(dme)MCl3(NNPh2) (dme = dimethoxyethane; M = Nb, Ta): A versatile synthon for [Ta - NNPh2] hydrazido(2-) complexes

Article abstract of DOI:10.1021/ic1004193

Complexes (dme)TaCl₃(NNPh₂) (1) and (dme)NbCl ₃(NNPh₂) (2) (dme =1,2-dimethoxyethane) were synthesized from MCl₅ and diphenylhydrazine via a Lewis-acid assisted dehydrohalogenation reaction. Monomeric 1 has been characterized by X-ray, IR, UV-vis, ¹H NMR, and ¹³C NMR spectroscopy and contains a κ¹-bound hydrazido(2-) moiety. Unlike the corresponding imido derivatives, 1 is dark blue because of an LMCT that has been lowered in energy as a result of an N_α-N_β antibonding interaction that raises the highest occupied molecular orbital (HOMO). Reaction of 1 with a variety of neutral, mono- and dianionic ligands generates the corresponding ligated complexes retaining the κ¹-bound [Ta-NNPh₂] moiety.

Full text of DOI:10.1021/ic1004193

4648 Inorg. Chem. 2010, 49, 4648–4656
DOI: 10.1021/ic1004193
(dme)MCl3(NNPh2) (dme=dimethoxyethane; M=Nb, Ta): A Versatile Synthon for
[TadNNPh2] Hydrazido(2-) Complexes†
Ian A. Tonks and John E. Bercaw*
Arnold and Mabel Beckman Laboratories of Chemical Synthesis, California Institute of Technology, Pasadena,
California 91125
Received March 2, 2010
Complexes (dme)TaCl3(NNPh2) (1) and (dme)NbCl3(NNPh2) (2) (dme =1,2-dimethoxyethane) were synthesized
from MCl5 and diphenylhydrazine via a Lewis-acid assisted dehydrohalogenation reaction. Monomeric 1 has been
characterized by X-ray, IR, UV-vis, 1H NMR, and 13C NMR spectroscopy and contains a κ1-bound hydrazido(2-)
moiety. Unlike the corresponding imido derivatives, 1 is dark blue because of an LMCT that has been lowered in energy
as a result of an NR-Nβ antibonding interaction that raises the highest occupied molecular orbital (HOMO). Reaction
of 1 with a variety of neutral, mono- and dianionic ligands generates the corresponding ligated complexes retaining the
κ1-bound [Ta-NNPh2] moiety.
Introduction
of Mountford,5 Odom,6 and Gade7 have been exploring the
reactivity of group 4 hydrazides and have made significant
advances in the implementation of these complexes in cata-
lytic nitrene transfer8 and hydrohydrazination reactions.
Additionally, Fryzuk and co-workers have reported an
interesting dinuclear tantalum complex with a bridging,
side-on, end-on bound N2 ligand that could be also consid-
ered a formal hydrazido moiety. This complex is particularly
susceptible to N-N bond cleavage and further functionaliza-
tion to afford silylamines.9
A longstanding goal in chemistry is the activation and
subsequent functionalization of molecular dinitrogen.1 One
of the proposed intermediates along a Chatt-type2 cycle of N2
reduction is an end-on (κ1-) bound hydrazide (2-) moiety
(M=NNH2), and accordingly significant research into possi-
ble models for these intermediates based on group 5-8
metals has been undertaken.3 In addition to efforts toward
the synthesis of ammonia from dinitrogen, recent work
toward the synthesis of other nitrogen-containing products
from [M=NNR2] moieties has proven to be an active area of
investigation. Following Bergman’s first report,4 the groups
While there exist examples of end-on (κ1-) hydrazide
(2-) vanadium complexes,3a,10 few complexes of the heavier
congeners Nb11 and Ta12 have been synthesized and
† Dedicated to Professor Uwe Rosenthal on the occasion of his 60th birthday.
*To whom correspondence should be addressed. E-mail: bercaw@
caltech.edu.
(1) (a) Fryzuk, M. D.; Johnson, S. A. Coord. Chem. Rev. 2000, 200, 379.
(b) MacKay, B. A.; Fryzuk, M. D. Chem. Rev 2004, 104, 385.
(2) Chatt, J.; Dilworth, J. R.; Richards, R. L. Chem. Rev. 1978, 78, 589.
(3) For representative examples, see: (a) Banerjee, S.; Odom, A. L. Dalton
Trans. 2008, 2005. (b) Yandulov, D. V.; Schrock, R. R. Science 2003, 301, 76.
(c) Schrock, R. R.; Glassman, T. E.; Vale, M. G.; Kol, M. J. Am. Chem. Soc.
1993, 115, 1760. (d) Dilworth, J. P.; Jobanputra, P.; Parrott, S. J.; Thompson,
R. M.; Povey, D. C.; Zubieta, J. A. Polyhedron 1992, 11, 147. (e) Huynh,
M. H. V.; Lee, D. G.; White, P. S.; Meyer, T. J. Inorg. Chem. 2001, 40, 3842.
(f) Huynh, M. H. V.; El-Samanody, E. S.; Demadis, K. D.; White, P. S.; Meyer,
T. J. Inorg. Chem. 2000, 39, 3075. (g) Coia, G M.; Devenney, M.; White, P. S.;
Meyer, T. J. Inorg. Chem. 1997, 36, 2341.
(6) (a) Li, Y.; Shi, Y.; Odom, A. L. J. Am. Chem. Soc. 2004, 126, 1794.
(b) Patel, S.; Li, Y.; Odom, A. L. Inorg. Chem. 2007, 46, 6373.
(7) (a) Herrmann, H.; Fillol, J. L.; Wadepohl, H.; Gade, L. H. Angew.
Chem., Int. Ed. 2007, 46, 8426. (b) Herrmann, H.; Fillol, J. L.; Gehrmann, T.;
Enders, M.; Wadepohl, H.; Gade, L. H. Chem.;Eur. J. 2008, 14, 8131.
(c) Herrmann, H.; Wadepohl, H.; Gade, L. H. J. Chem. Soc., Dalton Trans.
2008, 2111. (d) Herrman, H.; Gehrmann, T.; Wadepohl, H.; Gade, L. H. J. Chem.
Soc., Dalton Trans. 2008, 6231. (e) Weitershaus, K.; Wadepohl, H.; Gade, L. H.
Organometallics 2009, 28, 3381. (f) Weitershaus, K.; Fillol, J. L.; Wadepohl, H.;
Gade, L. H. Organometallics 2009, 28, 4747.
(8) Mindiola, D. J. Angew. Chem., Int. Ed. 2008, 47, 2.
(9) (a) Fryzuk, M. D. Acc. Chem. Res. 2009, 42, 127. (b) Shaver, M. P.;
Fryzuk, M. D. J. Am. Chem. Soc. 2005, 127, 500. (c) MacKay, B. A.; Munha,
R. F.; Fryzuk, M. D. J. Am. Chem. Soc. 2006, 128, 9472.
(4) Walsh, P. J.; Carney, M. J.; Bergman, R. G. J. Am. Chem. Soc. 1991,
113, 6343.
(10) (a) Davies, S. C.; Hughes, D. L.; Janas, Z.; Jerzykiewicz, L.; Richards,
R. L.; Sanders, J. R.; Sobota, P. Chem. Commun. 1997, 1261. (b) Henderson,
R. A.; Janas, Z.; Jerzykiewicz, L. B.; Richards, R. L.; Sobota, P. Inorg. Chim. Acta
1999, 285, 178. (c) Davies, S. C.; Hughes, D. L.; Janas, Z.; Jerzykiewicz, L.;
Richards, R. L.; Sanders, J. R.; Silverston, J. E.; Sobota, P. Inorg. Chem. 2000, 39,
3485. (d) Davies, S. C.; Hughes, D. L.; Konkol, M.; Richards, R. L.; Sanders, J. R.;
Sobota, P. J. Chem. Soc., Dalton Trans. 2002, 2811.
(11) Green, M. L. H.; James, J. T.; Saunders, J. F.; Souter, J. J. Chem.
Soc., Dalton Trans. 1997, 1281.
(12) Sebe, E.; Heeg, M. J.; Winter, C. H. Polyhedron 2006, 25, 2109.
(5) (a) Parsons, T. B.; Hazari, N.; Cowley, A. R.; Green, J. C.; Mountford,
P. Inorg. Chem. 2005, 44, 8442. (b) Selby, J. D.; Manley, C. D.; Feliz, M.; Schwarz,
A. D.; Clot, E.; Mountford, P. J. Chem. Soc., Chem. Commun. 2007, 4937.
(c) Selby, J. D.; Schulten, C.; Schwarz, A. D.; Stasch, A.; Clot, E.; Jones, C.;
Mountford, P. J. Chem. Soc., Chem. Commun. 2008, 5101. (d) Clulow, A. J.; Selby,
J. D.; Cushion, M. G.; Schwarz, A. D.; Mountford, P. Inorg. Chem. 2008, 47, 12049.
(e) Selby, J. D.; Manley, C. D.; Schwarz, A. D.; Clot, E.; Mountford, P.
Organometallics 2008, 27, 6479.
r
pubs.acs.org/IC
Published on Web 04/19/2010
2010 American Chemical Society

Article
Inorganic Chemistry, Vol. 49, No. 10, 2010 4649
characterized. In fact, only two related complexes containing
[TadNNR2] have been reported: [Ta(NNR2)Cl2(NH2NR2)-
(TMEDA)]Cl (R = Me, 1,5-(CH2)5).12 The utilization of
these complexes to prepare other related hydrazido com-
plexes appears limited;all attempts to replace the chloride
ligands with amides or alkoxides through salt metathesis
reactions have failed. The methodology used to prepare
[V=NNR2] complexes, aminolysis of vanadium oxo10c or
phenoxide10b ligands, is not viable for niobium and tantalum
because of their increased oxophilicity. Additionally, this
methodology typically requires installing the ancillary ligand
scaffold before the [M=NNR2] moiety. With this in mind,
we sought to develop a simple synthetic entry point into
niobium and tantalum terminal [M=NNR2] complexes and
investigate their reactivity relative to analogous tantalum
imido complexes and also to group 4 [M=NNR2] moieties.
Herein we report the synthesis of a versatile group 5 end-on
(κ1-) hydrazido synthon, (dme)M(NNPh2)Cl3 (dme=CH3-
OCH2CH2OCH3; M = Nb, Ta), along with initial results
for the tantalum complex demonstrating that dme and
chloride may be cleanly displaced by a variety of chelating
ligands.
˚
Figure 1. Thermal ellipsoid drawing of 1. Selected bond lengths (A)
and angles (deg): Ta1-N1 1.773(1); Ta1-O1 2.1638(7); Ta1-O2
2.2953(9); N1-N2 1.347(1); Ta1-N1-N2 173.65(8). H atoms removed
for clarity.
The N1-N2 distance of 1.347(1) is slightly shorter than that
of free diphenylhydrazine, which would be expected on the
basis of reduced NR-Nβ lone pair repulsion resulting from
NR lone pair donation to the metal center.
In some MNNR2 complexes it is possible that the hydra-
zide unit could be described as a formally neutral diazene
L-type ligand,15 but the short Ta-N distance, the only slightly
shortened NR-Nβ bond, and nearly linear Ta-NR-Nβ bond
angle indicate that the LX2-type hydrazido(2-) resonance
structure is the major contributor in 1.
Results and Discussion
Following a procedure similar to those utilizedby Williams
et al. to prepare group 5 [TadNR] imido complexes,13 TaCl5
and NbCl5 were treated with diphenylhydrazine and dime-
thoxyethane (dme) in the presence of pyridine and ZnCl2 to
generate (dme)TaCl3(NNPh2) (1) and (dme)NbCl3(NNPh2)
(2), respectively, through a Lewis acid assisted dehydrohalo-
genation reaction (eq 1).14 Unfortunately, similar reactions
involving Me2NNH2, MePhNNH2, or N-aminopiperidine
yield intractable mixtures of products, possibly a result of the
increased basicity of the Nβ lone pair and/or the better brid-
ging ability of these less bulky hydrazines. The dme ligand in
1 and 2 exhibits two signals in the 1H and 13C NMR spectra
for the methoxy protons, as well as two signals for the
methylene protons, indicating a cis, mer geometry as indi-
cated in eq 1.
A particularly interesting characteristic of 1 is its unique
dark blue color. UV-vis studies of 1 show a prominent
ligand-to-metal charge transfer (LMCT) band at 583 nm
with an extinction coefficient of 400 M-1 cm-1. In contrast,
the corresponding imido complexes (dme)TaCl3(NtBu) and
(dme)TaCl3(NPh) are colorless (342 nm) and pale yellow
(425 nm), respectively.13 The LMCT in these imido com-
plexes is postulated to arise from a transition from Ta dxz-
NR px π bonding orbital (HOMO) to the unoccupied Ta dxy
orbital (LUMO).16 We attribute the large red shift in the
LMCT for 1 to the interaction of the Nβ lone pair with the Ta
dxz-NR px π bonding orbital that serves to destabilize the
HOMO via an NR-Nβ antibonding interaction (Scheme 1).
A similar phenomenon is observed in (dme)TaCl3(NPh) as
a result of an antibonding contribution from the aryl ring,
although the effect is smaller (Scheme 1).17 DFT calculations
(see Experimental Section for computational details) of the
HOMO-LUMO gap performed on 1, (dme)TaCl3(NCMe3),
and (dme)TaCl3(NPh) qualitatively agree with this assess-
ment, and the NR-Nβ and NR-phenyl π antibonding inter-
actions for the HOMOs are clearly evident in 1 and
1 was crystallized by vapor diffusion of pentane into a
concentrated 1,2-dichloroethane solution of 1 to give large,
blue needles. The X-ray structure of 1 (Figure 1) confirms
that the complex is monomeric containing an end-on, κ1-
bound diphenylhydrazido(2-) ligand. In agreement with
NMR data, the ligands are arranged in a cis,mer fashion,
with one of the dme oxygens trans to a chloride and the other
trans to the hydrazide ligand. The Ta-N1 bond distance in 1
˚
is 1.773(1) A which indicates a Ta-N LX2 triple bond, as
does the nearly linear Ta-N1-N2 bond angle (173.65(8)°).
(13) Korolev, A. V.; Rheingold, A. L.; Williams, D. S. Inorg. Chem. 1997,
36, 2647.
(14) In all of the schemes in this paper, amido (LX) ligands will be
represented as double bonds and imido ligands (LX2) as triple bonds since
these representations most accurately describe the bonding within these
systems (as evidenced by simple electron counting and DFT calculations),
despite this notation not being the normal convention.
(15) Danopoulos, A. A.; Hay-Motherwell, R. S.; Wilkinson, G.; Sweet,
T. K. N.; Hursthouse, M. B. Polyhedron 1997, 16, 1081.
(16) Williams, D. S.; Thompson, D. W.; Korolev, A. V. J. Am. Chem. Soc.
1996, 118, 6526.
(17) Williams, D. S.; Korolev, A. V. Inorg. Chem. 1998, 37, 3809.

4650 Inorganic Chemistry, Vol. 49, No. 10, 2010
Tonks and Bercaw
Scheme 1
py2TaCl3(NNPh2) (3) (tmeda)TaCl3NNPh2 (4) and (bpy)-
TaCl3(NNPh2) (5), respectively. Adducts 3 and 4 are stable
1
in solution and were characterized by H and 13C NMR,
whereas 5 slowly decomposes in solution. Ligand substitu-
tion by THF, however, yields the bis-THF adduct 6 which
can be observed by 1H NMR, but rapidly decomposes to an
intractable purple mixture. Similarly, reaction with PPh3 or
chelating phosphines such as bis(dimethylphosphino)ethane
results in rapid decomposition of the complex. The instability
of these complexes likely is a result of weaker monodentate
ether or softer phosphine donors.
Figure 2. Schematic of HOMOs derived from DFT calculations per-
formed on (dme)TaCl3(NNPh2) (1) (left) and (dme)TaCl3(NPh) (right)
showing antibonding interactions between the Ta-N π bond and Nβ and
phenyl substituents, respectively.
(dme)TaCl3(NPh) (Figure 2).18 The calculated HOMO-LU-
MO gaps for all three compounds were consistently larger
than the observed values, so that quantitative comparisons on
the lone pair and aryl π effects are not possible. One particu-
larly enticing aspect of this effect is that the addition of a -lone
pair destabilizes the M=N multiple bond, which could incre-
ase the reactivity of hydrazido(2-) complexes toward [2 þ 2]
cyclization reactions as compared to the parent imidos.
1 undergoes ligand substitution with a variety of neutral
L-donors to generate new complexes bearing a terminal
diphenylhydrazido(2-) moiety (eq 2). The dme ligand is
readily substituted by nitrogen based L donors: pyridine,
tmeda, and bipyridine will react with 1 in benzene to yield
Precursor 1 also reacts cleanly with a variety of mono- and
dianionic ligands. Treatment of 1 with 2 equiv of NaCp
generates the tantalocene product Cp2TaCl(NNPh2) (7) in
good yield (eq 3). Treatment of 1 with only 1 equiv of NaCp
gives 0.5 equiv of 7 and 0.5 equiv of 1, and thus far we have
been unable to prepare monocyclopentadienyl complexes of
the type CpTaCl2(NNR2) via 1. Orange crystals of 7 were
obtained by layering pentane onto a concentrated toluene
solution cooled to -30 °C. The X-ray structure of 7 is
reported in Figure 3. The bonding in 7 is different from all
other [TadNNR2] complexes reported here. Since the vacant
orbital on Ta perpendicular to the tantalocene equatorial
plane that is capable of forming a second Ta-N π bond is
Ta-Cp antibonding,19 7 should have a weaker TatN triple
(18) One reviewer pointed out that in the NNPh2 case, in addition to the
lone pair effect, delocalization into the aryl rings may play an important role
in the HOMO. Our DFT calculations show that there appears to be
contribution from the aryl π system. This is further supported by some
related tungsten complexes, where the diphenylhydrazidos have a very low
energy LMCT when compared to the dialkylhydrazidos; see: Koller, J.;
Ajmera, H. M.; Abboud, K. A.; Anderson, T. J.; McElwee-White, L. Inorg.
Chem. 2008, 47, 4457. We are currently investigating this effect as it relates to
other heteroatom substituted imido derivatives.
(19) Parkin, G.; van Asselt, A.; Leahy, D. J.; Whinnery, L.; Hua, N. G.;
Quan, R. W.; Henling, L. M.; Schaefer, W. P.; Santarsiero, B. D.; Bercaw,
J. E. Inorg. Chem. 1992, 31, 82.

Article
Inorganic Chemistry, Vol. 49, No. 10, 2010 4651
˚
Figure 3. Thermal ellipsoid drawing of 7. Selected bond lengths (A) and
angles (deg): Ta1-N1 1.8153(16); N1-N2 1.3358(22); Ta1-N1-N2
167.04(1). Summation of angles about N2: 358°. H atoms removed for
clarity.
bond, approaching more of TadN double bond. This inter-
mediate bond order is reflected in the Ta-N bond distance,
˚
which at 1.8153(16)A is longer than all other Ta-N triple
bonds which are reported here. Because of the low symmetry
of this molecule, it is difficult to determine the occupation
of the Ta-Cp antibonding orbital based on Ta-C bond
lengths. The Ta-NR-Nβ bond angle is bent out of the
tantalocene wedge to 167.04(1)°, which might also be indi-
cative of some TadN character with a stereochemically
active NR lone electron pair as shown in eq 3, but this distor-
tion from linearity might be due at least in part to steric inter-
actions between cyclopentadienyl ligands and the large
[NβPh2] group (closest non-bonded H-H contacts between
Figure 4. Thermal ellipsoid drawing of 8. Side view and view the Cl-Ta
bond showing C2-symmetric arrangement of the (ONO) ligand. Selected
bond lengths (A) and angles (deg): Ta1-O1 1.9762(8); Ta1-O2 1.9856(7);
Ta1-N1 2.246(1); Ta1-N2 1.7925(8); Ta1-N4 2.3598(8); N2-N3
1.355(1); Ta1-N2-N3 174.62(8). H atoms removed for clarity.
˚
˚
the [NβPh2] group and the Cp ring are 2.263 and2.426 A).
Again, the low symmetry makes distinguishing between
electronic and steric effects difficult.
H2NNPh2 yielded no reaction, likely because of the increased
steric bulk of diphenylhydrazine versus dimethylhydrazine. We
have previously reported that sterically bulky primary amines
t
(e.g., BuNH2) do not react with (ONO)Ta(NMe2)2Cl or
(ONO)TaMe3, whereas less bulky amines such as aniline do
react to form imides.20a
Recently, our group has been interested in using aryl-
linked bis(phenolate) ligand sets as analogues of bis(cyclo-
pentadienyl) scaffolds.20 Hydrazide-containing tantalum
bis(phenolate) complexes have been synthesized through
two methods. First, the salt metathesis reaction of 1 with
(2,6-(OC6H2-tBu2)2C5H3N)K2 in benzene in the presence of
excess pyridine led to quantitative formation (NMR) of
(ONO)TaCl(NNPh2)(py) (8) (ONO = (2,6-(OC6H2-tBu2)2-
C5H3N)) (eq 4). The addition of a sixth ligand (e.g., pyridine)
to these reactions is required: attempts to synthesize the rela-
ted 5-coordinate complexes without an additional L donor
always yielded intractable, insoluble product mixtures. Alter-
nately, the complex (ONO)TaCl(NNMe2)(HNMe2) (9) could
be synthesized through hydrazinolysis of (ONO)Ta(NMe2)2Cl
with H2NNMe2 (eq 5). Similar metathesis attempts with
Both 8 and 9 have been characterized by X-ray diffraction.
The former contains a meridionally bound bis(phenolate) ligand
with the diphenylhydrazide ligand trans to an additional mole-
cule of pyridine (Figure 4). Similar to complex 1, the hydrazido-
(2-) ligand forms an LX2 triple bond with tantalum, evidenced
(20) (a) Tonks, I. A.; Henling, L. M.; Day, M. W.; Bercaw, J. E. Inorg.
Chem. 2009, 48, 5096. (b) Agapie, T.; Bercaw, J. E. Organometallics 2007, 26,
2957–2959. (c) Agapie, T.; Day, M. W.; Bercaw, J. E. Organometallics 2008, 27,
6123–6142. (d) Agapie, T.; Henling, L. H.; DiPasquale, A. G.; Rheingold, A. L.;
Bercaw, J. E. Organometallics 2008, 27, 6245–6246. (e) Golisz, S. R.; Bercaw,
J. E. Macromolecules 2009, 42, 8751.
˚
from the Ta-N bond length of 1.7925(8) A and an essentially
linear Ta-NR-Nβ angle of 174.62(8)°. The NR-Nβ bond
˚
distance of 1.355(1) A is again shorter than that in free diphenyl-
hydrazine because of reduced NR-Nβ lone pair repulsion.

4652 Inorganic Chemistry, Vol. 49, No. 10, 2010
Tonks and Bercaw
˚
Figure 6. Thermal ellipsoid drawing of 10. Selected bond lengths (A)
and angles (deg): Ta1-N1 1.7988(1); Ta1-N3 2.0197(1); Ta1-N4
2.3815(1); Ta1-N5 2.0113(1); N1-N2 1.363(1); Ta1-N1-N2 177.42.
H atoms removed for clarity.
Mountford,5b,c,e Odom,6 and Gade7 have utilized tri-
dentate, dianionic bis(amido)amine/pyridine ligand sets to
explore the structure and reactivity of group 4 hydrazido(2-)
complexes. These compounds can act as catalysts for hydro-
hydrazination reactions or as catalysts for a unique alkyne
bis-amination reaction. We sought to make analogous
cationic group 5 complexes, envisioning that the increa-
sed Lewis acidity of a cationic Ta center would promote
reactivity.
Figure 5. Thermal ellipsoid drawing of 9. Side view and view down the
Cl-T bond showing CS-symmetric arrangement of the (ONO) ligand.
˚
Selected bond lengths (A) and angles (deg): Ta1-O1 1.970(1); Ta1-
O2 1.968(1); Ta1-N1 2.303(1); Ta1-N2 1.789(1); Ta1-N4 2.443(1);
N2-N3 1.356(2); Ta1-N2-N3 175.2(1). H atoms (except for H on the
N4 amine) removed for clarity.
Reaction of 1 with MeN[(CH2)2NTMS)]2Li2 in benzene
produces the bis(amide)amine complex, (C2-N2NMe)TaCl-
(NNPh2) (10), inhigh yield (eq 6). The 1H NMR spectrum for
10 shows that the (C2-N2NMe) ligand is bound fac to Ta, as 4
non-equivalent protons for the methylenes of the backbone
of the ligand are observed as multiplets. Similar reaction of 1
with the propylene backbone ligand, MeN[(CH2)3NTMS)]2-
Li2, also produces the desired complex (C3-N2NMe)TaCl-
(NNPh2) (11), albeit in lower yield (eq 7). The methylene
backbone protons for 11 are much broader than in 10,
suggesting that the structure is fluxional at room tempera-
ture. Despite the ill-defined methylenes, 11 can be easily
Similar to 8, 9 contains a meridionally bound bis(pheno-
late) ligand with the dimethylhydrazido(2-) ligand trans to
the weakest trans influencing ligand HNMe2 (Figure 5). The
˚
short Ta-N distance of 1.789(1) A and linear Ta-NR-Nβ
angle of 175.2(1)° once again indicate a Ta-N triple bond for
the [TatN-NMe2] moiety. Complex 9 is the only dimethyl-
hydrazido(2-) complex that we have fully characterized and
provides a valuable structural contrast to 8, which contains
the same basic (ONO)TaLX(NR) framework. For 9 the
(ONO) ligand is bound in a CS-symmetric fashion, whereas
in 8 the ligand geometry is C2-symmetric. Given the close
similarity of the two complexes, we can only suggest that the
smaller methyl substituents of the dimethylhydrazido (2-)
complex 9 are able to accommodate the electronically pre-
ferred20a Cs-symmetric arrangement of (ONO), as is also
found in the corresponding phenyl imido derivative (ONO)-
Ta(HNMe2)Cl(ꢀNPh).20a The structure of 8 suggests that
the larger Nβ-phenyl groups would clash with the bulky tert-
butyl groups on the bis(phenolate) ligand such that the (ONO)
ligand twists to accommodate the less sterically hindered C2-
symmetric (ONO) geometry for the diphenylhydrazido com-
plex. The geometry about Nβ also generates greater steric
crowding for the diphenylhydrazido (2-) complex 8: while the
Ta-NR and NR-Nβ bonding metrics are roughly the same in 8
and 9, the geometry about Nβ is different in the two complexes.
In 8 (as in 1, and other diphenylhydrazido complexes), Nβ is
almost planar with bond angles of approximately 117° for
NR-Nβ-Cipso and 123° for Cipso-Nβ-Cipso. In contrast, 9 Nβ
is pyramidal with all angles near 111°. This geometry change
could also influence the overall ligand geometry.
1
identified in the H NMR from the characteristic NNPh2
resonances, the N-Me resonance, and the slightly broadened
SiMe3 resonance.
Large orange crystals of 10 were grown by slow diffusion
of a concentrated hexane solution of 10 into TMS2O. Com-
plex10 is monomeric, 5-coordinate trigonal bipyramidal with
the (C2-N2NMe) ligand bound in fac- manneras predictedby
1H NMR (Figure 6). The diphenyhydrazido ligand, which is
trans to the tertiary amine of the (C2-N2NMe) ligand, has a
˚
Ta-N bond length of 1.7988(1)A and a Ta-NR-Nβ bond
angle of 177.4(1)°, consistent with the metrics of an LX2
Ta-N triple bond as is the case for the other hydrazido
complexes reported here.
Perhaps the most notable feature of 10 is the position of the
hydrazido ligand relative to the (C2-N2NMe) ligand. In the
Mountford5b,e group 4 analogues, the diphenylhydrazido
ligand is located in the equatorial plane of the trigonal
bipyramid, whereas in 10 it lies in an axial position. From
an orbital overlap perspective, thetrans isomer observed in 10
would seem to be favored because the hydrazide and the
two amides would then not compete for the same metal

Article
Inorganic Chemistry, Vol. 49, No. 10, 2010 4653
˚
Figure 8. Thermal ellipsoid drawing of 13. Selected bond lengths (A)
and angles (deg): Ta1-N1 2.379(3); Ta1-N2 2.055(3); Ta1-N3 2.047(3);
Ta1-N4 2.314(4); Ta1-N5 2.280(4); Ta1-N6 1.762(3); N6-N7
1.402(4); Ta1-N6-N7 177.6(3). H atoms and BArF24 counteranion
removed for clarity.
Scheme 2
Figure 7. Thermal ellipsoid drawing of 11. Side view and top-down view
showing cis-fused decalin-type metallacycle structure. Selected bond
˚
lengths (A) and angles (deg): Ta1-N1 2.004(1); Ta1-N2 2.328(1);
Ta1-N3 2.006(1); Ta1-N4 1.791(1); N4-N5 1.374(2); Ta1-N4-N5
163.75(9). H atoms removed for clarity.
d π orbitals. Additionally, the strong trans influencing imido
should prefer to be opposite the very weakly trans influencing
tertiary amine. Because all of Mountford’s imido and hydra-
zido complexes have a cis conformation, this structure might
well require further investigation.
significantly bent compared to other Ta-NNPh2 complexes.
This bending could be caused by steric repulsion from one of
the SiMe3 groups also located in the equatorial plane. When
complex 10 was treated with Naþ[BArF24]- ([BArF24]- =
[B(3,5-(CF3)2C6H3)4]-) in CH2Cl2 in the presence of excess
pyridine, the cationic chloride-abstracted product [(C2-N2-
N
Me)Ta(NNPh2)(py)][BArF24] (12) was generated with con-
comitant precipitation of NaCl (Scheme 2). Without the
presence of pyridine, or in the presence of a weaker ligand
such as 2,6-lutidine, PPh3, or perfluoropyridine, reaction
with NaBArF24 led to fast decomposition after chloride
1
abstraction. Complex 12 has been identified by HNMR
and 13CNMR and is consistent with the coordination of one
molecule of pyridine to a cationic (C2-N2NMe)Ta(NNPh2)
fragment with [BArF24]- as the counteranion.
Attempts to carry out pyridine substitution reactions with
a variety of ligands (e.g., 4-tert-butyl pyridine, PPh3, THF),
as well as attempted and [2 þ 2] reactions with terminal and
internal alkynes resulted in no reaction. The inertness of 12
was unexpected, particularly considering that it is isoelec-
tronic with analogous neutral, group 4 imido complexes.
Attempts to crystallize 12 have instead yielded the bis-
(pyridine) adduct, [(C2-N2NMe)Ta(NNPh2)(py)2][BArF24]
(13), along with significant amounts of intractable noncrys-
talline solids (Scheme 2). Addition of 1 equiv of pyridine in
11 was crystallized by diffusion of pentane into a concen-
trated solution of 11 in CH2Cl2. 11 is a C1-symmetric mole-
cule with a fac-coordinated (C3-N2NMe) ligand that resem-
bles a cis-fused decalin bicyclic ring structure (Figure 7).
Unlike 10 and similar to the complexes observed by Mount-
ford and Gade, 11 contains a diphenylhydrazido ligand
roughly cis to the amine in the (C3-N2NMe) ligand. The
˚
Ta-N distance of 1.791(1) A is consistent with triple
bond, although the Ta-NR-Nβ bond angle (163.75(9)°) is

4654 Inorganic Chemistry, Vol. 49, No. 10, 2010
Tonks and Bercaw
the reaction of 10 with NaBArF24 yields 100% conversion to
12 (1H NMR), so we are confident that 12 is the major
product upon chloride abstraction rather than the crystal-
lographically observed 13. Additionally, elemental analysis
of 12 is consistent with a mono(pyridine) rather than a
bis(pyridine) adduct. Similar reaction with 4-tBu-pyridine
CaH2 and filtered through a plug of activated alumina. 1H and
13C spectra were recorded on Varian Mercury 300 or Varian
INOVA 500 spectrometers, and chemical shifts are reported
with respect to residual protio-solvent impurity for 1H (s, 7.16
ppm for C6D5H; t, 5.32 ppm for CDHCl2) and solvent carbons
for 13C (t, 128.39 for C6H6; p, 54.00 for CD2Cl2). It was difficult
to obtain satisfactory CHN combustion analysis for some of the
compounds prepared. For these compounds, spectroscopic data
is available in the Supporting Information.
t
gives an adduct with a 9:18 integration ratio of Bu:SiMe3
peaks in the 1H NMR, consistent with a product analogous
to12. As a result ofthis evidence, 13 is rather a decomposition
product of 12.
Computational Details. Density functional calculations were
carried out using Gaussian 03 Revision D.01.24 Calculations
were performed using the nonlocal exchange correction by
Becke25,26 and nonlocal correlation corrections by Perdew,27
as implemented using the b3lyp28,29 keyword in Gaussian.
The following basis sets were used: LANL2DZ30-32 for
Ta atoms and 6-31G** basis set for all other atoms. Pseudo-
potentials were utilized for Ta atoms using the LANL2DZ ECP.
All optimized structures were verified using frequency cal-
culations and did not contain any imaginary frequencies. Iso-
surface plots were made using the Gaussian 03 Revision D.01
program.24
Complex 13 contains a meridionally bound (C2-N2NMe
)
ligand with the diphenylhydrazido moiety trans to the
amine of the (C2-N2NMe) ligand and the two coordinated
pyridine molecules mutually trans (Figure 8). The Ta-N LX2
triple bond distance is 1.762(3), slightly shorter than in
10 as would be expected for a tantalum cation, and the
Ta-NR-Nβ bond angle is 177.6(3)°.
Conclusions
X-ray Crystal Data: General Procedure. Crystals were remo-
ved quickly from a scintillation vial to a microscope slide coated
with Paratone N oil. Samples were selected and mounted on a
glass fiber with Paratone N oil. Data collection was carried out
The complexes (dme)MCl3(NNPh2) (M = Ta, 1; Nb, 2)
have been prepared from MCl5 and diphenylhydrazine via a
Lewis-acid assisted dehydrohalogenation reaction. Complex
1 is blue whereas related imidos are colorless or yellow. This
color arises from an LMCT from a Ta-hydrazide π-bonding
HOMO that is destabilized because of an antibonding inter-
action with the lone pair of the hydrazido Nβ. Complex 1
has been shown to be a versatile synthon for installing
a [TadNNPh2] moiety into a variety of inorganic or organo-
metallic coordination complexes with other neutral, mono-
or dianionic ligand sets. The bonding metrics of all of the
reported [TadNNR2] complexes are consistent with LX2-
type Ta-N triple bonds based on short Ta-N distances and
mostly linear Ta-NR-Nβ bond angles. In an attempt to
generate cationic Ta analogues of reported group 4 hydrazi-
do complexes, a chloride abstraction for 10 was performed
with Naþ[BArF24]- to yield a pyridine adduct, cation, 12,
which is surprisingly inert to ligand substitution and [2 þ 2]
reactions with alkynes. We are currently further exploring the
reactivity of the tantalum-hydrazido moiety as it relates to
that for the analogous tantalum-imido complexes.
˚
on a Bruker KAPPA APEX II diffractometer with a 0.71073 A
MoKR source. The structures were solved by direct methods. All
non-hydrogen atoms were refined anisotropically. Some details
regarding refined data and cell parameters are available in
Tables 1 and 2.
Synthesis of (K2-CH3O(CH2)2OCH3)TaCl3(NNPh2) (1).
TaCl5 (500 mg, 1.4 mmol) and ZnCl2 (380 mg, 2.8 mmol) were
mixed in 10 mL of CH2Cl2 in an inert atmosphere glovebox.
Dimethoxyethane (0.25 mL) was added to the reaction mixture,
and the reaction stirred for 15 min, yielding a dark solution with
a white precipitate. The reaction was cooled to -30 °C and
1,1-diphenylhydrazine (230 μL, 258 mg, 1.4 mmol) and pyridine
(226 μL, 221 mg, 2.8 mmol) in 5 mL of CH2Cl2 was slowly added
to the reaction mixture. The initially orange solution slowly
turned deep blue and was left to stir overnight. The reaction was
then filtered to remove pyridinium-zinc chloride salts, CH2Cl2
was removed in vacuo, and the resulting blue solid was washed
with pentane and then was dissolved into 20 mL of benzene,
filtered, and lyophilized to yield 700 mg of 1 as a blue powder
(90%). Further purification was achieved by crystallization
Experimental Section
(24) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, Jr., J. A.; Vreven, T.; Kudin, K. N.;
Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.;
Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa,
J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li,
X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.;
Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.;
Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich,
S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.;
Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.;
Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz,
P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.;
Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson,
B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, revision
C.02; Gaussian, Inc.: Wallingford, CT, 2004.
(25) Becke, A. D. Phys. Rev. A: At., Mol., Opt. Phys. 1988, 38, 3098–3100.
(26) Becke, A. D. J. Chem. Phys. 1988, 88, 1053–1062.
(27) Perdew, J. P. Phys. Rev. B 1986, 33, 8800–8802.
(28) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785.
(29) Miehlich, B.; Savin, A.; Stoll, H.; Preuss, H. Chem. Phys. Lett. 1989,
157, 200.
(30) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270–283.
(31) Wadt, W. R.; Hay, P. J. J. Chem. Phys. 1985, 82, 284–298.
(32) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299–310.
General Considerations and Instrumentation. All air- and
moisture-sensitive compounds were manipulated using stan-
dard high vacuum and Schlenk techniques or manipulated in a
glovebox under a nitrogen atmosphere. Solvents for air- and
moisture-sensitive reactions were dried over sodium benzophe-
none ketyl and stored over titanocene where compatible or dried
by the method of Grubbs.21 Pyridine was dried over sodium and
distilled prior to use. TaCl5 was purchased from Strem Chemi-
cals and was sublimed prior to use. Diphenylhydrazine and
dimethylhydrazine were purchased from TCI and were distilled
from CaH2 and degassed prior to use. All other materials were
used as received. Naþ[BArF24]-,22 NaCp,23 and (2,6-(OC6H2-
tBu2)2C5H3N)K2
were prepared following literature proce-
20d
dures. Benzene-d6 was purchased from Cambridge Isotopes and
dried over sodium benzophenone ketyl, while methylene chlor-
ide-d2, also purchased from Cambridge Isotopes, was dried over
(21) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.
(22) Brookhart, M.; Grant, B.; Volpe, A. F., Jr. Organometallics 1992, 11,
3920.
(23) Panda, T. K.; Gamer, M. T.; Roesky, P. W. Organometallics 2003,
22, 877–878.

Article
Inorganic Chemistry, Vol. 49, No. 10, 2010 4655
Table 1. Crystal and Refinement Data for Complexes 1, 7, 8, and 9
1
7
8
9
empirical formula
formula weight
T (K)
C16H20N2O2Cl3Ta
559.64
100(2)
13.4839(6)
10.2768(4)
14.8254(7)
C22H20N2ClTa
528.80
100(2)
19.1261(8)
10.2503(4)
19.2383(8)
C50H58N4O2ClTa
963.40
100(2)
15.6102(8)
20.2128(10)
15.7963(8)
C37H56N4O2ClTa
805.26
100(2)
34.7022(12)
9.2582(3)
23.1835(9)
˚
a, A
˚
b, A
˚
c, A
R, deg
β, deg
γ, deg
volume, A
Z
108.079(2)
100.720(2)
113.066(3)
3
˚
1952.95(15)
4
3705.8(3)
8
4585.7(4)
4
7448.4(5)
8
crystal system
space group
dcalc, g/cm3
θ range, deg
μ, mm-1
monoclinic
P21/c
1.903
1.59 to 52.22
6.049
semi emp.
1.388
0.0285, 0.0362
monoclinic
P21/n
1.896
2.26 to 40.86
6.084
semi emp.
1.495
0.0271, 0.0400
monoclinic
P21/c
1.395
1.73 to 40.11
2.498
semi emp.
1.718
0.0250, 0.0380
orthorhombic
Pbcn
1.436
1.76 to 36.42
3.059
none
abs. correction
GOF
1.939
0.0401, 0.0439
R1, a wR2b [I > 2σ(I)]
P
P
P
P
a R1 = ||Fo| - |Fc||/ |Fo|. b wR2 = [ w(Fo2 - Fc2)2/ w(Fo2)2]1/2
.
Table 2. Crystal and Refinement Data for Complexes 10, 11, and 13
then dissolved into 10 mL of benzene, filtered, and then lyoph-
ilized to yield 2 as 220 mg (78%) of a dull green powder.
1HNMR (300 MHz, CD2Cl2) δ, ppm: 3.840 (s, 3H, OCH3);
3.944 (s, 3H, OCH3); 4.089 (s, 4H, OCH2); 7.166 (m, 2H, aryl);
7.454 (m, 8H, aryl). 13CNMR (125 MHz, CD2Cl2) δ, ppm:
63.22, 69.68, 72.08, 76.01 (CH3OCH2CH2OCH3); 120.90,
126.10, 129.70, 143.03 (aryl).
10
11
13
empirical
formula
formula
weight
C23H39N5-
Si2ClTa
658.17
C
25H43N5-
Si2ClTa
[C33H49N7Si2Ta]þ
[C32H12BF24
-
]
686.22
1644.15
T (K)
˚
˚
b, A
˚
c, A
100(2)
98(2)
100(2)
Synthesis of (py)2TaCl3(NNPh2) (3). 1 (72 mg, 0.13 mmol) was
dissolved in 1 mL of neat pyridine and stirred overnight. The
reaction quickly turned very dark green/blue. After 16 h, the
reaction was filtered and solvent removed in vacuo to give 3
quantitatively as a dark teal solid. 1HNMR (500 MHz, CD2Cl2)
δ, ppm: 7.02 (m, 2H, aryl); 7.35 (m, 8H, aryl); 7.48 (m, 6H,
pyridyl); 7.86 (t, 1H, pyridyl); 7.95 (t, 1H, pyridyl); 8.64 (d, 2H,
pyridyl); 9.07 (d, 2H, pyridyl). 13CNMR (125 MHz, CD2Cl2) δ,
ppm: 121.09, 124.87, 125.17, 125.46, 129.23, 139.85, 140.58,
143.17, 152.42, 152.75 (aryl).
a, A
13.1052(6)
12.9574(6)
16.9529(8)
8.1959(4)
10.4496(5)
34.5115(14)
22.0650(16)
13.9417(10)
24.4542(16)
R, deg
β, deg
γ, deg
volume, A
Z
90.622(3)
94.059(2)
114.312(4)
3
˚
2878.6(2)
4
monoclinic
P21/n
1.519
2948.3(2)
4
monoclinic
P21/n
1.546
6855.6(8)
4
monoclinic
P21/n
1.593
1.62 to 27.70
1.750
semi emp.
1.652
crystal system
space group
dcalc, g/cm3
θ range, deg
μ, mm-1
Synthesis of (tmeda)TaCl3(NNPh2) (4). 1 (60 mg, 0.1 mmol)
was dissolved in 1 mL of neat TMEDA. The reaction turned
dark blue and was stirred overnight. The reaction mixture was
filtered and solvent removed in vacuo to give 4 as a dark blue
solid (52 mg, 90%). 1HNMR (500 MHz, CD2Cl2) δ, ppm: 2.571
(s, 12H, N(CH3)2); 2.705 (s, 4H, NCH2); 6.604 (m, 2H, aryl);
7.254 (m, 8H, aryl). 13CNMR (125 MHz, CD2Cl2) δ, ppm: 48.08
(NCH3); 57.37 (NCH2); 118.14, 121.27, 124.88, 143.78 (aryl).
Synthesis of (bpy)TaCl3(NNPh2) (5). 1 (28 mg, 0.05 mmol,
1eq) in 2 mL of C6H6 was added to solid 2,20-bipyridine (78 mg,
0.5 mmol, 10 equiv) and stirred overnight. The reaction slowly
turned green. After 16 h, the reaction was filtered, solvent
removed in vacuo, and the remaining green residue was washed
successively with 35 mL portions of pentane to give 5 as a green
1.95 to 43.76 2.04 to 38.82
4.014
3.922
semi emp.
1.754
0.0235, 0.0341 0.0387,
0.0666
abs. correction semi emp.
GOF
2.205
0.0285,
R1, a wR2
b
[I > 2σ(I)]
0.0506
P
P
P
P
a R1 = ||Fo| - |Fc||/ |Fo|. b wR2 = [ w(Fo2 - Fc2)2/ w(Fo2)2]1/2
.
through vapor diffusion of pentane into a concentrated dichlo-
roethane solution of 1, yielding 1 as blue/royal blue dichroic
needles. 1HNMR (300 MHz, CD2Cl2) δ, ppm: 3.985 (s, 3H,
OCH3); 4.023 (s, 3H, OCH3); 4.136 (m, 2H, OCH2); 4.152 (m,
2H, OCH2); 7.05 (m, 2H, aryl); 7.425 (m, 8H, aryl). 13CNMR
(125 MHz, CD2Cl2) δ, ppm: 63.71, 70.91, 72.31, 76.45 (CH3-
OCH2CH2OCH3); 105.33, 120.86, 125.05, 129.35 (aryl). Calcd
for C16H20Cl3N2O2Ta: C 34.34, H 3.60, N 5.01; Found: C 34.57,
H 3.66, N 4.99%.
1
solid. HNMR (300 MHz, CD2Cl2) δ, ppm: 7.04(t, 2H, aryl);
7.39 (m, 4H, aryl); 7.50 (t, 1H, bpy); 7.58 (d, 4H, aryl); 7.90 (t,
1H, bpy); 8.23 (m, 2H, bpy); 8.31 (m, 2H, bpy); 9.08 (d, 1H, bpy);
9.69 (d, 1H, bpy).
Synthesis of (K2-CH3O(CH2)2OCH3)NbCl3(NNPh2) (2).
NbCl5 (160 mg, 0.6 mmol) and ZnCl2 (162 mg, 1.2 mmol) were
mixed in 10 mL of CH2Cl2 in an inert atmosphere glovebox.
Dimethoxyethane (0.2 mL) was added to the reaction mixture
and stirred for 15 min, yielding a dark solution with a yellowish
precipitate. The reaction was cooled to -30 °C, and 1,1-diphe-
nylhydrazine (110 mg, 0.6 mmol) and pyridine (94 mg, 96 μL,
1.2 mmol) in 2 mL of CH2Cl2 were slowly added to the reaction
mixture. The mixture turned dark blue/green, and was left to stir
overnight, during which period it turned dark green with a white
precipitate. The reaction was then filtered, and CH2Cl2 removed
in vacuo. The resulting green residue was washed with pentane,
Synthesis of (THF)2TaCl3(NNPh2) (6). 1 (20 mg, 0.036 mmol)
was dissolved in 2 mL of THF and stirred for 20 min. The
reaction mixture turned from blue to purple, and solvent was
removed in vacuo to yield 6 and some decomposition products. 6
is not stable in solution which precludes its pure isolation, but
can quickly be characterized by 1HNMR. 1HNMR (300 MHz,
CD2Cl2) δ, ppm: 1.95 (br, 8H, CH2CH2O); 4.20 (br, 8H,
CH2CH2O); 7.02 (m, 2H, aryl); 7.39 (m, 8H, aryl).
Synthesis of Cp2TaCl(NNPh2) (7). Solid 1 (91 mg, 0.163
mmol) and NaCp (28.4 mg, 0.326 mmol) were placed in a
50 mL round-bottom flask fitted with a needle valve and

4656 Inorganic Chemistry, Vol. 49, No. 10, 2010
Tonks and Bercaw
evacuated on a high vacuum line. A 20 mL portion of tetra-
hydrofuran (THF) was distilled onto the mixture at -78 °C,
then the reaction mixture was warmed to room temperature and
stirred overnight. Afterward, the reaction mixture was filtered,
solvent removed in vacuo, and the resulting red residue was
extracted into 20 mL of toluene. Removal of the toluene in
vacuo yielded 60 mg (70% yield) of 7 as an orange/red solid.
Further purification could be obtained by layering pentane onto
a concentrated, -30 °C solution of 7 in toluene which gave high
yields of orange, X-ray quality crystals of 7 upon cooling the
system to -30 °C. 1HNMR (300 MHz, CD2Cl2) δ, ppm: 5.990
(s, 10H, C5H5); 7.064 (m, 2H, aryl); 7.356 (m, 8H, aryl).
13CNMR (125 MHz, C6D6) δ, ppm: 110.09 (C5H5); 121.47,
124.36, 129.67, 145.46 (aryl).
Synthesis of (2,6-(OC6H2-tBu2)2C5H3N)TaCl(NNPh2)(py) (8).
(ONO)H2 (194.5 mg, 0.4 mmol) was deprotonated with KBn
(104.2 mg, 0.8 mmol) in 10 mL of C6H6 over the course of 2 h in
an inert atmosphere glovebox. After 2 h, (dme)TaCl3(NNPh2)
(244 mg, 0.4 mmol) and pyridine (31.6 mg, 0.4 mmol) in 10 mL
of C6H6 were added to the reaction mixture. The reaction was
stirred for 24 h, filtered, and solvent removed in vacuo. The
resulting orange residue was washed with pentane, yielding 8 as
350 mg (91%) of a yellow/orange solid. Yellow/orange crystals
suitable for X-ray diffraction were obtained through pentane
vapor diffusion into a concentrated CH2Cl2 solution. 1HNMR
(300 MHz, CD2Cl2) δ, ppm: 1.28 (s, 18H, C(CH3)3); 1.42 (s,
18H, C(CH3)3); 6.87 (m, 8H, aryl); 7.03 (m, 4H, aryl); 7.20 (s,
2H, aryl); 7.38 (s, 2H, aryl) 7.49 (t, 1H, pyridyl); 7.69 (d, 2H,
pyridyl); 7.91 (t, 1H, pyridyl); 8.30 (d, 2H, pyridyl). 13CNMR
(125 MHz, C6D6) δ, ppm: 30.40 (C(CH3)3); 31.91 (C(CH3)3);
34.66 (C(CH3)3); 35.58 (C(CH3)3); 120.12, 122.96, 123.69,
124.10, 124.63, 125.80, 126.79, 128.85, 136.85, 138.53, 138.86,
141.39, 145.21, 150.53, 155.55, 159.17 (aryl).
57.54 (NCH2CH2); 119.83, 122.19, 128.84, 144.10. Calcd for
C23H39ClN5Si2Ta: C 41.97, H 5.97, N 10.64; Found: C 42.49, H
6.43, N 9.99%.
Synthesis of (K3-MeN[(CH2)3NTMS)]2)TaCl(NNPh2) (11).
MeN[(CH2)3NTMS)]2Li2 (94.3 mg, 0.313 mmol) and (dme)-
TaCl3(NNPh2) (175 mg, 0.313 mmol) were mixed in 10 mL of
C6H6 in an inert atmosphere glovebox. The reaction quickly
turned from dark blue to deep orange/red, and was left to stir
overnight. The reaction was filtered and solvent removed in
vacuo, and the resulting orange residue was washed with
pentane. 11 was crystallized by vapor diffusion of pentane into
a concentrated solution of 11 in CH2Cl2, yielding 40% as
orange/red crystals. 1HNMR (300 MHz, CD2Cl2) δ, ppm:
0.172 (br s, 18H, NSi(CH3)3); 1.654 (br m, 4H, -CH2CH2-
CH2-); 2.853 (s, 3H, NCH3); 3.446 (br m, 8H, -CH2CH2-
CH2-); 6.962 (m, 2H, aryl); 7.315 (m, 8H, aryl). 13CNMR (125
MHz, C6D6) δ, ppm: 1.07 (Si(CH3)3); 27.85 (-CH2-); 53.18
(NCH3); 120.70, 123.37, 129.27, 146.29 (aryl). Calcd for
C25H43ClN5Si2Ta: C 43.76, H 6.32, N 10.21; Found: C 42.50,
H 6.49, N 9.99%.
Synthesis of [(K3-MeN[(CH2)2NTMS)]2)Ta(py)(NNPh2)][B-
(3,5-(CF3)2C6H3)4] (12). 10 (160 mg, 0.243 mmol) and pyridine
(19.2 mg, 19.6 μL, 0.243 mmol) were premixed in an inert
atmosphere glovebox in 4 mL of CH2Cl2. The solution of 10
and pyridine was then added to solid Naþ[BArF24]- (215.5 mg,
0.243 mmol). The reaction mixture quickly turned from yellow
to orange as the Naþ[BArF24]- went into solution. The reaction
mixture was stirred for 30 min; then the solvent was removed in
vacuo. The dark orange residue was washed with pentane,
yielding 346 mg 12 (91%) as a dark orange/red solid. 1HNMR
(500 MHz, CD2Cl2) δ, ppm: 0.207 (s, 18H, Si(CH3)3); 2.035 (s,
3H, NCH3); 2.712 (m, 4H, NCH2CH2); 4.124 (m, 2H, NCH-
HCH2); 4.256 (m, 2H, NCHHCH2); 6.281 (d, 4H, o-C6H5);
6.801 (t, 2H, p-C6H5); 6.871 (m, 4H m-C6H5); 7.570 (s, 4H, p-
C6H3(CF3)2); 7.738 (s, 8H, o-C6H3(CF3)2); 8.205 (t, 1H, pyridyl);
8.831 (d, 2H, pyridyl); 8.950 (br, 2H, pyridyl). 13CNMR (125
MHz, C6D6) δ, ppm: Calcd for C60H56BF24N6Si2Ta: C 46.05, H
3.61, N 5.37; Found: C 46.22, H 3.56, N 5.44%.
Synthesis of (2,6-(OC6H2-tBu2)2C5H3N)TaCl(NNMe2)(HN-
Me2) (9). A 10 mL Schlenk tube fitted with a Teflon needle valve
was charged with (ONO)Ta(NMe2)2Cl (106 mg, 0.135 mmol),
H2NNMe2 (8.08 mg, 10.2 μL, 0.135 mmol), a stirbar, and 5 mL
of C6H6 in an inert atmosphere glovebox. The vessel was sealed
and placed in an oilbath preheated to 90 °C and left to stir for 3
days, where it turned orange/red. After 3 days, the solvent and
HNMe2 were removed in vacuo, and the yellow-orange residue
was washed with 20 mL of hexanes to yield 50 mg of 9 as a
yellow-orange powder (43%). 1HNMR (300 MHz, CD2Cl2) δ,
ppm: 1.344 (s, 18H, C(CH3)3); 1.489 (s, 18H, C(CH3)3); 1.905 (br
s, 6H, HN(CH3)2); 2.082 (s, 6H, NN(CH3)2); 2.433 (m, 1H,
HNMe2); 7.358 (d, 2H, aryl); 7.497 (d, 2H, aryl); 7.758 (d, 2H,
pyridyl); 8.009 (t, 1H, pyridyl). 13CNMR (125 MHz, C6D6) δ,
ppm: 30.48 (C(CH3)3); 31.94 (C(CH3)3); 34.84 (CMe3); 35.66
(CMe3); 38.57 (HN(CH3)2); 47.97 (NN(CH3)2); 124.33, 124.91,
126.42, 127.02, 128.85, 137.41, 141.95, 157.94, 158.92 (aryl).
Synthesis of (K3-MeN[(CH2)2NTMS)]2)TaCl(NNPh2) (10).
MeN[(CH2)2NTMS)]2Li2 (418 mg, 1.53 mmol) and (dme)Ta-
Cl3(NNPh2) (856 mg, 1.53 mmol) were mixed in 20 mL of C6H6
in an inert atmosphere glovebox. The reaction quickly turned
from dark blue to deep orange, and was left to stir overnight.
The reaction was filtered and the benzene lyophilized off, and
the orange residue was extracted into 60 mL of pentane. The
pentane was removed in vacuo to yield 720 mg (71%) of 10 as a
sticky orange solid. Cystals suitable for X-ray diffraction were
grown from vapor diffusion out of a concentrated hexanes
Acknowledgment. We thank Dr. Nilay Hazari (Yale) for
assistance with the DFT calculations. DFT calculations were
carried out using the Molecular Graphics and Computa-
tion Facility, College of Chemistry, University of California,
Berkeley, CA, with equipment support from NSF Grant CHE-
0233882. We acknowledge Dr. Jay Labinger and Professor
Harry Gray (Caltech) and Professor Lisa McElwee-White
(University of Florida) for fruitful discussions. We also thank
Lawrence Henling and Dr. Michael Day for assistance with the
X-ray studies. The Bruker KAPPA APEXII X-ray diffract-
ometer was purchased via an NSF CRIF:MU award to the
California Institute of Technology, CHE-0639094. This work
has been supported by USDOE Office of Basic Energy Sciences
(Grant DE-FG03-85ER13431).
Supporting Information Available: Tables of bond lengths,
angles, and anisotropic displacement parameters for the pre-
sented solid-state structures. X-ray crystallographic data files
(CIF) of compounds 1, 7, 8, 9, 10, 11, and 13. NMR spectra for
compounds with unsatisfactory CHN combustion analysis.
This material is available free of charge via the Internet at
http://pubs.acs.org. The crystallographic data for compounds
1 (CCDC 719414), 7 (CCDC 767430), 8 (CCDC 719322), 9
(CCDC 754732), 10 (CCDC 719036), 11 (CCDC 752439), and
13 (CCDC 739782) have been deposited with the Cambridge
Crystallographic Data Center and can be obtained by request-
ing the deposition numbers.
1
solution into TMS2O. HNMR (500 MHz, CD2Cl2) δ, ppm:
0.03 (s, 18H, NSi(CH3)3); 2.76 (s, 3H, NCH3); 2.79 (m, 2H -
CHHCH2-); 3.15 (m, 2H -CHHCH2-); 3.83 (m, 2H, -
CH2CHH-); 3.91 (m, 2H, -CH2CHH-); 6.90 (t, 2H, aryl);
7.26 (m, 4H, aryl); 7.45 (d, 4H, aryl). 13CNMR (125 MHz, C6D6)
δ, ppm: 1.834 (Si(CH3)3); 45.87 (NCH3); 49.59 (NCH2CH2);