Synthesis and Group 4 Complexes of Tris(pyrrolyl-α-methyl)amine

Article abstract of DOI:10.1021/ic035049v

The tetradentate, trianionic ligand tris(pyrrolyl-α-methyl)amine (H₃tpa) is available in 84% yield in a single step by a triple Mannich reaction involving 3 equiv of pyrrole, 3 equiv of formaldehyde, and ammonium chloride. The new ligand is readily placed on titanium by transamination on Ti(NMe₂)₄, which generates Ti(NMe ₂)(tpa) (1) in 73% yield. Treating 1 with 1 equiv of 1,3-dimethyl-2-iminoimidazolidine (H-imd) in toluene provided a rare example of a titanium 2-iminoimidazolidinide, which displays some interesting structural features. Of note is the Ti-N(imd) distance of 1.768(2) A, a typical Ti-N double to triple bond distance. Reaction of Zr(NMe₂)₄ with H₃tpa gave a complex of variable composition, probably varying in the amount of labile dimethylamine retained. However, stable discreet compounds were available by addition of THF, pyridine, or 4,4′ -di-tert-butyl-2,2′-bipyridine (Bu^tbpy) to in situ generated Zr(NMe₂)(NHMe₂)_x(tpa). Three chloro zirconium complexes were generated using three different strategies. Treating Zr(tpa)(NMe₂)(Bu^tbpy) (5) with ClSiMe₃ afforded Zr(tpa)(Cl)(Bu^tbpy) (6) in 92% yield. Reaction of Li ₃tpa with ZrCl₄-(THF)₂ in THF gave a 72% yield of ZrCl(tpa)(THF)₂ (7). In addition, treatment of ZrCl(NMe ₂)₃ with H₃tpa cleanly generated ZrCl(NHMe ₂)₂(tpa) (8) in 95% yield. An organometallic zirconium complex was generated on treatment of 6 with LiC≡CPh; alkynyl Zr(C≡CPh)(tpa)(Bu^tbpy) (9) was isolated in 62% yield. 1, Ti(imd)(tpa) (2), 6, and 9 were characterized by X-ray diffraction.

Full text of DOI:10.1021/ic035049v

Inorg. Chem. 2004, 43, 275−281
Synthesis and Group 4 Complexes of Tris(pyrrolyl-r-methyl)amine
Yanhui Shi, Changsheng Cao, and Aaron L. Odom*
Department of Chemistry, Michigan State UniVersity, East Lansing, Michigan 48824
Received September 5, 2003
The tetradentate, trianionic ligand tris(pyrrolyl-R-methyl)amine (H tpa) is available in 84% yield in a single step by
3
a triple Mannich reaction involving 3 equiv of pyrrole, 3 equiv of formaldehyde, and ammonium chloride. The new
ligand is readily placed on titanium by transamination on Ti(NMe2)4, which generates Ti(NMe2)(tpa) (1) in 73%
yield. Treating 1 with 1 equiv of 1,3-dimethyl-2-iminoimidazolidine (H-imd) in toluene provided a rare example of a
titanium 2-iminoimidazolidinide, which displays some interesting structural features. Of note is the Ti−N(imd) distance
of 1.768(2) Å, a typical Ti−N double to triple bond distance. Reaction of Zr(NMe2)4 with H tpa gave a complex of
3
variable composition, probably varying in the amount of labile dimethylamine retained. However, stable discreet
t
compounds were available by addition of THF, pyridine, or 4,4′-di-tert-butyl-2,2′-bipyridine (Bubpy) to in situ generated
Zr(NMe2)(NHMe2)x(tpa). Three chloro zirconium complexes were generated using three different strategies. Treating
t
t
Zr(tpa)(NMe2)(Bubpy) (5) with ClSiMe3 afforded Zr(tpa)(Cl)(Bubpy) (6) in 92% yield. Reaction of Li3tpa with ZrCl4-
(THF)2 in THF gave a 72% yield of ZrCl(tpa)(THF)2 (7). In addition, treatment of ZrCl(NMe2)3 with H tpa cleanly
3
generated ZrCl(NHMe2)2(tpa) (8) in 95% yield. An organometallic zirconium complex was generated on treatment
t
of 6 with LiCtCPh; alkynyl Zr(CtCPh)(tpa)(Bubpy) (9) was isolated in 62% yield. 1, Ti(imd)(tpa) (2), 6, and 9
were characterized by X-ray diffraction.
Introduction
across the periodic table, including rare examples of multiple
bonds where late-transition metals are in relatively low
oxidation states.7
We have been examining the applications of pyrrolyl-based
ligands in early transition metal mediated C-N bond for-
mation,8 e.g., hydroamination9 and iminoamination10 of
alkynes. For these reactions, we sought ancillary ligands that
were readily prepared and that would afford Lewis acidic
metal centers. Multidentate amido ligands such as the well-
Multidentate ligands of approximate C3 symmetry have
been of particular recent interest in coordination chemistry
and include a diverse class of ligand structures (Chart 1)
including triazacyclononanes (A),1 tris(pyrazolyl)borates (B),2
tris(dialkylphosphinomethyl)borates (C),3 tris(alkylthio-
methyl)borates (D),4 tris[2-(N-alkylamido)ethyl]amine (tren)
derivatives (E),5 and several others.6 These C3 ancillary
ligands have been especially useful in the stabilization of
metal-ligand multiple bonds in transition-metal systems
(4) (a) Krishnan, R.; Voo, J. K.; Riordan, C. G.; Zahkorov, L.; Rheingold,
A. L. J. Am. Chem. Soc. 2003, 125, 4422-4423. (b) Craft, J. L.;
Mandimutsira, B. S.; Flujita, K.; Riordan, C. G.; Brunold, T. C. Inorg.
Chem. 2003, 42, 859-867. (c) Mandimutsira, B. S.; Yamarik, J. L.;
Brunold, T. C.; Gu, W. W.; Cramer, S. P.; Riordan, C. G. J. Am.
Chem. Soc. 2002, 124, 15336-15350.
(5) For a few examples see: (a) Schrock, R. R. Acc. Chem. Res. 1997,
30, 9-16. (b) Cummins, C. C.; Schrock, R. R.; Davis, W. M.
Organometallics 1992, 11, 1452-1454. (c) Verkade, J. G. Acc. Chem.
Res. 1993, 26, 483-489. (d) Yandulov, D. V.; Schrock, R. R. J. Am.
Chem. Soc. 2002, 124, 6252-6253. (e) Greco, G. E.; Schrock, R. R.
Inorg. Chem. 2001, 40, 3861-3878. (f) Greco, G. E.; Schrock, R. R.
Inorg. Chem. 2001, 40, 3850-3860. (g) Yandulov, D. V.; Schrock,
R. R.; Rheingold, A. L.; Ceccarelli, C.; Davis, W. M. Inorg. Chem.
2003, 42, 796-813.
* Author to whom correspondence should be addressed. E-mail: odom@
cem.msu.edu.
(1) For a review see: (a) Wainwright, K. P. Coord. Chem. ReV. 1997,
166, 35-90. For some recent examples see (b) Yang, J. Y.; Shores,
M. P.; Sokol, J. J.; Long, J. R. Inorg. Chem. 2003, 42, 1403-1419.
(c) Glaser, T.; Beissel, T.; Bill, E.; Weyhermuller, T.; Schunemann,
V.; Meyer-Klaucke, W.; Trautwein, A. X.; Wieghardt, K. J. Am. Chem.
Soc. 1999, 121, 1403-1419. (d) Mahapatra, S.; Halfen, J. A.;
Wilkinson, E. C.; Pan, G. F.; Wang, X. D.; Young, V. G.; Cramer, C.
J.; Que, L., Jr.; Tolman, W. B. J. Am. Chem. Soc. 1996, 118, 11555-
11574.
(2) Trofimenko, S. Scorpionates: The Coordination Chemistry of Poly-
pyrazolylborate Ligands; Imperial College Press: London, 1999.
(3) (a) Jenkins, D. M.; DiBilio, A. J.; Allen, M. J.; Beley, T. A.; Peters,
J. C. J. Am. Chem. Soc. 2002, 124, 15336-15350. (b) Feldman, J.
D.; Peters, J. C.; Tilley, T. D. Organometallics 2002, 21, 4050-4064.
(c) Feldman, J. D.; Peters, J. C.; Tilley, T. D. Organometallics 2002,
21, 4065-4075.
(6) For some recent reviews on multidentate amido ligands and amido
chemistry see: (a) Gade, L. H. Chem. Commun. 2000, 173-181. (b)
Kempe, R. Angew. Chem., Int. Ed. 2000, 39, 468-493. (c) Cummins,
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10.1021/ic035049v CCC: $27.50 © 2004 American Chemical Society
Published on Web 12/10/2003
Inorganic Chemistry, Vol. 43, No. 1, 2004 275

Shi et al.
Chart 1. Examples of Some Common C3 Ligands Employed in
Transition-Metal Chemistry and tpa
resonances. Chemical shifts are quoted in ppm and coupling
constants in hertz. Zr(NMe2)4 and Ti(NMe2)4 were prepared from
LiNMe2 and MCl4 using the literature procedure.14 1,3-Dimethyl-
2-iminoimidazolidine was synthesized using the literature prepara-
tion15 for the hydrochloride, which was basified by shaking with
aqueous K2CO3 and vacuum distilled. Pyrrole was purchased from
Fisher and distilled prior to use.
Preparation of ClZr(NMe2)3. This compound was obtained
using the procedure of Johnson and Cummins, which is reproduced
in brief.16 In an inert atmosphere drybox, a 250 mL Schlenk flask
was loaded with 75 mL of toluene, Zr(NMe2)4 (1.10 g, 4.11 mmol),
ZrCl4 (0.32 g, 1.37 mmol), and a stir bar. The vessel was removed
from the box and heated in a 95 °C oil bath for 5 min. The solution
was cooled to room temperature and then returned to the drybox.
The clear, yellow solution was concentrated in vacuo and then
cooled to -30 °C, which generated colorless crystals in 72% yield.
1H NMR (300 MHz, 23 °C, C6D6): δ ) 2.80 ppm. 13C{1H} NMR
(75 MHz, 23 °C, C6D6): δ ) 43.4 ppm.
Preparation of H3tpa. A 250 mL flask was charged with a stir
bar, pyrrole (18 g, 0.268 mol), formaldehyde (20 mL of a 37%
solution in water, 0.268 mol), NH4Cl (4.78 g, 0.0894 mol), 60 mL
of ethanol, and 20 mL of water. The reaction was heated at 40 °C
in an oil bath with stirring for 40 min. Volatiles were then removed
by rotary evaporation with the aid of an aspirator. To the residue
were added 40 mL of ether, 40 mL of THF, and 40 mL of NaOH
(20%). The organic layer was separated. The aqueous layer was
extracted three times with ether (20 mL). The combined organic
layers were dried over MgSO4. Volatiles were removed in vacuo.
The product was washed with 10 mL of pentane/ether (v:v ) 1:1),
which afforded H3tpa as a colorless solid. The product was
recrystallized from THF/pentane (19.20 g, 84%). Mp ) 137-8 °C.
1H NMR (300 MHz, CDCl3): δ ) 8.12 (br s, 3 H, NH), 6.70 (m,
explored tren derivatives are readily prepared, but alkylamido
subsituents can be quite π-basic, which quenches the Lewis
acidity of the metal. While the π-donating ability of the
amido substituents of tren ligands can be effectively tuned
by changing R, a different strategy where the amido nitrogen
is incorporated into a pyrrole ring also greatly reduces the
π-basicity of the nitrogen.11,12 Here we report the one-step
synthesis of a tetradentate, trianionic derivative of the tren
framework (Chart 1) incorporating pyrrolyl substituents into
the amido sites, tris(pyrrolyl-R-methyl)amine (H3tpa).13
Experimental Section
General Considerations. All manipulations of air-sensitive
compounds were carried out in an MBraun drybox under a purified
nitrogen atmosphere. Anhydrous ether (Columbus Chemical In-
dustries Inc.), THF (JADE Scientific), dichloromethane (EM
Science), and toluene (Spectrum Chemical Manufacturing Corp.)
were sparged with dry N2 and dried by being passed through
solvent-drying columns purchased from Solv-Tek. Pentane (Spec-
trum Chemical Manufacturing) and benzene (EM Science) were
distilled from purple sodium benzophenone ketyl. Acetonitrile
(Spectrum Chemical Manufacturing) was distilled from calcium
hydride. Deuterated solvents were dried over purple sodium
benzophenone ketyl (C6D6) or phosphoric anhydride (CDCl3) and
distilled under nitrogen. 1H and 13C spectra were recorded on Inova-
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V.; Atwood, J. L. J. Crystallogr. Spectrosc. Res. 1984, 14, 21. (b)
Atwood, J. L.; Rogers, R. D.; Bynum, R. V. Acta Crystallogr., Sect.
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A 1968, 1967-1969. (l) Yoshida, Y.; Matsui, S.; Takagi, Y.; Mitani,
M.; Nitabaru, M.; Nakano, T.; Tanaka, H.; Fujita, T. Chem. Lett. 2000,
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M.; Kuo, P.-C.; Zhou, C.-C.; Lee, G.-H.; Peng, S.-M. J. Chin. Chem.
Soc. 2000, 47, 895-900. (o) Yoshida, Y. Matsui, S.; Takagi, Y.;
Mitani, M.; Nakano, T.; Tanaka, H.; Kashiwa, N.; Fujita, T. Orga-
nometallics 2001, 20, 4793-4799. (p) Seo, W. S.; Cho, Y. J.; Yoon,
S. C.; Park, J. T.; Park, Y. J. Organomet. Chem. 2001, 640, 79-84.
(q) Yoshida, Y.; Saito, J.; Mitani, M.; Takagi, Y.; Matsui, S.; Ishii,
S.; Nakano, T.; Kashiwa, N.; Fujita, T. Chem. Commun. 2002, 1298-
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J. J. Chem. Soc., Dalton Trans. 2002, 4529-2531. (s) Novak, A.;
Blake, A. J.; Wilson, C.; Love, J. B. Chem. Commun. 2002, 2796-
2797. For related group 4 carbazole chemistry see: Riley, P. N.;
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181-186.
1
300 and VXR-500 spectrometers. H and 13C assignments were
confirmed when necessary with the use of two-dimensional
1H-1H and 13C-1H correlation NMR experiments. All spectra were
referenced internally to residual protiosolvent (1H) or solvent (13C)
(7) (a) Shirin, Z.; Hammes, B. S.; Young, V. G., Jr.; Borovik, A. S. J.
Am. Chem. Soc. 2000, 122, 1836-1837. (b) MacBeth, C. E.;
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M. P.; Borovik, A. S. Science 2000, 289, 938-941. (c) Jenkins, D.
M.; Betley, T. A.; Peters, J. C. J. Am. Chem. Soc. 2002, 124, 11238-
11239. (d) Brown, S. D.; Betley, T. A.; Peters, J. C. J. Am. Chem.
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Bukowski, M. R.; Costas, M.; Ho, R. Y. N.; Mu¨nck, E.; Nam, W.;
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(8) Katayev, E.; Li, Y.; Odom, A. L. Chem. Commun. 2002, 838-839.
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276 Inorganic Chemistry, Vol. 43, No. 1, 2004

Synthesis and Group 4 Complexes of tpa
3 H, 5-C4H3N), 6.15 (m, 3 H, 4-C4H3N), 6.06 (app s, 3 H, 3-C4H3N),
3.57 (s, 6 H, CH2). 13C{1H} NMR (CDCl3): δ ) 128.7 (2-C4H3N),
117.6 (5-C4H3N), 108.2 (4-C4H3N), 107.9 (3-C4H3N), 49.8 (CH2).
Anal. Found (Calcd) for C15H18N4: C, 70.84 (70.74); H, 7.13 (7.14);
N, 22.03 (22.24). MS (EI): m/z ) 254.2 (M+).
Preparation of Li3tpa. To a -95 °C suspension of H3tpa (0.5086
g, 2 mmol) in 30 mL of toluene was added LiBun (3.75 mL, 1.6 M
in hexanes, 6 mmol) slowly. The mixture was allowed to warm to
room temperature and stir for 2 h. Then, 20 mL of pentane was
added. The product was filtered, washed (3 × 20 mL of pentane),
and dried in vacuo, which yielded a white solid (0.52 g, 95%) that
was used without further purification.
allowed to warm to room temperature and stir for 2 h. Volatiles
were removed in vacuo to generate a yellow solid. Recrystallization
from toluene at -35 °C provided yellow microcrystals of 4 (68%,
1
0.185 g). H NMR (300 MHz, CDCl3): δ ) 8.02 (d, J ) 2 Hz, 4
H, 2-C5H5N), 7.71 (t, J ) 6 Hz, 2 H, 4-C5H5N), 7.26 (t, J ) 6 Hz,
4 H, 3-C5H5N), 6.39 (d, J ) 1 Hz, 3 H, 5-C4H3N), 5.95 (dd, J )
1 Hz, 3 H, 4-C4H3N), 5.92 (d, J ) 1 Hz, 3 H, 3-C4H3N), 4.15 (s,
6 H, C4H3NCH2N), 3.16 (s, 6 H, CH3). 13C NMR{1H} (300 MHz,
CDCl3): δ ) 150.1 (2-C5H5N), 138.1(4-C5H5N), 137.8 (2-C4H3N),
126.1 (3-C5H5N), 124.5 (5-C4H3N), 108.9 (4-C4H3N), 104.3
(3-C4H3N), 56.3 (C4H3NCH2N), 41.4 (CH3). Anal. Found (Calcd)
for C34H39N7Zr (MW ) 636.95): C, 63.60 (64.11); H, 6.41 (6.17);
N, 14.95 (15.39).
Preparation of Ti(NMe2)(tpa) (1). Under an inert atmosphere
of purified nitrogen, a nearly frozen solution of Ti(NMe2)4 (0.2242
g, 1 mmol) in 3 mL of Et2O was treated with a cooled solution of
H3tpa (0.2513 g, 1 mmol) in 3 mL of Et2O and 3 mL of CH2Cl2.
The reaction mixture was stirred at room temperature for 3 h.
Volatiles were removed in vacuo to generate a black solid. The
solid was dissolved in 3 mL of CH2Cl2 and layered with 3 mL of
Et2O. The layered solution was stored at -35 °C, which gave the
product as a dark red solid. A second recrystallization of the crude
product with CH2Cl2 and Et2O afforded dark red crystals (73%,
0.25 g). MW ) 343.29. 1H NMR (300 MHz, C6D6): δ ) 7.07 (m,
3 H, 5-C4H3N), 6.28 (m, 3 H, 4-C4H3N), 6.01 (m, 3 H, 3-C4H3N),
3.60 (s, 6 H, CH2), 3.14 (s, 6 H, NCH3). 13C{1H} NMR (300 Hz,
C6D6): δ ) 139.2 (2-C4H3N), 126.7 (5-C4H3N), 108.5(4-C4H3N),
105.2 (3-C4H3N), 55.4 (C4H3NCH2N), 42.5 (N(CH3)2). Anal. Found
(Calcd) for C17H21N5Ti: C, 59.82 (59.48); H, 6.28 (6.17); N, 20.12
(20.40).
Preparation of Zr(NMe2)(tpa)(Butbpy) (5). To a -90 °C
suspension of H3tpa (0.127 g, 0.5 mmol) and 4,4′-di-tert-butyl-
2,2′-bipyridine (Butbpy) (0.134 g, 0.5 mmol) in 10 mL of toluene
was added Zr(NMe2)4 0.134 g (0.5 mmol) in 10 mL of toluene
dropwise. The reaction mixture was allowed to warm to room
temperature and stir for 2 h. The volatiles were removed in vacuo
to generate a dark red solid. Recrystallization from toluene at -35
°C provided microcrystals of 5 (78%, 0.253 g). 1H NMR (300 MHz,
C6D6): δ ) 8.89 (d, 6,6′-C5H3N, J ) 6 Hz, 2 H), 7.98 (d, 3,3′-
C5H3N, J ) 2 Hz, 2 H), 7.15 (dd, 5,5′-C5H3N, J ) 2 and 1 Hz, 2
H), 6.73 (dd, 5-C4H3N, J ) 2 and 1 Hz, 2 H), 6.49 (dd, 4-C4H3N,
J ) 2 and 4 Hz, 2 H), 6.43 (dd, 3-C4H3N, J ) 1 and 2 Hz, 2 H),
6.16 (t, 5-C4H3N, J ) 1 Hz, 1 H), 6.10 (t, 4-C4H3N, J ) 2 Hz, 1
H), 5.42 (t, 3-C4H3N, J ) 1 Hz, 1 H), 4.58-3.86 (br m, C4H3-
NCH2N, 6 H), 2.65 (s, N(CH3)2, 6 H), 0.89 (s, 4,4′-C5H3NC(CH3)3,
18 H). 13C{1H} NMR (300 MHz, CDCl3): δ ) 164.4 (2,2′-C5H3N),
152.9 (6,6′-C5H3N), 150.6 (4,4′-C5H3N), 139.3 (2-C4H3N), 137.6
(2-C4H3N), 127.8 (5-C4H3N), 125.8 (5-C4H3N), 123.2 (3-C5H3N),
117.8 (5-C5H3N), 108.7 (4-C4H3N), 106.8 (4-C4H3N), 103.4
(3-C4H3N),102.5(3-C4H3N),56.6(C4H3NCH2N),56.5(C4H3NCH2N),
44.2 (br s, N(CH3)2), 35.5 (4,4′-C5H3NC(CH3)3), 30.4 (4,4′-C5H3-
NC(CH3)3). Anal. Found (Calcd) for C35H45N7Zr‚2CH2Cl2: C, 54.20
(53.88); H, 6.25 (5.99); N, 11.81 (11.89).
Preparation of Ti(imd)(tpa) (2). A solution of Ti(tpa)(NMe2)
(0.1716 g, 0.5 mmol) in 10 mL of toluene was cooled to -35 °C.
To the stirring cold solution was added 1,3-dimethyl-2-iminoimi-
dazolidine (H-imd) (0.0566 g, 0.5 mmol). The reaction mixture was
allowed to warm to room temperature and stir overnight. The
volatiles were removed in vacuo to give a light brown solid. The
solid was recrystallized at -35 °C in CH2Cl2 layered with toluene,
which afforded the product as a yellow powder (0.191 g, 93%). M
Preparation of ZrCl(tpa)(Butbpy) (6). To a nearly frozen
solution of 5 (0.655 g, 1.00 mmol) in 25 mL of THF was added
ClSiMe3 (127 µL, 1.00 mmol) dropwise. The reaction mixture was
allowed to warm to room temperature and stir for 3 h, after which
the volatiles were removed in vacuo to generate a yellow solid.
Purification was accomplished by recrystallization from THF/
toluene at -35 °C, which provided yellow microcrystals of 6
1
) 411.35. H NMR (300 MHz, CDCl3): δ ) 7.16 (q, 3 H, J ) 1
Hz, 5-C4H3N), 5.94 (t, 3 H, J ) 3 Hz, 4-C4H3N), 5.88 (q, 3 H, J
) 1 Hz, 3-C4H3N), 4.11 (d, 6 H, J ) 1 Hz, C4H3NCH2N), 3.57 (s,
4 H, NCH2CH2N), 3.16 (s, 6 H, CH3). 13C NMR (CDCl3): δ )
139.6 (2-C4H3N), 129.4 (5-C4H3N), 107.1 (4-C4H3N), 103.3 (3-
C4H3N), 55.6 (C4H3NCH2N), 46.7 (CH3), 33.6 (NCH2CH2N). Anal.
Found (Calcd) for C20H25N7Ti: C, 58.17 (58.40); H, 6.28 (6.13);
N, 23.48 (23.83).
1
(92%, 0.59 g). H NMR (300 MHz, CDCl3): δ ) 8.92-7.78 (br
s, 3,3′-C5H3N, 2 H), 8.20 (d, 6,6′-C5H3N, J ) 1 Hz, 2 H), 7.44
(d, 5,5′-C5H3N, J ) 4 Hz, 2 H), 7.10 (s, br s 5-C4H3N, 2 H), 6.08
(t, 4-C4H3N, J ) 2 Hz, 2 H), 5.97 (dd, 3-C4H3N, J ) 1 and 1 Hz,
2 H), 5.85 (t, 5-C4H3N, J ) 2 Hz, 1 H), 5.63 (t, 4-C4H3N, J ) 2
Hz, 1 H), 5.35 (dd, 3-C4H3N, J ) 1 and 1 Hz, 1 H), 5.12-3.72
(br s, C4H3NCH2N, 6 H), 1.44 (s, 4,4′-C5H3NC(CH3)3, 18 H).
13C{1H} NMR (300 MHz, CDCl3): δ ) 165.3 (2,2′-C5H3N),
153.0 (6,6′-C5H3N), 150.2 (br, 4-C4H3N), 138.7 (5-C4H3N), 130.6
(br, 5-C4H3N), 126.6 (5-C4H3N), 123.2 (3,3′-C5H3N), 118.8
(5,5′-C5H3N), 109.6 (4-C4H3N), 108.7 (4-C4H3N), 104.3 (br,
3-C4H3N), 103.9 (3-C4H3N), 57.0 (C4H3NCH2N), 35.7 (4,4′-
C5H3NC(CH3)3), 30.4 (C4H3NC(CH3)3). Anal. Found (Calcd) for
C40H47N6ClZr (MW ) 738.52): C, 65.05 (64.79); H, 6.41 (6.47);
N, 11.38 (11.01).
Preparation of Zr(NMe2)(tpa)(THF) (3). To a nearly frozen
solution of H3tpa (0.127 g, 0.5 mmol) in 3 mL of THF was added
Zr(NMe2)4 (0.134 g, 0.5 mmol) in 10 mL of THF. The reaction
mixture was allowed to warm to room temperature and stir for 4
h, after which time the volatiles were removed in vacuo, providing
1
product as a colorless solid (98%, 0.224 g). H NMR (300 MHz,
CDCl3): δ ) 6.90 (q, 3 H, J ) 1 Hz, 5-C4H3N), 6.07 (t, 3 H, J )
3 Hz, 4-C4H3N), 5.97 (t, 3 H, J ) 1 Hz, 3-C4H3N), 4.10 (s, 6 H,
C4H3NCH2N), 3.41 (m, 4 H, 2-C4H8O), 3.37 (s, 6 H, N(CH3)2),
1.67 (m, 4 H, 3-C3H8O). 13C{1H} NMR (300 MHz, CDCl3): δ )
138.1 (2-C4H3N), 125.2 (5-C4H3N), 108.8 (4-C4H3N), 104.6
(3-C4H3N), 70.9 (2-C4H8O), 55.8 (C4H3NCH2N), 39.1 (N(CH3)2),
25.1 (3-C4H8O). Anal. Found (Calcd) for C21H29N5OZr (MW )
458.71): C, 54.49 (54.99); H, 6.29 (6.37); N, 15.27 (15.27).
Preparation of Zr(NMe2)(tpa)(pyridine)2 (4). To a -90 °C
suspension of H3tpa (0.127 g, 0.5 mmol) and pyridine (1 mmol,
81 µL) in 10 mL of toluene was added Zr(NMe2)4 (0.134 g, 0.5
mmol) in 10 mL of toluene dropwise. The reaction mixture was
Preparation of ZrCl(tpa)(THF)2 (7). To a nearly frozen
suspension of ZrCl4(THF)2 (0.377 g, 1 mmol) in 20 mL of toluene
was added cold Li3tpa (0.272 g, 1 mmol) suspended in 20 mL of
toluene. The reaction mixture was allowed to warm to room
temperature. A yellow solution was isolated after filtration. Volatiles
Inorganic Chemistry, Vol. 43, No. 1, 2004 277

Shi et al.
Table 1. Structural Parameters for 1, 2, 6‚2CH2Cl2, and 9‚CH2Cl2
were removed under reduced pressure to give a yellow solid. The
product was recrystallized from CH2Cl2 at -35 °C (72%, 0.376
g). 1H NMR (300 MHz, CDCl3): δ ) 6.99 (s, 3H, 5-C4H3N), 6.07
(t, 3 H, 4-C4H3N, J ) 2 Hz), 5.94 (t, 3H, 3-C4H3N, J ) 2 Hz),
4.27 (s, 6H, C4H3NCH2N), 3.88 (m, 8H, 2-C4H8O), 1.94 (m,
8H, 3-C4H8O). 13C{1H} NMR (300 MHz, CDCl3): δ ) 137.9
(5-C4H3N), 127.7 (2-C4H3N), 109.7 (3-C4H3N), 103.7 (4-C4H3N),
69.9 (2-C4H8O), 57.1 (CH2), 25.5 (3-C4H8O). Anal. Found (Calcd)
for C23H31ClN4O2Zr (MW ) 522.19): C, 52.76 (52.90); H, 5.93
(5.98); N, 10.66 (10.73).
1
2
6
9
empirical
formula
fw
space group
a (Å)
b (Å)
c (Å)
C
17H21N5Ti
C20H25N7Ti C37H49Cl4N7Zr C20H29Cl3N6Zr
343.29
P21/n
411.37
P21/n
824.85
P21/c
551.06
P21/c
12.588(4)
12.147(4)
22.353(7)
99.518(6)
3370.9(18)
8
10.728(3)
10.672(3)
17.655(4)
95.078(4)
2013.3(8)
4
8.5527(18)
23.370(5)
20.101(4)
99.270(4)
3965.1(14)
4
12.468(3)
15.019(3)
13.703(3)
107.116(3)
2452.5(9)
4
â (deg)
vol (Å3)
Z
µ (mm-1
)
0.514
1.353
0.446
0.583
0.794
Preparation of ZrCl(NHMe2)2(tpa) (8). To a nearly frozen
suspension of H3tpa (0.102 g, 0.4 mmol) in 5 mL of CH2Cl2 was
added a cold solution of ZrCl(NMe2)3 (0.104 g, 0.4 mmol) in 5
mL of CH2Cl2. The reaction mixture was allowed to warm to
room temperature and stir for 2 h. Volatiles were removed in vacuo,
which provided a yellow solid. Then, the solid was dissolved in
CH2Cl2, which was layered by a mixture of Et2O and toluene (v:v
) 1:1). The layered solution was stored at -35 °C, which gave
the product as light yellow crystals (95%, 0.177 g). 1H NMR (300
MHz, CDCl3): δ ) 7.00 (br s, 3 H, 5-C4H3N,), 6.11 (d, 3 H, J )
2 Hz, 4-C4H3N), 5.94 (d, J ) 2 Hz, 3 H, 3-C4H3N), 4.24 (s, 6 H,
C4H3NCH2N), 3.08 (s, 2 H, NHMe2), 2.18 (br s, 12 H, NH(CH3)2).
13C{1H} NMR (300 MHz, CDCl3): δ ) 138.1 (2-C4H3N), 126.8
(br, 5-C4H3N), 110.5 (4-C4H3N), 104.4 (3-C4H3N), 57.1 (C4H3-
NCH2N), 39.3 (CH3). Anal. Found (Calcd) for C20H29Cl3N6Zr (MW
) 555.06): C, 43.45 (43.59); H, 5.70 (5.30); N, 15.05 (15.25).
D
calcd (g cm-3
)
1.357
1.382
1.492
no. of total
reflns
15191
16570
17955
10930
no. of unique
reflns (Rint
extinction
4852 (0.1658) 2890 (0.082) 5704 (0.1419) 3522 (0269)
)
0.0005(3)
0.0021(5)
0.0419
0.0043(6)
0.0623
0.0006(3)
0.0372
R(F0) (I > 2σ) 0.0576
Rw(F02) (I > 2σ) 0.1332
0.0879
0.1557
0.0923
Scheme 1. Synthesis of 1 and 2
Preparation of Zr(CtC-Ph)(tpa)(Butbpy) (9). To a nearly
frozen suspension of LiCtCPh (0.025 g, 0.5 mmol) in 10 mL of
toluene was added a cold solution of 6 (0.3232 g, 0.5 mmol) in 5
mL of THF dropwise. The reaction mixture was allowed to warm
to room temperature and stir overnight. Then, volatiles were
removed in vacuo. The residue was dissolved in 20 mL of toluene
and filtered, which provided a yellow solution. Concentration of
the resulting solution in vacuo and cooling to -35 °C afforded 9
as yellow microcrystals (0.221 g, yield 62%). 1H NMR (300 MHz,
CDCl3): δ ) 8.48 (d, J ) 5 Hz, 6,6′-C5H3N, 2 H), 8.18 (s, 3,3′-
C5H3N, 2 H), 7.41 (d, J ) 5 Hz, 5,5′-C5H3N, 2 H), 7.25 (br s,
5-C4H3N, 2 H), 6.99 (m, 3,4-Ph, 3 H), 6.85 (m, 2-Ph, 2 H), 6.05
(m, 4-C4H3N, 2 H), 5.98 (d, J ) 2 Hz, 3-C4H3N, 2 H), 5.85 (d, J
) 2 Hz, 5-C4H3N, 1 H), 5.65 (m, 4-C4H3N, 1 H), 5.42 (d, J ) 2
Hz, 3-C4H3N, 1 H), 4.42-4.18 (br, C4H3NCH2N, 6 H), 1.44 (d,
4,4′-C5H3NC(CH3)3, 18 H). 13C{1H} NMR (300 MHz, CDCl3): δ
) 164.7 (2,2′-C5H3N), 153.4 (6,6′-C4H3N), 150.6 (4,4′-C4H3N),
139.2 (2-C4H3N), 138.6 (2-C4H3N), 131.5 (2-Ph), 130.5 (3-Ph),
127.5 (2-Ph), 125.8 (5-C4H3N), 125.7 (5-C4H3N), 122.9 (3,3′-
C5H3N, 1-Ph), 118.4 (5,5′-C5H3N), 109.1 (4-C4H3N), 108.2
(4-C4H3N), 104.3 (3-C4H3N), 104.1 (3-C4H3N), 80.8 (C6H5C2), 56.8
(C4H3NCH2N), 35.6 (4,4′-C5H3NC(CH3)3), 30.4 (4,4′-C5H3NC-
(CH3)3). Anal. Found (Calcd) for C41H44N6Zr (MW ) 712.06): C,
69.35 (69.16); H, 6.36 (6.23); N, 11.81 (11.80).
program xprep. Some details on the structure refinement are found
in Table 1.
Results and Discussion
The tetradentate ligand H3tpa was prepared in 84% yield
on a 20 g scale by a triple Mannich reaction of 1 equiv of
ammonium chloride, 3 equiv of formaldehyde, and 3 equiv
of pyrrole in 3:1 ethanol/water (eq 1). The correct temper-
ature and time for the reaction are crucial for obtaining a
satisfactory quality and yield of the product.
Recently, a similar ligand, tris(indolyl-R-methyl)amine,
using indolyl instead of pyrrolyl groups was synthesized by
Tanski and Parkin through a multistep procedure.17 Several
tantalum complexes incorporating this tetradentate indolyl
ligand were reported.
Addition of an ethereal solution of H3tpa to a cold solution
of Ti(NMe2)4 afforded pseudo-trigonal-bipyramidal 1 in 73%
recrystallized yield (Scheme 1). The dark red complex was
structurally characterized by single-crystal X-ray diffraction
(Figure 1). The pseudo-trigonal-bipyramidal complex has
General Considerations for X-ray Diffraction. Crystals grown
at -35 °C were quickly moved from a scintillation vial to a
microscope slide containing Paratone N. Samples were selected and
mounted onto a glass fiber in wax and Paratone. The data collections
were carried out at a sample temperature of 173(2) K on a Bruker
AXS platform three-circle goniometer with a CCD detector. The
incident radiation was of wavelength 0.71073 Å, which was selected
with a graphite monochromator. The data were processed and
reduced utilizing the program SAINTPLUS supplied by Bruker
AXS. The structures were solved by direct methods (SHELXTL
v5.1, Bruker AXS) in conjunction with standard difference Fourier
techniques. Absorption corrections were done empirically using the
(17) Tanski, J. M.; Parkin, G. Inorg. Chem. 2003, 42, 264-266.
278 Inorganic Chemistry, Vol. 43, No. 1, 2004

Synthesis and Group 4 Complexes of tpa
Figure 1. Structure of 1 found by X-ray diffraction. Only one of the two
chemically identical but crystallographically distinct molecules in the
asymmetric unit is shown. Ellipsoids are at the 25% probability level.
Figure 3. Structure of 2 found by X-ray diffraction. Ellipsoids are at the
25% probability level.
Table 3. Selected Bond Distances (Å) and Angles (deg) from the
X-ray Diffraction Study on 2
Ti-N(1)
1.995(3)
2.009(2)
1.996(3)
2.296(2)
1.768(2)
1.321(4)
1.341(4)
1.440(4)
1.367(4)
1.434(4)
N(5)-Ti-N(1)
N(5)-Ti-N(2)
N(5)-Ti-N(3)
N(5)-Ti-N(4)
N(1)-Ti-N(2)
N(1)-Ti-N(3)
N(3)-Ti-N(2)
C(1)-N(5)-Ti
103.1(1)
106.6(1)
99.6(1)
175.7(1)
112.9(1)
114.2(1)
117.9(1)
169.1(2)
Ti-N(2)
Ti-N(3)
Ti-N(4)
Ti-N(5)
N(5)-C(1)
N(11)-C(1)
N(11)-C(1)
N(12)-C(1)
N(12)-C(2)
Figure 2. Possible resonance forms for 2 leading to the observed Ti-N
multiple bond. A second π-bond due to donation of the lone pair on the
imd imino nitrogen is not shown.
Scheme 2. Synthesis of Zr(NMe2)(tpa)Lx Complexes from Zr(NMe2)4
Table 2. Selected Bond Distances (Å) and Angles (deg) from the
X-ray Diffraction Study on 1
Ti(A)-N(1A)
Ti(A)-N(2A)
Ti(A)-N(3A)
Ti(A)-N(4A)
Ti(A)-N(5A)
1.992(6)
2.000(5)
1.977(5)
2.275(5)
1.843(6)
N(5A)-Ti(A)-N(1A)
N(5A)-Ti(A)-N(2A)
N(5A)-Ti(A)-N(3A)
N(5A)-Ti(A)-N(4A)
N(1A)-Ti(A)-N(2A)
N(1A)-Ti(A)-N(3A)
N(3A)-Ti(A)-N(2A)
98.3(3)
111.7(2)
99.3(2)
169.3(2)
111.4(2)
119.8(2)
114.2(2)
structural features common for titanium pyrrolyl compounds
of this class. The titanium dimethylamido, Ti(A)-N(5A),
has a distance consistent with significant π-bonding at 1.843-
(6) Å due to amido lone pair to titanium donation (Table 2).
The three pyrrolyl nitrogens reside in the approximate
trigonal plane with an average Ti-N(pyrrolyl) distance of
1.989(6) Å, consistent with the much lower π-donating
ability of pyrrolyl versus dimethylamido. The donor amine
occupies the other axial position 169.3(2)° away from the
dimethylamido and has a Ti(A)-N(4A) distance of 2.275-
(5) Å.
An electronically interesting ligand that has been little used
in titanium chemistry is the 2-iminoimidazolidinide, espe-
cially where the imidazolidine is substituted with donating
alkyl substituents in the 1- and 3-positions. Because of the
significant stabilization of the carbocation resulting from
Ti-N triple bond formation due to donation from the
adjacent nitrogens (Figure 2) and relatively high Lewis
acidity of the metal center due to poor π-donation from the
pyrrolyl ligands (vide supra), we expected a short Ti-N(imd)
bond. Reaction of H-imd with 1 generated 2 as a red
crystalline solid (Scheme 1).
The first X-ray diffraction study on a iminoimidazolidinide
titanium complex was recently reported by Kretschmer and
co-workers on Ti(Cp)Cl2(NdC[N(Ph)CH2]2), which exhib-
ited a Ti-N(imd) distance of 1.792(2) Å.18 Titanium tpa 2
was also characterized by X-ray diffraction (Figure 3, Table
3) and exhibited a short Ti-N(imd) distance of 1.768(2) Å.
The slightly shorter distance in 2 versus reported Ti(Cp)-
Cl2(NdC[N(Ph)CH2]2) may be a result of the more basic
methyl substituents on the imidazoline moiety and/or greater
Lewis acidity of the tpa ligand set. The typical Ti-N(imido)
bond length range is approximately 1.65-1.78 Å, which can
be thought of as a Ti-N double to triple bond distance.19
The Ti-N(imd) bond of 2 is in the typical titanium-imido
bond range, suggestive of some triple bond character. Indeed,
the Ti-N(imd) bond distance is similar to the Ti-N(imido)
bond distances in Ti(NSiBut)(OSiBut)(THF),19n [Ti(NSiMe3)-
(CH2SiR3)(N(SiMe3)2)2]-,19t and Ti(N-C6H3-2,6-Me)(OPMe3)-
(Cp)(NHC6H3-2,6-Me)19ai at 1.772(3), 1.751(5), and 1.752-
(18) Kretschmer, W. P.; Dijkhuis, C.; Meetsma, A.; Hessen, B.; Teuben,
J. H. Chem. Commun. 2002, 608-609.
Inorganic Chemistry, Vol. 43, No. 1, 2004 279

Shi et al.
(8) Å, respectively. In addition, the Ti-N(imd) bond is ∼0.1
Å shorter than the Ti-N(NMe2) bond in 1, suggestive of
significant additional bonding in the iminoimidazolidinide
complex.
That the nitrogens of the imidazoline strongly partici-
pate in π-bonding is also apparent from the solid-state
structure of 2. The N(11)-C(1) and N(12)-C(1) bond
distances of 1.341(4) and 1.367(4) Å, respectively, are
indicative of significant multiple bond character; cf. the C-N
bond distance in pyridine of 1.339(5) Å.20 By compari-
son, the imidazolidine N-Me average single bond distance,
i.e., N(11)-C(1′) and N(12)-C(2′), is much longer at
1.437(4) Å.
Figure 4. Structure of 5 found by X-ray diffraction. The compound
crystallized with 2 equiv of CH2Cl2 per Zr complex. Ellipsoids are at the
25% probability level.
We also explored the use of tpa in related zirconium
chemistry. Because of the larger van der Waals radius of
zirconium, additional donors on the metal center were in-
variably present in these initial studies. Several donors with
variable lability were studied to provide a selection of starting
materials. For example, reaction of H3tpa with Zr(NMe2)4
Table 4. Selected Bond Distances (Å) and Angles (deg) from the
X-ray Diffraction Study on 5
Zr-N(1)
Zr-N(2)
Zr-N(3)
Zr-N(4)
Zr-N(5)
Zr-N(6)
Zr-N(7)
2.200(7)
2.301(6)
2.202(6)
2.462(6)
2.365(6)
2.434(6)
2.054(6)
N(7)-Zr-N(1)
N(7)-Zr-N(3)
N(7)-Zr-N(2)
N(1)-Zr-N(4)
N(2)-Zr-N(4)
N(7)-Zr-N(5)
N(7)-Zr-N(6)
N(3)-Zr-N(6)
N(1)-Zr-N(5)
87.5(2)
87.9(2)
151.6(2)
70.0(2)
70.1(2)
77.9(2)
91.5(2)
162.9(2)
146.1(2)
(19) For representative examples of structurally characterized titanium imido
complexes see: (a) Jill, J. E.; Profilet, R. D.; Fanwick, P. E.; Rothwell,
I. P. Angew. Chem., Int. Ed. Engl. 1990, 29, 664-665. (b) Duchateau,
R.; Williams, A. J.; Gambarotta, S.; Chiang, M. Y. Inorg. Chem. 1991,
30, 4863-4866. (c) Hill, J. E.; Fanwick, P. E.; Rothwell, I. P. Inorg.
Chem. 1991, 30, 1143-1144. (d) Bai, Y.; Noltemeye, M.; Roesky,
H. W. Z. Naturforsh. 1991, 46b, 1357-1363. (e) Thorn, D. L.; Harlow,
R. L. Inorg. Chem. 1992, 31, 3917-3923. (f) Winter, C. H.; Sheridan,
P. H.; Lewdebandara, T. S.; Heeg, M. J.; Proscia, J. W. J. Am. Chem.
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Hill, J. E.; Fanwick, P. E.; Rothwell, I. P. Polyhedron 1993, 12, 689-
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1994, 2007-2008. (i) Mountford, P.; Swallow, D. Chem. Commun.
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Chem. Commun. 2001, 2738-2739. (ai) Johnson, J. S.; Bergman, R.
G. J. Am. Chem. Soc. 2001, 123, 2923-2924. (aj) Ong, T.-G.; Yap,
G. P. A.; Richeson, D. S. Organometallics 2002, 21, 2839-2841.
provided a complex that was of somewhat ill-defined com-
position, probably due to variable amounts of NHMe2 being
retained by the metal center (Scheme 2). A single compound,
Zr(THF)(Cl)(tpa) (3), is readily prepared by addition of THF
to in situ generated Zr(NMe2)(tpa)(NHMe2)x.
While excess THF generates the monoadduct 3, addi-
tion of 2 equiv of pyridine results in a stable complex with
two donor ligands Zr(NMe2)(tpa)(pyridine)2 (4). Simi-
larly, addition of 1 equiv of 4,4′-di-tert-butyl-2,2′-bipyridine
(Butbpy) to in situ generated Zr(NMe2)(tpa)(NHMe2)x gave
Zr(NMe2)(tpa)(Butbpy) (5).
Seven-coordinate 5 was characterized by X-ray diffraction
(Figure 4, Table 4) and displays a geometry most closely
resembling face-capped octahedral, where the donor nitrogen
of the tpa caps the trigonal face formed by the three pyrrolyl
substituents. The two pyrrolyl substituents trans to the
nitrogens of the Butbpy have similar zirconium-nitrogen
distances of 2.200(7) and 2.202(6) Å for Zr-N(1) and
Zr-N(3), respectively. However, Zr-N(2) is substantially
lengthened at 2.301(6) Å, presumably due to the trans
influence of the approximately coaxial dimethylamido ligand.
Another structural feature of 5 is the unequal Zr-N distances
to the two bpy nitrogens. The Zr-N(5) bond distance of
2.365(6) Å is substantially shorter than Zr-N(6) at 2.434-
(6) Å. The difference in bonding to the two pyridyl nitrogens
may be a result of differing trans influences by the tpa ligand
on the two sides of the bpy. The pyrrolyl nitrogen N(3) is
nearly trans to the longer bpy nitrogen with an angle of
162.9(2)°. Conversely, the shorter pyridyl-zirconium bond,
Zr-N(5), is farther from coaxial with its trans-pyrrolyl
nitrogen, and the N(1)-Zr-N(5) angle is 146.1(2)°.
(20) Gordon, A. J.; Ford, R. A. The Chemist’s Companion: A Handbook
of Practical Data, Techniques, and References; John Wiley & Sons:
New York, 1972.
280 Inorganic Chemistry, Vol. 43, No. 1, 2004

Synthesis and Group 4 Complexes of tpa
a ZrMe(Butbpy)(tpa) complex, which was unstable even at
-35 °C. However, reaction of 6 with LiCtCPh (eq 4)
provided the stable alkynyl 9 in 62% yield.
Scheme 3. Synthesis of Li3tpa and 7
Concluding Remarks
The tetradentate nitrogen ligand H3tpa is readily available
in a single step from commercially available compounds.
We set out to discover if the tetradentate tpa ligand frame-
work would provide a stable platform for group 4 complexes.
A wide selection of functionality was placed on the Ti(tpa)
and Zr(tpa) cores. In the zirconium system three different
synthetic protocols were used for the synthesis of ZrClL2-
(tpa) complexes. All the syntheses provided compounds in
high yields, consistent with a robust and useful ancillary
ligand set. In addition, a stable alkynyl complex of zirconium
was readily generated by simple metathesis.
The tpa ligand on titanium and zirconium provided stable
compounds bearing halides, amidos, 2-iminoimidazolidinide,
pyridine, alkynyl, and others. Due to the low π-donating
ability of the amide groups, the ligand may be useful in the
generation of complexes across the transition and main group
series.
The synthesis of potentially useful zirconium chloride tpa
complexes was also explored using several different routes
and donor ligands. Reaction of 5 with trimethylsilyl chloride
results in the formation of 6 in 92% yield as a crystalline
yellow solid (eq 2).
The zirconium halide complex 7 is available in 72% yield
through a reaction of ZrCl4(THF)2 with Li3tpa (Scheme 3).
The lithium salt of the tpa ligand was prepared in near
quantitative yield by deprotonation of the a toluene solution
of H3tpa with n-butyllithium in hexanes. Treatment of ZrCl4-
(THF)2 in THF with a toluene slurry of Li3tpa provides ZrCl-
(THF)2(tpa) in 72% recrystallized yield.
An alternative synthesis to zirconium chloride complexes
was explored using the starting material ClZr(NMe2)3 (eq
3). Treatment of a CH2Cl2 solution of ClZr(NMe2)3 with a
solution of H3tpa provides the bis(dimethylamine) complex
8 in 95% recrystallized yield. Bis(amine) 8 was also
characterized by X-ray diffraction, and the details are
included in the Supporting Information.
Acknowledgment. We gratefully acknowledge the finan-
cial support of the donors of the Petroleum Research Fund,
administered by the American Chemical Society, Department
of Energy-Defense Programs, Office of Naval Research, and
Michigan State University. A.L.O. thanks Mitch Smith for
many interesting and helpful discussions. The help of Bala
Ramanathan with spectroscopic characterization of some
compounds is greatly appreciated.
Supporting Information Available: Tables of crystallographic
data including refinement parameters, coordinates, bond distances,
and bond angles. This material is available free of charge via the
Internet at http://pubs.acs.org.
Zirconium organometallic complexes are available through
metathesis reactions involving the chloride tpa compounds.
Reaction of methyllithium with 6 results in the formation of
IC035049V
Inorganic Chemistry, Vol. 43, No. 1, 2004 281