Stable alkynyl palladium(II) and nickel(II) complexes with terdentate PNO and PNN hydrazone ligands

Article abstract of DOI:10.1016/S0022-328X(99)00519-7

Chloro and acetato complexes of palladium(II) and nickel(II) with terdentate PNO acylhydrazonic ligands derived from 2-(diphenylphosphino)benzaldehyde have been synthesized and characterized. The acetato complexes are able to activate the C-H bond of terminal alkynes, giving stable alkynyl complexes, one of which has been X-ray characterized. The coordination chemistry of the new PNN ligand 2-(diphenylphosphino)benzaldehyde 2-pyridylhydrazone (HL6) has been also investigated and the X-ray crystal structure of the complex [Pd(HL6)Cl][PdL6Cl]Cl·2H₂O is reported. Starting from the nickel(II) acetato complex of HL6, it has been possible to obtain a new stable alkynyl derivative.

Full text of DOI:10.1016/S0022-328X(99)00519-7

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 593–594 (2000) 180–191
Stable alkynyl palladium(II) and nickel(II) complexes with
terdentate PNO and PNN hydrazone ligands
Alessia Bacchi a, Mauro Carcelli a, Mirco Costa b, Andrea Fochi a, Claudio Monici b,
Paolo Pelagatti a, Corrado Pelizzi a, Giancarlo Pelizzi a,*, Luisa Maria Sanjuan Roca a,1
a Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica, Uni6ersita` degli Studi di Parma,
Parco Area delle Scienze 17/A, I-43100 Parma, Italy
b Dipartimento di Chimica Organica ed Industriale, Uni6ersita` degli Studi di Parma, Parco Area delle Scienze 17/A, I-43100 Parma, Italy
Received 4 June 1999; accepted 7 September 1999
Abstract
Chloro and acetato complexes of palladium(II) and nickel(II) with terdentate PNO acylhydrazonic ligands derived from
2-(diphenylphosphino)benzaldehyde have been synthesized and characterized. The acetato complexes are able to activate the CꢀH
bond of terminal alkynes, giving stable alkynyl complexes, one of which has been X-ray characterized. The coordination chemistry
of the new PNN ligand 2-(diphenylphosphino)benzaldehyde 2-pyridylhydrazone (HL6) has been also investigated and the X-ray
crystal structure of the complex [Pd(HL6)Cl][PdL6Cl]Cl·2H2O is reported. Starting from the nickel(II) acetato complex of HL6,
it has been possible to obtain a new stable alkynyl derivative. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Alkynyl complexes; Nickel complexes; Palladium complexes; Terdentate ligands; Hydrazone
1. Introduction
also
obtained
by
direct
synthesis
between
Pd(L2)(CH3COO) and phenylacetylene at room tem-
perature [7]. The mild conditions of this reaction are
remarkable, in fact most alkynylpalladium(II) com-
plexes were obtained by oxidative addition of an
alkynyl halide to a palladium(0) complex or via meta-
thetic substitution between a halopalladium(II) complex
and Li(CꢁCꢀR) [8]. There is a considerable interest in
metal complexes incorporating the alkyne moiety, e.g.
as material for non-linear optics [9], for luminescence
studies [10], and as rigid rod molecular wires [11]. In
this context, a set of PNO hydrazone ligands (Scheme
1) and the corresponding palladium(II) complexes
(Schemes 1 and 2) were synthesized and their reactivity
towards alkynes was studied. The PNN ligand 2-
(diphenylphosphino)benzaldehyde 2-pyridylhydrazone
(HL6, Scheme 1) was also synthesized, where the car-
bonyl oxygen donor is replaced by the pyridine nitro-
gen, but the monoprotic nature of the ligand is
retained; its nickel(II) and palladium(II) complexes
were characterized and their reactivity towards pheny-
lacetylene was examined.
Recently a considerable interest has been directed
towards the synthesis of complexes with terdentate
ligands, and their use in organometallic chemistry and
homogeneous catalysis is growing [1–3]. As part of our
ongoing research on the coordination properties of
hydrazones, we undertook the synthesis of terdentate,
semi-labile, multifunctional ligands having both hard
and soft donor atoms and of their palladium(II) com-
plexes [4]; the reactivity of these compounds towards
small molecules as hydrogen [5] and carbon monoxide
[6] was also studied. During the hydrogenation of
phenylacetylene catalyzed by Pd(L2)(CH3COO)
(HL2=2-(diphenylphosphino)benzaldehyde benzoylhy-
drazone)
the
alkynylpalladium(II)
complex
Pd(L2)(CꢁCꢀC6H5) was isolated; the same product was
* Corresponding author. Fax: +39-0521-905557.
E-mail address: chimic6@ipruniv.cce.unipr.it (G. Pelizzi)
1 Present address: Departimento de Quimica Inorganica, Universi-
dade de Santiago de Compostela, Av. das Ciencias s/n, A Corunha,
Spain.
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00519-7

A. Bacchi et al. / Journal of Organometallic Chemistry 593–594 (2000) 180–191
181
The synthesis of the ligands HL1–5 and the corre-
sponding complexes 1b(Pd)–5b(Pd), 2a(Pd) and 2c(Pd)
was already described [5,7]; X-ray quality crystals of
2a(Pd) were obtained by recrystallization from toluene.
2.1. Preparation of the ligand HL6
A methanol solution (20 ml) of 2-hydrazinopyridine
(0.120 g, 1.1 mmol) and 2-(diphenylphosphino)benzal-
dehyde (0.318 g, 1.1 mmol) was refluxed for 30 min; the
light yellow precipitate was filtered, washed with ethyl
ether and dried. Yield 78%; m.p. 201°C. IR (cm−1):
w(NH) 3201br, w(CHar) 3053m, w(CꢂN) 1601s, w(CꢀP)
1435m; 1H-NMR (DMSO-d6): l 10.95 (s, D2O ex-
changeable, 1H, NH), 8.59 (d, 1H, CHꢂN, J(PꢀH) 4
Hz), 8.05 (d, 1H, H1), 7.54 (m, 1H, H3), 7.45–7.18 (m,
14H), 7.38 (d, 1H, H4), 6.72 (t, 1H, H2). 31P-NMR
(CDCl3, 80 MHz): l −13.4 (s).
Scheme 1. Presentation of the ligands.
2.2. Preparation of the complexes
2.2.1. Complexes of the ligands HL1–HL5
A solution of the ligand (0.100 g) in dichloromethane
(20 ml) was slowly added to a solution containing an
equimolar amount of the metal salt (K2PdCl4,
NiCl2·6H2O or Ni(CH3COO)2·4H2O) in methanol–wa-
ter (25:10 ml). The mixture was stirred at room temper-
ature (r.t.) for 3 h, then the yellow organic phase was
dried with Na2SO4; after slow evaporation of the sol-
vent, a microcrystalline product was isolated.
1a(Pd) — M.p. \320°C. Yield 79%. IR (cm−1):
1
w(CꢂN) 1615br, 1518vs, w(CꢀP) 1432m, 1378w; H-NMR
(DMSO-d6): l 8.58 (d, 1H, CHꢂN, J(PꢀH) 4 Hz), 8.00
(m, 1H, J(ortho) 6 Hz), 7.80 (t, 1H, J(ortho) 7.4 Hz),
7.67–7.53 (m, 11H, Ph), 7.42 (t, 1H, H, J(ortho) 9.6
Hz), 2.00 (s, 3H, CH3). 31P-NMR (CDCl3, 80 MHz): l
32.1 (s).
Scheme 2. Structure and annotation for the complexes, M=Ni or
Pd.
3a(Pd) — M.p. 300°C (dec.). Yield 65%. IR (cm−1):
w(CꢂN) 1599vw, 1500vs, 1472s, w(CꢀP) 1436m, 1384vs,
1358s; 1H-NMR (CDCl3): l 8.58 (d, 1H, CHꢂN,
J(PꢀH) 4 Hz), 8.28 (d, 2H, J(ortho) 7.4 Hz), 7.93–7.62
(m, 13H, Ph), 7.56 (t, 1H, J(ortho) 9.2 Hz), 7.36 (d, 2H,
J(ortho) 7.5 Hz), 2.57 (s, 3H, CH3). 31P-NMR (CDCl3,
80 MHz): l 32.1 (s).
2. Experimental
All reactions were carried out under nitrogen; the
solvents were dried in accordance with literature meth-
ods. All reagents of commercial quality were used
without further purification, only phenylacetylene was
distilled prior to use. Elemental analyses (C, H, N) were
carried out on an automatic Carlo Erba CHNS-O
EA1108 elemental analyser. All new compounds gave
satisfactory elemental analyses. IR spectra (4000–400
cm−1) for KBr discs were recorded on a Nicolet 5PC
FTIR spectrometer, mass spectra (CI) on a Finnigan
SSQ710 instrument, 1H- and 31P-NMR spectra on a
Bruker ACX 300 instrument at 25°C; chemical shifts
(l) are relative to tetramethylsilane (1H-NMR) and
H3PO4 (31P{1H}-NMR). Melting points were obtained
with a Gallenkamp MFB-595 apparatus in open
capillaries.
4a(Pd) — M.p. \300°C. Yield 72%. IR (cm−1):
w(CꢂN) 1579w, 1504vs, 1472m, w(CꢀP) 1437m, 1381vs,
1355s; 1H-NMR (CDCl3): l 8.39 (d, 1H, CHꢂN,
J(PꢀH) 4 Hz), 8.06 (d, 2H, J(ortho) 7.4 Hz), 7.73–7.43
(m, 15H, Ph), 7.37 (t, 1H, J(ortho) 9 Hz). 31P-NMR
(CDCl3, 80 MHz): l 32.2 (s).
5a(Pd) — M.p. 300°C (dec.). Yield 83%. IR (cm−1):
w(CꢂN) 1610w, w(NO2)as 1529vs, w(CꢀP) 1437m, 1384mw
,
1
w(NO2)s 1341vs; H-NMR (DMSO-d6): l 8.50 (d, 1H,
CHꢂN, J(PꢀH) 2.8 Hz), 7.75–7.51 (m, 13H, Ph), 7.40
(t, 1H, J(ortho) 8 Hz). 31P-NMR (CDCl3, 80 MHz): l
32.5 (s).

182
A. Bacchi et al. / Journal of Organometallic Chemistry 593–594 (2000) 180–191
2a(Ni) — M.p. 243°C. Yield 60%. IR (cm−1):
Hz), 8.20 (d, 2H), 7.63–7.32 (m, 19H, Ph), 0.89 (m, 9H,
1
w(CꢂN) 1604s, 1507s, 1402br. H-NMR (CDCl3): l 8.42
(s, br, 1H, CHꢂN), 7.75 (d, 2H, J(ortho) 7.4 Hz),
7.70–7.31 (m, 17H). X-ray quality crystals were ob-
tained by recrystallization from methanol.
t-C4H9). 31P-NMR (CDCl3, 80 MHz): l 34.0 (s). X-ray
quality crystals were obtained by recrystallization from
CH2Cl2–ethyl ether.
2c(Ni) — M.p. 225–226°C. Yield 53%. IR (cm−1):
w(CꢁC) 2106s, w(CꢂN) 1586m, 1510s, 1384m.
2d(Ni) — M.p. 214–218°C. Yield 46%. IR (cm−1):
2b(Ni) — M.p. 238–239°C. Yield 75%. IR (cm−1):
w(CꢂN) 1604w, w(COO) 1559w, 1327s, 1514s, 1384mw
.
31P-NMR (CDCl3, 80 MHz): l 19.1 (s).
w(CꢁC) not observed, w(CꢀHar) 3052w, w(CꢀHalkyl
)
1c(Pd) — 0.04 g (0.078 mmol) of 2b(Pd) were dis-
solved in methanol (20 ml) with 0.09 ml (0.783 mmol)
of phenylacetylene. The solution was stirred at r.t. for 5
h. The solvent was removed under reduced pressure
and the resulting solution cooled at −20°C for 1 night.
An orange solid was filtered and washed with diethyl
ether. M.p. 210–211°C. Yield 88%. MS (CI) m/z: 552
(M−). IR (cm−1): w(CꢁC) 2112w, w(CꢂN) 1560vw,
2924–2854m, w(CꢂN) 1587m, 1495vs, 1370s.31P-NMR
(CDCl3, 80 MHz): l 30.6 (s).
Pd(HL2)Cl2 — 0.070 g of Pd(COD)Cl2 (0.245 mmol)
were added to 0.100 g (0.245 mmol) of HL2 in THF (20
ml). Instantly, a yellow powder precipitated, which was
filtered, washed with ethyl ether and dried. M.p. 180–
181°C. Yield 87%. IR (cm−1): w(CꢀH)ar 3055br, w(CꢂO)
1
1707s, w(CꢂN) 1603m, w(CꢀP) 1434. H-NMR (CDCl3):
1
1522vs, w(CꢀP) 1433s, 1392s. H-NMR (CDCl3): l 8.32
l 10.33 (s, 1H, NꢀH), 8.53 (d, 2H, Ph), 8.06 (t, 1H),
7.80 (t, 1H), 7.77–7.36 (m, 16H).
(d, 1H, CHꢂN, J(PꢀH) 2.6 Hz), 7.74–7.38 (m, 14H,
Ph), 7.05 (m, 3H, meta and para in CꢁCꢀC6H5), 6.85
(dd, 2H, ortho in CꢁCꢀC6H5, J(ortho) 6.6, J(meta) 4.2
Hz), 2.22 (s, 3H, CH3). 31P-NMR (CDCl3, 80 MHz): l
34.0 (s).
[Pd(HL2)Cl](TfO) — 0.044 g (0.17 mmol) of silver
trifluoromethanesulfonate in THF (10 ml) were
dropped in a CH2Cl2 solution (20 ml) of Pd(HL2)Cl2:
almost immediately AgCl separated from the reaction.
After 2 h AgCl was filtered and ethyl ether added, until
a yellow precipitate appeared. M.p. 178°C (dec.). Yield
65%. IR (cm−1): w(NꢀH) 3184, w(CꢀH)ar 3053br,
w(CꢂN) 1604s, w(CꢂO) 1551s, bands attributable to
Analogous procedures were followed for the other
alkynyl compounds.
3c(Pd) — A yellow solid precipitated during the
reaction. M.p. 232–233°C. Yield 60%. MS (CI) m/z:
628 (M−). IR (cm−1): w(CꢁC) 2117w, w(CꢂN) 1614w,
1
CF3SO−3 : 1238, 1221, 1026, 636. H-NMR (CDCl3): l
1
1492vs, 1471vs, w(CꢀP) 1436m, 1380vs, 1359s. H-NMR
13.85 (s, br, 1H, NꢀH), 9.55 (d, 1H, CHꢂN, J(PꢀH) 3.5
Hz), 8.28–7.43 (m, 19H).
(CDCl3): l 8.50 (d, 1H, CHꢂN, J(PꢀH) 2.6 Hz), 8.16
(d, 2H, J(ortho) 8.2 Hz), 7.78–7.36 (m, 14H, Ph), 7.18
(d, 2H, J(ortho) 8 Hz), 7.07 (dd, 3H, meta and para in
CꢁCꢀC6H5, J(ortho) 5.2, J(meta) 1.9 Hz), 6.89 (dd, 2H,
ortho in CꢁCꢀC6H5, J(ortho) 8.6, J(meta) 2 Hz), 2.38
(s, 3H, CH3). 31P-NMR (CDCl3, 80 MHz): l 34.3 (s).
4c(Pd) — M.p. 235–237°C. Yield 70%. MS (CI)
m/z: 693 (M−). IR (cm−1): w(CꢁC) 2117w, w(CꢂN)
2.2.2. Complexes of the ligand HL6
6a1(Pd) — 0.034 g (0.128 mmol) of Li2PdCl4 in
methanol (20 ml) were added to 0.049 g (0.128 mmol)
of HL6 in dry THF (15 ml), after which the solution
turned from yellow to orange. The solution was stirred
at r.t. for 1 h, concentrated and then ethyl ether added,
until a brown solid was obtained. The solid was washed
with ethyl ether and then dried. X-ray quality crystals
were obtained directly from the reaction solution. M.p.
86°C (dec.). Yield 86%. IR (cm−1): w(NꢀH) 3250w,
1
1578w, 1502vs, 1476vs, w(CꢀP) 1436m, 1380vs, 1356s. H-
NMR (CDCl3): l 8.49 (d, 1H, CHꢂN, J(PꢀH) 2.7 Hz),
8.14 (dd, 2H, J(ortho) 6.8, J(meta) 1.7 Hz), 7.77–7.37
(m, 16H, Ph), 7.08 (dd, 3H, meta and para in
CꢁCꢀC6H5, J(ortho) 7.8, J(meta) 4.1 Hz), 6.89 (dd, 2H,
ortho in CꢁCꢀC6H5, J(ortho) 6.7, J(meta) 2.0 Hz).
31P-NMR (CDCl3, 80 MHz): l 34.4 (s).
1
w(CꢀHar) 3050, w(CꢂN) 1617s, w(CꢀP) 1435s; H-NMR
(CDCl3): l 15.04 (s, 0.5H, NꢀH), 9.28 (d, 1H, CHꢂN,
J(PꢀH) 2.5 Hz), 8.40 (m, 1H, H1), 7.88 (t, 1H), 7.75–
7.26 (m, 15H), 6.93 (t, 1H). 31P-NMR (CDCl3, 80
MHz): l 29.0 (s).
5c(Pd) — M.p. 263–264°C. Yield 80%. MS (CI)
m/z: 660 (M−). IR (cm−1): w(CꢁC) 2129w, w(CꢂN)
1596m, w(NO2)as 1428vs–1485mw, w(CꢀP) 1436m, w(NO2)s
1380mw–1340vs. 1H-NMR (CDCl3): l 8.53(5) (d, 1H,
CHꢂN, J(PꢀH) 2.7 Hz), 8.43 (d, 2H), 8.22 (d, 2H),
7.79–7.40 (m, 14H, Ph), 7.09 (m, 3H, meta and para in
CꢁCꢀC6H5), 6.90 (m, 2H, ortho in CꢁCꢀC6H5). 31P-
NMR (CDCl3, 80 MHz): l 34.5 (s).
2d(Pd) — M.p. 250–253°C. Yield 70%. MS (CI)
m/z: 594 (M−). Raman (cm−1) w(CꢁC) 2122. IR
(cm−1): w(CꢁC) not observed, w(CꢀH)ar 3055w,
w(CꢀH)alkyl 2964vs, w(CꢂN) 1588m, 1500vs, 1378vs, 1359s.
1H-NMR (CDCl3): l 8.45 (d, 1H, CHꢂN, J(PꢀH) 3
6a2(Pd) — 0.100 g (0.245 mmol) of HL6 in dry THF
(25 ml) were reacted with an equimolar amount of
Pd(COD)Cl2 (0.077 g). After 30 min a pale yellow solid
began to precipitate. The solid was filtered, washed
with ethyl ether and dried. M.p. 260°C. Yield 62%. IR
(cm−1): w(NꢀH) 3175w, w(CꢀHar) 3052, w(CꢂN) 1624s,
w(CꢀP) 1437s; 1H-NMR (CDCl3): l 15.15 (s, 1H, NꢀH),
9.35 (d, 1H, CHꢂN, J(PꢀH) 3 Hz), 8.43 (m, 1H, H1),
7.91 (m, 1H, H5), 7.73–7.30 (m, 15H), 6.91 (m, 1H).
31P-NMR (CDCl3, 80 MHz): l 31.1 (s).

A. Bacchi et al. / Journal of Organometallic Chemistry 593–594 (2000) 180–191
183
6a(Pd) — 0.040 g of 6a1(Pd) were dissolved in dry
THF (15 ml) and an excess of Et3N added (10:1); the
yellow solution became scarlet. After 1 h, Et3NHCl was
removed by filtration, the solution concentrated under
vacuum and hexane added until a dark red solid precip-
itated. The solid was washed with cold water, ethyl
ether and then dried. The same result was obtained
starting from 6a2(Pd). M.p. 233°C. Yield 60%. MS (CI)
m/z: 522 (M−). IR (cm−1): w(CꢀHar) 3057, w(CꢂN)
m/z: 540 (M−). IR (cm−1): w(CꢀH)ar 3055w, w(CꢁC)
2102w, w(CꢂN) 1613m, w(CꢀP) 1434m. 1H-NMR
(CDCl3): l 8.86 (s, br, 1H, CHꢂN), 8.56 (s, br, 1H, H1),
7.76–7.11 (m, 19H), 6.74–6.65 (m, 3H). 31P-NMR
(CDCl3, 80 MHz): l 28.0 (s).
2.3. X-ray crystallography
Crystals suitable for X-ray diffraction analysis have
been obtained for compounds 2a(Ni), 2d(Pd), 6a1(Pd)
and 2a(Pd). A summary of relevant parameters con-
cerning data collection and structure refinement for all
compounds is reported in Table 1. In all cases the
intensity of one standard reflection was monitored
through data collection. None of the compounds
showed decay effects. The empirical „ scan correction
for absorption was applied for compound 6a1(Pd), for
compound 2d(Pd) the Walker and Stuart correction [12]
was applied, while no correction for absorption was
necessary for 2a(Pd) and 2a(Ni). In all cases the phase
problem was solved by direct methods using SIR-97
[13]. Structure refinement was carried out by full matrix
least-squares on F2 using SHELXL-97 [14]. All non hy-
drogen atoms were refined anisotropically. In com-
pound 2a(Ni) all hydrogen atoms were located on the
difference Fourier map and refined isotropically. In the
remaining compounds some or all hydrogen atoms were
put in calculated position riding on their carriers. Lists
of significant distances and angles are shown in Tables
2–5; all geometrical calculations were carried out with
PARST [15], while ZORTEP [16] diagrams of the com-
pounds are shown in Figs. 1, 2, 4 and 5.
1
1609s, w(CꢀP) 1431s; H-NMR (CDCl3): l 8.45 (d, 1H,
CHꢂN, J(PꢀH) 3 Hz), 8.27 (m, 1H, H1), 7.69–7.34 (m,
15H), 7.01 (d, 1H), 6.54 (t, 1H, H2). 31P-NMR (CDCl3,
80 MHz): l 29.2 (s).
6a(Ni) — An equimolar amount of NiCl2·6H2O in
water (10 ml) was added to a solution of HL6 (0.100 g)
in THF (15 ml); when Et3N was added, the solution
became scarlet. After 1 h, the ammonium salt was
removed by filtration, the solution concentrated under
vacuum and the solid washed with cold water, ethyl
ether and then dried. M.p. 212°C (dec.). Yield 40%. MS
(CI) m/z: 476 (M−). IR (cm−1): w(CꢂN) 1604s, w(CꢀP)
1
1437s; H-NMR (CDCl3): l 8.62 (s, br, 1H, CHꢂN),
8.05 (m, 1H, H1), 7.75–6.98 (m, 15H), 6.55 (s, br, 1H,
H2).
6b(Pd) — (a) 0.102 g of HL6 were dissolved in THF
(20 ml), then 0.068 g of Pd(CH3COO)2, dissolved in
acetonitrile (10 ml), were added. The solution was
refluxed for 2 h; a dark red solid precipitated when
ethyl ether was added (yield 75%). (b) 0.300 g of 6a(Pd)
were dissolved in THF (15 ml), then an equimolar
amount of Ag(CH3COO) in acetonitrile (10 ml) was
added. After 30 min the reaction was stopped, AgCl
filtered and the solution concentrated: a dark red solid
precipitated when ethyl ether was added (yield 60%).
M.p. \300°C. IR (cm−1): w(CꢂN) 1609s, w(COO)
2.4. Theoretical calculations
1
1632s, 1310s, w(CꢀP) 1437m; H-NMR (CDCl3): l 8.17
The bond orders and the charge distribution on the
bicyclic chelating system of molecules [Pd(HL6)Cl]+
and [Pd(L6)Cl] in 6a1(Pd) and of 2a(Pd) were obtained
by extended-Hu¨ckel calculations with the program CA-
CAO [17], using the X-ray coordinates as input.
(t, 1H), 8.07 (d, 1H), 7.92 (d, 1H), 7.73–7.16, 6.75 (m,
2H), 6.31 (m, 2H), 1.61 (m, 3H). 31P-NMR (CDCl3, 80
MHz): l 27.7(s), 25.0(s).
6b(Ni)
—
0.053
g
(0.20
mmol)
of
Ni(CH3COO)2·4H2O in methanol (20 ml) were added
to 0.076 g (0.020 mmol) of HL6 in dry THF (15 ml):
the solution changed colour from green to red. It was
stirred at r.t. for 1 h, concentrated in vacuo and then
ethyl ether added, obtaining a solid that was washed
with ethyl ether and then dried. M.p. 244°C (dec.).
Yield 65%. IR (cm−1): w(CꢂN) 1595s, w(COO) 1615m,
3. Results and discussion
The ligands HL1–HL5 (Scheme 1) react with potas-
sium tetrachloropalladate giving MLCl complexes
(Scheme 2, 1a(Pd)–5a(Pd)); the deprotonated ligands
behave as terdentate through the phosphorus, the imine
nitrogen and the oxygen. The square planar coordina-
tion around the metal is completed by a chlorine ion, as
shown by X-ray diffraction analysis on 2a(Pd) (see
Section 2.4). The main spectroscopic data of these
complexes are: (1) the disappearance of the CꢂO
stretching band, due to the deprotonation of the ligand
and the coordination of the oxygen that stabilizes the
CꢀO enolic form; (2) the disappearance of the NꢀH
1
1364s, w(CꢀP) 1437s; in the H-NMR spectrum all the
peaks were very broad: 8.02–6.89 (m), 6.89 (s), 6.60 (s),
6.24 (s), 1.41 (s, CH3COO). 31P-NMR (CDCl3, 80
MHz): l 20.0 (s).
6c(Ni) — 0.030 g of 6b(Ni) (0.061 mmol) in MeOH
(15 ml) were reacted with a large excess of pheny-
lacetylene (0.3 ml, 50:1) at r.t. for 24 h. The solution
was concentrated and a purple solid obtained by adding
ethyl ether. M.p. 138°C (dec.). Yield 61%. MS (CI)

184
A. Bacchi et al. / Journal of Organometallic Chemistry 593–594 (2000) 180–191
Table 1
Crystal and structure refinement data for compounds 6a1(Pd), 2a(Pd), 2a(Ni) and 2d(Pd)
Compound
6a1(Pd)
2a(Pd)
2a(Ni)
2d(Pd)
Empirical formula
C48H43Cl3N6O2P2Pd2
Mo–Ka, 0.7108
Philips PW1100
Triclinic
C
29.5H24ClN2OPPd
C26H20ClN2NiOP
Mo–Ka, 0.7108
Siemens AED
Monoclinic
C32H29N2OPPd
Cu–Ka, 1.5418
Enraf–Nonius CAD
Monoclinic
,
Radiation, u (A)
Mo–Ka, 0.7108
Siemens AED
Triclinic
Diffractometer
Crystal system
Space Group
4
(
(
P1
P1
P21/a
C2/c
Unit cell dimensions
,
a (A)
13.307(5)
15.810(5)
12.590(5)
100.43(5)
101.51(5)
67.66(5)
2384(2)
2
10.551(2)
14.251(3)
9.551(2)
99.77(2)
105.10(2)
104.77(2)
1297(1)
2
12.160(4)
26.855(8)
14.138(5)
22.014(2)
18.068(2)
14.476(2)
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
96.86(2)
102.38(5)
3
,
Volume (A )
4584(2)
8
5694(1)
8
Z
Crystal size (mm)
Crystal colour
q Range (°)
0.4×0.3×0.2
Dark red
3–25
0.5×0.3×0.2
Light yellow
3–30
0.5×0.4×0.4
Dark red
3–30
0.6×0.2×0.1
Pale yellow
3–70
Collected reflections
Independent reflections
Observed reflections (I\2|I)
Parameters/restraints
Final R indices
8378
8378
3158
538/392
7595
7595
5024
378/0
14 148
13 393
4054
5561
5346
3383
341/0
737/0
a
R1 [I\2|(I)]
0.0655
0.2066
0.0465
0.1397
0.0505
0.1519
0.0577
0.2071
b
Rw
a R=SꢀꢀFoꢀ−ꢀFcꢀꢀ/SꢀFoꢀ.
b Rw={S[w(Fo2−Fc2)2]/S[w(F2o)2]}1/2
.
1
peak in the H-NMR spectrum; (3) the large uppershift
of 31P resonance (:40 ppm) upon coordination to the
metal. Even if the different R substituents (Scheme 1)
modulate the acidic character of the hydrazonic proton
[5], they do not influence the course of the complexa-
tion reaction and the resulting coordination around the
metal.
1H- and 31P-NMR spectroscopies and it was also possi-
ble to undertake X-ray diffraction analysis of 2d(Pd)
(see Section 4). These compounds are air stable and are
recovered unchanged after prolonged refluxing in
methanol or toluene. 2c(Pd) seems to be more stable
than 2d(Pd), as it can be obtained by refluxing 2d(Pd)
at 50°C in THF with an excess of phenylacetylene.
These alkynyl complexes do not undergo oxidative
The deprotonation of the ligand also occurs in the
reactions of HL1–HL5 with palladium(II) acetate to
give the complexes 1b(Pd)–5b(Pd). The spectroscopic
features are the same along the series (31P chemical
shift, position of the acetate bands in the IR spectra)
and consequently the coordination already observed in
1b(Pd) [5] can be assumed for all of these complexes,
with the metal bonded to the phosphorus, the imine
nitrogen and the oxygen of the ligand and to the
monodentate acetate anion.
HL2 reacts with NiCl2·6H2O or Ni(CH3COO)2·
4H2O, giving 2a(Ni) and 2b(Ni), respectively. The spec-
troscopic data and the X-ray diffraction analysis on
2a(Ni) (see Section 4) indicate that the coordination is
the same as in palladium chlorides and acetates.
While the palladium and nickel chloro complexes do
not react with phenylacetylene or t-butylacetylene, the
acetato complexes are able to activate the CꢀH bond of
terminal alkynes, giving stable alkynyl complexes; the
products were characterized by elemental analyses, IR,
addition or CO insertion into PdꢀC bond:
a
dichloromethane solution of 2c(Pd) does not adsorb
CO at 1 atm nor at 30 atm; the same solution was
heated under nitrogen at 40°C with methyl iodide for 2
h, but the starting complex was recovered unaltered.
The ligand 2-(diphenylphosphino)benzaldehyde 2-
pyridylhydrazone (HL6) is obtained in good yield by
condensation of the aldehyde and 2-hydrazinopyridine;
as a solid it is air stable and it has been characterized
by means of the usual techniques. In solution a single
1
isomer is detectable by H-NMR, probably the E-iso-
mer; the imine proton is coupled to the 31P nucleus, as
in other 2-(diphenylphosphino)benzaldehyde derivatives
[18,19].
In many respects the reactivity of HL6 is different
from that of the acylhydrazonic ligands HL1–HL5.
In fact, it reacts with Li2PdCl4 giving a brown solid
that has been unequivocally characterized as
[Pd(HL6)Cl][Pd(L6)Cl]Cl·2H2O (6a1(Pd)) (see Section

A. Bacchi et al. / Journal of Organometallic Chemistry 593–594 (2000) 180–191
185
Table 3
4): the square planar geometry around the two indepen-
,
Selected bond distances (A) and angles (°) with S.U.S in parentheses
for 2a(Pd)
dent palladium(II) atoms is reached by means of the
phosphorus, the imine and the pyridine nitrogens of the
ligand, and a chlorine atom; half the molecules of the
ligand are deprotonated and an ionic chlorine balances
the charge. HL1–HL5 are, evidently, more acidic than
HL6, since in the same conditions they form neutral
PdLCl complexes. Despite its flexibility, HL6 has a
strong tendency to coordinate in a terdentate fashion,
as it has been already observed for the related PNN
PdꢀP
PdꢀCl
PdꢀO
PdꢀN1
PꢀC1
OꢀC8
N1ꢀN2
N1ꢀC7
N2ꢀC8
C1ꢀC6
C6ꢀC7
C8ꢀC9
2.208(1)
2.282(1)
2.067(3)
2.001(2)
1.821(3)
1.291(3)
1.405(4)
1.257(5)
1.321(5)
1.403(4)
1.473(5)
1.492(6)
ligand
N-(2-diphenylphosphinobenzylidene)-2-(2-py-
ridyl)ethylamine [20]. In fact, in solution the pyridine
ring results still coordinated, as can be inferred from
the uppershift of the H1 proton and from the presence
of a fine structure for this signal, due to the coupling
PꢀPdꢀCl
PꢀPdꢀO
90.06(4)
176.26(8)
96.08(8)
93.31(8)
173.47(9)
80.5(1)
111.7(1)
107.9(2)
115.3(3)
112.0(3)
123.0(2)
127.8(3)
128.6(3)
126.5(3)
117.2(3)
1
PꢀPdꢀN1
ClꢀPdꢀO
ClꢀPdꢀN1
OꢀPdꢀN1
PdꢀPꢀC1
PdꢀOꢀC8
N2ꢀN1ꢀC7
N1ꢀN2ꢀC8
PꢀC1ꢀC6
C1ꢀC6ꢀC7
N1ꢀC7ꢀC6
OꢀC8ꢀN2
OꢀC8ꢀC9
with the trans phosphorous [21] in the H-NMR spec-
1
trum. Strangely, in the H-NMR spectrum of 6a1(Pd)
in CDCl3 at r.t. it is not possible to distinguish two sets
of resonances for the deprotonated and neutral ligand,
but the NꢀH peak has half the area corresponding to a
proton; only one signal is present in the 31P spectrum
(29.0 ppm).
The complex 6a2(Pd) is easily obtained by reacting
HL6 and Pd(COD)Cl2 in dry THF. The ligand is
neutral (w(NꢀH) 3175 cm−1; NꢀH 15.15 ppm) and
Table 2
,
Selected bond distances (A) and angles (°) with S.U.S in parentheses
for compound 6a1(Pd)
Table 4
,
Selected bond distances (A) and angles (°) with S.U.S in parentheses
for compound 2a(Ni)
Pd1ꢀCl1
Pd1ꢀP1
Pd1ꢀN1
Pd1ꢀN3
P1ꢀC1
N1ꢀN2
N1ꢀC7
N2ꢀC8
N3ꢀC8
N3ꢀC12
C1ꢀC6
C6ꢀC7
C8ꢀC9
2.285(4)
2.219(3)
2.02(1)
2.079(9)
1.81(1)
1.35(2)
1.32(1)
1.37(1)
1.39(2)
1.33(1)
1.39(2)
1.42(2)
1.37(2)
Pd2ꢀCl2
Pd2ꢀP2
Pd2ꢀN4
Pd2ꢀN6
P2ꢀC25
N4ꢀN5
N4ꢀC31
N5ꢀC32
N6ꢀC32
N6ꢀC36
C25ꢀC30
C30ꢀC31
C32ꢀC33
2.273(3)
2.225(4)
1.985(9)
2.06(1)
1.79(1)
1.43(2)
1.28(2)
1.35(2)
1.30(2)
1.30(2)
1.43(2)
1.47(2)
1.43(3)
Ni1ꢀP1
Ni1ꢀCl1
Ni1ꢀO1
Ni1ꢀN1
P1ꢀC1
O1ꢀC8
N1ꢀN2
N1ꢀC7
N2ꢀC8
C1ꢀC6
C6ꢀC7
C8ꢀC9
2.148(1)
2.170(1)
1.878(3)
1.861(3)
1.803(4)
1.287(5)
1.410(5)
1.296(5)
1.309(5)
1.394(6)
1.436(6)
1.479(6)
Ni2ꢀP2
2.137(1)
2.154(1)
1.881(3)
1.847(3)
1.809(4)
1.285(5)
1.422(4)
1.306(5)
1.315(5)
1.400(6)
1.448(6)
1.480(5)
Ni2ꢀCl2
Ni2ꢀO2
Ni2ꢀN3
P2ꢀC27
O2ꢀC34
N3ꢀN4
N3ꢀC33
N4ꢀC34
C27ꢀC32
C32ꢀC33
C34ꢀC35
Cl1ꢀPd1ꢀP1
Cl1ꢀPd1ꢀN1
Cl1ꢀPd1ꢀN3
P1ꢀPd1ꢀN1
P1ꢀPd1ꢀN3
N1ꢀPd1ꢀN3
Pd1ꢀP1ꢀC1
C1ꢀP1ꢀC13
Pd1ꢀN1ꢀN2
Pd1ꢀN1ꢀC7
N2ꢀN1ꢀC7
N1ꢀN2ꢀC8
Pd1ꢀN3ꢀC8
P1ꢀC1ꢀC6
89.0(1)
175.1(3)
95.1(3)
95.2(3)
175.3(3)
80.8(4)
112.6(4)
104.2(5)
111.7(9)
130.9(8)
117(1)
Cl2ꢀPd2ꢀP2
Cl2ꢀPd2ꢀN4
Cl2ꢀPd2ꢀN6
P2ꢀPd2ꢀN4
P2ꢀPd2ꢀN6
N4ꢀPd2ꢀN6
Pd2ꢀP2ꢀC25
C25ꢀP2ꢀC43
Pd2ꢀN4ꢀN5
Pd2ꢀN4ꢀC31
N5ꢀN4ꢀC31
N4ꢀN5ꢀC32
Pd2ꢀN6ꢀC32
P2ꢀC25ꢀC30
C25ꢀC30ꢀC31
N4ꢀC31ꢀC30
N5ꢀC32ꢀN6
90.8(1)
175.3(3)
94.3(4)
93.7(4)
174.9(4)
81.2(5)
110.9(5)
107.3(5)
110.3(7)
135(1)
114(1)
116(1)
111(1)
123(1)
127(1)
125(2)
119(2)
P1ꢀNi1ꢀCl1
P1ꢀNi1ꢀO1
P1ꢀNi1ꢀN1
Cl1ꢀNi1ꢀO1
Cl1ꢀNi1ꢀN1
O1ꢀNi1ꢀN1
Ni1ꢀP1ꢀC1
Ni1ꢀO1ꢀC8
Ni1ꢀN1ꢀN2
Ni1ꢀN1ꢀC7
N2ꢀN1ꢀC7
N1ꢀN2ꢀC8
P1ꢀC1ꢀC6
89.90(4)
173.63(9)
95.1(1)
91.60(9)
174.4(1)
83.6(1)
113.6(1)
110.4(2)
113.4(2)
133.9(3)
112.8(3)
109.2(3)
121.0(3)
125.9(4)
128.7(4)
123.3(4)
P2ꢀNi2ꢀCl2
P2ꢀNi2ꢀO2
P2ꢀNi2ꢀN3
Cl2ꢀNi2ꢀO2
Cl2ꢀNi2ꢀN3
O2ꢀNi2ꢀN3
Ni2ꢀP2ꢀC27
Ni2ꢀO2ꢀC34
Ni2ꢀN3ꢀN4
Ni2ꢀN3ꢀC33
N4ꢀN3ꢀC33
N3ꢀN4ꢀC34
P2ꢀC27ꢀC32
C27ꢀC32ꢀC33
N3ꢀC33ꢀC32
O2ꢀC34ꢀN4
89.21(4)
175.22(9)
94.9(1)
91.70(8)
174.9(1)
84.0(1)
113.3(1)
110.2(2)
113.4(2)
134.9(3)
111.8(3)
108.7(3)
120.6(3)
125.9(4)
127.2(4)
123.4(3)
121(1)
111.5(9)
123.8(9)
129(1)
128(1)
115(1)
C1ꢀC6ꢀC7
N1ꢀC7ꢀC6
N2ꢀC8ꢀN3
C1ꢀC6ꢀC7
N1ꢀC7ꢀC6
O1ꢀC8ꢀN2

186
A. Bacchi et al. / Journal of Organometallic Chemistry 593–594 (2000) 180–191
again, terdentate: the H1 proton of the pyridine ring is
still coupled with phosphorous. The neutral HL1–HL5
PNO ligands show a smaller tendency to behave as
terdentate: in Pd(HL2)Cl2 (Scheme 3), obtained from
Table 5
,
Selected bond distances (A) and angles (°) with S.U.S in parentheses
for compound 2d(Pd)
PdꢀP
PdꢀO
PdꢀN1
PdꢀC27
PꢀC1
2.194(2)
2.069(5)
2.028(7)
1.99(1)
1.831(8)
1.29(1)
1.406(9)
1.27(1)
1.30(1)
1.42(1)
1.44(1)
1.50(1)
1.17(1)
1.49(1)
OꢀC8
N1ꢀN2
N1ꢀC7
N2ꢀC8
C1ꢀC6
C6ꢀC7
C8ꢀC9
C27ꢀC28
C28ꢀC29
Fig. 2. Perspective view of [Pd(L6)Cl], with thermal ellipsoids at 50%
probability level.
the reaction of HL2 with Pd(COD)Cl2, the ligand is
neutral but bidentate, the oxygen being outside the
coordination sphere (w(CꢂO)=1707 cm−1). The oxy-
gen coordinates the metal in [Pd(HL2)Cl](TfO)
(w(CꢂO)=1551 cm−1 [22,23]), where one chloride is
substituted by a triflate, whose poor coordinating abil-
ity is well known.
PꢀPdꢀO
174.8(1)
96.0(2)
88.5(2)
79.0(2)
96.6(3)
173.8(3)
111.7(2)
108.3(5)
114.0(5)
131.8(6)
114.1(6)
110.6(7)
123.9(6)
127.9(7)
128.4(8)
128.0(8)
PꢀPdꢀN1
PꢀPdꢀC27
OꢀPdꢀN1
OꢀPdꢀC27
N1ꢀPdꢀC27
PdꢀPꢀC1
PdꢀOꢀC8
PdꢀN1ꢀN2
PdꢀN1ꢀC7
N2ꢀN1ꢀC7
N1ꢀN2ꢀC8
PꢀC1ꢀC6
6a(Pd) is obtained by refluxing 6a1(Pd) or 6a2(Pd)
with Et3N in THF. The new compound has been
1
characterized by IR, H- and 31P-NMR spectroscopies,
and all the data suggest the deprotonation of the lig-
and; the coordination geometry of the starting com-
plexes is retained. It is interesting to compare the
UV–vis absorption spectra of 6a(Pd), 6a1(Pd) and
6a2(Pd); while in 6a2(Pd) and 6a(Pd) the lower energy
band is well resolved, in methanol the maximum being
at 397 and 528 nm, respectively, the spectrum of
6a1(Pd) is more complex and, besides a band with a
maximum at 528 nm, there is another, less resolved,
band near 400 nm.
C1ꢀC6ꢀC7
N1ꢀC7ꢀC6
OꢀC8ꢀN2
The corresponding complex 6a(Ni) was directly syn-
thesized by stirring NiCl2·6H2O, HL6 and Et3N in
THF. 6a(Pd) and 6a(Ni), as the chloro complexes of
HL1–HL5, do not react with phenylacetylene.
After the work-up of the reaction between HL6 and
Pd(CH3COO)2, the complex 6b(Pd) is isolated: the IR
1
and H-NMR spectra indicate the presence of the ac-
etate ion and the absence of hydrazino protons; in the
31P spectrum there are two peaks (27.8 and 25.2 ppm)
and in the 1H-NMR spectrum it seems possible to
recognize pyridine nitrogens which are coupled with 31
P
and others which, even if coordinated to the metal, are
not coupled. The multidentate nature of the ligand and
its flexibility make difficult to propose a plausible struc-
ture for 6b(Pd). The acetato complex could be also
obtained by methatesis from CH3COOAg and 6a(Pd),
Fig. 1. Perspective view of [Pd(HL6)Cl]+, with thermal ellipsoids at
50% probability level. Hydrogen bond NꢀH···Cl is shown in dashed
style.

A. Bacchi et al. / Journal of Organometallic Chemistry 593–594 (2000) 180–191
187
Scheme 3. The reaction between Pd(HL2)Cl2 and AgTfO to give [Pd(HL2)]OTf.
starting, in this way, with the ligand preorganised,
terdentate around the palladium, but, surprisingly, the
product of the reaction is again 6b(Pd).
On the contrary, 6b(Ni), which was obtained by the
direct synthesis between Ni(CH3COO)2 and HL6, pre-
sents the already-described monometallic structure,
with the deprotonated terdentate ligand and the anion
that completes the square planar coordination around
the metal atom. 6b(Ni) reacts with phenylacetylene
giving the corresponding alkynyl complex 6c(Ni).
lengths in the coordination sphere, apart from a slight
shortening of the bond between palladium and the
,
imine nitrogen: Pd1ꢀN1=2.02(1) A for the cationic
,
complex and Pd2ꢀN4=1.985(9) A for the neutral com-
plex. The analysis of the bond lengths along the two
chelation rings for the protonated complex
[Pd(HL6)Cl]+ shows that there is a certain degree of
resonance along the system C7ꢀN1ꢀN2ꢀC8ꢀN3
(C7ꢀN1=1.32(1), N1ꢀN2=1.35(2), N2ꢀC8=1.37(1),
,
C8ꢀN3=1.39(2), N3ꢀC12=1.33(1) A). This is consis-
tent with the values observed for analogous pyridine-2-
carbaldehyde 2%-pyridylhydrazone complexes, where
the following ranges are found: C7ꢀN1=1.252–
1.321, N1ꢀN2=1.318–1.358, N2ꢀC8=1.374–1.406,
4. X-ray crystal structures
,
C8ꢀN3=1.328–1.344, N3ꢀC12=1.334–1.362 A [24–
The strong tendency of HL6 to act as terdentate is
confirmed by the X-ray diffraction analysis carried on
6a1(Pd). Both neutral and anionic monodeprotonated
forms of HL6 are capable of complexing palladium by
acting as PNN terdentate ligands and by completing
the metal coordination sphere with a chlorine atom, to
give a cationic [Pd(HL6)Cl]+ and a neutral [Pd(L6)Cl]
complex, respectively. Interestingly, these two different
forms cocrystallize giving the compound 6a1(Pd). A
chloride anion and four disordered waters with 50%
occupancy complete the unit cell content. Figs. 1 and 2
show perspective views of the molecular structure of
[Pd(HL6)Cl]Cl and [Pd(L6)Cl], respectively, in the crys-
tals of 6a1(Pd), along with the labelling scheme. Table
2 lists the main bond distances and angles in the
structure. In both moieties the ligand chelates the metal
by the imine nitrogen, the pyridine nitrogen, and the
phosphorous atoms, originating a six-membered and a
five-membered chelation ring; a chlorine completes the
square geometry around the palladium and in both
26]. The deprotonation of the hydrazonic nitrogen
causes a relevant rearrangement of the bond lengths
and a redistribution of the charge on the hydrazonic
system. The examination of the bond lengths observed
for [Pd(L6)Cl] suggests that the electronic density delo-
calization is shifted from the CꢂNꢀN group towards the
pyridine ring (C31ꢀN4=1.28(2), N4ꢀN5=1.43(2),
N5ꢀC32=1.35(2),
C32ꢀN6=1.30(2),
N6ꢀC36=
,
,
1.30(2) A). Similar single-bond NꢀN distance (1.396 A)
,
and CꢀN shortening (1.302 A) have been observed for
nickel complex of (1,10-phenanthrolin-2-
a
yl)benzaldehyde hydrazone [27], where the possibility of
charge delocalization on the phenanthroline system is
even more effective than in the present pyridine ring. In
order to support this observation, an estimation of the
partial atomic charges and of bond orders for the
crystal structures of [Pd(HL6)Cl]Cl and [Pd(L6)Cl] has
been performed by means of extended-Hu¨ckel calcula-
tions. The results are shown in Fig. 3. It is seen that the
negative charge left on the ligand by the deprotonation
is mainly located on the hydrazonic nitrogen N5, but it
is also in part distributed on C33 and C35, which result
more negative than in the cationic complex. The palla-
dium atom is also slightly less positively charged, and
this could be due to the higher bond order between the
metal and the imine nitrogen PdꢀN4, related to a
diminution of the negative charge on N4. Interestingly,
the augmented negative charge on the pyridine ring has
no effects on the PdꢀN(py) bond, which remains un-
,
cases the coordination is planar within 0.08 A. The only
relevant angular distortion from a regular square is due
to the strain of the five-membered chelation ring, giving
a significant deviation from 90° of the angles involving
the imine and the pyridine nitrogens (NꢀPdꢀN=
80.8(4) and 81.2(5)°, respectively for [Pd(HL6)Cl]Cl and
[Pd(L6)Cl]). The comparison of the two molecules is
helpful in elucidating the effects of the deprotonation of
the ligand on the complex geometry. The deprotonation
of the ligand does not affect significantly the bond

188
A. Bacchi et al. / Journal of Organometallic Chemistry 593–594 (2000) 180–191
Fig. 3. Atomic partial charges (bold characters, ×1000) and bond orders (×1000) for the chelation systems in the two moieties of 6a1(Pd)
([Pd(HL6)Cl]+ and [Pd(L6)Cl]) and in 2a(Pd).
changed, although the pyridine nitrogen appears less
negatively charged than in the protonated complex. The
partial charges and bond orders on the phosphine–
imine moiety of 6a1(Pd) are substantially unaffected by
the deprotonation of the ligand; moreover the CꢂN
bond has a more pronounced multiple character in
[Pd(L6)Cl], showing that the negative charge is not
delocalized along the six-membered chelation ring. The
conformational analysis for both molecules shows that
in the cationic complex the chelation system comprising
atoms Pd1, P1, N1ꢀN3, C1ꢀC12 is planar within 0.20
turbed by torsions of 10° around the bonds C25ꢀC30
and C30ꢀC31, compared to values of 2° observed for
[Pd(HL6)Cl]+. The positive charge of the cationic com-
plex is balanced in the crystal by a chloride anion,
which is hydrogen bonded to the hydrazonic NꢀH, as
,
shown in Fig. 1 (N2···Cl3=3.07(1) A, NꢀH···Cl=
167(1)°).
The role of the pyridine ring on the negative charge
delocalization observed on the ligand backbone of
[Pd(HL6)Cl] has been compared with the one shown by
the phenylacyl group in 2a(Pd); in the crystal packing
of 2a(Pd) one toluene molecule is disordered around a
,
A, while in the neutral complex the planarity is per-

A. Bacchi et al. / Journal of Organometallic Chemistry 593–594 (2000) 180–191
189
Fig. 4. Perspective view of 2a(Ni), with thermal ellipsoids at 50% probability level.
centre of inversion2. Relevant bond distances and an-
gles are reported in Table 3; for labelling, refer to the
analogue nickel complex in Fig. 4. The charge distribu-
tion and bond orders of 2a(Pd) are shown in Fig. 3.
The main differences with respect to the 2-pyridylhy-
drazone ligand consist in the significantly higher bond
order of the N2ꢀC8 bond, accompanied by a large
decrease of the bond order C8ꢀO. The electronic den-
sity is transferred from the hydrazonic nitrogen to the
oxygen, and C8 is highly positive. The higher elec-
tronegativity of O with respect to N allows the location
of the negative charge on the oxygen, leaving the metal
more positive and decreasing the PdꢀO bond order.
The analogue nickel complex 2a(Ni) crystallizes with
two independent molecules in the asymmetric unit; one
of them is shown in Fig. 4, along with the labelling
scheme. As expected, the L2− anion coordinates the
metal in a square planar fashion and the coordination
is completed by a Cl atom trans to the imine nitrogen.
The planar coordination is slightly distorted as P1 and
ences between the nickel and the palladium complexes
are due to the steric strain introduced in the chelation
rings by the smaller dimensions of the former ion: in
the six-membered chelated ring the endocyclic angles on
metal, C1 and C6 are of about 2° smaller than in the
corresponding palladium complex, while the angles on
P1 and N1 are of about 2° larger. This is also associ-
ated to a slight but significant shortening of the P1ꢀC1
and C6ꢀC7 bonds in the nickel complex. In the five-
membered chelation ring, the endocyclic angles on
metal and O are of 4 and 2° larger, respectively, in the
Ni complex, while those on C8 and N2 are of about 3°
smaller. The examination of the NiꢀN and NiꢀO dis-
tances in complexes containing the same five-membered
chelation ring as 2a(Ni) reveals that the NiꢀN distances
fall well in the range observed for similar compounds
,
P2 deviate by 0.23 and 0.17 A, respectively, from the
plane defined by Ni, Cl, O and hydrazonic N atoms. As
seen from Table 4, that lists the relevant geometric
parameters for 2a(Ni), there are not significant differ-
ences in the bonding geometry of the chelation rings
between the two molecules. The most evident differ-
2 The crystal structure of the same compound as a dichloromethane
solvate, has been previously reported [7]. The molecular dimensions
of the complex are perfectly comparable in the two solvate forms.
The only differences are a rotation of 12° of the terminal phenyl
around the C8ꢀC9 bond in the toluene solvate, which causes a larger
,
deviation from planarity (maximum deviation=0.40 A) of the chela-
tion system Pd, P1, N1ꢀN3, C1ꢀC14 with respect to the one observed
in Ref. [7] (maximum deviation=0.15 A), and a different orientation
of the two phenyl rings bonded to the P atoms.
,
Fig. 5. Perspective view of 2d(Pd), with thermal ellipsoids at 50%
probability level.

190
A. Bacchi et al. / Journal of Organometallic Chemistry 593–594 (2000) 180–191
,
(1.828–1.910 A), while the NiꢀO distances are sensitive
organometallic species with the metal centres separated
by conjugated organic fragments, which are of interest
in the area of material and supramolecular chemistry.
to the trans effect of the phosphine group, falling on the
,
upper limit of the range observed (1.833–1.889 A), as
also observed in (thiodibenzoylmethane benzoylhydra-
zonato)-triphenylphosphine-nickel(II) [28], where the
oxygen is trans to the sulphur atom. The NiꢀP bond
lengths are comparable with the one observed in [Ni(a-
6. Supplementary material
,
cac)(PPh3)(CH3CH2)] [29] (2.143 A), where the P atom
is trans to an acetylacetonato oxygen.
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC Nos. 123605 for 2a(Pd), 123603
for 2a(Ni), 123602 for 2d(Pd) and 123604 for 6a1(Pd).
In 2d(Pd) (Fig. 5) the acetylenic ligand is situated
trans to the imine nitrogen, as already observed in the
analogue PhꢀCꢁC complex [7]. Table 5 lists the main
bond distances and angles for 2d(Pd). The comparison
with the chloro complex shows that there are no rele-
vant differences in the bonding geometry of the two
chelation rings. The coordination of the metal is planar
Acknowledgements
Thanks are due to the Centro di Studio per la
Strutturistica Diffrattometrica del CNR and Centro
Interfacolta` Misure ‘Giuseppe Casnati’ of the Univer-
sity of Parma.
,
within 0.07 A, and the same applies for the two chela-
tion rings. The overall planarity of the molecular sys-
tem Pd, P, N1, N2, O, C1ꢀC14 is perturbed by a slight
rotation of the terminal phenyl around the C8ꢀC9 bond
(OꢀC8ꢀC9ꢀC14= −15(1)°), as also observed for
2a(Pd). The PdꢀN distance is affected by the substitu-
tion of the group in the trans position and it is longer
in the alkynyl than in the chloro complex (2.028(7) and
2.001(2) A, respectively); a slight shortening of the
PdꢀP bond is also observed in 2d(Pd), 2.194(2) com-
pared to 2.208(1) A in 2a(Pd). The PdꢀO, C8ꢀO, and
References
[1] J.H. Groen, A. de Zwart, M.J.M. Vlaar, J.M. Ernsting,
P.W.N.M. van Leeuwen, K. Vrieze, H. Kooijman, W.J.J.
Smeets, A.L. Spek, P.H.M. Budzelaar, Q. Xiang, R.P. Thummel,
Eur. J. Inorg. Chem. (1998) 1129.
[2] M. Yang, M. Alvarez, N. Lugan, R. Mathieu, J. Chem. Soc.
Chem. Commun. (1995) 1721.
[3] Y. Kataoka, Y. Tsuji, O. Matsumoto, M. Ohashi, T. Yamagata,
K. Tani, J. Chem. Soc. Chem. Commun. (1995) 2099.
[4] A. Bacchi, M. Carcelli, M. Costa, P. Pelagatti, C. Pelizzi, G.
Pelizzi, J. Chem. Soc. Dalton Trans. (1996) 4239.
[5] P. Pelagatti, A. Bacchi, M. Carcelli, M. Costa, A. Fochi, P.
Ghidini, E. Leporati, M. Masi, C. Pelizzi, G. Pelizzi, J.
Organomet. Chem. 583 (1999) 94.
[6] P. Pelagatti, M. Carcelli, F. Franchi, C. Pelizzi, A. Bacchi, A.
Fochi, H.-W. Fru¨hauf, K. Goubitz, K. Vrieze, Eur. J. Inorg.
Chem. in press.
[7] A. Bacchi, M. Carcelli, M. Costa, P. Pelagatti, C. Pelizzi, G.
Pelizzi, Gazz. Chim. Ital. 124 (1994) 429.
[8] H.F. Klein, B. Zettel, U. Flo¨rke, H.J. Haupt, Chem. Ber. 125
(1992) 9.
[9] J.T. Lin, J.J. Wu, C. Li, Y.S. Wen, K.-J. Lin, Organometallics 15
(1996) 5028.
[10] M.J. Irwin, J.J. Vittal, R.J. Puddephatt, Organometallics 16
(1997) 3541.
,
,
C8ꢀN2 distances do not differ from those observed in
2a(Pd), showing that the enolate PdꢀOꢀCꢂNꢀ form is a
major contribution in the electronic distribution on the
PdꢀOꢀCꢀN system, as already evidenced by the calcula-
tion of bond orders (Fig. 3). This is also in agreement
with the values observed for the crystal structure of a
palladium complex with the enolate form of a similar
amide phosphine ligand (PdꢀO=2.108(4), CꢀO=
,
1.302(5) A) [30]. The coordination of the acetylenic
group is practically linear, with angles of 175.7(9) and
178(1)° on C27 and C28, respectively. The comparison
of the geometry of t-BuꢀCꢁC and PhꢀCꢁC in the two
complexes shows that the presence of the alkyl instead
of the aryl induces a shortening of the PdꢀC bond
(1.99(1) and 2.026(4) A, respectively) and a lengthening
of the CꢁC bond (1.17(1) and 1.092(6) A, respectively),
,
,
as a result of the different electronic characteristics of
the two ligands.
[11] V.W.-Wah Yam, W.K.-M. Fung, K.M.-Ch. Wong, V.C-Y. Lau,
K.-K. Cheung, J. Chem. Soc. Chem. Commun. (1998) 777.
[12] N. Walker, D. Stuart, Acta Crystallogr. Sect. A 39 (1983) 158.
[13] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi,
M.C. Burla, G. Polidori, M. Camalli, J. Appl. Crystallogr. 27
(1994) 435.
5. Conclusions
[14] G. Sheldrick, SHELXL-97, Program for structure refinement, Uni-
versity of Go¨ttingen, Germany, 1997.
[15] M. Nardelli, J. Appl. Crystallogr. 28 (1995) 659.
A procedure for the synthesis of stable acetylides was
found, starting from acetato complexes of terdentate
hydrazone ligands. The acetato anion plays a key role
in the process, in fact the corresponding chloro com-
plexes are not reactive. The mild conditions of the
reaction make appealing the possibility to extend this
method to di- and tri-functional acetylenes to obtain
[16] L. Zsolnai, H. Pritzkow, ZORTEP
. ORTEP original program
modified for PC, University of Heidelberg, Germany, 1994.
[17] C. Mealli, D.M. Proserpio, J. Chem. Educ. 67 (1990) 399.
[18] R.E. Rulke, V.E. Kaasjager, P. Wehman, C.J. Elsevier,
P.W.N.M. van Leeuwen, K. Vrieze, Organometallics 15 (1996)
3022.

A. Bacchi et al. / Journal of Organometallic Chemistry 593–594 (2000) 180–191
191
[24] T. Rojo, J.L. Mesa, M.I. Arriortua, J.M. Savariault, J. Galy, G.
Villeneuve, D. Beltran, Inorg. Chem. 27 (1988) 3904.
[25] E.W. Ainscough, A.M. Brodie, S.L. Ingham, J.M. Waters, In-
org. Chim. Acta 249 (1996) 47.
[26] J.L. Mesa, T. Rojo, M.L. Arriortua, G. Villeneuve, J.V. Fol-
gado, A. Beltran-Porter, D. Beltran-Porter, J. Chem. Soc. Dal-
ton Trans. (1989) 53.
[27] S. Choudhury, J. Bangladesh Acad. Sci. 21 (1997) 61.
[28] H. Kraudelt, U. Schilde, E. Uhlemann, F. Weller, Z. Natur-
forsch. Teil B 52 (1997) 1043.
[29] F.A. Cotton, B.A. Frenz, D.L. Hunter, J. Am. Chem. Soc. 96
(1974) 4820.
[19] A. Bacchi, M. Carcelli, M. Costa, A. Leporati, E. Leporati, P.
Pelagatti, C. Pelizzi, G. Pelizzi, J. Organomet. Chem. 535 (1997)
107.
[20] P. Wehman, R.E. Rulke, V.E. Kaasjager, P.C.J. Kamer, H.
Kooijman, A.L. Spek, C.J. Elsevier, P.W.N.M. van Leeuwen, K.
Vrieze, J. Chem. Soc. Chem. Commun. (1995) 331.
[21] M. Yabuta, S. Nakamura, T. Yamagata, K. Tani, Chem. Lett.
(1993) 323.
[22] J. Andrieu, P. Braunstein, A.D. Burrows, J. Chem. Res. (1993)
380.
[23] M.J. Green, G.J.P. Britovsek, K.J. Cavell, F. Gerhards, B.F.
Yates, K. Frankcombe, B.W. Skelton, A.H. White, J. Chem.
Soc. Dalton Trans. (1998) 1137.
[30] J. Andrieu, P. Braunstein, A. Tiripicchio, F. Ugozzoli, Inorg.
Chem. 35 (1996) 5975.
.