Structure, bonding, and reactivity of tantalum amides containing o-naphthyl- and o-indenylphenoxide ligation

Article abstract of DOI:10.1021/om0300934

The reaction of [Ta(NMe₂)₅] with the o-(2,3-dihydro-1-naphthyl)-, o-(1-naphthyl)-, and o-(inden-3-yl)phenols [HOC₆H₂Ar-2-Bu₂^t-4,6] (Ar = C₁₀H₉ (1), C₁₀H₇ (Np; 2), C₉H₇ (3)) has been investigated. In all three cases initial displacement of 1 equiv of dimethylamine occurs, yielding mono(aryloxides) [(ArO)Ta(NMe₂)₄]. Structural studies of the o-(2,3-dihydro-1-naphthyl) and o-(1-naphthyl) compounds 4 and 5 show they both adopt geometries best described as square pyramidal with an apical dimethylamido ligand and basal aryloxide oxygen. The Ta-O-Ar angles are 162° in both compounds, with no metal interaction with the ortho substituents. Compound 4 reacts with 2,3,5,6-tetraphenylphenol to form the corresponding bis(aryloxide) 6. The intermediate o-(inden-3-yl)phenoxide [(ArO)Ta(NMe₂)₄] 7 thermally eliminates a further 1 equiv of HNMe₂ with formation of the tris(amido) compound [Ta(OC₆H₂{η¹-Ind}-2-Bu^t-4,6)(NMe ₂)₃] 8. The coordination geometry about tantalum in 8 is best described as trigonal bipyramidal, with an oxygen and amido group in the axial positions: O-Ta-N = 170°. The carbon atom of the indenyl ring bound directly to the phenoxide nucleus is metalated, leading to a five-membered metallacycle. Hence, both deprotonation (CH bond activation) and tautomerization of the original inden-3-yl ring has occurred. The Ta-C(121) distance of 2.285(9) A is consistent with an η¹-indenyl ring being present in 8. Replacement of the dimethylamido ligands in 8 by chloride groups was achieved by reaction with SiCl₄. Structural analysis of the 4-phenylpyridine adduct [Ta(OC₆H₂{η³-Ind}-2- Bu^t-4,6)(NC₅H₄Ph-4)Cl₃] 9 showed the presence of an η³-indenyl interaction with the tantalum metal center. The bonding parameters for the η¹- and η³- indenyl rings are compared with those of related η⁵- cyclopentadienyl derivatives of niobium and tantalum.

Full text of DOI:10.1021/om0300934

4658
Organometallics 2003, 22, 4658-4664
Str u ctu r e, Bon d in g, a n d Rea ctivity of Ta n ta lu m Am id es
Con ta in in g o-Na p h th yl- a n d o-In d en ylp h en oxid e
Liga tion
Matthew G. Thorn, J ennifer R. Parker, Phillip E. Fanwick, and Ian P. Rothwell*
Purdue University, Department of Chemistry, 560 Oval Drive,
West Lafayette, Indiana 47907-2038
Received February 7, 2003
The reaction of [Ta(NMe2)5] with the o-(2,3-dihydro-1-naphthyl)-, o-(1-naphthyl)-, and
o-(inden-3-yl)phenols [HOC6H2Ar-2-But -4,6] (Ar ) C10H9 (1), C10H7 (Np; 2), C9H7 (3)) has
2
been investigated. In all three cases initial displacement of 1 equiv of dimethylamine occurs,
yielding mono(aryloxides) [(ArO)Ta(NMe2)4]. Structural studies of the o-(2,3-dihydro-1-
naphthyl) and o-(1-naphthyl) compounds 4 and 5 show they both adopt geometries best
described as square pyramidal with an apical dimethylamido ligand and basal aryloxide
oxygen. The Ta-O-Ar angles are 162° in both compounds, with no metal interaction with
the ortho substituents. Compound 4 reacts with 2,3,5,6-tetraphenylphenol to form the
corresponding bis(aryloxide) 6. The intermediate o-(inden-3-yl)phenoxide [(ArO)Ta(NMe2)4]
7 thermally eliminates a further 1 equiv of HNMe2 with formation of the tris(amido)
compound [Ta(OC6H2{η1-Ind}-2-But-4,6)(NMe2)3] 8. The coordination geometry about tan-
talum in 8 is best described as trigonal bipyramidal, with an oxygen and amido group in
the axial positions: O-Ta-N ) 170°. The carbon atom of the indenyl ring bound directly to
the phenoxide nucleus is metalated, leading to a five-membered metallacycle. Hence, both
deprotonation (CH bond activation) and tautomerization of the original inden-3-yl ring has
occurred. The Ta-C(121) distance of 2.285(9) Å is consistent with an η1-indenyl ring being
present in 8. Replacement of the dimethylamido ligands in 8 by chloride groups was achieved
by reaction with SiCl4. Structural analysis of the 4-phenylpyridine adduct [Ta(OC6H2{η3-
Ind}-2-But-4,6)(NC5H4Ph-4)Cl3] 9 showed the presence of an η3-indenyl interaction with the
tantalum metal center. The bonding parameters for the η1- and η3-indenyl rings are compared
with those of related η5-cyclopentadienyl derivatives of niobium and tantalum.
In tr od u ction
structure and reactivity of aryloxide ligands containing
o-naphthyl6 and o-indenyl ligation.7 These substituents
introduce a number of interesting stereochemical and
structural elements, while the indenyl ligand offers the
potential for formation of a constrained-geometry che-
late via CH bond activation.8 In this paper we report
on the tantalum amido chemistry of the three related
phenols 1, 2,6a and 37 with emphasis on the structure
and fluxionality of the compounds formed as well as the
possible bonding modes of the indenylphenoxide ligand.
A significant amount of our early research work has
focused upon the inorganic and organometallic chem-
istry of the group 5 metals niobium and tantalum that
can be supported by sterically bulky aryloxide ligands.1
A key feature of o-phenylphenoxide ligation has been
the involvement of the substituents within the chem-
istry, including their ability to be reduced (hydroge-
nated), to chelate via cyclometalation,2,3 or to form
π-bonding interactions with electron-deficient metal
centers.4,5 This has led to our recent interest in the
* To whom correspondence should be addressed. E-mail: rothwell@
purdue.edu.
(1) Bradley, D. C.; Mehrota, R. C.; Rothwell, I. P.; Singh, A. Alkoxo
and Aryloxo Derivatives of Metals; Academic Press: San Diego, CA,
2001.
(2) (a) Rothwell, I. P. Acc. Chem. Res. 1988, 21, 153. (b) Lefebvre,
F.; Leconte, M.; Pagano, S.; Mutch, A.; Basset, J .-M. Polyhedron 1995,
14, 3209. (c) Chesnut, R. W.; Durfee, L. D.; Fanwick, P. E.; Rothwell,
I. P.; Folting, K.; Huffman, J . C. Polyhedron 1987, 6, 2019.
(3) The cyclometalation of a variety of aryloxide ligands by low-
valent Mo and W systems has been demonstrated; see: (a) Hascall,
T.; Murphy, V. J .; J anak, K. E.; Parkin, G, J . Organomet. Chem. 2002,
652, 37. (b) Hascall, T.; Baik. M. H.; Bridgewater, B. A.; Shin, J . H.;
Churchill, D. G.; Friesner, R. A.; Parkin, G. Chem. Commun. 2002,
2644. (c) Rabinovich, D.; Zelman, R.; Parkin, G. J . Am. Chem. Soc.
1990, 112, 9632. (d) Rabinovich, D.; Zelman, R.; Parkin, G. J . Am.
Chem. Soc. 1992, 114, 4611.
10.1021/om0300934 CCC: $25.00 © 2003 American Chemical Society
Publication on Web 10/08/2003

Ta Amides Containing o-Naphthyl and o-Indenyl Ligation
Organometallics, Vol. 22, No. 23, 2003 4659
Sch em e 1
F igu r e 1. Molecular structure of [Ta(OC6H2{C10H8}-2-
But -4,6)(NMe2)4] (4).
2
Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for [Ta (OC6H2{C10H8}-2-Bu t2-4,6)(NMe2)4] (4)
Ta-O(1)
Ta-N(5)
Ta-N(3)
1.956(3)
2.013(4)
2.064(4)
Ta-N(4)
Ta-N(2)
1.956(4)
2.034(4)
N(4)-Ta-O(1)
N(4)-Ta-N(3)
O(1)-Ta-N(5)
O(1)-Ta-N(2)
N(5)-Ta-N(2)
Ta-O(1)-C(11)
104.0(2)
N(4)-Ta-N(5)
N(4)-Ta-N(2)
O(1)-Ta-N(3)
N(3)-Ta-N(2)
N(5)-Ta-N(3)
99.2(2)
99.7(2)
85.8(2)
157.5(2)
87.1(2)
102.8(2)
156.8(2)
88.7(1)
89.5(2)
162.4(3)
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion of Dim eth yla -
m id o Com p ou n d s. The treatment of hydrocarbon
solutions of the compound [Ta(NMe2)5]9 with phenols 1
and 2 leads to the displacement of 1 equiv of dimethy-
lamine and formation of the corresponding mono-
(aryloxides) 4 and 5 (Scheme 1). Both compounds have
been structurally characterized (Tables 1 and 2; Figures
1 and 2). In the solid state they both adopt geometries
best described as square pyramidal with an apical
dimethylamido ligand and basal aryloxide oxygen. The
N(axial)-Ta-N(basal) angles are smaller than the
F igu r e 2. Molecular structure of [Ta(OC6H2Np-2-But -
4,6)(NMe2)4] (5).
2
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for [Ta (OC6H2Np -2-Bu t2-4,6)(NMe2)4] (5)
Ta-O(1)
Ta-N(5)
Ta-N(3)
1.946(4)
1.939(6)
1.976(5)
Ta-N(4)
Ta-N(2)
2.031(5)
2.047(6)
(4) Maseras, F.; Lockwood, M. A.; Eisenstein, O.; Rothwell, I. P. J .
Am. Chem. Soc. 1998, 120, 6598.
N(4)-Ta-O(1)
N(4)-Ta-N(3)
O(1)-Ta-N(5)
O(1)-Ta-N(2)
N(5)-Ta-N(2)
Ta-O(1)-C(11)
90.0(2)
N(4)-Ta-N(5)
N(4)-Ta-N(2)
O(1)-Ta-N(3)
N(3)-Ta-N(2)
N(5)-Ta-N(3)
96.8(2)
164.2(2)
148.0(2)
87.6(2)
(5) (a) Lockwood, M. A.; Fanwick, P. E.; Eisenstein, O.; Rothwell, I.
P. J . Am. Chem. Soc. 1996, 118, 2762. (b) Kerschner, J . L.; Rothwell,
I. P.; Huffman, J . C.; Streib, W. E. Organometallics 1988, 7, 1871.
(6) (a) Vilardo, J . S.; Thorn, M. G.; Fanwick, P. E.; Rothwell, I. P.
Chem. Commun. 1998, 2425. (b) Thorn, M. G.; Vilardo, J . S.; Fanwick,
P. E.; Rothwell, I. P. Chem. Commun. 1998, 2427. (c) Riley, P. N.;
Thorn, M. G.; Vilardo, J . S.; Lockwood, M. A.; Fanwick, P. E.; Rothwell,
I. P. Organometallics 1999, 18, 3016. (d) Thorn, M. G.; Vilardo, J . S.;
Lee, J .; Hanna, B.; Fanwick, P. E.; Rothwell, I. P. Organometallics
2000, 19, 5636.
(7) (a) Thorn, M. G.; Fanwick, P. E.; Chesnut, R. W.; Rothwell, I. P.
J . Chem. Soc., Chem. Commun. 1999, 2543. (b) Turner, L. E.; Thorn,
M. G.; Fanwick, P. E.; Rothwell, I. P. J . Chem. Soc., Chem. Comm.
2003, 1034.
(8) Turner, L. E.; Swartz, R. D.; Thorn, M. G.; Chestnut, R. W.;
Fanwick, P. E.; Rothwell, I. P. J . Chem. Soc., Dalton Trans., in press.
(9) Serious safety concerns have been raised dealing with the
original procedure: Bradley, D. C.; Thomas, M. Can. J . Chem. 1962,
40, 1355. For a revised synthesis of [Ta(NMe2)5], see: Vilardo, J . S.;
Salberg, M. M.; Parker, J . R.; Fanwick, P. E.; Rothwell, I. P. Inorg.
Chim. Acta 2000, 299, 135. See also: Chesnut, R. W.; Rothwell, I. P.;
Banasak Holl, M.; Wolczanski, P. T. Chem. Eng. News 1990, 68, 2.
88.1(2)
107.3(2)
85.6(2)
99.0(3)
161.8(4)
104.7(2)
N(axial)-Ta-OAr angle in both 4 and 5, presumably
for steric reasons. It can be seen that the aryloxide
wedge is oriented to bring the o-aryl ring into the vacant
site of the square-based pyramid. The Ta-O-Ar angle
is 162° in both compounds. The basal N-Ta-N and
O-Ta-N angles are both 157° in 4. However, in 5 the
N-Ta-N angle of 164° is larger than the O-Ta-N
angle of 148°. Hence, there is a distinct distortion in 5
toward a trigonal-bipyramidal structure with axial
1
amido groups. The solution H NMR spectra of 4 and 5
show a single resonance for the Ta-NMe2 protons at

4660 Organometallics, Vol. 22, No. 23, 2003
Thorn et al.
4-But-6)2CH2}(NMe2)3].11 Surprisingly, compound 6 is
structurally very similar to the chelated tantalum
compound and significantly different from the niobium
example. In the niobium compound the two aryloxides
are mutually trans with an O-Nb-O angle of 145°,
whereas in the chelated compound this angle is 85°,
almost identical with that found in 6. These compounds
highlight the fact that there is a great deal of variety
in the solid-state structures that can be adopted by these
mixed aryloxy amides, with geometries being very close
in energy.
The substrate [Ta(NMe2)5] reacts with inden-3-ylphe-
nol 3 to initially form the tetrakis(dimethylamido)
compound 7 (Scheme 2). The spectroscopic properties
of 7 indicate that the indenyl ring remains protonated,
and presumably a structure is formed very similar to
that observed for 4 and 5. However, when compound 7
was heated to 100 °C under vacuum, displacement of a
second 1 equiv of dimethylamine occurred with forma-
tion of the tris(amide) 8 (Scheme 2). In the solid state 8
(Table 4, Figure 4) can be seen to contain a five-
coordinate tantalum atom with a new chelate ring. The
coordination geometry about tantalum is best described
as trigonal bipyramidal with an oxygen and amido
group in the axial positions: O-Ta-N ) 170°. The
equatorial ligands are two amido nitrogens and a carbon
atom on the aryloxide chelate. This carbon atom, C(121),
is the indenyl carbon bound directly to the phenoxide
nucleus, leading to a five-membered metallacycle. The
structural parameters for the tantalum-bound indenyl
ring show that there is a localized double bond between
C(122) and C(123) (Figure 4). Hence, both deprotonation
(CH bond activation) and tautomerization of the original
inden-3-yl ring has occurred. The Ta-C(121) distance
of 2.285(9) Å is consistent with a Ta-C(sp3) σ bond. The
distance is almost identical with the value of 2.216(3)
Å reported for the Ta-C bond in [Ta(OC6H3Pri-
F igu r e 3. Molecular structure of [Ta(OC6H2{C10H8}-2-
But -4,6)(OC6HPh4-2,3,5,6)(NMe2)3] (6).
2
Ta ble 3. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for [Ta (OC6H2{C10H8}-2-Bu t2-4,6)-
(OC6HP h 4-2,3,5,6)(NMe2)3] (6)
Ta-O(1)
Ta-N(3)
Ta-N(5)
1.948(3)
1.951(4)
2.005(3)
Ta-O(2)
Ta-N(4)
2.012(3)
1.995(4)
O(1)-Ta-O(2)
O(1)-Ta-N(4)
O(2)-Ta-N(4)
O(2)-Ta-N(5)
N(3)-Ta-N(5)
Ta-O(1)-C(11)
85.6(1)
148.7(1)
85.7(1)
167.1(1)
91.2(1)
154.9(2)
O(1)-Ta-N(3)
O(1)-Ta-N(5)
O(2)-Ta-N(3)
N(3)-Ta-N(4)
N(4)-Ta-N(5)
Ta-O(2)-C(21)
102.3(1)
93.1(1)
101.6(1)
108.8(2)
88.6(2)
159.3(3)
ambient temperatures. Hence, the molecules are highly
fluxional in solution, as the solid-state structure would
generate nonequivalent dimethylamido ligands. A vari-
able-temperature study of 5 (toluene-d8) showed that
at -80 °C the single resonance split into four equal-
intensity singlets at δ 2.38, 2.95, 3.17, and 3.30 ppm.
Hence, at low temperature there is not only slow
exchange of nonequivalent axial and basal ligands but
also restricted rotation about the phenoxy-naphthyl
bond. Previous NMR studies of 2,6-bis(1-naphthyl)-
phenol have shown the barrier to naphthyl rotation in
this molecule can be estimated as 18.0(5) kcal mol-1 at
67 °C. The barrier increases significantly in metal
derivatives of o-naphthylphenoxides.
CMe2)(OC6H3Pri -2,6)3], containing a cyclometalated
2
2,6-diisopropylphenoxide ligand.12 The Ta-O-C angles
are 122° in this compound and 123° in 8. Hence, all of
the structural data are consistent with an η1-indenyl
ring being present in 8. Previous examples of transition-
metal η1-indenyl compounds involved diruthenium com-
pounds.13 More recently examples of η1-indenyl rings
bound to titanium14 and rhenium15 have been reported.
1
In the H NMR spectrum of 8 at ambient tempera-
tures, the NMe2 protons appear as a single broad
resonance, indicating that the molecule is fluxional on
the NMR time scale. As the temperature is lowered, the
signal broadens and splits at -55 °C into four singlets
of intensity ratio 2:2:1:1 (Figure 5). We interpret this
observation as a freezing out of the trigonal-bipyramidal
structure on the NMR time scale, with the methyl
groups of the axial NMe2 group being nonequivalent due
to restricted rotation (Scheme 2, Figure 5).
Addition of 2,3,5,6-tetraphenylphenol to a solution of
4 leads to a further displacement of 1 equiv of dimethy-
lamine and formation of the bis(aryloxide) 6 (Scheme
1). The solid-state structure of 6 (Table 3, Figure 3)
displays a metal coordination geometry very similar to
that of 5, except that there are now two, mutually cis
basal aryloxide ligands. The O-Ta-O angle is very
small at 86°. The basal position of the distorted square
pyramid, trans O-Ta-N angles of 149 and 167°, is
occupied by the 3,4-dihydronaphthyl substituent (Figure
3). Bis(aryloxide) tris(amides) of niobium or tantalum
that have been structurally characterized are [Nb-
Rea ctivity of th e Dim eth yla m id o Com p ou n d s.
The fact that the indenyl ring in 8 adopts an η1 bonding
(11) Chisholm, M. H.; Huang, J .-H.; Huffman, J . C.; Streib, W. E.;
Tiedtke, D. Polyhedron 1997, 16, 2941.
(12) Yu, J . S.; Felter, L.; Potyen, M. C.; Clark, J . R.; Visciglio, V.
M.; Fanwick, P. E.; Rothwell, I. P. Organometallics 1996, 15, 4443.
(13) Blenkiron, P.; Enright, G. D.; Taylor, N. J .; Carty, A. J .
Organometallics 1996, 15, 2855.
(OC6H2Ph-2-But -4,6)2(NMe2)3]10 and the 2,2′-methyl-
2
enebis(4-methyl-6-tert-butylphenoxide) [Ta{(OC6H2Me-
(14) Guerin, F.; Beddie, C. L.; Stephan, D. W.; Spence, R. E. v. H.;
Wurz, R. Organometallics 2001, 20, 3466.
(15) Deck, P. A.; Fronczek, F. R. Organometallics 2000, 19, 327.
(10) Visciglio, V. M.; Fanwick, P. E.; Rothwell, I. P. Inorg. Chim.
Acta 1993, 211, 203.

Ta Amides Containing o-Naphthyl and o-Indenyl Ligation
Sch em e 2
Organometallics, Vol. 22, No. 23, 2003 4661
Ta ble 4. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for [Ta (OC6H2{η1-C9H6}-2-Bu t2-4,6)(NMe2)3] (8)
Ta-O(1)
2.025(7)
1.95(1)
1.95(1)
2.005(8)
2.285(9)
1.36(1)
1.39(1)
C(16)-C(121)
C(121)-C(122)
C(122)-C(123)
C(123)-C(124)
C(124)-C(129)
C(129)-C(121)
1.51(1)
1.49(1)
1.33(2)
1.47(2)
1.42(1)
1.49(1)
Ta-N(2)
Ta-N(3)
Ta-N(4)
Ta-C(121)
O(1)-C(11)
C(11)-C(16)
Ta-O(1)-C(11)
O(1)-Ta-N(2)
O(1)-Ta-N(3)
O(1)-Ta-N(4)
O(1)-Ta-C(121)
N(2)-Ta-N(3)
122.7(6)
90.8(3)
93.8(4)
169.9(3)
75.4(3)
117.6(5)
N(2)-Ta-N(4)
N(2)-Ta-C(121)
N(3)-Ta-N(4)
N(3)-Ta-C(121)
N(4)-Ta-C(121)
92.8(4)
123.6(4)
92.9(4)
117.7(4)
94.7(3)
mode can be ascribed to the presence of the dimethy-
lamido ligands. These groups form very stable bonds to
early d-block metals in high oxidation states due to the
presence of nitrogen p to metal d π-bonding.16 This
bonding requires empty d orbitals of the correct sym-
metery into which the electron density on the nitrogen
atom can be donated. The formation of an η3-indenyl or
η5-indenyl group would presumably reduce and weaken
these interactions.
Replacement of the three dimethylamido ligands in
8 by chloride groups was achieved by reaction with SiCl4
(Scheme 2). Spectroscopically it was not possible to
determine the hapticity of the indenyl ring in the
trichloride product (Figure 6). To isolate and character-
ize the resulting trichloride, it was found necessary to
add the donor ligands 4-phenylpyridine (forming 9) and
PMe3 (10). The solid-state structure of 9 was determined
to fully characterize the bonding of the indenyl ring
(Figure 7, Table 5). The molecular structure is best
F igu r e 4. Molecular structure of [Ta(OC6H2{η1-Ind}-2-
But-4,6)(NMe2)3] (8).
described as distorted octahedral, with the indenyl ring
occupying an axial site trans to the pyridine nitrogen.
The three chlorides and aryloxide oxygen are bent
toward the pyridine nitrogen with angles close to only
80°. Related structures have been found for the previ-
ously reported adducts [CpNbCl4(PMePh2)]17 and
[(MeCp)TaCl4(H2PC6H2Pri -2,4,6)],18 which both have
3
P-M-Cl angles slightly less than 80°. Previously in our
group we have isolated and structurally characterized
the mono(aryloxides) [CpNbCl3(OC6HPh2-2,6-But -3,5)]
2
and [Cp*TaCl3(OC6HPh2-2,6-But -3,5)]. The Ta-O dis-
2
tance of 1.968(3) Å in 9 is slightly shorter than the
(17) Fettinger, J . C.; Keogh, D. W.; Poli, R. Inorg. Chem. 1995, 34,
2343.
(16) Riley, P. N.; Fanwick, P. E.; Rothwell, I. P. J . Chem. Soc., Dalton
Trans. 2001, 181.
(18) Hadi, G. A. A.; Fromm, K.; Blaurock, S.; J elonek, S.; Hey-
Hawkins, E. Polyhedron 1997, 16, 721.

4662 Organometallics, Vol. 22, No. 23, 2003
Thorn et al.
F igu r e 7. Molecular structure of [Ta(OC6H2{η5-Ind}-2-
But-4,6)(NC6H4Ph-4)Cl3] (9).
F igu r e 8. “Radar” plot of the Ta-C(indenyl) (solid line)
and Ta-Cp (dashed line) distances in compound 9,
[CpNbCl4(PMePh2)], and [(MeCp)TaCl4(H2PC6H2Pri3-2,4,6)].
The coordination is exaggerated by using a plot scale of
2.2-2.7 Å from the metal center.
F igu r e 5. 1H NMR (toluene-d8) spectrum of [Ta(OC6H2-
{η1-Ind}-2-But-4,6)(NMe2)3] (8) at 40, -30, and -55 °C.
Ta ble 5. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for [Ta (OC6H2{η5-C9H6}-2-Bu t-4,6)-
(NC5H4P h -4)Cl3] (9)
Ta-O(1)
1.968(3)
2.326(4)
2.436(1)
2.449(1)
2.386(1)
2.443(4)
2.378(4)
2.412(4)
Ta-C(124)
2.578(5)
2.636(4)
1.415(6)
1.406(7)
1.420(7)
1.422(6)
1.426(7)
Ta-N(21)
Ta-Cl(3)
Ta-Cl(4)
Ta-Cl(5)
Ta-C(121)
Ta-C(122)
Ta-C(123)
Ta-C(129)
C(121)-C(122)
C(122)-C(123)
C(123)-C(124)
C(124)-C(129)
C(129)-C(121)
Ta-O(1)-C(11)
O(1)-Ta-Cl(3)
O(1)-Ta-Cl(4)
O(1)-Ta-Cl(5)
O(1)-Ta-N(21)
Cl(3)-Ta-Cl(4)
Cl(3)-Ta-Cl(5)
Cl(3)-Ta-N(21)
129.0(3)
90.75(9)
157.37(9)
87.24(9)
77.2(1)
86.52(4)
154.85(4)
76.6(1)
Cl(4)-Ta-Cl(5)
85.80(4)
80.34(9)
78.51(9)
148.3(1)
148.9(2)
151.7(2)
154.1(1)
152.5(1)
Cl(4)-Ta-N(21)
Cl(5)-Ta-N(21)
N(21)-Ta-C(121)
N(21)-Ta-C(122)
N(21)-Ta-C(123)
N(21)-Ta-C(124)
N(21)-Ta-C(129)
clarified by inspection of the “Radar” plot shown in
Figure 8. It can be seen that there is a distinct distortion
toward η3 bonding for the indenyl ring in 9 with none
of the contacts as short as the 2.285(9) Å distance
observed in 8. The Ta-C(indenyl) distances can be
compared to those reported for [CpNbCl4(PMePh2)] and
F igu r e 6. 1H NMR (C6D6) spectrum of the reaction
mixture of [Ta(OC6H2{η1-Ind}-2-But-4,6)(NMe2)3] (8) with
SiCl4.
[(MeCp)TaCl4(H2PC6H2Pri -2,4,6)] mentioned previ-
3
ously, where the M-C(cyclopentadienyl) distances are
all similar (Figure 8). As expected, the slippage of the
indenyl ring involves a distinct elongation of the Ta-C
distances to the two aromatic carbon atoms. The “slip
2.025(7) Å distance found in 8, consistent with an
increase in electron deficiency of the metal. There is also
a corresponding increase in interaction with the indenyl
ring upon replacing the dimethylamido groups by
chloride ligands. The details of this interaction can be
value” has been defined as ∆ ) d{M-C(3a,7a)}av
-
d{M-C(1,3)}av.19 This corresponds to ∆ ) d{M-C(124,-

Ta Amides Containing o-Naphthyl and o-Indenyl Ligation
Organometallics, Vol. 22, No. 23, 2003 4663
Ta ble 6. Cr ysta l Da ta a n d Da ta Collection P a r a m eter s
4
5
6
8
9
formula
formula wt
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
C
32H53N4OTa
C60H68N3O2Ta
1044.18
P21/n (No. 14)
15.7906(3)
14.8876(3)
23.0163(6)
90
107.864(1)
90
5149.9(4)
4
C32H51N4OTa
688.74
C29H44N3OTa
631.64
C34H35Cl3NOTa
760.97
690.75
P21/n (No. 14)
12.2706(2)
20.4323(5)
13.3871(3)
90
101.257(1)
90
3291.8(2)
4
P1h (No. 2)
10.4794(9)
11.6107(6)
14.392(1)
105.499(5)
104.203(4)
96.141(5)
1438.8(2)
2
P1h (No. 2)
9.6679(5)
12.1261(6)
13.9575(4)
86.118(3)
72.704(3)
67.257(2)
1438.8(2)
2
P21/n (No. 14)
13.5784(3)
14.7969(3)
16.9241(4)
90
111.549(1)
90
3162.7(2)
4
Z
F
calcd, g cm-3
1.458
193.
1.347
193.
1.423
193.
1.458
203.
1.598
193
temp, K
radiation (wavelength)
R
Rw
Mo KR (0.710 73 Å)
0.033
0.091
0.043
0.093
0.042
0.061
0.153
0.038
0.095
0.101
was removed under vacuum, resulting in an “off white”
powder. Pentane (2.0 mL) was added to the powder, and
cooling to -15 °C resulted in the precipitation of 6 as an off-
white solid. Crystals suitable for X-ray diffraction were
obtained from benzene/pentane solutions. Yield: 0.19 g (22%).
Anal. Calcd for C32H51N4OTa: C, 55.21; H, 7.46; N, 8.13.
Found: C, 55.26; H, 6.75; N, 8.46. H NMR (C6D6, 30 °C): δ
7.80-7.10 (m, 19H, aromatic region); 3.00 (s, 24H, NMe2); 1.32
(s, 18H, C(CH3)3).
Syn th esis of [Ta (OC6H2{C9H7}-2-Bu t2-4,6)(NMe2)4] (7).
A sample of [Ta(NMe2)5] (500 mg, 1.25 mmol) was dissolved
in benzene. This mixture was stirred as 2-(inden-3-yl)-4,6-di-
tert-butylphenol (400 mg, 1.25 mmol) dissolved in benzene was
slowly added. The mixture was stirred for 1 h and then
evacuated to dryness, affording a yellow glassy solid. Addition
of a minimal amount of pentane resulted in the formation of
white crystals (190 mg, 22%). Anal. Calcd for C31H51N4OTa:
C, 55.02; H, 7.60; N, 8.28. Found: C, 54.76; H, 7.64; N, 7.83.
1H NMR (C6D6, 30 °C): δ 7.17-7.73 (aromatics); 6.60 (t, CH);
3.48 (br, CH2); 3.15 (s, NMe2); 1.70 (s), 1.37 (s, CMe3). Selected
13C NMR (C6D6, 30 °C): δ 157.2 (Ta-O-C); 47.1 (NMe2); 39.1
(CH2); 35.8, 34.5 (CMe3); 31.8, 30.3 (CMe3).
129)}av - d{M-C(121,123)}av in the labeling used here.
For compound 8 ∆ ) 0.179 Å. For a “true η5-indenyl”
this value would be close to 0 Å, whereas values of ∼0.75
Å are calculated for “true η3-indenyl” compounds.19
Hence, although definitely slipped toward η3-indenyl,
compound 8 is not as “slipped” as possible. As the
database of structurally characterized group 5 metal
indenyl compounds increases, there will undoubtedly be
a spectrum of interactions in response to the electronic
and steric demands of the metal center.
1
Exp er im en ta l Section
Gen er a l Rem a r k s. All manipulations were carried out
using standard syringe, Schlenk line, and glovebox tech-
niques.20 Benzene, toluene, ether, THF, and n-hexane were
dried over sodium benzophenone ketyl and were freshly
distilled before use. Pentane was dried over sodium ribbon.
The substrate [Ta(NMe2)5] was obtained by literature proce-
dures. Caution! Explosions have been associated with the
synthesis of [Ta(NMe2)5].9 o-Dihydronaphthyl-, 1-naphthyl-,
and inden-3-ylphenols [HOC6H2Ar-2-But -4,6] (Ar ) C10H9 (1),
Syn th esis of [Ta (OC6H2{η1-In d }-2-Bu t-4,6)(NMe2)3] (8).
A sample of [Ta(NMe2)5] (1.0 g, 2.49 mmol) was dissolved in
benzene. This mixture was stirred as 2-(3-dihydroindenyl)-4,6-
di-tert-butylphenol (800 mg, 2.5 mmol) dissolved in benzene
was slowly added. The mixture was stirred for 1 h at room
temperature and then heated at 100 °C for 45 min and finally
evacuated to dryness, affording a yellow glassy solid. Recrys-
tallization from benzene/pentane afforded yellow crystals (350
mg, 23%). Anal. Calcd for C29H44N3OTa: C, 55.15; H, 7.02; N,
6.65. Found: C, 54.93; H, 6.91; N, 6.36. 1H NMR (C6D6, 30
°C): δ 7.58 (d), 7.51 (d), 7.28 (t), 7.05 (t, C6H4); 7.43 (d), 6.76
(d, m-H); 7.10 (d), 6.62 (d, C5H2); 2.76 (br, NMe2); 1.74 (s), 1.15
2
C
10H7 (Np; 2), C9H7 (3)) were prepared according to literature
procedures.6,8 1H NMR spectra were recorded on a Varian
INOVA-300 NMR spectrometer or a Bruker DRX-500 NMR
spectrometer and were referenced to residual protio impurities
in the NMR solvent. 13C NMR spectra were recorded on a
Bruker DRX-500 NMR spectrometer at 125.7 MHz and were
internally referenced to the solvent signal.
Syn th esis of [Ta (OC6H2{C10H8}-2-Bu t2-4,6)(NMe2)4] (4).
To a solution of [Ta(NMe2)5] (0.50 g, 1.25 mmol) in benzene
(8.0 mL) was slowly added 2-(3,4-dihydro-1-naphthyl)-4,6-di-
tert-butylphenol (0.416 g, 1.25 mmol). The mixture was stirred
for 6 h, and the solvent was removed under vacuum, resulting
in an “off white” powder. Pentane (2.0 mL) was added to the
powder, and cooling to -15 °C resulted in the precipitation of
4 as an off-white solid. Crystals suitable for X-ray diffraction
were obtained from benzene/pentane solutions. Yield: 0.20 g
(23%). Anal. Calcd for C32H53N4OTa: C, 55.64; H, 7.73; N, 8.11.
1
(s, CMe3). H NMR (C7D8, 40 °C): δ 7.56 (d), 7.49 (d), 7.25 (t),
7.05 (t, C6H4); 7.39 (d), 6.69 (d, 4J (1H-1H) ) 1.7 Hz, m-H); 7.09
1
(d), 6.64 (d, C5H2); 2.87 (s, NMe2); 1.73 (s), 1.21 (s, CMe3). H
NMR (C7D8, -30 °C): δ 6.59-7.63 (aromatics); 2.98 (br), 2.43
1
(br), 1.92 (br, NMe2); 1.79 (s), 1.18 (s, CMe3). H NMR (C7D8,
-55 °C): δ 6.57-7.64 (aromatics); 3.00 (s, 6H), 2.86 (s, 6H),
2.36 (s, 3H), 1.88(s, 3H, NMe2); 1.81 (s), 1.17 (s, CMe3). Selected
13C NMR (C6D6, 30 °C): δ 163.0 (Ta-O-C); 103.4 (Ta-C); 44.5
(NMe2); 35.1, 34.5 (CMe3); 32.0, 30.4 (CMe3).
1
Found: C, 55.44; H, 7.42; N, 8.00. H NMR (C6D6, 30 °C): δ
6.9-7.6 (aromatics); 3.48 (br, CH2); 3.13 (s, NMe2); 2.75 (m),
2.90 (m, CH2CH2); 1.64 (s), 1.29 (s, CMe3). Selected 13C NMR
(C6D6, 30 °C): δ 157.5 (Ta-O-C); 47.3 (NMe2); 39.1 (CH2);
35.8, 34.4 (CMe3); 31.9, 30.5 (CMe3); 28.5, 24.2 (CH2CH2).
Syn th esis of [Ta (OC6H2Np -2-Bu t2-4,6)(NMe2)4] (5). To a
solution of [Ta(NMe2)5] (0.50 g, 1.25 mmol) in benzene (8.0 mL)
was slowly added 2-(1-naphthyl)-4,6-di-tert-butylphenol (0.410
g, 1.24 mmol). The mixture was stirred for 6 h, and the solvent
Syn th esis of [Ta (OC6H2{η3-In d }-2-Bu t-4,6)(NC5H4P h -4)-
Cl3] (9). A solvent-sealed NMR tube was charged with [Ta-
(OC6H2{η1-Ind}-2-But-4,6)(NMe2)3] (8) and d6-benzene, afford-
ing a yellow solution to which was added several drops of SiCl4.
The solution immediately became red. Adding a few crystals
of 4-phenylpyridine and layering with pentane gave X-ray-
quality red crystals. Anal. Calcd for C34H35Cl3NOTa: C, 53.67;
(19) Westcott, S. A.; Kakkar, A. K.; Stringer, G.; Taylor, N. J .;
Marder, T. B. J . Organomet. Chem. 1990, 394, 777.
(20) Shriver, D. F.; Drezdzon, M. A. The Manipulation of Air-
Sensitive Compounds, 2nd ed.; Wiley: New York, 1986.
1
H, 4.64; N, 1.84. Found: C, 53.01; H, 4.71; N, 1.78. H NMR
(C6D6, 30 °C): δ 10.0 (d, o-NC6H4Ph-4); 6.81-7.76 (aromatics);
3
7.19 (d), 6.45 (d, J (1H-1H) ) 3.2 Hz, η5-CH); 1.36 (s), 1.30 (s,

4664 Organometallics, Vol. 22, No. 23, 2003
Thorn et al.
CMe3). Selected 13C NMR (C6D6, 30 °C): δ 172.1 (Ta-O-C);
104.9 (Ta-C); 35.4, 34.9 (CMe3); 31.9, 30.4 (CMe3).
included in the refinement but restrained to ride on the atom
to which they are bonded. The structure was refined in full-
matrix least squares, where the function minimized was
Syn t h esis of [Ta (OC6H 2{ηn -In d }-2-Bu t -4,6)(P Me3)Cl3]
(10). A solvent-sealed NMR tube was charged with [Ta(OC6H2-
{η1-Ind}-2-But-4,6)(NMe2)3] (8) and d6-benzene, affording a
yellow solution to which was added several drops of SiCl4. The
solution immediately became red. Adding 1 drop of trimeth-
ylphosphine and layering with pentane gave orange crystals.
Anal. Calcd for C26H35Cl3POTa: C, 45.80; H, 5.17. Found: C,
45.51; H, 5.09. 1H NMR (C6D6, 30 °C): δ 6.74-7.63 (aromatics);
2
2
2
∑w(|Fo| - |Fc| )2 and the weight w is defined as w ) 1/[σ2(Fo
)
+ (0.0585P)2 + 1.4064P] (P ) (Fo2 + 2Fc )/3). Scattering factors
were taken from ref 24. Refinement was performed on a
AlphaServer 2100 using SHELX-97.25 Crystallographic draw-
ings were done using ORTEP programs.26
2
Ack n ow led gm en t. We thank the National Science
Foundation (Grant No. CHE-0078405) for financial
support of this research.
3
2
6.99 (d), 6.24 (d, J (1H-1H) ) 3.2 Hz, η5-CH); 1.48 (d, J (1H-
31P) ) 10.5 Hz, PMe3); 1.40 (s), 1.34 (s, CMe3). 31P NMR (C6D6,
30 °C): δ 8.74 (s, PMe3).
X-r a y Da ta Collection a n d Red u ction . Crystal data and
data collection parameters are contained in Table 6. A suitable
crystal was mounted on a glass fiber in a random orientation
under a cold stream of dry nitrogen. Preliminary examination
and final data collection were performed with Mo KR radiation
(λ ) 0.710 73 Å) on a Nonius Kappa CCD instrument. Lorentz
and polarization corrections were applied to the data.21 An
empirical absorption correction using SCALEPACK was ap-
plied.22 Intensities of equivalent reflections were averaged. The
structure was solved using the structure solution program
PATTY in DIRDIF92.23 The remaining atoms were located in
succeeding difference Fourier syntheses. Hydrogen atoms were
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal-
lographic data for 4-6, 8, and 9. This material is available
free of charge via the Internet at http://pubs.acs.org.
OM0300934
(23) Beurskens, P. T.; Admirall, G.; Beurskens, G.; Bosman, W. P.;
Garcia-Granda, R S.; Gould, O.; Smits, J . M. M.; Smykalla, C. The
DIRDIF92 Program System; Technical Report; Crystallography Labo-
ratory, University of Nijmegen, Nijmegen, The Netherlands, 1992.
(24) International Tables for Crystallography; Kluwer Academic:
Dordrecht, The Netherlands, 1992; Vol. C, Tables 4.2.6.8 and 6.1.1.4.
(25) Sheldrick, G. M. SHELXS97. A Program for Crystal Structure
Refinement; University of Gottingen, Gottingen, Germany, 1997.
(26) J ohnson, C. K. ORTEPII; Report ORNL-5138; Oak Ridge
National Laboratory, Oak Ridge, TN, 1976.
(21) McArdle, P. C. J . Appl. Crystallogr. 1996, 239, 306.
(22) Otwinowski, Z.; Minor, W. Methods Enzymol. 1996, 276.