Coordination complexes bearing potentially tetradentate phenoxyamine ligands

Article abstract of DOI:10.1039/b607753f

A series of metal complexes containing potentially tetradentate phenoxyamine ligands is described. The ligands are found to bind to main-group metals and first-row transition-metal centres with variable denticity depending upon the requirements of the par

Full text of DOI:10.1039/b607753f

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Coordination complexes bearing potentially tetradentate phenoxyamine
ligands†
Andrew R. F. Cox, Vernon C. Gibson,* Edward L. Marshall, Andrew J. P. White and David Yeldon
Received 31st May 2006, Accepted 11th August 2006
First published as an Advance Article on the web 1st September 2006
DOI: 10.1039/b607753f
A series of metal complexes containing potentially tetradentate phenoxyamine ligands is described. The
ligands are found to bind to main-group metals and first-row transition-metal centres with variable
denticity depending upon the requirements of the particular metal centre. Bidentate [Al(III)], tridentate
[Mg(II), Ca(II), Zn(II)] and tetradentate [K(I), Cr(III), Fe(II), Co(II)] binding modes have been established
unambiguously through single-crystal X-ray structure determinations.
ether donors, and their coordination chemistry with metals across
Introduction
the first-row transition series [Cr(III), Fe(II), Co(II), Zn(II)] and for
Ligands containing phenoxide donors have enjoyed much success
several main-group metal ions [K(I), Mg(II), Ca(II), Al(III)].
in the stabilization of catalysts for numerous chemical transfor-
mations, ranging from oxidation1 and epoxidation,2 through to
carbon–carbon bond formation3 and controlled polymerization.4
The ligand types employed in these processes range from simple
bidentate (I) and tridentate (II, III) mono-phenoxide systems
through to bi- (IV), tri- (V) and tetra-dentate (VI, VII) bis-
phenoxideligands, manyofwhich are derivable via straightforward
Schiff-base or Mannich condensation procedures.
Results and discussion
Ligand synthesis
Ligands 1a–c were synthesised by treatment of 2,4-di-tert-
butylphenol with paraformaldehyde and the relevant secondary
amine in refluxing methanol, affording 1a–c as viscous oils in
high yield (Scheme 1). NMR data and elemental analyses were
consistent with the formation of the targeted phenols.
A potentially important category of phenoxide ligand which, to
date, has remained largely unexplored, is the series (VIII) based
on tetradentate mono-phenoxide coordination. Matyjaszewski
and coworkers recently introduced one ligand from this series,
containing diethylamino donors (IX), and described its copper
complex,5 while Kol and co-workers have recently reported
zirconium complexes stabilized by a derivative (X) containing
methoxy donors.6
Scheme 1
Complex synthesis and characterization
Group I complexes. Potassium salts of 1a,c were synthesised
by slow addition of the phenol to a slurry of potassium hydride
at −78 ◦C (Scheme 2). After 16 h the reaction mixtures were
concentrated under reduced pressure to afford waxy solids which
could be recrystallised from hot toluene to give 2a and 2c as
colourless crystals.
Herein, we describe the synthesis and characterization of a
family of phenoxyamine ligands bearing either additional amine or
Imperial College London, Department of Chemistry, South Kensington
Campus, London, UK SW7 2AZ. E-mail: v.gibson@imperial.ac.uk
† Electronic supplementary information (ESI) available: Table S1: Crystal
data, data collection and refinement parameters for compounds 4c and 5a.
Fig. S1–19: Molecular structures of 2a, 3b, 4c (I and II), 5a, 6c (I and II),
7a (I and II), 7b, 8a, 9c, 10c, and overlay diagrams for 6c and 7a. See DOI:
10.1039/b607753f
The X-ray structure of 2a showed the complex to be dimeric
with approximate C2 symmetry about an axis perpendicular to
the central four-membered K2O2 ring (Fig. 1). This ring has a
slightly folded conformation, the two KO2 planes being inclined
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Low-temperature 1H NMR spectra of 2a and 2c reveal in-
equivalent amino and methoxy donors, at 0.61 and 0.71 ppm
for the methyl protons of the NEt2 groups (213 K), and at 2.56
and 3.17 ppm for the methyl protons of the methoxy donors (at
193 K), consistent with the solid-state structure of 2a. As the
samples are warmed to room temperature, these signals coalesce
to single resonances (at 0.74 and 2.85 ppm, respectively) indicating
an averaging process on the NMR timescale, most likely a result
of motion within the dinuclear structure.
Scheme 2
Group II complexes. An alkyl magnesium complex, 3b, proved
accessible in good yield by deprotonation of ligand 1b (using
n-butyllithium) followed by reaction of the lithium salt with
iPrMgCl, (Scheme 3).
Scheme 3
Fig. 1 The molecular structure of 2a. The transannular K · · · K separa-
The solid-state structure of 3b revealed the expected distorted
tetrahedral coordination geometry at the magnesium centre, with
one of the amino side-arms not being bound (Fig. 2). The angles
at the metal are in the range 94.23(5)–129.58(6)◦, the smallest
being associated with the bite of the six-membered N,O chelate
ring (Table 2). This ring has a twisted boat geometry, with
˚
tion is 3.6417(5) A.
to each other by ca. 7◦. The two six-membered N,O chelate rings
have boat geometries. For the K(1) ring, {K(1),C(1),C(2),N(8)} is
˚
coplanar to within ca. 0.02 A with O(1) and C(7) ca. +0.65 and
˚
{Mg,C(1),C(6),N(8)} being coplanar to within ca. 0.06 A with
˚
+0.75 A out of this plane, corresponding to an approximate fold of
O(1) and C(7) ca. +0.33 and +0.68 A, respectively, out of this
plane; the fold about the O(1) · · · C(7) vector is ca. 41◦. The
six-membered N,Nꢀ chelate ring has a chair conformation, Mg
ca. 53◦ about the O(1) · · · C(7) vector, whilst for the counterpart at
˚
K(2), {K(2),C(31),C(32),N(38)} is coplanar to within ca. 0.06 A
˚
with O(31) and C(37) ca. +0.50 and +0.77 A out of the plane,
giving an approximate fold about the O(31) · · · C(37) vector of ca.
47◦. The four N,Nꢀ five-membered chelate rings all have the typical
twisted geometry. As expected, the bonds to the formally anionic
˚
oxygen centres, (ranging between 2.5919(12) and 2.6684(11) A)
are noticeably shorter than those to the neutral nitrogen donors
˚
(ranging between 2.8193(13) and 3.0402(15) A) (Table 1).
◦
˚
Table 1 Selected bond lengths (A) and angles ( ) for 2a
K1–O1
2.5919(12)
2.9659(15)
2.5977(11)
2.6092(12)
2.9035(16)
K1–N8
K1–N18
K2–O1
K2–N38
K2–N41
2.8193(13)
2.8798(15)
2.6684(11)
2.8340(13)
3.0402(15)
K1–N11
K1–O31
K2–O31
K2–N48
O1–K1–N8
78.59(4)
114.77(4)
63.84(4)
155.91(4)
139.90(4)
90.64(4)
151.30(4)
76.31(4)
116.52(4)
65.90(4)
87.61(3)
O1–K1–N11
O1–K1–O31
N8–K1–N18
N11–K1–N18
N18–K1–O31
O1–K2–N38
O1–K2–N48
O31–K2–N41
N38–K2–N41
N41–K2–N48
K1–O31–K2
109.05(4)
92.63(4)
66.24(4)
102.15(4)
98.35(4)
145.40(4)
93.18(4)
101.56(4)
63.29(4)
104.06(5)
88.76(3)
Fig. 2 The molecular structure of 3b.
O1–K1–N18
N8–K1–N11
N8–K1–O31
N11–K1–O31
O1–K2–O31
O1–K2–N41
O31–K2–N38
O31–K2–N48
N38–K2–N48
K1–O1–K2
◦
˚
Table 2 Selected bond lengths (A) and angles ( ) for 3b
Mg–O1
Mg–N12
1.9060(11)
2.1721(13)
Mg–N8
Mg–C30
2.1577(12)
2.1512(16)
O1–Mg–N8
O1–Mg–C30
N8–Mg–C30
94.23(5)
129.58(6)
114.91(6)
O1–Mg–N12
N8–Mg–N12
N12–Mg–C30
105.19(5)
97.00(5)
110.49(6)
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◦
˚
˚
Table 3 Selected bond lengths (A) and angles ( ) for the two independent
complexes (I and II) present in the crystals of 6c
and C(10) lying ca. +0.85 and −0.70 A, respectively, out of the
{N(8),C(9),C(11),N(12)} plane which is coplanar to within ca.
˚
0.02 A.
Mol. I
Mol. II
In addition to the magnesium mono-alkyl species, bis-chelate
complexes of magnesium and calcium are also accessible. De-
protonation of 1c with n-butyllithium, followed by reaction of
the lithium salt with isopropyl magnesium chloride, afforded the
homoleptic species 4c. Similarly the calcium complex 5a was
formed by the reaction of 1a sequentially with 1 equivalent of
K[N(SiMe3)2] and half an equivalent of CaI2. 4c and 5a can also be
synthesised directly by the reaction of 2c or 2a with the appropriate
metal dihalide precursor.
The quality of the single-crystal X-ray data for 4c and 5a are
poor, but nevertheless sufficient to establish the bis(tridentate)
ligand coordination within these products. The structure of 5a is
shown in Fig. 3 whilst 4c is shown in Fig. S15–S18 in the ESI.†
Al–O1
Al–C25
Al–N8
Al–C26
1.7735(15)
1.965(2)
2.0652(17)
1.962(2)
1.7752(16)
1.961(2)
2.0641(17)
1.961(2)
O1–Al–N8
O1–Al–C26
N8–Al–C26
O1–Al–C25
N8–Al–C25
C25–Al–C26
94.45(7)
104.61(9)
111.13(9)
106.65(10)
111.40(9)
123.96(12)
94.81(7)
105.76(10)
110.51(9)
106.94(10)
111.44(10)
123.25(12)
Fig. 4 The molecular structure of one (I) of the two independent
complexes present in the crystals of 6c.
arms being bound to the aluminium centre. The most notable
departure from an ideal tetrahedral geometry is an opening
out of the angle between the two methyl ligands, C(25)–Al–
C(26) 123.96(12)◦ [123.25(12)◦], the value in square parentheses
referring to molecule II. Associated with this is a close approach
of the non-coordinated methoxy oxygen atom O(11) at 2.7259(18◦)
Fig. 3 The molecular structure of the Ci-symmetric complex 5a.
Aluminium alkyl species. The aluminium alkyl complex 6c was
formed upon treatment of 1c with AlMe3 (Scheme 4). Refluxing
the reaction mixture, followed by crystallisation, afforded 6c in
25% yield.
˚
˚
A [2.7488(18) A]. The smallest angle at aluminium—94.45(7)
[94.81(7)◦]—is the bite of the six-membered N,O chelate ring which
˚
˚
has a folded geometry, Al and N(8) lying ca. 0.66 A [0.65 A] and
˚
˚
1.07 A [1.06 A], respectively, out of the {O(1),C(1),C(6),C(7)}
˚
˚
plane which is coplanar to within ca. 0.03 A [0.03 A].
Organometallic zinc complexes 7a–c were formed by the
reaction of diethyl zinc with ligands 1a–c (Scheme 5). The
ethyl zinc products were crystallised from heptane in reasonable
Scheme 4
The X-ray structure of complex 6c showed the presence of
two crystallographically independent molecules (I and II) in the
asymmetric unit, though with near identical geometries, the r.m.s.
˚
fit of all of the non-hydrogen atoms being ca. 0.06 A (molecule I is
shown in Fig. 4, molecule II in Fig. S3 in the ESI,† and an overlay
of the two molecules in Fig. S6, ESI†). The coordination geometry
is distorted tetrahedral (Table 3), with neither of the methoxy side-
Scheme 5
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◦
◦
˚
˚
Table 5 Selected bond lengths (A) and angles ( ) for 7b
Table 4 Selected bond lengths (A) and angles ( ) for the two independent
complexes (I and II) present in the crystals of 7a
Zn–O1
Zn–N12
1.9456(12)
2.1560(15)
Zn–N8
Zn–C29
2.1599(14)
1.9930(19)
Mol. I
Mol. II
O1–Zn–N8
O1–Zn–C29
N8–Zn–C29
93.85(5)
130.97(7)
114.27(7)
O1–Zn–N12
N8–Zn–N12
N12–Zn–C29
102.82(5)
97.43(6)
111.65(7)
Zn–O1
Zn–N11
Zn–N8
Zn–C31
1.952(2)
2.139(3)
2.139(2)
1.967(4)
1.948(2)
2.133(3)
2.155(2)
1.987(3)
O1–Zn–N8
O1–Zn–C31
N8–Zn–C31
O1–Zn–N11
N8–Zn–N11
N11–Zn–C31
93.67(9)
127.12(18)
121.97(17)
100.98(9)
85.26(11)
118.2(2)
93.52(9)
127.46(18)
121.64(14)
100.68(9)
85.57(12)
118.24(18)
X-Ray analysis of crystals of 7b revealed a structure (Fig. 6)
similar to that seen for each independent molecule of 7a (vide
supra). The phenoxyamine ligand is again tridentate, one of
the amine side-arms being non-coordinating. The coordination
geometry is distorted tetrahedral (Table 5) with angles in the range
93.85(5)–130.97(7)◦. In contrast to 7a, here the smallest angle is
associated with the bite of the six-membered N,O chelate ring, the
extra methylene in the six-membered N,Nꢀ chelate ring allowing
this latter chelate to adopt a less strained coordination geometry
[bite angle of 97.43(6)◦] than was possible for the five-memb◦ered
N,Nꢀ chelate ring in 7a [bite angles of 85.26(11) and 85.57(12) for
the two independent molecules]. The N,O chelate ring again has a
yields (>60%). The formation of the desired products was
confirmed by NMR spectroscopy, elemental analysis and mass
spectrometry.
As was observed for 6c, the structure of 7a also has two
crystallographically independent molecules (I and II) in the
asymmetric unit, and excluding the atoms of the non-coordinated
side-arm (vide infra) the two molecules have an r.m.s. fit of ca.
˚
boat conformation, O(1) and C(7) lying ca. +0.50 and +0.68 A out
of the {Zn,C(1),C(6),N(8)} plane which is coplanar to within ca.
˚
0.07 A (molecule I is shown in Fig. 5, molecule II in Fig. S7,
◦
˚
0.03 A; the associated fold about the O(1) · · · C(7) vector is ca. 48 .
and the overlay of the two molecules in Fig. S10, ESI†). The
geometry at the zinc centre is distorted tetrahedral (Table 4) with
one of the amino side-arms non-bound; this second side-arm is
disordered in both independent molecules. The angles at the metal
are in the range 85.26(11)–127.12(18)◦ [85.57(12)–127.46(18)◦ in
molecule II], the most acute being associated with the bite of
the five-membered N,Nꢀ chelate ring. This ring has a twisted
The N,Nꢀ chelate ring adopts a chair conformation, Zn and C(10)
˚
lying ca. +0.78 and −0.71 A out of the {N(8),C(9),C(11),N(12)}
˚
plane which is coplanar to within ca. 0.02 A.
˚
˚
conformation with C(9) and C(10) lying ca. +0.33 A [+0.32 A]
˚
˚
and −0.32 A [−0.33 A] respectively out of the ZnN2 plane. The
six-membered N,O chelate ring has a boat conformation, O(1) and
˚
˚
˚
˚
N(7) lying ca. +0.76 A [+0.76 A] and +0.60 A [+0.60 A] out of the
˚
{Zn,C(1),C(6),N(8)} plane which is coplanar to within ca. 0.09 A
˚
[0.09 A]; the associated fold about the O(1) · · · C(7) vector is ca.
58◦ [58◦].
Fig. 6 The molecular structure of 7b.
Room-temperature solution 1H NMR data for 7c revealed that
the bound and pendant OMe groups exchange rapidly on the
NMR timescale: a single methyl resonance is observed for the
methoxy donor at 2.85 ppm along with a single set of multiplets
(of a HABXY system) for the methylene protons of the donor arms.
A similar effect is observed for the amino donors 7a or 7b, which
gave a single resonance for the amino donor substituents. The
spectra remained largely unchanged, with only slight broadening,
to 213 K.
Chromium complex. We next explored the coordination of
these ligands to transition metals in order to gain further insight
Fig. 5 The molecular structure of one (I) of the two independent
complexes present in the crystals of 7a.
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into the possible coordination geometries adopted by these multi-
donor ligands.
˚
ca. 0.68 A out of the {Cr,N(8),C(17),N(18)} plane which is
˚
coplanar to within ca. 0.03 A. The six-membered N,O chelate
The chromium(III) complex 8a was formed by the addition of the
potassium salt 2a to CrCl3(THF)3, creating a green–black solution
(Scheme 6). Crystals suitable for X-ray diffraction studies were
obtained from a layered toluene–pentane solution.
ring has a twisted boat conformation, O(1) and C(7) lying ca.
˚
+0.42 and +0.41 A out of the {Cr,C(1),C(6),N(8)} plane which
˚
is coplanar to within ca. 0.10 A; the associated fold about the
O(1) · · · C(7) vector is ca. 35◦.
Iron complex. The iron(II) complex 9c was synthesised by
the transmetallation reaction between potassium salt 2c and
FeCl2(THF)1.5 (Scheme 7). The crude complex was recrystallised
from hot toluene to afford colourless needles.
Scheme 6
The structure of 8a shows the ligand to be tetradentate, with the
two amino side-arms coordinating in a mutually trans disposition
at the chromium centre (Fig 7). The coordination geometry
is distorted octahedral with cis angles in the range 82.11(11)–
98.96(7)◦, the two most acute angles [82.11(11) and 82.66(11)]
being the bites of the N(8)/N(18) and N(8)/N(11) five-membered
N,Nꢀ chelate rings, respectively (Table 6). Both of these rings adopt
envelope conformations; for the N(8)/N(11) ring, C(9) lies ca.
Scheme 7
˚
0.67 A out of the {Cr,N(8),C(10),N(11)} plane which is coplanar
The solid-state structure determination for 9c revealed a Ci-
symmetric dimer with a central, flat, Fe2Cl2 ring (Fig. 8). The
coordination geometry is distorted octahedral [cis angles in the
range 75.62(4)–105.80(3)◦], the aminophenolate ligand binding in
a tetradentate fashion (Table 7). The two most acute angles at the
iron centre are the bites of the five-membered N,O chelate rings,
both of which have envelope conformations. For the N(8)/O(11)
˚
to better than 0.01 A, whilst for the N(8)/N(15) ring C(16) lies
˚
ring, C(9) lies ca. 0.65 A out of the {Fe,N(8),C(10),O(11)}
˚
plane which is coplanar to within ca. 0.02 A. The N(8)/O(15)
˚
ring is a bit more distorted, C(14) lying ca. 0.64 A out of the
Fig. 7 The molecular structure of 8a.
◦
˚
Table 6 Selected bond lengths (A) and angles ( ) for 8a
Cr–Cl1
Cr–O1
Cr–N11
2.3615(11)
1.915(2)
2.259(3)
Cr–Cl2
Cr–N8
Cr–N18
2.3337(10)
2.107(3)
2.283(3)
Cl1–Cr–Cl2
Cl1–Cr–N8
Cl1–Cr–N18
Cl2–Cr–N8
Cl2–Cr–N18
O1–Cr–N11
N8–Cr–N11
N11–Cr–N18
91.79(4)
92.56(8)
87.47(8)
175.44(9)
96.74(7)
89.78(10)
82.66(11)
163.29(10)
Cl1–Cr–O1
Cl1–Cr–N11
Cl2–Cr–O1
Cl2–Cr–N11
O1–Cr–N8
O1–Cr–N18
N8–Cr–N18
175.56(8)
86.37(8)
86.62(7)
98.96(7)
89.13(10)
96.83(10)
82.11(11)
Fig. 8 The molecular structure of the centrosymmetric complex 9c. The
transannular Fe · · · Fe separation is 3.5866(4) A.
˚
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◦
˚
Table 7 Selected bond lengths (A) and angles ( ) for 9c
Fe–Cl
Fe–N8
Fe–O15
2.4192(4)
2.2027(12)
2.2905(12)
Fe–O1
Fe–O11
Fe–ClA
1.9449(10)
2.2815(11)
2.5453(4)
Cl–Fe–O1
105.80(3)
89.50(3)
87.520(14)
164.29(4)
98.92(4)
75.62(4)
80.36(4)
165.01(3)
Cl–Fe–N8
163.93(3)
95.58(3)
88.47(4)
94.35(5)
75.90(4)
97.70(3)
85.02(3)
92.480(14)
Cl–Fe–O11
Cl–Fe–ClA
O1–Fe–O11
O1–Fe–ClA
N8–Fe–O15
O11–Fe–O15
O15–Fe–ClA
Cl–Fe–O15
O1–Fe–N8
O1–Fe–O15
N8–Fe–O11
N8–Fe–ClA
O11–Fe–ClA
Fe–Cl–FeA
{Fe,N(8),C(13),O(15)} plane which is coplanar to within ca.
˚
0.09 A. The six membered N,O chelate ring has a bite angle of
88.47(4)◦ and adopts a folded geometry similar to that seen in the
˚
structure of 7, Fe and N(8) lying ca. 0.61 and 1.09 A, respectively
Fig. 9 The molecular structure of 10c.
out of the {O(1),C(1),C(6),C(7)} plane which is coplanar to better
˚
than 0.01 A.
The dimeric nature of 9c appears to be retained in solution, with
an Evans’ method magnetic moment determination affording a leff
value of 8.7 lB, attributable to the presence of magnetically isolated
high-spin Fe(II) centres.
Discussion
The solid-state structure determinations reveal useful insight into
the coordination flexibility of this ligand family. For example, for
the group of complexes 2a (K), 7a (Zn) and 8a (Cr) containing the
same diethylamino donors, the potassium and chromium deriva-
tives show tetradentate coordination while the zinc derivative has
one of the diethylamino groups non-bound, the latter clearly
being a consequence of the lower coordination number/electron
count requirements of the zinc centre. However, in the two
cases where the ligand is tetradentate, the potassium derivative
possesses a much smaller angle between the Et2N nitrogen donor
atoms (104.06(5) vs. 163.29(10)◦ for chromium). The pseudo-trans
displacement of the amino donors in this chromium complex
contrasts the cis arrangement of the MeO donors in the iron
complex, while the angle between the methoxy donors in the
cobalt derivative 10c is intermediate (121.31(4)◦) and compliant
with a trigonal bipyramidal coordination geometry at the cobalt
centre.
Cobalt complex. The high-spin cobalt(II) complex 10c (leff
=
3.7 lB) was formed by the metathesis reaction of cobalt dichloride
and the potassium salt 2c (Scheme 8). Crystals of 10c were isolated
as blue needles from hot toluene.
Scheme 8
The single-crystal X-ray structure revealed a five-coordinate
distorted trigonal bipyramidal coordination geometry (Fig. 9,
Table 8). The two most acute angles at the metal centre are the bites
of the N(8)/O(11) and N(8)/O(15) five-membered N,O chelate
rings, respectively, both of which have twisted geometries. The six-
membered N,O chelate ring [which has a bite angle of 90.62(4)◦]
adopts a boat conformation with O(1) and C(7) lying ca. +0.29 and
Solution NMR studies, e.g. on 7a–c, indicate that bound
and non-bound donor arms readily exchange, which may
have important implications for catalytic applications of these
complexes.
˚
+0.67 A out of the {Co,C(1),C(6),N(8)} plane which is coplanar to
˚
within ca. 0.07 A; the corresponding fold about the O(1) · · · C(7)
Conclusion
vector is ca. 39◦.
A series of metal complexes stabilised by a family of monoanionic
phenoxyamine ligands has been synthesised and characterised.
The denticity of the ligands is found to vary from bidentate
(Al) to tridentate (Mg, Zn, Ca) to tetradentate (K, Cr, Fe, Co)
depending on the coordination requirement of the metals. The
ligand is also found to accommodate a range of metal coordination
geometries, a consequence of the flexibility of the donor arms. Such
characteristics have considerable merit for their use in catalysis.
Current work is focused on exploring the potential of these
complexes as catalysts for small-molecule and macromolecule
synthesis.
◦
˚
Table 8 Selected bond lengths (A) and angles ( ) for 10c
Co–Cl
Co–N8
Co–O15
2.2932(4)
2.1773(10)
2.0934(10)
Co–O1
Co–O11
1.9040(9)
2.1256(10)
Cl–Co–O1
101.78(3)
93.60(3)
90.62(4)
108.98(4)
78.98(4)
Cl–Co–N8
167.53(3)
97.96(3)
124.44(4)
78.05(4)
121.31(4)
Cl–Co–O11
O1–Co–N8
O1–Co–O15
N8–Co–O15
Cl–Co–O15
O1–Co–O11
N8–Co–O11
O11–Co–O15
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Potassium 4,6-di-tert-butyl-2-bis(2-diethylamino)ethyl)-
aminomethylphenoxide, 2a
Experimental
General
To a stirring slurry of potassium hydride (0.18 g, 2.3 mmol) in
toluene (30 cm3) at −78 ◦C was added a solution of 1a (1 g,
2.3 mmol) in toluene (50 cm3). The mixture was stirred for 16 h
at room temperature after which the clear solution was filtered
and concentrated under reduced pressure to give a waxy solid.
This was recrystallised from hot toluene to afford 2a as colourless
crystals (0.73 g, 67%).
All solvents were distilled over standard drying agents un-
der nitrogen and deoxygenated before use. 4,6-di-tert-butyl-2-
bis(2-methoxyethyl)aminomethylphenol 1c,6 CrCl3·THF3,7 and
FeCl2·THF1.5,8 were synthesised using literature procedures. Potas-
sium hydride was bought as a dispersion over oil, which was
washed with heptane three times prior to use. All other chemicals
were bought from Aldrich Chemical Co. and used as received.
NMR spectra were recorded on Bruker AC-250 MHz, AV-
400 MHz or AM-500 MHz spectrometers. NMR chemical shifts
are quoted in ppm relative to the residual solvent resonances.
Magnetic susceptibilities were determined using the Evans’ NMR
method using 0.001–0.002 g ml−1 complex dissolved in 10%
CH2Cl2–90% CDCl3.9 Microanalysis were performed at the Lon-
don Metropolitan University. Mass spectra were recorded on
either a VG Autospec or a VG Platform II spectrometer.
1H NMR (400 MHz, C6D6): d 7.27 (d, J = 2.8 Hz,
1H, ArH), 7.15 (d, 1H, J = 2.8 Hz, ArH), 2.42 (br s,
N(CH2CH2N(CH2CH3)2)2), 1.62 (s, 9H, C(CH3)3), 1.46 (s, 9H,
1
C(CH3)3), 0.74 (t, J = 7.0 Hz, 12H, N(CH2CH3)2). 13C{ H} NMR
(100 MHz, C6D6): d 167.5, 135.8, 129.1, 129.0, 123.6, 123.0, 61.3,
51.4, 45.6, 35.4, 34.0, 33.6, 30.5, 9.9. MS data (FAB −ve, m/z):
432 [M − K]−. (Found: C, 68.80, H, 10.57, N, 8.86. C27H50KN3O
requires C, 68.73, H, 10.68, N, 8.91%).
Potassium 4,6-di-tert-butyl-2-bis(2-
methoxyethyl)aminomethylphenoxide, 2c
4,6-Di-tert-butyl-2-bis(2-(diethylamino)ethyl)aminomethylphenol,
1a
Complex 2c was prepared in an analogous manner to 2a using
1c (1 g, 2.8 mmol) and potassium hydride (0.23 g, 5.7 mmol).
Recrystallisation from hot toluene gave 2c as a white solid (0.61 g,
57%).
Paraformaldehyde (1.40 g, 46.4 mmol) and N,N,Nꢀ,Nꢀ-
tetraethyldiethylenetriamine (12.0 cm3, 46.4 mmol) were refluxed
in methanol (100 cm3) for 90 min. A solution of 2,4-di-tert-
butylphenol (9.58 g, 46.4 mmol) in methanol (50 cm3) was then
added and the mixture refluxed for a further 24 h. Removal of
the volatile components under reduced pressure afforded 1a as
a golden–brown oil, which was used without further purification
(17.4 g, 86% yield).
1H NMR (400 MHz, C6D6): d 7.52 (d, J = 2.8 Hz, 1H, ArH),
7.14 (d, J = 2.8, 1H, ArH), 3.67 (br s, 2H, ArCH2N), 3.07 (br s, 4H,
NCH2CH2O), 2.85 (s, 6H, OCH3), 2.44 (br s, 4H, NCH2CH2O),
1
1.68 (s, 9H, C(CH3)3), 1.52 (s, 9H, C(CH3)3). 13C{ H} NMR
(100 MHz, C6D6): d 167.8, 135.9, 129.3, 129.0, 123.7, 123.2, 70.5,
61.4, 58.0, 54.3, 35.4, 34.0, 32.6, 30.2. MS data (FAB −ve, m/z):
390 (45%, [M]−), 351 (100%, [M − K]−) (Found: C, 64.89, H, 9.42,
N, 3.49. C21H36KNO3 requires C, 64.74, H, 9.31, N, 3.60%).
1H NMR (250 MHz, CDCl3): d 10.55 (1H, br s, Ar–OH), 7.17
(1H, d, J = 2.3 Hz, ArH), 6.81 (1H, d, J = 2.3 Hz, ArH),
3.72 (2H, s, ArCH2N), 2.60 (4H, m, NCH2CH2NEt2), 2.57 (4H,
m, NCH2CH2N), 2.47 (8H, q, J = 7.1 Hz, NCH2CH3), 1.40
(9H, s, C(CH3)3), 1.26 (9H, s, C(CH3)3), 0.96 (12H, t, J = 7.1 Hz,
1
NCH2CH2); 13C{ H} NMR (100 MHz, CDCl3): d 154.0, 139.9,
Isopropyl magnesium 4,6-di-tert-butyl-2-bis(3-
(dimethylamino)propyl)aminomethylphenoxide, 3b
135.3, 123.5, 122.5, 121.7, 58.4, 51.9, 50.3, 47.0, 34.6, 31.5, 29.4,
11.4 (Found: C, 74.65, H, 11.84, N, 9.86. C27H51N3O requires: C,
74.77, H, 11.85, N, 9.69%).
At −78 ◦C, a 2.5 M hexanes solution of nBuLi (1.64 cm3, 4.1 mmol)
was added to a solution of 1b (1.63 g, 4.0 mmol) in toluene (20 cm3).
The mixture was allowed to warm to room temperature and, after
4,6-Di-tert-butyl-2-bis(3-(dimethylamino)propyl)-
aminomethylphenol, 1b
i
1 h, a 2 M PrMgCl solution in THF (2.05 cm3, 4.10 mmol) was
added. After stirring for a further 2 h, the solution was filtered, the
solid washed with pentane and the combined filtrates concentrated
under reduced pressure. A small amount of pentane was added to
the solid and then removed in vacuo at −78 ◦C, affording 3b as a
white solid (1.36 g, 71% yield). Crystals suitable for X-ray analysis
were grown from n-heptane.
Ligand 1b was prepared in an analogous manner to
1a using paraformaldehyde (1.6 g, 53.4 mmol), bis[3-
(dimethylamino)propyl]amine (11.9 cm3, 53.4 mmol) and 2,4-di-
tert-butylphenol (11.0 g, 53.4 mmol), affording 1b as a light brown
oil, which was used without further purification (19.5 g, 90%
yield).
1H NMR (250 MHz, C6D6): d 7.63 (d, 1H, J = 2.7 Hz, ArH),
6.94 (d, 1H, J = 2.6 Hz, ArH), 3.52 (br s, 2H, ArCH2N), 2.35
(m, 4H, NCH2CH2CH2), 2.13 (m, 4H, NCH2CH2CH2), 1.98 (s,
12H, N(CH3)2), 1.85 (6H, d, J = 8.7 Hz, Mg–CH(CH3)2), 1.84
(9H, s, C(CH3)3), 1.38 (4H, m, NCH2CH2CH2N), 1.52 (9H, s,
1H NMR (250 MHz, CDCl3): d 10.97 (1H, br s, Ar–OH), 7.18
(1H, d, J = 2.3 Hz, ArH), 6.81 (1H, d, J = 2.2 Hz, ArH), 3.72
(2H, s, ArCH2N), 2.55 (4H, t, J = 7.5 Hz, N(CH2CH2CH2)2), 2.18
(12H, s, N(CH3)2), 2.13 (4H, J = 7.5 Hz, N(CH2CH2CH2)2), 1.70
(4H, qnt, J = 7.4 Hz, N(CH2CH2CH2)2), 1.41 (9H, s, C(CH3)3,
1
ArC(CH3)3), 0.25 (1H, sept, J = 8.0, Mg–CH(CH3)2). 13C{ H}
1
1.27 (9H, s, C(CH3)3). 13C{ H} NMR (100 MHz, CDCl3): d 154.1,
NMR (100 MHz, C6D6): d 163.5, 137.4, 134.1, 126.0, 124.1, 121.5,
68.6, 58.7, 53.5, 45.4, 35.7, 32.4, 31.8, 30.2, 26.5, 25.2, 8.8 (Found:
C, 71.14, H, 11.30, N, 9.02. C28H53MgN3O requires C, 71.24, H,
11.32, N, 8.90%).
140.1, 135.2, 123.2, 122.4, 121.2, 59.0, 57.5, 51.3, 45.3, 34.6, 33.9,
31.6, 29.4, 24.4 (Found: C, 74.10; H, 11.70, N, 10.27. C25H47N3O
requires C, 74.02; H, 11.68, N, 10.36%).
5020 | Dalton Trans., 2006, 5014–5023
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Synthesis of magnesium bis(4,6-di-tert-butyl-2-bis(2-
methoxyethyl)aminomethylphenoxide), 4c
recrystallised from hot heptane to afford 7a as colourless crystals
(1.70 g, 61%).
1H NMR (400 MHz, C6D6): d 7.60 (d, J = 2.7 Hz, 1H, ArH),
7.00 (d, J = 2.6 Hz, 1H, ArH), 3.34 (s, 1H, ArCH2N), 2.63–2.56
(m, 2H, NCH2CH3), 2.46–2.30 (m, 12H, NCH2CH2N), 2.23–2.17
(m, 2H, (CH2CH3)2), 1.86 (s, 9H, C(CH3)3), 1.58 (t, J = 8.1 Hz,
3H, ZnCH2CH3), 1.48 (s, 9H, C(CH3)3), 0.82 (t, J = 7.1 Hz, 12H,
2c (1.17 g, 3 mmol) and MgCl2 (0.15 g, 1.6 mmol) were stirred in
THF (40 cm3) at room temperature for 16 h. The reaction mixture
was then filtered and concentrated in vacuo to afford a waxy white
solid which was recrystallised from hot toluene to give 4c (0.34 g,
29%).
1
N(CH2CH3)2), 0.37 (q, J = 8.1 Hz, 2H, ZnCH2CH3). 13C{ H}
1H NMR (250 MHz, C6D6): d 7.60 (d, J = 2.5, 1H, ArH),
6.98 (d, J = 2.5, 1H, ArH), 3.00 (br s, ArCH2N(CH2CH2–), 2.86
(s, 6H, OCH3), 1.74 (s, 9H, C(CH3)3), 1.50 (s, 9H, C(CH3)3).
NMR (100 MHz, C6D6): d 165.4, 138.2, 134.8, 125.3, 124.2, 122.8,
58.3, 53.7, 49.8, 46.3, 35.9, 32.2, 30.2, 22.7, 14.3, 13.7, 10.4, −1.4.
MS data (CI, m/z): 526 [M + H]+ (Found C, 66.18, H, 10.72, N,
7.97. C29H55N3OZn requires C, 66.07, H, 10.52, N, 7.97%).
1
13C{ H} NMR (100 MHz, C6D6): d 164.7, 136.3, 133.1, 125.7,
123.6, 122.4, 70.6, 69.1, 62.1, 58.7, 35.5, 34.1, 32.5, 30.4 (Found
C, 69.70, H, 9.84, N, 3.93. C42H72MgN2O6 requires C, 69.55, H,
10.01, N, 3.86%).
Ethyl zinc 4,6-di-tert-butyl-2-bis(2-dimethylamino)propyl)-
aminomethylphenoxide, 7b
Complex 7b was formed in an analogous manner to 7a using
1b (3.00 g, 6.5 mmol) and diethyl zinc (0.84 g, 6.8 mmol).
Recrystallisation from hot heptane afforded 7b as colourless
crystals (1.99 g, 62%).
Calcium bis(4,6-di-tert-butyl-2-bis(2-
diethylamino)ethyl)aminomethylphenoxide), 5a
2a (1.00 g, 2 mmol) and CaI2 (0.31 g, 1 mmol) were stirred in
THF (40 cm3) at room temperature for 16 h. The reaction mixture
was then filtered and concentrated in vacuo to afford a waxy white
solid which was recrystallised from hot toluene to afford 5a (0.27 g,
30%).
1H NMR (400 MHz, C6D6): d 7.60 (d, J = 2.7 Hz, 1H, ArH),
6.61 (d, J = 2.7 Hz, 1H, ArH), 3.72 (s, 1H, ArCH2N), 2.45–
2.30 (m, 4H, NCH2CH2CH2), 2.00 (s, 12H, N(CH3)2), 1.97–1.79
(m, 4H, NCH2CH2CH2), 1.85 (s, 9H, C(CH3)3) 1.63 (t, J =
8.1 Hz, 3H, ZnCH2CH3), 1.50 (s, 9H, C(CH3)3), 1.38–1.18 (m, 4H,
1H NMR (500 MHz, C6D6): d 7.61 (d, J = 2.8 Hz, 1H, ArH),
7.21 (d, 1H, J = 2.8 Hz, ArH), 4.01 (br s, ArCH2N), 2.53 (br s,
12H, N(CH2CH2N(CH2CH3)2), 1.81 (s, 9H, C(CH3)3), 1.46 (s, 9H,
1
NCH2CH2CH2), 0.37 (q, J = 8.1 Hz, 2H, ZnCH2CH3). 13C{ H}
NMR (100 MHz, C6D6): d 164.6, 137.9, 133.9, 125.6, 123.9, 121.0,
59.6, 55.0, 46.2, 35.9, 34.2, 32.5, 30.3, 22.7, 21.3, 14.3, −2.8. MS
data (CI, m/z): 498 [M]+ (Found C, 64.91, H, 10.19, N, 8.32.
C27H51N3OZn requires C, 64.97, H, 10.30, N, 8.42%).
C(CH3)3), 0.82 (s, 12H, N(CH2CH3)2). 13C{ H} NMR (100 MHz,
1
C6D6): d 165.4, 136.0, 132.5, 126.9, 124.1, 122.9, 61.1, 52.2, 47.2,
46.6, 35.7, 34.1, 32.4, 30.4, 12.0 (Found C, 71.57, H, 11.08, N,
9.37. C54H100CaN6O2 requires C, 71.63, H, 11.13, N, 9.28%).
Ethyl zinc 4,6-di-tert-butyl-2-bis(2-methoxyethyl)-
aminomethylphenoxide, 7c
Dimethyl aluminium 4,6-di-tert-butyl-2-bis(2-methoxyethyl)-
aminomethylphenoxide, 6c
Complex 7c was formed in an analogous manner to 7a using 1c
(3.00 g, 8.5 mmol) and diethyl zinc (1.11 g, 9 mmol). Recrystalli-
sation from hot heptane afforded 8c as a white crystalline solid
(4.71 g, 66%).
A 2 M trimethyl aluminium solution in toluene (11 cm3, 22 mmol)
was added to a solution of 1c (7.21 g, 21 mmol) in toluene
(100 cm3). The reaction was then stirred at reflux temperature
for 16 h. The resultant orange solution was concentrated under
reduced pressure to afford a waxy oil which was left to stand to
form crystals of 6c (2.12 g, 25%).
1H NMR (400 MHz, C6D6): d 7.57 (d, J = 2.7 Hz, 1H,
ArH), 6.88 (d, J = 2.6 Hz, 1H, ArH), 3.32 (s, 1H, ArCH2N),
2.97 (ddd, J = 3.7 Hz, J = 8.9 Hz, J = 10.0 Hz, 2H,
NCH2CH2O), 2.85 (s, 6H, OCH3), 2.82 (ddd, 1H, J = 4.5 Hz,
J = 4.5 Hz, J = 10.1 Hz, 2H, NCH2CH2O), 2.42 (ddd, 1H,
J = 4.4 Hz, J = 8.8 Hz, J = 13.3 Hz, 2H, NCH2CH2O),
2.18 (ddd, 1H, J = 4.1 Hz, J = 4.1 Hz, J = 13.4 Hz,
2H, NCH2CH2O), 1.86 (s, 9H, C(CH3)3), 1.62 (t, J = 8.1 Hz,
3H, ZnCH2CH3), 1.45 (s, 9H, C(CH3)3), 0.57 (q, J = 8.1 Hz, 2H,
1H NMR (500 MHz, C6D6): d 7.59 (d, J = 2.5 Hz, 1H, ArH),
6.79 (d, J = 2.5 Hz, 1H, ArH), 3.49 (s, 1H, ArCH2N), 3.23–
3.18 (m, 2H, NCH2CH2O), 3.03–2.98 (m, 2H, NCH2CH2O),
2.83 (s, 6H, OCH3), 2.79–2.64 (m, 4H, NCH2CH2O), 1.73 (s,
9H, C(CH3)3), 1.41 (s, 9H, C(CH3)3), −0.36 (s, 6H, Al(CH3)2).
1
13C{ H} NMR (100 MHz, C6D6): d 157.5, 138.2, 137.8, 125.1,
1
ZnCH2CH3). 13C{ H} NMR (100 MHz, C6D6): d 164.4, 138.4,
124.7, 120.0, 67.1, 59.3, 58.4, 50.4, 35.4, 34.2, 32.1, 30.3, 30.0,
−9.4. MS data (CI, m/z): 408 [M]+ (Found C, 67.68, H, 10.20, N,
3.28. C25H42AlNO3 requires C, 67.78, H, 10.39, N, 3.44%).
135.0, 125.2, 124.1, 122.4, 68.5, 59.5, 58.6, 56.5, 35.8, 34.2, 32.4,
30.2, 13.5, −1.9. MS data (CI, m/z): 444 [M + H]+ (Found: C,
62.00, H, 9.18, N, 3.14. C23H41NO3Zn requires C, 62.08, H, 9.29,
N, 3.15%).
Ethyl zinc 4,6-di-tert-butyl-2-bis(2-diethylamino)ethyl)-
aminomethylphenoxide, 7a
4,6-Di-tert-butyl-2-bis(2-diethylamino)ethyl)-
aminomethylphenoxide chromium dichloride, 8a
1a (2.07 g, 4.8 mmol) in toluene (40 cm3) was added to a solution of
diethyl zinc (0.62 g, 5.0 mmol) in toluene (20 cm3) at −78 ◦C. The
reaction mixture was allowed to warm to room temperature and
stirred for 16 h. The resultant colourless solution was concentrated
under reduced pressure to yield a waxy off-white solid, which was
2a (3.14 g, 6.7 mmol) in THF (20 cm3) was added to a solution of
CrCl3(THF)3 (2.49 g, 6.7 mmol) in THF (20 cm3). The mixture was
stirred for 16 h and then filtered and concentrated under reduced
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pressure to yield a dark green solid. Recrystallisation from layered
toluene–pentane afforded 8a (1.15 g, 31%).
X-Ray crystallography
Table 9 provides a summary of the crystallographic data for
compounds 2a, 3b, 6c, 7a, 7c, 8a, 9c and 10c. Analogous data for
4c and 5a may be found in Table S1 (ESI†). Data were collected
using Oxford Diffraction Xcalibur 3 (2a, 3b, 6c, 7a, 7c, 9c and
10c) and PX Ultra (8a) diffractometers, and the structures were
refined based on F2 using the SHELXTL and SHELX-97 program
systems.10
leff = 3.9 lB. MS data (FAB +ve, m/z): 555 (4%, [M]+),
519 (100%, [M − Cl]+) (Found: C, 58.27, H, 8.98, N, 7.64%.
C27H50Cl2CrN3O requires C, 58.37, H, 9.07, N, 7.56%).
4,6-Di-tert-butyl-2-bis(2-methoxyethyl)aminomethylphenoxide
iron(II) chloride, 9c
A solution of 2c (0.83 g, 2.4 mmol) in THF (20 cm3) was added
to a THF solution (20 cm3) of FeCl2.(THF)1.5 (0.50 g, 2.4 mmol).
The mixture was stirred for 16 h and then filtered and concentrated
under reduced pressure to yield a light blue solid. Recrystallisation
from hot toluene afforded 9c as colourless crystals (0.51 g, 49%).
leff = 8.7 lB. MS data (FAB +ve, m/z): 441 (38%, [M]+), 406
(47%, [M − Cl]+), 352 (100% [M − Cl − Fe]+) (Found: C, 56.95,
H, 8.28, N, 3.08. C42H72Cl2Fe2N2O6 requires C, 57.09, H, 8.21, N,
3.17%).
CCDC reference numbers 293279–293286, 293483 and 293484.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b607753f
References
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7432.
4,6-Di-tert-butyl-2-bis(2-methoxyethyl)aminomethylphenoxide
cobalt(II) chloride, 10c
A solution of 2c (0.94 g, 2.4 mmol) in THF (20 cm3) was added
to a THF solution (20 cm3) of CoCl2 (0.31 g, 2.4 mmol). The
solution was stirred for 16 h and then filtered and concentrated
under reduced pressure to yield a blue solid. Recrystallisation from
layered toluene–pentane gave 10c (0.51 g 49%).
6 S. Groysman, E. Sergeeva, I. Goldberg and M. Kol, Inorg. Chem., 2005,
44, 8188.
7 W. Herwig and H. Zeiss, J. Org. Chem., 1958, 23, 1404.
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10 SHELXTL PC version 5.1, Bruker AXS, Madison, WI, 1997;
G. M. Sheldrick, SHELX-97, Institut Anorg. Chemie, Tammannstr.
4, D37077 Go¨ttingen, Germany, 1998.
leff = 3.7 lB, MS data (FAB +ve, m/z): 444 (8%, [M]+), 408
(16%, [M − Cl]), 352 (100%, [M − Cl − Co]+) (Found: C, 56.61,
H, 8.21, N, 3.24. C21H36NClCoO3 requires C, 56.69, H, 8.16, N,
3.15%).
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