Synthesis and structures of bimetallic and polymeric zinc coordination compounds supported by salicylaldiminato and anilido-aldimine ligands

Article abstract of DOI:10.1039/b615080b

A series of bimetallic zinc complexes bearing salicylaldiminato (1b-3b) or anilido-aldimine (4c-5c) ligand frameworks, in which the metal centres are separated by aliphatic spacer groups containing 3-6 methylene units, were targeted. X-Ray analysis of sal

Full text of DOI:10.1039/b615080b

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Synthesis and structures of bimetallic and polymeric zinc coordination
compounds supported by salicylaldiminato and anilido–aldimine ligands†
David J. Doyle, Vernon C. Gibson* and Andrew J. P. White
Received 17th October 2006, Accepted 16th November 2006
First published as an Advance Article on the web 7th December 2006
DOI: 10.1039/b615080b
A series of bimetallic zinc complexes bearing salicylaldiminato (1b–3b) or anilido–aldimine (4c–5c)
ligand frameworks, in which the metal centres are separated by aliphatic spacer groups containing 3–6
methylene units, were targeted. X-Ray analysis of salicylaldiminato derivative 2b, with a 4 carbon
spacer group, revealed a coordination polymer in the solid state where each zinc centre is ligated by two
salicylaldiminato ligands. Contrastingly, the structure of the anilido–aldimine complex 4c, with a 3
carbon methylene spacer group, was found to be a discrete bimetallic complex. These differences are
attributed to the differing steric protection at the anilido vs phenoxy donors, the latter more readily
facilitating bridges between metal centres.
Introduction
Results and discussion
Catalytic pathways involving the cooperative reactivity between
two mutually interconnected metal complexes has been observed
in nature. One such example is the phosphomonoesterase enzyme
alkaline phosphatase which is known to contain two Zn centres
at the active site.1 Consequently, much attention has been directed
toward the synthesis of bimetallic zinc complexes which can po-
tentially mimic phosphomonoesterase activity in protic media.2,3
Contrastingly, organometallic binuclear zinc complexes that are
soluble in aprotic media are less commonly encountered.4,5 In
addition to their structural novelty, these complexes also have
potential applications in conventional catalysis. For example,
Coates and co-workers have shown that the copolymerisation
of cyclohexene oxide with the biorenewable feedstock CO2,
catalysed by b-dimiminate zinc complexes, occurs via a bimetallic
intermediate involving the cooperative effect of two discrete Zn
species.6 Further studies have suggested that bimetallic analogues
of such b-dimiminate zinc complexes can provide an enhancement
of catalytic activity over their monometallic derivatives.7 It has
also been proposed that zinc centres held at a certain fixed distance
apart, such as found in the zinc glutarate lattice, are beneficial for
copolymerisations of propylene oxide with carbon dioxide.8 With
these considerations in mind, we initiated a study to investigate
the synthesis and charaterisation of bimetallic salicylaldiminato
Zn complexes and anilido–aldimine zinc complexes in which
the ligated zinc centres are separated by aliphatic methylene
spacer groups of between 3–6 carbon atoms to allow for differing
separation of the two metal centres.
Bis-salicylaldiminato complexes
The pro-ligands 1a, 2a and 3a were prepared by standard
condensation reactions between two equivalents of 3,5-tBu sal-
icylaldehyde and one equivalent of the appropriate diamine in
methanol (Scheme 1).
Scheme 1 Synthesis of 1a–3a.
The ligands were isolated in high yield and were recrystallised
from pentane. 1H-NMR and 13C-NMR studies gave well resolved
resonances for all proton and carbon environments, while elemen-
tal analysis indicated that the compounds were formed in good
purity.
Compounds 1b–3b were prepared by the reaction of two
equivalents of ZnEt2 with one equivalent of the pro-ligands 1a–3a,
respectively, in toluene (Scheme 2). They were recrystallised from
toluene, pentane or mixtures of both to give bright yellow (1b, 2b)
and pale yellow (3b) crystalline aggregates. X-Ray quality crystals
of 2b could be obtained from a 50 : 50 toluene–pentane mixture
after standing for 6 days at −25 ◦C.
Department of Chemistry, Imperial College London, Exhibition Road,
London, UK SW7 2AZ. E-mail: v.gibson@imperial.ac.uk
† Electronic supplementary information (ESI) available: Crystal data for
2b, 4c and 5c; selected bond lengths and angles for 5c; structures of 2b, 4c
and 5c and environment of the Zn2O2 ring in the structure of 2b. See DOI:
10.1039/b615080b
358 | Dalton Trans., 2007, 358–363
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◦
˚
Table 1 Selected bond lengths (A) and angles ( ) for 2b
Zn(1)–O(1)
Zn(1)–O(18A)
Zn(2)–O(1)
Zn(2)–O(18A)
2.025(2) Zn(1)–N(7)
2.123(3) Zn(1)–C(35)
2.117(3) Zn(2)–N(12A)
2.032(2) Zn(2)–C(37)
2.048(3)
1.978(4)
2.027(3)
1.956(4)
O(1)–Zn(1)–N(7)
O(1)–Zn(1)–C(35)
N(7)–Zn(1)–C(35)
O(1)–Zn(2)–N(12A)
O(1)–Zn(2)–C(37)
N(12A)–Zn(2)–C(37) 132.15(19) O(18A)–Zn(2)–C(37)
Zn(1)–O(1)–Zn(2) 93.89(9) Zn(1)–O(18A)–Zn(2)
92.11(9)
O(1)–Zn(1)–O(18A)
85.49(9)
92.60(11)
126.05(16)
85.48(9)
93.07(10)
116.12(16)
93.53(10)
116.02(15) N(7)–Zn(1)–O(18A)
131.70(15) O(18A)–Zn(1)–C(35)
93.84(11) O(1)–Zn(2)–O(18A)
123.76(19) N(12A)–Zn(2)–O(18A)
the environment of the Zn2O2 ring has approximate C2 symmetry
about an axis perpendicular to the plane of the ring. The C4
linkage between the two salicylaldimine moieties adopts an all
anti conformation, the three C–C torsion angles being ca. −169,
◦
Scheme 2 Synthesis of 1b–3b.
=
+174 and +178 . The C N–C–C units, by contrast, have gauche
conformations, being ca. −123 and +123◦. This results in the
O(1) and O(18) aryl rings at each end of the bis(salicylaldimine)
ligand being inclined by only ca. 10◦. A similar arrangement is
seen for the closely related free ligand N,Nꢀ-bis(salicylidene)-1,4-
butanediamine,9 and for complexes of ligand 2a with aluminium10
and boron.11 The structure of the gallium complex12 of ligand 2a
has two independent molecules, one of which has the same anti–
anti–anti conformation for the C–C bonds of the C4 linkage as seen
here in the structure of 2b, whilst the other independent molecule
has a gauche–anti–gauche conformation. All of these metal com-
plexes are monomeric species, though polymers are known for
a couple of silver complexes13 and one manganese complex14 of
N,Nꢀ-bis(salicylidene)-1,4-butanediamine. These three polymeric
species all have all anti conformations along the C4 linkages.
Adjacent repeat units within the polymer here in the structure
of 2b are related by a glide plane along the crystallographic
b axis direction, and the {Zn2O2} centroid · · · {Zn2O2} centroid
˚
separation is ca. 10.4 A.
1H-NMR spectra of 1b–3b reveal sharp quartet resonances for
the methylene protons of the Zn-attached ethyl groups at 0.41, 0.40
and 0.43 ppm, respectively. The corresponding methyl resonances
are obscured by the presence of several broadened resonances
associated with the t-butyl groups of the phenoxy donors, the latter
indicating that a fluxional process is operating, possibly involving
Fig. 1 The asymmetric unit in the structure of 2b. Atom labels with an
“A” after the number are related to their counterparts without the letter
by a glide plane, e.g. Zn(1) and Zn(1A).
The single crystal X-ray structure determination on 2b
revealed the formation of an extended polymer with the
bis(salicylaldiminato) ligand linking neighbouring Zn2O2 rings;
Fig. 1 shows the basic repeating moiety (the crystallographic
asymmetric unit) and Fig. 2 shows part of one of the polymer
chains.
monomer–oligomer equilibria in solution. Room temperature 13
C
NMR spectra show the anticipated two pairs of resonances for
the t-butyl substituents which are now sharp, a consequence of
the longer relaxation time for the 13C nuclei. The similar NMR
features of 1–3 suggest closely related structures. However, there
is a marked decrease in solubility in toluene and pentane as the
spacer group is lengthened. A practical limit is reached at six
methylene units beyond which the bimetallic zinc ethyl complexes
can no longer be readily purified by re-crystallisation.
The Zn2O2 rings have a slightly folded geometry, the {Zn2O(1)}
and {Zn2O(18)} planes being inclined by ca. 14◦; the transannular
˚
Zn · · · Zn and O · · · O distances are 3.0276(5) and 2.817(3) A
respectively. The geometries at the zinc centres are distorted
tetrahedral with angles in the range 85.49(9)–131.70(15)◦ at Zn(1),
and 85.48(9)–132.15(19)◦ at Zn(2) (Table 1). The O(1)/N(7) and
O(18)/N(12) six-membered C3NOZn chelate rings both adopt
folded geometries. For the former Zn(1) and N(7) lie ca. 0.92
Bis-anilido–aldimine complexes
˚
and 0.41 A respectively out of the {C3O} plane (which is coplanar
Next we targeted derivatives containing anilido–aldimine ligands.
The ligands are comprised of two anilido–aldimine chelating
centres separated by a flexible aliphatic spacer group whose
length may be varied depending on the diamine employed. The
fluorinated diimine compounds 4a (n = 3) and 5a (n = 6)
were synthesised via the reation of two equivalents of
˚
to within ca. 0.04 A) in a direction away from Zn(2), whilst for
˚
the latter Zn(2A) and N(12) lie ca. 0.87 and 0.34 A respectively
˚
out of the {C3O} plane (which is coplanar to within ca. 0.01 A)
in a direction away from Zn(1). The ethyl ligands on each zinc
centre are in a syn relationship (see Fig. S2 in the ESI†) such that
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Fig. 2 Part of one of the extended chains present in the crystal of 2b.
2-fluorobenzaldehyde with the appropriate diamine in hexane. The
reaction of two equivalents of lithiated 2,6-diisopropylaniline with
the resultant fluorinated diimines, followed by the addition of an
extra equivalent of nBuLi yielded pro-ligands 4b (n = 3) and 5b
(n = 6) after workup (Scheme 3).
Scheme 4 Synthesis of 4c and 5c.
The two six-membered C3N2Zn chelate rings have noticeably
different conformations; that at Zn(1) has a folded geometry with
=
the carbon and nitrogen atoms of the C N(7) imine unit lying ca.
˚
0.24 and 0.37 A out of the {Zn(1),N(1),C(1),C(6)} plane (which is
˚
coplanar to within ca. 0.02 A), whilst that at Zn(2) has a slight sofa
˚
˚
conformation with the metal lying ca. 0.11 A out of the {C3N2}
plane (which is coplanar to within ca. 0.02 A). In contrast to the
all anti conformation seen for the C4 linkage between the two
imine units in the structure of 2b, here the C3 linkage has a mixed
conformation, the N(7)–C–C–C and C–C–C–N(11) torsion angles
◦
=
being ca. 60 (gauche) and 178 (anti) respectively. The C N–C–C
Scheme 3 Synthesis of 4b and 5b.
moieties have near orthogonal conformations, the torsion angles
Treatment of one equivalent of either 4b or 5b with two
equivalents of diethyl zinc in toluene gave compounds 4c and
5c, respectively, as yellow crystalline solids (Scheme 4). 4c and 5c
could be recrystallised from toluene–pentane (50 : 50) mixtures.
By contrast to the polymeric structure found for 2b, the structure
of 4c is a bimetallic species. The zinc centres here are trigonal
planar, the smallest angle at each corresponding to the bite of the
N,Nꢀ chelate ligand (Table 2, Fig. 3).
◦
˚
Table 2 Selected bond lengths (A) and angles ( ) for 4c
Zn(1)–N(1)
Zn(1)–C(42)
Zn(2)–N(17)
N(1)–Zn(1)–N(7)
N(7)–Zn(1)–C(42)
N(11)–Zn(2)–C(44)
1.942(2)
1.968(3)
Zn(1)–N(7)
Zn(2)–N(11)
1.9307(19) Zn(2)–C(44)
1.984(2)
2.001(2)
1.958(3)
130.87(12)
96.11(8)
141.04(10)
94.97(8)
133.82(12)
122.76(11)
N(1)–Zn(1)–C(42)
N(11)–Zn(2)–N(17)
N(17)–Zn(2)–C(44)
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cipitate formed from the yellow solution. The mixture was allowed
to stir for a further 2 h. The solid product was isolated by filtration
1
and dried under vacuum. Yield: 84% (6.81 g). H-NMR (298 K,
=
CDCl3, 250 MHz): d 8.41 (2H, s, HC N), 7.41 (2H, s, Ar), 7.10
(2H, s, Ar), 3.72 (4H, t, NCH2), 2.14 (2H, quint, CH2CH2CH2),
1.47 (18H, s, tBu), 1.32 (18H, s, tBu). 13C-NMR (CDCl3,
125.76 MHz): d 169.32, 158.13, 140.06, 136.70, 126.89, 125.86,
35.07, 34.15, 31.74, 29.47. Elem. Anal. Cald. for C33H50N2O2: C,
78.21; H, 9.94; N, 5.53. Found: C, 78.12; H, 9.96; N, 5.59%.
Synthesis of 2a. An analogous procedure to that described
for the synthesis of 1a was employed, using 3,5-di-t-butyl sali-
cylaldehyde (10.16 g, 0.043 mol) and 1,4-diaminobutane (1.91 g,
0.022 mol). The mixture was allowed to stir overnight before work-
Fig. 3 The molecular structure of 4c. The Zn(1) · · · Zn(2) separation is
˚
6.3840(6) A.
1
up. Yield: 79% (9.05 g). H-NMR (298 K, CDCl3, 250 MHz):
being ca. 95 and 102◦ for the N(7) and N(11) containing moieties
respectively. As a result, the two anilido–aldimine aryl rings are
oriented approximately orthogonally (inclined by ca. 79◦) cf. the
near co-planar arrangement in 2b (inclined by ca. 10◦). Similar
gauche–anti conformations for the C3 linkage are seen in the
structures of the free ligand N,Nꢀ-bis(2-tosylaminobenzylidene)-
1,3-propanediamine15 and its zinc16 and nickel17 complexes. The
crystal structure of 5c shows similar features to 4c with minimal
differences between the Zn–O and Zn–N bond distances and
angles. Further details for this structure are provided in the ESI.†
=
d 13.90 (2H, s, –OH), 8.38 (2H, s, –HC N), 7.40 (2H, s, Ar),
7.09 (2H, s, Ar), 3.64 (4H, br, CH2N), 1.82 (4H, br, CH2CH2N),
1.47 (18H, s, Bu), 1.33 (18H, s, Bu). 13C-NMR (298 K, CDCl3,
125.76 MHz): d 165.97, 158.13, 139.95, 136.66, 126.79, 125.78,
117.83, 59.26, 35.03, 34.13, 31.52, 29.45, 28.56. Elem. Anal. Cald.
for C34H52N2O2: C, 78.41; H, 10.06; N, 5.38. Found: C, 78.67; H,
10.15; N, 5.29%.
t
t
Synthesis of 3a. An analogous procedure to that described
for the synthesis of 1a was employed, using 3,5-di-t-butyl sal-
icylaldehyde (8.00 g, 0.034 mol) and 1,6-diaminohexane (1.99 g,
0.017 mol). The mixture was allowed to stir overnight before work-
up. Yield 72% (6.71 g). 1H-NMR (298 K, CDCl3, 250 MHz): d 8.35
Conclusions
=
(2H, s, –C NH), 7.38 (2H, s, Ar), 7.09 (2H, s, Ar), 3.58 (4H, t,
CH2N), 1.72 (4H, m, CH2CH2N), 1.46 (18H, s, Bu), 1.45 (4H,
A successful synthetic strategy has been developed for the synthesis
of bi- and multi-metallic complexes containing zinc centres
separated by different length aliphatic spacer groups. In the case
of salicylaldiminato derivatives, extended coordination polymers
form via bis-chelation of the zinc centres, a consequence of the
steric accessibility of the phenoxide oxygen donors for bridging
between metals. The greater steric hindrance of anilido–aldimine
ligands bearing the 2,6-diisopropylphenyl amide donor results in
discrete dimeric products.
t
m, CH2CH2CH2N), 1.31 (18H, s, tBu). 13C-NMR (298 K, CDCl3,
125.76 MHz): d 165.61, 158.32, 139.77, 136.62, 126.65, 125.64,
117.79, 59.38, 35.01, 34.11, 31.50, 30.73, 29.43, 26.85. Elem. Anal.
Cald. for C36H56N2O2: C, 78.78; H, 10.28; N, 5.10. Found: C, 78.98;
H, 10.20; N, 5.06%.
Synthesis of 1b. To a solution of 1a (3.53 g, 0.007 mol) in
toluene (100 cm3) was added ZnEt2 (1.44 cm3, 0.014 mol) at
0 ◦C. After warming the mixture to room temperature and stirring
overnight, the resultant yellow precipitate was isolated by filtration
and re-crystallised from toluene (20 cm3). Yield 60% (2.91 g). 1H-
Experimental
=
NMR (298 K, C6D6, 250 MHz): d 7.72–7.36 (2H, m, –HC N),
General considerations
7.06–6.82 (4H, m, Ar), 3.52–2.66 (2H, m, CH2CH2N), 1.73–1.61
t
t
All reactions were carried out using standard Schlenk techniques
unless otherwise stated. Toluene and pentane were dried by passing
through a cylinder filled with commercially available Q-5 catalyst
(13% Cu(II) oxide on Al2O3) and activated Al2O3 (3 mm, pellets)
under a stream of nitrogen. All other solvents were distilled over
standard drying agents under nitrogen. The solvents were degassed
before use. All reagents were obtained from Aldrich Chemical Co.
and used as received except for 2,6-diisopropylaniline which was
purified by vacuum distillation prior to use. NMR spectra were
recorded on Bruker 250 MHz, DRX-400 MHz or AM-500 MHz
spectrometers. NMR chemical shifts are quoted in ppm relative to
the residual protio solvent resonances.
(18H, m, Bu), 1.48–1.34 (18H, m, Bu and 6H, m, ZnCH2CH3;
overlapping resonances), 0.41 (4H, quintet, ZnCH2CH3). 13C-
NMR (298 K, CD2Cl2, 63 MHz): d173.36, 171.48, 169.13,
166.40, 141.68, 137.81, 136.04, 130.67, 129.89, 129.49, 128.69,
125.78, 119.74, 117.51, 58.56, 35.97, 34.34, 31.81, 30.39, 39.86,
12.23 (ZnCH2CH3), 1.82 (CH2CH3). Elem. Anal. Cald. for
C37H58N2O2Zn2: C, 64.07; H, 8.43; N, 4.04. Found: C, 63.78; H,
8.67; N, 3.97%.
Synthesis of 2b. To a solution of 2a (4.31 g, 0.0083 mol) in
toluene (100 cm3) was added ZnEt2 (1.69 cm3, 0.0166 mol) at
0 ◦C. After warming the mixture to room temperature and stirring
overnight, the resultant yellow precipitate was isolated by filtration
and re-crystallised from toluene (20 cm3). Yield 57% (3.35 g). 1H-
Preparations
=
NMR (298 K, C6D6, 400 MHz): d 7.72 (2H, s, HC N), 7.53 (2H, s,
Synthesis of 1a. To a solution of 3,5-di-t-butyl salicylaldehyde
(7.57 g, 0.032 mol) in ethanol was added 1,3-diaminopropane
(1.35 cm3, 0.016 mol). After several minutes, a bright yellow pre-
Ar), 6.90 (2H, s, Ar), 3.50–2.74 (4H, br, CH2CH2), 1.75–1.68
t
t
(18H, m, Bu), 1.40–1.28 (18H, m, Bu and 6H, m, ZnCH2CH3;
overlapping resonances), 0.40 (4H, q, ZnCH2CH3). 13C-NMR
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(298 K, C6D6, 100.61 MHz): d 172.02, 170.68, 141.51, 136.20,
129.88, 60.27, 59.62, 35.69, 33.83, 31.43, 29.72, 11.40, 2.52. Elem.
Anal. Cald. for C38H60N2O2Zn2: C, 64.49; H, 8.55; N, 3.96. Found:
C, 64.53; H, 8.72; N, 3.85%.
CH2CH2), 6.28 (2H, m, Ar), 6.69 (2H, m, Ar), 7.09–7.37 (10H, m,
Ar), 8.47 (2H, s, N CH), 10.62 (NH). 13C NMR (298 K, CDCl3,
=
100.61 MHz): d −1.79, 11.89, 24.27, 27.87, 34.38, 58.82, 112.69,
113.73, 116.09, 123.72, 124.98, 133.83, 137.00, 143.53, 144.55,
157.34, 169.40. Elem. Anal. Cald. for C41H52N4: C, 81.95; H, 8.72;
N, 9.32. Found: C, 82.03; H, 8.72; N, 9.19%.
Synthesis of 3b. To a solution of 3a (4.31 g, 0.0083 mol) in
toluene (100 cm3) was added ZnEt2 (1.69 cm3, 0.0166 mol) at
0 ◦C. After warming the mixture to room temperature and stirring
overnight, the resultant yellow precipitate was isolated by filtration
and re-crystallised from toluene (30 cm3). Yield 53% (0.74 g). 1H-
Synthesis of 5b. Using an analogous procedure to that de-
scribed for the synthesis of 4b, n-BuLi (2.5 M solution in
hexane; 56 cm3, 140 mmol) was added to a solution of 2,6-
diisopropylaniline (27.3 cm3, 140 mmol) in THF (100 cm3) while
stirring at 0 ◦C. The resultant light red coloured solution was added
to a colourless solution of 5a (22.99 g, 70 mmol) in THF (100 cm3).
=
NMR (298 K, C6D6, 250 MHz): d 7.76–7.67 (2 H, m, HC N),
7.59 (2H, s, Ar), 6.93 (2H, s, Ar), 3.16–2.79 (4H, br, CH2N) 1.39–
t
1.35 (18H, m, Bu and 6H, CH2CH2; overlapping resonances),
1
t
Yield 27% (24.0 g). H NMR (298 K, CDCl3, 400 MHz): d 1.17
1.76–1.67 (18H, m, Bu), 1.18–0.90 (6H, br, ZnCH2CH3) 0.43
i
i
(4H, q, ZnCH2CH3). 13C-NMR (298 K, C6D6, 100.61 MHz): d
170.55, 141.47, 136.23, 129.75, 60.74, 35.69, 33.77, 31.43, 29.72,
26.35, 11.42 (ZnCH2CH3), 2.33 (ZnCH2CH3). Elem. Anal. Cald.
for C40H64N2O2Zn2: C, 65.30; H, 8.77; N, 3.81. Found: C, 65.11;
H, 8.75; N, 8.82%.
(12H, m, Pr), 1.18 (12H, m, Pr), 1.45 (4H, m, CH2CH2), 1.71
(4H, m, NCH2CH2), 3.16 (4H, sept, iPr), 3.63 (4H, t, NCH2), 6.25
(2H, d, Ar), 6.69 (2H, t, Ar), 7.09–7.37 (8H, m, Ar), 8.46 (2H, s,
N CH), 10.65 (NH). 13C NMR (298 K, CDCl3, 100.61 MHz): d
=
22.88, 24.93, 27.16, 28.49, 31.36, 61.47, 111.62, 114.90, 116.75,
123.70, 127.16, 130.88, 133.38, 135.30, 147.54, 149.43, 164.04.
Elem. Anal. Cald. for C44H58N4: C, 82.19; H, 9.09; N, 8.71. Found:
C, 80.85; H, 8.66; N, 8.52%.
Synthesis of 4a. To a solution of 1,3-diaminopropane (2.98 g,
40 mmol) in hexane (30 cm3) was added 2-fluorobenzaldehyde
(10 g, 81 mmol). After stirring for 12 h, a quantity of water was
seen to collect at the bottom of the reaction flask. The solution
was dried over MgSO4 and the product then re-crystallised from
hexane by standing for one day at −25 ◦C, yielding white needle-
like crystals. Yield 89% (10.2 g) 1H NMR (298 K, CDCl3,
400 MHz): d 2.04 (2H, quintet, CH2CH2), 3.64 (4H, t, CH2CH2),
Synthesis of 4c. To a solution of compound 4b (2.45 g,
4.08 mmol) in toluene–pentane (50 : 50, 100 cm3) at 0 ◦C
was added ZnEt2 (1.00 g, 8.15 mmol). The colourless solution
immediately became bright yellow and was stirred for a further
12 h at room temperature. The solution was concentrated under
reduced pressure and left to stand at −25 ◦C for 12 h after which
7.00–7.96 (8H, m, Ar), 8.50 (2H, s, N CH). 13C NMR (298 K,
=
1
yellow crystals of 4c had formed. Yield 57% (1.83 g). H NMR
CDCl3, 100.61 MHz): d 31.91, 59.42, 115.66, 124.15, 127.65,
131.94, 154.18, 160.83, 163.33. Elem. Anal. Cald. for C17H16F2N2:
C, 71.31; H, 5.63; N, 9.78. Found: C, 71.23; H, 5.74; N, 9.86%.
(298K, CDCl3, 400 MHz): d 0.25 (4H, q, ZnCH2CH3), 0.91 (6H,
t, ZnCH2CH3), 1.12 (12H, d, iPr), 1.20 (12H, d, iPr), 2.30 (2H, p,
CH2CH2), 3.08 (4H, septet, iPr), 3.88 (4H, t, CH2CH2), 6.32 (6H,
Synthesis of 5a. Using a procedure analogous to that described
for 4a, 2-fluorobenzaldehyde (20 g, 16 mmol) was added to
a solution of 1,3-diaminohexane (9.36 g, 81 mmol) in hexane
(30 cm3). The product was isolated as white needle-like crystals.
m, Ar), 7.93 (2H, m, Ar), 8.50 (2H, s, N CH). 13C NMR (298 K,
=
CDCl3, 100.61 MHz): d −1.79, 11.89, 24.27, 27.87, 34.38, 58.82,
112.69, 113.73, 116.09, 123.72, 124.98, 133.83, 137.00, 143.53,
144.55, 157.34, 169.40. Elem. Anal. Cald. for C45H60N4Zn2: C,
68.61; H, 7.68; N, 7.11. Found: C, 68.56; H, 7.81; N, 7.09%.
1
Yield 91% (24.2 g). H NMR (298 K, CDCl3, 400 MHz): d 1.38
(4H, p, CH2CH2), 1.67 (4H, m, CH2CH2), 3.56 (4H, t, CH2CH2),
6.92–7.27 (6H, m, Ar), 7.93 (2H, m, Ar), 8.50 (2H, s, N CH). 13C
=
Synthesis of 5c. Using an analogous procedure to that de-
scribed for the synthesis of 4c, ZnEt2 (1.10 g, 8.93 mmol) was
added to a solution of 5b (2.87 g, 4.46 mmol) in toluene (100 cm3)
at 0 ◦C. The product 5c was isolated as yellow crystals. Yield 52%
NMR (298 K, CDCl3, 100.61 MHz): d 27.11, 30.79, 61.90, 115.66,
124.17, 127.64, 131.85, 153.70, 160.80, 163.31. Elem. Anal. Cald.
for C20H22F2N2: C, 73.15; H, 6.75; N, 8.53. Found: C, 73.21; H,
6.90; N, 8.62%.
1
(1.92 g). H NMR (298 K, CDCl3, 400 MHz): d 0.26 (4H, q,
i
ZnCH2CH3), 0.98 (6H, t, ZnCH2CH3), 1.14 (12H, d, Pr), 1.22
Synthesis of 4b. To a solution of 2,6-diisopropylaniline
(24.38 cm3, 140 mmol) in THF (100 cm3) was added n-BuLi
2.5 M solution in hexane (56 cm3, 140 mmol) while stirring at
0 ◦C. The solution was allowed to warm to room temperature and
stirred for 12 h, after which the solution was light red in colour.
This solution was added to a colourless solution of compound
4a (20 g, 70 mmol) in THF (100 cm3). The resultant dark orange
solution was stirred overnight. An add◦itional equivalent of BuLi
was then added (28 cm3, 70 mmol) at 0 C. The solution darkened
considerably and was left to stir for a further 12 h. Distilled
water (200 cm3) was then carefully added and the organic layer
was separated and dried over MgSO4. After removal of solvent
under reduced pressure, the resultant residue was recrystallised
from pentane to yield a cream-coloured crystalline solid. Yield
37% (31 g). 1H NMR (298 K, CDCl3, 400 MHz): d 1.19 (24H, m,
(12H, d, iPr), 1.53 (4H, m, CH2CH2), 1.87 (4H, m, CH2CH2), 3.08
(4H, septet, iPr), 3.81 (4H, t, CH2CH2), 6.31 (2H, d, Ar), 6.50 (2H,
t, Ar), 7.08–7.31 (10H, m, Ar), 8.41 (2H, s, N CH). 13C NMR
=
(298 K, CD2Cl2, 100.61 MHz), 100.62 MHz): d −1.57, 12.23,
24.51, 27.10, 28.27. 32.53, 61.91, 112.81, 114.60, 116.17, 124.10,
125.26, 133.84, 137.48, 144.10, 145.34, 157.49, 169.44. Elem. Anal.
Cald. for C48H66N4Zn2: C, 69.47; H, 8.02; N, 6.75 Found: C, 69.59;
H, 8.13; N, 6.72%.
X-Ray crystallography
Crystal data for 2b. C38H60N2O2Zn2, M = 707.62, orthorhom-
bic, Aba2 (no. 41), a = 18.1320(8), b = 18.8215(7), c =
3
−3
˚
˚
23.1100(9) A, V = 7886.8(54) A , Z = 8, Dc = 1.192 g cm ,
l(Mo-Ka) = 1.248 mm−1, T = 173 K, 12497 independent
measured reflections, R1 = 0.063, wR2 = 0.149.
i
iPr), 2.11 (2H, quintet, CH2CH2), 3.18 (4H, p, Pr), 3.78 (4H, t,
362 | Dalton Trans., 2007, 358–363
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¯
4 M. T. Gamer and P. W. Roesky, Eur. J. Inorg. Chem., 2003, 2145.
5 S. D. Allen, D. M. Moore, E. B. Lobovsky and G. W. Coates,
J. Organomet. Chem., 2003, 683, 137.
Crystal data for 4c. C45H60N4Zn2, M = 787.71, triclinic, P1
˚
˚
(no. 2), a = 8.9147(5), b = 14.7627(9), c = 16.4967(9) A, a =
◦
3
88.863(6), b = 86.406(4), c = 72.948(5) , V = 2071.5(2) A , Z =
6 D. Moore, M. Cheng, E. B. Lobovsky and G. W. Coates, J. Am. Chem.
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Y. P a r k , J. Am. Chem. Soc., 2005, 127, 3031.
2, Dc = 1.263 g cm−3, l(Cu-Ka) = 1.676 mm−1, T = 173 K, 7684
independent measured reflections, R1 = 0.042, wR2 = 0.120.
8 (a) K. Soga, E. Imai and I. Hattori, Polym. J., 1981, 13, 407; (b) M.
Ree, J. Y. Bae, J. H. Jung and T. J. Shin, J. Polym. Sci., Part A: Polym.
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Crystal data for 5c. C48H66N4Zn2, M = 829.79, monoclinic,
˚
P21/n (no. 14), a = 11.5694(6), b = 13.4841(8), c = 14.3159(7) A,
◦
3
−3
˚
b = 98.626(4) , V = 2208.1(2) A , Z = 2, Dc = 1.248 g cm ,
l(Mo-Ka) = 1.122 mm−1, T = 173 K, 7658 independent measured
reflections, R1 = 0.045, wR2 = 0.095.
CCDC reference numbers 621015–621017.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b615080b
12 M. S. Hill, P. Wei and D. A. Atwood, Polyhedron, 1998, 17, 811.
13 M.-L. Tong, X.-M. Chen, B.-H. Ye and L.-N. Ji, Angew. Chem., Int.
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1545.
Acknowledgements
BASF is thanked for a studentship to DJD.
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This journal is
The Royal Society of Chemistry 2007
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©