Synthesis and structure of a linked-bis(amidate) ligand and some complexes with titanium

Article abstract of DOI:10.1021/ic010533o

The synthesis of a new ligand system in which two amides are coupled via a rigid phenylene spacer is readily accomplished in a high-yield, single-step reaction. The dilithio salt (NO)₂Li₂(THF)_x reacts with Ti(NR₂)₄ (R = Me, Et) to yield the titanium amides [(NO)₂Ti(NR₂)₂]₂. The latter react with excess Me₃SiCl to produce the dichloride (NO)₂TiCl₂, which was also obtained by the reaction of [(NO)₂Ti(NMe₂)₂]₂ with TiCl₄(THF)₂ in refluxing toluene, and in a lower-yielding route, by salt metathesis between the dilithio salt and TiCl₄(THF)₂.

Full text of DOI:10.1021/ic010533o

Inorg. Chem. 2001, 40, 6069-6072
6069
synthesis of a new linked bis-amidate ligand and a series of
titanium complexes supported by this ligand system.
Synthesis and Structure of a Linked-Bis(amidate)
Ligand and Some Complexes with Titanium
Results and Discussion
Garth R. Giesbrecht, Alex Shafir, and John Arnold*
The linked-amidate ligand 1 is easily prepared in high yield
by the reaction of p-tBu-benzoyl chloride with phenylenediamine
in the presence of triethylamine in refluxing CH2Cl2 (eq 1).13,21
Department of Chemistry, University of California,
Berkeley, California 94720-1460, and the
Chemical Sciences Division, Lawrence Berkeley
National Laboratory, Berkeley, California 94720-1460
ReceiVed May 21, 2001
Introduction
The development of new ligands that are capable of support-
ing novel reactivity is one of the cornerstones of organotransition
metal chemistry. Since the discovery of group 4 metallocene
catalyst systems, there has been increasing interest in well-
defined transition-metal complexes that contain ligands other
than cyclopentadienyl.1-3 Nitrogen-based ligands have been
actively studied in this regard, and we ourselves have been
particularly interested in the synthesis and reaction chemistry
of amidinates for group 3-5 metals.4-9 In contrast to the wealth
of information now available for these systems, the related
amidate ligands are virtually unknown in transition-metal
chemistry. Although titanium amidates have been invoked as
intermediates in numerous catalytic cycles,10,11 the number of
well-defined group 4 η2-amide complexes remains low, and
those reported are generally the result of isocyanate insertion
into a metal-alkyl bond.12
The p-tBu group aids in solubility and provides a convenient
spectroscopic handle within the ligand framework. Compound
1 is isolated as an air-stable white solid, which is soluble in
solvents such as diethyl ether, benzene, toluene, or tetrahydro-
1
furan. The H NMR spectrum is indicative of a Cs-symmetric
species in solution; additionally, the IR spectrum shows
characteristic NH stretches from 3270 to 3240 cm-1 along with
strong absorbances around 1650 cm-1 due to νCdO. Cooling a
saturated diethyl ether solution of 1 to -30 °C resulted in
colorless crystals that were suitable for X-ray diffraction.
An ORTEP view of the molecular structure of (NO)2H2 (1)
is shown in Figure 1; bond lengths and angles are given in Table
1. Complete details of the crystallographic analyses of com-
pounds 1 and 3 are given in Table 3. The X-ray analysis shows
a monomeric compound with two amides bound to a rigid
phenylene spacer. All hydrogen atoms were found and refined.
There is an intramolecular hydrogen bond between H14 on N1
and O2 on the other amide group (1.99 Å), with an angle of
142.3°. This interaction results in the two amide groups facing
in opposing directions in relation to the phenylene backbone.
No intermolecular contacts were noted. The C-N and CdO
bond lengths of the two amide groups are similar to each other
and are unremarkable.
(NO)2H2 (1) is readily deprotonated with LiN(SiMe3)2 (2
equiv) in cold THF to yield the dilithio salt, (NO)2Li2(THF)x
(2) (Scheme 1). The product is insoluble in hydrocarbon and
aromatic solvents, with only limited solubility in THF. The 1H
NMR spectrum of 2 suggests a Cs-symmetric structure in
solution as found for the starting amide. The NH proton
resonance of 1 (10.23 ppm) is absent in the spectrum of
compound 2, and peaks corresponding to coordinated THF are
present. Integration suggests approximately one THF molecule
per lithium atom, although this number decreases upon pro-
longed exposure to vacuum; microanalytical data are consistent
with an unsolvated compound. We have been unable to obtain
X-ray quality crystals of 2, although the low solubility and high
Our goal here was to investigate the utility of η2-amides as
supporting ligands for early transition metals; additionally, we
sought to link two of these ligands together in a constrained
manner analogous to ansa-cyclopentadienyls.8,13 These com-
pounds may represent an attractive alternative to traditional salen
complexes and/or Schiff base complexes utilizing a dianionic
N2O2 coordination sphere for use in the polymerization of
olefins,14-18 or asymmetric catalysis.19,20 Here we report the
(1) Gade, L. H. Chem. Commun. 2000, 173.
(2) Kempe, R. Angew. Chem., Int. Ed. 2000, 39, 468.
(3) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem., Int.
Ed. 1999, 38, 428.
(4) Hagadorn, J. R.; Arnold, J. Organometallics 1994, 13, 4670.
(5) Hagadorn, J. R.; Arnold, J. J. Am. Chem. Soc. 1996, 118, 893.
(6) Hagadorn, J. R.; Arnold, J. J. Chem. Soc., Dalton Trans. 1997, 3087.
(7) Hagadorn, J. R.; Arnold, J. Inorg. Chem. 1997, 36, 2829.
(8) Hagadorn, J. R.; Arnold, J. Angew. Chem., Int. Ed. 1998, 37, 1729.
(9) Hagadorn, J. R.; Arnold, J. Organometallics 1998, 17, 1355.
(10) Patten, T. E.; Novak, B. M. J. Am. Chem. Soc. 1996, 118, 1906.
(11) Zhang, Y.; Jiang, J.; Chen, Y. Tetrahedron Lett. 1987, 28, 3815.
(12) Braunstein, P.; Nobel, D. Chem. ReV. 1989, 89, 1927 and references
therein.
(13) Whitener, G. D.; Hagadorn, J. R.; Arnold, J. J. Chem. Soc., Dalton.
Trans. 1999, 1249.
(14) Matsui, S.; Mitani, M.; Saito, J.; Matsukawa, N.; Tanaka, H.; Nakano,
T.; Fujita, T. Chem. Lett. 2000, 11, 554.
(15) Matsui, S.; Mitani, M.; Saito, J.; Tohi, Y.; Makio, H.; Tanaka, H.;
Fujita, T. Chem. Lett. 1999, 10, 1263.
(16) Matsui, S.; Tohi, Y.; Mitani, M.; Saito, J.; Makio, H.; Tanaka, H.;
Nitabaru, M.; Nakano, T.; Fujita, T. Chem. Lett. 1999, 10, 1065.
(17) Strauch, J.; Warren, T. H.; Erker, G.; Frohlich, R.; Saarenketo, P. Inorg.
Chim. Acta 2000, 300, 810.
(18) Tian, J.; Coates, G. W. Angew. Chem., Int. Ed. 2000, 39, 3626.
(19) Kim, G. J.; Shin, J. H. Catal. Lett. 1999, 63, 83.
(20) Belokon, Y. N.; Cepas, S. C.; Green, B.; Ikonnikov, N. S.; Khrustalev,
V. N.; Larichev, V. S.; Moscalenko, M. A.; North, M.; Orizu, C.;
Tararov, V. I.; Tasinazzo, M.; Timofeeva, G. I.; Yashkina, L. V. J.
Am. Chem. Soc. 1999, 121, 3968.
(21) Kubota, N.; Mashita, S. Adeka Argus Chemical Co., Ltd., Japanese
Patent 50105558, 1975.
10.1021/ic010533o CCC: $20.00 © 2001 American Chemical Society
Published on Web 10/03/2001

6070 Inorganic Chemistry, Vol. 40, No. 23, 2001
Notes
Table 3. Crystallographic Data
compd
formula
fw
cryst syst
(NO)2H2 (1)
C28H32N2O2
428.57
monoclinic
P21/c
[(NO)2Ti(NMe2)2]2(Et2O)2 (3)
C72H104N8O6Ti2
1273.46
monoclinic
P21/c
space group
a, Å
b, Å
c, Å
12.5782(4)
14.5619(4)
13.7768(4)
100.902(1)
2477.85(19)
4
13.899(1)
28.319(1)
18.516(1)
101.330(2)
7145.9(8)
4
â, °
V, Å3
Z
total reflns
11548
4305
0.72
0.06
19397
5779
2.78
0.16
indep reflns
µ(Mo KR), cm-1
Rint
R
0.055
0.072
Rw
T, °C
0.055
-143
0.069
-93
Scheme 1
Figure 1. ORTEP view of (NO)2H2 (1) drawn with 50% probability
ellipsoids.
Table 1. Selected Bond Distances (Å) and Angles (deg) for
(NO)2H2 (1)
C11-O1
C11-N1
N1-H14
1.238(4)
1.355(5)
0.89(4)
C18-O2
C18-N2
N2-H19
1.232(4)
1.356(5)
0.87(4)
O1-C11-C8
O1-C11-N1
C8-C11-N1
C11-N1-C12
120.0(3)
122.7(4)
117.3(3)
124.0(3)
O2-C18-C19
O2-C18-N2
C19-C18-N2
C18-N2-C17
122.4(4)
132.2(4)
114.4(3)
127.3(3)
1
pounds 3 and 4 exhibit highly symmetric H NMR spectra as
found for 1 and 2. Cooling a saturated diethyl ether solution of
3 to -30 °C resulted in deep red crystals that were amenable
to X-ray diffraction.
Table 2. Selected Bond Distances (Å) and Angles (deg) for
[(NO)2Ti(NMe2)2]2 (3)
Ti1-N1
Ti1-N3
Ti1-N5
Ti1-N6
Ti1-O1
Ti1-O3
O1-C77
N1-C77
O3-C79
N3-C79
2.22(8)
2.23(1)
1.88(2)
1.90(2)
2.05(1)
2.01(1)
1.35(2)
1.22(2)
1.27(2)
1.32(2)
Ti2-N2
Ti2-N4
Ti2-N7
Ti2-N8
Ti2-O2
Ti2-O4
O2-C78
N2-C78
O4-C80
N4-C80
2.23(2)
2.22(2)
1.88(2)
1.87(2)
2.01(1)
2.02(1)
1.33(2)
1.32(2)
1.29(2)
1.31(2)
The molecular structure of compound 3 can be found in
Figure 2. Selected bond distances and angles are presented in
Table 2. The compound cocrystallizes with two molecules of
diethyl ether, which do not interact with the metal centers and
are omitted for the sake of clarity. As seen in Figure 2,
compound 3 is dimeric in the solid state. Each dianionic ligand
binds two titanium centers, with each of the two amidate groups
binding different metal centers. The titanium atoms are ligated
by two amidate groups and two NMe2 units, generating an
octahedral geometry. The steric constraints of the ligand result
in some distortion from an idealized geometry; for example,
the trans O-Ti-O linkages exhibit angles of 150.4(6)o and
154.4(6)o. The dimeric nature of 3 also results in a cis orientation
of the two NMe2 groups, which may have favorable implications
with regard to the use of these complexes as olefin polymeri-
zation catalysts.15,16,22,23 A similar orientation of NMe2 groups
has been reported for unlinked bis(salicylaldiminato) and
â-diketiminato complexes of zirconium.17,24 The Ti-N(amidate)
bonds are longer than the Ti-N(amido) bond lengths (∼2.22
Å vs ∼1.88 Å) due to the delocalized nature of the amidate
double bond. The Ti-N(amido) bond lengths (1.87(2)-1.90-
(2) Å) are similar to those reported for Ti(NMe2)3Cl (1.866(4)
Å);25 additionally, the Ti-N(amidate) bonds are comparable to
those found in previously reported titanium-salen complexes.26-29
[(NO)2Ti(NMe2)2]2 (3) and [(NO)2Ti(NEt2)2]2 (4) react with
excess Me3SiCl in toluene to yield the dichloride (NO)2TiCl2
N1-Ti1-N3
N1-Ti1-N5
N1-Ti1-N6
N1-Ti1-O1
N1-Ti1-O3
N3-Ti1-N5
N3-Ti1-N6
N3-Ti1-O1
N3-Ti1-O3
N5-Ti1-N6
N5-Ti1-O1
N5-Ti1-O3
N6-Ti1-O1
N6-Ti1-O3
O1-Ti1-O3
O1-C77-N1
O2-C78-N2
87.2(6)
93.5(7)
150.4(8)
61.1(6)
97.4(6)
155.1(7)
92.5(7)
95.1(5)
61.8(5)
98.8(8)
107.1(6)
93.4(7)
89.5(7)
108.6(7)
150.4(6)
115(2)
N2-Ti2-N4
N2-Ti2-N7
N2-Ti2-N8
N2-Ti2-O2
N2-Ti2-O4
N4-Ti2-N7
N4-Ti2-N8
N4-Ti2-O2
N4-Ti2-O4
N7-Ti2-N8
N7-Ti2-O2
N7-Ti2-O4
N8-Ti2-O2
N8-Ti2-O4
O2-Ti2-O4
O3-C79-N3
O4-C80-N4
84.6(6)
94.0(7)
153.7(7)
61.7(6)
98.2(6)
152.2(7)
93.0(7)
98.6(6)
61.8(6)
99.9(8)
105.2(7)
91.0(7)
93.0(7)
103.8(6)
154.4(6)
115(2)
112(2)
115(2)
melting point of this compound suggest a polymeric structure
in the solid state.
(NO)2H2 (1) also reacts with the homoleptic titanium amides
Ti(NR2)4 (R ) Me, Et) to directly generate the titanium
complexes [(NO)2Ti(NMe2)2]2 (3) and [(NO)2Ti(NEt2)2]2 (4)
(Scheme 1). The amine elimination reactions were carried out
in cold THF, yielding deep red solutions of 3 and 4. Both
titanium complexes are soluble in diethyl ether, benzene,
toluene, and THF but only slightly soluble in pentane. Com-
(22) Tjaden, E. B.; Swenson, D. C.; Jordan, R. F. Organometallics 1995,
14, 371.
(23) Corden, J. P.; Errington, W.; Moore, P.; Wallbridge, M. G. H. Chem.
Commun. 1999, 323.
(24) Kakaliou, L.; Scanlon, W. J.; Qian, B.; Baek, S. W.; Smith, M. R.;
Motry, D. H. Inorg. Chem. 1999, 38, 5964.

Notes
Inorganic Chemistry, Vol. 40, No. 23, 2001 6071
and the dichloro compound 5 exhibit only modest activities as
ethylene polymerization catalysts in the presence of MAO (500
equiv).
Experimental Section
General Considerations. Standard Schlenk-line and glovebox
techniques were used unless stated otherwise. Pentane, diethyl ether,
toluene, tetrahydrofuran, and methylene chloride were purified by
passage through a column of activated alumina and degassed with argon.
C6D6 was vacuum transferred from sodium/benzophenone. p-tBu-
benzoyl chloride was purchased from Aldrich and used as received.
Phenylenediamine was purchased from Aldrich and recrystallized from
benzene prior to use. Triethylamine was purchased from Aldrich and
distilled over Na. Chlorotrimethylsilane was purchased from Strem and
distilled over CaH2 prior to use. LiN(SiMe3)2,30 Ti(NMe2)4,31 Ti(NEt2)4,31
32
and TiCl4(THF)2 were prepared according to literature procedures.
Melting points were determined in sealed capillary tubes under nitro-
1
gen and are uncorrected. H NMR spectra were recorded at ambient
temperature; chemical shifts are given relative to C6D5H (7.15 ppm)
or CD2HCN (1.94 ppm). 13C NMR chemical shifts are given relative
to C6D6 (128.39 ppm). IR samples were prepared as Nujol mulls and
taken between KBr plates. Elemental analyses were determined at the
College of Chemistry, University of California, Berkeley. Single-crystal
X-ray structure determinations were performed at CHEXRAY, Uni-
versity of California, Berkeley.
Figure 2. ORTEP view of [(NO)2Ti(NMe2)2]2 (3) drawn with 50%
probability ellipsoids. Amidate aryl groups have been omitted for clarity.
(5) (Scheme 1). Compound 5 may also be synthesized via a
disproportionation reaction between [(NO)2Ti(NMe2)2]2 (3) and
1 equiv of TiCl4(THF)2 in refluxing toluene. In both cases,
(NO)2TiCl2 (5) was isolated as a pentane soluble red/brown
solid. Attempts to prepare compound 5 by salt metathesis
between the dilithio salt 2 and TiCl4(THF)2 were partially
successful; although the dichloride was also formed by this
route, we were unable to separate the product from other ligand-
containing impurities formed in the reaction. Notable in the 1H
and 13C{1H} NMR spectra of 5 are the absence of resonances
corresponding to NR2 groups and a doubling of all of the ligand
peaks, in contrast to that found for compounds 1-4. This
suggests an asymmetric solution structure, as a result of either
aggregation or a rigid monomeric structure. A similar asymmetry
has been noted for a series of monomeric Schiff base complexes
of titanium.23 The extremely high solubility of 5 has prevented
us thus far from obtaining X-ray quality crystals of this
compound.
(NO)2H2 (1). This reaction was performed without the exclusion of
air. A three-neck round-bottomed flask equipped with a reflux condenser
and a dropping funnel was charged with 4-tert-butylbenzoyl chloride
(14.1 g, 71.7 mmol), triethylamine (7.25 g, 71.7 mmol,) and 250 mL
of CH2Cl2. A methylene chloride solution (50 mL) of phenylenediamine
(3.88 g, 35.9 mmol) was added to the dropping funnel and added
dropwise to the benzoyl chloride/triethylamine solution at 0 °C over a
period of 15 min. This resulted in a cloudy yellow slurry. The mixture
was heated to reflux for 12 h. The clear yellow solution was then cooled
to room temperature and the solvent removed under vacuum. The yellow
solid was then extracted with water (3 × 300 mL) and filtered to yield
a white solid. The solid was dried under vacuum at 100 °C to remove
residual water (13.5 g, 88% yield). Cooling a saturated diethyl ether
solution to -30 °C resulted in small colorless blocks suitable for X-ray
1
diffraction. Mp: 235-238 °C. H NMR (C6D6, 300 MHz): δ 10.23
3
(br s, 2H, NH), 8.37 and 7.31 (AB dd, 8H, amidate phenyl, JH-H
)
3
8.5 Hz), 7.52 and 6.51 (AB dd, 4H, backbone phenyl, JH-H ) 8.0
Hz), 1.14 (s, 18H, tert-butyl). 13C{1H} NMR (CDCl3, 400 MHz): δ
166.5, 155.5 and 130.7 (tertiary phenyl), 127.6, 125.9, 125.8, and 125.6
(phenyl CH), 35.0 (CMe3), 31.2 (CMe3), amidate carbon not observed.
IR (cm-1): 3269 (w), 3243 (w), 1649 (m), 1609 (m), 1598 (m), 1529
(m), 1506 (m), 1365 (m), 1320 (m), 1308 (m), 1270 (w), 759 (w).
Anal. Calcd for C28H32N2O2: C, 78.47; H, 7.53; N, 6.54. Found: C,
78.39; H, 7.54; N, 6.44.
(NO)2Li2(THF)x (2). To a THF solution of 1 (1.00 g, 2.33 mmol)
maintained at -78 °C was slowly added a THF solution of LiN(SiMe3)2
(780 mg, 4.66 mmol) via cannula, generating a yellow solution. After
stirring overnight, the solvent was removed in vacuo and the resulting
white powder washed with pentane to remove HN(SiMe3)2 (1.01 g,
85% yield). Mp: >350 °C. 1H NMR (CD3CN, 300 MHz): δ 7.99 and
7.45 (AB dd, 8H, amidate phenyl, 3JH-H ) 8.0 Hz), 7.90 and 6.91 (AB
m, 4H, backbone phenyl), 1.33 (s, 18H, tert-butyl). The solubility of
compound 2 was too low to obtain a suitable 13C NMR spectrum. IR
(cm-1): 1654 (s), 1596 (s), 1576 (s), 1520 (s), 1504 (s), 1263 (m),
1102 (w), 1044 (m), 1016 (m), 904 (w), 852 (w), 794 (m), 776 (m),
754 (m), 709 (m). Anal. Calcd for C28H30Li2N2O2: C, 76.36; H, 6.87;
N, 6.36. Found: C, 76.05; H, 7.08; N, 6.02.
Preliminary screening of some of the compounds reported
here (bis-amido 3 and dichloro 5) indicates that these systems
exhibit only modest activities for polymerization of ethylene
(1 atm) when activated with methylalumoxane (500 equiv).
Conclusions
The synthesis of a new ligand system in which two amides
are coupled via a rigid phenylene spacer is readily accomplished
in a high-yield, single-step reaction. This reaction should be
easily extended to incorporate a chiral spacer into the ligand
backbone, i.e., trans-1,2-diaminocyclohexane or (1S,2S)-1,2-
diphenylethylenediamine, resulting in a new class of C2-
symmetric ligands. This report also illustrates that the ami-
date ligand is a suitable spectator ligand for titanium, pro-
viding the metal center with an N2O2 coordination sphere sim-
ilar to that found in the more well-studied salen, bis(salicyl-
aldiminato), and â-diketiminate systems. Bis-amido complex 3
(25) Dick, D. G.; Rousseau, R.; Stephan, D. W. Can. J. Chem. 1991, 69,
357.
(26) Coles, S. J.; Hursthouse, M. B.; Kelly, D. G.; Toner, A. J.; Walker,
N. M. J. Chem. Soc., Dalton Trans. 1998, 3489.
(27) Gilli, G.; Cruickshank, D. W. J.; Beddoes, R. L.; Mills, O. S. Acta
Crystallogr. 1972, B28, 1889.
[(NO)2Ti(NMe2)2]2 (3) and [(NO)2Ti(NEt2)2]2 (4). For 3: A pentane
solution of Ti(NMe2)4 (520 mg, 2.33 mmol) was added to a THF
(30) Bartsch, R.; Drost, C.; Klingbeil, V. in Synthetic Methods of Organo-
metallic and Inorganic Chemistry; Herrman, W. A., Ed.; Thieme: New
York, 1996; Vol. 2, p 15.
(28) Choudhary, N. F.; Hitchcock, P. B.; Leigh, G. J. Inorg. Chim. Acta
2000, 306, 24.
(29) Repo, T.; Klinga, M.; Leskela, M.; Pietikainen, P.; Brunow, G. Acta
Crystallogr. 1996, C52, 2742.
(31) Bradley, D. C.; Thomas, L. M. J. Chem. Soc. 1960, 3857.
(32) Manzer, L. E. Inorg. Synth. 1982, 21, 135.

6072 Inorganic Chemistry, Vol. 40, No. 23, 2001
Notes
solution of 1 (1.00 g, 2.33 mmol) maintained at -78 °C. The
homogeneous red solution was stirred overnight and allowed to warm
to room temperature. The solvent was then removed under vacuum,
and the orange solid was washed with pentane. The solid was then
dissolved in a minimum amount of diethyl ether and cooled to -30
°C, resulting in small red blocks (435 mg, 33% yield). Compound 4
was prepared in a similar manner from 1 and Ti(NEt2)4.
and the solvent was removed under vacuum to yield a dark red/brown
solid (393 mg, 72% yield).
Method C. A THF solution of TiCl4(THF)2 (195 mg, 0.585 mmol)
was added via cannula to a THF solution of the dilithio salt 3 (300
mg, 0.585 mmol) at -78 °C. The resultant dark red solution was left
to stir overnight and warm to room temperature. The solvent was
removed under vacuum, and the residue was extracted with toluene,
forming a red solution over a white preciptate. The reaction mixture
was filtered to remove LiCl, and the solvent was removed to yield a
red solid. The product could not be fully separated from other ligand-
containing impurities (160 mg, 50% yield (estimated)). Mp: 135-
138 °C. 1H NMR (C6D6, 300 MHz): δ 8.04, 7.54, 7.17, and 7.03 (AB
dd, 4H, backbone phenyl, 3JH-H ) 6.0 Hz), 7.72, 7.46, 7.00, and 6.92
(AB dd, 8H, amidate phenyl, 3JH-H ) 8.6 Hz), 1.04 and 0.99 (s, 18H,
tert-butyl). 13C{1H} NMR (CDCl3, 400 MHz): δ 169.1, 158.1, 154.2,
152.9, 143.0, 135.0, 130.2, and 127.5 (tertiary phenyl), 130.7, 128.9,
125.6, 125.2, 124.3, 124.1, 120.0, and 113.0 (phenyl CH), 35.2 and
34.7 (CMe3), 31.0 and 30.9 (CMe3). IR (cm-1): 1702 (s), 1605 (s),
1334 (s), 1288 (s), 1264 (s), 1230 (m), 1193 (m), 1148 (m), 1017 (m),
930 (m), 907 (m), 837 (s), 762 (m), 735 (s). Independently prepared
samples of 5 consistently analyzed low in carbon. Anal. Calcd for
C28H30Cl2N2O2Ti: C, 61.67; H, 5.55; N, 5.14. Found: C, 55.90; H,
Data for 3. Mp: 180-182 °C. 1H NMR (C6D6, 300 MHz): δ 7.65
and 6.97 (AB dd, 8H, amidate phenyl, 3JH-H ) 8.5 Hz), 6.69 and 6.54
(AB m, 4H, backbone phenyl), 3.62 (s, 12H, NCH3), 1.09 (s, 18H,
tert-butyl). 13C{1H} NMR (C6D6, 300 MHz): δ 172.5, 153.4 and 143.4
(tertiary phenyl), 131.6, 127.0, 124.9, and 124.2 (phenyl CH), 46.8
(NCH3), 35.0 (CMe3), 31.5 (CMe3), amidate carbon not observed. IR
(cm-1): 1608 (s), 1576 (s), 1542 (s), 1505 (s), 1412 (s), 1266 (s), 1194
(s), 1108 (m), 1018 (m), 957 (m), 937 (m), 843 (m), 800 (m), 716 (m),
695 (m), 654 (m). Anal. Calcd for C32H42N4O2Ti(Et2O)2: C, 67.91; H,
8.23; N, 8.80. Found: C, 67.05; H, 7.57; N, 9.45.
Data for 4. Mp: 216-218 °C. 1H NMR (C6D6, 300 MHz): δ 7.59
3
and 6.96 (AB dd, 8H, amidate phenyl, JH-H ) 8.5 Hz), 6.72 and
6.67 (AB m, 4H, backbone phenyl), 4.71 and 3.15 (m, 8H, NCH2CH3,
3
3JH-H ) 6.7 Hz), 1.35 (t, 12H, NCH2CH3, JH-H ) 6.7 Hz), 1.12 (s,
18H, tert-butyl). 13C{1H} NMR (C6D6, 400 MHz): δ 172.3, 153.2
and 143.4 (tertiary phenyl), 131.5, 126.7, 124.9, and 124.3 (phenyl
CH), 48.3 (NCH2CH3), 35.0 (CMe3), 31.6 (CMe3), 15.4 (NCH2CH3),
amidate carbon not observed. IR (cm-1): 1610 (m), 1575 (m), 1543
(m), 1505 (m), 1411 (m), 1268 (w), 1187 (w), 999 (w), 930 (w), 884
(m), 842 (m), 786 (m), 753 (w), 716 (w), 694 (w). Anal. Calcd for
C36H50N4O2Ti: C, 69.89; H, 8.15; N, 9.06. Found: C, 69.66; H, 8.25;
N, 8.93.
1
6.28; N, 5.13. (See Supporting Information for a copy of H NMR
spectrum.)
General Procedures for X-ray Crystallography. Pertinent details
for the individual compounds can be found in Table 3. For compound
1, all non-hydrogen atoms were refined anisotropically. Hydrogen atoms
were assigned idealized positions and were included in structure factor
calculations. For compound 3, only a low-quality data set was obtained;
thus only the titanium atoms were refined anisotropically. The aromatic
rings were treated as rigid groups, and all hydrogen atoms were assigned
idealized positions and were included in structure factor calculations,
but were not refined.
(NO)2TiCl2 (5). Method A. Me3SiCl (7.6 mL, 60.0 mmol) was
added to a toluene solution of 4 (3.70 g, 6.00 mmol) via syringe, causing
the solution to darken. The solution was stirred at room temperature
for 24 h, after which time the volatiles were removed under vacuum.
The remaining oily solid was extracted with pentane, forming a dark
red solution and a red solid. The pentane layer was filtered away from
the insoluble material, and the solvent was removed to yield a red solid
(2.80 g, 86% yield). Compound 5 may also be generated starting with
the dimethylamido derivative 3.
Method B. Compound 3 (563 mg, 1.00 mmol) and TiCl4(THF)2
(334 mg, 1.00 mmol) were combined in a Schlenk tube. Toluene was
added, and the contents were heated to 100 °C for 24 h, forming a
dark brown solution and some insoluble material. The reaction mixture
was then cooled to room temperature. The reaction mixture was filtered,
Acknowledgment. We thank the Department of Energy for
support of this work.
Supporting Information Available: Tables of positional and
thermal parameters and bond distances and angles for compounds 1
and 3. This material is available free of charge via the Internet at
http://pubs.acs.org.
IC010533O