Disubstituted 1,8-Diamidonaphthalene Ligands as a Flexible, Responsive, and Reactive Framework for Tantalum Complexes

Article abstract of DOI:10.1021/ic1003963

Deprotonated N,N'-disubstituted 1,8-diaminonaphthalenes (R ₂DAN^2-; R = (CH₃)₂CH, C ₆H₅, 3,5-Me₂C₆H₃) were incorporated into Ta(V) complexes employing two methods. The direct proton transfer reaction of the parent amine, 1,8-(RNH)₂C₁₀H ₆, with TaMe₃Cl₂ led to elimination of methane and formation of TaCl₃[1,8-(RN)₂C₁₀H ₆] (1, 2). Reaction of the dilithiated amido species, Li ₂R₂DAN, with TaMe₃Cl₂ or [Ta(NEt₂)₂Cl₃] yielded TaMe₃[1,8- (RN)₂C₁₀H₆] (3, 4) and TaCl(NEt ₂)₂[1,8-(RN)₂C₁₀H₆] (5, 6), respectively. X-ray structural studies of these complexes revealed the flexible coordination behavior of R₂DAN^2- by demonstrating that the ligand bonded to Ta with a coordination array dependent on the identity of the other ligands bonded to tantalum. Computational analysis of these complexes confirmed that the energetic components for binding of R ₂DAN^2- to these TaX₃²⁺ fragments were dominated by the electronic features of the metal fragment. Chemical transformations of the bound ligand were evaluated by reaction of compounds 5 and 6 with LiNMe₂ and MeLi. Simple metathesis products Ta(NEt ₂)₂NMe₂[1,8-(ⁱPrN)₂C ₁₀H₆] (R = ⁱPr 7, R = 3,5-Me₂(C ₆H₃) 8) were obtained from reactions with LiNMe ₂. In contrast, when the R group of the DAN ligand was ⁱPr, reaction with MeLi ultimately led to activation of the isopropyl group and formation of the metallaziridine [κ³-(Me ₂CN)(ⁱPrN)C₁₀H₆]Ta(NEt ₂)₂ (9) species via the elimination of methane.

Full text of DOI:10.1021/ic1003963

Inorg. Chem. 2010, 49, 5231–5240 5231
DOI: 10.1021/ic1003963
Disubstituted 1,8-Diamidonaphthalene Ligands as a Flexible, Responsive, and
Reactive Framework for Tantalum Complexes
Nathalie Lavoie,† Serge I. Gorelsky,† Zhixian Liu,† Tara J. Burchell,† Glenn P. A. Yap,‡ and Darrin S. Richeson*,†
†Department of Chemistry and the Center for Catalysis Research and Innovation, University of Ottawa, Ottawa,
‡
Ontario, Canada K1N 6N5, and Department of Chemistry and Biochemistry, University of Delaware, Newark,
Delaware 19716
Received February 26, 2010
Deprotonated N,N0-disubstituted 1,8-diaminonaphthalenes (R2DAN2-; R = (CH3)2CH, C6H5, 3,5-Me2C6H3) were
incorporated into Ta(V) complexes employing two methods. The direct proton transfer reaction of the parent amine,
1,8-(RNH)2C10H6, with TaMe3Cl2 led to elimination of methane and formation of TaCl3[1,8-(RN)2C10H6] (1, 2).
Reaction of the dilithiated amido species, Li2R2DAN, with TaMe3Cl2 or [Ta(NEt2)2Cl3 ] yielded TaMe3-
[1,8-(RN)2C10H6] (3, 4) and TaCl(NEt2)2[1,8-(RN)2C10H6] (5, 6), respectively. X-ray structural studies of these
complexes revealed the flexible coordination behavior of R2DAN2- by demonstrating that the ligand bonded to Ta with
a coordination array dependent on the identity of the other ligands bonded to tantalum. Computational analysis of
these complexes confirmed that the energetic components for binding of R2DAN2- to these TaX32þ fragments were
dominated by the electronic features of the metal fragment. Chemical transformations of the bound ligand were
evaluated by reaction of compounds 5 and 6 with LiNMe2 and MeLi. Simple metathesis products Ta(NEt2)2NMe2-
[1,8-(iPrN)2C10H6] (R = iPr 7, R = 3,5-Me2(C6H3) 8) were obtained from reactions with LiNMe2. In contrast, when the
R group of the DAN ligand was iPr, reaction with MeLi ultimately led to activation of the isopropyl group and formation of
the metallaziridine [κ3-(Me2CN)(iPrN)C10H6]Ta(NEt2)2 (9) species via the elimination of methane.
Introduction
of new ligands remains an important endeavor with the goal
of revealing both fundamental and applied impact of the
ligand in chemical transformation and catalysis. One of our
general interests, the design and implementation of rigid
chelating ligands with delocalized π-electrons, led us to
investigate the utilization of a family of diamido ligands,
{1,8-(RN)2C10H6}2- (A, R2DAN2-), in transition metal
complexes.3 In particular, we reported the reaction of
1,8-(iPrNH)2C10H6 with TaMe3Cl2 to produce an unusual
metallaaziridine complex, {[κ3-(Me2CN)(iPrN)C10H6]TaCl2}2
(B).3a This species apparently arose from a σ-bond metathesis
involving the ipso-CH function of the isopropyl substituents
of the diamidonaphthalene ligand and elimination of
methane from a Ta-Me function, yielding this novel triden-
tate trianionic ligand, [(Me2CN)(Me2CHN)C10H6]3-. We
now report on the elaboration of this chemistry along two
avenues. The first involves changing the N-substituents of the
{1,8-(RN)2C10H6}2- ligand in an effort to control the reac-
tivity of these groups when this scaffold is bonded to
tantalum. The second explores the influence on the bonding
and reactivity of the R2DAN2- through variation of the
remaining ligands bonded to Ta. Through these efforts we
Exploring ligand-metal bonding and the associated im-
pact on the stability and reactivity of metal complexes is a
central theme in inorganic and organometallic chemistry.
With d0, early transition metal complexes, amido ligands
have a well-established position, and the role of such species
in a host of small molecule transformations continues to
stimulate interest in this area.1,2 Expanding the investigation
*To whom correspondence should be addressed. E-mail: darrin@
uottawa.ca.
(1) (a) Decams, J. M.; Daniele, S.; Hubert-Pfalzgraf, G. L.; Vaissermann,
J.; Lecocq, S. Polyhedron 2001, 20, 2405. (b) Ketterer, A. N.; Fan, H.;
Blackmore, J. K.; Yang, X.; Ziller, W. J.; Baik, M.-H.; Heyduk, A. F. J. Am.
Chem. Soc. 2008, 130, 4364. (c) Ison, E. A.; Ortiz, C. O.; Abboud, K.; Boncella,
J. M. Organometallics 2005, 24, 6310. (d) Ketterer, A. N.; Ziller, W. J.;
Rheingold, L. A.; Heyduk, A. F. Organometallics 2007, 26, 5330. (e) Ison,
A. E.; Abboud, A. K.; Ghiviriga, I.; Boncella, J. M. Organometallics 2004, 23,
929. (f) Cameron, M. T.; Ghiviriga, I.; Abboud, A. K.; Boncella, J. M.
Organometallics 2001, 20, 4378. (g) Aoyagi, K.; Gantzel, K. P.; Kalai, K.;
Tilley, T. D. Organometallics 1996, 15, 923.
(2) For selected reviews see: (a) Britovsek, G. J. P.; Gibson, V. C.; Wass,
D. F. Angew. Chem., Int. Ed. 1999, 38, 428, and references therein.
(b) Arndtsen, B. A.; Bergman, R. G.; Mobley, T. A.; Peterson, T. H. Acc. Chem.
Res. 1995, 28, 154, and references therein.. (c) Berresford, D. J.; Bolm, C.;
Sharpless, K. B. Angew. Chem., Int. Ed. Engl. 1995, 34, 1059, and references
therein. (d) Negishi, E.; Takahashi, T. Acc. Chem. Res. 1994, 27, 124, and
references therein. (e) Tilley, T. D. Acc. Chem. Res. 1993, 26, 22, and references
therein.
(3) (a) Bazinet, P.; Yap, G. P. A.; Richeson, D. S. Organometallics 2001,
20, 4129. (b) Lavoie, N.; Ong, T. G.; Gorelsky, S. I.; Korobkov, I.; Yap, G. P. A.;
Richeson, D. S. Organometallics 2007, 26, 6586.
r
2010 American Chemical Society
Published on Web 05/14/2010
pubs.acs.org/IC

5232 Inorganic Chemistry, Vol. 49, No. 11, 2010
Lavoie et al.
Scheme 1
Table 1. Selected Crystal Data and Structure Refinement Parameters for TaCl3[1,8-(PhN)2C10H6] (1), TaMe3[1,8-(PhN)2C10H6] (3), TaNEt2Cl[1,8-(iPrN)2C10H6] (5), and
TaNEt3NMe[1,8-(iPrN)2C10H6] (7)
1
3
5
7
empirical formula
formula mass
temp (K)
C25H23Cl3N2Ta
638.75
203(2)
C25H25N2Ta
534.42
203(2)
0.71073
triclinic
10.5074(11)
10.5509(11)
11.9869(13)
96.708(2)
113.601(2)
113.073(2)
1059.64(19)
2
C24H40ClN4Ta
601.00
201(2)
0.71073
monoclinic
14.8426(12)
11.4911(9)
16.5518(13)
90
113.9450(10)
90
2580.1(4)
4
1.547
C26H46N5Ta
609.63
293(2)
0.71073
triclinic
10.5712(12)
10.6469(12)
14.3310(17)
74.850(2)
73.189(2)
65.1710(10)
1383.0(3)
2
ꢀ
˚
λ (A)
cryst syst
0.71073
triclinic
7.906(5)
12.406(8)
13.806(9)
70.028(7)
85.467(7)
78.172(7)
1245.7
ꢀ
˚
a (A)
ꢀ
˚
b (A)
ꢀ
˚
c (A)
R (deg)
β (deg)
γ (deg)
3
ꢀ
˚
V (A )
Z
2
1.703
4.748
F(calc) (Mg/m3)
1.675
5.198
1.464
3.995
μ (mm-1
)
4.381
semiempirical from equivalents
absorp corr
final R indices
[I > 2σ(I)]
a
R1
wR2
0.0581
0.1138
0.0372
0.1674
0.0367
0.0762
0.0446
0.1065
b
P
P
P
P
a R1 = ||Fo|-|Fc||/ |Fo|. b wR2 = ( w(|Fo|-|Fc|)2/ w(|Fo|2)1/2
.
demonstrate the versatility and flexibility of this ligand class
in bonding with metal centers, its responsiveness to the
electronic demands of the metal center, and conditions to
provoke reaction and CH activation.
Results and Discussion
Synthesis and Characterization of R2DAN2- Complexes
of Ta(V). The introduction of the dianionic 1,8-diamido-
naphthalene ligand, R2DAN2-, into the coordination
sphere of a metal complex can be achieved using two
complementary approaches. The first avenue involves the
direct reaction of the parent amine, 1,8-(RNH)2C10H6
(R2DANH2), with a metal complex possessing two basic
ligands that are capable of undergoing a proton transfer
reaction. Elimination of the metal-bound ligand results
in incorporation of dianion R2DAN2- into the metal
coordination sphere. A second method involves a two-
step process that first deprotonates R2DANH2 with
butyllithium to generate a dilithiated amido species,
Figure 1. Thermal ellipsoid plot showing the molecular structure and
partial atom numbering scheme for TaCl3[1,8-(PhN)2C10H6] (1). Ellip-
soids are drawn at 20% probability. Hydrogen atoms have been omitted
for clarity.
Li2R2DAN. A subsequent metathesis reaction between
this reagent and a dichloro metal complex would incor-
porate the R2DAN2- ligand onto the metal center along
with elimination of two equivalents of LiCl.

Article
Inorganic Chemistry, Vol. 49, No. 11, 2010 5233
Table 2. Selected Bond Lengths and Angles for TaCl3[1,8-(PhN)2C10H6] (1), TaMe3[1,8-(PhN)2C10H6] (3), TaNEt2Cl[1,8-(iPrN)2C10H6] (5), and TaNEt3NMe-
[1,8-(iPrN)2C10H6] (7)
ꢀ
˚
Bond Lengths (A)
1
3
5
7
Ta-N(1)
1.892(8)
1.931(9)
2.393(3)
2.396(3)
2.414(3)
1.432(12)
1.422(12)
1.445(12)
1.450(13)
Ta-N(1)
2.064(7)
1.954(7)
Ta(1)-N(1)
Ta(1)-N(2)
Ta(1)-N(3)
Ta(1)-N(4)
Ta(1)-Cl(1)
N(1)-C(1)
N(1)-C(11)
N(2)-C(9)
N(2)-C(14)
1.938(5)
2.084(5)
1.948(5)
1.965(5)
2.468(2)
1.443(8)
1.491(8)
1.391(8)
1.488(8)
N(1)-Ta(1)
N(2)-Ta(1)
N(4)-Ta(1)
N(5)-Ta
2.064(18)
2.04(3)
Ta-N(2)
Ta-N(2)
Ta-Cl(3)
Ta-Cl(2)
Ta-Cl(1)
N(2)-C(13)
N(2)-C(22)
N(1)-C(7)
N(1)-C(6)
Ta-C(23)
Ta-C(25)
Ta-C(24)
N(2)-C(22)
N(2)-C(13)
N(1)-C(7)
N(1)-C(6)
2.120(10)
2.153(11)
2.181(10)
1.397(10)
1.420(10)
1.430(9)
1.899(10)
1.987(10)
2.086(10)
1.405(15)
1.50(2)
N(3)-Ta
N(1)-C(1)
N(1)-C(11)
N(2)-C(10)
N(2)-C(14)
1.418(15)
1.45(3)
1.430(10)
Bond Angles (deg)
1
3
C(7)-N(1)-C(6)
C(7)-N(1)-Ta
C(6)-N(1)-Ta
C(22)-N(2)-C(13)
C(22)-N(2)-Ta
C(13)-N(2)-Ta
N(1)-Ta-N(2)
121.4(8)
136.1(7)
102.4(6)
123.8(9)
99.9(6)
C(7)-N(1)-C(6)
C(7)-N(1)-Ta
C(6)-N(1)-Ta
C(22)-N(2)-C(13)
C(22)-N(2)-Ta
C(13)-N(2)-Ta
N(2)-Ta-N(1)
114.8(7)
111.2(5)
133.4(5)
120.5(7)
135.7(6)
101.0(5)
87.4(3)
134.9(7)
85.3(4)
Bond Angles (deg)
5
7
C(1)-N(1)-C(11)
C(11)-N(1)-Ta(1)
C(1)-N(1)-Ta(1)
C(9)-N(2)-C(14)
C(9)-N(2)-Ta(1)
C(14)-N(2)-Ta(1)
N(1)-Ta(1)-N(2)
116.9(5)
110.3(4)
128.7(4)
118.9(5)
130.9(4)
109.8(4)
83.5(2)
C(1)-N(1)-C(11)
C(11)-N(1)-Ta(1)
C(1)-N(1)-Ta(1)
C(10)-N(2)-C(14)
C(14)-N(2)-Ta(1)
C(10)-N(2)-Ta(1)
N(2)-Ta(1)-N(1)
116.3(17)
108.1(10)
135.2(15)
117(2)
118.9(13)
123.8(16)
81.9(7)
We found that TaMe3Cl2 was a readily accessible
and functional starting material to demonstrate both
approaches. The direct reaction of the N,N0-diaryl-1,8-
diaminonaphthalene with TaMe3Cl2 produced two ana-
logous species TaCl3[1,8-(RN)2C10H6] (1 R=Ph; 2 R=
3,5-Me2C6H3) as red-brown powders in good yields
(Cl2-Ta-Cl3 = 169.0(1)°). The equatorial plane is de-
fined by the remaining chloride (Cl1) and the N1 and N2
P
centers of the R2DAN2- ligand ( angles=360°). The
two nitrogen centers (N1, N2) for the DAN ligand are
P
planar ( N angles 359.9° and 358.3°), and these planes
are coincident with the plane of the naphthyl group,
which aligns the lone pairs of electrons on these centers
for π overlap with their adjacent atoms. The Ta-N bond
1
(Scheme 1). The H NMR spectra for these compounds
provided the first indication for the formation of the sym-
metrical structures for 1 and 2 as represented in Scheme 1.
Specifically, the spectrum for 2 displayed a singlet, inte-
grating for the 12 protons, consistent with four equivalent
methyl groups on the N-Ar0 substituents. Furthermore,
the simple 13C NMR spectra for both 1 and 2 also sug-
gested a symmetrical structure for both species. Impor-
tantly, neither complex displayed spectroscopic indica-
tions of remaining Ta-Me functions, suggesting that the
reaction involved exchange of Cl and Me groups bonded
to tantalum during the reaction. This is an established
phenomenon.4
Details of the molecular connectivity and level of
aggregation for 1 were revealed through X-ray crystal-
lography (Table 1). These results are displayed in Figure 1
and summarized in Table 2. Examination of Figure 1
indicated that the coordination geometry for 1 is derived
from a distorted trigonal-bipyramidal ligand array with
two chloro ligands (Cl2 and Cl3) in the axial positions
˚
lengths in 1 average 1.91 A, while the Ta-Cl distances
˚
average 2.40 A. A distinctive feature of the coordination
of the diamidonaphthalene ligand to the Ta center is the
planar orientation of the naphthyl moiety and the plane
defined by N1-Ta-N2. While this is similar to our
observations with Ge(II)5 and our reported pnictogenium
cations,6 this observation differs significantly from the
previously reported tungsten3b and tin7 complexes bear-
ing this ligand. For example, in the W(VI) complex
W(dNtBu)2[1,8-(iPr N)2C10H6] the naphthyl moiety
and the N(1)-W(1)-N(2) plane exhibit a fold angle of
122.6°.
The starting material TaMe3Cl2 also represented an
excellent choice for investigating a second approach for
(5) Bazinet, P.; Yap, G. P. A.; Richeson, D. S. J. Am. Chem. Soc. 2001,
123, 11162.
(6) Spinney, H. S.; Korobkov, I.; DiLabio, G. A.; Yap, G. P. A.;
Richeson, D. S. Organometallics 2007, 26, 4972.
(7) Bazinet, P.; Yap, G. P. A.; DiLabio, G. A.; Richeson, D. S. Inorg.
Chem. 2005, 44, 4616.
(4) Fowles, G. W. A.; Rice, D. A.; Wilkins, J. D. J. Chem. Soc., Dalton
Trans. 1973, 961.

5234 Inorganic Chemistry, Vol. 49, No. 11, 2010
Lavoie et al.
introducing the R2DAN2- ligand (Scheme 1). The stoichio-
metric reaction of the in situ generated species (R2DAN2-)-
(Liþ)2 with one equivalent of TaMe3Cl2 led to the forma-
tion of TaMe3[1,8-(RN)2C10H6] (R = Ph 3; R =
3,5-Me2C6H3 4) as dark orange and red materials, re-
spectively. As with compounds 1 and 2, complexes 3 and 4
1
displayed simple H NMR spectra providing only one
singlet for the three Ta-bonded methyl groups. Although
this initially might suggest a symmetrical structure for 3,
structural analysis revealed nonequivalent methyl groups
(vide infra). Therefore, the simplicity of the NMR spectra
are likely a consequence of fluxionality of 3 and 4 on the
1
NMR time scale. Finally, neither the H nor 13C NMR
spectra indicated evidence of an R-agostic interaction of
the Ta-Me groups.
Single crystals suitable for X-ray analysis where obtai-
ned for 3 from cooled solutions in diethyl ether (Table 1).
These results, summarized in Figure 2 and Table 2, not
only establish the connectivity for this compound but
allow for comparison of this trimethyl species with the
trichloro complex 1. Similar to compound 1, the Ta center
of 3 resides in a distorted trigonal-bipyramidal coordina-
tion geometry. However, several key structural features
of 3 contrast with those of 1. Notably, in 3 the three
methyl moieties are coordinated in a facial array and the
DAN ligand is bonded to Ta through axial and equatorial
sites, leading to the pseudoaxial positions being defined
by a methyl group and one of the nitrogen centers of the
DAN ligand (C24-Ta-N1=159.2(4)°). The equatorial
positions are occupied by the remaining two methyl
groups (C23, C25) and the second N center (N2) of the
R2DAN2- ligand. The Ta-N bond lengths in 3 are
Figure 2. Thermal ellipsoid plot showing the molecular structure and
partial atom-numbering scheme for TaMe3[1,8-(PhN)2C10H6] (3). Ellip-
soids are drawn at 20% probability. Hydrogen atoms have been omitted
for clarity.
naphthyl moiety and the N1-Ta-N2 plane is 61.4°. This
feature is reminiscent of the reported tungsten3b and tin7
complexes with the R2DAN2- ligand. Furthermore, it is
similar to structural features that have been observed in
high-valent group 4,1g Ta,8,9 Mo,10 and W11 species bear-
ing N,N0-bis(trialkylsilyl)-o-phenylene diamide (PDA)
ligands. In the case of the PDA complexes, the fold of
the ligand about the N-N vector has been attributed
to an increase in metal ligand interaction through a
π donation from the phenylene component of the ligand
into the metal orbitals.8,10 In order to better understand
the origin of these structural differences, we have exam-
ined 1 and 3 computationally, and the results of our
analysis are presented below.
Similarly versatile Ta starting materials are represented
by the two readily available Ta diethylamido species {Ta-
(NEt2)2Cl3}2 and the mononuclear analogue Ta(NEt2)2-
Cl3py).12 These species allow for further investigation of
the role of the tantalum ligand scaffold on R2DAN2-
bonding. Both of these starting complexes undergo me-
tathesis reactions with an equimolar ratio of Li2(R2DAN)
to yield the analogous products Ta[1,8-(RN)2C10H6]-
(NEt2)2Cl (R=(CH3)2CH 5, 3,5-Me2C6H3 6) (Scheme 2),
which were isolated as orange-red solids in 63% yield.
The structure of Ta(NEt2)Cl[1,8-(iPrN)C10H6] (5) was
initially proposed on the basis of the 1H NMR spectrum,
which displayed single sets of resonances for the two
diethyl amido groups and for two isopropyl groups on
the DAN ligand. Significantly, the NMR data indicated
that the ipso-CH signals of the isopropyl groups are intact
in compound 5 and that both the ethyl CH2 signals and
the ipso-CH signals appeared as broad signals. These
features point to two conclusions regarding 5. First, in
spite of the presence of basic amido sites within the
tantalum complex, there is no reaction of these Ta-NR2
groups with the isopropyl C-H bond. This contrasts
with the reported reaction of 1,8-(iPrNH)2C10H6 and
ꢀ
˚
slightly longer (∼0.1 A) than those observed for 1.
Furthermore the axial Ta-N bond length is, as antici-
ꢀ
˚
pated, slightly longer (Ta-N1 = 2.064(7) A) than the
ꢀ
˚
equatorial Ta-N2 bond at 1.954(7) A. One of the most
pronounced differences between the ligand binding in 3
compared to 1 is the orientation of the N-substituents
relative to the naphthyl plane. Importantly, while the two
N centers in the (PhN)2C10H62- ligand are planar with the
sums of the angle around N1 and N2 being 360.0° and
359.4°, it is quite clear that the ligand in 3 is not planar. It
is the relative orientation of the ligand components that
clearly differentiates the DAN ligands of 1 and 3. While
TaCl3[1,8-(PhN)2C10H6] (1) exhibited N planes that are
coplanar with the naphthyl group, in the trimethyl com-
plex 3, only the plane for N1 is aligned with the napthyl
moiety, while the N2 plane is almost perpendicular (77.2°)
to the naphthyl plane. This orients the phenyl group
bonded to N2 vertical to the ligand plane. As a result,
the ligand in 3 is not coordinated to the Ta center in a
planar fashion and the observed fold angle between the
(8) Aoyagi, K.; Gantzel, P. K.; Tilley, T. D. Polyhedron 1996, 15, 4299.
(9) Pindado, G. J.; Thornton-Pett, M.; Bochmann, M. J. Chem. Soc.,
Dalton Trans. 1998, 393.
(10) (a) Cameron, T. M.; Abboud, K. A.; Boncella, J. M. Chem. Commun.
2001, 1224. (b) Ortiz, C. G.; Abboud, K. A.; Boncella, J. M. Organometallics
1999, 18, 4253.
(11) (a) Cameron, T. M.; Ortiz, C. G.; Abboud, K. A.; Boncella, J. M.;
Baker, R. T.; Scott, B. L. Chem. Commun. 2000, 573. (b) Wang, S. Y. S.;
Vanderlende, D. D.; Abboud, K. A.; Boncella, J. M. Organometallics 1998, 17,
2628. (c) Wang, S. Y. S.; Abboud, K. A.; Boncella, J. M. J. Am. Chem. Soc. 1997,
119, 11990. (d) VanderLende, D. D.; Abboud, K. A.; Boncella, J. M. Organo-
metallics 1994, 13, 3378.
(12) Chao, Y.-W.; Wexler., P. A.; Wigley., D. E. Inorg. Chem. 1989, 28,
3860.

Article
Inorganic Chemistry, Vol. 49, No. 11, 2010 5235
Scheme 2
TaMe3Cl2, which involved the elimination of the isopropyl
C-H bond and a Ta-Me group with formation of the
metallaaziridine [(Me2CN)(Me2CHN)(C10H6)TaCl2]2.3a
Second, complex 5 appeared to be fluxional on the
NMR time scale at room temperature.
The connectivity of 5 was firmly established by X-ray
crystallography (Table 1), with the results summarized in
Figure 3 and Table 2. The Ta core is reminiscent of 3, and,
once again, the coordination geometry of the tantalum
center can be described as a distorted trigonal bipyrami-
dal with N(2) and Cl defining the axial positions
(N(2)-Ta(1)-Cl(1)=176.18(14)°). The sum of the angles
in the equatorial plane defined by N1, N3, and N4 is 360°.
The Ta-N1 and Ta-N2 bond lengths of 1.983(5) and
1a,3a
ꢀ
˚
2.084(5) A are comparable to reported complexes.
The Ta-NEt2 bond lengths are slightly shorter at
ꢀ
ꢀ
˚
˚
1.948(5) A (Ta-N3) and 1.965(5) A (Ta-N4). Within
the chelating {1,8-(iPrN)2C10H6}2- ligand, nitrogen cen-
ter N2 is planar, while N1 deviates very slightly from
Figure 3. Thermal ellipsoid plot showing the molecular structure and
partial atom-numbering scheme for Ta(NEt2)2Cl[1,8-(NiPr)2C10H6] (5).
Ellipsoids are drawn at 20% probability. Hydrogen atoms have been
omitted for clarity.
P
planarity ( angles N1= 355.9°). The plane of nitrogen
N2 approaches alignment with the naphthyl plane. How-
ever, the mean plane for the N1 nitrogen makes an angle
of 57° with the naphthyl plane. As a result, the isopropyl
substituent on N1 points away from the napthyl plane.
The overall coordination geometry and the relative or-
ientation of the DAN ligand in 5 are similar to those
observed in compound 3.
to the trimethyl compound 3 and the amido compound 5
were examined computationally using density functional
theory(DFT).13 Optimizations of [TaCl3(1,8-(PhN)2C10H6)]
(1), [TaMe3(1,8-(PhN)2C10H6)] (3), and Ta(NEt2)2Cl-
[1,8-(NiPr)2C10H6] (5) using the B3LYP functional14 with
a LANL2DZ basis set15 yielded computed structures that
were similar to the experimental X-ray structures of these
species in terms of metal coordination geometry, ligand
orientation, and bond distances, thus supporting this
approach. Our examination of these results begins with
a comparison of the electronic features of 1 and 3 and is
followed by inclusion of compound 5.
Computational Studies of Complexes 1, 3, and 5. The
fundamental electronic features that led to the observed
structural differences for the trichloro complex 1 compared
(13) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; 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.
In the case of compound 1 the computed structure
displayed an R2DAN2- ligand with a planar coordina-
tion, as observed experimentally. An electronic analysis
was first carried out by examination of the interaction of
the diamido ligand ((PhN)2C10H6)2- fragment orbitals
with those of the TaCl3 fragment.16 The key donor
2þ
orbitals of the ligand fragment are the four highest
(14) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. Lee, C.; Yang, W.; Parr,
R. G. Phys. Rev. B 1988, 37, 785.
(15) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299.

5236 Inorganic Chemistry, Vol. 49, No. 11, 2010
Lavoie et al.
this in turn leads to a reduced bond order between the
fragments of 2.10. The reduced donation is also reflected
by the higher NPA charge on the Ta center in 3 of þ1.97
au compared to 1.
From this orbital interaction analysis it is clear that the
degree of R2DAN2- donation and the ligand-metal frag-
ment bond order is lower for the trimethyl complex 3
compared to the trichloro complex 1. In order to deter-
mine the origin for these differences, the trimethyl com-
plex [TaMe3(1,8-(PhN)2C10H6)] (3) was examined with
two different structural models. Specifically, the energy of
the experimentally obtained structure for 3, with a facial
orientation of the Me groups, was compared to a model
structure in which, analogously to complex 1, positions of
the methyl ligands were in a meridional array and a planar
Ta-R2DAN is maintained.18 These two structures are
displayed in Figure 5 along with their relative electronic
energies. The relative energies for the two R2DAN2-
ligand fragments of these species are also included in this
figure. Interestingly, these results indicate that the planar
geometry for the R2DAN2- fragment is slightly lower in
energy (0.9 kcal mol-1) than the nonplanar orientation
that was observed in the experimental structure of 3.
More importantly, the electronic interaction energy be-
tween the R2DAN2- and TaMe32þ fragments is 40.9 kcal
mol-1 more negative (stable) for the planar ligand con-
figuration than for the nonplanar configuration. How-
ever, the overall electronic energy of the nonplanar
structure of 3 is 6.9 kcal mol-1 lower in energy than the
model structure with the planar ligand and meridional
methyl moieties.
Figure 4. Highest occupied fragment orbitals (HOFOs) for the
R2DAN2- ligand that participate in bonding with the TaCl32þ fragment
in complex1 (left) and with the Ta(CH3)32þ fragmentin complex3 (right).
The ligand-metal bond order and net electron donation as well as the
change in occupancy for each HOFO are given.
occupied fragment orbitals (HOFOs) shown in Figure 4.
The HOFO and HOFO-1 of the ligand participate in
π donation to the metal fragment, and HOFO-2 and
HOFO-3 participate in σ donation to the metal frag-
ment. The changes in the orbital populations upon the
formation of the complex are indicated by the percentage
values next to each HOFO in the figure. Since these ligand
orbitals are doubly occupied, charge donation from the
ligand orbitals to the TaCl32þ fragment can be evaluated.
For example, the π donation from the interaction of the
HOFO of the ligand with the unoccupied orbitals of the
These results directed our attention to the features that
stabilize the facial orientation of the methyl groups in
TaMe3 compared to the meridional chloro ligands in
2þ
2þ
TaCl3 fragment is 0.327 ꢀ 2 = 0.65 electron. Adding
TaCl32þ as the driving force for the determining the over-
contributions from all orbital interactions together, 1.88
electrons are donated from the R2DAN2- fragment to the
TaCl32þ fragment, giving a total bond order of 2.69. The
donation from the ligand reduces the NPA charge17 on Ta
in the TaCl32þ fragment from þ1.75 to þ1.54 au.
all structures of 3 and 1. A comparison of the energies for
the two orientations of the methyl substituents in TaMe3
2þ
revealed that the facial disposition, experimentally obser-
ved for 3, is 48.7 kcal mol-1 lower in energy than a
meridional orientation of these groups in the model
complex. The ultimate origin of this energy difference is
revealed by examining the electrostatic interactions with-
The optimization calculation for the trimethyl species
3 also reflected the orientation of the two amido moieties
and the nonplanar orientation of the R2DAN2- ligand
that was obtained from X-ray analysis. Again, the inter-
actions of the diamido fragment, ((PhN)2C10H6)2-, and
the metal fragment TaMe32þ were examined. The donor
HOFOs for the ligand orientation represented in complex
3 are shown in Figure 4, and the energies of these
fragment orbitals are similar to the orbital energies of
those in 1. The distortion from planarity changes the
nature of the HOFOs to a mixture of σ and π overlap with
the metal fragment. Again, the donor contribution from
each ligand fragment orbital is shown by the percentage
value of the change in electron population. Significant
reduction in donation from the HOFO and HOFO-2 are
the most important differences of 3 from 1. With the
nonplanar ligand orientation, the R2DAN2- fragment
donates only 1.31 electrons to the TaMe32þ fragment, and
2þ
in the TaMe3 fragment. The C atoms of the methyl
ligands in the TaMe3 fragment bear large negative
2þ
charges (from -0.97 to -1.02 au). The electrostatic repul-
sion between these negative moieties results in the mer-
idionally ligated TaMe32þ lying 30.5 kcal mol-1 higher in
energy than the facially ligated TaMe32þ fragment. This
electrostatic component appears to be the major contri-
butor to stabilizing the experimentally observed structure
of 3.
A
similar examination can be made for
[TaCl3(1,8-(PhN)2C10H6)], 1. In this case, the electronic
energy of a model structure of 1 with nonplanar
R2DAN2- and facial chloro groups is 12.4 kcal mol-1
higher in energy than that of the experimentally observed
structure. Similar to the TaMe32þ fragment, the meridio-
nal TaCl32þ fragment is 33.5 kcal mol-1 higher in energy
2þ
than the computed facially ligated TaCl3 fragment.
This indicates that the stabilizing energy for the observed
(16) Gorelsky, S. I.; Ghosh, S.; Solomon, E. I. J. Am. Chem. Soc. 2006,
128, 278. Gorelsky, S. I. AOMix software for molecular orbital analysis, www.
sg-chem.net.
(17) Reed, A. E.; Weinstock, R. B.; Weinhold, F. J. Chem. Phys. 1985,
83, 735.
(18) The atomic coordinates for the optimized structures are provided in
the Supporting Information.

Article
Inorganic Chemistry, Vol. 49, No. 11, 2010 5237
Figure 5. Comparison of the calculated energies for the experimental structure of 3 (I) and a model structure (II) for this compound. The hydrogen atoms
on the two structures are omitted for clarity. The largest energy differences between these two isomers are the electronic interaction (ΔEint) between the
TaMe32þ and R2DAN2- fragments and the relative energies between the two orientations of the TaMe32þ fragments given by ΔE(TaMe3). The difference in
energy between the two R2DAN2- fragments is given by ΔE(R2DAN). For reference, the charges on the Ta and Me centers are provided in red.
structure of 1 must originate from a different interaction
than for 3. In fact, the major stabilizing feature for comp-
lex 1 turns out to be the electronic interaction energy
between the R2DAN2- and TaCl32þ fragments. This inter-
action is 42.4 kcal mol-1 more negative for the planar ligand
configuration than for the nonplanar configuration and
arises from the stronger charge transfer interaction.
From these results we can conclude that the observed
geometries of 1 and 3 are dictated by the balance between
the energetics of the TaX32þ fragment and the TaX3-R2-
DAN interaction energy. The loss of energy in distorting
the DAN ligand from planarity is rather minor.
The similarity in the bonding array displayed by com-
pound 5, [Ta(NEt2)2Cl(1,8-(iPrN)2C10H6)], to trimethyl
compound 3 suggested that a similar electronic analysis of
5 should be carried out. Again the computed optimized
structure for 5 at the B3LYP/DGDZVP level of theory
was in accordance with the X-ray structure. The
R2DAN2- ligand fragment of 5 displayed a set of donor
HOFOs that correlated with the analogous fragment in 3.
The donation level of each of the ligand fragment frontier
orbitals to the Ta(NEt2)2Cl2þ fragment was very similar
to what we observed in 3 with a total donation of 1.33
electrons, a bond order of 2.1, and a resulting NPA charge
of þ1.95 for the Ta(V) ion. The energy of this nonplanar
ligand orientation is slightly higher than was observed for
the nonplanar orientation observed for compound 3 and
is 14.9 kcal mol-1 less stable than the planar R2DAN
ligand.
Calculations on a model structure of 5 with planar
R2DAN2- and mer-Ta(NEt2)2Cl ligand arrangement
gave an electronic energy that was 20.8 kcal mol-1 higher
in energy than that of the experimentally observed struc-
ture. As observed with 3, the energy required to reorga-
nize from the facial to the meridional Ta(NEt2)2Cl2þ
orientation is the dominant component for this increased
energy. This mer orientation was computed to be 53.1 kcal
mol-1 higher in energy than the fac-Ta(NEt2)2Cl2þ frag-
ment. Even though the planar R2DAN2- ligand would
provide a more stabilizing interaction energy, by 17.5 kcal
mol-1, with the Ta(NEt2)2Cl2þ fragment compared to the
nonplanar configuration, this is not adequate to over-
come the favored fac-Ta(NEt2)2Cl2þ configuration.
Overall, these computational results correlate with
experiment and demonstrate that the R2DAN2- ligand
bonding configuration and the corresponding donation
to the metal fragment is flexible. Significantly, the
R2DAN ligand-metal interactions respond to the de-
mands of the Ta(V) fragment, which in turn is largely
controlled by the nature of the ligands of the TaX3
fragment.
2þ
Reactivity and Transformations of Ta(NEt2)2Cl[1,8-
(NR)2C10H6] (R = iPr 5; R = 3,5-Me2(C6H3) 6). The
reactivity of compounds 5 and 6 provided an attractive
avenue for exploring the stability and bonding of the
R2DAN2- ligand coupled with the effects of metal co-
ordination environment. Specifically, substitution of the
chloro ligand of these species with both LiNMe2 and
LiMe was examined as summarized in Scheme 2. The
reaction of either 5 or 6 with LiNMe2 proceeded to intro-
duce the dimethyl amido group on the tantalum center
with elimination of LiCl and generation of compounds 7
1
and 8. The H and 13C NMR spectra of these reaction
products appear similar to the corresponding starting
materials with the addition, in each case, of resonances
corresponding to the incorporated dimethyl amido protons.
Suitable crystals for single-crystal X-ray diffraction
analysis of Ta(NEt2)2NMe2[1,8-(iPrN)2C10H6] (7) were
obtained from hexanes (Table 1). The results are sum-
marized in Figure 6 and Table 2. Most striking is the
similarity of 7 to the starting material 5 with the replace-
ment of a chloro group with a dimethylamido ligand. The
tantalum center remains in a distorted trigonal-bipyra-
midal coordination geometry with the R2DAN2- ligand
spanning axial/equatorial sites (N1-Ta-N3=172.1(5)°)
and with N2, N4, and N5 defining the equatorial plane
P
(
angles=360°). The nitrogen centers of the R2DAN2-
P
P
ligand are planar ( angles N1=359.6°,
angles N2=
359.7°). The plane of nitrogen N1 approaches alignment
with the naphthyl plane with the angle between these
planes being only 21°. On the other hand, the mean plane
for the N2 nitrogen makes an angle of 55° with the mean
naphthyl plane. The net result is an R2DAN2- ligand
geometry that is twisted and similar to that obtained in
compound 5.
A notable feature of 7 is that the iPr groups of the DAN
ligand remain intact in the formation of this compound.
There is no deprotonation of the ispo-CH group even in
the presence of three strongly basic amido ligands. This
contrasts with the documented reactivity of the methyl

5238 Inorganic Chemistry, Vol. 49, No. 11, 2010
Lavoie et al.
was a minor energy debt. Furthermore, the nonplanar ligand
did exhibit a lower R2DAN-TaX3 interaction energy, which
led to reduced electron donation from the ligand and dimin-
ished bond order between the ligand and Ta. In opposition to
these destabilizing features was a rather large energy con-
tribution favoring a facial arrangement of the ligands in the
TaX32þ fragments. Interestingly, the balance of these energy
terms demonstrated the flexibility of the R2DAN2- ligand in
bonding to a metal center and the responsiveness of this
2þ
donor speciesto the demands of the Ta(V) fragment, TaX3
,
which in turn was dictated by the nature of the groups
constituting this fragment.
Finally, the substitution reactions of the chloro ligand
in Ta(NEt2)2Cl[1,8-(iPrN)2C10H6] (5) provided a probe for
the σ-bond metathesis transformation of the Ta-NCHMe2
moiety into a metallaziridine κ2-(Me2CN)Ta. This conver-
sion was observed in the reaction of 5 with MeLi but not with
LiNMe2.
Figure 6. Thermal ellipsoid plot showing the molecular structure and
partial atom-numbering scheme of Ta(NEt2)2NMe2[1,8-(iPrN)2C10H6]
(7). Ellipsoids are drawn at 20% probability. Hydrogen atoms have been
omitted for clarity.
Experimental Section
General Methods. All manipulations were carried out either in
a nitrogen-filled drybox or under nitrogen using standard
Schlenk line techniques. Unless otherwise noted, solvents were
sparged with nitrogen and then dried by passage through a
column of activated alumina using an apparatus purchased
from Anhydrous Engineering. Deuterated benzene and methy-
lene chloride were dried by vacuum transfer from molecular
sieves. TaCl5 was purchased from Strem and used without
further purification. N,N-Diethyltrimethylsilylamine was pur-
chased from Aldrich and used without further purification.
1H NMR spectra were recorded at room temperature and run
on either a Bruker Avance 300 MHz or a Bruker 500 MHz
spectrometer with deuterated benzene or methylene chloride as
a solvent and internal standard. Elemental analyses were carried
out by Robertson Microlit Laboratories, Inc. (Madison, NJ) or
Midwest Microlab, LLC (Indianapolis, IN). Multiple attempts
to obtain microanalyses of compounds 1-4 were unsuccessful.
Samples of these compounds changed color from orange to
dark brown during overnight shipping. [Ta(NEt2)2Cl3],12 Ta-
(NEt2)2Cl3Py,12 1,8-(2,6-Me2C6H3NH)2C10H6,19 1,8-(NHiPr)2-
groups in TaMe3Cl2 with 1,8-(iPrNH)2C10H6, which
ultimately led to metallaziridine via deprotonation of
the isopropyl CH group.
These observations prompted our deployment of met-
hyllithium in a reaction with Ta(NEt2)2Cl[1,8-(iPrN)2-
C10H6] (5). The goal was to determine if this reaction
would proceed by simple metathetical substitution of the
chloro ligand with a methyl group or would involve
transformation of the isopropyl CH group. From this
reaction, an orange powder was obtained. Our previous
experience with the appearance of the 1H NMR spectrum
for the tridentate trianionic metallaziridine ligand (Me2CN)-
(Me2CHN)C10H6]3- allowed us to rapidly identify com-
pound 9 (Scheme 2) as the metallacyclic product. In
i
particular, the spectrum for 9 displayed one intact Pr
group, exhibiting a doublet for the methyl moieties, and
the methyl signals of the metallacycle appearing as a
singlet with an integration value of six hydrogens. The
remaining 1H and 13C NMR signals supported the structural
assignment for [(Me2CN)(Me2CHN)C10H6]Ta(NEt2)2 (9).
20
C10H6, and TaMe3Cl2 were prepared according to literature
methods.
Preparation of TaCl3[1,8-(Ph)2C10H6] (1). A dark brown
solution was formed after stirring 1,8-(C6H5NH)2C10H6 (0.191 g,
0.64 mmol) and TaMe3Cl2 (0.201 g, 0.65 mmol) in 10 mL of
diethyl ether under nitrogen for 24 h. Ether was removed under
vacuum from the reaction mixture, and the solid was extracted
with 4 mL of toluene. Addition of hexanes to this solution and
cooling to -20 °C gave red crystals (0.151 g, 39.6%) of com-
pound 1.
Conclusions
A set of N,N0-disubstituted 1,8-diaminonaphthalenes have
been employed in the preparation of a series of Ta(V) comp-
lexes with general formulas (R2DAN)TaX3. Characteriza-
tion of these complexes allowed an examination of the
influence of the R2DAN ligand substituents as well as the
influenceof theother ligands onthe structures and stability of
the tantalum complexes. The use of aromatic substituents
enabled the isolation of trichloro, trimethyl, and mixed bis-
(amido)/chloro Ta compounds with an analogous bis-
(amido)/chloro complex also being accessible with iPr ligand
substituents. While all of these species displayed distorted
trigonal-bipyramidal Ta coordination geometries, there were
significant differences in bonding of the R2DAN2- ligand
1H NMR (300 MHz, C6D6): δ 6.38 (d, 2H), 7.02 (m, 6H), 7.19
(m, 2H), 7.23(m, 2H), 7.80 (m, 4H). 13C NMR (300 MHz, C6D6):
δ 115.5 (CHAr), 125.6 (CAr), 126.6 (CAr), 127.3 (CHAr), 128.5
(CHAr), 129.2 (CHAr), 129.3 (CHAr), 132.9 (CAr), 134.2 (CHAr),
135.5 (CAr).
Preparation of TaCl3[1,8-(3,5-Me2C6H3N)2C10H6] (2). In a
nitrogen-filled glovebox, TaMe3Cl2 (0.243 g, 0.82 mmol) and
1,8-(3,5-Me2C6H3NH)2C10H6 (300 mg, 0.82 mmol) were dis-
solved in toluene, and the reaction mixture was allowed to stir
overnight at room temperature. The resulting red solution was
dried by vacuum evaporation of the reaction solvent. A brown
powder was obtained, which was dissolved in hexanes cooled to
-20 °C to give a red powder of 2 (269 mg, 51.0%).
2þ
to Ta and in the ligand orientation within the TaX3
fragments.
A DFT computational analysis and modeling of the inter-
action between the R2DAN2- and TaX32þ fragments revea-
led that the distortion of the R2DAN2- ligand from planarity
(19) Bazinet, P.; Ong, T. G.; O’Brien, S. J.; Lavoie, N.; Bell, E.; Yap,
G. P. A.; Korobkov, I.; Richeson, D. S. Organometallics 2007, 26, 2885.
(20) Juvinall, G. L. J. Am. Chem. Soc. 1964, 86, 4202.

Article
1H NMR (300 MHz, C6D6): δ 2.02 (s, 12H, CH3), 6.45 (s, 2H,
CHAr) 6.55 (s, 4H, CHAr), 7.18-7.27 (m, 4H, CHAr), 7.43
(d, 2H, CHAr). 13C NMR (500 MHz, CD2Cl2): δ 21.6 (CH3),
116.8 (CHAr), 117.4 (CHAr), 122.2 (CAr), 123.6 (CHAr), 126.5
(CAr), 126.6 (CHAr), 137.7 (CAr),139.5 (CHAr), 141.3 (CAr), 145.4
(CAr).
Inorganic Chemistry, Vol. 49, No. 11, 2010 5239
6.73 (br, 2H, Ar-H), 7.06-7.14 (br, 4H, Ar-H), 7.17-7.25
(m, 4H, Ar-H). 13C NMR (300 MHz, C6D6): δ 13.0 (NCH2CH3),
21.5 (CArCH3), 45.6 (NCH2CH3), 117.1 (CHAr), 117.5 (CAr),
123.8 (CAr), 125.7 (CHAr), 126.5 (CAr), 126.7 (CHAr), 127.5
(CHAr), 129.5 (CAr), 136.9 (CAr), 139.2 (CHAr). Anal. Calcd for
C34H44N4ClTa: C 56.32, H 6.12, N 7.73. Found: C 56.53, H
6.21, N 7.59.
Preparation of TaMe3[1,8-(Ph)2C10H6] (3). In a nitrogen-filled
glovebox, 1,8-(C6H5NH)2C10H6 (0.62 g, 2 mmol) was dissolved
in 5 mL of diethyl ether and cooled to -30 °C. To this solution
was added dropwise methyllithium (2.9 mL of a 1.4 M solution in
diethyl ether, 4.06 mmol). The reaction mixture was maintained
at -30 °C and stirred for 30 min. TaMe3Cl2 (0.59 g, 1 mmol),
which had been dissolved in 5 mL of diethyl ether, was then added
slowly to the reaction mixture. This mixture was allowed to stir
for 1 h at room temperature. After filtration, the resulting dark
red solution was cooled to -30 °C. Dark orange crystals of 3 were
obtained after several hours (0.31 g, 29%).
Preparation of Ta(NEt2)2NMe2[1,8-(NiPr)2C10H6] (7). In a
round-bottomed flask, compound 5 (0.18 g, 0.30 mmol) was
dissolved in 40 mL of diethyl ether. To this solution was added
LiNMe2 (0.015 g, 0.30 mmol), and the reaction mixture was
allowed to stir overnight. The reaction mixture was filtered, and
the solvent was removed under vacuum. Orange crystals of
7 (117 mg, 65.1%) were obtained by recrystallization from hex-
anes cooled to -20 °C.
1H NMR (300 MHz, C6D6): δ 0.90 (t, 12H, NCH2CH3), 1.26
(d, 12H, CH(CH3)2), 3.35 (s, 6H, NCH3), 3.39 (q, 4H, NCH2CH3),
3.68 (q, 4H, NCH2CH3), 4.16 (sept, 2H, CH(CH3)2), 6.96-6.99
(m, 2H, Ar-H), 7.34-7.38 (m, 4H, Ar-H). 13C NMR (300 MHz,
C6D6): δ 14.5 (NCH2CH3), 23.6 (CHCH3), 46.4 (NCH3), 48.6
(NCH2CH3), 51.6 (CH(CH3)2), 115.2 (CAr), 119.8 (CAr), 125.8
(CHAr), 128.8 (CHAr), 137.7 (CHAr), 147.7 (CAr). Anal. Calcd
for C32H42N5Ta: C 51.22, H 7.62, N 11.49. Found: C 50.74, H
7.27, N 11.15.
1H NMR (300 MHz, C6D6): δ 1.20 (s, 9H), 6.73 (m 2H), 6.95
(m, 4H), 7.06 (m, 2H), 7.18 (m, 6H), 7.24 (m, 2H). 13C NMR
(300 MHz, C6D6): δ 75.3 (CH3), 120.1 (CHAr), 123.9 (CHAr),
125.2 (CHAr), 125.8 (CHAr), 126.4 (CAr), 129.5 (CAr), 130.2
(CHAr), 137.0 (CAr), 143.1 (CAr), 146.4 (CHAr).
Preparation of TaMe3[1,8-(3,5-Me2C6H3N)2C10H6] (4). In a
round-bottom flask 1,8-(3,5-Me2C6H3NH)2C10H6 (300 mg,
0.82 mmol) was dissolved in diethyl ether at room temperature.
To this solution was added dropwise nBuLi (1.02 mL of 1.6 M
solution in ether, 1.6 mmol). The reaction mixture was allowed
to stir for 1 h. TaMe3Cl2 (0.243 g, 0.82 mmol) was then added
slowly to the reaction flask. The reaction mixture was then
stirred for an additional 3 h and filtered, and the solvent was
evaporated under vacuum to yield a brown solid. Compound 4
was purified by precipitation from toluene (208 mg, 89%).
1H NMR (300 MHz, C6D6): δ 1.24 (s, 9H, Me), 1.98 (s, 12H,
Me) 6.60 (s, 2H, CHAr), 6.80 (s, 4H, CHAr), 6.87 (d, 2H, CHAr),
7.15-7.27 (m, 4H, CHAr). 13C NMR (300 MHz, C6D6): δ 21.4
(CArCH3), 73.6 (TaCH3), 119.2 (CAr), 123.8 (CHAr), 123.9
(CHAr), 126.5 (CAr), 127.7 (CHAr), 127.8 (CHAr), 137.4 (CAr),
140.3 (CHAr), 144.4 (CAr), 144.7 (CAr).
Preparation of Ta(NEt2)2NMe2[1,8-(2,6-Me2C6H3N)2C10H6]
(8). In a round-bottom flask, compound 6 (0.765 g, 1.05 mmol)
was dissolved in 40 mL of diethyl ether. To this solution was
added LiNMe2 (0.057 g, 1.12 mmol), and the reaction mixture
was allowed to stir overnight. The reaction mixture was filtered,
and the solvent was removed under vacuum. Orange crystals of
8 (0.607 g, 78.8%) were obtained by recrystallization from
hexanes and THF.
1H NMR (300 MHz, C6D6): δ 0.64 (t, 12H, NCH2CH3), 2.15
(s, 12H, CArCH3), 3.01 (s, 6H, N(CH3)2), 3.31 (q, 4H, NCH2CH3),
3.81 (q, 4H, NCH2CH3), 6.58 (s, 4H, Ar-H), 6.71 (s, 4H, Ar-H),
7.14-7.30 (m, 4H, Ar-H). 13C NMR (300 MHz, C6D6): δ 14.4
(NCH2CH3), 21.7 (CArCH3), 46.1 (N(CH3)), 47.8 (NCH2CH3),
115.0 (CAr), 119.6 (CAr), 124.8 (CHAr), 124.9 (CAr), 125.2
(CHAr), 127.3 (CHAr), 128.2 (CAr), 137.9 (CAr), 138.6 (CHAr),
Preparation of Ta(NEt2)2Cl[1,8-(NiPr)2C10H6] (5). In a round-
bottom flask 1,8-(iPrNH)2C10H6 (0.50 g, 2.06 mmol) was dissolved
in diethyl ether at room temperature. To this solution was added
151.3 (CAr), 153.4 (CHAr). Anal. Calcd for [C36H50N5Ta]
2[THF]: C 60.19, H 7.58, N 7.98. Found: C 60.59, H 7.49,
N 8.24.
3
n
dropwise BuLi (2.58 mL of a 1.6 M solution in diethyl ether,
Preparation of η3-C10H6(Me2CN)(Me2CHN)Ta(NEt2)2 (9).
In a round-bottomed flask, compound 5 (469 mg, 0.78 mmol)
was dissolved in 30 mL of diethyl ether. To this solution
was added MeLi (0.49 mL of a 1.6 M solution in diethyl ether
(0.78 mmol)), and the reaction mixture was allowed to stir
overnight. The reaction mixture was filtered, and the solvent
was removed under vacuum to give an orange solid. Orange
crystals of 9 (224 mg, 50.8%) were obtained by recrystallization
from ether at -20 °C.
4.13 mmol). The reaction mixture was allowed to stir for 1 h.
[Ta(NEt2)2Cl3]2 (0.89 g, 1.03 mmol) was then added to the reaction
flask. This mixture was then allowed to stir overnight and filtered
through Celite, and the solvent was evaporated under vacuum. The
resulting orange solid was recrystallized from hexanes cooled to
-20 °C to yield 5 (0.782 g, 63.2%) as orange crystals.
1H NMR (300 MHz, C6D6): δ 0.88 (t, 12H, NCH2CH3), 1.25
(d, 12H, CH(CH3)2), 3.62-3.44 (br, 8H, NCH2CH3), 4.67-4.24
(br, 2H, CH(CH3)2), 6.75-7.14 (m, 2H, Ar-H), 7.26-7.47 (m,
4H, Ar-H). 13CNMR (300 MHz, C6D6): δ 13.8 (NCH2CH3),
21.7 (CHCH3), 45.8 (NCH2CH3), 50.4 (CH(CH3)2, 55.3 (CH-
(CH3)2, 113.6 (CAr), 119.5 (CAr), 124.3 (CAr), 126.1 (CHAr),
128.9 (CHAr), 137.2 (CHAr). Anal. Calcd for C24H40N4ClTa:
C 47.96, H 6.71, N 9.32 Found: C 47.69, H 6.43, N 9.16
Preparation of Ta(NEt2)2Cl[1,8-(3,5-Me2C6H3N)2C10H6] (6).
In a round-bottomed flask 1,8-(3,5-Me2C6H3NH)2C10H6 (0.5 g,
1.36 mmol) was dissolved in diethyl ether at room temperature.
To this solution was added dropwise nBuLi (1.71 mL of a 1.6 M
solution in diethyl ether, 2.7 mmol). The reaction mixture was
allowed to stir for 1 h. Ta(NEt2)2Cl3Py (0.697 g, 1.36 mmol) was
then added to the reaction flask. This mixture was then allowed
to stir overnight and filtered through Celite, and the solvent was
evaporated under vacuum. The resulting red solid was recrys-
tallized from hexanes cooled to -20 °C to yield 6 (612 mg,
62.5%).
1H NMR (300 MHz, C6D6): δ 0.83 (t, 12H, NCH2CH3), 1.57
(d,6H,CH(CH3)2),2.16(s,6H,C(CH3)2, 3.02 (br, 8H, NCH2CH3),
4.47 (sept, 1H, CH(CH3)2), 6.90-6.96 (m, 2H, Ar-H), 7.34-7.47
(m, 4H, Ar-H). 13C NMR (300 MHz, C6D6):
δ 16.7
(NCH2CH3), 21.8 (CH3), 27.4 (CH3), 42.6 (NCH2CH3), 52.6
(CH(CH3)2), 107.0 (CHAr), 109.1 (CHAr), 118.8 (CHAr), 125.3,
(CHAr), 126.3 (CHAr), 126.7 (CHAr), 128.7 (CAr), 129.9 (CAr),
139.1 (CAr), 145.3 (CAr). Anal. Calcd for C24H39N4Ta: C 51.06,
H 6.96, N 9.92. Found: C 50.93, H 6.84, N 9.84.
Computational Details
DFT calculations with the B3LYP functional were car-
ried out using the Gaussian 03 (revision D.01) suite of pro-
grams. Spin-restricted treatment was used for all closed-
shell species. The basis set LANL2DZ was employed.
Atomic charges were calculated by natural population
analysis (NPA) as implemented in Gaussian 03. Mayer
1H NMR (300 MHz, C6D6): δ 0.65 (t, 12H, NCH2CH3), 2.05
(12H, s, CArCH3), 3.60 (q, 8H, NCH2CH3), 6.57 (s, 2H, Ar-H),

5240 Inorganic Chemistry, Vol. 49, No. 11, 2010
Lavoie et al.
bond orders were obtained using the AOMix-L program.
The analysis of molecular orbitals (MOs) in terms of frag-
ment orbital (FO) contributions and calculations of the FO
overlap matrices and FO populations were carried out using
the AOMix-CDA program. The converged wave functions
were tested to confirm that they represent the true ground
state.
Acknowledgment. This work was supported by the NSERC
of Canada.
Supporting Information Available: Atomic coordinates for the
optimized experimental and model structures of 1, 3, and 5. Crystal-
lographic files (cif) for compounds 1, 3, 5, and 7. This material is
available free of charge via the Internet at http://pubs.acs.org.