Imido complexes of titanium bearing η2-pyrazolato ancillary ligand sets

Article abstract of DOI:10.1021/om980802r

Treatment of dichlorobis(3,5-di-tert-butylpyrazolato)titanium(IV) with Grignard (CH₃MgCl, C₆H₅CH₂MgCl) or organolithium (LiCH₂Si(CH₃)₃) reagents (2 equiv) afforded the dialkyl de

Full text of DOI:10.1021/om980802r

1168
Organometallics 1999, 18, 1168-1176
Im id o Com p lexes of Tita n iu m Bea r in g η2-P yr a zola to
An cilla r y Liga n d Sets
Carlos Ye´lamos, Mary J ane Heeg, and Charles H. Winter*
Department of Chemistry, Wayne State University, Detroit, Michigan 48202
Received September 25, 1998
Treatment of dichlorobis(3,5-di-tert-butylpyrazolato)titanium(IV) with Grignard (CH3MgCl,
C6H5CH2MgCl) or organolithium (LiCH2Si(CH3)3) reagents (2 equiv) afforded the dialkyl
derivatives dimethylbis(3,5-di-tert-butylpyrazolato)titanium(IV) (93%), dibenzylbis(3,5-di-
tert-butylpyrazolato)titanium(IV) (43%), and bis(methyltrimethylsilyl)bis(3,5-di-tert-butyl-
pyrazolato)titanium(IV) (49%). Analogous methylation of chlorotris(3,5-di-tert-butylpyrazolato)-
titanium(IV) with CH3MgCl afforded methyltris(3,5-di-tert-butylpyrazolato)titanium(IV)
(52%). Attempted alkylation of trichloro(3,5-di-tert-butylpyrazolato)titanium(IV) with CH3-
MgCl (3 equiv) afforded dimethylbis(3,5-di-tert-butylpyrazolato)titanium(IV) (35%), along
with extensive decomposition. This experiment indicates that trimethyl(3,5-di-tert-butylpyra-
zolato)titanium(IV) is unstable at ambient temperature. The reactivity of dichlorobis(3,5-
di-tert-butylpyrazolato)titanium(IV) and dimethylbis(3,5-di-tert-butylpyrazolato)titanium(IV)
toward primary amines was studied. Treatment of dichlorobis(3,5-di-tert-butylpyrazolato)-
titanium(IV) with excess tert-butylamine afforded tert-butylimido(chloro)(3,5-di-tert-butyl-
pyrazolato)titanium(IV) dimer (10%), chlorotris(3,5-di-tert-butylpyrazolato)titanium(IV)
(56%), and tert-butylammonium chloride (85%). Analogous treatment of dimethylbis(3,5-di-
tert-butylpyrazolato)titanium(IV) with tert-butylamine gave the monomeric imido complex
tert-butylimidobis(3,5-di-tert-butylpyrazolato)(tert-butylamine)titanium(IV) (33%). Addition
of pyridine to the reaction between dimethylbis(3,5-di-tert-butylpyrazolato)titanium(IV) and
tert-butylamine or isopropylamine afforded the pyridine adducts tert-butylimidobis(3,5-di-
tert-butylpyrazolato)(pyridine)titanium(IV) (80%) and isopropylimidobis(3,5-di-tert-butylpyra-
zolato)(tert-butylamine)titanium(IV) (46%), respectively. Treatment of dimethylbis(3,5-di-
tert-butylpyrazolato)titanium(IV) with 1-amino-4-methylpiperazine led to the hydrazide(1-)
complex 1-amido-4-methylpiperazine(methyl)bis(3,5-di-tert-butylpyrazolato)titanium(IV) (64%),
which contains both a titanium-methyl bond and a primary hydrazide(1-) ligand. It is
proposed that the thermal stability of this compound arises from bidentate coordination of
the hydrazide(1-) ligand, which places the reactive nitrogen-hydrogen bond distal to the
titanium-methyl bond. The reactivity of tert-butylimidobis(3,5-di-tert-butylpyrazolato)(tert-
butylamine)titanium(IV) toward acetylenes, nitriles, and ketones is discussed. The X-ray
crystal structures of bis(methyltrimethylsilyl)bis(3,5-di-tert-butyl-pyrazolato)titanium(IV),
tert-butylimido(chloro)(3,5-di-tert-butylpyrazolato)titanium(IV) dimer, and isopropylimidobis-
(3,5-di-tert-butylpyrazolato)(tert-butylamine)titanium(IV) were determined.
In tr od u ction
sive research has established that mid to late transition
metal complexes exhibit either bridging or η1-pyrazolato
ligand coordination modes,7 the analogous situation
with the early transition metals has not received enough
attention to make general statements. Our work and
the result of Erker6 suggested that η2-pyrazolato ligands
might be common among the early transition metals.
Since there has been considerable recent interest in the
development of new ancillary ligand sets for reactive
early transition metal complexes,8-11 we wondered if the
η2-pyrazolato ligand would be sufficiently stable to serve
as a spectator ligand. The η2-pyrazolato coordination
We have recently described the synthesis, structure,
and properties of a series of early transition metal
complexes that contain η2-pyrazolato ligands.1-5 Prior
to our reports, the only structurally characterized
d-block metal complex bearing a η2-pyrazolato ligand
was [Cp2Zr(C3H3N2)(THF)]BPh4‚(THF)0.5.6 While exten-
(1) Guzei, I. A.; Baboul, A. G.; Yap, G. P. A.; Rheingold, A. L.;
Schlegel, H. B.; Winter, C. H. J . Am. Chem. Soc. 1997, 119, 3387.
(2) Guzei, I. A.; Yap, G. P. A.; Winter, C. H. Inorg. Chem. 1997, 36,
1738.
(3) Guzei, I. A.; Winter, C. H. Inorg. Chem. 1997, 36, 4415.
(4) Ye´lamos, C.; Heeg, M. J .; Winter, C. H. Inorg. Chem., in press.
(5) See also: (a) Ye´lamos, C.; Heeg, M. J .; Winter, C. H. Inorg. Chem.
1998, 37, 3892. (b) Pfeiffer, D.; Heeg, M. J .; Winter, C. H. Angew.
Chem., Int. Ed. 1998, 37, 2517. (c) Culp, T. D.; Cederberg, J . G.; Bieg,
B.; Kuech, T. F.; Bray, K. L.; Pfeiffer, D.; Winter, C. H. J . Appl. Phys.
1998, 83, 4918.
(7) For reviews, see: Trofimenko, S. Chem. Rev. 1972, 72, 497.
Sadimenko, A. P.; Basson, S. S. Coord. Chem. Rev. 1996, 147, 247. La
Monica, G.; Ardizzoia, G. A. Progr. Inorg. Chem. 1997, 46, 151. Cosgriff,
J . E.; Deacon, G. B. Angew. Chem., Int. Ed. 1998, 37, 286.
(8) For recent reviews on early transition metal alkoxides, see:
Rothwell, I. P. J . Chem. Soc., Chem. Commun. 1997, 1331. Wolczanski,
P. T. Polyhedron 1995, 14, 3335.
(6) Ro¨ttger, D.; Erker, G.; Grehl, M.; Fro¨lich, R. Organometallics
1994, 13, 3897.
10.1021/om980802r CCC: $18.00 © 1999 American Chemical Society
Publication on Web 02/19/1999

Imido Complexes of Titanium
Organometallics, Vol. 18, No. 7, 1999 1169
mode would be most desirable for such applications,
since reactions involving the basic nitrogen lone pairs
of electrons associated with η1-structures would be
eliminated or attenuated. Moreover, bridging pyrazolato
ligands could lead to intractable or poorly soluble
oligomeric complexes. We recently demonstrated that
titanium complexes bearing both chloride and η2-pyra-
zolato ligands have significant structural and chemical
analogy with cyclopentadienyltitanium trichloride and
titanocene dichloride.4 Titanium complexes bearing
cyclopentadienyl ligands are widely used in many
reactive systems,12 and it seemed possible that titanium
complexes bearing η2-pyrazolato ligands might serve in
similar roles.
2 equiv of methylmagnesium chloride, benzylmagne-
sium chloride, or methyltrimethylsilyllithium afforded
dimethylbis(3,5-di-tert-butylpyrazolato)titanium(IV) (1,
93%), dibenzylbis(3,5-di-tert-butylpyrazolato)titanium-
(IV) (2, 43%), and bis(methyltrimethylsilyl)bis(3,5-di-
tert-butylpyrazolato)titanium(IV) (3, 49%), respectively,
as yellow (1, 3) or red (2) crystalline solids (eq 1).
Herein we describe the synthesis, structure, and
reactivity of complexes that contain the bis(η2-3,5-di-
tert-butylpyrazolato)titanium(IV) structural fragment.
The starting material for this chemistry, dichlorobis-
(3,5-di-tert-butylpyrazolato)titanium(IV),3,4 is easily pre-
pared in high yield and can be alkylated with organo-
lithium or organomagnesium reagents to afford the
dialkyl derivatives in moderate to high yields. There is
no evidence for side reactions that involve the pyrazolato
ligands. Monomeric and dimeric imido complexes result
upon treatment of the dichloro or dialkyl complexes with
primary alkylamines. The reactivity of the monomeric
imido complexes toward unsaturated organic molecules
is presented. Finally, the crystal structures of repre-
sentative complexes are described. The combined results
suggest that η2-pyrazolato ligands are stable during
several types of reactions that occur at the titanium
center and may therefore find utility as new ancillary
ligands for early transition metal complexes.
Compounds 1-3 are air sensitive in solution and in the
solid state, but are stable at ambient temperature for
at least weeks under argon. A benzene-d6 solution of 1
1
did not show any changes in its H NMR spectrum after
heating at 70 °C for 48 h. Structures of 1-3 were
assigned by 1H and 13C{1H} NMR spectroscopy, infrared
spectroscopy, microanalysis, and an X-ray structure
determination for 3 (vide infra).
Similar reactions of chlorotris(3,5-di-tert-butylpyra-
zolato)titanium(IV) and trichloro(3,5-di-tert-butylpyra-
zolato)titanium(IV) with methylmagnesium chloride
were also studied (eqs 2, 3). In the first case (eq 2),
Resu lts
Syn t h esis of Alk yl Der iva t ives. Treatment of
dichlorobis(3,5-di-tert-butylpyrazolato)titanium(IV)3,4 with
(9) For leading references to early transition metal amidinate
complexes, see: Hagadorn, J . R.; Arnold, J . Angew. Chem., Int. Ed.
1998, 37, 1729. Hagadorn, J . R.; Arnold, J . Organometallics 1998, 17,
1355. Hagadorn, J . R.; Arnold, J . J . Chem. Soc., Dalton Trans. 1997,
3087. Littke, A.; Sleiman, N.; Bensimon, C.; Richeson, D. S.; Yap, G.
P. A.; Brown, S. J . Organometallics 1998, 17, 446. Edelmann, F. T.
Coord. Chem. Rev. 1994, 137, 403. Barker, J .; Kilner, M. Coord. Chem.
Rev. 1994, 133, 219.
(10) For recent reviews of pyrazolylborate complexes, see: Reger,
D. L. Coord. Chem. Rev. 1996, 147, 571. Kitajima, N.; Tolman, W. B.
Prog. Inorg. Chem. 1995, 43, 419. Parkin, G. Adv. Organomet. Chem.
1995, 42, 291. Trofimenko, S. Chem. Rev. 1993, 93, 943.
(11) For recent selected examples of other new ligands that have
been used in early transition metal complexes, see: Gantzel, P.; Walsh,
P. J . Inorg. Chem. 1998, 37, 3450. Martin, A.; Uhrhammer, R.;
Gardner, T. G.; J ordan, R. F.; Rogers, R. D. Organometallics 1998, 17,
382. Fryzuk, M. D.; Love, J . B.; Rettig, S. J . Organometallics 1998,
17, 846. Scott, M. J .; Lippard, S. J . Organometallics 1998, 17, 1769.
Muller, E.; Muller, J .; Olbrich, F.; Bruser, W.; Knapp, W.; Abeln, D.;
Edelmann, F. T. Eur. J . Inorg. Chem. 1998, 1, 87. Schrock, R. R.;
Schattenmann, F.; Aizenberg, M.; Davis, W. M. J . Chem. Soc., Chem.
Commun. 1998, 199. Warren, T. H.; Schrock, R. R.; Davis, W. M.
Organometallics 1998, 17, 308. Armistead, L. T.; White, P. S.; Gagne´,
M. R. Organometallics 1998, 17, 216. Lee, C. H.; La, Y.-H.; Park, S.
J .; Park, J . W. Organometallics 1998, 17, 3648. Guzei, I. A.; Liable-
Sands, L. M.; Rheingold, A. L.; Winter, C. H. Polyhedron 1997, 16,
4017.
(12) For leading references to group 4-based systems, see: Boch-
mann, M. In Comprehensive Organometallic Chemistry II; Abel, E. W.,
Stone, F. G. A., Wilkinson, G., Eds.; Pergamon: Oxford, 1995; Vol. 4,
pp 273-431. J ubb, J .; Song, J .; Richeson, D.; Gambarotta, S. In
Comprehensive Organometallic Chemistry II; Abel, E. W., Stone, F.
G. A., Wilkinson, G., Eds.; Pergamon: Oxford, 1995; Vol. 4, pp 543-
588. Guram, A. S.; J ordan, R. F. In Comprehensive Organometallic
Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.;
Pergamon: Oxford, 1995; Vol. 4, pp 589-625.
methyltris(3,5-di-tert-butylpyrazolato)titanium(IV) (4,
52%) was obtained as yellow crystals after crystalliza-
tion from hexane. However, the reaction of trichloro-
(3,5-di-tert-butylpyrazolato)titanium(IV) with methyl-
magnesium chloride (3 equiv) was more complicated (eq

1170 Organometallics, Vol. 18, No. 7, 1999
Ye´lamos et al.
Sch em e 1. P r op osed Rea ction P a th
3). A yellow suspension immediately resulted when the
reagents were mixed at -78 °C. However, upon warm-
ing to ambient temperature, the solution gradually
turned to a black color. Workup afforded 1 in 35% yield
as the sole tractable product. This result implies that
trimethyl(3,5-di-tert-butylpyrazolato)titanium(IV) is un-
stable at or near room temperature. A possible route to
the formation of 1 involves a redistribution reaction of
trimethyl(3,5-di-tert-butylpyrazolato)titanium(IV) to af-
ford 1 and tetramethyltitanium. Tetramethyltitanium
is known to be thermally unstable and decomposes near
-78 °C to metallic titanium and other products in the
absence of donor ligands.13 Due to the low-yield forma-
tion of 1, the preparation of trimethyl(3,5-di-tert-bu-
tylpyrazolato)titanium(IV) was not pursued further.
R ea ct ivit y of Bis(3,5-d i-ter t-b u t ylp yr a zola t o)-
tita n iu m (IV) Der iva tives w ith P r im a r y Am in es.
The reactivity of dichlorobis(3,5-di-tert-butylpyrazolato)-
titanium(IV) with tert-butylamine was examined as a
route to a complex bearing tert-butylimido ligands (eq
4). When the reaction was run in hexane at ambient
titanocene dichloride with primary amines to afford
stable complexes of the formula Cp2Ti(NHR)(Cl).14 The
tert-butylamide complex then eliminates 3,5-di-tert-
butylpyrazole to afford the fragment (tBu2pz)Ti(NtBu)-
(Cl), which dimerizes to give 5. Finally, 3,5-di-tert-
butylpyrazole reacts with dichlorobis(3,5-di-tert-butyl-
pyrazolato)titanium(IV) in the presence of tert-butyl-
amine to afford chlorotris(3,5-di-tert-butylpyrazolato)-
titanium(IV) and tert-butylammonium chloride. We
have reported that chlorotris(3,5-di-tert-butylpyrazola-
to)titanium(IV) can be prepared in high yield by treat-
ment of dichlorobis(3,5-di-tert-butylpyrazolato)titanium-
(IV) with 3,5-di-tert-butylpyrazole using triethylamine
as a base to neutralize the hydrogen chloride that is
generated.4 It is clear that tert-butylamine plays a role
similar to that of triethylamine in the present reaction.
We next examined the reaction of the dimethyl
derivative 1 with primary amines. Use of tert-butyl-
amine led to elimination of methane (2 equiv) to afford
the monomeric imido complex 6 (33%) after crystalliza-
tion from hexane (eq 5). In 6, the neutral tert-butyl-
temperature for 16 h, the hexane solution gradually took
on a deep orange coloration and a fine white precipitate
formed. Upon workup, the white precipitate was deter-
mined to be tert-butylammonium chloride (85% of
theory) by comparison of its 1H and 13C{1H} NMR
spectra with those of authentic material. A pale orange
powder was obtained after decanting the hexane layer
from the tert-butylammonium chloride and removing the
hexane under reduced pressure. Analysis of the powder
by 1H and 13C{1H} NMR spectroscopy showed it to be a
30:70 mixture of imido complex 5 and chlorotris(3,5-di-
tert-butylpyrazolato)titanium(IV).4,5a Pure 5 was ob-
tained as dark orange crystals in 10% yield by fractional
crystallization. Further crystallization afforded chloro-
tris(3,5-di-tert-butylpyrazolato)titanium(IV) as pure
yellow crystals in 56% yield. Intermediate crops of
crystals were mixtures of 5 and chlorotris(3,5-di-tert-
butylpyrazolato)titanium(IV), which is why the yields
were substantially reduced from the 33% and 67%
theoretical values, respectively. The composition of 5
was established by a combination of spectral and
analytical data and by an X-ray crystal structure
determination (vide infra).
amine ligand completes the coordination sphere and
stabilizes the potentially reactive terminal imido link-
age. However, 6 was exceptionally soluble in hexane and
was correspondingly difficult to isolate. More tractable
compounds were obtained by replacing the neutral
primary amine donor with a pyridine ligand. Treatment
of 1 with tert-butylamine or isopropylamine (5 equiv)
in the presence of pyridine (5 equiv) afforded the imido
complexes 7 (80%) and 8 (46%) as orange solids after
crystallization from hexane. The structures of 6-8 were
A reaction path that rationalizes the products is
outlined in Scheme 1. Treatment of dichlorobis(3,5-di-
tert-butylpyrazolato)titanium(IV) with tert-butylamine
would result in the formation of a tert-butylamide
complex along with production of tert-butylammonium
chloride. A similar reaction occurs upon treatment of
(13) For leading references, see: Berthold, H. J .; Groh, G. Z. Anorg.
Allg. Chem. 1963, 319, 230. Thiele, K. H.; Mu¨ller, J . Z. Z. Anorg. Allg.
Chem. 1968, 362, 113.
(14) Baye, L. J . Synth. Inorg. Met.-Org. Chem. 1972, 2, 47.

Imido Complexes of Titanium
Organometallics, Vol. 18, No. 7, 1999 1171
1
established from the spectral and analytical data and
by an X-ray crystal structure determination for 8. The
13C NMR chemical shifts of the carbons attached to the
imido nitrogens in 6-8 resonated between 65.6 and
68.74 ppm. Such chemical shifts are about 10 ppm more
shielded than the related resonance associated with the
bridging imido ligand in 5. The -80 °C 1H NMR
spectrum of 8 showed a single resonance for the tert-
butyl methyl groups on the pyrazolato ligands.
We next sought to prepare hydrazide(2-) complexes
that would be analogous to 6-8 through treatment of 1
with 1,1-dialkylhydrazines. Whereas 1,1-dimethylhydra-
zine and 1-aminopiperidine gave intractable mixtures,
1-amino-4-methylpiperazine afforded clear yellow crys-
tals of (1-amido-4-methylpiperazine)(methyl)bis(3,5-di-
tert-butylpyrazolato)titanium(IV) (9) in 64% yield after
crystallization from hexane (eq 6). Complex 9 was
erazine. We suggest that the sharpening of the ring H
NMR resonances upon cooling corresponds to freezing
out of a dynamic process involving a chair-chair inter-
conversion of the piperazine ring. The H and 13C{1H}
1
NMR data for 9 demonstrate that there are four
chemically distinct sites for the protons and two chemi-
cally distinct sites for the carbon atoms. A static, chiral
structure of the type proposed in eq 6 for 9 should have
diastereotopic ring hydrogens and carbons on the pip-
erazine ring, i.e., eight different hydrogen resonances
and four different carbon resonances. Clearly, the
solution structure of 9 is not static in the temperature
range studied. One possibility is that the η2-1-amido-
4-methylpiperazine does not rotate fully on the NMR
time scale, but only has enough motion to racemize the
∆ and Λ isomers. Such a windshield wiper-like motion
would lead to the observed number of resonances for
the piperazine ring in 9, but would not place the
nitrogen-hydrogen bond near the titanium-methyl
bond. Alternatively, the η2-1-amido-4-methylpiperazine
ligand may undergo rapid rotation on the NMR time
scale, but the nitrogen-hydrogen and titanium-carbon
bonds do not achieve the correct geometry for methane
elimination. We are unable to differentiate between the
two arguments with the limited data that could be
collected. However, pyrazolato ligand rotation is fast,
even at -40 °C, as evidenced by the sharp singlet that
was observed for the tert-butyl methyl groups at this
temperature. Rapid pyrazolato group rotation suggests
that η2-1-amido-4-methylpiperazine ligand rotation may
also be fast and tends to support the idea that the
correct transition state structure for methane elimina-
tion from 9 is not accessible at moderate temperatures.
characterized by spectroscopic and analytical methods.
Despite several data collections, crystals of 9 were found
to be of insufficient quality to allow determination of
the molecular structure by crystallographic methods.
The most striking feature of 9 is the presence of the
titanium-methyl bond, despite the acidic hydrogen
bonded to the hydrazide(1-) ligand.
Rea ctivity of 6 w ith Un sa tu r a ted Or ga n ic Com -
p ou n d s. The reactivity of zirconocene imido complexes
toward unsaturated organic compounds has been ex-
tensively explored.16 To provide a comparison, we
examined the reactions of 6 with several organic com-
pounds containing multiple bonds. Compound 6 was
chosen for reactivity studies, since we reasoned that the
pyridine ligands in 7 and 8 would be too strongly bonded
to allow access of the unsaturated organic compounds
to the titanium center. Treatment of 6 with dipheny-
lacetylene or acetonitrile (3-4 equiv) in refluxing tolu-
ene for 24 h did not give any detectable reaction, as
assessed by 1H NMR spectroscopy, and 6 was recovered
quantitatively. The reaction between 6 and benzophe-
none in benzene-d6 was followed by NMR spectroscopy
(eq 7). The 1H and 13C{1H} NMR spectra after 48 h
showed complete reaction and revealed resonances for
tert-butylamine, the tert-butylimine of benzophenone,
and new pyrazolato resonances that we propose cor-
respond to an oxo complex 11. Spectra taken after 0.5
h of reaction revealed complete consumption of 6, with
concomitant formation of free tert-butylamine, the tert-
butylimine of benzophenone, and two compounds in a
68:32 ratio that only showed resonances from 3,5-di-
tert-butylpyrazolato ligands. We propose that these
latter two compounds correspond to oligomeric forms of
We propose that the hydrazide(1-) ligand in 9 adopts
a bidentate coordination mode in which the nitrogen-
hydrogen bond is distal to the titanium-methyl bond.
Such a structure would be very similar to those of
dimethylamidotris(3,5-di-tert-butylpyrazolato)titanium-
(IV)15 and chlorotris(3,5-di-tert-butylpyrazolato)hafnium-
(IV),4 which contain chiral, seven-coordinate metal
centers with η2-pyrazolato ligands. Complex 9 could be
refluxed in toluene for 18 h without decomposition or
1
any reaction, as determined by H NMR spectroscopy.
To probe the origins of the thermal stability, the
variable-temperature NMR spectra of 9 were recorded.
1
In the H NMR spectrum of 9 in toluene-d8 at 20 °C,
the piperazine ring hydrogens appeared as very broad
resonances centered at δ 2.75 and 2.17. At -40 °C,
sharper equal intensity multiplets for the piperazine
ring hydrogens were observed at δ 2.78, 2.62, 2.22, and
2.05. Below -40 °C, 9 precipitated. The 13C{1H} NMR
spectrum in benzene-d6 at 20 °C showed the piperazine
ring carbons at 60.13 and 54.15 ppm. These values can
be compared to carbon chemical shifts of 59.77 and 55.36
ppm for the ring carbons of free 1-amino-4-methylpip-
(16) For leading references, see: Walsh, P. J .; Hollander, F. J .;
Bergman, R. G. J . Am. Chem. Soc. 1988, 110, 8729. Walsh, P. J .;
Baranger, A. M.; Bergman, R. G. J . Am. Chem. Soc. 1992, 114, 1708.
Baranger, A. M.; Walsh, P. J .; Bergman, R. G. J . Am. Chem. Soc. 1993,
115, 2753. Walsh, P. J .; Hollander, F. J .; Bergman, R. G. Organome-
tallics 1993, 12, 3705.
(15) Guzei, I. A.; Baboul, A. G.; Ye´lamos, C.; Liable-Sands, L. M.;
Rheingold, A. L.; Schlegel, H. B.; Winter, C. H. Manuscript in
preparation.

1172 Organometallics, Vol. 18, No. 7, 1999
Ye´lamos et al.
Ta ble 1. Exp er im en ta l Cr ysta llogr a p h ic Da ta for
3, 5, a n d 8
3
5
8
empirical formula
fw
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
C30H60N4Si2Ti C15H28N3ClTi C30H50N6Ti
580.90
P1h
333.75
P2(1)/c
12.4152(6)
10.0217(5)
15.7552(9)
90
542.66
P1h
10.0187(4)
11.6437(5)
16.7533(7)
81.414(2)
113.5780(10)
75.711(2)
1860.17(13)
2
10.399(10)
10.87(2)
15.79(2)
94.67(8)
90.07(2)
106.63(7)
1704(4)
2
97.9090(10)
90
1941.6(2)
4
Z
T (K)
295(2)
0.71073
1.037
0.316
6.06
295(2)
0.71073
1.1142
0.574
295(2)
0.71073
1.058
0.276
5.70
λ (Å)
F calcd (g cm3)
µ (mm-1
R(F) (%)
)
4.42
Rw(F) (%)
12.52
12.01
12.57
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 3
Ti(1)-N(1)
Ti(1)-N(2)
Ti(1)-C(5)
N(1)-N(2)
2.015(4)
2.028(3)
2.079(3)
1.370(4)
Ti(1)-N(3)
Ti(1)-N(4)
Ti(1)-C(1)
N(3)-N(4)
2.015(4)
2.045(3)
2.084(4)
1.366(4)
N(1)-Ti(1)-N(3) 96.70(12)
N(3)-Ti(1)-N(2) 108.24(13) N(1)-Ti(1)-N(4) 106.92(12)
N(3)-Ti(1)-N(4) 39.30(11) N(2)-Ti(1)-N(4) 138.57(14)
N(1)-Ti(1)-N(2) 39.62(10)
oxo complexes containing the bis(3,5-di-tert-butylpyra-
zolato)titanium(IV) fragment (10, 11; x * y; x, y g 2).17
The initial major compound 10 converted to 11 over
about 48 h at 23 °C in benzene-d6. To gain evidence that
10 and 11 were oxo complexes, the analogous reaction
of 6 with acetophenone was conducted in an NMR tube.
After 0.5 h, 1H and 13C{1H} NMR spectroscopy revealed
complete conversion to free tert-butylamine and the tert-
butylimine of acetophenone as the organic products.
Additionally, 10 and 11 were observed in a 78:22 ratio.
As per the case with benzophenone, 10 converted to 11
over 48 h at ambient temperature. Despite considerable
effort, we were unable to provide more structural insight
into 10 and 11. The proposed structures are tentative,
particularly with respect to the degree of oligomeriza-
tion.
X-r a y Cr ysta l Str u ctu r es of 3, 5, a n d 8. The X-ray
crystal structures of 3, 5, and 8 were determined in
order to establish the geometry about the metal centers
and the bonding modes of the pyrazolato ligands.
Experimental crystallographic data are summarized in
Table 1, selected bond lengths and angles are given in
Tables 2-4, and perspective views are presented in
Figures 1-3. Further data are available in the Sup-
porting Information.
N(1)-Ti(1)-C(5) 134.13(14) N(3)-Ti(1)-C(5) 98.90(14)
N(2)-Ti(1)-C(5) 94.52(13)
N(1)-Ti(1)-C(1) 90.00(14)
N(4)-Ti(1)-C(5) 112.40(13)
N(3)-Ti(1)-C(1) 134.03(14)
N(2)-Ti(1)-C(1) 110.76(14) N(4)-Ti(1)-C(1) 94.73(14)
C(5)-Ti(1)-C(1)
101.3(2)
Si(1)-C(1)-Ti(1) 122.9(2)
Si(2)-C(5)-Ti(1) 122.9(2)
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 5
Ti(1)-N(3)
Ti(1)-N(1)
Ti(1)-Cl(1)
Ti(1)‚‚‚Ti(1)#1
1.854(2)
2.030(2)
2.2876(7)
2.7670(7)
Ti(1)-N(3)#1
Ti(1)-N(2)
N(1)-N(2)
1.923(2)
2.035(2)
1.386(3)
N(3)-Ti(1)-N(3)#1 85.81(8)
N(3)-Ti(1)-N(1)
125.98(8)
107.93(8)
39.87(7)
N(3)#1-Ti(1)-N(1) 136.21(8) N(3)-Ti(1)-N(2)
N(3)#1-Ti(1)-N(2) 107.37(8) N(1)-Ti(1)-N(2)
N(3)-Ti(1)-Cl(1)
N(1)-Ti(1)-Cl(1)
C(12)-N(3)-Ti(1)
106.91(6) N(3)#1-Ti(1)-Cl(1) 104.82(6)
94.28(6)
137.6(2)
N(2)-Ti(1)-Cl(1)
C(12)-N(3)-Ti(1)# 128.1(2)
133.59(6)
Ti(1)-N(3)-Ti(1)# 94.19(8)
Ta ble 4. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 8
Ti(1)-N(6)
Ti(1)-N(4)
Ti(1)-N(5)
N(1)-N(2)
1.692(3)
2.049(3)
2.183(3)
1.385(3)
Ti(1)-N(2)
Ti(1)-N(3)
Ti(1)-N(1)
N(3)-N(4)
2.027(3)
2.109(3)
2.251(4)
1.387(3)
Complex 3 contains two η2-pyrazolato ligands and two
methyltrimethylsilyl groups. The titanium atom pos-
sesses approximate tetrahedral geometry, if the centers
of the nitrogen-nitrogen bonds in the 3,5-di-tert-bu-
tylpyrazolato groups are considered to be monodentate
N(6)-Ti(1)-N(2) 111.22(14) N(6)-Ti(1)-N(4)
N(2)-Ti(1)-N(4) 109.85(12) N(6)-Ti(1)-N(3)
N(2)-Ti(1)-N(3) 131.80(11) N(4)-Ti(1)-N(3)
103.3(2)
111.8(2)
38.93(9)
102.76(12)
92.09(10)
37.33(10)
96.97(12)
N(6)-Ti(1)-N(5) 97.65(14)
N(2)-Ti(1)-N(5)
N(4)-Ti(1)-N(5) 130.94(10) N(3)-Ti(1)-N(5)
N(6)-Ti(1)-N(1) 148.47(11) N(2)-Ti(1)-N(1)
N(4)-Ti(1)-N(1) 90.86(13)
N(5)-Ti(1)-N(1) 93.79(13)
N(3)-Ti(1)-N(1)
C(28)-N(6)-Ti(1) 172.7(3)
(17) For crystal structures of terminal titanium oxo complexes with
non-porphyrinato and non-phthalocyaninato ligands, see: Crescenzi,
R.; Solari, E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. Organometallics
1996, 15, 5456. Gallo, E.; Solari, E.; Franceschi, F.; Floriani, C.; Chiesi-
Villa, A.; Rizzoli, C. Inorg. Chem. 1995, 34, 2495. De Angelis, S.; Solari,
E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. Organometallics 1995, 14,
4505. J eske, P.; Haselhorst, G.; Weyhermu¨ller, T.; Wieghardt, K.;
Nuber, B. Inorg. Chem. 1994, 33, 2462. Smith, M. R.; Matsunaga, P.
T.; Andersen, R. A. J . Am. Chem. Soc. 1993, 115, 7049. Bodner, A.;
J eske, P.; Weyhermu¨ller, T.; Wieghardt, K.; Dubler, E.; Schmalle, H.;
Nuber, B. Inorg. Chem. 1992, 31, 3737. Hill, J . E.; Fanwick, P. E.;
Rothwell, I. P. Inorg. Chem. 1989, 28, 3602.
ligands. The pseudotetrahedral angles about the tita-
nium atom span 94.5-138.6°. The carbon-titanium-
carbon angle associated with the methyltrimethylsilyl
ligands (C(1)-Ti-C(5)) is 101.3(2)°. The 3,5-di-tert-
butylpyrazolato ligands are symmetrically coordinated
in a η2-fashion, with the titanium-nitrogen distances
ranging from 2.015 to 2.045 Å. These characteristics are

Imido Complexes of Titanium
Organometallics, Vol. 18, No. 7, 1999 1173
atom. The dimer is held together by the two bridging
imido ligands. Molecules of 5 lie on a crystallographic
inversion center. Each titanium atom possesses ap-
proximate tetrahedral geometry, if the centers of the
nitrogen-nitrogen bonds in the 3,5-di-tert-butylpyra-
zolato groups are considered to be monodentate ligands.
The pyrazolato groups are symmetrically coordinated
in a η2-fashion, with titanium-nitrogen distances of
2.030(2) and 2.035(2) Å. These values are identical to
the related values observed in 3. The titanium chlorine
bond length (2.2876(7) Å) is slightly longer than the
values found in dichlorobis(3,5-di-tert-butylpyrazolato)-
titanium(IV) (2.247-2.251 Å).3 The difference probably
reflects the less electrophilic metal center present in 5,
due to the strong donor characteristics of the imido
ligands. The titanium-nitrogen bond lengths associated
with the imido linkages (Ti-N(3) 1.854(2), Ti-N(3)#1
1.923(2) Å) are longer than the average value for known
monomeric alkylimido complexes (1.704 Å)19-22 and are
similar to those found in other structurally character-
ized dimeric titanium imido complexes.23 The geometry
at the bridging nitrogen atoms is nearly trigonal planar
(sum of angles ) 359.9(5)°). The structural and bonding
characteristics of dinuclear imido complexes with core
structures similar to that of 5 have been the subject of
a recent theoretical study.20
F igu r e 1. Perspective view of (But pz)2Ti(CH2SiMe3)2 (3)
with thermal ellipsoids at the 50% probability level. The
tert-butyl groups have been removed for clarity.
2
Complex 8 is a monomeric complex that bears two η2-
pyrazolato, one isopropylimido, and one pyridine ligand.
The titanium atom possesses approximate tetrahedral
geometry, if the centers of the nitrogen-nitrogen bonds
in the 3,5-di-tert-butylpyrazolato groups are considered
to be monodentate ligands. The pseudo-tetrahedral
angles around the titanium atom span 90.8-148.5°. The
titanium-nitrogen-carbon angle associated with the
imido ligand (172.7(3)°) is nearly linear and is consistent
F igu r e 2. Perspective view of [(But pz)TiCl(µ-NtBu)]2 (5)
2
with thermal ellipsoids at the 50% probability level.
(18) For selected examples of structurally characterized titanium
complexes with methyltrimethylsilyl ligands, see: Latesky, S. L.;
McMullen, A. K.; Rothwell, I. P.; Huffman, J . C. J . Am. Chem. Soc.
1985, 107, 5981. Chamberlain, L. R.; Durfee, L. D.; Fanwick, P. E.;
Kobriger, L.; Latesky, S. L.; McMullen, A. K.; Rothwell, I. P.; Folting,
K.; Huffman, J . C.; Streib, W. E.; Wang, R. J . Am. Chem. Soc. 1987,
109, 390. Chesnut, R. W.; Durfee, L. D.; Fanwick, P. E.; Rothwell, I.
P.; Folting, K.; Huffman, J . C. Polyhedron 1987, 6, 2019. Go´mez-Sal,
P.; Mena, M.; Palacios, F.; Royo, P.; Serrano, R.; Carreras, S. M. J .
Organomet. Chem. 1989, 375, 59. Eisch, J . J .; Caldwell, K. R.; Werner,
S.; Kru¨ger, C. Organometallics 1991, 10, 3417. McAlexander, L. H.;
Hung, M.; Li, L.; Diminnie, J . B.; Xue, Z.; Yap, G. P. A.; Rheingold, A.
L. Organometallics 1996, 15, 5231.
(19) Winter, C. H.; Sheridan, P. H.; Lewkebandara, T. S.; Heeg, M.
J .; Proscia, J . W. J . Am. Chem. Soc. 1992, 114, 1085. Lewkebandara,
T. S.; Sheridan, P. H.; Heeg, M. J .; Rheingold, A. L.; Winter, C. H.
Inorg. Chem. 1994, 33, 5879.
(20) Collier, P. E.; Blake, A. J .; Mountford, P. J . Chem. Soc., Dalton
Trans. 1997, 2911.
F igu r e 3. Perspective view of (But pz)2Ti(NiPr)(py) (8)
with thermal ellipsoids at the 50% probability level. The
2
(21) Monomeric titanium imido complexes reported to date show an
average titanium-nitrogen bond distance of 1.704 Å: Swallow, D.;
McInnes, J . M.; Mountford, P. J . Chem. Soc., Dalton Trans. 1998, 2253.
Stewart, P. J .; Blake, A. J .; Mountford, P. Organometallics 1998, 17,
3271. Hagadorn, J . R.; Arnold, J . Organometallics 1998, 17, 1355.
Dunn, S. C.; Mountford, P.; Robson, D. A. J . Chem. Soc., Dalton Trans.
1997, 293. Blake, A. J .; Collier, P. E.; Gade, L. H.; McPartlin, M.;
Mountford, P.; Schubart, M.; Scowen, I. J . J . Chem. Soc., Chem.
Commun. 1997, 1555. Dunn, S. C.; Mountford, P.; Shishkin, O. V.
Inorg. Chem. 1996, 35, 1006. Collier, P. E.; Dunn, S. C.; Mountford,
P.; Shishkin, O. V.; Swallow, D. J . Chem. Soc., Dalton Trans. 1995,
3743. Dunn, S. C.; Batsanov, A. S.; Mountford, P. J . Chem. Soc., Chem.
Commun. 1994, 2007. Duchateau, R.; Williams, A. J .; Gambarotta, S.;
Chiang, M. Y. Inorg. Chem. 1991, 30, 4863. Bai, Y.; Noltemeyer, M.;
Roesky, H. W. Z. Naturforsch. 1991, B46, 1357.
tert-butyl groups have been removed for clarity.
similar to those found in dichlorobis(3,5-di-tert-bu-
tylpyrazolato)titanium(IV) ((Ti-N 1.972-1.986 Å, Cl-
Ti-Cl 100.5(2)°).3 The slightly longer titanium-nitrogen
distances in 3, as compared to dichlorobis(3,5-di-tert-
butylpyrazolato)titanium(IV), can be rationalized by the
change of two methyltrimethylsilyl ligands for the two
chlorine atoms, which makes the central metal less
electrophilic and more crowded in 3. The titanium-
carbon bond lengths and the titanium-carbon-silicon
angles are typical and compare well to those found in
other methyltrimethylsilyl derivatives of titanium.18
Complex 5 is dimeric, with one 3,5-di-tert-butylpyra-
zolato, one chloride, and one imido ligand per titanium
(22) For reviews of early transition metal imido complexes, see:
Mountford, P. J . Chem. Soc., Chem. Commun. 1997, 2127. Wigley, D.
E. Progr. Inorg. Chem. 1994, 42, 239. Nugent, W. A.; Mayer, J . A.
Metal-Ligand Multiple Bonds; Wiley-Interscience: New York, 1988.
Nugent, W. A.; Haymore, B. L. Coord. Chem. Rev. 1980, 31, 123.

1174 Organometallics, Vol. 18, No. 7, 1999
Ye´lamos et al.
with triple bonding between titanium and nitrogen. The
titanium-nitrogen distance in the imido group (1.692-
(3) Å) is similar to the related distances in known
monomeric imido complexes.19-22 One of the pyrazolato
ligands is bonded to the titanium atom with essentially
ideal η2-bonding (Ti-N(4) 2.049(3), Ti-N(3) 2.109(3) Å),
while the other pyrazolato ligand adopts a “slipped” η2-
bonding mode (Ti(1)-N(2) 2.027(3), Ti(1)-N(1) 2.251-
(4) Å). In the “slipped” η2-ligand, one titanium-nitrogen
bond is 0.224 Å longer than the other. We have found
this type of bonding in situations where the coordination
sphere is extremely crowded.2 It is also likely that the
extremely strong trans-influence of the imido ligand
weakens the bonding between titanium and nitrogen-
(1). Nitrogen(1) is the nitrogen atom that is closest to
being trans to the imido group.
serve as an ancillary ligand in reactive early transition
metal complexes. In this regard, we envisioned that
there would be a significant analogy between cyclopen-
tadienyl and η2-pyrazolato ligands.4 Since many reactive
systems employ cyclopentadienyltitanium fragments,12
new reactive complexes with unique steric and elec-
tronic characteristics might be constructed from pyra-
zolato building blocks. From the experiments described
herein, we predict that the bis(η2-pyrazolato) ligand set
will be stable during transformations that do not lead
to the generation of acidic element-hydrogen bonds in
the coordination sphere. When acidic element-hydrogen
bonds are generated in the coordination sphere, the
stability of the pyrazolato ligands will depend on the
other ligands present about the metal. If other highly
reactive metal-ligand bonds are present, i.e., titanium-
alkyl linkages, the pyrazolato ligands should be pre-
served. If, however, the other ligands in the coordination
sphere are unreactive, i.e., chloride ligands, then the
pyrazolato ligand may be eliminated as the neutral
pyrazole. We are continuing to explore these predictions
in the context of olefin polymerizations promoted by
catalysts derived from 1-3 and related molecules.25
The results of this study suggest that the pyrazolato
ligand can be added to the list of new useful ligands for
early transition metals. Related ligands that have been
the subject of much recent study in early transition
metal systems include alkoxides,8 amidinates,9 and
pyrazolylborates,10 as well as many others.11 The struc-
tural and electronic features of η2-pyrazolato ligand
coordination may impart unique reactivity patterns to
metal centers that bear these groups.
Discu ssion
Since early transition metal complexes containing η2-
pyrazolato ligands remain very rare,7 it is instructive
to compare the titanium complexes prepared herein
with previous titanium pyrazolato complexes that have
been structurally characterized. In 1978, Fieselman and
Stucky reported the crystal structure of µ-pyrazolatobis-
(cyclopentadienyl)titanium(III) (12), which contains bridg-
ing pyrazolato ligands.24 We have recently reported the
crystal structures of dichlorobis(3,5-di-tert-butylpyra-
zolato)titanium(IV),3 tetrakis(3,5-dimethylpyrazolato)-
titanium(IV) (13),1 and tetrakis(3,5-diphenylpyrazolato)-
titanium(IV) (14).1 Complex 12 possesses d1 titanium(III)
centers, while 13 and 14 possess the d0 titanium(IV)
oxidation state. It is possible that a partially filled
d-shell destabilizes the η2-pyrazolato coordination mode
through filled/filled d-orbital/pyrazolato repulsive in-
teractions. The question of η2-pyrazolato ligand coordi-
nation in d-block metal complexes with partially filled
d-shells remains open, but we are working on this issue
both experimentally and theoretically.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All manipulations were carried
out under argon using Schlenk line or glovebox techniques.
Hexane and toluene were distilled from sodium just prior to
use. Tetrahydrofuran was distilled from a purple solution of
sodium/benzophenone ketyl immediately prior to use. The
primary amines and pyridine (purchased from Aldrich Chemi-
cal Co.) were distilled from sodium and calcium hydride,
respectively. Methylmagnesium chloride (3.0 M in tetrahy-
drofuran) and benzylmagnesium chloride (1.0 M in diethyl
ether) were used as received from Aldrich Chemical Co.
Methyltrimethylsilyllithium was purchased from Aldrich Chemi-
cal Co. as a 1.0 M solution in hexane, but was used as white
solid after removing the solvent under reduced pressure.
1-Amino-4-methylpiperazine was used as received from Acros.
Dichlorobis(3,5-di-tert-butylpyrazolato)titanium(IV)3,4 and chlo-
rotris(3,5-di-tert-butylpyrazolato)titanium(IV)4 were prepared
according to published procedures.
A central goal of the present study was to determine
if the η2-pyrazolato ligand would be inert enough to
Samples for infrared spectroscopy were prepared as Nujol
(23) Alcock, N. W.; Pierce-Butler, M.; Willey, G. R. J . Chem. Soc.,
Chem. Commun. 1974, 627. Alcock, N. W.; Pierce-Butler, M.; Willey,
G. R. J . Chem. Soc., Dalton Trans. 1976, 707. Thorn, D. L.; Nugent,
W. A.; Harlow, R. L. J . Am. Chem. Soc. 1981, 103, 357. Olmstead, M.
M.; Power, P. P.; Viggiano, M. J . Am. Chem. Soc. 1983, 105, 2927.
Vroegop, C. T.; Teuben, J . H.; van Bolhuis, F.; van der Linden, J . G.
M. J . Chem. Soc., Chem. Commun. 1983, 550. J ekel-Vroegop, C. T.;
Teuben, J . H. J . Organomet. Chem. 1985, 286, 309. Wollert, R.;
Wocadlo, S.; Dehnicke, K.; Goesmann, H.; Fenske, D. Z. Naturforsch.
1992, B47, 1386. Bai, Y.; Roesky, H. W.; Schmidt, H.-G.; Noltemeyer,
M. Z. Naturforsch. 1992, B47, 603. Schlichenmaier, R.; Strahle, J . Z.
Anorg. Allg. Chem. 1993, 619, 1526. Ovchinnikov, Y. E.; Ustinov, M.
V.; Igonin, V. A.; Struchkov, Y. T.; Kalikhman, I. D.; Voronkov, M. G.
J . Organomet. Chem. 1993, 461, 75. Wagner, O.; J ansen, M.; Baldus,
H.-P. Z. Anorg. Allg. Chem. 1994, 620, 366. Grigsby, W. J .; Olmstead,
M. M.; Power, P. P. J . Organomet. Chem. 1996, 513, 173. Liu, F.-Q.;
Herzog, A.; Roesky, H. W.; Uson, I. Inorg. Chem. 1996, 35, 741.
Bettenhausen, R.; Milius, W.; Schnick, W. Chem. Eur. J . 1997, 3, 1337.
(24) Fieselmann, B. F.; Stucky, G. D. Inorg. Chem. 1978, 17, 2074.
1
mulls unless stated otherwise. H and 13C{1H} NMR spectra
were recorded at 500, 300, 125, or 75 MHz. Chemical shifts
(δ, ppm) are given relative to residual protons or to the carbon
of the solvent. Melting points were determined in sealed
capillary tubes under argon and are uncorrected. Elemental
analyses were performed by Midwest Microlab, Indianapolis,
IN.
P r ep a r a tion of Dim eth ylbis(3,5-d i-ter t-bu tylp yr a zola -
to)tita n iu m (IV) (1). A 3.0 M solution of methylmagnesium
chloride in tetrahydrofuran (3.10 mL, 9.21 mmol), diluted in
tetrahydrofuran (30 mL), was slowly added to a solution of
dichlorobis(3,5-di-tert-butylpyrazolato)titanium(IV) (2.00 g,
4.19 mmol) in hexane (60 mL) at 0 °C. The reaction mixture
(25) Ye´lamos, C.; Nickias, P. N.; Winter, C. H. Work in progress.

Imido Complexes of Titanium
Organometallics, Vol. 18, No. 7, 1999 1175
was allowed to warm to room temperature and was stirred
for 20 h. The volatile components were removed under reduced
pressure, and the resultant yellow solid was extracted with
hexane (60 mL). Filtration of the hexane extract through a 2
cm pad of Celite on a coarse glass frit afforded a yellow
solution. Removal of the solvent under reduced pressure gave
1 as a yellow crystalline solid (1.67 g, 93%): dec 90 °C; IR
(Nujol, cm-1) 1528 (w), 1508 (s), 1363 (s), 1252 (s), 1234 (s),
1206 (w), 1102 (w), 1020 (m), 944 (w), 883 (w), 812 (s), 719
C(CH3)3); 13C{1H} NMR (C6D6, 22 °C, ppm) 159.15 (CC(CH3)3),
108.75 (pz ring CH), 68.80 (TiCH3), 32.22 (CC(CH3)3), 30.85
(CC(CH3)3).
Anal. Calcd for C34H60N6Ti: C, 67.97; H, 10.07; N, 13.99.
Found: C, 67.62; H, 10.12; N, 14.06.
R ea ct ion of Tr ich lor o(3,5-d i-ter t-b u t ylp yr a zola t o)-
tita n iu m (IV) w ith Meth ylm a gn esiu m Ch lor id e. A 3.0 M
solution of methymagnesium chloride in tetrahydrofuran (1.20
mL, 3.60 mmol), diluted with tetrahydrofuran (30 mL), was
slowly added to a suspension of trichloro(3,5-di-tert-butylpyra-
zolato)titanium(IV) (0.400 g, 1.20 mmol) in hexane (50 mL) at
-78 °C. After 0.25 h at this temperature, the yellow solution
was allowed to warm to ambient temperature and was stirred
for 3 h to afford a black suspension. The volatile components
were removed under reduced pressure, and the resultant black
solid was extracted with hexane (60 mL). Filtration of the
hexane extract through a 2 cm pad of Celite on a coarse glass
frit afforded a yellow solution. Removal of the solvent under
reduced pressure afforded 1 (0.18 g, 35%) as a yellow crystal-
1
(m); H NMR (CDCl3, 22 °C, δ) 6.68 (s, 2H, ring CH), 1.43 (s,
6H, TiCH3), 1.30 (s, 36H, C(CH3)3); 13C{1H} NMR (CDCl3, 22
°C, ppm) 160.89 (CC(CH3)3), 109.84 (ring CH), 68.19 (TiCH3),
32.31 (CC(CH3)3), 30.72 (CC(CH3)3).
Anal. Calcd for C22H44N4Ti: C, 66.03; H, 10.16; N, 12.83.
Found: C, 64.82; H, 9.36; N, 12.73.
P r ep a r a tion of Diben zylbis(3,5-d i-ter t-bu tylp yr a zola -
to)tita n iu m (IV) (2). A 1.0 M solution of benzylmagnesium
chloride in diethyl ether (3.01 mL, 3.06 mmol), diluted with
diethyl ether (30 mL), was slowly added to a solution of
dichlorobis(3,5-di-tert-butylpyrazolato)titanium(IV) (0.730 g,
1.53 mmol) in toluene (50 mL) at 0 °C. During the addition,
the initial yellow color turned to deep red. After stirring at
room temperature for 16 h, the volatile components were
removed under reduced pressure and the resultant red solid
was extracted with hexane (50 mL). Filtration of the hexane
extract through a 1 cm pad of Celite on a coarse glass frit gave
a red solution. This solution was concentrated under reduced
pressure to ca. 10 mL. After 2 days at -20 °C, deep red crystals
of 2 (0.39 g, 43%) were isolated by decanting the hexane
solution: mp 109-112 °C; IR (Nujol, cm-1) 3057 (w), 1593 (s),
1571 (w), 1527 (w), 1507 (s), 1485 (s), 1360 (s), 1286 (w), 1250
(m), 1229 (m), 1205 (m), 1087 (w), 1028 (m), 1017 (m), 986 (s),
1
line solid. The H and 13C{1H} NMR spectra of this solid were
identical to those of authentic 1.
P r ep a r a tion of ter t-Bu tylim id o(ch lor o)(3,5-d i-ter t-bu -
tylp yr a zola to)tita n iu m Dim er (5). tert-Butylamine (0.400
mL, 3.66 mmol) was added to a solution of dichlorobis(3,5-di-
tert-butylpyrazolato)titanium(IV) (0.35 g, 0.73 mmol) in hex-
anes (40 mL). After stirring at room temperature for 16 h, the
orange solution was separated from a fine white powder by
filtration. The powder was isolated and dried to yield tert-
butylammonium chloride (0.068 g, 85%). The volatile compo-
nents were removed from the filtrate under reduced pressure
to afford an orange solid. Analysis of this solid by 1H NMR
showed it to be a 30:70 mixture of 5 and chlorotris(3,5-di-tert-
butylpyrazolato)titanium(IV). Fractional crystallization from
hexane (5 mL) at -15 °C gave pure 5 as dark orange crystals
(0.050 g, 10%). Intermediate fractions obtained were mixtures
of orange crystals of 5 and yellow crystals of chlorotris(3,5-di-
tert-butylpyrazolato)titanium(IV). The last fraction, obtained
by cooling the solution to -20 °C for 20 days, afforded pure
chlorotris(3,5-di-tert-butylpyrazolato)titanium(IV) (0.26 g, 56%)
as yellow crystals. Spectral and analytical data for 5: mp 246
°C dec; IR (Nujol, cm-1) 1508 (m), 1363 (m), 1308 (w), 1252
(w), 1236 (w), 1173 (m), 1017 (w), 988 (w), 816 (m), 720 (m),
664 (s); 1H NMR (C6D6, 22 °C, δ) 6.63 (s, 2H, pz ring CH),
1.59 (s, 36H, CC(CH3)3), 0.96 (s, 18H, NC(CH3)3); 13C{1H} NMR
(C6D6, 22 °C, ppm) 162.14 (CC(CH3)3), 110.97 (pz ring CH),
77.60 (NC(CH3)3), 32.95 (CC(CH3)3), 31.24 (NC(CH3)3), 31.08
(CC(CH3)3).
1
889 (w), 813 (s), 794 (m), 747 (s), 720 (m), 693 (s), 656 (s); H
NMR (C6D6, 22 °C, δ) 7.06 (m, 4H, Ph meta-CH), 6.80-6.84
(m, 6H, Ph ortho-CH and para-CH), 6.70 (s, 2H, pz ring CH),
3.45 (s, 4H, CH2Ph), 1.23 (s, 36H, C(CH3)3); 13C{1H} NMR
(C6D6, 22 °C, ppm) 160.53 (CC(CH3)3), 146.37 (Ph ipso-C),
128.24 (Ph ortho-CH), 127.84 (Ph meta-CH), 122.79 (Ph para-
CH), 111.66 (pz ring CH), 95.25 (CH2C6H5), 32.36 (CC(CH3)3),
30.77 (CC(CH3)3).
Anal. Calcd for C36H52N4Ti: C, 73.44; H, 8.90; N, 9.52.
Found: C, 73.21; H, 9.01; N, 9.65.
P r ep a r a t ion of Bis(m et h ylt r im et h ylsilyl)b is(3,5-d i-
ter t-bu tylp yr a zola to)tita n iu m (IV) (3). A 100 mL Schlenk
flask was charged with dichlorobis(3,5-di-tert-butylpyrazolato)-
titanium(IV) (0.70 g, 1.47 mmol), methyltrimethylsilyllithium
(0.28 g, 2.93 mmol), and hexane (90 mL). The reaction mixture
was stirred at ambient temperature for 24 h. At this point,
the reaction mixture was filtered through a 2 cm pad of Celite
on a coarse glass frit to afford a clear yellow solution. The
volume of this solution was concentrated to about 10 mL under
reduced pressure. Crystallization at -20 °C for 2 days afforded
Anal. Calcd for C30H56N6Cl2Ti2: C, 53.98; H, 8.46; N, 12.59.
Found: C, 53.60; H, 8.61; N, 12.79.
tert-Butylammonium chloride and chlorotris(3,5-di-tert-bu-
tylpyrazolato)titanium(IV) were identified by comparison of
their 1H and 13C{1H} NMR spectra with those of authentic
materials.
3 as yellow crystals (0.42 g, 49%): dec 136 °C; IR (Nujol, cm-1
)
1508 (m), 1363 (m), 1252 (m), 1240 (s), 1206 (w), 1092 (s), 1019
(m), 990 (w), 898 (s), 844 (m), 816 (s), 740 (w), 720 (m), 698
(w), 677 (w); 1H NMR (C6D6, 22 °C, δ) 6.70 (s, 2H, pz ring CH),
2.82 (s, 4H, CH2SiMe3), 1.36 (s, 36H, C(CH3)3), 0.00 (s, 18H,
CH2Si(CH3)3); 13C{1H} NMR (C6D6, 22 °C, ppm) 160.96 (CC-
(CH3)3), 111.00 (pz ring CH), 91.60 (CH2SiMe3), 32.52
(CC(CH3)3), 31.02 (CC(CH3)3), 2.05 (CH2Si(CH3)3).
P r epar ation of ter t-Bu tylim idobis(3,5-di-ter t-bu tylpyr a-
zola to)(ter t-bu tyla m in e)tita n iu m (IV) (6). tert-Butylamine
(0.480 mL, 4.58 mmol) was added to a solution of 1 (0.40 g,
0.92 mmol) in toluene (30 mL) at ambient temperature. After
stirring for 3 days at room temperature, the volatile compo-
nents were removed under reduced pressure. The resultant
orange solid was extracted with hexane (40 mL), and the
hexane extract was filtered through a 1 cm pad of Celite on a
coarse glass frit. The yellow-orange filtrate was concentrated
to a volume of about 10 mL. Crystallization at -20 °C for 24
h afforded 6 as orange crystals (0.17 g, 33%): mp 149 °C dec;
IR (Nujol, cm-1) 3312 (m), 1569 (m), 1524 (s), 1404 (m), 1285
(w), 1261 (m), 1160 (w), 1091 (s), 1039 (m), 1026 (m), 799 (s),
727 (w), 676 (w), 660 (w); 1H NMR (C6D6, 22 °C, δ) 6.23 (s,
2H, pz ring CH), 3.38 (s broad, 2H, NH2But), 1.42 (s, 36H, CC-
(CH3)3), 1.22 (s, 9H, NC(CH3)3), 1.10 (s, 9H, NH2C(CH3)3); 13C-
{1H} NMR (C6D6, 22 °C, ppm) 158.92 (CC(CH3)3), 102.27 (pz
Anal. Calcd for C30H60N4Si2Ti: C, 62.03; H, 10.41; N, 9.64.
Found: C, 61.82; H, 10.51; N, 9.54.
P r ep a r a tion of Meth yltr is(3,5-d i-ter t-bu tylp yr a zola -
to)tita n iu m (IV) (4). In a fashion similar to the preparation
of 1, chlorotris(3,5-di-tert-butylpyrazolato)titanium(IV) (0.60
g, 0.96 mmol) and a 3.0 M solution of methylmagnesium
chloride in tetrahydrofuran (0.35 mL, 1.06 mmol) were reacted
to afford 4 as large yellow crystals (0.30 g, 52%): mp 155 °C;
IR (Nujol, cm-1) 1505 (m), 1363 (s), 1252 (m), 1233 (m), 1205
(w), 1019 (m), 997 (w), 804 (s), 718 (m); 1H NMR (C6D6, 22 °C,
δ) 6.55 (s, 3H, pz ring CH), 2.31 (s, 3H, TiCH3), 1.25 (s, 54H,

1176 Organometallics, Vol. 18, No. 7, 1999
Ye´lamos et al.
ring CH), 68.39 (NC(CH3)3), 51.14 (NH2C(CH3)3), 32.75 (NC-
(CH3)3), 32.28 (CC(CH3)3), 31.33 (CC(CH3)3), 30.91 (NH2C-
(CH3)3).
Data for tert-butylamine: 1H NMR (C6D6, 22 °C, δ) 0.98 (s,
9H), 0.68 (s, 2H); 13C{1H} NMR (C6D6, 22 °C, ppm) 47.01 (s,
H2NC(CH3)3), 37.70 (s, H2NC(CH3)3).
Data for the tert-butylimine of benzophenone: 1H NMR
(C6D6, 22 °C, δ) 7.83 (m, 4H, o-C6H2H2′H′′), 7.12-6.95 (m, 6H,
m,p-C6H2H2′H′′), 1.23 (s, 9H, C(CH3)3); 13C{1H} NMR (C6D6,
22 °C, ppm) 142.21 (s, CdNtBu), 140.31 (s, ipso-phenyl
carbon), 129.56 (s, p-phenyl carbons), 128.69 (s, o- or m-phenyl
carbons), 128.60 (s, o- or m-phenyl carbons), 57.02 (s, C(CH3)3),
31.83 (s, C(CH3)3).
Anal. Calcd for C30H58N6Ti: C, 65.43; H, 10.62; N, 15.26.
Found: C, 64.61; H, 10.56; N, 15.22.
P r epar ation of ter t-Bu tylim idobis(3,5-di-ter t-bu tylpyr a-
zola to)(p yr id in e)tita n iu m (IV) (7). tert-Butylamine (0.72
mL, 6.87 mmol) and pyridine (0.55 mL, 6.87 mmol) were added
to a solution of 1 (0.60 g, 1.37 mmol) in toluene (30 mL). After
stirring for 3 days at room temperature, the volatile compo-
nents were removed under reduced pressure to afford an
orange solid. The solid was extracted with hexane (40 mL).
The resulting extract was filtered through a 1 cm pad of Celite
on a coarse glass frit and was then concentrated in volume to
ca. 20 mL. Crystallization at -20 °C for 24 h afforded 7 as
orange crystals (0.61 g, 80%): mp 151 °C; IR (Nujol, cm-1) 1604
(s), 1508 (s), 1360 (s), 1302 (m), 1248 (s), 1230 (s), 1211 (s),
1117 (m), 1070 (m), 1043 (m), 1018 (m), 999 (w), 990 (m), 801
(s), 792 (m), 758 (m), 723 (m), 696 (s), 642 (m); 1H NMR (C6D6,
22 °C, δ) 9.07 (m, 2H, py ortho-CH), 6.77 (m, 1H, py para-
CH), 6.53 (m, 2H, py meta-CH), 6.32 (s, 2H, pz ring CH), 1.43
(s, 36H, CC(CH3)3), 1.26 (s, 9H, NC(CH3)3); 13C{1H} NMR
(C6D6, 22 °C, ppm) 159.03 (CC(CH3)3), 152.35 (py ortho-CH),
138.43 (py para-CH), 123.95 (py meta-CH), 102.53 (pz ring
CH), 68.74 (NC(CH3)3), 32.64 (NC(CH3)3), 32.37 (CC(CH3)3),
31.32 (CC(CH3)3).
Data for 10: 1H NMR (C6D6, 22 °C, δ) 6.33 (s, 2H), 1.29 (s,
36H);13C{1H} NMR (C6D6, 22 °C, ppm) 160.69 (s, C-C(CH3)3),
107.41 (s, pz ring C-H), 32.48 (s, C(CH3)3), 30.68 (s, C(CH3)3).
Data for 11: 1H NMR (C6D6, 22 °C, δ) 6.30 (s, 2H), 1.25 (s,
36H); 13C{1H} NMR (C6D6, 22 °C, ppm) 159.40 (s, C-C(CH3)3),
106.81 (s, pz ring C-H), 32.26 (s, C(CH3)3), 30.73 (s, C(CH3)3).
X-r a y Cr ysta l Str u ctu r e Deter m in a tion of 2, 5, a n d 8.
Samples for X-ray structural determinations were mounted
in thin-walled capillaries under a nitrogen atmosphere. Crys-
tallographic data were collected at room temperature on a
Bruker automated P4/CCD diffractometer with monochro-
mated Mo radiation. A hemisphere of data was collected for
each sample at 10 s/frame and integrated with the manufac-
turer’s SMART and SAINT software, respectively. Absorption
corrections were applied with Sheldrick’s SADABS, and the
structures were solved and refined using the programs of
SHELXS-86 and SHELXL-93.26
Anal. Calcd for C31H52N6Ti: C, 66.88; H, 9.42; N, 15.10.
Found: C, 66.92; H, 9.44; N, 15.10.
For 2, 10 793 total data were averaged to yield 7175 (Rint
)
0.072) independent reflections. The compound crystallizes as
a molecular complex with no associated solvent or ions.
Hydrogen atoms were calculated and assigned to ride on the
carbons to which they were bound. The tert-butyl groups and
trimethylsilyl groups in the molecule displayed a typical
rotational disorder that is reflected in the large thermal
parameters associated with these atoms.
P r epar ation of Isopr opylim idobis(3,5-di-ter t-bu tylpyr a-
zola to)(p yr id in e)tita n iu m (IV) (8). In a fashion similar to
the preparation of 7, isopropylamine (0.390 mL, 4.58 mmol),
pyridine (0.370 mL, 4.58 mmol), and 1 (0.40 g, 0.92 mmol) were
reacted to afford 8 as orange crystals (0.23 g, 46%): mp 108
°C dec; IR (Nujol, cm-1) 1604 (m), 1507 (m), 1360 (m), 1300
(m), 1250 (m), 1231 (s), 1111 (w), 1070 (w), 1044 (w), 1018 (m),
For 5, 10 662 total data were averaged to yield 4240 (Rint
)
1
0.038) independent reflections. The compound crystallizes as
a binuclear molecular complex with no associated solvents or
ions. Hydrogen atoms were calculated and assigned to ride on
the carbons to which they were bound or were placed in
observed positions and refined. The molecule occupies a
crystallographic inversion center, but all atoms occupy general
positions in the cell. The asymmetric unit consists of one-half
dimer. Moderate disorder in the tert-butyl groups was observed
and is reflected in the large thermal parameters associated
with the atoms contained in these groups.
991 (w), 801 (s), 759 (w), 723 (w), 696 (m); H NMR (C6D6, 22
°C, δ) 9.03 (m, 2H, py ortho-CH), 6.80 (m, 1H, py para-CH),
6.54 (m, 2H, py meta-CH), 6.33 (s, 2H, pz ring CH), 3.81
(septuplet, J HH ) 6.6 Hz, 1H, NCH(CH3)2), 1.43 (s, 36H, CC-
(CH3)3), 1.17 (d, J HH ) 6.6 Hz, 6H, NCH(CH3)2); 13C{1H} NMR
(C6D6, 22 °C, ppm) 159.10 (CC(CH3)3), 152.24 (py ortho-CH),
138.29 (py para-CH), 124.00 (py meta-CH), 102.65 (pz ring
CH), 65.60 (NCH(CH3)2), 32.36 (CC(CH3)3), 31.27 (CC(CH3)3),
26.36 (NCH(CH3)2).
Anal. Calcd for C30H50N6Ti: C, 66.40; H, 9.29; N, 15.49.
Found: C, 65.53; H, 9.00; N, 15.38.
For 8, 9174 total data were averaged to yield 6527 (Rint
)
0.038) independent reflections. The compound crystallizes as
a molecular complex with no associated solvent or ions.
Hydrogen atoms were calculated and assigned to ride on the
carbons to which they were bound or were placed in observed
positions and refined. The tert-butyl groups in the molecule
displayed a typical rotational disorder. The two tert-butyl
groups most subject to disorder were modeled with partial
(occupancy ) 0.5) carbon atoms, viz., C(5)-C(7) and C(20)-
C(22).
P r ep a r a tion of 1-Am id o-4-m eth ylp ip er a zin e(m eth yl)-
bis(3,5-di-ter t-bu tyl-pyr azolato)titan iu m (IV) (9). In a fash-
ion similar to the preparation of 6, 1-amino-4-methylpiperazine
(0.620 mL, 5.15 mmol) and 1 (0.450 g, 1.03 mmol) were reacted
in toluene (50 mL) to afford 9 as yellow crystals (0.35 g, 64%):
mp 104-107 °C dec; IR (Nujol, cm-1) 3292 (νNH, m), 1517 (m),
1507 (s), 1489 (w), 1362 (s), 1283 (m), 1251 (s), 1235 (s), 1206
(w), 1141 (w), 1092 (m), 1019 (m), 1003 (s), 926 (w), 809 (s),
794 (s), 706 (m), 668 (w); 1H NMR (C6D6, 22 °C, δ) 6.84 (s broad,
1H, NHN(CH2CH2)2NCH3), 6.38 (s, 2H, pz ring CH), 2.76
(broad m, 4H, NHN(CH2CH2)2NCH3), 2.16 (broad m, 4H,
NHN(CH2CH2)2NCH3), 2.02 (s, 3H, NHN(CH2CH2)2NCH3),
1.34 (s, 36H, CC(CH3)3), 1.11 (s, 3H, TiCH3); 13C{1H} NMR
(C6D6, 22 °C, ppm) 158.25 (CC(CH3)3), 106.43 (ring CH), 60.12
(NHN(CH2CH2)2NCH3), 54.15 (NHN(CH2CH2)2NCH3), 49.50
(TiCH3), 45.58 (NHN(CH2CH2)2NCH3), 32.21 (CC(CH3)3), 31.10
(CC(CH3)3).
Ack n ow led gm en t. We are grateful to the National
Science Foundation (Grants Nos. CHE-9510712 and
CHE-9807269) and the Ministerio de Educacio´n y Cul-
tura of Spain (postdoctoral fellowship to C.Y.) for
support of this research.
Su p p or tin g In for m a tion Ava ila ble: Tables listing full
experimental details for data collection and refinement, atomic
coordinates, bond distances and angles, and thermal param-
eters for 3, 5, and 8. This material is available free of charge
via the Internet at http://pubs.acs.org.
Anal. Calcd for C28H53N7Ti: C, 62.78; H, 9.97; N, 18.30.
Found: C, 62.54; H, 10.04; N, 18.34.
Rea ction of 6 w ith Ben zop h en on e. A 5 mm NMR tube
was charged with 6 (0.040 g, 0.073 mmol), benzophenone
(0.014 g, 0.077 mmol), and benzene-d6 (1.00 mL). The tube was
flame sealed, and the course of the reaction was monitored by
1H and 13C{1H} NMR spectroscopy. For a description of the
reaction, see the text.
OM980802R
(26) Sheldrick, G. SHELX-S and SHELXL-93; University of Go¨t-
tingen: FDR, 1986 and 1993, respectively.