Tantalum complexes of diphenyldipyrrolide dianion: Partial hydrogenation of a phenyl ring

Article abstract of DOI:10.1021/om020406f

The reactivity of the pentavalent dipyrrolide complex {[Ph₂C(C₄H₃N)₂]₂TaCl ₂}{Li(THF)₄}·2THF was investigated. While an isostructral dimethyl derivative was readily prepared by treatment with MeLi, reaction with NaHBEt₃ gave a major reorganization, affording a mixture of [Ph₂C(C₄H₃N)₂]Ta[(1,4-η¹ :η¹-2,3-η²-C₆H₇PhC(C ₄H₃N)₂][Na(OEt₂)] and [Ph₂C-(C₄H₃N)₂]₃Ta[Na(OEt ₂)]₂·(OEt₂). The first complex arises from partial hydrogenation of one of the ligand phenyl rings performed by an intermediate Ta hydride. In the second case, ligand scrambling occurred along with reduction of the metal center.

Full text of DOI:10.1021/om020406f

Organometallics 2002, 21, 4257-4263
4257
Ta n ta lu m Com p lexes of Dip h en yld ip yr r olid e Dia n ion :
P a r tia l Hyd r ogen a tion of a P h en yl Rin g
Ghazar Aharonian, Sandro Gambarotta,* and Glenn P. A. Yap
Department of Chemistry, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada
Received May 22, 2002
The reactivity of the pentavalent dipyrrolide complex {[Ph2C(C4H3N)2]2TaCl2}{Li(THF)4}‚
2THF was investigated. While an isostructral dimethyl derivative was readily prepared by
treatment with MeLi, reaction with NaHBEt3 gave a major reorganization, affording a
mixture of [Ph2C(C4H3N)2]Ta[(1,4-η1:η1-2,3-η2-C6H7PhC(C4H3N)2][Na(OEt2)] and [Ph2C-
(C4H3N)2]3Ta[Na(OEt2)]2‚(OEt2). The first complex arises from partial hydrogenation of one
of the ligand phenyl rings performed by an intermediate Ta hydride. In the second case,
ligand scrambling occurred along with reduction of the metal center.
In tr od u ction
uration enable other features such as cluster formation
and metal-metal interactions.8
Recent work in this group has shown that dipyr-
romethane dianions provide a versatile class of sup-
porting ligands. These species display a remarkable
flexibility in terms of bonding mode (pure σ-donor, pure
π-donor, and σ/ π-donor).1 At least in the case of low-
valent lanthanides, these ligands may stabilize highly
reactive metals yet increase the reactivity of the metal
center2 with respect to the isoelectronic cyclopentadienyl
derivatives. Finally, these dianions often retain alkali
cations in the molecular structure of the complex. The
additional coordination of a Lewis acid to the pyrrolide
ring, via either σ- or π-bonding, directly affects the
metal-ligand interaction, thus allowing for the fine-
tuning of the metal redox potential.3
Given the ability of the dipyrrolide ligand to assemble
large cluster structures,9 we became interested in
studying the ability of this versatile class of ligand to
support low-valent tantalum. Aiming to prepare highly
reactive Ta hydrides supported by this ligand system
that may work as precursors for further reduction, we
have now obtained a curious case of phenyl ring partial
hydrogenation. In this first paper, we describe our
findings.
Resu lts a n d Discu ssion
Diphenyldipyrromethane1a undergoes an easy depro-
tonation by MeLi in ether and at room temperature,
Among low-valent early transition metals, niobium
and tantalum occupy a special place. The few deriva-
tives reported in the literature are able to perform a
wide variety of reactions, including pyridine ring-
opening,4 pyrrole denitrogenation,5 C-N bond cleavage,6
C-H bond oxidative addition,7 etc. In addition, the low
oxidation state and the electron-rich electronic config-
(7) See for example: (a) Steffey, B. D.; Chamberlain, L. R.; Chesnut,
R. W.; Chebi, D. E.; Fanwick, P. E.; Rothwell, I. P. Organometallics
1989, 8, 1419. (b) Chamberlain, L. R.; Kerschner, J .; Rothwell, A. P.;
Rothwell, I. P.; Huffman, J . C. J . Am. Chem. Soc. 1987, 109, 6471. (c)
Chamberlain, L. R.; Rothwell, A. P.; Rothwell, I. P. J . Am. Chem. Soc.
1984, 106, 1847. (d) Chamberlain, L. R.; Keddington, J .; Rothwell, I.
P.; Huffman, J . C. Organometallics 1982, 1, 1538. (e) Chamberlain, L.
R.; Rothwell, I. P.; Huffman, J . C. J . Am. Chem. Soc. 1986, 108, 1502.
(f) Schaller, C. P.; Wolczanski, P. T. Inorg. Chem. 1993, 32, 131. (g)
Chamberlain, L. R.; Rothwell, I. P. J . Am. Chem. Soc. 1983, 105, 1665.
(h) Chamberlain, L. R.; Rothwell, I. P.; Huffman, J . C. J . Am. Chem.
Soc 1982, 104, 7338. (i) Ballard, K. R.; Gardiner, I. M.; Wigley, D. E.
J . Am. Chem. Soc. 1989, 111, 2159. (j) Tayebani, M.; Feghali, K.;
Gambarotta, S.; Yap, G. P. A. Organometallics 1998, 17, 4282.
(8) See for example: (a) Hubert-Pfalzgraf, L. G.; Riess, J . G. Inorg.
Chim. Acta 1978, 29, L251. (b) Hubert-Pfalzgraf, L. G.; Riess, J . G.
Inorg. Chim. Acta 1980, 41, 283. (c) Allen, A. D.; Naito, S. Can. J .
Chem. 1976, 54, 2948. (d) Maas, E. T.; McCarley, R. E. Inorg. Chem.
1973, 12, 1096. (e) Templeton, J . L.; McCarley, R. E. Inorg. Chem. 1978,
17, 2293. (f) Cotton, F. A.; Falvello, L. R.; Najjar, R. C. Inorg. Chem.
1983, 22, 375. (g) Cotton, F. A.; Najjar, R. C. Inorg. Chem. 1981, 20,
2716. (h) Cotton, F. A.; Roth, W. J . Inorg. Chem. 1983, 22, 3654. (i)
Cotton, F. A.; Roth, W. J . Inorg. Chim. Acta 1983, 71, 175. (j)
Sattelberger, A. P.; Wilson, R. B.; Huffman, J . C. Inorg. Chem. 1982,
21, 2392. (k) Sattelberger, A. P.; Wilson, R. B.; Huffman, J . C. J . Am.
Chem. Soc. 1980, 102, 7111. (l) Hey, E.; Weller, F.; Dehnicke, K. Z.
Anogr. Allg. Chem. 1984, 25, 514. (m) Canich, J . A. M.; Cotton, F. A.
Inorg. Chem. 1987, 26, 4236. (n) Canich, J . A. M.; Cotton, F. A. Inorg.
Chem. 1987, 26, 3473. (o) Cotton, F. A.; Duraj, S. A.; Roth, W. J . Acta
Crystallogr., Sect. C 1985, 41, 878. (p) Cotton, F. A.; Matonic, J . H.;
Murillo, C. A. J . Am. Chem. Soc. 1997, 119, 7889. (q) Cotton, F. A.;
Diebold, M. P.; Roth, W. J . J . Am. Chem. Soc. 1987, 109, 5506. (r)
Cotton, F. A.; Shang, M. J . Am. Chem. Soc. 1988, 110, 7719. (s) Cotton,
F. A.; Matonic, J . H.; Murillo, C. A. J . Am. Chem. Soc. 1998, 120, 6047.
(9) Dube´, T.; Gambarotta, S.; Yap, G. P. A.; Conoci, S. Organome-
tallics 2000, 19, 115.
(1) (a) Freckmann, D. M. M.; Dube´, T.; Be´rube´, C. D.; Gambarotta,
S.; Yap, G. P. A. Organometallics, in press. (b) Mani, G.; Lalonde, M.
P.; Gambarotta, S.; Yap, G. P. A. Organometallics 2001, 20, 2443, (c)
Dube´, T.; Conoci, S.; Gambarotta, S.; Yap, G. P. A. Organometallics
2000, 19, 1182. (d) Dube´, T.; Freckmann, D. M. M.; Conoci, S.;
Gambarotta, S.; Yap, G. P. A. Organometallics 2000, 19, 209.
(2) (a) Dube´, T.; Mani, G.; Conoci, S.; Gambarotta, S.; Yap, G. P. A.
Organometallics 2000, 19, 3716. (b) Mani, G.; Gambarotta, S.; Yap,
G. P. A. Angew. Chem., Int. Ed. 2001, 40, 766. (c) Dube´, T.; Conoci, S.;
Gambarotta, S.; Yap, G. P. A.; Vasapollo, G. Angew. Chem., Int. Ed.
1999, 38, 3657.
(3) (a) Dube´, T.; Gambarotta, S.; Yap, G. P. A. Angew. Chem., Int.
Ed. 1999, 38, 1432. (b) Mani, G.; Be´rube´, C. D.; Gambarotta, S.; Yap,
G. P. A. Organometallics, in press.
(4) (a) Kleckley, T. S.; Bennett, J . L.; Wolczanski, P. T.; Lobkovsky,
E. B. J . Am. Chem. Soc. 1997, 119, 247. (b) Gray, S. D.; Weller, K. J .;
Bruck, M. A.; Briggs, P. M.; Wigley, D. E. J . Am. Chem. Soc. 1995,
117, 10678.
(5) Tayebani, M.; Gambarotta, S.; Yap, G. P. A. Angew. Chem., Int.
Ed. 1998, 37, 3002.
(6) See for example: (a) Bonanno, J . B.; Henry, T. P.; Neithamer,
D. R.; Wolczanski, P. T.; Lobkovsky, E. B. J . Am. Chem. Soc. 1996,
118, 5132. (b) Tayebani, M.; Kasani, A.; Feghali, K.; Gambarotta, S.;
Yap, G. P. A. J . Chem. Soc., Chem. Commun. 1997, 20, 2001. (c)
Tayebani, M.; Feghali, K.; Gambarotta, S.; Bensimon, C.; Yap, G. P.
A. Organometallics 1997, 16, 5084. (d) Tayebani, M.; Gambarotta, S.;
Yap, G. P. A. Organometallics 1998, 17, 3639.
10.1021/om020406f CCC: $22.00 © 2002 American Chemical Society
Publication on Web 08/24/2002

4258 Organometallics, Vol. 21, No. 20, 2002
Aharonian et al.
F igu r e 2. Thermal ellipsoid plot of 2. Thermal ellipsoids
are drawn at 30% probability.
of bent-metallocene type of geometry and is also σ-bond-
ed to two N atoms of the other two pyrrolyl rings from
two different ligands [Li(1)-N(2) ) 2.028(12) Å, Li(1)-
N(3) ) 2.033(12) Å]. The simplicity of the NMR spectra
of 1, showing only one type of pyrrolyl and phenyl rings,
indicates that a rapid exchange between the nonequiva-
lent lithium atoms occurs in solution.
The room-temperature reaction of 1 with 1 equiv of
TaCl5 in ether gave a green-brown solution, from which
red-brown microcrystals of the diamagnetic {[Ph2C-
(C4H3N)2]2TaCl2}{Li(THF)4}‚2THF (2) were isolated
(Scheme 1). In agreement with the solid state structure
(Figure 2), the NMR spectra showed two different
phenyl rings and four nonequivalent pyrrolide rings.
Crystals suitable for X-ray diffraction were grown from
THF/hexane. The coordination sphere of the tantalum
center is distorted octahedral (Figure 2) with two
chloride ligands [Ta-Cl(1) ) 2.3741(12) Å, Ta-Cl(2) )
2.3746(13) Å] situated cis to one another [Cl(1)-Ta-
Cl(2) ) 87.83(5)°] and the N atoms of two diphenyl-
dipyrrolide ligands occupying the remaining four coor-
F igu r e 1. Thermal ellipsoid plot of 1. Thermal ellipsoids
are drawn at 30% probability.
affording the corresponding tetranuclear [Ph2C(C4H3N)2]2-
Li4(OEt2)3 (1). This derivative was readily isolated from
an ether solution and fully characterized including by
X-ray analysis (Figure 1). The structure is somewhat
unusual, showing that two lithium atoms, each π-bond-
ed to two pyrrolyl rings from two different ligands [Li-
(1)-N(1) ) 2.034(11) Å, Li(1)-C(1) ) 2.777(12) Å,
Li(1)-C(4) ) 2.665(12) Å, Li(1)-N(4) ) 2.050(12) Å, Li-
(1)-C(30) ) 2.777(12) Å, Li(1)-C(29) ) 2.772(13) Å],
hold together the dinuclear frame. Each of the other two
lithium cations are instead σ-bonded to the two N atoms
of each ligand [Li(3)-N(1) ) 1.970(12) Å, Li(3)-N(2) )
2.051(12) Å, Li(4)-N(3) ) 2.041(12) Å, Li(4)-N(4) )
1.956(12) Å]. One molecule of ether completes the
coordination sphere of the two σ-bonded lithium atoms
as well as that of one of the two π-bonded lithium
cations. The second π-bonded lithium cation has a sort
Sch em e 1

Ta Complexes of Diphenyldipyrrolide Dianion
Organometallics, Vol. 21, No. 20, 2002 4259
F igu r e 3. Thermal ellipsoid plot of 3. Thermal ellipsoids
are drawn at 30% probability.
F igu r e 4. Thermal ellipsoid plot of 4. Thermal ellipsoids
are drawn at 30% probability.
dination sites [N(1)-Ta-Cl(1) ) 89.66(10)°, N(1)-Ta-
N(2) ) 83.94(14)°, N(3)-Ta-N(4) ) 84.43(14)°, Cl(2)-
Ta-N(4) ) 173.83(10)°]. The dipyrrolide ligands are
σ-bound to the metal through the pyrrole nitrogen with
no π-donation from the ring. The Ta-N bond lengths
[Ta-N(1) ) 2.094(4) Å, Ta-N(2) ) 2.082(3) Å, Ta-N(3)
) 2.086(3) Å, Ta-N(4) ) 2.078(4) Å] are indicative of
tantalum-nitrogen single bonds. A lithium cation sol-
vated by four molecules of THF and unconnected with
the anionic portion completes the structure.
Treatment of 2 with MeLi in THF afforded the
expected dimethyl product {[Ph2C2(C4H3N)2]2TaMe2}-
{Li(THF)4} (3) as yellow crystals. An X-ray diffraction
analysis of crystals grown from THF/hexane revealed
that the tantalum metal center has a trigonal prismatic
geometry (Figure 3). The methyl ligands are cis to each
other but form with the metal center an angle [C(43)-
Ta-C(44) ) 130.35(13)°] that is substantially larger
than that formed by the chlorine atoms in the corre-
sponding chloride derivative 2 [Cl(1)-Ta-Cl(2) ) 87.83-
(5)°]. This is possibly the result of the fact that the Me
ligand is a pure σ-donor while the Cl ligand acts
additionally as a π-donor. In addition, the Ta-Me bond
lengths [Ta-C(43) ) 2.179(3) Å, Ta-C(44) ) 2.175(3)
Å], which are in the normal range of Ta-alkyl bond
distances, are substantially shorter than the Ta-Cl
distances of 2. This may cause a significant increase in
the steric congestion around the Ta center with conse-
quent further distortion of the octahedral geometry.
Similar to complex 2, the Ta-N bond lengths [Ta-N(1)
) 2.156(3) Å, Ta-N(2) ) 2.085(2) Å, Ta-N(3) ) 2.098-
(3) Å, Ta-N(4) ) 2.130(2) Å] are essentially single bond
in character.
Compound 3 is thermally robust and chemically inert
toward several reagents including H2. The alkyl signals
were readily located in both the 1H and 13C NMR spectra
at 1.36 and 95.4 ppm, respectively. In sharp contrast
with the NMR spectrum of the nearly isostructural 2,
the NMR spectrum was remarkably simpler, showing
only one kind of phenyl and pyrrolide ring. We speculate
that the fact the structure of 3 deviates substantially
from the octahedral geometry toward a trigonal pris-
matic coordination is possibly enhancing pseudorotation
with consequent symmetrization of the NMR spectra.
Attempts to use 2 as a starting material for the
preparation of highly reactive lower valent compounds
were carried out with hydrides. The reaction with
NaHBEt3 in toluene yielded two products that have
been successfully isolated and characterized by X-ray
crystallography. The two complexes, separated by frac-
tional crystallization from ether as red and yellow
crystalline solids, respectively, are [Ph2C(C4H3N)2][(1,4-
η1:η1-2,3-η2-C6H5)PhC(C4H3N)2]Ta[Na(OEt2)] (4) and
[Ph2C(C4H3N)2]3Ta[Na(OEt2)]2‚(OEt2) (5).
Complex 4 is diamagnetic. Its crystal structure (Fig-
ure 4) reveals that the tantalum center is bound by two
dipyrrolide ligands and one Na cation. The metal is
further both σ- and π-bonded to one of the former phenyl
rings from one dipyrrolide moiety that has been partly
hydrogenated. As a result of the bonding interaction
with the metal center and of the partial hydrogenation,
the ring is severely distorted, adopting a “boat” type of
conformation. The corresponding Ta-C bond distances
for 4 are comparable to those observed in the structure
of an arene/Ta derivative10 and of a η4-cyclohexadiene
Nb complex previously reported in the literature.11 The
structure shows that bonding of the ring is better
described in terms of both σ-bonding [Ta-C(12) ) 2.222-
(8) Å, Ta-C(15) ) 2.247(7) Å] and π-bonding [Ta-C(13)
) 2.424(9) Å, Ta-C(14) ) 2.506(9) Å] to the metal
rather than slipped η4-hexadienyl. The other two CH2
groups completing the ring form long nonbonding
contacts [Ta-C(11) ) 3.084(8) Å, Ta-C(10) ) 3.129(8)
Å]. The C-C bond distances within the ring are com-
parable [C(11)-C(10) ) 1.492(11) Å, C(12)-C(13) )
1.466(12) Å, C(12)-C(11) ) 1.453(11) Å, C(15)-C(10)
) 1.509(11) Å] with the exception of one [C(13)-C(14)
) 1.435(12) Å] indicating a small yet significant local-
ization of residual C-C double-bond character. Unfor-
tunately, the hydrogen atoms could not be located. One
atom of sodium is π-bonded to two pyrrolide rings from
the same ligand [Na-N(1) ) 2.924(6) Å, Na-C(1) )
2.984(8) Å, Na-C(2) ) 2.984(8) Å, Na-C(3) ) 2.914(7)
Å, Na-C(4) ) 2.886(7) Å, Na-N(2) ) 2.802(6) Å, Na-
C(5) ) 2.907(7) Å, Na-C(6) ) 3.045(8) Å] that has one
phenyl ring bonded to tantalum. Interestingly, there is
a loose π-coordination of Na to one Ph ring [Na-C(33)
) 2.995(8) Å, Na-C(32) ) 3.260(8) Å, Na-C(34) )
3.189(8) Å] of the second dipyrrolide ligand, probably
an artifact of ligand geometry optimization. One mol-
ecule of ether completes the coordination geometry of
Na.
(10) Bruck, M. A.; Copenhaver, A. S.; Wigley, D. E. J . Am. Chem.
Soc. 1987, 109, 6525.
(11) (a) Steffey, B. D.; Chesnut, R. W.; Kerschner, J . L.; Pellechia,
P. J .; Fanwick, P. E.; Rothwell, I. P. J . Am. Chem. Soc 1989, 111, 378.
(b) Steffey, B. D.; Rothwell, I. P. J . Chem. Soc., Chem. Commun. 1990,
213.

4260 Organometallics, Vol. 21, No. 20, 2002
Aharonian et al.
are detected as transient intermediates.12,14 Since the
formation of 4 was obtained in the absence of H2, its
formation is most likely the result of the intramolecular
attack of the Ta-H groups of an intermediate [H2Ta-
{Ph2C(C4H3N)2}2] anion at two contiguous ortho and
meta positions of a ligand phenyl ring. The reaction is
conceptually different, from the partial hydrogenation
of an aromatic ring performed by a transient (RO)3Nb
under H2 atmosphere, where the reaction is triggered
by oxidative addition of the metal into the C-H bond
followed by hydrogenolysis.11 Similar to the Nb case
however, the two hydrogen atoms have been placed cis
to each other. However, the hydrogenation in this
particular case did not involve the ipso C atom but
instead has directed the H atoms to the aromatic ring
ortho and meta positions. Since the reaction occurred
rapidly at room temperature, we believe that the
hydrogenation of the ligand is an indication for a very
high reactivity of Ta-H species supported by the dipyr-
rolide ligand system.
F igu r e 5. Thermal ellipsoid plot of 5. Thermal ellipsoids
are drawn at 30% probability.
The formation of 5 is more difficult to rationalize, but
the presence of three dipyrrrolide ligands around the
metal center indicates that the reduction is accompanied
by ligand scrambling and suggests that another product
might be present in the reaction mixture.
The NMR spectra were characterized by large ani-
sotropy, clearly showing the resonances of three distinct
phenyl and four pyrrolyl rings. The partly hydrogenated
ring shows the resonances of the two distinct CH2
groups at 32.26 and 34.13 ppm of the DEPT 13C NMR
spectrum. The corresponding two couples of gem-
hydrogen atoms feature four distinct well-solved mul-
tiplets at 2.27 (endo) and 3.05 ppm (exo) and at 2.88
(endo) and 3.03 (exo), respectively. The hydrogen atom
at the ring para position that is directly bonded to Ta
is present as a doublet at 2.16 ppm, while the quater-
nary C also bonded to Ta features a resonance at 114.05
ppm of the 13C NMR spectrum. Finally, the other two
hydrogen atoms attached to the two last C atoms
forming the residual C-C double bond resonate at 6.51
and 6.36 ppm, and their coupling with the resonance
at 2.16 ppm was clearly visible in the COSY NMR
spectrum.
In conclusion, it has been shown that the dipyrrolide
ligand may both activate and stabilize tantalum metal
complexes. The preparation of {[Ph2C(C4H3N)2]2TaCl2}-
{Li (THF)4}‚2THF is facile and provides a promising
route to tantalum-dipyrrolide chemistry. A stable bis-
alkyl complex has been isolated, while attempts to form
hydrides afforded both reduction of the metal center and
partial hydrogenation of an aromatic ring. This confirms
once again the ability of dipyrrolide ligand to increase
the reactivity of the metal center and encourages further
work toward the synthesis and characterization of
hydride derivatives of other dipyrrolides with lower
possibility of being involved in the reactivity of the metal
center.
The structure of 5 (Figure 5) shows that the tantalum
center is pseudo-octahedral and coordinated by three
dipyrrolide ligands, two of which are in turn π-bound
to the two Na atoms. The Ta-N bond lengths are
similar to those already discussed for complexes 2 and
3 and warrant no further comment. Most importantly
however, the metal center has undergone a one-electron
reduction to the tetravalent state. The magnetic mo-
ment (1.71 µB) is consistent with a single unpaired
electron, thus confirming the reduction to Ta(IV).
The ability of Nb and Ta hydrides to perform hydro-
genation reactions and in a few cases even in catalytic
fashion is documented in the literature.12 However, the
reactivity of the Ta-H function seems to be particularly
sensitive to the nature of the ligand. For example, while
the Cp derivatives seem to be sufficiently stable to allow
full characterization,12a,13 a more enhanced reactivity
has been found for alkoxide derivatives that typically
Exp er im en ta l Section
Gen er a l P r oced u r es. All operations were performed under
inert atmosphere by using standard Schlenk type techniques
and in the drybox. TaCl5 was purchased from STREM and
sublimed prior to use; diphenyldipyrrolmethane was prepared
by a published procedure.1a Methyllithium (1.4 M solution in
ether) and NaBH(C2H5)3 (1 M solution in toluene) were
obtained from Aldrich and used as received. Infrared spectra
were recorded on a Mattson 9000 and Nicolet 750-Magna FTIR
instruments from Nujol mulls prepared in a drybox. Samples
for magnetic susceptibility measurements were weighed inside
a drybox equipped with an analytical balance and sealed into
calibrated tubes. Magnetic measurements were carried out
with a Gouy balance (J ohnson Matthey) at room temperature.
Magnetic moments were calculated following standard meth-
ods,15
and corrections for underlying diamagnetism were
applied to data.16 Elemental analyses were carried out with a
Perkin-Elmer 2400 CHN analyzer. Data for X-ray crystal
(12) (a) Wigley, D. E.; Gray, S. D. In Comprehensive Organometallic
Chemistry, 2nd ed.; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.;
Oxford, 1995. (b) Ankianiec, B. C.; Fanwick, P. E.; Rothwell, I. P. J .
Am. Chem. Soc. 1991, 113, 4710. Chesnut, R. W.; Steffey, B. D.;
Rothwell, I. P. Polyhedron 1989, 8, 1607. Yu, J . S.; Rothwell, I. P. J .
Chem. Soc., Chem. Commun. 1992, 632.
(13) See for example: (a) Fei, P.; Khan, M. A.; Nicholas, L. M. J .
Am. Chem. Soc. 1992, 114, 6579. (b) Belmonte, P.; Schrock, R. R.;
Churchill, M. R.; Youngs W. J . J . Am. Chem. Soc. 1980, 102, 2858.
(14) (a) Miller, R. L.; Toreki, R.; LaPointe, R. E.; Wolczanski, P. T.;
Van Duyne, G. D.; Roe, D. C. J . Am. Chem. Soc. 1993, 115, 5570. (b)
Bishop, P. T.; Dilworth, J . R.; Nicholson, T.; Zubieta, J . A. J . Chem.
Soc., Chem. Commun. 1986, 1123. (c) Yu, J . S.; Felter, L.; Potyen, M.
C.; Clark, J . R.; Visciglio, V. M.; Fanwick, P. E.; Rothwell, I. P.
Organometallics 1996, 15, 4443.
(15) Mabbs, M. B.; Machin, D., Magnetism and Transition Metal
Complexes; Chapman and Hall: London, 1973.

Ta Complexes of Diphenyldipyrrolide Dianion
Organometallics, Vol. 21, No. 20, 2002 4261
Ta ble 1. Cr ysta l Da ta a n d Str u ctu r e An a lysis Resu lts
1
2
3
4
5
formula
fw
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
C
54H62Li4N4O3
C
66H80Cl2LiN4O6Ta
C60H70LiN4O4Ta
1099.09
monoclinic, P2(1)/ c
14.570(1)
19.954(2)
18.371(1)
90
91.129(1)
90
5339.8(7)
4
C46H44N4NaOTa
872.79
C75H78N6Na2O3Ta
1338.36
triclinic, P1h
13.290(1)
13.448(1)
18.868(2)
81.324(1)
77.388(2)
85.026(1)
3248.1(5)
2
842.84
1284.13
monoclinic, P2(1)/ n
14.224(2)
32.518(4)
14.335(2)
90
112.804(9)
90
6112(1)
4
monoclinic, P2(1)/ c
14.787(5)
22.026(8)
15.134(5)
90
90.331(7)
90
4929(3)
4
triclinic, P1h
8.551(3)
11.671(3)
19.577(6)
86.697(2)
80.432(3)
74.575(3)
1857.0(9)
2
Z
radiation (KR, Å)
0.71073
236(2)
1.136
0.69
1800
0.71073
203(2)
1.395
1.940
2648
0.71073
203(2)
1.367
2.108
2264
0.71073
203(2)
1.561
3.014
880
0.71073
203(2)
1.368
1.758
1378
T (K)
D
calcd (g cm-3
)
µcalcd (mm-1
)
F000
R, Rw
2 a
0.0711, 0.1606
1.026
0.0471, 0.0934
1.025
0.0294, 0.0633
1.037
0.0384, 0.0737
0.952
0.0340, 0.0854
1.091
GoF
R ) ∑|Fo| - |Fc||/∑|Fo|. Rw ) [(∑(|Fo| - |Fc|)2/∑wFo2)]1/2
.
a
structure determination were obtained with a Bruker diffrac-
tometer equipped with a Smart CCD area detector.
Hz, 4H), 7.22(CH-Ph, t, J H-H ) 6.1 Hz, 4H), 5.77(CH-pyr, br
s, 1H), 5.56(CH-pyr, dd, J H-H ) 1.3 and 1.5 Hz, 1H), 5.49(CH-
pyr, t, J H-H ) 2.9 Hz, 1H), 6.21(CH-pyr, dd, J H-H ) 8.2 Hz,
1H), 6.13(CH-pyr, pseudo q, J H-H ) 1.3 and 1.5 Hz, 1H), 5.65-
(CH-pyr, dd, J H-H ) 1.3 and 1.5 Hz, 1H), 8.22(CH-pyr, br s,
1H), 6.09(CH-pyr, pseudo q, J H-H ) 1.4 and 1.6 Hz, 1H), 6.05-
(CH-pyr, t, J H-H ) 3.0 Hz, 1H), 7.01 and 6.81(CH-pyr,
overlapping m, 3H), 3.30(24H, m, CH2-THF), 0.95(24H, m,
CH2-THF). 13C{1H} NMR [125.72 MHz, C6D6, 25 °C] δ: 159.7
and 157.5(C-Ph), 148.7, 147.2, 146.4, and 143.9(C-pyr), 128.29,
128.19, 128.00, 127.42, 127.23, and 127.16(CH-Ph), 147.9,
128.0, 127.1, 126.8, 126.7, 114.6, 113.86, 113.82, 113.70,
110.94, 110.83, 103.14(CH-pyr), 59.5 and 59.0(C-ligand), 67.7-
(CH2-THF), 25.5(CH2-THF).
P r ep a r a tion of [P h 2C(C4H3 N)2]2Li4(OEt2)3 (1). A solu-
tion of MeLi in ether (3.5 mL, 1.4 M, 5 mmol) was added to a
suspension of diphenyldipyrrolmethane (0.74 g, 2.5 mmol) in
ether (50 mL) cooled to 0 °C, causing a vigorous gas evolution.
The solution was allowed to slowly warm to room temperature.
After stirring for 24 h, the ether solution was concentrated to
small volume (20 mL) and layered with hexane. Colorless
crystals of 1 (0.85 g, 1.0 mmol, 78%) separated upon standing
for 2 days at 4 °C. Anal. Calcd (found) for C54H62Li4N4O3: C
76.95 (76.38), H 7.67 (7.51), N 6.65 (6.73). IR (Nujol mull, cm-1
)
ν: 1596(w), 1484(m), 1421(w), 1377(m), 1274(w), 1184(w),
1153(m), 1090(m), 1067(m), 1028(m), 979(w), 960(w), 901(m),
876(w), 847(m), 785(w), 726(m), 702(m), 656(m), 625(m), 553-
(m). 1H NMR [500 MHz, C6D6, 25 °C] δ: 7.0-7.2(10H, m, CH-
Ph), 7.09(2H, s, R-CH-pyr), 6.35(2H, s, â-CH-pyr), 6.15(2H, s,
γ-CH-pyr), 2.95(12H, q, J H-H ) 7.0 Hz, CH2-ether), 0.95(18H,
t, J H-H ) 7.0 Hz, CH3-ether). 13C{1H} NMR [125.72 MHz, C6D6,
25 °C] δ: 150(C-Ph), 149(C-pyr), 130.4(CH-pyr), 128.8(CH-Ph),
127.7(CH-Ph), 126.2(CH-Ph), 110.4(CH-pyr), 107.3(CH-pyr),
59.2(C-ligand), 65.7 (CH2 ether), 14.8(CH3 ether).
P r ep a r a tion of {[P h 2C(C4H3N)2]2Ta Me2}{Li(THF )4} (3).
A solution of MeLi in ether (1.0 mL, 1.4 M, 1.4 mmol) was
added to the dark red solution of 2 (0.9 g, 0.7 mmol) in THF
(80 mL) at 0 °C. The color immediately changed from red to
yellow, and the solution was allowed to warm slowly to room
temperature. After stirring the reaction mixture for another
24 h, the clear yellow solution was concentrated (40 mL),
layered with hexane, and allowed to stand at 4 °C for 1 week,
upon which yellow crystals of 3 (0.57 g, 0.52 mmol, yield 76%)
separated. Anal. Calcd (found) for C60H70LiN4O4Ta: C 65.57
(65.88), H 6.42 (6.35), N 5.10 (5.23). IR (Nujol mull, cm-1) ν:
1593(w), 1404(m), 1282(m), 1244(w), 1223(w), 1136(m), 1109-
(m), 1078(s), 1078(m), 1043(s), 989(s), 887(m), 796(m), 758-
(m), 746(s), 719(m), 700(m), 656(w), 629(w). 1H NMR [500
MHz, C6D6, 25 °C] δ: 7.44(4H, d, J H-H ) 6.9 Hz, CH-Ph), 7.10-
(6H, dd, J H-H ) 8.4 and 8.0 Hz, CH-Ph), 6.68(2H, s, R-CH-
pyr), 6.01(2H, s, â-CH-pyr), 5.92(2H, s, γ-CH-pyr), 3.33(8H,
m, CH2-THF), 1.36(3H, s, CH3-Ta), 1.30(8H, m, CH2-THF). 13C-
{1H} NMR [125.72 MHz, C6D6, 25 °C] δ: 148.5(C-Ph), 147.2-
(C-pyr), 131.2(CH-Ph), 129.1(CH-pyr), 127.5(CH-Ph), 127.2-
(CH-Ph), 110.9(CH-pyr), 107.7(CH-pyr), 95.4(CH3-Ta), 58.6(C-
ligand), 68.0(CH2-THF), 25.5(CH2-THF).
Isola tion of [Ta {P h 2C(C4H3N)2}{P h C(C4H3N)2(1,4-η1:η1-
2,3-:η2-C6H7)Na (OEt2)} (4) a n d [Ta {P h 2C(C4H3N)2}3[Na -
(OEt2)]2‚(OEt2) (5). A solution of NaBH(C2H5)3 in toluene (1.8
mL, 1 M, 1.8 mmol) was added to a flask containing a solution
of 2 (2.3 g, 1.8 mmol) in toluene (70 mL) at 0 °C. The color
changed from dark red to green-brown after 3 min, and the
solution was allowed to warm slowly to room temperature.
After stirring for an additional 24 h, the solvent was removed
in vacuo and ether (80 mL) was added to the remaining
residue. The red solution was centrifuged to remove a light
yellow precipitate. The ether solution was concentrated (40
mL). Red crystals of 4 separated upon standing at 4 °C for 3
days (0.35 g, 0.4 mmol, yield 22%). Anal. Calcd (found) for
P r ep a r a t ion of {[P h 2C(C4H 3N)2]2Ta Cl2}{Li(TH F )4}‚
2THF (2). A solution of MeLi in ether (33 mL, 1.4 M, 46 mmol)
was added to a suspension of diphenyldipyrromethane (6.8 g,
23 mmol) in ether (100 mL) at 0 °C. A clear solution was
obtained by the end of the addition. The solution was allowed
to warm slowly to room temperature and then transferred via
cannula to a flask containing a suspension of TaCl5 (4.1 g, 11.4
mmol) in ether (100 mL). The color changed immediately from
yellow to green and finally to green-brown. After stirring for
24 h, a green-brown compound was precipitated. Ether was
removed in vacuo, and the resulting residue was dissolved in
toluene (100 mL). The dark red solution was centrifuged to
remove LiCl, and toluene was removed from the dark red-
brown solution in vacuo and replaced by THF (40 mL). The
dark red-brown solution was layered with hexane, from which
dark red crystals of 2 were obtained upon standing for a week
at room temperature (10.6 g, 8.3 mmol, 72%). Anal. Calcd
(found) for C66H80Cl2LiN4O6Ta: C 61.73 (62.1), H 6.28 (6.35),
N 4.36 (4.23). IR (Nujol mull, cm-1) ν: 1595(w), 1486(m), 1423-
(w), 1377(m), 1260(s), 1213(m), 1109(m), 1093(m), 1075(m),
1045(s), 982(s), 886(m), 748(m), 731(m), 702(s), 654(s), 626-
1
(m), 553(m). H NMR [500 MHz, C6D6, 25 °C] δ: 7.47(CH-Ph,
dd, J H-H ) 6.1 and 1.6 Hz, 2H), 7.10(CH-Ph, m, 8H), 7.53-
(CH-Ph, dd, J H-H ) 7.5 Hz, 2H), 7.31(CH-Ph, t, J H-H ) 7.5
(16) Foese, G.; Gorter, C. J .; Smits, L. J . Constantes Se´lectionne´es
Diamagne´tisme, Paramagne´tisme, Relaxation Paramagne´tique; Mas-
son: Paris, 1957.

4262 Organometallics, Vol. 21, No. 20, 2002
Aharonian et al.

Ta Complexes of Diphenyldipyrrolide Dianion
Organometallics, Vol. 21, No. 20, 2002 4263
C
46H44N4NaOTa: C 63.30 (63.71), H 5.08 (4.95), N 6.42 (6.23).
the data collection temperature. Data were collected on a
Bruker AXS SMART 1k CCD diffractometer using 0.3° ω-scans
at 0°, 90°, and 180° in φ. Initial unit-cell parameters were
determined from 60 data frames collected at different sections
of the Ewald sphere. Semiempirical absorption corrections
based on equivalent reflections were applied.17 Systematic
absences in the diffraction data and unit-cell parameters were
uniquely consistent with the reported space group for 1 and
3, P21/ c, and for 2, P21/ n. No symmetry higher than triclinic
was observed for 5 and 4, and solution in the centrosymmetric
space group option yielded chemically reasonable and compu-
tationally stable results of refinement. The structures were
solved by direct methods, completed with difference Fourier
syntheses, and refined with full-matrix least-squares proce-
dures based on F2. Symmetry unique solvent molecules were
located cocrystallized in 5 (one diethyl ether molecule) and 2
(two tetrahydrofuran molecules). Phenyl groups in 1 were
refined as idealized, flat, rigid hexagons.
IR (Nujol mull cm-1) ν: 1591(w), 1313(w), 1300(w), 1259(m),
1219(w), 1182(w), 1165(w), 1140(m), 1115(m), 1093(m), 1080-
(m), 1047(m), 1022(s), 981(w), 871(w), 798(s), 733(s), 719(w),
1
709(w), 679(w), 656(w), 509(w). H NMR [500 MHz, THF-d8,
25 °C] δ: CH-hydrogenated ring: 6.51(t, J H-H ) 6.5 Hz, 1H),
6.36(d, J H-H ) 5.9 Hz, 1H), 3.05-3.03(two m, 2H), 2.88(m, 1H),
2.27(m, 1H), 2.16(dd, 1H); CH-Ph: 7.95(dd, J H-H ) 1.0 and
7.1 Hz, 2H), 7.29(t, J H-H ) 7.7 Hz, 2H), 7.16(overlapping d,
1H); CH-Ph: 7.13(br s, 5H); CH-Ph: 7.04(dd, J H-H ) 1.0 and
7.1 Hz, 2H), 6.89(t, J H-H ) 7.8 Hz, 2H), 6.77(pseudo t, J H-H
7.2 Hz, 1H); CH-pyrr: 7.13(overlapping m, 1H), 5.86(t, J H-H
) 2.7 Hz, 1H), 5.34(m, 1H); CH-pyrr: 6.94(pseudo q, J H-H
1.4 Hz, 1H), 5.96(t, J H-H ) 2.7 Hz, 1H), 5.49(pseudo q, J H-H
1.4 Hz, 1H); CH-pyrr: 5.29(br s, 1H), 5.22(t, J H-H ) 2.6 Hz,
1H), 5.18(pseudo q, J H-H ) 1.4 Hz, 1H); CH-pyrr: 6.39(pseudo
q, J H-H ) 1.1 amd 1.4 Hz, 1H), 5.78(pseudo q, J H-H ) 1.1 and
1.6 Hz, 1H), 5.34(br s, 1H); 3.41(4H, q, J H-H ) 7.0 Hz, CH2-
ether), 1.05(6H, t, J H-H ) 7.0 Hz, CH3-ether). 13C{1H} NMR
[125.72 MHz, THF-d8, 25 °C] δ: 163.9, 152.6, and 151.0(C-
Ph), 150.6, 148.6, 148.4, and 146.5(s, C-pyr), hydrogenated
ring: 114.05(C-Ta), 130.19(CHd), 122.94(CHd), 80.47(CH-Ta),
34.13(CH2), 32.26(CH2); CH-Ph: 130.12, 129.09, and 12.13;
CH-Ph: 135.95, 131.86, and 127.94; CH-Ph: 126.06, 126.67,
and 130.52; CH-pyr: 103.01, 105.39, and 130.17; CH-pyrr:
104.79, 107.19, and 127.47; CH-pyrr: 112.09, 106.62, and
126.23; CH-pyr: 10.91, 107.99, and 125.90; CH2-ether: 67.04;
(CH3-ether): 15.65.
After separation of 4, the mother liquor was further
concentrated (20 mL). Yellow crystals of 5 (0.45 g, 0.33 mmol,
19%) separated after upon standing 1 week at 4 °C. Anal. Calcd
(found) for C75H78N6Na2O3Ta: C 67.31 (67.71), H 5.87 (5.95),
N 6.28 (6.23). IR (Nujol mull cm-1) ν: 1650(w), 1595(w), 1261-
(s), 1209(w), 1180(w), 1133(s), 1097(s), 1079(m), 1045(s), 974-
(m), 899(w), 889(w), 872(w), 802(s), 746(m), 729(w), 698(s),
)
)
)
All non-hydrogen atoms were refined with anisotropic
displacement coefficients. All hydrogen atoms were treated as
idealized contributions. All scattering factors are contained in
the SHELXTL 6.12 program library (Sheldrick, G. M., Bruker
AXS, Madison, WI, 2001).
Ack n ow led gm en t. This work was supported by the
Natural Sciences and Engineering Council of Canada
(NSERC) and by Canada Foundation for Innovation
(CFI) through an infrastructure grant.
Su p p or tin g In for m a tion Ava ila ble: Complete crystal-
lographic data (CIF and PDF) for complexes 1, 2, 3, 4, and 5.
This material is available free of charge via the Internet at
http://pubs.acs.org.
OM020406F
655(s). µeff ) 1.71 µBM
.
X-r a y Cr ysta llogr a p h y. Suitable crystals were selected,
mounted on thin, glass fibers using paraffin oil, and cooled to
(17) Blessing, R. Acta Crystallogr. 1995, A51, 33-38.