The complexation of nickel(II) and palladium(II) by heterotridentate ligands with [P,N,O] donor sets

Article abstract of DOI:10.1016/S0020-1693(99)00531-9

Phosphorus-containing heterotridentate ligands prepared by the condensation of 2-(diphenylphosphino)aniline with 5-chlorosalicylaldehyde (HL¹), 5-nitrosalicylaldehyde (HL²), 5-bromosalicylaldehyde (HL³), 5-methoxysalicylaldehyde (HL⁴) or 3-methoxysalicylaldehyde (HL⁵) react directly with NiCl₂·6H₂O or [(cod)PdCl₂] to form complexes of general formula [η³(L)M(II)Cl]. These are characterised by spectroscopic, microanalytical and crystallographic methods. The crystal structures of [η³(L³)Ni(II)Cl] (3) and [η³(L²)Pd(II)Cl] (6) confirm tridentate [P,N,O] coordination of the deprotonated ligands to the metal centres, forming both five- and six-membered rings. (C) 2000 Elsevier Science S.A.

Full text of DOI:10.1016/S0020-1693(99)00531-9

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Inorganica Chimica Acta 303 (2000) 116–120
The complexation of nickel(II) and palladium(II) by
heterotridentate ligands with [P,N,O] donor sets
Jonathan Parr *, Alexandra M.Z. Slawin
Department of Chemistry, Loughborough Uni6ersity, Loughborough, Leicestershire LE11 3TU, UK
Received 29 July 1999; accepted 8 November 1999
Abstract
Phosphorus-containing heterotridentate ligands prepared by the condensation of 2-(diphenylphosphino)aniline with 5-chlorosal-
icylaldehyde (HL1), 5-nitrosalicylaldehyde (HL2), 5-bromosalicylaldehyde (HL3), 5-methoxysalicylaldehyde (HL4) or 3-
methoxysalicylaldehyde (HL5) react directly with NiCl2·6H2O or [(cod)PdCl2] to form complexes of general formula
[h3(L)M(II)Cl]. These are characterised by spectroscopic, microanalytical and crystallographic methods. The crystal structures of
[h3(L3)Ni(II)Cl] (3) and [h3(L2)Pd(II)Cl] (6) confirm tridentate [P,N,O] coordination of the deprotonated ligands to the metal
centres, forming both five- and six-membered rings. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Crystal structures; Nickel complexes; Palladium complexes; Tridentate ligand complexes
1. Introduction
condensation of 2-(diphenylphosphino)-aniline with
substituted salicylaldehydes, Fig. 1.
Bidentate ligands, which comprise mixed hard/soft
donor sets, continue to attract the attention of coordi-
nation chemists. In particular, those ligands, which can
be described as functionalised phosphines, are fre-
quently used to form complexes with middle and late
transition metals [1].
2. Experimental
2.1. Materials
A number of groups have expanded upon this
premise and have prepared mixed tridentate ligands
with [P,N,E] donor sets (E=O, S or N%) and explored
their complexation behaviour. In the cases where E=
O, the ligands are either monobasic, with ionisable
protons, [2–8] or neutral, where the oxygen donor is
part of an ether function [9–12]. From amongst the
former we have previously reported the ligand prepared
from the Schiff base condensation of 2-(diphenylphos-
phino)aniline with salicylaldehyde and its complexes
with Group 10 metals [7] and ruthenium [8]. To extend
the study of these ligands, we report the preparation of
a range of complexes of general formula [h3(L)M(II)-
Cl], where (L) is a monobasic ligand prepared by the
Complexation reactions were performed under an
atmosphere of oxygen-free nitrogen; diethyl ether and
dichloromethane were distilled under nitrogen from
sodium–benzophenone ketyl and calcium hydride re-
spectively; all other solvents were analytical grade and
used without further purification. The compounds
[(cod)Pd(II)Cl2] (cod=cycloocta-1,5-diene) [13] and 2-
(diphenylphosphino)aniline [14] were prepared by liter-
* Corresponding author. Tel.: +44-1509-22 2588; fax: +44-1509-
22 3925.
E-mail address: j.parr@lboro.ac.uk (J. Parr)
Fig. 1. The preparation of 1–10.
0020-1693/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(99)00531-9

J. Parr, A.M.Z. Slawin / Inorganica Chimica Acta 303 (2000) 116–120
117
Table 1
Crystal data and structure determination parameters for 3 and 6·CHCl3
Compound
3
6·CHCl3
Empirical formula
M
C25H18BrClNNiOP
553.44
C25H18Cl2NOPPd·CHCl3
676.04
Temperature (K)
Crystal size (mm)
Crystal system
Space group
293(2)
293(2)
0.1×0.1×0.2
triclinic
0.08×0.1×0.2
monoclinic
P21/n
(
P1
Unit cell dimensions
,
a (A)
12.3042(4)
12.3559(4)
14.9487(5)
90
100.395(1)
90
9.6740(4)
10.5463(4)
13.2275(5)
87.3610(10)
77.5690(10)
88.7600(10)
1316.40(9)
2
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
3
,
U (A )
2235.34(13)
4
Z
F000
Dcalc
1112
1.645
2.865
672
1.706
1.295
v (mm−1
)
Total data
9580
6739
Unique data
Rint
3218
0.0337
3109
0.0198
R1, wR2
Residual electron density
Absorption correction
0.0274, 0.0566
0.426, −0.483
SADABS
0.0281, 0.0617
0.395, −0.364
SADABS
ature methods; ligands HL1–5 were prepared according
to a published method [8]; nickel chloride hexahydrate
and the substituted salicylaldehydes were obtained
commercially (Aldrich) and used as received.
and all of the non-hydrogen atoms refined with an-
isotropic displacement parameters. Refinement was by
full-matrix least-squares methods on F2, calculations
were performed using the program SHELXTL-PC [15].
2.2. Instrumentation
2.3. Preparation of complexes
2.3.1. [p3(L1)Ni(II)Cl] (1)
To a solution of NiCl2·6H2O (0.057 g, 0.24 mmol) in
95% ethanol (5 ml) was added solid [HL1] (0.10 g, 0.24
mmol). The solution was stirred at room temperature
Infrared spectra were recorded as KBr pellets over
the range 4000–200 cm−1 using a Perkin–Elmer sys-
tem 2000 FT spectrometer. The H NMR spectra were
1
recorded on a Bruker AC250 FT spectrometer (250
MHz) with chemical shifts (l) reported relative to
external TMS. The 31P{1H} NMR spectra were
recorded on a Jeol FX90Q spectrometer (36.2 MHz)
with chemical shifts (l) reported relative to external
85% H3PO4; NMR spectra for 6–10 were recorded in
CDCl3 solutions. Elemental analyses were performed
using a Perkin–Elmer 2400 CHN Elemental Analyser
by the Loughborough University Microanalytical Ser-
vice within the Department of Chemistry.
Table 2
a
,
Selected bond lengths (A) and angles (°) for 3 and 6
3
6
Bond lengths
MꢀP
MꢀN
MꢀO
MꢀCl
CꢁN
CꢀO
2.1487(9)
1.887(2)
1.881(2)
2.1857(8)
1.304(3)
1.295(3)
2.1908(9)
2.020(2)
2.034(2)
2.3006(9)
1.307(4)
1.292(4)
2.2.1. X-ray crystallography
X-ray crystallographic studies were performed on 3
and 6·CHCl3 at ambient temperatures using a Siemens
SMART diffractometer with graphite-monochromated
Bond angles
NꢀMꢀO
NꢀMꢀP
OꢀMꢀCl
PꢀMꢀCl
OꢀMꢀP
93.40(9)
86.35(7)
90.70(6)
89.53(7)
179.11(7)
175.59(7)
93.91(10)
85.88(8)
89.26(7)
91.10(3)
175.73(8)
176.32(8)
,
Mo Ka radiation (u=0.71073 A) and ꢀ scans. The
crystal data, a summary of the data collections and the
structure refinements for these compounds are given in
Table 1, selected bond lengths and angles are collected
in Table 2. All structures were solved by direct methods
NꢀMꢀCl(1)
a Estimated S.D. in parentheses.

118
J. Parr, A.M.Z. Slawin / Inorganica Chimica Acta 303 (2000) 116–120
for 30 min and then warmed to reflux for 5 min. The
deep-red solution was cooled to room temperature and
the solvent was removed under reduced pressure. The
red–brown residue was extracted into 2 ml of CHCl3
from which the product was obtained as red crystals
after addition of 10 ml of diethyl ether. The product 1
was collected by suction filtration and dried in vacuo.
Yield: 0.076 g of red–brown crystals, 72%. Complexes
2–5 were prepared by the same route and on the same
scale. Complex 2. Yield: 0.090 g of brown crystals,
68%. Complex 3. Yield: 0.082 g of deep-red crystals,
66%. Complex 4. Yield: 0.080 g of brown crystals, 72%.
Complex 5. Yield: 0.088 g of brown crystals, 78%.
plexes 7–10 were prepared by the same route and on
the same scale. Complex 7. Yield: 0.104 g of yellow–or-
ange crystals, 79%. Complex 8. Yield: 0.111 g of yel-
low–orange crystals, 81%. Complex 9. Yield: 0.089 g of
scarlet crystals, 71%. Complex 10. Yield: 0.111 g of
brick red crystals, 88%.
3. Results and discussion
The stoichiometric reaction of HL1–5 with either
NiCl2·6H2O in ethanol or [(cod)Pd(II)Cl2] in di-
chloromethane gives the complexes [h3(L1–5)M(II)Cl]
1–10 in moderate to high yields. This formulation is
supported by elemental analysis, spectroscopic data and
in two cases by crystallographic investigations.
2.3.2. [p3(L1)Pd(II)Cl] (6)
To a solution of [(cod)PdCl2] (0.068 g, 0.24 mmol) in
10 ml of CH2Cl2 was added solid [HL1] (0.10 g, 0.24
mmol). The solution was stirred at room temperature
for 30 min and then warmed to reflux for 5 min. The
orange solution was cooled to room temperature and
the solvent was removed under reduced pressure. After
addition of 10 ml of diethyl ether the orange residue
was extracted into 2 ml of CHCl3 from which the
product was obtained as yellow crystals. The product 6
was collected by suction filtration and dried in vacuo.
Yield: 0.104 g of yellow–orange crystals, 88%. Com-
3.1. IR spectroscopy
Selected IR data for the complexes 1–10 and the
ligands HL1–5 are presented in Table 3. The bands due
to w(CꢁN) are readily identified in both the complexes
and in the free ligands and serve as a useful indication
that complexation has occurred. There is a distinct
bathochromic shift on complexation typical for imines
on coordination to transition metal centres. In the
Table 3
Microanalytical and selected IR data for 1–10
Complex
Microanalysis (calc.) (%)
M.p. (°C)
IR (cm−1
)
C
H
N
w(CꢁN)
w(MꢀCl)
1
2
3
4
5
6
7
8
9
58.5 (59.0)
55.7 (55.9) a
52.9 (52.8)
62.0 (61.9)
61.5 (61.9)
53.7 (53.9)
52.7 (52.9)
49.7 (50.0)
58.2 (57.6)
58.2 (57.8)
3.4 (3.4)
3.5 (3.7) a
3.4 (3.2)
4.4 (4.2)
4.0 (4.2)
3.3 (3.3)
3.1 (3.2)
3.2 (3.0)
3.9 (3.9)
3.7 (4.0)
2.8 (2.5)
5.2 (5.2) a
2.6 (2.5)
2.8 (2.8)
2.5 (2.8)
2.3 (2.5)
4.6 (4.9)
2.2 (2.3)
2.5 (2.6)
2.9 (2.6)
\340
1608
1608
1601
1590
1588
1606
1606
1600
1591
1588
393
393
390
383
394
347
347
345
341
346
196 (d)
296–297
282–283
312–313
316–317
194–195
202 (d)
274–275
306–307
10
a As monohydrate.
Table 4
NMR data for 6–10 (free ligand values included for comparison)
Complex
31P{1H} (ligand) a
HꢀCꢁN (ligand) b
Aromatic (ligand) b
ꢀOCH3 (ligand) b
6
7
8
9
10
47.8 (−14.6)
46.9 (−14.6)
46.9 (−14.5)
49.1 (−14.9)
49.4 (−15.4)
8.95 (8.19)
8.59 (8.27)
8.78 (8.27)
8.56 (8.33)
8.70 (8.36)
8.22–6.89 (7.50–6.75)
8.01–6.82 (7.49–6.75)
7.82–6.47 (7.70–6.47)
8.00–6.45 (7.70–6.60)
8.10–6.73 (7.44–6.39)
3.75 (3.84)
3.77 (3.71)
a l in ppm relative to external 85% phosphoric acid.
b l in ppm relative to external TMS.

J. Parr, A.M.Z. Slawin / Inorganica Chimica Acta 303 (2000) 116–120
119
brought about by an increased donation of electron
density from the imine nitrogen to the nickel or palla-
dium centres.
3.2. NMR spectroscopy
1
Selected NMR data (31P{1H}, H) for 6–10 are col-
lected in Table 4. For the complexes of Ni(II) 1–5 there
were no NMR spectra observed, indicating that in
solution these samples are paramagnetic. Since com-
plexes of Ni(II), which have a square planar geometry
are expected to be diamagnetic, this observation implies
that these complexes are distorted from idealised geo-
metry in solution. Inspection of the complex 3 in the
solid state also indicates a somewhat distorted struc-
ture, which is in agreement with this observation.
The 31P{1H} NMR spectra show singlets for the
Pd(II) complexes with a downfield shift of between 61.4
and 64.8 ppm on coordination. The values of 31P
chemical shift, both in the free ligands and in their
complexes, are quite similar indicating that the substitu-
tion on the aldehyde fragment has little effect on the
Fig. 2. Crystal structure of [h3(L3)Ni(II)Cl] (3) (hydrogen atoms
omitted for clarity).
1
chemical shift. In the H NMR spectra of the Pd(II)
complexes, the azomethine proton is shifted downfield
by between 0.23 and 0.76 ppm with respect to the free
ligand value, and no intramolecular coupling of the
imine proton with the 31P nuclei was observed. The
aromatic protons also show a similar shift on complex-
ation, entirely consistent with expectations.
3.3. Single-crystal X-ray diffraction studies
The crystal structures of complexes 3 and 6 (Figs. 2
and 3; selected bond lengths and angles are presented in
Table 2) reveal in general a square planar geometry at
the metal atom with tridentate [P,N,O] coordination of
the ligand, where the remaining bound chloride ligand
is obligatorily disposed trans to N(1). The complexes
1–10 are neutral owing to the deprotonation of the
oxygen atom of the tridentate ligand upon com-
plexation.
Crystal structures 3 and 6 both exhibit distortions
from idealised square planar geometry at the metal,
probably due to the bulk of the phosphine group and to
the bite angle of the P,N chelate. The trans OꢀMꢀP
[179.11(7)–175.73(8)°] and trans NꢀMꢀCl [175.59(7)–
176.32(8)°] axes are less than 180° in both complexes,
and the cis PꢀMꢀN and cis NꢀMꢀO angles are also
principally dependent upon the sizes of the N,O and
P,N chelate rings, so that cis NꢀMꢀO for 3 and 6,
which both comprise a six-membered N,O ring, are
93.40(9) and 93.91(10)°, respectively, both greater than
90°. The five-membered P,N chelate rings have con-
comitantly smaller PꢀMꢀN angles of 86.35(7) and
85.88(8)° and are indicative of the reduced bite pre-
sented by this smaller ring size.
Fig. 3. Crystal structure of [h3(L2)Pd(II)Cl] (6) (hydrogen atoms
omitted for clarity).
protonated free ligand, there is a strong intramolecular
hydrogen-bonding interaction between the phenolic
proton and the basic imine nitrogen, forming a pseudo
six-membered ring. This can be observed in the solid
state structures of such ligands and in their IR spectra
[16]. When coordination to a metal centre displaces this
proton, there is a change in the (CꢁN) stretching fre-
quency, which depends upon the acidity of the proton
in the free ligand and the Lewis acidity of the coordi-
nated metal. In all the complexes 1–10 there is a shift
to lower wavenumber with respect to the free ligand,
suggesting an increase in the length of the (CꢁN) bond

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J. Parr, A.M.Z. Slawin / Inorganica Chimica Acta 303 (2000) 116–120
4. Conclusions
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Acknowledgements
We are grateful to Johnson–Matthey for the loan of
precious metals, and Dr Steve Aucott for the kind gift
of 2-(diphenylphosphino)aniline.
.