Group 4 and 5 metal derivatives of 2,2'-methylene-bis(6-phenylphenoxide)

Article abstract of DOI:10.1016/S0277-5387(99)00319-8

Addition of the phenol 2,2'-methylene-bis(6-phenylphenol) [(HOC₆H₃Ph)₂CH₂] (1) (1 equiv. per Ti) to hydrocarbon solutions of [TiCl₄] or [Ti(OPr(i))₄] leads to dimeric products [Ti{(OC₆H₃Ph)₂CH₂}Cl₂]₂ (2) and [Ti{(OC₆H₃Ph)₂CH₂} (μ-OPr(i)) (OPr(i))]₂ (3). Structural studies show 2 (CHCl₃ solvate) to consist in the solid state of two tetrahedral titanium centers linked by one end of two di-aryloxide ligands. In contrast, 3 contains five-coordinate titanium atoms linked directly by two bridging isopropoxide ligands. Treatment of [MCl₅] (M = Nb, Ta) with 1 equiv. of 1 leads to sparingly soluble trichlorides 4 and 5 which react with pyridine to form soluble adducts [M{(OC₆H₃Ph)₂CH₂}Cl₃(py)] (M = Nb, 6; M=Ta, 7). Compounds 6 and 7 are isostructural in the solid state (benzene solvates) with a mer arrangement of chloride groups and the pyridine trans to one of the di-aryloxide oxygen atoms. Treatment of 7 with PMe₂Ph leads to the products [Ta{(OC₆H₃Ph)₂CH₂}Cl₃(PMe₂Ph)] (8) and [HPMe₂Ph] [Ta{(OC₆H₃Ph)₂CH₂}Cl₄] (9). Structurally characterized 9 (benzene solvate) presumably arises via the presence of trace amounts of water during workup. Reaction of 1 with [Ta(NMe₂)₅] allows isolation of derivatives [Ta{(OC₆H₃Ph)₂CH₂ }₂(NMe₂) (HNMe₂)] (10) (cis-nitrogen atoms by NMR) and [H₂NMe₂] [Ta{(OC₆H₃Ph)₂CH₂}₃] (11) depending on the stoichiometry. The anion in 11 was shown by crystallography to contain an octahedral arrangement of oxygen atoms about the tantalum metal center. The crystallographic study of 11 is complicated by a disorder of the cation and partial occupancies for the three types of benzene solvate molecule. The niobium trichloride 4 acts as a catalyst precursor for benzene hydrogenation although with lower activity than reported for monodentate aryloxide precursors. During the catalysis the ortho-phenyl rings of the di-aryloxide ligand are not hydrogenated. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0277-5387(99)00319-8

www.elsevier.nl/locate/poly
Polyhedron 19 (2000) 35–42
Group 4 and 5 metal derivatives of 2,29-methylene-bis(6-
phenylphenoxide)
*
Douglas R. Mulford, Phillip E. Fanwick, Ian P. Rothwell
Department of Chemistry, 1393 Brown Building, Purdue University, West Lafayette, IN 47907, USA
Received 21 June 1999; accepted 29 September 1999
Abstract
Addition of the phenol 2,29-methylene-bis(6-phenylphenol) [(HOC6H3Ph)2CH2] (1) (1 equiv. per Ti) to hydrocarbon solutions of
[TiCl4] or [Ti(OPri)4] leads to dimeric products [Ti{(OC6H3Ph)2CH2}Cl2]2 (2) and [Ti{(OC6H3Ph)2CH2}(m-OPri)(OPri)]2 (3).
Structural studies show 2 (CHCl3 solvate) to consist in the solid state of two tetrahedral titanium centers linked by one end of two di-aryloxide
ligands. In contrast, 3 contains five-coordinate titanium atoms linked directly by two bridging isopropoxide ligands. Treatment of [MCl5]
(MsNb, Ta) with 1 equiv. of 1 leads to sparingly soluble trichlorides 4 and 5 which react with pyridine to form soluble adducts
[M{(OC6H3Ph)2CH2}Cl3(py)] (MsNb, 6; MsTa, 7). Compounds 6 and 7 are isostructural in the solid state (benzene solvates) with a
mer arrangement of chloride groups and the pyridine trans to one of the di-aryloxide oxygen atoms. Treatment of 7 with PMe2Ph leads to the
products [Ta{(OC6H3Ph)2CH2}Cl3(PMe2Ph)] (8) and [HPMe2Ph][Ta{(OC6H3Ph)2CH2}Cl4] (9). Structurally characterized 9 (benzene
solvate) presumably arises via the presence of trace amounts of water during workup. Reaction of 1 with [Ta(NMe2)5] allows isolation of
derivatives [Ta{(OC6H3Ph)2CH2}2(NMe2)(HNMe2)] (10) (cis-nitrogen atoms by NMR) and [H2NMe2][Ta{(OC6H3Ph)2CH2}3] (11)
depending on the stoichiometry. The anion in 11 was shown by crystallography to contain an octahedral arrangement of oxygen atoms about
the tantalum metal center. The crystallographic study of 11 is complicated by a disorder of the cation and partial occupancies for the three
types of benzene solvate molecule. The niobium trichloride 4 acts as a catalyst precursor for benzene hydrogenation although with lower
activity than reported for monodentate aryloxide precursors. During the catalysis the ortho-phenyl rings of the di-aryloxide ligand are not
hydrogenated.
q2000 Elsevier Science Ltd All rights reserved.
Keywords: Titanium; Tantalum; Nobium; Aryloxide; Bisphenol; Hydrogenation
1. Introduction
2. Results and discussion
There has recently been increased interest in the chemistry
of 2,6-di-aryl-phenoxide ligation attached to early d-block
metal centers [1–8]. Part of this work has been stimulated
by the demonstrated ability of niobium and tantalum hydride
compounds containing aryloxide ligation to catalyze the
hydrogenation of a variety of arene substrates [9]. In the case
of 2,6-diphenylphenoxide ligands, both partial andtotalintra-
molecular hydrogenation of ortho-phenyl rings has been
observed [10,11]. As an extension of this research we have
examined the early d-block metal chemistry of the chelating
2.1. Synthesis and spectroscopy of compounds
The addition of the parent phenol 2,29-methylene-bis(6-
phenylphenol) ((HOC6H3Ph)2CH2 1) (1 equiv. per Ti) to
hydrocarbon solutions of [TiCl4] or [Ti(OPri)4] leads to
formation of the corresponding mono(di-aryloxide) com-
pounds 2 and 3 respectively (Scheme 1). The di-chloride 2
is only sparingly soluble and hence purification was difficult.
The 1H NMR spectrum of 2 in C6D6 is not very informative,
showing, in addition to the aromatic resonances, a single pair
of doublets for the methylene protons CH2 of the ligand.
Previous work on 2,29-methylene-bisphenoxides [13–17]
has shown that the puckered eight-membered ring formed by
chelation to metal centers undergoes slow flipping on the
NMR timescale. Hence the methylene protons in the chelate
backbone are typically diastereotopic at ambient tempera-
tures. The 1H NMR spectral data for 3 are equally uninform-
ligand
2,29-methylene-bis(6-phenylphenol)
[(HOC6H3Ph)2CH2] (1) [12]. This paper reports the syn-
thesis and characterization of Group 4 and 5 metalderivatives
of this ligand as well as an evaluation of the hydrogenation
activity of niobium and tantalum catalyst precursors.
* Corresponding author. Tel.: q1-765-494-7012; fax: q1-765-494-0239;
e-mail: rothwell@chem.purdue.edu
0277-5387/00/$ - see front matter q2000 Elsevier Science Ltd All rights reserved.
PII S0277-5387(99)00319-8
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D.R. Mulford et al. / Polyhedron 19 (2000) 35–42
In the case of 4 and 5, the bidentate aryloxide is probably not
sufficiently bulky to generate a monomeric environment. A
dimeric structure in hydrocarbon solvents is consistent with
the low solubility, but whether there are chloride or aryloxide
bridges is unknown. The addition of the donorligandpyridine
leads
to
much
more
soluble
adducts
[M{(OC6H3Ph)2CH2}Cl3(py)] (MsNb, 6; M5Ta, 7,
Scheme 2). In the 1H NMR spectra of 6 and 7 (Fig. 1), well
resolved sharp multiplets are observed. The diastereotopic
methylene protons in the chelate ring are separated by over
2 ppm. The solid state structure (vide infra) would lead to a
virtual plane of symmetry in the molecule if the eight-mem-
bered chelate were undergoing rapid flipping. The sharp AX
pattern observed for the methylene group of 6 and 7 shows
that inversion is much slower than the NMR timescale. A
similar phosphine adduct of 7 is generated by addition of
PMe2Ph. In this case the resulting product 8 shows broad
ligand resonances consistent with partial ligand dissociation
in solution. During the workup of 8, a few well-formed crys-
tals
of
a
salt
identified
as
[HPMe2Ph][Ta{(OC6H3Ph)2CH2}Cl4] (9) were obtained.
It is believed that adventitious amounts of water led to the
formation of 9 which has the elements of HCl added to 8.
The addition of 1 to [Ta(NMe2)5] is found to lead to a
mixture of substitution products (serious safety concerns
have been raised with respect to the original procedure [21],
for the synthesis of [Ta(NMe2)5], see [22]). With 2 equiv.
of 1, a six-coordinate dimethylamine adduct is produced of
formula [Ta{(OC6H3Ph)2CH2}2(NMe2)(HNMe2)] (10)
(Scheme 2). In the 1H NMR spectrum of 10 two diastereo-
topic methylene groups CH2 indicate non-equivalence of the
two di-aryloxide ligands. The spectrum also shows a pair of
broad doublets at d 1.73 and 0.87 ppm. These we assign to
the diastereotopic HNMe2 methyl groups shifted upfield of
their normal position by the anisotropy of adjacent phenyl
groups of the aryloxides. Two geometries are possible for
six-coordinate 10 (Scheme 2). In one the amine is located
trans to the amido nitrogen while in the second these groups
are mutually cis. The assigned cis-geometry (Scheme 2)
automatically gives rise to non-equivalent di-aryloxide
groups as well as diastereotopic HNMe2 methyl groups. Even
if the di-aryloxide rings in the trans geometry fold so as to
become non-equivalent, they will still maintain a plane of
symmetry through the Ta-HNMe2 group. The reaction of
[Ta(NMe2)5] with the bulkier ligand 2,29-methylene-bis(6-
tert-butyl-4-methylphenoxide) has been shown to produe
[Ta{(OC6H2But-6-Me-4)2CH2}(NMe2)3] with one amide
and di-aryloxide oxygen atom trans within a tbp structure
[16]. When more than 2 equiv. of 1 are reacted with
[Ta(NMe2)5], a mixture (NMR) is produced from which a
sparingly soluble product 11 precipitates. This compound
was identified by crystallographic methods as a salt,
[H2NMe2][Ta{(OC6H3Ph)2CH2}3] (11). Disorder of the
cation and the presence of three benzene molecules of solvate
complicated solution of the crystal structure of 11. Two of
the benzene molecules had partial occupancies of 0.59 and
Scheme 1.
ative, simply showing broad resonances for the di-aryloxide
ligands and OPri groups.
The reaction of 1 with the chlorides [M2Cl10] (MsNb,
Ta)
produces
sparingly
soluble
trichlorides
[M2{(OC6H3Ph)2CH2}Cl3] (MsNb, 4; MsTa, 5)
(Scheme 2). Previous work with monodentatearyloxideshas
shown that for bulky ligands square pyramidal structures are
formed for trichlorides [M(OAr)2Cl3] (MsNb, Ta;
OArsOC6H3But2-2,6, various 2,6-diphenylphenoxides)
with an axial aryloxide [18,19]. With a slightly smaller ary-
loxide a dimeric structure [(ArO)2Cl2Ta(m-Cl)]2 isformed,
where the 2,6-di-isopropylphenoxide ligands are trans to the
bridging chloride groups [20]. Previously the compound
[Nb{(OC6H2But2-4,6)2CH2}2Cl] has been reported and
shown to adoptatbp structurewithanequatorialcloride[17].
Scheme 2.
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D.R. Mulford et al. / Polyhedron 19 (2000) 35–42
37
Table 2
Selected
0.72, respectively, possibly due to loss of solvent from the
unit cell. However, the anion clearly contains a tantalum
metal center chelated by three di-aryloxide ligands (vide
infra).
˚
bond
distances
(A)
and
angles
(8)
for
[Nb{(OC6H3Ph)2CH2}Cl3(py)]P1/2C6H6 (6)
Nb–O(2)
Nb–O(1)
Nb–N
1.867(2)
1.863(2)
2.329(3)
Nb–Cl(1)
Nb–Cl(2)
Nb–Cl(3)
2.371(1)
2.377(1)
2.383(1)
2.2. Structural studies
O(1)–Nb–O(2)
O(1)–Nb–N
O(1)–Nb–Cl(1)
O(1)–Nb–Cl(2)
O(1)–Nb–Cl(3)
O(2)–Nb–N
O(2)–Nb–Cl(1)
O(2)–Nb–Cl(2)
Nb–O(2)–C(13)
93.0(1)
174.2(1)
99.06(9)
93.80(8)
91.45(8)
88.1(1)
88.69(8)
172.53(9)
161.6(2)
O(2)–Nb–Cl(3)
N–Nb–Cl(1)
N–Nb–Cl(2)
93.14(9)
86.62(9)
85.39(8)
82.84(9)
87.26(5)
91.45(3)
89.81(4)
141.5(2)
The solid-state structures of 2, 6, 7, 9 and 11 were deter-
mined (Tables 1–5, Figs. 2–6). All five compounds formed
crystals containing solvent molecules within the unit cell. In
the case of 2, two molecules of chloroform per di-titanium
unit were present while the other four compounds contained
varying amounts of benzene of solvation. Previous work on
the bulky ligand 2,29-methylene-bis(6-tert-butyl-4-methyl-
phenol) ((HOC6H2But-6-Me-4)2CH2) has led to the isola-
N–Nb–Cl(3)
Cl(1)–Nb–Cl(2)
Cl(1)–Nb–Cl(3)
Cl(2)–Nb–Cl(3)
Nb–O(1)–C(1)
tion
of
a
series
of
monomeric
species
[Ti{(OC6H2But-6-Me-4)2CH2}X2] (XsCl, OR, R) [13].
Fig. 1. 1H NMR (C6D6, 500 MHz) of [Nb{(OC6H3Ph)2CH2}Cl3(py)] (6).
Table 3
Selected
Structural studies show a pseudo-tetrahedral geometry about
Ti with O–Ti–O angles of 106.5(2)8 (XsCl) and 112.7(2)8
(XsMe). In the case of the dichloride a five-coordinate thf
adduct was also isolated and structurally characterized as
Table 1
˚
bond
distances
(A)
and
angles
(8)
for
[Ta{(OC6H3Ph)2CH2}Cl3(py)]P1/2C6H6 (7)
Ta–O(2)
Ta–O(1)
Ta–N
1.865(2)
1.871(2)
2.311(3)
Ta–Cl(1)
Ta–Cl(2)
Ta–Cl(3)
2.360(1)
2.376(1)
2.368(1)
˚
Selected
bond
distances
(A)
and
angles
(8)
for
[Ti{(OC6H3Ph)2CH2}Cl2]2P2CHCl3 (2)
O(1)–Ta–O(2)
O(1)–Ta–N
O(1)–Ta–Cl(1)
O(1)–Ta–Cl(2)
O(1)–Ta–Cl(3)
O(2)–Ta–N
O(2)–Ta–Cl(1)
O(2)–Ta–Cl(2)
Ta–O(2)–C(13)
93.8(1)
88.1(1)
O(2)–Ta–Cl(3)
N–Ta–Cl(1)
N–Ta–Cl(2)
91.57(9)
86.40(9)
85.15(9)
83.4(1)
87.38(5)
169.63(3)
89.73(5)
161.5(2)
Ti–O(10)
Ti–O(20)
1.746(5)
1.754(5)
Ti–Cl(1)
Ti–Cl(2)
2.216(3)
2.219(3)
89.21(9)
172.60(8)
92.48(8)
174.7(1)
98.53(9)
93.20(9)
139.9(2)
N–Ta–Cl(3)
Cl(1)–Ta–Cl(2)
Cl(1)–Ta–Cl(3)
Cl(2)–Ta–Cl(3)
Ta–O(1)–C(1)
O(10)–Ti–O(20)
O(10)–Ti–Cl(1)
O(10)–Ti–Cl(2)
O(20)–Ti–Cl(1)
111.7(2)
110.0(2)
111.1(2)
109.4(2)
Cl(1)–Ti–Cl(2)
C(11)–O(10)–Ti
C(21)–O(20)–Ti
O(20)–Ti–Cl(2)
105.9(1)
161.9(5)
168.2(5)
108.6(2)
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D.R. Mulford et al. / Polyhedron 19 (2000) 35–42
Table 4
Selected
about the metal center. In contrast the dichloride 2 can be
seen to adopt a dinuclear structure in the solid state (Fig. 2).
Each Ti metal center is pseudo-tetrahedral and bound to one
end of two di-aryloxides. The O–Ti–O angle is 111.7(2)8,
only slightly larger than that found for [Ti{(OC6H2But-6-
Me-4)2CH2}Cl2]. The question arises as to what factors are
important in determining whether a monomeric structure is
formed or a dimeric unit as in 2. The dimeric structure does
˚
bond
distances
(A)
and
angles
(8)
for
[HPMe2Ph][Ta{(OC6H3Ph)2CH2}Cl4]PC6H6 (9)
Ta–Cl(1)
Ta–Cl(2)
Ta–Cl(3)
2.384(1)
2.416(1)
2.400(1)
Ta–Cl(4)
Ta–O(1)
Ta–O(9)
2.422(1)
1.851(3)
1.892(3)
O(1)–Ta–O(9)
O(1)–Ta–Cl(1)
O(1)–Ta–Cl(2)
O(1)–Ta–Cl(3)
O(1)–Ta–Cl(4)
O(9)–Ta–Cl(1)
O(9)–Ta–Cl(2)
O(9)–Ta–Cl(3)
91.5(1)
92.0(1)
177.1(1)
89.7(1)
92.8(1)
88.7(1)
88.1(1)
94.2(1)
O(9)–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)
174.5(1)
90.8(5)
176.5(1)
92.7(1)
87.5(1)
87.8(1)
89.3(1)
Table 5
Selected
˚
bond
distances
(A)
and
angles
(8)
for
[H2NMe2][Ta{(OC6H3Ph)2CH2}3]P2.31C6H6 (11)
Ta–O(11)
Ta–O(12)
Ta–O(21)
1.939(5)
1.941(5)
1.938(5)
Ta–O(22)
Ta–O(31)
Ta–O(32)
1.973(9)
2.014(9)
1.96(1)
O(11)–Ta–O(12)
O(21)–Ta–O(22)
O(31)–Ta–O(32)
O(12)–Ta–O(22)
O(21)–Ta–O(31)
O(11)–Ta–O(32)
92.7(2)
93.8(2)
89.8(2)
88.8(2)
87.9(2)
88.7(2)
O(12)–Ta–O(32)
O(22)–Ta–O(31)
O(11)–Ta–O(21)
O(12)–Ta–O(31)
O(22)–Ta–O(32)
90.8(2)
90.7(2)
176.1(2)
178.8(2)
176.0(2)
Fig. 4. Molecular structure of [Ta{(OC6H3Ph)2CH2}Cl3(py)]P1/2C6H6
(7).
Fig.
5.
Molecular
structure
of
Fig. 2. Molecular structure of [Ti{(OC6H3Ph)2CH2}Cl2]2P2CHCl3 (2).
[HPMe2Ph][Ta{(OC6H3Ph)2CH2}Cl4]PC6H6 (9).
Fig. 3. Molecular structure of [Nb{(OC6H3Ph)2CH2}Cl3(py)]P1/2C6H6
(6).
pseudo-trigonal bipyramidal about Ti with the thf axial and
trans to one end of the chelating di-aryloxide [15]. The O–
Ti–O angle of 96.2(1)8 for the chelate shows the flexibility
of the eight-membered ring in occupying coordination sites
Fig. 6. Molecular structure of [H2NMe2][Ta{(OC6H3Ph)2CH2}3]PC6H6
(11).
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D.R. Mulford et al. / Polyhedron 19 (2000) 35–42
39
not contain either chloro or oxygen bridges which might
alleviate the electron deficiency of the metal center. It may
very well be that the bulkier ortho-tert-butyl substituentspre-
clude formation of a dimer. However, an electronic rationale
for the dimeric structure is that it allows for larger Ti–O–Ar
angles. In monomeric [Ti{(OC6H2But-6-Me-4)2CH2}Cl2]
these angles are 143.6(4) and 155.8(4)8 while in 2 they open
up to 161.9(5) and 168.2(5)8. This could imply greater oxy-
gen-p to metal-d p-bonding. However, the Ti–O distances in
angle in 9 of 91.5(1)8 accommodates the octahedral geom-
etry very well. The bite of the three chelates in the anion of
11 scans the range 89.8(2)–93.8(2)8. Also in tris(chelate)
11 the folding of the chelate rings is such that there are two
types of di-aryloxide. Unfortunately the lack of solubility of
this compound precluded confirmation of this by NMR. The
closest analog of 9 is the salt [HPMe2Ph][Nb(OC6H3Pri2-
2,6)3Cl3] formed as a minor product by addition of PMe2Ph
to [Nb(OC6H3Pri2-2,6)2Cl3] [20]. The anion in
tris(chelate) 11 can be related to the hexa(aryloxide) anion
[Nb(OC6H3Me2-3,5)6] [28].
[Ti{(OC6H2But-6-Me-4)2CH2}Cl2],
1.760(4)
and
˚
1.742(4) A, are essentially identical to values of 1.746(5)
˚
and 1.754(5) A found for 2. It is now well established that
the degree of p-donation does not correlate with M–O–Ar
angles for early d-block metal aryloxides [23,24]. It appears
that a larger database of related compounds is needed to reach
any conclusions concerning the relative stabilities of these
two structural motifs. The formation of dimericunitshasbeen
enforced by use of fluorenediol ligation where the di-arylox-
ide structure precludes chelation [25].
A data set collected on the isopropoxide 3 indicates a
dimeric structure in the solid state with terminal chelated di-
aryloxide and bridging isopropoxides as shown in Scheme 1.
Unfortunately the refinement could not be completed owing
to disorder among the methyl units of the Pri groups [26]. It
would appear in this case that the electron deficiency of the
titanium atoms is relieved by the formation of alkoxide
bridges leading to a pseudo square pyramidal geometryabout
each metal center.
Both of the pyridine adducts 6 and 7 have been structurally
characterized (Figs. 3 and 4). A large number of adducts
[M(OAr)x(Cl)5yx(L)] (MsNb, Ta; OArsvarious mon-
odentate aryloxides; LsO, N or P donor ligands) have been
reported [20]. Structural studies of the tri-chlorides (xs3)
show a cis-mer geometry with the donor ligand trans to one
of the aryloxides. These molecules consistently show a dis-
tortion from octahedral geometry in which four of the anionic
ligands are bent towards the cis-donor ligand. This distortion
has been studied theoretically [20,27]. It can be seen that
compounds 6 and 7 are related to the previously isolated
monodentate aryloxide complexes. The chloride ligands are
arranged in a mer fashion with the pyridine trans to one of
the chelating aryloxide oxygen atoms. The O–M–O angles
are 93–948, again showing the flexibility of this ligand. The
metal–ligand distances (Tables 2 and 3) are very similar to
those reported for cis-mer-[M(OC6H3Pri2-2,6)2Cl3(py)]
(MsNb, Ta). In order to quantify the distortion from octa-
hedral geometry in adducts of this type, the parameter Sa
defined as follows, SasS[(cis-L-M-X)y90], was intro-
duced [20]. The value of Sa is y17.6 and y17.0 for 6 and
7, respectively. These values are slightly smaller than values
of y23.5 and y22.6 found in cis-mer-[M(OC6H3Pri2-
2,6)2Cl3(py)] (MsNb, Ta) but still indicate a significant
distortion from octahedral geometry.
2.3. Reactivity studies
The potential of the trichloride compounds 4 and 5 as
catalyst precursors for the hydrogenation of arene rings was
evaluated. A sample of the trichloride (0.5 mmol)wasplaced
in benzene and activated with a standardized solution of n-
BuLi (3 equiv.). The resulting mixture (20 ml total volume)
was pressurized with H2 (1200 psi) and heated at 1208C for
24 h. The tantalum compound showed no detectable activity
for benzene hydrogenation. However, the niobium precursor
4 did produce cyclohexane (80 equiv. per Nb). This com-
pares with 240 equiv. previously reported to be produced by
the precursor [Nb(OC6HPh4-2,3,5,6)2Cl3] under the same
conditions [9]. Under these conditions in the presence of 20
equiv. of PPh3, compound 4 showed some conversion to
PCyPh2 and PCy2Ph, but the activity was much lower than
when the monodenate precursor [Nb(OC6HPh4-
2,3,5,6)2Cl3] was used. Analysis of these reaction mixtures
after hydrolysis showed (NMR and GC) the presence of 1
with only very minor signals that may be attributable to
cyclohexyl phenols. It therefore appears that the chelation of
the di-aryloxide at niobium metal centers inhibits the intra-
molecular hydrogenation of theortho-phenyl rings, areaction
that is facile for monodentate ortho-phenylphenoxides
[10,11].
3. Experimental
3.1. General
All operations were carried out under a dry nitrogenatmos-
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. Reagents were purchased from
˚
Aldrich Chemical Co. and were dried over 3 A molecular
sieves prior to use. The 1H NMR spectra were recorded on a
Varian Associates Gemini 200 and a General Electric QE-
300 spectrometer and were referenced using protioimpurities
of commercial benzene-d6 as an internal standard. Microan-
alytical data were obtained in-house at Purdue. All high-
pressure reactions were performed in a Parr model 4561, 300
The molecular structures of the anions in 9 and 11 (Figs.
5 and 6) are unexceptional. In both cases the geometry about
the metal center is very close to octahedral. The O–Ta–O
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D.R. Mulford et al. / Polyhedron 19 (2000) 35–42
ml internal volume minireactor. The X-ray diffractionstudies
were completed in-house at Purdue University.
resulting solution was stirred for 1 day during which time the
solution changed from brown to red. The solutionwaslayered
with pentane and the resulting solid 6 was washed once with
pentane and dried in vacuo. Yield 0.48 g (83.0%). Anal.
Calc. for NbNO2Cl3C30H23P0.5C6H6: C, 59.35; H, 3.92; N,
2.10; Cl, 15.92. Found: C, 58.82; H, 4.06; N, 2.14; Cl,
16.04%. 1H NMR (C6D6, 308C): d 8.48 (d, aromatic); 7.83
(d, aromatic); 7.48 (t, aromatic); 7.16 (d, aromatic); 6.78
(t, aromatic); 6.70 (t, aromatic); 6.51 (t, aromatic); 6.39 (d,
aromatic); 5.93 (t, aromatic); 5.88 (d, 1H, CH2); 3.33 (d,
1H, CH2).
3.2. Synthesis of compounds
3.2.1. [Ti{(OC6H3Ph)2CH2}Cl2]2 (2)
To a suspension of 2,29-methylene-bis(6-phenylphenol)
(4.23 g, 12.0 mmol) in benzene (100 ml) was added[TiCl4]
(2.0 g, 10.5 mmol) by standard Schlenk techniques under a
dry N2 atmosphere. The resulting red solution was stirred for
3 h before being dried in vacuo to produce a red solid which
was washed twice with pentane to yield compound 2. Yield
4.10 g (83.2%). Anal. Calc. for TiCl2O2C25H18: C, 63.99; H,
3.2.6. [Ta{(OC6H3Ph)2CH2}Cl3(py)] (7)
1
3.86; Cl, 15.11. Found: C, 62.41; H, 4.03; Cl, 15.31%. H
To a suspension of 5 (0.50 g, 0.78 mmol) in benzene was
added pyridine (0.09 g 1.14 mmol, 1.5 equiv.) resulting in
the formation of a yellow solution. The solution was layered
with pentane causing yellow crystals of 7 to form, whichwere
dried in vacuo. Yield 0.30 g (52.8%). Anal. Calc. for
TaNO2Cl3C30H23P0.5C6H6: C, 52.44; H, 3.47; N, 1.85; Cl,
NMR (CDCl3, 308C): d 7.16–7.56 (m, 16H, aromatics);
4.32 (d, 1H, CH2); 3.92 (d, 1H, CH2). Crystals suitable for
X-ray diffraction were obtained from CHCl3–pentane
mixtures.
3.2.2. [Ti{(OC6H3Ph)2CH2}(m-OPri)(OPri)]2 (3)
1
14.07. Found: C, 51.77; H, 3.81; N, 1.50; Cl, 13.94%. H
A mixture of 2,29-methylene-bis(6-phenylphenol) (24.6
g, 69.8 mmol) and [Ti(OPri)4] (20.0 g, 70.4 mmol) in
benzene (100 ml) was stirred for 1 h then dried in vacuo.
The resulting red/orange solid was washed three times with
hexane and recrystallized from toluene. The resulting orange
plate-like crystals of 3 were dried in vacuo. Yield 13.85 g
(38.1%). Anal. Calc. for TiO4C31H32: C, 72.01; H, 6.24.
Found: C, 72.17; H, 6.25%. 1H NMR (C6D6, 308C): d 7.45
(d, 2H, aromatic); 7.09 (m, 12H, aromatic); 6.73 (t, 2H,
aromatic); 4.35 (broad, 2H, CHMe2); 4.19 (broad, 1H,
CH2); 3.45 (broad, 1H, CH2); 0.85 (broad, 12H, CHMe2).
NMR (C6D6, 308C): d 8.52 (d, aromatic); 7.84 (d, aro-
matic); 7.47 (t, aromatic); 7.14 (d, aromatic); 6.77 (t, aro-
matic); 6.70 (t, aromatic); 6.50 (t, aromatic); 6.43 (d,
aromatic); 5.93 (t, aromatic); 5.81 (d, 1H, CH2); 3.42 (d,
1H, CH2).
3.2.7. [Ta{(OC6H3Ph)2CH2}Cl3(PMe2Ph)] (8) and
[HPMe2Ph][Ta{(OC6H3Ph)2CH2}Cl4] (9)
To a suspension of 5 (0.32 g, 0.50 mmol) in benzene was
added PMe2Ph (0.155 g, 1.12 mmol) and the solution was
stirred for 20 min. Yellow powder of 8 formed overnight and
was washed twice with pentane and dried in vacuo. Yield
0.35 g (70%). Anal. Calc. for TaO2Cl3PC33H29: C, 51.08; H,
3.79; P, 3.99; Cl, 13.71. Found: C, 50.82; H, 3.83; P, 3.61;
Cl, 13.57%. 1H NMR (C6D6, 308C): d 6.89–7.17 (m, 21H,
aromatic); 5.95 (broad, 1H, CH2); 3.25 (broad, 1H, CH2);
1.026 (s, 6H, PMe2Ph). 31P NMR (C6D6, 308C): d y10.536
(s, 1P, PMe2Ph). Layering of the supernatant with pentane
resulted in the formation of a few well formed crystals of 9
(benzene solvate) presumably due to adventitious amounts
of moisture. 1H NMR (C6D6, 308C): d 6.89–7.17 (m, 21H,
aromatic); 5.95 (broad, 1H, CH2); 3.25 (broad, 1H, CH2);
0.489 (d, 6H, PMe2Ph). 31P NMR (C6D6, 308C): d y10.505
(d, 1P, HPMe2Ph, 2JP-Hs461.43 Hz).
3.2.3. [Nb{(OC6H3Ph)2CH2}Cl3] (4)
A sample of 2,29-methylene-bis(6-phenylphenol) (13.3
g, 37.76 mmol) was added to a solution of [NbCl5] (10.2 g,
37.7 mmol) in benzene (100 ml) to give a red solution which
was stirred for 5 h under a dry N2 atmosphere. The resulting
red/brown precipitate of 5 was dried in vacuo. Yield 17.5 g
(84%). Anal. Calc. for NbCl3O2C25H18: C, 54.63; H, 3.30;
1
Cl, 19.35. Found: C, 53.89; H, 3.40; Cl, 17.33%. H NMR
(C6D6, 308C): d 6.65–7.24 (m, 16H, aromatics); 3.10 (s,
2H, CH2).
3.2.4. [Ta{(OC6H3Ph)2CH2}Cl3] (5)
A sample of 2,29-methylene-bis(6-phenylphenol) (1.02
g, 2.89 mmol) was added to a solution of [TaCl5] (1.02 g,
2.87 mmol) in benzene (25 ml) to give a brown/red solution
which was stirred for 1.5 h under a dry N2 atmosphere. The
resulting yellow/orange precipitate of 4 was dried in vacuo.
Yield 1.47g (75%). Anal. Calc. for TaCl3O2C25H18: C,
47.10; H, 2.84; Cl, 16.68. Found: C, 47.10; H, 2.84; Cl,
14.59%. 1H NMR (C6D6, 308C): d 6.65–7.44 (m, 16H, aro-
matics); 3.24 (s, 2H, CH2).
3.2.8. [Ta{(OC6H3Ph)2CH2}2(NMe2)(HNMe2)] (10)
To a suspension of [Ta(NMe2)5] (0.25 g, 0.62 mmol) in
benzene was added 2,29-methylene-bis(6-phenylphenol)
(0.44 g, 1.24 mmol) by standard Schlenk techniques under
an N2 atmosphere. The solution was stirred for 2 h and
allowed to stand overnight before being dried in vacuo to
produce a yellow powder. The resulting powder was sus-
pended in a minimum amount of benzene and layered with
pentane, resulting in the formation of a yellow crystalline
3.2.5. [Nb{(OC6H3Ph)2CH2}Cl3(py)] (6)
To a suspension of 4 (0.50 g, 0.91 mmol) in benzene was
added pyridine (0.13 g 1.64 mmol, 1.80 equiv.) and the
material. Yield 0.486 g (78.4%). Anal. Calc. for
TaN2O4C54H49PC6H6: C, 68.70; H, 5.28; N, 2.67. Found: C,
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D.R. Mulford et al. / Polyhedron 19 (2000) 35–42
41
68.84; H, 5.33; N, 2.44%. 1H NMR (C6D6, 308C): d 6.73–
7.86 (m, 32H, aromatics); 6.41 (d, 1H, CH2); 5.56 (d, 1H,
CH2); 3.59 (d, 1H, CH2); 3.46 (d, 1H, CH2); 2.51 (s, 16H,
NCH3); 1.73 (d, 3H, HNCH3); 0.87 (d, 3H, HNCH3).
Table 7
Crystal data and data collection parameters
9
11
Formula
TaCl4O2C33H30PPC6H6 TaO6NC77
H
62P2.31C6H6
Formula weight
890.45
1458.75
3.2.9. [H2NMe2][Ta{(OC6H3Ph)2CH2}3] (11)
¯
Space group
P21/c (no. 14)
15.1411(2)
12.2725(3)
21.3744(3)
90
110.5051(12)
90
3720.1(2)
4
P1 (no. 2)
14.1691(5)
15.2004(5)
18.5104(6)
96.427(2)
94.398(2)
105.3996(19)
3795.8(5)
2
To a suspension of [Ta(NMe2)5] (0.25 g, 0.62 mmol) in
benzene was added 2,29-methylene-bis(6-phenylphenol)
(0.66 g, 1.86 mmol) by standard Schlenk techniques under
an N2 atmosphere. Upon stirring for 1 h a small amount of
11 was formed as a white precipitate which was isolated.
Upon standing, the supernatant produced a few crystals of 11
(benzene solvate) suitable for X-ray analysis. Anal. Calc. for
TaNO6C77H62P2C6H6: C, 74.52; H, 5.20; N, 1.00. Calc. for
TaNO6C77H62P3C6H6: C, 75.43; H, 5.33; N, 0.93. Found: C,
74.22; H, 5.40; N, 1.65%. The crystals analyzed by crystal-
lography contained 2.31 equiv. of benzene per Ta within the
unit cell.
˚
a (A)
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
3
˚
V (A )
Z
rcalc (g cmy3
)
1.590
203.
Mo Ka (0.71073)
1.276
193.
Mo Ka (0.71073)
Temperature (K)
Radiation (wave-
˚
length, A)
R
RW
0.025
0.055
0.065
0.148
3.2.10. Hydrogenation experiment
lographic Data Center, CCDC numbers 133328 (2), 133329
(6), 133330 (7), 133331 (9) and 133332 (11). Copies of
this information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK
A sample of [Nb{(OC6H3Ph)2CH2}Cl3] (4) (0.28 g,
0.51 mmol) was suspended in benzene (17 ml, 400 equiv.)
in a 50 nl round bottomed flask. To this was added n-BuLi
(3 equiv. in hexane). The flask containing the mixture was
placed in a Parr model 4561, 300ml highpressureminireactor
and pressurized to 1200 psi hydrogen and heated to 808C for
24 h. After cooling, a small amount of the resulting solution
wasdiluted with C6D6 andthedegreeofhydrogenation(20%,
80 equiv.) of cyclohexane determined by 1H.
(fax:
q44-1223-336-033)
or
e-mail
deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk.
Acknowledgements
We thank the Department of Energy, Basic Energy Sci-
ences, for financial support of this research.
4. Supplementary data
References
Crystal data and data collection parameters are contained
in Tables 6 and 7. Crystallographic data for the structural
analyses have been deposited with the Cambridge Crystal-
[1] M.G. Thorn, Z.C. Etheridge, P.E. Fanwick, I.P. Rothwell, Organo-
metallics 17 (1998) 3636.
Table 6
Crystal data and data collection parameters
2
6
7
Formula
Formula weight
Ti2Cl4O4C50
1177.21
P1 (no. 2)
H
36P2CHCl3
NbCl3O2NC30
667.85
P1 (no. 2)
H
23P1/2C6H6
TaCl3O2NC30
755.89
P1 (no. 2)
H23P1/2C6H6
¯
¯
¯
Space group
˚
a (A)
8.5013(14)
10.8086(4)
11.0418(4)
13.6563(5)
67.0451(17)
84.929(2)
87.293(2)
1494.75(14)
2
10.683(4)
11.023(3)
13.579(3)
67.15(2)
84.59(2)
86.90(2)
1466.7(9)
2
˚
b (A)
10.2239(16)
15.117(2)
85.736(12)
84.716(9)
78.217(11)
1278.7(5)
1
˚
c (A)
a (8)
b (8)
g (8)
3
˚
V (A )
Z
rcalc (g cmy3
)
1.529
1.484
1.711
Temperature (K)
Radiation (wavelength, A)
R
203.
296.
203.
˚
Mo Ka (0.71073)
0.087
Mo Ka (0.71073)
0.049
Mo Ka (0.71073)
0.026
RW
0.244
0.130
0.071
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42
D.R. Mulford et al. / Polyhedron 19 (2000) 35–42
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