Synthesis and characterization of new cyclometallated Pd(II) complexes with bridging or terminal imidato ligands. Crystal structures of [{Pd(μ-succinimide)(phpy)}2] and [Pd(azb)(succinimide)(PPh3)] (phpy = 2-phenylpyridine; azb = azo

Article abstract of DOI:10.1016/S0277-5387(02)01041-0

Two series of new dinuclear cyclometallated palladium complexes [{Pd(μ-NCO)(C∧N)}₂] containing asymmetric imidato NCO- bridging units have been synthesized [C^N = azobenzene (azb); -NCO- = succinimide (1a), phthalimide (2a) or maleimide (3a); C

Full text of DOI:10.1016/S0277-5387(02)01041-0

Polyhedron 21 (2002) 1589ꢁ1596
/
www.elsevier.com/locate/poly
Synthesis and characterization of new cyclometallated Pd(II)
complexes with bridging or terminal imidato ligands.
Crystal structures of [{Pd(m-succinimide)(phpy)}2]
and [Pd(azb)(succinimide)(PPh3)]
(phpy ꢀ
/
2-phenylpyridine; azbꢀ
/
azobenzene)
Jose´ Luis Serrano a,*, Luis Garc´ıa a, Jose´ Pe´rez a,d, Eduardo Pe´rez a, Jorge Vives b,
Gregorio Sa´nchez b, Gregorio Lo´pez b, Elies Molins c, A. Guy Orpen d
a
´
Departamento de Ingenier´ıa Minera, Geolo´gica y Cartogra´fica, Area de Qu´ımica Inorga´nica, 30203 Cartagena, Spain
b Departamento de Qu´ımica Inorga´nica, Universidad de Murcia, 30071 Murcia, Spain
c Institut de Cie`ncia de Materials de Barcelona, CSIC, Campus Universitari de Bellaterra, E-08193 Bellaterra, Barcelona, Spain
d School of Chemistry, University of Bristol, Bristol, BS8 1 TS, UK
Received 12 November 2001; accepted 31 January 2002
Abstract
Two series of new dinuclear cyclometallated palladium complexes [{Pd(m-NCO)(CfflN)}2] containing asymmetric imidato ꢁ
NCOꢁ azobenzene (azb); ꢁNCOꢁ succinimide (1a), phthalimide (2a) or maleimide
bridging units have been synthesized [CfflNꢀ
(3a); CfflNꢀ
2-phenylpyridine (phpy); ꢁNCOꢁ succinimide (1b), phthalimide (2b) or maleimide (3b)]. The reaction of both
succinimidato precursors with tertiary phosphines to form the mononuclear N-bonded imidato derivatives of general formula
[Pd(CfflN)(suc)(L)] [CfflNꢀ C6H4)3 (8a); CfflNꢀ
azb; LꢀPPh3 (4a), PPh2Me (5a), PPhMe2 (6a), P(4-FꢁC6H4)3, (7a), P(4-MeOꢁ
C6H4)3 (8b)] has been investigated. The new
/
/
/
/
/
ꢀ
/
/
/
/
ꢀ
/
/
/
/
/
/
phpy; Lꢀ
/
PPh3 (4b), PPh2Me (5b), PPhMe2 (6b), P(4-Fꢁ
/
C6H4)3 (7b), P(4-MeOꢁ
/
complexes were characterized by partial elemental analyses and spectroscopic methods (IR, FAB, H, 13C and 31P). The single-
1
crystal structures of compounds 1b and 4a have been established. # 2002 Elsevier Science Ltd. All rights reserved.
Keywords: Imidato complexes; Cyclometallated paladium(II) complexes; Crystal structures
1. Introduction
there has been a growing interest in this kind of
compound.
Azobenzenes and heteroaromatic ligands such as 2-
phenylpyridine can easily be orthometallated by Pd(II)
On the other hand, investigation of various deriva-
tives of imidate-bridged compounds has received great
attention since it was noted that some Pt(II) derivatives
had higher activity against L1210 leukaemia in vivo than
the corresponding amidate-bridged compounds [20,21].
The synthesis of several maleimide compounds for the
preparation of chemoinmunoconjugates has also been
recently reported [22,23]. In this sense, the most
common routes to get imidato complexes of palladiu-
m(II) and platinum(II) are oxidative addition to low
salts via C(sp2)-H bond cleavage [1ꢁ
3] to usually give
/
the corresponding acetato or halide-bridged dimers.
These complexes have been thoroughly studied [4] and
employed as convenient precursors of mononuclear and
dinuclear cyclometalates [5ꢁ12]. Furthermore, since a
/
number of orthometallated complexes of the platinum
group elements were implicated as potential photosensi-
tizers [13ꢁ19], and mononuclear palladium derivatives
/
have been tested for nonlinear optical properties [12],
valent precursors [24ꢁ
by imide deprotonation [27ꢁ
/
26], the use of imide salt [10,27] or
32]. The replacement of the
/
bridging halide or acetate groups in classical binuclear
cyclometallated complexes by succinimidato was also
* Corresponding author
0277-5387/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S 0 2 7 7 - 5 3 8 7 ( 0 2 ) 0 1 0 4 1 - 0

1590
J.L. Serrano et al. / Polyhedron 21 (2002) 1589ꢁ1596
/
described [10] some years ago, showing a new mode of
bidentate coordination for this ligand, involving an Nꢁ
CꢁO bridging unit.
for 2 h and then concentrated to one-fifth of the initial
volume. Slow addition of diethyl ether caused the
precipitation of the title complexes, which were filtered
/
/
We report here the preparation of new dinuclear
orthometallated palladium(II) derivatives with bridging
succinimide, maleimide or phthalimide ligands acting in
the coordination mode mentioned above. We also
present a novel synthesis route of mononuclear N-
bonded succinimidato derivatives, by reaction of the
corresponding dinuclear precursor with neutral ligands.
Spectroscopic characterization of the new compounds
and the structure elucidation by X-ray diffraction
analyses of both mononuclear and binuclear derivatives
is also given.
off, air-dried and recrystallized from acetoneꢁ
/
ether.
2.2.1. [{Pd(m-suc)(azb)}2] (1a)
Yield: 57% (Anal. Calc. for C32H26N6O4Pd2: C, 49.8;
H, 3.4; N, 10.9. Found: C, 49.7; H, 3.5; N, 10.7%). IR
(cmꢂ1): 1722s, 1566s (CÄ
/
O str.). FAB MS (positive
[{Pd(m-suc)(azb)}2]ꢃ,
673
[{Pd2(suc)(azb)2}]ꢃ, 575 [{Pd(azb)}2]ꢃ, 287 [Pd(azb)]ꢃ.
13C{1H} NMR ((CD3)2CO, d ppm): 194.2 (coordi-
O, suc), 187.9 (non-coordinated CÄO, suc),
mode)
m/z:
772
.
nated CÄ
/
/
163.5 (azb), 152.6 (azb), 150.5 (azb), 134.5 (azb), 132.0
(azb), 130.7 (azb), 130.0 (azb), 127.8 (azb), 125.4 (azb),
123.6 (azb), 32.0 (ꢁ
ppm, J Hz): 7.31 (m, 10H, H2,3,4,5,6), 7.15 (m, 2H, H5?),
7.12 (d, 2H, H6?, JHH 7.5), 6.74 (m, 2H, H4?), 6.19 (d,
2H, H3?, JHH
7.8), 2.69 (m, 8H, ꢁCH2ꢁ suc).
/
CH2ꢁ
/
, suc). 1H NMR ((CD3)2CO, d
2. Experimental
ꢀ
/
2.1. Materials and physical measurements
ꢀ
/
/
/
C, H and N analysis were carried out with a Perkinꢁ
Elmer 240C microanalyser. IR spectra were recorded on
a PerkinꢁElmer spectrophotometer 16F PC FT-IR,
/
2.2.2. [{Pd(m-phtal)(azb)}2] (2a)
Yield: 65% (Anal. Calc. for C40H26N6O4Pd2: C, 55.4;
H, 3.0; N, 9.7. Found: C, 55.6; H, 3.0; N, 9.7%). IR
/
using nujol mulls between polyethylene sheets. NMR
data (1H, 13C, 31P) were recorded on a Bruker AC 200E
or a Varian Unity 300 spectrometer. Mass spectrometric
analyses were performed on a Fisons VG Autospec
double-focusing spectrometer, operated in the positive
mode. Ions were produced by fast atom bombardment
(FAB) with a beam of 25-KeV Cs atoms. The mass
spectrometer was operated with an accelerating voltage
of 8 kV and a resolution of at least 1000.
(cmꢂ1): 1731s, 1569s (CÄ
/
O str.). FAB MS (positive
[{Pd(m-phtal)(azb)}2]ꢃ,
722
[{Pd2(phtal)(azb)2}]ꢃ, 287 [Pd(azb)]ꢃ, 13C{1H} NMR
((CD3)2CO, d ppm): 183.6 (coordinated CÄO, phtal),
178.0 (non-coordinated CÄO, phtal), 163.2 (azb), 152.6
mode)
m/z:
868
/
/
(azb), 150.6 (azb), 136.8 (phtal), 135.5 (phtal), 134.5
(azb), 132.4 (phtal), 132.3 (phtal), 132.0 (azb), 130.6
(azb), 129.8 (azb), 127.7 (azb), 125.3 (azb), 123.5 (azb),
123.2 (phtal), 122.1 (phtal). 1H NMR ((CD3)2CO, d
ppm, J Hz): 7.69 (m, 6H, H6?, 4H phtal), 7.56 (m, 4H,
phtal), 7.40 (m, 4H, H2,6), 7.12 (m, 8H, H3,4,5, H5?), 6.59
The cyclometallated precursors [{Pd(m-OOCMe)-
(CfflN)}2] [CfflNꢀ
azobenzene or 2-phenylpyridine]
/
were prepared as described in the literature [12]. The
commercially available chemicals were purchased from
Aldrich Chemical Co. and were used without further
purification, and all the solvents were dried by standard
methods before use.
(m, 2H, H4?), 6.22 (d, 2H, H3?, JHH
ꢀ7.4).
/
2.2.3. [{Pd(m-mal)(azb)}2] (3a)
Yield: 69% (Anal. Calc. for C32H22N6O4Pd2: C, 50.1;
H, 2.9; N, 10.9. Found: C, 50.3; H, 3.1; N, 10.9%). IR
(cmꢂ1): 1727s, 1571s (CÄ
/
O str.). FAB MS (positive
mode) m/z: 768 [{(Pd(m-mal)2(azb)}]ꢃ, 672 [{Pd2(mal)-
2.2. Preparation of the complexes [{Pd(m-NCO)-
(CfflN)}2] [CfflNꢀ
/
azobenzene (azb); ꢁ
succinimide (suc) (1a), phthalimide (2a) (phtal) or
maleimide (mal) (3a); CfflNꢀ
2-phenylpyridine (phpy);
NCOꢁ succinimide (1b), phthalimide (2b) or
/
NCOꢁ
/
ꢀ
/
(azb)2}]ꢃ, 575 [{Pd(azb)}2]ꢃ, 287 [Pd(azb)]ꢃ, 13C{1H}
NMR ((CD3)2CO, d ppm): 186.9 (coordinated CÄ
/
O,
/
mal), 180.9 (non-coordinated CÄO, mal), 163.2 (azb),
/
ꢁ
/
/
ꢀ
/
152.5 (azb), 150.6 (azb), 136.1 (mal), 134.7 (mal), 132.4
(azb), 132.0 (azb), 131.8 (azb), 131.4 (azb), 127.8 (azb),
125.1 (azb), 123.1 (azb). 1H NMR ((CD3)2CO, d ppm, J
Hz): 7.72 (m, 2H, H6?), 7.26 (m, 12H, H2,3,4,5,6, H5?), 6.46
(m, 6H, H4?, 4H mal), 6.19 (m, 2H, H3?).
maleimide (3b)]
The azobenzene or 2-phenylpyridine complexes were
obtained by treating the appropriated precursor ([{Pd(m-
OOCMe)(azb)}2] or [{Pd(m-OOCMe)(phpy)}2], respec-
tively) with the corresponding imide (molar ratio 1:2) in
acetone, according to the following general method. To
2.2.4. [{Pd(m-suc)(phpy)}2] (1b)
Yield: 63% (Anal. Calc. for C30H24N4O4Pd2: C, 50.2;
H, 3.4; N, 7.8. Found: C, 50.5; H, 3.4; N, 7.8%). IR
an
OOCMe)(CfflN)}2] (0.07 g, 0.101 mmol if CfflNꢀ
0.07 g, 0.109 mmol if CfflNꢀ
phpy) the stoichiometric
amount of ligand was added. The solution was refluxed
acetone
(20
ml)
solution
of
[{Pd(m-
/
azb;
(cmꢂ1): 1720s, 1587s (CÄ
/
O str.). FAB MS (positive
mode) m/z: 718 [{Pd(m-suc)(phpy)}2]ꢃ, 620 [{Pd2(suc)-
/
(phpy)2}]ꢃ, 415 [{Pd(phpy)}2]ꢃ, 260 [Pd(phpy)]ꢃ.

J.L. Serrano et al. / Polyhedron 21 (2002) 1589ꢁ
/
1596
1591
13C{1H} NMR ((CD3)2CO, d ppm): 195.1 (coordinated
O, suc), 163.7
(phpy), 150.8 (phpy), 148.8 (phpy), 144.9 (phpy), 137.8
(phpy), 133.7 (phpy), 128.8 (phpy), 123.8 (phpy), 122.7
solution was refluxed for 2 h, then concentrated until
approximately one-fifth of the initial volume. Slow
addition of hexane caused the precipitation of the title
complexes, which were filtered off, washed with hexane,
CÄ
/
O, suc), 187.9 (non-coordinated CÄ
/
(phpy), 121.2 (phpy), 117.2 (phpy), 32.2 (ꢁ
/
CH2ꢁ
/
, suc),
CH2ꢁ
, suc). 1H NMR ((CD3)2CO, d ppm, J Hz):
air-dried and recrystallized from acetoneꢁ
/
hexane.
32.0 (ꢁ
/
/
7.63 (m, 2H, H6), 7.28 (m, 2H, H3), 7.01 (m, 2H, H4),
6.72 (m, 6H, H5, H5?,6?), 6.51 (m, 4H, H3?,4?), 2.76 (m,
2.3.1. [Pd(azb)(suc)(PPh3)] (4a)
Yield: 62% (Anal. Calc. for C34H28N3O2PPd: C, 63.0;
H, 4.4; N, 6.5. Found: C, 63.0; H, 4.4; N, 6.5%). IR
8H, ꢁ
/
CH2ꢁ
/
suc).
(cmꢂ1): 1580s (CÄ
/
O str.); 534m, 514m, 493m (PPh3). 1H
2.2.5. [{Pd(m-phtal)(phpy)}2] (2b)
Yield: 76% (Anal. Calc. for C38H24N4O4Pd2: C, 56.1;
H, 3.0; N, 6.9. Found: C, 56.4; H, 2.7; N, 6.9%). IR
NMR ((CD3)2CO, d ppm, J Hz): 7.81 (d, 1H, H6?,
JHH 6.2), 7.72, (m, 6H, Ph), 7.52 (m, 3H, Ph), 7.38 (m,
11H, H2,3,4,5,6, 6H Ph), 7.09 (m, 2H, H5?), 6.69 (m, 2H,
ꢀ
/
(cmꢂ1): 1728s, 1597s (CÄ
/
O str.). FAB MS (positive
H4?), 6.50 (m, 2H, H3?), 1.80 (dd, 2H, ꢁ
/
CH2ꢁ
/
suc,
suc,
mode) m/z: 812 [{Pd(m-phtal)(phpy)}2]ꢃ, 668
[{Pd2(phtal)(phpy)2}]ꢃ, 415 [{Pd(phpy)}2]ꢃ, 260
[Pd(phpy)]ꢃ. 13C{1H} NMR ((CD3)2CO, d ppm):
JHH syn
JHH syn
d ppm): 42.3 (s, PPh3).
ꢀ
/
5, JHH anti
5, JHH anti
ꢀ
/
16), 1.55 (dd, 2H, ꢁCH2ꢁ
/
/
ꢀ
/
ꢀ
/
16). 31P{1H} NMR ((CD3)2CO,
184.6 (coordinated CÄ
/
O, phtal), 178.6 (non-coordinated
CÄO, phtal), 163.7 (phpy), 151.0 (phpy), 148.9 (phpy),
/
2.3.2. [Pd(azb)(suc)(PPh2Me)] (5a)
Yield: 68% (Anal. Calc. for C29H26N3O2PPd: C, 59.5;
H, 4.5; N, 7.2. Found: C, 59.4; H, 4.7; N, 7.5%). IR
144.7 (phpy), 137.3 (phpy), 137.0 (phtal), 135.9 (phtal),
134.1 (phpy), 132.2 (phtal), 132.0 (phtal), 128.7 (phpy),
123.7 (phpy), 122.6 (phpy), 122.0 (phpy), 121.7 (phpy),
121.2 (phpy), 117.1 (phpy). 1H NMR ((CD3)2CO, d
ppm, J Hz): 7.70 (m, 2H, H6), 7.50 (m, 8H, phtal), 7.33
(m, 2H, H3), 7.05 (m, 2H, H4), 6.68 (m, 2H, H6?), 6.62
(m, 8H, H5, H3?,4?,5?).
(cmꢂ1): 1572s (CÄ
/
O str.); 512m, 482m, 446m (PPh2Me).
1H NMR ((CD3)2CO, d ppm, J Hz): 7.76 (d, 1H, H6?,
JHH
7.4), 7.28, (m, 15H, H2,3,4,5,6, 10H Ph), 7.19 (m,
1H, H5?), 7.12 (m, 1H, H4?), 6.68 (m, 1H, H3?), 2.19 (m,
3H, Meꢁ
), 1.88 (m, 2H, suc), 1.57 (m, 2H, suc). 31P{1H}
ꢀ
/
/
NMR ((CD3)2CO, d ppm): 23.4 (s, PPh2Me).
2.2.6. [{Pd(m-mal)(phpy)}2] (3b)
Yield: 71% (Anal. Calc. for C30H20N4O4Pd2: C, 50.5;
H, 2.8; N, 7.8. Found: C, 50.8; H, 3.0; N, 7.9%). IR
2.3.3. [Pd(azb)(suc)(PPhMe2)] (6a)
Yield: 72% (Anal. Calc. for C24H24N3O2PPd: C, 55.0;
H, 4.6; N, 8.0. Found: C, 55.2; H, 4.8; N, 7.9%). IR
(cmꢂ1): 1724s, 1620s (CÄ
/
O str.). FAB MS (positive
mode) m/z: 714 [{Pd(m-mal)(phpy)}2]ꢃ, 618 [{Pd2(mal)-
(phpy)2}]ꢃ, 415 [{Pd(phpy)}2]ꢃ, 260 [Pd(phpy)]ꢃ.
13C{1H} NMR ((CD3)2CO, d ppm): 195.0 (coordinated
(cmꢂ1): 1580s (CÄ
/O str.); 540m, 510m, 488m (PPhMe2).
1H NMR ((CD3)2CO, d ppm, J Hz): 7.91 (m, 3H, H6?,
2H Ph), 7.41, (m, 8H, H2,3,4,5,6, 3H Ph), 7.19 (m, 1H,
H5?), 6.96 (m, 1H, H4?), 6.66 (m, 1H, H3?), 2.24 (m, 4H,
suc), 1.71 (m, 6H, Me). 31P{1H} NMR ((CD3)2CO, d
ppm): 11.2 (s, PPhMe2).
CÄ
/
O, mal), 188.5 (non-coordinated CÄ/O, mal), 163.7
(phpy), 148.9 (phpy), 144.9 (phpy), 137.9 (mal), 137.6
(mal), 134.1 (phpy), 131.8 (phpy), 129.6 (phpy), 128.9
(phpy), 123.9 (phpy), 122.7 (phpy), 121.0 (phpy), 117.4
1
(phpy). H NMR ((CD3)2CO, d ppm, J Hz): 7.78 (m,
2H, H6), 7.26 (m, 2H, H3), 7.06 (m, 2H, H4), 6.65 (m,
10H, H5, H5?,6?, 4H mal), 6.45 (m, 4H, H3?,4?).
2.3.4. [Pd(azb)(suc)(P(4-FꢁC6H4)3)] (7a)
/
Yield: 63% (Anal. Calc. for C34H25F3N3O2PPd: C,
58.2; H, 3.6; N, 6.0. Found: C, 58.3; H, 3.7; N, 6.2%). IR
(cmꢂ1): 1586s (CÄ
C6H4)3). H NMR ((CD3)2CO, d ppm, J Hz): 8.02 (d,
/
O str.); 536m, 518m, 452m (P(4ꢁ
/
Fꢁ
/
2.3. Preparation of complexes [Pd(CfflN)(suc)(L)]
1
[CfflNꢀ
(6a), P(4-Fꢁ
CfflNꢀ
phpy; Lꢀ
(6b), P(4-FꢁC6H4)3 (7b), P(4-MeOꢁ
/
azb; Lꢀ
/
PPh3 (4a), PPh2Me (5a), PPhMe2
1H, H6?, JHH
ꢀ7.0), 7.75, (m, 6H, Ph ortho), 7.53 (m,
/
/
C6H4)3 (7a), P(4-MeOꢁ
/
C6H4)3 (8a);
6H, Ph meta), 7.38 (m, 6H, H2,3,4,5,6, H5?), 6.72 (m, 1H,
H4?), 6.40 (m, 1H, H3?), 1.91 (m, 2H, suc), 1.62 (m, 2H,
suc). 31P{1H} NMR ((CD3)2CO, d ppm): 40.0 (s, P(4-
/
/
PPh3 (4b), PPh2Me (5b), PPhMe2
/
/
C6H4)3 (8b)]
Fꢁ
/
C6H4)3).
The complexes were obtained by treating the pre-
cursors [{Pd(m-suc)(azb)}2] (1a) or [{Pd(m-suc)(phpy)}2]
(1b) with the corresponding neutral ligand (molar ratio
1:2) in dichloromethane, according to the following
general method. To a dichloromethane (20 ml) solution
of 1a (0.07 g, 0.091 mmol) or 1b (0.07 g, 0.112 mmol) the
stoichiometric amount of ligand (a compounds: 0.183
mmol; b compounds: 0.225 mmol) was added. The
2.3.5. [Pd(azb)(suc)(P(4-MeOꢁ
/
C6H4)3)] (8a)
Yield: 70% (Anal. Calc. for C37H34N3O5PPd: C, 60.2;
H, 4.6; N, 5.7. Found: C, 60.2; H, 4.7; N, 5.7%). IR
(cmꢂ1): 1566s (CÄ
/
O str.); 538m, 518m, 498m (P(4-Meꢁ
C6H4)3). H NMR ((CD3)2CO, d ppm, J Hz): 7.99 (d,
1H, H6?, JHH 6.2), 7.58, (m, 8H, H2,6, 6H Ph ortho),
7.33 (m, 3H, H3,4,5), 7.10 (m, 1H, H5?), 6.85 (m, 6H Ph
/
1
ꢀ
/

1592
J.L. Serrano et al. / Polyhedron 21 (2002) 1589ꢁ1596
/
meta), 6.73 (m, 1H, H4?), 6.54 (m, 1H, H3?), 3.79 (s, 9H,
MeOꢁ), 1.86 (dd, 2H, CH2ꢁ suc, JHH syn 5.2,
JHH anti 16.4), 1.58 (dd, 2H, ꢁCH2ꢁ suc, JHH syn
5.2, JHH anti
16.4). 31P{1H} NMR ((CD3)2CO, d
ppm): 38.9 (s, P(4-MeOꢁC6H4)3).
2H, suc), 1.71 (m, 2H, suc). 31P{1H} NMR ((CD3)2CO,
d ppm): 39.4 (s, P(4-MeOꢁC6H4)3).
/
ꢁ
/
/
ꢀ
/
/
ꢀ
/
/
/
ꢀ
/
ꢀ
/
/
2.4. Crystal structure determination of [{Pd(phpy)(m-
suc)}2] (1b) and [Pd(azb)(suc)(PPh3)] (4a)
2.3.6. [Pd(phpy)(suc)(PPh3)] (4b)
Yield: 71% (Anal. Calc. for C33H27N2O2PPd: C, 63.8;
H, 4.4; N, 4.5. Found: C, 63.9; H, 4.2; N, 4.7%). IR
Data for 1b were collected using a single crystal of
approximate dimensions 0.5ꢄ
/
0.5ꢄ0.3 mm. Accurate
/
(cmꢂ1): 1614s (CÄ
/
O str.); 534m, 514m, 492m (PPh3). 1H
NMR ((CD3)2CO, d ppm, J Hz): 8.19 (m, 1H, H6), 7.82,
(m, 7H, H3,4, 5H Ph), 7.46 (d, 1H, H6?, JHH
7.8), 7.40
(m, 10H, Ph), 7.11 (m, 1H, H5), 6.91 (m, 1H, H5?), 6.52
(m, 2H, H3?,4?), 2.22 (dd, 2H, ꢁ
CH2ꢁ suc, JHH syn 3,
JHH anti 11.6), 1.25 (m, 2H, ꢁCH2ꢁ
suc). 31P{1H}
cell parameters were determined by least-squares fitting
of 25 high-angle reflections. The scan method was v
ꢀ
/
with the range of hkl (ꢂ
/
225
/
h 5
/
22, ꢂ
/
145
/
k 5
/
0, 05
/
l 523) corresponding to 2Umax
/
ꢀ
/
60.848. The structure
/
/
ꢀ
/
was solved by direct methods and refined anisotropically
on F2 [33]. Hydrogen atoms were introduced in calcu-
ꢀ
/
/
/
NMR ((CD3)2CO, d ppm): 42.1 (s, PPh3).
lated positions. The final R factor was 0.0481 [Rwꢀ
/
2
0.1139, where wꢀ
/
1/s2(Fo )ꢃ
2Fc )/3] over 5115 observed reflections [I ꢀ
Data for 4a were collected using a single crystal of
approximate dimensions 0.2ꢄ0.4ꢄ0.3 mm on a Sie-
/
(0.0678P)2 and Pꢀ
/
2.3.7. [Pd(phpy)(suc)(PPh2Me)] (5b)
Yield: 66% (Anal. Calc. for C28H25N2O2PPd: C, 60.2;
2
2
(Fo ꢃ
/
/2s(I)].
H, 4.5; N, 5.0. Found: C, 60.2; H, 4.6; N, 5.1%). IR
(cmꢂ1): 1634s (CÄ
/
O str.); 516m, 488m, 448m (PPh2Me).
1H NMR ((CD3)2CO, d ppm, J Hz): 8.10 (m, 1H, H6),
/
/
mens SMART diffractometer under a stream of N2 at
173 K. Crystallographic data are summarized in Table
1. An empirical absorption (SADABS) was applied [34].
The structure was solved by direct methods and refined
on all F2 data using the SHELX suite of programs on a
Silicon Graphics computer [35]. All non-hydrogen
atoms were anisotropic refined, hydrogen atoms were
7.68, (m, 5H, H3,4, 3H Ph), 7.45 (d, 1H, H6?, JHH
ꢀ7.8),
/
7.31 (m, 7H Ph), 6.89 (m, 2H, H3?,4?), 2.18 (m, 5H, ME,
2H suc), 1.63 (m, 2H, suc). 31P{1H} NMR ((CD3)2CO,
d ppm): 23.5 (s, PPh2Me).
2.3.8. [Pd(phpy)(suc)(PPhMe2)] (6b)
Yield: 76% (Anal. Calc. for C23H23N2O2PPd: C, 55.6;
H, 4.7; N, 5.6. Found: C, 55.5; H, 4.6; N, 5.5%). IR
introduced in calculated positions. The final R factor
1/[s2(Fo )ꢃ
/
2
was 0.0264 [Rwꢀ
(0.0652P)2ꢃ
6.4628P] and Pꢀ
observed reflections [I ꢀ2s(I)].
/
0.0712, where wꢀ
/
(cmꢂ1): 1622s (CÄ
/
O str.); 488m, 470m, 442m (PPhMe2).
2
2
/
/
(Fo ꢃ2Fc )/3] over 5439
/
1H NMR ((CD3)2CO, d ppm, J Hz): 8.10 (s, 1H, H6),
7.71, (m, 2H, Ph), 7.66 (m, 2H, H3,4), 7.36 (m, 5H, H6?, 4
Ph), 7.06 (m, 1H, H5), 6.90 (m, 1H, H5?), 6.57 (m, 2H,
H3?,4?), 2.60 (m, 4H, suc), 1.69 (m, 6H, Me). 31P{1H}
NMR ((CD3)2CO, d ppm): 10.8 (s, PPhMe2).
/
Table 1
Crystal data and summary of data collection and refinement for
2.3.9. [Pd(phpy)(suc)(P(4-FꢁC6H4)3)] (7b)
/
[{Pd(phpy)(m-suc)}2] (1b) and [Pd(azb)(suc)(PPh3)] (4a)
Yield: 81% (Anal. Calc. for C33H24F3N2O2PPd: C,
58.7; H, 3.6; N, 4.1. Found: C, 58.8; H, 3.8; N, 4.3%). IR
1b
4a
(cmꢂ1): 1622s (CÄ
C6H4)3). H NMR ((CD3)2CO, d ppm, J Hz): 8.16 (m,
/
O str.); 540m, 454m, 441m (P(4-Fꢁ
/
1
Empirical formula
Formula weight
Crystal system
C30H24N4O4Pd2
717.33
C34H28N3O2PPd
647.96
1H, H6), 7.49, (m, 8H, H3,4, 6H Ph ortho), 7.10 (d, 1H,
monoclinic
P21/n
monoclinic
P21/n
H6?, JHH
ꢀ
7.2), 6.92 (m, 8H, H5, H5?, 6H Ph), 6.47 (m,
/
Space group
Unit cell dimensions
2H, H3?, H4?), 2.33 (m, 2H, suc), 0.86 (m, 2H, suc).
31P{1H} NMR ((CD3)2CO, d ppm): 40.8 (s, P(4-Fꢁ
C6H4)3).
˚
a (A)
16.090(4)
10.323(3)
16.571(2)
105.97(2)
2646.0(11)
4
10.8781(19)
16.079(3)
16.014(3)
91.560(3)
2799.9(9)
4
/
˚
b (A)
˚
c (A)
b (8)
V (A )
3
2.3.10. [Pd(phpy)(suc)(P(4-MeOꢁC6H4)3)] (8b)
/
˚
Yield: 67% (Anal. Calc. for C36H33N2O5PPd: C, 60.8;
H, 4.7; N, 3.9. Found: C, 60.9; H, 4.7; N, 3.9%). IR
Z
Dcalc (Mg mꢂ3
F (mmꢂ1
)
1.801
1.404
1.537
0.758
(cmꢂ1): 1624s (CÄ
/
O str.); 544m, 506m, 494m (P(4-
C6H4)3). H NMR ((CD3)2CO, d ppm, J Hz):
8.18 (m, 1H, H6), 7.74 (m, 1H, H6?), 7.72, (m, 8H, H3,4
6H Ph ortho), 6.94 (m, 1H, H5), 6.92 (m, 7H, H5?, 6H Ph
meta), 6.56 (m, 2H, H3?,4?), 3.78 (s, 9H, MeOꢁ
), 2.25 (m,
)
˚
l (A)
0.71073
5115
0.71073
5439
1
MeOꢁ
/
Observed reflections
R1, wR2
Goodness-of-fit
,
0.0481, 0.1139
1.043
0.0264, 0.0712
0.663
/

J.L. Serrano et al. / Polyhedron 21 (2002) 1589ꢁ
/
1596
1593
3. Results and discussion
cyclometallated ligands. The 1H spectra exhibit the
expected resonances for these ligands, together with
the corresponding signals of the bridging imidato units
that are partly overlapped with the former in the case of
phthalimide and maleimide derivatives. Moreover, the
succinimidato protons in the 2-phenylpyridine derivative
(1b) appear as a broad singlet at 2.76 ppm, whereas the
spectrum of the azobenzene analogue (1a) shows a
complex multiplet centered at 2.69 ppm. By analogy
with previously reported results in related systems [10],
this behaviour may be explained in view of the fact that
the azophenyl and methylene groups were close in
complex 1a. On the other hand, the distinction of two
different carbonyl signals, shifted downfield from the
one observed for the corresponding free ligand, is the
only remarkable feature in the 13C NMR spectra of the
new compounds. On the basis of previously reported
data [27,28], the singlet that appears at lowest field has
been assigned to the carbonyl atom coordinated to
palladium.
We have also investigated the reaction of the succini-
midato-bridged compounds (1a,1b) with tertiary phos-
phines, in an attempt to obtain a parallel behaviour to
that shown by the well known halide-bridged dimers:
bridge splitting to yield the mononuclear derivatives
[Pd(CfflN)(X)(L)]. The halogen-like character of the
succinimido ligand suggested by McCleverty and co-
workers [10] should play an important role in the
formation of the mononuclear N-bonded imidato deri-
vatives presented in Scheme 2.
In acetone, the acetato-bridged cyclometallated di-
mers [{Pd(m-OOCMe)(CfflN)}2] (CfflNꢀ
react under the conditions described in the experimental
/
azb or phpy)
section with succinimide, phthalimide or maleimide to
give dinuclear complexes (1aꢁ
imidato ligands replace the bridging acetate group as
presented in Scheme 1.
The new azobenzene derivatives are air-stable brown
solids, while the 2-phenylpyridine complexes present a
yellow colour. Infrared spectra of all compounds show
the characteristic absorptions of the corresponding
cyclometallated ligand, partially overlapped with those
/
3a, 1bꢁ3b) in which the
/
attributed to imidatoꢁcarbonyl stretching. Thus, two
/
medium intensity bands at 1595 and 1552 cmꢂ1 were
occasionally observed in the IR spectra of the azoben-
zene compounds, whilst relevant bands for 2-phenylpyr-
idine derivatives appeared at 1604 and 1576 cmꢂ1. Two
strong bands in the range 1731ꢁ
cmꢂ1 suggested coordination of one carbonyl group to
the metal as a part of an ꢁNCOꢁ bridging unit,
according to previously reported data [10]. It has been
claimed that this bridging structure would remove the
twofold symmetry of the free or N-bonded imidato
ligand increasing the intensity of the symmetric absorp-
tion. This higher frequency mode nsym(CO) is normally
weak in cyclic imides, as shown later for compounds
/
1720 and 1600ꢁ1566
/
/
/
(4aꢁ
/
8a, 4bꢁ8b) in whose spectra the band has negligible
/
intensity compared with the antisymmetric n(CO) ab-
sorption.
Further evidence for the dinuclearity of complexes
(1aꢁ
/
3a, 1bꢁ3b) comes from the FAB mass spectro-
/
metry, as can be implied by the m/z values for the
observed fragments (see Section 2). Spectra of the new
bridged compounds show a similar fragmentation
pattern which includes the peaks corresponding to
[{Pd(NCO)(CfflN)}2]ꢃ and [{Pd2(NCO)(CfflN)2}]ꢃ.
The abundances of the signals around the pattern ion
are consistent with the natural isotopic abundances.
The 1H and 13C NMR data are collected in the
experimental section and Scheme 1 shows the labelled
Scheme 2.
Scheme 1.

1594
J.L. Serrano et al. / Polyhedron 21 (2002) 1589ꢁ1596
/
Table 2
lated and succinimidato ligands, together with those
attributed to the corresponding coordinated phosphine.
The assignment of the cyclometallated protons was
made by comparison with our previously published
data [11]. An interesting aspect, also found before in
cyclometallated complexes with iminophosphines [11], is
the appreciable coupling to the phosphorus atom
exhibited by the H3? in azobenzene derivatives, and
H3?, H6 in compounds with 2-phenylpyridine. On the
other hand, basically two different behaviours were
observed for aliphatic protons of succinimidato, de-
pending on the steric hindrance introduced by the
phosphine ligand in the cis-position. Thus, rotation
˚
Selected bond lengths (A) and bond angles (8) for 1b and 4a
1b
4a
Bond lengths
Pd(1)ꢁ
Pd(1)ꢁ
Pd(1)ꢁ
Pd(1)ꢁ
Pd(1)ꢁ
Pd(2)ꢁ
Pd(2)ꢁ
Pd(2)ꢁ
Pd(2)ꢁ
C(12)ꢁ
C(19)ꢁ
C(15)ꢁ
C(16)ꢁ
C(12)ꢁ
C(15)ꢁ
C(16)ꢁ
C(19)ꢁ
/
C(1)
N(1)
N(2)
O(3)
Pd(2)
C(26)
N(4)
N(3)
O(2)
1.970(4)
2.028(3)
2.048(3)
2.162(3)
2.9544(7)
1.963(4)
2.023(3)
2.046(3)
2.179(3)
1.219(5)
1.202(5)
1.238(5)
1.239(5)
1.371(5)
1.328(5)
1.339(5)
1.403(5)
Pd(1)ꢁ
Pd(1)ꢁ
Pd(1)ꢁ
Pd(1)ꢁ
C(13)ꢁ
C(16)ꢁ
C(13)ꢁ
C(16)ꢁ
/
C(1)
N(3)
N(1)
P(1)
2.008(2)
2.0970(18)
2.0998(18)
2.2580(6)
1.222(3)
1.220(3)
1.361(3)
1.362(3)
/
/
/
/
/
/
/
/
O(1)
O(2)
N(3)
N(3)
/
/
/
/
/
/
/
/
O(1)
O(4)
O(2)
O(3)
N(2)
N(2)
N(3)
N(3)
about the PdꢁN axis might be hindered when bulky
/
/
/
phosphines (4, 5, 7, 8a,b) coordinate the metal, and two
resonances that integrate two protons each (syn-/anti-,
see Scheme 2) are observed, while just one multiplet
signal appears in the spectra of compounds 6a and 6b
/
/
/
/
1
with less voluminous substituents. VT H NMR experi-
ments were carried out in an attempt to get coalescence
of signals and to calculate the energy barrier associated
/
Bond angles
C(1)ꢁPd(1)ꢁ
C(1)ꢁPd(1)ꢁ
N(1)ꢁPd(1)ꢁ
C(1)ꢁPd(1)ꢁ
N(1)ꢁPd(1)ꢁ
N(2)ꢁPd(1)ꢁ
C(26)ꢁ
C(26)ꢁ
N(4)ꢁPd(2)ꢁ
C(26)ꢁPd(2)ꢁ
N(4)ꢁPd(2)ꢁ
N(3)ꢁPd(2)ꢁ
N(2)ꢁC(12)ꢁ
N(3)ꢁC(19)ꢁ
N(2)ꢁC(15)ꢁ
N(3)ꢁC(16)ꢁ
/
/
N(1)
81.47(15) C(1)ꢁ
95.96(15) C(1)ꢁ
173.60(13) N(3)ꢁ
172.76(14) C(1)ꢁPd(1)ꢁ
93.57(13) N(3)ꢁPd(1)ꢁ
89.51(12) N(1)ꢁPd(1)ꢁ
81.55(16) O(1)ꢁC(13)ꢁ
95.32(15) O(2)ꢁC(16)ꢁ
173.51(14)
173.88(14)
94.03(13)
89.49(12)
123.4(4)
/
Pd(1)ꢁ
Pd(1)ꢁ
Pd(1)ꢁ
/
N(3)
174.71(8)
78.45(8)
97.10(7)
93.28(6)
91.15(5)
171.74(5)
124.9(2)
125.1(2)
/
/N(2)
/
/N(1)
with the PdꢁN rotation, but it could not be achieved in
/
/
/
N(2)
/
/
N(1)
the range of temperatures allowed by usual deuterated
solvents. Nevertheless, similarly hindered rotations
/
/O(3)
/
/P(1)
/
/
O(3)
O(3)
/
/
P(1)
P(1)
about MꢁN bonds have been attributed previously to
/
/
/
/
/
steric factors [27,36,37].
/
Pd(2)ꢁ
/N(4)
/
/
N(3)
/
Pd(2)ꢁ
/N(3)
/
/
N(3)
/
/
N(3)
O(2)
3.1. X-ray structures of [{Pd(m-suc)(phpy)}2] (1b) and
[Pd(azb)(suc)(PPh3)] (4a)
/
/
/
/
O(2)
O(2)
/
/
/
/
O(1)
O(4)
O(2)
O(3)
Selected bond distances and angles are presented in
Table 2. The coordination around the Pd atoms is
/
/
124.4(4)
/
/
126.2(4)
/
/
126.2(4)
Reactions take place in dichloromethane under con-
tinued reflux, yielding brown (a compounds) or yellow
(b compounds) air stable solids with negligible molar
conductivity values. Acetone was avoided as a solvent
since we found that it tends to stay occluded (lost at
118 8C) in the new complexes. The subsequent strong
IR band around 1720 cmꢂ1 interfered the monitoring of
the reactions by this technique, as it appears in the
typical range of absorption for imidato bridging units
discussed before. Thus, the spectra show the expected
bands for the corresponding cyclometallated backbone,
together with those attributed to the incoming neutral
ligand and one strong carbonyl band in the range 1566ꢁ
1586 or 1600ꢁ
1634 cmꢂ1 for azobenzene and 2-phe-
nylpyridine derivatives, respectively.
/
/
The 1H and 31P NMR data of the mononuclear
complexes are collected in Section 2, the latter consisting
of singlets with chemical shifts in the usual range for
1
Pd(II) complexes. With regard to the H NMR spectra,
they show the expected resonances of the cyclometal-
Fig. 1. Molecular structure of complex 1b.

J.L. Serrano et al. / Polyhedron 21 (2002) 1589ꢁ
/
1596
1595
CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK
(fax: ꢃ44-1223-336033; e-mail: deposit@ccdc.cam.ac.uk
or www: http://www.ccdc.cam.ac.uk).
/
Acknowledgements
Financial support of this work by the Direccio´n
General de Investigacio´n (project BQU2001-0979) Spain
is acknowledged. Jose´ Pe´rez thanks the PFMP-UPCT-
2001 program for a grant to visit the University of
Bristol.
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