Synthesis and structure of niobium and tantalum compounds containing 2,6-diphenyl-3,5-di-tert-butylphenoxide ligation

Article abstract of DOI:10.1016/S0020-1693(99)00448-X

A series of mononuclear derivatives of niobium(V) and tantalum(V) containing the new ligand 2,6-diphenyl-3,5-di-tert-butylphenoxide (OC₆HPh₂-2,6-(t)Bu₂-3,5) have been isolated. The addition of the parent phenol (2 equiv. per Nb) to a benzene solution of [Nb₂Cl₁₀] leads to formation of the trichloride [Nb(OC₆HPh₂-2,6-(t)Bu₂-3,5)₂Cl₃] (1), while treatment of the tetra-chlorides [Cp*TaCl₄] and [CpNbCl₄] with [LiOC₆HPh₂-2,6-(t)Bu₂-3,5] leads to the mixed cyclopentadienyl, aryloxides [Cp*Ta(OC₆HPh₂-2,6-(t)Bu₂-3,5)Cl₃] (2) and [CpNb(OC₆HPh₂-2,6-(t)Bu₂-3,5)Cl₃] (3), respectively. Structural studies show a square pyramidal geometry for trichlorides 1-3 with a basal aryloxide in each case. An axial aryloxide, Cp* and Cp ligand are present for 1, 2 and 3, respectively. The addition of HOC₆HPh₂-2,6-(t)Bu₂-3,5 to the precursor [Ta(NMe₂)₅] results in formation of the mono-aryloxide [Ta(OC₆HPh₂-2,6-(t)Bu₂-3,5)(NMe₂)₄] (4), which is also square pyramidal with a basal aryloxide ligand. Activation of a solution of 1 in benzene with 3 equiv. of (n)BuLi, followed by treatment with H₂ (1200 psi, 100°C) results in intramolecular hydrogenation of ortho-phenyl rings. Hydrolysis of the reaction mixture leads to isolation of 2,6-dicyclohexyl-3,5-di-tert-butylphenol (5), which has been structurally characterized. (C) 2000 Elsevier Science S.A.

Full text of DOI:10.1016/S0020-1693(99)00448-X

www.elsevier.nl/locate/ica
Inorganica Chimica Acta 299 (2000) 135–141
Synthesis and structure of niobium and tantalum compounds
containing 2,6-diphenyl-3,5-di-tert-butylphenoxide ligation
Jonathan S. Vilardo, Michelle M. Salberg, Jennifer R. Parker, Phillip E. Fanwick,
Ian P. Rothwell *
Department of Chemistry, 1393 Brown Building, Purdue Uni6ersity, West Lafayette, IN 47907-1393, USA
Received 27 May 1999; accepted 1 October 1999
Abstract
A series of mononuclear derivatives of niobium(V) and tantalum(V) containing the new ligand 2,6-diphenyl-3,5-di-tert-butyl-
phenoxide (OC6HPh2-2,6-tBu2-3,5) have been isolated. The addition of the parent phenol (2 equiv. per Nb) to a benzene solution
of [Nb2Cl10] leads to formation of the trichloride [Nb(OC6HPh2-2,6-tBu2-3,5)2Cl3] (1), while treatment of the tetra-chlorides
[Cp*TaCl4] and [CpNbCl4] with [LiOC6HPh2-2,6-tBu2-3,5] leads to the mixed cyclopentadienyl, aryloxides [Cp*Ta(OC6HPh2-2,6-
tBu2-3,5)Cl3] (2) and [CpNb(OC6HPh2-2,6-tBu2-3,5)Cl3] (3), respectively. Structural studies show a square pyramidal geometry for
trichlorides 1–3 with a basal aryloxide in each case. An axial aryloxide, Cp* and Cp ligand are present for 1, 2 and 3, respectively.
The addition of HOC6HPh2-2,6-tBu2-3,5 to the precursor [Ta(NMe2)5] results in formation of the mono-aryloxide [Ta(OC6HPh2-
2,6-tBu2-3,5)(NMe2)4] (4), which is also square pyramidal with a basal aryloxide ligand. Activation of a solution of 1 in benzene
n
with 3 equiv. of BuLi, followed by treatment with H2 (1200 psi, 100°C) results in intramolecular hydrogenation of ortho-phenyl
rings. Hydrolysis of the reaction mixture leads to isolation of 2,6-dicyclohexyl-3,5-di-tert-butylphenol (5), which has been
structurally characterized. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Crystal structures; Tantalum complexes; Niobium complexes; Phenoxide complexes
1. Introduction
ducing meta-substituents on the phenoxide nucleus of
2,6-di-arylphenoxides has been explored. This has led
to the development of new chiral phenols in which the
meta-substituent acts as a blocking group to hinder
rotation of two-substituted phenyl or 1-naphthyl sub-
stituents [4,5]. It has also been demonstrated that in-
creasing the bulk of meta-substituents will inhibit the
ease of cyclometallation of 2,6-diphenyl-3,5-dialkylphen-
oxides (OC6HPh2-2,6-R2-3,5) at transition metal centers
[6]. The rate of cyclometallation in the compound
[Ta(OC6HPh2 - 2,6 - R2 - 3,5)2(ꢀCHSiMe3)(CH2SiMe3)]
drops of in the sequence H\Ph\Me\iPr\tBu with
the 3,5-di-tert-butyl derivative failing to undergo cy-
clometallation. We wish to report in this paper further
investigations into the coordination properties if the
2,6-diphenyl-3,5-di-tert-butyl-phenoxide (OC6HPh2-2,6-
tBu2-3,5) ligand at niobium and tantalum metal centers.
This work also demonstrates that despite the immunity
to cyclometallation, the ortho-phenyl rings can undergo
hydrogenation.
The use of 2,6-di-arylphenoxide ligands has had a
considerable impact on both inorganic and organo-
metallic chemistry in recent years. The ortho-aryl sub-
stituents in these ligands typically play a pivotal role in
the chemistry that can be developed. Hence, in the case
of simple 2,6-diphenylphenoxide the ortho-phenyl ring
can undergo chelation to metal centers either via hn-in-
teractions [1] or by intramolecular CH bond activation
(cyclometallation) [2]. It has also been shown possible
to carry out either the partial (to cyclohexadienyl or
cyclohexenyl rings) [3] or total (to the cyclohexyl group)
hydrogenation of initial ortho-phenylphenoxides at
early d-block metal centers. Recently the effect of intro-
* Corresponding author. Tel.: +1-765-494 7012; fax: +1-765-494
0239.
E-mail address: rothwell@purdue.edu (I.P. Rothwell)
0020-1693/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(99)00448-X

136
J.S. Vilardo et al. / Inorganica Chimica Acta 299 (2000) 135–141
2. Results and discussion
The reaction of the tetra-chlorides [Cp*TaCl4] and
[CpNbCl4] with [LiOC6HPh2-2,6-tBu2-3,5] leads to the
mixed cyclopentadienyl, aryloxides [Cp*Ta(OC6HPh2-
2,6-tBu2-3,5)Cl3] (2) and [CpNb(OC6HPh2-2,6-tBu2-
2.1. Synthesis and characterization of compounds
1
The 2,6-diphenyl-3,5-di-tert-butylphenoxide ligand
can be introduced onto early d-block metal centers via
two synthetic strategies. The first involves the addition
of the parent phenol [7] to a metal halide, dialkylamide
or alkyl derivative. In these cases formation of the
metal aryloxide is accompanied by the elimination of
HCl, HNMe2 or alkane, respectively. Alternatively, use
can be made of the lithium derivative [LiOC6HPh2-2,6-
tBu2-3,5] which has been shown to be soluble in ben-
zene and toluene solvents and to exist as a cyclic trimer
in the solid state [8]. The addition of the parent phenol
(2 equiv. per Nb) to a benzene solution of [Nb2Cl10]
leads to formation of the trichloride [Nb(OC6HPh2-2,6-
tBu2-3,5)2Cl3] (1) (Scheme 1), which is obtained as the
toluene solvate from toluene–hexane. The tantalum
analogue was previously obtained (as the benzene sol-
vate) and structurally characterized [6]. Despite the
non-equivalence of the aryloxide ligands in the solid
state (vide-infra) the 1H NMR spectrum of 1 shows
only one set of sharp ligand resonances indicating that
the molecule is fluxional on the NMR time-scale.
3,5)Cl3] (3), respectively (Scheme 1). In the H NMR
spectrum of 2 the C5Me5 protons resonate at l 1.88
ppm compared to l 2.16 ppm in [Cp*TaCl4]. Similarly
the C5H5 protons in 3 appear at l 5.66 ppm, upfield of
the position of l 6.02 ppm found in [CpNbCl4]. The
upfield shifting of these proton resonances can be ac-
counted for by the diamagnetic anisotropy of the adja-
cent aryloxide ligands. Previous studies have shown
that the ortho-phenyl rings of 2,6-diphenylphenoxide
ligands cause an upfield shift (diamagnetic shielding) of
adjacent protons within the metal coordination sphere
[6]. The decrease in conformational flexibility imparted
by meta-substituents correlates with an increase in this
upfield shifting.
The addition of HOC6HPh2-2,6-tBu2-3,5 to the pre-
cursor [Ta(NMe2)5] [9] results in the formation of the
mono-aryloxide
[Ta(OC6HPh2-2,6-tBu2-3,5)(NMe2)4]
(4)1,2. Further substitution of dimethylamido groups by
the bulky phenol does not occur over weeks at ambient
1
temperatures. The H NMR spectrum of 4 at ambient
temperatures shows only one set of NMe2 resonances.
Hence either a square pyramidal structure is adopted in
solution with an axial aryloxide or, more likely given
the observed solid-state structure (vide infra), the
molecule is highly fluxional in solution.
The niobium chloro, aryloxides [Nb(OAr)2Cl3] are
catalyst precursors for the hydrogenation of a variety of
arenes and aryl-phosphine substrates [10]. In the case of
2,6-diphenylphenoxide supporting ligands, studies have
shown that the ortho-phenyl rings undergo partial and
total hydrogenation, eventually leading to 2,6-di-cyclo-
hexylphenoxide groups, which yield the corresponding
phenol upon hydrolytic work-up [3]. We therefore
chose to investigate whether the presence of the meta-
tert-butyl groups in 1 (which shut down cyclometalla-
tion) would inhibit the intramolecular hydrogenation of
the adjacent phenyl rings. A solution of 1 in benzene
n
was activated with 3 equiv. of BuLi, pressurized with
H2, and heated at 100°C for 6 h. Work-up of the
resulting mixture resulted in the isolation of 2,6-dicyclo-
hexyl-3,5-di-tert-butylphenol (5). The solid-state struc-
ture of 5 (Fig. 1, Table 5) shows that the chair
cyclohexyl rings (phenoxide nucleus occupying an equa-
torial position) are oriented as shown for steric reasons
with the axial proton pointing towards the bulky meta-
substituent (Scheme 2). This is the exact conformation
1 Serious safety concerns have been raised dealing with the original
procedure.
Scheme 1.
2 For the synthesis of [Ta(NMe2)5], see [9b].

J.S. Vilardo et al. / Inorganica Chimica Acta 299 (2000) 135–141
137
Fig. 2. Molecular structure of [Nb(OC6HPh2-2,6-tBu2-3,5)2Cl3] (1).
Fig. 1. Molecular structure of 2,6-di-cyclohexyl-3,5-di-tert-butylphe-
nol (5).
interestingly the tri-iodide [Nb(OC6HPh4-2,3,5,6)2I3]
adopts a trigonal bipyramidal structure with trans axial
aryloxides [12]. The axial aryloxide in 1 has an essen-
tially linear NbꢁOꢁAr angle of 177.5(1)° while for the
basal aryloxide this angle is 141.3(1)°. It can be seen
that the bending of the basal aryloxide results in one of
Scheme 2.
previously predicted for the ligand 2,6-dicyclohexyl-3,5-
diphenylphenol on the basis of NMR data [3]. This
spectroscopic work implied that for 2,6-dicyclohexyl-
phenol and 2,6-dicyclohexyl-4-phenylphenol, the ortho-
cyclohexyl rings are oriented as shown in Scheme 2
with the axial proton pointing towards the hydroxyl
group.
Fig. 3. Molecular structure of [Cp*Ta(OC6HPh2-2,6-tBu2-3,5)Cl3] (2).
2.2. Solid-state structure of metal compounds
The molecular structures of compounds 1–4 are
shown in Figs. 2–5 while crystal data and data collec-
tion parameters are shown in Table 6. All four struc-
tures are best described as
a square pyramidal
arrangement of ligands about the central metal center
(Tables 1–4). In compound 1 there is an axial aryloxide
ligand. The (axial)OꢁNbꢁCl angles lie in the narrow
range of 102.11(4)–103.96(4)° with the (axial)-
OꢁNbꢁO(basal) angle of 105.30(6)° being only slightly
larger, presumably for steric reasons. A similar struc-
ture is found for other monomeric bis(aryloxides)
[M(OAr)2Cl3] of niobium and tantalum [11], although
Fig. 4. Molecular structure of [CpNb(OC6HPh2-2,6-tBu2-3,5)Cl3] (3).

138
J.S. Vilardo et al. / Inorganica Chimica Acta 299 (2000) 135–141
Table 3
,
Selected bond lengths (A) and angles (°) for [CpNb(OC6HPh2-2,6-
tBu2-3,5)Cl3] (3)
Bond lengths
NbꢁO(10)
NbꢁCl(1)
1.872(4)
2.420(1)
NbꢁCl(3)
NbꢁCl(2)
2.384(1)
2.388(2)
Bond angles
O(10)ꢁNbꢁCl(1)
O(10)ꢁNbꢁCl(2)
O(10)ꢁNbꢁCl(3)
Cl(1)ꢁNbꢁCl(2)
Cl(1)ꢁNbꢁCl(3)
Cl(3)ꢁNbꢁCl(2)
82.51(8)
136.5(1)
88.96(8)
81.86(6)
148.41(5)
83.73(6)
CpꢁNbꢁCl(1)
CpꢁNbꢁCl(2)
CpꢁNbꢁCl(3)
CpꢁNbꢁO(10)
NbꢁO(1)ꢁC(11)
105.9(3)
104.4(6)
104.9(3)
118.9(6)
155.2(3)
Table 4
Fig. 5. Molecular structure of [Ta(OC6HPh2-2,6-tBu2-3,5)(NMe2)4]
(4).
t
,
Selected bond lengths (A) and angles (°) for [Ta(OC6HPh2-2,6- Bu2-
3,5)(NMe2)4] (4)
Bond lengths
Table 1
t
TaꢁN(2)
TaꢁN(3)
TaꢁO(1)
2.016(6)
1.938(5)
1.950(3)
TaꢁN(4)
TaꢁN(5)
2.071(6)
1.985(6)
,
Selected bond lengths (A) and angles (°) for [Nb(OC6HPh2-2,6- Bu2-
3,5)2Cl3]0.5C7H8 (1)
Bond lengths
Bond angles
NbꢁCl(1)
NbꢁCl(2)
NbꢁCl(3)
2.3158(5)
2.3505(5)
2.3520(5)
NbꢁO(1)
NbꢁO(2)
1.809(1)
1.881(1)
O(1)ꢁTaꢁN(2)
O(1)ꢁTaꢁN(3)
O(1)ꢁTaꢁN(4)
O(1)ꢁTaꢁN(5)
N(2)ꢁTaꢁN(3)
N(2)ꢁTaꢁN(4)
86.3(2)
109.4(2)
85.2(2)
151.2(2)
98.0(3)
N(2)ꢁTaꢁN(5)
N(3)ꢁTaꢁN(4)
N(3)ꢁTaꢁN(5)
N(4)ꢁTaꢁN(5)
TaꢁO(1)ꢁC(11)
90.9(3)
100.5(2)
99.4(2)
88.4(3)
172.1(3)
Bond angles
Cl(1)ꢁNbꢁCl(2)
Cl(1)ꢁNbꢁCl(3)
Cl(2)ꢁNbꢁCl(3)
Cl(1)ꢁNbꢁO(1)
Cl(1)ꢁNbꢁO(2)
Cl(2)ꢁNbꢁO(1)
153.42(2)
87.23(2)
84.64(2)
103.96(4)
91.82(4)
102.47(4)
Cl(2)ꢁNbꢁO(2)
Cl(3)ꢁNbꢁO(1)
Cl(3)ꢁNbꢁO(2)
O(1)ꢁNbꢁO(2)
NbꢁO(1)ꢁC(11)
NbꢁO(2)ꢁC(21)
83.80(4)
102.11(4)
151.95(4)
105.30(6)
177.6(1)
141.3(1)
161.3(3)
respectively. As with compound 1, the basal aryloxide
is bent so that one of the ortho-phenyl rings occupies
the open site trans to the axial group.
Table 2
In all three tri-chlorides 1–3 the MꢁCl distances scan
,
Selected bond lengths (A) and angles (°) for [Cp*Ta(OC6HPh2-2,6-
tBu2-3,5)Cl3] (2)
,
the range 2.3158(5)–2.420(1) A. These distances are
well within the range found for neutral, monomeric
chloride derivatives of Nb(V) and Ta(V) [13].
Bond lengths
TaꢁO(10)
TaꢁCl(1)
1.902(3)
2.403(2)
TaꢁCl(3)
TaꢁCl(2)
2.328(1)
2.404(1)
The tetrakis(dimethylamido) derivative 4 can be seen
to have the aryloxide oxygen in a basal position. The
(axial)NꢁTaꢁN(basal) angles of 98.0(3)–100.5(2)° are
smaller than the (axial)NꢁTaꢁOAr angle of 109.4(2)°
again presumably for steric reasons. Again it can be
seen that the aryloxide wedge is oriented to bring the
ortho-phenyl ring into the vacant site, although in this
case the TaꢁOꢁAr angle is almost linear. Previously it
Bond angles
O(10)ꢁTaꢁCl(1)
O(10)ꢁTaꢁCl(2)
O(10)ꢁTaꢁCl(3)
Cl(1)ꢁTaꢁCl(2)
Cl(1)ꢁTaꢁCl(3)
Cl(3)ꢁTaꢁCl(2)
81.6(1)
84.1(1)
129.6(1)
149.96(5)
83.64(5)
85.38(5)
Cp*ꢁTaꢁCl(1)
Cp*ꢁTaꢁCl(2)
Cp*ꢁTaꢁCl(3)
Cp*ꢁTaꢁO(10)
TaꢁO(10)ꢁC(11)
105.4(2)
104.4(2)
104.4(1)
126.1(2)
149.9(3)
t
was shown that the bis(aryloxide) [Nb(OC6H2 Bu2-2,4-
Ph-6)2(NMe2)3] also adopted a square pyramidal geo-
metry with trans-basal aryloxide ligands [14].
The MꢁOAr distances for trichlorides 1–3, 1.809(1)–
the ortho-phenyl rings occupying the pocket trans to
the axial aryloxide.
,
1.902(3) A are slightly shorter than the value of
In compounds 2 and 3 the cyclopentadiene groups
occupy the axial site with a resulting four legged piano
stool geometry. In both compounds the Cp*(Cp)ꢁMꢁCl
angles lie in the very narrow range of 104.4(1)–
105.9(3)°. However the Cp*(Cp)ꢁMꢁOAr angle is
opened up to 126.1(2)° and 118.9(6)° for 2 and 3,
[Ta(OC6HPh2-2,6-tBu2-
,
1.950(3)
A
found
in
3,5)(NMe2)4] (4). In the latter compound one would
predict that the presence of the four p-donating
dimethylamido groups [15] would decrease the amount
of aryloxide oxygen-p to metal-d p-bonding, hence

J.S. Vilardo et al. / Inorganica Chimica Acta 299 (2000) 135–141
139
Table 5
Selected bond lengths (A) [HOC6HCy2-2,6- Bu2-3,5] (5)
fraction studies were also carried out ‘in house’ at
Purdue University. General operating procedures have
been reviewed elsewhere [18]. High-pressure reactions
using hydrogen gas were performed using a Parr Instru-
ment, Model 4561, 300 ml stainless steel, bench top
mini-reactor equipped with a pressure gauge, thermo-
couple and a gas inlet–outlet system. The reactors were
thermally controlled using a Parr 4841 proportional
controller. Preparative layer chromatography plates
(silica gel 60 F254, 200 mm×200 mm×2 mm) were
purchased from EM Separations.
t
,
OꢁC(1)
1.380(3)
1.401(2)
1.406(2)
1.526(2)
1.395(2)
1.545(2)
1.521(3)
1.524(3)
C(22)ꢁC(23)
C(23)ꢁC(24)
C(24)ꢁC(25)
C(25)ꢁC(26)
C(31)ꢁC(33)
C(31)ꢁC(34)
C(31)ꢁC(32)
1.512(3)
1.508(3)
1.505(3)
1.513(3)
1.533(3)
1.537(3)
1.546(3)
C(1)ꢁC(2)
C(2)ꢁC(3)
C(2)ꢁC(21)
C(3)ꢁC(4)
C(3)ꢁC(31)
C(21)ꢁC(22)
C(21)ꢁC(26)
leading to the observed elongation. It is interesting that
,
the shortest, 1.809(1) A in 1, and the longest, 1.950(3)
3.2. Synthesis of the compounds
,
A in 4, MꢁOAr distances are both associated with
essentially linear MꢁOꢁAr angles. The failure of the
MꢁOꢁAr angle as a measure of p-donation has been
noted [16].
3.2.1. [Nb(OC6HPh2-2,6-tBu2-3,5)2Cl3] (1)
To a benzene solution of [Nb2Cl10] (3.8 g, 14 mmol)
was added
2
equiv. of 3,5-di-tert-butyl-2,6-di-
phenylphenol (10.0 g, 28 mmol). HCl gas was evolved
and the reaction mixture was refluxed for approxi-
mately 1 h. The solvent was then removed under vac-
3. Experimental
uum yielding
a light orange solid, which was
3.1. General
recrystallized from toluene–hexane giving 1 as large
purple crystals (toluene solvate, 10.3 g, 81%). Anal.
Calc. for C55.5H62Cl3ONb·1/2C7H8: C, 69.41; Cl, 11.07;
H, 6.51. Found: C, 68.85; Cl, 11.25; H, 6.45%. 1H
NMR (C6D6, 30°C): l 7.73 (s, 2H, para-H); 7.30–7.10
(m, 20H, aromatics); 1.16 (s, 36H, CMe3).
All operations were carried out under a dry nitrogen
atmosphere using standard Schlenk techniques [17].
The hydrocarbon solvents were distilled from sodium
benzophenone and stored over sodium ribbons under
nitrogen until use. Reagents were purchased from
1
Aldrich and used without further purification. The H
3.2.2. [Cp*Ta(OC6HPh2-2,6-tBu2-3,5)Cl3] (2)
and 13C NMR spectra were recorded on a Varian
Associates Gemini-200 spectrometer and referenced to
protio impurities of commercial benzene-d6 or deuter-
ated chloroform as internal standards. Mass spectra,
elemental analyses and molecular structures were ob-
tained in-house at Purdue University. The X-ray dif-
To a stirred solution of [Cp*TaCl4] (0.6 g, 1.3 mmol)
in benzene (10 ml) was added lithium-2,6-diphenyl-3,5-
di-tert-butylphenoxide (0.48 g, 1.3 mmol). The solution
immediately became orange. The solution was stirred
for 24 h, filtered, and the solvent removed under vac-
uum. The remaining orange powder was recrystallized
Table 6
Crystal data and data collection parameters
1
2
3
4
5
Formula
NbCl3O2C52H58·1/2C7H8 TaCl3OC36H44
NbCl3OC31H34·C6H6 TaN4O2C34H53
C26H42O
Formula weight
Space group
960.38
P1 (no. 2)
780.06
P21/n (no. 14)
700.00
C2/c (no. 15)
714.78
P21/n (no. 14)
370.62
I2/a (no. 15)
Unit cell dimensions
,
a (A)
10.3762(19)
13.0571(14)
19.948(2)
70.703(8)
84.378(13)
78.429(13)
2497.5(7)
2
18.2271(4)
9.9041(2)
20.1969(4)
90
115.4930(13)
90
3291(2)
4
1.574
28.5355(10)
16.3062(8)
18.6971(5)
90
128.094(2)
90
6846.8(9)
8
1.358
16.0424(5)
11.8157(3)
18.1424(6)
90
91.4216(16)
90
3437.9(3)
4
1.381
9.7614(19)
20.610(4)
11.514(2)
90
99.787(16)
90
2282.7(14)
4
1.577
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
V (A )
3
,
Z
Dcalc (g cm−3
)
1.277
Temperature, K
203.
203.
296.
203.
296.
,
,
,
,
,
Radiation (wavelength) Mo Ka (0.71073 A)
Mo Ka (0.71073 A) Mo Ka (0.71073 A)
Mo Ka (0.71073 A) Mo Ka (0.71073 A)
0.043
0.102
R
0.033
0.047
0.043
0.106
0.065
0.174
0.046
0.121
Rw

140
J.S. Vilardo et al. / Inorganica Chimica Acta 299 (2000) 135–141
as X-ray quality crystals from a minimum amount of
hexane giving (0.8 g, 78%). Anal. Calc. for
contained the 2,6-dicyclohexyl-3,5-di-tert-butylphenol
(5) (240 mg, 73%). White crystals of the phenol were
grown by slow evaporation of a CH2Cl2 solution. H
NMR (C6D6, 30°C): l 7.22 (s, 1H, para-H), 4.97 (s,
1H, OH), 3.32 (tt, 2H), 1.6–2.2 (m), 1.37(s, 9H, CMe3).
13C{1H} NMR (C6D6, 30°C): l 157.1 (CꢁOH), 145.1,
129.5, 117.2, 36.2 (CMe3), 31.9 (CMe3), 53.0, 39.7, 30.0,
27.6. EI MS: 57(100), 287(3.9), 370(M+, 19.2). CI MS:
315(28.8), 371(MH+, 100).
2
1
C36H44Cl3OTa: C, 55.43; H, 5.69; Cl, 13.63. Found: C,
1
55.82; H, 5.73; Cl, 13.37%. H NMR (C6D6, 30 °C): l
7.82 (s, 1H para-H); 7.71–7.05 (m, 18H, aromatics);
1.88 (s, 15H, C5Me5); 1.11 (s, 36H, CMe3). Selected 13C
NMR (C6D6, 30 °C): l 165.3 (TaOC); 37.9 (CMe3);
33.2 (CMe3); 14.2 (C5Me5); 12.8 (C5Me5).
3.2.3. [CpNb(OC6HPh2-2,6-tBu2-3,5)Cl3] (3)
To a stirred solution of [CpNbCl4] (1.0 g, 3.3 mmol)
in toluene (50 ml) was added lithium-2,6-diphenyl-3,5-
di-tert-butylphenoxide (1.2 g, 3.3 mmol). The solution
immediately became purple. The solution was stirred
for 24 h, filtered, and the solvent removed under vac-
uum. The remaining purple powder was recrystallized
as X-ray quality crystals from a minimum amount of
4. Supplementary material
Crystal data and data collection parameters are con-
tained in Table 6. Crystallographic data for the struc-
tural analyses have been deposited with the Cambridge
Crystallographic Data Center, CCDC nos. 135067 (1),
135068 (2), 135069 (3), 135070 (4) and 135071 (5).
Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road,
Cambridge, CB2 1EZ (fax: +44-1223-336033 or e-
mail: deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.
ac.uk).
1
hot benzene giving 3 (1.45 g, 70%). H NMR (C6D6,
30°C): l 7.81 (s, 1H, para-H); 7.43–7.05 (m, 10H,
aromatics); 5.66 (s, 5H, C5H5); 1.15 (s, 36H, CMe3).
Selected 13C NMR (C6D6, 30°C): l 168.9 (NbOC);
121.7 (C5H5); 37.6 (CMe3); 32.9 (CMe3).
3.2.4. [Ta(OC6HPh2-2,6-tBu2-3,5)(NMe2)4] (4)
To a benzene (5.0 ml) solution of [Ta(NMe2)5] (0.50
g, 1.2 mmol), was slowly added 1.0 equiv. of 2,6-
diphenyl-3,5-di-tert-butylphenol (0.44 g, 1.2 mmol).
The resulting yellow solution was stirred for 6 h and the
solvent was removed in vacuo resulting in an off-white
powder, which was recrystallized from benzene–hexane
yielding X-ray quality crystals (0.41 g, 46%). Anal.
Calc. for C34H53N4OTa: C, 57.13; H, 7.47; N, 7.84.
Acknowledgements
We thank the National Science Foundation (Grant
CHE-9700269) for financial support of this research.
References
1
Found: C, 56.31; H, 7.23; N, 7.05%. H NMR (C6D6,
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.