Directed regioselectivity in cyclometallated palladium(II) compounds of N-benzylidenebenzylamines. Crystal and molecular structure of [Pd{3,4-(OCH2O)C6H2C(H)=NCH2- [3,4-(OCH2O)C6H3]-C2,N}(μ-O 2CME)]2

Article abstract of DOI:10.1016/S0277-5387(01)00876-2

The reaction of the Schiff base ligand 3,4-(OCH₂O)C₆H₃C(H)=NCH₂[3,4- (OCH₂O)C₆H₃] (a) with Pd(OAc)₂ yields two endocyclic cyclometallated compounds: [Pd{3,4-(OCH₂O)C₆H₂C(H)=NCH₂ [3,4-(OCH₂O)C₆H₃]-C2,N}(μ-O ₂CMe)]₂ (C2,N-bonded) (1a), and [Pd{3,4-(OCH₂O)C₆H₂C(H)=NCH₂ [3,4-(OCH₂O)C₆H₃]-C6,N}(μ-O ₂CMe)]₂ (C6,N-bonded) (1b), which may be separated by fractional crystallization. The corresponding cyclopalladated dimers with bridging chloride ligands, 2a, 2b, have been prepared by a metathesis reaction with aqueous sodium chloride. Treatment of the latter compounds with tertiary phosphines in the appropriate molar ratio gave the mono and dinuclear compounds, 3a-8a and 3b-5b, respectively. The structure of compound 1a has been determined by X-ray diffraction analysis. The molecular configuration is a dimeric form of the anti isomer with the cyclopalladated moieties in an 'open-book' arrangement linked by two acetate bridging ligands.

Full text of DOI:10.1016/S0277-5387(01)00876-2

Polyhedron 20 (2001) 2925–2933
www.elsevier.com/locate/poly
Directed regioselectivity in cyclometallated palladium(II)
compounds of N-benzylidenebenzylamines. Crystal and molecular
structure of [Pd{3,4-(OCH2O)C6H2C(H)ꢀNCH2-
[3,4-(OCH2O)C6H3]-C2,N}(m-O2CMe)]2
Samuel Castro-Juiz a, Margarita Lo´pez-Torres a, Alberto Ferna´ndez a,
Roberto Mosteiro a, Antonio Sua´rez a, Jose´ M. Vila b,*, Jesu´s J. Ferna´ndez a,*
a Departamento de Qu´ımica Fundamental, Uni6ersidad de La Corun˜a, E-15071 La Corun˜a, Spain
b Departamento de Qu´ımica Inorga´nica, Uni6ersidad de Santiago de Compostela, E-15782 Santiago de Compostela, Spain
Received 3 April 2001; accepted 12 June 2001
Abstract
The reaction of the Schiff base ligand 3,4-(OCH2O)C6H3C(H)ꢀNCH2[3,4-(OCH2O)C6H3] (a) with Pd(OAc)2 yields two
endocyclic cyclometallated compounds: [Pd{3,4-(OCH2O)C6H2C(H)ꢀNCH2[3,4-(OCH2O)C6H3]-C2,N}(m-O2CMe)]2 (C2,N-
bonded) (1a), and [Pd{3,4-(OCH2O)C6H2C(H)ꢀNCH2[3,4-(OCH2O)C6H3]-C6,N}(m-O2CMe)]2 (C6,N-bonded) (1b), which may be
separated by fractional crystallization. The corresponding cyclopalladated dimers with bridging chloride ligands, 2a, 2b, have been
prepared by a metathesis reaction with aqueous sodium chloride. Treatment of the latter compounds with tertiary phosphines in
the appropriate molar ratio gave the mono and dinuclear compounds, 3a–8a and 3b–5b, respectively. The structure of compound
1a has been determined by X-ray diffraction analysis. The molecular configuration is a dimeric form of the anti isomer with the
cyclopalladated moieties in an ‘open-book’ arrangement linked by two acetate bridging ligands. © 2001 Elsevier Science Ltd. All
rights reserved.
Keywords: C–H activation; Phosphorus ligands; Palladium; Schiff base
1. Introduction
cording to the metal, the donor atom, or the chelate
ring size; by far the most well studied examples are
five-membered palladacycles containing nitrogen donor
organic substrates [8]. We have been interested in cyclo-
palladation reactions of differently substituted Schiff
base ligands derived from amines [9], diamines [10] and
dialdehydes [11] and we have also reported five-mem-
bered metallacycles derived from substituted imidazoles
[12]. When cyclometallation involves polyfunctional lig-
ands the question of regioselectivity immediately arises.
Thus, N-benzylidenebenzylamines may yield either en-
docyclic or exocyclic compounds, depending on
whether or not the CꢀN group is included in the
metallated ring. Endocyclic compounds are obtained
when the ortho positions are occupied by hydrogen
atoms, whereas exocyclic derivatives are obtained when
the ortho positions of the benzylidene ring are occupied
by halogens, methyl or methoxy groups [13] or when
The last two decades have seen a growing interest in
reactions that produce cyclometallated palladium(II)
complexes [1] in view of their novel and outstanding
applications, for instance the use as intermediates in
organic and organometallic synthesis [2], and the design
of liquid crystals [3] or antitumor drugs [4]. Therefore,
the characterization of new cyclopalladated compounds
has been of great interest in a wide variety of areas, and
many of them have been described as efficient catalytic
materials [5], chiral discriminators in asymmetric syn-
thesis [6] or interesting photochemical reagents [7].
Cyclometallated compounds are usually classified ac-
* Corresponding authors. Jose´ M. Vila. Tel.: +34-981-563100 x.
14255; fax: +34-981-595012.
E-mail address: qideport@usc.es (J.M. Vila).
0277-5387/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0277-5387(01)00876-2

2926
S. Castro-Juiz et al. / Polyhedron 20 (2001) 2925–2933
the reaction is carried out via oxidative addition with
ligands derived from 2-bromobenzylamine [14].
We have studied the influence of different sub-
stituents adjacent to the potential metallation sites
[15,16], showing that MeO or OCH2CH2O groups hin-
der direct metallation by palladium(II), in contrast to
the less sterically demanding Me or OCH2O groups
which allow attack of the palladium atom at the ortho
position of the ring substituent.
In the present paper, we report the synthesis and
characterization of new examples of mono- and polynu-
clear cyclometallated compounds of palladium(II)
derived from a polyfunctional Schiff base ligand, N-
benzylidenebenzylamine (a), which may undergo metal-
lation on different carbon atoms.
2.3. Synthesis of the complexes
2.3.1. Synthesis of [Pd{3,4-(OCH2O)C6H2C(H)ꢀNCH2-
[3,4-(OCH2O)C6H3]-C2,N}(v-O2CMe)]2 (1a) and
[Pd{3,4-(OCH2O)C6H2C(H)ꢀNCH2[3,4-(OCH2O)-
C6H3]-C6,N}(v-O2CMe)]2 (1b)
3,4-(OCH2O)C6H3C(H)ꢀNCH2[3,4-(OCH2O)C6H3]
(0.640 g, 2.249 mmol) and palladium(II) acetate (0.500
g, 2.227 mmol) were added to 25 cm3 of dry toluene to
give a yellow solution which was heated at 80°C for 3
h under argon. After cooling to room temperature (r.t.)
the solution was filtered to eliminate the small amount
of black palladium formed. The solvent was removed
under vacuum and the product recrystallized from chlo-
roform–n-hexane to give a mixture of 1a–1b in 20:1
molar ratio. Both compounds could be obtained in
pure form from the mixture by fractional crystalliza-
tion. The mixture was dissolved in 50 cm3 of warm
dichloromethane, filtered, n-hexane carefully added and
the resultant solution slowly evaporated. The yellow
crystals formed were filtered to give compound 1a. The
mother liquor was evaporated to dryness to give a
mixture of 1a–1b in 2:1 molar ratio and the residue was
added to a mixture of dichloromethane–n-hexane, kept
at −15°C for 48 h and filtered, yielding a further batch
of compound 1a as a crystalline precipitate and a
solution from which compound 1b was obtained after
solvent elimination. Overall yield: 80%. Anal. Found:
C, 48.3; H, 3.5; N, 3.2. Calc.: C, 48.2; H, 3.4; N, 3.1%.
IR (1a): w(CꢀN) 1607s, was(COO) 1580m; ws(COO)
1425m,sh cm−1. IR (1b): w(CꢀN) 1610s, was(COO)
2. Experimental
2.1. Materials and instrumentation
Solvents were dried according to the standard meth-
ods [17]. The following compounds were used as sup-
plied from commercial sources: palladium(II) acetate
from Johnson Matthey, PPh3, P(p-C6H4OMe)3, Ph2P(p-
C6H4NMe2), Ph2P(CH2)4PPh2 (dppb), Ph2PC5H4FeC5-
H4PPh2 (dppf) and cis-Ph2PCHꢀCHPPh2 (cis-dppe)
from Aldrich-Chemie. Elemental analyses were carried
out by the Servicios Generales de la Universidad de La
Corun˜a using a Carlo-Erba elemental analyzer, model
1108. IR spectra were recorded as Nujol mulls or
polythene discs on a Perkin–Elmer 1330 spectrophoto-
meter. NMR spectra were obtained as CDCl3 solutions
and referenced to SiMe4 [(1H) and 13C{1H}] or 85%
H3PO4 (31P{1H}) and were recorded on a Bruker AC
200F spectrometer (200 MHz for 1H, 81 MHz for
31P{1H}). Mass spectra were obtained in a VG QUAT-
TRO mass spectrometer with Cs ion-gun and 3-NBA
matrix. Conductivity measurements were made on a
CRISON GLP 32 conductivimeter using 10−3 mol
dm−3 solutions in dry acetonitrile.
1580m; ws(COO) 1430m,sh cm−1 13C{1H} NMR (1a):
.
l 182.2 (O2CMe); 171.4 (CꢀN); 151.5 (C2); 148.5 (C3);
147.9 (C4); 147.4 (C9); 141.7 (C10); 128.5 (C7); 128.0
(C1); 123.4, 123.2 (C5, C11); 109.9, 108.4 (C8, C12);
104.3 (C6); 101.1, 100.3 (OCH2O); 60.4 (NCH2); 23.4
(O2CMe). 13C{1H} NMR (1b): l 181.8 (O2CMe); 170.2
(CꢀN); 151.3 (C6); 147.2 (C3); 147.5(C4); 144.7 (C9);
142.1 (C10); 137.8 (C1); 128.7 (C7); 123.1 (C11); 112.3
(C5); 106.8 (C2); 100.7 (OCH2O); 60.5 (NCH2); 23.3
(O2CMe). m/z (FAB) (1a): 837 [M+−OAc], 388 [(L–
H)Pd+]. m/z (FAB) (1b): 837 [M+−OAc], 388 [(L–
H)Pd+].
2.2. Synthesis of 3,4-(OCH2O)C6H3C(H)ꢀNCH2-
[3,4-(OCH2O)C6H3] (a)
2.3.2. Synthesis of [Pd{3,4-(OCH2O)C6H2C(H)ꢀNCH2-
[3,4-(OCH2O)C6H3]-C2,N}(v-Cl)]2 (2a)
Aqueous sodium chloride (ca. 10−2 M) was added
dropwise to 1a (0.400 g, 0.446 mmol) in acetone (ca. 20
cm3). The mixture was stirred for 24 h after which a
yellow solid precipitated which was filtered off, washed
with water and cold acetone and dried in vacuo. Yield:
\95%. Anal. Found: C, 45.2; H, 3.0; N, 3.2. Calc.: C,
45.3; H, 2.9; N, 3.3%. IR: w(CꢀN) 1605s,
The preparation of ligand a was performed by heat-
ing a chloroform solution of piperonal (2 g, 13.321
mmol) and piperonylamine (2.014 g, 13.323 mmol) in a
Dean–Stark apparatus under reflux. Yield: 85.0%.
Anal. Found: C, 68.0; H, 4.5; N, 5.0. Calc.: C, 67.8; H,
4.6; N, 4.9%. IR: w(CꢀN) 1635s cm−1 13C{1H} NMR:
.
l 160.8 (CꢀN); 149.9, 148.3 (C3, C4); 147.7, 146.5 (C9,
C10); 133.4 (C7); 131.0 (C1); 124.5 (C5); 121.0 (C11);
108.6, 108.2 (C8, C12); 108.0, 106.7 (C2, C6); 104.4,
100.9 (OCH2O); 64.5 (NCH2). m/z (FAB): 282 [M+].
w(Pd–Cltrans-N) 325m, w(Pd–Cltrans-C) 290m cm−1
.
Compound 2b was prepared similarly and isolated as
a solid. [Pd{3,4-(OCH2O)C6H2C(H)ꢀNCH2[3,4-(OCH2-

S. Castro-Juiz et al. / Polyhedron 20 (2001) 2925–2933
2927
O)C6H3]-C6,N}(m-Cl)]2 (2b). Yield: 89.4%. Anal.
Found: C, 45.1; H, 3.0; N, 3.4. Calc.: C, 45.3; H, 2.9;
N, 3.3%. IR: w(CꢀN) 1607s, w(Pd–Cltrans-N) 320m,
2.3.5. Synthesis of [Pd{3,4-(OCH2O)C6H2C(H)ꢀNCH2-
[3,4-(OCH2O)C6H3]-C2,N}{cis-Ph2PCHꢀCHPPh2-
P,P%}](ClO4) (8a)
w(Pd–Cltrans-C) 290m cm−1
.
To a solution of 2a (35 mg, 0.041 mmol) in acetone
(ca. 15 cm3), cis-dppe (33 mg, 0.083 mmol) was added.
The mixture was stirred for 1 h at r.t., and sodium
perchlorate (22 mg, 0.084 mmol) was added. The result-
ing mixture was stirred for 1 h, and water added
dropwise until a precipitate formed, which was filtered
off, washed with water, cold acetone and ethanol, dried
in vacuo, and recrystallized from chloroform–n-hex-
ane. Yield: 92.4%. Anal. Found: C, 56.8; H, 4.0; N, 1.7.
Calc.: C, 57.0; H, 3.9; N, 1.6%. IR: w(CꢀN) 1610s
cm−1. m/z (FAB): 785 [M+], 502 [Pd(PP)+].
Compound 5b was prepared similarly and isolated as
a solid.
2.3.3. Synthesis of [Pd{3,4-(OCH2O)C6H2C(H)ꢀNCH2-
[3,4-(OCH2O)C6H3]-C2,N}(PPh3)(Cl)] (3a)
To a solution of 2a (50 mg, 0.059 mmol) in acetone
(ca. 15 cm3), PPh3 (31 mg, 0.118 mmol) was added. The
mixture was stirred for 3 h at r.t., after which the
precipitate formed was filtered off, washed with cold
acetone and dried in vacuo. Yield: 81.1%. Anal. Found:
C, 59.2; H, 3.9; N, 2.1. Calc.: C, 59.5; H, 4.0; N, 2.0%.
IR: w(CꢀN) 1610s, w(Pd–Cl) 280m cm−1. m/z (FAB):
650 [M+−Cl].
Compounds 4a, 5a, 3b and 4b were prepared simi-
larly and isolated as solids.
[Pd{3,4-(OCH2O)C6H2C(H)ꢀNCH2[3,4-(OCH2O)-
C6H3]-C6,N}{cis-Ph2PCHꢀCHPPh2-P,P%}](ClO4) (5b).
Yield: 83.7%. Anal. Found: C, 56.9; H, 4.0; N, 1.8.
Calc.: C, 57.0; H, 3.9; N, 1.6%. IR: w(CꢀN) 1610s
cm−1. m/z (FAB): 785 [M+], 502 [Pd(PP)+].
[Pd{3,4-(OCH2O)C6H2C(H)ꢀNCH2[3,4-(OCH2O)-
C6H3]-C2,N}{P(p-OMeC6H4)3}(Cl)] (4a). Yield: 78.0%.
Anal. Found: C, 57.4; H, 4.2; N, 1.9. Calc.: C, 57.2; H,
4.3; N, 1.8%. IR: w(CꢀN) 1602s, w(Pd–Cl) 285m cm−1
.
[Pd{3,4-(OCH2O)C6H2C(H)ꢀNCH2[3,4-(OCH2O)-
C6H3]-C2,N}{P(p-NMe2C6H4)Ph2}(Cl)] (5a). Yield:
75.9%. Anal. Found: C, 59.5; H, 4.5; N, 4.0. Calc.: C,
59.3; H, 4.4; N, 3.8%. IR: w(CꢀN) 1605s, w(Pd–Cl)
2.4. Single-crystal X-ray diffraction analysis
Crystal data for 1a: C36H30N2O12Pd2·CH2Cl2, Mr=
980.35, crystal dimensions 0.40×0.20×0.20 mm, a=
275m cm−1
.
,
A,
12.590(1),
b=12.994(1),
c=13.733(1)
[Pd{3,4-(OCH2O)C6H2C(H)ꢀNCH2[3,4-(OCH2O)-
C6H3]-C6,N}{P(p-OMeC6H4)3}(Cl)] (3b). Yield: 80.2%.
Anal. Found: C, 56.9; H, 4.4; N, 1.9. Calc.: C, 57.2; H,
h=68.769(1)°, i=73.559(1)°, k=65.011(1)°, V=
3
1875.65(2) A , v(Mo Ka)=1.168 mm−1, u=0.71073
,
,
(
A, Z=2, T=293(2) K, triclinic, space group P1. Crys-
tal structure determination: three-dimensional, room
temperature X-ray data were collected in the range
1.61BqB28.31° on a Siemens Smart CCD diffrac-
4.3; N, 1.8%. IR: w(CꢀN) 1610s, w(Pd–Cl) 280m cm−1
.
[Pd{3,4-(OCH2O)C6H2C(H)ꢀNCH2[3,4-(OCH2O)-
C6H3]-C6,N}{P(p-NMe2C6H4)Ph2}(Cl)] (4b). Yield:
79.0%. Anal. Found: C, 59.1; H, 4.6; N, 3.9. Calc.: C,
59.3; H, 4.4; N, 3.8%. IR: w(CꢀN) 1610s, w(Pd–Cl)
tometer by the
ꢀ scan method using graphite-
monochromated Mo Ka radiation. Of the 13042
reflections measured, all of which were corrected for
Lorentz and polarization effects and for absorption by
semi-empirical methods based on symmetry-equivalent
and repeated reflections [minimum and maximum
transmission coefficients 0.800, 0.652], 6908 indepen-
dent reflections exceeded the significance level ꢀFꢀ/
|(ꢀFꢀ)\4.0. The structure was solved by direct
methods and refined by full matrix least squares on F2.
Hydrogen atoms were included in calculated positions
and refined in riding mode. Refinement converged at a
final R=0.0500 (observed data, F) and wR2=0.1281
(8980 unique data, F2), with allowance for thermal
anisotropy of all non-hydrogen atoms. Minimum and
maximum final electron density were −1.271 and 1.184
275m cm−1
.
2.3.4. Synthesis of [{Pd{3,4-(OCH2O)-
C6H2C(H)ꢀNCH2[3,4-(OCH2O)C6H3]-C2,N}(Cl)}2-
{v-Ph2P(CH2)4PPh2}] (6a)
To a solution of 2a (50 mg, 0.059 mmol) in acetone
(ca. 15 cm3), dppb (25 mg, 0.059 mmol) was added. The
mixture was stirred for 8 h at r.t., after which the
precipitate formed was filtered off, washed with cold
acetone, dried in vacuo, and recrystallized from
dichloromethane–n-hexane. Yield: 84.9%. Anal.
Found: C, 56.7; H, 3.9; N, 2.3. Calc.: C, 56.5; H, 4.1;
N, 2.2%. IR: w(CꢀN) 1600s, w(Pd–Cl) 280m cm−1. m/z
(FAB): 1239 [M+−Cl], 957 [M+−(L–H)–Cl], 815
[(L–H)Pd(PP)+], 532 [Pd(PP)+].
e A−3. The structure solution and refinement were
,
Compound 7a was prepared similarly and isolated as
a solid.
carried out using the program package SHELX-97 [18].
[{Pd{3,4-(OCH2O)C6H2C(H)ꢀNCH2[3,4-(OCH2O)-
C6H3]-C2,N}(Cl)}2(m-Ph2PC5H4FeC5H4–PPh2)]
(7a).
3. Results and discussion
Yield: 79.3%. Anal. Found: C, 56.8; H, 3.9; N, 1.9.
Calc.: C, 56.5; H, 3.7; N, 2.0%. IR: w(CꢀN) 1605s,
For the convenience of the reader the compounds
and reactions are shown in Schemes 1–3. The com-
w(Pd–Cl) 275m cm−1
.

2928
S. Castro-Juiz et al. / Polyhedron 20 (2001) 2925–2933
pounds described in this paper were characterized by
elemental analysis (C, H, N) and by IR (data in Section
2) and by 1H and 31P{1H} NMR spectroscopy (Table 1)
and (in part) by 13C{1H} NMR spectroscopy and mass
spectrometry (Section 2).
[3,4-(OCH2O)C6H3]-C2,N}(m-Cl)]2 (2a) and [Pd{3,4-
(OCH2O)C6H2C(H)ꢀNCH2[3,4-(OCH2O)C6H3]-C6,N}-
(m-Cl)]2 (2b), respectively, with exchange of the acetate-
bridging groups by chloride-bridging ligands. The IR
spectra showed the absence of the acetate bands and
the appearance of two w(Pd–Cl) bands, consistent with
an asymmetric Pd2Cl2 bridging unit [21].
Reaction of the Schiff base ligand 3,4-(OCH2O)-
C6H3C(H)ꢀNCH2[3,4-(OCH2O)C6H3] (a) with palladiu-
m(II) acetate in toluene at 80°C for 3 h gave a yellow
solid as a mixture of two products, both of which are
five-membered endo-palladacycles: [Pd{3,4-(OCH2O)-
C6H2C(H)ꢀNCH2[3,4-(OCH2O)C6H3]-C2,N}(m-O2-
CMe)]2 (1a), and [Pd{3,4-(OCH2O)C6H2C(H)ꢀNCH2-
[3,4-(OCH2O)C6H3]-C6,N}(m-O2CMe)]2 (1b), in 20:1
(1a–1b) molar ratio, showing C(2)–H and C(6)–H
activation, respectively (see Scheme 1). These results,
together with our previous findings [15,16], allow us to
confirm unambiguously that the OCH2O moiety is not
only a weak sterically demanding group, as opposed to
the bulkier OCH2CH2O substituent which imposes
metallation at the C6 atom exclusively, but also that it
seems to direct metallation preferably at the C2 carbon
atom. Furthermore, in the present case we have suc-
cessfully achieved total separation of both isomers in
pure form by fractional crystallization from dichloro-
methane–n-hexane.
The shift of the CꢀN stretch towards lower
wavenumbers, as compared to a (ca. 1610 vs. 1635
cm−1), indicates N-coordination of the CꢀN group
[19]. The HCꢀN proton resonance in the 1H NMR
spectra is upfield shifted by ca. 1.2 ppm from its
position in the free ligand, in accordance with Pd–N
bonding. Previous studies [20] have shown that for
cyclometallated complexes derived from Schiff bases,
the position of the imine proton is also indicative of the
conformation of the ligand in the complexes. In the
Treatment of 2a or 2b with tertiary monophosphines
in 1:2 molar ratio gave the mononuclear derivatives
[Pd{3,4-(OCH2O)C6H2C(H)ꢀNCH2[3,4-(OCH2O)C6-
H3]}(PR3)(Cl)] (3a–5a and 3b–4b, respectively) after
cleavage of the Pd2Cl2 moiety, which were fully charac-
terized (see Section 2). The IR spectra show a band at
ca. 280 cm−1 assigned to the w(Pd–Cl) stretching vibra-
tion consistent with a trans-Cl–Pd–C geometry [22].
1
The H NMR spectra showed the HCꢀN proton reso-
nance coupled to the phosphorus atom [4J(PH5) ca. 8.0
Hz]. For complexes 3a–5a, the OCH2O resonance was
strongly shifted to lower frequency, ca. 1.00 ppm, due
to the shielding effect of the phosphine phenyl rings.
This is in accordance with a P trans to N arrangement
and within the terms of the ‘transphobic effect’ as
coined by Vicente et al. [23]. For complexes 3b and 4b
the H5 resonance was coupled to the phosphorus atom
[4J(PH5)=7.8 Hz], thus confirming the cis geometry of
the phosphine and of the metallated phenyl group. The
31P{1H} NMR spectra showed a singlet resonance in all
cases, shifted to higher frequency from the free phos-
phine, in agreement with phosphorus coordination to
metal center [24].
The reaction of 2a with dppb and dppf in 1:1 molar
ratio afforded the dinuclear complexes [{Pd[3,4-
(OCH2O)C6H2C(H)ꢀNCH2[3,4-(OCH2O)C6H3]-C2,N]-
(Cl)}2(m-Ph2PR–PPh2)] (6a [R=(CH2)4] and 7a [R=
C5H4FeC5H4]), respectively, which were fully character-
ized (see Section 2). The phosphorus resonance in the
31P{1H} NMR spectra was a singlet showing the equiv-
alence of the two phosphorus nuclei. The MS-FAB
spectrum of complex 6a shows, among others, a peak
assigned to [M+−Cl] ions, thereby confirming the
dinuclear nature of these complexes [25].
present paper the l(HCꢀN)complexesBl(HCꢀN)free ligand
,
which suggests that the ligand adopts the anti-form in
the palladacycles. The C(2)–H (2a) and C(6)–H (2b)
proton resonances are absent showing metallation of
the C(2) and C(6) atoms, respectively.
Complexes 1a and 1b react with aqueous sodium
chloride to give [Pd{3,4-(OCH2O)C6H2C(H)ꢀNCH2-
Scheme 1.

Table 1
1H a and 31P{1H} b NMR data c
l(Hi)
l(H2)
l(H5)
l(H6)
l(NCH2)
4.69d
l(OCH2O)
l(P)
d
a
8.24t, 4J(HiNCH2)=1.5
7.41d,
6.83d, 3J(H5H6)=8.3 7.13dd
6.54d, 3J(H5H6)=8.3 6.71d
6.62s
5.99s, 5.94s
4J(H2H6)=1.9
1a e 7.05t, 4J(HiNCH2)=1.5
1b f 7.02t, 4J(HiNCH2)=1.5
2a g 7.51b
4.53d, 3.99d,
5.95s, 5.89d, 5.79d,
J
gem=15.6
J
gem=1.5
5.96s, 5.92d, 5.89d,
gem=1.5
o
6.64s
J
6.51d, 3J(H5H6)=7.8 6.80d
6.42d, 3J(H5H6)=7.8 6.88d
4.68b
5.09b
5.97s, 5.94s
3a h 7.87dt, 4J(PHi)=7.8, 4J(HiNCH2)=1.5
5.97s, 4.61s
37.9s
4a i 7.83dt, 4J(PHi)=8.3, 4J(HiNCH2)=1.5
5a j 7.83dt, 4J(PHi)=7.8, 4J(HiNCH2)=1.5
6.42d, 3J(H5H6)=7.8 6.88d
6.40d, 3J(H5H6)=7.8 6.87d
6.38d, 3J(H5H6)=7.8 6.85d
5.05b
5.09b
5.05b
5.96s, 4.70s
5.96s, 4.65s
5.93s, 4.70s
30.0s
35.7s
30.0s
o
6a k
7a l 7.88d, 4J(PHi)=7.8
8a m 8.00dt, 4J(PHi)=7.8, 1.5,
4J(HiNCH2)=1.5
6.39d, 3J(H5H6)=7.8 6.89d
6.55d, 3J(H5H6)=7.8 7.09d,
4.95b
4.49b
5.90s, 4.62s
5.94s, 5.06s
27.5s
62.4d p, 54.5d,
3J(PP)=11.0
5J(PH6)=2.3
/
2b n 7.53d, 4J(PHi)=7.7
6.69s
6.68s
4.69b
4.90b
4.91b
4.46b
5.96s, 5.92s
5.94s, 5.71s
5.97s, 5.70s
5.83s, 4.99s
3b n 7.76dt, 4J(PHi)=7.8, 4J(HiNCH2)=1.5 6.72s
4b n 7.75dt, 4J(PHi)=7.8, 4J(HiNCH2)=1.5 6.71s
6.39d, 4J(PH5)=7.8
6.38d, 4J(PH5)=7.8
39.20s
40.94s
2
1
5b n 7.60d, 4J(PHi)=7.6
6.90d,
6.28dd,
63.9d p, 53.1d,
5J(PH2)=2.3
4J(PH5)=5.5, 2.3 q
3J(PP)=11.1
295
a In CDCl3. Measured at 200 MHz (ca. 20 °C), chemical shifts (l) in ppm (90.01) to high frequency of SiMe4.
b In CDCl3. Measured at 81 MHz (ca. 20 °C), chemical shifts (l) in ppm (90.01) to high frequency of 85% H3PO4.
c Coupling contants in Hz; s, singlet; d, doublet, dd, doublet of doublets, t, triplet; dt, doublet of triplets; b, broad; m, multiplet.
d l(H8, H11, H12)=6.80m.
2
e l(H8)=6.31d, 4J(H8H12)=1.5; l(H11)=6.73d, 3J(H11H12)=7.8; l(H12)=6.44dd; l(MeCO2)=2.09s.
f l(H8)=6.26d, 4J(H8H12)=1.5; l(H11)=6.73d, 3J(H11H12)=7.8; l(H12)=6.37dd; l(MeCO2) occluded.
g l(H8, H11, H12)=6.81m.
h l(H8)=6.86d, 4J(H8H12)=1.5; l(H11)=6.80d, 3J(H11H12)=7.8; l(H12)=6.92dd.
i l(H8)=6.99d, 4J(H8H12)=1.5; l(H11)=6.78d, 3J(H11H12)=7.8; l(H12)=6.95dd; l(OMe)=3.80s.
j l(H8)=6.94d, 4J(H8H12)=1.5; l(H11)=6.83d, 3J(H11H12)=7.8; l(H12)=6.65dd; l(NMe2)=2.99s.
k l(H8)=7.00d, 4J(H8H12)=1.5; l(H11)=6.79d, 3J(H11H12)=7.8; l(H12)=6.89dd.
l l(H8)=6.94d, 4J(H8H12)=1.5; l(H11)=6.77d, 3J(H11H12)=7.8; l(H12)=6.86dd; l(C5H4)=5.05d, 4.41d, 3J(HaHb)=2.9 Hz.
m l(H8)=6.25d, 4J(H8H12)=1.5; l(H11)=6.68d, 3J(H11H12)=7.8; l(H12)=6.40dd; l(HC=CH) occluded.
n l(H8), l(H11), l(H12) occluded; l(OMe)=3.82s (3b); l(NMe2)=3.01s (4b); l(HCꢀCH) occluded (5b).
o Occluded.
p l(Ptrans-N)\l(Ptrans-C).
q 4J(PtransH)\4J(PcisH).

2930
S. Castro-Juiz et al. / Polyhedron 20 (2001) 2925–2933
Scheme 2. (i) NaCl, Me2CO–H2O. (ii) PPh3 (3a), P(p-C6H4OMe)3 (4a), PPh2(p-C6H4NMe2) (5a) (1:2 molar ratio), Me2CO. (iii) dppb (1:1 molar
ratio), Me2CO. (iv) dppf (1:1 molar ratio), Me2CO. (v) cis-dppe (1:2 molar ratio), NaClO4, Me2CO–H2O.
Treatment of the chlorine-bridged complexes 2a and
2b with cis-dppe in 1:2 molar ratio and sodium perchlo-
rate yielded the mononuclear cyclometallated
[M+−diphosphine] ions. The conductivity data (125–
150 V−1cm2 mol−1 in 10−3 mol dm−3 solutions in dry
acetonitrile) showed them to be 1:1 electrolytes [26].
1
compounds
[Pd{3,4-(OCH2O)C6H2C(H)ꢀNCH2[3,4-
The HCꢀN resonance in the H NMR spectra at ca.
(OCH2O)C6H3]}{cis-Ph2PCHꢀCHPPh2-P,P%}](ClO4)
(8a (C2,N-bonded) and 5b (C6,N-bonded)), respec-
tively. The MS-FAB spectra showed similar fragmenta-
tion patterns, containing peaks assigned to [M+] and
7.60 ppm appeared as a doublet due to coupling with
the 31P nucleus [4J(PHi)=7.6 Hz] trans to nitrogen.
For complex 8a, long-range coupling was observed for
the H6 resonance, which appeared as a doublet by

S. Castro-Juiz et al. / Polyhedron 20 (2001) 2925–2933
2931
coupling to the phosphorus atom trans to the metal-
lated carbon atom [5J(PH6)=2.3 Hz]. For complex 5b,
the H5 resonance in the 1H NMR spectrum of 5b
appeared as a doublet of doublets by coupling to both
phosphorus atoms. Selective decoupling experiments
allowed the correct assignment of the corresponding
coupling constants [trans-4J(PH5)=5.5, cis-4J(PH5)=
2.3 Hz]. The 31P{1H} NMR spectra showed two dou-
blets, indicating the two phosphorus atoms to be
non-equivalent in each case. Selective irradiation al-
lowed the assignment of the doublets, in accordance
with the assumption that a ligand of greater trans
influence shifts the resonance of the phosphorus atoms
trans to it to lower frequency [24].
isomer with the cyclopalladated moieties in an ‘open
book’ arrangement linked by two acetate bridging lig-
ands between the palladium atoms, as observed in the
related dimers [27]. The species possesses approximate
(non-crystallographic) C2 symmetry with the two-fold
axis perpendicular to the Pd–Pd vector. In accordance
with the spectroscopic results, the molecular structure
of 1a corresponds to the endo isomer in which the
palladium atom is bonded to the carbon atom adjacent
to the OCH2O and CꢀN groups of the benzylidene ring.
,
The palladium···palladium distance is 2.9330(5) A,
which may be regarded as non-bonding (the covalent
radius of square-planar Pd(II) has been estimated as
,
approximately 1.31 A) [28]. Each palladium atom is in
a slightly distorted square-planar coordination environ-
ment. The coordination sphere around each palladium
atom consists of an ortho carbon of the phenyl ring, the
CꢀN nitrogen atom, and two oxygen atoms, one from
each of the bridging acetate ligands. The angles be-
tween adjacent atoms in the coordination sphere are
close to the expected value of 90°, in the range 81.2–
94.3°, with the more noticeable distortions in the ‘bite’
angles C(6)–Pd(1)–N(1) and C(26)–Pd(2)–N(2),
81.2(2)° consequent upon chelation.
4. Molecular structure of complex 1a
Suitable crystals of the title compound were grown
by slow evaporation of a cooled dichloromethane–n-
hexane solution of the complex. The numbering scheme
is shown in Fig. 1. Crystallographic data and selected
bond lengths and angles are listed in Table 2. The
crystal structure consists of discrete dinuclear molecules
separated by normal van der Waals distances. The
molecular configuration is a dimeric form of the anti
The palladium–nitrogen bond lengths [Pd(1)–
,
N(1)=2.009(4) and Pd(2)–N(2)=2.005(4) A] are in
Scheme 3. (i) NaCl, Me2CO–H2O. (ii) P(p-C6H4OMe)3 (3b), PPh2(p-C6H4NMe2) (4b) (1:2 molar ratio), Me2CO. (iii) cis-dppe (1:2 molar ratio),
NaClO4, Me2CO–H2O.

2932
S. Castro-Juiz et al. / Polyhedron 20 (2001) 2925–2933
Fig. 1. Labeling of atoms in [Pd-{3,4-(OCH2O)C6H2C(H)ꢀNCH2(3,4-{OCH2O}C6H3)-C2,N}(m-O2CMe)]2 (1a).
,
,
0.0071, 0.0061 and 0.0065, 0.0037 A, respectively. The
good agreement with the predicted value of 2.01 A,
based on the sum of covalent radii for nitrogen(sp2)
angles between planes are as follows: plane 1/plane 2
3.9°, plane 1/plane 3 6.4°, plane 2/plane 3 3.8° and
plane 4/plane 5 3.8°, plane 4/plane 6 5.2°, plane 5/plane
6 1.4°.
,
and palladium, 0.701 and 1.31 A, respectively [29].
However, the palladium–carbon bond lengths, [Pd(1)–
C(6)=1.967(5) and Pd(2)–C(26)=1.964(5) A], are
,
,
rather shorter than the predicted value of 2.081 A,
based on the sum of covalent radii for carbon(sp2) and
Table 2
,
palladium, 0.771 and 1.31 A, respectively, suggesting
,
Selected bond lengths (A) and angles (°) for 1a
some degree of multiple-bond character in the Pd–
C(aryl) linkage, as has been observed before [30].
The trans influence of s-bonded carbon is put for-
ward by the lengthening of the palladium–oxygen dis-
tances trans to carbon [Pd(1)–O(7)=2.125(3),
Bond lengths
Pd(1)–C(6)
Pd(1)–N(1)
Pd(1)–O(5)
Pd(1)–O(7)
Pd(1)–Pd(2)
N(1)–C(7)
N(1)–C(8)
O(1)–C(4)
O(1)–C(15)
O(2)–C(5)
O(2)–C(15)
O(3)–C(11)
O(3)–C(16)
O(4)–C(12)
O(4)–C(16)
C(1)–C(7)
1.967(5)
2.009(4)
2.033(3)
2.125(3)
2.9330(5)
1.290(6)
1.473(6)
1.383(7)
1.425(10)
1.363(6)
1.420(8)
1.373(7)
1.406(10)
1.378(7)
1.423(11)
1.441(6)
Pd(2)–C(26)
Pd(2)–N(2)
Pd(2)–O(8)
Pd(2)–O(6)
1.964(5)
2.005(4)
2.041(3)
2.120(4)
,
Pd(2)–O(6)=2.120(4) A] as opposed to the shorter
Pd–O bond lengths trans to nitrogen [Pd(1)–O(5)=
N(2)–C(27)
N(2)–C(28)
O(9)–C(24)
O(9)–C(35)
O(10)–C(25)
O(10)–C(35)
O(11)–C(31)
O(11)–C(36)
O(12)–C(32)
O(12)–C(36)
C(21)–C(27)
1.276(6)
1.477(6)
1.373(7)
1.400(10)
1.368(7)
1.440(8)
1.366(6)
1.426(8)
1.374(6)
1.422(8)
1.442(7)
,
2.033(3), Pd(2)–O(8)=2.041(3) A].
As a result of the Pd(1) and Pd(2) atoms being
bridged by two mutually cis m-acetate ligands, the
chelating C,N bonded Schiff bases are forced to lie
above one another in the dimeric molecule. This leads
to interligand repulsions on the ‘open’ side of the
molecule and results in the coordination planes of the
palladium atoms being tilted at an angle of 34.6° to one
another. The two acetate bridges are separated by
dihedral angles of 85.1°.
The cyclometallated moiety is almost planar. The
mean deviations from the least squares planes deter-
mined by the coordination spheres of palladium (plane
1: Pd1, N1, C6, O5, O7; plane 4: Pd2, N2, C26, O8,
O6), the metallacycles (plane 2: Pd1, N1, C7, C1, C6;
plane 5: Pd2, N2, C27, C21, C26) and the metallated
phenyl rings (plane 3: C1, C2, C3, C4, C5, C6; plane 6:
C21, C22, C23, C24, C25, C26) are 0.0295, 0.0380;
Bond angles
C(6)–Pd(1)–N(1)
C(6)–Pd(1)–O(5)
N(1)–Pd(1)–O(5)
C(6)–Pd(1)–O(7)
N(1)–Pd(1)–O(7)
O(5)–Pd(1)–O(7)
C(3)–C(4)–O(1)
O(2)–C(5)–C(6)
81.18(17) C(26)–Pd(2)–N(2)
93.98(17) C(26)–Pd(2)–O(8)
174.12(15) N(2)–Pd(2)–O(8)
172.59(16) C(26)–Pd(2)–O(6)
94.07(14) N(2)–Pd(2)–O(6)
90.39(15) O(8)–Pd(2)–O(6)
81.20(18)
94.32(18)
175.01(15)
172.48(16)
94.25(15)
89.97(15)
125.0(6)
126.0(6)
129.3(5)
C(23)–C(24)–O(9)
O(10)–C(25)–C(26) 128.9(5)
O(3)–C(11)–C(10)
C(13)–C(12)–O(4)
C(30)–C(31)–O(11) 128.1(5)
C(33)–C(32)–O(12) 128.8(5)
127.9(6)
127.3(6)

S. Castro-Juiz et al. / Polyhedron 20 (2001) 2925–2933
2933
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5. Supplementary data
Full details of data collection and structure refine-
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compound 1a. Copies of this information may be ob-
tained free of charge from The Director, CCDC, 12
Union Road, Cambridge, CB2 1EZ, UK (fax: +44-
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Acknowledgements
We wish to thank the DGESIC (Spain, Proyecto
PB98-0638-C02-01/02) for financial support. RM ac-
knowledges a fellowship from the Ministerio de Ciencia
y Tecnolog´ıa (Spain).
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