Mononuclear Titanium Complexes That Contain Aminopyridinato Ligands

Article abstract of DOI:10.1021/ic951177a

2-(Methylamino)pyridine (Me-APy-H), 2-anilinopyridine (Ph-APy-H), and 4-methyl-2-((trimethylsilyl)amino)-pyridine (TMS-APy-H) were used to synthesize mononuclear monochloro complexes that contain two or three such aminopyridines as strained amido ligands. The reaction of 2 or 3 equiv of in situ generated lithium aminopyridinate with TiCl₄(THF)₂ or TiCl₄ afforded just in the case of Me-APy-H a red crystalline product (Me-APy)₃TiCl (1a) but in unacceptably low yield. An alternative way to synthesize 1a and (Ph-APy)₃TiCl (1b) is amine elimination, starting from mixed chlorodimethylamido complexes like (Me₂N)₃TiCl or (Me₂N)₂TiCl₂. The reaction of (Me₂N)₃TiCl with 2 equiv of Me-APy-H, Ph-APy-H or TMS-APy-H afforded (Me-APy)₂Ti-(NMe₂)Cl (2a), (Ph-APy)₂Ti(NMe₂)Cl (2b), or (TMS-APy)₂Ti(NMe₂)Cl (2c). These compounds represent novel unusual highly nitrogen-coordinated titanium complexes. X-ray diffraction studies of la established its monomeric structure as having a disturbed pentagonal bipyramidal coordination geometry. X-ray crystal structure investigations of 2a - c proved these compounds to be monomeric with a slightly distorted octahedral coordination geometry. The η² binding mode of the strained aminopyridinato ligands is discussed in comparison to the related amidinato ligand system by averaging bond distances and angles of the determined structures. The N_Py - C - N_amido angle of 108(1)° instead of the desired 120° Indicates the highly strained tweezers-like bonding mode. The Ti - N_Py distances vary within the known range. The Ti - N_amido distances are more than 0.1 A? longer than the expected values and indicate weak amido bonds. Variable-temperature NMR investigations of complex 2c are indicative of exchange processes which proceed most likely via tetrahedral transition states. Crystallographic data (distances, A?; angles, deg): 1a, C₁₈H₂₁ClN₆Ti, a = 9.313(1), b = 10.277(1), c = 11.302(1), α = 98.15(1), β= 108.28(1), γ = 102.98-(1), triclinic, P1, Z = 2; 2a, C₁₄H₂₀ClN₅Ti, a = 8.725(1). b = 9.258(1), c = 10.778(1), α = 83.288(7), β= 79.977(9), γ = 78.766(8), triclinic, P1?, Z = 2; 2b, C₂₄H₂₄ClN₅Ti, a = 17.652(3), b = 7.959(1), c = 18.017(3), β = 111.37(1), monoclinic, P2₁/a, Z = 4; 2c, C₂₀H₃₆ClN₅Si₂Ti, a = 10.786(1), b = 14.053(1), c = 18.144(1), β = 97.06(1), monoclinic, P2₁/c, Z = 4.

Full text of DOI:10.1021/ic951177a

2644
Inorg. Chem. 1996, 35, 2644-2649
Mononuclear Titanium Complexes That Contain Aminopyridinato Ligands
Rhett Kempe* and Perdita Arndt
MPG AG “Komplexkatalyse” an der Universita¨t Rostock, Buchbinderstrasse 5-6,
18055 Rostock, Germany
ReceiVed September 8, 1995X
2-(Methylamino)pyridine (Me-APy-H), 2-anilinopyridine (Ph-APy-H), and 4-methyl-2-((trimethylsilyl)amino)-
pyridine (TMS-APy-H) were used to synthesize mononuclear monochloro complexes that contain two or three
such aminopyridines as strained amido ligands. The reaction of 2 or 3 equiv of in situ generated lithium
aminopyridinate with TiCl4(THF)2 or TiCl4 afforded just in the case of Me-APy-H a red crystalline product
(Me-APy)3TiCl (1a) but in unacceptably low yield. An alternative way to synthesize 1a and (Ph-APy)3TiCl (1b)
is amine elimination, starting from mixed chlorodimethylamido complexes like (Me2N)3TiCl or (Me2N)2TiCl2.
The reaction of (Me2N)3TiCl with 2 equiv of Me-APy-H, Ph-APy-H or TMS-APy-H afforded (Me-APy)2Ti-
(NMe2)Cl (2a), (Ph-APy)2Ti(NMe2)Cl (2b), or (TMS-APy)2Ti(NMe2)Cl (2c). These compounds represent novel
unusual highly nitrogen-coordinated titanium complexes. X-ray diffraction studies of 1a established its monomeric
structure as having a disturbed pentagonal bipyramidal coordination geometry. X-ray crystal structure investigations
of 2a-c proved these compounds to be monomeric with a slightly distorted octahedral coordination geometry.
The η2 binding mode of the strained aminopyridinato ligands is discussed in comparison to the related amidinato
ligand system by averaging bond distances and angles of the determined structures. The NPy-C-Namido angle of
108(1)° instead of the desired 120° indicates the highly strained tweezers-like bonding mode. The Ti-NPy distances
vary within the known range. The Ti-Namido distances are more than 0.1 Å longer than the expected values and
indicate weak amido bonds. Variable-temperature NMR investigations of complex 2c are indicative of exchange
processes which proceed most likely via tetrahedral transition states. Crystallographic data (distances, Å; angles,
deg): 1a, C18H21ClN6Ti, a ) 9.313(1), b ) 10.277(1), c ) 11.302(1), R ) 98.15(1), â ) 108.28(1), γ ) 102.98-
(1), triclinic, P1h, Z ) 2; 2a, C14H20ClN5Ti, a ) 8.725(1), b ) 9.258(1), c ) 10.778(1), R ) 83.288(7), â )
79.977(9), γ ) 78.766(8), triclinic, P1h, Z ) 2; 2b, C24H24ClN5Ti, a ) 17.652(3), b ) 7.959(1), c ) 18.017(3),
â ) 111.37(1), monoclinic, P21/a, Z ) 4; 2c, C20H36ClN5Si2Ti, a ) 10.786(1), b ) 14.053(1), c ) 18.144(1), â
) 97.06(1), monoclinic, P21/c, Z ) 4.
Introduction
or group 4 metal complexes have been published so far. Such
ligands are interesting because they combine a number of
features which would make them attractive ligands for early
transition metals in high oxidation states if they are bound in a
η2 fashion. Electronic requirements of highly Lewis acidic
Alternative amido-based ligands that stabilize early transition
metal complexes in a Cp analogous fashion have been inves-
tigated intensively.1,18 Recently catalytic activity of such
titanium complexes was reported in hydroboration2 and olefin
polymerization.3 With regard to possible catalytic applications,
we are currently examining the chemistry of mononuclear early
transition metal complexes that contain 2-aminopyridinato
ligands.
(4) Cotton, F. A.; Walton, R. A. Multiple Bonds Between Metal Atoms;
John Wiley and Sons: New York, 1982; see also references cited
therein. Cotton, F. A.; Niswander, R. H.; Sekutowski J. C. Inorg.
Chem. 1978, 17, 3541. Cotton, F. A.; Ilsley, W. H.; Kaim, W. Inorg.
Chem. 1979, 18, 2717. Chakravarty, A. R.; Cotton, F. A.; Shamshoum,
E. S. Inorg. Chem. 1984, 23, 4216. Chakravarty, A. R.; Cotton, F.
A.; Tochter, D. A. Inorg. Chem. 1984, 23, 4693.
(5) Cotton, F. A.; Dori, Z.; Marler, D. O.; Schwotzer, W. Inorg. Chem.
1984, 23, 4023. Chakravarty, A. R.; Cotton, F. A.; Tochter, D. A.
Inorg. Chem., 1985, 24, 172. Chakravarty, A. R.; Cotton, F. A.;
Falvello, L. R. Inorg. Chem. 1986, 25, 214. Yao, C.-L.; Park, K. H.;
Khokhar, A. R.; Jun, M.-J.; Bear, J. L. Inorg. Chem. 1990, 29, 4033.
Bear, J. L.; Yao, C.-L.; Liu, L.-M.; Capdeville, F. J.; Korp, J. D.;
Albright, T. A.; Kang, S.-K.; Kadish, K. M. Inorg. Chem. 1989, 28,
1254.
(6) Deeming, A. J.; Peters, R.; Hursthous, M. B.; Backer-Dirks, J. D. J.
J. Chem. Soc., Dalton Trans. 1982, 1205. Burgess, K.; Johnson, B. F.
G.; Lewis, J; Raithby, P. R. J. Chem. Soc., Dalton Trans. 1983, 1661.
Andreu, P. L.; Cabeza, J. A.; Riera, V.; Jeannin, Y.; Miguel, D. J.
Chem Soc., Dalton Trans. 1990, 2201. Lugan, N.; Laurent, F.; Lavigne,
G.; Newcomb, T. P.; Liimatta, E. W.; Bonnet, J.-J. J. Am. Chem. Soc.
1990, 112, 8607. Andreu, P. L.; Cabeza, J. A.; Pellinghelli, M. A.;
Riera, V.; Tiripicchio, A. Inorg. Chem. 1991, 30, 4611. Cabeza, J.
A.; Llamazares, A.; Riera, V.; Triki, S.; Ouahab, L. Organometallics
1992, 11, 3334.
(7) Chakravarty, A. R.; Cotton, F. A.; Shamshoum, E. S. Inorg. Chim.
Acta 1984, 86, 5. Calhorda, M. J.; Carrondo, M. A. A. F. D. C. T.;
Gomes da Costa, R.; Dias, A. R.; Duarte, M. T. L. S.; Hursthouse,
M. B. J. Organomet. Chem. 1987, 320, 53. Edema, J. J. H.;
Gambarotta, S.; Meetsma, A; Spek, A. L.; Veldman, N. Inorg. Chem.
1991, 30, 2062.
Ligands of this type have been used to stabilize metal-metal
multiple bonds,4 to synthesize polynuclear transition metal
complexes5 and small clusters.6 Only a few examples of well
characterized mononuclear transition metal complexes7 that
contain a η2-bound aminopyridinato ligand are described. To
our knowledge no group 3 (including lanthanides and actinides)
X Abstract published in AdVance ACS Abstracts, March 15, 1996.
(1) Edelmann, F. T. Coord. Chem. ReV. 1994, 137, 403.
(2) Bijpost, E. A.; Duchateau, R.; Teuben, J. H. J. Mol. Catal. A 1995,
95, 121.
(3) Flores, J. C.; Chien, J. C. W.; Rausch, M. D. Organometallics 1995,
14, 1827. Flores, J. C.; Chien, J. C. W.; Rausch, M. D. Organometallics
1995, 14, 2106.
0020-1669/96/1335-2644$12.00/0 © 1996 American Chemical Society

Ti Complexes Containing Aminopyridinato Ligands
Inorganic Chemistry, Vol. 35, No. 9, 1996 2645
Table 1. Crystallographic Data for 1a and 2a-c
1a
2a
2b
2c
empirical formula
fw
space group (No.)
temp, °C
F, g cm-3
a, Å
C18H21ClN6Ti
404.8
C14H20ClN5Ti
341.7
C24H24ClN5Ti
465.8
P21/a (14)
20
1.31
17.652(3)
7.959(1)
18.017(3)
C20H36ClN5Si2Ti
486.1
P21/c (14)
20
1.18
10.786(1)
14.053(1)
18.144(1)
P1h (2)
P1h (2)
20
1.38
20
1.36
9.313(1)
10.277(1)
11.302(1)
98.15(1)
108.28(1)
102.98(1)
974.2(2)
2
8.725(1)
9.258(1)
10.778(1)
83.288(7)
79.977(9)
78.766(8)
837.8(2)
2
b, Å
c, Å
R, deg
â, deg
111.37(1)
97.06(1)
γ, deg
V, Å3
2357.2(6)
4
0.50
94.0
100.0
0.055
0.171
2729.3(4)
4
Z
µ mm-1
0.59
0.67
0.51
transm min %
transm max %
R1a (I > 2σ(I))
wR2b (all data)
90.6
88.0
77.2
100.0
100.0
99.8
0.036
0.035
0.048
0.146
0.112
0.107
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. wR2 ) {∑[w(Fo - Fc2)]2/∑[w(Fo )]2}1/2
.
b
2
2
by direct methods (SHELXS-86)13 and refined by full-matrix least-
squares techniques against F2 (SHELXL-93).14 XP (SIEMENS Ana-
lytical X-ray Instruments, Inc.) and SCHAKAL-92 (E. Keller, Uni-
versity of Freiburg, Germany) were used for structure representations.
metal centers are fulfilled by the strong basicity of amide and
pyridine ligands.8 Complex stability is supported by a chelating
effect, and the strained η2 binding mode causes an unusual
reactivity. Substitution at the amide nitrogen and at the pyridine
ring allows fine tuning of electronic properties, of bulkiness
(stabilization of the metal complexes by steric shielding), and
of solubility (including crystallization behavior). The offered
set of electrons is similar to those of a Cp ligand, which suggests
that the ligand could be considered as Cp analogous. The
objectives of the present study were to develop syntheses of
monomolecular monochloro titanium complexes that contain
aminopyridinato ligands. Interest is also focused on structural
aspects.
4-Methyl-2-((trimethylsilyl)amino)pyridine. To a solution of
2-amino-4-picoline (12.8 g, 0.12 mmol) in ether (120 mL) was added
slowly via syringe 47.6 mL of n-BuLi in hexane (2.5 M, 0.118 mol) at
0 °C. The mixture was allowed to warm to room temperature over a
period of 20 min and stirred for another 90 min. The mixture was
cooled to 0 °C, and trimethylsilyl chloride (23.2 mL, 0.183 mol) was
added slowly via syringe at 0 °C. The mixture was allowed to warm
to room temperature and was stirred for 12 h. The solution was filtered,
and solvents were removed under vacuum. Distillation at 43 °C (0.03
mbar) afforded a colorless liquid. Yield: 18.0 g, 0.100 mol, 85%. 1H
NMR (303 K, C6D6): δ 8.04 (dd, 1H, Py H6), 6.21 (dd, 1H, Py H5),
5.87 (s, 1H, Py H3), 3.80 (s, 1H, NH), 1.90 (s, 3H, Me), 0.33 (s, 9 H,
SiMe3). 13C NMR (303 K, C6D6): δ 160.6 (Py C2), 148.3 (Py C6),
147.8 (Py C4), 114.6, 110.6 (Py C3/C5), 20.8 (Me), 0.33 (SiMe3).
Experimental Section
Materials and Procedures. The complexes (Me2N)3TiCl12 and
12
(Me2N)2TiCl2 were prepared according to a previously published
(Me-APy)3TiCl (1a). A solution of 600 mg (2.78 mmol) of (Me2N)3-
TiCl in 15 mL of ether was added slowly via syringe to a solution of
8.95 mmol of 2-(methylamino)pyridine in 50 mL of ether. The color
became immediately red. The mixture was stirred over a period of 30
min. The solution was filtered, and the volume was reduced under
vacuum to approximately 20 mL. Cooling to -30 °C overnight
afforded a red crystalline material. Yield: 721 mg, 1.78 mmol, 64%.
1H NMR (303 K, C6D6): δ 7.56 (d, 1H, Py H6), 6.95 (m, 1H, Py H4),
6.02 (m, 1H, Py H5), 5.77 (d, 1H, Py H3), 3.20 (s, 3H, Me). 13C NMR
(303 K, C6D6): δ 171.3 (Py C2), 141.6 (Py C6), 139.6 (Py C4), 101.2,
101.0 (Py C3/C5), 38.1 (Me). Anal. Calcd for C18H21N6TiCl: C, 53.42;
H, 5.23; N, 20.76. Found: C, 52.22; H, 5.02; N, 20.08. Mp
(uncorrected): 138 °C.
procedure. 2-(Methylamino)pyridine was degassed and stored over 4
Å molecular sieves. All other reagents were obtained commercially
and used as supplied. All manipulations of air-sensitive materials were
performed with rigorous exclusion of oxygen and moisture in (at 140
°C) dried Schlenk-type glassware on a dual-manifold Schlenk line,
interfaced to a high-vacuum line, or in an argon-filled Vacuum
Atmospheres glovebox (mBraun labmaster 130) with a high-capacity
recirculator (<1.5 ppm of O2 ). Solvents (Aldrich) and NMR solvents
(Cambridge Isotope Laboratories, all 99 atom % D) were freshly
distilled from sodium tetraethylaluminate.
Physical Measurements. The NMR spectra were recorded on a
Bruker ARX 400 NMR spectrometer with a variable-temperature unit.
Chemical shifts were referenced to signals of the solvents THF-d8 (â-
CH2: δH ) 1.73 ppm, δC ) 25.2 ppm) and C6D6 (δH ) 7.16 ppm, δC
) 128.0 ppm). The spectra were assigned with the help of Dept and
COSY experiments. Melting points were determined in sealed capil-
laries on a Bu¨chi 535 apparatus. Elemental analyses were performed
with a Leco CHNS-932. X-ray diffraction data were collected on a
CAD4 MACH3 diffractometer using graphite-monochromated Mo KR
radiation. The crystals were sealed inside capillaries. Absorption
corrections were carried out by Ψ-scans. The structures were solved
(Ph-APy)3TiCl (1b). A solution of 432 mg (2.00 mmol) of (Me2N)3-
TiCl in 20 mL of ether was added slowly via syringe to a solution of
1.056 g (6.20 mmol) of 2-anilinopyridine in 30 mL of ether. A red-
purple color was seen. The mixture was stirred over a period of 30
min. The solution was filtered, and the volume was reduced under
vacuum to approximately 20 mL. Cooling to -30 °C overnight
afforded a purple crystalline material. Yield: 843 mg, 1.43 mmol,
71%. 1H NMR (303 K, THF-d8): 7.5 (br, 1H, Py H6), 7.35 (t, 1H, Py
H4), 7.00 (t, 2H, m Ph), 6.86 (m, 1H, p Ph), 6.68 (d, 2H, o Ph), 6.45
(t, 1H, Py H5), 6.10 (d, 1H, Py H3). 13C NMR (303 K, THF-d8): δ
149.5 (Py C2), 142.9 (ipso-C Ph), 141.8 (Py C6), 140.6 (Py C4), 129.2
(m-C Ph), 125.0 (o-C Ph), 124.3 (p-C Ph), 112.5 (Py C5), 104.3 (Py
C3). Anal. Calcd for C33H27N6TiCl: C, 67.07; H, 4.61; N, 14.22.
Found: C, 67.07; H, 4.91; N, 14.75. Mp (uncorrected): 140 °C.
(8) Lappert, M. F.; Power, P. P.; Sanger, A. R.; Srivastava, R. C. Metal
and Metalloid Amides; Ellis Norwood Ltd.: Chichester, England, 1980.
(9) Engelhardt, L. M.; Jacobsen, G. E.; Junk, P. C.; Raston, C. L.; Skelton,
B. W.; White, A. H. J. Chem. Soc., Dalton Trans. 1988, 1011.
Engelhardt, L. M.; Jacobsen, G. E.; Patalinghug, W. C.; Skelton, B.
W.; Raston, C. L.; White, A. H. J. Chem. Soc., Dalton Trans. 1991,
2859.
(10) Phillion, D. P.; Neubauer, R.; Andrew S. S. J. Org. Chem. 1986, 51,
1610.
(11) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson, D.
G.; Taylor R., J. Chem. Soc., Dalton Trans. 1989, S1.
(12) Benzinger, E.; Kornicker, W. Chem. Ber. 1961, 94, 2263.
(13) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467.
(14) Sheldrick G. M. SHELXL-93: A program for crystal structure
refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1993.
(15) QUESD3D and VISTA statistics from 18 Ti-NPy bond distances.
(16) QUESD 3D and VISTA statistics from 117 Ti-Namido bond distances.

2646 Inorganic Chemistry, Vol. 35, No. 9, 1996
Kempe and Arndt
(Me-APy)2Ti(NMe2)Cl (2a). A solution of 307 mg (1.42 mmol)
of (Me2N)3TiCl in 5 mL of ether was added slowly via syringe to a
solution of 307 µL (2.99 mmol) of 2-(methylamino)pyridine in 15 mL
of ether. The color became immediately red. The mixture was stirred
over a period of 10 min, during which a purple-red crystalline product
precipitated. The product was isolated by filtration and washed with
cold hexane. Yield: 192 mg, 0.56 mmol, 40%. 1H NMR (303 K,
THF-d8): δ 7.61 (d, 2H, Py H6), 7.44 (m, 2H, Py H4), 6.36 (m, 2H, Py
H5), 6.16 (d, 2H, Py H3), 3.68 (s, 6H, NMe2), 3.15 (s, 6H, Py-NMe).
13C NMR (303 K, THF-d8): δ 169.4 (Py C2), 144.5 (Py C6), 140.7 (Py
C4), 111.4 (Py C5), 101.6 (Py C3), 49.5 (NMe2), 36.4 (Py-NMe). Anal.
Calcd for C14H20N5TiCl: C, 49.21; H, 5.90; N, 20.50. Found: C, 47.77;
H, 5.33; N, 19.56. Mp (uncorrected): 140 °C.
synthesize 1a is amine elimination, starting from mixed chloro
dimethylamido complexes like (Me2N)3TiCl or (Me2N)2TiCl2,
which are easily prepared via the conproportionation reactions
between Ti(NMe2)4 and TiCl4.12 As anticipated, the reaction
between (Me2N)3TiCl and 3 equiv of Me-APy-H proceeds
1
without any significant side reaction (observed by H NMR).
The yield depends upon the solubility.
(Ph-APy)2Ti(NMe2)Cl (2b). A solution of 343 mg (1.59 mmol) of
(Me2N)3TiCl in 20 mL of ether was added slowly via syringe to a
solution of 541 mg (3.18 mmol) of 2-anilinopyridine in 30 mL of ether.
The color became immediately red-purple. The mixture was stirred
over a period of 30 min. The solution was filtered, and the volume
was reduced under vacuum to approximately 20 mL. Cooling to -30
°C overnight afforded a purple crystalline material. Yield: 563 mg,
1.21 mmol, 76%. 1H NMR (303 K, THF-d8): δ 7.8 (br, 2H, Py H6),
7.4, 7.3, 7.0, 6.5 (m, 16H, Ph and Py), 3.55 (s, 6H, NMe2). 13C NMR
(303 K, THF-d8): δ 166.9 (Py C2), 148.9 (ipso-C Ph), 144.7 (Py C6),
141.0 (Py C4), 129.5, 124.3, 122.9 (o-, m-, p-C Ph), 112.9 (Py C5),
104.9 (Py C3), 49.7 (NMe2). Anal. Calcd for C24H24N5TiCl: C, 61.88;
H, 5.19; N, 15.03. Found: C, 61.34; H, 5.32; N, 14.82. Mp
(uncorrected): 175 °C.
(TMS-APy)2Ti(NMe2)Cl (2c). A solution of 315 mg (1.46 mmol)
of (Me2N)3TiCl in 20 mL of ether was added slowly via syringe to a
solution of 553 µL (2.92 mmol) of 4-methyl-2-((trimethylsilyl)amino)-
pyridine in 20 mL of ether. The color became orange immediately.
The mixture was stirred over a period of 30 min, after which the solution
was filtered and the volume was reduced under vacuum to ap-
proximately 10 mL. Cooling to -30 °C afforded overnight an orange
crystalline material. Yield: 647 mg, 1.33 mmol, 91%. 1H NMR (303
K, C6D6): δ 7.8 (br, 2H, Py H6), 6.20 (s, 2H, Py H3), 5.91 (d, 2H, Py
H5), 3.70 (s, 6H, NMe2), 1.73 (s, 6H, Py-Me), 0.36 (s, 18H, SiMe3).
1H NMR (230 K, THF-d8): δ 8.15 (s, 1H, Py H6), 7.01 (s, 1H, Py′
H′6), 6.45 (d, 1H, Py H5), 6.29 (s, 2H, Py H3), 6.29 (d, 1H, Py′ H′5),
3.62 (s, 6H, NMe2), 2.24 (s, 3H, Py-Me), 2.20 (s, 3H, Py′-Me′), 0.30
(s, 9H, SiMe3), 0.03 (s, 9H, Si′Me′3). 13C NMR (303 K, C6D6): δ
167.2 (Py C2), 150.8 (Py C4), 143.1 (br, Py C6), 113.2 (br, Py C5),
110.7 (Py C3), 51.7 (NMe2), 21.5 (Py-NMe), 1.2 (SiMe3). Anal. Calcd
for C20H36N5TiCl: C, 49.47; H, 7.48; N, 14.43. Found: C, 49.51; H,
7.57; N, 14.27. Mp (uncorrected): 156 °C.
Unexpectedly, the reaction of only 2 equiv of Me-APy-H and
(Me2N)2TiCl2 affords the same product (1a). In situ generated
dimethylamine acts as a base and deprotonates the aminopyri-
dine. Me2NH‚HCl was observed as a byproduct. A smooth
synthesis of (Ph-APy)3TiCl (1b) proceeds via amine elimination
according to eq 2. The reaction of (Me2N)3TiCl with 2 or 3
equiv of TMS-APy-H did not afford a complex of the type (R-
APy)3TiCl, presumably owing to steric repulsion. The 1H and
13C NMR spectra of the product crystallized from hexane are
indicative of two-coordinated aminopyridinato ligands and a
“leftover” dimethylamide.
Elemental analysis is consistent with (TMS-APy)3Ti(NMe2)Cl
(2c). Complexes of the type (R-APy)2Ti(NMe2)Cl were also
synthesized from (Me2N)3TiCl and 2 equiv of Me-APy-H or
Ph-APy-H to afford (Me-APy)2Ti(NMe2)Cl (2a) or (Ph-APy)2-
Ti(NMe2)Cl (2b) as a red crystalline compound, analogous to
eq 3. All the aminopyridinato-containing complexes described
herein are sensitive to air and moisture. The 1H NMR spectrum
of 2c at room temperature shows broad or missing signals for
the aminopyridinato ligand, indicating that exchange processes
are occurring. The results from low-temperature NMR studies
reveal that the aminopyridinato ligands are in two different
environments, in accordance with the structure determined by
X-ray diffraction studies. It is proposed that this exchange
proceeds most likely via a tetrahedral transition state without
pyridine coordination.
Results and Discussion
Synthesis of Complexes of the Types (R-APy)3TiCl and
(R-APy)2Ti(NMe2)Cl. 2-(Methylamino)pyridine (Me-APy-H)
and 2-anilinopyridine (Ph-APy-H) are commercially available,
and the synthesis of trimethylsilyl-substituted 2-aminopyridines
was reported.9 4-Methyl-2-((trimethylsilyl)amino)pyridine (TMS-
APy-H) was prepared by method of Phillion.10 The reaction
of 3 equiv of in situ generated lithium (methylamino)pyridinate
(Me-APy-Li) with TiCl4(THF)2 or TiCl4 affords a red crystalline
product in only 10% yield.
1H and 13C NMR spectra indicate an overall 3-fold molecular
symmetry showing the expected signals of one type of coor-
dinated (methylamino)pyridinato ligand. Elemental analysis is
consistent with the formula (Me-APy)3TiCl (1a). Synthesis of
the analogous phenyl- or trimethylsilyl-substituted aminopy-
ridinato titanium complexes failed. An alternative way to

Ti Complexes Containing Aminopyridinato Ligands
Inorganic Chemistry, Vol. 35, No. 9, 1996 2647
Table 2. Atomic Coordinates (×104) and Equivalent Isotropic
Displacement Parameters (Å2 × 103) for 1aa
x
y
z
U(eq)a
C(1)
C(2)
C(3)
3867(4)
45(4)
1919(4)
1973(3)
-86(4)
4070(3)
4981(4)
6333(5)
6817(4)
5885(3)
3251(2)
3666(3)
4442(3)
4816(3)
4387(3)
30(3)
-1259(3)
-1525(3)
-564(3)
690(3)
2709(3)
4565(2)
2507(2)
3627(2)
578(2)
2625(4)
-148(3)
3795(3)
3258(3)
3512(3)
3826(3)
3875(3)
3608(3)
811(2)
-242(3)
-55(4)
1128(4)
2131(3)
2592(2)
2560(3)
2022(3)
1567(3)
1668(3)
2985(2)
3293(2)
927(2)
95(1)
79(1)
79(1)
58(1)
75(1)
86(1)
77(1)
62(1)
47(1)
67(1)
79(1)
73(1)
55(1)
52(1)
67(1)
75(1)
72(1)
61(1)
64(1)
52(1)
53(1)
44(1)
55(1)
50(1)
55(1)
43(1)
1577(4)
3444(3)
4932(3)
5111(4)
3880(4)
2447(3)
-926(3)
-1801(4)
-2727(4)
-2811(4)
-1920(3)
-1004(3)
-1921(4)
-3526(4)
-4211(4)
-3233(3)
2914(3)
2239(2)
85(3)
C(10)
C(11)
C(12)
C(13)
C(14)
C(20)
C(21)
C(22)
C(23)
C(24)
C(30)
C(31)
C(32)
C(33)
C(34)
N(1)
N(2)
N(3)
N(4)
N(5)
N(6)
Cl
Figure 1. Structural representation of 1a. Hydrogen atoms are omitted
for clarity. The thermal ellipsoids correspond to 40% probability.
Selected bond distances (Å) and angles (deg): N(1)-Ti 2.012(2), N(2)-
Ti 2.183(2), N(3)-Ti 2.010(2), N(4)-Ti 2.191(2), N(5)-Ti 2.004(2),
N(6)-Ti 2.204(2), Cl-Ti 2.3492(7), N(5)-Ti-N(3) 108.99(9), N(5)-
Ti-N(1) 85.67(10), N(3)-Ti-N(1) 90.56(10), N(5)-Ti-N(2) 142.80-
(9), N(3)-Ti-N(2) 89.80(9), N(1)-Ti-N(2) 61.65(10), N(5)-Ti-
N(4) 137.99(9), N(3)-Ti-N(4) 61.70(8), N(1)-Ti-N(4) 132.30(9),
N(2)-Ti-N(4) 79.13(8), N(5)-Ti-N(6) 61.79(9), N(3)-Ti-N(6)
84.52(9), N(1)-Ti-N(6) 142.99(9), N(2)-Ti-N(6) 154.50(8), N(4)-
Ti-N(6) 76.28(7), N(5)-Ti-Cl 90.73(7), N(3)-Ti-Cl 153.06(7),
N(1)-Ti-Cl 109.58(7), N(2)-Ti-Cl 84.66(6), N(4)-Ti-Cl 91.36-
(5), N(6)-Ti-Cl 89.22(6).
-1010(2)
1975(2)
3001(2)
2161(2)
4818(1)
2793(1)
567(3)
-1685(2)
476(1)
970(2)
3103(1)
2495(1)
Ti
645(1)
a U(eq) is defined as one-third of the trace of the orthogonalized Uij
tensor.
Molecular modeling experiments suggest that no exchange
mechanism in which the Namido- and NPy-titanium bonds pass
through an octahedral transition state is possible due to the cis
arrangement of both the pyridines and the aminopyridinato
amides. The temporary loss of the pyridines is supported by
the highly strained binding mode. Furthermore it is proposed
that 2a and 2b have similar dynamic behaviors which could
not be slowed down to the NMR time scale at 230 K.
Solid State Structures of (Me-APy)3TiCl (1a), (Me-
APy)2Ti(NMe2)Cl (2a), (Ph-APy)2Ti(NMe2)Cl (2b), and
(TMS-APy)2Ti(NMe2)Cl (2c). Large dark red crystals of 1a
suitable for X-ray analysis could be grown by layering a
saturated ether solution with hexane. The single-crystal X-ray
structure analysis of 1a established its monomeric structure, as
shown in Figure 1, including principal bond distances and
angles. Atomic coordinates and equivalent isotropic displace-
ment parameters are listed in Table 2. Some important
crystallographic features are shown in Table 1. The solid state
structure shows a highly nitrogen-coordinated titanium complex.
Coordination geometry is described best as pentagonal bipyra-
midal where the atoms N(1), N(2), N(4), N(5), and N(6) occupy
the central plane and the Cl atom stands perpendicular to this
plane. The “leftover” nitrogen cannot bind exactly opposite to
the Cl atom because of the strained binding mode. Thus the
coordination geometry is disturbed. The amide nitrogen atoms
have an almost planar geometry, as has been found in virtually
all structurally characterized transition metal amido complexes.8
As seen in Table 2, bond lengths and angles are almost identical
for all three aminopyridinato ligands. The Ti-Cl bond distance
of 2.3492(7) Å in 1a is slightly longer than the average Ti-Cl
bond distance (2.305 Å11) and almost equivalent with the upper
quartile (2.352 Å11). Suitable crystals for X-ray diffraction
studies of 2a-c could be obtained by slowly cooling a saturated
solution (2a, an ether solution to -30 °C; 2b, an ether solution
to 0 °C; 2c, a hexane solution to -30 °C). Perspective ORTEP
drawings of the molecular structures of 2a-c are represented
Figure 2. Structural representation of 2a. Hydrogen atoms are omitted
for clarity. The thermal ellipsoids correspond to 40% probability.
Selected bond distances (Å) and angles (deg): N(1)-Ti(1) 2.016(2),
N(2)-Ti(1) 2.185(2), N(3)-Ti(1) 1.968(2), N(4)-Ti(1) 2.299(2),
N(5)-Ti(1) 1.899(2), Cl(1)-Ti(1) 2.3512(8), N(5)-Ti(1)-N(3) 96.73-
(10), N(5)-Ti(1)-N(1) 97.30(10), N(3)-Ti(1)-N(1) 98.65(10), N(5)-
Ti(1)-N(2) 109.30(10), N(3)-Ti(1)-N(2) 149.25(10), N(1)-Ti(1)-
N(2) 62.84(9), N(5)-Ti(1)-N(4) 158.48(10), N(3)-Ti(1)-N(4) 61.77(9),
N(1)-Ti(1)-N(4) 85.72(9), N(2)-Ti(1)-N(4) 91.09(9), N(5)-Ti(1)-
Cl(1) 97.99(8), N(3)-Ti(1)-Cl(1) 104.60(8), N(1)-Ti(1)-Cl(1) 150.34-
(8), N(2)-Ti(1)-Cl(1) 88.10(6), N(4)-Ti(1)-Cl(1) 89.24(6).
in Figure 2-4, including selected bond distances and angles.
Crystallographic details are given in Table 1. Atomic coordi-
nates, including equivalent isotropic displacement parameters,
are listed in Table 3 for 2a, in Table 4 for 2b, and in Table 5
for 2c. The coordination geometries of all three compounds
are almost identical and described best as disturbed octahedral.
The chloride atom stands perpendicular to the nitrogen plane.
The pyridine nitrogen-titanium bond distances (NPy-Ti) of the
aminopyridinato ligands in these planes are approximately 0.1
Å longer (average 2.26 Å) than the out-of-plane NPy-Ti bond
(average 2.16 Å). The Ti-Ndimethylamido and the Ti-Cl bond

2648 Inorganic Chemistry, Vol. 35, No. 9, 1996
Kempe and Arndt
Table 3. Atomic Coordinates (×104) and Equivalent Isotropic
Displacement Parameters (Å2 × 103) for 2a
x
y
z
U(eq)a
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
C(10)
C(11)
C(12)
C(13)
C(14)
N(1)
N(2)
N(3)
N(4)
N(5)
Cl(1)
Ti(1)
4581(3)
5783(4)
6970(4)
7003(4)
5809(4)
2972(6)
2259(4)
2118(5)
3458(6)
4897(5)
4960(4)
-507(5)
-113(5)
-181(6)
3260(3)
4616(3)
1132(3)
3678(3)
675(3)
2220(3)
1870(4)
714(4)
-82(4)
315(3)
818(3)
-198(3)
-14(4)
1165(4)
2127(3)
-142(4)
3325(3)
3662(3)
3832(4)
3666(3)
3351(3)
3211(5)
1339(4)
3281(5)
909(2)
1966(2)
3106(2)
3178(2)
2435(2)
4729(1)
2734(1)
39(1)
53(1)
63(1)
58(1)
48(1)
64(1)
42(1)
58(1)
67(1)
60(1)
49(1)
65(1)
65(1)
75(1)
43(1)
40(1)
44(1)
41(1)
42(1)
49(1)
35(1)
4358(5)
5449(3)
6887(4)
7343(4)
6424(4)
5014(4)
5466(5)
2404(5)
913(6)
3259(3)
1425(2)
4723(3)
4534(3)
1921(3)
1521(1)
2768(1)
Figure 3. Structural representation of 2b. Hydrogen atoms are omitted
for clarity. The thermal ellipsoids correspond to 40% probability.
Selected bond distances (Å) and angles (deg): N(1)-Ti(1) 2.257(5),
N(2)-Ti(1) 2.007(4), N(3)-Ti(1) 2.101(4), N(4)-Ti(1) 2.144(4),
N(5)-Ti(1) 1.890(5), Cl(1)-Ti(1) 2.310(2), N(5)-Ti(1)-N(2) 99.9-
(2), N(5)-Ti(1)-N(3) 94.4(2), N(2)-Ti(1)-N(3) 99.4(2), N(5)-Ti-
(1)-N(4) 103.5(2), N(2)-Ti(1)-N(4) 151.2(2), N(3)-Ti(1)-N(4)
62.4(2), N(5)-Ti(1)-N(1) 161.6(2), N(2)-Ti(1)-N(1) 62.2(2), N(3)-
Ti(1)-N(1) 85.2(2), N(4)-Ti(1)-N(1) 92.7(2), N(5)-Ti(1)-Cl(1)
99.5(2), N(2)-Ti(1)-Cl(1) 102.12(14), N(3)-Ti(1)-Cl(1) 151.85(13),
N(4)-Ti(1)-Cl(1) 90.50(13), N(1)-Ti(1)-Cl(1) 89.02(12).
2687(1)
2378(1)
a U(eq) is defined as one-third of the trace of the orthogonalized Uij
tensor.
Table 4. Atomic Coordinates (×104) and Equivalent Isotropic
Displacement Parameters (Å2 × 103) for 2b
x
y
z
U(eq)a
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
6006(3)
6663(3)
6931(4)
6556(4)
5913(4)
3650(3)
4201(3)
3972(4)
3165(4)
2595(4)
2838(3)
3594(3)
2951(4)
2775(4)
3213(4)
3840(4)
5824(3)
5864(3)
6018(4)
6139(4)
6065(4)
5910(4)
3812(4)
4200(4)
5650(3)
5624(3)
3927(2)
4015(3)
4242(3)
5588(1)
4814(1)
3143(7)
3995(8)
5431(9)
6008(8)
5085(8)
3869(6)
4512(7)
5195(7)
5260(8)
4641(8)
3929(7)
3425(7)
4453(8)
4527(9)
3639(10)
2655(8)
800(7)
7980(3)
8518(4)
8272(4)
7502(4)
6995(4)
7559(3)
8258(3)
8841(4)
8733(4)
8047(4)
7470(4)
6202(3)
5754(3)
4947(4)
4583(4)
5056(3)
8777(3)
9482(3)
10171(4)
10171(4)
9468(4)
8786(4)
7604(4)
6665(5)
7223(3)
8053(2)
6998(2)
5842(3)
7055(3)
6281(1)
6936(1)
36(1)
48(2)
59(2)
57(2)
51(2)
33(1)
39(1)
49(2)
55(2)
56(2)
44(2)
36(1)
50(2)
62(2)
65(2)
54(2)
33(1)
45(2)
54(2)
56(2)
54(2)
47(2)
67(2)
75(2)
39(1)
36(1)
35(1)
40(1)
41(1)
64(1)
36(1)
C(9)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
C(24)
N(1)
1550(7)
634(8)
-1085(8)
-1854(8)
-933(7)
-525(9)
-2087(9)
3700(6)
1670(5)
3145(5)
2537(6)
-477(6)
261(2)
Figure 4. Structural representation of 2c. Hydrogen atoms are omitted
for clarity. The thermal ellipsoids correspond to 40% probability.
Selected bond distances (Å) and angles (deg): N(1)-Ti 1.892(3), N(2)-
Si(2) 1.747(3), N(2)-Ti 2.031(3), N(3)-Ti 2.141(3), N(4)-Ti 2.220-
(3), N(5)-Si(1) 1.729(3), N(5)-Ti 2.096(3), Cl-Ti 2.3241(13), N(1)-
Ti-N(2) 106.92(13), N(1)-Ti-N(5) 95.93(13), N(2)-Ti-N(5)
100.96(12), N(1)-Ti-N(3) 102.32(13), N(2)-Ti-N(3) 148.29(13),
N(5)-Ti-N(3) 63.58(12), N(1)-Ti-N(4) 169.38(13), N(2)-Ti-N(4)
63.51(12), N(5)-Ti-N(4) 82.07(12), N(3)-Ti-N(4) 86.19(12), N(1)-
Ti-Cl 96.10(10), N(2)-Ti-Cl 100.01(10), N(5)-Ti-Cl 151.58(10),
N(3)-Ti-Cl 88.70(9), N(4)-Ti-Cl 90.37(9).
N(2)
N(3)
N(4)
N(5)
Cl(1)
Ti(1)
1450(1)
a U(eq) is defined as one-third of the trace of the orthogonalized Uij
tensor.
distances are similar to known values. In order to express ligand
steric properties, an angle æ similar to a cone angle17 was
defined as the angle formed by the outermost H atom of the
pyridine ring, the titanium atom, and the outermost H atom of
the substituent (data were taken from the results of the X-ray
diffraction studies). The TMS-substituted aminopyridinato
ligand, which was expected to be the most sterically demanding
ligand, has an angle æ ) 143°. The cone angles of the phenyl-
substituted (æ ) 120°) and the methyl-substituted ligand (æ )
119°) are similar. This fact explains that complexes of type 1
could not be prepared using the sterically demanding TMS-
APy ligand. The binding mode of the complexes described
herein is illustrated in Chart 1 and compared with analogous
bonding in titanium complexes that contain related amidinato
ligands.18 The listed bond distances and angles are averaged
by using all available structures. The standard deviation is the
usual sample standard deviation resulting from the 9 observa-
tions (aminopyridinato ligands) or 12 observations (amidinato
ligands). The Cn-Namido (the carbon atom between the two
(17) Brown, T. L.; Lee, K. J. Coord. Chem. ReV. 1993, 128, 89.

Ti Complexes Containing Aminopyridinato Ligands
Inorganic Chemistry, Vol. 35, No. 9, 1996 2649
Table 5. Atomic Coordinates (×104) and Equivalent Isotropic
Cn-Namidinato distance (1.329(4) Å) and equivalent to the Cn-
NPy length. The Ti-NPy distance is well in the range of such
distances (2.247(7) Å15). The Ti-Namido distance is more than
0.1 Å longer as the expected value of the averaged titanium-
amido bond length (1.889(2) Å16) and 0.1 Å shorter as the Ti-
Namidinato distance. All these findings are indicative that a
delocalization of titanium-nitrogen bonds as in case of the
amidinato ligand system does not take place for aminopyridinato
ligands. Instead, a typical Ti-NPy and a weak Ti-Namido bond
is observed. Nevertheless, the flexibility of both the amido and
the pyridine nitrogen titanium distances may attest to a
sensitivity of the binding situation depending on the substituents
at the amido nitrogen and/or the pyridine ring. The NPy-Cn-
Namido angle of 108(1)° instead of the desired 120° or the
observed value for amidinato ligands (114.5(8)°) verifies the
strained bonding mode.
Displacement Parameters (Å2 × 103) for 2c
x
y
z
U(eq)a
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
N(1)
N(2)
N(3)
N(4)
N(5)
Si(1)
Si(2)
Cl
1293(3)
1527(4)
2430(4)
3100(4)
2830(4)
3312(3)
4544(4)
4829(4)
3930(4)
2749(4)
549(4)
2625(4)
4893(5)
4347(5)
-483(5)
-1751(4)
-1835(5)
-620(4)
2686(5)
6139(4)
254(3)
1990(3)
1690(3)
1008(3)
649(3)
8562(2)
9305(2)
9504(2)
8959(3)
8242(2)
6912(2)
6711(2)
6136(2)
5775(2)
5987(2)
6896(3)
8796(3)
8653(3)
7670(3)
9453(3)
8870(3)
7902(3)
6014(3)
10288(3)
5904(3)
6682(2)
8248(2)
6542(2)
8046(2)
7445(2)
8123(1)
8616(1)
6667(1)
7225(1)
40(1)
48(1)
51(1)
58(1)
52(1)
43(1)
54(1)
62(1)
62(1)
55(1)
65(1)
65(1)
90(2)
96(2)
79(2)
73(1)
91(2)
68(1)
77(2)
96(2)
44(1)
41(1)
43(1)
43(1)
42(1)
54(1)
47(1)
61(1)
39(1)
973(3)
2830(3)
2845(3)
2284(4)
1696(4)
1686(3)
4662(3)
4447(3)
3265(5)
5038(4)
3819(4)
2012(3)
3773(4)
3646(4)
648(4)
2310(5)
3671(2)
2671(2)
2241(2)
1612(2)
3321(2)
4004(1)
3066(1)
1461(1)
2650(1)
Conclusion and Outlook
Several conclusions can be drawn from this study. First, the
best way to prepare mononuclear titanium complexes that
contain aminopyridinato ligands is via amine elimination starting
from mixed chloro(dialkylamido)titanium complexes. The
reactions are smooth and can be scaled up easily to a multigram
scale. Second, despite the fact that aminopyridinato ligands can
donate formally 6 electrons, they are not Cp analogous. They
act because of their steric properties as an amide type ligand.
For instance, complexes of the general type (R2N)3TiCl are
described8,12,19 and are similar to complexes of the type (R-
APy)3TiCl. Complexes 2a-c represent the first examples of
nonsymmetric group 4 tris(amido) complexes. Third, aminopy-
ridinato ligands give rise to highly nitrogen-coordinated titanium
complexes. Fourth, the strained binding mode and the flexibility
in the Ti-Namido and/or Ti-NPy bond may cause an unusual
reactivity. The results may also provide the general conclusion
that strained bound aminopyridinato ligands may act as the basis
of a novel ligand system to stabilize mononuclear early transition
metal complexes with unusual coordination geometries. The
reactivity of the complexes presented in this paper is under
investigation, and our interest is extended to other early
transition metals and to other aminopyridinato ligands.
481(3)
2455(3)
1958(3)
2804(3)
3650(1)
-851(1)
-223(1)
1063(1)
Ti
a U(eq) is defined as one-third of the trace of the orthogonalized Uij
tensor.
Chart 1. Selected Averaged Bond Distances (Å) and Bond
Angles (deg) To Illustrate the Binding Mode of
Aminopyridinato Ligands in Comparison with That of the
Related Amidinato Ligand System
Acknowledgment. We thank Prof. U. Rosenthal for gener-
ous support and helpful discussions. Financial support from
the Fonds der Chemischen Industrie and the Max-Planck-
Gesellschaft is gratefully acknowledged.
nitrogen atoms is called Cn) distance of the aminopyridinato
ligand (1.35(2) Å) is shorter as the expected value of the general
Caromatic-NH2 bond length (1.375(25) Å11) but longer as the
Supporting Information Available: Tables of experimental details
and crystal data, hydrogen positional parameters, full bond distances
and angles, and thermal parameters (23 pages). Ordering information
is given on any current masthead page.
(18) Fachinetti, G.; Biran, C.; Floriani, C.; Villa, A. C.; Guastini, C. J.
Chem. Soc., Dalton Trans. 1979, 792. Fenske, D.; Hartmann, E.;
Dehnicke, K. Z. Naturforsch. 1988, 43B, 1611. Roesky, H. W.; Meller,
B.; Noltemeyer, M.; Schmidt, H.-G.; Scholz, U.; Sheldrick, G. M.
Chem. Ber. 1988, 121, 1403. Dick, H. G.; Duchateau, R.; Edema, J.
J. H.; Gamarotta, S. Inorg. Chem. 1993, 32, 1959. Cotton, F. A.;
Wojtczak, W. A. Gazz. Chim. Ital. 1993, 123, 499. Sotoodeh, M.;
Leichtweis, I.; Roesky, H. W.; Noltemeyer, M.; Schmidt, H.-G. Chem.
Ber. 1993, 126, 913.
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(19) Airoldi, C.; Breadley, D. C.; Chudzynska, H.; Hursthouse, M. B.;
Abdul-Malik, K. M.; Raithby, P. R. J. Chem. Soc., Dalton Trans. 1980,
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