Tetrahydroquinolinyl Amido and Indolinyl Amido Complexes of Tantalum as Models for Substrate-Catalyst Adducts in Hydrodenitrogenation Catalysis

Article abstract of DOI:10.1021/ic960298n

The reactions of TaCl₅ with Me₃SiNC₉H₁₀ or LiNC₉H₁₀, where [NC₉H₁₀]^- = tetrahydroquinolinyl (the amido anion of tetrahydroquinoline), afford selective preparative routes to the complete series of amido halide complexes of tantalum(V)Ta(NC₉H₁₀)_nCl_5-n for n = 1-5 (compounds 1-5, respectively). The monokis(tetrahydroquinolinyl) complex is isolated as an ether adduct Ta(NC₉H₁₀)Cl₄(OEt₂) while the complexes Ta(NC₉H₁₀)_nCl_5-n (n = 2-5) are found to be base-free, monomeric species. The related complexes of indolinyl [NC₈H₈]^- (the amido anion of indoline), Ta(NC₈H₈)_nCl_5-n(THF) for n = 1 (6) or 2 (7), have been prepared from TaCl₅, Me₃SiNC₈H₈, and THF. An X-ray structural determination of Ta(NC₉H₁₀)₂Cl₃ (2) reveals that it adopts a trigonal bipyramidal geometry with equatorial amido ligands that are closer to lying parallel (within) than perpendicular to the TBP equatorial plane. Routes to mixed-ligand aryloxide-amide complexes have been developed from either aryloxide or amido precursors but not from both. Thus, Ta(NC₉H₁₀)(OAr)Cl₃(OEt₂) (8), where Ar = 2,6-C₆H₃ⁱPr₈, and Ta(NC₈H₈)(OAr)Cl₃(OEt₂) (9) are available from reacting Ta(OAr)Cl₄(OEt₂) with Me₃SiNC₈H₈ and Me₃SiNC₈H₉, respectively, while Ta(NC₉H₁₀)₂(OAr)₂Cl (10) is available from Ta(NC₉H₁₀)₂Cl₃ (2) and excess LiOAr·OEt₂. The alkyl derivatives Ta(NC₉H₁₀)(OAr)Me₂Cl (11), Ta(NC₉H₁₀)(OAr)Et₂Cl (12), Ta(NC₉H₁₀)₂(OAr)₂Me (13), and Ta(NC₉H₁₀)Me₂Cl₉ (14) are prepared from AlR₃ or ZnR₂ reagents and the appropriate precursor. Thermolyzing compounds 4, 5, and 11-14 in solution afforded no evidence for the formation of any η²(N,C)-heterocyclic complexes arising from metalation of a NC₉H₁₀ ligand.

Full text of DOI:10.1021/ic960298n

Inorg. Chem. 1996, 35, 6027-6036
6027
Tetrahydroquinolinyl Amido and Indolinyl Amido Complexes of Tantalum as Models for
Substrate-Catalyst Adducts in Hydrodenitrogenation Catalysis
Peter A. Fox, Steven D. Gray, Michael A. Bruck, and David E. Wigley*
Carl S. Marvel Laboratories of Chemistry, Department of Chemistry, University of Arizona,
Tucson, Arizona 85721
ReceiVed March 20, 1996X
The reactions of TaCl5 with Me3SiNC9H10 or LiNC9H10, where [NC9H10]- ) tetrahydroquinolinyl (the amido
anion of tetrahydroquinoline), afford selective preparative routes to the complete series of amido halide complexes
of tantalum(V) Ta(NC9H10)nCl5-n for n ) 1-5 (compounds 1-5, respectively). The monokis(tetrahydroquinolinyl)
complex is isolated as an ether adduct Ta(NC9H10)Cl4(OEt2) while the complexes Ta(NC9H10)nCl5-n (n ) 2-5)
are found to be base-free, monomeric species. The related complexes of indolinyl [NC8H8]- (the amido anion
of indoline), Ta(NC8H8)nCl5-n(THF) for n ) 1 (6) or 2 (7), have been prepared from TaCl5, Me3SiNC8H8, and
THF. An X-ray structural determination of Ta(NC9H10)2Cl3 (2) reveals that it adopts a trigonal bipyramidal
geometry with equatorial amido ligands that are closer to lying parallel (within) than perpendicular to the TBP
equatorial plane. Routes to mixed-ligand aryloxide-amide complexes have been developed from either aryloxide
i
or amido precursors but not from both. Thus, Ta(NC9H10)(OAr)Cl3(OEt2) (8), where Ar ) 2,6-C6H3 Pr2, and
Ta(NC8H8)(OAr)Cl3(OEt2) (9) are available from reacting Ta(OAr)Cl4(OEt2) with Me3SiNC9H10 and Me3SiNC8H8,
respectively, while Ta(NC9H10)2(OAr)2Cl (10) is available from Ta(NC9H10)2Cl3 (2) and excess LiOAr‚OEt2.
The alkyl derivatives Ta(NC9H10)(OAr)Me2Cl (11), Ta(NC9H10)(OAr)Et2Cl (12), Ta(NC9H10)2(OAr)2Me (13),
and Ta(NC9H10)Me2Cl2 (14) are prepared from AlR3 or ZnR2 reagents and the appropriate precursor. Thermolyzing
compounds 4, 5, and 11-14 in solution afforded no evidence for the formation of any η2(N,C)-heterocyclic
complexes arising from metalation of a NC9H10 ligand.
Introduction
Scheme 1
The catalytic removal of nitrogen from petroleum is necessary
to reduce NOx emissions upon combustion of its fuel products
and to reduce organonitrogen compounds, which can poison
re-forming and hydrocracking catalysts used in petroleum
refining.1-6 Under standard hydrodenitrogenation (HDN) con-
ditions (300-450 °C, up to 200 atm of H2), N-heterocycles are
readily hydrogenated, although they are slow to undergo C-N
bond hydrogenolysis reactions.7-10 A generalized HDN reaction
scheme for the model substrates quinoline and indole is
presented in Scheme 1.3,11,12 The most efficient and selective
method of quinoline HDN involves the a f b f c pathway in
which the carbocyclic ring is not hydrogenated, however most
of the quinoline follows the a f d f e f f pathway (perhaps
involving f′) where the carbocycle is also hydrogenated before
C-N bonds are cleaved. In either case, the most facile step is
X Abstract published in AdVance ACS Abstracts, September 1, 1996.
(1) Angelici, R. J. In Encyclopedia of Inorganic Chemistry; King, R. B.,
Ed.; John Wiley and Sons: New York, 1994; Vol. 3; pp 1433-1443.
(2) Gary, J. H.; Handwerk, G. E. Petroleum Refining: Technology and
Economics, 3rd ed.; Marcel Dekker, Inc.: New York, 1993.
(3) Satterfield, C. N. Heterogeneous Catalysis in Industrial Practice, 2nd
ed.; McGraw-Hill, Inc.: New York, 1991.
(4) Kasztelan, S.; des Courie`res, T., Breysse, M. Catal. Today 1991, 10,
433.
(5) Ho, T. C. Catal. ReV.sSci. Eng. 1988, 30, 117.
(6) Ledoux, M. J. Catalysis; The Chemical Society: London, 1985; Vol.
7, pp 125-148.
(7) Katzer, J. R.; Sivasubramanian, R. Catal. ReV.sSci. Eng. 1979, 20,
155.
hydrogenation of the heterocycle (step a); therefore, quinoline
HDN invariably involves the intermediacy of tetrahydroquino-
line, just as indole HDN proceeds Via indoline, Scheme 1.
While there are several reports of quinoline complexes,13-17
and catalytic HDN studies invariably examine quinoline and
(8) Laine, R. M. Ann. N.Y. Acad. Sci. 1983, 415, 271.
(9) Laine, R. M. Catal. ReV.sSci. Eng. 1983, 25, 459.
(10) Fish, R. H. Ann. NY Acad. Sci. 1983, 415, 292.
(11) Satterfield, C. N.; Modell, M.; Wilkers, J. A. Ind. Eng. Chem. Process
Des. DeV. 1980, 19, 154.
(13) Allen, K. D.; Bruck, M. A.; Gray, S. D.; Kingsborough, R. P.; Smith,
D. P.; Weller, K. J.; Wigley, D. E. Polyhedron 1995, 14, 3315.
(14) Baralt, E.; Smith, S. J.; Hurwitz, J.; Horva´th I. T.; Fish, R. H. J. Am.
Chem. Soc. 1992, 114, 5187.
(12) Satterfield, C. N.; Yang, S. H. Ind. Eng. Chem. Process Des. DeV.
1984, 23, 11.
(15) Fish, R. H.; Kim, H.-S.; Fong, R. H. Organometallics 1989, 8, 1375.
S0020-1669(96)00298-4 CCC: $12.00 © 1996 American Chemical Society

6028 Inorganic Chemistry, Vol. 35, No. 21, 1996
Fox et al.
Scheme 2
Results
Figure 1. Binding modes and metalated forms of piperidine, tetrahy-
Preparation and Properties of Tetrahydroquinolinyl Com-
plexes of Tantalum(V). By the reaction of TaCl5 with 1 equiv
of Me3SiNC9H10 in C6H6/Et2O, intense burgundy-colored,
almost black crystalline rods of compound 1 can be isolated in
nearly quantitative yield, Scheme 2. Analytical and spectro-
scopic data are consistent with the formulation of 1 as the
monokis(amido) complex Ta(NC9H10)Cl4(OEt2). On the basis
of the structures observed or proposed for Ta[OSi(2-C6H4Me)3]-
Cl4(OEt2),31 Ta(OAr)Cl4(OEt2),32 and M(NR2)Cl4(OEt2) (M )
Nb, Ta),33 we formulate Ta(NC9H10)Cl4(OEt2) (1) as the trans
isomer. The 1H and 13C NMR data for 1 are entirely consistent
with the simple η1(N) mode of amido bonding to the d0 metal;
e.g., the 1H NMR resonances attributed to the H2 and H8 protons
of the NC9H10 ligand are shifted downfield with respect to those
of the free tetrahydroquinoline (C6D6, probe temperature). This
shift appears to be a manifestation of these protons’ proximity
to the electrophilic d0 metal when the heterocycle is coordinated
in this fashion.13 However, the 13C chemical shifts do not
consistently track the proton shifts, as demonstrated by the
HETCOR spectrum of 1 (see Experimental Section).
When Ta(NC9H10)Cl4(OEt2) (1) reacts with 1 equiv of Me3-
SiNC9H10 in toluene, burgundy-colored, microcrystalline
Ta(NC9H10)2Cl3 (2) is observed to precipitate in moderate yield,
Scheme 2. While samples of Ta(NC9H10)2Cl3 (2) collected in
this fashion were found to be analytically pure, the dark red
filtrate obtained from isolating these microcrystals contains a
mixture of Ta(NC9H10)Cl4(OEt2) (1), Ta(NC9H10)2Cl3 (2), and
Ta(NC9H10)3Cl2 (3) (Vide infra). The last compound is obtained
in high yield from reacting TaCl5 with excess Me3SiNC9H10
(toluene, 100 °C), suggesting that the tris(amido) complex Ta-
(NC9H10)3Cl2 (3) is a thermodynamic product that arises from
droquinoline, and indoline.
indole substrates,14,18-23 complexes of their hydrogenated
derivatives tetrahydroquinoline or indoline are scarce.14,24,25 In
this report, we describe the preparation and properties of
tantalum aryloxide complexes containing the amido ligands of
tetrahydroquinoline and indoline, namely tetrahydroquinolinyl
([NC9H10]-, the anion of tetrahydroquinoline) and indolinyl
([NC8H8]-, the anion of indoline), Figure 1. (The amide of
indoline, indolinyl [NC8H8]-, is not to be confused with the
amide of indole, the [NC8H6]- ligand.) These compounds were
deemed worthy synthetic targets for two reasons. First, in an
effort to closely model substrate-catalyst complexes at the
active site in HDN, early transition metal complexes26 of these
partially hydrogenated ligands should be examined. Second,
because the η2(N,C) binding mode provides excellent reactivity
models for fundamental HDN reactions of pyri-
dines,27-30 we wanted to determine whether η1 complexes of
tetrahydroquinoline, or of its amide, might serve as precursors
to related η2 species. We note that one mechanistic proposal
for piperidine HDN includes an η2(N,C)-piperidyl ligand, Figure
1.8,9 (Our terminology for metalated forms of selected ligands
is also presented in Figure 1.)
(16) Fish, R. H.; Kim, H.-S.; Babin, J. E.; Adams, R. D. Organometallics
1988, 7, 2250.
(17) Fish, R. H.; Kim, H.-S.; Fong, R. H. Organometallics 1991, 10, 770.
(18) Perot, G. Catal. Today 1991, 10, 447.
(19) Moreau, C.; Bekakra, L.; Durand, R.; Geneste, P. Catal. Today 1991,
10, 681.
(20) Laine, R. M. New. J. Chem. 1987, 11, 543.
(21) Dzidic, I.; Balicki, M. D.; Petersen, H. A.; Nowlin, J. G.; Evans, W.
E.; Siegel, H.; Hart, H. V. Energy Fuels 1991, 5, 382.
(22) Fish, R. H. In Aspects of Homogeneous Catalysis; Ugo, R., Ed.; Kluwer
Academic Publishers: Amsterdam, 1990; pp 65-83.
(23) Fish, R. H.; Michaels, J. N.; Moore, R. S.; Heinemann, H. J. Catal.
1990, 123, 74.
(24) Rosales, M.; Alvarado, Y.; Boves, M.; Rubio, R.; Soscu´n, H.; Sa´nchez-
Delgado, R. A. Transition Met. Chem. 1995, 20, 246.
(25) Maurya, R. C.; Mishra, D. D.; Pandey, M.; Awasthi, S. Natl. Acad.
Sci. Lett. 1990, 13, 443.
(26) Industrial HDN catalysis is generally effected over sulfided CoMo/
γ-Al2O3 or NiMo/γ-Al2O3 under rather severe hydrogenation condi-
tions (e.g. 350-500 °C and g200 atm of H2), which ultimately
removes the nitrogen as NH3.1,5,7 See also: Prins, R.; de Beer, V. H.
J.; Somorjai, G. A. Catal. ReV.sSci. Eng. 1989, 31, 1.
(27) Gray, S. D.; Smith, D. P.; Bruck, M. A.; Wigley, D. E. J. Am. Chem.
Soc. 1992, 114, 5462.
maximizing the total bond energies in the Ta(NC9H10)nCl5-n
+
(5 - n)Me3SiNC9H10 + nMe3SiCl mixtures. This feature is
confirmed by reacting Ta(NC9H10)5 (Vide infra) with 5 equiv
of Me3SiCl, which affords the same mixture of Ta(NC9H10)3-
Cl2 (3), Me3SiCl, and Me3SiNC9H10 as that obtained from TaCl5
and 5 equiv of Me3SiNC9H10 under identical conditions. These
observations demonstrate the kinetic accessibility of Ta(NC9H10)3-
Cl2 from either direction and suggest the series of facile
metathesis reactions shown in eq 1. This kinetic feature has
found considerable synthetic utility in early metal alkoxide and
amide chemistry.32-39
(28) Gray, S. D.; Fox, P. A.; Kingsborough, R. P.; Bruck, M. A.; Wigley,
D. E. Prepr.sAm. Chem. Soc., DiV. Pet. Chem. 1993, 39, 706.
(29) Gray, S. D.; Weller, K. J.; Bruck, M. A.; Briggs, P. M.; Wigley, D.
E. J. Am. Chem. Soc. 1995, 117, 10678.
(30) Weller, K. J.; Gray, S. D.; Briggs, P. M.; Wigley, D. E. Organome-
tallics 1995, 14, 5588.
(31) Bott, S. G.; Sullivan, A. C. J. Chem. Soc., Chem. Commun. 1988,
1577.
(32) Arney, D. J.; Wexler, P. A.; Wigley, D. E. Organometallics 1990, 9,
1282.
(33) Chao, Y.-W.; Polson, S.; Wigley, D. E. Polyhedron 1990, 9, 2709.

Models for Substrate-Catalyst Adducts
Inorganic Chemistry, Vol. 35, No. 21, 1996 6029
Scheme 3
TaCl5 + 5Me3SiNC9H10 a
Ta(NC9H10)Cl4 + Me3SiCl + 4Me3SiNC9H10 a
Ta(NC9H10)2Cl3 + 2Me3SiCl + 3Me3SiNC9H10 a
Ta(NC9H10)3Cl2 + 3Me3SiCl + 2Me3SiNC9H10 a
Ta(NC9H10)4Cl + 4Me3SiCl + Me3SiNC9H10 a
Ta(NC9H10)5 + 5Me3SiCl (1)
Table 1. Crystallographic Data for Ta(NC9H10)2Cl3 (2)a
Both Ta(NC9H10)2Cl3 (2) and Ta(NC9H10)3Cl2 (3) display
1
equivalent NC9H10 amido ligands in their H and 13C NMR
empirical
C18H20Cl3N2Ta
space
group
T
monoclinic
P21/c (No. 14)
20 ( 1 °C
0.710 73 Å
1.96 g cm-3
62.3 cm-1
0.025
formula
spectra, suggesting either the static structures shown in Scheme
2, presumably with free rotation about Ta-NR2 bonds, or
fluxional five-coordinate molecules. The solid state structure
of Ta(NC9H10)2Cl3 (2) has been determined to be that shown
in Scheme 2; Vide infra.
fw
a
551.68
15.409(1) Å
9.946(1) Å
12.310(1) Å
96.62(8)°
1874.0(7) Å3
4
λ
b
c
â
V
Z
Fcalcd
µ
R
Rw
0.034
Since the reaction of any Ta(NC9H10)nCl5-n (n ) 0-3)
complex with excess Me3SiNC9H10 affords only Ta(NC9H10)3-
Cl2, further amidation of the metal center was attempted using
more nucleophilic reagents. When Ta(NC9H10)3Cl2 is reacted
with 1 equiv of LiNC9H10‚2THF (in THF), orange crystals of
the tetrakis(amido) complex Ta(NC9H10)4Cl (4) can be isolated
in high yield, Scheme 2. Similarly, reacting Ta(NC9H10)2Cl3
with 3 equiv of LiNC9H10‚2THF (in C6H6/THF) affords an
orange powder that analyzes as the pentakis(amido) complex
Ta(NC9H10)5 (5). Although samples of Ta(NC9H10)5 (5) isolated
in this manner are analytically pure, attempts to grow crystals
a R ) ∑||Fo| - |Fc||/∑|Fo|; Rw ) [∑w(|Fo| - |Fc|)2/∑w(Fo)2]1/2
.
for this compound are also consistent with a simple η1(N) mode
of amido bonding to the d0 metal. Further reaction of Ta-
(NC8H8)Cl4(THF) (6) with 1 equiv of Me3SiNC8H8 (in C6H6)
forms Ta(NC8H8)2Cl3(THF) (7) as a brown powder. The
inequivalent NC8H8 ligands observed in the NMR spectra of
Ta(NC8H8)2Cl3(THF) (7) support its formulation as the cis-mer
isomer as shown in Scheme 3. The observation that Ta-
(NC9H10)2Cl3 (2) does not coordinate Et2O (Vide supra) and
appears to only loosely coordinate THF suggests that the
isolation of 7 may reflect the slight steric difference between
coordinated NC9H10 and NC8H8 amido ligands.
X-ray Structural Study of Ta(NC9H10)2Cl3. Red single
crystals of Ta(NC9H10)2Cl3 (2) suitable for an X-ray structural
determination were grown directly from the toluene reaction
solution at -35 °C. A summary of the crystal data and
structural analysis is given in Table 1, and relevant bond
distances, bond angles, and torsional angles are provided in
Table 2. Figure 2 presents two views of Ta(NC9H10)2Cl3 (2)
in which the complex can be seen to adopt a trigonal bipyramidal
1
of this compound have failed. The H and 13C NMR spectra
of 4 and 5 reveal equivalent NC9H10 ligands, implying fluxional
five-coordinate species. Complex 5 is also accessible from
reacting Ta(NC9H10)3Cl2 with 2 equiv of LiNC9H10‚2THF. The
reaction of TaCl5 with 5 equiv of LiNC9H10‚2THF also affords
Ta(NC9H10)5 (5) in low yield, along with byproducts arising
from tantalum reduction; therefore, this direct synthesis is not
the preferred route to 5. Pentakis(amido) complexes of nio-
bium40,41 and tantalum41,42 have been reported from reacting
MCl5 with 5 LiNR2, and the structures of Nb(NMe2)5,43 Nb-
44
(NC5H10)5,43 and Ta(NEt2)5 have been determined crystallo-
graphically.
geometry with equatorial NC9H10 amido ligands. The Cl1axial
-
Preparation and Properties of Indolinyl Complexes of
Tantalum(V). Indolinyl analogues of the tetrahydroquinolinyl
complexes are also accessible from metathetical reactions using
the appropriate (trimethylsilyl)amine. Thus, reacting TaCl5 with
1 equiv of Me3SiNC8H8 (in C6H6/Et2O) affords a dark purple,
insoluble solid presumed to be either [Ta(NC8H8)Cl4]n or Ta-
(NC8H8)Cl4‚OEt2. (We note that moderately soluble [Ta(OAr)-
Cl4]2 readily forms adducts with THF or Et2O.32) Upon
dissolution of this solid in THF, a soluble monokis(amido)
complex can be isolated in high yield as the dark purple adduct
Ta(NC8H8)Cl4(THF) (6), Scheme 3. The 1H and 13C NMR data
Ta-Cl3axial linkage is almost linear (170.27(7)°), while the
Laxial-Ta-Lequatorial angles that span a narrow range of 84.92-
(7)-93.6(2)° (averaging 90.1°) are clearly indicative of a
trigonal bipyramid.
The NC9H10 amido ligands are closer to lying parallel (within)
than perpendicular to the equatorial plane of the trigonal
bipyramid. However, significant tilting of the NC9H10 rings
toward a propeller arrangement is apparent, as the phenyl rings
of both amido ligands are 35.9(3) and 21.6(4)° out-of-plane with
the best equatorial TaN2Cl plane for the N11 amide and the
N21 amide, respectively. The saturated ring of the N21 NC9H10
ligand, however, is twisted more out-of-plane than that of the
N11 ligand, as judged from the torsional angles about the Cl-
Ta-N-C bonds, Table 2. Although N(pπ)fTa(dπ) bonding
from both amido ligands is possible if they are either parallel
or perpendicular to the TBP equatorial plane, a steric preference
for parallel amido ligands (within the plane) seems more likely,
since a nearly perpendicular orientation of these ligands would
eclipse the NC9H10 H8 and H2 protons with the axial chloride
ligands. However, steric restriction imposed by the neighboring
NC9H10 ligand does not allow both amides to lie completely
within the equatorial plane, thereby accounting for the observed
twisting.
(34) Handy, L. B.; Sharp, K. G.; Brinckman, F. F. Inorg. Chem. 1977, 11,
523.
(35) Akiyama, M.; Chisholm, M. H.; Cotton, F. A.; Extine, M. W.; Murillo,
C. A. Inorg. Chem. 1977, 16, 2407.
(36) Bradley, D. C.; Mehrotra, R. C.; Gaur, D. P. Metal Alkoxides;
Academic Press: London, 1978.
(37) Chisholm, M. H.; Huffman, J. C.; Tan, L.-S. Inorg. Chem. 1981, 20,
1859.
(38) Gibson, V. C.; Kee, T. P.; Shaw, A. Polyhedron 1988, 7, 2217.
(39) Gibson, V. C.; Kee, T. P. J. Chem. Soc., Chem. Commun. 1989, 656.
(40) Bradley, D. C.; Thomas, M. Can. J. Chem. 1962, 40, 449.
(41) Bradley, D. C.; Gitlitz, M. H. J. Chem. Soc. A 1969, 980.
(42) Bradley, D. C.; Thomas, M. Can. J. Chem. 1962, 40, 1355.
(43) Heath, C.; Hursthouse, M. B. J. Chem. Soc., Chem. Commun. 1971,
143.
(44) Heath, C. E.; Hursthouse, M. B. Unpublished results. As referenced
in: Chisholm, M. H.; Rothwell, I. P. In ComprehensiVe Coordination
Chemistry; Wilkinson, G., Gillard, R. D., McCleverty, J. A., Eds.;
Pergamon Press: Oxford, U.K., 1987; Vol. 2, pp 161-188.
Ligand twisting is accompanied by a smaller N-Ta-N angle
than one might expect: the N11-Ta-N21 angle of 116.8(2)°
contrasts with the Cl2-Ta-N angles of 121.4(1) and 121.8-

6030 Inorganic Chemistry, Vol. 35, No. 21, 1996
Fox et al.
Table 2. Selected Bond Distances (Å), Bond Angles (deg), and
Torsional Angles (deg) in Ta(NC9H10)2Cl3 (2)a
Scheme 4
Bond Distances
Ta-Cl1
2.381(2)
2.340(2)
2.383(2)
1.932(5)
1.932(5)
1.493(7)
1.412(8)
1.502(9)
1.52(1)
1.498(9)
1.409(9)
1.391(9)
1.38(1)
C17-C18
C18-C19
N21-C21
N21-C29
C21-C22
C22-C23
C23-C24
C24-C29
C24-C25
C25-C26
C26-C27
C27-C28
C28-C29
1.37(1)
1.392(8)
1.498(8)
1.429(8)
1.51(1)
1.51(1)
1.49(1)
1.399(8)
1.39(1)
1.39(1)
1.36(1)
1.369(9)
1.395(9)
Ta-Cl2
Ta-Cl3
Ta-N11
Ta-N21
N11-C11
N11-C19
C11-C12
C12-C13
C13-C14
C14-C19
C14-C15
C15-C16
C16-C17
1.37(1)
of the amido ligands out of the equatorial plane. Likewise, the
equatorial N-Ta-N angle in Ta[N(SiMe3)2]2Cl3 measures only
115°. While the small N-Ta-N angle may reflect an enhance-
ment in N(pπ)fTa(dπ) overlap, the authors suggest that
interactions between the equatorial chloride and methyl groups
from both N(SiMe3)2 ligands induce larger than expected
equatorial Cl-Ta-N angles and simultaneously reduce the
equatorial N-Ta-N angle to minimize these interactions.46
Preparation and Properties of Aryloxide and Alkyl
Derivatives of Ta(NC9H10)nCl5-n (n ) 1, 2). Recently, we
described excellent structural and reactivity HDN model com-
plexes supported by aryloxide ancillary ligands, in particular
Bond Angles
Cl1-Ta-Cl2
Cl1-Ta-Cl3
Cl1-Ta-N11
Cl1-Ta-N21
Cl2-Ta-Cl3
Cl2-Ta-N11
Cl2-Ta-N21
Cl3-Ta-N11
84.92(7)
170.27(7)
92.9(2)
Cl3-Ta-N21
N11-Ta-N21
Ta-N11-C11
Ta-N11-C19
C11-N11-C19
Ta-N21-C21
Ta-N21-C29
C21-N21-C29
92.7(2)
116.8(2)
110.0(4)
135.3(4)
114.5(5)
112.4(4)
132.3(4)
115.1(5)
90.8(2)
85.51(7)
121.4(1)
121.8(2)
93.6(2)
Torsional Angles
Cl1-Ta-N11-C11
Cl1-Ta-N11-C19
Cl2-Ta-N11-C11
100.44(34) Cl1-Ta-N21-C21
128.82(38)
-56.48(50)
-84.62(52) Cl1-Ta-N21-C29
14.61(41) Cl2-Ta-N21-C21 -146.68(33)
t
i
Cl2-Ta-N11-C19 -170.45(46) Cl2-Ta-N21-C29
28.02(57)
-60.26(38)
114.44(50)
35.16(45)
[η2(N,C)-2,4,6-NC5 Bu3H2]Ta(OAr)2Cl (Ar ) 2,6-C6H3 Pr2) that
was used to uncover the mechanistic details of C-N bond
scission reactions.27-30 We set out, therefore, to prepare η1-
Cl3-Ta-N11-C11
Cl3-Ta-N11-C19
-72.32(34) Cl3-Ta-N21-C21
102.62(52) Cl3-Ta-N21-C29
N21-Ta-N11-C11 -167.21(34) N11-Ta-N21-C21
i
(N)-NC9H10 compounds containing ancillary O-2,6-C6H3 Pr2
N21-Ta-N11-C19
7.72(60) N11-Ta-N21-C29 -150.14(48)
ligands, with a particular view to develop routes to alkyl
complexes of the form Ta(NC9H10)x(OAr)yRz. These species
would allow us to test whether their thermolysis would lead to
NC9H10 cyclometalation and alkane elimination and thereby
afford η2(N,C) heterocycles such as those in Figure 1.
a Numbers in parentheses are estimated standard deviations in the
least significant digits.
The most facile entry into mixed-ligand compounds was
determined to be from the aryloxide chlorides. Thus, an Et2O
solution of Ta(OAr)Cl4(OEt2)32 reacts with Me3SiNC9H10 to
provide dark red crystals of Ta(NC9H10)(OAr)Cl3(OEt2) (8), one
possible structure of which is shown in Scheme 4. Ta(NC9H10)-
(OAr)Cl3(OEt2) (8), however, has not been prepared from
reacting Ta(NC9H10)Cl4(OEt2) (1) with Me3SiOAr or LiOAr‚
OEt2, although this preparative route would seem viable. We
previously reported a similar reactivity feature in the preparation
of Ta(NEt2)(OAr)Cl3(OEt2), a complex that is accessible from
Ta(OAr)Cl4(OEt2) and Me3SiNEt2 but not from Ta(NEt2)Cl4(OEt2)
and Me3SiOAr or LiOAr‚OEt2.33 Similarly, the indolinyl
compound Ta(NC8H8)(OAr)Cl3(OEt2) (9) may be prepared from
Ta(OAr)Cl4(OEt2) and Me3SiNC8H8 in Et2O, eq 2. Attempts
to further alkoxylate Ta(NC9H10)(OAr)Cl3(OEt2) (8) using
LiOAr‚OEt2 led to disproportionation products, since the
principal species isolable from this reaction was identified as
Ta(NC9H10)2(OAr)2Cl (10); this complex is readily accessible
from its bis(amide) precursor. When Ta(NC9H10)2Cl3 (2) is
Figure 2. Two views of the molecular structure of Ta(NC9H10)2Cl3
(2) with atoms represented as 50% ellipsoids.
(2)°. This structural feature was also noted in Ta[N(SiMe3)2]2-
Cl3,45 the structure of which has been communicated.46
Ta[N(SiMe3)2]2Cl3 also adopts a trigonal bipyramidal geometry
with equatorial N(SiMe3)2 ligands and a propeller-like twisting
(45) Andersen, R. A. Inorg. Chem. 1979, 18, 3622.
(46) Bradley, D. C.; Hursthouse, M. B.; Malik, K. M. A.; Vuru, G. B. C.
Inorg. Chim. Acta 1980, 44, L5.

Models for Substrate-Catalyst Adducts
Inorganic Chemistry, Vol. 35, No. 21, 1996 6031
reacted with excess LiOAr‚OEt2 (in C6H6/Et2O), Ta(NC9H10)2-
(OAr)2Cl (10) can be isolated in essentially quantitative yield.
When less than 1 equiv of LiOAr‚OEt2 is employed in this
reaction, 10 is simply isolated in lower yield along with
unreacted 2. Ta(NC9H10)2(OAr)2Cl (10) is also available, but
in low yield, from reacting Ta(OAr)2Cl3(OEt2)32 with 2 equiv
of LiNC9H10‚2THF.
Scheme 5
The desired alkyl complexes were accessed from reacting
compounds 8 and 10 with AlR3 or ZnR2 reagents, which
afforded more tractable reactions and higher yields than alkyl-
lithium or Grignard reagents. When a benzene solution of Ta-
(NC9H10)(OAr)Cl3(OEt2) (8) is treated with excess ZnMe2,
yellow crystals of Ta(NC9H10)(OAr)Me2Cl (11) can be obtained
in 64% yield, Scheme 4. Ta(NC9H10)(OAr)Cl3(OEt2) and excess
ZnEt2 react to afford Ta(NC9H10)(OAr)Et2Cl (12) in comparable
yield. Attempts to either monoalkylate or exhaustively alkylate
Ta(NC9H10)(OAr)Cl3(OEt2) (8) led simply to lower yields of
the dialkyl complexes. The 1H and 13C NMR spectra of these
compounds reveal equivalent alkyl groups, most likely indicating
fluxional species in solution. Treating toluene solutions of Ta-
(NC9H10)2(OAr)2Cl (10) with AlMe3 (1 equiv) affords yellow
in Scheme 5 for comparison. Similar amido cyclometalations
were observed more recently in η5-C5Me5-supported tantalum
complexes; for example, Cp*Ta(η2-MeNdCH2)Me2 is isolated
when solutions of Cp*Ta(NMe2)Me3 are warmed to room
temperature,49 and Cp*2Ta(η2-MeNdCH2)H is formed as the
kinetic product from [Cp*2Ta(NMe2)].50,51 Moreover, Gam-
barotta and co-workers have found a similar cyclometalation
reaction in the preparation of Nb[η2-CyNdC6H10](NCy2)2Cl (Cy
) C6H11) from NbCl4(THF)2 and LiNCy252 and in the prepara-
tion of its tantalum analog Ta[η2-CyNdC6H10](NCy2)2Cl from
TaCl5 and LiNCy2.53
1
crystals of Ta(NC9H10)2(OAr)2Me (13) in 77% yield. The H
and 13C NMR data for this compound reveal equivalent NC9H10
and equivalent OAr ligands at probe temperature.
An interesting spectroscopic feature of the ethyl derivative
Ta(NC9H10)(OAr)Et2Cl (12) is the coincidence of the methylene
CH2 and methyl CH3 protons of the ethyl ligand at δ 2.11 in its
1H NMR spectrum (250 MHz, C6D6, probe temperature). The
13C NMR spectrum (62.9 MHz, C6D6) of 12 clearly shows
inequiValent methylene CH2 and methyl CH3 carbon atoms (at
δ 78.08 and 15.68, respectively), and the HETCOR spectrum
of 12 correlates both CH2 and CH3 carbons with the single
CH2CH3 1H NMR resonance. To confirm this assignment, the
500 MHz H NMR spectrum of 12 was obtained where the
methylene CH2 and methyl CH3 protons are observed at δ 2.112
and 2.104, respectively (C6D6, probe temperature).
We additionally prepared one amido alkyl complex without
aryloxide ancillary ligands. Ta(NC9H10)Cl4(OEt2) (1) can be
smoothly alkylated with 2 equiv of ZnMe2 in benzene solution
to provide high yields of orange, crystalline Ta(NC9H10)Me2-
Cl2 (14), eq 3. Attempts to prepare the ethyl analog of 14 from
Unfortunately, thermolyzing 11-14 in C6D6 solution (80 °C,
up to 24 h) afforded no evidence for the formation of any η2-
(N,C) heterocycles; intractable mixtures that included paramag-
netic species were slowly formed. While thermolysis of
Ta(NC9H10)4Cl (4) and Ta(NC9H10)5 (5) under similar conditions
(C6D6, g80 °C) produced free tetrahydroquinoline, HNC9H10,
no evidence for the formation of an η2(N,C) complex was
obtained in either case; intractable, paramagnetic products were
again obtained. In order to test whether a reVersible metalation
of a NC9H10 ligand occurs under these conditions,54,55 a sample
of Ta(NC9H10)5 (5) was thermolyzed in the presence of excess
DNC9H10 and examined by 1H and 13C NMR.56 No incorpora-
tion of deuterium into either H2 or H8 (or any position) of the
coordinated NC9H10 amide ligand was observed. When the
reaction mixture was hydrolyzed with aqueous base (which
exchanged any N-bound deuterium), a GC/mass spectral analysis
of the organic phase revealed that no significant deuterium
incorporation into HNC9H10 occurred, thereby precluding a
reversible C-H activation of this ligand.
1
Discussion
We recently prepared niobium and tantalum complexes (M
) Nb, Ta) of the form M(NEt2)Cl4(OEt2), [M(NEt2)2Cl3]2,
Ta(NEt2)2Cl3L (L ) OEt2, THF, py), and [Nb(NEt2)2Cl3]2
directly from the halides and Me3SiNEt2 under the appropriate
conditions.33,57 This synthetic procedure allows selective forma-
tion of the mixed amido halides and circumvents any reduction
Ta(NC9H10)Cl4(OEt2) and ZnEt2 afforded a thermally unstable
complex that could not be completely characterized.
Attempts To Prepare η2(N,C)-Heterocyclic Ligands by
Cyclometalation. The alkyl derivatives Ta(NC9H10)(OAr)Me2-
Cl (11), Ta(NC9H10)(OAr)Et2Cl (12), and Ta(NC9H10)2(OAr)2-
Me (13), as well as the amido derivatives Ta(NC9H10)4Cl (4),
Ta(NC9H10)5 (5), and Ta(NC9H10)Me2Cl2 (14), were all ther-
molyzed in an attempt to cyclometalate a NC9H10 ligand and
eliminate alkane or HNC9H10, much in the way that Ta(NEt2)5
undergoes thermolysis to form the N-ethylethanimine complex
Ta(η2-EtNdCHCH3)(NEt2)3, Scheme 5.41,42,47,48 The proposed
complex arising from cyclometalation of an amido ligand in
Ta(NC9H10)5 (5), Viz. Ta(η2-NC9H9)(NC9H10)3 (A), is presented
(49) Mayer, J. M.; Curtis, C. J.; Bercaw, J. E. J. Am. Chem. Soc. 1983,
105, 2651.
(50) Parkin, G.; Bunel, B. J.; Trimmer, M. S.; van Asselt, A.; Bercaw, J.
E. J. Mol. Catal. 1987, 41, 21.
(51) We note that most η2-imine compounds of tantalum are prepared from
CtNR insertions into metal-alkyl bonds. See: Durfee, L. D.;
Rothwell, I. P. Chem. ReV. 1988, 88, 1059.
(52) Berno, P.; Gambarotta, S. Organometallics 1995, 14, 2159.
(53) Gambarotta, S. Abstracts of Papers, International Chemical Congress
of Pacific Basin Societies, Honolulu, HI, 1995; American Chemical
Society: Washington, DC, 1995; INOR 631.
(54) Fish, R. H.; Baralt, E.; Smith, S. J. Organometallics 1991, 10, 54.
(55) Giandomenico, C. M.; Eisenstadt, A.; Fredericks, M. F.; Hirschon,
A. S.; Laine, R. M. In Catalysis of Organic Reactions; Augustine, R.
L., Ed.; Marcel Dekker, Inc.: New York, 1955; pp 73-92.
(56) Nugent, W. A.; Ovenall, D. W.; Holmes, S. J. Organometallics 1983,
2, 161.
(47) Takahashi, Y.; Onoyama, N.; Ishikawa, Y.; Motojima, S.; Sugiyama,
K. Chem. Lett. 1978, 525.
(48) Bradley, D. C.; Thomas, I. M. Proc. Chem. Soc., London 1959, 225.

6032 Inorganic Chemistry, Vol. 35, No. 21, 1996
Fox et al.
Scheme 6
of the NCy2 amides relative to NC9H10, as well as possible one-
electron pathways that are operative in the niobium system.
Experimental Section
General Details. All experiments were performed under a nitrogen
atmosphere either by standard Schlenk techniques58 or in a Vacuum
Atmospheres HE-493 drybox at room temperature (unless otherwise
indicated). Solvents were distilled under N2 from an appropriate drying
agent59 and were transferred to the drybox without exposure to air.
NMR solvents were passed down a short (5-6 cm) column of activated
alumina prior to use. The “cold” solvents used to wash isolated
products were typically cooled to -35 °C before use. In all preparations
i
Ar ) 2,6-C6H3 Pr2, [NC8H8]- ) the amido anion of indoline (indolinyl),
and [NC9H10]- ) the amido anion of tetrahydroquinoline (tetrahydro-
quinolinyl). Ring numbering:
problems or the formation of product mixtures that can arise
when the more powerful alkali metal amidating agents are used.
The viability of this approach is evident in the present work
since the entire series of mixed-ligand complexes are selectively
prepared; thus, sequential amidation of TaCl5 using Me3-
SiNC9H10 affords the Ta(NC9H10)nCl5-n for n ) 1-3 complexes
and subsequent reaction with LiNC9H10 provides selective routes
to the n ) 4 and 5 species.
Physical Measurements. 1H and 13C NMR spectra were recorded
at probe temperature (unless otherwise specified) on a Bruker AM-
250, Varian Gemini 200, or Varian Unity 300 spectrometer in C6D6,
CDCl3, or toluene-d8 solvent. Chemical shifts are referenced to protio
impurities (δ: 7.15, C6D6; 7.24, CDCl3; 2.09, toluene-d8) or solvent
13C resonances (δ: 128.0, C6D6; 77.0, CDCl3; 20.4, toluene-d8) and
are reported downfield of SiMe4. Routine coupling constants are not
reported. NMR assignments were assisted by COSY, APT, HETCOR,
The impetus for preparing these complexes is suggested in
Scheme 1, where quinoline HDN is shown to proceed Via the
intermediacy of tetrahydroquinoline. The motivation for at-
tempting the cyclometalation reactions suggested in Scheme 5
is realized by examining the Laine proposal for C-N bond
cleavage in piperidine, outlined in Scheme 6.8,9 An important
feature of this proposal is the initial formation of an η2(N,C)-
piperidyl amine complex (B of Scheme 6) that arises from
metalation of a piperidine ligand. If the subsequent C-N bond
cleavage results from hydride transfer to CR, then formation of
a ring-opened amido complex (C) occurs. In our model studies,
we have observed that an η2(N,C)-pyridine complex, containing
a formal amido nitrogen, can be transformed to a formal imido
complex upon C-N scission. Specifically, we observed that
hydride can attack the metal and migrate to CR of [η2(N,C)-
1
or gated 13C{1H} decoupled spectra. The H NMR multiplet signals
for H2 and H3 of both NC9H10 and NC8H8 ligands often appear as
pseudotriplets but are nominally recorded as multiplets throughout.
Electron ionization mass spectra (70 eV) were recorded to m/z ) 999
on a Hewlett Packard 5970 mass selective detector and RTE-6/VM
data system. For GC mass spectra, the sample was introduced into
the mass spectrometer by a Hewlett Packard Model 5890 gas chro-
matograph equipped with an HP-5 column. Microanalytical samples
were handled under nitrogen and were combusted with WO3 (Desert
Analytics, Tucson, AZ).
Starting Materials. TaCl5 was obtained from Cerac and used as
received. Tetrahydroquinoline, HNC9H10, indoline, HNC8H8, and
chlorotrimethylsilane, Me3SiCl, were obtained from Aldrich and distilled
prior to use. n-Butyllithium (1.6 M in hexanes) was obtained from
Aldrich and used as received. ZnMe2 (Alfa), ZnEt2 (Aldrich), and
AlMe3 (Aldrich) were obtained from commercial sources and prepared
t
2,4,6-NC5 Bu3H2]Ta(OAr)2Cl to afford the C-N bond scission
product Ta(dNCtBudCHCtBudCHCHtBu)(OAr)2 (2), shown
in Scheme 6.29,30 A complex such as Ta(η2-NC9H9)(NC9H10)3
(A) of Scheme 5 was desired to test whether nucleophilic
addition would cleave the C-N bond of the η2-NC9H9 ligand
in a substrate more relevant to HDN. Furthermore, the
likelihood of protonating the heterocycle nitrogen of an η2-
NC9H9 complex like A (Scheme 5) to afford a direct analog of
the Laine intermediate B (Scheme 6) was an attractive prospect.
Unfortunately, in our hands, the initial cyclometalation step was
not realized and therefore reactions of η2-NC9H9 complexes with
electrophiles and nucleophiles could not be carried out.
32
as either 1.0 or 2.0 M solutions in heptane. [Ta(OAr)Cl4]2 and
57
LiOAr‚OEt2 were prepared as previously described.
Ligand Preparations. LiNC9H10‚2THF. A solution of tetrahy-
droquinoline (40.2 mL, 42.6 g, 0.320 mol) in 500 mL of pentane was
prepared and cooled to 0 °C. This cold solution was stirred rapidly
while 1 equiv of n-butyllithium (1.6 M in hexanes, 200 mL, 0.320
mol) was added slowly. After this mixture was stirred at room
temperature for 21 h, the reaction volatiles were removed under reduced
pressure to afford a pale yellow powder that was dissolved in THF
(ca. 500 mL), and the solution was stirred for an additional 2 h. The
reaction volatiles were removed from this solution under reduced
pressure, and the resulting light yellow solid was placed on a frit,
washed with pentane (ca. 125 mL), and dried in vacuo to yield 71.16
g of LiNC9H10‚2THF as a pale yellow, almost white solid. An
additional 5.61 g of product was obtained by concentrating the filtrate
to ca. 25 mL in volume, adding minimal THF (ca. 2 mL) to redissolve
the precipitate that formed during concentration of the solution, and
cooling to -35 °C for a total yield of 76.77 g (0.271 mol, 85%) of
LiNC9H10‚2THF. Analytically pure compound was obtained as large
white crystals by recrystallization from THF/pentane solutions at -35
°C. 1H NMR (C6D6): δ 7.06, 7.00 (overlapping t and d, 1 H each, H6
and H8), 6.42, 6.40 (overlapping t and d, 1 H each, H7 and H5), 3.69
Finally, we note that Gambarotta and co-workers recently
described the preparation of Nb[η2(N,C)-CyNdC6H10](NCy2)2-
Cl (Cy ) C6H11) from NbCl4(THF)2 and LiNCy2, containing
one metalated cyclohexyl ring.52 The proposal is made that
intermediate Nb(NCy2)3Cl is formed, which undergoes a formal
elimination of hydrogen; therefore, under the appropriate
conditions, these cyclometalations are facile.52 Gambarotta has
also described the tantalum analog Ta[η2(N,C)-CyNdC6H10]-
(NCy2)2Cl from TaCl5 and LiNCy2, which could form by
HNCy2 elimination from the intermediate Ta(NCy2)4Cl.53 These
reactions are perhaps facilitated by the greater steric congestion
(58) Shriver, D. F.; Drezdzon, M. A. The Manipulation of Air-SensitiVe
Compounds, 2nd ed.; John Wiley and Sons: New York, 1986.
(59) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals, 3rd ed.; Pergamon Press: Oxford, U.K., 1988.
(57) Chao, Y.-W.; Wexler, P. A.; Wigley, D. E. Inorg. Chem. 1989, 28,
3860.

Models for Substrate-Catalyst Adducts
Inorganic Chemistry, Vol. 35, No. 21, 1996 6033
(m, 2 H, H2), 3.38 (m, 8 H, HR THF), 2.97 (t, 2 H, H4), 1.95 (m, 2 H,
H3), 1.25 (m, 8 H, Hâ THF). 13C NMR (C6D6): δ 159.05 (C8a), 130.53
(C8 or C6), 127.68 (C6 or C8), 120.77 (C4a), 112.88, 109.41 (C5,
C7), 68.11 (CR THF), 48.40 (C2), 30.29 (Câ THF), 25.43 (C4), 24.82
(C3). Anal. Calcd for C17H26LiNO2: C, 72.07; H, 9.25; N, 4.93.
Found: C, 72.03; H, 8.89; N, 5.58.
stir at room temperature. Over several minutes, a precipitate was
observed to form, and after 18 h, the reaction volatiles were removed
under reduced pressure to yield an oily residue. This product was
transferred to a short-path distillation apparatus and vacuum distilled
(ca. 10-2
Torr, 80 °C) to afford the product as a white crystalline solid
(27.55 g, 0.144 mol, 90%). 1H NMR (C6D6): δ 7.08-7.02 (overlapping
m, 2 H total, H7 and H5), 6.74 (t, 1 H, H6), 6.66 (d, 1 H, H4), 3.25 (t,
2 H, H2), 2.70 (t, 2 H, H3), 0.15 (s, 9 H, SiMe3). 13C NMR (C6D6):
δ 142.95 (C7a), 131.91 (C3a), 127.57 (C7), 124.82 (C5), 117.56 (C6),
109.36 (C4), 49.09 (C2), 30.19 (C3), -0.75 (SiMe3). Anal. Calcd
for C11H17NSi: C, 69.00; H, 8.88; N, 7.32. Found: C, 69.08; H, 8.96;
N, 7.53.
Me3SiNC9H10. (i) A solution of LiNC9H10‚2THF (40.0 g, 0.141
mol) in 400 mL of Et2O was prepared and cooled to 0 °C. A slight
excess of neat Me3SiCl (18.8 mL, 16.09 g, 0.148 mol) was added
dropwise to this rapidly stirred solution, whereupon an exothermic yet
smooth reaction ensued as the pale yellow solution decolorized and a
white precipitate formed. After 17 h, solvent was removed from the
mixture in vacuo to form a clear oil and a white solid. The product
was extracted from this residue with pentane (ca. 300 mL), the extract
was filtered through Celite to remove the large amount of white solid,
and the clear, pale yellow filtrate was stripped of solvent to yield a
clear yellow oil. This product was distilled under reduced pressure to
afford 25.40 g (0.124 mol, 84%) of N-(trimethylsilyl)-1,2,3,4-tetrahy-
droquinoline (Me3SiNC9H10) as a clear oil with a boiling range of 64-
67 °C at ca. 10-2 Torr.
Complex Preparations. Ta(NC9H10)Cl4(OEt2) (1). Neat Me3-
SiNC9H10 (4.60 g, 22.4 mmol) was slowly added to a rapidly stirred
solution of TaCl5 (8.00 g, 22.3 mmol) in 70 mL of benzene and 10 mL
of Et2O. The clear TaCl5 solution turned deep red instantly upon Me3-
SiNC9H10 addition. The mixture was stirred for 20 h, after which the
reaction volatiles were removed under reduced pressure to yield the
product as a burgundy-colored powder. This powder was washed with
cold pentane (2 × 25 mL) and dried in vacuo to yield 11.47 g (21.7
mmol, 97%) of Ta(NC9H10)Cl4(OEt2) as an analytically pure, intense
burgundy-colored solid. Samples of Ta(NC9H10)Cl4(OEt2) can be
readily recrystallized as black rods from Et2O at -35 °C. 1H NMR
(C6D6): δ 8.59 (d, 1 H, H8), 7.22 (t, 1 H, H6), 6.86 (d, 1 H, H5), 6.64
(t, 1 H, H7), 5.13 (m, 2 H, H2), 4.19 (q, 4 H, OCH2CH3), 2.48 (t, 2 H,
H4), 1.88 (m, 2 H, H3), 0.96 (t, 6 H, OCH2CH3). 13C NMR (CDCl3):
δ 148.30 (C8a), 130.82 (C8), 128.80 (C4a), 128.18 (C5), 127.45 (C7),
125.27 (C6), 67.75 (OCH2CH3), 55.05 (C2), 25.75 (C4), 20.97 (C3),
12.70 (OCH2CH3). Anal. Calcd for C13H20Cl4NOTa: C, 29.51; H,
3.81; N, 2.65. Found: C, 29.07; H, 3.66; N, 2.67.
(ii) A solution of tetrahydroquinoline (40.2 mL, 42.6 g, 0.320 mol)
in 500 mL of pentane was prepared and cooled to 0 °C. This cold
solution was stirred rapidly while 1 equiv of n-butyllithium (1.6 M in
hexanes, 200 mL, 0.320 mol) was added slowly. After this mixture
was stirred at room temperature for 24 h, the reaction mixture was
stripped of solvent to afford a pale yellow powder, which was dissolved
in 400 mL of Et2O and 100 mL of THF. This orange solution was
cooled to 0 °C, and a slight excess of Me3SiCl (45.0 mL, 38.52 g,
0.355 mol) was added dropwise over the course of 30 min, which
induced rapid bleaching of the solution and formation of a white
precipitate. After 24 h, the solvent was removed from the mixture in
vacuo to provide a clear oil and a white solid. The product was
extracted from this residue with pentane (ca. 100 mL), the extract was
filtered through Celite, and the pale yellow filtrate was stripped of
solvent to afford a clear yellow oil. This oil was distilled under reduced
pressure as described above to yield 59.84 g (0.291 mol, 91%) of Me3-
SiNC9H10 as a clear oil. 1H NMR (C6D6): δ 7.03, 6.98 (overlapping
t and d, 1 H each, H6 and H8), 6.88, 6.78 (overlapping d and t, 2 H,
H5 and H7), 3.01 (m, 2 H, H2), 2.58 (t, 2 H, H4), 1.54 (m, 2 H, H3),
0.20 (s, 9 H, SiMe3). 13C NMR (C6D6): δ 146.50 (C8a), 130.18, 126.19
(C6 and C8), 125.65 (C4a), 118.35 (coincident C5, C7), 44.73 (C2),
28.14 (C4), 24.28 (C3), 0.97 (SiMe3). One resonance of the C5, C7
pair is not observed and is presumed to be coincident with the δ 118.35
resonance. Anal. Calcd for C12H19NSi: C, 70.11; H, 9.25; N, 6.81.
Found: C, 70.28; H, 9.26; N, 7.16.
Ta(NC9H10)2Cl3 (2). A toluene solution of Me3SiNC9H10 (1.17 g,
5.70 mmol in 7 mL of toluene) was added dropwise to a rapidly stirred
solution of Ta(NC9H10)Cl4(Et2O) (3.00 g, 5.67 mmol) in 10 mL of
toluene. During Me3SiNC9H10 addition, the reaction solution underwent
a rapid but subtle color change as it darkened slightly. After Me3-
SiNC9H10 addition was complete, the mixture was set aside without
stirring for 2 d, after which the solution was cooled to -35 °C for 24
h. The dark burgundy-colored crystals that formed were collected by
filtration, washed with cold pentane (ca. 10 mL), and dried in vacuo
to afford 2.20 g (3.99 mmol, 70%) of Ta(NC9H10)2Cl3 as an analytically
pure, deep burgundy-colored microcrystalline product. Solvent was
removed from the dark red filtrate under reduced pressure to provide
1
a red solid that was shown by H NMR spectroscopy to consist of a
mixture of Ta(NC9H10)Cl4(OEt2), Ta(NC9H10)2Cl3, and Ta(NC9H10)3-
Cl2. 1H NMR (C6D6): δ 7.76 (d, 1 H, H8), 6.91 (t, 1 H, H6), 6.81 (d,
1 H, H5), 6.66 (t, 1 H, H7), 3.88 (m, 2 H, H2), 2.23 (t, 2 H, H4), 1.59
(m, 2 H, H3). 13C NMR (C6D6): δ 144.33 (C8a), 129.66 (C5), 126.66
(overlapping C6, C8), 126.24 (C7), 125.60 (C4a), 44.26 (C2), 25.29
(C4), 20.12 (C3). Anal. Calcd for C18H20Cl3N2Ta: C, 39.19; H, 3.65;
N, 5.08. Found: C, 39.02; H, 3.68; N, 4.92.
LiNC8H8‚2THF. A solution of 5.00 g (41.9 mmol) of indoline in
40 mL of pentane was prepared and cooled to 0 °C in a ice bath. To
this rapidly stirred, cold solution was added over several minutes a
26.2 mL (41.9 mmol) aliquot of n-butyllithium solution (1.6 M in
hexanes). Within minutes, a white precipitate was observed, and over
the next few hours, the mixture became a pasty, off-white suspension.
After 3 h, the precipitate was collected by filtration and washed with
pentane to remove any unreacted starting materials. This product (base-
free LiNC8H8) was then dissolved in a minimal volume of THF, and
the solution was cooled to -35 °C, during which 8.60 g (31.9 mmol,
76%) of white crystals formed, were collected by filtration, and dried
in vacuo. 1H NMR (C6D6): δ 7.24 (d, 1 H, H7), 7.12 (t, 1 H, H5),
6.48, 6.47 (overlapping t and d, 1 H each, H6 and H4), 3.87 (t, 2 H,
H2), 3.44 (m, 8 H, HR THF), 3.15 (t, 1 H, H3), 1.29 (m, 8 H, Hâ
THF). 13C NMR(C6D6): δ 147.35 (C7a), 131.86 (C3a), 128.21, 124.19,
110.22, 104.39 (C4, C5, C6, and C7), 67.96 (CR THF), 53.30 (C2),
33.29 (C3), 25.57 (Câ THF). Anal. Calcd for C16H24LiNO2: C, 71.32;
H, 8.91; N, 5.20. Found: C, 71.50; H, 9.14; N, 5.55.
Ta(NC9H10)3Cl2 (3). A solution of TaCl5 (5.00 g, 14.0 mmol) in
75 mL of toluene and 15 mL of Et2O was rapidly stirred while an
excess of neat Me3SiNC9H10 (17.2 g, 0.084 mol, 6 equiv) was slowly
added, whereupon the solution rapidly changed from pale yellow to
dark red. This mixture was heated in a 100 °C oil bath for 22 h, after
which it was allowed to cool and the reaction volatiles were removed
in vacuo to provide an oily, bright red solid. Trituration of this mixture
with ca. 25 mL of cold (-35 °C) pentane afforded a bright red solid,
which was quickly filtered off, washed with cold pentane (2 × 25 mL),
and dried in vacuo. This procedure provided 8.60 g (13.3 mmol, 95%)
of Ta(NC9H10)3Cl2 as a bright orange-red powder. The red pentane
filtrate was stripped of solvent to yield a red oil, shown by 1H NMR to
be relatively pure Me3SiNC9H10 with a trace of Ta(NC9H10)3Cl2
impurity. The excess Me3SiNC9H10 reagent could be reclaimed and
purified by vacuum distillation. Performing this synthesis with only 3
equiv of Me3SiNC9H10 yields inseparable mixtures of Ta(NC9H10)2Cl3
and Ta(NC9H10)3Cl2, even under high temperatures (120 °C) and/or
long reaction times (3 d). 1H NMR (C6D6): δ 8.15 (d, 1 H, H8), 7.10
(t, 1 H, H6), 6.96 (d, 1 H, H5), 6.80 (t, 1 H, H7), 3.81 (m, 2 H, H2),
2.35 (t, 2 H, H4), 1.71 (m, 2 H, H3). 13C NMR (C6D6): δ 146.87
(C8a), 130.10 (C5), 126.57 (C6), 124.65 (C4a), 124.48 (C8), 124.14
Me3SiNC8H8 (N-(Trimethylsilyl)indoline). A large Schlenk tube
was charged with 18.70 g (0.157 mol) of indoline (HNC8H8) and 200
mL of Et2O and cooled to -78 °C. To this rapidly stirred solution
was slowly added 98.0 mL (0.157 mmol) of n-butyllithium solution
(1.6 M in hexanes). After this mixture was stirred for 5 min, a solution
of Me3SiCl (20.3 mL, 17.38 g, 0.160 mol) in 100 mL of Et2O was
added over a period of several minutes. When the addition was
complete, the solution was removed from the cold bath and allowed to

6034 Inorganic Chemistry, Vol. 35, No. 21, 1996
Fox et al.
(C7), 46.19 (C2), 26.19 (C4), 19.22 (C3). Anal. Calcd for C27H30-
Cl2N3Ta: C, 50.01; H, 4.66; N, 6.48. Found: C, 49.54; H, 4.86; N,
6.10.
32.86 (C3), 31.72 (C3′), 25.61 (Câ THF). Anal. Calcd for C20H24-
Cl3N2OTa: C, 40.32; H, 4.06; N, 4.70. Found C, 40.06; H, 4.07; N,
4.60.
Ta(NC9H10)4Cl (4). A solution of LiNC9H10‚2THF (0.88 g, 3.10
mmol) in 5 mL of THF was added dropwise to a stirred solution of
Ta(NC9H10)3Cl2 (2.00 g, 3.10 mmol) in 20 mL of THF. This mixture
was stirred for 20 h, during which the solution developed an lighter,
orange color. Removing the reaction volatiles in vacuo afforded an
orange-red oil from which the product was extracted with Et2O (100
mL). This extract was filtered through Celite, the Celite was washed
with Et2O (ca. 50 mL) until the washings were colorless, and the
volatiles were removed from the orange filtrate under reduced pressure,
yielding an orange crystalline solid. This solid was washed with cold
pentane (2 × 25 mL) and dried in vacuo to provide 2.02 g (2.71 mmol,
87%) of Ta(NC9H10)4Cl as a bright orange solid. Analytically pure
samples were obtained by recrystallization from Et2O at -35 °C. 1H
NMR (C6D6): δ 7.42 (d, 1 H, H8), 6.90, 6.86 (overlapping t and d, 2
H total, H6 and H5), 6.68 (t, 1 H, H7), 4.23 (m, 2 H, H2), 2.53 (t, 2
H, H4), 1.85 (m, 2 H, H3). 13C NMR (C6D6): δ 149.73 (C8a), 129.15
(C5), 127.30 (C4a), 125.20 (C6), 124.12 (C8), 123.33 (C7), 51.64 (C2),
26.61 (C4), 23.26 (C3). Anal. Calcd for C36H40ClN4Ta: C, 58.03; H,
5.41; N, 7.52. Found: C, 57.91; H, 5.51; N, 7.46.
Ta(NC9H10)5 (5). A solution of 0.31 g (1.09 mmol) of LiNC9H10‚
2THF in 10 mL of benzene was added to a rapidly stirred solution of
0.20 g (0.36 mmol) of Ta(NC9H10)2Cl3 in 10 mL of benzene, whereupon
the solution changed from dark red to orange. After the addition was
complete, the mixture was stirred for 20 h, after which it was filtered
through Celite and the reaction volatiles were removed under reduced
pressure to afford the product as an orange powder; yield 0.256 g (0.304
mmol, 84%). Samples of Ta(NC9H10)5 obtained in this fashion were
analytically pure. 1H NMR (C6D6): δ 7.38 (d, 1 H, H8), 6.87, 6.83
(overlapping t and d, 2 H total, H6 and H5), 6.65 (t, 1 H, H7), 4.26 (t,
2 H, H2), 2.51 (t, 2 H, H4), 1.72 (m, 2 H, H3). 13C NMR (C6D6): δ
150.40 (C8a), 128.79 (C5), 126.90 (C4a), 125.37 (C6), 124.45 (C8),
121.58 (C7), 51.30 (C2), 27.48 (C4), 24.50 (C3). Anal. Calcd for
C45H50N5Ta: C, 64.20; H, 5.99; N, 8.32. Found: C, 64.18; H, 5.88;
N, 8.10.
Ta(NC8H8)Cl4(THF) (6). A solution of 1.49 g (7.79 mmol) of Me3-
SiNC8H8 in 10 mL of benzene was added dropwise to a rapidly stirred
solution of 2.78 g (7.76 mmol) of TaCl5 in 10 mL of benzene and 1
mL of Et2O. Upon Me3SiNC8H8 addition, the tantalum solution rapidly
changed from pale yellow to dark purple. After 24 h, the volatiles
were removed from the solution under reduced pressure, the dark residue
was dissolved in 5 mL of THF, and this solvent was removed in vacuo
to afford 3.85 g (7.50 mmol, 96%) of dark purple, solid Ta(NC8H8)-
Cl4(THF). Analytically pure samples were obtained by recrystallization
from 3:1 (v/v) Et2O/THF solutions. 1H NMR (C6D6): δ 8.10 (d, 1 H,
H7), 7.27 (t, 1 H, H6), 6.88 (d, 1 H, H4), 6.65 (m, 2 H, H2), 6.51 (t,
1 H, H5), 4.31 (m, 4 H, HR THF), 2.98 (m, 2 H, H3), 1.07 (m, 4 H,
Hâ THF). 13C NMR (C6D6): δ 149.79 (C7a), 133.01 (C3a), 127.39,
126.97, 122.72 (C4, C5, C6, C7), 77.25 (C2), 63.69 (CR THF), 31.45
(C3), 25.41 (Câ THF). One resonance from the C4, C5, C6, C7 set is
not observed and is presumed to be coincident with another resonance.
Anal. Calcd for C12H16Cl4NOTa: C, 28.09; H, 3.14; N, 2.73. Found:
C, 27.59; H, 3.11; H, 2.58.
Ta(NC8H8)2Cl3(THF) (7). A solution of 0.36 g (1.88 mmol) of
Me3SiNC8H8 in 10 mL of benzene was added slowly to a solution of
1.00 g (1.95 mmol) of Ta(NC8H8)Cl4(THF) in 10 mL of benzene. Upon
Me3SiNC8H8 addition, the Ta(NC8H8)Cl4(THF) solution rapidly changed
from dark purple to orange-brown. After 46 h, the volatiles were
removed in vacuo to afford a brown powder, which was washed with
pentane (10 mL) to yield 1.12 g (1.88 mmol; 96% based upon tantalum,
quantitative based on Me3SiNC8H8) of Ta(NC8H8)2Cl3(THF) as a brown
powder. Analytically pure samples were obtained by recrystallization
from THF at -35 °C. 1H NMR (C6D6): δ 7.27-7.19 (overlapping d,
2 H total, H7, H7′), 7.11-7.03 (m, 2 H, H4, H6′), 6.92-6.83
(overlapping m, 2 H total, H4′, H6), 6.66, 6.53 (t, 1 H each, H5′, H5),
5.88, 4.99 (m, 2 H each, H2, H2′), 4.06 (m, 4 H, HR THF), 2.90, 2.82
(t, 2 H each, H3′, H3), 1.11 (m, 4 H, Hâ THF). 13C NMR (C6D6): δ
151.10, 150.83 (C7a, C7a′), 133.11, 132.30 (C3a, C3a′), 127.11 (C6),
126.97 (C6′), 125.69 (C5), 124.84 (C5′), 123.67 (C4), 123.29 (C4′),
123.06 (C7), 122.14 (C7′), 75.93 (CR THF), 60.92 (C2), 58.81 (C2′),
Ta(NC9H10)(OAr)Cl3(OEt2) (8). A solution of 10.00 mmol of Ta-
(OAr)Cl4(OEt2) was prepared by dissolving 5.00 g (5.00 mmol) of [Ta-
(OAr)Cl4]2 in 60 mL of Et2O. This mixture was stirred rapidly while
a solution of 2.00 g (9.74 mmol) of Me3SiNC9H10 in 40 mL of Et2O
was added dropwise. Over the course of the addition, the yellow-orange
solution became dark red-orange and after 1 h had developed a dark
cherry red color. After 24 h, the reaction solution was filtered through
Celite, and the reaction volatiles were removed in vacuo to provide an
orange, iridescent foam. This product was dissolved in ca. 75 mL of
Et2O, and the mixture was stored at -35 °C to afford the desired
compound as analytically pure, dark red crystals; these were collected
by filtration and dried in vacuo; yield 5.85 g (8.72 mmol, 87%). 1H
NMR (C6D6): δ 8.11 (d, 1 H, H8), 6.90 (d, 2 H, Hm OAr), 6.85-6.74
(overlapping m, 3 H total, Hp OAr, H5, and H6), 6.48 (t, 1 H, H7),
5.09 (m, 2 H, H2), 3.89 (q, 4 H, OCH2CH3), 3.80 (spt, 2 H, CHMe2),
2.49 (t, 2 H, H4), 1.94 (m, 2 H, H3), 1.11 (d, 12 H, CHMe2), 0.95 (t,
6 H, OCH2CH3). 1H NMR (CDCl3): δ 7.68 (d, 1 H, H8), 7.11 (d, 1
H, H5), 7.01-6.83 (overlapping m, 4 H total, Haryl OAr, H6), 6.73 (t,
1 H, H7), 5.19 (m, 2 H, H2), 4.01 (q, 4 H, OCH2CH3), 3.54 (spt, 2 H,
CHMe2), 3.00 (t, 2 H, H4), 2.31 (m, 2 H, H3), 1.28 (t, 6 H, OCH2CH3),
1.02 (d, 12 H, CHMe2). 13C NMR (C6D6): δ 155.10 (Cipso), 147.12
(C8a), 141.44 (Co), 129.06 (C5), 128.27 (C4a), 126.26 (C7), 125.83
(C6), 125.75 (Cp), 124.11 (Cm), 66.68 (OCH2CH3), 56.14 (C2), 26.35
(CHMe2), 26.12 (C4), 25.04 (CHMe2), 21.18 (C3), 12.63 (OCH2CH3).
Anal. Calcd for C25H37Cl3NO2Ta: C, 44.75; H, 5.56; N, 2.09.
Found: C, 44.44; H, 5.69; N, 2.17.
Ta(NC8H8)(OAr)Cl3(OEt2) (9). A solution of 4.28 mmol of Ta-
(OAr)Cl4(OEt2) was prepared by dissolving 2.14 g (2.14 mmol) of [Ta-
(OAr)Cl4]2 in 10 mL of Et2O. This mixture was stirred rapidly while
a solution of 0.82 g (4.29 mmol) of Me3SiNC8H8 in 10 mL of Et2O
was added dropwise. Over the course of the addition, the pale yellow
solution became dark red, and after 24 h of stirring, the reaction volatiles
were removed in vacuo to afford a dark red solid. This solid was
washed with pentane, filtered off, and dried in vacuo to afford 1.90 g
(2.89 mmol, 68% yield) of product as a microcrystalline burgundy-
colored solid. Samples of Ta(NC8H8)(OAr)Cl3(OEt2) prepared in this
fashion were sufficiently pure for futher reactions; analytically pure
samples were obtained by recrystallization from Et2O at -35 °C. 1H
NMR (C6D6): δ 7.53 (d, 1 H, H7), 6.99 (d, 2 H, Hm), 6.87-6.76
(overlapping m, 3 H total, Hp OAr, H4, H6), 6.44 (t, 1 H, H5), 6.02
(m, 2 H, H2), 4.06 (q, 4 H, OCH2CH3), 3.81 (spt, 2 H, CHMe2), 2.83
(m, 2 H, H3), 1.11 (d, 12 H, CHMe2), 0.93 (t, 6 H, OCH2CH3). 13C
NMR (C6D6): δ 155.40 (Cipso), 147.20 (C7a), 141.20 (Co), 132.70
(C3a), 127.20, 126.32, 125.72, 124.32, 123.52, 122.49 (Cm, Cp, C4,
C5, C6, C7), 67.19 (C2), 63.05 (OCH2CH3), 31.77 (C3), 26.17
(CHMe2), 24.99 (CHMe2), 12.43 (OCH2CH3). Anal. Calcd for C24-
H35Cl3NO2Ta: C, 43.89; H, 5.37; N, 2.13. Found: C, 44.29; H, 5.54;
N, 2.15.
Ta(NC9H10)2(OAr)2Cl (10). A solution of Ta(NC9H10)2Cl3 (1.87
g, 3.39 mmol) in 10 mL of benzene was rapidly stirred while a solution
of 1.75 g (6.78 mmol) of LiOAr‚OEt2 in 10 mL of Et2O was added
dropwise. Over the course of the addition, the reaction solution
underwent a subtle color change from dark red to yellow-orange, with
the concomitant formation of a precipitate. The mixture was stirred at
room temperature for 24 h and filtered through Celite, and the solvent
was removed from the filtrate in vacuo to afford the product as a yellow-
orange solid (2.77 g, 3.32 mmol, 98%) sufficiently pure for further
reactions. Analytically pure, yellow-orange needles were obtained by
recrystallization from pentane at -35 °C. 1H NMR (C6D6): δ 7.59
(d, 2 H, H8), 7.08-6.81 (overlapping m, 10 H total, Haryl OAr, H6,
H5) 6.62 (t, 2 H, H7), 4.54 (m, 4 H, H2), 3.46 (spt, 4 H, CHMe2), 2.59
(t, 4 H, H4), 1.89 (m, 4 H, H3), 1.20 (d, 24 H, CHMe2). 13C NMR
(C6D6): δ 156.34 (Cipso), 148.50 (C8a), 138.93 (Co), 129.56 (C5),
126.82 (C4a), 126.30 (C6), 124.77 (C8), 124.00 (C7), 123.78 (overlap-
ping Cm and Cp), 53.44 (C2), 27.58 (CHMe2), 26.79 (C4), 25.05 (C3),
24.95 (CHMe2). Anal. Calcd for C42H54ClN2O2Ta: C, 60.39; H, 6.52;
N, 3.35. Found: C, 60.00; H, 6.68; N, 3.22.
Ta(NC9H10)(OAr)Me2Cl (11). A 2.88 mL aliquot of ZnMe2 (1.0
M in heptane, 2.88 mmol) was added to a rapidly stirred solution of

Models for Substrate-Catalyst Adducts
Inorganic Chemistry, Vol. 35, No. 21, 1996 6035
1.00 g (1.49 mmol) of Ta(NC9H10)(OAr)Cl3(OEt2) in 18 mL of benzene,
whereupon the mixture changed from dark red to yellow. After the
solution was stirred for 1 h, the solvent was removed in vacuo to provide
a pale yellow, oily solid. The product was extracted with ca. 20 mL
of pentane, the extract was filtered through Celite, and the filtrate was
stripped of solvent to afford the yellow microcrystalline product. The
crystals were collected on a frit, washed with cold (-35 °C) pentane,
and dried in vacuo to afford 0.53 g (0.95 mmol, 64%) of analytically
pure, golden yellow crystals. 1H NMR (C6D6): δ 7.26 (d, 1 H, H8),
7.06-6.86 (overlapping m, 5 H total, Haryl OAr, H5, H6), 6.66 (t, 1 H,
H7), 3.51 (m, 2 H, H2), 3.36 (spt, 2 H, CHMe2), 2.37 (t, 2 H, H4),
1.66 (m, 2 H, H3), 1.53 (s, 6 H, TaMe), 1.02 (d, 12 H, CHMe2). 13C
NMR (C6D6): δ 155.85 (Cipso), 139.58 (Co), 130.35 (C5), 126.88 (C6),
124.35 (Cm), 124.17 (C4a), 123.89 (Cp), 122.75 (C7), 120.29 (C8),
66.10 (TaMe), 38.84 (C2), 27.14 (CHMe2), 23.95 (C4), 23.73 (CHMe2),
20.81 (C3). The resonance for C8a was not observed. Anal. Calcd
for C23H33ClNOTa: C, 49.69; H, 5.98; N, 2.52. Found: C, 49.89; H,
6.17; N, 2.58.
Ta(NC9H10)(OAr)Et2Cl (12). A 2.00 mL aliquot of ZnEt2 (1.0 M
in heptane, 2.00 mmol) was added dropwise to a rapidly stirred solution
of 1.00 g (1.49 mmol) of Ta(NC9H10)(OAr)Cl3(OEt2) in 20 mL of
benzene. Over the course of the addition, the solution changed from
deep red to pale yellow with the concomitant formation of a precipitate.
After 5 min, the mixture was filtered through Celite, and the solvent
was removed from the filtrate in vacuo to afford a yellow, oily solid.
The product was extracted from this solid with 25 mL of pentane, the
pentane extract was filtered, and the filtrate was concentrated in vacuo,
whereupon a bright yellow microcrystalline solid formed. This product
was collected by filtration and dried in vacuo to afford 0.55 g (0.94
mmol, 63%) of product. Analytically pure samples were obtained by
recrystallization from pentane at -35 °C. 1H NMR (C6D6): δ 7.23
(d, J ) 7.9 Hz, 1 H, H8), 6.89-7.07 (overlapping m, 5 H total, Haryl
OAr, H5, H6), 6.68 (t, J ) 7.5 Hz, 1 H, H7), 3.51 (t, J ) 5.9 Hz, 2 H,
H2), 3.44 (spt, 2 H, CHMe2), 2.43 (t, J ) 6.5 Hz, 2 H, H4), 2.11 (br
s, 10 H, TaEt), 1.77 (m, 2 H, H3), 1.06 (d, 12 H, CHMe2). 13C NMR
(C6D6): δ 154.5 (Cipso), 139.45 (Co), 130.45 (C5), 126.82 (C6), 124.88
(C4a), 124.00 (Cm), 123.89 (Cp), 122.55 (C7), 120.02 (C8), 78.08
(TaCH2CH3), 40.66 (C2), 26.95 (CHMe2), 26.42 (C4), 24.13 (CHMe2),
20.49 (C3), 15.68 (TaCH2CH3). Anal. Calcd for C25H37ClNOTa: C,
51.42; H, 6.39; N, 2.40. Found: C, 51.39; H, 6.14; N, 2.36.
Ta(NC9H10)2(OAr)2Me (13). A 1.20 mL aliquot of AlMe3 (1.0 M
in heptane, 1.20 mmol) was added dropwise to a rapidly stirred solution
of 1.00 g (1.20 mmol) of Ta(NC9H10)2(OAr)2Cl in 20 mL of toluene.
This yellow-orange solution was stirred for 24 h, during which it
gradually darkened. The reaction volatiles were removed in vacuo to
afford an orange oil. The product was extracted with pentane, the
extract was filtered through Celite, and the solvent was removed from
the filtrate (in vacuo) to yield an oily orange solid. This solid was
dissolved in minimal pentane and the solution cooled to -35 °C to
provide the product as yellow crystals, which were filtered off and dried
in vacuo; yield 0.75 g (0.92 mmol, 77%). 1H NMR (C6D6): δ 7.37
(d, 2 H, H8), 7.06-6.83 (overlapping m, 10 H total, Haryl OAr, H6,
H5), 6.61 (t, 2 H, H7), 3.92 (m, 4 H, H2), 3.71 (spt, 4 H, CHMe2),
2.51 (t, 4 H, H4), 1.68 (m, 4 H, H3), 1.63 (s, 3 H, TaMe), 1.09 (d, 24
H, CHMe2). 13C NMR (C6D6): δ 156.25 (Cipso), 148.78 (C8a), 139.31
(Co), 129.77 (C8), 124.66 (C4a), 123.84 (Cm), 126.25, 122.89, 121.77,
121.37 (C5, C6, C7, Cp), 55.11 (TaMe), 47.21 (C2), 27.04 (C4), 26.79
(CHMe2), 24.59 (CHMe2), 24.04 (C3). Anal. Calcd for C43H57N2O2-
Ta: C, 63.38; H, 7.05; N, 3.44. Found: C, 62.70; H, 7.12; N, 3.32.
H5, H7), 6.667 (t, 1 H, H5), 3.507 (m, 2 H, H2), 2.285 (t, 2 H, H4),
1.822 (s, 6 H, TaMe), 1.579 (m, 2 H, H3) 13C NMR (C6D6): δ 141.51
(C8a), 130.24 (C5), 126.89 (C6), 125.63 (C7), 125.25 (C4a), 121.70
(C8), 37.34 (C2), 25.55 (C4), 19.56 (C3). The TaCH3 carbon
resonances were not observed. Anal. Calcd for C11H16Cl2NTa: C,
31.95; H, 3.87; N, 3.34. Found: C, 32.14; H, 3.86; N, 3.27.
Equilibration Experiments of Ta(NC9H10)nCl5-n + (5 - n)Me3-
SiNC9H10 + nMe3SiCl (n ) 0, 5) Mixtures. (i) A 5 mm NMR tube
was charged with 0.024 g (0.028 mmol) of Ta(NC9H10)5 in 400 µL of
toluene-d8. A 17.5 µL (0.149 mmol) aliquot of Me3SiCl was added,
the solution was frozen in liquid nitrogen, and the tube was flame-
sealed. The dark, red-orange solution was heated in a 100 °C oil bath
1
for 36 h. Examining the solution by H NMR indicated the presence
of Ta(NC9H10)3Cl2, Me3SiNC9H10, and Me3SiCl in an approximate 1:2:3
ratio.
(ii) A 5 mm NMR tube was charged with 0.010 g (0.028 mmol) of
TaCl5 in 400 µL of toluene-d8. A 30.2 µL (0.140 mmol) aliquot of
Me3SiNC9H10 was added, the solution was frozen in liquid nitrogen,
and the tube was flame-sealed. The dark red solution was heated in a
100 °C oil bath for 24 h. Examining the solution by 1H NMR indicated
the the presence of Ta(NC9H10)3Cl2, Me3SiNC9H10, and Me3SiCl in
approximately a 1:2:3 molar ratio.
Thermolysis Experiments of Ta(NC9H10)4Cl (4) and Ta(NC9H10)5
(5). (i) A 5 mm NMR tube was charged with 0.020 g (0.027 mmol)
of Ta(NC9H10)4Cl (4) and 0.60 mL of C6D6 and was sealed in vacuo.
The sample was heated in an 80 °C oil bath for 30 h and examined by
1H NMR; the formation of HNC9H10 was observed, along with a small
amount of Ta(NC9H10)3Cl2. The tube was then opened, the mixture
was hydrolyzed with 10 mL of 0.5 M aqueous NaOH, and the organic
products were extracted with 10 mL of Et2O. Examining this organic
phase by GC/mass spectroscopy confirmed the presence of HNC9H10,
along with quinoline as a minor component (HNC9H10:quinoline ≈ 100:
8).
(ii) The thermolysis of 0.020 g (0.024 mmol) of Ta(NC9H10)5 (5)
was carried out in a 5 mm NMR tube in a manner identical with that
described above for Ta(NC9H10)4Cl (4), except that the sample was
1
examined by H NMR after 14 h (80 °C oil bath). The presence of
HNC9H10 and unreacted Ta(NC9H10)5 was noted. After hydrolysis (as
described above for Ta(NC9H10)4Cl), an examination of the organic
phase by GC/mass spectroscopy confirmed the presence of HNC9H10,
along with quinoline as a minor component (HNC9H10:quinoline ≈ 100:
3).
(iii) A sample of DNC9H10 was prepared by quenching 0.046 mL
(0.214 mmol) of Me3SiNC9H10 with 0.040 mL (2.00 mmol) of D2O in
THF/benzene solution (1:1 by volume). The resulting DNC9H10 was
isolated as an oil by removing the reaction volatiles in vacuo. The
DNC9H10 was added to a solution of 0.036 g (0.042 mmol) of Ta-
(NC9H10)5 (5) and ca. 0.50 mL of C6D6 in a 5 mm NMR tube, and the
tube was sealed under partial vacuum. The sample was heated in an
80 °C oil bath for 18 h and examined by 1H and 13C NMR; the formation
of HNC9H10 was observed, along with a corresponding decrease in the
concentration of Ta(NC9H10)5, but no incorporation of deuterium into
the H2 or H8 positions of the coordinated tetrahydroquinolinyl NC9H10
amide ligand was observed. The NMR tube was then opened, the
mixture was hydrolyzed with 10 mL of 0.5 M aqueous NaOH (thereby
exchanging the N-bound deuterium only), and the organic products
were extracted with 10 mL of Et2O. Examining this organic phase by
GC/mass spectroscopy confirmed that no significant deuterium incor-
poration into HNC9H10 had occurred.
Ta(NC9H10)Me2Cl2 (14). A solution of 0.500 g (0.945 mmol) of
Ta(NC9H10)Cl4(OEt2) in 20 mL of benzene was prepared and stirred
rapidly while a 0.945 mL aliquot of ZnMe2 solution (2.0 M in heptane,
1.89 mmol) was added dropwise. Upon ZnMe2 addition, the dark
purple solution smoothly developed a light orange color with the
simultaneous formation of a sticky precipitate. After 24 h, the orange
solution was decanted from the precipitate, the reaction volatiles were
removed in vacuo, and the product was extracted from the residue with
minimal pentane. This extract was filtered through Celite, and the
filtrate was stripped of solvent in vacuo to provide 0.34 g (0.82 mmol,
87%) of product as an orange solid. Analytically pure Ta(NC9H10)Me2-
Cl2 was obtained by recrystallization from pentane solution at -35 °C.
1H NMR (C6D6): δ 7.331 (d, 1 H, H8), 6.70-6.94 (unresolved, 2 H,
X-ray Structural Determination of Ta(NC9H10)2Cl3 (2). A red
hexagonal block-shaped crystal of C18H20Cl3N2Ta (grown directly from
the toluene reaction solution at -35 °C) having approximate dimensions
of 0.21 × 0.21 × 0.16 mm was mounted in a glass capillary in a random
orientation. Preliminary examination and data collection were per-
formed with Mo KR radiation (λ ) 0.710 73 Å) on a Syntex P21
diffractometer equipped with a graphite monochromator and a Crystal
Logics computer control system. Cell constants and an orientation
matrix for data collection were obtained from least-squares refinement,
using the setting angles of 53 reflections in the range 20 < 2θ < 30°.
The monoclinic cell parameters and calculated volume are a ) 15.409-
(1) Å, b ) 9.946(1) Å, c ) 12.310(1) Å, â ) 96.62(8)°, V ) 1874.0
Å3. For Z ) 4 and fw ) 551.68, the calculated density is 1.96 g/cm3.

6036 Inorganic Chemistry, Vol. 35, No. 21, 1996
Fox et al.
As a check on crystal quality, ω scans of several intense reflections
were measured; the width at half-height was 0.25°, indicating good
crystal quality. From the systematic absences of h0l, l ) 2n + 1, and
0k0, k ) 2n + 1, and from subsequent least-squares refinement, the
space group was determined to be P21/c (No. 14).
parameters and converged (largest parameter shift was 0.00 times its
esd) with agreement factors of R ) 0.025, Rw ) 0.034, and S ) 0.98.
There were three correlation coefficients greater than 0.50. The highest
correlations were between the scale factor and the Ta (U11, U22, U33)
parameters. The highest peak in the final difference Fourier map had
a height of 0.84(12) e/Å3;63 the minimum negative peak had a height
of -0.26(12) e/Å3. The maximum peaks were in the vicinity of the
Ta and Cl positions. Plots of ∑w(|Fo| - |Fc|)2 versus |Fo|, reflection
order in data collection, (sin θ)/λ, and various classes of indices showed
no unusual trends. All calculations were performed on a VAX computer
using MolEN.64
The data were collected at 20 ( 1 °C using the ω-2θ scan technique
(octants +h,+k,(l). The scan rate was fixed at 3.0°/min. Data were
collected to a maximum 2θ of 50.0°. The scan range was determined
as a function of θ to correct for the separation of the KR doublet; the
scan width was calculated from (2θ(KR1) - 1.30) to (2θ(KR2) + 1.60).
The diameter of the incident beam collimator was 0.75 mm. A total
of 3693 reflections were collected, of which 3308 were unique and
not systematically absent. As a check on crystal and electronic stability,
3 representative reflections were measured after every 97 reflections.
The intensities of these standards remained constant within experimental
error throughout data collection; therefore, no decay correction was
applied. Lorentz and polarization corrections were applied to the data.
The linear absorption coefficient is 62.3 cm-1 for Mo KR radiation.
An absorption correction based on ψ-scan data was applied (minimum
1.00, maximum 1.35, average 1.20). Intensities of equivalent reflections
were averaged. The agreement factors for the averaging of the 276
observed and accepted reflections was 1.5% based on intensity and
1.1% based on Fo.
Acknowledgment is made to the Division of Chemical
Sciences, Office of Basic Energy Sciences, Office of Energy
Research, U. S. Department of Energy (Contract DE-FG03-
93ER14349), for support of this research and to the donors of
the Petroleum Research Fund, Administered by the American
Chemical Society, for partial support of this work. We also
thank the Materials Characterization Program (State of Arizona)
for partial support.
Supporting Information Available: Text giving details of the
structure solution and refinement, tables of crystal data and data
collection parameters, atomic positional and thermal parameters, bond
distances, bond angles, least-squares planes, and torsional angles, and
ORTEP figures for Ta(NC9H10)2Cl3 (17 pages). Ordering information
is given on any current masthead page.
The structure was solved using the Patterson heavy-atom method,
which revealed the position of the Ta atom. The remaining atoms were
located in succeeding difference Fourier syntheses. Hydrogen atom
positions were visible in a difference map after anisotropic refinement
of the non-hydrogen atoms. Hydrogen atoms were added at idealized
positions. Hydrogen atoms were included in the refinement but
constrained to ride on the atom to which they are bonded. The structure
was refined in full-matrix least-squares procedures, where the function
IC960298N
(60) Cromer, D. T.; Waber, J. T. International Tables for X-Ray Crystal-
lography; The Kynoch Press: Birmingham, England, 1974; Vol. IV,
Table 2.2B.
(61) Ibers, J. A.; Hamilton, W. C. Acta Crystallogr. 1964, 7, 781.
(62) Cromer, D. T. International Tables for X-Ray Crystallography; The
Kynoch Press: Birmingham, England, 1974; Vol. IV, Table 2.3.1.
(63) Cruickshank, D. W. J. Acta Crystallogr. 1949, 2, 154.
(64) MolEN: An InteractiVe Structure Solution Procedure; Enraf-Nonius:
Delft, The Netherlands, 1990.
2
minimized was ∑w(|Fo| - |Fc|)2 and the weight w is defined as 4Fo /
2
σ2(Fo ).
Scattering factors were taken from Cromer and Waber.60 Anomalous
dispersion effects were included in Fc;61 the values for ∆f′ and ∆f′′
were those of Cromer.62 Only the 2427 reflections having intensities
greater than 3.0 times their standard deviation were used in the
refinements. The final cycle of refinement included 217 variable