Synthetic and mechanistic investigations of trimethylsilyl-substituted triamidoamine complexes of tantalum that contain metal-ligand multiple bonds

Article abstract of DOI:10.1021/ja953826n

[N₃N]Ta=PPh ([N₃N]^3- = [(Me₃SiNCH₂CH₂)₃N]^3-) reacts with excess lithium metal in tetrahydrofuran to give '[N₃N]Ta=PLi', as judged by NMR studies and by reactions with RX at -35°C to afford the phosphinidene complexes [N₃N]Ta=PR (R = Me, n-Bu, SiMe₃, SiMe₂Ph). [N₃N]TaCl₂ reacts with 2 equiv of LiN(H)R (R = H, CMe₃, Ph) to produce 1 equiv of RNH₂ and imido complexes [N₃N]Ta=NR and with 2 equiv of benzylmagnesium chloride or ((trimethylsilyl)methyl)lithium to afford the alkylidene complexes [N₃N]Ta=CHR (R = Ph or SiMe₃). The ethylene complex [N₃N]Ta(C₂H₄) is formed quantitatively upon addition of 2 equiv of ethylmagnesium chloride to [N₃N]TaCl₂. [N₃N]Ta(C₂H₄) decomposes in a first-order manner in solution over a period of days at room temperature to give a complex in which a C-N bond in the TREN backbone has been cleaved. Alkylation of [N₃N]TaCl₂ with 2 equiv of RCH₂CH₂MgX (R = CH₃, CH₂CH₃, CH(CH₃)₂, C(CH₃)₃; X = Cl or Br) produces a mixture of alkylidene and products derived from decomposition of the incipient olefin complex. When R = t-Bu, only an alkylidene complex is formed as a consequence of a sterically disfavored β abstraction process. [N₃N]TaCl₂ reacts with 2 equiv of vinylmagnesium bromide to afford white crystalline [N₃N]Ta(C₂H₂). An analogous benzyne complex can be prepared by refluxing [N₃N]TaCl₂ with 2 equiv of phenyllithium in toluene. [N₃N]Ta(C₂H₄) reacts with a catalytic amount of phenylphosphine to afford [N₃N]Ta=CHMe, while reactions with ammonia, aniline, or pentafluoroaniline yield [N₃N]Ta=NR complexes. In contrast, excess Me₃SiAsH₂ reacts with [N₃N]Ta(C₂H₄) to afford [N₃N]Ta=CHMe first, and then what is proposed to be [N₃N]Ta=AsSiMe₃. [N₃N]Ta(C₂H₄) reacts with dihydrogen to give [N₃N]Ta(H)(C₂H₅) reversibly. [N₃N]Ta(C₆H₄) reacts with ArNH₂ (Ar = Ph, C₆F₅) to give [N₃N]Ta=NAr complexes, but [N₃N]Ta(C₂H₂) is relatively unreactive. X-ray structures of [N₃N]Ta(Me)Et and [N₃N]Ta(C₂H₂) are included.

Full text of DOI:10.1021/ja953826n

J. Am. Chem. Soc. 1996, 118, 3643-3655
3643
Synthetic and Mechanistic Investigations of
Trimethylsilyl-Substituted Triamidoamine Complexes of
Tantalum That Contain Metal-Ligand Multiple Bonds
Joel S. Freundlich, Richard R. Schrock,* and William M. Davis
Contribution from the Department of Chemistry 6-331, Massachusetts Institute of Technology,
Cambridge, Massachusetts 02139
ReceiVed NoVember 14, 1995X
Abstract: [N3N]TadPPh ([N3N]3- ) [(Me3SiNCH2CH2)3N]3-) reacts with excess lithium metal in tetrahydrofuran
to give “[N3N]TadPLi”, as judged by NMR studies and by reactions with RX at -35 °C to afford the phosphinidene
complexes [N3N]TadPR (R ) Me, n-Bu, SiMe3, SiMe2Ph). [N3N]TaCl2 reacts with 2 equiv of LiN(H)R (R ) H,
CMe3, Ph) to produce 1 equiv of RNH2 and imido complexes [N3N]TadNR and with 2 equiv of benzylmagnesium
chloride or ((trimethylsilyl)methyl)lithium to afford the alkylidene complexes [N3N]TadCHR (R ) Ph or SiMe3).
The ethylene complex [N3N]Ta(C2H4) is formed quantitatively upon addition of 2 equiv of ethylmagnesium chloride
to [N3N]TaCl2. [N3N]Ta(C2H4) decomposes in a first-order manner in solution over a period of days at room
temperature to give a complex in which a C-N bond in the TREN backbone has been cleaved. Alkylation of
[N3N]TaCl2 with 2 equiv of RCH2CH2MgX (R ) CH3, CH2CH3, CH(CH3)2, C(CH3)3; X ) Cl or Br) produces a
mixture of alkylidene and products derived from decomposition of the incipient olefin complex. When R ) t-Bu,
only an alkylidene complex is formed as a consequence of a sterically disfavored â abstraction process. [N3N]-
TaCl2 reacts with 2 equiv of vinylmagnesium bromide to afford white crystalline [N3N]Ta(C2H2). An analogous
benzyne complex can be prepared by refluxing [N3N]TaCl2 with 2 equiv of phenyllithium in toluene. [N3N]Ta-
(C2H4) reacts with a catalytic amount of phenylphosphine to afford [N3N]TadCHMe, while reactions with ammonia,
aniline, or pentafluoroaniline yield [N3N]TadNR complexes. In contrast, excess Me3SiAsH2 reacts with [N3N]Ta-
(C2H4) to afford [N3N]TadCHMe first, and then what is proposed to be [N3N]TadAsSiMe3. [N3N]Ta(C2H4) reacts
with dihydrogen to give [N3N]Ta(H)(C2H5) reversibly. [N3N]Ta(C6H4) reacts with ArNH2 (Ar ) Ph, C6F5) to give
[N3N]TadNAr complexes, but [N3N]Ta(C2H2) is relatively unreactive. X-ray structures of [N3N]Ta(Me)Et and
[N3N]Ta(C2H2) are included.
Introduction
num and tungsten terminal phosphido complexes.10 Key
features of complexes that contain a [(RNCH2CH2)3N]3- ligand
include the sterically protected “pocket” formed by the bulky
R groups and the presence of one σ-type and two orthogonal π
metal orbitals directed toward the remaining (fifth) coordination
site. This orbital arrangement is ideally suited for forming d0
complexes that contain a triple bond or pseudo triple bond
between the metal and the ligand in the apical coordination site,
a double and a single bond, or (sterically least feasibly) three
single bonds. (The [(RNCH2CH2)3N]3- ligand itself is only a
12-electron donor (4σ,2π) since one of the three linear combina-
tions of atomic orbitals constructed from the p orbitals on the
three amido nitrogens is a ligand-centered nonbonding orbital.)
In view of tantalum’s ability to form multiple bonds to C, N,
or O,20 and because many starting materials are readily available,
we chose to explore the chemistry of [(Me3SiNCH2CH2)3N]-
Ta(X) complexes that contain a multiple Ta-X bond. We first
Recent efforts in these laboratories1-10 and others11-19 have
focused on the preparation of complexes of metals in groups 4,
5, and 6 that contain tetradentate triamidoamine ligands,
[(RNCH2CH2)3N]3-. When R is a bulky silyl group (usually
SiMe3), rare types of complexes can be prepared, e.g., a
tantalum(V) phosphinidene,3 a VdNH species,6 and molybde-
X Abstract published in AdVance ACS Abstracts, April 1, 1996.
(1) Cummins, C. C.; Schrock, R. R.; Davis, W. M. Organometallics 1992,
11, 1452.
(2) Cummins, C. C.; Lee, J.; Schrock, R. R. Angew. Chem., Int. Ed. Engl.
1992, 31, 1501.
(3) Cummins, C. C.; Schrock, R. R.; Davis, W. M. Angew. Chem., Int.
Ed. Engl. 1993, 32, 756.
(4) Kol, M.; Schrock, R. R.; Kempe, R.; Davis, W. M. J. Am. Chem.
Soc. 1994, 116, 4382.
(5) Freundlich, J. S.; Schrock, R. R.; Cummins, C. C.; Davis, W. M. J.
Am. Chem. Soc. 1994, 116, 6476.
(6) Cummins, C. C.; Schrock, R. R.; Davis, W. M. Inorg. Chem. 1994,
33, 1448.
reported that [N3N]TaCl2 ([N3N]3- ) [(Me3SiNCH2CH2)3N]3-
)
reacts with 2 equiv of a lithium phosphide LiP(H)R (R ) Ph,
Cy, t-Bu) to afford 1 equiv of RPH2 and gold crystalline d0
phosphinidene complexes, [N3N]TadPR, in moderate to high
yields.3 An X-ray crystal structure of [N3N]TadPCy revealed
(7) Shih, K.-Y.; Schrock, R. R.; Kempe, R. J. Am. Chem. Soc. 1994,
116, 8804.
(8) Shih, K.-Y.; Totland, K.; Seidel, S. W.; Schrock, R. R. J. Am. Chem.
Soc. 1994, 116, 12103.
(9) Schrock, R. R.; Shih, K.-Y.; Dobbs, D.; Davis, W. M. J. Am. Chem.
Soc. 1995, 117, 6609.
(10) Zanetti, N.; Schrock, R. R.; Davis, W. M. Angew. Chem., Int. Ed.
Engl. 1995, 34, 2044.
(11) Christou, V.; Arnold, J. Angew. Chem., Int. Ed. Engl. 1993, 32,
1450.
(12) Naiini, A. A.; Menge, W. M. P. B.; Verkade, J. G. Inorg. Chem.
1991, 30, 5009.
(13) Plass, W.; Verkade, J. G. J. Am. Chem. Soc. 1992, 114, 2275.
(14) Naiini, A. A.; Ringrose, S. L.; Su, Y.; Jacobson, R. A.; Verkade, J.
G. Inorg. Chem. 1993, 32, 1290.
(15) Plass, W.; Verkade, J. G. Inorg. Chem. 1993, 32, 3762.
(16) Verkade, J. G. Acc. Chem. Res. 1993, 26, 483.
(17) Duan, Z.; Verkade, J. G. Inorg. Chem. 1995, 34, 1576.
(18) Schubart, M.; O’Dwyer, L.; Gade, L. H.; Li, W.-S.; McPartlin, M.
Inorg. Chem. 1994, 33, 3893.
(19) Hill, P. L.; Yap, G. A.; Rheingold, A. L.; Maatta, E. A. J. Chem.
Soc., Chem. Commun. 1995, 737.
(20) Schrock, R. R. In Reactions of Coordinated Ligands; Braterman,
P. R., Ed.; Plenum: New York, 1986.
0002-7863/96/1518-3643$12.00/0 © 1996 American Chemical Society

3644 J. Am. Chem. Soc., Vol. 118, No. 15, 1996
Freundlich et al.
Table 1. 31P NMR Data and Yields for Phosphinidene Complexes
ligands in related neutral d0 complexes, [N3N]MotP,10
[N3N]WtP,10 and [(t-Bu)NAr]3MotP21 (Ar ) 3,5-Me2C6H3),
range from 1080 to 1346 ppm. Therefore a chemical shift of
575 ppm, even though it is ∼400 ppm larger than that in a
typical TadPR species (∼200 ppm), we believe to be too small
to ascribe to a “{[N3N]TatP}-” species, i.e., one in which
lithium is not bound to the phosphorus. Since bent phosphin-
idenes are characterized by a more downfield resonance (335
ppm in (t-Bu3SiO)3TadPPh22 and 600-800 ppm in Cp2MdPR
complexes (M ) Mo, W, Zr)23-25), a chemical shift of 575 ppm
would be more consistent with a “[N3N]TadPLi” species in
which the Ta-P-Li bond angle is less than 180°. Unfortu-
nately, we could find no way to separate the “[N3N]TadPLi”
species from phenyllithium, the other product of the cleavage
reaction, and so could not isolate and structurally characterize
it.
RX
MeI
n-BuBr
Me3SiCl
PhMe2SiCl
product
31P δ
yielda (%)
1a
1b
1c
1d
157
33
68
58
77
186
212b
203c
a Determined via 1H NMR with a (Me3Si)2O internal standard. b ∆ν1/2
≈ 3600 Hz (23 °C), 400 Hz (-30 °C), 300 Hz (-60 °C). c ∆ν1/2
3600 Hz (23 °C), 800 Hz (-30 °C), 400 Hz (-60 °C).
≈
an essentially linear Ta-P-C angle and a Ta-P bond length
(2.145 Å) consistent with a pseudo triple bond between Ta and
P. We subsequently turned to the synthesis and reactions of
alkylidene, olefin, and acetylene complexes.5 Full details and
additional results in both areas are reported here.
Results
All attempts to prepare [N3N]TadPH so far have failed. For
example, the reaction of [N3N]TaCl2 with 2 equiv of LiPH2 in
1,2-dimethoxyethane at -78 °C afforded intractable products,
while quenching “[N3N]TadPLi” with proton sources such as
HNMe3Cl or 2,6-lutidinium triflate led to complex mixtures in
which no species could be identified.
Synthesis of Tantalum Phosphinidene and Imido Com-
plexes. We became interested in the possibility of preparing
the parent phosphinidene complex, [N3N]TadPH, or the
terminal phosphido complex, {[N3N]TatP}-. We found that
[N3N]TadPPh reacts with excess lithium metal in tetrahydro-
furan to give a species whose 31P NMR spectrum reveals a
resonance at 575 ppm (∆ν1/2 ≈ 600 Hz). This species reacts at
-35 °C with alkyl and silyl halides to yield the phosphinidene
complexes [N3N]TadPR (R ) Me, n-Bu, SiMe3, SiMe2Ph),
1a-d (eq 1), according to 31P NMR data. The yields of the
[N3N]TaCl2 reacts with 2 equiv of LiN(H)R (R ) H, CMe3,
Ph) to produce 1 equiv of RNH2 and imido complexes 2a-c in
62-95% yield (eq 3). The synthesis of 2a is noteworthy, as
parent imido complexes are relatively rare.6,26-29 NMR and IR
spectra of 2a are similar to those for [N3N]VdNH, which has
been structurally characterized.6 A notable difference is that
the imido proton resonance is observed as a broad 1:1:1 triplet
1. 5 equiv of Li, THF
[N3N]TadPPh 2. 3 equiv of RX, THF, -35 °C8
1
1
14
( J
) 50 Hz) in 2a whereas it is not seen in the H NMR
NH
[N3N]TadPR + PhR + 2LiX (1)
1a-d
spectrum of [N3N]VdNH, presumably as a consequence of
additional coupling to 51V (I ) 7/2, 99.75%). Resolved coupling
between the imido proton and 14N has also been observed in
Cp*MMe3(NH) (M ) Mo, W) complexes27,28 and was attributed
to a low electric field gradient about the imido nitrogen.30 The
white crystalline imido complexes are stable when heated as
∼0.1 M solutions in toluene-d8 in sealed NMR tubes to 110 °C
for several days. They do not react with benzaldehyde in
benzene-d6 (∼0.1 M in Ta, 2 days) at ∼25 °C to yield known
[N3N]TadO.3
R ) Me (1a), n-Bu (1b), SiMe3 (1c), SiMe2Ph (1d)
phosphinidene complexes, as judged by proton NMR versus
an internal standard, are listed in Table 1. The NMR yields
are modest, and isolated yields are poor (10-20%) as a
consequence of the extreme solubility of the phosphinidene
complexes in common organic solvents. The formulations of
1a-d are confirmed by reactions with pivaldehyde to yield
[N3N]TadO and the corresponding trans-phosphaalkenes, which
2LiN(H)R
[N3N]TaCl2
8 [N3N]TadNR + RNH2 (3)
2a-c
Et2O (R ) CMe3, Ph)
THF (R ) H)
-35 °C
1
were identified by H and 31P NMR, a reaction that is known
for several isolated tantalum phosphinidene complexes.3 We
have also prepared complex 1b as shown in eq 2, although the
isolated yield is again low (10%) as a consequence of the high
solubility of 1b in common organic solvents.
R ) H (2a), CMe3 (2b), Ph (2c)
Synthesis and Reactivity of Tantalum Alkylidene Com-
plexes. [N3N]TaCl2 reacts with 2 equiv of ((trimethylsilyl)-
[N3N]TaCl2 2LiP(H)-n-Bu8 [N3N]TadP-n-Bu + n-BuPH2 (2)
Et2O, -35 °C
1b
(21) Laplaza, C. E.; Davis, W. M.; Cummins, C. C. Angew. Chem., Int.
Ed. Engl 1995, 34, 2042.
(22) Bonanno, J. B.; Wolczanski, P. T.; Lobkovsky, E. B. J. Am. Chem.
Soc. 1994, 116, 11159.
(23) Ho, J.; Rousseau, R.; Stephan, D. W. Organometallics 1994, 13,
1918.
(24) Hou, Z.; Breen, T. L.; Stephan, D. W. Organometallics 1993, 12,
3158.
(25) Hitchcock, P. B.; Lappert, M. F.; Leung, W.-P. J. Chem. Soc., Chem.
Commun. 1987, 1282.
(26) Parkin, G.; van Asselt, A.; Leahy, D. J.; Whinnery, L.; Hua, N. G.;
Quan, R. W.; Henling, L. M.; Schaefer, W. P.; Santarsiero, B. D.; Bercaw,
J. E. Inorg. Chem. 1992, 31, 82.
(27) Schrock, R. R.; Glassman, T. E.; Vale, M. G. J. Am. Chem. Soc.
1991, 113, 725.
(28) Glassman, T. E.; Vale, M. G.; Schrock, R. R. Organometallics 1991,
10, 4046.
(29) Chatt, J.; Choukroun, R.; Dilworth, J. R.; Hyde, J.; Vella, P.; Zubieta,
J. Transition Met. Chem. 1979, 4, 59.
A puzzling fact is that the phosphorus resonances in
compounds 1 are broad, especially those in 1c and 1d. Alkyl-
and arylphosphinidenes exhibit a 31P resonance with a half-
height width of 100-200 Hz at 25 °C, while the analogous
resonances in 1c and 1d have widths of 300-400 Hz at -60
°C. We currently attribute the broadened phosphinidene
phosphorus resonances to coupling to 181Ta, but why coupling
is greater in the silyl-substituted phosphinidene complexes is
unclear. Broadened resonances are not found in proton NMR
spectra.
The intermediate whose 31P NMR spectrum contains a
resonance at 575 ppm (∆ν1/2 ≈ 600 Hz) we propose to be
“[N3N]TadPLi”, rather than {[N3N]TatP}-. The primary
reason is that the chemical shifts of the terminal phosphido
(30) Mason, J. In Multinuclear NMR; Mason, J., Ed.; Plenum Press: New
York, 1987; Chapter 2.

Triamidoamine Complexes of Tantalum
J. Am. Chem. Soc., Vol. 118, No. 15, 1996 3645
2EtMgCl
methyl)lithium or benzylmagnesium chloride to afford the
alkylidene complexes 3a and 3b (eq 4) in >90% yield. We
[N3N]TaCl2
8 [N3N]Ta(C2H4)
(6)
Et2O, -35 °C
4
[N3N]TaCl2 dialkylation 8 [N3N]TadCHR + RCH3 (4)
Et2O, -35 °C
NMR time scale, even at -90 °C. The ethylene ligand is
observed as a singlet at 2.15 ppm in the proton NMR spectrum
and a triplet (1JCH ) 144 Hz) at 62.6 ppm in the 13C NMR
spectrum. We propose that 4 has a structure similar to that of
[N3N]Ta(C2H2) (vide infra) in the solid state, i.e., one in which
the C-C axis of the ethylene is lined up with one of the Ta-N
bonds, but that the ethylene rotates readily in solution to give
a C3-symmetric species on the NMR time scale as a consequence
of the degeneracy of the dxz and dyz orbitals.
3a,b
R ) SiMe3 (3a; LiCH2SiMe3), Ph (3b; PhCH2MgCl)
propose that dialkyl complexes are intermediates in these
reactions for several reasons. First, if only 1 equiv of alkylating
agent is employed, [N3N]Ta(CH2Ph)Cl and [N3N]Ta(CH2-
SiMe3)Cl can be isolated by fractional crystallization, and each
is converted into the expected alkylidene upon reaction with
Reaction of [N3N]TaCl2 with only 1 equiv of ethyl Grignard
reagent yields the yellow crystalline monoethyl derivative 5 in
72% yield (eq 7). 5 reacts immediately with 1 equiv of
ethylmagnesium chloride to yield 4, and with 1 equiv of CD3-
CD2MgBr to afford a 5.7:1 mixture of [N3N]Ta(C2H4) and
[N3N]Ta(C2D4). The labeling experiment suggests that the
intramolecular isotope effect for â abstraction in the diethyl
intermediate is 5.7.
an additional 1 equiv of the appropriate metal alkyl. Second,
32
reaction of Li3[N3N] with Ta(CH2R)2Cl3 (R ) Ph,31 CMe3
)
gives 3b and 3c (eq 5) in yields of 86% and 56%, respectively.
Complexes 3a-c show no signs of decomposition in toluene-
d8 (∼0.1 M) after being heated for days in sealed tubes at 110
°C. They react rapidly with aldehydes to afford a mixture of
[N3N]TadO and cis- and trans-isomers of the expected olefin.
A variety of tantalum alkylidene complexes are known to react
readily with aldehydes in this manner.20,33
EtMgCl
[N3N]TaCl2
8 [N3N]Ta(Et)Cl
(7)
Et2O, -35 °C
Li3[N3N]
5
Ta(CH2R)2Cl3
8 [N3N]TadCHR + RCH3 (5)
Et2O, -35 °C
3b,c
Although 4 is formed upon treatment of [N3N]Ta(Me)OTf
with 1 equiv of ethylmagnesium chloride over a period of 1
day, [N3N]Ta(Me)Cl reacts with 1 equiv of ethyl Grignard under
the same conditions to afford a 2:1 mixture of 4 and [N3N]Ta-
(Me)Et (6, eq 8). [N3N]Ta(Me)Et can be isolated as a yellow
R ) Ph (3b), CMe3 (3c)
Complexes 3a-c all have NMR spectra consistent with 3-fold
symmetry on the NMR time scale. HR resonances are found
near 0 ppm in 1H NMR spectra, a region characteristic of
alkylidenes that are highly “distorted” through an R-agostic34
CH interaction,20,35 and 13C NMR spectra show an alkylidene
carbon resonance in the range 200-215 ppm. We were
EtMgCl
[N3N]Ta(Me)Cl Et O, -35 °C8
2
[N3N]Ta(C2H4) + [N3N]Ta(Me)Et (8)
1
4
6
surprised by the unusually low values for JCH (∼70 Hz), the
R
lowest known for d0 alkylidene complexes.20 The alkylidene
ligands are effectively pseudo triply bound to tantalum as 1σ,2π
ligands. In spite of the fact that the π interactions in the apical
position are of two distinct types, all alkylidene complexes show
3-fold symmetry on the NMR time scale down to -90 °C.
Apparently only steric constraints would lead to a breaking of
the dxz/dyz degeneracy and slowing of “rotation” of the alkylidene
about the Ta-C bond. Such steric constraints would seem to
be minimal, if the TadCRsCâ angle is relatively large. No
crystals suitable for X-ray studies have yet been obtained,
although an X-ray study of a related Et3SiTREN alkylidene
complex of tantalum has recently confirmed that the TadCRsCâ
angle is indeed large (>170°)36 and, therefore, that a large
TadCRsCâ angle should be expected for any alkylidene
complex in this category.
crystalline solid via fractional recrystallization. It shows 3-fold
symmetry on the NMR time scale. Over a period of 1 day at
∼25 °C, 6 decomposes to yield 4 and methane. At 52 °C in
toluene-d8, decomposition of 6 was shown to follow first-order
kinetics with k ) 2.4(1) × 10-4 s-1 (two runs). [N3N]Ta(Me)-
Et is also formed in the reaction between [N3N]Ta(Et)Cl and 1
equiv of methylmagnesium chloride.
An X-ray structure of 6 (Table 2; Figure 1) shows it to be a
six-coordinate species with methyl and ethyl ligands in apical
coordination sites that lie approximately in the N(2)-Ta-N(4)
plane. (Relevant bond lengths and angles are listed in Table
3.) The smaller methyl group is pointed toward N(2). Con-
sequently, the Ta-N(2)-Si(2) angle (136°) is somewhat larger
than the other two Ta-N-Si angles (129° and 132°), but all
are larger than the usual values of 125-126 °C in crystallo-
graphically characterized M[N3N] species.1-3,6,9,10,19 Since the
ethyl ligand points away from the methyl group and between
N(1) and N(3), the N(1)-Ta-N(3) angle opens to 133°,
compared to 104° and 100° for the other two N-Ta-N angles.
The distance between Câ of the ethyl group and Ta is 3.14 Å,
too far for any â agostic interaction; in any case there is no
readily available orbital with which the methyl CH bond can
interact when the ethyl group is oriented in the observed manner.
Therefore we propose that â abstraction first involves rotation
of the ethyl group past one SiMe3 group, possibly with
concomitant “dissociation” of the amine nitrogen donor from
the metal, followed by activation of Hâ through an agostic
interaction with the remaining π orbital that lies in a plane
approximately 90° to that containing Ta, C(9), and C(7). The
Synthesis of a Tantalum Ethylene Complex. r versus â
Abstraction Processes. An ethylene complex (4) is formed
quantitatively upon addition of 2 equiv of ethylmagnesium
chloride to [N3N]TaCl2 (eq 6). An alternate route to 4 consists
of alkylation of [N3N]Ta(Me)OTf5 with 1 equiv of ethylmag-
nesium chloride. Proton and carbon NMR spectra of 4 are
consistent with it being a 3-fold-symmetric complex on the
(31) Messerle, L. W.; Jennische, P.; Schrock, R. R.; Stucky, G. D. J.
Am. Chem. Soc. 1980, 102, 6744.
(32) Schrock, R. R.; Fellmann, J. D. J. Am. Chem. Soc. 1978, 100, 3359.
(33) Schrock, R. R. J. Am. Chem. Soc. 1976, 98, 5399.
(34) Brookhart, M.; Green, M. L. H.; Wong, L. Prog. Inorg. Chem. 1988,
36, 1.
(35) Schultz, A. J.; Williams, J. M.; Schrock, R. R.; Rupprecht, G. A.;
Fellmann, J. D. J. Am. Chem. Soc. 1979, 101, 1593.
(36) Freundlich, J. S.; Schrock, R. R.; Davis, W. M. Submitted for
publication.

3646 J. Am. Chem. Soc., Vol. 118, No. 15, 1996
Freundlich et al.
Table 2. Crystallographic Data, Collection Parameters, and
Refinement Parameters for [N3N]Ta(Me)Et (6) and
[N3N]Ta(C2H2) (8)
Table 3. Selected Intramolecular Distancesa and Anglesb for the
Non-Hydrogen Atoms of [N3N]Ta(Me)Et and [N3N]Ta(C2H2)
Bond Lengths
[N3N]Ta(Me)Et
[N3N]Ta(C2H2)
[N3N]Ta(Me)Et
Ta-N(1)
Ta-N(2)
Ta-N(3)
Ta-N(4)
Ta-C(7)
Ta-C(9)
C(7)-C(8)
[N3N]Ta(C2H2)
empirical formula
formula wt
cryst color, habit
cryst dimens (mm)
C18H47N4Si3Ta
584.80
yellow, plate
0.150 × 0.150 ×
0.05
C17H41N4Si3Ta
566.74
colorless, needle
0.280 × 0.120 ×
0.120
2.00(1)
2.071(9)
1.956(9)
2.444(8)
2.21(1)
2.21(1)
1.55(2)
Ta-N(1)
2.07(1)
2.02(1)
2.04(1)
2.30(1)
2.09(1)
2.10(1)
1.26(2)
Ta-N(2)
Ta-N(3)
Ta-N(4)
Ta-C(7)
Ta-C(8)
C(7)-C(8)
cryst syst
no. reflns used for unit
cell determination
(2θ range, deg)
a (Å)
b (Å)
c (Å)
monoclinic
25 (14.0- 22.0)
orthorhombic
25 (15.0- 25.0)
Bond Angles
10.0504(8)
15.010(1)
17.937(1)
95.79(1)
2692.1(6)
P21/n
17.154(1)
16.756(1)
34.365(3)
90.0
9878(2)
Pbca
[N3N]Ta(Me)Et
[N3N]Ta(C2H2)
Ta-N(1)-Si(1)
Ta-N(2)-Si(2)
Ta-N(3)-Si(3)
N(1)-Ta-N(2)
N(1)-Ta-N(3)
N(2)-Ta-N(3)
Ta-C(7)-C(8)
131.6(5)
136.1(5)
128.8(5)
99.6(4)
133.1(4)
103.7(4)
112.0(9)
Ta-N(1)-Si(1)
Ta-N(2)-Si(2)
Ta-N(3)-Si(3)
N(1)-Ta-N(2)
N(1)-Ta-N(3)
N(2)-Ta-N(3)
126.1(6)
125.7(6)
126.4(6)
110.5(5)
110.6(4)
122.5(5)
â (deg)
V (Å3)
space group
Z
4
8
D
calc (g/cm3)
1.443
1192
41.75
1.525
4528
F000
µ(Mo KR) (cm-1
scan type
temp (°C)
)
45.47
ω-2θ
-72
a In angstroms. b In degrees.
ω-2θ
-86
total no. of unique reflns
3679
9483
no. of observations with
2270
5137
I > 3.00σ(I)
no. of variables
235
439
R
Rw
GOF
0.041
0.035
1.25
0.048
0.053
3.42
ethyl ligand are found at 1.93 and 1.46 ppm, respectively.
Heating of a toluene-d8 solution of [N3N]Ta(C2D4) at 110 °C
in a sealed tube yields a product analogous to 7b that contains
a TaCD2CD2H group. At 70 °C kD ) 1.53(2) × 10-4 s-1 for
a kH/kD of 0.89(2), consistent with a change in hybridization of
the ethylene carbon atoms from sp2 to sp3 in the rate-limiting
step.37 Proton and carbon NMR spectral data are similar to
those for the product resulting from the thermolysis of [(Et3-
SiNCH2CH2)3N]Ta(C2H4), whose structure has been determined
in an X-ray study.36 Thermolysis of [N3N]Ta(C2D4) (0.03 M
Figure 1. X-ray crystal structure of [N3N]Ta(Me)Et (6).
Ta-N(4) distance (2.444 Å) is comparable to that found in
[N3N]TadTe (2.487 Å),11 but is somewhat longer than found
in [N3N]Ta(HCtCH) (2.30 Å; see later).
[N3N]Ta(Et)Cl reacts with 1 equiv of benzylmagnesium
chloride to yield 4. If only 0.5 equiv of Grignard is used, the
proton NMR spectrum shows no evidence for [N3N]Ta(CH2-
Ph)Cl formed by alkyl exchange. [N3N]Ta(CH2Ph)Cl similarly
reacts with 1 equiv of ethylmagnesium chloride to afford 4.
We propose that [N3N]Ta(Et)(CH2Ph) is the intermediate in each
of these reactions. The benzylidene complex (3b) is not formed
in either reaction.
in toluene-d8) in the presence of 1 atm of ethylene produces
only a TaCD2CD2H species. All of these data are consistent
with decomposition of 4 by intramolecular â abstraction of a
proton from the side chain of the amido ligand. The TREN
backbone must turn and flex to a considerable degree, possibly
after dissociation of the apical nitrogen donor atom, in order to
present the C-Hâ bond to the metal for removal of Hâ and
transfer to the ethylene ligand. Formation of 7b′ would
constitute removal of a γ proton if the apical donor nitrogen
were not coordinated at the time.
[N3N]Ta(C2H4) is not stable in solution. After a period of
several days at ∼25 °C, solutions of 4 show signs of decom-
position; the red color lightens, and NMR spectra consistent
with formation of the yellow ethyl complex 7b (eq 9) are
observed. Decomposition of a toluene solution of 4 ([4] )
0.0059, 0.0089, 0.010, 0.012 M) was followed by UV/vis at
494 nm and shown to be first order in tantalum with k ) 1.37-
5
[N3N]TaMe2 decomposes when heated above 60 °C to
1
produce 7a, according to H and 13C NMR spectra (eq 10).
1
(1) × 10-4 s-1 at 70 °C. Most prominent in the H NMR
Thermolysis of [N3N]Ta(CD3)2 produces CD3H and 7a that
1
2
contains a CD3 ligand, according to H and H NMR spectra.
Therefore we can rule out [N3N]Ta(CD2) as an intermediate.
spectrum of 7b are the vinyl resonances, a doublet of doublets
at 6.49 ppm and a doublet at 4.25 ppm. (The latter is obscured
by the 4.07 ppm resonance for the diastereotopic ligand
methylene protons.) The triplet and quartet resonances for the
(37) Carpenter, B. K. Organic Reaction Mechanisms; John Wiley &
Sons: New York, 1984.

Triamidoamine Complexes of Tantalum
J. Am. Chem. Soc., Vol. 118, No. 15, 1996 3647
Table 4. Percent Yields of Alkylidene and Decomposition
Products Resulting from the Reaction between [N3N]TaCl2 and
2RCH2CH2MgX
% olefin
or dec prod.
R
% alkylidene
H
CH3
0
32
96b
66
CH2Me
CHMe2
CMe3
42
54
15
<1
([N3N]Ta(CH2) is still an unknown compound.) It is interesting
to note that in [N3N]TaMe2, as in 4, only two of the three orbitals
in the apical position are used for bonding to apical ligands,
i.e., one orbital is empty. Other species discussed in this paper
in which all three orbitals are involved in bonding to a ligand
in the apical position do not decompose upon heating for days
at 100 °C.
84 (76b)
83 (77b)
a Determined by 1H NMR versus an internal standard of (Me3Si)2O,
unless otherwise noted. b Isolated yield.
Reactions between [N3N]TaCl2 and 2 equiv of RCH2CH2-
MgX (X ) Cl or Br) in which R is not a proton do not yield
olefin complexes analogous to 4, but alkylidene complexes in
yields that correlate with the bulk of the R group, and products
whose NMR spectra are analogous to those of 7a and 7b. We
propose that the latter products arise via facile decomposition
of intermediate olefin complexes. For example, n-propylmag-
nesium chloride affords a mixture of a propylidene complex
(3e) in 32% yield and a decomposition product (7c) in 66%
1
yield, as determined by H NMR versus an internal standard
(eq 11). The spectra of 3e are analogous to those of other
alkylidenes described here; in this case HR is a triplet at -0.28
ppm in the proton NMR spectrum. We propose that 3e and 7c
arise via competitive R and â abstraction, respectively, in a
dipropyl intermediate.
Figure 2. X-ray crystal structure of [N3N]Ta(C2H2) (8).
scale at -90 °C, consistent with rapid “rotation” of the acetylene
about the acetylene-tantalum bond relative to the TREN ligand.
The IR spectrum of 8 shows an acetylenic CtC stretch at 1725
cm-1. [N3N]Ta(C2H2) can be heated to 100 °C for weeks as a
0.01 M toluene-d8 solution in a sealed NMR tube with no sign
of decomposition.
[N3N]TaCl2 2H CdCHMgBr8 [N3N]Ta(C2H2) + H2CdCH2
2
Et2O, -35 °C
Increasing the size of the alkyl group in the alkylation reaction
affords the expected alkylidene complex formed via R abstrac-
tion and less of the decomposition product that ultimately is
formed as a consequence of a â abstraction process (eq 12). As
8
(13)
An X-ray crystal study of 8 revealed two independent
molecules in the unit cell. (See Table 2 for crystallographic
details and Table 3 for selected intramolecular distances and
angles.) A drawing of one of the two molecules is shown in
Figure 2. In the other, the acetylene ligand is disordered; the
site disorder is not imposed by any space group symmetry. Bond
distances and angles in the two molecules are not statistically
different. (For further information, see supporting information.)
8 is best described as a distorted trigonal bipyramid in which
the two axial sites are occupied by the acetylene and the amine
nitrogen donor. The tantalum-Neq distances of 2.02-2.07 Å
and the Ta-Nax bond length of 2.30 Å are similar to those found
in [N3N]TadPCy3 and [N3N]TadSe (2.349 Å).11 The C-C
bond length in the acetylene ligand (1.26 Å) is consistent with
a bond order of ∼2.5. The acetylene C-C bond axis lines up
with the Ta(1)-N(1) bond, therefore opening the N(2)-Ta-
N(3) angle to 123° for steric reasons. The remaining two
N-Ta-N angles are 111°. However, all three Ta-N-Si bond
angles are 126°. Therefore we can say that steric crowding in
the trigonal pocket in 8 is not as severe as it is in 6.
shown in Table 4 the percent yield of alkylidene (by NMR)
increases from 32% (for R ) CH3) to 84% (for R ) CHMe2),
while the amount of decomposition product falls to 66% and
15%, respectively. The reaction between [N3N]TaCl2 and 2
equiv of Me3CCH2CH2MgCl affords an 83% yield of 3h and
1
no observable decomposition product 7e (<1% via H NMR).
This last reaction contrasts markedly with that in which R )
H, in which no alkylidene is formed and 4 is isolated in 96%
yield.
Synthesis of a Tantalum Acetylene and a Benzyne Com-
plex. [N3N]TaCl2 reacts with 2 equiv of vinylmagnesium
bromide to afford white crystalline 8 in 80% yield (eq 13). 8
also can be prepared in 61% yield by treating [N3N]Ta(Me)-
OTf with 1 equiv of vinyl Grignard. The acetylene protons
are observed as a singlet at 12.22 ppm and the acetylenic carbon
atoms as a doublet (1JCH ) 169 Hz) at 219.9 ppm (cf. δ Cacet
at 217 ppm with 1JCH ) 169 Hz in (t-Bu3SiO)3Ta(C2H2)38). 1H
NMR spectra show that 8 is C3 symmetric on the NMR time
A white crystalline benzyne complex (9) can be prepared in
70% yield by refluxing [N3N]TaCl2 with 2 equiv of phenyl-
lithium in toluene for 1 day (eq 14). [N3N]Ta(Ph)Cl can be
observed as an intermediate in the reaction and can be generated
by treating 9 with a stoichiometric amount of hydrochloric acid.
(38) Covert, K. J.; Neithamer, D. R.; Zonnevylle, M. C.; LaPointe, R.
E.; Schaller, C. P.; Wolczanski, P. T. Inorg. Chem. 1991, 30, 2494.

3648 J. Am. Chem. Soc., Vol. 118, No. 15, 1996
Freundlich et al.
HR resonance is a quartet at -0.41 ppm, and the CR resonance
1
is a doublet at 191.2 ppm with JCH ) 69 Hz. We speculate
that the lower energy of 3d relative to 4 in this case is achieved
via the strong interaction between the ethylidene’s C-HR bond
and the metal. Like other alkylidene complexes in this class,
3d reacts with benzaldehyde to afford [N3N]TadO and (in this
case) a mixture of the cis- and trans-isomers of â-methylstyrene.
RPH2
[N3N]Ta(C2H4)
8 [N3N]TadCHMe
(15)
Et2O
4
3d
R ) H, n-Bu, Ph, Cy
Two equivalents of a 9:1 mixture of PhPD2 and PhPHD in
diethyl ether at ∼25 °C converts 4 (0.04 M) to 3d over a period
of 2 days. In this sample of 3d the percent deuterium at the
alkylidene methyl and HR positions is equal. Similarly, [N3N]-
Ta(C2D4) (0.02 M) reacts with 1 equiv of PhPH2 in diethyl ether
over a period of 1 day at ∼25 °C to provide 3d with the H
label washed into both alkylidene positions equally. Monitoring
the same reaction in benzene-d6 via 1H NMR immediately after
PhPH2 has been added shows the initial buildup of 4 that has
protons in the ethylene ligand. Finally, addition of 1 equiv of
the 9:1 PhPD2/PhPHD mixture to [N3N]TadCHMe (0.04 M)
in diethyl ether for 2 days at ∼25 °C leads to incorporation of
the deuterium label into the alkylidene HR and methyl locations
in roughly the same percentage. These results are consistent
with a mechanism in which all steps are reversible. We propose
the essential features to be those shown in eq 16. The key
intermediate is [N3N]Ta(Et)(PHPh), in which an R hydrogen
migrates from the ethyl group back to the phosphide. In theory,
ethane could be lost to yield the known phenylphosphinidene
complex. However, 3d (0.02 M) does not react with 10 equiv
of phenylphosphine in toluene-d8 at 85 °C over 24 h. (Both
3d and [N3N]TadPPh are stable in toluene-d8 when solutions
are heated to 100 °C in sealed NMR tubes.) Loss of ethane
from [N3N]Ta(Et)(PHPh) evidently is simply too slow.
Figure 3. Plot of ln(k/T) vs 1/T for the formation of [N3N]Ta(C6H4)
(9) from [N3N]Ta(Me)Ph (10) (ten runs; see Experimental Section for
a list of individual values).
The proton NMR spectrum of 9 exhibits the expected downfield
resonances for the benzyne ligand at 7.52 and 8.45 ppm, and
the ipso carbon resonances are found in the 13C NMR spectrum
at 215.1 ppm. Cooling a toluene-d8 solution of the benzyne
complex in the NMR probe to -90 °C does not lead to
significant broadening of the aromatic proton or carbon reso-
nances, and the compound maintains its C3 symmetry on the
NMR time scale.
2LiPh
[N3N]TaCl2 toluene, 80 °C, 1 day8 [N3N]Ta(C6H4) + C6H6 (14)
9
Addition of 1 equiv of phenylmagnesium bromide in toluene
to [N3N]Ta(Me)Cl followed by heating of the mixture to 55 °C
also affords 9 in 77% yield. In this case [N3N]Ta(Me)Ph (10)
can be observed as an intermediate. If the reaction is conducted
at room temperature for ∼8 h, mixtures containing ∼80% 10
can be obtained. Following the disappearance of 10 in such
mixtures in toluene-d8 in a sealed tube (ferrocene standard)
demonstrates that conversion of 10 to 9 is first order in 10
through several half-lives. Data were collected between 31 and
74 °C (Figure 3). The resulting activation parameters (∆Hq )
21.3(5) kcal/mol and ∆Sq ) -11(1) cal/(mol K)) are comparable
[N3N]Ta(C2H4) reacts differently with amines. Upon mixing
4 with ammonia, aniline, or pentafluoroaniline, 2a, 2c, and 2d
(eq 17) are formed in yields of 62-78%. 4 does not react with
to those for thermolysis of Cp* Ti(Me)Ph to produce transient
2
Cp* Ti(C6H4) (∆Hq ) 23.0 kcal/mol, ∆Sq ) -9.8 cal/(mol
2
K)39). Labeling experiments conducted at 74 °C (see Experi-
mental Section) suggest that the primary isotope effect is 3.6-
(6), a value that is significantly smaller than that measured for
RNH2
[N3N]Ta(C2H4)
8 [N3N]TadNR
(17)
Et2O
4
2a,c,d
decomposition of Cp* Ti(Me)(C6R5) (R ) H or D; kH/kD ) 5.1
2
at 80 °C in benzene-d639). A comparison of the rates of
decomposition of [N3N]Ta(CH3)(C6H5) and [N3N]Ta(CD3)-
(C6H5) suggests that the secondary isotope effect is negligible
(1.1(1)).
R ) H (2a), Ph (2c), C6F5 (2d)
tert-butylamine under similar conditions. 3d is not observed
by 1H NMR during the reaction of 4 with ArNH2 (Ar ) C6H5,
C6F5). The reaction of 3d (0.05 M) with 1 equiv of aniline in
toluene-d8 at ∼25 °C is slow; it is only 23% complete after 8
Reactions of Ethylene, Acetylene, and Benzyne Complexes.
[N3N]Ta(C2H4) has proven to be relatively reactive, probably
largely because one empty orbital is available to which
nucleophiles can bind. Fortunately, decomposition of 4 to 7b
(eq 9) is rarely a competitive reaction, although it sometimes is
a complication.
One unusual reaction is that between 4 and a catalytic amount
of phenylphosphine (0.3 equiv) to afford the ethylidene complex
(3d) in 88% yield (eq 15). Less acidic phosphines RPH2 (R )
H, n-Bu, Cy) require longer reaction times. NMR studies
suggest that 3d is entirely analogous to 3a-c; the alkylidene
1
days, as determined via H NMR (internal standard). These
two observations argue against the formation of imido com-
plexes via 3d as an intermediate. We propose that ethane is
lost rapidly and irreversibly from [N3N]Ta(CH2CH3)(NHR)
intermediates.
Addition of 10 equiv of Me3SiAsH2 to an NMR tube
containing a toluene-d8 solution of 4 (0.03 M) affords 3d rapidly,
according to proton NMR. However, over a period of days at
∼25 °C, 3d is converted into what we propose to be the
1
(39) Luinstra, G. A.; Teuben, J. H. Organometallics 1992, 11, 1793.
arsinidene complex, [N3N]TadAsSiMe3, according to H and

Triamidoamine Complexes of Tantalum
J. Am. Chem. Soc., Vol. 118, No. 15, 1996 3649
Scheme 1. Proposed Mechanism for Ethylene Complex 4
Reacting with EH2R
diazomethane instantly to form yellow crystalline [N3N]-
TadNNdCHSiMe3 in 91% yield. The doublet at 166.1 ppm
(1JCH ) 138 Hz) in the 13C NMR spectrum is characteristic of
6
diazoalkane adducts6,43-45 (cf. [N3N]VdNNdCHSiMe3 ). Heat-
ing a 0.02 M toluene-d8 solution of [N3N]TadNNdCHSiMe3
in a sealed tube at 110 °C for weeks failed to induce loss of
dinitrogen and formation of [N3N]TadCHSiMe3. In contrast,
4 (0.07 M in toluene-d8) reacts with 1 equiv of trimethylsilyl
azide over a period of 3 weeks in a sealed NMR tube at ∼25
°C to afford [N3N]TadNSiMe3 (2d) quantitatively as determined
via 1H NMR versus an internal standard. We presume that the
azide adduct [N3N]TadNNdNSiMe3 is an intermediate, as such
species have now been observed,46,47 although we have not yet
observed an azide adduct in this case. The ethylene ligand in
4 does not exchange readily with free ethylene as determined
Scheme 2. Some Reactions of [N3N]Ta(C2H4) (4)
1
by monitoring via H NMR a toluene-d8 solution of [N3N]Ta-
(C2D4) (0.03 M) under 1 atm of ethylene in a sealed tube at
∼25 °C.
[N3N]Ta(C2H4) reacts with 0.5 atm of hydrogen gas to afford
white [N3N]Ta(H)(Et). The reversibility of addition of dihy-
drogen to [N3N]Ta(C2H4) is demonstrated by monitoring the
reactions of 4 with 0.25 atm of D2 and [N3N]Ta(C2D4) with
1
2
0.25 atm of H2 in toluene-d8 (∼0.02 M in Ta) by H or H
NMR. In all cases, H and D are scrambled between the metal,
CR, and Câ sites. [N3N]Ta(H)(Et) can be obtained as a white
crystalline solid in 93% yield via fractional recrystallization from
diethyl ether. The hydride resonance at 24.77 ppm remains
sharp down to -80 °C. The Ta-H stretch is found in the IR
spectrum at 1816 cm-1 (νTaD ) 1301 cm-1). A 0.40 M solution
of [N3N]Ta(H)(Et) in toluene-d8 decomposes at 100 °C over a
period of hours to yield Me3SiH and a colorless oil whose proton
and carbon NMR are consistent with it being “EtTa[(NCH2-
CH2)N(CH2CH2NSiMe3)2]”. Unfortunately, we have been
unable to obtain crystals of “EtTa[(NCH2CH2)N(CH2CH2-
NSiMe3)2]” in order to provide further support for its formula-
tion. On the basis of its solubility and an X-ray structure of a
related monomeric complex of tungsten,48 we assume at this
point that “EtTa[(NCH2CH2)N(CH2CH2NSiMe3)2]” is a mono-
mer (eq 19). Loss of trimethylsilane is one example of what is
likely to be a general tendency to lose the silyl group in some
manner in silylated TREN complexes.
13C NMR and its reaction with pivaldehyde to form the unstable
arsaalkene Me3SiAsdC(H)CMe3. If the mechanism of reaction
of Me3SiAsH2 with 4 is the same in principle as the reactions
of 4 with amines and phosphines (Scheme 1), then we must
conclude that path a is unobservable when E ) P, path b is
slow relative to path a when E ) N, and both paths can be
observed (with the rate of path b being greater than that of path
a) when E ) As. These results should be compared with those
obtained by Wolczanski for a series of Ta(silox)3(ER) complexes
prepared by loss of hydrogen from Ta(silox)3(EHR)(H) com-
plexes.22,40
Two reactions in which ethylene is protonated to give an ethyl
complex are shown in Scheme 2. 4 is cleanly protonated by
2,6-lutidinium triflate (LutHOTf) to afford [N3N]Ta(CH2CH3)-
(OTf) in 91% yield. When [N3N]Ta(C2D4) is employed, the
1
2
product is [N3N]Ta(CD2CD2H)(OTf), as judged by H and H
NMR. 4 also is protonated cleanly by phenylacetylene to afford
yellow crystalline [N3N]Ta(CH2CH3)(η1-CtCPh) in 87% yield.
When [N3N]Ta(C2D4) is employed in this reaction, the product
1
2
is [N3N]Ta(CD2CD2H)(η1-CtCPh), according to H and H
NMR. In contrast, acetylene itself adds to 4 to form the
metallacyclopentene complex 11 in 91% yield. We assume that
phenylacetylene is sterically prohibited from adding to the
ethylene complex to form a similar tantalacyclopentene complex.
Similar reactivity toward acetylenes has been reported for Cp* -
2
Ti(C2H4).41,42 Upon heating of a 0.03 M benzene-d6 solution
of 11 to 70 °C in a sealed tube for 1 day, ethylene is extruded
to yield [N3N]Ta(C2H2) quantitatively (eq18).
In contrast, 8 and 9 are relatively unreactive. For example,
8 does not react with ethylene, pyridine N-oxide, phenylphos-
phine, or ArNH2 (Ar ) Ph or C6F5) at 100 °C for weeks, while
9 does not react with PH3 (1 atm; 1 week in diethyl ether at
∼25 °C) or 10 equiv of phenylphosphine (toluene-d8 at 110 °C
for 3 weeks). Solutions of 9 in toluene-d8 (0.01 M) also do
not react with 1 atm of ethylene or acetylene at 100 °C for 3
days in sealed NMR tubes. However, solutions of 9 in toluene-
Several reactions of 4 resulted in displacement of ethylene
(Scheme 2). Mixing of 2 equiv of pyridine N-oxide with a 0.02
M toluene-d8 solution at room temperature in a sealed tube of
4 for 2 days afforded [N3N]TadO in 90% yield plus ethylene
and pyridine. [N3N]Ta(C2H4) reacts with (trimethylsilyl)-
(43) Roland, E.; Walborsky, E. C.; Dewan, J. C.; Schrock, R. R. J. Am.
Chem. Soc. 1985, 107, 5795.
(44) Chisholm, M. H.; Folting, K.; Huffman, J. C.; Raterman, A. L. Inorg.
Chem. 1984, 23, 2303.
(45) Hillhouse, G. L.; Haymore, B. L. J. Am. Chem. Soc. 1982, 104,
1537.
(40) Wolczanski, P. T. Polyhedron 1995, 14, 3335.
(41) Cohen, S. A.; Bercaw, J. E. Organometallics 1985, 4, 1006.
(42) Cohen, S. A.; Ashburn, P. R.; Bercaw, J. E. J. Am. Chem. Soc.
1983, 105, 1136.
(46) Fickes, M. G.; Davis, W. M.; Cummins, C. C. J. Am. Chem. Soc.
1995, 117, 6384.
(47) Proulx, G.; Bergman, R. G. J. Am. Chem. Soc. 1995, 117, 6382.
(48) Dobbs, D. A.; Davis, W. M.; Schrock, R. R. unpublished results.

3650 J. Am. Chem. Soc., Vol. 118, No. 15, 1996
Freundlich et al.
d8 (0.02-0.03 M) do react with 1 equiv of ArNH2 (Ar ) Ph,
C6F5) in sealed NMR tubes over a period of days at 110 °C to
give 2c and 2d, respectively, in quantitative yields (eq 20).
of a pseudo triple bond between the metal and the apical ligand.
It is interesting to note that π bonding to an apical ligand in
Ta(silox)3 complexes40 is considerably weaker than in [N3N]Ta
complexes, judging from the fact that the phosphinidene ligand
in (silox)3TadPR complexes is bent rather than linear. Another
way to increase “steric pressure” in the pocket, by increasing
the size of the amide nitrogen silyl substituent, will be described
in a forthcoming publication.36
RNH2
[N3N]Ta(C6H4)
8 [N3N]TadNR
(20)
toluene-d8
9
2c,d
R ) Ph (2c), C6F5 (2d)
The demonstration that R elimination or abstraction processes
are preferred over analogous â processes in a sterically crowded
environment can be taken as evidence that alkylidene ligands
could be formed in classical olefin metathesis systems51 from
alkyls that have â protons. There is other evidence in the
literature that R and â processes in Ta complexes can be
competitive. An equilibrium between Ta(CHCMe3)(Et)Cl2-
(PMe3)2 and Ta(CH2CMe3)(C2H4)Cl2(PMe3)2 has been demon-
strated via magnetization transfer experiments.52 Decomposition
Discussion
One of the themes that runs through the chemistry reported
here is the stability and relatively low reactivity of [N3N]Ta-
(X) complexes that contain pseudo triply bound X ligands
(where X ) CHR, O, NR, PR, or alkyne). Such compounds
attain an 18-electron count as long as the apical nitrogen remains
bound to the metal, and they are sterically protected against
intermolecular decomposition reactions by the bulky TMS
groups. (Only two π bonds can form between the three nitrogen
p orbital combinations and the metal; the third is a ligand-based
nonbonding orbital.) Intramolecular reactions, such as CH
activation of a methyl group in a TMS substituent,1 are also
slow in such species. Conversely, 16-electron [N3N]Ta(olefin)
complexes decompose relatively easily by abstraction of a â
proton in the TREN backbone to give species in which the cage
structure of the TREN ligand is disrupted and a vinyl amido
ligand is formed. Attempts to reduce [N3N]TaCl2 to [N3N]Ta,
or to prepare species such as [N3N]TaH2 so far have been
unsuccessful, possibly for the same reason. It should also be
noted that [N3N]Ta(H)(C2H5) does not lose ethane to give
“[N3N]Ta.” Ultimate decomposition of [N3N]Ta(H)(C2H5) via
loss of trimethylsilane points out a pervasive and not entirely
unexpected problem with the Me3Si-substituted TREN system
that also will limit the utility of this ligand system, at least for
preparing complexes in which the metal is aggressively reactive.
Another characteristic of the chemistry reported here is the
“steric pressure” that the three TMS substituents exert on ligands
bound in the apical position. The degree of steric hindrance in
the apical “pocket” is evident from the structure of 6 (Figure
1) and also from the tendency to form alkylidene complexes
by R abstraction instead of olefin complexes by â abstraction
as the size of the R group increases in the hypothetical
intermediate [N3N]Ta(CH2CH2R)2 species formed by alkylation
of [N3N]TaCl2. The question is still open as to whether ligands
that could be bent instead of linear (alkylidene and phosphin-
idene species, in particular) are linear solely for electronic
reasons, or whether steric factors also play a major role in
stabilizing the linear form. At this stage we believe that the
metal π orbitals involved in formation of a pseudo triple bond
to a ligand in the apical position are extraordinarily electrophilic,
and that π donation to give a pseudo triple bond is an important
stabilizing feature of such compounds. For example, alkylidene
complexes of Ta(V) that contain â-protons are rare20,49 because
they usually rearrange to the olefin complex readily. They are
stable in [N3N]TadCHR complexes because the C-HR electron
pair is strongly donated to the metal. Steric repulsion between
the substituent on a “bent” apical ligand and the bulky TMS
groups is believed simply to reinforce linearity, although we
have not been able to prepare a species such as [N3N]TadCH2
that would allow us to test this supposition. We suspect that
the methylene ligand in [N3N]TadCH2 would be “T-shaped”,
as observed in unstable Cp*Me3WdCH2,50 a result that would
confirm that electronic factors alone can account for formation
of Cp* (H)TadCdCH2 is believed to involve Cp*(η5-C5Me4-
2
CH2CH2CH2)Ta as an intermediate, from which the kinetic
product is Cp*(H)TadCHCH2CH2(η5-C5Me4) and the thermo-
dynamic product is Cp*(η5-C5Me4CH2CHdCH2)TaH.53 Finally,
Ta(CHCMe3)(H)(PMe3)3I2 is known to react with n equiv of
ethylene to afford the R-H elimination product Ta[CH(CH2-
CH2)nCMe3](H)(PMe3)3I2.54,55 There are other examples in the
literature where R-H processes are proposed to occur pre-
ferentially.54-57 Most recently and convincingly,9 deuterium-
labeling experiments have shown that R-elimination in [N3N]W-
(cyclopentyl) to give [N3N]W(cyclopentylidene)(H) proceeds
more rapidly than â elimination, the slowest step being loss of
cyclopentene from intermediate [N3N]W(cyclopentene)(H) to
give [N3N]W(H).
Several extensions of the work reported here currently are
being pursued. For example, we would like to isolate and
determine the structure of an arsinidene complex in order to
compare it with the bent arsinidene (107°) in (silox)3-
TadAsPh;22,40 we expect the TadAsR linkage in [N3N]TadAsR
to be linear, as is the TadPsR linkage in [N3N]TadPCy.3 We
also hope to find a way to generate “[N3N]TadPLi” cleanly
and isolate it in high yield. However, the main focus will be
on new TREN-like ligands. On the basis of the decomposition
reactions described here, it seems likely that complexes that
contain aggressively reactive metal centers, e.g., “trigonal
monopyramidal” [N3N]Ta, are likely to be short-lived and to
decompose readily in an intramolecular fashion. Therefore it
is imperative to design TREN-like ligands that are more resistant
to cage decomposition reactions, metalation reactions involving
the substituents on the amido nitrogen atoms,1 or loss of amido
substituents than is [N3N]3-
.
Experimental Section
General Procedures. All experiments were carried out under a
nitrogen atmosphere in a Vacuum Atmospheres drybox or by standard
Schlenk techniques, unless otherwise mentioned. Reagent grade
solvents were purified by standard methods. Li3[N3N],1,6 [N3N]TaCl2,3
(51) Ivin, K. J. Olefin Metathesis; Academic: New York, 1983.
(52) Fellmann, J. D.; Schrock, R. R.; Traficante, D. D. Organometallics
1982, 1, 481.
(53) Parkin, G.; Bunel, E.; Burger, B. J.; Trimmer, M. S.; Van Asselt,
A.; Bercaw, J. E. J. Mol. Catal. 1987, 41, 21.
(54) Turner, H. W.; Schrock, R. R. J. Am. Chem. Soc. 1982, 104, 2331.
(55) Turner, H. W.; Schrock, R. R.; Fellmann, J. D.; Holmes, S. J. J.
Am. Chem. Soc. 1983, 105, 4942.
(56) Kiel, W. A.; Lin, G.-Y.; Gladysz, J. A. J. Am. Chem. Soc. 1980,
102, 3299.
(49) Sharp, P. R.; Schrock, R. R. J. Organomet. Chem. 1979, 171, 43.
(50) Liu, A. H.; Murray, R. C.; Dewan, J. C.; Santarsiero, B. D.; Schrock,
R. R. J. Am. Chem. Soc. 1987, 109, 4282.
(57) Burk, M. J.; McGrath, M. P.; Crabtree, R. H. J. Am. Chem. Soc.
1988, 110, 620.

Triamidoamine Complexes of Tantalum
J. Am. Chem. Soc., Vol. 118, No. 15, 1996 3651
Ta(CH2CMe3)2Cl3,32 and Ta(CH2Ph)2Cl331 were prepared according to
literature methods.
Sample Procedure for Reaction of a Phosphinidene [N3N]TadPR
with Me3CCHO. Observation of trans-Me3C(H)CdPMe by NMR.
Pivaldehyde (21 µL, 0.194 mmol) was added via syringe to an NMR
tube containing [N3N]TadPMe (57 mg, 0.0971 mmol) in 700 µL of
C6D6. Within minutes the red-brown solution turned colorless: 1H
1H and 13C NMR data are listed in parts per million downfield from
TMS while 31P NMR data are listed in parts per million downfield
from triphenylphosphine (δ -4.51), and 19F NMR data are listed in
parts per million downfield from trifluoroacetic acid (δ -76.53).
Routine coupling constants are usually not reported; those listed are in
units of hertz. IR spectra were recorded on a Perkin-Elmer 1600 FT-
IR spectrometer. Elemental analyses (C, H, N) were performed by
Oneida Research Services, Whitesboro, NY, or in our laboratory using
a Perkin-Elmer 2400 CHN analyzer. X-ray data were collected on an
Enraf-Nonius CAD-4 diffractometer. A complete description of data
collection, structure solution, and structure refinement can be found in
the supporting information. NMR tube reactions were carried out in a
Wilmad 512-7 in. or 512-9 in. NMR tube sealed to a 14/20 outer joint.
This joint was connected to a gas adapter outfitted with a 28/15 ball
joint and a Teflon stopcock. The contents of the tube were degassed
on a high-vacuum line using three freeze(-196 °C)-pump-thaw cycles
before flame-sealing under a static vacuum.
2
NMR (C6D6) δ 8.56 (dq, JPH ) 25, 1, PdCHCMe3), 1.34 (m, 3,
4
MePdC), 1.12 (d, JPH ) 2, 9, PdCHCMe3); 31P{1H} (C6D6) δ 229.
2
trans-Me3C(H)CdP(n-Bu): 1H NMR (C6D6) δ 8.65 (m, JPH
)
25, 1, PdCHCMe3), 1.85 (m, 2, PCH2CH2CH2CH3), 1.59 (m, 2,
PCH2CH2CH2CH3), 1.30 (m, 2, PCH2CH2CH2CH3), 1.16 (d, 3JPH ) 2,
9, PdCHCMe3), 0.81 (t, 3, PCH2CH2CH2CH3); 31P{1H} (C6D6) δ 243.
1
2
trans-Me3C(H)CdPSiMe3: H NMR (C6D6) δ 9.52 (d, JPH ) 24,
1, PdCHCMe3), 1.18 (d, 9, PdCHCMe3), 0.21 (d, 9, PSiMe3); 31P{1H}
(C6D6) δ 244.
2
trans-Me3C(H)CdPSiMe2Ph: 1H NMR (CD2Cl2) δ 9.44 (d, JPH
4
) 24, 1, PdCHCMe3), 7.56 (m, 2, Ph), 7.37 (m, 3, Ph), 1.16 (d, JPH
) 2, 9, PdCHCMe3), 0.56 (d, 4JPH ) 3, 6, PSiMe2Ph); 31P{1H} (CD2-
Cl2) δ 238.
[N3N]TadNH (2a). [N3N]TaCl2 (200 mg, 0.327 mmol) was added
to a -35 °C slurry of lithium amide (16 mg, 0.687 mmol) in 12 mL of
tetrahydrofuran. After 23 h, the solvents were removed from the
reaction mixture in vacuo and the residue was extracted with 50 mL
of pentane. The extract was filtered through Celite, and the pale yellow
filtrate was taken to dryness in vacuo to yield a pale yellow solid.
Recrystallization of the solid from pentane at -35 °C gave 112 mg
(0.201 mmol, 62%) of white crystalline product: 1H NMR (C6D6) δ
Kinetic Studies via 1H NMR Spectroscopy. An NMR tube sealed
to a 14/20 outer joint was charged with a solution of the reactant and
ferrocene (internal standard) in 1 mL of toluene-d8 and then fitted with
a gas adapter. The tube was sealed according to the above procedure
and placed in the preshimmed NMR probe for monitoring. Probe
temperature was calibrated prior to the run utilizing neat ethylene glycol
and was maintained to within (0.1 °C of the set point.
1
14
Sample Procedure for Synthesis of [N3N]TadPR via P-Ph
Cleavage: Preparation of [N3N]TadPSiMe3 (1c). A yellow solution
of [N3N]TadPPh (0.500 g, 0.771 mmol) in 50 of mL tetrahydrofuran
was transfered via cannula to a 100 mL Schlenk flask containing clean
Li ribbon (27 mg, 3.89 mmol). The reaction mixture was stirred at
room temperature for 19 h and was then decanted from the remaining
Li ribbon. Trimethylsilyl chloride (0.250 g, 2.31 mmol) was added to
the red-brown liquid at -35 °C, and the mixture was allowed to warm
to 25 °C. After 45 min, the reaction mixture was taken to dryness in
vacuo and the residue was extracted with 30 mL of pentane. The extract
was filtered through a bed of Celite to remove LiCl, and the filtrate
was concentrated in vacuo to yield a red-brown solid. The solid was
recrystallized from pentane at -35 °C to yield 37 mg (0.060 mmol,
8%) of a gold powder: 1H NMR (C6D6) δ 3.51 (t, 6, CH2), 2.05 (t, 6,
5.59 (br t (1:1:1), J NH ) 50, NH), 3.39 (t, 6, CH2), 2.22 (t, 6, CH2),
0.40 (s, 27, SiMe3); 13C NMR (C6D6) δ 53.9 (t, CH2), 49.2 (t, CH2),
3.3 (q, SiMe3); IR (diethyl ether solution, KBr cells, background
subtracted) cm-1 3436 (s, ν NH). Anal. Calcd for TaSi3N5C15H40: C,
32.42; H, 7.25; N, 12.60. Found: C, 32.35; H, 7.36; N, 12.37.
[N3N]TadNCMe3 (2b). [N3N]TaCl2 (1.00 g, 1.64 mmol) was added
to a -35 °C solution of LiN(H)CMe3 (271 mg, 3.43 mmol) in 60 mL
of diethyl ether. After 15 h, the pale yellow-orange mixture was filtered
through Celite. The pale yellow filtrate was taken to dryness in vacuo
to yield a pale yellow solid. Recrystallization of the yellow solid from
pentane at -35 °C gave 727 mg (1.19 mmol, 73%) of off-white
crystalline product: 1H NMR (C6D6) δ 3.22 (t, 6, CH2), 2.18 (t, 6,
CH2), 1.66 (s, 9, CMe3), 0.37 (s, 27, SiMe3); 13C NMR (C6D6) δ 64.8
(s, CMe3), 60.1 (t, CH2), 47.6 (t, CH2), 35.4 (q, CMe3), 2.9 (q, SiMe3).
Anal. Calcd for TaSi3N5C19H48: C, 37.30; H, 7.91; N, 11.45. Found:
C, 37.55; H, 7.87; N, 11.37.
[N3N]TadNPh (2c). [N3N]TaCl2 (250 mg, 0.409 mmol) was added
to a -35 °C solution of LiN(H)Ph (85 mg, 0.858 mmol) in 12 mL of
diethyl ether. After 22 h, the cloudy white mixture was passed through
Celite. The solvents were removed from the filtrate in vacuo to provide
an off-white solid. Recrystallization of this solid from diethyl ether at
-35 °C gave 246 mg (0.389 mmol, 95%) of white crystalline product:
1H NMR (C6D6) δ 7.42 (m, 2, Ph), 7.34 (m, 3, Ph), 3.42 (t, 6, CH2),
2.23 (t, 6, CH2), 0.40 (s, 27, SiMe3); 13C NMR (CD2Cl2) δ 159.5 (s,
Ph), 128.7 (dt, Ph), 127.6 (dd, Ph), 56.0 (t, CH2), 49.8 (t, CH2), 3.2 (q,
SiMe3). Anal. Calcd for TaSi3N5C21H44: C, 39.92; H, 7.02; N, 11.08.
Found: C, 39.91; H, 7.03; N, 10.95.
3
CH2), 0.63 (s, 27, NSiMe3), 0.55 (d, JPH ) 5, 9, PSiMe3); 13C{1H}
3
4
NMR (C6D6) δ 53.7 (s, CH2), 51.7 (d, JPC ) 6, CH2), 6.0 (d, JPC
)
4, NSiMe3), 5.3 (d, 2JPC ) 6, PSiMe3); 31P{1H} NMR (toluene-d8, -60
°C) δ 212 (∆ν1/2 ) 300).
“[N3N]TadPLi” can be observed as an intermediate in reactions
of this general type: 1H NMR (C6D6) δ 3.75 (t, 6, CH2), 3.60 (br t, 4,
THF), 2.13 (t, 6, CH2), 1.42 (br t, 4, THF), 0.91 (s, 27, SiMe3); 13C{1H}
NMR (C6D6) δ 68.5 (THF), 54.4 (CH2), 51.3 (CH2), 25.8 (THF), 6.5
(SiMe3); 31P{1H} NMR (C6D6) δ 575 (∆ν1/2 ≈ 600).
[N3N]TadPMe (1a): 1H NMR (C6D6) δ 3.49 (t, 6, CH2), 2.56 (d,
2JPH ) 20, 3, CH3), 2.18 (t, 6, CH2), 0.56 (s, 27, SiMe3); 13C{1H} NMR
3
1
(C6D6) δ 54.1 (s, CH2), 51.0 (d, JPC ) 9, CH2), 30.8 (d, JPC ) 33,
CH3), 5.8 (s, SiMe3); 31P{1H} NMR (C6D6) δ 157.
[N3N]TadP-n-Bu (1b). [N3N]TaCl2 (1.500 g, 2.45 mmol) was
added to a suspension of LiP(H)-n-Bu (0.500 g, 5.15 mmol) in 100
mL of diethyl ether at -35 °C. The reaction mixture turned dark red
immediately. After 19 h the mixture was filtered through a bed of
Celite, and the filtrate was taken to dryness in vacuo. The red solid
was recrystallized from pentane at -35 °C to yield 150 mg (0.239
mmol, 10%) of a gold powder: 1H NMR (C6D6) δ 3.51 (t, 6, CH2),
3.20 (m, 2, PCH2CH2CH2CH3), 2.14 (t, 6, CH2), 1.86 (m, 2, PCH2CH2-
CH2CH3), 1.42 (m, 2, PCH2CH2CH2CH3), 0.88 (t, 3, PCH2CH2-
CH2CH3), 0.61 (s, 27, SiMe3); 13C{1H} NMR (C6D6) δ 53.8 (s, CH2),
[N3N]TaMe2. Methyllithium (2.34 mL, 1.4 M in diethyl ether, 3.28
mmol) was added via syringe to a -35 °C solution of [N3N]TaCl2 (910
mg, 1.49 mmol) in 50 mL of diethyl ether. A white LiCl precipitate
was observed in a few minutes. After 3 h, the reaction mixture was
taken to dryness in vacuo. The off-white solid was extracted with 40
mL of pentane, the extract was filtered through Celite, and the pentane
was removed from the filtrate in vacuo to provide 840 mg (1.47 mmol,
99%) of a waxy, beige solid. The complex may be isolated as colorless
crystals by recrystallization from pentane at -35 °C: 1H NMR (C6D6)
δ 3.34 (t, 6, CH2), 2.09 (t, 6, CH2), 1.27 (s, 6, TaMe2), 0.29 (s, 27,
SiMe3); 13C NMR (C6D6) δ 64.6 (q, 1JCH ) 117, TaMe2), 60.3 (t, 1JCH
) 138, CH2), 50.3 (t, JCH ) 136, CH2), 2.3 (q, JCH ) 118, SiMe3).
Anal. Calcd for TaSi3N4C17H45: C, 35.77; H, 7.95; N, 9.82. Found:
C, 35.40; H, 8.40; N, 9.68.
[N3N]Ta(Me)OTf. [FeCp2][O3SCF3] (373 mg, 1.11 mmol) was
added to a -35 °C solution of [N3N]TaMe2 (607 mg, 1.11 mmol) in
50 mL of tetrahydrofuran. The color of the stirred reaction mixture
changed to gold as the blue [FeCp2][O3SCF3] dissolved. After 1 h,
the reaction mixture was concentrated in vacuo. The residue was
1
51.1 (s, CH2), 48.0 (d, JPC ) 29, PCH2), 33.4 (s, PCH2CH2), 24.1 (s,
PCH2CH2CH2), 13.8 (s, PCH2CH2CH2CH3), 6.1 (s, SiMe3); 31P{1H}
NMR (C6D6) δ 186.
1
1
[N3N]TadPSiMe2Ph (1d): 1H NMR (CD2Cl2) δ 7.65 (m, 2, Ph),
3
7.33 (m, 3, Ph), 3.80 (t, 6, CH2), 2.76 (t, 6, CH2), 0.66 (d, JPH ) 4,
SiMe2Ph), 0.27 (s, 27, SiMe3); 13C{1H} NMR (CD2Cl2) δ 140.3 (d,
2JPC ) 12, Ph), 134.5 (s, Ph), 129.0 (s, Ph), 127.9 (s, Ph), 54.9 (s,
2
CH2), 51.8 (s, CH2), 5.25 (s, SiMe3), 3.76 (d, JPC ) 7, SiMe2Ph);
31P{1H} NMR (CD2Cl2, -60 °C) δ 203 (∆ν1/2 ) 400).

3652 J. Am. Chem. Soc., Vol. 118, No. 15, 1996
Freundlich et al.
washed with 40 mL of pentane, collected on a frit, and dried to afford
585 mg (0.83 mmol, 75%) of a tan powder. The complex may be
isolated as colorless crystals by recrystallization from diethyl ether at
-35 °C: 1H NMR (C6D6) δ 3.53 (t, 6, CH2), 2.04 (t, 6, CH2), 1.42 (s,
3, Me), 0.27 (s, 27, SiMe3); 13C NMR (C6D6) δ 67.0 (q, TaMe), 60.4
(t, CH2), 53.0 (t, CH2), 1.8 (q, SiMe3). Anal. Calcd for TaSi3N4O3-
SF3C17H42: C, 28.97; H, 6.01; N, 7.95. Found: C, 28.93; H, 6.14; N,
7.67.
-35 °C solution of [N3N]TaCl2 (187 mg, 0.306 mmol) in 8 mL of
diethyl ether. After 17 h, the cloudy orange mixture was filtered
through Celite and the orange filtrate concentrated in vacuo to yield
an orange solid. The solid was recrystallized from diethyl ether at
-35 °C, and two crops of orange needles were collected to yield 175
mg (0.277 mmol, 91%) of product: 1H NMR (C6D6) δ 7.34 (m, 3,
Ph), 6.80 (m, 2, Ph), 3.39 (t, 6, CH2), 2.16 (t, 6, CH2), 2.01 (s, 1, CHPh),
1
0.39 (s, 27, SiMe3); 13C NMR (C6D6) δ 201.4 (d, JCH ) 72, CHPh),
152.6 (s, Ph), 129.5 (d, Ph), 127.4 (d, Ph), 122.4 (m, Ph), 56.4 (t, CH2),
49.8 (t, CH2), 3.7 (q, SiMe3). Anal. Calcd for TaSi3N4C22H45: C,
41.89; H, 7.19; N, 8.88. Found: C, 41.68; H, 7.09; N, 8.81.
[N3N]Ta(Me)Cl. To a -35 °C solution of [N3N]Ta(Me)OTf (300
mg, 0.426 mmol) in 8 mL of methylene chloride was added tetraethy-
lammonium chloride (71 mg, 0.426 mmol). After 23 h, the yellow
solution was concentrated in vacuo, extracted with 30 mL of diethyl
ether, and filtered through Celite. The yellow filtrate was concentrated
in vacuo to provide 175 mg (0.296 mmol, 69%) of yellow powder.
The complex may be isolated as yellow crystals by recrystallization
from diethyl ether at -35 °C: 1H NMR (C6D6) δ 3.56 (t, 6, CH2),
2.04 (t, 6, CH2), 1.49 (s, 3, Me), 0.35 (s, 27, SiMe3); 13C NMR (C6D6)
δ 64.4 (q, 1JCH ) 118, TaMe), 61.7 (t, 1JCH ) 136, CH2), 53.6 (t, 1JCH
If only 1 equiv of PhCH2MgCl is added to [N3N]TaCl2, then [N3N]-
Ta(CH2Ph)Cl can be isolated by fractional crystallization: 1H NMR
(C6D6) δ 7.21 (t, 2, Ph), 6.98 (d, 2, Ph), 6.74 (t, 1, Ph), 3.45 (t, 6,
CH2), 3.13 (s, 2, CH2Ph), 2.10 (t, 6, CH2), 0.42 (s, 27, SiMe3); 13C
1
NMR (C6D6) δ 149.0 (s, Ph), 131.9 (dd, JCH ) 156 Hz, Ph), 127.0
(dd, Ph), 121.7 (dt, 1
JCH ) 157 Hz, Ph), 91.4 (t, 1JCH ) 129 Hz, CH2-
1
Ph), 57.5 (t,
1JCH ) 138 Hz, CH2), 52.4 (t, JCH ) 136 Hz, CH2), 3.3
1
1
) 136, CH2), 2.0 (q, JCH ) 119, SiMe3). Anal. Calcd for TaSi3N4-
(q, JCH ) 119 Hz, SiMe3).
ClC16H42: C, 32.51; H, 7.16; N, 9.48. Found: C, 32.55; H, 7.21; N,
9.54.
(b) From Ta(CH2Ph)2Cl3. Ta(CH2Ph)2Cl3 (250 mg, 0.532 mmol)
was added to a -35 °C solution of Li3[N3N] (203 mg, 0.532 mmol) in
10 mL of diethyl ether. After 20 h, the reaction mixture was filtered
through Celite and the solvents were removed from the red-orange
filtrate in vacuo to afford a red-brown solid. Recrystallization of the
red-brown solid from diethyl ether at -35 °C gave several crops of
orange needles; yield 288 mg (0.456 mmol, 86%).
[N3N]Ta(Et)Cl (5). Ethylmagnesium chloride (164 µL, 2.27 M in
diethyl ether, 0.373 mmol) was added via syringe to a solution of [N3N]-
TaCl2 (228 mg, 0.373 mmol) in 30 mL of diethyl ether at -35 °C.
After 45 h, the light orange reaction mixture was taken to dryness in
vacuo and the residue was extracted with 30 mL of pentane. The extract
was filtered through Celite, and the filtrate was concentrated in vacuo
to give a yellow-orange solid that was recrystallized from pentane at
-35 °C to afford 163 mg (0.269 mmol, 72%) of yellow-orange
crystals: 1H NMR (C6D6) δ 3.58 (t, 6, CH2), 2.60 (t, 3, CH3), 2.07 (t,
6, CH2), 1.86 (q, 2, CH2), 0.37 (s, 27, SiMe3); 13C NMR (C6D6) δ 76.8
[N3N]TadCHCMe3 (3c). A solution of Ta(CH2CMe3)2Cl3 (2.41 g,
5.61 mmol) in 40 mL of diethyl ether was prepared, as was a solution
of Li3[N3N] (2.14 g, 5.61 mmol) in 40 mL of diethyl ether. Both
solutions were chilled to -35 °C and then combined. After 2.5 h, the
yellow reaction mixture was filtered through a bed of Celite and the
filtrate was concentrated in vacuo to yield an orange solid. Recrys-
tallization of the orange solid from pentane at -35 °C yielded several
crops of crystals; yield 1.92 g (3.14 mmol, 56%):
1
1
1
(t, JCH ) 114, CH2CH3), 61.8 (t, JCH ) 136, CH2), 53.6 (t, JCH
)
136, CH2), 21.2 (q, 1JCH ) 125, CH2CH3), 2.1 (q, 1JCH ) 119, SiMe3).
Anal. Calcd for TaSi3N4ClC17H44: C, 33.74; H, 7.33; N, 9.26.
Found: C, 33.51; H, 7.49; N, 8.82.
1H NMR (C6D6) δ
3.25 (t, 6, CH2), 2.12 (t, 6, CH2), 1.54 (s, 9, CHCMe3), 0.93 (s, 1,
1
CHCMe3), 0.39 (s, 27, SiMe3); 13C NMR (C6D6) δ 213.3 (d, JCH
)
[N3N]Ta(Me)Et (6). A -35 °C solution of [N3N]Ta(Et)Cl (166
mg, 0.274 mmol) in 5 mL of diethyl ether was subjected to the addition
of methylmagnesium chloride (100 µL, 0.302 mmol, 3.0 M in
tetrahydrofuran) via syringe. The orange mixture was stirred for 3.5 h
and was then taken to dryness in vacuo. The resulting orange solid
was extracted with 5 mL of diethyl ether and filtered through Celite to
afford an orange solution. The filtrate was concentrated in vacuo to
afford 151 mg of an orange solid, which was shown to be an 8:1 mixture
of [N3N]Ta(Me)Et (6) and [N3N]Ta(C2H4) (4) by 1H NMR. Four
recrystallizations from pentane at -35 °C afforded X-ray quality yellow
plates of 6: 1H NMR (C6D6) δ 3.42 (t, 6, CH2), 2.16 (t, 6, CH2), 1.89
(t, 3, CH2CH3), 1.69 (q, 2, CH2CH3), 1.35 (s, 3, CH3), 0.28 (s, 27,
72, CHCMe3), 59.4 (t, CH2), 48.7 (t, CH2), 47.7 (s, CMe3), 35.7 (q,
CHMe3), 3.0 (q, SiMe3). Anal. Calcd for TaSi3N4C20H49: C, 39.33;
H, 8.09; N, 9.17. Found: C, 39.05; H, 7.95; N, 9.02.
Observation of [N3N]TadCHCH2CH3 (3e). n-Propylmagnesium
chloride (700 µL, 2.5 M in diethyl ether, 1.75 mmol) was added via
syringe to a -35 °C solution of [N3N]TaCl2 (510 mg, 0.834 mmol) in
10 mL of diethyl ether. After 23 h, the mixture was taken to dryness
in vacuo and the residue was extracted with 40 mL of pentane. The
extract was filtered through Celite, and the solvent was removed from
1
the yellow filtrate in vacuo to afford a yellow solid. Via H NMR
with a (Me3Si)2O internal standard, the solid was determined to contain
[N3N]TadCHCH2CH3 (3e) and (n-Pr)Ta[N(CH2CH2NSiMe3)2][N(SiMe3)-
(CHdCH2)] (7c) in 32% and 66% yields, respectively. [N3N]Tad
CHCH2CH3 (3e): 1H NMR (C6D6) δ 3.43 (t, 6, CH2), 3.29 (m, 2,
TaCHCH2), 2.21 (t, 6, CH2), 1.19 (t, 3, TaCHCH2CH3), 0.38 (s, 27,
1
SiMe3); 13C NMR (C6D6) δ 78.7 (t, JCH ) 117, CH2CH3), 65.6 (q,
1JCH ) 117, CH3), 59.7 (t, 1JCH ) 136, CH2), 51.1 (t, 1JCH ) 135, CH2),
1
1
17.0 (q, JCH ) 123, CH2CH3), 2.6 (q, JCH ) 118, SiMe3).
[N3N]TadCHSiMe3 (3a). ((Trimethylsilyl)methyl)lithium (96 mg,
1.02 mmol) was added to a solution of [N3N]TaCl2 (250 mg, 0.409
mmol) in 8 mL of diethyl ether at -35 °C. After 24 h, the cloudy
yellow solution was filtered through Celite and the yellow filtrate
concentrated in vacuo to provide a yellow solid. The solid was
recrystallized from diethyl ether at -35 °C to afford 234 mg (0.373
mmol, 91%) of yellow crystalline product: 1H NMR (C6D6) δ 3.29 (t,
6, CH2), 2.55 (s, 1, CHSiMe3), 2.03 (t, 6, CH2), 0.47 (s, 9, CHSiMe3),
1
SiMe3), -0.28 (t, 1, TaCH); 13C NMR (C6D6) δ 201.5 (d, JCH ) 68,
1
1
TaCH), 54.2 (t, JCH ) 136, CH2), 50.3 (t, JCH ) 135, CH2), 38.5 (t,
1JCH ) 125, TaCHCH2), 18.1 (q, JCH ) 121, TaCHCH2CH3), 4.5 (q,
1
1JCH ) 117, SiMe3). (n-Pr)Ta[N(CH2CH2NSiMe3)2][N(SiMe3)(CHd
CH2)] (7c): 1H NMR (C6D6) δ 6.61 (dd, 1, CHdCH2), 4.20 (d, 1,
CHdCH2), 4.06 (m, 3, CH2 and CHdCH2), 3.87 (m, 4, CH2), 3.65
(m, 2, CH2), 2.21 (m, 2, TaCH2CH2CH3), 1.45 (t, 2, TaCH2CH2CH3),
1.04 (t, 3, TaCH2CH2CH3), 0.22 (s, 18, NSiMe3), 0.20 (s, 9, NSiMe3);
13C NMR (toluene-d8) δ 137.9 (d, 1JCH ) 159, CHdCH2), 92.8 (t, 1JCH
1
0.41 (s, 27, NSiMe3); 13C NMR (C6D6) δ 206.5 (d, JCH ) 72,
1
1
CHSiMe3), 57.9 (t, JCH ) 135, CH2), 49.6 (t, JCH ) 136, CH2), 5.2
(q, 1JCH ) 118, CHSiMe3), 3.4 (q, 1JCH ) 118, NSiMe3). Anal. Calcd
for TaSi3N4C22H45: C, 36.40; H, 7.88; N, 8.94. Found: C, 36.18; H,
7.53; N, 8.92.
1
1
) 157, CHdCH2), 73.1 (t, JCH ) 116, TaCH2CH2CH3), 66.7 (t, JCH
) 133, CH2), 55.7 (t, 1JCH ) 133, CH2), 26.7 (t, 1JCH ) 127, TaCH2CH2-
1
1
CH3), 21.3 (q, JCH ) 125, TaCH2CH2CH3), 1.8 (q, JCH ) 118,
1
If only 1 equiv of (trimethylsilyl)methyl)lithium is added, then [N3N]-
Ta(CH2SiMe3)Cl can be isolated by fractional crystallization: 1H NMR
(C6D6) δ 3.63 (t, 6, CH2), 2.12 (t, 6, CH2), 1.29 (s, 2, CH2SiMe3), 0.50
(s, 9, CH2SiMe3), 0.36 (s, 27, NSiMe3); 13C NMR (C6D6) δ 76.8 (t,
NSiMe3), 0.06 (q, JCH ) 119, NSiMe3).
Observation of [N3N]TadCHCH2CH2CH3 (3f). n-Butylmagne-
sium chloride (692 µL, 2.5 M in diethyl ether, 1.73 mmol) was added
via syringe to a -35 °C solution of [N3N]TaCl2 (504 mg, 0.834 mmol)
in 10 mL of diethyl ether. After 23 h, the mixture was taken to dryness
in vacuo and the residue was extracted with 40 mL of pentane. The
extract was filtered through Celite, and the solvents were removed from
1
1
CH2SiMe3), 62.1 (t, JCH ) 136 Hz, CH2), 53.7 (t, JCH ) 136 Hz,
1
1
CH2), 4.7 (q, JCH ) 119 Hz, CH2SiMe3), 2.5 (q, JCH ) 118 Hz,
NSiMe3).
1
[N3N]TadCHPh (3b). (a) From [N3N]TaCl2. PhCH2MgCl (642
µL, 1.0 M in diethyl ether, 0.642 mmol) was added via syringe to a
the yellow filtrate in vacuo to afford a yellow solid. Via H NMR
with a (Me3Si)2O internal standard, the solid was determined to contain

Triamidoamine Complexes of Tantalum
J. Am. Chem. Soc., Vol. 118, No. 15, 1996 3653
[N3N]TadCHCH2CH2CH3 (3f) and (n-Bu)Ta[N(CH2CH2NSiMe3)2]-
[N(SiMe3)(CHdCH2)] (7d) in 42% and 54% yields, respectively.
[N3N]TadCHCH2CH2CH3 (3f): 1H NMR (C6D6) δ 3.42 (t, 6, CH2),
3.26 (m, 2, TaCHCH2), 2.20 (t, 6, CH2), 1.71 (m, 2, TaCHCH2CH2),
0.95 (t, 3, TaCHCH2CH2CH3), 0.41 (s, 27, SiMe3), -0.20 (t, 1, TaCH);
Anal. Calcd for TaSi3N4C17H43: C, 35.90; H, 7.62; N, 9.85. Found:
C, 35.94; H, 7.41; N, 9.61.
EtTa[N(SiMe3)(CHdCH2)][N(CH2CH2NSiMe3)2] (7b). A solution
of [N3N]Ta(C2H4) (82 mg, 0.144 mmol) in ∼1 mL of toluene-d8 was
added to an NMR tube, which was then sealed. The tube was then
heated to 50 °C in an oil bath for 24 h. 1H NMR demonstrated the
sole reaction product to be 7b: 1H NMR (toluene-d8) δ 6.59 (dd, 1,
CHdCH2), 4.25 (d, 1, CHdCH2), 4.07 (m, 3, CH2 and CHdCH2),
3.87 (m, 4, CH2), 3.67 (m, 2, CH2), 1.99 (t, 3, CH2CH3), 1.46 (q, 2,
CH2CH3), 0.23 (s, 18, NSiMe3), 0.21 (s, 9, NSiMe3); 13C NMR (toluene-
d8) δ 137.1 (d, 1JCH ) 160, CHdCH2), 92.9 (t, 1JCH ) 158, CHdCH2),
66.7 (t, 1JCH ) 133, CH2), 60.4 (t, 1JCH ) 118, CH2CH3), 55.7 (t, 1JCH
1
1
13C NMR (C6D6) δ 199.7 (d, JCH ) 70, TaCH), 53.5 (t, JCH ) 136,
CH2), 50.3 (t, 1JCH ) 135, CH2), 48.4 (t, 1JCH ) 126, TaCHCH2), 27.1
1
1
(t, JCH ) 126, TaCHCH2CH2), 14.8 (q, JCH ) 125, TaCHCH2-
CH2CH3), 4.4 (q, 1JCH ) 117, SiMe3). (n-Bu)Ta[N(CH2CH2NSiMe3)2]-
[N(SiMe3)(CHdCH2)] (7d): 1H NMR (C6D6) δ 6.64 (dd, 1, CHdCH2),
4.21 (d, 1, CHdCH2), 4.07 (m, 3, CH2 and CHdCH2), 3.87 (m, 4,
CH2), 3.66 (m, 2, CH2), 2.21 (m, 2, TaCH2CH2CH2CH3), 1.47 (t, 2,
TaCH2CH2CH2CH3), 1.36 (m, 2, TaCH2CH2CH2CH3), 0.94 (t, 3,
TaCH2CH2CH2CH3), 0.23 (s, 18, NSiMe3), 0.20 (s, 9, NSiMe3); 13C
1
1
) 135, CH2), 18.0 (q, JCH ) 125, CH2CH3), 1.7 (q, JCH ) 118,
1
NSiMe3), 0.08 (q, JCH ) 118, NSiMe3).
NMR (toluene-d8) δ 137.8 (d, 1JCH ) 160, CHdCH2), 92.8 (t, 1JCH
)
MeTa[N(SiMe3)(CHdCH2)][N(CH2CH2NSiMe3)2] (7a). A solu-
tion of [N3N]TaMe2 (277 mg, 0.485 mmol) in ∼1 mL of toluene-d8
was added to an NMR tube, which was then sealed. The tube was
then heated to 110 °C in an oil bath for 24 h. 1H NMR demonstrated
the sole reaction products to be methane (δ 0.17) and 7a: 1H NMR
(toluene-d8) δ 6.55 (dd, 1, CHdCH2), 4.27 (d, 1, CHdCH2), 4.10 (d,
1, CHdCH2), 3.97 (m, 2, CH2), 3.83 (m, 4, CH2), 3.68 (m, 2, CH2),
0.75 (s, 3, CH3), 0.19 (s, 9, NSiMe3), 0.16 (s, 18, NSiMe3); 13C NMR
156, CHdCH2), 69.9 (t, 1JCH ) 117, TaCH2CH2CH2CH3), 66.7 (t, 1JCH
) 134, CH2), 55.7 (t, 1JCH ) 134, CH2), 35.7 (t, 1JCH ) 125, TaCH2CH2-
1
1
CH2CH3), 29.6 (t, JCH ) 124, TaCH2CH2CH2CH3), 14.1 (q, JCH
)
1
1
124, TaCH2CH2CH2CH3), 1.8 (q, JCH ) 118, NSiMe3), 0.05 (q, JCH
) 119, NSiMe3).
[N3N]TadCHCH2CHMe2 (3g). A -35 °C solution of [N3N]TaCl2
(318 mg, 0.520 mmol) in 10 mL of diethyl ether was subjected to the
addition of isopentylmagnesium bromide (642 µL, 1.7 M in diethyl
ether, 1.09 mmol) via syringe. After 23 h, the cloudy yellow mixture
was concentrated in vacuo, extracted with 30 mL of pentane, and filtered
through Celite. The filtrate was concentrated in vacuo to afford a
yellow solid, which was determined via 1H NMR spectroscopy with a
(Me3Si)2O internal standard to contain [N3N]TadCHCH2CH(CH3)2 (3g)
and (Me2CHCH2CH2)Ta[N(CH2CH2NSiMe3)2][N(SiMe3)(CHdCH2)]
(7e) in 84% and 15% yields, respectively. The crude reaction product
was recrystallized to provide [N3N]TadCHCH2CHMe2 (3g) free of the
decomposition product. Yellow crystals of the alkylidene were
collected to afford 242 mg (0.396 mmol, 76%) of product: 1H NMR
(C6D6) δ 3.41 (t, 6, CH2), 3.37 (dd, 2, TaCHCH2CHMe2), 2.15 (t, 6,
CH2), 2.03 (m, 1, CHMe2), 1.14 (d, 6, CHMe2), 0.46 (s, 27, NSiMe3),
0.10 (t, 1, TaCHCH2CHMe2); 13C NMR (C6D6) δ 199.7 (d, 1JCH ) 71,
1
1
(tol-d8) δ 135.2 (d, JCH ) 160, CHdCH2), 93.7 (t, JCH ) 157,
CHdCH2), 67.0 (t, 1JCH ) 132, CH2), 55.4 (t, 1JCH ) 136, CH2), 40.5
(q, JCH ) 120, CH3), 1.6 (q, JCH ) 119, NSiMe3), -0.1 (q, JCH
1
1
1
)
120, NSiMe3). Anal. Calcd for TaSi3N4C16H41: C, 34.64; H, 7.45;
N, 10.10. Found: C, 34.38; H, 6.90; N, 9.94.
[N3N]Ta(C2H2) (8). Vinylmagnesium bromide (1.37 mL, 1.0 M in
tetrahydrofuran, 1.37 mmol) was added to a -35 °C solution of [N3N]-
TaCl2 (400 mg, 0.654 mmol) in 25 mL of diethyl ether. After 17 h,
the pale gold mixture was concentracted in vacuo and the residue was
extracted with 50 mL of pentane. The extract was filtered through
Celite, and the pale gold filtrate was taken to dryness in vacuo to yield
an off-white solid, which was recrystallized from pentane at -35 °C
to afford 298 mg (0.526 mmol, 80%) of colorless needles. X-ray quality
needle crystals were obtained by recrystallization of the product from
pentane at -35 °C: 1H NMR (C6D6) δ 12.22 (s, 2, HCCH), 3.51 (t, 6,
CH2), 2.42 (t, 6, CH2), 0.20 (s, 27, SiMe3); 13C NMR (C6D6) δ 219.9
1
TaCHCH2CHMe2), 54.9 (t, JCH ) 122, TaCHCH2CHMe2), 54.8 (t,
1
1
1JCH ) 136, CH2), 50.1 (t, JCH ) 135, CH2), 31.3 (d, JCH ) 129,
1
1
1
(dd, JCH ) 169, HCCH), 54.2 (t, JCH ) 136, CH2), 51.0 (t, JCH
)
1
1
CHMe2), 23.7 (q, JCH ) 125, CHMe2), 4.3 (q, JCH ) 118, NSiMe3).
Anal. Calcd for TaSi3N4C20H49: C, 39.33; H, 8.09; N, 9.17. Found:
C, 39.18; H, 8.25; N, 9.03.
1
134, CH2), 4.3 (q, JCH ) 118, SiMe3); IR (Nujol, background
subtracted) cm-1 1725 (s, νCtC). Anal. Calcd for TaSi3N4C17H41: C,
36.03; H, 7.29; N, 9.89. Found: C, 35.97; H, 7.19; N, 10.01.
[N3N]Ta(C6H4) (9). (a) From [N3N]TaCl2. A mixture of [N3N]-
TaCl2 (257 mg, 0.420 mmol) and phenyllithium (81 mg, 92 mol %
solid, 0.882 mmol) in 10 mL of toluene was heated at ∼80 °C for 24
h. The reaction mixture was taken to dryness in vacuo, and the residue
was extracted with 10 mL of pentane. The extract was filtered through
Celite, and the solvents were removed in vacuo from the yellow-orange
filtrate to give a solid. Recrystallization of this solid from pentane at
-35 °C provided 166 mg (0.269 mmol, 64%) of white crystals: 1H
[N3N]TadCHCH2CMe3 (3h). A -35 °C solution of [N3N]TaCl2
(500 mg, 0.818 mmol) in 8 mL of diethyl ether was subjected to the
addition of neohexylmagnesium chloride (818 µL, 2.1 M in diethyl
ether, 1.72 mmol) via syringe. After 23 h, the cloudy yellow-orange
mixture was concentrated in vacuo, extracted with 30 mL of pentane,
and filtered through Celite. The filtrate was concentrated in vacuo to
afford an orange solid, which was determined to be [N3N]TadCHCH2-
CMe3 (3h) contaminated by a trace (<1%) amount of (Me3CCH2-
CH2)Ta[N(SiMe3)(CHdCH2)][N(CH2CH2NSiMe3)2] (7f) via 1H NMR
spectroscopy. The crude reaction product was recrystallized to provide
3h free of the decomposition product. Orange crystals of the alkylidene
were collected to afford 393 mg (0.629 mmol, 77%) of product: 1H
NMR (C6D6) δ 3.71 (d, 2, TaCHCH2CMe3), 3.34 (t, 6, CH2), 2.13 (t,
6, CH2), 1.21 (s, 9, CMe3), 0.75 (t, 1, TaCHCH2CMe3), 0.41 (s, 27,
NMR (C6D6) δ 8.45 (m, 2, Ph), 7.52 (m, 2, Ph), 3.59 (t, 6, CH2), 2.49
2
(t, 6, CH2), 0.06 (s, 27, SiMe3); 13C NMR (C6D6) δ 215.1 (d, JCH
)
1
1
6, C6H4), 136.5 (d, JCH ) 158, C6H4), 132.6 (d, JCH ) 156, C6H4),
1
1
1
55.7 (t, JCH ) 136, CH2), 51.2 (t, JCH ) 136, CH2), 3.2 (q, JCH
)
118, SiMe3). Anal. Calcd for TaSi3N4C21H43: C, 40.89; H, 7.03; N,
9.08. Found: C, 40.89; H, 7.02; N, 8.84.
1
NSiMe3); 13C NMR (C6D6) δ 200.6 (d, JCH ) 75, TaCHCH2CMe3),
[N3N]Ta(Ph)Cl can be observed as an intermediate in the reaction
to form 9. It can be generated by treating 9 in toluene or benzene
with a stoichiometric amount of ethereal hydrochloric acid: 1H NMR
(C6D6) δ 7.37 (t, 3, Ph), 7.15 (m, 2, Ph), 3.68 (t, 6, CH2), 2.32 (t, 6,
CH2), 0.21 (s, 27, SiMe3).
58.6 (t, 1JCH ) 124, TaCHCH2CMe3), 57.5 (t, 1JCH ) 135, CH2), 49.3
(t, 1JCH ) 135, CH2), 34.3 (s, CMe3), 30.5 (q, 1JCH ) 124, CMe3), 3.9
(q, 1JCH ) 118, NSiMe3). Anal. Calcd for TaSi3N4C21H51: C, 40.37;
H, 8.23; N, 8.97. Found: C, 40.43; H, 8.25; N, 8.62.
[N3N]Ta(C2H4) (4). Ethylmagnesium chloride (1.17 mL, 2.2 M in
diethyl ether, 2.58 mmol) was added via syringe to a -35 °C solution
of [N3N]TaCl2 (750 mg, 1.23 mmol) in 30 mL of diethyl ether. After
1 h, the mixture was taken to dryness in vacuo and the residue was
extracted with 60 mL of pentane. The extract was filtered through
Celite, the solvents were removed from the red filtrate in vacuo, and
the red solid was recrystallized from pentane at -35 °C to provide
673 mg (1.18 mmol, 96%) of magenta crystals: 1H NMR (C6D6) δ
3.38 (t, 6, CH2), 2.29 (t, 6, CH2), 2.15 (s, 4, H2CdCH2), 0.20 (s, 27,
(b) From [N3N]Ta(Me)Cl. Phenylmagnesium bromide (209 µL,
3.5 M in tetrahydrofuran, 0.731 mmol) was added to a solution of [N3N]-
Ta(Me)Cl (393 mg, 0.665 mmol) in 10 mL of toluene. The mixture
was heated at 55 °C for 2 days. The cloudy yellow-orange solution
was subsequently concentrated in vacuo, and the residue was extracted
with 20 mL of diethyl ether. The orange extract was filtered through
Celite, and the filtrate was concentrated in vacuo to yield a light orange
solid, which was recrystallized from pentane at -35 °C to produce
316 mg (0.512 mmol, 77%) of product as white crystals.
1
SiMe3); 13C NMR (C6D6) δ 62.6 (t, JCH ) 144, H2CdCH2), 59.7 (t,
[N3N]Ta(Me)Ph (10) can be observed as an intermediate in this
reaction. If the reaction is conducted at room temperature for ∼8 h,
1JCH ) 135, CH2), 49.7 (t, 1JCH ) 135, CH2), 3.2 (q, 1JCH ) 118, SiMe3).

3654 J. Am. Chem. Soc., Vol. 118, No. 15, 1996
Freundlich et al.
mixtures containing ∼80% 10 can be obtained: 1H NMR (C6D6) δ
8.11 (dd, 2, Ph), 7.44 (t, 2, Ph), 7.24 (t, 1, Ph), 3.43 (t, 6, CH2), 2.24
(t, 6, CH2), 1.81 (s, 3, CH3), 0.11 (s, 27, SiMe3).
was then added via syringe, and the tube was sealed. After 24 h at
∼25 °C, the mixture was found by 1H NMR to contain a 62% yield of
[N3N]TadNPh (vs ferrocene internal standard).
Kinetics of Decomposition of [N3N]Ta(CH3)(C6H5). Decomposi-
tion reactions were followed by NMR (see earlier description). The
(f) With 2,6-Lutidinium Triflate To Give [N3N]Ta(Et)OTf. 2,6-
Lutidinium triflate (226 mg, 0.879 mmol) was added to a -35 °C
solution of [N3N]Ta(C2H4) (500 mg, 0.879 mmol) in 20 mL of
dichloromethane. The red solution immediately turned orange. After
8 h the solvents were removed in vacuo, and the resulting solid was
extracted with 40 mL of diethyl ether. The extract was filtered through
Celite, and the filtrate was taken to dryness in vacuo to yield a yellow
solid. Recrystallization of the yellow solid from diethyl ether at -35
°C gave 578 mg (0.804 mmol, 91%) of yellow crystalline product: 1H
individual values for runs at a given temperature (K) are (k × 106 s-1
)
304 (9.58, 9.84), 315 (36.8, 36.8), 325 (110, 119), 335 (250, 337), 347
(858, 937). The resulting activation parameters are ∆Hq ) 21.3(5)
kcal/mol and ∆Sq ) -11 (1) cal/(mol K).
The rate of decomposition of [N3N]Ta(CH3)(C6H5) was found to be
1.4 times faster than that of [N3N]Ta(CD3)(C6H5) for a secondary
isotope effect (per D) of {1.4(2)}1/3 or 1.1(1), while comparison of the
rates of decomposition of [N3N]Ta(CH3)(C6H5) and [N3N]Ta(CH3)-
(C6D5) yielded a primary isotope effect of 3.6(6).
NMR (C6D6) δ 3.62 (t, 6, CH2), 2.26 (t, 6, CH2), 2.11 (t, 3, CH3), 1.78
1
(q, 2, CH2), 0.30 (s, 27, SiMe3); 13C NMR (C6D6) δ 80.0 (t, JCH
)
1
1
In order to calculate the uncertainties in the reported rate constants,
kinetic isotope effects, and activation parameters, methods similar to
112, CH2CH3), 60.8 (t, JCH ) 137, CH2), 54.1 (t, JCH ) 137, CH2),
17.5 (q, 1JCH ) 126, CH2CH3), 2.0 (q, 1JCH ) 119, SiMe3). Anal. Calcd
for TaSi3N4O3SF3C18H44: C, 30.08; H, 6.17; N, 7.79. Found: C, 29.77;
H, 6.50; N, 7.75.
those described in a recent paper by Xue58 were employed.
A
systematic uncertainty of 5% was averaged with the calculated random
uncertainty in root-mean-square fashion to determine the total uncer-
tainty in k. This value was utilized in error propagation formulas
derived by Girolami and co-workers59 to calculate the uncertainties in
∆Hq and ∆Sq.
(g) With Phenylacetylene To Give [N3N]Ta(CH2CH3)(CtCPh).
Phenylacetylene (24.3 µL, 0.211 mmol) was added via syringe to a
solution of [N3N]Ta(C2H4) (100 mg, 0.176 mmol) in 4 mL of diethyl
ether. After 45 h, the gold solution was filtered through Celite and
the filtrate was stripped to yield a yellow oily solid. Recrystallization
of the solid from pentane at -35 °C afforded 103 mg (0.153 mmol,
87%) of yellow crystalline product: 1H NMR (CD2Cl2) δ 7.38 (m, 2,
Ph), 7.27 (m, 2, Ph), 7.20 (m, 1, Ph), 3.86 (t, 6, CH2), 2.95 (t, 6, CH2),
1.85 (q, 2, CH2CH3), 1.66 (t, 3, CH2CH3), 0.24 (s, 27, SiMe3); 13C
NMR (CD2Cl2) δ 172.0 (s, CCPh), 132.1 (s, Ph), 129.4 (m, Ph), 128.5
Reactions of [N3N]Ta(C2H4). (a) With PPhH2 To Give [N3N]-
TadCHCH3 (3d). Phenylphosphine (17 µL, 0.158 mmol) was added
via syringe to a solution of [N3N]Ta(C2H4) (300 mg, 0.527 mmol) in
2 mL of diethyl ether. After 24 h, the gold solution was filtered through
Celite and the gold filtrate was concentrated in vacuo to yield an oily
yellow solid. The oily solid was recrystallized from pentane at -35
°C to afford 264 mg (0.464 mmol, 88%) of product as yellow crystals:
1H NMR (C6D6) δ 3.42 (t, 6, CH2), 2.84 (d, 3, CH3), 2.16 (t, 6, CH2),
0.44 (s, 27, SiMe3), -0.41 (q, 1, CHCH3); 13C NMR (C6D6) δ 191.2
1
(m, Ph), 128.1 (s, CCPh), 126.1 (m, Ph), 79.5 (t, JCH ) 124, CH2-
1
1
CH3), 59.1 (t, JCH ) 136, CH2), 52.0 (t, JCH ) 136, CH2), 16.1 (q,
1JCH ) 122, CH2CH3), 3.0 (q, JCH ) 118, SiMe3); IR (diethyl ether
1
(d, 1JCH ) 69, CHCH3), 53.9 (t, CH2), 50.1 (t, CH2), 30.5 (dq, 1JCH
)
solution, KBr cells, background subtracted) cm-1 1963 (s, νCtC). Anal.
Calcd for TaSi3N4C25H49: C, 44.76; H, 7.36; N, 8.35. Found: C, 44.26;
H, 7.26; N, 8.35.
126, CH3), 4.1 (q, SiMe3). Anal. Calcd for TaSi3N4C17H43: C, 35.90;
H, 7.62; N, 9.85. Found: C, 36.08; H, 7.75; N, 9.73.
(b) With AsSiMe3H2 to give [N3N]TadAsSiMe3: 1H NMR (C6D6)
δ 3.52 (t, 6, CH2), 2.05 (t, 6, CH2), 0.65 (s, 27, NSiMe3), 0.63 (s, 9,
(h) With Pyridine N-Oxide To Give [N3N]TadO. Pyridine
N-oxide (12 mg, 0.127 mmol) was added to a solution of [N3N]Ta-
(C2H4) (36 mg, 0.0633 mmol) in 3 mL of tetrahydrofuran. After 2
days, the gold reaction mixture was stripped, to afford a light yellow
solid, which by 1H NMR spectroscopy with a (Me3Si)2O internal standard
AsSiMe ); 13C NMR (C6D6) δ 53.6 (t, 1JCH ) 136, CH2), 51.3 (t, 1JCH
3
1
1
) 136, CH2), 6.4 (q, JCH ) 118, NSiMe3), 6.3 (q, JCH ) 118,
AsSiMe3).
1
Addition of pivaldehyde to [N3N]TadAsTMS at -35 °C yields Me3-
SiAsdC(H)CMe3: 1H NMR (C6D6) δ 11.46 (s, 1, CHCMe3), 1.20 (s,
9, CHCMe3), 0.29 (s, 9, AsSiMe3).
was determined to contain a 90% yield of [N3N]TadO. The H and
13C NMR spectra for [N3N]TadO have been reported previously.3
(i) With (Trimethylsilyl)diazomethane To Give [N3N]TadNNd
CHSiMe3. (Trimethylsilyl)diazomethane (500 µL, 2.0 M in hexanes,
1.00 mmol) was added via syringe to a -35 °C solution of [N3N]Ta-
(C2H4) (400 mg, 0.703 mmol) in 5 mL of pentane. The red solution
immediately turned bright yellow and was stirred for 45 min. The
yellow solution was filtered through Celite, and the filtrate was
concentrated in vacuo to provide a yellow solid, which was recrystal-
lized from pentane at -35 °C. Yellow crystals were collected to afford
422 mg (0.644 mmol, 91%) of product: 1H NMR (C6D6) δ 8.39 (s, 1,
CHSiMe3), 3.44 (t, 6, CH2), 2.27 (t, 6, CH2), 0.43 (s, 27, NSiMe3),
(c) With Ammonia To Give [N3N]TadNH. A 100 mL glass bomb
fitted with a Teflon stopcock was charged with a solution of [N3N]-
Ta(C2H4) (42 mg, 0.0738 mmol) in 5 mL of diethyl ether. The mixture
was subjected to three freeze(-196 °C)-pump-thaw cycles. Am-
monia (0.148 mmol) was condensed into the bomb at -196 °C. The
reaction mixture was allowed to warm to room temperature and stirred
for 19 h. The resulting light orange solution was filtered through Celite
and concentrated in vacuo to afford a light yellow solid. The reaction
1
product was determined by H NMR spectroscopy with a (Me3Si)2O
1
0.32 (s, 9, CHSiMe3); 13C NMR (C6D6) δ 166.1 (d, JCH ) 138,
internal standard to contain a 78% yield of [N3N]TadNH.
1
1
(d) With Pentafluoroaniline To Give [N3N]TadNC6F5 (2d).
Pentafluoroaniline (66 mg, 0.362 mmol) was added to a -35 °C solution
of [N3N]Ta(C2H4) (206 mg, 0.362 mmol) in 5 mL of diethyl ether.
Over a period of 3 days the red solution turned light yellow. The
solvents were removed in vacuo, and the resulting solid was extracted
with 5 mL of pentane. The extract was filtered through Celite, and
the solvents were removed from the filtrate to provide a light yellow
solid. The solid was recrystallized from pentane at -35 °C to afford
191 mg (0.264 mmol, 73%) of product: 1H NMR (C6D6) δ 3.36 (t, 6,
CH2), 2.25 (t, 6, CH2), 0.22 (s, 27, SiMe3); 13C NMR (C6D6) δ 56.9 (t,
1JCH ) 136, CH2), 49.3 (t, 1JCH ) 136, CH2), 2.3 (q, 1JCH ) 119, SiMe3);
19F NMR (C6D6) δ -146.6 (d, 3JFF ) 24, C6F5), -165.2 (dt, 3JFF ) 24,
CHSiMe3), 54.2 (t, JCH ) 135, CH2), 49.7 (t, JCH ) 135, CH2), 3.5
(q, 1JCH ) 118, NSiMe3), -1.8 (q, 1JCH ) 120, CHSiMe3). Anal. Calcd
for TaSi4N6C19H49: C, 34.84; H, 7.54; N, 12.83. Found: C, 34.99; H,
7.48; N, 12.86.
(j) With Trimethylsilyl Azide To Give [N3N]TadNSiMe3. [N3N]-
Ta(C2H4) (30 mg, 0.0527 mmol) and ferrocene (10 mg, 0.0580 mmol)
were dissolved in ∼1 mL of toluene-d8 in an NMR tube. Trimethylsilyl
azide (8.0 µL, 0.0580 mmol) was then added via syringe, and the tube
1
was sealed. After 3 weeks at ∼25 °C, the mixture was found by H
NMR to contain a >99% yield of [N3N]TadNSiMe3 (vs ferrocene
internal standard): 1H NMR (C6D6) δ 3.26 (t, 6, CH2), 2.17 (t, 6, CH2),
0.45 (s, 9, dNSiMe3), 0.34 (s, 27, NSiMe3); 13C{1H} NMR (C6D6) δ
58.7 (CH2), 48.6 (CH2), 5.7 (dNSiMe3), 2.8 (NSiMe3).
3
C6F5), -168.2 (dt, JFF ) 23, C6F5). Anal. Calcd for TaSi3F5N5C21-
H39: C, 34.95; H, 5.45; N, 9.70. Found: C, 35.15; H, 5.62; N, 9.64.
(e) With Aniline To Give [N3N]TadNPh. [N3N]Ta(C2H4) (15 mg,
0.0264 mmol) and ferrocene (5 mg, 0.0269 mmol) were dissolved in
∼1 mL of toluene-d8 in an NMR tube. Aniline (2.4 µL, 0.0264 mmol)
(58) Li, L.; Hung, M.; Xue, Z. J. Am. Chem. Soc. 1995, 117, 12746.
(59) Morse, P. M.; Spencer, M. D.; Wilson, S. R.; Girolami, G. S.
Organometallics 1994, 13, 1646.
(k) With Acetylene To Give [N3N]Ta(CHCHCH2CH2) (11). A
100 mL glass bomb fitted with a Teflon stopcock was charged with a
solution of [N3N]Ta(C2H4) (381 mg, 0.670 mmol) in 10 mL of diethyl
ether. The mixture was subjected to three freeze(-196 °C)-pump-
thaw cycles. Acetylene (1.61 mmol) was condensed into the bomb at
-196 °C. The reaction vessel was allowed to warm to room
temperature and was stirred for 19 h. The purple reaction mixture was

Triamidoamine Complexes of Tantalum
J. Am. Chem. Soc., Vol. 118, No. 15, 1996 3655
filtered through Celite in order to remove the polyacetylene, and the
solvents were removed from the yellow-orange filtrate. The resulting
solid was recrystallized from pentane at -35 °C to give yellow crystals
(364 mg, 0.612 mmol, 91%): 1H NMR (C6D6) δ 8.62 (dd, J ) 9, 1.6,
1, TaCH), 8.12 (dd, J ) 9, 2, 1, TaCHCH), 3.64 (m, 2, TaCHCHCH2),
3.35 (t, 6, CH2), 2.17 (t, 6, CH2), 2.14 (t, 2, TaCHCHCH2CH2), 0.25
(s, 27, SiMe3); 13C NMR (C6D6) δ 208.4 (dt, 1JCH ) 126, TaCH), 159.2
(d, 1JCH ) 145, TaCHCH), 80.3 (t, 1JCH ) 116, TaCHCHCH2), 60.0 (t,
Hellma 221-QS quartz cell (path length ) 10 mm) sealed to a gas
adapter fitted with a Teflon stopcock was charged with 2 mL of a stock
solution of [N3N]Ta(C2H4) (4) via syringe. The cell was placed in the
HP 8452 diode array spectrophotometer, and the temperature was then
set utilizing a HP 89090A Peltier temperature control accessory. Upon
reaching the desired temperature, the reaction was monitored by
observing the decrease in the absorbance of the solution at 494 nm at
fixed time intervals via an interface to a HP 9000 Series 300 computer.
The reaction temperature was maintained to within (0.2 °C of the set
point. Decomposition of a toluene solution of 4 ([4] ) 0.0059, 0.0089,
0.010, 0.012 M) was shown to be first order in tantalum with k )
1.37(1) × 10-4 s-1 at 70 °C. At 70 °C kD ) 1.53(2) × 10-4 s-1, for
a kH/kD of 0.89(2). The fractional uncertainty in the measured rate
constants was assumed to be 1% on the basis of inspection of the
sensitivity of the fits to the absorbance versus time plots.
1
1
1JCH ) 136, CH2), 50.1 (t, JCH ) 135, CH2), 44.0 (t, JCH ) 124,
1
TaCHCHCH2CH2), 2.5 (q, JCH ) 118, SiMe3). Anal. Calcd for Ta-
Si3N4C19H45: C, 38.37; H, 7.62; N, 9.42. Found: C, 38.50; H, 7.60;
N, 9.35.
(l) With Dihydrogen To Give [N3N]Ta(H)(C2H5). A 100 mL glass
bomb fitted with a Teflon stopcock was charged with a solution of
[N3N]Ta(C2H4) (319 mg, 0.561 mmol) in 10 mL of diethyl ether. The
mixture was subjected to three freeze(-196 °C)-pump-thaw cycles,
and 0.5 atm of hydrogen gas was then added. The magenta color of
the solution bleached over a period of 1 h to yield a colorless solution.
After 2 h, the solution was filtered through Celite and the filtrate was
concentrated in vacuo to provide a white solid containing small amounts
of red solid. Examination of the product mixture via 1H NMR revealed
that the white [N3N]Ta(H)(Et) was contaminated with ∼5% [N3N]Ta-
(C2H4). Recrystallization of the mixture from diethyl ether at -35 °C
afforded [N3N]Ta(H)(Et) as a white crystalline solid; yield 298 mg
(0.522 mmol, 93%): 1H NMR (C6D6) δ 24.77 (s, 1, TaH), 3.44 (t, 6,
CH2), 2.26 (t, 8, CH2 and CH2CH3), 1.50 (t, 3, CH2CH3), 0.25 (s, 27,
Reactions of [N3N]Ta(C6H4). (a) With Aniline To Give [N3N]-
TadNPh. An NMR tube was charged with a solution of [N3N]Ta-
(C6H4) (20 mg, 0.0324 mmol) and ferrocene (3 mg, 0.0161 mmol) in
∼1 mL of toluene-d8. Aniline (2.9 µL, 0.0324 mmol) was then added
via syringe, and the tube was sealed and placed in an oil bath at 90 °C
for 4 days. The reaction mixture was determined by 1H NMR
spectroscopy with a ferrocene internal standard to contain a >99% yield
of [N3N]TadNPh.
(b) With Pentafluoroaniline To Give [N3N]TadNC6F5. An NMR
tube was charged with a solution of [N3N]Ta(C6H4) (10 mg, 0.0162
mmol), pentafluoroaniline (3 mg, 0.0162 mmol), and ferrocene (2 mg,
0.0122 mmol) in ∼1 mL of toluene-d8. The tube was then sealed and
placed in an oil bath at 110 °C for 7 days. The reaction mixture was
shown by 1H NMR spectroscopy with a ferrocene internal standard to
contain a 98% yield of [N3N]TadNC6F5.
1
SiMe3); 13C NMR (C6D6) δ 62.4 (t, JCH ) 124, TaCH2CH3), 56.3 (t,
1
1
1JCH ) 137, CH2), 51.1 (t, JCH ) 134, CH2), 11.2 (q, JCH ) 123,
TaCH2CH3), 2.3 (q, 1JCH ) 119, SiMe3); IR (Nujol) cm-1 1816 (s, νTaH).
Under a dynamic vacuum [N3N]Ta(Et)H loses hydrogen gas slowly in
solution at 25 °C to regenerate [N3N]Ta(C2H4) quantitatively.
A 0.40 M toluene-d8 solution of [N3N]Ta(Et)H in a sealed NMR
tube decomposed upon heating in an oil bath at 100 °C for 5 h. The
1H NMR was consistent with formation of EtTa[N(CH2CH2NSiMe3)2-
Acknowledgment. R.R.S. thanks the National Science
Foundation for research support (CHE 91 22827). J.S.F. thanks
Professor Christopher C. Cummins, Dr. Harold H. Fox, Profes-
sor Klaus H. Theopold, and Professor Peter T. Wolczanski for
helpful discussions.
3
(CH2CH2N)] and Me3SiH [δ 4.12 (m, 1, Me3SiH), 0.02 (d, JHH ) 4,
9, Me3SiH)], contaminated by a small amount (<5%) of EtTa-
[N(SiMe3)(CHdCH2)][N(CH2CH2NSiMe3)2] resulting from dihydrogen
loss to give [N3N]Ta(C2H4) followed by decomposition of [N3N]Ta-
(C2H4). The light yellow reaction mixture was concentrated in vacuo
to provide a yellow oil. Recrystallization of the yellow oil from diethyl
ether at -35 °C afforded EtTa[N(SiMe3)(CHdCH2)][N(CH2CH2-
NSiMe3)2] as yellow crystals. The mother liquor was concentrated in
vacuo to afford “EtTa[N(CH2CH2NSiMe3)2(CH2CH2N)]” as a colorless
oil: 1H NMR (C6D6) δ 4.40 (br m, 2, CH2), 3.74 (br m, 2, CH2), 3.58
(br m, 2, CH2), 3.37 (br m, 2, CH2), 2.58 (br s, 4, CH2), 2.07 (t, 3,
CH2CH3), 1.08 (q, 2, CH2CH3), 0.46 (s, 18, NSiMe3); 13C NMR (C6D6)
Supporting Information Available: A detailed description
of X-ray data collection, structure solution, and refinement,
labeled ORTEP diagrams, and tables of fractional coordinates,
isotropic and anisotropic thermal parameters, intramolecular
distances, intramolecular angles, and torsional angles for [N3N]-
Ta(Me)Et and [N3
N]Ta(C H ) (26 pages). This material is
2
2
1
1
contained in many libraries on microfiche, immediately follows
this article in the microfilm edition of this journal, can be ordered
from the ACS, and can be downloaded from the Internet; see
any current masthead page for ordering information and Internet
access instructions.
δ 54.6 (t, JCH ) 141, dNCH2), 52.6 (t, JCH ) 134, CH2), 51.7 (t,
1JCH ) 135, CH2), 49.5 (t, 1JCH ) 135, CH2), 46.2 (t, 1JCH ) 115, CH2-
CH3), 18.3 (q, JCH ) 124, CH2CH3), 3.4 (q, JCH ) 115, SiMe3).
“EtTa[N(CH2CH2NSiMe3)2(CH2CH2N)]” could not be induced to
crystallize.
1
1
Kinetics of Decomposition of [N3N]Ta(C2H4). Decomposition
reactions were followed by UV/vis spectroscopy. In UV/vis runs a
JA953826N