Tl(I), Fe(II), and Co(II) complexes supported by a monoanionic N,N,N′-heteroscorpionate ligand bis(3,5-di-tertbutylpyrazol-1-yl)-1- CH2NAr (Ar = 2,6-iPr2C6H 3)

Article abstract of DOI:10.1021/ic051704i

The lithium salt (L)Li(THF) (L^- = bis(3,5-di-tertbutylpyrazol-1- yl)-1-CH₂NAr1 Ar = 2,6-ⁱPr₂C₆H ₃) can be readily prepared from lithium bis(3,5-di-tertbutylpyrazol- 1-yl)methide and the N-methyleneaniline H₂C=NAr. This N,N,N′-heteroscorpionate lithium reagent can be transmetalated with Tl(OTf), FeCl₂(THF)_1.5, and CoCl₂ to yield the (L)Tl, (L)FeCl, and (L)CoCl complexes, respectively. Single crystal structural data for compounds (L)Li(THF), (L)Tl, (L)FeCl, and (L)CoCl reveal in each case the hapticity of the sterically demanding, monoanionic L^- ligand to be κ³-N₃.

Full text of DOI:10.1021/ic051704i

Inorg. Chem. 2006, 45, 1604−1610
Tl(I), Fe(II), and Co(II) Complexes Supported by a Monoanionic
N,N,N -Heteroscorpionate Ligand
Bis(3,5-di-tertbutylpyrazol-1-yl)-1-CH2NAr (Ar
′
)
2,6-iPr2C6H3)
Debashis Adhikari, Guangyu Zhao, Falguni Basuli, John Tomaszewski, John C. Huffman, and
Daniel J. Mindiola*
Department of Chemistry and Molecular Structure Center, Indiana UniVersity,
Bloomington, Indiana 47405
Received October 3, 2005
The lithium salt (L)Li(THF) (L-
from lithium bis(3,5-di-tertbutylpyrazol-1-yl)methide and the N-methyleneaniline H2C
)
bis(3,5-di-tertbutylpyrazol-1-yl)-1-CH2NAr, Ar
)
2,6-iPr2C6H3) can be readily prepared
NAr. This N,N,N -heteroscor-
d
′
pionate lithium reagent can be transmetalated with Tl(OTf), FeCl2(THF)1.5, and CoCl2 to yield the (L)Tl, (L)FeCl,
and (L)CoCl complexes, respectively. Single crystal structural data for compounds (L)Li(THF), (L)Tl, (L)FeCl, and
(L)CoCl reveal in each case the hapticity of the sterically demanding, monoanionic L- ligand to be
κ
3-N3.
Introduction
1-yl)methane skeleton. These systems can be readily prepared
via replacement of one methylene hydrogen for a carboxylate,
dithiocarboxylate, alkoxide, aryloxide, or 1,1-diphenylmeth-
ylcyclopentadienyl group. Likewise, Parkin and others6 have
also synthesized several heteroscoropionate hybrids with the
Tris(pyrazolyl)borate ligands constitute an invaluable class
of ligands for the stabilization of elements ranging from
early- and late-transition metals, to main group, as well as
the lanthanides and actinides.1 One of several traits which
makes these ligands attractive is their ability to coordinate
in a κ3 mode via the nitrogen lone pairs of the three pyrazolyl
fragments. In addition, these ligands are tripodal yet mo-
nanionic, thus, they allow a greater degree of substitution
chemistry at a sterically protected metal center.
(3) (a) Otero, A.; Ferna´ndez-Baeza, J.; Antin˜olo, A.; Carrillo-Hermosilla,
F.; Tejeda, J.; Lara-Sa´nchez, A.; Sa´nchez-Barba, L.; Ferna´ndez-Lo´pez,
M.; Rodr´ıguez, A. M.; Lo´pez-Solera, I. Inorg. Chem. 2002, 41, 5193-
5202. (b) Otero, A.; Ferna´ndez-Baeza, J.; Antin˜olo, A.; Tejeda, J.;
Lara-Sa´nchez, A.; Sa´nchez-Barba, L.; Ferna´ndez-Lo´pez, M.; Rod-
r´ıguez, A. M.; Lo´pez-Solera, I. Inorg. Chem. 2004, 43, 1350-1358.
(c) Otero, A.; Ferna´ndez-Baeza, J.; Antin˜olo, A.; Tejeda, J.; Lara-
Sa´nchez, A.; Sa´nchez-Barba, L.; Rodr´ıguez, A. M.; Maestro, M. A.
J. Am. Chem. Soc. 2004, 126, 1330-1331. (d) Otero, A.; Ferna´ndez-
Baeza, J.; Antin˜olo, A.; Tejeda, J.; Lara-Sa´nchez, A.; Sa´nchez-Barba,
L.; Mart´ınez-Caballero, E.; Rodr´ıguez, A. M.; Lo´pez-Solera, I. Inorg.
Chem. 2005, 44, 5336-5344. (e) Otero, A.; Ferna´ndez-Baeza, J.;
Antin˜olo, A.; Tejeda, J.; Lara-Sa´nchez, A.; Sa´nchez-Barba, L.;
Ferna´ndez-Lo´pez, M.; Lanfranchi, M.; Pellinghelli, M. A. J. Chem.
Soc., Dalton Trans. 1999, 3537-3539. (f) Otero, A.; Ferna´ndez-Baeza,
J.; Tejeda, J.; Antin˜olo, A.; Carrillo-Hermosilla, F.; Diez-Barra, E.;
Lara-Sa´nchez, A.; Ferna´ndez-Lo´pez, M. J. Chem. Soc., Dalton Trans.
2000, 2367-2374.
(4) (a) Hammes, B. S.; Chohan, B. S.; Hoffman, J. T.; Einwa¨chter, S.;
Carrano, C. J. Inorg. Chem. 2004, 43, 7800-7806. (b) Hammes, B.
S.; Carrano, C. J. Inorg. Chem. 1999, 38, 3562-3568. (c) Hammes,
B. S.; Carrano, C. J. J. Chem. Soc., Dalton Trans. 2000, 3304-3309.
(d) Smith, J. N.; Shirin, Z.; Carrano, C. J. J. Am. Chem. Soc. 2003,
125, 868-869. (e) Hammes, B. S.; Kieber-Emmons, M. T.; Latizia,
J. A.; Shirin, Z.; Carrano, C. J.; Rheingold, A. L. Inorg. Chim. Acta
2003, 346, 227-238.
To this extent, we have drawn our attention to a new class
of tris(pyrazolyl)borate hybrids having instead the putative
tris(3,5-ditertbutylpyrazol-1-yl)methane framework,2 where
one pyrazole pendant arm has been replaced with a hard
monoanionic group, such as a methyleneanilide. Replacing
the borate group avoids 1,2-borotropic rearrangements as well
as bond cleavage reactions inflicted by the B-N linkages.
In addition, these systems also allow one to introduce a hard
donor as well as a monoanionic charge without sacrificing
both the fac mode of coordination and steric protection.
Otero,3 Carrano,4 and Burzlaff5 have reported an attractive
class of heteroscorpionate ligands containing the bis(pyrazol-
* To whom correspondence should be addressed. Email:
mindiola@indiana.edu. Fax: 812 855 8300. Tel: 812 855 2399.
(1) (a) Trofimenko, S. Chem. ReV. 1993, 93, 943-980. (b) Trofimenko,
S. Scorpionates. The Coordination Chemistry of Polypyrazolylborate
Ligands; Imperial College Press: London, 1999. (c) Parkin, G. AdV.
Inorg. Chem. 1995, 42, 291-393.
(5) (a) Beck, A.; Barth, A.; Hubner, E.; Burzlaff, N. Inorg. Chem. 2003,
42, 7182-7188. (b) Beck, A.; Weibert, B.; Burzlaff, N. Eur. J. Inorg.
Chem. 2001, 521-527. (c) Burzlaff, N.; Hegelmann, I.; Weibert, B.
J. Organomet. Chem. 2001, 626, 16-23. (d) Lopez-Hernandez, A.;
Muller, R.; Kopf, H.; Burzlaff, N. Eur. J. Inorg. Chem. 2002, 671-
677. (e) Hegelmann, I.; Beck, A.; Eichhorn, C.; Weibert, B.; Burzlaff,
N. Eur. J. Inorg. Chem. 2003, 339-347.
(2) Reger, D. L. Comments Inorg. Chem. 1999, 21, 1-28.
1604 Inorganic Chemistry, Vol. 45, No. 4, 2006
10.1021/ic051704i CCC: $33.50
© 2006 American Chemical Society
Published on Web 01/13/2006

NoWel Heteroscorpionate Ligand
bis(3,5-R2pyrazol-1yl) methane (R ) tBu or CH3) framework.
Inspired by their work, we report the N,N,N′-heteroscorpi-
onate analogue bis(3,5-di-tertbutylpyrazol-1-yl)-1-CH2NAr,
where Ar ) 2,6-iPr2C6H3. This scorpionate-anilide hybrid
can support Tl(I) as well as divalent Fe(II) and Co(II)
scaffolds via κ3 coordination of the ligand. For the latter two
transition metals, the ligand enforces a tetrahedral geometry,
which is a common trait among the parent tris(pyrazolyl)-
borate system.1
diameter, Bioanalytical Systems), a platinum wire, and silver wire
were employed as the working, auxiliary, and reference electrodes,
respectively. A one-compartment cell was used in the CV measure-
ment. The electrochemical response was collected with the as-
sistance of an E2 Epsilon (BAS) autolab potentiostat/galvanostat
with BAS software. The IR drop correction was applied when
significant resistance was noted. All potentials were reported against
the ferrocenium/ferrocene couple (0 V) measured as an internal
standard, and the spectra were recorded under an N2 atmosphere.
In a typical CV experiment, 15-20 mg of crystalline 3 or 4 were
dissolved in ∼5 mL of a TBAH solution in THF at 26 °C. X-ray
diffraction data were collected on a SMART6000 (Bruker) system
under a stream of N2(g) at low temperatures.
Synthesis of 1. In a 500 mL round-bottom flask bis(3,5-di-tert-
butylpyrazole-1-yl)-methane (3.5 g, 9.4 mmol) was dissolved in
THF (200 mL), and the solution cooled to -78 °C. An analogously
cold nBuLi solution (1.6 M solution, 6.17 mL, 9.87 mmol) was
added to the cold solution via cannula. The solution was stirred
for 1.5 h at this temperature and then allowed to warm to -51 °C.
N-methyleneaniline H2CdNAr [1.78 gm, 9.4 mmol] was added by
cannula transfer, and the mixture was allowed to stir for 30 min at
-51 °C. The reaction mixture was then warmed slowly to room
temperature (using an ice bath) and stirred for an additional hour.
The volatiles were evaporated completely to yield a solid which
was washed with cold hexane to give pure product (L)Li(THF) (1)
(L- ) bis(3,5-di-tertbutylpyrazol-1-yl)-1-CH2NAr, Ar ) 2,6-
iPr2C6H3) (4.61 gm, 7.2 mmol, 76.6% yield). 1H NMR (24 °C, 300.1
MHz, C6D6): δ 7.22 (d, Ar, 2H), 7.05 (t, CHCH2NAr, 1H), 6.92
(t, Ar, 1H), 5.88 (s, Ar, 2H), 4.32 (d, CHCH2NAr, 2H), 3.48 (septet
overlapped with THF resonance, CHMe2, 6H), 1.30-1.17 (br,
CHMe2, CMe3 and THF resonance, 34H), 1.09 (s, CMe3, 18H).
13C NMR (23 °C, 75.46 MHz, C6D6): δ 160.5, 160.0, 152.7, 142.9,
123.4, 115.5, 101.5, 74.9 (CHCH2NAr, JC-H ) 142 Hz), 69.0
(THF), 63.4 (CHCH2NAr, JC-H ) 129 Hz), 32.7 (CMe3), 32.3
(CMe3), 31.84 (CMe3), 30.9 (CMe3), 28.3 (CHMe2), 25.6 (THF),
25.2 (CHMe2). Anal. Calcd for C40H66N5LiO: C, 75.08; H, 10.40;
N, 10.94. Found: C, 74.74; H, 10.46; N, 11.25.
Experimental Section
General Considerations. Unless otherwise stated, all operations
were performed in a M. Braun Lab Master double-drybox under
an atmosphere of purified nitrogen or using high-vacuum standard
Schlenk techniques under an argon atmosphere.7 Anhydrous n-
hexane, pentane, toluene, and benzene were purchased from Aldrich
in sure-sealed reservoirs (18 L) and were further dried by passage
through one column of activated alumina and one of Q-5.8 Diethyl
ether and CH2Cl2 were dried by passage through two columns of
activated alumina.8 THF was distilled, under nitrogen, from purple
sodium benzophenone ketyl and stored over sodium metal. Distilled
THF was transferred under vacuum into bombs before being
transferred into a drybox. C6D6 was purchased from Cambridge
Isotope Laboratory (CIL), degassed, and dried over 4 Å molecular
sieves and CaH2, respectively. Celite, alumina, and 4 Å molecular
sieves were activated under vacuum overnight at 200 °C. Di-
tertbutylpyrazole,9 bis(3,5-di-tertbutylpyrazol-1-yl)methane,5b lithium
bis(3,5-di-tertbutylpyrazol-1-yl)methide (generated and used in
situ),5b methyleneaniline H2CdNAr (Ar ) 2,6-iPr2C6H3),10 and
FeCl2(THF)1.5 11 were prepared according to the literature. All other
chemicals were used as received. Infrared spectra (KBr plates,
Nujol) were measured using a Nicolet 510P FTIR spectrometer.
CHN analysis was performed by Desert Analytics, Tucson, AZ.
1H and 13C spectra were recorded on Varian 400 or 300 MHz NMR
spectrometers. 1H and 13C NMR spectra are reported with reference
to solvent resonances (residual C6D5H in C6D6, 7.16 and 128.0
ppm). 205Tl NMR spectral data were collected on a Varian Inova
500 instrument. Chemical shifts were externally referenced to 0.1
M aqueous Tl(NO3) at 0.0 ppm.12 Cyclic voltammetry was
performed in predried solutions of THF (0.3-0.5 M of predried
and recrystallized TBAH, Aldrich). A platinum disk (2.0 mm
Synthesis of the Free Base HL. In a Schlenk flask the lithium
salt 1 (2.0 g, 3.1 mmol) was dissolved in THF, and degassed water
(56.26 mg, 3.1 mmol) was added dropwise. The mixture was stirred
for 1 h, and the THF was evaporated under reduced pressure to
1
afford HL as a white solid (1.68 g, 2.98 mmol, 96% yield). H
NMR (24 °C, 300.1 MHz, C6D6): δ 7.52 (t, CHCH2NHAr,1H),
7.16 (m, Ar, 3H), 6.09 (s, Ar, 2H), 4.22 (br, CHCH2NHAr, 1H),
4.12 (dd, CHCH2NHAr, 2H), 3.46 (septet, CHMe2, 2H), 1.45 (s,
CMe3, 18 H), 1.34 (d, CHMe2, 12H), 1.17(s, CMe3, 18H). 13C NMR
(24 °C, 75.46 MHz, C6D6): δ 159.9, 154.7, 143.5, 142.9, 124.7,
124.5, 103.7, 78.89 (CHCH2NHAr), 55.14 (CHCH2NHAr), 33.03
(CMe3) 32.89 (CMe3), 31.29 (CMe3), 30.86 (CMe3), 28.52 (CHMe2),
25.12 (CHMe2). MS-CI, [M + H]+: calcd 562.89, found 562.48.
Deprotonation of HL to Afford 1. HL was dissolved (300 mg,
0.53 mmol) in toluene (∼10 mL) and cooled to -35 °C. nBuLi
(1.6 M solution, 0.33 mL, 0.53 mmol) was diluted in hexane (∼5
mL) and added dropwise to the H(L) solution after it was cooled
to -35 °C. The mixture was stirred for 1 h, and the white precipitate
was collected by drying the solution in vacuo. That white residue
was washed with cold hexane to yield LLi (most likely [LLi]x) (314
mg, 0.49 mmol, 92% yield). Exposure of the white solid to THF
and evaporation of the solvent lead to clean formation of 1 as shown
(6) For some other examples of complexes bearing tripodal ligands with
the bis(3,5-R2pyrazol-1-yl)methane framework, see: (a) Dowling, C.;
Parkin, G. Polyhedron 1996, 15, 2463-2465. (b) Tang, L.-F.; Zhao,
S.-B.; Jia, W.-L.; Yang, Z.; Song, D.-T.; Wang, J.-T. Organometallics
2003, 22, 3290-3298. (c) Ortiz, M.; D´ıaz, A.; Cao, R.; Otero, A.;
Ferna´ndez-Baeza, J. Inorg. Chim. Acta 2004, 357, 19-24. (d) Porchia,
M.; Papini, G.; Santini, C.; Lobbia, G. G.; Pellei, M.; Tisato, F.;
Bandoli, G.; Dolmella, A. Inorg. Chem. 2005, 44, 4045-4054.
(7) For a general description of the equipment and techniques used in
carrying out this chemistry, see: Burger, B. J.; Bercaw, J. E. In
Experimental Organometallic Chemistry; Wayda, A. L., Darensbourg,
M. Y., Eds.; ACS Symposium Series 357; American Chemical
Society: Washington D. C., 1987; pp 79-98.
(8) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518-1520.
(9) (a) Kitajima, N.; Fujisawa, K.; Fujimoto, C.; Moro-oka, Y.; Hashimoto,
S.; Kitagawa, T.; Toriumi, K.; Tatsumi, K.; Nakamura, A. J. Am.
Chem. Soc. 1992, 114, 1277-1291. (b) Ferna´ndez-Castan˜o, C.; Foces-
Foces, C.; Jageronic, N.; Elguero, J. J. Mol. Struct. 1995, 355, 265-
271.
(10) Verardo, G.; Cauci, S.; Giumanini, A. G. J. Chem. Soc., Chem.
Commun. 1985, 1787-1788.
1
by H NMR in C6D6 (vide supra).
(11) Kern, R. J. J. Inorg. Nucl. Chem. 1962, 24, 1105-1109.
(12) Spectra were recorded using 16 scans with 45° pulse width over a
spectral window of 1728 ppm. The acquisition time was 0.524 s, and
the relaxation delay was 5 s.
Synthesis of 2. Complex 1 (181 mg, 0.283 mmol) was dissolved
in THF (∼5 mL) and cooled to -35 °C in a vial. In an another
vial Tl(OTF) (100 mg, 0.283 mmol) in THF (∼5 mL) was cooled
Inorganic Chemistry, Vol. 45, No. 4, 2006 1605

Adhikari et al.
to -35 °C. Complex 1 was added dropwise to the Tl(OTF) solution
and stirred for 1 h. THF was removed in vacuo, and the residue
was extracted with benzene. The solution was filtered, and the
filtrate was dried in vacuo and extracted in diethyl ether. The Et2O
solution was concentrated and cooled to -35 °C to yield colorless
crystals of (L)Tl (2) (172 mg, 0.225 mmol, 79.4% yield). The
solution and the white crystals of 2 begin to rapidly decompose to
a dark precipitate. Workup of the reaction mixture must be rapid,
and the solids must be stored cold and in the absence of light to
actual data collection after integration (SAINT).14 The structure was
solved using SHELXS-97 and refined with SHELXL-97.15 A direct-
methods solution was calculated which provided most non-hydrogen
atoms from the E-map. Full-matrix least squares/difference Fourier
cycles were performed which located the remaining non-hydrogen
atoms. All non-hydrogen atoms were refined with anisotropic
displacement parameters, and all hydrogen atoms were refined with
isotropic displacement parameters (unless otherwise specified).
Complex 1. Transparent colorless crystals of various morphol-
ogies were grown at -35 °C from a saturated THF solution.
Intensity statistics and systematic absences suggested the cen-
trosymmetric space group P1h, and subsequent solution and refine-
ment confirmed this choice. All hydrogen atoms were located in
subsequent Fourier maps and included as isotropic contributors in
the final cycles of refinement.
Complex 2. Colorless elongated prisms were grown at -35 °C
from a saturated toluene solution. Intensity statistics and systematic
absences suggested the centrosymmetric space group C2/c, and
subsequent solution and refinement confirmed this choice. An
analytical absorption correction was applied (SADABS).16 All
hydrogen atoms were located in subsequent Fourier maps and
included as isotropic contributors in the final cycles of refinement.
Complex 3. Pale yellow single needles were grown at -35 °C
from a saturated CH2Cl2 solution layered with pentane. Intensity
statistics and systematic absences suggested the centrosymmetric
space group P21/n, and subsequent solution and refinement
confirmed this choice.
1
prevent decomposition. H NMR (24 °C, 300.1 MHz, C6D6): δ
7.38 (d, Ar, 2H), 7.12 (t, Ar, 1H), 6.96 (br, CHCH2NAr, 1H), 6.08
(s, Ar, 2H), 5.70 (br, CHCH2NAr, 2H), 3.78 (septet, CHMe2, 2H),
1.41-1.38 (br, CHMe2 and CMe3, 30H), 1.14 (s, CMe3, 18H). 13
C
NMR (24 °C, 75.46 MHz, C6D6): δ 160.6, 153.2, 146.6, 127.8,
123.5, 121.1, 102.7, 78.0 (CHCH2NAr), 61.6 (CHCH2NAr), 32.6
(CMe3), 32.3 (CMe3), 31.1 (CMe3), 27.1 (CHMe2), 25.2 (CHMe2).
One carbon resonance was not located. 205Tl NMR (24 °C, 289.35,
C6D6): 3300 (∆ν1/2 ) 4492 Hz). MS-CI, [M + H]+: calcd 766.39,
found 766.39. Multiple attempts to obtain satisfactory elemental
analysis failed given the sensitivity of the complex.
Synthesis of 3. Complex 1 (272 mg, 0.426 mmol) was dissolved
in toluene (∼5 mL), and FeCl2(THF)1.5 (100 mg, 0.426 mmol) in
toluene (∼5 mL) was added dropwise after both solutions were
cooled to -35 °C. The reaction mixture was stirred for 12 h, and
the yellow solution was filtered. The filtrate was evaporated in
vacuo. The residue was extracted with toluene and filtered. The
solution was slowly concentrated, and yellow crystals of (L)FeCl
(3) were obtained by cooling the solution to -35 °C (186 mg, 0.302
mmol, 70.8% yield). 1H NMR (24 °C, 300.1 MHz, C6D6): δ 14.1
Complex 4. Dark wedge-shaped crystals were grown at -35
°C from a saturated toluene solution. Intensity statistics and
systematic absences suggested the centrosymmetric space group
P21/c, and subsequent solution and refinement confirmed this
choice. All hydrogen atoms were located in subsequent Fourier
maps and included as isotropic contributors in the final cycles of
refinement.
(∆ν1/2 ) 119 Hz), 12.3 (∆ν1/2 ) 36 Hz), 11.16 (br), 6.99 (∆ν1/2
)
61 Hz), 6.42 (∆ν1/2 ) 69 Hz), 2.37 (∆ν1/2 ) 273 Hz), -21.9 (br),
-22.2 (∆ν1/2 ) 35 Hz), -29.1 (∆ν1/2 ) 32 Hz). IR (KBr plates,
Nujol): 1542 (s), 1477 (m), 1432 (s), 1361 (s), 1315 (s), 1253 (s),
1227 (m), 1204 (m), 1121 (m), 908 (m) cm-1. µeff: 4.92 µΒ (C6D6,
25 °C, Evan’s method). Anal. Calcd for C36H58N5FeCl: C, 66.30;
H, 8.96; N, 10.74. Found: C, 66.18; H, 8.78; H, 10.61.
Results and Discussion
Treatment of lithium bis(3,5-di-tertbutylpyrazol-1-yl)-
methide,5b prepared in situ from nBuLi and bis(3,5-di-
tertbutylpyrazol-1-yl)methane5b at -78 °C, with the N-me-
thyleneaniline H2CdNAr (Ar ) 2,6-iPr2C6H3),10 elicited a
rapid color change from colorless to yellow. Workup of the
reaction mixture gives (L)Li(THF) (1) (L- ) bis(3,5-di-
tertbutylpyrazol-1-yl)-1-CH2NAr) as an off-white crystalline
Synthesis of 4. Complex 1 (300 mg, 0.469 mmol) was dissolved
in THF (∼10 mL) and added dropwise to a cold (-35 °C)
suspension of CoCl2 (60.6 mg, 0.468 mmol) in THF (∼5 mL). After
the mixture was stirred for 12 h, THF was evaporated in vacuo,
and the dark green residue was extracted with toluene. The toluene
solution was then filtered, and the filtrate was concentrated and
cooled to give green crystals of (L)CoCl (4) (194 mg, 0.313 mmol,
1
material in a 77% yield (Scheme 1). H and 13C NMR
1
66.7% yield). H NMR (24 °C, 300.1 MHz, C6D6): δ 72.6 (∆ν1/2
) 58 Hz), 58.6 (∆ν1/2 ) 22 Hz), 13.1 (∆ν1/2 ) 53 Hz), -4.69
(∆ν1/2 ) 11 Hz), -19.8 (∆ν1/2 ) 15 Hz). IR (KBr plates, Nujol):
3071(m), 3040(m), 1959(m), 1814(m), 1526(m), 1474 (s), 1030
(s) cm-1. µeff: 3.83 µΒ (C6D6, 25 °C, Evan’s method). Anal. Calcd
for C36H58N5CoCl: C, 66.03; H, 8.93; N, 10.70. Found: C, 65.69;
H, 8.84; N, 10.58.
solution spectra of 1 are consistent with this complex
retaining Cs symmetry in solution, which is manifested by
only two inequivalent tertbutyl groups as well as only one
isopropyl methine environment. The methylene protons
connecting the bis(3,5-di-tertbutylpyrazol-1-yl)methane unit
to the anilide are broad suggesting that a dynamic process
is occurring in this system. Unfortunately, variable-temper-
X-ray Crystallography. Inert atmosphere techniques were used
to place the crystal onto the tip of a glass capillary (0.06-0.20
mm diameter) mounted on a SMART6000 (Bruker) at 121-126-
(2) K. A preliminary set of cell constants was calculated from
reflections obtained from three nearly orthogonal sets of 20-30
frames. The data collection was carried out using graphite-
monochromated Mo KR radiation with a frame time of 5-30 s ad
a detector distance of 5.0 cm. A randomly oriented region of a
sphere in reciprocal space was surveyed. Three sections of 606
frames were collected with 0.30° steps in ω at different φ settings
with the detector set at -43° in 2θ. Final cell constants were
calculated from the xyz centroids of strong reflections from the
1
ature H NMR studies (-50 °C) of 1 did not resolve the
resonance.
To ascertain the coordination mode of the novel L-
surrogate, we obtained single-crystal X-ray diffraction data
(13) (a) Sur, S. K. J. Magn. Reson. 1989, 82, 169-173. (b) Evans, D. F.
J. Chem. Soc. 1959, 2003-2005.
(14) SAINT, version 6.1; Bruker Analytical X-ray Systems: Madison, WI.
(15) SHELXTL-Plus, version 5.10; Bruker Analytical X-ray Systems:
Madison, WI.
(16) An empirical correction for absorption anisotropy. Blessing, R. Acta
Crystallogr. 1995, A51, 33-38.
1606 Inorganic Chemistry, Vol. 45, No. 4, 2006

NoWel Heteroscorpionate Ligand
Figure 1. Molecular structures of complexes 1-4 depicting thermal ellipsoids at the 50% probability level. Hydrogen atoms and solvent molecules have
been excluded for the purpose of clarity. Crystallographic data for each structure is displayed in Table 1, and selected metrical parameters are shown in
Table 2.
Scheme 1. Synthesis of Compound 1 and the Free Base HL
served. The reaction mixture must be filtered rapidly to avoid
the gradual decomposition of the thallium complex. Hence,
extraction of the product with C6H6, followed by filtration
and cooling, gives the Tl(I) complex (L)Tl (2) as a pale
yellow solid in a 72% isolated yield (Scheme 2). Solids must
be stored cold and in the absence of light to avoid the
1
formation of thallium metal. The H NMR spectrum of 2
corroborates well with the lithium derivative 1, but the
methylene hydrogens are much broader suggesting a slower
dynamic process occurring on the NMR time scale. Most
notably, the 205Tl NMR spectrum of 2 reveals a broad
resonance at 3355 ppm (∆ν1/2 ≈ 4493 Hz) and unambigu-
ously confirms formation of a thallium(I) complex bearing
this ligand.19
Thallium(I) is a soft metal, and as a result, Tl-amide
linkages are exceedingly reactive and often decompose
thermally or photolytically to give Tl metal.20 Despite bearing
a hard amide donor group, complex 2 is remarkably stable
allowing for spectroscopic and structural elucidation. Ac-
cordingly, the single-crystal structure analysis of 2 depicts
a highly distorted κ3 tripodal ligand where the anilide N-Tl
distance (2.274(4) Å) deviates significantly from that of the
two pyrazolyl N-Tl bonds (2.670(5) and 2.702(4) Å, Figure
1). To accommodate the large Tl(I) ion, the two nitrogen
atoms from the pyrazolyl arms (N2 and N12) are skewed in
a propellerlike fashion, while the Tl(I) atom is displaced
∼1.80 Å above the imaginary N3 plane thus conforming the
complex to a pseudo-trigonal pyramid geometry. Complex2
represents a structurally characterized heteroscorpionate
analogue of Tl(I) tris(pyrazolyl)borate systems.21 Crystal-
lographic data for the structure of 2 are displayed in Table
1, and selected metrical parameters are shown in Table 2.
Ar represents the 2,6-iPr2C6H3 aryl group.
of 1. As shown in Figure 1, the geometry at lithium is
tetrahedral, where one THF molecule occupies the apical site
and the L- displays a κ3 coordination mode. The anilido
distance is significantly shorter (1.929(3) Å) than the two
nitrogen donors from two pyrazolyl arms (2.109(3) and
2.270(3) Å). Crystallographic data for 1 are displayed in
Table 1, and selected metrical parameters are shown in Table
2.17 Over extended periods of time complex 1 decomposes
slowly to the free aniline H(L). As a result, solids of 1 are
best stored in the protonated form. To generate H(L) cleanly,
THF solutions of 1 are treated with H2O to afford the free
ligand as a white solid which can be stored indefinitely.
Anhydrous THF solutions of H(L) react smoothly with nBuLi
at -35 °C to produce the salt 1 (Scheme 1), which can be
utilized for subsequent transmetalation reactions.
(19) For 205Tl NMR of a mononuclear 3-coordinate Tl(I) species, see:
Shapiro, I. R.; Jenkins, D. M.; Thomas, J. C.; Day, M. W.; Peters, J.
C. Chem. Commun. 2001, 2152-2153.
To probe the coordination ability of 1, we carried out
transmetalation reactions of this ligand with Tl(I), Fe(II),
and Co(II) precursors. Accordingly, when a cold THF
solution of 1 is added dropwise to a cold THF solution
containing Tl(OTf),18 an orange color is immediately ob-
(20) (a) Wright, R. J.; Brynda, M.; Power, P. P. Inorg. Chem. 2005, 44,
3368-3370. Unlike complex 2, trispyrazolylborate complexes of Ti-
(I) are remarkably stable, an attribute likely originated by these ligands
being weaker π donors than the bis(3,5-di-tertbutylpyrazol-1-yl)-1-
CH2NAr reported in this paper. (b) Janiak, C. Coord. Chem. ReV. 1997,
163, 107-216.
(17) A monoanionic complex of lithium has been prepared with the tris-
(pyrazol-1yl)methane ligand. Reger, D. L.; Collins, J. E.; Mathews,
M. A.; Rheingold, A. L.; Liable-Sands, L. M.; Guzei, I. A. Inorg.
Chem. 1997, 36, 6266-6269.
(18) Bruno, J. W.; Marks, T. J.; Lewis, F. D. J. Am. Chem. Soc. 1982,
104, 5580-5585.
(21) For some structurally characterized Tl(I) monomers bearing 3-tBu-
substituted tris(pyrazolyl)borate ligands, see: (a) Ghosh, P.; Churchill,
D. G.; Rubinshtein, M.; Parkin, G. New J. Chem. 1999, 23, 961-
963. (b) Cowley, A. H.; Geerts, R. L.; Nunn, C. M.; Trofimenko, S.
J. Organomet. Chem. 1989, 365, 19-22. (c) Yoon, K.; Parkin, G.
Polyhedron 1995, 14, 811-821.
Inorganic Chemistry, Vol. 45, No. 4, 2006 1607

Adhikari et al.
Table 1. Crystallographic Data for Complexes 1-4
1
2
3
4
empirical formula
fw
C40H66LiN5O
639.92
C36H58N5Tl
765.24
C36H58ClFeN5
652.17
C36H58ClCoN5
655.25
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
triclinic
P1h
monoclinic
C2/c
24.613(2)
20.2102(16)
17.7282(14)
monoclinic
P2(1)/n
11.507(5)
17.699(10)
19.360(12)
monoclinic
P2(1)/c
15.0257(18)
12.0207(14)
21.061(3)
9.9605(12)
11.5019(14)
18.077(2)
102.866(3)
91.019(4)
98.275(4)
1995.3(4)
2
125.337(2)
106.927(19)
98.543(3)
7194.0(10)
8
1.413
3772(4)
4
1.148
3761.8(8)
4
1.157
Z
D
calcd (g cm-3
)
1.065
cryst size (mm)
solvent habit, color
h, k, l
0.25 × 0.20 × 0.20
X, colorless
-12 e h e 12
-14 e k e 14
-23 e l e 23
704
0.35 × 0.15 × 0.15
X, colorless
-34 e h e 34
-28 e k e 28
-24 e l e 24
3120
0.20 × 0.10 × 0.06
CH2Cl2/Et2O, yellow
-12 e h e 14
-11 e k e 22
-25 e l e 25
1408
0.30 × 0.20 × 0.20
X, dark
-21 e h e 20
-16 e k e 14
-29 e l e 29
1412
F(000)
Θ range
1.94-27.55
2.33-30.05
2.08-27.47
2.22-30.03
linear abs coeff (mm-1
total reflns collected
independent reflns
unique reflns
Rint
)
0.064
4.520
0.500
0.557
25559
9180
4336
0.0947
97311
10531
8925
0.0454
13975
8375
2515
0.1295
34515
10967
6883
0.0669
data/params
R1, R2 (for I > 2σ(I)
GOF
9180/710
0.0460, 0.0765
0.751
10500/611
0.0183, 0.0402
1.020
8375/404
0.0570, 0.0982
0.655
10125/620
0.0362, 0.0687
0.852
peak/hole (e/Å-3
)
0.252/-0.205
2.748/-2.130
0.487/-0.284
0.401/-0.529
Table 2. Selected Interatomic Distances (Å) and Angles (deg)
1
Li42-N3
N3-C2
N16-N17
1.929(3)
1.428(2)
1.367(9)
Li42-N30
C2-C1
N29-N30
2.109(3)
1.541(2)
1.378(8)
Li42-N17
C1-N16
2.270(3)
1.468(2)
Li42-O43
C1-N29
2.038(3)
1.459(2)
O43-Li42-N3
O43-Li42-N17
116.8(6)
133.2(5)
O43-Li42-N30
N3-Li42-N30
122.8(6)
95.0(4)
N3-Li42-N17
94.3(4)
N17-Li42-N30
85.0(2)
2
3
Tl1-N30
N30-C29
N8-N12
2.274(4)
1.438(2)
1.370(9)
Tl1-N12
C29-C7
2.670(5)
1.544(2)
Tl1-N2
C7-N6
2.702(4)
1.476(2)
N6-N2
C7-N8
1.368(8)
1.463(2)
N30-Tl1-N12
78.65(5)
N30-Tl1-N2
76.75(5)
N2-Tl1-N12
64.66(4)
Fe1-Cl2
N30-C29
N16-N28
2.288(8)
1.438(5)
1.380(4)
Fe1-N30
C29-C15
N9-N3
1.925(4)
1.532(5)
1.380(5)
Fe1-N3
C15-N9
2.115(4)
1.453(5)
Fe1-N28
C15-N16
2.203(4)
1.479(5)
Cl2-Fe1-N30
N30-Fe1-N28
124.7(3)
95.7(5)
Cl2-Fe1-N3
N3-Fe1-N28
123.4(2)
81.0(4)
Cl2-Fe1-N28
126.8(1)
N30-Fe1-N3
93.6(6)
4
Co1-Cl2
N5-C4
N31-N35
2.2195(5)
1.441(8)
1.376(6)
Co1-N5
C4-C3
N18-N22
1.887(3)
1.526(2)
1.378(6)
Co1-N22
C3-N18
2.059(3)
1.470(9)
Co1-N35
C3-N31
2.100(3)
1.469(9)
Cl2-Co1-N5
N5-Co1-N35
113.59(4)
94.27(5)
Cl2-Co1-N22
N35-Co1-N22
132.81(4)
82.20(5)
Cl2-Co1-N35
130.31(4)
N5-Co1-N22
92.86(5)
11
When 1 is added to FeCl2(THF)1.5 in a cold toluene
slurry, yellow (L)FeCl (1) is isolated in an ∼71% yield
(Scheme 2) upon workup of the reaction mixture. 1H NMR
spectra display broad resonances ranging from 14 to -29
ppm, consistent with a paramagnetic material. As expected
for a monomeric high-spin Fe(II) system, the solution
magnetic susceptibility measurement of complex 3 is in
agreement with four unpaired electrons (µeff ) 4.92 µΒ).
Cyclic voltammetry of a solution of 3 (THF/TBAH) showed
one reversible oxidation wave and an irreversible reduction
wave at -0.269 V and -3.31 V (Figure 2), respectively
(referenced vs FeCp2/FeCp2 ). The remarkably negative
+
reduction potential in 3 suggests that this species is highly
electron rich and that chemical access of Fe(III) is far more
likely than for Fe(I). Not surprisingly, attempts to chemically
reduce 3 with powerful one-electron reductants such as
22
KC8 have so far been unsuccessful.
The identity of complex 3 has been scrutinized not only
by a combination of physical methods including Evans and
elemental analysis but also by single-crystal X-ray diffraction
1608 Inorganic Chemistry, Vol. 45, No. 4, 2006

NoWel Heteroscorpionate Ligand
Figure 2. Cyclic voltamograms of complexes 3 and 4 in 0.3 M TBAPF6 in THF using a scan rate of 250 mV/s and referenced to the FeCp20/+ couple (0.0
V).
Scheme 2. Synthesis of Compounds 2-4 from 1
oxidation wave and one reduction wave at 0.388 V and
-2.915 V, respectively (Figure 2). Chemically, it was found
that reductants such as Na/Hg or Mg (powder) do not react
with 4 in THF suggesting that this species is far more electron
rich than the tris(pyrazolyl)borate Co(II) derivatives.24 Single-
crystal X-ray diffraction analysis of 4 exposes a mononuclear
Co(II) center, but unlike 3 the geometry at the cobalt ion is
that of a distorted tetrahedron. This is reflected by the
imaginary C(3)-Co-Cl(2) angle, which is slightly deviated
from linearity (168.7°) from that of the ferrous analogue 3
(C(15)-Fe-Cl(2), 177.8°). The distortion observed in the
crystal structure of complex 4 is significant when compared
to the close relative (Tp′)CoCl reported by Parkin and co-
workers (Tp′ ) tris(3-tertbutylpyrazol-1-yl)hydroborate).23b
Close inspection of the Cl-Co-N (120.3(2), 122.2(1), and
122.2(2)) and N-Co-N (95.3(1), 94.8(2), and 95.3(1))
angles in (Tp′)CoCl reveals differences in the metrical
parameters when compared with the structure of 4. Hence
we speculate that such distortion (toward the anilide nitrogen)
originates from the amide component of the ligand in
complex 4. However, the exact reason for the axial distortion
is currently unclear to us. Axial distortion observed in the
crystal structure of 4 does break down the symmetry in the
molecule but does not appear to change the multiplicity of
the system (from triplet to singlet), thus implying that the
splitting of the singly occupied molecular orbitals are not
significant enough to promote electron pairing in 4.25
Ar represents the 2,6-iPr2C6H3 aryl group.
studies (Figure 1). The molecular structure of complex 3 is
depicted in Figure 1, and the gross structural features of the
FeN3 core resemble the tetrahedral homoscorpionate ferrous
i
analogues (Tp)FeCl (Tp ) HB(3,5-R2py; R ) CH3, Pr; py
) pyrazol-1-yl).23 As observed previously with 1 and 2, the
anilido N-metal distance is significantly shorter (1.925(4)
Å) than the pyrazolyl N-metal distances (2.203(4) and
2.115(4) Å). Given the steric encumbrance of the ligand,
we speculate that the aryl group on the amide nitrogen is
oriented parallel to the ligand N3 plane, thus placing the
isopropyl groups away from both the chloride and sterically
imposing tertbutyl groups.
Conclusion
Combining a hard amide donor with the bis(3,5-di-
tertbutylpyrazol-1-yl)methane skeleton has produced a steri-
cally encumbering scorpionate hybrid ligand. This monoan-
ionic bis(3,5-di-tertbutylpyrazol-1-yl)-1-CH2NAr ligand appears
to be an excellent platform for tripodal frameworks of Li+,
CoCl2 can be also transmetalated smoothly with 1 in THF
at -35 °C to produce dark green crystals of (L)CoCl (4) in
a 67% yield. 1H NMR solution spectra reveal several broad
resonances ranging from 73 to -20 ppm, and solution
magnetic measurements are consistent with a tetrahedral
high-spin d7 species (µeff ) 3.83 µΒ). A cyclic voltammogram
of a solution of 4 (THF/TBAH) showed one irreversible
(24) For tetrahedral Co(II) complexes bearing tris(pyrazolyl)borate ligands
(ref 23b), see (a) Trofimenko, S.; Rheingold, A. L.; Liable-Sands, L.
M. Inorg. Chem. 2002, 41, 1889-1896. (b) Rheingold, A. L.; Liable-
Sands, L. M.; Golan, J. A.; Trofimenko, S. Eur. J. Inorg. Chem. 2003,
2767-2773. (c) Rheingold, A. L.; Liable-Sands, L. M.; Golen, J. A.;
Yap, G. P. A.; Trofimenko, S. Dalton Trans. 2004, 598-604. (d)
Olson, M. D.; Rettig, S. J.; Storr, A.; Trotter, J.; Trofimenko, S. Acta
Crystallogr. 1991, C47, 1543-1544. (e) Uehara, K.; Hikichi, S.; Akita,
M. Dalton Trans. 2002, 3529-3538. (f) Reinaud, O. M.; Rheingold,
A. L.; Theopold, K. H. Inorg. Chem. 1994, 33, 2306-2308. (g) Huang,
J.; Lee, L.; Haggerty, B. S.; Rheingold, A. L.; Walters, M. A. Inorg.
Chem. 1995, 34, 4268-4270.
(22) Schwindt, M.; Lejon, T.; Hegedus, L. Organometallics 1990, 9, 2814-
2819.
(23) For tetrahedral Fe(II) complexes bearing tris(pyrazolyl)borate ligands,
see: (a) Brunker, T. J.; Hascall, T.; Cowley, A. R.; O’Hare, D. Inorg.
Chem. 2001, 40, 3170-3176. (b) Gorrell, I. B.; Parkin, G. Inorg.
Chem. 1990, 29, 2452-2456. (c) Ito, M.; Amagai, H.; Fukui, H.;
Kitajima, N.; Moro-oka, Y. Bull. Chem. Soc. Jpn. 1996, 69, 1937-
1945.
(25) Jenkins, D. M.; Di Bilio, A. J.; Allen, M. J.; Betley, T. A.; Peters, J.
C. J. Am. Chem. Soc. 2002, 124, 15336-15350.
Inorganic Chemistry, Vol. 45, No. 4, 2006 1609

Adhikari et al.
Tl+, and transition metals such as Fe2+ and Co2+. Judging
from the electrochemical reduction waves for both (L)FeCl
and (L)CoCl, it is postulated that the “M(II)L” scaffold is
highly electron rich, a factor which we attribute to the
donating ability of the hard anilide pendant arm.
and PECASE award to D.J.M.). The authors wish to thank
the Howard Hughes Medical Institute (HHMI) at Brandeis
University for allowing us to borrow an NMR probe.
Supporting Information Available: Complete experimental,
spectroscopic, analytical, crystallographic details (in CIF files) for
complexes 1-4. This material is available free of charge via the
Internet at http://pubs.acs.org.
Acknowledgment. For financial support of this research,
we thank Indiana University-Bloomington, the Camille and
Henry Dreyfus Foundation, the Alfred P. Sloan Foundation,
and the U.S. National Science Foundation (CHE-0348941
IC051704I
1610 Inorganic Chemistry, Vol. 45, No. 4, 2006