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)]

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; azb�/azobenzene)

Jose Luis Serrano a,*, Luis Garcıa a, Jose Perez a,d, Eduardo Perez a, Jorge Vives b,Gregorio Sanchez b, Gregorio Lopez b, Elies Molins c, A. Guy Orpen d

a Departamento de Ingenierıa Minera, Geologica y Cartografica, Area de Quımica Inorganica, 30203 Cartagena, Spainb Departamento de Quımica Inorganica, Universidad de Murcia, 30071 Murcia, Spain

c Institut de Ciencia de Materials de Barcelona, CSIC, Campus Universitari de Bellaterra, E-08193 Bellaterra, Barcelona, Spaind 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 �/

NCO�/ bridging units have been synthesized [CfflN�/azobenzene (azb); �/NCO�/�/succinimide (1a), phthalimide (2a) or maleimide

(3a); CfflN�/2-phenylpyridine (phpy); �/NCO�/�/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)] [CfflN�/azb; L�/PPh3 (4a), PPh2Me (5a), PPhMe2 (6a), P(4-F�/C6H4)3, (7a), P(4-MeO�/C6H4)3 (8a); CfflN�/

phpy; L�/PPh3 (4b), PPh2Me (5b), PPhMe2 (6b), P(4-F�/C6H4)3 (7b), P(4-MeO�/C6H4)3 (8b)] has been investigated. The new

complexes were characterized by partial elemental analyses and spectroscopic methods (IR, FAB, 1H, 13C and 31P). The single-

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

Azobenzenes and heteroaromatic ligands such as 2-

phenylpyridine can easily be orthometallated by Pd(II)

salts via C(sp2)-H bond cleavage [1�/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 [5�/12]. Furthermore, since a

number of orthometallated complexes of the platinum

group elements were implicated as potential photosensi-

tizers [13�/19], and mononuclear palladium derivatives

have been tested for nonlinear optical properties [12],

there has been a growing interest in this kind of

compound.

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

valent precursors [24�/26], the use of imide salt [10,27] or

by imide deprotonation [27�/32]. The replacement of the

bridging halide or acetate groups in classical binuclear

cyclometallated complexes by succinimidato was also* Corresponding author

Polyhedron 21 (2002) 1589�/1596

www.elsevier.com/locate/poly

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

described [10] some years ago, showing a new mode of

bidentate coordination for this ligand, involving an N�/

C�/O bridging unit.

We report here the preparation of new dinuclearorthometallated 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 diffractionanalyses of both mononuclear and binuclear derivatives

is also given.

2. Experimental

2.1. Materials and physical measurements

C, H and N analysis were carried out with a Perkin�/

Elmer 240C microanalyser. IR spectra were recorded on

a Perkin�/Elmer spectrophotometer 16F PC FT-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.

The cyclometallated precursors [{Pd(m-OOCMe)-

(CfflN)}2] [CfflN�/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 furtherpurification, and all the solvents were dried by standard

methods before use.

2.2. Preparation of the complexes [{Pd(m-NCO)-

(CfflN)}2] [CfflN�/azobenzene (azb); �/NCO�/�/

succinimide (suc) (1a), phthalimide (2a) (phtal) or

maleimide (mal) (3a); CfflN�/2-phenylpyridine (phpy);

�/NCO�/�/succinimide (1b), phthalimide (2b) or

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

an acetone (20 ml) solution of [{Pd(m-OOCMe)(CfflN)}2] (0.07 g, 0.101 mmol if CfflN�/azb;

0.07 g, 0.109 mmol if CfflN�/phpy) the stoichiometric

amount of ligand was added. The solution was refluxed

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

off, air-dried and recrystallized from acetone�/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

(cm�1): 1722s, 1566s (C�/O str.). FAB MS (positive

mode) m /z : 772 [{Pd(m-suc)(azb)}2]�, 673

[{Pd2(suc)(azb)2}]�, 575 [{Pd(azb)}2]�, 287 [Pd(azb)]�.

. 13C{1H} NMR ((CD3)2CO, d ppm): 194.2 (coordi-nated C�/O, suc), 187.9 (non-coordinated C�/O, suc),

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 (�/CH2�/, suc). 1H NMR ((CD3)2CO, d

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, �/CH2�/ suc).

2.2.2. [{Pd(m-phtal)(azb)}2] (2a)


H, 3.0; N, 9.7. Found: C, 55.6; H, 3.0; N, 9.7%). IR


mode) m /z : 868 [{Pd(m-phtal)(azb)}2]�, 722

[{Pd2(phtal)(azb)2}]�, 287 [Pd(azb)]�, 13C{1H} NMR

((CD3)2CO, d ppm): 183.6 (coordinated C�/O, phtal),

178.0 (non-coordinated C�/O, phtal), 163.2 (azb), 152.6

(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

(m, 2H, H4?), 6.22 (d, 2H, H3?, JHH�/7.4).

2.2.3. [{Pd(m-mal)(azb)}2] (3a)


H, 2.9; N, 10.9. Found: C, 50.3; H, 3.1; N, 10.9%). IR


mode) m /z : 768 [{(Pd(m-mal)2(azb)}]�, 672 [{Pd2(mal)-

(azb)2}]�, 575 [{Pd(azb)}2]�, 287 [Pd(azb)]�, 13C{1H}

NMR ((CD3)2CO, d ppm): 186.9 (coordinated C�/O,

mal), 180.9 (non-coordinated C�/O, 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?).

2.2.4. [{Pd(m-suc)(phpy)}2] (1b)


H, 3.4; N, 7.8. Found: C, 50.5; H, 3.4; N, 7.8%). IR(cm�1): 1720s, 1587s (C�/O str.). FAB MS (positive

mode) m /z : 718 [{Pd(m-suc)(phpy)}2]�, 620 [{Pd2(suc)-

(phpy)2}]�, 415 [{Pd(phpy)}2]�, 260 [Pd(phpy)]�.

J.L. Serrano et al. / Polyhedron 21 (2002) 1589�/15961590

13C{1H} NMR ((CD3)2CO, d ppm): 195.1 (coordinated

C�/O, suc), 187.9 (non-coordinated C�/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(phpy), 121.2 (phpy), 117.2 (phpy), 32.2 (�/CH2�/, suc),

32.0 (�/CH2�/, suc). 1H NMR ((CD3)2CO, d ppm, J Hz):

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,

8H, �/CH2�/ suc).

2.2.5. [{Pd(m-phtal)(phpy)}2] (2b)


H, 3.0; N, 6.9. Found: C, 56.4; H, 2.7; N, 6.9%). IR(cm�1): 1728s, 1597s (C�/O str.). FAB MS (positive

mode) m /z : 812 [{Pd(m-phtal)(phpy)}2]�, 668

[{Pd2(phtal)(phpy)2}]�, 415 [{Pd(phpy)}2]�, 260

[Pd(phpy)]�. 13C{1H} NMR ((CD3)2CO, d ppm):

184.6 (coordinated C�/O, phtal), 178.6 (non-coordinated

C�/O, phtal), 163.7 (phpy), 151.0 (phpy), 148.9 (phpy),

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?).

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


mode) m /z : 714 [{Pd(m-mal)(phpy)}2]�, 618 [{Pd2(mal)-

(phpy)2}]�, 415 [{Pd(phpy)}2]�, 260 [Pd(phpy)]�.13C{1H} NMR ((CD3)2CO, d ppm): 195.0 (coordinated

C�/O, mal), 188.5 (non-coordinated C�/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

(phpy). 1H 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. Preparation of complexes [Pd(CfflN)(suc)(L)]

[CfflN�/ azb; L�/PPh3 (4a), PPh2Me (5a), PPhMe2

(6a), P(4-F�/C6H4)3 (7a), P(4-MeO�/C6H4)3 (8a);

CfflN�/phpy; L�/PPh3 (4b), PPh2Me (5b), PPhMe2

(6b), P(4-F�/C6H4)3 (7b), P(4-MeO�/C6H4)3 (8b)]

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) solutionof 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

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,air-dried and recrystallized from acetone�/hexane.

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

(cm�1): 1580s (C�/O str.); 534m, 514m, 493m (PPh3). 1H

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,

H4?), 6.50 (m, 2H, H3?), 1.80 (dd, 2H, �/CH2�/ suc,

JHH syn �/5, JHH anti �/16), 1.55 (dd, 2H, �/CH2�/ suc,

JHH syn �/5, JHH anti �/16). 31P{1H} NMR ((CD3)2CO,

d ppm): 42.3 (s, PPh3).

2.3.2. [Pd(azb)(suc)(PPh2Me)] (5a)


H, 4.5; N, 7.2. Found: C, 59.4; H, 4.7; N, 7.5%). IR(cm�1): 1572s (C�/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, Me�/), 1.88 (m, 2H, suc), 1.57 (m, 2H, suc). 31P{1H}

NMR ((CD3)2CO, d ppm): 23.4 (s, PPh2Me).

2.3.3. [Pd(azb)(suc)(PPhMe2)] (6a)


H, 4.6; N, 8.0. Found: C, 55.2; H, 4.8; N, 7.9%). IR

(cm�1): 1580s (C�/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).

2.3.4. [Pd(azb)(suc)(P(4-F�/C6H4)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

(cm�1): 1586s (C�/O str.); 536m, 518m, 452m (P(4�/F�/

C6H4)3). 1H NMR ((CD3)2CO, d ppm, J Hz): 8.02 (d,

1H, H6?, JHH�/7.0), 7.75, (m, 6H, Ph ortho ), 7.53 (m,

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-

F�/C6H4)3).

2.3.5. [Pd(azb)(suc)(P(4-MeO�/C6H4)3)] (8a)


H, 4.6; N, 5.7. Found: C, 60.2; H, 4.7; N, 5.7%). IR

(cm�1): 1566s (C�/O str.); 538m, 518m, 498m (P(4-Me�/

C6H4)3). 1H 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

J.L. Serrano et al. / Polyhedron 21 (2002) 1589�/1596 1591

meta), 6.73 (m, 1H, H4?), 6.54 (m, 1H, H3?), 3.79 (s, 9H,

MeO�/), 1.86 (dd, 2H, �/CH2�/ suc, JHH syn �/5.2,

JHH anti �/16.4), 1.58 (dd, 2H, �/CH2�/ suc, JHH syn �/

5.2, JHH anti �/16.4). 31P{1H} NMR ((CD3)2CO, d

ppm): 38.9 (s, P(4-MeO�/C6H4)3).

2.3.6. [Pd(phpy)(suc)(PPh3)] (4b)


H, 4.4; N, 4.5. Found: C, 63.9; H, 4.2; N, 4.7%). IR

(cm�1): 1614s (C�/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, �/CH2�/ suc, JHH syn �/3,

JHH anti �/11.6), 1.25 (m, 2H, �/CH2�/ suc). 31P{1H}

NMR ((CD3)2CO, d ppm): 42.1 (s, PPh3).

2.3.7. [Pd(phpy)(suc)(PPh2Me)] (5b)


H, 4.5; N, 5.0. Found: C, 60.2; H, 4.6; N, 5.1%). IR

(cm�1): 1634s (C�/O str.); 516m, 488m, 448m (PPh2Me).1H NMR ((CD3)2CO, d ppm, J Hz): 8.10 (m, 1H, H6),

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

(cm�1): 1622s (C�/O str.); 488m, 470m, 442m (PPhMe2).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).

2.3.9. [Pd(phpy)(suc)(P(4-F�/C6H4)3)] (7b)

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

(cm�1): 1622s (C�/O str.); 540m, 454m, 441m (P(4-F�/

C6H4)3). 1H NMR ((CD3)2CO, d ppm, J Hz): 8.16 (m,

1H, H6), 7.49, (m, 8H, H3,4, 6H Ph ortho ), 7.10 (d, 1H,

H6?, JHH�/7.2), 6.92 (m, 8H, H5, H5?, 6H Ph), 6.47 (m,

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-F�/

C6H4)3).

2.3.10. [Pd(phpy)(suc)(P(4-MeO�/C6H4)3)] (8b)


H, 4.7; N, 3.9. Found: C, 60.9; H, 4.7; N, 3.9%). IR

(cm�1): 1624s (C�/O str.); 544m, 506m, 494m (P(4-

MeO�/C6H4)3). 1H 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, MeO�/), 2.25 (m,

2H, suc), 1.71 (m, 2H, suc). 31P{1H} NMR ((CD3)2CO,

d ppm): 39.4 (s, P(4-MeO�/C6H4)3).

2.4. Crystal structure determination of [{Pd(phpy)(m-

suc)}2] (1b) and [Pd(azb)(suc)(PPh3)] (4a)

Data for 1b were collected using a single crystal of

approximate dimensions 0.5�/0.5�/0.3 mm. Accurate

cell parameters were determined by least-squares fitting

of 25 high-angle reflections. The scan method was v

with the range of hkl (�/225/h 5/22, �/145/k 5/0, 05/

l 5/23) corresponding to 2Umax�/60.848. The structure

was solved by direct methods and refined anisotropically

on F2 [33]. Hydrogen atoms were introduced in calcu-

lated positions. The final R factor was 0.0481 [Rw�/

0.1139, where w�/1/s2(Fo2)�/(0.0678P)2 and P�/

(Fo2�/2Fc

2)/3] over 5115 observed reflections [I �/2s (I )].

Data for 4a were collected using a single crystal of

approximate dimensions 0.2�/0.4�/0.3 mm on a Sie-

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

introduced in calculated positions. The final R factor

was 0.0264 [Rw�/0.0712, where w�/1/[s2(Fo2)�/

(0.0652P )2�/6.4628P ] and P�/(Fo2�/2Fc

2)/3] over 5439

observed reflections [I �/2s(I )].

Table 1

Crystal data and summary of data collection and refinement for

[{Pd(phpy)(m-suc)}2] (1b) and [Pd(azb)(suc)(PPh3)] (4a)

1b 4a

Empirical formula C30H24N4O4Pd2 C34H28N3O2PPd

Formula weight 717.33 647.96

Crystal system monoclinic monoclinic

Space group P 21/n P21/n

Unit cell dimensions

a (A) 16.090(4) 10.8781(19)

b (A) 10.323(3) 16.079(3)

c (A) 16.571(2) 16.014(3)

b (8) 105.97(2) 91.560(3)

V (A3) 2646.0(11) 2799.9(9)

Z 4 4

Dcalc (Mg m�3) 1.801 1.537

F (mm�1) 1.404 0.758

l (A) 0.71073 0.71073

Observed reflections 5115 5439

R1, wR2 0.0481, 0.1139 0.0264, 0.0712

Goodness-of-fit 1.043 0.663


3. Results and discussion

In acetone, the acetato-bridged cyclometallated di-

mers [{Pd(m-OOCMe)(CfflN)}2] (CfflN�/azb or phpy)

react under the conditions described in the experimental

section with succinimide, phthalimide or maleimide to

give dinuclear complexes (1a�/3a, 1b�/3b) in which the

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

attributed to imidato�/carbonyl stretching. Thus, two

medium intensity bands at 1595 and 1552 cm�1 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 cm�1. Two

strong bands in the range 1731�/1720 and 1600�/1566

cm�1 suggested coordination of one carbonyl group to

the metal as a part of an �/NCO�/ 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

(4a�/8a, 4b�/8b) in whose spectra the band has negligible

intensity compared with the antisymmetric n (CO) ab-

sorption.

Further evidence for the dinuclearity of complexes

(1a�/3a, 1b�/3b) 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]� and [{Pd2(NCO)(CfflN)2}]�.

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

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.

Scheme 1.

Scheme 2.


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 cm�1 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 1566�/

1586 or 1600�/1634 cm�1 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

Pd(II) complexes. With regard to the 1H NMR spectra,

they show the expected resonances of the cyclometal-

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 publisheddata [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 thephosphine ligand in the cis -position. Thus, rotation

about the Pd�/N 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

with less voluminous substituents. VT 1H NMR experi-

ments were carried out in an attempt to get coalescenceof signals and to calculate the energy barrier associated

with the Pd�/N rotation, but it could not be achieved in

the range of temperatures allowed by usual deuterated

solvents. Nevertheless, similarly hindered rotations

about M�/N bonds have been attributed previously to

steric factors [27,36,37].

3.1. X-ray structures of [{Pd(m-suc)(phpy)}2] (1b) and

[Pd(azb)(suc)(PPh3)] (4a)

Selected bond distances and angles are presented in

Table 2. The coordination around the Pd atoms is

Table 2

Selected bond lengths (A) and bond angles (8) for 1b and 4a

1b 4a

Bond lengths

Pd(1)�/C(1) 1.970(4) Pd(1)�/C(1) 2.008(2)

Pd(1)�/N(1) 2.028(3) Pd(1)�/N(3) 2.0970(18)

Pd(1)�/N(2) 2.048(3) Pd(1)�/N(1) 2.0998(18)

Pd(1)�/O(3) 2.162(3) Pd(1)�/P(1) 2.2580(6)

Pd(1)�/Pd(2) 2.9544(7) C(13)�/O(1) 1.222(3)

Pd(2)�/C(26) 1.963(4) C(16)�/O(2) 1.220(3)

Pd(2)�/N(4) 2.023(3) C(13)�/N(3) 1.361(3)

Pd(2)�/N(3) 2.046(3) C(16)�/N(3) 1.362(3)

Pd(2)�/O(2) 2.179(3)

C(12)�/O(1) 1.219(5)

C(19)�/O(4) 1.202(5)

C(15)�/O(2) 1.238(5)

C(16)�/O(3) 1.239(5)

C(12)�/N(2) 1.371(5)

C(15)�/N(2) 1.328(5)

C(16)�/N(3) 1.339(5)

C(19)�/N(3) 1.403(5)

Bond angles

C(1)�/Pd(1)�/N(1) 81.47(15) C(1)�/Pd(1)�/N(3) 174.71(8)

C(1)�/Pd(1)�/N(2) 95.96(15) C(1)�/Pd(1)�/N(1) 78.45(8)

N(1)�/Pd(1)�/N(2) 173.60(13) N(3)�/Pd(1)�/N(1) 97.10(7)

C(1)�/Pd(1)�/O(3) 172.76(14) C(1)�/Pd(1)�/P(1) 93.28(6)

N(1)�/Pd(1)�/O(3) 93.57(13) N(3)�/Pd(1)�/P(1) 91.15(5)

N(2)�/Pd(1)�/O(3) 89.51(12) N(1)�/Pd(1)�/P(1) 171.74(5)

C(26)�/Pd(2)�/N(4) 81.55(16) O(1)�/C(13)�/N(3) 124.9(2)

C(26)�/Pd(2)�/N(3) 95.32(15) O(2)�/C(16)�/N(3) 125.1(2)

N(4)�/Pd(2)�/N(3) 173.51(14)

C(26)�/Pd(2)�/O(2) 173.88(14)

N(4)�/Pd(2)�/O(2) 94.03(13)

N(3)�/Pd(2)�/O(2) 89.49(12)

N(2)�/C(12)�/O(1) 123.4(4)

N(3)�/C(19)�/O(4) 124.4(4)

N(2)�/C(15)�/O(2) 126.2(4)

N(3)�/C(16)�/O(3) 126.2(4)

Fig. 1. Molecular structure of complex 1b.


approximately planar. The narrow NPdC angle, (80.88and 78.48 in the dinuclear and mononuclear complexes,

respectively), in the ortho -metallated moiety is similar to

that found in complexes containing the same ligand [11].

The structural analysis of complex 4a confirms the

relative cis -position of the phosphine ligand and the

metallated carbon atom suggested by the NMR data.This is the typical arrangement of the phosphine group

in cyclopalladated complexes of the type

[Pd(CfflN)(phosphine)(X)] (X�/anionic monodentate

ligand) due to the so-called transphobia effect [38,39].

In the succinimide ligand the C�/O distance, 1.239(5)

A, is elongated in the bridged group with respect to the

non-coordinated C�/O, 1.211(5) A, and to the mono-

nuclear one, 1.221(3) A. The Pd�/N distance is larger inthe mononuclear complex and the Pd(1)�/Pd(2) distance

in dinuclear compound 1b is rather short (2.9544(7) A).

The angle between the best plane through the succini-

mide and the coordination plane is 72.408 in dinuclear

1b (Fig. 1) and 79.228 in mononuclear 4a (Fig. 2). In the

bridged complex the 2-phenylpyridine ligands are nearly

parallel, (dihedral angle�/12.898), while the planes

through the succinimide ligands form an angle of 85.968.

4. Supplementary material

Crystallographic data for the structural analysis have

been deposited with the Cambridge CrystallographicData Centre, CCDC Nos. 173327 for compound 1b and

173328 for compound 4a. Copies of this information

may be obtained free of charge from The Director,

CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK

(fax: �/44-1223-336033; e-mail: [email protected]

or www: http://www.ccdc.cam.ac.uk).

Acknowledgements

Financial support of this work by the Direccion

General de Investigacion (project BQU2001-0979) Spain

is acknowledged. Jose Perez thanks the PFMP-UPCT-

2001 program for a grant to visit the University of

Bristol.

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Documents

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)]