, 0.43 mmol) dissolved in 10 mL of toluene
at room temperature, followed by stirring for 2 h at ambient
temperature. The dark red solution was then concentrated in
vacuo to give the dark red solid 2b, which was purified by
recrystallization from toluene/hexanes at -35 °C (120 mg, 52%
yield). 1H NMR (250 MHz, C6D6): δ 7.05 (m, 2H), 6.70 (m, 4H),
2.10 (s, 6H), 1.55 ppm (s, 18H). 13C{1H} NMR (50.28 MHz, CD2-
Cl2): δ 19.1, 30.7, 35.5, 125.0, 125.2, 129.6, 131.7, 137.9, 169.5
ppm. Anal. Calcd for
C22H30Br2O2Ti: C, 49.47; H, 5.66.
Found: C, 49.62; H, 5.94.
(Ar O)2TiI2 (2c). Meth od 1. SiI4 (683 mg, 1.27 mmol) was
added to (ArO)2Ti(NEt2)2 (132 mg, 0.25 mmol) (1a ) dissolved
in 10 mL of toluene at room temperature. The dark red
solution was stirred for 6 h at 60 °C and then concentrated in
vacuo to give a dark red tar containing 2c, SiI4, and Et2NSiI3.
The silicon-containing byproducts were removed by sublima-
tion onto a cold probe (60 °C, <1 mTorr), and then the red
powder 2c was recrystallized from pentane at -35 °C (20.0
mg, 12.5% yield).
Meth od 2. BI3 (175 mg, 0.45 mmol) was added to (ArO)2TiCl2
(181 mg, 0.41 mmol) dissolved in 10 mL of toluene at room
temperature. The dark red solution was stirred for 3 h at 23
°C and then concentrated in vacuo to give the dark red solid
2c. The product was purified by recrystallizing from pentane
at -35 °C (90 mg, 35% yield). 1H NMR (250 MHz, C6D6): δ
7.05 (m, 2H), 6.75 (m, 4H), 2.00 (s, 6H), 1.65 ppm (s, 18H).
13C{1H} NMR (50.28 MHz, CD2Cl2): δ 19.7, 31.0, 35.7, 125.0,
125.1, 129.6, 132.0, 137.5, 169.9 ppm. Anal. Calcd for C22H30I2O2-
Ti: C, 42.06; H, 4.81. Found: C, 42.37; H, 4.86.
(p-vin yl-Ar O)2Ti(NEt2)2 (1b). A 3 mL solution of p-vinyl-
ArOH1 (1.02 g, 5.34 mmol) in toluene was added dropwise to
a 10 mL solution of Ti(NEt2)4 (0.895 g, 2.67 mmol) in toluene
(23 °C). The orange solution was stirred for 2 h at 23 °C,
followed by solvent removal in vacuo to give the yellow solid
1b. The yellow product was purified by recrystallization from
Et2O/pentane at -35 °C (1.33 g, 87% yield). 1H NMR (250
MHz, C6D6): δ 0.80 (t, J ) 7.1 Hz, 12 H), 1.60 (s, 18H), 2.34
(s, 6H), 3.70 (q, J ) 7.1 Hz, 8H), 5.10 (dd, J ) 10.8, 1.1 Hz,
2H), 5.68 (dd, J ) 17.6, 1.1 Hz, 2H), 6.70 (dd, J ) 17.6, 10.8
Hz, 2H), 7.20 (m, 2H), 7.40 (m, 2H). 13C{1H} NMR (50.28 MHz,
CD2Cl2): δ 13.3, 18.0, 29.8, 34.6, 45.7, 109.9, 122.5, 126.2,
128.6, 137.0, 162.7. Anal. Calcd for C34H54N2O2Ti: C, 71.56;
H, 9.54; N, 4.91. Found: C, 71.33; H, 9.72; N, 5.05.
P 1. Metallomonomer 1b (100.0 mg, 0.175 mmol), AIBN (20.0
mg, 0.12 mmol), toluene (1.39 mL), styrene (0.30 mL), and tech
grade divinylbenzene (1.09 mL) were combined in a 20 mL
scintillation vial under nitrogen and sealed with a Teflon-lined
cap. The vial was heated for 12 h at 80 °C followed by 12 h at
120 °C. The yellow-orange insoluble polymer was dried under
high vacuum (<1 mTorr) for 12 h at 40 °C to give an isolated
yield of 1.32 g of dried polymer. Anal. Calcd for P 1: Ti, 0.61.
Found: Ti, 0.59. Surface area: 570 m2/g polymer.
P 2Cl. Under a nitrogen atmosphere, toluene (10 mL) was
added to a sample of solvated P 1 (2.55 g polymer, 0.175 mmol
Ti), giving a colorless liquid over a yellow polymer. SiCl4 (0.4
mL, 20 equiv) was added at 23 °C, the reaction mixture was
slowly stirred for 6 h at room temperature, and then the
solvent was removed in vacuo. The red polymer was rinsed
with Et2O in a Soxhlet extractor for 6 h and then dried under
(Ar O)2TiCl2 (2a ). Meth od 1.9 TiCl4 (1.63 mL, 14.6 mmol)
was added to 2-tert-butyl-6-methylphenol (ArOH, 29.2 mmol)
dissolved in 50 mL of Et2O at 0 °C, and then the homogeneous
(7) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J . Organometallics 1996, 15, 1518-1520.
(8) Ho, G. J .; Mathre, D. J . J . Org. Chem. 1995, 60, 2271-2273.
(9) Duff, A. W.; Kamarudin, R. A.; Lappert, M. F.; Norton, R. J . J .
Chem. Soc., Dalton Trans. 1986, 489-498.
vacuum (<1 mTorr) for 12 h at 40 °C to yield 1.32 g of P 2Cl
.
Anal. Calcd for P 2Cl: Ti, 0.61; Cl, 0.90. Found: Ti, 0.67; Cl,
0.89. Surface area: 530 m2/g polymer.

2560 Organometallics, Vol. 18, No. 13, 1999
Notes
Ta ble 1. Cr ysta llogr a p h ic Da ta a n d Collection
P a r a m eter s for 2a
P 2Br . Under a nitrogen atmosphere, SiBr4 (0.44 mL, 20
equiv) was added to a sample of P 1 (2.55 g polymer, 0.175
mmol Ti) in toluene at room temperature. The reaction mixture
was slowly stirred for 6 h at 23 °C, and then the solvent was
removed in vacuo. The red polymer was rinsed with Et2O in a
Soxhlet extractor for 6 h and then dried under vacuum (<1
mTorr) for 12 h at 40 °C to yield 1.33 g of P 2Br . Anal. Calcd
for P 2Br : Ti, 0.61; Br, 2.03. Found: Ti, 0.58; Br, 2.74. Surface
area: 580 m2/g polymer.
formula
TiCl2C22H30O2
fw
445.28
red, crystal
0.40 × 0.40 × 0.25
orthorhombic
Pbca
19.133(9)
11.394(7)
21.204(6)
4623(4)
8
color, habit
cryst size, mm
cryst syst
space group
a, Å
b, Å
P 2I. Under a nitrogen atmosphere, SiI4 (2.8 g, 20 eq) was
added to a sample of P 1 (2.55 g polymer, 0.175 mmol Ti) in
toluene at room temperature. The reaction mixture was slowly
stirred for 6 h at 60 °C, and then the solvent was removed in
vacuo. The red polymer was rinsed with Et2O in a Soxhlet
extractor for 6 h and then dried under vacuum (<1 mTorr)
for 12 h to yield 1.36 g of P 2I. Anal. Calcd for P 2I: Ti, 0.61; I,
3.22. Found: Ti, 0.61; I, 4.19. Surface area: 620 m2/g polymer.
P olym er An a lysis. For a concise introduction to neutron
activation analysis, visit the North Carolina State University
Nuclear Science Center website at www.ne.ncsu.edu/NRP/
naa.html. Theoretical amounts of titanium in the dried
polymer catalysts were calculated as follows: initial amount
of titanium added to the polymerization mixture × (weight of
dried polymer sample/(total weight of all polymerizable com-
ponents + weight of residual toluene)). Control experiments
indicate that no styrene, DVB, or metallomonomer 1b are
rinsed out of the polymer, and roughly 0.5% residual toluene
remains using the described drying procedure. Analyses of
P 2Br and P 2I are slightly high for halide analysis, possibly
due to SiX4 trapped within the polymer matrix. Extracting the
polymers for a longer time period led to decomposition of the
titanium complexes. Control experiments also indicated that
SiX4 is not a catalyst for the Diels-Alder reaction (vide supra).
Unfortunately, neutron activation is not amenable to silicon
and nitrogen analysis.
Solu tion Ca ta lysis. In the glovebox under a nitrogen
atmosphere, Ti(OAr)2X2 (X ) Cl, Br, I, NEt2; 0.018 mmol),
3-acryloyloxazolidin-2-one (25.5 mg, 0.18 mmol), and 1,3-
cyclohexadiene (255 µL, 2.7 mmol) were added to a 20 mL
scintillation vial with 1 mL of CH2Cl2 at 33 °C. The reactions
were monitored by periodically withdrawing aliquots via pipet
and quenched by passing through a plug of silica gel with
EtOAc, followed by GC analysis. Concentrations of 3-acryloyl-
oxazolidin-2-one and cyclized product were obtained using
known relative response factors for these materials (GC
response factor was determined to be 1:2.75 for a dienophile:
product concentration ratio of 1:1). The Ti(OAr)2(NEt2)2-
catalyzed reactions remained homogeneous throughout the
course of the reaction, but extraneous peaks appeared in the
GC after 48 h. Reaction kinetics were determined under
pseudo-first-order conditions in dienophile (15-fold excess), and
rate constants were obtained by plotting ln[dienophile] vs time
(s).
c, Å
V, Å3
Z
T, °C
-100
Dc, g/cm3
F(000)
1.280
1877.39
Mo KR (0.71073)
0.61
ω
h, k, l
50.0
13393
4020
0.112
radiation, Å
µ, mm-1
scan mode
data collected
2θmax,deg
total no. rflns
no. of unique rflns
Rmerge
no. of rflns with I > 2.5σ(I)
2323
245
0.066
0.077
no. of variables
a
Rf
b
Rw
GoFc
2.22
max ∆/σ
0.080
-0.89, 2.03
residual density, e/Å3
a
b
2 1/2
Rf ) ∑(Fo - Fc)/∑Fo. Rw ) [∑w(Fo - Fc)2/∑wFo
] .
c GoF )
[∑w(Fo - Fc)2/(n - p)]1/2, where n ) number of reflections and p )
number of parameters.
The reaction kinetics were determined under pseudo-first-
order conditions in dienophile (15-fold excess), and rate
constants obtained by plotting ln[dienophile] vs time (s).
Internal standards (e.g., decane) were not helpful, as they were
observed to adsorb into the polymer matrix. Rate constants
therefore reflect the rate of product formation in the solution
above the polymer as determined from dienophile:product
ratios.
X-r a y Da ta for 2a . Data were collected at -100 °C on a
Rigaku AFC-6/S diffractometer using graphite-monochromated
Mo KR radiation. The structure of this weakly diffracting
crystal was solved by direct methods, and non-hydrogen atoms
were refined anisotropically (see Table 1).
Ack n ow led gm en t. This work was partially sup-
ported by the NSF, under the auspices of a CAREER
Development Award to M.R.G. (CHE-9624852), the
Petroleum Research Fund, administered by the ACS,
and the DuPont Company for a Grant in Aid. We wish
to thank Dr. Ken Moloy at DuPont CR&D for the
polymer surface area analysis.
P olym er Ca ta lysis. In the glovebox under N2 atmosphere,
3-acryloyloxazolidin-2-one (25.5 mg, 0.18 mmol), 1,3-cyclo-
hexadiene (213.0 mg, 2.7 mmol), and 149 mg P 2Br (18 µmol
based on 121 µmol Ti/g polymer) were added to a 20 mL
scintillation vial with 1 mL of CH2Cl2 at 33 °C. The reaction
was monitored by periodically taking aliquots via pipet,
passing through a plug of silica gel with EtOAc, and analyzing
by GC using the same protocol as the solution catalysis studies.
Su p p or tin g In for m a tion Ava ila ble: Tables of metrical
parameters for 2a . This material is available free of charge
via the Internet at http://pubs.acs.org.
OM9808099