Synthesis, structural characterization, and cyclometalation chemistry of tantalum terphenyl compounds

Article abstract of DOI:10.1021/acs.organomet.5b00158

The κ¹-m-terphenyl complex of tantalum, [ArTol₂]Ta(NMe₂)₃Cl ([ArTol₂] = 2,6-di-p-tolylphenyl), has been synthesized by the reaction of [Ta(NMe₂)₃Cl₂]₂ with two equivalents of [ArTol₂]Li. [ArTol₂]Ta(NMe₂)₃Cl provides access to a variety of monoalkyl compounds, [ArTol₂]Ta(NMe₂)₃R (R = Me, Et, Prⁿ, Buⁿ, and Np; Np = CH₂BuT), via the reactions with the corresponding RLi. In addition, the reaction of [Ta(NMe₂)₃Cl₂]₂ with excess [ArTol₂]Li affords the bis(terphenyl) complex, [ArTol₂]₂Ta(NMe₂)₃, while the reaction of [ArTol₂]Ta(NMe₂)₃Cl with LiBH₄ gives the borohydride complex, [ArTol₂]Ta(NMe₂)₃(κ²-BH₄). The dichloride compound, [ArTol₂]Ta(NMe₂)₂Cl₂, which is obtained via the reaction of [ArTol₂]Ta(NMe₂)₃Cl with Me₃SiCl, provides access to a series of dialkyl derivatives, [ArTol₂]Ta(NMe₂)₂R₂ (R = Me, Et, Prⁿ, Buⁿ, and Np), via the reactions with the corresponding RLi. The κ¹-m-terphenyl ligands in these complexes are susceptible to metalation. Thus, [ArTol₂]Ta(NMe₂)₃R eliminates RH to afford [κ²-ArTol,Tol′]Ta(NMe₂)₃ (Tol′ = C₆H₃Me), while [ArTol₂]Ta(NMe₂)₂Np₂ eliminates NpH to form [κ²-ArTol,Tol′]Ta(NMe₂)₂Np.

Full text of DOI:10.1021/acs.organomet.5b00158

Article
pubs.acs.org/Organometallics
Synthesis, Structural Characterization, and Cyclometalation
Chemistry of Tantalum Terphenyl Compounds
Aaron Sattler and Gerard Parkin*
Department of Chemistry, Columbia University, 3000 Broadway, MC 3115, New York, New York 10027, United States
*
S Supporting Information
1
Tol
2
ABSTRACT: The κ -m-terphenyl complex of tantalum, [Ar ]Ta-
(
Tol
2
NMe ) Cl ([Ar ] = 2,6-di-p-tolylphenyl), has been synthesized by
2 3
2
Tol
the reaction of [Ta(NMe ) Cl ] with two equivalents of [Ar ]Li.
2
3
2 2
Tol
2
[
Ar ]Ta(NMe ) Cl provides access to a variety of monoalkyl
2 3
2
Tol
n
n
compounds, [Ar ]Ta(NMe ) R (R = Me, Et, Pr , Bu , and Np; Np
2
3
t
=
CH Bu ), via the reactions with the corresponding RLi. In addition,
2
2
Tol
the reaction of [Ta(NMe ) Cl ] with excess [Ar ]Li affords the
2
3
2 2
2
Tol
bis(terphenyl) complex, [Ar ] Ta(NMe ) , while the reaction of
2
2 3
Tol
2
Tol
2
2
[
[
Ar ]Ta(NMe ) Cl with LiBH gives the borohydride complex, [Ar ]Ta(NMe ) (κ -BH ). The dichloride compound,
2 3 4 2 3 4
2 2
Tol
Tol
Ar ]Ta(NMe ) Cl , which is obtained via the reaction of [Ar ]Ta(NMe ) Cl with Me SiCl, provides access to a series of
2
2
2
2 3
3
Tol
2
n
n
1
dialkyl derivatives, [Ar ]Ta(NMe ) R (R = Me, Et, Pr , Bu , and Np), via the reactions with the corresponding RLi. The κ -m-
2
2 2
Tol
2
2
terphenyl ligands in these complexes are susceptible to metalation. Thus, [Ar ]Ta(NMe ) R eliminates RH to afford [κ -
2
3
Tol,Tol′
Tol
2
2
Tol,Tol′
Ar
]Ta(NMe ) (Tol′ = C H Me), while [Ar ]Ta(NMe ) Np eliminates NpH to form [κ -Ar
]Ta(NMe ) Np.
2
3
6
3
2 2
2
2 2
([ArTol ]) to synthesize [ArTol ]TaMe Cl and [Ar ]TaMe Cl
2
2
Tol
2
INTRODUCTION
3 2 2
■
represents, to the best of our knowledge, the first application of
Ancillary ligands play a critical role in organometallic chemistry
by allowing tunable properties of a metal center. One such
6
1
terphenyl ligands to tantalum chemistry.
class that has received considerable attention is that of the m-
Ar
2
terphenyl ligand ([Ar ]) (Figure 1), which provides significant
steric protection by virtue of the outer aryl rings. Two common
Mes
2
Dipp
2
2
examples are [Ar ] and [Ar
] (Figure 1). Indeed,
1
Figure 2. Elements for which κ -m-terphenyl compounds have been
structurally characterized by X-ray diffraction (blue), and those for
which there are no structurally characterized examples listed in the
Cambridge Structural Database (red).
1
Figure 1. Examples of [κ -m-terphenyl] ligands.
While many of the applications of m-terphenyl ligands have
1
Ar
2
focused on the use of steric protection to allow for the isolation
structurally characterized [κ -Ar ]M compounds are known
2
of uncommon and low coordination complexes, our interest
for a substantial number of metals, including transition metals
3
3,4
5
6
7
8
7d,9
7d,9a−f,10
7d,9b−d,11
pertains to the potential of using such ligands to construct
multidentate variants via cyclometalation. As an illustration, we
recently employed this approach to obtain the first examples of
(
Sc, Y, Ti, Ta, Cr, Mo, Mn,
Fe,
Co,
1
2
12a,13
18
14
15 16
17
24
Cu, Ag,
Au ), main group metals (Li, Na, Be,
6
,11a
19 19a,20 16,19a 21 15d,22 23
Mg,
Ca, Zn, Cd,
Hg,
Al, Ga,
In, Tl,
2
5
26
27
28d,29
28
28d,30
transition metal compounds that feature a [CCC] X -donor
3
Ge, Sn, Pb, As,
4,34Sb, Bi,
), and lanthanides
3
6
3
Tol′2
3
3
1,32b
32d
33
3,4,32
35
pincer ligand, namely [κ -Ar ]Ta(PMe ) MeCl, [κ -
3 2
(
Sm,
Eu, Er, Tm, Yb,
Lu ). However, despite
this interest in the use of terphenyl ligands, there are still many
elements that have received little attention (Figure 2). In this
regard, our recent use of the 2,6-di-p-tolylphenyl ligand
Received: November 17, 2014
Published: May 11, 2015
©
2015 American Chemical Society
1828
DOI: 10.1021/acs.organomet.5b00158
Organometallics 2015, 34, 1828−1843

Organometallics
Article
Tol′
2
3
Tol′
2
3
Ar ]Ta(PMe ) Me , [κ -Ar ]Ta(PMe ) Cl , and [κ -
Scheme 2
3
2
2
3
2
2
Tol′
2
6
6
Ar ]Ta(PMe ) (η -C H ) (Tol′ = C H Me). For example,
3
2
6
6
6
3
3
Tol′
2
the pincer complex, [κ -Ar ]Ta(PMe ) MeCl was obtained
3
2
by both (i) addition of PMe to the terphenyl complex,
3
Tol
2
[
[
Ar ]TaMe Cl, and (ii) treatment of Ta(PMe ) Me Cl with
3 3 2 3 2
2
Tol
Ar ]Li. Such compounds provide valuable complements to
3
7,38
other complexes that feature X -donor pincer ligands
and
3
39
40
also those that feature LX2 and L2X [CCC] donors.
Remarkably, even though hundreds of metal−terphenyl
complexes have been synthesized, there were no examples of
structurally characterized cyclometalated transition metal
4
1,42
derivatives listed in the Cambridge Structural Database
prior to our report of the use of cyclometalation to form a
6
43
[
CCC] pincer ligand. Thus, while cyclometalation is a widely
44
studied and well-known subset of C−H bond activation, it is
essentially absent with respect to terphenyl chemistry. There-
fore, we report here the synthesis of other terphenyl tantalum
compounds and their subsequent C−H bond cleavage
cyclometalation reactions.
RESULTS AND DISCUSSION
■
Synthesis of [ArTol ]Ta(NMe ) X (X = Cl, R, BH ). In
2
2
3
4
Tol
2
addition to utilizing [Ar ]TaMe Cl to provide access to
3
pincer complexes via formal hydrogen atom abstraction from an
6
aryl group, we have investigated related compounds that have
the potential to undergo similar transformations. Specifically,
since Me N ligands are capable of hydrogen atom abstraction
2
45
reactions via elimination of Me NH, we decided to synthesize
the dimethylamido counterpart of [Ar ]TaMe Cl, namely
Ar ]Ta(NMe ) Cl (1−Cl). Indeed, the latter compound can
be obtained via the reaction of [Ta(NMe ) Cl ]
2
Tol
2
3
Tol
2
[
2
3
46,47
with two
2
3
2 2
Tol
2
equivalents of [Ar ]Li, as illustrated in Scheme 1.
Tol
2
Furthermore, the bis(terphenyl) complex, [Ar ]2Ta(NMe2)3
Figure 3. Molecular structure of [ArTol2]Ta(NMe ) Cl.
Tol
2
2 3
(
1−Ar ), can be obtained upon treatment of [Ta-
Scheme 1
Tol
2
(
[
NMe ) Cl ] with excess [Ar ]Li or by reaction of
2 3 2 2
2 2
Tol
Tol
Ar ]Ta(NMe ) Cl with [Ar ]Li (Scheme 2).
2 3
2
Tol
The molecular structures of [Ar ]Ta(NMe ) Cl and
2
3
2
Figure 4. Molecular structure of [ArTol ] Ta(NMe ) .
2
Tol
[
Ar ] Ta(NMe ) have been determined by X-ray diffraction,
2 2 3
2
2 3
as illustrated respectively in Figures 3 and 4. The geometries of
five-coordinate compounds are often expressed in terms of the
the axial sites of [ArTol ] Ta(NMe ) are occupied by two
2
2 2 3
τ five-coordinate geometry index, which corresponds to (β −
NMe ligands [with N−Ta−N = 160.8(2)°].
5
2
Tol
2
α)/60, where β − α is the difference between the two largest
Another interesting feature of the structures of [Ar ]Ta-
4
8
Tol
2
angles. In this regard, the τ values (Table 1) indicate that
(NMe ) Cl and [Ar ] Ta(NMe ) is that the tantalum atoms
5
2 3
2
2 3
Tol
2
Tol
2
both [Ar ]Ta(NMe ) Cl (0.37) and [Ar ]2Ta(NMe2)3
are displaced from the plane of the terphenyl ligands (i.e., the
2
3
(
0.36) adopt geometries that are significantly distorted from
plane of the central aryl group), as measured by their Ta−
trigonal bipyramidal (with an idealized value of 1.00) towards a
square pyramidal geometry (with an idealized value of 0.00).
Nevertheless, from the perspective of the trigonal bipyramidal
description, the axial sites of [Ar ]Ta(NMe ) Cl are occupied
by NMe and Cl ligands [with N−Ta−Cl = 162.1(1)°], while
C
−C
angles (Table 1). Thus, the displacement of the
para
2
ipso
Tol
tantalum atom of [Ar ]Ta(NMe ) Cl is characterized by a
2
3
Ta−C −C angle of 162.8°, while the two terphenyl ligands
ipso
Tol
para
Tol
2
2
of [Ar ] Ta(NMe ) exhibit displacements of 154.4° and
2
3
2
2 3
49
177.3°, despite the fact that the Ta−C bond lengths are
2
1
829
DOI: 10.1021/acs.organomet.5b00158
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Organometallics
Article
Table 1. Selected Metrical Data Pertaining to {[ArTol2]Ta} Derivatives
τ5
Ta−Cipso−Cpara (deg)
d(Ta−C ) (Å)
d(Ta−C ) (Å)
Δ (Å)
Ar
R
Tol
2
[
[
Ar ]Ta(NMe ) Cl
0.366
0.359
162.8
177.3
2.248(3)
2.296(6)
2.307(6)
2.255(3)
2.240(4)
2.246(4)
2.268(2)
2.274(2)
2.260(2)
2.208(5)
2.197(5)
2.221(2)
2.198(3)
2
3
Tol
2
Ar ] Ta(NMe )
2 3
2
1
54.4
Tol
2
[
[
[
[
[
[
[
Ar ]Ta(NMe ) Me
0.342
0.729
0.578
0.419
0.489
0.366
0.433
174.5
161.0
160.7
176.9
179.3
174.9
166.5
168.0
180.0
169.2
2.162(3)
2.196(4)
2.210(4)
2.161(3)
2.174(2)
0.093
0.044
0.036
0.107
0.100
2
3
Tol
2
Ar ]Ta(NMe ) Et
2
3
Tol
2
n
Ar ]Ta(NMe ) Pr
2
3
Tol
2
n
Ar ]Ta(NMe ) Bu
2
3
Tol
2
Ar ]Ta(NMe ) Np
2
3
Tol
2
2
a
Ar ]Ta(NMe ) (κ -BH )
2
3
4
Tol
2
b
c
c
Ar ]Ta(NMe ) Cl
2
2
2
0
.477
Tol
2
[
[
Ar ]Ta(NMe ) Me
0.491
0.823
2.167(2)
2.170(4)
0.054
0.028
0.023
0.052
0.056
0.057
0.037
0.032
0.055
0.053
0.018
0.034
0.074
0.004
0.018
2
2
2
Tol
2
Ar ]Ta(NMe ) Et
2
2
2
2
.175(4)
2.177(4)
.173(5)
2.164(3)
2
n
[
[
ArTol ]Ta(NMe ) Pr
0.537
0.517
178.3
176.3
2.229(4)
2.221(2)
2
2
2
2
ArTol ]Ta(NMe ) Bu
2
n
d
2
2
2
f
f
2
.184(4)
.189(7)
2
2
[
[
ArTol ]Ta(NMe ) Np
0.781
0.629
177.2
145.1
2.225(3)
2.116(3)
2.170(3)
.172(3)
2.134(4)
2
2
2
2
ArTol ]TaMe Cl
2
e
3
2
2
.150(4)
.190(4)
ArTol ]TaMe Cl2
2
e
0.843
0.640
0.348
157.1
171.9
162.3
2.141(4)
2.297(3)
[
[
[
2.145(5)
.159(4)
2
2
κ2-ArTol,Tol′]Ta(NMe2)3
κ2-ArTol,Tol′]Ta(NMe ) Np
2
.204(3)
2.264(5)
.219(5)
2.200(5)
0.064
0.019
2
2
2
a
b
The listed τ value assumes that the borohydride ligand occupies a single coordination site that is represented by boron. Values for two
5
c
d
crystallographically independent molecules. The values correspond to an in-plane, rather than out-of-plane distortion. Value does not include a
minor component of a disordered n-butyl group. Data taken from ref 6. Two components of a disordered butyl group.
e
f
As observed for [ArTol ]Ta(NMe ) Cl, the tantalum coordi-
2
similar [2.296(6) Å and 2.307(6) Å]. The variable displace-
ments of the metal from the plane indicate that the κ -terphenyl
2
3
1
Tol
2
nation geometries in the alkyl compounds [Ar ]Ta(NMe ) R
2 3
ligand is rather flexible in this system and can adjust its position
to accommodate the steric demands of other ligands. κ -
are distorted from trigonal bipyramidal towards a square
pyramidal geometry (Table 1). However, in contrast to
1
Tol
2
[
Ar ]Ta(NMe ) Cl, in which the chloride ligand is located
Terphenyl compounds do not typically exhibit displacements of
2 3
5
0
in an axial site with respect to the perspective of a trigonal
this magnitude, although substantial distortions have been
Tol
2
3
2a,d
bipyramidal geometry, the alkyl ligands of [Ar ]Ta(NMe2)3R
are located in equatorial sites, similar to the aryl ligands of
observed in compounds that feature two terphenyl ligands,
as illustrated by the observation that [ArPh ] Eu(THF)
possesses Eu−Cipso−Cpara angles of 145.4° and 159.9°. It is
also pertinent to note that not only do κ -terphenyl ligands
2
2
2
Tol
2
32d
[Ar ]2Ta(NMe2)3 (Figure 4). This site preference is in
0
1
accord with previous studies which predict that, for d metal
complexes with a trigonal bipyramidal geometry, the more
exhibit out-of-plane distortions, but in-plane distortions have
51
electronegative ligands favor the axial sites. On this basis, the
alkyl groups would be expected to reside in the equatorial site,
although other factors, such as steric interactions and π-donor
effects, could also play a role.
also been observed. For example, the chromium complex
i
2
Pr
{
[Ar ]Cr(μ-Cl)} exhibits Cr−Cipso−Cortho angles of 99.9°
2
9d
and 142.0°, which deviate considerably from the average
value of 122.5° for structurally characterized M−aryl
compounds listed in the Cambridge Structural Database.
In addition to metathesis of the chloride ligand of
Tol
2
Tol2
Similar to [Ar ]Ta(NMe ) Cl and [Ar ] Ta(NMe ) , the
41
2 3
2
2 3
Tol
2
tantalum atoms of [Ar ]Ta(NMe ) R are also displaced from
2
3
the aryl plane (Table 1). Thus, the Ta−C −C angles of
ipso
para
Tol
2
Tol
2
[Ar ]Ta(NMe ) Cl with [Ar ]Li providing access to the
Tol
2
2
3
[Ar ]Ta(NMe ) R range from 160.7° to 179.3° but,
2 3
Tol
2
Tol
2
bis(terphenyl) complex [Ar ] Ta(NMe ) , [Ar ]Ta-
2
2
3
interestingly, there is no discernible trend based on steric
2
Tol
(
NMe ) Cl also provides a means to obtain a series of alkyl
2 3
2
factors. For example, the neopentyl compound [Ar ]Ta-
Tol
n
n
derivatives, [Ar ]Ta(NMe ) R (1−R: R = Me, Et, Pr , Bu ,
or Np; Np = CH Bu ), via reaction with RLi (Scheme 2). The
2
3
(NMe ) Np (179.3°) exhibits the smallest displacement, while
2
3
t
Tol
2
2
the ethyl derivative [Ar
]Ta(NMe ) Et (161.0°) exhibits a
2 3
molecular structures of each of the tantalum alkyl complexes
has been determined by X-ray diffraction, as illustrated in
Figures 5−9.
substantial displacement. Moreover, in contrast to the ethyl
Tol
2
complex, the methyl derivative [Ar ]Ta(NMe ) Me (174.5°)
2
3
shows relatively little displacement. Despite the substantial
1
830
DOI: 10.1021/acs.organomet.5b00158
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Organometallics
Article
Figure 8. Molecular structure of [ArTol ]Ta(NMe ) Bu .
2
n
Figure 5. Molecular structure of [ArTol2]Ta(NMe ) Me.
2 3
2
3
Figure 6. Molecular structure of [ArTol2]Ta(NMe ) Et.
2
3
Figure 9. Molecular structure of [ArTol2]Ta(NMe ) Np.
2
3
Figure 7. Molecular structure of [ArTol2]Ta(NMe ) Pr .
n
2
3
Figure 10. Molecular structure of [ArTol ]Ta(NMe ) (κ -BH ).
2
2
2
3
4
Tol
2
range of Ta−C −C
angles, however, the Ta−[Ar
]
ipso
para
Tol
2
bonds in [Ar ]Ta(NMe ) X fall in the narrow range of
(Figure 10). Tantalum borohydride compounds are not
common, with there being only one structurally characterized
2
3
2
.240(4)−2.307(6) Å (i.e., 0.067 Å) and are comparable to the
2
52
mean bond length of 2.22 Å for structurally characterized
tantalum aryl compounds listed in the Cambridge Structural
example, namely Ta (μ-BH )(μ-dmpm) (κ -BH ) , listed in
2 3 3 4 2
41,53
the Cambridge Structural Database.
The Ta···B distance
4
1
Tol
2
2
Database. Furthermore, the Ta−R bond lengths also have a
within [Ar ]Ta(NMe ) (κ -BH ) [2.570(2) Å] is comparable
2 3 4
52
2
narrow range of 2.161(3)−2.210(4) Å (i.e., 0.05 Å), all of
to those in Ta (μ-BH )(μ-dmpm) (κ -BH ) (2.54−2.59 Å),
2
3
3
4 2
Tol
2
which are slightly shorter than the Ta−[Ar ] bonds by 0.04−
and the bonding in both complexes may be viewed as
0
.11 Å (Table 1).
comprising two 3-center-2-electron Ta−H−B bonding inter-
54
In addition to affording a series of alkyl compounds,
actions.
Tol
2
Tol
2
In solution, the terphenyl compounds [ArTol ]Ta(NMe2)3R
exhibit limited stability and undergo cyclometalation at elevated
temperatures (100 °C), with concomitant elimination of RH, to
2
[
(
[
Ar ]Ta(NMe ) R, the borohydride compound [Ar ]Ta-
NMe ) (κ -BH ) has also been obtained by treatment of
Ar ]Ta(NMe ) Cl with LiBH (Scheme 2) and the
2 3
2
2
2
3
4
Tol
2
3
4
2
Tol,Tol′
molecular structure has been determined by X-ray diffraction
form [κ -Ar
]Ta(NMe ) (2), as illustrated in Scheme 3.
2 3
1
831
DOI: 10.1021/acs.organomet.5b00158
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Organometallics
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Scheme 3
Table 2. Ta−C Bond Lengths Pertaining to Coordination of
2
Tol,Tol′
3
Tol′
2
[
κ -Ar
] and [κ -Ar ] Ligands
Ta−C
Ta−C
Ta−C
latt#2
cent
Å)
latt#1
(Å)
(
(Å)
2
Tol,Tol′
[
[
[
[
[
[
κ -Ar
]Ta(NMe2)3
2.297(3)
2.264(5)
2.200(5)
2.227(4)
2.190(3)
2.243(2)
2.204(3)
2.219(5)
2.230(5)
2.207(3)
2.230(3)
2.356(2)
2
Tol,Tol′
κ -Ar
]Ta(NMe ) Np
2 2
3
Tol′
2
a
κ -Ar ]Ta(PMe ) Me
2.243(5)
2.207(3)
2.227(3)
2.362(2)
3
2
2
3
Tol′
2
a
κ -Ar ]Ta(PMe ) Cl
2
3
2
3
Tol′
2
a
κ -Ar ]Ta(PMe ) MeCl
3
2
3
Tol′
2
6
a
κ -Ar ]Ta(PMe ) (η -C H )
3
2
6
6
a
Data taken from ref 6.
The borohydride compound, [ArTol ]Ta(NMe ) (κ -BH )
2
2
2
3
4
(
1−BH ), is stable at room temperature but may be induced to
4
undergo cyclometalation by addition of PMe . It is postulated
that the cyclometalation of [Ar ]Ta(NMe ) (κ -BH ) occurs
via elimination of H from a hydride intermediate, [[Ar ]Ta-
3
Tol
2
2
The bis(terphenyl) compound, [ArTol2] Ta(NMe ) , also
2 3
4
2
2 3
Tol
2
2
Tol,Tol′
undergoes cyclometalation to form [κ -Ar
and [Ar ]H. However, the transformation is much more
facile for [Ar ] Ta(NMe ) , occurring over a period of 1 day
]Ta(NMe2)3
2
5
6
Tol
2
(
NMe ) H], which is generated by release of Me P→BH
2 3 3 3
2
Tol
Tol
2
upon addition of PMe . Despite the fact that [Ar ] Ta-
3
2
2
2 3
Tol
2
Tol
2
2
(
NMe ) , [Ar ]Ta(NMe ) R, and [Ar ]Ta(NMe ) (κ -
at room temperature.
Spectroscopically, the formation of [κ -ArTol,Tol′]Ta(NMe2)3
2 3 2 3 2 3
BH ) undergo cyclometalation with different facility, a common
feature is that the transformations do not involve elimination of
2
4
is indicated by a loss of symmetry associated with the terphenyl
Me NH. As such, this observation indicates that, in this system,
2
Tol,Tol′
2
ligand. Thus, the [κ -Ar
] moiety is characterized by the
Tol
2
the Me N ligands are less prone than either [Ar ], R, or H to
abstract a hydrogen from an [Ar ] ligand. This result could be
2
observation of (i) two inequivalent methyl groups in both the
Tol
2
1
1
13
13
1
H [δ( H) = 2.19 and 2.38 ppm] and C [δ( C{ H}) = 21.2
and 21.9 ppm] NMR spectra, (ii) eight aromatic CH signals,
a reflection of (i) Ta−N bonds (accompanied by π-donation)
57,58
being stronger than Ta−H and Ta−C bonds
and (ii) C−H
Tol
2
rather than the four observed for [Ar ]Ta(NMe ) X
complexes, and (iii) two C signals with chemical shifts of
59
2
3
and H−H bonds being stronger than N−H bonds, both of
1
3
1
97.7 and 199.6 ppm that are distinctive for aryl carbons
Scheme 4
55
bonded to tantalum.
2
Tol,Tol′
The molecular structure of [κ -Ar
]Ta(NMe ) has also
2 3
been determined by X-ray diffraction (Figure 11) and possesses
Figure 11. Molecular structure of [κ -ArTol,Tol′]Ta(NMe ) .
2
2
3
a τ value of 0.64, which indicates a significant distortion from a
5
2
trigonal bipyramidal geometry. With respect to the κ -
coordination mode, it is pertinent to note that although the
Ta−C bond lengths of 2.204(3) Å and 2.297(3) Å (Table 2)
2
Tol,Tol′
1
for [κ -Ar
]Ta(NMe ) are comparable to those of the κ -
2 3
terphenyl compounds (Table 1), the Ta−C bond involving the
lateral aryl group is distinctly shorter (by 0.093 Å) than that for
the central aryl group. This observation also contrasts with the
fact that the central Ta−C bond is shorter than the lateral
3
Ta−C bond in the majority of the κ -pincer complexes (Table
2).
1
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Article
Figure 15. Molecular structure of [ArTol ]Ta(NMe ) Pr .
2
n
2
2
2
Figure 12. Molecular structure of [ArTol2]Ta(NMe ) Cl .
2
2
2
Figure 16. Molecular structure of [ArTol ]Ta(NMe
2
)
Bun
.
Figure 13. Molecular structure of [ArTol2]Ta(NMe ) Me .
2
2
2
2
2
2
Figure 17. Molecular structure of [ArTol ]Ta(NMe ) Np .
2
2
2
2
Figure 14. Molecular structure of [ArTol2]Ta(NMe ) Et .
2
2
2
Tol
2
n
n
(
NMe ) Cl and [Ar ]Ta(NMe ) R (R = Me, Et, Pr , Bu ,
2
2
2
2 2 2
which would provide a driving force for elimination of RH or
H rather than Me NH.
and Np) have been determined by X-ray diffraction, as
illustrated in Figures 12−17.
2
2
Tol
2
Synthesis of [Ar ]Ta(NMe ) X (X = Cl, R). In addition
An interesting feature of the structures of the dialkyl
2
2 2
Tol
2
Tol
2
to synthesizing the monoalkyl compounds, [Ar ]Ta-
NMe ) R, we have also synthesized dialkyl compounds,
compounds, [Ar ]Ta(NMe ) R , is that, by comparison to
2 2 2
2
Tol
(
[
the monoalkyls, [Ar ]Ta(NMe ) R, the terphenyl ligands do
2
2
3
2 3
Tol
Ar ]Ta(NMe ) R (3-R), by the sequence illustrated in
not display any significant distortions and the tantalum lies
2
2 2
Tol
2
60
Scheme 4. Specifically, the [Ar ]Ta(NMe ) R complexes are
close to the aryl plane. For example, the Ta−C −C
2
2
2
2
ipso
para
Tol
obtained via the dichloride complex [Ar ]Ta(NMe ) Cl (3-
Cl), which is formed by treatment of [Ar ]Ta(NMe ) Cl
with Me SiCl. The molecular structures of [Ar ]Ta-
angles are in the range of 169.2−180.0° (Table 1). Thus, the
dialkyls have molecular geometries that have approximate C
2
2
2
Tol
2
2
2
3
2
Tol
symmetry, with the alkyl groups located in the equatorial plane
3
1
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Article
Scheme 5
Scheme 6
2
Tol,Tol′
Figure 18. Molecular structure of [κ -Ar
]Ta(NMe ) Np.
2 2
pendent molecules of [ArTol ]Ta(NMe ) Cl exhibit Ta−C−C
2
2
2
2
angles of (i) 111.1(3)° and 131.0(4)° and (ii) 113.4(3)° and
28.0(4)°. However, while significant, these distortions are not
as extreme as noted above for {[Ar ]Cr(μ-Cl)} (99.9° and
1
i
2
Pr
2
9d
1
42.0°).
Although the dialkyls [Ar ]Ta(NMe ) R (R = Me, Et, Pr ,
Tol
2
n
2
2 2
n
61
Bu ) are stable in solution at room temperature, the
Tol
2
dineopentyl complex, [Ar ]Ta(NMe ) Np , is unstable and
2
2
2
2
Tol,Tol′
cyclometalates to give [κ -Ar
]Ta(NMe ) Np (4), as
2 2
62
illustrated in Scheme 5. As observed for the monoalkyls,
[Ar ]Ta(NMe ) R, cyclometalation of [Ar ]Ta-
Tol
2
Tol
2
which, as noted above, is in accord with the prediction that
2 3
51
electronegative substituents favor the axial sites. In contrast to
(NMe ) Np also involves abstraction of the aryl hydrogen
2 2 2
Tol
2
the alkyl compounds, the dichloride complex, [Ar ]Ta-
NMe ) Cl , exhibits an in-plane distortion of the aryl group, as
by a Np ligand rather than by a Me N ligand. The molecular
2
2
Tol,Tol′
(
structure of [κ -Ar
]Ta(NMe ) Np has been determined
2 2
2
2
2
indicated by a significant deviation of the Ta−C−C aryl bond
angles from the average value of 122.5° for M−aryl
by X-ray diffraction and is illustrated in Figure 18. As described
2
Tol,Tol′
2
for [κ -Ar
]Ta(NMe ) , the lateral Ta−C bond of [κ -
2
3
4
1
Tol,Tol′
compounds. Specifically, the two crystallographically inde-
Ar
]Ta(NMe ) Np is shorter than the central Ta−C bond
2
2
Scheme 7
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Organometallics
Table 2), although the difference (0.045 Å) is less significant
Article
(
than for the former compound.
Tol
2
The kinetics of cyclometalation of [Ar ]Ta(NMe ) Np to
2
2
2
2
Tol,Tol′
form [κ -Ar
]Ta(NMe ) Np have been measured by using
2 2
1
H NMR spectroscopy. As illustrated in Figure 19, the
conversion is characterized by first-order kinetics with a rate
−4 −1
constant of 3.7(1) × 10 s , corresponding to a free energy of
⧧
−1
activation (ΔG ) of 23.8(1) kcal mol at 47 °C.
2
Tol,Tol′
Interestingly, rather than [κ -Ar
]Ta(NMe ) Np under-
2 2
going subsequent cyclometalation and eliminating NpH at
2
Tol,Tol′
elevated temperatures, [κ -Ar
]Ta(NMe ) Np undergoes a
2 2
transformation to form a compound that is proposed to be an
2
Tol,Tol′
isomer, [κ -Ar*
]Ta(NMe ) Np (4*), in which the
2 2
tantalum is attached to a different position on the central
63,64
ring, as indicated by the “*” (Scheme 6).
NMR spectroscopic characterization of [κ -Ar*
NMe ) Np, additional information pertaining to the rear-
In addition to the
Figure 20. Sequential conversion of [ArTol2]Ta(NMe ) Np to [κ -
2
2
Tol,Tol′
2
2
2
]Ta-
ArTol,Tol′]Ta(NMe ) Np and [κ -Ar*
2
Tol,Tol′
]Ta(NMe ) Np at 67 °C as
2 2
2
2
(
2
2
1
measured by H NMR spectroscopy. Data points were acquired at 1.14
min intervals.
rangement is provided by analysis of the isotopomer of
Tol
2
[
Ar ]H that is released upon addition of CD OD.
3
1
2
Specifically, a combination of H and H NMR spectroscopy
demonstrates that deuterium of the d -[Ar ]H released is not
Tol
2
2
located on a central ring position that is ortho to both tolyl
groups; rather, it is located on a position that is ortho to one
tolyl group and para to the other, as illustrated in Scheme 7. In
2
Tol,Tol′
contrast, addition of CD OD to [κ -Ar
]Ta(NMe ) Np
3
2 2
Tol
2
releases d -[Ar ]H which is enriched with deuterium in the
2
site that is mutually ortho to both tolyl groups, an assignment
Tol
2
that is confirmed by analysis of the [Ar ]D that is released
Tol
2
upon reaction of [Ar ]Li with CD OD.
3
The kinetics of the isomerization have been measured by
1
using H NMR spectroscopy (Figure 20), which indicates that
the reaction is first-order (Figure 21), with a rate constant of
.2(1) × 10− s , corresponding to a free energy of activation
4
−1
1
Figure 21. First-order plot for the conversion of [κ -ArTol,Tol′]Ta-
2
2
Tol,Tol′
(
NMe ) Np to [κ -Ar*
]Ta(NMe ) Np at 67 °C using the data
2 2
2
2
in Figure 20. The data starts at 20 min, which is the point at which
Tol
2
[
Ar ]Ta(NMe ) Np was effectively consumed.
2 2 2
Two possibilities for the mechanism of the transformation
involve (i) α-H abstraction of a methylene hydrogen of the
neopentyl ligand (Scheme 8) and (ii) β-H abstraction of a
methyl hydrogen of the Me N ligand (Scheme 9). For example,
2
an α-H abstraction reaction involving the neopentyl group
would cleave the Ta−C bond (forming a neopentylidene
intermediate and a new C−H bond) and subsequent rotation
of the terphenyl ligand about its C−C bond would allow for the
formation of a new Ta−C bond via the formal reverse of the
cleavage reaction, i.e., 1,2-addition across the TaC double
bond. The alternative mechanistic scenario in which cleavage of
the Ta−C bond is accompanied by a β-H abstraction proceeds
similarly, with the principal difference being the fact that the
intermediate possesses a metallaaziridine moiety (Scheme 9).
Evidence to distinguish between these two possibilities has
Figure 19. First-order plot for the conversion of [ArTol2]Ta-
2
Tol,Tol′
(
NMe ) Np to [κ -Ar
]Ta(NMe ) Np at 47 °C (data points
2 2
2
2
2
were acquired at 0.66 min intervals).
⧧
−1
(
ΔG ) of 26.1(1) kcal mol at 67 °C. The mechanism of
2
Tol,Tol′
formation of [κ -Ar*
]Ta(NMe ) Np is of interest since it
2 2
requires several bond cleavage and formation reactions. In this
regard, a mechanism that involves simple cleavage of a Ta−C
bond can be discounted because it is expected to be a high
energy process that is considerably more endoergic than the
been provided by examining the isomerization of the d -
2
2
Tol,Tol′
t
66
isotopologue [κ -Ar
]Ta(NMe ) (CD Bu ). Specifically,
2 2 2
isomerization via α-H abstraction would be accompanied by
incorporation of hydrogen into the methylene moiety of the
neopentyl ligand and deuterium into the arene, whereas no
scrambling would be observed for a mechanism involving β-H
⧧
−1 65
measured value of ΔG [26.1(1) kcal mol ]. As such, it is
evident that the Ta−C bond cleavage step must be coupled
with C−H bond formation.
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Article
Scheme 8
complexes is susceptible to intramolecular C−H bond cleavage
reactions, thereby affording unprecedented examples of
structurally characterized cyclometalated transition metal
terphenyl derivatives. For example, the monoalkyl compounds
Tol
2
2
[
Ar ]Ta(NMe ) R undergo cyclometalation to form [κ -
2 3
Tol,Tol′
Ar
]Ta(NMe2)3 via elimination of RH. Likewise, the
2
Tol
dineopentyl compound [Ar ]Ta(NMe ) Np eliminates
2
2
2
2
Tol,Tol′
NpH to form [κ -Ar
]Ta(NMe ) Np. A common feature
2 2
of both of these transformations is that the abstraction of the
hydrogen from the terphenyl ligand is achieved by an alkyl
group rather than by a dimethylamido ligand.
EXPERIMENTAL SECTION
■
General Considerations. All manipulations were performed using
a combination of glovebox, high vacuum, and Schlenk techniques
under an argon atmosphere unless otherwise specified. Solvents were
purified and degassed by using standard procedures. H NMR spectra
6
9
1
were measured on Bruker 300 DRX, Bruker 300 DPX, Bruker 400
Avance III, Bruker 400 Cyber-enabled Avance III, and Bruker 500
1
DMX spectrometers. H chemical shifts are reported in ppm relative
to SiMe (δ = 0) and were referenced internally with respect to the
4
7
0
13
protio solvent impurity (δ 7.16 for C D H).
C NMR spectra are
6
5
reported in ppm relative to SiMe4 (δ = 0) and were referenced
Scheme 9
70 11
internally with respect to the solvent (δ 128.06 for C D ).
B NMR
6
6
are reported in ppm relative to BF ·Et O (δ = 0) and were referenced
3
2
1
71
electronically by using the solvent H frequency. Coupling constants
n
are given in hertz. MeLi, EtLi, and Bu Li were obtained commercially
n
72
73
Tol
2
6
from Aldrich, while Pr Li, NpLi, and [Ar ]Li, were prepared by
literature methods. In each case, solvent was removed from the
t
74
solution of RLi prior to use. Bu CD Li was prepared from
2
t
75,76
Bu CD I.
Me SiCl was obtained from Aldrich, dried over CaH
2
3
2
prior to use, and vacuum transferred directly into the reaction vessel.
4
6
[
Ta(NMe ) Cl ] was prepared by the literature method.
2 3 2 2
X-ray Structure Determinations. X-ray diffraction data were
collected on a Bruker Apex II diffractometer. Crystal data, data
collection, and refinement parameters are summarized in Table S1 in
the Supporting Information. The structures were solved using direct
methods and standard difference map techniques and were refined by
2
full-matrix least-squares procedures on F with SHELXTL (version
7
7
2
008/4).
Synthesis of [ArTol ]Ta(NMe ) Cl. A solution of [Ar ]Li (760
2
Tol
2
2
3
mg, 2.88 mmol) in Et O (10 mL) was added to a stirred suspension of
2
[
Ta(NMe ) Cl ] (1.0 g, 1.30 mmol) in Et O (15 mL) over a period
2 3 2 2 2
of 5 min. The mixture was then stirred for an additional 30 min, after
which period the volatile components were removed in vacuo. The
resulting solid was first washed with pentane (15 mL) and then
extracted into pentane (100 mL). The volatile components were
removed from the extract in vacuo to give a golden-yellow/brown
powder. The powder was washed twice with pentane (ca. 5 and 3 mL)
abstraction from NMe . Significantly, isomerization of
2
2
Tol,Tol′
t
2
Tol,Tol′
67
Tol
2
and dried in vacuo to afford [Ar ]Ta(NMe ) Cl (427 mg, 28%
[
(
κ ‑Ar
]Ta(NMe ) (CD Bu ) yields [κ -Ar*
2
]Ta-
2 3
2
2
2
t
yield). X-ray quality crystals were obtained from a solution in pentane
NMe ) (CD Bu ), with no scrambling of deuterium, thereby
2
2
at −15 °C. Anal. Calcd: C, 51.5%, H, 5.8%, N, 6.9%. Found: C, 51.4%,
indicating that a mechanism involving α-H abstraction does not
occur. Thus, a mechanism involving β-H abstraction is the
more likely possibility. Further evidence in support of this
1
Tol
2
H, 5.9%, N, 6.8%. H NMR (C D ): 2.17 [s, 6H of Me of Ar ], 2.86
6
6
3
Tol
2
3
[
=
s, 18H of (NMe ) ], 7.05 [d, J
= 8, 4H of Ar ], 7.19 [dd, J
H−H H−H
2
2
3
3
Tol
2
3
Tol
8, J
= 7, 1H of Ar ], 7.30 [d, J
= 8, 2H of Ar ], 7.74 [br
H−H
2
H−H
suggestion is provided by the fact that cyclometalation of Me N
Tol
2
13
1
Tol
2
s, 4H of Ar ]. C{ H} NMR (C D ): 21.1 [s, 2C of Me of Ar ],
6 6
2
6
8
Tol
ligands on tantalum has been previously observed.
4
6.9 [s, 6C of (NMe ) ], 126.0 [s, 1C of Ar ], 128.8 [s, 4C of
2 3
2 2 2
Tol
Tol
Tol
Ar ], 130.4 [s, 2C of Ar ], 130.9 [br s, 4C of Ar ], 136.0 [s, 2C
Tol
2
Tol
2
Tol
2
SUMMARY
of Ar ], 144.7 [s, 2C of Ar ], 146.5 [s, 2C of Ar ], 202.5 [s, 1C
2
■
Tol
1
Tol
2
of Ar ].
Synthesis of [Ar ]Ta(NMe ) Me. A solution of [Ar ]Ta-
In conclusion, a series of κ -m-terphenyl [Ar ] tantalum
Tol
2
Tol
2
2
3
complexes that feature dimethylamido ligands, namely
Tol
2
n
n
Tol
2
(NMe ) Cl (30 mg, 0.05 mmol) in d -benzene (ca. 0.7 mL) in an
2
3
6
[
Ar ]Ta(NMe ) X (X = Me, Et, Pr , Bu , Np, [Ar ], and
2 3
2
NMR tube equipped with a J. Young valve was treated with MeLi (10
Tol
n
n
BH ) and [Ar ]Ta(NMe ) R (R = Me, Et, Pr , Bu , and Np)
4
2 2
2
mg, 0.45 mmol) in Et O (ca. 0.1 mL). The mixture was analyzed by
2
Tol
2
have been synthesized. Together with [Ar ]TaMe Cl and
1
3
H NMR spectroscopy, thereby demonstrating conversion to
2
Tol
2
[
Ar ]TaMe Cl , these complexes constitute the first examples
Tol
2
2
[Ar ]Ta(NMe ) Me. The mixture was lyophilized and extracted
2 3
1
Tol
2
of structurally characterized κ -m-terphenyl [Ar ] tantalum
into pentane (ca. 1 mL) and filtered through Celite. The extract was
placed at −15 °C, thereby depositing light-yellow crystals of
compounds. Interestingly, the terphenyl ligand in these
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ArTol ]Ta(NMe ) Me over a period of 1 day. The mother liquor was
2
the period of ca. 1 week. The crystals were dried in vacuo, giving
[
2
3
Tol
2
n
removed using a pipet, and the crystals were washed with cold (−15
[Ar ]Ta(NMe ) Bu (9 mg, 29% yield). X-ray quality crystals were
2 3
Tol
2
1
°
(
C) pentane (2 × 1 mL), and dried in vacuo, giving [Ar ]Ta-
obtained from a solution in pentane at −15 °C. H NMR (C D ): 0.25
[m, 2H of TaCH CH CH CH ], 0.91 [t,
6
6
3
NMe ) Me (15 mg, 52% yield). X-ray quality crystals were obtained
J
= 7, 3H of
2
3
2
2
2
3
H−H
from a solution in pentane at −15 °C. Anal. Calcd: C, 55.4%, H, 6.5%,
TaCH CH CH CH ], 1.23 [m, 2H of TaCH CH CH CH ], 1.76
2 2 2 3 2 2 2 3
2
1
Tol
N, 7.2%. Found: C, 55.4%, H, 6.6%, N, 7.0%. H NMR (C D ): 0.25
[m, 2H of TaCH CH CH CH ], 2.22 [s, 6H of Me of Ar ], 3.01 [br
2 2 2 3
2
6
6
Tol
2
3
Tol
3
[
(
s, 3H of TaMe], 2.20 [s, 6H of Me of Ar ], 3.01 [br s, 18H of
s, 18H of (NMe ) ], 7.08 [d, J
= 8, 4H of Ar ], 7.20 [t, J
=
H−H
= 8,
2
3
H−H
3
Tol
2
3
Tol
2
3
Tol
2
3
NMe ) ], 7.08 [d, J
= 8, 4H of Ar ], 7.20 [t, J
= 8, 2H of Ar ], 7.46 [d, J
= 8, 1H of
= 8, 4H of
8, 1H of Ar ], 7.35 [d, J
= 8, 2H of Ar ], 7.47 [d, J
2
3
H−H
H−H
H−H
H−H
Tol
2
3
Tol
2
3
Tol
2
13
1
Ar ], 7.35 [d, J
4H of Ar ].
C{ H} NMR (C D ): 13.7 [s, 1C of
6 6
2
H−H
H−H
Tol
2
13
1
Tol
2
Tol
Ar ]. C{ H} NMR (C D ): 21.2 [s, 2C of Me of Ar ], 46.6 [s,
TaCH CH CH CH ], 21.2 [s, 2C of Me of Ar ], 30.4 [s, 1C of
6
6
2
2
2
3
Tol
2
6
[
1
C of (NMe ) ], 53.3 [s, 1C of TaMe], 125.2 [s, 1C of Ar ], 129.0
TaCH CH CH CH ], 33.1 [s, 1C of TaCH CH CH CH ], 46.8 [s,
2
3
2 2 2 3 2 2 2 3
Tol
2
Tol
2
Tol
2
br s, 4C of Ar ], 129.8 [s, 4C of Ar ], 130.4 [s, 2C of Ar ],
35.8 [very br, 2C of Ar ], 145.9 [very br, 4C of Ar ], 200.3 [s, 1C
of Ar ].
Synthesis of [Ar ]Ta(NMe ) Et. EtLi (2 mg, 0.05 mmol) was
added to [Ar ]Ta(NMe ) Cl (30 mg, 0.05 mmol) in d -benzene (ca.
6C of (NMe ) ], 79.3 [s, 1C of TaCH CH CH CH ], 125.1 [s, 1C of
2 3 2 2 2 3
2 2 2
Tol
2
Tol
2
Tol
Tol
Tol
Ar ], 128.9 [br s, 4C of Ar ], 130.1 [br s, 4C of Ar ], 130.3 [s,
2 2
Tol
2
Tol
Tol
2C of Ar ], 136.1 [very br, 2C of Ar ], 146.0 [very br, 4C of
2 2
Tol
2
Tol
Tol
Ar ], 200.8 [s, 1C of Ar ].
2
3
Tol
2
Tol
2
Synthesis of [Ar ]Ta(NMe ) Np. NpLi (5 mg, 0.06 mmol) was
2 3
Tol
2
2
3
6
0.7 mL) in a small vial. The suspension was mixed for 1 min, filtered
added to [Ar ]Ta(NMe ) Cl (30 mg, 0.05 mmol) in d -benzene (ca.
2 3 6
through Celite, and transferred to an NMR tube equipped with a J.
0.7 mL) in a small vial. The suspension was mixed for 1 min, filtered
1
Young valve. The pale-yellow to colorless solution was analyzed by H
through Celite, and transferred to an NMR tube equipped with a J.
Tol
2
1
NMR spectroscopy, thereby demonstrating conversion to [Ar ]Ta-
Young valve. The pale-yellow to colorless solution was analyzed by H
Tol
2
(
NMe ) Et. The mixture was then lyophilized and extracted into
NMR spectroscopy, thereby demonstrating conversion to [Ar ]Ta-
(NMe ) Np. The mixture was then lyophilized and extracted into
2
3
pentane (ca. 1 mL). The extract was allowed to evaporate slowly at
2
3
room temperature to give [ArTol2]Ta(NMe ) Et as light-yellow
pentane (ca. 1 mL). The extract was placed at −15 °C, thereby
2
3
Tol
2
crystals. The crystals were isolated, washed with cold (−15 °C)
depositing light-yellow crystals of [Ar ]Ta(NMe ) Np over the
2 3
Tol
2
pentane (1 mL), and dried in vacuo to give [Ar ]Ta(NMe ) Et (8
period of ca. 1 week. The mother liquor was removed by using a pipet,
2
3
mg, 27% yield). X-ray quality crystals were obtained from a solution in
and the crystals were washed with cold (−15 °C) pentane (2 × 1 mL)
1
3
Tol
2
pentane at −15 °C. H NMR (C D ): 0.42 [q, J
= 8, 2H of
= 8, 3H of TaCH CH ], 2.20 [s, 6H of Me
and dried in vacuo, giving [Ar ]Ta(NMe ) Np (10 mg, 31% yield).
6
6
H−H
2 3
3
TaCH CH ], 1.77 [t, J
X-ray quality crystals were obtained from a solution in pentane at −15
2
3
H−H
2
3
Tol
2
3
of Ar ], 3.00 [br s, 18H of (NMe ) ], 7.08 [d, J
Ar ], 7.20 [t, J
Ar ], 7.46 [d, J
s, 1C of TaCH CH ], 21.2 [s, 2C of Me of Ar ], 46.8 [s, 6C of
= 8, 4H of
= 8, 2H of
°C. Anal. Calcd: C, 58.0%, H, 7.2%, N, 6.6%. Found: C, 57.5%, H,
2
3
H−H
Tol
2
3
Tol
2
3
1
= 8, 1H of Ar ], 7.34 [d, J
= 8, 4H of Ar ]. C{ H} NMR (C D ): 15.2
6.7%, N, 6.2%. H NMR (C D ): 0.04 [s, 2H of TaCH CMe ], 0.98
H−H
H−H
6
6
2
3
Tol
2
3
Tol
2
13
1
Tol
2
[s, 9H of TaCH CMe ], 2.23 [s, 6H of Me of Ar ], 3.05 [br s, 18H
2 3
2 2
H−H
6
6
Tol
2
Tol
3
Tol
[
of (NMe ) ], 7.07 [br, 4H of Ar ], 7.21 [t, J
= 8, 1H of Ar ],
2
3
2
3
H−H
Tol
2
Tol
2
Tol
2
13 1
(
NMe ) ], 67.2 [s, 1C of TaCH CH ], 125.1 [s, 1C of Ar ], 128.9
7.40 [br, 4H of Ar ], 7.52 [br, 2H of Ar ]. C{ H} NMR (C D ):
6 6
2
2
3
2
3
Tol
2
Tol
2
Tol
2
Tol
[
br s, 4C of Ar ], 130.0 [br s, 4C of Ar ], 130.4 [s, 2C of Ar ],
21.2 [s, 2C of Me of Ar ], 34.3 [s, 1C of TaCH CMe ], 37.7 [s, 1C
2 3
Tol
2
Tol
2
1
36.2 [very br, 2C of Ar ], 146.1 [very br, 4C of Ar ], 200.5 [s, 1C
of TaCH CMe ], 46.8 [s, 6C of (NMe ) ], 98.7 [s, 1C of
2 3 2 3
2 2
Tol
2
Tol
Tol
of Ar ].
Synthesis of [Ar ]Ta(NMe ) Pr . Pr Li (5 mg, 0.10 mmol) was
TaCH CMe ], 124.7 [s, 1C of Ar ], 129.2 [br s, 4C of Ar ],
2 3
2 2
Tol
2
n
n
Tol
Tol
129.8 [br s, 4C of Ar ], 130.8 [br s, 2C of Ar ], 135.3 [br s, 1C of
2
3
Tol
2
Tol
2
Tol
2
Tol
2
added to [Ar ]Ta(NMe ) Cl (30 mg, 0.05 mmol) in d -benzene (ca.
Ar ], 136.7 [br s, 1C of Ar ], 143.8 [br s, 1C of Ar ], 144.8 [br s,
2 2 2
2
3
6
Tol
Tol
Tol
0
.7 mL) in a small vial. The suspension was mixed for 1 min, filtered
1C of Ar ], 145.6 [br s, 1C of Ar ], 146.8 [br s, 1C of Ar ],
2
Tol
through Celite, and transferred to an NMR tube equipped with a J.
Young valve. The pale-yellow to colorless solution was analyzed by H
NMR spectroscopy, thereby demonstrating conversion to [Ar ]Ta-
201.3 [s, 1C of Ar ].
2
1
Tol
Tol
2
Synthesis of [Ar ] Ta(NMe ) . [Ar ]Li (15 mg, 0.06 mmol)
2 2 3
Tol
2
Tol
2
was added to a solution of [Ar ]Ta(NMe ) Cl (25 mg, 0.04 mmol)
2 3
n
(
NMe ) Pr . The mixture was lyophilized and extracted into pentane
in d -benzene (ca. 0.7 mL) in a small vial. The suspension was mixed
2
3
6
(
ca. 1 mL). The extract was placed at −15 °C, thereby depositing light-
for 1 min, filtered through Celite, and transferred to an NMR tube
Tol
2
n
1
yellow crystals of [Ar ]Ta(NMe ) Pr over a period of ca. 1 week.
The mother liquor was removed using a pipet, and the crystals were
equipped with a J. Young valve. The sample was analyzed by H NMR
2
3
Tol
2
spectroscopy, thereby demonstrating conversion to [Ar ]2Ta-
(NMe ) . The sample was then lyophilized and extracted with
washed with cold (−15 °C) pentane (1 mL) and dried in vacuo, giving
2
3
Tol
2
n
[
Ar ]Ta(NMe ) Pr (6 mg, 20% yield). X-ray quality crystals were
pentane (ca. 1 mL). The extract was placed at −15 °C for 1 week,
2
3
Tol
2
obtained from a solution in pentane at −15 °C. Anal. Calcd: C, 56.8%,
H, 6.9%, N, 6.8%. Found: C, 56.0%, H, 6.7%, N, 5.8%. H NMR
thereby depositing yellow crystals of [Ar ] Ta(NMe ) ·0.5(C H )
2 2 3 5 12
1
over a period of ca. 1 week. The mother liquor was removed by using a
3
(
C D ): 0.28 [m, 2H of TaCH CH CH ], 0.93 [t, J
= 7, 3H of
pipet, and the crystals were washed with cold (−15 °C) pentane (2 ×
6
6
2
2
3
H−H
Tol
2
TaCH CH CH ], 1.80 [m, 2H of TaCH CH CH ], 2.22 [s, 6H of Me
1 mL), giving [Ar ] Ta(NMe ) ·0.5(C H ) (14 mg, 39% yield). X-
2
2
3
2
2
3
2 2 3 5 12
Tol
2
3
of Ar ], 3.00 [br s, 18H of (NMe ) ], 7.08 [d, J
Ar ], 7.20 [t, J
Ar ], 7.46 [d, J
= 8, 4H of
= 8, 2H of
ray quality crystals were obtained from a solution in pentane at −15
°C. Anal. Calcd: C, 66.7%, H, 6.3%, N, 5.1%. Found: C, 65.6%, H,
2
3
H−H
Tol
2
3
Tol
2
3
= 8, 1H of Ar ], 7.35 [d, J
2
H−H
H−H
Tol
2
3
Tol
13
1
1
Tol
2
= 8, 4H of Ar ]. C{ H} NMR (C D ): 21.2
6.3%, N, 4.5%. H NMR (C D ): 2.19 [s, 12H of Me of Ar ], 2.51
6 6
2
H−H
6
6
Tol
2
3
Tol
3
[
s, 2C of Me of Ar ], 22.3 [s, 1C of TaCH CH CH ], 24.6 [s, 1C of
[s, 18H of (NMe ) ], 7.08 [d, J
= 7, 8H of Ar ], 7.10 [t, J
=
H−H
2
2
3
2
3
H−H
Tol
2
3
Tol
2
3
TaCH CH CH ], 46.8 [s, 6C of (NMe ) ], 79.6 [s, 1C of
8, 2H of Ar ], 7.24 [d, J
= 7, 4H of Ar ], 7.40 [d, J
= 7,
H−H
2
2
2
3
2
3
H−H
Tol
2
Tol
2
Tol
2
13
1
Tol
TaCH CH CH ], 125.1 [s, 1C of Ar ], 128.9 [br s, 4C of Ar ],
1
Ar ], 146.1 [very br, 4C of Ar ], 200.9 [s, 1C of Ar ].
8H of Ar ]. C{ H} NMR (C D ): 21.1 [s, 4C of Me of Ar ],
6 6
2
2
2
3
Tol
2
Tol
2
Tol
30.0 [br s, 4C of Ar ], 130.3 [s, 2C of Ar ], 136.2 [very br, 2C of
47.0 [s, 6C of (NMe ) ], 125.4 [s, 2C of Ar ], 128.4 [s, 8C of
2 3
2 2 2
Tol
2
Tol
2
Tol
2
Tol
Tol
Tol
Ar ], 130.1 [s, 8C of Ar ], 131.3 [s, 4C of Ar ], 134.9 [s, 4C of
2 2 2
Tol
2
n
n
Tol
Tol
Tol
Synthesis of [Ar ]Ta(NMe ) Bu . A solution of Bu Li (3 mg,
Ar ], 147.8 [s, 4C of Ar ], 152.2 [s, 4C of Ar ], 199.2 [s, 2C of
2
2
3
Tol
2
Tol
0
.05 mmol) in d -benzene (0.2 mL) was added to [Ar ]Ta-
Ar ].
Synthesis of [Ar ]Ta(NMe ) (κ -BH ). A mixture of [Ar ]Ta-
6
Tol
2
2
Tol
2
(
NMe ) Cl (30 mg, 0.05 mmol) in d -benzene (ca. 1 mL) in a small
2
3
6
2 3
4
vial. The suspension was mixed for 1 min, filtered through Celite, and
(NMe ) Cl (50 mg, 0.08 mmol) and LiBH (3 mg, 0.14 mmol) was
2
3
4
transferred to an NMR tube equipped with a J. Young valve. The pale-
treated with Et O (ca. 0.5 mL). The volatile components were
2
1
yellow to colorless solution was analyzed by H NMR spectroscopy,
removed in vacuo after 30 min, and the off-white solid obtained was
extracted with pentane (2 mL). The solution was placed at −15 °C,
Tol
2
n
thereby demonstrating conversion to [Ar ]Ta(NMe ) Bu . The
2
3
Tol
2
2
mixture was then lyophilized and extracted into pentane (ca. 1 mL).
thereby depositing colorless crystals of [Ar ]Ta(NMe ) (κ -BH )
2 3 4
The extract was placed at −15 °C and allowed to evaporate slowly,
over a period of 1 day. The mother liquor was removed using a pipet,
and the crystals were washed with cold (−15 °C) pentane (2 × 1 mL)
thereby forming light-yellow crystals of [ArTol ]Ta(NMe ) Bu over
2
n
2
3
1
837
DOI: 10.1021/acs.organomet.5b00158
Organometallics 2015, 34, 1828−1843

Organometallics
Article
and dried in vacuo, giving [ArTol2]Ta(NMe ) (κ -BH ) (13 mg, 27%
2
Ar
Tol,Tol′
]Ta(NMe ) , Me PBH (δ 0.61 [d, J = 10, 9H, PMe ], 1.33
2 3 3 3 PH 3
2
2
3
4
2
1
yield). X-ray quality crystals were obtained from a solution in pentane
at −15 °C. Anal. Calcd: C, 53.3%, H, 6.7%, N, 7.2%. Found: C, 51.7%,
H, 6.2%, N, 6.9%. H NMR (C D ): 2.17 [s, 6H of Me of Ar ], 2.92
[d, J = 16, 1:1:1:1 q, J = 96, 3H, BH ]) and H .
PH
BH
3
2
Tol
2
Tol
2
Synthesis of [Ar ]Ta(NMe ) Cl . [Ar ]Ta(NMe ) Cl (100
mg, 0.17 mmol) in d -benzene (ca. 1 mL) in an NMR tube equipped
6
with a J. Young valve was treated with excess Me SiCl (ca. 0.7 mL) via
vapor transfer. The mixture was shaken for 1 min and allowed to stand
2 2 2 2 3
1
Tol
2
6
6
3
[
s, 18H of (NMe ) ], 3.28 [very br, 4H of Ta(BH )], 7.03 [d, J
=
2
3
4
H−H
3
Tol
2
3
3
Tol
2
8
, 4H of Ar ], 7.20 [dd, J
JH−H = 8, 2H of Ar ], 7.48 [d, J
= 8, J
= 7, 1H of Ar ], 7.31 [d,
= 8, 4H of Ar ]. C{ H}
NMR (C D ): 21.1 [s, 2C of Me of Ar ], 48.9 [s, 6C of (NMe ) ],
H−H
H−H
3
Tol
2
3
Tol
2
13
1
1
at room temperature for 10 min. The sample was analyzed by H
H−H
Tol
Tol
2
2
NMR spectroscopy, thereby demonstrating conversion to [Ar ]Ta-
(NMe Cl and Me SiNMe . The volatile components were removed
6
6
2 3
Tol
2
Tol
2
Tol
2
1
1
25.9 [s, 1C of Ar ], 128.6 [s, 4C of Ar ], 130.1 [s, 2C of Ar ],
2
)
2
2
3
2
Tol
2
Tol
2
30.8 [br s, 4C of Ar ], 135.5 [s, 2C of Ar ], 145.7 [s, 2C of
in vacuo, leaving a yellow oily residue, which was extracted into
pentane (5 × 1 mL), with each extract being placed in a small vial. The
extracts were placed at −15 °C, thereby depositing yellow crystals of
Tol
2
Tol
2
Tol
2
11
Ar ], 148.0 [s, 2C of Ar ], 198.4 [s, 1C of Ar ]. B NMR
(
C D ): −8.4 [br, 1B of Ta(BH )].
Synthesis of [κ -Ar
6
6
4
Tol
2
[
Ar ]Ta(NMe ) Cl . The mother liquor was removed from each vial
2
Tol,Tol′
2 2 2
]Ta(NMe ) . NpLi (7 mg, 0.09 mmol)
was added to a suspension of [Ar ]Ta(NMe ) Cl (50 mg, 0.08
mmol) in d -benzene (ca. 0.7 mL) in a small vial. The suspension was
mixed for 1 min and then filtered through Celite into an NMR tube
equipped with a J. Young valve. The solution was analyzed by H
NMR spectroscopy, thereby demonstrating formation of [Ar ]Ta-
2
2
3
using a pipet, and the crystals were washed with cold (−15 °C)
Tol
2
3
pentane (1 mL each), combined, and dried in vacuo to give
6
Tol
2
[
Ar ]Ta(NMe ) Cl (30 mg). Additionally, the yellow solid
2
2
2
remaining after the pentane extractions was extracted into benzene
and lyophilized to give an additional batch of [Ar ]Ta(NMe ) Cl
23 mg). The total yield of [Ar ]Ta(NMe ) Cl is 53 mg (54%). X-
ray quality crystals were obtained by evaporation of a solution in
benzene. Anal. Calcd: C, 48.3%, H, 4.9%, N, 4.7%. Found: C, 49.1%,
1
Tol
2
Tol
2
2
2
2
Tol
2
(
2 2 2
(
NMe ) Np. The sample was then heated at 100 °C for 2 h, thereby
2
3
2
Tol,Tol′
demonstrating complete conversion to [κ -Ar
]Ta(NMe ) and
2 3
neopentane. The mixture was lyophilized and extracted into pentane.
The volatile components were allowed to evaporate, thereby
]Ta(NMe ) , which contained a
small amount (ca. 10%) [Ar ]H (27 mg total, ca. 55% yield of [κ -
1
Tol
2
H, 4.5%, N, 4.2%. H NMR (C D ): 2.18 [s, 6H of Me of Ar ], 2.94
6
6
3
Tol
2
[
s, 12H of (NMe ) ], 7.07 [d, J
= 8, 4H of Ar ], 7.16 [m, 1H of
H−H
2
2
Tol,Tol′
2
2
depositing crystals of [κ -Ar
Tol
3
Tol
3
2
3
2
Ar ], 7.29 [d, J
= 7, 2H of Ar ], 7.72 [br d, J
= 7, 4H of
2
Tol
2
2
H−H
H−H
ArTol2]. C{ H} NMR (C D ): 21.3 [s, 2C of Me of Ar ], 47.7 [s,
13
1
Tol
Tol,Tol′
6
6
Ar
]Ta(NMe ) ). X-ray quality crystals were obtained from a
Tol
2
2
3
4
C of (NMe ) ], 128.3 [s, 1C of Ar , under C D signal, located by
2 2 6 6
2 2
1
solution in pentane at −15 °C. H NMR (C D ): 2.19 [s, 3H of Me of
Tol
Tol
6
6
HSQC], 129.3 [s, 4C of Ar ], 130.4 [s, 2C of Ar ], 131.4 [s, 4C of
Tol,Tol′
.11 [d, 3J
Tol,Tol′
Ar
7
], 2.38 [s, 3H of Me of Ar
], 3.03 [s, 18H of (NMe ) ],
Tol
Tol
Tol
2
2
3
2
2
Ar ], 137.5 [s, 2C of Ar ], 139.4 [br s, 2C of Ar ], 144.4 [s, 2C
Tol,Tol′
Tol,Tol′
= 8, 2H of Ar
], 7.16 [m, 1H of Ar
under C D H signal confirmed by 2D COSY and homonuclear
; location
Tol
Tol
2
H−H
2
of Ar ], 201.4 [s, 1C of Ar ].
6
5
Synthesis of [ArTol ]Ta(NMe ) Me . A solution of [ArTol2]Ta-
2
3
4
2 2
2
decoupling experiments], 7.63 [dd, J
= 7, J
= 2, 1H of
= 7, 1H of
= 2, 1H of
H−H
H−H
H−H
(
NMe ) Cl (20 mg, 0.03 mmol) in d -benzene (ca. 0.7 mL) in an
Tol,Tol′
Tol,Tol′
Tol,Tol′
3
2 2 2 6
Ar
Ar
], 7.68 [m, 3H of Ar
], 7.90 [d, J
], 7.85 [d, J
H−H
NMR tube equipped with a J. Young valve was treated with MeLi (10
mg, 0.45 mmol) in Et O (ca. 0.2 mL), and mixture was allowed to
stand for ca. 1 h. The sample was analyzed by H NMR spectroscopy,
thereby demonstrating conversion to [Ar ]Ta(NMe ) Me . The
3
= 8, 1H of ArTol,Tol′], 8.24 [d, J
4
H−H
ArTol,Tol′]. C{ H} NMR (C D ): 21.2 [s, 1C of Me of Ar
13
1
Tol,Tol′
], 21.9
], 42.6 [s, 6C of (NMe ) ], 119.6 [s, 1C of
2
6
6
1
Tol,Tol′
[
s, 1C of Me of Ar
Tol
2
3
2
Tol,Tol′
Tol,Tol′
Tol,Tol′
2
2
2
Ar
], 121.2 [s, 1C of Ar
], 125.5 [s, 1C of Ar
], 127.5 [s,
1
sample was lyophilized, extracted into d -benzene, and analyzed by H
Tol,Tol′
Tol,Tol′
Tol,Tol′
6
2
1
C of Ar
], 129.7 [s, 2C of Ar
], 129.9 [s, 1C of Ar
],
NMR spectroscopy, thereby demonstrating that the sample consisted
Tol,Tol′
Tol,Tol′
35.7 [s, 1C of Ar
], 136.5 [s, 1C of Ar
], 139.8 [s, 2C of
Tol
2
Tol
2
of [Ar ]Ta(NMe ) Me as the major product, in addition to [Ar
]
2
Tol,Tol′
Tol,Tol′
Tol,Tol′
2
2
2
Ar
], 140.4 [s, 1C of Ar
], 142.2 [s, 1C of Ar
], 154.2 [s,
Tol
2
H (<5%). The sample was lyophilized to give [Ar ]Ta(NMe ) Me
12 mg, 65% yield) as a light-brown powder. X-ray quality crystals
Tol,Tol′
Tol,Tol′
Tol,Tol′
2
2
1
1
C of Ar
], 158.3 [s, 1C of Ar
], 197.7 [s, 1C of Ar
],
(
Tol,Tol′
99.6 [s, 1C of Ar
].
1
were obtained from a solution in pentane at −15 °C. H NMR
2
Tol,Tol′
Tol
2
Formation of [κ -Ar
]Ta(NMe ) via Cyclometalation. (i)
A solution of [Ar ]Ta(NMe ) Me (5 mg, 0.01 mmol) in d -benzene
ca. 0.7 mL) in an an NMR tube equipped with a J. Young valve was
(C D ): −0.41 [s, 6H of TaMe ], 2.15 [s, 6H of Me of Ar ], 2.89 [s,
2
3
6
6
2
Tol
2
3
Tol
2
12H of (NMe ) ], 6.99 [d, J
= 8, 4H of Ar ], 7.22 [m, 1H of
2
3
6
2
2
H−H
Tol
2
Tol
2
13
1
(
Ar ], 7.28 [m, 6H of Ar ]. C{ H} NMR (C D ): 21.2 [s, 2C of
6
6
Tol
2
heated at 100 °C for 1 day, thereby demonstrating the formation of,
Me of Ar ], 43.0 [s, 4C of (NMe ) ], 56.1 [s, 2C of TaMe ], 125.1
2 2 2
2 2
2
Tol,Tol′
Tol
2
Tol
Tol
inter alia, [κ -Ar
(
]Ta(NMe ) and methane.
[s, 1C of Ar ], 128.8 [s, 4C of Ar ], 129.6 [s, 4C of Ar ], 130.5
2 2 2
2
3
Tol
2
Tol
Tol
Tol
ii) A solution of [Ar ]Ta(NMe ) Et (5 mg, 0.01 mmol) in d -
benzene (ca. 0.7 mL) in an NMR tube equipped with a J. Young valve
was heated at 100 °C for 3 h, thereby demonstrating the formation of,
[s, 2C of Ar ], 136.4 [s, 2C of Ar ], 141.0 [s, 2C of Ar ], 143.6
2 2
2
3
6
Tol
Tol
[s, 2C of Ar ], 195.6 [s, 1C of Ar ].
Tol
2
Synthesis of [Ar ]Ta(NMe
added to [Ar ]Ta(NMe
(ca. 0.7 mL) in a small vial. The suspension was mixed for 1 min,
)
2
Et . EtLi (3 mg, 0.08 mmol) was
(15 mg, 0.03 mmol) in d
6
2
2
2
Tol,Tol′
Tol
2
inter alia, [κ -Ar
(
]Ta(NMe ) and ethane.
2
)
2
Cl
2
-benzene
2
3
Tol
2
n
iii) A solution of [Ar ]Ta(NMe ) Pr (5 mg, 0.01 mmol) in d -
2
3
6
benzene (ca. 0.7 mL) in an NMR tube equipped with a J. Young valve
filtered through Celite, and then added to an NMR tube equipped
1
was heated at 100 °C for 3 h, thereby demonstrating the formation of,
with a J. Young valve. The solution was analyzed by H NMR
2
Tol,Tol′
Tol
2
inter alia, [κ -Ar
(
]Ta(NMe ) and propane.
spectroscopy, thereby demonstrating conversion to [Ar ]Ta-
(NMe Et . The mixture was then lyophilized, extracted into pentane
(ca. 1 mL), and allowed to evaporate slowly at −15 °C, thereby giving
2
3
Tol
2
n
iv) A solution of [Ar ]Ta(NMe ) Bu (5 mg, 0.01 mmol) and
2
)
2
2
2
3
d6-benzene (ca. 0.7 mL) in an NMR tube equipped with a J. Young
valve was heated at 100 °C for 3 h, thereby demonstrating the
Tol
2
light-yellow crystals of [Ar ]Ta(NMe
) Et . X-ray quality crystals
2 2 2
2
Tol,Tol′
1
formation of, inter alia, [κ -Ar
(
]Ta(NMe ) and n-butane.
were obtained from a solution in pentane at −15 °C. H NMR
2 3
Tol
2
3
3
v) A solution of [Ar ]Ta(NMe ) Np (5 mg, 0.01 mmol) in d -
(C
6H of Ta(CH
(NMe ], 7.05 [d, JH−H = 8, 4H of Ar ], 7.18 [m, 1H of Ar ],
7.25 [d, JH−H = 7, 2H of Ar ], 7.32 [d, JH−H = 8, 4H of Ar ].
6
D
6
): 0.15 [q, JH−H = 8, 4H of Ta(CH
CH ) ], 1.32 [t, JH−H = 8,
2 3 2
2
2
3
6
Tol
benzene (ca. 0.7 mL) in an NMR tube equipped with a J. Young valve
2
CH ], 2.18 [s, 6H of Me of Ar ], 2.99 [s, 12H of
)
3 2
3
Tol
2
Tol
Tol
2
was heated at 100 °C for 2 h, thereby demonstrating the formation of,
)
2 2
2
Tol,Tol′
3
Tol
2
3
2
inter alia, [κ -Ar
(
]Ta(NMe ) and neopentane.
2 3
2
Tol
13
1
vi) A solution of [Ar ] Ta(NMe ) (10 mg, 0.01 mmol) in d -
C{ H} NMR (C
6
D
6
): 13.6 [s, 2C of Ta(CH
Me of Ar ], 43.4 [s, 4C of (NMe ) ], 71.1 [s, 2C of Ta(CH CH ) ],
CH ) ], 21.2 [s, 2C of
2 3 2
2
2
3
6
Tol
2
benzene (ca. 0.7 mL) in an NMR tube equipped with a J. Young valve
2
2
2
3 2
Tol
2
Tol
2
Tol
2
was allowed to stand at 22 °C for 1 day, thereby demonstrating the
126.0 [s, 1C of Ar ], 128.8 [s, 4C of Ar ], 130.1 [s, 4C of Ar ],
2 2 2
2
Tol,Tol′
Tol
2
Tol
Tol
Tol
formation of, inter alia, [κ -Ar
(
]Ta(NMe ) and [Ar ]H.
130.4 [s, 2C of Ar ], 136.5 [s, 2C of Ar ], 142.0 [s, 2C of Ar ],
2 2
2
3
Tol
2
2
Tol
Tol
vii) A solution of [Ar ]Ta(NMe ) (κ -BH ) (10 mg, 0.02 mmol)
145.3 [s, 2C of Ar ], 197.8 [s, 1C of Ar ].
2
2
3
4
Tol
n
n
in d -benzene (ca. 0.7 mL) in an NMR tube equipped with a J. Young
Synthesis of [Ar ]Ta(NMe ) Pr . Pr Li (3 mg, 0.06 mmol) was
2 2 2
Tol
2
6
valve was treated with PMe (ca. 0.05 mL) and allowed to stand at 22
added to [Ar ]Ta(NMe ) Cl (15 mg, 0.03 mmol) in d -benzene
2 2 2 6
3
2
°
C for 1 day, thereby demonstrating the formation of, inter alia, [κ -
(ca. 0.7 mL) in a small vial. The suspension was mixed for 1 min,
1
838
DOI: 10.1021/acs.organomet.5b00158
Organometallics 2015, 34, 1828−1843

Organometallics
Article
2
filtered through Celite, and transferred to an NMR tube equipped with
(b) A solution of [ArTol ]Ta(NMe ) Np (5 mg, 0.01 mmol) in
2 2 2
1
a J. Young valve. The solution was analyzed by H NMR spectroscopy,
pentane was allowed to stand at room temperature for 2 days in a
sealed vial. After this period, the mixture was filtered. The filtrate was
Tol
2
n
2
thereby demonstrating conversion to [Ar ]Ta(NMe ) Pr . The
2
2
2
mixture was then lyophilized and extracted into pentane (ca. 1 mL).
placed at −15 °C, thereby depositing yellow crystals of [κ -
Tol,Tol′
The extract was allowed to evaporate slowly at −15 °C, thereby giving
Ar
]Ta(NMe ) Np. The mother liquor was removed by using a
2 2
Tol
2
n
light-yellow crystals of [Ar ]Ta(NMe ) Pr . X-ray quality crystals
pipet, and the crystals were washed with cold (−15 °C) pentane (0.5
2
2
2
1
2
Tol,Tol′
1
were obtained from a solution in pentane at −15 °C. H NMR
C D ): 0.04 [m, 4H of Ta(CH CH CH ) ], 0.80 [t, J = 7, 6H of
mL), giving [κ -Ar
]Ta(NMe
CMe
], 2.38 [s, 3H of Me of Ar
2
)
2
Np (2 mg, 45% yield). H NMR
], 1.52 [s, 2H of TaCH CMe ],
], 2.59 [s,
= 8, 2H of Ar ], 7.16 [m, 1H of
3
(
(C ): 0.96 [s, 9H of TaCH
6
D
6
2
3
2
3
6
6
2
2
3
2
H−H
Tol,Tol′
Tol,Tol′
2
1
Ar
.22 [s, 3H of Me of Ar
2H of (NMe ) ], 6.99 [d, J
H−H
Ta(CH CH CH ) ], 1.32 [m, 4H of Ta(CH CH CH ) ], 2.21 [s, 6H
2
2
3
2
2
2
3
2
3
Tol,Tol′
Tol
2
3
of Me of Ar ], 2.97 [s, 12H of (NMe ) ], 7.02 [d, J
Ar ], 7.19 [t, J
Ar ], 7.30 [d, J
s, 2C of Me of Ar ], 22.0 [s, 2C of Ta(CH CH CH ) ], 23.1 [s, 2C
= 8, 4H of
= 7, 2H of
H−H
2
2
2
2
2
H−H
Tol,Tol′
3
Tol
2
3
Tol
3
, under C D H signal, located by 2D COSY], 7.21 [d, J
=
= 7, 1H of Ar ], 7.26 [d, J
= 8, 4H of Ar ]. C{ H} NMR (C D ): 21.2
6
5
H−H
H−H
H−H
Tol,Tol′
Tol,Tol′
3
Tol
2
3
Tol
2
13
1
8, 2H of Ar
], 7.33 [m, 2H of Ar
= 7, J = 2, 1H of Ar
]. C{ H} NMR (C D ): 21.1 [s, 1C of Me of
], 7.83 [d, J
= 8, 1H of
], 8.24 [br s,
H−H
6
6
Tol,Tol′
3
4
Tol,Tol′
Tol
2
Ar
1
Ar
], 7.84 [dd, J
[
H−H
H−H
2
2
3 2
Tol,Tol′
13
1
H of Ar
of Ta(CH CH CH ) ], 43.5 [s, 4C of (NMe ) ], 83.1 [s, 2C of
6
6
2
2
3
2
2 2
Tol,Tol′
Tol,Tol′
Tol
2
Tol
2
], 21.9 [s, 1C of Me of Ar
], 35.7 [s, 3C of TaCH CMe ],
Ta(CH CH H ) ], 125.6 [s, 1C of Ar ], 128.8 [s, 4C of Ar ],
29.9 [s, 4C of Ar ], 130.4 [s, 2C of Ar ], 136.5 [s, 2C of Ar ],
41.9 [s, 2C of Ar ], 144.7 [s, 2C of Ar ], 197.6 [s, 1C of Ar ].
Synthesis of [Ar ]Ta(NMe ) Bu . Bu Li (2 mg, 0.03 mmol)
2 3
2
2
3 2
Tol
2
Tol
2
Tol
2
37.4 [s, 1C of TaCH CMe ], 39.1 [br s, 4C of (NMe ) ], 96.2 [very br
1
1
2 3 2 2
Tol,Tol′
Tol
2
Tol
2
Tol
2
s, 1C of TaCH CMe ], 119.4 [s, 1C of Ar
], 122.1 [s, 1C of
, obscured by the solvent but the
assignment is supported by 2D HSQC and HMBC spectroscopy],
2
3
Tol,Tol′
Tol,Tol′
Tol
2
n
n
Ar
], 128.7 [s, 2C of Ar
2
2
2
Tol
2
was added to [Ar ]Ta(NMe ) Cl (10 mg, 0.03 mmol) in d6-
2
2
2
Tol,Tol′
Tol,Tol′
1
Ar
28.7 [s, 2C of Ar
], 129.5 [s, 2C of Ar
], 130.0 [s, 1C of
benzene (ca. 0.7 mL) in a small vial. The suspension was mixed for 1
Tol,Tol′
Tol,Tol′
Tol,Tol′
], 135.0 [s, 1C of Ar
], 135.2 [s, 1C of Ar
], 141.9 [s,
min, filtered through Celite, and transferred to an NMR tube equipped
Tol,Tol′
Tol,Tol′
Tol,Tol′
1
1C of Ar
], 145.3 [s, 1C of Ar
], 154.9 [s, 1C of Ar
, confirmed by 2D HMBC spectroscopy], 201.5 [s, 1C
], 152.2 [s, 1C of Ar
],
with a J. Young valve. The solution was analyzed by H NMR
Tol,Tol′
Tol,Tol′
Tol
2
154.3 [s, 1C of Ar
], 197.7 [very br s,
spectroscopy, thereby demonstrating conversion to [Ar ]Ta-
Tol,Tol′
n
1C of Ar
of Ar
(
NMe ) Bu . The mixture was then lyophilized and extracted into
2 2 2
Tol,Tol′
].
pentane (ca. 1 mL). The extract was allowed to evaporate slowly at
Kinetics of Elimination of Neopentane from [ArTol2]Ta-
NMe ) Np . A solution of [Ar ]Ta(NMe ) Np (10 mg, 0.02
mmol) in d -benzene was transferred to an NMR tube equipped with a
Tol
2
n
−
15 °C, thereby giving light-yellow crystals of [Ar ]Ta(NMe ) Bu .
Tol
2
2
2
2
(
2
2
2
2
2
2
X-ray quality crystals were obtained from a solution in pentane at −15
1
6
°
t, J
C. H NMR (C D ): 0.04 [m, 4H of Ta(CH CH CH CH ) ], 0.83
Tol
2
6
6
2
2
2
3
2
J. Young valve. The kinetics of the conversion of [Ar ]Ta-
3
3
[
= 7, 6H of Ta(CH CH CH CH ) ], 1.10 [sextet, J
= 7,
2
Tol,Tol′
H−H
2
2
2
3
2
H−H
(NMe ) Np to [κ -Ar
]Ta(NMe ) Np and neopentane were
2
2
2
2 2
4
H of Ta(CH CH CH CH ) ], 1.28 [m, 4H of Ta-
2 2 2 3 2
2
measured at 47 °C by monitoring the intensity of the (NMe ) groups
for both compounds in the probe of the NMR spectrometer.
2 2
Tol
(
(
CH CH CH CH ) ], 2.21 [s, 6H of Me of Ar ], 2.99 [s, 12H of
2 2 2 3 2
2
3
Tol
3
NMe ) ], 7.03 [d, J
= 8, 4H of Ar ], 7.19 [m, J
= 7, 1H of
= 8, 4H of
2
2
H−H
H−H
2
Tol,Tol′
]Ta(NMe )
Np to [κ2-
2 2
Tol
2
Tol
2
3
Tol
2
3
Isomerization of [κ -Ar
Ar ], 7.26 [m, J
Ar
= 7, 2H of Ar ], 7.31 [d, J
Tol,Tol′
H−H
H−H
Ar*
]Ta-(NMe ) Np. A solution of [Ar ]Ta(NMe ) Np (10
2 2 2 2 2
T ol
2
1 3
1
].
C{ H} NMR (C D ): 13.8 [s, 2C of Ta-
6 6
2
mg, 0.02 mmol) in d -benzene was transferred to an NMR tube
equipped with a J. Young valve and heated at 80 °C for ca. 6 h.
Analysis by H NMR spectroscopy demonstrated conversion to, inter
]Ta-(NMe ) Np. H NMR (C D ) (2D COSY
experiment was also conducted to assist with assignment, which is
tentative due to the presence of an unidentified compound): 1.10 [s,
Tol
6
(
CH CH CH CH ) ], 21.2 [s, 2C of Me of Ar ], 30.1 [s, 2C of
2
2
2
3 2
Ta(CH CH CH CH ) ], 31.6 [s, 2C of Ta(CH CH CH CH ) ], 43.4
1
2
2
2
3
2
2
2
2
3 2
[
s, 4C of (NMe ) ], 79.5 [s, 2C of Ta(CH CH CH CH ) ], 125.6 [s,
2
Tol,Tol′
1
2
2
2
2
2
3 2
alia, [κ -Ar*
Tol
2
Tol
2
Tol
2
2 2 6 6
1
2
2
C of Ar ], 128.8 [s, 4C of Ar ], 130.0 [s, 4C of Ar ], 130.4 [s,
Tol
2
Tol
2
Tol
2
C of Ar ], 136.5 [s, 2C of Ar ], 142.0 [s, 2C of Ar ], 144.8 [s,
Tol
2
Tol
2
C of Ar ], 200.8 [s, 1C of Ar ].
9
H of TaCH CMe ], 1.85 [s, 2H of TaCH CMe ], 2.18 [s, 3H of Me
2 3 2 3
Tol
2
Synthesis of [Ar ]Ta(NMe ) Np . NpLi (19 mg, 0.24 mmol)
Tol,Tol′
Tol,Tol′
2
2
2
of Ar
], 2.39 [s, 3H of Me of Ar
], 2.83 [s, 12H of (NMe ) ],
2
2
Tol
2
was added to a suspension of [Ar ]Ta(NMe ) Cl (60 mg, 0.10
3
Tol,Tol′
Tol,Tol′
3
2
2
2
7.11 [d, J
8, J
= 8, 1H of Ar
= 2, 1H of Ar
and 2H of Ar
], 7.66 [d, J
], 7.62 [dd, J
H−H
H−H
mmol) in pentane (ca. 2 mL), and the mixture was stirred for ca. 5
min. After this period, the mixture was the filtered through Celite. The
filtrate was placed at −15 °C, thereby depositing yellow crystals of
4
Tol,Tol′
3
Tol,Tol′
=
= 8, 2H of Ar
],
], 8.11 [d,
H−H
H−H
3
Tol,Tol′
Tol,Tol′
7
.81 [d, J
= 8, 1H of Ar
], 7.90 [s, 1H of Ar
H−H
3
Tol,Tol′
4
Tol,Tol′
J
= 8, 1H of Ar
], 8.15 [d, J
= 2, 1H of Ar
].
H−H
H−H
Tol
2
13
1
[
Ar ]Ta(NMe ) Np over a period of ca. 1 day. The mother liquor
C{ H} NMR (C D ) (assignment is tentative because obtained as a
2 2 2
6
6
was removed by using a pipet, and the crystals were washed with cold
mixture of compounds; 2D HSQC and 2D HMBC experiments were
also conducted to assist with assignment): 21.1 [s, 1C of Me of
Tol
2
(
−15 °C) pentane (2 × 0.5 mL), giving [Ar ]Ta(NMe ) Np (27
2
2
2
Tol,Tol′
Tol,Tol′
mg, 40% yield). X-ray quality crystals were obtained from a solution in
pentane at −15 °C. Anal. Calcd: C, 61.1%, H, 7.7%, N, 4.2%. Found:
C, 60.9%, H, 7.7%, N, 4.2%. 1H NMR (C D ): 0.12 [s, 4H of
Ar
], 22.0 [s, 1C of Me of Ar
], 35.1 [s, 3C of TaCH CMe ],
2 3
37.9 [s, 1C of TaCH CMe ], 40.0 [s, 4C of (NMe ) ], 99.5 [s, 1C of
2
3
2 2
Tol,Tol′
Tol,Tol′
TaCH
125.4 [s, 1C of Ar
CMe
], 119.5 [s, 1C of Ar
], 121.2 [s, 1C of Ar
],
], 129.7 [s, 2C of
], 135.6 [s, 1C of Ar
6
6
2
3
Tol,Tol′
Tol,Tol′
Ta(CH CMe ) ], 0.93 [s, 18H of Ta(CH CMe ) ], 2.23 [s, 6H of Me
], 127.5 [s, 2C of Ar
2
3
2
2
3
2
Tol
2
3
Tol
2
Tol,Tol′
Tol,Tol′
Tol,Tol′
of Ar ], 3.30 [s, 12H of (NMe ) ], 7.08 [d, J
.13 [m, 1H of Ar ], 7.23 [m, 6H of Ar ]. C{ H} NMR (C D ):
1.2 [s, 2C of Me of Ar ], 34.8 [s, 6C of Ta(CH CMe ) ], 38.5 [s,
C of Ta(CH CMe ) ], 47.7 [s, 4C of (NMe ) ], 111.5 [s, 2C of
= 8, 4H of Ar ],
Ar
1C of Ar
], 130.0 [s, 1C of Ar
], 136.6 [s,
2
2
H−H
Tol
2
Tol
2
13
1
Tol,Tol′
Tol,Tol′
Tol,Tol′
7
2
2
], 139.7 [s, 2C of Ar
], 140.2 [s, 1C of Ar
],
6
6
Tol
2
Tol,Tol′
Tol,Tol′
142.2 [s, 1C of Ar
], 154.1 [s, 1C of Ar
], 158.1 [s, 1C of
2
3 2
Tol,Tol′
Tol,Tol′
Tol,Tol′
Ar
], 199.7 [s, 1C of Ar
], 201.2 [s, 1C of Ar
].
2
3
2
2 2
Tol
2
2
Tol
2
Tol
2
Kinetics of Conversion of [Ar ]Ta(NMe ) Np to [κ -
Ta(CH CMe ) ], 125.9 [s, 1C of Ar ], 129.0 [s, 4C of Ar ], 130.3
2 2
2
2
3 2
Tol,Tol′
2
Tol
2
Tol
2
Tol
2
Ar
]Ta(NMe ) Np and Subsequent Isomerizaton to [κ -
2 2
Tol
2
[
[
s, 4C of Ar ], 130.4 [s, 2C of Ar ], 136.5 [s, 2C of Ar ], 143.9
s, 2C of Ar ], 146.2 [s, 2C of Ar ], 201.6 [s, 1C of Ar ].
Tol,Tol′
Tol
2
Tol
2
Tol
2
Ar*
]Ta(NMe ) Np. A solution of [Ar ]Ta(NMe ) Np (10
2 2 2 2 2
mg, 0.02 mmol) in d -benzene was transferred to an NMR tube
6
2
Tol,Tol′
Synthesis of [κ -Ar
]Ta(NMe ) Np. (a) A solution of
2 2
equipped with a J. Young valve. The kinetics of the conversion of
Tol
2
Tol
2
2
Tol,Tol′
[
Ar ]Ta(NMe ) Np (10 mg, 0.02 mmol) in d -benzene in an
2 2 2 6
[Ar ]Ta(NMe ) Np to [κ -Ar
]Ta(NMe ) Np and neopen-
2
2
2
2 2
2
Tol,Tol′
NMR tube equipped with a J. Young valve was allowed to stand at
tane and subsequent isomerization to [κ -Ar*
]Ta(NMe ) Np
2 2
1
room temperature for 2 days. Analysis by H NMR spectroscopy
was measured at 67 °C by monitoring the intensity of the (NMe2)2
groups for all three compounds in the probe of the NMR
spectrometer.
2
Tol,Tol′
demonstrated conversion to, inter alia, [κ -Ar
]Ta(NMe ) Np
2 2
(
ca. 90%) and NpH. The mixture was lyophilized and extracted into
Tol
2
t
pentane (1 mL). The extract was placed at −15 °C, thereby depositing
Synthesis of d -[Ar ]Ta(NMe ) (CD Bu ) . A suspension of
4 2 2 2 2
Tol
2
2
Tol,Tol′
yellow crystals of [κ -Ar
]Ta(NMe ) Np, which were used for X-
[Ar ]Ta(NMe ) Cl (30 mg, 0.05 mmol) in pentane (ca. 2 mL) was
2 2 2
added to d -Bu CD Li (12 mg, 0.15 mmol) and stirred for ca. 5 min.
2
2
t
ray diffraction studies.
2 2
1
839
DOI: 10.1021/acs.organomet.5b00158
Organometallics 2015, 34, 1828−1843

Organometallics
Article
The mixture was then filtered through Celite. The filtrate was placed at
C.; Lei, H.; Power, P. P. Organometallics 2010, 29, 1988−1991. (g) Ni,
C.; Fettinger, J. C.; Power, P. P. Organometallics 2010, 29, 269−272.
(10) (a) Ni, C.; Long, G. J.; Power, P. P. Organometallics 2009, 28,
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263−267. (b) Lei, H.; Ellis, B. D.; Ni, C.; Grandjean, F.; Long, G. J.;
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A.; Long, G. J.; Power, P. P. Chem. Commun. 2010, 46, 4466−4468.
−
15 °C for several days, thereby depositing yellow crystals of d -
4
2
Tol t
[
Ar ]Ta(NMe ) (CD Bu ) . The mother liquor was removed by
2 2 2 2
using a pipet, and the crystals were washed with cold (−15 °C)
Tol
2
t
pentane (3 × 0.5 mL), giving d -[Ar ]Ta(NMe ) (CD Bu ) (5 mg,
4
2
2
2
2
1
1
5% yield). H NMR (C D ): 0.93 [s, 18H of Ta(CD CMe ) ], 2.23
s, 6H of Me of Ar ], 3.30 [s, 12H of (NMe ) ], 7.08 [d, J
H of Ar ], 7.13 [m, 1H of Ar ], 7.23 [m, 6H of Ar ]. H NMR
6
6
2
3
2
Tol
2
3
[
4
= 8,
2
3
H−H
Tol
2
Tol
2
Tol
2
2
(
C D ): 0.03 [s, 4D of Ta(CD CMe ) ].
6 6 2 3 2
(
12) (a) Lang, H.; Ko
M.; Driess, A.; Huttner, G.; Strah
05. (b) Groysman, S.; Holm, R. H. Inorg. Chem. 2009, 48, 621−627.
c) He, X.; Olmstead, M. M.; Power, P. P. J. Am. Chem. Soc. 1992, 114,
̈
hler, K.; Rheinwald, G.; Zsolnai, L.; Bu
̈
chner,
ASSOCIATED CONTENT
Supporting Information
̈
le, J. Organometallics 1999, 18, 598−
■
6
*
S
(
Crystallographic data for structurally characterized compounds
PDF, CIF). This material is available free of charge via the
9
1
1
9
668−9670. (d) Hwang, C.-S.; Power, P. P. J. Am. Chem. Soc. 1998,
20, 6409−6410. (e) Hwang, C.-S.; Power, P. P. Organometallics 1999,
8, 697−700. (f) Schiemenz, B.; Power, P. P. Organometallics 1996, 15,
58−964. (g) Niemeyer, M. Z. Anorg. Allg. Chem. 2003, 629, 1535−
(
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
E-mail: parkin@columbia.edu.
■
1540. (h) Niemeyer, M. Z. Anorg. Allg. Chem. 2004, 630, 252−256.
(13) Hwang, C.-S.; Power, P. P. J. Organomet. Chem. 1999, 589, 234−
2
38.
*
(
14) Rabe, G. W.; Mitzel, N. W. Inorg. Chim. Acta 2001, 316, 132−
34.
15) (a) Schiemenz, B.; Power, P. P. Angew. Chem., Int. Ed. 1996, 35,
150−2152. (b) Hardman, N. J.; Twamley, B.; Stender, M.; Baldwin,
Notes
1
The authors declare no competing financial interest.
(
2
ACKNOWLEDGMENTS
R.; Hino, S.; Schiemenz, B.; Kauzlarich, S. M.; Power, P. P. J.
Organomet. Chem. 2002, 643−644, 461−467. (c) Girolami, G. S.;
Riehl, M. E.; Suslick, K. S.; Wilson, S. R. Organometallics 1992, 11,
■
We thank the U.S. Department of Energy, Office of Basic
Energy Sciences (DE-FG02-93ER14339), for support of this
research.
3
907−3910. (d) Crittendon, R. C.; Beck, B. C.; Su, J.; Li, X.-W.;
Robinson, G. H. Organometallics 1998, 18, 156−160.
(
16) The terphenyl ligand {[Ar ]Na}2 does not exhibit κ1
Mes
2
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(
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M−H bond energy data for tantalum, stronger bonds to NMe have
2
1
842
DOI: 10.1021/acs.organomet.5b00158
Organometallics 2015, 34, 1828−1843

Organometallics
Article
t
t
(
76) Bu CD I is prepared from Bu CD OH, which is obtained by
2
2
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̈
̈
1
1
843
DOI: 10.1021/acs.organomet.5b00158
Organometallics 2015, 34, 1828−1843