Synthesis and molecular structures of α-diimines and their zinc and palladium dichloride complexes

Article abstract of DOI:10.1016/j.poly.2004.06.023

Three α-iimines have been prepared and structurally characterised by single-crystal X-ray diffraction. In addition, molecular structures of some of their tetrahedral ZnCl₂ and square-planar PdCl₂ complexes are reported allowing a comparison as a function of coordination geometry. Three α-diimines, 2,3-dimethyl-N,N′-bis(cyclohexyl)-diaza-1,4-butadiene, Cy-DAD (1), (DAD = diaza-1,4-butadiene), bis{2,8-(4-methoxyphenylimino)} acenaphthene, p-OMe-BIAN (3), (BIAN = 2,8-bis(arylimino)acenaphthene) and bis{2,8-(2,6-di-isopropylphenylimino)}acenaphthene, 2,6-ⁱPr-BIAN (4), were synthesised either via their zinc complexes, as a template, or by the direct reaction of the appropriate primary amine with the diketone. Compound 1 is a non-constrained analogue of the rigid, bidentate nitrogen ligands 3 and 4. Syntheses of the zinc and palladium complexes of 3 and 4, namely 2, 5, 6 and 7, are also reported herein. All compounds have been characterised spectroscopically, and the molecular structures of 1, 3, 4, ZnCl ₂(p-OMe-BIAN)·1/2CH₂Cl₂ (2), PdCl ₂(p-OMe-BIAN) (6) and PdCl₂(2,6-ⁱPr-BIAN) (7) have been determined by single-crystal X-ray diffraction. Compound 1 adopts a transoid geometry and possesses a crystallographic inversion centre midway along the N=C-C=N backbone. Compounds 3 and 4 are inherently cisoidal and X-ray analysis highlights a twofold axis through the backbone. The Pd(II) centres of 6 and 7 both adopt square planar geometries whilst 6 contains four molecules per asymmetric unit and 1/2 molecule of benzonitrile per Pd atom and complex 7 is isomorphous with the known structure of PdCl(Me)(2,6-ⁱPr-BIAN). The Zn complex 2 is pseudo tetrahedral as expected for Zn(II).

Full text of DOI:10.1016/j.poly.2004.06.023

Polyhedron 23 (2004) 2789–2795
www.elsevier.com/locate/poly
Synthesis and molecular structures of a-diimines and their zinc
and palladium dichloride complexes
David N. Coventry, Andrei S. Batsanov, Andres E. Goeta,
*
Judith A.K. Howard, Todd B. Marder
Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, UK
Received 28 April 2004; accepted 16 June 2004
Available online 3 September 2004
Abstract
Three a-diimines, 2,3-dimethyl-N,N0-bis(cyclohexyl)-diaza-1,4-butadiene, Cy-DAD (1), (DAD = diaza-1,4-butadiene), bis{2,8-
(4-methoxyphenylimino)}acenaphthene, p-OMe-BIAN (3), (BIAN = 2,8-bis(arylimino)acenaphthene) and bis{2,8-(2,6-di-isopro-
pylphenylimino)}acenaphthene, 2,6-iPr-BIAN (4), were synthesised either via their zinc complexes, as a template, or by the direct
reaction of the appropriate primary amine with the diketone. Compound 1 is a non-constrained analogue of the rigid, bidentate
nitrogen ligands 3 and 4. Syntheses of the zinc and palladium complexes of 3 and 4, namely 2, 5, 6 and 7, are also reported herein.
All compounds have been characterised spectroscopically, and the molecular structures of 1, 3, 4, ZnCl2
i
1
2
ðp-OMe-BIANÞ ꢀ CH2Cl2 ð2Þ, PdCl2(p-OMe-BIAN) (6) and PdCl2(2,6- Pr-BIAN) (7) have been determined by single-crystal X-
ray diffraction. Compound 1 adopts a transoid geometry and possesses a crystallographic inversion centre midway along the
N‚C–C‚N backbone. Compounds 3 and 4 are inherently cisoidal and X-ray analysis highlights a twofold axis through the back-
bone. The Pd(II) centres of 6 and 7 both adopt square planar geometries whilst 6 contains four molecules per asymmetric unit and
1/2 molecule of benzonitrile per Pd atom and complex 7 is isomorphous with the known structure of PdCl(Me)(2,6-iPr-BIAN). The
Zn complex 2 is pseudo tetrahedral as expected for Zn(II).
ꢀ 2004 Elsevier Ltd. All rights reserved.
Keywords: X-ray structure; Diimine; Coordination complex; Zinc; Palladium
1. Introduction
dentate nitrogen donor ligands have been used in many
catalytic studies including the enantioselective carbony-
lation of olefins [3], hydrogenation and hydrosilylation
[4], the borylation of alkanes and alkenes [5], diboration
[6] and reduction of nitrobenzene to aniline [7]. Routes
to the diimines have been previously developed by Else-
vier and co-worker [8a], Fukuda and co-worker [8b] and
Dieck and Dietrich [8c].
Over the past decade there has been considerable in-
terest in alternative ligands to phosphines, for the devel-
opment of late transition metal catalysts. Examples of
this include the substantial development by Brookhart
and co-workers [1] of a-diimine ligands for nickel and
palladium catalysed olefin polymerisation and recent de-
velopments in the zinc catalysed ring-opening polymeri-
sation of epoxides and e-caprolactone reported by
Bochmann and co-workers [2]. Furthermore, other bi-
Whilst most studies of the a-diimines have concen-
trated on the reactivity of their complexes, very little
crystallographic information has been obtained. We re-
port herein the synthesis and structural characterisation
of p-OMe-BIAN (3), 2,6-iPr-BIAN (4), Cy-DAD (1),
*
Corresponding author. Tel.: +44 191 334 2037; fax: +44 191 384
1
2
ZnCl2ðp-OMe-BIANÞ ꢀ CH2Cl2 ð2Þ,
PdCl2(p-OMe-
4737.
E-mail address: todd.marder@durham.ac.uk (T.B. Marder).
BIAN) (6) and PdCl2(2,6-iPr-BIAN) (7) (shown in
0277-5387/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2004.06.023

2790
D.N. Coventry et al. / Polyhedron 23 (2004) 2789–2795
1
166 [M ꢁ C6H10]+. H NMR [CD2Cl2, 200 MHz]: d 3.5
(m, 4H, CH2), 2.05 (s, 6H, CH3), 1.8 (m, 4H, CH2),
1.65 (m, 4H, CH2), 1.4 (m, 8H, CH2).
1
2
2.3. Synthesis of ZnCl2ðp-OMe-BIANÞ ꢀ CH2Cl2 (2)
Cy
N
N
Cy
Ar
N
N
Ar
1
3, Ar = C4H4-p-OMe
4, Ar = 2,6-iPr2C6H3
This complex was synthesised in a similar manner to
that described in the literature [8a]. A mixture of ace-
naphthenequinone (2.00 g, 11 mmol), anhydrous ZnCl2
(1.71 g, 12.5 mmol) and 4-methoxyaniline was heated to
170 ꢁC in a closed YoungÕs-tap tube for 4 h. The mixture
was then cooled to 20 ꢁC and transferred to a beaker
with Et2O (2 · 50 ml) and glacial acetic acid (2 · 50
ml). Aluminium foil was placed over the beaker and
the following day the red precipitate which had formed
was collected by filtration and washed with Et2O (5 · 20
ml). Crystals suitable for X-ray diffraction studies were
grown from CH2Cl2. Yield: 5.51 g, 95%. (Found: C,
N
N
N
N
Ar
Ar
Ar
Ar
Zn
Pd
Cl
Cl
Cl
Cl
6, Ar = C4H4-p-OMe
7, Ar = 2,6-iPr2C6H3
2, Ar = C4H4-p-OMe
5, Ar = 2,6-iPr2C6H3
1
2
56.49; H, 3.71; N, 5.09. C26H20Cl2N2O2Zn ꢀ CH2Cl2 re-
Scheme 1.
quires: C, 55.72; H, 3.71; N, 4.90%). This suggests that
CH2Cl2 may be slowly evaporating from the crystal lat-
tice.) ES-MS [CH2Cl2, m/z]: 528 [M]+, 391
[M ꢁ H ꢁ ZnCl2]+. 1H NMR [DMSO; 200 MHz]: d
8.12 (d, 2H, J = 8.3, C10H6), 7.57 (dd, 2H, J = 8.3, 7.2,
C10H6), 7.09 (s, 8H, C6H4), 6.96 (d, 2H, J = 7.2,
C10H6), 3.85 (s, 6H, OMe).
Scheme 1). Although the structure of 2,6-iPr-BIAN has
been published previously [9a,9b] we note that the space
group reported was wrong [9c].
2.4. Synthesis of p-OMe-BIAN (3)
2. Experimental
Compound 3 was prepared in a similar manner to
that described in the literature [8a]. Thus, ZnCl2
2.1. General
1
ðp-OMe-BIANÞ ꢀ CH2Cl2 ð2Þ ð3:00 g; 5:25 mmolÞ was
All chemicals were commercially available and were
1
used as received. H NMR spectra were obtained using
2
added to a solution of K2CO3 (25.00 g, 180 mmol) in
water (250 ml) and the mixture was heated at reflux with
vigorous stirring. After 17 h, the solid was collected by
filtration and washed with water (5 · 30 ml) and then
was extracted by soxhlet with ethanol for two days.
On cooling, red crystals suitable for X-ray diffraction
studies grew from solution. The reaction was filtered
and the mother liquor concentrated to half volume to
promote the formation of a second crop of crystals.
Yield: 1.80 g, 81%. (Found: C, 79.32; H, 5.03; N, 7.17.
C26H20N2O2 requires: C, 79.57; H, 5.14; N, 7.14%),
EI-MS [CH2Cl2, m/z]: 391 [M ꢁ 1]+, 377 [M ꢁ CH3]+,
361 [M ꢁ OCH3]+. 1H NMR [DMSO; 200 MHz]: d
8.07 (d, 2H, J = 7.8, C10H6), 7.53 (dd, 2H, J = 7.8, 7.0,
C10H6), 7.07 (apparent d, 8H, J = 3.1, C6H4), 6.92 (d,
2H, J = 7.0, C10H6), 3.83 (s, 6H, OMe).
a 400 MHz Bruker Avance and Mercury-200, Unity-300
and Inova-500 MHz Varian spectrometers; coupling con-
stants are given in Hz. Mass spectra were obtained with
Micromass AutoSpec (EI) and Micromass-LCT (ES)
spectrometers. The elemental analyses were carried out
with an Exeter Analytical Inc. CE-440 elemental analyser.
2.2. Synthesis of (Cy-DAD) (1)
The compound 2,3-dimethyl-N,N0-bis(cyclohexyl)-
diaza-1,4-butadiene was prepared in a similar manner
to that used by Dieck and Dietrich [8c]. Cyclohexylamine
(20.25 ml, 180 mmol) was added dropwise to a cooled (0
ꢁC) mixture of butane-2,3-dione (7.8 ml, 90 mmol), mo-
˚
lecular sieves (10 g, 4 A) and formic acid (1 ml, 98%) in
chloroform (100 ml). After stirring for one day, the mix-
ture was filtered and the chloroform removed in vacuo.
The remaining yellow-white solid was re-crystallised
from ethanol yielding colourless plates suitable for X-
ray diffraction. Yield: 8.9 g, 40%. (Found: C, 77.40; H,
11.60; N, 11.28. C16H28N2 requires: C, 77.36; H, 11.36;
N, 11.28%). ES-MS [m/z]: 248 [M]+, 205 [M ꢁ C3H7]+,
2.5. Synthesis of (2,6-iPr-BIAN) (4)
This compound was prepared via a similar method
to that of Fukuda and co-workers [8b]. Acenaphthen-
equinone (1.35 g, 7.4 mmol) was dissolved in acetonit-
rile (65 ml) and glacial acetic acid (12 ml) and heated

D.N. Coventry et al. / Polyhedron 23 (2004) 2789–2795
2791
to reflux. 2,6-Diisopropylaniline (3 ml, 16 mmol) was
2.8. Synthesis of PdCl2(2,6-iPr-BIAN) (7)
added dropwise and the mixture refluxed for 1.5 h.
After cooling to room temperature the yellow solid
was filtered, washed with hexane and re-crystallised
with hexane/CH2Cl2 to yield crystals suitable for X-
ray diffraction. Yield: 3.15 g, 85%. (Found: C, 86.20;
H, 7.98; N, 5.65 C36H40N2 requires: C, 86.35; H,
8.05; N, 5.59%). EI-MS [CH2Cl2, m/z]: 500 [M]+,
457 [M ꢁ C3H7]+, 340 [M ꢁ C6H3(C3H7)2 + 1]+. 1H
NMR [CD2Cl2; 400 MHz]:d 7.91 (d, 2H, J = 8.3,
C10H6), 7.58 (dd, 2H, J = 8.3, 7.1, C10H6), 7.3 (m,
6H, C6H3), 6.69 (d, 2H, J = 7.1, C10H6), 2.98 (sept,
2H, J = 6.8, CHCH3), 1.30 (d, 6H, J = 6.8, CH3),
1.0 (d, 6H, J = 6.8, CH3).
This complex was prepared and crystallised as for 6
with the following quantities of materials: cyclooctene
(0.166 ml, 1.27 mmol), PdCl2(NCPh)2 (0.244 g, 0.637
mmol) in benzonitrile (10 ml) and 2,6-iPr-BIAN (0.319
g, 0.637 mmol) in benzonitrile (10 ml). Yield: 0.314 g,
72%. (Found: C, 63.62; H, 5.95; N, 4.13. C36H40
Cl2N2Pd requires: C, 63.77; H, 5.95; N, 4.13%.) EI-MS
[CH2Cl2, m/z]: 500 [M ꢁ PdCl2]+, 457 [M ꢁ
PdCl2 ꢁ C3H7]+, 340.1 [M ꢁ PdCl2 ꢁ C6H3(C3H7)2 +
1]+. 1H NMR [CD2Cl2; 200 MHz]: d 8.18 (d, 2H,
J = 8.4, C10H6), 7.69 (m, 6H, C6H3), 7.41 (dd, 2H,
J = 8.4, 7.2, C10H6), 6.55 (d, 2H, J = 7.2, C10H6), 3.50
(sept, 2H, J = 6.8, CHCH3), 1.52 (d, 6H, J = 6.8,
CH3), 1.00 (d, 6H, J = 6.8, CH3).
2.6. Synthesis of ZnCl2(2,6-iPr-BIAN) (5)
2.9. X-ray crystallography
This zinc complex was prepared using a different
method to that published by Asselt et al. [8a]. Thus,
2,6-iPr-BIAN (4) (2 g, 3.99 mmol) was added in one por-
tion to a stirring solution of anhydrous ZnCl2 (0.544 g,
3.99 mmol) in glacial acetic acid (50 ml). The yellow-or-
ange solid which formed was collected by filtration,
washed with Et2O (3 · 30 ml) and dried in air. The prod-
uct was recrystallised by layering Et2O over CH2Cl2.
Yield: 2.34 g, 92%. (Found: C, 67.77; H, 6.33; N, 4.42.
C36H40Cl2N2Zn requires: C, 67.88; H, 6.33; N, 4.40%).
EI-MS [CH2Cl2, m/z]: 600 [M ꢁ Cl + 1]+ 500
[M ꢁ ZnCl2]+, 457 [M ꢁ ZnCl2 ꢁ C3H7]+, 340 [M ꢁ Zn
Cl2 ꢁ C6H3(C3H7)2 + 1]+. 1H NMR [CD2Cl2; 200
MHz]: d 8.17 (d, 2H, J = 7.9, C10H6), 7.58 (dd, 2H,
J = 7.9, 7.4, C10H6), 7.46 (m, 6H, C6H3), 6.75 (d, 2H,
J = 7.4, C10H6), 3.26 (sept, 2H, J = 6.8, CHCH3), 1.36
(d, 6H, J = 6.8, CH3), 0.87 (d, 6H, J = 6.8, CH3).
X-ray diffraction experiments were performed on
Bruker 3-circle diffractometers with SMART 6000
CCD area detectors, using graphite-monochromated
ꢀ
˚
Mo Ka radiation ðk ¼ 0:71073 AÞ. The low temperature
of the crystals was maintained with Cryostream (Oxford
Cryosystems) open-flow N2 cryostats. The structures
were solved by direct methods and refined by full-matrix
least squares against F2 of all reflections, using SHELXTL
software [10]. All non-H atoms were refined with aniso-
tropic ADP and all H atoms were located by difference
Fourier synthesis and refined isotropically. The absolute
structure of 5 has been determined from the anomalous
dispersion of sulfur, the Flack parameter converging at
0.26(16) [11]. Crystal data and experimental details are
given in Table 1.
1
2
3. Results and discussion
2.7. Synthesis of PdCl2ðp-OMe-BIANÞ ꢀ C6H5CN (6)
3.1. Crystal structures
Cyclooctene (0.341 ml, 2.61 mmol) was added in
one portion to a stirring solution of PdCl2(NCPh)2
(0.5 g, 1.324 mmol) in benzonitrile (10 ml). A solution
of p-OMe-BIAN (3) (1.023 g, 2.608 mmol) in benzo-
nitrile (10 ml) was then added and the reaction was
stirred for 2 h. The solid formed was collected by fil-
tration, washed with Et2O and recrystallised from re-
fluxing CH2Cl2/benzonitrile. Yield: 0.511 g, 67%.
Molecule 1 (shown in Fig. 1) lies at a crystallographic
inversion centre, the C(1)–N‚C(7)–C(70)‚N0–C(10)
moiety is planar, and transoid with respect to the central
C(7)–C(70) bond; the C(1)–N–C(7)–C(70) torsion angle
is ꢁ179.95(7)ꢁ. This E, s-trans-E conformation has been
observed in CyN‚CHCH‚NCy [12] and is typical for
previously reported 2,3-dimethyl-azabutadienes [13],
while their analogues with larger substituents in the
2,3-positions usually adopt gauche conformations. The
cyclohexyl ring adopts a chair conformation. The bond
distances are usual, and indicative of localised C‚N
double bonds.
(Found:
C,
56.65;
1
H,
3.64;
N,
5.64.
C26H20Cl2N2O2Pd ꢀ C6H5CN requires: C, 57.02; H,
2
3.65; N, 5.64%). EI-MS [CH2Cl2, m/z]: 570 [M]+,
391 [M ꢁ PdCl2 ꢁ 1]+, 377 [M ꢁ PdCl2 ꢁ CH3]+, 361
[M ꢁ PdCl2 ꢁ OCH3]+. 1H NMR [DMSO; 300
MHz]: d 8.27 (d, 2H, J = 8.4, C10H6), 7.63 (dd, 2H,
J = 8.4, 7.3, C10H6), 7.34 (d, 4H, J = 8.7, C6H4),
7.13 (d, 4H, J = 8.7, C6H4), 6.73 (d, 2H, J = 7.3,
C10H6), 3.86 (s, 6H, OMe).
1
2
In the structure of 2 ꢀ CH2Cl2, molecule 2 (Fig. 2)
has no crystallographic symmetry, while the CH2Cl2 is
chaotically disordered around an inversion centre. The

2792
D.N. Coventry et al. / Polyhedron 23 (2004) 2789–2795
Table 1
Crystal data and experimental parameters
Compound
1
2
3
4
6
7
Formula
Formula weight
T (K)
C16H28N2
248.40
120(2)
C26H20N2O2Cl2Zn ꢀ 1 CH2Cl2 C26H20N2O2
C36H40N2
500.70
120(2)
C26H20N2O2Cl2Pd ꢀ 1 C7H5N C36H40N2Cl2Pd
2
2
571.17
120(2)
392.44
120(2)
621.30
120(2)
678.00
120(2)
orthorhombic
Pbca (# 61)
11.429(1)
21.330(1)
26.984(1)
90
Crystal system
Space group
monoclinic monoclinic
P21/c (# 14) P21/c (# 14)
orthorhombic monoclinic monoclinic
Pbcn (# 60)
19.851(4)
8.913(1)
10.936(2)
90
C2/c (# 15) P21/n (# 14)
˚
a (A)
14.076(5)
5.8507(7)
9.222(2)
93.81(2)
757.8(3)
2
12.402(1)
11.736(1)
17.574(2)
95.99(1)
2543.9(4)
4
15.414(2)
8.860(1)
21.452(3)
93.56(1)
2923.8(7)
4
19.360(3)
23.573(4)
23.871(4)
105.93(1)
10476(3)
16
˚
b (A)
˚
c (A)
b (ꢁ)
3
˚
V (A )
1934.9(6)
4
6578.1(5)
8
1.369
Z
qcalcd (g cmꢁ3
)
1.089
0.06
1.491
1.31
60
1.347
0.09
58
1.137
0.07
58
1.576
0.94
60
l (mmꢁ1
2hmax (ꢁ)
Total reflections
)
0.75
60
60
10 161
2211
31 064
7424
5762
30 778
2569
2159
19 346
4261
3053
158 533
30 528
18 993
1349
86 119
9562
7306
Unique reflections
Reflections I > 2r(I) 2006
Parameters
Rint
138
330
177
181
394
0.052
0.071
0.040
0.119
0.035
0.035
0.103
0.034
0.038
0.110
0.059
0.053
0.156
0.063
0.037
0.114
R (F, I > 2r(I))
wR (F2, all data)
0.033
0.092
In 2, the phenyl rings form angles of 54.1ꢁ and 57.7ꢁ
with the A plane and 13.1ꢁ between themselves. Thus,
the molecule has an approximate mirror plane perpen-
dicular to the acenaphthene plane (violated, however,
by opposite orientations of the methyl groups) but loses
the mirror plane coinciding with the acenaphthene
plane. The two Cl ligands are sterically non-equivalent:
Cl(2) faces more overcrowding than Cl(1), with the fol-
Fig. 1. Molecular structure of 1. Atoms generated by the inversion
centre are primed.
˚
lowing results: (i) the Zn–Cl(2) bond is 0.017 A longer
than Zn–Cl(1); (ii) the Zn atom tilts out of the A plane
˚
by 0.12 A in the direction of Cl(1); (iii) the N–Zn–Cl(1)
Zn atom has a distorted tetrahedral coordination with
two Cl ligands and a nearly-planar chelating diazabut-
adiene moiety N(1)C(11)–C(12)N(2). In similar com-
plexes with phenyl (and especially substituted phenyl)
groups at the N atoms, the phenyl rings usually adopt
a perpendicular orientation with respect to the diazabut-
adiene plane (plane A).
angles are wider than N–Zn–Cl(2), averaging 116.5ꢁ and
110.2ꢁ, respectively; (iv) the naphthalene moiety is tilted
out of the A plane by 5.1ꢁ towards Cl(2), i.e., in the di-
rection of less hindrance on its side. Distortions (ii), (iii)
and (iv) together make the angle between the acenaph-
thene plane and the Zn–Cl(2) bond 70.9ꢁ compared to
44.5ꢁ for Zn–Cl(1).
Molecule 3 lies on a crystallographic twofold axis,
passing through atoms C(5), C(6) and the midpoint of
the C(7)–C(70) bond (Fig. 3(a)). The diazabutadiene
moiety is planar, and the phenyl rings are inclined to
its plane (A) by 57.6ꢁ; hence, the molecule has no local
mirror symmetry but adopts a twisted overall conforma-
tion. The A and naphthalene planes form an angle
u = 6.0ꢁ, while the N–C(8) bond is tilted out of plane
A in the opposite direction, with the torsion angles
C(70)–C(7)–N–C(8) 11.0ꢁ and C(2)–C(1)ꢀ ꢀ ꢀN–C(8)
15.5ꢁ.
Molecule 4 also has crystallographic C2 symmetry
i
(Fig. 3(b)). Bulky Pr groups enforce a more perpendic-
ular orientation of the phenyl rings, which are inclined
Fig. 2. Molecular structure of 2 in the crystal of 2 ꢀ 1 CH2Cl2.
2

D.N. Coventry et al. / Polyhedron 23 (2004) 2789–2795
2793
(a)
(a)
(b)
(b)
Fig. 3. Molecular structures of 3 (a) and 4 (b). Atoms generated by the
twofold axis in each structure are primed.
Fig. 4. Molecular structures of 6 (a) (one of the four independent
molecules in the crystal of 6 ꢀ 12 PhCN) and 7 (b).
by 78.7ꢁ to the A plane, and the twist of the molecule is
correspondingly smaller than in 3, with the angles
u = 2.8ꢁ, C(70)–C(7)–N–C(8) 3.5ꢁ and C(2)–C(1)ꢀ ꢀ ꢀN–
C(8) 5.1ꢁ.
While this work was in progress, the crystal structure
of 4 was determined [9a,9b] at room temperature in
space group Cc (No. 9), with the molecule in a general
position. The lattice parameters reported, a = 15.587(2)
pendent molecules is similar, with square-planar coordi-
nation of the Pd atom. Phenyl rings are approximately
normal to the diazabutadiene moiety (interplanar angles
74.8ꢁ–89.9ꢁ). The acenaphthene moiety in molecule (ii) is
practically planar and in three others show minor twist,
of the same order as in molecule 4.
The crystal structure of 7 (Fig. 4(b)) is isomorphous
with that of chloro-bis{2,8-(2,6-di-isopropylphenylimi-
no)-acenaphthene-N,N)-methylpalladium [5], which dif-
fers from 7 by a substitution of a methyl group for one
of the chloro-ligands. The asymmetric unit comprises
one molecule, without crystallographic symmetry. Mol-
ecule 7 is similar to 6 in the nearly perpendicular orien-
tation of the phenyl rings (dihedral angles of 83.3ꢁ and
82.6ꢁ with plane A) and other conformational features.
˚
˚
˚
A, b = 8.856(2) A, c = 21.780(7) A, b = 93.85(2)ꢁ,
V = 2999.7 A , were identical with our results (allowing
3
˚
for thermal expansion). A search for additional symme-
try, performed on the atomic coordinates (ref. code
WUSLIF) deposited at the CSD, using PLATON soft-
ware [14], revealed the missing inversion centre with
the coordinates (ꢁ0.030, 0, ꢁ0.212). Thus, the structure
[9a,9b] is identical with the one reported herein, in the
correct space group C2/c (No. 15) as already pointed
out by Marsh [9c].
The ionic radius of square-planar Pd2+ (0.64 A) ex-
˚
ceeds that of tetrahedral Zn2+ (0.60 A) [20]. In fact,
˚
the Pd–Cl bond distances in 6 and 7 exceed Zn–Cl in 2
˚
by an average of 0.065 A, while the Pd–N bonds are ac-
˚
tually shorter than Zn–N, by ca. 0.035 A (Table 2). This
is probably due to dp ! pp back donation in the Pd
complexes. The resulting p delocalisation in the chelate
ring is indicated by small but significant lengthening of
C‚N bonds and shortening of the intermediate C–C
bond in the Pd complexes compared to the free mole-
cules, while coordination with Zn affects these distances
insignificantly. It is noteworthy that coordination with
1
2
The asymmetric unit of 6 ꢀ PhCN comprises four
molecules of the complex and two of benzonitrile, all
of them devoid of crystallographic symmetry (Fig.
4(a)). Acenaphthene systems of all molecules 6 in the
structure are approximately parallel to the (1 0 ꢁ1)
plane, and the four independent Pd atoms (although
not the rest of the molecules) are related by peculiar
pseudo-symmetrical operations, viz: (i) x, y, z; (ii) x,
y + 1/2, z; (iii) 1/2 ꢁ x, y ꢁ 1/4, 1 ꢁ z; (iv) 1/2 ꢁ x,
y ꢁ 1/4, 1 ꢁ z. The geometry and conformation of inde-

2794
D.N. Coventry et al. / Polyhedron 23 (2004) 2789–2795
Table 2
Bond distances (A) in diimine ligands and their complexes
˚
M–Cl
M–N
C‚N
C–C
Nꢀ ꢀ ꢀN
1
2
–
2.2013(6)
2.2180(6)
–
2.085(2)
2.071(2)
1.281(1)
1.281(3)
1.285(3)
1.277(1)
1.280(1)
1.510(1)
1.520(3)
–
2.713(3)
–
3
4
6
–
–
–
–
1.527(2)
1.530(2)
2.815(2)
2.812(2)
Minimum
Maximum
Average
2.2731(7)
2.2817(7)
2.277(3)
2.033(2)
2.055(2)
2.041(8)
2.053(2)
2.051(2)
1.275(3)
1.295(3)
1.289(6)
1.293(2)
1.292(2)
1.495(3)
1.499(3)
1.497(2)
1.486(3)
–
2.652(3)
2.664(3)
2.660(5)
2.679(2)
–
7
2.2665(5)
2.2689(5)
˚
Zn reduces the transannular Nꢀ ꢀ ꢀN distance by ca. 0.1 A
tion B does not shift on complexing to Zn but moves
upfield when 4 is bound to Pd. As in compound 3, it
1
is the H signals for the aryl side arm that show the
compared to free molecules, and coordination with Pd
˚
reduces it by 0.15 A.
most significant shifts. The C6H3 signal remains a
multiplet regardless of complexation; however, it
moves downfield on binding to Zn (0.16 ppm) and
Pd (0.39 ppm). This is also the case for the CH of
1
3.2. H NMR properties
The 1H NMR spectrum of compound 3 shows
three signals at d 8.07, 7.53 and 6.92 corresponding
to positions A, B and C, respectively (see Fig. 5) of
the acenaphthenequinone backbone, and an apparent
doublet (AB spin system) at d 7.07 for the C6H4 aro-
matic protons. On complexation to Zn, a very small
downfield shift is observed for all of these signals
and the apparent doublet collapses to a singlet, i.e.,
the two chemical environments lead to absolutely co-
incident signals. When Pd occupies the cavity, a more
pronounced effect is observed. The signals relating to
protons at positions A and B move downfield while
that of C moves upfield. The major difference, how-
ever, is the splitting of the C6H4 AB signal into two
doublets.
i
the Pr groups. There are two signals present for the
methyl groups in compound 4 (Dd = 0.3 ppm), indica-
tive of restricted rotation. The magnitude of separa-
tion increases on complexation to Zn (Dd = 0.49
ppm) and Pd (Dd = 0.52 ppm).
4. Conclusions
Three a-diimines have been synthesised and two of
these have been complexed to both ZnCl2 and PdCl2.
1
The H NMR spectra have been compared and com-
pounds 1, 2, 3, 4, 6 and 7 have been structurally charac-
terised by single-crystal X-ray diffraction, revealing the
changes resulting from coordination to both tetrahedral
Zn(II) and square-planar Pd(II) metal centres.
These effects may well be due to the Pd–N interac-
tion being stronger than the analogous Zn–N interac-
tion. Very little change is observed in the shift of the
methoxy signal. An increase in all of the coupling
constants is also observed in complexation of 3 to ei-
ther Zn or Pd.
5. Supplementary material
The proton signals of compound 4 exhibit very sim-
1
ilar behaviour to that observed in 3. While the H sig-
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic
data centre, CCDC Nos. 236150–236155. Copies of this
data may be obtained free of charge from The Director
CCDC, 12 Union Road, Cambridge, CB2 1EZ (fax:
+44-1223-336-033 or e-mail: deposit@ccdc.cam.ac.uk
or www: http://www.ccdc.cam.ac.uk).
nals at positions A and C move upfield and downfield
as described for 3, the signal for the protons at posi-
C
C
B
A
B
A
Acknowledgements
Ar
N
N
Ar
We thank EPSRC for research support and Professor
C.J. Elsevier for helpful discussions.
Fig. 5. Assignment of acenaphthenequinone proton positions.

D.N. Coventry et al. / Polyhedron 23 (2004) 2789–2795
2795
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