Synthesis of cyclopalladated derivatives of (E)-N-Benzylidene-2-(2,6- dichlorophenyl)ethanamine and their reactivity towards monodentate and symmetric bidentate lewis bases

FULL PAPER

DOI: 10.1002/ejic.201100293

Synthesis of Cyclopalladated Derivatives of (E)-N-Benzylidene-2-(2,6-

dichlorophenyl)ethanamine and Their Reactivity towards Monodentate and

Symmetric Bidentate Lewis Bases

Joan Albert,*^[a]Ramón Bosque,^[a]Lucía D’Andrea,^[a]Jaume Granell,*^[a]

Mercè Font-Bardia,^[b,c]and Teresa Calvet^[b]

Keywords: Metalation / Palladium / Imines / Density functional calculations

Treatment of the monoimine (E)-N-benzylidene-2-(2,6-

dichlorophenyl)ethanamine (1) with a stoichiometric amount {C₆H₄CH=N(CH₂)₂(2,6-Cl₂C₆H₃)}Cl)₂{μ-L₂}] [8: L₂

high yields of the dinuclear compounds trans-N,L-[(Pd-

Ph₂-

PCH₂CH₂PPh₂; 9: L₂= trans-Ph₂PCH=CHPPh₂; 10: L₂= 4,4Ј-

bipyridine; 11: L₂= NH₂CH₂CH₂OCH₂CH₂OCH₂CH₂NH₂;

12: L₂= NH₂CH₂(CHOH)CH₂NH₂)] in which the symmetric

bidentate Lewis base bridged two identical cyclopalladated

units. Compounds 1–3 and 6–12 were fully characterized by

=

of Pd(OAc)₂in acetic acid at 60 °C under nitrogen produced

the corresponding acetato-bridged endo five-membered

ortho-cyclopalladated dimer [Pd{C₆H₄CH=N(CH₂)₂(2,6-

Cl₂C₆H₃)}(μ-OAc)]₂(2), which was isolated in pure form in

80% yield. Reaction of 2 with an excess of LiCl in acetone

gave rise to the corresponding chlorido-bridged cyclopallad- elemental analysis, mass spectrometry, IR and ¹H and

ated dimer [Pd{C₆H₄CH=N(CH₂)₂(2,6-Cl₂C₆H₃)}(μ-Cl)]₂(3) in

88% yield. Compounds 2 and 3 reacted with an excess of

[D₅]pyridine or a stoichiometric amount of PPh₃to give the

mononuclear compounds trans-N,L-[Pd{C₆H₄CH=N(CH₂)₂-

(2,6-Cl₂C₆H₃)}(X)(L)] (4: X = OAc, L = [D₅]py; 5: X = Cl, L =

[D₅]py; 6: X = OAc, L = PPh₃; 7: X = Cl, L = PPh₃). Compounds

4 and 5 were prepared in a CDCl₃/[D₅]py solution and

¹³C{¹H} NMR spectroscopy. In addition, the crystal structures

of 2, 8·2CH₂Cl₂, 10·4CHCl₃and 11·2CH₂Cl₂were deter-

mined by single-crystal X-ray diffraction analysis. Also re-

ported is the theoretical study of the differences in the abso-

lute Gibbs free energies in acetone or CHCl₃solution be-

tween the cis- and trans-N,L stereoisomers of compounds

[Pd(C-N)(X)(L)] in which Pd(C-N) is a model of an endo five-

membered ortho-cyclopalladated imine, X is OAc, Cl, Br or I

and L is py, NH₃or PH₃.

1

studied by H and ¹³C{¹H} NMR spectroscopy, but they were

not isolated. Compound 3 was treated with different types of

symmetric bidentate Lewis bases in a 1:1 molar ratio to give

Introduction

Since Onoue and Moritani reported the synthesis of the

first endo five-membered ortho-cyclopalladated imines,^[1]

compounds of this kind (Figure 1) have attracted attention

due to their use as starting materials in organic synthesis,^[2]

as pre-catalysts in Heck and Suzuki C–C coupling reac-

tions^[3]and as liquid crystals if they possess appropriate

substituents on the imine ligands and co-ligands at the pal-

ladium(II) centres.^[4]In 1987, Clark et al.^[5]introduced the

descriptors endo and exo to differentiate between structural

isomers of ortho-cyclopalladated benzyl-benzylidene-

amines (Figure 2). Since then, the use of these descriptors

has been extended to refer to cyclometallated imines, oxaz-

[a] Institut de Biomedicina, Departament de Química Inorgànica,

Universitat de Barcelona,

Martí i Franquès 1–11, 08028 Barcelona, Spain

E-mail: joan.albert@qi.ub.es

jaume.granell@qi.ub.es

[b] Departament de Cristal·lografia, Mineralogia i Dipòsits

Minerals, Universitat de Barcelona,

Martí i Franquès s/n, 08028 Barcelona, Spain

[c] Unitat de Difracció de RX, Centre Científic i Tecnològic de la

Universitat de Barcelona,

Figure 1. Most common structural formulae of endo five-mem-

bered ortho-cyclopalladated imines.

Solé i Sabarís 1–3, 08028 Barcelona, Spain

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olines and iminophosphoranes with a C=N or P=N bond molecules found in the solid state were also assumed to be

inside the metallacycle (endo-cyclometallated compounds) present in solution.^[2b,10–12]This should be the case because

or outside the metallacycle (exo-cyclometallated com- the bidentate L₂bridging ligands are biphosphane ligands

pounds).^[6]

and the formation of palladium(II)–phosphane complexes

is quite exergonic at the experimental temperature,^[14]which

points to the stability of the Pd^II–P(phosphane) bond. For

compounds IV, although other oligomeric structures would

be compatible with the NMR spectroscopic data in solu-

tion, the mass spectrometry data are consistent with the

structure depicted in Figure 3.^[13]Interestingly, some of the

compounds shown in Figure 3 can be classified as me-

tallomacrocycles or molecular cages.

In this paper we present the synthesis of cyclopalladated

derivatives of the monoimine (E)-N-benzylidene-2-(2,6-

dichlorophenyl)ethanamine and a study of their reactivity

towards monodentate and symmetric bidentate Lewis bases.

These studies have allowed the preparation of dinuclear

compounds with different types of symmetric bidentate

Lewis bases acting as bridging ligands between two iden-

tical cyclopalladated units. Note that the synthesis of cyclo-

palladated compounds derived from (E)-N-benzylidene-2-

phenylethanamines has not been described in detail.^[15]In

addition, we report a theoretical study of the differences in

the absolute Gibbs free energies in acetone or CHCl₃solu-

tion between the cis- and trans-N,L stereoisomers of com-

pounds [Pd(C-N)(X)(L)] in which Pd(C-N) is a model of an

endo five-membered ortho-cyclopalladated imine, X is OAc,

Cl, Br or I and L is py, NH₃or PH₃.

Figure 2. endo and exo structural isomers of ortho-cyclopalladated

benzyl-benzylidene-amine.

In recent years, the reactivity of endo-cyclopalladated im-

ines towards bidentate Lewis bases has been extensively

studied by Vila and co-workers.^[2b,7–13]These studies are rel-

evant to the field of supramolecular chemistry. Figure 3

shows schematically the structures proposed for the com-

pounds obtained in the reactions between mono- or di-

endo-cyclopalladated imines and bidentate Lewis bases in a

Pd/bidentate Lewis base molar ratio of 2:1 in which the

bidentate Lewis base acts as a bridging ligand. In Figure 3,

the L₂bridging ligand is generally a biphosphane, X is Cl,

–

Y is PF₆and Pd(C-N) is an endo five-membered ortho-

cyclopalladated imine. A large number of compounds I

have been prepared,^[7]as have a few compounds II.^[8]In

addition, in one case,^[9]a compound characterized as II in

solution adopts structure I in the solid state. The molecular

structures of representative compounds III,^[10]V,^[2b]VI^[11]

Results and Discussion

Scheme 1 shows the structural formulae of the new com-

and VII^[12]have been determined by X-ray diffraction. The pounds prepared in this study and the numbering of their

Figure 3. Structural formulae of compounds with a bridging bidentate ligand obtained by reactions between mono- or dicyclopalladated

compounds and bidentate Lewis bases in a Pd/bidentate Lewis base molar ratio of 2:1. In general, L₂is a biphosphane, X is Cl, Y is

–

PF₆and Pd(C-N) is an endo five-membered ortho-cyclopalladated imine.

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Eur. J. Inorg. Chem. 2011, 3617–3631

Cyclopalladated N-Benzylidene-2-(dichlorophenyl)ethanamines

Scheme 1. Reagents and conditions: i) Pd(OAc)₂(stoichiometric), HOAc, 60 °C, 5 h, under N₂; ii) LiCl (excess), acetone, room temp.,

24 h; iii) 4 and 5: [D₅]py (excess), CDCl₃, room temp.; 6: PPh₃(stoichiometric), acetone, room temp., 2 h; 7: PPh₃(stoichiometric), acetone,

room temp., 48 h; iv) 8: Ph₂PCH₂CH₂PPh₂(stoichiometric), CHCl₃, room temp., 6 h, under N₂; 9: trans-Ph₂PCH=CHPPh₂(stoichiomet-

ric), acetone, room temp., 3 h, under N₂; 10: 4,4Ј-bipyridine (stoichiometric), CHCl₃, room temp., 3 h, under N₂; 11: NH₂CH₂CH₂OCH_2-

CH₂OCH₂CH₂NH₂(stoichiometric), CHCl₃, room temp., 3 h, under N₂; 12: NH₂CH₂(CHOH)CH₂NH₂(stoichiometric), CHCl₃, room

temp., 4 h, under N₂.

protons and carbon atoms for the discussion that follows. an intense signal at m/z = 278.2, which corresponds to [M

Compounds 1–3 and 6–12 were fully characterized by ele- + H]⁺.

mental analysis (C, H and N), mass spectrometry, IR and

Treatment of imine 1 with a stoichiometric amount of

Pd(OAc)₂in acetic acid at 60 °C under nitrogen produced

the corresponding acetato-bridged endo five-membered or-

tho-cyclopalladated dimer 2, which was easily converted by

a metathesis reaction with LiCl into the chlorido-bridged

cyclopalladated dimer 3 (Scheme 1). Compounds 2 and 3

were isolated in pure form in 80 and 88% yields, respec-

tively. Compound 2 is a deep-yellow solid that is very solu-

ble in CDCl₃and compound 3 is a yellow solid that is par-

tially soluble in CDCl₃. The solutions of compounds 2 and

3 in CDCl₃were stable on contact with air.

¹H and ¹³C{¹H} NMR spectroscopy. Compounds 6–9 were

1

also studied by ³¹P{¹H} and H{³¹P} NMR spectroscopy.

Compounds 4 and 5 were prepared in CDCl₃/[D₅]py solu-

1

tion and studied by H and ¹³C{¹H} NMR spectroscopy,

1

but they were not isolated. The assignments of the H and

¹³C{¹H} NMR spectra were inferred from the results of

two-dimensional COSY, NOESY, HSQC and HMBC ex-

periments. In addition, the crystal structures of 2,

8·2CH₂Cl₂, 10·4CHCl₃and 11·2CH₂Cl₂were determined

by single-crystal X-ray diffraction analysis.

Intense C=N stretching bands for compounds 2 and 3

appear at 1609 cm^–1, shifted to lower wavenumbers in rela-

tion to 1, which is consistent with the coordination of the

Synthesis and Characterization of Compounds 1–3

Imine 1 was prepared by a condensation reaction be- iminic nitrogens to the palladium(II) centres.^[1]The asym-

tween benzaldehyde and 2-(2,6-dichlorophenyl)ethanamine. metric and symmetric stretchings of the carboxylic func-

Imine 1 is a solid that is highly soluble in CDCl₃; in this tions of 2 produced broad intense bands at 1568 and

solvent, H and ¹³C{¹H} NMR analysis produced a single 1433 cm^–1, respectively, which indicates that the acetato li-

1

set of signals. These NMR spectroscopic data suggested gands of 2 present a bridging coordination mode.^[17]On the

that imine 1 consists of only the E geometrical isomer.^[16]other hand, the Pd–Cl stretchings of the chlorido-bridged

In agreement with this assumption, the NOESY spectrum cyclopalladated dimer 3 gave rise to two bands at 296 and

of 1 shows a cross-peak between the CH=N and the N– 264 cm^–1, which have been assigned to Pd–Cl stretching

CH₂protons. The methinic proton and carbon atom of 1 trans to the iminic nitrogen and trans to the palladated car-

appear at 8.26 and 161.7 ppm, respectively, and C=N bon atom, respectively.^[18]In addition, MALDI-TOF(+)

stretching produced an intense band at 1645 cm^–1. In ad- MS analysis of compounds 2 and 3 produced intense peaks

dition, the MALDI-TOF(+) MS analysis of 1 gave rise to for the cations [M – X]⁺, in which X is acetate for 2 and

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chloride for 3, in agreement with dimeric structures with

acetato- and chlorido-bridged ligands, respectively.^[2c]

The principal features of the ¹H NMR spectrum of com-

pound 2 in CDCl₃solution are i) the upfield shift by

0.70 ppm of the methinic proton in relation to the free im-

ine, ii) the diastereotopic nature of the N–CH₂–CH₂– meth-

ylene protons and iii) the single singlet produced by the

methyl protons of the acetato ligands at δ = 2.20 ppm.

These data are consistent with a dimeric folded structure

with a trans configuration for compound 2, which is the

usual structure adopted for acetato-bridged cyclopalladated

dimers in CDCl₃solution and in the solid state.^[19]In this

dimeric structure, the acetato ligands bridge two palladi-

um(II) centres and the imines are coordinated to them in a

chelate mode through their iminic nitrogen and C1 aro-

matic carbon atoms (Figure 4, A). Furthermore, the ¹H

NMR spectrum of compound 2 in CDCl₃solution is also

consistent with its ortho-cyclopalladated nature as two ortho

Figure 4. A) trans-folded structure of compound 2. B) Planar trans

and cis geometrical isomers of compound 3. C-N stands for

C₆H₄CH=N(CH₂)₂(2,6-Cl₂C₆H₃).

X-ray Crystal Structure of Compound 2

Yellow crystals of compound 2 suitable for a single-crys-

protons, one from each imine ligand, are absent from the tal X-ray diffraction analysis were obtained by evaporating

spectrum. In accord with the structure proposed for com- the solvent of a saturated solution of 2 in diethyl ether.

pound 2, its ¹³C{¹H} NMR spectrum in CDCl₃produced Compound 2 crystallized in the triclinic space group P1

¯

a single set of signals, which presented as principal features with Z = 2. Figure 5 shows an ORTEP view of the X-ray

i) a downfield shift of 10.6 and 27.2 ppm of the methinic molecular structure of 2 and also gives selected bond

and metallated carbon atoms, respectively, in relation to the lengths and angles. The X-ray molecular structure con-

free imine ligand and ii) a single set of signals afforded by firmed the proposed structure for compound 2. Thus, com-

the carbon atoms of the acetato ligands at 181.3 and pound 2 presents a dimeric trans folded structure with the

24.6 ppm. Note that compound 2 in CDCl₃solution pres- acetato ligands bridging the two palladium(II) centres with

ents an apparent C₂symmetry, as deduced from the ¹H and the imines chelated to them through the N1 and C1 and

¹³C{¹H} NMR spectra at 298 K. In addition, the ¹H NMR the N2 and C21 atoms, respectively. The molecule of 2 in

spectrum of compound 3 in CDCl₃at 298 K produced two the crystal form is asymmetric. The two halves differ in the

set of signals, which we tentatively assigned to its planar conformation of the CH₂CH₂(2,6-Cl₂C₆H₃) groups [com-

trans and cis geometrical isomers (Figure 4, B).^[20]

pare the torsion angles N1–C8–C9–C10 –172.5(4)° and C9–

Figure 5. ORTEP view of the X-ray molecular structure of compound 2 and labelling of the atoms. Selected bond lengths [Å] and bond

angles [°]: Pd1–C1 1.979(4), Pd1–N1 2.114(4), Pd1–O1 2.126(3), Pd1–O3 2.147(3), Pd2–C21 1.998(5), Pd2–N2 2.028(4), Pd2–O4 2.058(3),

Pd2–O2 2.194(3), C21–Pd2–N2 80.10(19), C21–Pd2–O4 93.77(18), N2–Pd2–O4 173.66(15), C1–Pd1–N1 80.38(16), C1–Pd1–O1 92.62(16),

N1–Pd1–O1 172.69(13), C1–Pd1–O3 176.80(15), N1–Pd1–O3 97.68(14), O1–Pd1–O3 89.41(13), C21–Pd2–O2 173.80(15), N2–Pd2–O2

95.93(15), O4–Pd2–O2 90.31(14).

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Cyclopalladated N-Benzylidene-2-(dichlorophenyl)ethanamines

C10–C11–Cl1 0.0(7)° with N2–C28–C29–C30 67.8(5)° and are shifted upfield in relation to the free imine by around

C29–C30–C31–Cl3 2.0(6)°] and in the small differences in 1.20 ppm for compounds 4 and 5 and by around 1.00 pm

the distances and angles [for instance, compare Pd1–N1 for compounds 6 and 7. Further indications of the stereo-

2.114(4) Å with Pd2–N2 2.028(4) Å and O3–Pd1–C1 chemistry of compounds 6 and 7 are given by ³¹P{¹H}

176.80(15)° with O2–Pd2–C21 173.80(15)°].

NMR, with resonances observed at 40.0 and 42.0 ppm,

The two palladacycles Pd1–N1–C1–C6–C7 and Pd2– respectively. These chemical shifts are in the range expected

N2–C21–C26–C27 are almost planar [maximum deviations: for mononuclear cyclopalladated compounds of general

C1 –0.073(5) Å and N2 0.052(4) Å] and the angle between formula trans-N,P-[Pd(C-N)(X)(PPh₃)] (X = OAc, Cl, Br, I)

them is 25.0(2)°. In addition, i) the distances Pd1–O3 containing a five-membered palladacycle and a phenyl- or

2.147(3) Å and Pd2–O2 2.194(3) Å are greater than the dis- naphthyl-metallated carbon atom (43–40 ppm).^[6e,8a,24]

tances Pd1–O1 2.126(3) Å and Pd2–O4 2.058(3) Å due to

In the ¹³C{¹H} NMR spectra of compounds 4–7, the

the greater trans influence of the metallated carbon atom in CH=N and the C1-metallated carbon atoms appear down-

relation to the iminic nitrogen atom^[18]and ii) the chelate field shifted by around 14 and 30 ppm, respectively, in rela-

bite angles C1–Pd1–N1 80.38(16)° and C21–Pd2–N2 tion to the free imine, which is in agreement with the chelate

80.10(19)° are those of the coordination spheres of the pal- coordination mode of the imine ligand through the iminic

ladium(II) centres with the largest deviations from the ideal nitrogen and the C1 carbon atoms. In addition, for com-

angles. The distance between the palladium atoms pound 6, the acetato ligand produced singlet signals at δ =

[2.9881(10) Å] is at the upper limit accepted for a palla- 177.0 and 23.5 ppm. Interestingly, for compounds 4 and 5

dium–palladium single bond length, which is between 2.5 the [D₅]py coordinated molecules are not observed in the

and 3.0 Å.^[21]

¹³C{¹H} NMR spectra in CDCl₃/[D₅]py solution at 298 K.

This is an indication that compounds 4 and 5 in CDCl₃/

[D₅]py solution are involved in a dynamic process in which

coordinated and free [D₅]py molecules are exchanged.

Analogous dynamic processes have been described for re-

lated systems.^[25]

Reactivity of Compounds 2 and 3 Towards Monodentate

Lewis Bases

Compounds 2 and 3 reacted with an excess of [D₅]py or

a stoichiometric amount of PPh₃to give the mononuclear

compounds 4–7. Compounds 4 and 5 were prepared in

CDCl₃/[D₅]py solution and studied by ¹H and ¹³C{¹H}

NMR, but they were not isolated. Compounds 4 and 5 are

highly soluble in CDCl₃/[D₅]py. Compounds 6 and 7 were

Reactivity of Compound 3 Towards Symmetric Bidentate

Lewis Bases

Compound 3 reacted in a 1:1 molar ratio with the sym-

prepared in acetone and isolated in pure form as pale-yel- metric bidentate Lewis bases Ph₂PCH₂CH₂PPh₂, trans-

low solids in 83 and 74% yields, respectively, and are quite Ph₂PCH=CHPPh₂, 4,4Ј-bipyridine, NH₂CH₂CH₂OCH₂-

soluble in CDCl₃. Solutions of compounds 6 and 7 in CH₂OCH₂CH₂NH₂and NH₂CH₂(CHOH)CH₂NH₂to

CDCl₃as well as solutions of compounds 4 and 5 in give high yields of the dinuclear compounds trans-N,L-

CDCl₃/[D₅]py were stable on contact with air. The [(Pd{C₆H₄CH=N(CH₂)₂(2,6-Cl₂C₆H₃)}Cl)₂{μ-L₂}] [8: L₂=

MALDI-TOF(+) MS analyses of compounds 6 and 7 pro- Ph₂PCH₂CH₂PPh₂; 9: L₂= trans-Ph₂PCH=CHPPh₂; 10: L₂

duced intense peaks for the cations [M – X]⁺for which X

= 4,4Ј-bipyridine; 11: L₂= NH₂CH₂CH₂OCH₂CH_2-

is acetate for 6 and chloride for 7. The C=N stretching and OCH₂CH₂NH₂; 12: L₂= NH₂CH₂(CHOH)CH₂NH₂] in

the q X-sensitive mode of the coordinated PPh₃appear at which the symmetric bidentate L₂Lewis base bridges two

1620 and 1097 cm^–1for compound 6 and at 1624 and identical cyclopalladated units. The high chemo- and

1096 cm^–1for compound 7.^[22]In addition, the carboxylate stereoselectivity of these reactions are remarkable, espe-

function of the acetato ligand of compound 6 produced in- cially the reactions with the ligands Ph₂PCH₂CH₂PPh₂(a),

tense bands at 1601 and 1369 cm^–1, in agreement with its NH₂CH₂CH₂OCH₂CH₂OCH₂CH₂NH₂(b) and NH₂CH₂-

monodentate coordination mode.^[16]In addition, the Pd–Cl (CHOH)CH₂NH₂(c), which could alternatively act as che-

stretching of compound 7 appears at 300 cm^–1.

late (a–c) or chelate-bridging ligands (b–c), for instance.

1

The H NMR spectroscopic data for the mononuclear

These results confirm previous work by our group on the

compounds 4–7 are consistent with their proposed stereo- reactivity of cyclopalladated derivatives with 1,2-bis(di-

chemistry, with the L ligand located trans to the iminic ni- phenylphosphanyl)ethane (dppe)^[6g]in which the dppe li-

trogen and the X ligand trans to the palladated carbon gand bridges cyclopalladated units if the reaction is per-

atom (see Scheme 1). We refer to this arrangement as trans- formed with a palladium/dppe molar ratio of 2:1. In con-

N,L stereochemistry. In accord with this stereochemistry, trast, when the same reaction was performed with a palla-

the aromatic protons of the palladated ring of compounds dium/dppe molar ratio of 1:1, anionic compounds [Pd(C-

4–7 appear upfield shifted in relation to the free imine be- N)(dppe)]Br or neutral derivatives with no Pd–N bond of

cause they are located in the shielding zone of the aromatic formula [Pd(C-N)(Br)(dppe)] were obtained.

ring of the [D₅]py ligand in compounds 4 and 5 and of the

Compounds 8–12 are pale-yellow solids quite soluble in

phenyl substituents of the PPh₃ligand for compounds 6 CDCl₃, with the exception of compound 9, which is more

and 7.^[23]As a result, the H2 protons of compounds 4–7 soluble in CD₂Cl₂than in CDCl₃. The deuteriated solutions

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of these compounds were air-stable, with the exception of protons. Thus, the protons of the same NH₂or CH₂group

that of compound 12, which slowly evolved to yield un- in the bridging ligand are not equivalent. This is consistent

identified compounds. In the IR spectra of compounds 8– with the proposed apparent C_ssymmetry for this com-

12, the C=N stretching bands appear at 1626, 1624, 1608, pound in CDCl₃solution. In addition, for compound 12,

1613 and 1612 cm^–1, respectively. For compounds 8 and 9, the OH proton appears as a broad signal at δ = 5.38 ppm.

the

Ph₂PCH₂CH₂PPh₂and trans-Ph₂PCH=CHPPh₂ligands 8 and 9 were virtually coupled with the two phosphorus

appear at 1101 or 1099 cm^–1, respectively.^[22]For compound atoms

of the Ph₂PCH₂CH₂PPh₂and trans-

q

X-sensitive modes of the coordinated

Interestingly, the CH=N and H2 protons of compounds

10, which contains the 4,4Ј-bipyridine ligand, the band Ph₂PCH=CHPPh₂bridging ligands, respectively. For in-

equivalent to the ν₄stretching mode of the pyridine ligand stance, for compound 9, the CH=N and H2 protons af-

appears at 1608 cm^–1,^[26]which coincides with the C=N forded signals of multiplicity three and five, respectively,

stretching of the imine ligand. For compound 11, the NH₂both signals showing second-order effects. These virtual

asymmetric and symmetric stretchings produced bands at couplings were corroborated by ¹H{³¹P} NMR as the

3321 and 3263 cm^–1, and for compound 12, the bands at CH=N and H2 protons of compounds 8 and 9 appear as a

3385, 3295 and 3236 cm^–1were assigned to NH₂and OH singlet and doublet, respectively, in these latter experiments.

stretchings. Furthermore, the far-IR spectra of compounds The most interesting features of the ¹³C{¹H} NMR spectra

8–12 present bands at around 300 cm^–1, which have been of compounds 8–12 are the downfield shifts of around 13–

assigned to terminal Pd–Cl stretching. In addition, the mass 14 and 30 ppm for the CH=N and C1 carbon atoms, respec-

spectrometry experiments for compounds 8–11 produced tively, relative to the free imine ligand, which is consistent

intense signals with appropriate isotopic patterns for cat- with the chelate coordination mode of the imine ligands

ions [M – Cl]⁺. However, a mass spectrum providing evi- through the iminic nitrogen and C1 carbon atoms to the

dence for the dinuclear structure of compound 12 could not palladium(II) centres.

be obtained.

The ¹H and ¹³C{¹H} NMR spectra of compounds 8 and

1

10–12 in CDCl₃and the H and ¹³C{¹H} NMR spectra of

X-ray Crystal Structures of the Adducts 8·2CH₂Cl₂,

10·4CHCl₃and 11·2CH₂Cl₂

compound 9 in CD₂Cl₂at 298 K show that these com-

pounds present a molecular structure with an apparent cen-

tre of inversion (compounds 8–11) or an apparent plane of

Yellow single crystals of the adducts 8·2CH₂Cl₂,

symmetry (compound 12), which divides the molecules into 10·4CHCl₃and 11·2CH₂Cl₂were obtained by slow evapo-

two symmetrical parts. This is in agreement with the struc- ration of the solvent of a dichloromethane solution of 8 and

tures proposed for these compounds with symmetric L₂li- a chloroform solution of 10 and by slow diffusion of hex-

gands i) bridging the two palladium(II) centres and ii) coor- anes into a CH₂Cl₂solution of 11, respectively. These three

¯

dinated to the cyclopalladated units with trans-N,L stereo- adducts crystallized in the triclinic space group P1 with Z

chemistry. In addition, the ³¹P{¹H} NMR spectra of com- = 1 with the molecules 8, 10 and 11 located in an inversion

pounds 8 and 9 in CDCl₃each show a singlet at δ = 38.2 centre. Therefore these molecules consist of two symmetri-

and 34.7 ppm, respectively, as expected for the proposed cally equivalent parts in these crystals. Figures 6, 7 and 8

structures. Furthermore, for compounds 8–10, in accord show ORTEP views of 8, 10 and 11 and also give selected

with the presence of aromatic rings in the bridging ligand bond lengths and angles for these molecules.

close to the H2 protons, the H2 protons are shifted upfield

The X-ray molecular structures of compounds 8, 10 and

by between 0.8 and 1.0 ppm in relation to the free ligand. 11 confirmed the structures proposed upon NMR analysis.

In contrast, for compounds 11 and 12, which do not have Thus, in the X-ray molecular structures of compounds 8,

aromatic rings in the bridging ligand, the H2 protons are 10 and 11, the symmetric bidentate Lewis bases bridge the

shifted upfield by only between 0.4 and 0.5 ppm in relation two palladium(II) centres and are coordinated to the cyclo-

to the free ligand.

palladated units in a trans-N,L stereochemistry. The pallad-

For compound 8, the aliphatic P–CH₂protons produced acycles of compounds 8, 10 and 11 are almost planar. The

an apparent doublet at δ = 2.97 ppm with an apparent cou- maximum deviations from the best plane of the pallada-

pling constant with the phosphorus atom of 2.1 Hz. For cycles are C7 –0.057(7) Å for 8, N1 0.017(2) Å for 10 and

compound 9, the alkenyl protons of the trans- N1 –0.017(6) Å for 11. The chelate bite angles C1–Pd1–N1

Ph₂PCH=CHPPh₂bridging ligand afforded an apparent 80.2(2)° for 8, N1–Pd1–C1 81.01(11)° for 10 and N1–Pd2–

triplet by their virtual coupling with the two phosphorus C1 79.7(3)° for 11 are those of the coordination spheres of

atoms. For compound 10, the 4,4Ј-bipyridine bridging li- the palladium(II) centres with the largest deviations from

gand afforded doublets at δ = 9.11 and 7.72 ppm with a the ideal angles. The palladium–nitrogen iminic distances

coupling constant of around 6 Hz. For compound 11, the are 2.028(3) Å for 10, 2.092(5) Å for 11 and 2.086(5) Å for

coordinated NH₂groups produced a broad triplet centred 8. The variations in these distances did not match those

at δ = 3.40 ppm. In contrast, for compound 12, the protons expected taking into account the trans influence of the li-

of the coordinated NH₂groups and the CH₂groups of the gand trans to the iminic nitrogen in these compounds: a

bridging ligand produced four signals centred at 3.42, 3.29, pyridine ligand in compound 10, a primary amine ligand in

3.15 and 2.93 ppm, each signal integration revealing two compound 11 and a phosphane ligand in compound 8.^[27]

3622

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Eur. J. Inorg. Chem. 2011, 3617–3631

Cyclopalladated N-Benzylidene-2-(dichlorophenyl)ethanamines

Figure 6. ORTEP view of the X-ray molecular structure of compound 8 and labelling of the atoms. Selected bond lengths [Å] and bond

angles [°]: Pd–C1 2.068(3), Pd–N1 2.086(5), Pd–P 2.2647(17), Pd–Cl1 2.387(2), C1–Pd–N1 80.16(18), C1–Pd–P 94.22(12), N1–Pd–P

174.36(16), C1–Pd–Cl1 171.49(11), N1–Pd–Cl1 91.38(16), P–Pd–Cl1 94.24(7).

Figure 7. ORTEP view of the X-ray molecular structure of compound 10 and labelling of the atoms. Selected bond lengths [Å] and bond

angles [°]: Pd1–C1 2.010(3), Pd1–N1 2.028(3), Pd1–N2 2.054(3), Pd1–Cl1 2.4092(13), C1–Pd1–N1 81.01(11), C1–Pd1–N2 95.66(11), N1–

Pd1–N2 176.02(8), C1–Pd1–Cl1 174.06(8), N1–Pd1–Cl1 95.71(7), N2–Pd1–Cl1 87.80(7).

Figure 8. ORTEP view of the X-ray molecular structure of compound 11 and labelling of the atoms. Selected bond lengths [Å] and bond

angles [°]: Pd2–C1 2.001(6), Pd2–N2 2.073(5), Pd2–N1 2.092(5), Pd2–Cl1 2.410(2), C1–Pd2–N2 94.3(3), C1–Pd2–N1 79.7(3), N2–Pd2–

N1 172.9(2), C1–Pd2–Cl1 175.9(2), N2–Pd2–Cl1 88.74(16), N1–Pd2–Cl1 97.02(16).

For compounds 8, 10 and 11, their P–C28–C28a–Pa, these atoms are 180°. This is because the molecules are lo-

C19–C18–C18a–C19a and O1–C18–C18a–O1a central cated in an inversion centre of the crystal. For compound

fragments are planar and the torsion angles defined by 11, the torsion angles C18a–C18–O1–C17, C18–O1–C17–

Eur. J. Inorg. Chem. 2011, 3617–3631

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3623

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FULL PAPER

C16 and O1–C17–C16–N2 are –176.3(5), –173.0(6) and Lewis base molar ratio of 2:1 (see chapter Reactivity of

57.3(7)°, respectively. For compounds 8, 10 and 11, the Compound 3 Towards Symmetric Bidentate Lewis Bases

angles between the cyclopalladated rings and the central and ref.^[2c,7–13]).

planar fragments P–C28–C28a–Pa, C19–C18–C18a–C19a

and O1–C18–C18a–O1a are 73.0(9), 64.01(13) and 68.0(4)°,

respectively. In addition, for compound 11, the torsion an-

gle C16–N2–Pd2–Cl1 is 63.3(4)° and the distance N2–Pd2

[2.073(5) Å] is greater than the Pd1–N2 distance in com-

pound 10 [2.053(3) Å]. The variations in these distances

agree with the expectation that the length of a Pd–N(sp³) σ

bond should be greater than the length of a Pd–N(sp²) σ

bond.

Compound 11 does not present intermolecular N–H···O

hydrogen bonds. Nevertheless, the conformation adopted

by the O1–C17–C16–N2 fragment of this molecule in the

crystal [torsion angle O1–C17–C16–N2 57.3(7)°] may be a

consequence of the intramolecular N2–H2A···O1 hydrogen

bond with a H2A···O1 distance of 2.50 Å.

The high selectivity of these splitting reactions has

formed the basis for the successful application of cyclopal-

ladated compounds of optically active N-donor ligands i) as

derivatizing agents for the optical resolution of chiral phos-

phanes^[28]and for the determination by NMR of the optical

purity of optically active phosphanes and α-amino acids^[29]

and ii) as chiral Lewis acid templates for the promotion of

asymmetric Diels–Alder, hydroamination, hydrophosphin-

ation and hydroarsination reactions.^[30]Furthermore, this

trans-N,L stereochemistry also allows the self-assembly of

mono- or di-cyclopalladated compounds and the bidentate

Lewis bases discussed in the Introduction to produce the

metallomacrocycles and molecular cages II–VII shown in

Figure 1.

In a few cases, compounds of the type [Pd(C-N)(Cl)(py)]

with cis-N,N stereochemistry have been observed (com-

pounds a; see Figure 9 for the schematic structural formulae

of compounds a–d)^[31]and metallated compounds of gene-

ral formula trans-[Pd(C-N)(X)(monophosphane)₂] (X = Cl

or Br), in which the Pd–N bond has been broken, have also

been reported. The formation of these latter compounds

depends on the stability of the metallacycle and the basicity

of the monophosphane ligand.^[1,32]

Theoretical Study of the Stereochemistry of Compounds of

Formula [Pd(C-N)(X)(L)]

The results obtained in this study (see chapter Reactivity

of Compounds 2 and 3 Towards Monodentate Lewis Bases)

confirm the high selectivity of the splitting reactions of cy-

clopalladated dimers of N-donor ligands of general formula

[Pd(C-N)(μ-X)]₂(X = OAc or Cl) with Lewis bases such as

monophosphanes, -pyridines or -amines, which transformed

these dimers with complete selectivity into the mononuclear

compounds trans-N,L-[Pd(C-N)(X)(L)] (X = OAc or Cl; L

= monophosphane, -pyridine or -amine) in most of the

cases (see this work and ref.^[23–25]). Furthermore, the selec-

tivity of these reactions is also maintained in more complex

situations when mono- or di-cyclopalladated complexes re-

act with rigid or flexible bidentate Lewis bases such as di-

Recently, examples of compounds of formula [Pd(C-

N)(X)(py)] with X = Br or I and a cis-N,N stereochemistry

have also been described (compounds b).^[33]In addition,

two compounds of formula [Pd(C-N)(Br)(py)] with trans-

N,N stereochemistry (compounds c) have also been re-

ported^[25]as well as compounds of formula [Pd(C-N)-

(X)(monophosphane)] with X = Br or I that adopt trans-

N,P stereochemistry.^[6e,23b,25]

Interestingly, for compounds a and b, with the exception

phosphanes, bipyridines or diamines in a Pd/bidentate of one of the compounds a (compound aЈ), the C–N ligand

Figure 9. Schematic structural formulae of compounds a–d. Compounds a, b and d1 are endo cyclopalladated compounds with an

aromatic- or ferrocenylic-metallated carbon atom. Compound d2 is an exo compound with a naphthylic-metallated carbon atom.

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Eur. J. Inorg. Chem. 2011, 3617–3631

Cyclopalladated N-Benzylidene-2-(dichlorophenyl)ethanamines

is an imine ligand, whereas for compounds c the C–N li- CH=CH₂) more stable than the geometrical isomers with

gand is an amine ligand. Thus, on going from compounds the chlorido ligand trans to the nitrogen atom. These results

a and b to compounds c, the nitrogen atom of the C–N are consistent with experimental observations.^[37]Interested

ligand changes from an sp²to a softer sp³nitrogen atom in this theoretical work, we calculated the differences in the

and the pyridine ligand changes from cis to the iminic nitro- electronic energies, absolute enthalpies and absolute Gibbs

gen atom (compounds a and b) to trans to the aminic nitro- free energies in vacuo and in acetone or CHCl₃solutions

gen atom (compounds c). In compound aЈ, which has cis- between the cis- and trans-N,L stereoisomers of the endo

N,N stereochemistry, the C–N ligand is an amine ligand, five-membered ortho-cyclopalladated imine models of for-

but instead of a pyridine, compound aЈ contains 3,4,5-tri- mula [Pd(CH=CH–CH=NH)(X)(L)], hereafter referred to

chloropyridine, which is harder than pyridine itself.^[34]

as compounds A, in which X is OAc, Cl, Br or I and L is py,

Note that in all compounds a, the iminic nitrogen atom NH₃or PH₃. Table 1 summarizes the results and Figure 10

of the C–N ligand is bonded to a σ-acceptor group, such as shows the structures of the cis- and trans-N,L stereoisomers

phenyl or 1-naphthyl,^[31]but compounds of general formula of compounds A. To facilitate a comparison with the exper-

[Pd(C–N)(Cl)(py)], in which C–N is an iminic ligand with imental results, we have focused the discussion on the differ-

a σ-donor group, such as –CHMePh, –CH₂–CH₂–aryl or ences in the absolute Gibbs free energies in acetone and

–CH₂–(1-naphthyl) bonded to the iminic nitrogen atom of chloroform solution between the cis- and trans-N,L stereo-

the C–N ligand (compounds d), adopt a trans-N,N stereo- isomers of compounds A [ΔG(a) and ΔG(c), respectively;

chemistry (see, for instance, this work and ref.^[2c,24a]). Thus, columns with values printed in bold in Table 1].

on going from compounds d to compounds a, the hardness

of the iminic nitrogen of the C–N ligand increases and the

pyridine ligand moves from trans to the iminic nitrogen in

compounds d to cis to the iminic nitrogen in compounds a.

Thus, if we consider that the pyridine ligand is slightly

harder than the chlorido ligand,^[35]these results are consis-

tent with the finding that the splitting reactions of cyclopal-

ladated dimers of general formula [Pd(C-N)(μ-X)]₂with

monodentate Lewis bases lead generally to mononuclear

compounds of formula [Pd(C-N)(X)(L)] with complete ster-

eoselectivity. This is as expected, according to the anti-sym-

biotic effect, which establishes that two soft ligands in mut-

Figure 10. Structures of the cis- and trans-N,L stereoisomers of

ual trans positions have a destabilizing effect on each other

when attached to a soft metal atom.^[36]Thus, in compounds

[Pd(C-N)(X)(L)], the hardest X or L ligand tends to be

compounds A.

With the anionic X ligand fixed, comparison of the

trans to the palladated carbon atom and the softest X or L ΔG(a) and ΔG(c) values for neutral L ligands shows that in

ligand tends to be trans to the nitrogen atom. all cases the order of stabilization of the trans-N,L stereo-

Previous theoretical studies with model compounds of isomer is PH₃Ͼ NH₃Ͼ py. Thus, an increment in the hard-

type [PdCl(R)(P–N)] (R = CH₃or η¹-CH₂–CH=CH₂; P– ness of the ligand L leads to a stabilization of the cis-N,L

N = PH₂–O–CH₂–CH=NH] showed that the geometrical stereoisomer (see, for instance, entries 10–12). On the other

isomers with the chlorido ligand trans to the phosphorus hand, for the anionic X ligand, if we take as reference the

atom are 7.1 (R = CH₃) and 5.3 kcalmol^–1(R = η¹-CH₂– compounds containing the PH₃ligand (entries 3, 6, 9 and

Table 1. Energy differences between cis- and trans-N,L stereoisomers of compounds A. Positive values indicate that the trans-N,L isomer

is more stable.^[a]

Entry

X

L

ΔE [kcalmol^–1]

ΔE(v)

ΔE(a)

ΔE(c)

ΔH(v)

ΔH(a)

ΔH(c)

ΔG(v)

ΔG(a)

ΔG(c)

1

2

3

4

5

6

7

8

OAc

Cl

Br

I

py

NH₃

PH₃

py

NH₃

PH₃

py

NH₃

PH₃

py

NH₃

PH₃

5.90

–0.88

5.60

0.02

0.13

0.25

–0.86

5.31

1.14

2.25

4.90

0.63

1.70

4.52

0.27

1.07

4.01

1.45

–0.64

5.46

0.96

1.99

4.81

0.53

1.35

4.43

0.03

0.82

3.94

5.79

–1.02

5.26

–0.09

–0.10

3.64

–0.56

–0.57

3.34

–1.11

–1.13

2.92

0.14

–1.01

4.98

1.04

2.02

4.62

0.50

1.44

4.19

0.14

0.81

3.71

1.34

–0.78

5.12

0.86

1.75

4.53

0.40

1.09

4.10

–0.11

0.57

3.63

3.53

–1.07

4.85

–0.71

–0.44

3.21

–1.15

–0.91

2.81

–1.67

–1.44

2.42

–2.12

–1.05

4.57

0.41

1.68

4.19

–0.08

1.10

3.67

–0.43

0.50

3.20

–0.92

–0.83

4.71

0.23

1.42

4.09

–0.19

0.75

3.58

–0.67

0.25

3.13

3.92

–0.43

–0.31

3.66

–0.97

–0.87

3.22

9

10

11

12

I

[a] ΔE = electronic energy_cis-N,L– electronic energy_trans-N,L, ΔH = absolute enthalpy_cis-N,L– absolute enthalpy_trans-N,L, ΔG = absolute Gibbs

free energy_cis-N,L– absolute Gibbs free energy_trans-N,L. v = vacuum, a = acetone solution, c = chloroform solution.

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3625

J. Albert, J. Granell et al.

FULL PAPER

3.80 mmol) was gently heated at reflux in absolute ethanol (40 mL)

for approximately 5 h. After this period, the slightly pink solution

was concentrated to a final volume of around 1 mL by rotary evap-

oration. The oily product was then refrigerated overnight to pro-

mote precipitation. The salmon-coloured precipitate was filtered

12), the order of stabilization of the trans-N,L stereoisomer

is OAcϾClϾBrϾI, that is, it increases with the hardness

of the anionic X ligand. The solvent (acetone or chloro-

form) seems to have little influence on the difference be-

tween the absolute Gibbs free energies of the cis and trans

isomers, except for the combination OAc and py (entry 1)

in which the acetone solvent seems to favour the cis isomer

more than chloroform does.

off and dried in air (1051 mg, 99% yield). IR (KBr): ν = 1645

˜

(CH=N st) cm^–1. ¹H NMR (400 MHz, CDCl₃, 298 K): δ = 8.26 (s,

1 H, CH=N), 7.74–7.72 (m, 2 H, 1-H), 7.42–7.40 (m, 3 H, 2-H, 3-

3

H), 7.28 (d, J_HH= 8.0 Hz, 2 H, 12-H), 7.08 (t, J_HH= 8.0 Hz, 1

3

4

Interestingly, despite the simplicity of these models, the

H, 13-H), 3.84 (td, J_HH= 7.7, J_HH= 1.1 Hz, 2 H, 8-H), 3.34 (t,

calculations predict quite well the extreme situations found ³J_HH= 7.7 Hz, 2 H, 9-H) ppm. ¹³C{¹H} NMR (101 MHz, CDCl₃,

298 K): δ = 161.7 (s, CH=N), 136.2 (s, C-6), 135.8 (s, C-11), 135.6

(s, C-10), 130.6 (s, C-3), 128.5 (s, C-2), 128.2 (s, overlapped, C-1 +

C-12), 127.9 (s, C-13), 59.2 (s, C-8), 32.9 (s, C-9) ppm. MS

(MALDI-TOF, +, DHB): calcd. for [M + H]⁺278.0; found 278.2.

C₁₅H₁₃Cl₂N (278.18): calcd. C 64.76, H 4.71, N 5.04; found C

64.26, H 4.76, N 5.23.

experimentally. Thus, if L is PH₃, independently of the an-

ionic X ligand (OAc, Cl, Br or I), the favoured stereoisomer

is the trans-N,P isomer, which is the result observed experi-

mentally. Thus, compounds of the type [Pd(C-N)(X)(mono-

phosphane)] (X = OAc, Cl, Br or I) adopt a trans-N,P

stereochemistry (see, for instance, ref.^{[6e,7–13,23–25]}). On the

other hand, the combination X = Br or I and L = py fav-

ours the cis isomer (entries 7 and 10), but can give rise ex-

perimentally to the trans-N,N isomer,^[25]mixtures of trans-

N,N and cis-N,N isomers or only the cis-N,N isomer.^[33]

Furthermore, the combination Cl and py (entry 4), accord-

ing to theoretical calculations, favours the trans-N,N isomer,

which is the result most often observed experimentally (see,

Preparation of 2: A Schlenk tube was charged with palladium(II)

acetate (509 mg, 2.27 mmol) and (E)-N-benzylidene-2-(2,6-dichlo-

rophenyl)ethanamine (635 mg, 2.28 mmol). An evacuation/nitrogen

backfill cycle was applied three times. Then glacial acetic acid

(35 mL) was added to suspend the solids. The resulting mixture

was heated at 60 °C for 5 h whilst stirring and subsequently concen-

trated to dryness. Ethanol (5 mL) was next poured into the Schlenk

tube and concentrated under vacuum to efficiently remove the re-

for instance, ref.^[23a,24a]), although there are some exceptions sidual acetic acid. The crude was purified by silica gel chromatog-

that give rise to the cis-N,N isomer.^[31]

Finally, it should be noted that our computational stud-

ies failed to reproduce the relative stability of the cis and

trans isomers for the combinations OAc/pyridine (entry 1)

and OAc/NH₃(entry 2) as they favour the cis-N,N isomer,

but compounds of formula [Pd(C-N)(OAc)(L)] with L =

raphy eluting with 100:1 to 100:4 chloroform/methanol. The col-

oured eluted band was concentrated to yield an orange resin. A

small amount of diethyl ether (2 mL) was then added to the flask.

The mixture was allowed to cool for 10 min to ensure complete

precipitation of the product. The deep-yellow solid obtained was

collected by suction filtration and air-dried (801 mg, 80% yield).

An additional crop may be obtained from the ether mother liquor.

pyridine or monoamine adopt a trans-N,L stereochemistry

IR (KBr): ν = 1609 (CH=N st), 1568 (COO as st), 1433 (COO sym

˜

(see, for instance, ref.^[2a,24a]).

1

3

st) cm^–1. H NMR (400 MHz, CDCl₃, 298 K): δ = 7.24 (d, J_HH

=

8.0 Hz, 2 H, 12-H), 7.12 (s, 1 H, CH=N), 7.09–7.05 (m, partially

3

overlapped, 1 H, 13-H), 7.06 (d, J_HH= 8.3 Hz, partially over-

Experimental Section

lapped, 1 H, 2-H), 6.96–6.90 (m, 3 H, 3-H, 4-H, 5-H), 3.49–3.42

(m, 2 H, 8-H, 9-H), 3.14–3.05 (m, 1 H, 9-H), 2.71–2.62 (m, 1 H,

8-H), 2.20 (s, 3 H, CH₃) ppm. ¹³C{¹H} NMR (101 MHz, CDCl₃,

298 K): δ = 181.3 (s, COO), 172.3 (s, CH=N), 155.4 (s, C-1), 145.6

(s, C-6), 135.7 (s, C-11), 134.6 (s, C-10), 132.1 (s, C-2), 129.1 (s, C-

5), 128.2 (s, C-13), 128.1 (s, C-12), 126.3 (s, C-3), 123.7 (s, C-4),

57.0 (s, C-8), 31.9 (s, C-9), 24.6 (s, CH₃) ppm. MS (MALDI-TOF,

Instruments and Reagents: NMR spectra were recorded with the

following spectrometers: a Varian Inova 500, a Varian Mercury

400, a Varian Unity 300, a Varian Inova 300 or a Bruker DRX

250. Chemical shifts (in ppm) were measured relative to SiMe₄for

¹H, to residual solvent peaks for ¹³C and to 85% H₃PO₄for ³¹P.

Shifts are reported as δ and coupling constants are expressed in

Hz. CHN microanalyses were performed with a Carlo–Erba EA

1108 instrument. IR spectra were collected with a Thermo Nicolet

5700 and Nicolet Avatar 300 FT-IR spectrometers using KBr discs.

Far-IR spectra were recorded with a Bomem DA3 FT-IR instru-

ment using polyethylene (PE) pellets. MALDI-TOF(+) mass spec-

tra were registered with a VOYAGER-DE-RP spectrometer using

dithranol (DTH), 2,5-dihydroxybenzoic acid (DHB) or trans-2-[3-

(4-tert-butylphenyl)-2-methyl-2-propenylidene]malononitrile

(DCTB) as matrix. ESI(+) mass spectra were acquired with a LC/

MSD-TOF mass spectrometer using 1:1 H₂O/CH₃CN as eluent.

Abbreviations used for fragments in the mass spectra are as follows:

L indicates the metallated ligand (E)-N-benzylidene-2-(2,6-dichlo-

rophenyl)ethanamine, NN expresses the corresponding [N,N] bi-

dentate Lewis base (1,3-diamino-2-propanol or 4,4Ј-bipyridine)

and PP refers to the corresponding diphosphane [1,2-bis(diphenyl-

phosphanyl)ethane or trans-1,2-bis(diphenylphosphanyl)ethylene].

All chemicals were of commercial grade and used as received.

+, DTH): calcd. for [M

–

OAc]⁺822.9; found 822.4.

C₃₄H₃₀Cl₄N₂O₄Pd₂(885.23): calcd. C 46.13, H 3.42, N 3.16; found

C 46.63, H 3.53, N 3.13.

Preparation of 3: An excess of lithium chloride (79 mg, 1.86 mmol)

was added to an orange solution of 2 (266 mg, 0.30 mmol) in ace-

tone (50 mL). The reaction mixture was stirred at room tempera-

ture for 1 d. The crude was then concentrated to dryness. Upon

addition of diethyl ether (5 mL) a pale-yellow precipitate appeared,

which was filtered off and placed in a flask. Deionised water

(15 mL) was added and the resulting suspension stirred vigorously

overnight. After this time, the solid was collected by filtration and

washed exhaustively with further portions of water (5ϫ5 mL). The

salt-free product was next transferred to a flask along with acetone

(20 mL). The solvent was removed under reduced pressure and di-

ethyl ether (5 mL) was added to yield the required product as a

pale-yellow powder (222 mg, 88% yield). IR (KBr): ν = 1609

˜

(CH=N st) cm^–1. Far-IR (PE): ν = 296 ([Pd–Cl

]

st), 264

˜

transN bridge

1

Preparation of 1: A mixture of benzaldehyde (403 mg, 386 μL,

3.80 mmol) and 2,6-dichlorophenethylamine (723 mg, 553 μL,

([Pd–Cl_{transC bridge}

]

st) cm^–1. H NMR (400 MHz, CDCl₃, 298 K): δ

= 7.57 (br. s, 0.56 H, CH=N), 7.48 (br. s, 0.44 H, CH=N), 7.43

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Eur. J. Inorg. Chem. 2011, 3617–3631

Cyclopalladated N-Benzylidene-2-(dichlorophenyl)ethanamines

(dd, J_HH= 7.6, J_HH= 1.2 Hz, 1 H, 2-H or 5-H), 7.30–7.26 (m, ³J_HH= 7.9 Hz, 6 H, o-C₆H₅), 7.71 (s, 1 H, CH=N), 7.46–7.34 (m,

3

4

obscured by residual solvent peak, 2 H, 12-H), 7.13–6.99 (m, 4 H,

9 H, m-C₆H₅+ p-C₆H₅), 7.26 (d, ³J_HH= 7.9 Hz, 2 H, 12-H), 7.12–

7.06 (m, 2 H, 5-H, 13-H), 6.83 (td, J_HH= 7.3, J_HH= 0.9 Hz, 1

3

4

2-H or 5-H, 3-H, 4-H, 13-H), 3.93 (t, J_HH= 6.9 Hz, 2 H, 8-H),

3

4

3.54 (t, J_HH= 6.9 Hz, 2 H, 9-H) ppm. The poor solubility of 3 in

H, 4-H), 6.51 (td, J_HH= 7.6, J_HH= 1.5 Hz, 1 H, 3-H), 6.41 (d,

3

common deuteriated solvents precluded the acquisition of mean-

ingful carbon NMR spectroscopic data. MS (MALDI-TOF, +,

DHB): calcd. for [M – Cl]⁺798.8; found 799.0. C₃₀H₂₄Cl₆N₂Pd₂

(838.05): calcd. C 42.99, H 2.89, N 3.34; found C 42.22, H 3.11, N

3.24.

³J_HH= 7.8 Hz, 1 H, 2-H), 3.91 (t, J_HH= 6.6 Hz, 2 H, 8-H), 3.48

3

(t, J_HH= 6.6 Hz, 2 H, 9-H), 1.32 (s, 3 H, CH₃-COO) ppm.

¹³C{¹H} NMR (101 MHz, CDCl₃, 298 K): δ = 177.0 (s, COO),

3

2

174.7 (d, J_CP= 3.6 Hz, CH=N), 155.7 (d, J_CP= 4.0 Hz, C-1),

148.0 (s, C-6), 138.6 (d, ³J_CP= 10.5 Hz, C-2), 136.0 (s, C-11), 135.5

2

1

(d, J_CP= 12.2 Hz, o-C₆H₅), 135.0 (s, C-10), 130.6 (d, J_CP

49.0 Hz, i-C₆H₅), 130.5 (s, p-C₆H₅), 129.6 (d, J_CP= 5.0 Hz, C-3),

128.2 (s, overlapped, C-12, C-13), 128.1 (d, J_CP= 10.9 Hz, m-

=

Preparation of 4 and 5 in CDCl₃/[D₅]py Solution: An orange solu-

tion or a suspension formed by mixing the dimeric cyclopalladated

compound 2 or 3 (10 mg), respectively, in CDCl₃(0.7 mL) was

treated with 2 drops of deuteriated pyridine and shaken for a few

seconds. The formation of a yellow or colourless solution (com-

pound 4 or 5, respectively) indicated the quantitative formation of

the corresponding monomeric cyclopalladated derivative. Charac-

4

3

C₆H₅), 127.8 (s, C-5), 123.6 (s, C-4), 56.5 (s, C-8), 31.9 (s, C-9),

23.5 (s, CH₃) ppm. ³¹P{¹H} NMR (101 MHz, CDCl₃, 298 K): δ =

40.0 (s) ppm. MS (MALDI-TOF, +, DCTB): calcd. for [M –

OAc]⁺644.0; found 644.3. C₃₅H₃₀Cl₂NO₂PPd (704.91): calcd. C

59.63, H 4.29, N 1.99; found C 59.60, H 4.45, N 2.00.

terization data for compound 4: ¹H NMR (400 MHz, CDCl₃

+

3

[D₅]py, 298 K): δ = 7.70 (s, 1 H, CH=N), 7.29 (d, J_HH= 8.0 Hz,

Preparation of 7: Chlorido-bridged dimer 3 (191 mg, 0.23 mmol)

3

4

2 H, 12-H), 7.18 (dd, J_HH= 7.4, J_HH= 1.4 Hz, 1 H, 5-H), 7.11 and PPh₃(119 mg, 0.45 mmol) were combined in acetone (50 mL)

3

(t, J_HH= 8.0 Hz, 1 H, 13-H), 6.99 (t, J_HH= 7.4 Hz, 1 H, 4-H),

and stirred for 48 h at room temperature. The yellow filtrate ob-

tained was then concentrated to dryness, redissolved in a minimum

amount of 100:0.5 chloroform/methanol and loaded onto a

chromatography column packed with silica. The eluent polarity was

gradually increased from 100:0.5 to 100:2 and 100:5. The coloured

3

4

3

6.90 (td, J_HH= 7.5, J_HH= 1.4 Hz, 1 H, 3-H), 6.20 (d, J_HH

=

3

7.5 Hz, 1 H, 2-H), 3.82 (t, J_HH= 7.2 Hz, 2 H, 8-H), 3.51 (t, J_HH

= 7.3 Hz, 2 H, 9-H), 1.96 (s, 3 H, CH₃) ppm. ¹³C{¹H} NMR

(101 MHz, CDCl₃+ [D₅]py, 298 K): δ = 178.1 (s, COO), 175.0 (s,

CH=N), 156.6 (s, C-1), 146.7 (s, C-6), 135.8 (s, C-11), 134.7 (s, C- eluted band was concentrated to dryness with a rotary evaporator

10), 132.6 (s, C-2), 130.0 (s, C-3), 128.3 (s, C-13), 128.2 (s, C-12), to afford a yellowish solid after the addition of diethyl ether (5 mL).

127.3 (s, C-5), 124.1 (s, C-4), 57.4 (s, C-8), 32.1 (s, C-9), 24.8 (s,

CH₃) ppm. Owing to the rapid exchange between the coordinated

and free [D₅]pyridine, carbon NMR signals of the coordinated

[D₅]pyridine were not observed. Characterization data for com-

The product was filtered off and air-dried (230 mg, 74% yield). IR

(KBr): ν = 1624 (CH=N st), 1096 (q X-sensitive mode of coordi-

˜

nated PPh ) cm^–1. Far-IR (PE): ν = 300 ([Pd–Cl]_terminalst) cm^–1. ¹H

˜

3

NMR (400 MHz, CDCl₃, 298 K): δ = 7.76 (ddd, ³J_HP= 11.6, ³J_HH

1

4

pound 5: H NMR (300 MHz, CDCl₃+ [D₅]py, 298 K): δ = 7.43

= 8.3, J_HH= 1.2 Hz, 6 H, o-C₆H₅), 7.56 (d, J_HP= 7.8 Hz, 1 H,

CH=N), 7.46–7.42 (m, 3 H, p-C₆H₅), 7.39–7.34 (m, 6 H, m-C₆H₅),

3

(s, 1 H, CH=N), 7.26 (d, J_HH= 7.4 Hz, partially obscured by

residual solvent peak, 2 H, 12-H), 7.10 (d, ³J_HH= 7.4 Hz, partially

overlapped, 1 H, 5-H), 7.09 (t, ³J_HH= 7.4 Hz, partially overlapped,

7.26 (d, ³J_HH= 8.0 Hz, 2 H, 12-H), 7.08 (t, J_HH= 8.0 Hz, slightly

3

4

overlapped, 1 H, 13-H), 7.05 (dd, J_HH= 7.4, J_HH= 1.5 Hz,

3

4

1 H, 13-H), 6.99 (td, J_HH= 7.3, J_HH= 1.0 Hz, 1 H, 4-H), 6.92

slightly overlapped, 1 H, 5-H), 6.83 (td, ³J_HH= 7.4, ⁴J_HH= 0.8 Hz,

3

4

(t, J_HH= 7.4 Hz, 1 H, 3-H), 6.16 (d, J_HH= 7.2 Hz, 1 H, 2-H), 1 H, 4-H), 6.51 (td, J_HH= 7.4, J_HH= 1.1 Hz, 1 H, 3-H), 6.39

3

4

4.17 (t, J_HH= 6.2 Hz, 2 H, 8-H), 3.63 (t, J_HH= 6.3 Hz, 2 H, 9-

(app. t, J_HH= J_HP= 7.0 Hz, 1 H, 2-H), 4.27 (m, 2 H, 8-H), 3.58

H) ppm. ¹³C{¹H} NMR (101 MHz, CDCl₃+ [D₅]py, 298 K): δ =

(t, J_HH= 6.3 Hz, 2 H, 9-H) ppm. ¹H{³¹P} NMR (300 MHz,

3

175.0 (s, CH=N), 158.3 (s, C-1), 146.6 (s, C-6), 136.1 (s, C-11), CDCl₃, 298 K): δ = 7.78–7.74 (m, 6 H, o-C₆H₅), 7.56 (s, 1 H,

3

4

134.8 (s, C-10), 131.7 (s, C-2), 130.2 (s, C-3), 128.3 (s, C-13), 128.2

CH=N), 7.43 (tt, J_HH= 7.2, J_HH= 1.5 Hz, 3 H, p-C₆H₅), 7.39–

3

(s, C-12), 127.1 (s, C-5), 124.2 (s, C-4), 58.4 (s, C-8), 32.1 (s, C- 7.33 (m, 6 H, m-C₆H₅), 7.26 (d, J_HH= 8.1 Hz, 2 H, 12-H), 7.10–

3

4

9) ppm. Owing to the rapid exchange between the coordinated and

free [D₅]pyridine, carbon NMR signals of the coordinated [D₅]pyr-

idine were not observed.

7.03 (m, 2 H, 5-H, 13-H), 6.83 (td, J_HH= 7.2, J_HH= 0.9 Hz, 1

3

4

H, 4-H), 6.51 (td, J_HH= 7.5, J_HH= 1.6 Hz, 1 H, 3-H), 6.40 (d,

³J_HH= 7.8 Hz, 1 H, 2-H), 4.28 (t, ³J_HH= 6.2 Hz, 2 H, 8-H), 3.58 (t,

³J_HH= 6.3 Hz, 2 H, 9-H) ppm. ¹³C{¹H} NMR (101 MHz, CDCl₃,

Preparation of 6: A deep-yellow solution of acetato-bridged dimer

2 (56 mg, 0.06 mmol) in acetone (20 mL) was treated at room tem-

perature with a stoichiometric amount of PPh₃(33 mg, 0.13 mmol).

Approximately 1 h later, the solution began to lighten. The reaction

mixture was stirred for an additional hour, after which time vola-

tiles were evaporated under reduced pressure. Trituration with di-

ethyl ether (ca. 4 mL) rendered an extremely pale-yellow solid,

3

298 K): δ = 175.0 (d, J_CP= 3.1 Hz, CH=N), 158.4 (s, C-1), 147.9

3

(s, C-6), 138.1 (d, J_CP= 10.3 Hz, C-2), 136.2 (s, C-11), 135.5 (d,

²J_CP= 12.0 Hz, o-C₆H₅), 135.3 (s, C-10), 131.2 (d, J_CP= 50.7 Hz,

1

4

i-C₆H₅), 130.7 (d, J_CP= 2.4 Hz, p-C₆H₅), 129.7 (d, ⁴J_CP= 5.1 Hz,

3

C-3), 128.2 (s, C-12), 128.1 (s, C-13), 128.0 (d, J_CP= 10.9 Hz, m-

C₆H₅), 127.6 (s, C-5), 123.7 (s, C-4), 57.5 (s, C-8), 32.4 (s, C-9) ppm.

³¹P{¹H} NMR (101 MHz, CDCl₃, 298 K): δ = 42.0 (s) ppm. MS

(MALDI-TOF, +, DHB): calcd. for [M – Cl]⁺644.0; found 644.1;

calcd. for [M – Cl – Pd]⁺538.1; found 538.1. C₃₃H₂₇Cl₃NPPd

(681.32): calcd. C 58.17, H 3.99, N 2.06; found C 58.41, H 4.12, N

2.09.

which was filtered and air-dried (74 mg, 83% yield). IR (KBr): ν =

˜

1620 (CH=N st), 1601 (C=O st), 1369 (C–O st), 1096 (q X-sensitive

mode of coordinated PPh₃) cm^–1. ¹H NMR (400 MHz, CDCl₃,

4

298 K): δ = 7.83–7.78 (m, 6 H, o-C₆H₅), 7.71 (d, J_HP= 7.4 Hz, 1

3

H, CH=N), 7.45–7.41 (m, 3 H, p-C₆H₅), 7.37 (td, J_HH= 7.3, ⁴J_HP

3

= 1.8 Hz, 6 H, m-C₆H₅), 7.26 (d, J_HH= 8.0 Hz, 2 H, 12-H), 7.09 Preparation of 8: 1,2-Bis(diphenylphosphanyl)ethane (44 mg,

3

(t, J_HH= 8.2 Hz, partially overlapped, 1 H, 13-H), 7.09 (dd, ³J_HH

0.11 mmol) was added to a stirred suspension of chlorido-bridged

dimer 3 (90 mg, 0.11 mmol) in chloroform (30 mL) under nitrogen.

= 7.3 Hz, 1 H, 4-H), 6.51 (td, J_HH= 7.5, J_HH= 1.2 Hz, 1 H, 3- The mixture was allowed to stand at room temperature for 6 h.

= 7.3, ⁴J_HH= 1.3 Hz, partially overlapped, 1 H, 5-H), 6.83 (t, ³J_HH

3

4

3

4

H), 6.41 (dd, J_HH= 7.4, J_HP= 5.4 Hz, 1 H, 2-H), 3.93–3.89 (m,

After this period, the resulting light-yellow solution was filtered

through a 2-cm-thick pad of silica and washed through with ace-

3

2 H, 8-H), 3.48 (t, J_HH= 6.6 Hz, 2 H, 9-H), 1.33 (s, 3 H,

CH₃) ppm. H{³¹P} NMR (300 MHz, CDCl₃, 298 K): δ = 7.80 (d, tone and then dichloromethane. After removal of the solvent, the

1

Eur. J. Inorg. Chem. 2011, 3617–3631

www.eurjic.org

3627

J. Albert, J. Granell et al.

FULL PAPER

desired product precipitated on addition of diethyl ether (5 mL).

The pale-yellow solid obtained was isolated by filtration and air-

m-C₆H₅), 129.0 (s, C-13), 128.9 (s, C-12), 128.54 (d, ¹J_CP= 50.0 Hz,

i-C₆H₅), 128.4 (s, C-5), 124.5 (s, C-4), 57.4 (s, C-8), 32.7 (s, C-

9) ppm. ³¹P{¹H} NMR (101 MHz, CH₂Cl₂, 298 K): δ = 34.3

(s) ppm. MS (MALDI-TOF, +, DHB): calcd. for [M – Cl]⁺1195.0;

found 1195.2; calcd. for [Pd(L)(PP)]⁺778.0; found 778.2.

C₅₆H₄₆Cl₆N₂P₂Pd₂(1234.46): calcd. C 54.48, H 3.76, N 2.27; found

C 54.46, H 3.82, N 2.22.

dried (102 mg, 77% yield). IR (KBr): ν = 1626 (CH=N st), 1101

˜

(q X-sensitive mode of coordinated PPh₂CH₂CH₂PPh₂) cm^–1. Far-

IR (PE): ν = 296 ([Pd–Cl]

st) cm^–1. ¹H NMR (400 MHz,

˜

terminal

CDCl₃, 298 K): δ = 8.01–7.96 (m, 4 H, o-C₆H₅), 7.54–7.52 (m, 1

3

H, CH=N), 7.41–7.33 (m, 6 H, m-C₆H₅, p-C₆H₅), 7.25 (d, J_HH

=

8.0 Hz, partially obscured by residual solvent peak, 2 H, 12-H),

Preparation of 10: Compound 10 was synthesized under nitrogen

by adding 4,4Ј-bipyridine (0.0200 g, 0.13 mmol) to a suspension of

chlorido-bridged dimer 3 (106 mg, 0.13 mmol) in chloroform

(30 mL). After 3 h of stirring at room temperature, the resulting

yellow solution was concentrated under reduced pressure. Upon

addition of diethyl ether (ca. 5 mL) a yellow solid precipitated,

which was recovered by filtration, thoroughly washed with toluene

(5ϫ 1 mL) and acetone (3ϫ 0.5 mL) and finally dried in vacuo

3

7.08 (dd, J_HH= 8.4, J_HH= 7.7 Hz, 1 H, 13-H), 6.99 (dd, J_HH

=

7.4, ⁴J_HH= 1.4 Hz, 1 H, 5-H), 6.78 (td, ³J_HH= 7.4, ⁴J_HH= 0.7 Hz,

3

4

1 H, 4-H), 6.49 (td, J_HH= 7.6, J_HH= 1.4 Hz, 1 H, 3-H), 6.33–

3

6.30 (m, 1 H, 2-H), 4.25 (br. s, 2 H, 8-H), 3.58 (t, J_HH= 6.3 Hz,

2

2 H, 9-H), 2.97 (d, J_HP= 2.1 Hz, 2 H, CH₂–P) ppm. ¹H{³¹P}

3

4

NMR (300 MHz, CDCl₃, 298 K): δ = 7.99 (dd, J_HH= 7.9, J_HH

= 1.6 Hz, 4 H, o-C₆H₅), 7.53 (s, 1 H, CH=N), 7.42–7.31 (m, 6 H,

3

m-C₆H₅, p-C₆H₅), 7.25 (d, J_HH= 8.0 Hz, 2 H, 12-H), 7.08 (dd,

(95 mg, 75% yield). IR (KBr): ν = 1608 (CH=N st and st equiva-

˜

³J_HH= 8.6, J_HH= 7.4 Hz, 1 H, 13-H), 6.99 (dd, J_HH= 7.4, J_HH

3

4

lent to the ν₄stretching of pyridine for 4,4Ј-bipyridine) cm^–1. Far-

3

4

= 1.5 Hz, 1 H, 5-H), 6.78 (td, J_HH= 7.4, J_HH= 1.0 Hz, 1 H, 4-

H), 6.49 (td, J_HH= 7.6, J_HH= 1.6 Hz, 1 H, 3-H), 6.32 (d, J_HH

IR (PE): ν = 309 ([Pd–Cl]

st) cm^–1. ¹H NMR (400 MHz,

˜

3

4

3

terminal

3

CDCl₃, 298 K): δ = 9.11 (d, J_HH= 6.5 Hz, 2 H, 14-H), 7.72 (d,

3

= 7.9 Hz, 1 H, 2-H), 4.26 (t, J_HH= 6.3 Hz, 2 H, 8-H), 3.58 (t,

³J_HH= 6.4 Hz, 2 H, 15-H), 7.45 (s, 1 H, CH=N), 7.23 (d, J_HH

=

3

³J_HH= 6.3 Hz, 2 H, 9-H), 2.97 (s, 2 H, CH₂-P) ppm. ¹³C{¹H}

NMR (101 MHz, CDCl₃, 298 K): δ = 174.7 (br. s, CH=N), 158.5

8.0 Hz, 2 H, 12-H), 7.13–7.09 (m, 2 H, 5-H, 13-H), 7.02 (t, ³J_HH

3

4

7.4 Hz, slightly overlapped, 1 H, 4-H), 6.97 (td, J_HH= 7.6, J_HH

2

(d, J_CP= 2.3 Hz, C-1), 147.7 (s, C-6), 137.7–137.6 (m, C-2), 136.2

3

= 1.4 Hz, slightly overlapped, 1 H, 3-H), 6.26 (d, J_HH= 7.4 Hz, 1

(s, C-11), 135.2 (s, C-10), 134.9 (app. t, J_CP= 6.2 Hz, o-C₆H₅), 130.8

(s, p-C₆H₅), 129.9–129.8 (m, C-3), 128.5–128.2 (m, overlapped, C-

12, C-13, m-C₆H₅), 127.5 (s, C-5), 123.6 (s, C-4), 56.7 (s, C-8), 32.3

(s, C-9), 25.9 (br. s, CH₂-P) ppm. The carbon signal of i-C₆H₅could

not be identified owing to its weak intensity. ³¹P{¹H} NMR

(101 MHz, CDCl₃, 298 K): δ = 34.7 (s) ppm. MS (MALDI-TOF,

+, DHB): calcd. for [M – Cl]⁺1197.0; found 1196.8; calcd. for

[Pd(L)(PP)]⁺780.1; found 780.2. C₅₆H₄₈Cl₆N₂P₂Pd₂(1236.47):

calcd. C 54.40, H 3.91, N 2.26; found C 53.82, H 3.64, N 2.35.

3

H, 2-H), 4.18 (t, J_HH= 6.3 Hz, 2 H, 8-H), 3.63 (t, J_HH= 6.4 Hz,

2 H, 9-H) ppm. ¹³C{¹H} NMR (101 MHz, CDCl₃, 298 K): δ =

175.2 (s, CH=N), 158.3 (s, C-1), 154.2 (s, C-14), 146.6 (s, C-6),

145.9 (s, C-16), 136.1 (s, C-11), 134.7 (s, C-10), 131.6 (s, C-2), 130.4

(s, C-3), 128.4 (s, C-13), 128.3 (s, C-12), 127.3 (s, C-5), 124.5 (s, C-

4), 123.0 (s, C-15), 58.6 (s, C-8), 32.1 (s, C-9) ppm. MS (ESI, +,

H₂O/CH₃CN, 1:1): calcd. for [M – Cl + CH₃CN]⁺995.9; found

995.9; calcd. for [M – Cl]⁺954.9; found 954.9; calcd. for

[Pd(L)(NN)]⁺538.0; found 538.0; calcd. for [Pd(L)(NN)-

(CH₃CN)]⁺579.0; found 579.0; calcd. for [Pd(L)(CH₃CN)]⁺423.0;

found 423.0. C₄₀H₃₂Cl₆N₄Pd₂(994.24): calcd. C 48.32, H 3.24, N

5.64; found C 47.60, H 3.25, N 5.58.

Preparation of 9: A Schlenk tube was loaded with chlorido-bridged

dimer 3 (89 mg, 0.11 mmol) and then evacuated and backfilled with

nitrogen (three times). Acetone (30 mL) was then added to suspend

the solid. trans-1,2-Bis(diphenylphosphanyl)ethylene (42 mg,

0.10 mmol) was the added to give a yellow solution. After 3 h of

stirring, the solvent was removed under reduced pressure. Crude

mixture was then subjected to column chromatography (SiO₂) elut-

ing with 100:2 to 100:5 dichloromethane/methanol to yield the

Preparation of 11: A suspension of 3 (0.0804 g, 0.096 mmol) in

chloroform (30 mL) was treated with 2,2Ј-(ethylenedioxy)bis(ethyl-

amine) (0.0142 g, 14.00 μL, 0.096 mmol). The reaction mixture was

stirred at room temperature for around 3 h under nitrogen. The

resulting yellow solution was concentrated to dryness. The subse-

quent addition of diethyl ether (5 mL) led to a light-yellow solid,

which was filtered off and dried under vacuum (79 mg, 83% yield).

product as a pale-yellow solid (117 mg, 89% yield). IR (KBr): ν =

˜

1624 (CH=N st), 1099 (q X-sensitive mode of coordinated trans-

Ph PCH=CHPPh ) cm^–1. Far-IR (PE): ν = 302 ([Pd–Cl]

˜

2

terminal

IR (KBr): ν = 3321 (NH as st), 3263 (NH sym st), 1613 (CH=N

˜

2

st) cm^–1. H NMR (400 MHz, CD₂Cl₂, 298 K): δ = 7.83–7.78 (m,

1

st) cm^–1. Far-IR (PE): ν = 296 ([Pd–Cl]

st) cm^–1. ¹H NMR

˜

terminal

3

4 H, o-C₆H₅), 7.55–7.53 (m, 1 H, CH=N), 7.48 (t, J_HH= 7.4 Hz,

(400 MHz, CDCl₃, 298 K): δ = 7.29 (s, 1 H, CH=N), 7.23 (d, ³J_HH

3

2 H, p-C₆H₅), 7.40 (t, J_HH= 7.3 Hz, 4 H, m-C₆H₅), 7.27 (d, J_HH

= 8.0 Hz, 2 H, 12-H), 7.11–7.05 (m, 3 H, 3-H, 5-H, 13-H), 7.00

3

= 7.9 Hz, 2 H, 12-H), 7.12 (dd, J_HH= 8.5, J_HH= 7.5 Hz, 1 H,

3

(app. t, J_HH= 7.1 Hz, 2 H, 2-H, 4-H), 3.97 (t, J_HH= 6.4 Hz, 2

3

4

13-H), 7.06 (dd, J_HH= 7.4, J_HH= 1.4 Hz, partially overlapped,

1 H, 5-H), 7.01 (app. t, J_HP= 20.3 Hz, partially overlapped, 1 H,

3

H, 8-H), 3.77 (t, J_HH= 4.6 Hz, 2 H, 15-H), 3.71 (s, 2 H, 16-H),

3

3.50 (t, J_HH= 6.5 Hz, 2 H, 9-H), 3.42-3.39 (br. t, 2 H, NH₂),

3

4

=CH–P), 6.85 (td, J_HH= 7.4, J_HH= 0.8 Hz, 1 H, 4-H), 6.53 (td,

3.31–3.26 (m, 2 H, 14-H) ppm. ¹³C{¹H} NMR (101 MHz, CDCl₃,

298 K): δ = 174.2 (s, CH=N), 155.9 (s, C-1), 147.0 (s, C-6), 136.0

(s, C-11), 134.8 (s, C-10), 130.1 (s, overlapped, C-2, C-3), 128.3 (s,

C-13), 128.2 (s, C-12), 127.4 (s, C-5), 124.4 (s, C-4), 70.7 (s, C-15),

70.4 (s, C-16), 58.5 (s, C-8), 45.6 (s, C-14), 32.0 (s, C-9) ppm. MS

(ESI, +, H₂O/CH₃CN, 1:1): calcd. for [M – Cl]⁺947.0; found 947.0;

calcd. for [Pd(L)(CH₃CN)₂]⁺464.0; found 464.0; calcd. for

[Pd(L)(CH₃CN)]⁺423.0; found 423.0; calcd. for [Pd(L)]⁺381.9;

found 381.9; C₃₆H₄₀Cl₆N₄O₂Pd₂(986.26): calcd. C 43.84, H 4.09,

N 5.68; found C 43.62, H 3.89, N 5.51.

³J_HH= 7.6, J_HH= 1.5 Hz, 1 H, 3-H), 6.40–6.36 (m, 1 H, 2-H),

4

3

4.24 (br. s, 2 H, 8-H), 3.56 (t, J_HH= 6.1 Hz, 2 H, 9-H) ppm.

¹H{³¹P} NMR (300 MHz, CDCl₃, 298 K): δ = 7.90 (d, J_HH

=

3

8.1 Hz, 4 H, o-C₆H₅), 7.50 (s, 1 H, CH=N), 7.43–7.34 (m, 6 H, m-

3

C₆H₅, p-C₆H₅), 7.24 (d, J_HH= 7.8 Hz, 2 H, 12-H), 7.11–7.01 (m,

3

2 H, 5-H, 13-H), 6.89 (s, 1 H, =CH–P), 6.82 (t, J_HH= 7.4 Hz, 1

3

H, 4-H), 6.52 (t, J_HH= 7.5 Hz, 1 H, 3-H), 6.40 (d, J_HH= 7.7 Hz,

1 H, 2-H), 4.29 (t, ³J_HH= 6.0 Hz, 2 H, 8-H), 3.59 (t, ³J_HH= 6.0 Hz,

2 H, 9-H) ppm. ¹³C{¹H} NMR (101 MHz, CD₂Cl₂, 298 K): δ =

3

175.7 (d, J_CP= 1.8 Hz, CH=N), 158.8 (s, C-1), 148.6 (s, C-6),

140.3-139.9 (m, =CH-P), 138.2 (app. t, J_CP= 5.2 Hz, C-2), 136.7

Preparation of 12: A Schlenk tube was loaded with dimer 3 (75 mg,

(s, C-11), 135.8 (app. t, J_CP= 6.3 Hz, o-C₆H₅), 135.6 (s, C-10), 0.09 mmol) and then evacuated and backfilled with nitrogen (three

131.8 (s, p-C₆H₅), 130.5–130.4 (m, C-3), 129.1 (app. t, J_CP= 5.5 Hz, times). Chloroform (24 mL) was then added to suspend the solid.

3628

www.eurjic.org

Eur. J. Inorg. Chem. 2011, 3617–3631

Cyclopalladated N-Benzylidene-2-(dichlorophenyl)ethanamines

A chloroform solution of 1,3-diamino-2-propanol (0.09 m, 1 mL)

was then added and the crude was stirred for 4 h at room tempera-

ture. After this period, the solvent was removed in vacuo and di-

ethyl ether (5 mL) was added to furnish the desired product as a

yellow solid, which was recovered by filtration (75 mg, 90% yield).

The sample must be stored under nitrogen and kept under refriger-

hybrid functional.^[39]The basis set was chosen as follows: for Pd,

Br and I LANL2DZ was used^[40]with an effective core potential

to replace the 36 innermost electrons of Pd and I and the 18 inner-

most electrons of Br; a polarization function was added for Br and

I.^[41]For H, C, N, O, P, and Cl the 6-31G(d) basis set including

polarization functions for non-hydrogen atoms^[42]was used. Geom-

etry optimizations and frequency calculations were performed in

vacuo with no imposed symmetry restrictions. Solvent effects were

ation to avoid decomposition. IR (KBr): ν = 3385, 3295, 3236

˜

(NH and OH stretchings), 1612 (CH=N st) cm^–1. Far-IR (PE): ν =

˜

2

300 ([Pd–Cl]_terminalst) cm^–1. ¹H NMR (400 MHz, CDCl₃, 298 K): δ calculated on the pre-optimized geometries using the C-PCM

3

= 7.38 (s, 2 H, CH=N), 7.25 (d, J_HH= 8.0 Hz, partially obscured

by residual solvent peak, 4 H, 12-H), 7.15 (td, J_HH= 7.4, J_HH

model.^[43]

3

4

=

X-ray Diffraction Studies: Yellow single crystals of 2, 8·2CH₂Cl₂,

10·4CHCl₃and 11·2CH₂Cl₂were obtained by slow evaporation of

the solvent of a diethyl ether solution of 2, a dichloromethane solu-

tion of 8 and a chloroform solution of 10 and by slow diffusion of

hexanes into a CH₂Cl₂solution of 11, respectively. In each case, a

prismatic crystal was mounted on a MAR345 diffractometer with

an image plate detector. Unit cell parameters were determined from

586 reflections for 2, 171 for 8·2CH₂Cl₂, 101 for 10·4CHCl₃and 67

for 11·2CH₂Cl₂(3ϽθϽ31°) and refined by least-squares methods.

Intensities were collected with graphite-monochromatized Mo-K_α

radiation. For 2, 7898 reflections were measured in the range

2.51ՅθՅ31.62°, 6828 reflections were assumed as observed apply-

ing the condition IϾ2σ(I). For 8·2CH₂Cl₂, 15791 reflections were

measured in the range 2.79ՅθՅ32.45°, 8393 were non-equivalent

by symmetry [R_int(I) = 0.049] and 5358 were assumed as observed

applying the condition IϾ2σ(I). For 10·4CHCl₃, 15981 reflections

1.6 Hz, 2 H, 3-H), 7.11–7.00 (m, 6 H, 4-H, 5-H, 13-H), 6.93 (d,

³J_HH= 7.5 Hz, 2 H, 2-H), 5.38 (br. s, 1 H, OH), 4.72 (br. s, 1 H,

3

CH-OH), 4.05–3.94 (m, 4 H, 8-H), 3.48 (t, J_HH= 6.8 Hz, 4 H, 9-

H), 3.45–3.39 (m, slightly overlapped, 2 H, NH₂), 3.31–3.27 (br. t,

2 H, NH₂), 3.19–3.12 (m, 2 H, CH₂-NH₂), 2.97–2.89 (m, 2 H, CH₂-

NH₂) ppm. ¹³C{¹H} NMR (101 MHz, CDCl₃, 298 K, under nitro-

gen): δ = 174.3 (s, CH=N), 155.7 (s, C-1), 146.7 (s, C-6), 136.0 (s,

C-11), 134.7 (s, C-10), 130.6 (s, C-3), 130.2 (s, C-2), 128.3 (s, C-13),

128.2 (s, C-12), 127.4 (s, C-5), 124.4 (s, C-4), 70.7 (s, CH-OH), 58.3

(s, C-8), 48.6 (s, CH₂-NH₂), 32.0 (s, C-9) ppm. MS (MALDI-TOF,

+, DHB): calcd. for [Pd(L)(NN)]⁺472.0; found 472.0.

C₃₃H₃₄Cl₆N₄OPd₂(928.18): calcd. C 42.70, H 3.69, N 6.04; found

C 42.50, H 3.58, N 5.96.

Theoretical Calculations: All DFT calculations were carried out

with the Gaussian 03^[38]package of programs using the B3LYP

Table 2. Selected crystal data and structure refinement for 2, 8·2(CH₂Cl₂), 10·4(CHCl₃) and 11·2(CH₂Cl₂).

2

8·2CH₂Cl₂

10·4CHCl₃

11·2CH₂Cl₂

Formula

C₃₄H₃₀Cl₄N₂O₄Pd₂

885.20

0.15ϫ0.09ϫ0.08

203(2)

C₅₈H₅₂Cl₁₀N₂P₂Pd₂

1406.26

0.20ϫ0.10ϫ0.09

293(2)

C₄₄H₃₆Cl₁₈N₄Pd₂

1471.67

0.09ϫ0.08ϫ0.07

293(2)

C₃₈H₄₄Cl₁₀N₄O₂Pd₂

1156.07

0.09ϫ0.08ϫ0.08

293(2)

Formula mass

Crystal size [mm³]

Temperature [K]

Wavelength [Å]

Crystal system

Space group

0.71073

triclinic

¯

P1

a [Å]

b [Å]

c [Å]

α [°]

8.950(4)

12.202(4)

17.117(5)

71.41(2)

82.22(2)

83.22(2)

1749.9(11)

2

10.795(6)

11.908(5)

14.377(6)

68.62(4)

68.40(3)

65.29(3)

1511.7(12)

1

10.690(7)

10.971(4)

14.073(7)

97.06(4)

109.40(3)

104.52(3)

1468.1(13)

1

9.865(8)

11.733(7)

12.634(6)

117.09(4)

99.95(4)

103.75(5)

1196.0(16)

1

β [°]

γ [°]

Volume [Å³]

Z

Calcd. density [Mgm^–3]

Absorption coefficient [mm^–1]

F(000)

1.680

1.373

880

1.545

1.128

706

1.665

1.467

726

1.605

1.347

578

θ range for data collection [°]

Limiting indices

2.51 to 31.62

–11 Յ h Յ 10

–15 Յ k Յ 16

0 Յ l Յ 23

7898

0.0557

2.79 to 32.45

–14 Յ h Յ 16

–16 Յ k Յ 17

–21 Յ l Յ 21

15791

8393

0.0496

2.67 to 32.41

–16 Յ h Յ 16

–16 Յ k Յ 13

–17 Յ l Յ 17

15981

8639

0.0320

2.89 to 32.38

–14 Յ h Յ 14

–17 Յ k Յ 17

–18 Յ l Յ 18

13416

7132

0.0707

Reflections collected

Reflections unique

R(int)

Completeness to θ = 25.00° [%]

Absorption correction

Max. and min. transmission

Refinement method

Data / restraints / parameters

Goodness-of-fit on F²

Final R indices

87.3

93.6

93.5

93.7

empirical

0.86 and 0.84

0.87 and 0.84

0.89 and 0.87

0.91 and 0.89

full-matrix least-squares on F²

7898 / 1 / 416

1.132

R₁= 0.0444

wR₂= 0.1414

R₁= 0.0508

wR₂= 0.1444

8393 / 5 / 286

1.121

R₁= 0.0744

wR₂= 0.1607

R₁= 0.1216

wR₂= 0.1824

1.261 and –0.776

8639 / 4 / 325

0.870

R₁= 0.0399

wR₂= 0.0746

R₁= 0.0858

wR₂= 0.0822

0.381 and –0.422

7132 / 13 / 271

1.316

R₁= 0.0741

wR₂= 0.1572

R₁= 0.0811

wR₂= 0.1605

1.316 and –0.770

[IϾ2σ(I)]

R indices

(all data)

Largest diff. peak and hole [eÅ^–3] 1.108 and –0.884

Eur. J. Inorg. Chem. 2011, 3617–3631

www.eurjic.org

3629

J. Albert, J. Granell et al.

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11·2CH₂Cl₂, 13416 reflections were measured in the range 2.89Յ

θ Յ32.38°, 7132 were non-equivalent by symmetry [R_int(I) = 0.071]

and 2521 were assumed as observed applying the condition

IϾ2σ(I). Lorentzian polarization and absorption corrections were

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program.^[45]The function minimized was Σw||F_o|²–|F_c|²|², w =

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2.7466P]^–1for 8·2CH₂Cl₂, w = [σ²(I) + (0.0276P)²]^–1for 10·4CHCl₃

and w = [σ²(I) + (0.0471P)²+ 2.9985P]^–1for 11·2CH₂Cl₂, and P =

(|F_o|²+ 2|F_c|²)/3. Values of f, fЈ and fЈЈ were taken from the Inter-

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data and structure refinement for 2, 8·2CH₂Cl₂, 10·4CHCl₃and

11·2CH₂Cl₂.

[7]

CCDC-780754 (for 2), -780755 (for 8·2CH₂Cl₂), -780756 (for

10·4CHCl₃) and -780757 (for 11·2CH₂Cl₂) contain the crystallo-

graphic data for this paper. These data can be obtained free of

charge from The Cambridge Crystallographic Data Centre via

www.ccdc.cam.ac.uk/data_request/cif.

Acknowledgments

We are grateful to the Ministerio de Ciencia y Tecnología (MCYT)

for financial support (grant number CTQ2009-11501/BQU).

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Received: March 23, 2011

Published Online: July 20, 2011

Eur. J. Inorg. Chem. 2011, 3617–3631

www.eurjic.org

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Synthesis of cyclopalladated derivatives of (E)-N-Benzylidene-2-(2,6- dichlorophenyl)ethanamine and their reactivity towards monodentate and symmetric bidentate lewis bases

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