Versatility in the mode of coordination {(N), (N,O)-, (C,N)- or (C,N,O)2-} of [(η5-C5H5)Fe{(η5-C 5H4)-CH{double bond, long}N-(C6H4-2OH)] to palladium(II)

Journal of Organometallic Chemistry 692 (2007) 2402–2414

www.elsevier.com/locate/jorganchem

Versatility in the mode of coordination {(N), (N,O)^ꢀ, (C,N)^ꢀ

or (C,N,O)^2ꢀ} of [(g⁵-C₅H₅)Fe{(g⁵-C₅H₄)–CH@N–(C₆H₄-2OH)}]

to palladium(II)

a

a,

a

b

Sonia Perez , Concepcion Lopez ^*, Amparo Caubet , Xavier Solans ,

´

b

c

`

´

Merce Font-Bardıa , Martı Gich , Elies Molins

a

` `

´

Departament de Quı´mica Inorganica, Facultat de Quımica, Universitat de Barcelona, Martı i Franques 1-11, 08028 Barcelona, Spain

´

` `

Departament de Cristal.lograﬁa, Mineralogia i Diposits Minerals, Facultat de Geologia, Martı i Franques s/n. 08028 Barcelona, Spain

b

´

c

` `

Institut de Ciencia de Materials de Barcelona (ICMAB-CSIC), Campus de la Universitat Autonoma de Barcelona, 08193 Bellaterra, Spain

Received 18 December 2006; received in revised form 31 January 2007; accepted 31 January 2007

Available online 8 February 2007

Abstract

The study of the reactivity of the ferrocenyliminoalcohol [(g⁵-C₅H₅)Fe{(g⁵-C₅H₄)–CH@N–(C₆H₄-2OH)}] (1b) with Na₂[PdCl₄] or

Pd(OAc)₂has allowed the isolation and characterization of the heterotrimetallic complexes: trans-[Pd{(g⁵-C₅H₅)Fe[(g⁵-C₅H₄)–

CH@N–(C₆H₄-2OH)]}₂Cl₂] (2b), [Pd{[(g⁵-C₅H₃)–CH@N–(C₆H₄-2O)]Fe(g⁵-C₅H₅)}{(g⁵-C₅H₅)Fe[(g⁵-C₅H₄)–CH@N–(C₆H₄-2OH)]}]

(3b) and trans-[Pd{(g⁵-C₅H₅)Fe[(g⁵-C₅H₄)–CH@N–(C₆H₄-2O)]}₂] (4b). Ligand 1b acts as a (N) (in 2b) or a (N,O)^ꢀ(in 4b) ligand; while

in 3b the two units of the iminoalcohol exhibit simultaneously diﬀerent modes of binding {(N) and [C(sp², ferrocene),N,O]^2ꢀ}. The crys-

tal structures of 2b Æ 3H₂O and 3b Æ 1/2CHCl₃are also reported and conﬁrm the mode of binding of the ligand in these compounds. The

relative importance of the factors aﬀecting the preferential formation of products (2b–4b) is also discussed. The study of the reactivity of

3b with PPh₃has enabled the obtention of the cyclopalladated complexes [Pd{[(g⁵-C₅H₃)–CH@N–(C₆H₄-2O)]Fe(g⁵- C₅H₅)}(PPh₃)] (6b)

and [Pd{[(g⁵-C₅H₃)–CH@N–(C₆H₄-2OH)]Fe(g⁵-C₅H₅)}Cl(PPh₃)] (7b), in which 1b behaves as a [C(sp², ferrocene),N,O]^2ꢀ(in 6b) or

[C(sp², ferrocene),N]^ꢀ(in 7b) ligand. Treatment of 3b with MeO₂C–C„C–CO₂Me produces [Pd{[(MeO₂C–C@C–CO₂Me)₂(g⁵-

C₅H₃)–CH@N–(C₆H₄-2O)]Fe(g⁵-C₅H₅)}] (8b), that arises from the bis(insertion) of the alkyne into the r[Pd–C(sp², ferrocene)] bond.

The comparison of the results obtained for 1b and [C₆H₅–CH@N–(C₆H₄-2OH)] (1a) has allowed to establish the inﬂuence of the sub-

stituents on the imine carbon on their reactivity in front of palladium(II) as well as on the lability of the Pd-ligands bond. ⁵⁷Fe Mo¨ss-

bauer studies of 2b–4b and 6b provide conclusive evidence of the eﬀect induced by the mode of binding of 1b on the environment of the

iron(II).

Keywords: Ferrocene derivatives; Iminoalcohols; Cyclopalladation; 57-Fe Mo¨ssbauer spectra; Alkyne insertions

1. Introduction

due to their potential hemilability [2], which may be partic-

ularly important in diﬀerent areas including homogeneous

catalysis [3]. A wide variety of palladacycles having

[C,N,X] (X = N, S, P) ligands and a r[Pd–C(sp², aryl)]

or to a lesser extent r[Pd–C(sp³)] bonds have been

described in the literature during the last decade [4].

Although the incorporation of a harder donor atom such

as the oxygen in the ‘‘C,N,X’’ backbone is expected to

Organometallic palladium(II) complexes derived from

polydentate ligands containing two or more donor atoms

with diﬀerent hardness [1] have attracted great interest

*

Corresponding author. Tel.: +34 934039134; fax: +34 9340907725.

´

E-mail address: conchi.lopez@qi.ub.es (C. Lopez).

doi:10.1016/j.jorganchem.2007.01.054

S. Pe´rez et al. / Journal of Organometallic Chemistry 692 (2007) 2402–2414

2403

introduce signiﬁcant diﬀerences in the physical and chemi-

cal properties of the complexes, palladacycles with terden-

tate [C,N,O] ligands are not common [5–9], although they

are especially attractive from diﬀerent points of view. For

instance, some compounds of this kind exhibit unusual

structural features, such as [Pd{C₆H₄–CH@N–(C₆H₄-

2O)}]₄, which arises from the iminoalcohol [C₆H₅–

CH@N–(C₆H₄-2OH)] (1a) (Fig. 1) by the self-assembly of

enable us to elucidate the importance of the substituents

on the imine carbon {a phenyl (in 1a) or a ferrocenyl unit

(in 1b)} on the nature and nuclearity of the ﬁnal product

as well as on the versatility of the modes of bindings of

1a and 1b.

2. Results and discussion

four cyclopalladated units containing

a

terdentate

The reaction of [(g⁵-C₅H₅)Fe{(g⁵-C₅H₄)–CH@N–

(C₆H₄-2OH)}] (1b) [16] with an equimolar amount of

Na₂[PdCl₄] in methanol at 298 K for 24 h produced a

red solid. Its characterization data (see Section 4) agreed

with those expected for trans-[Pd{(g⁵-C₅H₅)Fe[(g⁵-C₅H₄)–

CH@N–(C₆H₄-2OH)}]₂Cl₂] (2b) (Table 1, entry I and

Scheme 1, step (A)) in which two units of the iminoalco-

hol are bound to the palladium(II) through the imine

nitrogen exclusively. Complex 2b was isolated in a 74%

yield.

(C,N,O)^2ꢀligand [5]. Besides that, the coexistence of a

r(Pd–C) and a r(Pd–O) bond make them especially

interesting in view of their potential utility as precursors

in organic or organometallic synthesis [3,6,10]. For

instance, the two palladacycles depicted in Fig. 2 were used

in the total synthesis of the central core of Teleodicin B4

[9].

In recent years these studies have been extended to

ligands derived from ferrocene and several palladacycles

with [C(sp², ferrocene),N,X]^ꢀ(X = N⁰, S) ligands have also

been described [11,12]. However, their analogues with

X = oxygen are extremely scarce [13,14]. Mak et al. [13]

reported the ﬁrst palladacycles containing a mer-terdentate

[C(sp², ferrocene),N,O]^ꢀligand. More recently, the study

of the reaction between 2-ferrocenyl-2,4-dihydro-1H-3,1-

benzoxazine [15] and Na₂[PdCl₄] has lead to [Pd{[(g⁵-

The crystal structure of 2b Æ 3H₂O¹(Fig. 3) contains

molecules of trans-[Pd{(g⁵-C₅H₅)Fe[(g⁵-C₅H₄)–CH@N–

(C₆H₄-2OH)]}₂Cl₂] and water in a 1:3 molar ratio. In each

one of the heterotrimetallic molecules, the palladium(II)

atom is in a square-planar environment, where it is bound

to two chlorides {Cl and Cl(A)} in a trans arrangement.

The remaining coordination sites are occupied by the imine

nitrogen of two iminoalcohols. The Pd–N and Pd–Cl bond

lengths fall in the range reported for other palladium(II)

complexes of the type trans-[Pd(L)₂Cl₂] where L represents

an N-donor ferrocenyl ligand [17,18].

C₅H₃)–CH@N–(C₆H₄-2CH₂OH)]Fe(g⁵-C₅H₅)}Cl]

[14],

which is a useful precursor for the synthesis of 1,2-disubsti-

tuted ferrocenyl products containing two unsaturated

groups in adjacent positions [14].

˚

In view of these facts and due to the potential utility

of heterodimetallic complexes with ferrocenyl units we

were prompted to study the reactivity of [(g⁵-

The C@N– bond length {1.28(4) A} is similar to those

found for 1b {average value for the two non-equivalent

˚

molecules: 1.26(2) A [16]} and related ferrocenyl Schiﬀ

C₅H₅)Fe{(g⁵-C₅H₄)–CH@N–(C₆H₄-2OH)}]

(1b)

[16]

bases [18,19]. The values of the torsion angles C(10)–

towards palladium(II). Since this product can be easily

visualized as derived from 1a by replacement of the phe-

nyl group by a ferrocenyl unit, the comparison of the

results obtained for 1b with those reported for 1a will

C(11)–N–C(12)

{179.4(3)ꢁ} agree with an anti-(E) conformation of the

ligand.

and

C(10A)–C(11A)–N(A)–C(12A)

The imine group is practically orthogonal to the ‘‘PdCl₂’’

moiety and forms an angle of 8.7ꢁ with the C₅H₄ring. As a

consequence of this arrangement, the separation between

the palladium(II) atom and the hydrogen atoms H(9) and

˚

H(9A) is 2.63 A. This ﬁnding, together with the values of

the angles involving the H(9) or H(9A), the palladium(II)

and the nitrogen or the chloride atoms, suggests the exis-

tence of transanular Pdꢁ ꢁ ꢁH(9) and Pdꢁ ꢁ ꢁH(9A) contacts,

similar to those reported for trans-[Pd{(g⁵-C₅H₅)Fe[(g⁵-

C₅H₄)–CH@N–NMe₂]}₂Cl₂] [17] and other mono- and

dinuclear complexes with ‘‘PdN₂Cl₂’’ cores [18–20].

Fig. 1. Schiﬀ base [(C₆H₅)–CH@N–(C₆H₄-2OH)] (1a).

1

Crystallographic data: C₃₄H₃₀Cl₂Fe₂N₂O₂Pd (2b) Æ 3H₂O, MAR345

˚

diﬀractometer (Mo Ka radiation), monoclinic, a = 14.803(1) A,

b = 13.968(1) A, c = 17.702(1) A, a = c = 90ꢁ and b = 112.190(1)ꢁ, space

group: C2/c, V = 3389.1(4) A , Z = 4, T = 273(2) K, k = 0.71069 A,

D_calc= 1.639 g cm^ꢀ3, l = 1.572 mm^ꢀ1, F(000) = 1768, 2607 reﬂections

collected of which 2207 were assumed as independent (R_int= 0.0249), R

indices: R₁= 0.0529 and wR₂= 0.1505 {for I > 2r(I)} and R₁= 0.0618

and wR₂= 0.1590 (for all data).

˚

3

˚

Fig. 2. Palladacycles containing (C,N,O)^2ꢀligands used in the total

synthesis of the central core of Teleocidin B4.

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S. Pe´rez et al. / Journal of Organometallic Chemistry 692 (2007) 2402–2414

Table 1

Summary of the experimental conditions {reagents, solvents, temperature (T) and reaction periods (t)} used to prepare the palladium(II) complexes

containing the iminoalcohol 1b acting as a (N), (N,O)^ꢀor [C(sp², ferrocene),N,O]^2ꢀdonor ligand

Entry

Reagents (molar ratios)

Solvent

T (K)

t

Products

Yields^a

I

1b and Na₂[PdCl₄] (1:1)

1b, Na₂[PdCl₄] and NaOAc Æ 3H₂O (1:1:1)

1b and Pd(OAc)₂(1:1)

1b and Pd(OAc)₂(2:1)

MeOH

Toluene

MeOH

298

Reﬂux

298

24 h

2.5 h

20 min

24 h

2b

3b

74

51

55

c

II

III

IV

V

VI

a

3b

3b, 4b, 5b^b

3b and 4b^d

3b

c

2b and NaOAc (1:1) or (1:2)

Reﬂux

31 and 45^e

In %.

b

c

Compounds 3b and 4b were isolated in a molar ratio 3b:4b = 1.00:0.65 and only traces (ꢂ5 mg) of 5b were isolated (see text).

In this case competitive chemical reactions take place.

d

e

The molar ratio 3b:4b was 1:4.

For molar ratios NaOAc:2b = 1.0 or 2.0, respectively.

Scheme 1. Reagents and conditions: R = CO₂Me. (i) Equimolar amount of Na₂[PdCl₄] in methanol at 298 K for 24 h. (ii) Treatment with Na₂[PdCl₄] and

NaOAc Æ 3H₂O (in a molar ratio 1b:Pd(II):OAc^ꢀ= 1:1:1) at 298 K for 24 h or addition of Pd(OAc)₂in reﬂuxing toluene for 2.5 h. (iii) NaOAc (in a molar

ratio OAc^ꢀ:2b of 2) in reﬂuxing methanol for 24 h. (iv) Addition of the equimolar amount of PPh₃in CH₂Cl₂at 298 K followed by SiO₂column

chromatography. (v) In CDCl₃followed by the addition of DCl (in a proportion DCl:6b = 0.8) in methanol-d₄at 298 K. (vi) In NaOD (molar ratio

OD^ꢀ:7b = 0.5) in methanol-d₄. (vii) Addition of R–C„C–C–R (in a molar ratio alkyne:3b = 4) in CH₂Cl₂under reﬂux for 8 h followed by SiO₂column

chromatography.

The phenyl ring is planar and its main plane forms an

angle of 104.9ꢁ with the imine group, as a result of this

arrangement and of the relative orientation between the

C₆H₄-2OH group of one of the ligands and the ferrocenyl

moiety of the other one, the separation between the

C(8)–H(8) bond {or the C(8A)–H(8A)} and the phenyl

group deﬁned by the set of atoms [C(12)–C(17)] {or

[C(12A)–C(17A)]} suggest the existence of a weak C–

Hꢁ ꢁ ꢁp interaction [21].

Bond lengths and angles of the ferrocenyl moieties agree

with data reported for most ferrocene derivatives [18], the

pentagonal rings are practically parallel (tilt angle = 2.9ꢁ)

and they deviate by 15.6ꢁ from the ideal eclipsed

conformation.

S. Pe´rez et al. / Journal of Organometallic Chemistry 692 (2007) 2402–2414

2405

Fig. 3. ORTEP plot of trans-[Pd{(g⁵-C₅H₅)Fe[(g⁵-C₅H₄)–CH@N–(C₆H₄-

2OH)]}₂Cl₂] Æ 3H₂O (2b Æ 3H₂O). The water molecules as well as hydrogen

˚

atoms have been omitted for clarity. Selected bond lengths (A) and angles

(ꢁ): Pd–N, 2.016(2); Pd–Cl, 2.305(5); C(10)–C(11), 1.43(3); C(11)-N,

1.28(4); N–C(12), 1.44(4); C(12)–C(13), 1.38(3); C(13)–C(14), 1.39(3);

C(14)–C(15), 1.33(4); C(15)–C(16), 1.37(4); C(16)–C(17), 1.36(3); C(17)–

O(1), 1.35(3); C(12)–C(17), 1.39(3); N–Pd–Cl, 90.0(5); C(10)–C(11)-N,

128.4(18); C(11)–N–C(12), 118.7(16); N–C(12)–C(13), 121.0(18); O(1)–

C(17)–C(12), 123.4(19) and O(1)–C(17)–C(16), 117(2).

The separation between the Pd(II) and the Fe(II) atoms

˚

(4.541 A) clearly exceeds the sum of their van der Waals

radii [22] thus suggesting that there is no direct interaction

between them.

When the reaction was carried out in the presence of an

equimolar amount of NaOAc Æ 3H₂O (Table 1, entry II and

Scheme 1, step (B)) a deep red solid (hereafter referred to as

1

3b) was isolated. The H NMR spectrum of 3b (Fig. 4a)

showed two sets of superimposed signals of identical inten-

sity suggesting the presence of two non-equivalent units of

the ligand.

1

One of the two sets of signals detected in the H and

¹³C{¹H} NMR spectra of 3b (in the ranges 3.50–

5.50 ppm and 65.0–80.0 ppm, respectively) (Fig. 4a–c)

was consistent with the typical pattern of monosubsti-

tuted ferrocene derivatives. For the other set, the number

of resonances due to the ferrocenyl moiety, the low ﬁeld

shift of the signals due to the C¹and C²nuclei of the

ferrocenyl moiety (when compared with those of 1b)

and the absence of a cross-peak between signals due to

C²and to any proton in the {¹H–¹³C} HSQC spectrum,

suggested that the metallation of the ferrocenyl unit had

taken place. In addition,₀the ₀diﬀerenc₀es detected in the

chemical shifts of the C¹, C²and C⁶nuclei of 3b and

1b were very similar to those reported for [Pd{C₆H₄–

CH@N–(C₆H₄-2O)}]₄(3a) {with a [C(sp², phenyl),N,O]^2ꢀ

terdentate ligand} and its parent ligand 1a [5]. All these

ﬁndings suggested that 3b contained two units of the imi-

noalcohol exhibiting diﬀerent modes of binding {(N) and

[C(sp², ferrocene),N,O]^2ꢀ}.

Fig. 4. Partial views of the ¹H NMR and ¹³C{¹H} NMR spectra (a and b,

respectively) of 3b in CDCl₃at 298 K. An expansion of the ¹³C{¹H} NMR

spectrum in the range 66.8 ppm < d < 76.2 ppm is shown in (c). In all

cases, characters in itallics correspond to the non-cyclopalladated ligand

(see text and Scheme 1).

In order to conﬁrm the nuclearity of the complex and

the mode of binding of 1b, crystals suitable for X-ray anal-

ysis were grown. The crystal structure of 3b²contains mol-

2

Crystallographic data: C₃₄H₂₈Fe₂N₂O₂Pd (3b) Æ 1/2CHCl₃, Mar 345

˚

diﬀractometer (Mo Ka radiation), monoclinic, a = 19.4190(5) A,

b = 10.349(1) A, c = 17.003(1) A, a = c = 90ꢁ and b = 101.47(1)ꢁ, space

group: P2₁/c, V = 3348.8(4) A , Z = 4, T = 293(2) K, k = 0.71069 A,

D_calc= 1.536 g cm^ꢀ3, l = 1.538 mm^ꢀ1, F(000) = 1566, 49529 reﬂections

collected of which 8455 were assumed as independent (R_int= 0.0294), R

indices: R₁= 0.0373 and wR₂= 0.1175 {for I > 2r(I)} and R₁= 0.0441

and wR₂= 0.1239 (for all data).

˚

3

˚

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S. Pe´rez et al. / Journal of Organometallic Chemistry 692 (2007) 2402–2414

The distances between the palladium and the iron(II)

˚

atoms Fe(1) and Fe(2) (3.611 and 4.617 A, respectively)

clearly exceed the sum of the van der Waals radii of these

atoms [22], this precludes the existence of any direct inter-

action. As expected bond lengths and angles of the two

ferrocenyl units are consistent with the values reported

for most ferrocene derivatives [17–19]. In both cases the

pentagonal rings are planar, practically parallel {tilt angles

of 1.3ꢁ and 1.5ꢁ for the moieties containing Fe(1) and

Fe(2), respectively} and they deviate from the ideal eclipsed

conformation by 1.5ꢁ (in the cyclometallated unit) and 0.9ꢁ

(for the other unit).

The existence of two bands at ca. 1591 and 1616 cm^ꢀ1in

the IR spectrum of 3b is consistent with the results

obtained from X-ray studies. Previous works on IR spec-

troscopy of cyclopallada- and cycloplatinated complexes

derived from imines have shown the shift of the band due

to the stretching of the C@N– group to lower frequencies

is greater for the metallated derivatives than for the com-

plexes where the same ligand acts as a N-donor group

[23]. On this basis, we tentatively assign the absorption at

1591 cm^ꢀ1to the imine group of the terdentate ligand

and that at 1616 cm^ꢀ1to the N-bonded iminoalcohol.

The remaining characterization data of 3b (see Section 4)

are consistent with the results presented above and with

the chemical formulae presented in Scheme 1. As far as

we know organometallic palladium(II) complexes contain-

ing two units of the same ligand adopting simultaneously a

(N) and a (C,N,O)^2ꢀmode of binding have not been

described so far, and consequently 3b is particularly inter-

esting from this point of view.

It should be noted that 3b was also obtained when 1b

was reacted with Pd(OAc)₂(in a 1:1 molar ratio) in reﬂux-

ing toluene for 2.5 h (Table 1, entry III) and evidence of the

formation of any other by-product was not detected. This

procedure has greater advantages than that described

above (entry II of Table 1) since it allows the isolation of

3b in slightly higher yield (55% versus 51% in entry II)

and in less than one day. More interesting were the results

obtained when equimolar amounts of the ligand and

Pd(OAc)₂were reﬂuxed in methanol for 2.5 h (Table 1,

entry IV). This reaction gave 3b, a red solid (here after

referred to as 4b) (in a molar ratio 3b:4b = 1.00:0.65) and

traces (ꢃ5 mg) of a minor component (5b).

Fig. 5. ORTEP diagram of the heterotrimetallic complex 3b. The CHCl₃

molecule as well as hydrogen atoms have been omitted for clarity. Selected

˚

bond lengths (A) and angles (ꢁ): Pd–N(1), 2.028(2); Pd–N(2), 1.973(2); Pd–

O(2), 2.094(2); Pd–C(23), 1.970(3); C(10)–C(11), 1.450(3); C(11)–N(1),

1.268(3); N(1)–C(12), 1.433(3); C(17)–O(1), 1.368(5); C(27)–C(28),

1.447(4); C(28)–N(2), 1.290(3); N(2)–C(29), 1.414(4); C(34)–O(2),

1.324(4); O(1)–C(17), 1.368(5); N(1)–Pd–C(23), 99.02(10); C(23)–Pd–

N(2), 81.95(10); C(23)–Pd–O(2), 164.51(10); O(2)–Pd–N(1), 96.4(8);

C(10)–C(11)–N(1), 126.4(2); C(11)–N(1)–C(12), 116.7(2); C(16)–C(17)–

O(1), 117.7(4); C(12)–C(17)–O(1), 124.8(3); C(28)–N(2)–C(29), 129.0(2);

N(2)–C(29)–C(30), 123.7(2); C(29)–C(34)–O(2), 122.0(3) and C(33)–

C(34)–O(2), 121.1(3).

ecules of 3b and CHCl₃(in a 2:1 molar ratio). In each one

of the heterotrimetallic molecules (Fig. 5), the palladium is

in a slightly distorted square-planar environment, where it

is bound to the deprotonated oxygen {O(2)}, the imine

nitrogen {N(2)} and the C(23) atom of the ferrocenyl unit

of one molecule of the iminoalcohol, thus conﬁrming the

[C(sp², ferrocene),N,O]^2ꢀmode of binding. The remaining

coordination site is occupied by the nitrogen {N(1)} of the

other molecule of ligand 1b. Thus conﬁrming the conclu-

sions reached by NMR.

˚

The Pd–N(1) bond length {2.028(2) A} is larger than the

˚

values obtained for 2b {2.016(2) A}, where the ligand also

acts as a N-donor group, and for the Pd–N(2) bond. The

values of the bond angles C(23)–Pd–N(2) and N(2)–

Pd–O(2) agree with those reported for 3a where the imino-

alcohol 1a exhibits a similar mode of binding. In the

non-metallated unit of the ligand the bond length of the

The IR spectra of 4b did not show the typical band due

to the stretching of the –OH group [24], thus suggesting

that deprotonation of the alcohol group had taken place.

In addition, no evidence of the presence of OAc^ꢀgroups

was detected by IR or NMR spectroscopy [25,26]. Charac-

terization data of 4b were consistent with those expected

for the trimetallic complex [Pd{(g⁵-C₅H₅)Fe[(g⁵-C₅H₄)–

CH@N–(C₆H₄-2O)]}₂] (Fig. 6a), where two deprotonated

units of the ligand are bound to the palladium in a trans-

arrangement.

˚

imine group {1.268(3) A} is smaller than for the other unit

˚

of the ligand {1.290(3) A} but the N–C(phenyl) and O–

C(phenyl) bond distances are larger than those of the

ligand acting as a (C,N,O)^2ꢀdonor group.

The complex contains a [5.5.5.6] tetracyclic system

which is formed by the 1,2-disubstituted C₅H₃ring, a

ﬁve-membered palladacycle, the pentagonal chelate,

formed by the binding of the N(2) and O(2) atoms and

the phenyl ring. Bond lengths and angles of metallacycles

are similar to those found for palladacycles derived from

ferrocenylimines and palladium(II) complexes holding

(N,O) bidentate ligands, respectively [17,18].

It should be noted that the synthesis of 4b can be

improved if the reaction is performed in methanol at

298 K using palladium(II) acetate {in a molar ratio

S. Pe´rez et al. / Journal of Organometallic Chemistry 692 (2007) 2402–2414

2407

the reﬂuxing periods were varied in the range

(30 min < t < 3.5 h).

On this basis and with the results obtained in the reac-

tion of 5b with PPh₃(vide infra), we tentatively postulate

for 5b the chemical formula (b) depicted in Fig. 6 with

n = 2. Unfortunately, attempts to obtain crystals of 5b suit-

able for X-ray diﬀraction failed.

The comparison of the chemical formula of 2b and those

of 3b, 4b and 5b suggests that in principal 4b could be easily

visualized as derived from 2b by deprotonation of the –OH

groups and the subsequent replacement of the Cl^ꢀligands

by the oxygen; while 3b could arise from 2b by activation of

the r[C(sp², ferrocene)-H], deprotonation of the O–H

group and coordination of the oxygen of one of the two

ligands of 2b. The formation of 5b could involve the

dissociation of the N-donor ligand in 3b, followed by the

assembling of the ‘‘[Pd{[(g⁵-C₅H₃)–CH@N–(C₆H₄-2O)]Fe

(g⁵-C₅H₅)}]’’ units. Previous work on cyclopallada- and

cycloplatination reactions have shown that some [M(N-

donor imine ligand)₂Cl₂] and [M(N,X-donor ligand)Cl₂]

complexes (M = Pd or Pt and X = N⁰or S) may undergo

Fig. 6. Chemical formulae of the trimetallic complex 4b (a) and of the

polymeric compound holding a ‘‘Pd_nO_n’’ central core (b) (see text).

1b:Pd(II) = 2} (Table 1, entry V). Besides that, the treat-

ment of a CDCl₃solution of 4b with DCl (dissolved in

methanol-d₄) in a molar ratio 4b:DCl = 0.5 showed the

presence of FcCHO and the presence of compound 2b

1

was not detected by H NMR. These results indicate that

4b is unstable under acidic conditions.

1

The H NMR spectrum of the minor component 5b as

the cyclometallation in the presence of

a

base

well as its reactivity with PPh₃(see below) suggested the

existence of cyclopalladated units containing a terdentate

[C(sp², ferrocene),N,O]^2ꢀligand. Besides that, the diﬀer-

ences detected in the ¹H chemical shifts of the 1,2-disubsti-

tuted phenyl ring for 1b and 5b were very similar to those

reported for 1a and [Pd{C₆H₄–CH@N–(C₆H₄-2O)}]₄(3a)

[5]. These ﬁndings suggested that 5b could arise from the

self-assembly of the cyclopalladated units ‘‘[Pd{[(g⁵-

[4a,4b,11c,30,31]. In view of this, several additional exper-

iments were performed in order to elucidate: (a) if 2b could

be an intermediate product in the formation of 3b–5b, and

(b) the potential ability of 2b to undergo the activation of

the r(C–H) bond and/or the deprotonation of the –OH

moiety.

Treatment of 2b with NaOAc in methanol under reﬂux

for 24 h (Table 1, entry VI and Scheme 1, step (C)) gave

3b and the presence of either 4b or 5b was not detected by

NMR studies of the crude of the reactions. In addition

the relative abundance of 3b was greater when the molar

ratio AcO^ꢀ:Pd(II) increases from 1 to 2. These ﬁndings

conﬁrm that 2b is an intermediate product in the forma-

tion of 3b. In addition, when the NaOAc was replaced

C₅H₃)–CH@N–(C₆H₄-2O)]Fe(g⁵-C₅H₅)}]’’ forming

a

central ‘‘Pd_nO_n’’ ring (Fig. 6b). A few palladacycles with

central ‘‘Pd_nO_n’’ cores have been reported [5,6a,6b,

6c,20,27,28], among them those with a 4-membered central

ring (n = 2) are more common than the tri- or tetrameric

derivatives [27,28].

1

Due to: (a) the formal similarity between the ligands 1a

and 1b, (b) the tetranuclear nature of the product obtained

in the reaction of 1a with Pd(OAc)₂under identical exper-

imental conditions as for 1b, and (c) presence of a peak at

m/z = 1638.5 in the mass spectrum, we tentatively postu-

lated a tetrameric structure for 5b. However, the use of

molecular models for [Pd{[(g⁵-C₅H₃)–CH@N–(C₆H₄-

2O)]Fe(g⁵-C₅H₅)}]₄revealed that the self-assembly of the

four cyclopalladated units is unlikely to occur due to

the steric eﬀects arising from the proximity between the

‘‘Fe(g⁵-C₅H₅)’’ moiety of one of the units and the protons

of the phenyl ring of a neighbouring fragment. This would

reduce signiﬁcantly the stability of the [Pd{[(g⁵-C₅H₃)–

CH@N–(C₆H₄-2O)]Fe(g⁵-C₅H₅)}]₄in comparison with

that of [Pd{C₆H₄–CH@N–(C₆H₄-2O)}]₄(3a), where the

substituent on the imine carbon (a phenyl) is smaller than

the ferrrocenyl group [29].

by a stronger base (NaOH) the H NMR spectra of the

crude reaction mixtures indicated the existence of FcCHO

(due to partial hydrolysis of the ligand), but 4b or 5b were

not detected. Thus suggesting that the formation of 4b

and 5b possibly takes place directly from the free ligand

1b by a diﬀerent pathway. All these studies suggest that

the ﬁnal products isolated in entries IV and V are pro-

duced in diﬀerent chemical reactions that take place

simultaneously.

Treatment of 3b with an equimolar amount of PPh₃in

CH₂Cl₂at 298 K involved the replacement of the N-

bonded unit of 1b by the phosphine giving [Pd{[(g⁵-

C₅H₃)–CH@N–(C₆H₄-2O)]Fe(g⁵-C₅H₅)}(PPh₃)]

(6b)

(Scheme 1, step (D)). The position of the signal detected

in the ³¹P{¹H} NMR spectrum of 6b is very similar to that

of [Pd{[(g⁵-C₅H₃)–CH@N–(C₆H₄-2CH₂O)]Fe(g⁵-C₅H₅)}-

(PPh₃)] [14] where the ferrocenyl ligand also acts as a

[C(sp², ferrocene),N,O]^2ꢀgroup. It should be noted that

evidence of the formation of any other palladium(II) com-

plex was not detected even when the molar ratio PPh₃:3b

increased. All these ﬁndings indicate that the r(Pd–O)

Molecular models also show that this type of steric hin-

drance vanishes for the dimeric molecule [Pd{[(g⁵-C₅H₃)–

CH@N–(C₆H₄-2O)]Fe(g⁵-C₅H₅)}]₂. It should be noted

that the yield of 5b did not improve signiﬁcantly when

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S. Pe´rez et al. / Journal of Organometallic Chemistry 692 (2007) 2402–2414

bond exhibits low lability and this agrees with the results

obtained for [Pd{C₆H₄–CH@N–(C₆H₄-2O)}]₄(3a) [5] and

[Pd{[(g⁵-C₅H₃)–CH@N–(C₆H₄-2-CH₂O)]Fe(g⁵-C₅H₅)}]₂

(5c) [14], that contain terdentate [C(sp², phenyl),N,O]^2ꢀ

and [C(sp², ferrocene),N,O]^2ꢀligands, respectively.

When 5b was treated with PPh₃{in a molar ratio

Pd(II):phosphine of 1}, a red solid was isolated. Its charac-

terization data based on NMR, IR and mass spectra were

identical to those of 6b. This results supports the existence

of cyclopalladated ‘‘Pd{[(g⁵-C₅H₃)–CH@N–(C₆H₄-2O)]-

Fe(g⁵-C₅H₅)}’’ units in 5b. The comparison of the reactiv-

ity of the palladacycles holding a [C,N,O]^2ꢀterdentate

ligand (3a, 3b, 5b and 5c), shows that in 5c the lability of

the Pd–O bond is greater than for 3a, 3b and 5b. This could

be related to the steric eﬀects arising from the diﬀerent size

of the chelate a ﬁve- (in 3a, 3b and 5b) or a six- (in 5c) mem-

bered ring.

gesting the formation of a new product. Its characterization

data were consistent with those expected for [Pd{[(g⁵-

C₅H₃)–CH@N–(C₆H₄-2OH)]Fe(g⁵-C₅H₅)}Cl(PPh₃)] (7b).

The formation of 7b requires the protonation of the oxygen

atom of the terdentate ligand, the cleavage of the Pd–O bond

and the incorporation of the Cl^ꢀligand in the coordination

sphere of the palladium in a cis-arrangement to the phospho-

rus, in good agreement with the transphobia eﬀect [32].

It has been recently reported that freshly prepared solu-

tions of the cyclopalladated complex [Pd{[(g⁵-C₅H₃)–

CH@N–(C₆H₄-2-CH₂O)]Fe(g⁵-C₅H₅)}(PPh₃)] (6c) [14]

(which can be easily visualized as derived from 6b by incor-

poration of a –CH₂– unit between the oxygen and the phe-

nyl ring), in CDCl₃changed with time giving a mixture of

6c and [Pd{[(g⁵-C₅H₃)–CH@N–(C₆H₄-2-CH₂OH)]Fe(g⁵-

C₅H₅)}Cl(PPh₃)] (7c) where the ligand acts as a [C(sp², fer-

rocene),N]^ꢀgroup and the molar ratio 6c:7c decreased to

0.9 after 5 days. The comparison of the results obtained

for 6c and those of 6b indicate that the ﬁve-membered che-

late ring of 6b is less prone to undergo the opening of the

ﬁve-membered chelate ring than 6c where the chelate is

hexagonal.

In a ﬁrst attempt to induce the cleavage of the Pd–O bond

of 6b and the subsequent modiﬁcation of the mode of bind-

ing of the ligand, the reactivity of this product with HCl was

1

also studied on a NMR scale. As shown in Fig. 7, the H

NMR spectrum of a CDCl₃solution of 6b changed substan-

tially upon the addition of a DCl solution (in methanol-d₄) in

a molar ratio DCl: 6b = 0.8 (Scheme 1, step (E)) thus sug-

An interesting feature of 7b is that it reacts with NaOD

(molar ratio NaOD:7b = 0.5) giving 6b (Scheme 1, step (F))

Fig. 7. Partial views of the ¹H NMR spectra (at 298 K) of a freshly prepared solution of 6b (in CDCl₃) (a) and after the addition of DCl (in methanol-d₄)

(b), together with their ³¹P{¹H} NMR spectra (c and d, respectively).

S. Pe´rez et al. / Journal of Organometallic Chemistry 692 (2007) 2402–2414

2409

and subsequent cycles exposing 6b (or 7b) to acidic (or

basic) conditions showed that the transformations

6b « 7b (Scheme 1, steps (E) and (F)) are reproducible

and robust. Therefore, the mode of binding of 1b to the

palladium(II) in 6b and 7b can be easily tuned by manipu-

lating the acidity/basicity of the media. Examples of palla-

dacycles exhibiting this behaviour are not known. Previous

studies on the coordinating ability of the pendant –OH

group in palladacycles containing bidentate [C(sp²,

phenyl),N]^ꢀligands derived from organic iminoalcohols

{i.e. 4,5-(MeO)₂-C₆H₃–CH@N–(CH₂)₂-OH} [8] have

shown that the formation of the complexes where these

ligands behave as a terdentate group requires the use of

Ag⁺salts. In none of these cases the change of the denticity

of the ligand (from bidentate to terdentate or vice versa)

could be so easily achieved as for the pair of compounds

6b and 7b reported here.

Fig. 9. ⁵⁷Fe Mo¨ssbauer spectra of a solid sample of compound 3b at 80 K

(see text). Experimental data (dots), ﬁtting of the experimental data (solid

line, A) and the results obtained from the ﬁtting assuming the presence of

two iron(II) centres in diﬀerent environments (lines B and C, respectively).

To elucidate the inﬂuence of the mode of binding of the

ligand in compounds 2b–4b and 6b upon the environment

of the iron(II) centre, ⁵⁷Fe Mo¨ssbauer studies of solid sam-

ples at 80 K were carried out. The spectra of 2b, 4b and 6b

consisted of a single quadrupole doublet indicating a

unique iron site (Fig. 8).³

Previous studies have shown that the quadrupole split-

ting parameter (DE_q) is very sensitive to the nature of the

substituents [33]. In general electron-withdrawing groups

produce a decrease of the DE_qvalue relative to ferrocene

(hereafter referred to as FcH), while for electron-donating

susbtituents the eﬀect is opposite. The comparison of the

data for 1b [16], 2b, 4b and 6b³and FcH [34] reveals that

the DE_qparameter decreases according to the sequence

FcH > 1b > 2b > 4b > 6b, which reﬂects an increase of

the electron-pulling nature of the substituent on the

‘‘(g⁵-C₅H₅)Fe(g⁵-C₅H₄)’’ moiety. Additionally the diﬀer-

ences detected in the DE_qvalues for 2b and 4b indicate

that the binding of the palladium(II) to the imine nitro-

gen exclusively has a weaker electron-withdrawing eﬀect

than in 4b that contains two bidentate (N,O)^ꢀunits of

the iminoalcohol; while in 6b,³where the palladium(II)

is directly attached to the ferrocenyl moiety, this eﬀect

is stronger.

In the ⁵⁷Fe-Mossbauer spectrum of 3b, that contains

two molecules of the ligand adopting diﬀerent hapticities

and modes of binding, a single quadrupole doublet

(Fig. 9) was also observed, but the full-width at half-height

3

Summary of ⁵⁷Fe Mo¨ssbauer hyperﬁne parameters {isomer shift (i.s.),

quadrupole splitting (DE_q) and full-width at half-height (C) in mm/s} at

80 K for compounds 2b, 4b and 6b. For 2b: i.s. = 0.520(3), DE_q= 2.218(6)

and C = 0.235(9); for 4b: i.s. = 0.5063(1), DE_q= 2.1646(2) and

C = 0.2444(4) and for 6b: i.s. = 0.5049(9), DE_q= 2.126(3) and

C = 0.236(5).

Fig. 8. ⁵⁷Fe Mo¨ssbauer spectra of solid samples of compounds 2b, 4b and

6b at 80 K.

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S. Pe´rez et al. / Journal of Organometallic Chemistry 692 (2007) 2402–2414

(C)^4(a)was sligthly greater than those obtained for 2b, 4b or

6b.³In addition, the DE_qobtained for 3b is intermediate

between those of 6b and 2b, where the iminophenol acts

as a terdentate [C(sp², ferrocene),N,O]^2ꢀ(in 6b) or a

monodentate N-donor ligand (in 2b). These ﬁndings sug-

gested that the observed signal could be the result of the

existence of two superimposed doublets due to the presence

of two iron(II) centres with slightly diﬀerent environments.

Thus, we ﬁtted the experimental data^4(b)according to this

hypothesis and the sets of values obtained for the i.s.,

DE_qand C for each one of the two iron(II) centres of 3b

agreed with those of compounds 6b and 2b, respectively.

As mentioned above, one of the main interest in pallada-

cycles containing terdentate ligands arises from their

potential utility as precursors in organic or organometallic

synthesis [3,6,9,10]. Commonly these processes are based

on the insertions of small molecules (i.e. alkynes, alkenes,

CO, etc.) into the r(Pd–C) bond. As a ﬁrst attempt to eval-

uate the ability of 3b to undergo this sort of reactions, we

studied its reactivity toward MeO₂C–C„C–CO₂Me.

Treatment of 3b with this alkyne in a 1:4 molar ratio under

reﬂux for 8h gave, after work up, [Pd{[(Me₂OC–C@

C–CO₂Me)₂(g⁵-C₅H₃)–CH @N–(C₆H₄-2O)] Fe(g⁵-C₅H₅)}]

(8b) (Scheme 1, step (G)) as the major product. Complex 8b

arises from the bis(insertion) of the alkyne into the r(C–H)

bond. NMR studies of 8b suggested that the four substitu-

ents on the g³-butadienyl unit are in a trans-, cis-

arrangement.

coordination of the alkyne to the Pd(II) in a cis-arrange-

ment to the metallated carbon. For 3b this would require

the release of the Schiﬀ base 1b, which could later on react

with the alkyne and undergo an hydrolysis process to give

9b and ferrocenecarboxaldehyde.

Additionally, the greater proclivity of 3b to react with

MeO₂C–C„C–CO₂Me, when compared with that of 3a⁶

could be related to several factors arising from: (a) the

greater lability of the bond between the palladium and

the donor atom in a cis-arrangement to the metallated car-

bon {a N (in 3b) or a O_alcoxo(in 3a)} or (b) steric eﬀects

aﬀecting diﬀerent accesibility of the alkyne to the palla-

dium(II), this may be particularly important for the com-

plexes containing central ‘‘Pd_nO_n’’ cores.

On the other hand, it should be noted that 3b is more

prone to react with this alkyne than the palladacycle

[Pd{[(g⁵-C₅H₃)–CH@N–(C₆H₄-2SMe)]Fe(g⁵-C₅H₅)}Cl]

(3d) that contains a [C(sp², ferrocene),N,S]^ꢀligand [12b].

For 3d, the formation of the bis(insertion) product

[Pd{[(Me₂OC–C@C–CO₂Me)₂(g⁵-C₅H₃)–CH@N–(C₆H₄-

2SMe)]Fe(g⁵-C₅H₅)}][BF₄] (8d) required the presence of

thallium(I) salts to induce the cleavage of the Pd–Cl

bond; while for 3b the reaction proceeds without this

requirement.

3. Conclusions

The results presented here show that 1b exhibits an

interesting coordination ability. These studies have allowed

us to establish the best experimental conditions to selec-

tively control the mode of binding [(N) (in 2b and 3b);

(N,O)^ꢀ(in 4b); {C(sp², ferrocene),N}^ꢀ(in 7b) or {C(sp²,

ferrocene),N,O}^2ꢀ(in 3b and 6b)] of ligand 1b to palla-

dium(II). The versatility of the modes of binding of 1b is

greater that of the iminoalcohol 1a which diﬀers from 1b

in the nature of the substituent on the imine carbon {a phe-

nyl in 1a or a ferrocenyl unit in 1b}. These diﬀerences are

important as to aﬀect the number and the nature of the pal-

ladium(II) complexes formed, their nuclearity, the modes

of binding of the ligand in the complexes as well as their

reactivity. The results obtained from the reaction between

the alkyne MeO₂C–C„C–CO₂Me and 3b indicated that

3b is more prone to undergo the bis(insertion) of the alkyne

than 3d where the Schiﬀ base behaves as a [C(sp², ferro-

cene),N,S]^ꢀgroup. All these ﬁndings together with the

recent interest generated by the potential utility of pallada-

cycles holding terdentate (C,N,O)^qꢀ(q = 1 or 2) ligands as

precursors in organometallic and organic synthesis, indi-

cate that 3b is particularly relevant from these points of

In this reaction small amounts of 3b, ferrocenecarboxal-

dehyde and yellow needles of (Z)-methyl-2(2-oxo-2H-

benzo[b][1,4]oxazin-3(4H)-ylidene) acetate (9b) were also

isolated as by-products. Compound 9b⁵and the aldehyde

were also obtained when the Schiﬀ base 1b was treated with

the alkyne (in a 1:1 molar ratio) in reﬂuxing CH₂Cl₂.

According to the mechanistic studies reported by Rya-

bov et al. [35] on the bis(insertion) of alkynes into the

r[Pd–C(sp², aryl)] bond of cyclopalladated complexes, in

these reactions the ﬁrst step of the process consists of the

4

Iron-57 Mo¨ssbauer hyperﬁne parameters {isomer shift (i.s.), quadru-

pole splitting (DE_q) and full-width at half-height (C) in mm/s} at 80 K for

3b. (a) Parameters obtained from the ﬁtting of the experimental data:

i.s. = 0.510(2), DE_q= 2.191(4) and C = 0.287(7); (b) results of the ﬁtting

assuming the existence of two superimposed doublets due to the two

iron(II) centres in diﬀerent environments: for the Fe(II) of the ferrocenyl

moiety that is linked to the palladium(II) through the nitrogen atom

exclusively: i.s. = 0.512(3), DE_q= 2.289(7) and C = 0.235 and for the

other Fe(II) centre: i.s. = 0.507(3), DE_q= 2.092(7) and C = 0.236. The

areas of the two doublets have been imposed to be equal and full-width at

half-height has been ﬁxed to the values obtained for 2b and 4b,

respectively, in order to avoid correlation between the ﬁtting parameters.

5

Compound 9b was previously prepared by treatment of the H₂N–

(C₆H₄-2OH) and the alkyne in absolute ethanol at 273 K (G.W. Danswan,

P.W. Hairsine, D.A. Rowlands, J.B. Taylor, R. Westwood, J. Chem. Soc.,

Perkin Trans. I 4 (1982) 1049–1058). In order to conﬁrm that this product

could also be formed under the experimental conditions used to isolate 8b,

we also studied the reaction between the aminoalcohol and MeO₂C–

C„C–CO₂Me in reﬂuxing CH₂Cl₂. In this case 9b was also isolated, but

the yield was smaller than that reported.

6

No evidence of the formation of any product arising from the mono-

or bis(insertion) of MeO₂C–C„C–CO₂Me was detected when the

tetrameric complex 3a and this alkyne (in a alkyne:Pd(II) molar ratio of

4) were reﬂuxed in CH₂Cl₂for 8h. After this period the ¹H NMR spectrum

of the solid isolated by after concentration to dryness of the reaction

mixture revealed the presence of the starting materials exclusively.

S. Pe´rez et al. / Journal of Organometallic Chemistry 692 (2007) 2402–2414

2411

view. Further studies on this ﬁeld are currently under

study.

7.51(s, 1H, –CH@N–), 4.40(s, 10H, C₅H₅), 5.76(s, 4H, H²

3

and H⁵), 4.67(s, 4H, H³and H⁴), 7.14(dd, 2H, J = 7.5

0

and ⁴J = 1.5, H³), 7.33(td, 2H, ³J = 7.5 and ⁴J = 1.5,

0

3

4

4. Experimental

H⁴), 6.99(td, 2H, J = 7.5 and J = 1.5, H⁵) and 7.25(s,

0

2H, H⁶). ¹³C{¹H}₀NMR data:⁷d = 175.6(–CH@N–),

4.1. Materials and methods

70.7(C₅H₅), 73.9(C¹), 72.9(C²and C⁵), 74.6(C³and C⁴),

0

139.2(C¹), 149.9(C²), 118.6(C³), 129.2(C⁴), 120.9(C⁵)

0

Compound 1b was synthesized as reported before [16]

and the remaining reagents used in this work were obtained

from commercial sources and used as received. The sol-

vents were dried and distilled before use [36]. Some of the

preparations described below require the use of HIGHLY

HAZARDOUS materials such toluene which should be

handled with CAUTION!

and 125.7(C⁶).

4.2.2. [Pd{[(g⁵-C₅H₃)–CH@N–(C₆H₄-2O)]Fe-

(g⁵-C₅H₅)}{(g⁵-C₅H₅)Fe[(g⁵-C₅H₄)–CH@N–

(C₆H₄-2OH)]}] (3b) Æ 1/2CHCl₃

Although this compound can be isolated by treatment of

equimolar amounts of 1b, Na₂[PdCl₄] and NaOAc Æ 3H₂O

and following the same procedure as described for 2b, or

as a by-product during the synthesis of 4b. The method

described here allowed its obtention in higher yield.

Ligand 1b (295 mg, 9.67 · 10^ꢀ4mol) was treated with

25 mL of toluene, then a solution of Pd(OAc)₂(215 mg,

9.67 · 10^ꢀ4mol) in toluene (5 mL) was added. The reaction

mixture was protected from the light and reﬂuxed for 2.5 h.

After this period the hot solution was carefully ﬁltered and

the ﬁltrate was concentrated on a rotary evaporator to ca.

5 mL. The red solid formed upon cooling was collected by

ﬁltration and air-dried (yield: 396 mg, 55%). Anal. Calc. for

C₃₄H₂₈Fe₂N₂O₂Pd: C, 57.14; H, 3.95; N, 3.92. Found: C,

57.4; H, 4.2; N, 4.0%. MS(FAB⁺): m/z = 714{[M]⁺}. IR:

Elemental analyses (C, H and N) were carried out at the

`

Serveis de Recursos Cientı´ﬁcs i Tecnics (Univ. Rovira i Vir-

gili, Tarragona). Mass spectra {MALDI-TOF⁺(for 5b),

ESI⁺(for 8b) and FAB⁺(for the remaining compounds)}

were performed at the Servei d’Espectrometria de Masses

(Univ. Barcelona) with a VOYAGER-DE-RP, Waters

Micromass and VG-Quattro instruments, respectively,

using 2,5-dihydroxybenzoic acid {(DHB), for MALDI-

TOF⁺} and 3-nitrobenzylalcohol {(NBA), for FAB⁺} as

matrix. IR spectra were recorded with a Nicolet-400FTIR

instrument using KBr pellets. Routine ¹H and ¹³C{¹H}

NMR spectra were obtained with a Gemini 200 MHz, a

Bruker 250-DXR or a Mercury 400 MHz instrument. High

resolution mono- and two-dimensional [{¹H–¹H}-NOESY

and COSY and {¹H–¹³C}-HSQC and HMBC] NMR

experiments were recorded with either a Varian VRX-500

or with a Bruker Avance DMX 500 instruments at

298 K. The solvent used for the NMR studies was CDCl₃

(99.8%) and SiMe₄was used as internal reference.

³¹P{¹H} NMR spectra of 6b and 7b were obtained with a

Bruker 250-DXR instrument in CDCl₃(99.9%) and

using trimethylphosphite as reference [d³¹P{P(OMe)₃}

= 140.17 ppm]. The chemical shifts (d) are given in ppm

and the coupling constants (J) in Hz.

1

1591 and 1616 cm^ꢀ1m(C@N–). H NMR data:⁷for the

metallated fragment d = 7.98(s, 1H, –CH@N–), 3.89(s, 5

H, C₅H₅), 4.34(br, 2H, H³and H⁵), 4.39(s, 1H, H⁴),

0

6.80(dd, 1H, ³J = 8.0 and ⁴J = 1.5, H³), 7.05(td, 1H,

0

³J = 8.0 and ⁴J = 1.5, H⁴), 6.48(td, 1H, ³J = 8.0 and

0

⁴J = 1.5, H⁵) and 7.11(dd, 1H, ³J = 8.0 and ⁴J = 1.5,

0

H⁶) and for the non-cyclometallated moiety d = 8.36(s,

1H, –CH@N–), 4.36(s, 5 H, C₅H₅), 5.31(s, 1H, H²),

4.59(br.s, 1H, H³), 4.65(s, 1H, H⁴), 6.37(s, 1H, H⁵),

0

7.0₀9(dd, 1H, ³J = 8.0 and ⁴J = 1.5, H³),₀7.21(br, 1H,

3

4

H⁴), 6.94(m, 1H, J = 8.0 and J = 1.5, H⁵) and 6.95(m,

0

1H, H⁶). ¹³C{¹H} NMR data:⁷for the cyclometallated

4.2. Preparation of the compounds

unit d = 157.9(–CH@N–), 70.6(C₅H₅), 93.5(C¹), 95.1 (C²),

0

67.5(C³), 69.3 (C⁴), 75.0(C⁵₀), 137.4(C¹), 168.3(C²), 122.0

0

4.2.1. trans-[Pd{(g⁵-C₅H₅)Fe[(g⁵-C₅H₄)–CH@N–(C₆H₄-

2OH)]}₂Cl₂] (2b)

(C³), 129.9(C⁴), 115.4(C⁵) and 115.3(C⁶) and for the

non-cyclometallated unit d = 172.3(–CH@N–),

70.7(C₅H₅), 75.6(C¹), 72.7(C²), 73.4(C³), 73.9(C⁴₀),

To a suspension formed by 1b (202 mg, 6.62 · 10^ꢀ4mol)

and 20 mL of methanol, Na₂[PdCl₄] (195 mg,

6.63 · 10^ꢀ4mol) was added. The reaction ﬂask was pro-

tected from the light with aluminium foil and the mixture

was stirred at 298 K for 24 h. The red solid that formed

was isolated by ﬁltration and air-dried (yield: 190 mg,

74%). Anal. Calc. for C₃₄H₃₀Cl₂Fe₂N₂O₂Pd: C, 51.84; H,

3.84; N, 3.56. Found: C, 51.7; H, 3.7; N, 3.5%. MS(FAB⁺):

m/z = 788{[M]⁺} and 751{[MꢀCl]⁺}. IR: 1609 cm^ꢀ1

m(C@N–). ¹H NMR data:⁷d = 7.73(s, 1H, –CH@N–),

0

71.8(C⁵), 141.9(C¹), 151.0(C²), 120.3(C³), 128.8(C⁴),

0

120.2(C⁵) and 122.4(C⁶).

4.2.3. trans-[Pd{(g⁵-C₅H₅)Fe[(g⁵-C₅H₄)–CH@N–(C₆H₄-

2O)]}₂] (4b)

Compound 1b (272 mg, 8.91 · 10^ꢀ4mol) was dissolved

in 10 mL of methanol, then a solution formed by Pd(OAc)₂

(100 mg, 4.45 · 10^ꢀ4mol) and 5 mL of methanol was

added. The reaction mixture was protected from the light

and stirred at 298 K for 20 min. The red solid formed

(4b) was isolated by ﬁltration and air-dried (yield:

120 mg). Slow evaporation of the ﬁltrate gave small

amounts (30 mg) of 3 b. Anal. Calc. for C₃₄H₂₈Fe₂N₂O₂Pd:

7

Labelling of the atoms corresponds to those presented in Scheme 1 (for

1b–3b and 6b–8b) and Fig. 6 (for 4b and 5b).

2412

S. Pe´rez et al. / Journal of Organometallic Chemistry 692 (2007) 2402–2414

0

C, 57.13; H, 3.95; N, 3.92. Found: C, 57.0; H, 4.3; N, 3.9%.

MS(FAB⁺): m/z = 714{[M]⁺}. IR: 1616 cm^ꢀ1m(C@N–).

¹H NMR data:⁷d = 7.95(s, 2H, –CH@N–), 4.38(s, 10H,

C₅H₅), 4.76(t, 2H, ³J = 2.0, H²and H⁵), 4.61(t, 2H,

1.5, H⁶) and 7.30-7.80(m, 15H, PPh₃). ¹³C{¹H} NMR:^7,8

d = 155.8(–CH@N–), 70.7(C₅H₅), 97.9(C²), 75.7(C³₀),

0

69.3(C⁴), 67.9(C⁵),₀137.6(C⁴), 171.7(C²), 121.6(C³),

0

129.8(C⁴), 113.8(C⁵), 115.2(C⁶) and four additional dou-

blets centred at ca. 128, 129, 131 and 135 due to the four

types of non-equivalent ¹³C nuclei of the PPh₃ligand.

³¹P{¹H} NMR: d = 31.0.

3

4

³J = 2.0, H³and H⁴), 6.84(dd, 2H, J = 7.5 and J = 1.5,

0

3

4

H³), 6.95(td, 2H, J = 7.5 and J = 1.5, H⁴), 6.30(td, 2H,

0

³J = 7.5 and₀J = 1.5, H⁵) and 7.44(dd, 2H, J = 7.5 and

⁴J = 1.5, H⁶). ¹³C{¹H} NMR data:⁷d = 159.4(–CH@N–

), 71.2(C₀₅H₅), 76.0(C¹), 71.9(C²and C⁵), 72.7(C³and C⁴),

4

1

4.2.6. [Pd{[(g⁵-C₅H₃)–CH@N–(C₆H₄-2OH)]Fe(g⁵-

C₅H₅)}Cl(PPh₃)] (7b)

0

139.2(C¹), 168.9(C²), 118.4(C³), 129.6(C⁴), 113.4(C⁵)

0

and 121.5(C⁶).

This product was prepared on a NMR scale as follows:

Complex 6b (10 mg, 1.49 · 10^ꢀ5mol) was dissolved in

0.7 mL of CDCl₃. Then 0.25 lL of a 0.465 M solution of

HCl in methanol-d₄were added. The reaction mixture

was stirred at 298 K for 30 min and then ﬁltered. The ﬁl-

trate was concentrated to dryness on a rotary evaporator

giving a red solid, which was collected and air-dried (yield:

9 mg, 85%). MS(FAB⁺): m/z = 673{[MꢀCl]⁺}. IR:

4.2.4. [Pd{[(g⁵-C₅H₃)–CH@N–(C₆H₄-2O)]Fe(g⁵-

C₅H₅)}]_n(5b)

This complex was obtained as a by-product using the

following procedure: a mixture containing Pd(OAc)₂

(100 mg, 4.45 · 10^ꢀ4mol), 1b (136 mg, 4.45 · 10^ꢀ4mol)

and 50 mL of methanol was reﬂuxed for 2.5 h. After this

period the reaction mixture was allowed to cool to

298 K. The nearly black solid that formed (contained

metallic palladium, compounds 4b and 5b) was collected

by ﬁltration and air-dried. Then it was dissolved in the min-

imum amount of CH₂Cl₂and passed through a SiO₂col-

umn. The elution with CH₂Cl₂produced a narrow brown

band that gave after concentration to dryness complex 5b

(5 mg). The major component 4b was isolated after work

up of the second band released. Slow evaporation of the ﬁl-

trate obtained after the separation of the blackish solid at

298 K gave 3b (40 mg). MS(MALDI-TOF⁺): m/z =

1638.5{[M₄]⁺} and 819.8 {[M₂]⁺}. ¹H NMR data:⁷d =

1569 cm^ꢀ1m(C@N–) and 3420 cm^ꢀ1m(–OH). H NMR

1

data:⁷d = 8.24(d, 1H, J_P–H= 6.8, –CH@N–), 3.97(s, 5H,

4

C₅H₅), 3.56(s, 1H, H³), 4.21(t, 1H, J = 2.0, H⁴), 4.52(d,

3

0

1H, J = 2.0, H⁵), 7.04(d, 1H, J = 8.4, H³), 7.18(t, 1H,

3

0

³J = 7.4, H⁴), 6.99(m, 2H, H⁵and H⁶) and 7.30-7.80(m,

15H, PPh₃). ¹³C{¹H} NMR:⁷d = 175.1(–CH@N–),

70.8(C₅H₅), 86.9(C¹), 104.2(C²), 77.7(C³), 71.1(C⁴₀),

0

67.8(C⁵), 142.1(C¹), 149.5(C²), 121.2(C³), 128.0(C⁴),

0

122.5(C⁵), 122.8.(C⁶) and four additional doublets centred

at ca. 128, 129, 131 and 135 due to the four types of non-

equivalent ¹³C nuclei of the PPh₃ligand. ³¹P{¹H} NMR:

d = 38.8.

7.33(s, 1H, –CH@N–), 4.25(s, 5H, C₅H₅), 4.15(s, 2H, H⁴

4.2.7. [Pd{[(MeO₂C–C@C–CO₂Me)₂(g⁵-C₅H₃)–CH@N–

(C₆H₄-2O)]Fe(g⁵-C₅H₅)}] (8b)

0

and H⁵), 3.79(s, 1H, H³), 7.83(d, 1H, ³J = 7.8,₀H³),

0

3

7.04(t, 1H, J = 7.8, H⁴₀), 6.41(t, 1H, J = 7.8, H⁵) and

Compound 3b (145 mg, 2.03 · 10^ꢀ4mol) was dissolved

in CH₂Cl₂(7 mL), then 0.1 mL of MeO₂C–C„C–CO₂Me

(8.12 · 10^ꢀ4mol) was added. The reaction mixture was

reﬂuxed for 8h and then ﬁltered. The undissolved materials

were discarded and the ﬁltrate was concentrated to dryness

on a rotary evaporator. The residue was dissolved in the

minimum amount of CH₂Cl₂and passed through a SiO₂

column (4.5 cm · 2.0 cm). Elution with CH₂Cl₂produced

the release of three bands. The ﬁrst one was yellow and

gave after concentration to dryness small amounts of 9b.

Small amounts of ferrocenecarboxaldehyde (15 mg) and

traces of 3b (ꢃ3 mg) were isolated from the second and

third band, respectively. Once these bands had been col-

lected a CH₂Cl₂:MeOH (100:0.4) mixture was used as elu-

6.69(d, 1H, J = 7.8, H⁶).

3

4.2.5. [Pd{[(g⁵-C₅H₃)–CH@N–(C₆H₄-2O)]Fe(g⁵-

C₅H₅)}(PPh₃)] (6b)

Complex 3b (155 mg, 2.17 · 10^ꢀ4mol) was dissolved in

15 mL of CH₂Cl₂, then PPh₃(57 mg, 2.17 · 10^ꢀ4mol)

was added. After stirring of the mixture at 298 K for 1 h,

the undissolved materials were removed by ﬁltration and

discarded and the ﬁltrate was concentrated to dryness on

a rotary evaporator. The residue was treated with 5 mL

of CH₂Cl₂and passed through a short (4.5 cm · 2.5 cm)

SiO₂column. The orange-red band collected after the elu-

tion with a CH₂Cl₂:MeOH (100:0.3) solution was concen-

trated to dryness on a rotary evaporator, air-dried and

then dried in vacuum (yield: 84 mg, 58%). Anal. Calc. for

C₃₅H₂₈FeNOPPd: C, 62.57; H, 4.20; N, 2.08. Found: C,

62.3; H, 4.5; N, 2.1%. MS(FAB⁺): m/z = 673{[M+1]⁺}.

IR: 1582 cm^ꢀ1m(C@N–). ¹H NMR data:⁷d = 8.12(d,

ant this produced

a deep red band, which after

concentration produced 8b (49 mg, 35%). Anal. Calc. for

C₂₉H₂₅NO₅FePd: C, 50.21; H, 3.63; N, 2.02. Found: C,

49.7; H, 3.5; N, 2.0%. MS(ESI⁺): m/z = 694{[M]⁺}. IR:

1733 cm^ꢀ1m(COO) and 1597 cm^ꢀ1m(C@N–). H NMR

1

4

1H, J_P–H= 9, –CH@N–), 4.08(s, 5H, C₅H₅), 3.19(d, 1H,

data:⁷d = 8.35(s, 1H, –CH@N–), 4.35(s, 5H, C₅H₅),

³J = 2.2, H³), 4.24(t, 1H, ³J = 2.2, H⁴), 4.67(d, 1H,

0

³J = 2.2, H²), 6.73(dd, 1H, ³J = 7.5 and ⁴J = 1.5, H³),

0

7.00(td, 1H, ³J = 7.5 and ⁴J = 1.5, H⁴), 6.39(td, 1H,

The signal due to the C¹carbon was not detected in the ¹³C{¹H} NMR

spectrum.

8

0

4

³J = 7.5 and J = 1.5, H⁵) and 7.19(dd, 1H, J = 7.5 and

S. Pe´rez et al. / Journal of Organometallic Chemistry 692 (2007) 2402–2414

2413

3

4.77(s, 1H, H³), 4.91(t, 1H, J = 2.4, H⁴), 5.28(s, 1H, H⁵₀),

(b) P.W. Jolly, G. Wilke, W.A. Kermann, B. Cornils (Eds.), Applied

Homogeneous Catalysis with Organometallic Compounds, VCH,

Weinheim, 1996;

(c) I. Omae, Applications of Organometallic Compounds, Wiley,

Chichester, 1998 (Chapter 20).

0

6.92(d, 1H, ³J = 8.4, H³), 7.11(t, 1H, ³J = 8.4, H⁴),

0

6.59(d, 1H, J = 8.4, H⁵), 7.33(d, 1H, J = 8.4, H⁶), four

singlets at 3.95, 3.94, 3.74 and 3,58 (12H, 4OMe).

¹³C{¹H} NMR:⁷d = 152.6(–CH@N–), 72.0(C₅H₅), 78.0(C¹),

3

[4] (a) For recent advances on palladacycles containing terdentate

[C(sp²,aryl),N,X]^ꢀor [C(sp³),N,X]^ꢀligands with X = N⁰or S see

for instance: I. Favier, M. Go´mez, J. Granell, M. Mart´ınez, X.

Solans, Dalton Trans. (2005) 123–132;

0

77.9(C²), 73.1(C³), 74.1(C⁴), 75.8(C⁵), 136.7(C¹), 168.6(C²),

0

120.3(C³), 130.7(C⁴), 116.5(C⁵), 114.6(C⁶), four singlets at

53.3, 52.6, 52.3 and 53.1(4OMe) and 159.2, 164.1, 166.6

and 167.2 (4 COO) and four additional singlets at 149.5,

136.3 119.8 and 119.5 due to the C^a, C^b, C^dand C^ccarbon

nuclei of the inserted g³-butadienyl unit, respectively.

´

(b) C. Lopez, S. Perez, X. Solans, M. Font-Bardıa, J. Organomet.

Chem. 650 (2002) 258–267;

´

(c) A. Fernandez, P. Urıa, J.J. Fernandez, M. Lopez-Torres, A.

´

Suarez, D. Vazquez-Garcıa, M.T. Pereira, J.M. Vila, J. Organomet.

Chem. 620 (2001) 8–19;

´

(d) J.M. Vila, T. Pereira, A. Amoedo, M. Grana, J. Martınez, M.

˜

4.3. Mo¨ssbauer spectra

´

Lopez-Torres, A. Fernandez, J. Organomet. Chem. 623(2001)176–184.

´

[5] C. Lopez, A. Caubet, S. Perez, X. Solans, M. Font-Bardıa, J.

⁵⁷Fe Mo¨ssbauer spectra were recorded using powdered

solid samples. The samples were placed inside an Oxford

Instrument cryostat and the spectra were collected at

80 K using a constant acceleration Mo¨ssbauer spectrom-

eter with a ⁵⁷Co/Rh source. The source was moved via

triangular velocity wave and the c-counts were collected

in a 512 multi-channel analyser. The data were folded,

plotted and ﬁtted by a computer procedure. Velocity cal-

ibration was done using a 25 lm thick metallic iron foil

and the Mo¨ssbauer spectral parameters are given to this

standard.

Organomet. Chem. 681 (2003) 82–90.

[6] (a) A. Ferna´ndez, D. Va´zquez-Garc´ıa, J.J. Ferna´ndez, M. Lo´pez-

´

Torres, A. Suarez, S. Castro-Juiz, J.M. Vila, New J. Chem. 26 (2002)

398–404;

(b) A. Fernandez, E. Pereira, J.J. Fernandez, M. Lopez-Torres, A.

Suarez, R. Mosteiro, J.M. Vila, Polyhedron 21 (2002) 39–48;

(c) H. Yang, M.A. Khan, K.M. Nicholas, J. Chem. Soc., Chem.

Commun. (1992) 210–212;

(d) J. Albert, A. Gonzalez, J. Granell, R.M. Moragas, C. Puerta, P.

´

Valerga, Organometallics 16 (1997) 3775–3778.

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[7] (a) D. Sole, S. Dıaz, X. Solans, M. Font-Bardıa, Organometallics 25

(2006) 1995–2001;

(b) S. Das, S. Pal, J. Organomet. Chem. 691 (2006) 2575–2583.

´

[8] C. Cativiela, L.R. Falvello, J.C. Gines, R. Navarro, E.P. Urriolabei-

tia, New J. Chem. 25 (2001) 344–352.

[9] B.D. Dangel, K. Godula, S.W. Youn, B. Sezen, D. Sames, J. Am.

Chem. Soc. 124 (2002) 11856–11857.

[10] (a) For recent advances in the utility of palladacycles containing

oxygen atoms see for instance: G. Lu, J.L. Portscheller, H.C.

Malinakova, Organometallics 24 (2005) 945–961;

Acknowledgement

This work was supported by the Ministerio de Edu-

´

cacion y Ciencia of Spain.

(b) W.E. Lindsell, D.D. Palmer, P.N. Preston, G.M. Rosair, R.V.H.

Jones, A.J. Whitton, Organometallics 24 (2005) 1119–1133;

(c) M. Kang, A. Sen, Organometallics 24 (2005) 3508–3515;

Appendix A. Supplementary material

CCDC 622635 and 622636 contain the supplementary

crystallographic data for 2b Æ 3H₂O and 3b Æ 1/2CHCl₃.

These data can be obtained free of charge via http://

www.ccdc.cam.ac.uk/conts/retrieving.html, or from the

Cambridge Crystallographic Data Centre, 12 Union Road,

Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or

e-mail: deposit@ccdc.cam.ac.uk. Supplementary data asso-

ciated with this article can be found, in the online version,

at doi:10.1016/j.jorganchem.2007.01.054.

´

(d) J. Vicente, J.A. Abad, M.J. Lopez-Saez, P.G. Jones, Organomet-

allics 25 (2006) 1851–1856;

(e) M. Nagel, A. Sen, Organometallics 25 (2006) 4722–4724.

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(d) S. Perez, C. Lopez, A. Caubet, A. Pawełczyk, X. Solans, M.

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Article Doi

Versatility in the mode of coordination {(N), (N,O)-, (C,N)- or (C,N,O)2-} of [(η5-C5H5)Fe{(η5-C 5H4)-CH{double bond, long}N-(C6H4-2OH)] to palladium(II)

DOI: 10.1016/j.jorganchem.2007.01.054

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