Mono- vs. bi-metallic assembly on a bulky bis(imino)terpyridine framework: A combined experimental and theoretical study

Article abstract of DOI:10.1039/b516083a

The bis(imino)terpyridine ligands, 6,6″-{(2,6-i-Pr₂C ₆H₃)NCR}₂-2,2′:6′,2″-C ₁₅H₉N₃ (R = H L1, Me L2), have been prepared in high yield from the condensation reaction of the corre

Full text of DOI:10.1039/b516083a

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www.rsc.org/dalton | Dalton Transactions
Mono- vs. bi-metallic assembly on a bulky bis(imino)terpyridine framework:
a combined experimental and theoretical study
Yohan D. M. Champouret,a Jean-Didier Mare´chal,a,b Ishaq Dadhiwala,a John Fawcett,a Donna Palmer,a
Kuldip Singha and Gregory A. Solan*a
Received 14th November 2005, Accepted 6th February 2006
First published as an Advance Article on the web 22nd February 2006
DOI: 10.1039/b516083a
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The bis(imino)terpyridine ligands, 6,6 -{(2,6-i-Pr2C6H3)N CR}2-2,2 :6 ,2 -C15H9N3 (R = H L1, Me
L2), have been prepared in high yield from the condensation reaction of the corresponding carbonyl
compound with two equivalents of 2,6-diisopropylaniline. The molecular structure of L2 reveals a
transoid relationship between the imino and pyridyl nitrogen groups throughout the ligand framework.
Treatment of aldimine-containing L1 with one equivalent or an excess of MX2 in n-BuOH at 110 ◦C
gives the mononuclear five-coordinate complexes, [(L1)MX2] (M = Fe, X = Cl 1a; M = Ni, X = Br
1b; M = Zn, X = Cl 1c), in which the metal centre occupies the terpyridine cavity and the imino groups
pendant. Conversely, reaction of ketimine-containing L2 with excess MX2 in n-BuOH at 110 ◦C affords
the binuclear complexes, [(L2)M2X4] (M = Fe, X = Cl 3a; M = Ni, X = Br 3b; M = Zn, X = Cl 3c), in
which one metal centre occupies a bidentate pyridylimine cavity while the other a tridentate
bipyridylimine cavity. 1H NMR studies on diamagnetic 3c suggests a fluxional process is operational at
ambient temperature in which the central pyridine ring undergoes an exchange between metal
coordination. Under less forcing conditions (room temperature in dichloromethane), the monometallic
counterpart of 1b [(L2)NiBr2] (2b) has been isolated which can be converted to 3b by addition of one
equivalent of (DME)NiBr2 (DME = 1,2-dimethoxyethane) in n-BuOH at 110 ◦C. Quantum mechanical
calculations (DFT) have been performed on [(L1)ZnCl2] and [(L2)ZnCl2] for different monometallic
conformations and show that 1a is the energetically preferred structure for L1 while there is evidence for
dynamic behaviour in L2-containing species leading to bimetallic formation. Single-crystal X-ray
diffraction studies have been performed on 1a, 1b, 1c, 2b, 3a, 3b(H2O) and 3c.
1
Introduction
The application of 2,6-linked oligopyridine ligands, C5H4N-
(C5H3N)nC5H4N (n = 2–7), in coordination chemistry is now well
established with mono-, double- or triple-stranded helicates being
a feature of the structural types.1 For example quinquepyridine
(n = 3) can readily form homobimetallic salts of the type
[(quinquepyridine)2M2]n+ with a variety of 3d metal ions including
cobalt,2 nickel3 and copper.4
Fig. 1 Oligopyridylimines (R = H or hydrocarbyl, Ar = aryl).
the family, bis(imino)terpyridine (Lx). To the knowledge of the
authors, Lx has received scarcely any attention as a supporting
ligand for binding to transition metals.6 Specifically, we focus on
We have been interested recently in developing oligopyri-
dine ligands featuring sterically demanding imino end-groups,
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the reactivity of 6,6 -{(2,6-i-Pr2C6H3)N CR}2-2,2 :6 ,2 -C15H9N3
(Lx = L1 R = H; Lx = L2 R = Me) towards divalent metal
halides of iron, nickel and zinc and pay particular attention to the
effect of the imino-carbon substituent R on the nuclearity of the
product. Furthermore, DFT calculations are used to support and
complement the synthetic work.
=
=
ArN CR(C5H3N)nCR NAr (n = 3, 4, 5; Ar = 2,6-substituted
aryl group; R = H or hydrocarbyl), and have termed this family
of ligands as oligopyridylimines (Fig. 1).5 It was envisaged that
the steric attributes of these ligands would to some extent inhibit
multi-stranded helicate formation and allow access to well-defined
polymetallic complexes of the form [(oligopyridylimine)MxXy]
(X = anionic monodentate ligand) that could be amenable to
further functionalisation at the metal centres and/or for catalytic
applications.
2
Results and discussion
(a) Syntheses of the ligands
Herein we report our efforts at developing the coordination
chemistry of the potentially pentadentate (n = 3) member of
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The ligands 6,6 -{(2,6-i-Pr2C6H3)N CR}2-2,2 :6 ,2 -C15H9N3
(R = H L1, R = Me L2) were synthesised in good yield by the
acid catalysed condensation reaction of 6,6ꢀꢀ-bis-formyl-2,2ꢀ:6ꢀ,2ꢀꢀ-
terpyridine5,7 and 6,6ꢀꢀ-bis-acetyl-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine5 with two
equivalents of 2,6-diisopropylaniline in ethanol, respectively
(Scheme 1). Alternatively, L2 can be prepared by carrying out
aDepartment of Chemistry, University of Leicester, University Road, Leices-
ter, UK LE1 7RH. E-mail: gas8@leicester.ac.uk
bDepartment of Biochemistry, University of Leicester, University Road,
Leicester, UK LE1 7RH
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Scheme 1 Reagents and conditions: 2 eq. 2,6-i-Pr2C6H3NH2, EtOH, cat. H+, heat.
◦
˚
1a; M = Ni, X = Br 1b; M = Zn, X = Cl 1c) in high yield
(Scheme 2). No evidence for bimetallic products was apparent
on addition of two equivalents or greater of MX2 or after
stirring for longer periods. All products have been characterised
by microanalysis, FAB mass spectrometry, IR spectroscopy and,
in the cases of 1a and 1b, by magnetic measurements and 1c by
1H NMR spectroscopy (see Table 2 and Experimental section). In
addition, crystals of 1a, 1b and 1c have been subjected to single-
crystal X-ray diffraction studies.
Crystals of 1a, 1b and 1c suitable for the X-ray determinations
were grown by slow cooling of hot acetonitrile solutions containing
the complexes. The structures of 1a, 1b and 1c are similar and only
1a will be discussed in any detail. A view of 1a is depicted in
Fig. 3; selected bond distances and angles for 1a, 1b and 1c are
listed in Table 3. The molecular structure of 1a depicts a single iron
centre bound by L1 and two terminal chloride ligands. The metal
centre occupies the tridentate terpyridine cavity with the two imine
groups pendant and exo to the coordinated terpyridine moiety. The
geometry at the metal centre can be best described as distorted
trigonal bipyramidal with N(2) and N(2A) defining the axial sites
[N(2)–Fe(1)–N(2A) 150.8(3)◦] and N(3), Cl(1) and Cl(1A) the
equatorial ones [N(3)–Fe(1)–Cl(1) 120.99(5); Cl(1)–Fe(1)–Cl(1A)
118.03(9)◦]. The complex has molecular C2 symmetry about an
axis containing the metal, the pyridyl–N(3) and C(21) atoms.
Table 1 Selected bond distances (A) and angles ( ) for L2
C(13)–N(1)
C(29)–N(5)
1.284(6)
1.255(6)
C(18)–C(19)
C(23)–C(24)
1.506(6)
1.458(7)
C(29)–N(5)–C(30)
119.8(4)
the reaction in neat 2,6-diisopropylaniline at elevated temperature
over short time periods.5 Both ligands have been characterised
by IR, 1H and 13C NMR spectroscopy along with ES mass
spectrometry (see Experimental section). L2 has also been the
subject of a single-crystal X-ray diffraction study.
Pale yellow crystals of L2 suitable for the X-ray determination
were grown by the slow evaporation of a dichloromethane solution
containing the compound. A view of L2 is shown in Fig. 2; selected
bond distances and angles are listed in Table 1. The structure of L2
consists of three 2,6-linked pyridine rings with the imino groups
occupying the ends of the oligopyridylimine chain. The nitrogen
atoms of the pyridine groups adopt a mutually transoid conforma-
tion which is also extended to the terminal imine groups in a man-
ner reminiscent of that found in 2,6-oligopyridines.1,8 A slight twist
[torsion angles: N(1)–C(13)–C(14)–N(2) 1.8◦; N(2)–C(18)–C(19)–
N(3) 6.9◦; N(3)–C(23)–C(24)–N(4) 3.4◦; N(4)–C(28)–C(29)–N(5)
3.5◦] from planarity is displayed throughout the imine-pyridine
backbone as has been observed for L1.5 The 2,6-diisopropyl
substituents on the terminal aryl groups sit above and below the
planes of the nearest pyridine units within the chain. The N(1)–
˚
The central M–Npyridyl distance [2.073(6) A] is noticeably less than
˚
the M–N(2)pyridyl and M–N(2A)pyridyl bond lengths [2.234(5) A],
probably as a consequence of satisfying the tridentate chelating
constraint of the ligand and that it occupies a equatorial site within
˚
C(13) and N(5)–C(29) bond lengths of 1.284(6) and 1.255(6) A are
consistent with their being double bond character. The IR spectra
˚
=
the trigonal bipyramid. The C N bond distance [1.283(8) A] is
˚
=
similar to that found in L2 [av. 1.258 A].
of L1 and L2 confirm the presence of the imine with m(C N) bands
at ca. 1645 cm−1 which is supported by the 13C NMR spectra which
show peaks at d 163.5 (L1) and d 166.1 (L2) corresponding to the
imino carbon atoms.
The FAB mass spectra for 1a–c show fragmentation peaks cor-
responding to the loss of one halide group from the corresponding
=
molecular ion peak. The IR spectra for 1a–c display m(C N) bands
at ca. 1635 cm−1 and in a similar region to that for free L1,
supporting the pendant nature of the imino groups. Complexes
1a and 1b are paramagnetic and display magnetic moments of
5.3 and 2.8 lB (Evans Balance at ambient temperature) which
are consistent with high spin configurations possessing four and
two unpaired electrons, respectively. In contrast, complex 1c is
(b) Complexation reactions
(i) Reaction of MX2 with L1. The reaction of L1 with one
equivalent of MX2 [MX2 = FeCl2, (DME)NiBr2, ZnCl2] in n-
◦
butanol at 110 C gave complexes [(L1)MX2] (M = Fe, X = Cl
Fig. 2 Molecular structure of L2 including the atom numbering scheme.
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Scheme 2 Reagents and conditions: (i) 1 eq. or xs. MX2 [MX2 = FeCl2, (DME)NiBr2, ZnCl2], n-BuOH, 110 ◦C; (ii) 1 eq. (DME)NiBr2, CH2Cl2, RT;
(iii) 2 eq. MX2 [MX2 = FeCl2, (DME)NiBr2, ZnCl2], n-BuOH, 110 ◦C; (iv) 1 eq. (DME)NiBr2, n-BuOH, 110 ◦C; (v) CHCl3/H2O, RT (Ar = 2,6-i-Pr2C6H3).
Table 2 Characterisation data for the new complexes 1–3
a
−1
leffb/lB
1H NMRc (d)
FAB mass
=
Compound
Colour
m(C N) /cm
d
d
1a
1b
Brown
Yellow
1635
1640
5.3
2.8
733 [M]+,698 [M − Cl]+
746 [M − Br]+, 665
[M − 2Br]+
e
1c
Yellow
1638
1.49 (d, 24H, 3JHH 6.7 Hz, CH(CH3)2), 3.06
(sept, 4H, 3JHH 6.7 Hz, CH(CH3)2), 7.07 (m,
6H, ArH), 8.10 (dd, 2H, 3JHH 7.6 Hz,
744 [M]+, 706 [M −
Cl]+, 669 [M − 2Cl]+
7.9 Hz, PyH), 8.21 (d, 2H, 3JHH 7.6 Hz,
PyH), 8.28 (m, 3H, PyH), 8.60 (d, 2H, 3JHH
7.9 Hz, PyH), 9.30 (s, 2H, HCN)
d
2b
3a
3b
3c
Yellow
Brown
Orange
Yellow
1594,1630
1592
2.4
7.0
774 [M − Br]+, 693
[M − 2Br]+
d
d
854 [M − Cl]+, 817
[M − 2Cl]+
1591
4.3
992 [M − Br]+, 913
[M − 2Br]+
e
1590
0.93 (d, 12H, 3JHH 7.0 Hz, CH(CH3)2), 1.17
(d, 12H, 3JHH 6.4 Hz, CH(CH3)2), 2.31 (s,
6H, CH3CN), 3.06 (sept, 4H, 3JHH 6.7 Hz,
CH(CH3)2), 7.12 (m, 6H, ArH), 8.08 (d, 2H,
3JHH 7.9 Hz, PyH), 8.24 (dd, 1H, 3JHH 7.9,
3JHH 7.6 Hz, PyH), 8.31 (dd, 2H, 3JHH 7.9,
3JHH 7.9 Hz, PyH), 8.45 (d, 2H, 3JHH 7.6 Hz,
PyH), 8.68 (d, 2H, 3JHH 7.9 Hz, PyH).
872 [M − Cl]+, 837
[M − 2Cl]+,734 [M −
2Cl − Zn]+
a Recorded on a Perkin-Elmer Spectrum One FT-IR spectrometer on solid samples. b Recorded on an Evans Balance at room temperature. c Recorded in
CDCl3 solution at room temperature. d Broad paramagnetically shifted resonances. e Diamagnetic.
diamagnetic and exhibits a 1H NMR spectrum (in CDCl3 at
ambient temperature) that is consistent with the molecular C2
symmetry observed in the solid state with five signals for the
pyridyl protons. In comparison with L1, the signals are slightly
(ii) Reaction of MX2 with L2. The reaction of L2 with two
equivalents of MX2 [MX2 = FeCl2, (DME)NiBr2, ZnCl2] in n-
butanol at elevated temperatures gave complexes [(L2)M2X4] (M =
Fe, X = Cl 3a; M = Ni, X = Br 3b; M = Zn, X = Cl 3c) in high yield
(Scheme 2). No evidence for monometallic products was apparent
under these experimental conditions nor when one equivalent of
MX2 was employed. All products have been characterised by FAB
mass spectrometry, IR spectroscopy and, in the cases of 3a and 3b,
=
shifted with, for example, the singlet for the CH N protons in
L1 (d 8.36) being shifted by ca. 1 ppm downfield in 1c (d 9.30).
The 1H NMR spectra for paramagnetic 1a and 1b were broad and
uninformative.
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◦
˚
Table 3 Selected bond distances (A) and angles ( ) for 1a, 1b and 1c
1a (M = Fe, X = Cl)
1b (M = Ni, X = Br)
1c (M = Zn, X = Cl)
M(1)–N(2)
M(1)–N(3)
M(1)–N(2A)
M(1)–X(1)
M(1)–X(1A)
C(13)–N(1)
2.234(5)
2.073(6)
2.234(5)
2.2889(17)
2.2889(17)
1.283(8)
2.110(6)
1.982(6)
2.110(6)
2.3919(9)
2.3919(9)
1.251(9)
2.242(7)
2.036(8)
2.242(7)
2.247(2)
2.247(2)
1.278(12)
N(2)–M(1)–N(3)
N(2)–M(1)–N(2A)
X(1)–M(1)–X(1A)
X(1)–M(1)–N(2)
X(1)–M(1)–N(3)
X(1)–M(1)–N(2A)
75.42(13)
150.8(3)
118.03(9)
93.50(13)
120.99(5)
101.42(14)
78.33(13)
156.7(3)
129.51(6)
91.76(15)
115.24(3)
98.15(15)
76.16(18)
152.3(4)
119.10(14)
93.71(18)
120.45(7)
100.24(19)
Atoms with suffix A are generated by symmetry.
are both nearly planar with each of the planes being disposed
almost orthogonally to one another [torsion angles: N(3)–C(18)–
C(19)–N(4) 91.5◦ (3a), 90.6◦ (3c)]. For M(1) the two M(1)–Cl bond
˚
lengths are a essentially equivalent [3a 2.273(2) vs. 2.281(2) A; 3c
˚
2.2254(12) vs. 2.2367(12) A], while the M(1)–N distances vary with
˚
˚
˚
˚
M(1)–N(2) [3a 2.061(6) A; 3c 2.064(3) A] being shorter than the
M(1)–N(1) [3a 2.278(6) A; 3c 2.270(3) A] and the M(1)–N(3) [3a
˚
˚
2.267(5) A; 3c 2.285(3) A] bond lengths. At M(2), the M(2)–Nimine
distance is similar to the M(2)–Npyridyl bond length [3a 2.109(5)
vs. 2.102(6) A; 3c 2.071(3) vs. 2.056(3) A]. There is no apparent
delocalisation of the imino double bond into the adjacent pyridyl
group.
˚
˚
Attempted crystallisation of 3b using the conditions applied for
3a and 3c proved unsuccessful. However, by prolonged standing
in chloroform adventitious reaction with water occurs to give
[(L2)Ni2Br4(OH2)] [3b(H2O)] as orange crystals (Scheme 2). The
dataset obtained for the single-crystal X-ray determination was,
unfortunately, of poor quality. Nevertheless, the structure was
unequivocal in revealing a bimetallic species displaying structural
features similar to that observed in 3a and 3c (vide supra) but with
one molecule of water additionally bound to the nickel centre
[Ni(2)] occupying the bidentate cavity in L2. For comparison,
Table 4 also contains the corresponding bond lengths and angles
for 3b(H2O).
Fig. 3 Molecular structure of 1a; the atoms labelled with an additional
A are generated by symmetry (1 − x, −y, z). All hydrogen atoms, apart
from H13, have been omitted for clarity.
The FAB mass spectra for 3a–c show fragmentation peaks
corresponding to the loss of one or two halide groups from the
by magnetic measurements and for 3c by 1H NMR spectroscopy
(see Table 2 and Experimental section). In addition, crystals of
3a and 3c have been the subject of single-crystal X-ray diffraction
studies.
corresponding molecular ion peak. In the IR spectra for 3a–c,
−1
=
the m(C N) bands are seen at ca. 1590 cm (in both solid and
solution state) and shifted to a lower wavenumber by ca. 52 cm−1
in comparison with the free ligand L2; supporting coordination
of both imine groups. Complexes 3a and 3b are paramagnetic and
display magnetic moments of 7.0 lB and 4.3 lB (Evans Balance at
ambient temperature) which are consistent with non-spin coupled
Crystals of 3a and 3c were grown by slow cooling of hot acetoni-
trile solutions of the corresponding complexes. The structures of
3a and 3c are essentially the same and will be discussed together. A
view of 3c is depicted in Fig. 4; selected bond distances and angles
are listed for both 3a and 3c in Table 4. The molecular structures
reveal bimetallic complexes in which the two metal centres are
supported on the same L2 ligand frame and each bound terminally
by two chloride ligands. One of the metal centres [M(2)] occupies
a bidentate pyridylimine pocket while the other [M(1)] a tridentate
dipyridylimine cavity so as to generate a tetrahedral geometry at
M(2) and a distorted square pyramidal geometry at M(1). Within
the ligand frame the pyridylimine and dipyridylimine moieties
Fe(II) (S = 2)–Fe(II) (S = 2) and Ni(II) (S = 1)–Ni(II) (S = 1)
ꢀ
systems (using l2 = li2, where li is the magnetic moment of the
individual metal centres).9
The 1H NMR spectrum of 3c in CDCl3 (at ambient temperature)
indicates that the molecule has average C2 symmetry in solution
with only five resonances for the pyridyl hydrogen atoms occurring
at d 8.08, 8.24, 8.31, 8.45 and 8.68. In addition, there is only one
resonance for the methyl protons on the imine groups. Attempts
to lower the symmetry by recording the spectrum at lower
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◦
˚
Table 4 Selected bond distances (A) and angles ( ) for 3a, 3b(H2O) and 3c
3a (M = Fe, X = Cl)
3b(H2O) (M = Ni, X = Br)
3c (M = Zn, X = Cl)
M(1)–N(1)
M(1)–N(2)
M(1)–N(3)
M(1)–X(1)
M(1)–X(2)
M(2)–N(4)
M(2)–N(5)
Ni(2)–O(1)H
M(2)–X(3)
M(2)–X(4)
C(7)–N(1)
C(24)–N(5)
2.278(6)
2.061(6)
2.267(5)
2.273(2)
2.281(2)
2.102(6)
2.109(5)
—
2.221(2)
2.237(2)
1.269(9)
1.268(8)
2.157(17)
1.933(17)
2.192(17)
2.421(4)
2.394(4)
2.079(17)
2.036(17)
2.042(17)
2.468(4)
2.427(4)
1.26(3)
2.270(3)
2.064(3)
2.285(3)
2.2254(12)
2.2367(12)
2.056(3)
2.071(3)
—
2.1848(13)
2.2212(13)
1.289(5)
1.274(5)
2 O
1.38(2)
N(1)–M(1)–N(2)
N(1)–M(1)–N(3)
X(1)–M(1)–N(1)
X(2)–M(1)–N(1)
X(1)–M(1)–X(2)
X(1)–M(1)–N(2)
N(4)–M(2)–N(5)
N(4)–M(2)–X(3)
N(4)–M(2)–X(4)
N(4)–Ni(2)–O(1)H
X(3)–M(2)–X(4)
73.9(2)
149.4(2)
95.98(16)
101.62(16)
131.37(8)
115.44(17)
77.0(2)
119.75(18)
103.73(17)
—
78.0(7)
154.0(6)
99.5(4)
94.8(4)
110.29(13)
96.5(5)
79.1(7)
172.3(5)
89.3(5)
85.8(7)
95.88(13)
74.47(13)
149.61(12)
97.20(9)
101.41(9)
126.33(4)
117.20(10)
79.40(13)
119.86(10)
104.53(10)
—
2 O
118.76(9)
116.80(5)
Fig. 4 Molecular structure of 3c including the atom numbering scheme. All hydrogen atoms have been omitted for clarity.
temperature were, however, hampered by solubility problems.
Scheme 3 indicates a possible fluxional process that could be oper-
ating at room temperature in solution in which the central pyridine
group could be flipping between metal centre coordination. An
alternative explanation may be that the central pyridine nitrogen
donor is not coordinated in solution.
With the intent of synthesising monometallic complexes bound
by L2, the reaction with MX2 was attempted under milder
conditions. Thus, when a cooled dichloromethane solution of
(DME)NiBr2 is treated with one equivalent of L2 and left to stir
overnight at room temperature, the yellow mononuclear complex
[(L2)NiBr2] (2b) can be obtained in good yield. Attempted
Scheme 3 Possible dynamic process operating for 3.
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isolation of the mononuclear zinc analogue of 2b, [(L2)ZnCl2] (2c),
under the same reaction conditions as employed above, proved
problematic with 3c and L2 being the main species identifiable in
one of the exterior pyridine units than the other [Ni(1)–N(2)
˚
2.040(2) vs. Ni(1)–N(4) 2.316(2) A], while the central pyridine
˚
remains strongly bound [Ni(1)–N(3) 1.982(2) A]. The effect of
1
the H NMR spectrum. Complex 2b was characterised by FAB
partial coordination on the C–N double bond length in the imine
is minimal.
The FAB mass spectrum for 2b shows fragmentation peaks
corresponding to the loss of one or two bromide groups from
mass spectrometry, IR spectroscopy and by magnetic measure-
ments (see Table 2 and Experimental section). In addition, a crystal
of 2b has been the subject of a single-crystal X-ray diffraction
study.
=
the molecular ion peak. In the IR spectra for 2b, m(C N) bands
Crystals of 2b suitable for the X-ray determination were grown
by prolonged standing in chloroform. A view of 2b is shown in
Fig. 5; selected bond distances and angles are listed in Table 5. The
molecular structure consists of a single nickel atom bound by both
L2 and two terminal bromide ligands. As with its L1-containing
counterpart, 1b, the metal centre occupies the terpyridine cavity of
the bis(imino)terpyridine ligand. In this case, however, only one of
the imino groups is exo while the other is endo and forms a partial
at 1594 and 1630 cm−1 support the presence of both bound and
free imino groups, respectively. As with 1b, 2b is paramagnetic
exhibiting a magnetic moment of 2.4 lB (Evans Balance at ambient
temperature) which is consistent with presence of two unpaired
electrons.
Conversion of yellow 2b to orange 3b can be achieved in
good yield by treating 2b with one equivalent of (DME)NiBr2
in n-butanol at 110 ◦C for 30 min (Scheme 2). Similarly, 2b
could be converted to 3b on refluxing 2b with one equivalent
of (DME)NiBr2 in dichloromethane for two days, these condi-
tions also proving successful for the preparation of 3b directly
from L2.
˚
interaction with the nickel centre [Ni(1) · · · N(1) 2.537(2) A].
The effect of the interaction in comparison with 1b is two-fold.
Firstly, an increase in the Br–Ni–Br angle from 129.51(6)◦ in
1b to 172.84(2)◦ in 2b occurs so that the nickel assumes a more
octahedral geometry in 3b. Secondly, the occupation of terpyridine
cavity is more uneven with the nickel centre more disposed towards
2.3 Density functional theory calculations
The capacity of Lx, depending on the nature of the imino-carbon
substituent, to have a selectivity for the number of metal(II)
halide units it binds was unexpected. Although it could be argued
that differences in electronic properties within the two ligand
manifolds (e.g., donor capability of the nitrogen donors within Lx
is expected to follow the order: pyridine > ketimine > aldimine10)
should be influential, such a dramatic change in binding affinity
was nevertheless surprising. Therefore, a theoretical study on the
relative stability of mononuclear [(L2)MX2] and [(L1)MX2] was
carried out in order to investigate in more detail the energetic
properties of these systems. Specifically, density functional calcu-
lations have been performed on ZnCl2-containing complexes and
is likely, given the similarity of the experimental results, to be
representative of the other metal halide systems employed in this
work.
For both L1 and L2, B3LYP calculations have been undertaken
on mono-zinc dichloride species in conformations 1Lx and 2Lx
(Fig. 6) which are based on the conformations adopted in
structurally determined 1c and 2b. In addition, hypothetical
species 4Lx derived from the removal of one zinc dichloride unit
from the bidentate pocket in bimetallic 3c are also studied. As
1c is the only monometallic ZnCl2 structure characterised by
X-ray diffraction, it was used to test our theoretical approach.
For this configuration, theoretical (1L1) and experimental (1c)
structures are in good agreement with the discrepancies found
Fig. 5 Molecular structure of 2b including the atom numbering scheme.
All hydrogen atoms have been omitted for clarity.
◦
˚
being less than 0.07 A for the bond lengths and 10 for the
angles (see Tables 3 and 6). The coordinated terpyridine portion
of the ligand remains planar with an out of plane displacement of
◦
˚
Table 5 Selected bond distances (A) and angles ( ) for 2b
Ni(1) · · · N(1)
Ni(1)–N(2)
Ni(1)–N(3)
Ni(1)–N(4)
2.537(2)
2.040(2)
1.982(2)
2.316(2)
Ni(1)–Br(1)
Ni(1)–Br(2)
N(1)–C(13)
N(5)–C(29)
2.4827(7)
2.4780(7)
1.269(4)
1.277(4)
˚
0.03 and 0.05 A for the theoretical and experimental structures,
respectively [Fig. 7(ii)]. It is likely that any discrepancies can be
attributed to the vacuum conditions of the calculations. Therefore,
it was viewed that this initial study demonstrated that using the
B3LYP functional with our basis set is viable for studying such
large systems. To extend the investigation, we have applied this
theoretical approach to mono-zinc complexes that have not been
characterised crystallographically.
N(2)–Ni(1)–N(3)
N(3)–Ni(1)–Br(2)
N(3)–Ni(1)–N(4)
N(3)–Ni(1)–Br(1)
N(2)–Ni(1)–Br(2)
79.76(10)
92.49(7)
76.51(9)
90.81(7)
93.80(7)
N(2)–Ni(1)–Br(1)
N(2)–Ni(1)–N(4)
N(4)–Ni(1)–Br(1)
N(4)–Ni(1)–Br(2)
Br(2)–Ni(1)–Br(1)
93.04(7)
156.26(9)
86.80(6)
87.78(6)
172.84(2)
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◦
˚
Table 6 Selected calculated bond distances (A) and angles ( ) for [(L1)ZnCl2] and [(L2)ZnCl2] in types-1, -2 and -4 conformations
Conformation based on 3c with one
ZnCl2 unit removed
Conformation based on 1c
Conformation based on 2b
1L1
1L2
2L2
2L1
4L2
4L1
Zn(1) · · · N(1)
Zn(1)–N(2)
Zn(1)–N(3)
Zn(1)–N(2A)
Zn(1) · · · N(1A)
Zn(1)–Cl(1)
Zn(1)–Cl(1A)
C(13)–N(1)imine
C(13A)–N(1A)imine
4.68
2.29
2.17
2.29
4.68
2.33
2.33
1.29
1.28
5.06
2.42
2.12
2.41
5.06
2.35
2.32
1.29
1.29
Zn(1)–N(1)
Zn(1)–N(2)
Zn(1)–N(3)
Zn(1)–N(4)
Zn(1) · · · N(5)
Zn(1)–Cl(1)
Zn(1)–Cl(2)
C(13)–N(1)imine
C(29)–N(5)imine
2.55
2.70
2.26
2.24
2.44
4.80
2.35
2.36
1.28
1.29
Zn(1)–N(1)
Zn(1)–N(2)
Zn(1)–N(3)
Zn(1)–Cl(1)
Zn(1)–Cl(2)
C(7)–N(1)imine
C(24)–N(5)imine
2.35
2.18
2.38
2.35
2.30
1.29
1.28
2.39
2.18
2.37
2.35
2.30
1.28
1.28
2.22
2.21
2.54
5.15
2.39
2.40
1.29
1.28
N(2)–Zn(1)–N(3)
N(2)–Zn(1)–N(2A)
Cl(1)–Zn(1)–Cl(1A)
Cl(1)–Zn(1) · · · N(1)
Cl(1)–Zn(1)–N(2)
Cl(1)–Zn(1)–N(3)
Cl(1)–Zn(1)–N(2A)
Cl(1)–Zn(1) · · · N(1A)
Cl(1A)–Zn(1)–N(2)
Out of plane
74.1
75.6
N(2)–Zn(1)–N(3)
N(2)–Zn(1)–N(4)
Cl(1)–Zn(1)–Cl(2)
Cl(1)–Zn(1)–N(1)
Cl(1)–Zn(1)–N(2)
Cl(1)–Zn(1)–N(3)
Cl(1)–Zn(1)–N(4)
Cl(1)–Zn(1)–N(5)
Cl(2)–Zn(1)–N(2)
Out of plane
72.8
74.2
N(1)–Zn(1)–N(2)
N(1)–Zn(1)–N(3)
Cl(1)–Zn(1)–N(1)
Cl(2)–Zn(1)–N(1)
Cl(1)–Zn(1)–Cl(2)
Cl(1)–Zn(1)–N(2)
72.3
143.5
98.7
95.6
131.5
94.5
73.2
145.1
99.4
92.3
135.1
96.7
148.3
129.0
78.0
96.0
116.0
97.5
75.1
97.5
0.03
151.0
147.1
94.9
92.0
94.0
95.7
95.9
95.4
146.0
168.9
92.1
92.6
91.0
88.4
84.1
92.8
143.7
155.0
90.8
95.8
97.5
89.1
76.3
95.8
0.31
0.21
0.37
Out of plane
displacementb
0.21
0.19
displacementa
displacementa
a Out of plane displacement of the eighteen atoms in the three pyridine moieties. b Out of plane displacement of the fifteen atoms in the imino-bipyridine
moiety.
Fig. 6 Monometallic zinc conformations to be investigated by DFT including the atom numbering scheme (Ar = 2,6-i-Pr2C6H3).
Firstly, 1L2 has been optimised. The resulting structure exhibits
a geometry substantially distorted when compared with its coun-
terpart 1L1 [Fig. 7(iii) vs. (ii)]. Inspection of the coordination sphere
around zinc in 1L2 indicates that N2 and N2A atoms lie further
2b [Fig. 7(iv)], was undertaken. As a first observation, it is noted
that the optimised structure of 2L2 does not show any noticeable
changes when compared with 2b, apart from the expected variation
in metal–nitrogen distances [Fig. 7(v) vs. (iv) and Tables 5 and 6].
Indeed, 2L2 remains in a distorted octahedral geometry with its
four nitrogen donor ligands from L2 occupying the equatorial
sites and the halide ligands axial. Two of the Zn–N distances are
˚
away from the metal centre [Zn(1)–N(2)/N(2A) 2.42 A (1L2) vs.
˚
Zn(1)–N(2)/N(2A) 2.29 A (1L1)] implying that the chelating ability
of L2 in this coordination mode is substantially reduced (Table 6).
This observation is likely linked to the steric constraints imposed
by the methyl units of the imino-carbon groups which are in close
proximity in this conformation [Fig. 7(iii)]. The geometry around
the metal is also altered in the fact that both chlorine atoms while
equivalent in 1L1 are non-equivalent in 1L2 leading to a distorted
structure intermediate between trigonal-bipyramidal and square-
based pyramidal. The planarity of the tridentate portion of the
ligand is significantly reduced in comparison with 1L1 [out of plane
˚
˚
elongated [Zn(1)–N(1) 2.55 A and Zn(1)–N(4) 2.54 A] indicative
of a weaker coordination to the metal centre. In addition, the
planarity of the pyridine rings within L2 is reduced when compared
with structurally determined 2b with an increase in the out of plane
˚
displacement evident [0.08 (2b) vs. 0.21 A (2L2)]. Nevertheless,
based on these observations, it would seem that [(L2)ZnCl2]
when adopting a type-2 conformation is structurally possible. By
contrast, the optimised structure for [(L1)ZnCl2] (2L1) indicates a
more distorted geometry than in 2L2 [Fig. 7(vi) vs. (v)]. Although
the Zn(1)–N(4) distance is slightly shorter in this complex [2.44
˚
˚
displacement: 0.31 A (1L2) vs. 0.03 A (1L1)]. Overall, a monometallic
zinc dichloride species supported by L2 exhibits a considerable
deformation when it is forced to adopt a type-1 conformation.
Secondly, a theoretical study of mono-zinc dichloride complexes
bound by respectively L2 (2L2) or L1 (2L1) in conformations
adopted in the structurally characterised nickel bromide complex
˚
(2L1) vs. 2.54 A (2L2)], the Zn(1)–N(1) distance is substantially
˚
longer [2.70 A (2L1)], while the out of plane displacement of the
˚
pyridine rings is increased further than in 2L2 [0.37 A (2L1) vs.
˚
0.21 A (2L2)]. Indeed, the geometry at metal centre in 2L1 could be
2356 | Dalton Trans., 2006, 2350–2361
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Fig. 7 Calculated structures for [(Lx)ZnCl2] (1Lx, 2Lx, 4Lx) in conformations based on structurally determined 1c, 2b and 3c. All hydrogen atoms have
been omitted for clarity.
described as more five-coordinate than six-coordinate. Therefore,
on comparison of the hypothetical zinc complexes 2L2 and 2L1, it
would seem that the presence of an endo-oriented imino group
stabilises an octahedral-type conformation in the L2 system while
it leads to a significant structural rearrangement for the L1 system.
Thirdly, to examine the possibility for equilibration of
monometallic species in solution (Scheme 4, vide supra) and
to probe potential intermediates in the formation of bimetallic
species (e.g., 3c), a hypothetical mono-zinc species has been
generated by removing one ZnCl2 molecule from structurally
characterised 3c. Specifically, we have focused on a conformation
(4L2), in which the single ZnCl2 unit is bound in the tridentate
iminobipyridine pocket within L2 [N(1), N(2) and N(3)]; the
corresponding 4L1 has also been studied [Fig. 7(viii) and (ix)].
A structural reorganisation is observed on inspection of the
theoretical (4Lx) and experimental structures (3c) and consists of a
change of the relative positions of the chloride ligands on the metal
centre. This structural rearrangement is linked to a permutation
in and out of the medium plane of the N(2)- and N(3)-containing
pyridine rings. These changes are most likely due to the absence of
a second metal centre and the isolated condition of the complex in
the theoretical calculations. The most important feature though,
is that both theoretical structures do not produce any noticeable
structural discrepancies (see Tables 4 and 6) with a difference in
◦
˚
bond lengths of 0.04 A and in angles of 4.2 .
Several points emerge from inspection of the relative energies of
the optimised structures established for the mono-zinc dichloride
species, 1L1 (1c), 1L2, 2L2, 2L1, 4L2 and 4L1 (Table 7). Firstly, a
comparison of the [(L1)ZnCl2] structures indicates that a con-
formation based on type-1 is substantially preferred to the other
two possible conformations [DE = 9.56 (2L1) and 8.75 kcal mol−1
(4L1)]. Secondly, all the [(L2)ZnCl2] structures display energies
Scheme 4 Possible equilibria for [(Lx)ZnCl2] in solution (Ar = 2,6-i-Pr2C6H3; X = halide).
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Table 7 Relative potential energies (kcal.mol−1) for [(L1)ZnCl2] and
[(L2)ZnCl2] in various conformations; calculations have been performed
as DE (Ey − E1Lx
behaviour is likely for L2-supported species leading to bimetallic
formation.
)
y
L1
L2
0.0
1.21
−1.32
4
Experimental
1Lx
2Lx
4Lx
0.0
9.56
8.75
4.1 General
All reactions, unless otherwise stated, were carried out under an
atmosphere of dry, oxygen-free nitrogen, using standard Schlenk
techniques or in a nitrogen purged glovebox. Solvents were dis-
tilled under nitrogen from appropriate drying agents and degassed
prior to use.11 The IR spectra were recorded on a Perkin-Elmer
Spectrum One FT-IR spectrometer on solid samples. The ES and
the FAB mass spectra were recorded using a micromass Quattra
LC mass spectrometer and a Kratos Concept spectrometer with
methanol or NBA as the matrix respectively. Accurate Mass
FABMS were recorded on Kratos Concept spectrometer (xenon
that are very close to one another with a slightly more stable
conformation apparent for 4L2 [DE = 1.21 (2L2) and −1.32 kcal
mol−1 (4L2)]. Overall, the data for these species indicate a clear
preference for [(L1)ZnCl2] to exist in a type-1 conformation, while
for [(L2)ZnCl2], the closeness in the relative energies between the
different conformations (1L2, 2L2, 4L2) suggests that an equilibrium
is likely in the gas phase but with a slight preference towards 4L2. It
is worthy of note that for both ligands the type-2 conformation is
the least stable of all although, given the accuracy of the theoretical
method employed, the significance of this inference should be
treated with some caution. However, the isolation and structural
characterisation only in the case NiBr2 derivative 2b suggests that
the nature of the halide group may have a stabilising influence for
this particular conformation. This will be the subject of further
study elsewhere.
In summary, the density functional study carried out on the
monometallic ZnCl2 species with L1 and L2 as the ligand frame
supports the experimental observations and indicates that the
nature of the substituent on the imino-carbon moiety has a
dramatic effect on the stability of the monometallic species. Several
points emerge from the study. Firstly, it is apparent that the
difference in the stability of species adopting conformation 1Lx
is mainly steric in origin which in turn directly influences the
chelating properties around the metal. In the case of L1 steric
interactions are minimised while good coordination within the
terpyridine moiety is maximised. This stability allied with the
substantial reduction of the solvent accessibility to the metal
centre in this conformation would appear to suggest why 1L1
(1c) does not react with a further molecule of ZnCl2 to form a
bimetallic complex. Secondly, for L2, all three conformations 1L2,
2L2 and 4L2 are distorted and can be considered as isoenergetic.
These two points together indicate that an equilibrium could be
operational in solution for L2 but not for L1 (Scheme 4). It would
be expected, therefore, that further addition of a molecule of ZnCl2
to [(L2)ZnCl2] would drive the equilibrium towards the right hand
side and allow occupation of the bidentate pocket in 4 to furnish
bimetallic complex 3.
1
gas, 7 kV) with NBA as matrix. H and 13C NMR spectra were
recorded on a Bruker ARX spectrometer (250 or 300 MHz);
chemical shifts (d) are referred to the residual protic solvent
peaks. Magnetic Susceptibility studies were performed using an
Evans Balance (Johnson Matthey) at room temperature. The
magnetic moments were calculated following standard methods12
and corrections for underlying diamagnetism were applied to the
data.13 Elemental analyses were performed at the Science Technical
Support Unit, London Metropolitan University.
The metal dichlorides and (DME)NiBr2 (DME = 1,2-
dimethoxyethane) were purchased from Aldrich Chemical Co. and
used without further purification while 2,6-diisopropylaniline was
distilled prior to use. The compounds, 6,6ꢀꢀ-bis-formyl-2,2ꢀ:6ꢀ,2ꢀꢀ-
terpyridine5,7 and 6,6ꢀꢀ-bis-acetyl-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine5 were pre-
pared according to previously reported procedures. All other
chemicals were obtained commercially and used without further
purification.
4.2 Synthesis of 6,6ꢀꢀ-bis(iminoformyl)-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine-
bis(2,6-diisopropylanil) (L1)
6,6ꢀꢀ-Diformyl-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine (1.031 g, 3.57 mmol) was
suspended in absolute ethanol (20 ml) and 2,6-diisopropylaniline
(1.390 g, 7.85 mmol, 2.2 eq.) introduced along with a catalytic
amount of glacial acetic acid. The mixture was stirred and heated
vigorously at 60 ◦C for 12 h. The solution was cooled and the re-
sulting precipitate collected by filtration and washed with ethanol
(60 ml). The residue was crystallised from a dichloromethane–
hexane (1 : 9) mixture at room temperature and the crystalline
material filtered, washed with hexane and dried under vacuum
ꢀꢀ
ꢀ
ꢀ
ꢀꢀ
=
to afford 6,6 -{(2,6-i-Pr2C6H3)N CH}2-2,2 :6 ,2 -C15H9N3 (L1)
as a pale yellow solid. Yield: 1.411 g, 65%. Anal. Calc. for
C41H45N5·0.5H2O: C, 79.87; H, 7.46; N, 11.36%. Found: C, 79.62;
H, 7.63; N, 10.81%. 1H NMR (300 MHz, CDCl3): d 1.14 (d, 3JH–H
7.0, 24H, CH(CH3)2), 2.92 (sept, 3JH–H 7.0, 4H, CH(CH3)2), 7.03–
7.16 (m, 6H, Ar–H), 7.91 (app. t, 3JH–H 7.6, 3JH–H 7.6, 1H, Py–H),
3
Conclusions
The bulky bis(imino)terpyridine ligand Lx has been used as an
effective scaffold to support one or two metal(II) halide units.
The nature of the imino-carbon substituent is found to have an
effect on the number of metal halide units the ligand can bind
with the aldimine ligand L1 showing a strong preference for a
single unit while the ketimine L2 has the capacity to bind one
or two metal centres. These experimental results have been further
complemented by DFT calculations which reveal that a significant
energy gap is apparent for L1-containing systems leading to a
stabilised conformation of type-1 and also suggests that dynamic
7.96 (app. t, 3JH–H 7.9, 3JH–H 7.9, 2H, Py–H), 8.29 (d, 3JH–H 7.6, 2H,
3
=
Py–H), 8.36 (s, 2H, HC N), 8.52 (d, JH–H 7.9, 2H, Py–H) and 8.71
(d, 3JH–H 7.6, 2H, Py–H). 13C { H} NMR (75 MHz, CDCl3): d 23.5
1
(CH3), 28.0 (CH), 121.1 (Py), 121.4 (Py), 122.7 (Py), 122.8 (Py),
123.1 (Ar), 124.5 (Ar), 137.3 (Py), 137.6 (Py), 148.6 (Ar), 154.0
−1
=
(Ar), 155.0 (Py), 156.1 (Py) and 163.5 (C N). IR (cm ): 2952(m),
2358 | Dalton Trans., 2006, 2350–2361
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=
1648(m, m(C N)), 1563(s), 1434(s), 1361(w), 1190(w), 1115(s),
(c) 1c, M = Zn, X = Cl. Using an analogous procedure
to that described in 4.4(a) employing anhydrous ZnCl2 (0.022 g,
0.164 mmol) and L1 (0.100 g, 0.164 mmol, 1 eq.) gave [6,6ꢀꢀ-{(2,6-i-
795(s), 786(s) and 760(s). ESI positive mass spectrum (m/z): 608
[(M + H)+]. Acc. Mass FABMS positive spectrum (m/z): required
for (C43H49N5H+) 608.37532. Found 608.37532. Mp 220–222 ◦C.
ꢀ
ꢀ
ꢀꢀ
=
Pr2C6H3)N CH}2-2,2 :6 ,2 -C15H9N3]ZnCl2 (1c) as a yellow solid.
Crystallisation of 1c from a mixture of acetonitrile/chloroform
gave 1c as yellow needles. Yield: 0.085 g, 70%. Anal. Calc. for
C41H45N5ZnCl2·1/3CHCl3: C, 63.33; H, 5.79; N, 8.94%. Found:
C, 62.99; H, 5.72; N, 8.91%.
4.3 Synthesis of 6,6ꢀꢀ-bis(iminoacetyl)-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine-
bis(2,6-diisopropylanil) (L2)
6,6ꢀꢀ-Diacetyl-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine (1.00 g, 3.15 mmol) was sus-
pended in absolute ethanol (16 ml) and 2,6-diisopropylaniline
(1.228 g, 6.94 mmol, 2.2 eq.) introduced along with a catalytic
amount of formic acid (98%). The mixture was stirred and
heated vigorously at 100 ◦C for 36 h. The solution was cooled
and the resulting precipitate collected by filtration and washed
with ethanol (60 ml). The residue was crystallised from a
dichloromethane–hexane (1 : 9) mixture at room temperature and
4.5 Synthesis of [6,6ꢀꢀ-bis(iminoacetyl)-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine-
bis(2,6-diisopropylanil)]NiBr2 (2b)
Under an atmosphere of nitrogen a mixture of L2 (0.178 g,
0.280 mmol) and (DME)NiBr2 (0.086 g, 0.280 mmol, 1 eq.) were
added to a Schlenk flask containing dichloromethane (10 ml) at
0 ◦C. The stirred reaction mixture was allowed to warm to room
temperature and stirring continued for a further 12 h. The volatiles
the resulting crystalline material filtered, washed with hexane and
ꢀꢀ
=
were removed under reduced pressure and the residue was washed
dried under vacuum to afford 6,6 -{(2,6-i-Pr2C6H3)N CMe}2-
ꢀꢀ
2,2ꢀ:6ꢀ,2ꢀꢀ-C15H9N3 (L2) as a pale yellow solid. Yield: 1.10 g, 55%.
=
with hexane (20 ml) to yield [6,6 -{(2,6-i-Pr2C6H3)N CH}2-
2,2ꢀ:6ꢀ,2ꢀꢀ-C15H9N3]NiBr2 (2b) as a yellow solid. Crystallisation of
2b from a mixture of acetonitrile–chloroform gave 2b as yellow
blocks. Yield: 0.167 g, 70%. Anal. Calc. for C43H49N5NiBr2: C,
60.39; H, 5.73; N, 8.19%. Found: C, 60.23; H, 5.92; N, 7.99%.
Anal. Calc. for C43H49N5: C, 81.26; H, 7.72; N, 11.02%. Found:
C, 81.16; H, 7.86; N, 10.92%. H NMR (300 MHz, CDCl3): d
1.11 (d, 3JH–H 6.7, 24H, CH(CH3)2), 2.29 (s, 6H, CH3C N), 2.72
1
=
3
(sept, JH–H 6.7, 4H, CH(CH3)2), 7.0–7.1 (m, 6H, Ar–H), 7.91
3
3
3
(app. t, JH–H 7.9, JH–H 7.9, 1H, Py–H), 7.92 (app. t, JH–H 7.9,
4.6 Synthesis of [6,6ꢀꢀ-bis(iminoacetyl)-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine-
bis(2,6-diisopropylanil)]M2X4 (3)
3JH–H 7.9, 2H, Py–H), 8.37 (dd, JH–H 7.9, JH–H 0.9, 2H, Py–H),
3
4
3
3
4
8.54 (d, JH–H 7.9, 2H, Py–H) and 8.71 (dd, JH–H 7.9, JH–H 0.9,
2H, Py–H). 13C{ H} NMR (75 MHz, CDCl3): d 16.3 (CH3C N),
1
=
(a) 3a, M = Fe, X = Cl. An oven-dried Schlenk flask
equipped with a magnetic stir bar was evacuated and backfilled
with nitrogen. The flask was charged with anhydrous FeCl2
(0.040 g, 0.315 mmol) in n-BuOH (10 ml) and the contents
stirred at 110 ◦C until the iron salt had completely dissolved. L2
(0.100 g, 0.157 mmol, 0.5 eq.) was added and the mixture heated
to 110 ◦C for a further 20 min. After cooling to room temperature,
the suspension was concentrated and washed several times with
hexane. The solid was dried overnight under reduced pressure to
21.9 (CH3), 22.2 (CH3), 27.3 (CH), 120.0 (Py), 120.3 (Py), 121.0
(Py), 122.0 (Ar), 122.6 (Ar), 134.8 (Ar), 136.3 (Py), 136.8 (Py),
145.5 (Py), 136.3 (Py), 136.8 (Py), 145.4 (Ar), 154.0 (Py), 154.2
(Py), 154.6 (Py) and 166.1 (C N). IR (cm ): 2960(m), 1642(m,
m(C N)), 1563(s), 1430(s), 1362(w), 1256(w), 1184(w), 1108(m),
800(s), 784(s) and 760(s).◦ESI positive mass spectrum (m/z): 636
[(M + H)+]. Mp 252–254 C.
−1
=
=
4.4 Synthesis of [6,6ꢀꢀ-bis(iminoformyl)-2,2ꢀ:6ꢀ,2ꢀꢀ-terpyridine-
bis(2,6-diisopropylanil)]MX2 (1)
ꢀꢀ
ꢀ
ꢀ
ꢀꢀ
=
afford [6,6 -{(2,6-i-Pr2C6H3)N CMe}2-2,2 :6 ,2 -C15H9N3]Fe2Cl4
(3a) as a brown solid. Crystallisation of 3a from hot acetonitrile
solution gave 3a as red blocks. Yield: 0.109 g, 78%.
(a) 1a, M = Fe, X = Cl. An oven-dried Schlenk flask
equipped with a magnetic stir bar was evacuated and backfilled
with nitrogen. The flask was charged with anhydrous FeCl2
(0.021 g, 0.164 mmol) in n-BuOH (10 ml) and the contents stirred
at 110 ◦C until the iron salt had completely dissolved. L1 (0.100 g,
0.164 mmol, 1 eq.) was added and the mixture heated to 110 ◦C for
a further 20 min. After cooling to room temperature, the suspen-
sion was concentrated and washed several times with hexane. The
solid was dried overnight under reduced pressure to afford [6,6ꢀꢀ-
{(2,6-i-Pr2C6H3)N CH}2-2,2 :6 ,2 -C15H9N3]FeCl2 (1a) as a red–
brown solid. Crystallisation of 1a from hot acetonitrile solution
gave 1a as red needles. Yield: 0.096 g, 80%. Anal. Calc. for
C41H45N5FeCl2·1.5H2O·0.5MeCN: C, 64.49; H, 6.35; N, 9.85%.
Found: C, 64.78; H, 6.06; N, 9.63%.
(b) 3b, M = Ni, X = Br. Using an analogous procedure
to that described in 4.6(a) employing (DME)NiBr2 (0.097 g,
0.315 mmol) and L2 (0.100 g, 0.157 mmol, 0.5 eq.) gave [6,6ꢀꢀ-{(2,6-
ꢀ
ꢀ
ꢀꢀ
=
i-Pr2C6H3)N CMe}2-2,2 :6 ,2 -C15H9N3]Ni2Br4 (3b) as an orange
solid. Yield: 0.135 g, 80%. Crystallisation of 3b by prolonged
standing in chloroform gave 3b(H2O) as green needles.
(c) 3c, M = Zn, X = Cl. Using an analogous procedure
to that described in 4.6(a) employing anhydrous ZnCl2 (0.043 g,
0.315 mmol) and L2 (0.100 g, 0.157 mmol, 0.5 eq.) gave [6,6ꢀꢀ-{(2,6-
ꢀ
ꢀ
ꢀꢀ
=
ꢀ
ꢀ
ꢀꢀ
=
i-Pr2C6H3)N CMe}2-2,2 :6 ,2 -C15H9N3]Zn2Cl4 (3c) as a yellow
solid. Crystallisation of 3c from hot acetonitrile solution gave 1b as
yellow plates. Yield: 0.107 g, 75%. Anal. Calc. for C43H49N5Zn2Cl4:
C, 56.84; H, 5.40; N, 7.71%. Found: C, 56.96; H, 5.48; N, 7.68%.
(b) 1b, M = Ni, X = Br. Using an analogous procedure
to that described in 4.4(a) employing (DME)NiBr2 (0.051 g,
0.164 mmol) and L1 (0.100 g, 0.164 mmol, 1 eq.) gave [6,6ꢀꢀ-{(2,6-i-
4.7 Conversion of 2b to 3b
ꢀ
ꢀ
ꢀꢀ
=
Pr2C6H3)N CH}2-2,2 :6 ,2 -C15H9N3]NiBr2 (1b) as a yellow solid.
Crystallisation of 1b from hot acetonitrile solution gave 1b as
yellow needles. Yield: 0.108 g, 80%. Anal. Calc. for C41H45N5NiBr2:
C, 59.59; H, 5.45; N, 8.48%. Found: C, 59.50; H, 5.61; N, 8.39%.
An oven-dried Schlenk flask equipped with a magnetic stir
bar was evacuated and backfilled with nitrogen. The flask was
charged with (DME)NiBr2 (0.048 g, 0.157 mmol) and n-BuOH
(10 ml) and the suspension heated to 110 ◦C until the nickel
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salt had partially dissolved. 2b (0.134 g, 0.157 mmol, 1 eq.)
was added and the mixture heated to 110 ◦C for a further
30 min. After cooling to room temperature, the suspension was
concentrated and washed several times with hexane. The solid
was dried overnight under reduced pressure to afford [6,6ꢀꢀ-{(2,6-
ꢀ
ꢀ
ꢀꢀ
=
i-Pr2C6H3)N CMe}2-2,2 :6 ,2 -C15H9N3]Ni2Br4 (3b) as an orange
solid. Yield: 0.143 g, 85%.
4.8 Density functional calculations
Quantum mechanical calculations have been carried out using
the Gaussian 03 package of programs.14 The density functional
theory (DFT) was applied, in particular the functional Becke’s
three-parameter hybrid exchange method combined with LYP
correlation functional (B3LYP).15 The quasi-relativistic effective
core potential (ECP) LANL2DZ was used for the metal atoms
(Zn).16 The basis set for both atoms in the valence double-f
contraction associated to this ECP.14,16 The valence double-f with
polarisation 6–31 G(d)17,18 basis was used for N and Cl and the
minimal basis STO-3G for C and H.
4.9 Crystallography
Data for L2, 1a–1c 2b, 3a, 3b(H2O) and 3c were collected
on a Bruker APEX 2000 CCD diffractometer. Details of data
collection, refinement and crystal data are listed in Table 8.
The data were corrected for Lorentz and polarisation effects
and empirical absorption corrections applied. Structure solution
by direct methods and structure refinement on F2 employed
SHELXTL version 6.10.19 Hydrogen atoms were included in
˚
calculated positions (C–H = 0.96 A) riding on the bonded atom
with isotropic displacement parameters set to 1.5 Ueq(C) for methyl
H atoms and 1.2 Ueq(C) for all other H atoms. With the exception
of 3b(H2O) (only Ni and Br refined anisotropically) and 1c (all
atoms apart from C21 and C9), all non-H atoms were refined
with anisotropic displacement parameters. Disordered MeCN was
omitted using the SQUEEZE option in PLATON for 1b and 2b.
CCDC reference numbers 289324–289331.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b516083a
Acknowledgements
We thank the University of Leicester for financial assistance.
ExxonMobil Chemical are also thanked for Undergraduate sum-
mer Bursaries (to I. D. and D. P.).
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©