The isolation and chemistry of niobium and tantalum dimethylamides containing mono- and di-aryloxide ancillary ligands

Article abstract of DOI:10.1039/b101723n

The salt complex [Me₂NH₂][Ta(NMe₂)₂Cl₄] 4 has been isolated from the reaction of [Ta₂Cl₁₀] with Me₂NH and the anion shown to contain mutually cis-dimethylamido ligands. 4 reacts with Me₂NH and pyridine to produce the neutral adducts mer,cis-[Ta(NMe₂)₂Cl₃(HNMe₂)] 1 (known compound) and [Ta(NMe₂)₂Cl₃(py)] 5. The solid state structure of [Ta(NMe₂)₂Cl₃(py-4Ph)] 7 shows a mer,cis arrangement of Cl and NMe₂ groups. The addition of 2,3,5,6-tetraphenyl- or 2,6-di-isopropyl-phenol (2 equiv) to solutions of 1 in benzene was found to produce a mixture of two isomers each containing a residual Ta-NMe₂ and Ta-NHMe₂ group. These were formulated as [Ta(OAr)₂Cl₂(NMe₂)-(NHMe₂)] with the coordinated amine trans to the Ta-NMe₂ group and aryloxide ligands either mutually cis or trans. The cis isomer was found to thermally convert to the trans form. The trans isomers [M(OAr)₂Cl₂(NMe₂)(NHMe₂)] (M = Ta, OAr = 2,3,5,6-tetraphenyl- or 2,6-di-isopropyl-phenoxide; M = Nb, OAr = 2,3,5,6-tetraphenylphenoxide) are obtained in high yield by treatment of the corresponding tri(chlorides) [M(OAr)₂Cl₃] with excess Me₂NH. The isomorphous/isostructural compounds [M(OC₆HPh₄-2,3,5,6)₂Cl₂(NMe₂ )(py)] (M = Nb, Ta) were structurally characterized and shown to contain the pyridine ligand trans to the Ta-NMe₂ group with mutually trans aryloxides. Addition of 2,2′-methylenebis(6-phenylphenol) {(HOC₆H₃Ph)₂CH₂} to 1 resulted in formation of the compound [Ta{(OC₆H₃Ph)₂CH₂}Cl₂(NMe ₂)(HNMe₂)] 15. The solid state structure of 15 shows the nitrogen atoms to be mutually trans with cis aryloxide oxygen atoms. The eight-membered dioxametallacycle ring is puckered with the methylene bridge folded up towards the Ta-NMe₂ group. The reaction pathways leading to these products are discussed.

Full text of DOI:10.1039/b101723n

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The isolation and chemistry of niobium and tantalum
dimethylamides containing mono- and di-aryloxide ancillary
ligands
Scott W. Schweiger, Dana L. Tillison, Matt G. Thorn, Phillip E. Fanwick and Ian P. Rothwell*
1393 Brown Building, Department of Chemistry, Purdue University, West Lafayette,
IN 47907-1393, USA. E-mail: rothwell@purdue.edu
Received 22nd February 2001, Accepted 8th June 2001
First published as an Advance Article on the web 2nd August 2001
The salt complex [Me2NH2][Ta(NMe2)2Cl4] 4 has been isolated from the reaction of [Ta2Cl10] with Me2NH and the
anion shown to contain mutually cis-dimethylamido ligands. 4 reacts with Me2NH and pyridine to produce the
neutral adducts mer,cis-[Ta(NMe2)2Cl3(HNMe2)] 1 (known compound) and [Ta(NMe2)2Cl3(py)] 5. The solid state
structure of [Ta(NMe2)2Cl3(py-4Ph)] 7 shows a mer,cis arrangement of Cl and NMe2 groups. The addition of 2,3,5,6-
tetraphenyl- or 2,6-di-isopropyl-phenol (2 equiv) to solutions of 1 in benzene was found to produce a mixture of two
isomers each containing a residual Ta–NMe2 and Ta–NHMe2 group. These were formulated as [Ta(OAr)2Cl2(NMe2)-
(NHMe2)] with the coordinated amine trans to the Ta–NMe2 group and aryloxide ligands either mutually cis or trans.
The cis isomer was found to thermally convert to the trans form. The trans isomers [M(OAr)2Cl2(NMe2)(NHMe2)]
(M = Ta, OAr = 2,3,5,6-tetraphenyl- or 2,6-di-isopropyl-phenoxide; M = Nb, OAr = 2,3,5,6-tetraphenylphenoxide)
are obtained in high yield by treatment of the corresponding tri(chlorides) [M(OAr)2Cl3] with excess Me2NH. The
isomorphous/isostructural compounds [M(OC6HPh4-2,3,5,6)2Cl2(NMe2)(py)] (M = Nb, Ta) were structurally
characterized and shown to contain the pyridine ligand trans to the Ta–NMe2 group with mutually trans aryloxides.
Addition of 2,2Ј-methylenebis(6-phenylphenol) {(HOC6H3Ph)2CH2} to 1 resulted in formation of the compound
[Ta{(OC6H3Ph)2CH2}Cl2(NMe2)(HNMe2)] 15. The solid state structure of 15 shows the nitrogen atoms to be
mutually trans with cis aryloxide oxygen atoms. The eight-membered dioxametallacycle ring is puckered with the
methylene bridge folded up towards the Ta–NMe2 group. The reaction pathways leading to these products are
discussed.
Table 1 Selected bond distances (Å) and angles (Њ) for [Me2NH2]-
[Ta(NMe2)2Cl4] 4
Introduction
The inorganic and organometallic chemistry associated with
Ta–N(1)
Ta–N(2)
Ta–Cl(1)
1.954(5)
1.945(5)
2.483(1)
Ta–Cl(2)
Ta–Cl(3)
Ta–Cl(4)
2.510(1)
2.404(1)
2.400(1)
niobium and tantalum chloro(aryloxide) compounds continues
to be an area of research interest.1–5 These compounds are
typically synthesized by reaction of the metal chloride with
either the parent phenol, the lithium aryloxide or the trimethyl-
silyl ether. An initial exploration of the reaction of niobium or
tantalum halides with either parent 3,3Ј-disubstituted-1,1Ј-bi-2-
naphthol or its di-lithium derivative failed to provide tractable
products. We have therefore begun to explore the reactivity of
mixed chloro(dialkylamido) compounds with phenolic reagents
as an alternative strategy for the synthesis of chloro(aryloxides)
of niobium and tantalum. In this paper we report an investi-
gation of the reaction chemistry of the compound mer,cis-
[Ta(NMe2)2Cl3(HNMe2)] 1 (first reported by Carnell and
Fowles6 and later characterized by Chisholm and Tan7) with
mono- and di-phenols.8
N(1)–Ta–N(2)
N(1)–Ta–Cl(1)
N(1)–Ta–Cl(2)
N(1)–Ta–Cl(3)
N(1)–Ta–Cl(4)
N(2)–Ta–Cl(1)
N(2)–Ta–Cl(2)
N(2)–Ta–Cl(3)
95.3(2)
171.6(2)
89.0(1)
89.2(2)
96.2(2)
92.0(2)
174.7(2)
96.1(2)
N(2)–Ta–Cl(4)
Cl(1)–Ta–Cl(2)
Cl(1)–Ta–Cl(3)
Cl(1)–Ta–Cl(4)
Cl(2)–Ta–Cl(3)
Cl(2)–Ta–Cl(4)
Cl(3)–Ta–Cl(4)
91.2(2)
83.99(5)
85.76(6)
87.84(5)
87.00(5)
85.35(5)
170.50(5)
Cl4] 4 in moderate yield as a crystalline sample from benzene–
hexane mixtures. Compound 4 is formally the result of the
reaction of [Ta2Cl10] with only 4 equivalents of Me2NH and
analysis of the supernatant showed the presence of both 1
and 2. The isolation of 4 further highlights the complexity of
the reaction of [Ta2Cl10] with dimethylamine in hydrocarbon
solvents observed by Chisholm and Tan.7 It is possible that
variations from experiment to experiment are caused by the rate
of warming of the frozen toluene solution that has the con-
densed dimethylamine “frost” on the surface. We found that
compound 1 could be isolated reproducibly in high yield by
carrying out the reaction in a toluene–diethyl ether solvent
mixture.
Results and discussion
Synthesis of chloro(dimethylamido) compounds
The reaction of [Ta2Cl10] with dimethylamine in hydrocarbon
solvents was shown previously to produce a variety of products
including 1,6,7 [Ta(NMe2)3Cl2(HNMe2)] 2 and the oxo impurity
[{Ta(NMe2)2Cl2(HNMe2)}2(µ-O)] 3 (Scheme 1). Adduct 1 was
found to undergo sublimation with no loss of coordinated
dimethylamine. While attempting the synthesis of 1 by conden-
sation of Me2NH (5 equiv per Ta) to a frozen toluene solution
of [Ta2Cl10] we isolated the salt complex [Me2NH2][Ta(NMe2)2-
Compound 4 was structurally characterized (Fig. 1, Table 1)
and shown to contain a distorted octahedral metal center with
the dimethylamido ligands mutually cis. The distortion from
DOI: 10.1039/b101723n
J. Chem. Soc., Dalton Trans., 2001, 2401–2408
This journal is © The Royal Society of Chemistry 2001
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Scheme 1
Fig. 2 Molecular structure of [{Ta(NMe2)(py)Cl3}2(µ-O)] 6.
Fig. 1 Molecular structure of [Me2NH2][Ta(NMe2)2Cl4] 4.
octahedral geometry involves an opening up of the N–Ta–N
angle to 95.3(2)Њ while the four chloride ligands are slightly
compressed. The cis-geometry is expected given the strong
π-donor properties of the dimethylamido ligands.
The addition of Me2NH to a C6D6 solution of 4 was found to
produce a mixture of 1 and 2 (1H NMR) and a precipitate taken
to be [Me2NH2][Cl] (Scheme 1).
Addition of pyridine (py) to 4 was found to produce the
neutral pyridine adduct [Ta(NMe2)2Cl3(py)] 5 along with a pre-
cipitate of [Me2NH2][Cl] (Scheme 2). During the recrystalliz-
ation of 5, a few crystals of the sparingly soluble µ-oxo
compound [{Ta(NMe2)Cl3(py)}2(µ-O)] 6 were also isolated and
structurally characterized (Fig. 2, Table 2). Compound 5 is the
direct pyridine analogue of the dimethylamine compound 1.
Compound 6 is structurally related to 3 but has a different ratio
of amide to chloride ligands. As stated for the formation of 3,
the origins of 6 “could conceivably arise from an oxide impurity
in the commercially available TaCl5 or by trace hydrolysis
during the course of these reactions or crystallizations”. The
formation of an unbridged, linear M–O–M (M = Nb, Ta) core
is not an unusual occurrence for these metals in their highest
oxidation state.9 The linearity at oxygen can be readily
accounted for by the presence of oxygen-p to metal-d
π-bonding to both metals. What is unusual about the structure
of 6 is the slight asymmetry in the oxide bridge. The Ta(1)–O
distance of 1.877(9) Å is significantly shorter than the Ta(2)–O
distance of 1.929(9) Å and the Ta–O distances of 1.917(6) and
1.928(6) Å reported for 3. We have no ready explanation for this
anomaly as all the other types of ligands have essentially identi-
cal distances to each tantalum metal center. Although crystals
of the pyridine adduct 5 suitable for X-ray diffraction could
not be isolated, use of 4-phenylpyridine led to crystals of
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[Ta(NMe2)2Cl3(py-4Ph)]
7
(Scheme 2) whose underlying
2.371(4) Å in 7 is identical to the Ta–N(HNMe2) distance
molecular structure was successfully elucidated by X-ray dif-
fraction (Fig. 3, Table 3). The Ta–N(py-4Ph) distance of
reported for 1, and much longer than the Ta–NMe2 bond dis-
tances. There are definite distortions away from octahedral
geometry involving a bending of chloride ligands towards the
pyridine ligand, away from the strongly π-bonding dimethyl-
amido ligands. The influence of these ligands is also seen in
the Ta–Cl(2) distance of 2.442(2) Å which is longer than the
corresponding distances of 2.377(1) and 2.404(1) Å for
the mutually trans chloride ligands.
Table 2 Selected bond distances (Å) and angles (Њ) for [{Ta(NMe2)-
(py)Cl3}2(µ-O)] 6
Ta(1)–O
1.877(9)
2.370(3)
2.383(3)
2.399(3)
1.92(1)
Ta(2)–O
1.929(9)
2.358(3)
2.382(3)
2.382(3)
1.92(1)
Ta(1)–Cl(11)
Ta(1)–Cl(12)
Ta(1)–Cl(13)
Ta(1)–N(1)
Ta(1)–N(11)
Ta(2)–Cl(21)
Ta(2)–Cl(22)
Ta(2)–Cl(23)
Ta(2)–N(2)
Ta(2)–N(21)
Synthesis of aryloxy(dimethylamido) compounds
2.389(9)
2.36(1)
The addition of 2,3,5,6-tetraphenyl- or 2,6-di-isopropyl-phenol
(2 equiv) to solutions of 1 in benzene was found to produce a
mixture of two compounds. Spectroscopic data (1H NMR) was
consistent with the presence of two isomers containing a
residual Ta–NMe2 and Ta–NHMe2 group. We formulated these
as the cis/trans isomers 8–11 (Scheme 3) based upon other
experiments (see below). These isomers contain the amine
coordinated trans to the amide group. There are four other
geometric isomers possible for this particular formulation
(Scheme 3). However, we feel there will be a strong electronic
driving force (in the absence of overwhelming steric factors) for
the amine to coordinate trans to the strongest π-donor ligand,
which in this case is clearly the dimethylamido group. This
hypothesis is not contradicted by any of the structures obtained
in this study, where the donor ligand is consistently trans to the
dimethylamido group. When C6D6 solutions of these mixtures
were heated at 100 ЊC for several hours, isomer 8 or 9 were
found to isomerize to the alternative isomer 10 or 11 respec-
tively. It was found that isomers 10 and 11 could be formed
exclusively by the addition of excess dimethylamine to the
chloro(aryloxides) [Ta(OC6HPh4-2,3,5,6)2Cl3] or [Ta(OC6H3-
Pri2-2,6)2Cl3] in hydrocarbon solvents. The niobium analogue
12 was also obtained from the corresponding substrate (Scheme
3). Although crystals of 10–12 suitable for X-ray diffraction
could not be obtained, addition of pyridine to benzene
solutions of 10 or 12 led to formation of well formed crystals of
the sparingly soluble pyridine adducts 14 and 13 respectively.
Ta(1)–O–Ta(2)
O–Ta(1)–Cl(11)
O–Ta(1)–Cl(12)
O–Ta(1)–Cl(13)
O–Ta(1)–N(1)
O–Ta(1)–N(11)
Cl(11)–Ta(1)–Cl(12)
Cl(11)–Ta(1)–Cl(13)
Cl(11)–Ta(1)–N(1)
Cl(11)–Ta(1)–N(11)
Cl(12)–Ta(1)–Cl(13)
Cl(12)–Ta(1)–N(1)
Cl(12)–Ta(1)–N(11)
Cl(13)–Ta(1)–N(1)
Cl(13)–Ta(1)–N(11)
N(1)–Ta(1)–N(11)
176.0(5)
91.8(3)
166.4(2)
88.4(3)
97.6(4)
83.5(3)
88.1(1)
170.2(1)
95.8(3)
85.3(3)
89.4(1)
96.0(3)
82.9(3)
94.0(3)
85.0(3)
178.5(4)
O–Ta(2)–Cl(21)
O–Ta(2)–Cl(22)
O–Ta(2)–Cl(23)
O–Ta(2)–N(2)
93.3(3)
165.5(2)
88.1(3)
97.5(4)
82.2(3)
87.3(1)
170.5(1)
93.9(3)
84.9(3)
88.9(1)
96.9(3)
83.4(3)
95.2(3)
86.0(3)
178.7(4)
O–Ta(2)–N(21)
Cl(21)–Ta(2)–Cl(22)
Cl(21)–Ta(2)–Cl(23)
Cl(21)–Ta(2)–N(2)
Cl(21)–Ta(2)–N(21)
Cl(22)–Ta(2)–Cl(23)
Cl(22)–Ta(2)–N(2)
Cl(22)–Ta(2)–N(21)
Cl(23)–Ta(2)–N(2)
Cl(23)–Ta(2)–N(21)
N(2)–Ta(2)–N(21)
Table 3 Selected bond distances (Å) and angles (Њ) for [Ta(NMe2)2-
(NC6H4Ph-4)Cl3] 7
Ta–N(1)
Ta–N(2)
Ta–N(3)
2.371(4)
1.951(5)
1.936(5)
Ta–Cl(1)
Ta–Cl(2)
Ta–Cl(3)
2.404(1)
2.442(2)
2.377(1)
N(1)–Ta–N(2)
N(1)–Ta–N(3)
N(1)–Ta–Cl(1)
N(1)–Ta–Cl(2)
N(1)–Ta–Cl(3)
N(2)–Ta–N(3)
N(2)–Ta–Cl(1)
N(2)–Ta–Cl(2)
85.7(2)
177.3(2)
84.4(1)
83.2(1)
83.6(1)
96.0(2)
87.9(2)
167.4(2)
N(2)–Ta–Cl(3)
N(3)–Ta–Cl(1)
N(3)–Ta–Cl(2)
N(3)–Ta–Cl(3)
Cl(1)–Ta–Cl(2)
Cl(1)–Ta–Cl(3)
Cl(2)–Ta–Cl(3)
95.7(2)
97.8(2)
95.4(2)
94.2(2)
85.14(6)
167.11(5)
88.87(6)
Fig. 3 Molecular structure of [Ta(NMe2)2(NC6H4Ph-4)Cl3] 7.
Scheme 2
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Scheme 3
Table 4 Selected bond distances (Å) and angles (Њ) for [M(OC6HPh4-
2,3,5,6)2Cl2(NMe2)(py)] (M = Nb, 13; Ta, 14)
13
14
M–O(1)
M–O(2)
M–Cl(1)
M–Cl(2)
M–N(31)
M–N(41)
1.926(3)
1.913(3)
2.397(1)
2.391(1)
1.935(4)
2.395(4)
1.927(3)
1.932(4)
2.370(1)
2.386(1)
1.929(5)
2.400(5)
O(1)–M–O(2)
O(1)–M–N(31)
O(2)–M–N(31)
O(1)–M–N(41)
O(2)–M–N(41)
O(1)–M–Cl(1)
O(1)–M–Cl(2)
O(2)–M–Cl(1)
O(2)–M–Cl(2)
N(31)–M–N(41)
N(31)–M–Cl(1)
N(31)–M–Cl(2)
N(41)–M–Cl(1)
N(41)–M–Cl(2)
Cl(1)–M–Cl(2)
168.7(1)
95.9(2)
95.4(2)
84.0(1)
84.7(1)
90.0(9)
90.2(9)
88.9(1)
89.2(1)
179.3(2)
93.4(1)
95.4(1)
86.0(1)
85.3(1)
171.2(5)
167.3(2)
96.6(2)
96.1(2)
83.5(2)
83.8(2)
90.1(1)
90.1(1)
88.9(1)
88.9(1)
179.8(2)
94.5(2)
94.8(2)
85.7(1)
85.1(1)
170.7(5)
Fig.
4
Molecular structure of [Ta(OC6HPh4-2,3,5,6)2Cl2(NMe2)-
(py)]ؒ5C6H6 14. The niobium compound 13 is isomorphous and
the compound [Ta{(OC6H3Ph)2CH2}Cl2(NMe2)(HNMe2)] 15
(Scheme 4). The solid-state structure of 15 (Fig. 5, Table 5)
shows the nitrogen atoms to be mutually trans with cis
aryloxide oxygen atoms. The eight-membered ring formed by
this bis(aryloxide) has been shown to typically adopt a
puckered conformation in which the methylene linker is folded
above the chelate ring.10 Inversion of this ring is typically slow
on the NMR timescale resulting in a distinctive AB(AX)
pattern for the non-equivalent methylene protons. In the case of
15 the solid-state structure shows that the methylene group
is folded towards the Ta–NMe2 group. It is possible that the
molecule could exist as two isomers in solution with the chelate
ring folded either towards the amide group (as in the solid state)
isostructural.
Crystallographic studies showed 13 and 14 to be isomorphous,
with five molecules of benzene per Nb/Ta in the unit cell. The
molecular structure of these isomorphous/isostructural com-
pounds (Fig. 4, Table 4) shows the pyridine to be bound trans
to the dimethylamido group and the aryloxide ligands to be
mutually trans. It can be seen (Table 4) that the chloride and
aryloxide ligands are bent slightly away from the p-donating
dimethylamido group towards the neutral donor amine ligand.
Addition of 2,2Ј-methylenebis(6-phenylphenol) {(HOC6H3-
Ph)2CH2} to benzene solutions of 1 resulted in formation of
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Table 5 Selected bond distances (Å) and angles (Њ) for [Ta{(OC6H3-
Ph)2CH2}Cl2(NMe2)(HNMe2)] 15
site, i.e. displacement of the amine ligand. This can readily lead
to an intermediate mono(aryloxide), mono(amido) compound
as shown (Scheme 5). However, the protonolysis of the last
remaining amido group is problematic in this system as the
incoming phenol will coordinate trans to the Ta–NMe2 bond.
Hence, elimination of HCl (trapped by HNMe2) will occur to
produce the cis/trans isomers observed (Scheme 5). In the case
of the bis(phenol), only the cis isomer can be formed.
Ta–O(2)
Ta–N(4)
Ta–Cl(1)
1.887(2)
1.961(2)
2.4105(8)
Ta–O(1)
Ta–N(3)
Ta–Cl(2)
1.896(2)
2.372(7)
2.4180(7)
O(2)–Ta–O(1)
O(1)–Ta–N(4)
O(1)–Ta–N(3)
O(2)–Ta–Cl(1)
N(4)–Ta–Cl(1)
O(2)–Ta–Cl(2)
N(4)–Ta–Cl(2)
Cl(1)–Ta–Cl(2)
C(21)–O(2)–Ta
92.15(9)
98.2(1)
78.5(2)
89.77(7)
93.44(8)
170.88(6)
92.80(7)
87.58(3)
155.2(2)
O(2)–Ta–N(4)
O(2)–Ta–N(3)
N(4)–Ta–N(3)
O(1)–Ta–Cl(1)
N(3)–Ta–Cl(1)
O(1)–Ta–Cl(2)
N(3)–Ta–Cl(2)
C(11)–O(1)–Ta
96.08(9)
90.8(2)
172.5(2)
167.93(6)
89.6(2)
88.67(7)
80.4(2)
154.5(2)
Experimental
All operations were carried out under a dry nitrogen atmos-
phere or in vacuo either in a Vacuum Atmosphere Dri-Lab or by
standard Schlenk techniques. Hydrocarbon solvents were dried
by distillation from sodium–benzophenone and stored under
dry nitrogen. All reagents were dried over 3 Å molecular sieves
1
prior to use. H and 13C NMR spectra were recorded on a
Varian Associates Gemini 200 and an Inova 300 spectrometer
and were referenced using protio impurities of commercial
benzene-d6 as an internal standard. Microanalytical data were
obtained in-house; however in some cases accurate micro-
analytical data were difficult to obtain due to partial loss of
hydrocarbon solvate during analysis. This is compounded by
the fact that poly(phenylated)phenoxide ligands tend to gener-
ate low carbon analyses due to incomplete combustion. The
X-ray diffraction studies were completed in-house at Purdue
University.
[Me2NH2][Ta(NMe2)2Cl4] (4)
A 1 L round-bottomed flask was charged with TaCl5 (13 g, 0.04
mol) and toluene (300 mL) forming a yellow suspension. This
suspension was frozen at Ϫ178 ЊC and Me2NH (0.185 mol)
added via a calibrated glass manifold. The mixture was slowly
warmed to room temperature, stirred overnight, and the solvent
evaporated. The mixture was then extracted with benzene,
filtered and evacuated to dryness affording an orange solid
that could be recrystallized from benzene–hexane. Yield: 10.7 g
(63%). Anal. Calc. for C6H20Cl4N3Ta: C, 15.77; H, 4.41; N, 9.19;
Scheme 4
1
Cl, 31.03. Found: C, 15.97; H, 4.45; N, 9.07; Cl, 30.95%. H
NMR (C6D6, 30 ЊC): δ 7.87 (br, NH2); 4.10 (s, H2NMe2); 2.39 (s,
Ta–NMe2).
Alternative synthesis of [TaCl3(NMe2)2(HNMe2)] (1)
TaCl5 (43.55 g, 0.12 mol) was suspended in a 50 : 50 (v/v) solu-
tion of toluene–ether (100 mL/100 mL). The yellow suspension
was frozen in a liquid nitrogen bath (Ϫ178 ЊC). HNMe2 (11.74
mL, 0.48 mol) was condensed in via a calibrated glass manifold.
The suspension was allowed to warm to room temperature and
stirred overnight. The red solution was dried under vacuum,
suspended in benzene and filtered to remove salts. The red
supernatant was collected and dried to yield the product as a
fine red powder. Yield: 48.03 g (94.0%). 1H NMR (C6D6, 25 ЊC):
δ 4.04 (s, NMe2); 3.60 (s, NMe2); 2.49 (m, HNMe2); 2.24 (s,
HNMe); 2.20 (s, HNMe).
Fig.
5
Molecular structure of [Ta{(OC6H3Ph)2CH2}Cl2(NMe2)-
(HNMe2)] 15.
or towards the amine donor ligand. However, in solution only
one sharp AB pattern is observed at δ 4.76 and 3.24. A possible
reason for the observed folding of the chelate lies in the distor-
tion from octahedral geometry imposed by the dimethylamido
ligand. It can be seen (Table 5) that the N(amide)–Ta–O angles
are opened up to 96 and 98Њ. It seems reasonable, therefore, that
the chelate would fold towards the amide instead of towards the
amine towards which the bis(aryloxide) is being “pushed”.
[Ta(NMe2)2Cl3(py)] (5) and [{TaCl3(NMe2)(py)}2(ꢀ-O)] (6)
A round-bottomed flask was charged with 4 (1.6 g, 3.5 mmol)
and benzene (20 mL). This red solution was stirred as pyridine
(0.3 mL, 4.2 mmol) was slowly added. Stirring was continued
for 30 minutes whereupon the solution was filtered and the
filtrate evacuated to dryness affording a red solid that could be
recrystallized from benzene–hexane. Yield: 1.4 g (88%). Anal.
Calc. for C9H17Cl3N3Ta, 5: C, 23.78; H, 3.77; N, 9.24. Found: C,
Mechanistic discussion
1
The addition of either the mono- or bis-(phenol) reagents to
[TaCl3(NMe2)2(HNMe2)] 1 does not lead to displacement of
both amido ligands. This observation can be rationalized
by considering the probable intermediates in the reaction. In
order for protonolysis of the first Ta–NMe2 function to
occur, the phenolic reagent must coordinate to a vacant metal
23.88; H, 3.66; N, 8.53%. H NMR (C6D6, 30 ЊC): δ 8.95 (d,
ortho-pyH); 6.46–6.80 (meta and para-pyH); 4.11 (s, NMe2),
3.61 (s, NMe2). 13C NMR (C6D6, 30 ЊC): δ 151.8, 138.6, 124.1
(py); 48.9, 48.0 (NMe2). A minor amount of oxo-bridged 6
formed during either the reaction or workup and was identified
by X-ray analysis.
J. Chem. Soc., Dalton Trans., 2001, 2401–2408
2405

View Article Online
Scheme 5
[TaCl3(NMe2)2(py-4Ph)] (7)
Reaction of 1 with 2,6-di-isopropylphenol
A round-bottomed flask was charged with 4 (1.0 g, 2.2
mmol) and benzene (20 mL). This red solution was stirred
as 4-phenylpyridine (370 mg, 2.4 mmol) was slowly added as a
solid. Stirring was continued for 30 minutes whereupon the
solution was filtered and the filtrate evacuated to dryness
affording a red solid that could be recrystallized from
benzene–hexane. Yield: 1.1 g (92%). Anal. Calc. for C15H21-
Cl3N3Ta: C, 33.95; H, 3.99; N, 7.92. Found: C, 34.23; H,
3.96; N, 7.77%. 1H NMR (C6D6, 30 ЊC): δ 9.05 (d, ortho-pyH);
6.70–7.40 (meta and para-pyH); 4.18 (s, NMe2), 3.70 (s,
NMe2).
To a solution of 1 (1.0 g, 2.4 mmol) in benzene (25 mL) was
added 2,6-di-isopropylphenol (0.84 g, 4.8 mmol). The reaction
mixture turned yellow almost instantly. It was stirred for 1 hour,
filtered and the yellow supernatant collected. The supernatant
was dried under vacuum to yield a yellow powder as a mixture
of 9 and 11 (NMR data identical with following experiment).
Yield: 1.51 g (92%). 1H NMR (C6D6, 25 ЊC) of 9: δ 6.9–7.3 (m,
aromatics); 4.37 (septet, CHMe2); 4.14 (s, NMe2); 2.41 (d,
HNMe2); 1.24 (d, CHMe2); 0.90 (m, HNMe2).
[Ta(OC6H3Pri2-2,6)2Cl2(NMe2)(HNMe2)] (11)
In a round-bottomed flask, [Ta(OC6H3Pri2-2,6)2Cl3] (1.0 g, 1.56
mmol) was dissolved in benzene (25 mL). The flask was
exposed to one atmosphere of dimethylamine using a calibrated
gas manifold. The reaction flask became warm and the solution
turned pale yellow. A precipitate formed on the side of the
flask. Benzene and any left over dimethylamine was removed
by vacuum after two hours. The resulting yellow powder was
dissolved in benzene (25 mL) and filtered using Celite as a
filter aid. The benzene was again removed by vacuum to
yield a yellow powder. Yield: 0.81 g (73%). Anal. Calc. for
TaC28H47Cl2N2O2: C, 48.35; H, 6.81; N, 4.02; Cl, 10.19.
Found: C, 48.09; H, 6.64; N, 4.00; Cl, 10.26%. 1H NMR
(C6D6, 25 ЊC): δ 7.15 (d, m-H); 6.96 (t, m-H); 4.33 (septet,
CHMe2), 3.90 (s, NMe2); 2.73 (m, HNMe2); 2.08 (d,
HNMe2); 1.35 (d, CHMe2). 13C NMR (C6D6, 25 ЊC): δ 154.7
(C-O); 141.5–124.0 (aromatics), 49.9 (s, NMe2), 40.3 (s,
HNMe2), 26.6 (s, CHMe2), 25.3 (s, CHMe2).
Reaction of 1 with 2,3,5,6-tetraphenylphenol
To a solution of 1 (1.0 g, 2.4 mmol) in benzene (25 mL) was
added 2,3,5,6-tetraphenylphenol (1.89 g, 4.8 mmol). The red
reaction mixture was stirred overnight. The reaction was fil-
tered to remove salts and the yellow supernatant was collected
and dried under vacuum to yield a yellow powder as a 60–40
mixture of 8 and 10 (NMR data identical with following
experiment). Yield: 2.69 g (83.3%). 1H NMR (C6D6, 25 ЊC) of 8:
δ 6.9–7.5 (m, aromatics); 3.79 (s, NMe2); 2.08 (d, HNMe2); 0.70
(m, HNMe2).
[Ta(OC6HPh4-2,3,5,6)2Cl2(NMe2)(HNMe2)] (10)
In a round-bottomed flask, [Ta(OC6HPh4-2,3,5,6)2Cl3] (1.00 g,
0.8525 mmol) was dissolved in benzene (25 mL). The flask
was exposed to one atmosphere of dimethylamine using a
calibrated gas manifold. The reaction flask became warm and
the solution turned pale yellow. A precipitate formed on the
side of the flask. Benzene and any left over dimethylamine
was removed by vacuum after two hours. The resulting yellow
powder was dissolved in benzene (25 mL) and filtered using
Celite as a filter aid. The benzene was again removed by
vacuum to yield a yellow powder. Yield: 0.65 g (71%). The
1H NMR spectrum clearly showed the presence of benzene
solvate trapped within the solid. This is consistent with the
microanalytical data. Anal. Calc. for C64H55Cl2N2O2Ta: C,
67.67; H, 4.88; N, 2.47; Cl, 6.24. For C64H55Cl2N2O2Taؒ
2C6H6: C, 70.64; H, 5.22; N, 2.17; Cl, 5.48. Found: C, 69.89;
[Nb(OC6HPh4-2,3,5,6)2Cl2(NMe2)(HNMe2)] (12)
In a round-bottomed flask, [Nb(OC6HPh4-2,3,5,6)2Cl3] (1.00 g,
1.01 mmol) was dissolved in benzene (25 mL). The flask was
exposed to one atmosphere of dimethylamine using a calibrated
gas manifold. The reaction flask became warm and the solution
turned pale yellow. A precipitate formed on the side of the
flask. Benzene and any left over dimethylamine was removed by
vacuum after two hours. The resulting yellow powder was dis-
solved in benzene (25 mL) and filtered using Celite as a filter
aid. The benzene was again removed by vacuum to yield a dark
1
1
H, 5.10; N, 1.78; Cl, 5.08%. H NMR (C6D6, 25 ЊC): δ 6.9–
red powder, 0.81g (77.14%). H NMR (C6D6, 25 ЊC): δ 6.8–7.3
7.5 (m, aromatics); 3.43 (s, NMe2); 1.76 (d, HNMe2); 0.37 (m,
HNMe2).
(m, aromatics); 3.11 (s, NMe2); 1.71 (d, HNMe2); 0.32 (m, 1H,
HNMe2).
2406
J. Chem. Soc., Dalton Trans., 2001, 2401–2408

View Article Online
Table 6 Crystallographic data for complexes 4, 6, 7 and 13–15
4
6
7
13
14
15
Formula
C6H20Cl4N3-
Ta
C14H22Cl6N4-
OTa2
C15H21Cl3N3-
Ta
C67H53Cl2N2O2Nbؒ
5C6H6
C67H53Cl2N2O2Taؒ
5C6H6
C29H31Cl2N2O2Taؒ
C6H6
Formula weight
Space group
a/Å
b/Å
c/Å
α/Њ
β/Њ
457.01
836.97
530.66
1472.57
Pna21 (no. 33)
30.4539(2)
22.0854(4)
11.4593(9)
90
90
90
7707.4(5)
4
1.27
1560.61
Pna21 (no. 33)
30.47090(10)
22.0751(2)
11.4756(4)
90
90
90
7719.0(2)
4
1.343
769.55
P2l/n (no. 14)
8.6567(3)
17.9638(7)
10.2052(3)
90
107.121(2)
90
1516.7(2)
4
2.001
P2l2l2l (no. 19)
11.9310(6)
14.3050(4)
14.3949(7)
90
90
90
2456.8(3)
4
2.263
173
0.045, 0.107
P2l/c (no. 14)
19.1788(7)
7.2144(4)
14.3129(6)
90
104.191(3)
90
1919.3(3)
4
1.836
P1 (no. 2)
10.0975(2)
11.1400(2)
15.5664(3)
80.5543(8)
84.6022(8)
67.3869(7)
1593.55(8)
2
γ/Њ
V/Å3
Z
ρcalc/g cmϪ3
T /K
R, RW
1.604
150
0.027, 0.058
173
0.041, 0.107
173
0.037, 0.085
150
0.058, 0.095
150
0.046, 0.085
[Nb(OC6HPh4-2,3,5,6)2Cl2(NMe2)(py)] (13)
aged and the structures solved using the structure solution pro-
gram PATTY in DIRDIF92.13 The remaining atoms were
located in succeeding difference Fourier syntheses. Hydrogen
atoms were included in the refinement but restrained to ride
on the atom to which they are bonded. The structures were
refined in full-matrix least-squares where the function mini-
mized was Σw(|Fo|2 Ϫ |Fc|2)2 and the weight w is defined as
A sample of 12 (0.62 g, 0.591 mmol) was dissolved in benzene.
To this, an excess (100 µL) of pyridine was added. The mixture
was then layered with pentane and left overnight. Red crystals
of product were formed within a 24 hour period. The benzene–
pentane solution was decanted away and the crystals (0.38 g,
60.3%) were dried by vacuum. 1H NMR analysis of the crystals
was unobtainable due to low solubility. X-Ray analysis showed
five benzene molecules in the coordination sphere. Anal. Calc.
for C67H53Cl2N2O2Nbؒ5C6H6: C, 79.12; H, 5.68; N, 1.90; Cl,
4.82. Found: C, 79.02; H, 5.47; N, 2.17; Cl, 5.40%.
2
w = 1/[σ2(Fo ) ϩ (0.0585P)2 ϩ 1.4064P] where P = (Fo2 ϩ 2Fc2)/
3. Scattering factors were taken from the International Tables
for Crystallography.14 Refinement was performed on a Alpha-
Server 2100 using SHELX-97.15 Crystallographic drawings
were done using the program ORTEPII.16
CCDC reference numbers 159025–159030.
See http://www.rsc.org/suppdata/dt/b1/b101723n/ for crystal-
lographic data in CIF or other electronic format.
[Ta(OC6HPh4-2,3,5,6)2Cl2(NMe2)(py)] (14)
In a vial, 10 (0.69 g, 0.607 mmol) was dissolved in benzene. To
this, three drops of pyridine were added. The mixture was then
layered with pentane and left overnight. Orange crystals of
product were formed within a 24 hour period. The benzene–
pentane solution was decanted away and the crystals (0.35 g,
Acknowledgements
We thank the National Science Foundation (Grant
CHE-0078405) for financial support of this research.
1
49.3%) were dried by vacuum. H NMR analysis was again
unobtainable due to low solubility of crystals. X-Ray analysis
showed five benzene molecules in the coordination sphere.
Anal. Calc. for C67H53Cl2N2O2Taؒ5C6H6: C, 74.66; H, 5.36; N,
1.80; Cl, 4.54. Found: C, 73.90; H, 5.40; N, 1.85; Cl, 4.15%.
References
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[Ta{(OC6H3Ph)2CH2}Cl2(NMe2)(HNMe2)] (15)
To a solution of 1 (1.0 g, 2.4 mmol) in benzene (20 mL) was
added
a 10 mL benzene solution of 2,2Ј-methylenebis-
(6-phenylphenol) (0.84 g, 2.4 mmol). The solution was stirred
for 24 hours, filtered to remove salts and the red supernatant
collected. The supernatant was layered with pentane and
allowed to stand for 24 hours resulting in an orange crystalline
precipitate. Crystallographic studies indicated one benzene
molecule of crystallization per Ta. Microanalytical data indi-
cated some loss of these solvate molecules. Anal. Calc. for
TaC29H31Cl2N2O2: C, 50.38; H, 4.52. For TaC29H31Cl2N2O2ؒ
C6H6: C, 54.63; H, 4.85. Found: C, 53.49; H, 4.86. Repeat: C,
1
52.76; H, 4.68%. Yield: 1.63 g (98%). H NMR (C6D6, 25 ЊC):
δ 6.70–7.61 (m, aromatics); 4.76 (d, CH2); 3.24 (d, CH2); 3.92 (s,
NMe2); 1.40 (d, HNMe2).
X-Ray crystallography data
Crystal data and data collection parameters are contained in
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data.11 An empirical absorption correction using SCALEPACK
was applied.12 Intensities of equivalent reflections were aver-
J. Chem. Soc., Dalton Trans., 2001, 2401–2408
2407

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2408
J. Chem. Soc., Dalton Trans., 2001, 2401–2408