Unexpected rearrangement of palladacycles derived from 2-oxopropionaldehyde phenylhydrazones. Synthesis of palladium complexes containing a bianionic tridentate C, N, O ligand

Article abstract of DOI:10.1021/om970240w

The synthesis of bidentate monoanionic C-N derivatives of 2-oxopropionaldehyde phenylhydrazones, compounds 3, [Pd(2-{NH-N=CH-C(O)Me}-3-RC₆H₃)Cl(PPh₃)] is described. The structure of 3b (R = Me) was determined by X-ray diffraction. The bond distances and angles are similar to those reported for related metallacycles. The distance N(2)?O(1) (2.583-(7) ?) shows the existence of a strong intramolecular hydrogen bond between the NH and COCH₃ groups. The C(9)-O(1) (1.224(9) ?), C(8)-C(9) (1.46(1) ?), C(8)-N(1) (1.307(8) ?), and N1-N2 (1.325(7) ?) bond lengths indicate that 3b exists mainly in the keto-hydrazo form. The action of NaMeO on 3 in MeOH afforded deep violet compounds which did not contain chlorine atoms. The analytical data, the infrared spectra, and the NMR studies, including ¹H-¹H COSY and NOESY experiments, showed that deprotonation of the N-H bond took place to give 4, [Pd(2-{N=N-CH=C(O)Me}-3-RC₆H₃)(PPh₃)] by means of an unexpected hydrazo-azo tautomerization. The structure of 4c (R = Et) was determined by X-ray diffraction. The C(10)-O(1) (1.32(1) ?), C(10)-C(9) (1.37(1) ?), C(9)-N(2) (1.33(1) A), and N(1)-N(2) (1.25(1) ?) bond lengths indicate that 4c exists mainly in the azo-enol form. The action of HCl (0.5 N) on the tridentate metallacycles 4 regenerated the bidentate derivatives 3, showing the reversibility of this process.

Full text of DOI:10.1021/om970240w

Organometallics 1997, 16, 3775-3778
3775
Un exp ected Rea r r a n gem en t of P a lla d a cycles Der ived
fr om 2-Oxop r op ion a ld eh yd e P h en ylh yd r a zon es.
Syn th esis of P a lla d iu m Com p lexes Con ta in in g a
Bia n ion ic Tr id en ta te C, N, O Liga n d
J oan Albert,† Asensio Gonza´lez,‡ J aume Granell,*,† Rosa Moragas,†
Carmen Puerta,§ and Pedro Valerga§
Departament de Qu´ımica Inorga`nica, Universitat de Barcelona, Diagonal 647,
08028 Barcelona, Spain, Departament de Qu´ımica Orga`nica, Facultat de Farma`cia,
Universitat de Barcelona, 08028 Barcelona, Spain, and Departamento de Ciencia de los
Materiales, Ingenierı´a Metalu´rgica y Quı´mica Inorga´nica, Facultad de Ciencias,
Universidad de Ca´diz, Apdo. 40, 11510 Puerto Real, Ca´diz, Spain
Received March 24, 1997X
The synthesis of bidentate monoanionic C-N derivatives of 2-oxopropionaldehyde phen-
ylhydrazones, compounds 3, [Pd(2-{NHsNdCHsC(O)Me}-3-RC6H3)Cl(PPh3)] is described.
The structure of 3b (R ) Me) was determined by X-ray diffraction. The bond distances and
angles are similar to those reported for related metallacycles. The distance N(2)‚‚‚O(1) (2.583-
(7) Å) shows the existence of a strong intramolecular hydrogen bond between the NH and
COCH3 groups. The C(9)-O(1) (1.224(9) Å), C(8)-C(9) (1.46(1) Å), C(8)-N(1) (1.307(8) Å),
and N1-N2 (1.325(7) Å) bond lengths indicate that 3b exists mainly in the keto-hydrazo
form. The action of NaMeO on 3 in MeOH afforded deep violet compounds which did not
contain chlorine atoms. The analytical data, the infrared spectra, and the NMR studies,
1
including H-1H COSY and NOESY experiments, showed that deprotonation of the N-H
bond took place to give 4, [Pd(2-{NdN-CHdC(O)Me}-3-RC6H3)(PPh3)] by means of an
unexpected hydrazo-azo tautomerization. The structure of 4c (R ) Et) was determined by
X-ray diffraction. The C(10)-O(1) (1.32(1) Å), C(10)-C(9) (1.37(1) Å), C(9)-N(2) (1.33(1)
Å), and N(1)-N(2) (1.25(1) Å) bond lengths indicate that 4c exists mainly in the azo-enol
form. The action of HCl (0.5 N) on the tridentate metallacycles 4 regenerated the bidentate
derivatives 3, showing the reversibility of this process.
In tr od u ction
tridentate C-N-O ligand from cyclopalladated hydra-
zones by deprotonation of the N-H bond and tautomer-
ization of the metalated ligand.
In recent years, many multidentate ligands have been
developed in order to obtain new organometallic com-
plexes. Among these, the palladium complexes with
polydentate ligands are especially interesting because
of their reactivity and catalytic activity. It has recently
been shown that palladacycles with anionic P-C or
N-C ligands are efficient catalysts for a range of
processes including the Heck olefination of chloro and
bromoarenes,1 aryl coupling reactions,2 telomerization
of butadiene with alcohols,3 and asymmetric cyclopro-
panation.4
Organopalladium compounds containing tridentate
ligands have been extensively studied,5 but only a few
of these species are reported to contain a bianionic
tridentate ligand.6 In this paper, we describe the
synthesis of palladacycles containing the bianionic
The equilibrium between the hydrazo-keto and azo-
enol forms of organic molecules, containing the HNs
N)CsCdO fragment, is well-known,7 and it has been
shown that the presence of a specific organic fragment
may shift the equilibrium in favor of one of the two
tautomeric forms.8 In contrast, to the best of our
knowledgement, this tautomerization process has not
been studied in organometallic derivatives in which the
(5) For a review on tridentate N-donor ligands, see: van Kotten G.
Pure Appl. Chem. 1989, 61, 1681. For specific and recent palladium
examples, see: (a) Alsters, P. L.; Engel, P. F.; Hogerheide, M. P.;
Copijn, M.; Spek, A. L.; van Koten, G. Organometallics 1993, 12, 1831.
(b) Garcia-Herbosa, G.; Mun˜oz, A.; Miguel, D.; Garcia-Granda, S.
Organometallics 1994, 13, 1775 (c) Cross, R. J .; Kennedy, A. R.; Muir,
K. W. J . Organomet. Chem. 1995, 487, 227. (d) Kraatz, H.; Milstein,
D. J . Organomet. Chem. 1995, 488, 223. (e) Chan, C.; Mingos, D. M.
P.; White, A. J . P.; Williams, D. J . J . Chem. Soc., Chem. Commun.
1996, 81. (f) Perera, S. D.; Shaw, B. L. J . Chem. Soc., Dalton Trans.
1995, 641.
(6) For some examples of bianionic tridentate ligands, see: (a)
Hedden, D.; Roundhill, D. M.; Fultz, W. C.; Reingold, A. L. Organo-
metallics 1986, 5, 336. (b) Mahapatra, A. K.; Bandyopadhyay, D.;
Bandyopadhyay, P.; Chakravorty, D. Inorg. Chem. 1986, 25, 2214. (c)
Yang, H.; Khan, M. A.; Nicholas, K. M. J . Chem. Soc. Chem. Commun.
1992, 210. (d) Yoneda, A.; Newkome, G. R.; Theriot, K. J . J . Organomet.
Chem. 1991, 401, 217. (e) Yoneda, A.; Hakushi, T.; Newkome, G. R.;
Fronczek, F. R. Organometallics 1994, 13, 4912. (f) Albert, J .; Granell,
J .; Sales, J .; Font-Bardia, M.; Solans, X. Organometallics 1995, 14,
1393.
† Departament de Qu´ımica Inorga`nica, Universitat de Barcelona.
‡ Departament de Qu´ımica Orga`nica, Universitat de Barcelona.
§ Universidad de Ca´diz.
X Abstract published in Advance ACS Abstracts, J uly 15, 1997.
(1) Hermann, W. A.; Brossmer, C.; O¨ fele, K.; Reisinger, C.; Prier-
meier, T.; Beller, M.; Fischer, H. Angew. Chem., Int. Ed. Engl. 1995,
34, 1844.
(2) (a) Beller, M.; Fischer, H.; Hermann, W. A.; O¨ fele, K.; Brossmer,
C. Angew. Chem., Int. Ed. Engl. 1995, 34, 1848. (b) Hermann, W. A.;
Reisinger, C.; O¨ fele, K.; Brossmer, C.; Beller, M.; Fischer, H. J . Mol.
Catal. 1996, 108, 51.
(3) Camargo, M.; Dani, P.; Dupont, J .; de Souza, R. F.; Pfeffer, M.;
Tkatchenko, I. J . Mol. Catal. 1996, 109, 127
(7) Cox, R. C.; Buncel, E. In The Chemistry of the Hydrazo, Azo and
Azoxy Groups; Patai, S., Ed; Wiley: Chichester, U.K. 1970; pp 838-
851 and references therein.
(4) Navarro, R.; Urriolabeitia, E. P.; Cativiela, C.; Diaz de Villegas,
M. D.; Lo´pez, M. P.; Alonso, E. J . Mol. Catal. 1996, 105, 111.
S0276-7333(97)00240-9 CCC: $14.00 © 1997 American Chemical Society

3776 Organometallics, Vol. 16, No. 17, 1997
Albert et al.
Sch em e 1a
(i) PdCl2, EtOH, 3 days, room temperature. (ii) PPh3, acetone, 30 min, room temperature. (iii) NaMeO, MeOH, 2 h, room
temperature. (iv) 0.5 N HCl, room temperature, 5 min.
presence of a transition metal atom, strongly bonded
to the organic ligand and with available coordination
positions, can influence the equilibrium position.
Resu lts a n d Discu ssion
The action of PdCl2 on hydrazones 1, derived from
2-oxopropionaldehyde, leads to the cyclopalladated com-
plexes 2 in high yield (80-90%). The dinuclear com-
pounds obtained react with PPh3 affording the cyclo-
metalated complexes [PdCl(C-N)PPh3] 3 (see Scheme
1). The new compounds obtained were characterized
1
by elemental analysis, IR spectra, and H and 31P NMR
spectra.9 In several cases, COSY experiments were
carried out to complete the NMR studies. The aromatic
protons of the palladated ring in 3 appear high-field-
1
shifted in the H NMR spectra, indicating a cis arrange-
F igu r e 1. Molecular structure of 3b.
ment of the phosphine and the metalated carbon atom.6f
The signal assigned to the methinic proton in the
3. The crystal structure consists of discrete molecules
cyclometalated compounds is low-field-shifted in rela-
separated by van der Waals distances. The bond
tion to the free ligand. This shift can be explained by
distances and angles are similar to those reported for
the paramagnetic anisotropy of the palladium atom and
indicates that the metalated phenyl ring and the COCH3
group adopt a cis disposition around the CdN bond,
thus an E-Z isomerization occurs during the cyclomet-
alation process,10 as reported for similar cyclopalladated
derivatives from imines.11 The signal assigned to the
NH proton in the 1H NMR spectra appears strongly
shifted to low fields (δ ) 13.9-14.5 ppm), indicating a
strong hydrogen bond between the CH3CO and the NH
groups.8,12 The crystal structure of 3b has been deter-
mined (Figure 1). Crystallographic data and selected
bond lengths and angles are listed in Tables 1, 2, and
related metallacycles.6f,11 The palladium atom is in a
slightly distorted square-planar environment coordi-
nated to phosphorus, carbon, chloride, and the iminic
nitrogen atom (the largest deviation from the mean
plane determined by the five atoms is 0.14 Å for N(1)).
The iminic nitrogen and the phosphine molecule adopt
a trans arrangement. The metalated phenyl ring and
the COCH3 groups adopt a cis disposition around the
CdN bond. The distance N(2)‚‚‚O(1) (2.583(7) Å) con-
firms a strong intramolecular hydrogen bond between
the NH and COCH3 groups, similar to those found for
related free hydrazones. The C(9)-O(1) (1.224(9) Å),
C(8)-C(9) (1.46(1) Å), C(8)-N(1) (1.307(8) Å), and N1-
N2 (1.325(7) Å) bond lengths indicate that 3b exists
mainly in the keto-hydrazo form.8,12
The action of NaMeO on 3 in MeOH affords deep
violet compounds which do not contain chlorine atoms.
The analytical data, the infrared spectra (absence of the
strong bands of the CdO and CdN bonds and the
existence of a weak band assigned to the NdN group),
and the NMR studies, including 1H-1H COSY and
NOESY experiments, show that deprotonation of the
N-H bond takes place to give 4 by means of an
unexpected hydrazo-azo tautomerization.
(8) (a) Connor, J . A.; Kennedy, R. J .; Dawes, H. M.; Hursthouse, M.
B.; Walker, N. P. C. J . Chem. Soc., Perkin Trans. 1990, 203. (b) Olivieri,
A. C.; Wilson, R. B.; Paul, I. C.; Curtin, D. Y. J . Am. Chem. Soc. 1989,
111, 5525.
(9) Due to the insolubility of 2, their NMR spectra were recorded in
the presence of pyridine-d5, which affords the mononuclear complexes
[PdCl(C-N)(py-d5)].
(10) The coordination of palladium to methinic nitrogen changes the
order of precedence order, and strictly speaking, the ligand is in the
E-form in 2 and 3.
(11) Albert, J .; Go´mez, M.; Granell, J .; Sales, J .; Solans, X. Orga-
nometallics 1990, 9, 1405.
(12) The model RAHB (resonance-assisted hydrogen bonding) has
been used to interpret the intramolecular hydrogen bond in the
OdCsCdNsNH fragments, see: (a) Bertolasi, V.; Ferreti, V; Gilli,
G.; Issa, Y. M.; Sherif, O. E. J . Chem. Soc., Perkin Trans. 1993, 2223.
(b) Bertolasi, V.; Nanni, L.; Gilli, P.; Ferreti, V.; Gilli, G.; Issa, Y. M.;
Sherif, O. E. New J . Chem. 1994, 18, 251 and references therein.
The crystal structure of 4c has been determined
(Figure 2). Crystallographic data and selected bond

Unexpected Rearrangement of Palladacycles
Organometallics, Vol. 16, No. 17, 1997 3777
Ta ble 3. Selected Bon d An gles (d eg) for 3b
Cl(1)-Pd(1)-P(1)
Cl-Pd(1)-N(1)
P(1)-Pd(1)-C(1)
N(1)-Pd(1)-C(1)
N(2)-C(6)-C(5)
N(1)-N(2)-C(8)
93.32(7)
91.1(2)
93.8(2)
81.9(3)
118.3(6)
119.3(6)
N(1)-N(2)-C(6)
N(1)-C(8)-C(9)
O(1)-C(9)-C(8)
O(1)-C(9)-C(10)
C(8)-C(9)-C(10)
117.5(5)
124.5
122.1(7)
121.7(7)
116.2(7)
Ta ble 4. Selected Bon d Len gth s (Å) for 4c
Pd(1)-P(1)
Pd(1)-O(1)
Pd(1)-N(2)
Pd(1)-C(1)
O(1)-C(10)
2.262(2)
2.166(7)
2.011(7)
1.975(9)
1.32(1)
N(1)-N(2)
N(1)-C(6)
N(2)-C(9)
C(9)-C(10)
C(10)-C(11)
1.25(1)
1.41(1)
1.33(1)
1.37(1)
1.47(1)
Ta ble 5. Selected Bon d An gles (d eg) for 4c
Pd(1)-Pd(1)-O(1)
O(1)-Pd(1)-N(2)
P(1)-Pd(1)-C(1)
N(2)-Pd(1)-C(1)
N(2)-N(1)-C(6)
N(1)-N(2)-C(9)
103.3(2)
79.9(3)
97.9(2)
78.8(3)
110.9(7)
126.2(8)
N(1)-C(6)-C(5)
N(2)-C(9)-C(10)
O(1)-C(10)-C(9)
O(1)-C(10)-C(11)
C(9)-C(10)-C(11)
118.8(8)
118.4(9)
121.4(9)
116.1(1)
123.1(1)
(1.32(1) Å), C(10)-C(9) (1.37(1) Å), C(9)-N(2) (1.33(1)
Å), and N(1)-N(2) (1.25(1) Å) bond lengths indicate that
4c exists mainly in the azo-enol form.8,12
F igu r e 2. Molecular structure of 4c.
When the deprotonation reaction was performed with
benzylamine in toluene, a white compound precipitated,
which was identified as benzylamine hydrochloride, and
compounds 4 and a small quantity of the starting
materials 3 were obtained from the solution. The action
of HCl (0.5 N) on the tridentate metallacycles 4 regen-
erates the bidentate derivatives 3, showing the revers-
ibility of this process.
The results here described contrasts with those previ-
ously reported by Espinet et al.13 which have shown that
the deprotonation of cyclopalladated hydrazone deriva-
tives affords binuclear amido complexes. The main
difference between both types of hydrazones relies in
the presence, in our case, of the COCH3 group which
permits the hydrazone to act as a tridentate ligand by
the tautomerization reaction here described.
The deprotonation of the N-H bond, leading to a
highly conjugated anion which can adopt the “azoben-
zene-like” resonance structure, has recently been pro-
posed to explain the metalation of aromatic hydrazones.5b
Here, for the first time, we show the existence of this
metalated azobenzene derivative and the reversibility
of the rearrangement between the hydrazo and azo
tautomers in palladium metallacyles, which produces
a reversible change in the coordination mode of the
ligand from monoanionic bidentate C,N to bianionic
tridentate C,N,O.
Ta ble 1. Su m m a r y of Cr ysta l Da ta Collection a n d
Str u ctu r e An a lysis
compound
formula
fw
4c
3b
C
29H27N2OPPd
C28H26ClN2OPPd
579.35
556.92
cryst size (mm)
cryst syst
space group
cell param
0.14 × 0.07 × 0.40 0.34 × 0.14 × 0.17
monoclinic
P21/c (No. 14)
a ) 15.633(4) Å
b ) 8.602(3) Å
c ) 18.809(3) Å
â ) 96.66(2)°
2512(1) Å3
4
monoclinic
P21/c (No. 14)
a ) 18.082(5) Å
b ) 9.184(2) Å
c ) 18.752(6) Å
â ) 114.66(2)°
2830(1) Å3
4
volume
Z
Fcalcd
1.472 g cm-3
0.710 69 Å
8.14 cm-1
1136
1.360 g cm-3
0.710 69 Å
8.18 cm-1
1176
λ(Mo KR)
µ(Mo KR)
F(000)
transmission factors
decay
0.89-1.00
no correction
-7.80%
-1.66%
temperature
scan speed (ω)
2θ interval
no. of measd reflns
no. of unique reflns
no. of obsd reflns
(I > 3σI)
290(1) K
290(1) K
8° min-1
4° min-1
5° < 2θ < 50°
4582
5° < 2θ < 50°
4066
3936 (Rint ) 0.090) 4447 (Rint ) 0.089)
2172
3161
no. of params
refln/param ratio
Ra
307
7.07
0.048
0.055
335
9.44
0.047
0.057
1.37
1.75
-2
b
Rw (w ) σF
)
max ∆/σ in final cycle 1.06
gof
1.48
a
b
2 1/2
R ) ∑(|Fo| - |Fc|)/∑|Fo|. Rw ) [∑w(|Fo| - |Fc|)2/∑wFo
] .
Exp er im en ta l Section
Ta ble 2. Selected Bon d Len gth s (Å) for 3b
1H NMR spectra at 200 MHz and 500 MHz and 31P{1H}
NMR spectra at 101.26 MHz were recorded, respectively, on
Varian Gemini 200, Varian VXR 500, and Bruker DRX 250
spectrometers. Chemical shifts (in ppm) were measured
relative to SiMe4 for the 1H NMR and to 85% H3PO4 for the
31P NMR studies. The solvents used were CDCl3 in the 1H
NMR and CHCl3 in the 31P NMR studies. Microanalyses were
performed at the Institut de Qu´ımica Bio-Orga`nica de Barce-
lona and the Serveis Cient´ıfico-Te`cnics de la Universitat de
Barcelona.
Pd(1)-Cl(1)
2.360(2)
2.257(2)
2.098(6)
2.004(7)
1.224(9)
N(1)-N(2)
N(1)-C(8)
N(2)-C(6)
C(8)-C(9)
C(9)-C(10)
1.325(7)
1.307(8)
1.402(8)
1.46(1)
Pd(1)-P(1)
Pd(1)-N(1)
Pd(1)-C(1)
O(1)-C(9)
1.49(1)
lengths and angles are listed in Tables 1, 4, and 5. The
crystal structure consists of discrete molecules sepa-
rated by van der Waals distances. The palladium atom
is in a square-planar environment coordinated to phos-
phorus, carbon, oxygen, and the iminic nitrogen atom,
(the largest deviation from the mean plane determined
by the five atoms is 0.076 Å for N(2)). The C(10)-O(1)
(13) Espinet, P.; Garcia, G.; Herrero, F. J .; J eannin, Y.; Philoche-
Levisalles, M. Inorg. Chem. 1989, 28, 4207.

3778 Organometallics, Vol. 16, No. 17, 1997
Albert et al.
Cr ysta llogr a p h ic Stu d ies. A crystal was selected and
mounted on a Rigaku AFC6S diffractometer. Unit cell pa-
rameters were determined from automatic centering of 25
reflections (12.5 e θ e 15°) and refined by the least-squares
method. Intensities were collected with graphite-monochro-
mated Mo KR radiation, using the ω-scan technique. Reflec-
tions having I g 3σ(I) were used for structure resolution. All
calculations for data reduction, structure solution, and refine-
ment were carried out using the TEXSAN software system.14
The structures were solved by Patterson synthesis and refined
by the full-matrix least-squares method. Hydrogen atoms
were included in idealized positions. Crystal parameters, data
collection details, and results of the refinements are sum-
marized in Table 1.
Ma ter ia ls a n d Syn th eses. All chemicals and solvents
were commercial grade and used as received, except ethanol,
chloroform, methanol, and acetone which were dried over
CaCl2 and distilled before use. Hydrazones were obtained
according to procedures described elsewhere.15 X-ray quality
crystals were obtained by slow evaporation (at room temper-
ature ca. 20 °C) of a saturated CHCl3 solution layered with
MeOH.
(97%). Anal. Calcd (found) for C27H24N2OClPPd: C, 57.36
(57.3); H, 4.28 (4.4); N, 4.95 (4.9).1H NMR: δ 14.20 (d, J HP
)
3.0 Hz, 1H, NH), 8.16 (d, J HP ) 3.5 Hz, 1H, HCdN), 7.76-
7.34 (br m, 15H, PPh3), 6.85 (td, J HH ) 7.0, 1.0 Hz, 1H, H4),
6.72 (dd, J HH ) 7.5, 1.0 Hz, 1H, H3), 6.30 (td, J HH ) 7.0, 1.0
Hz, 1H, H5), 6.22 (td, J HH ) 7.5 Hz, J HP ) 1.0 Hz, 1H, H6),
2.37 (s, 3H, CH3CO). 31P NMR: δ 43.83 ppm. 3b: yield 365
mg (78%). Anal. Calcd (found) for C28H26N2OClPPd: C, 58.05
(57.8); H, 4.53 (4.5); N, 4.84 (4.8).1H NMR: δ 14.39 (d, J HP
)
3.5 Hz, 1H, NH), 8.19 (d, J HP ) 3.5 Hz, 1H, HCdN), 7.59-
7.34 (br m, 15H, PPh3), 6.68 (t, J HH ) 7.5 Hz, 1H, H5), 6.16
(m, 2H, H4, H6), 2.37 (s, 3H, CH3CO), 2.28 (s, 3H, CH3). 31P
NMR: δ 44.28 ppm. 3c: yield 322 mg (93%). Anal. Calcd
(found) for C29H28N2OClPPd: C, 57.70 (57.9); H, 4.76 (4.7); N,
4.73 (4.6). 1H NMR: δ 14.54 (d, J HP ) 2.0 Hz, 1H, NH), 8.19
(d, J HP ) 3.5 Hz, 1H, HCdN), 7.76-7.24 (br m, 15H, PPh3),
6.70 (dd, J HH ) 8.5, 1.5 Hz, 1H, H4), 6.20-6.18 (m, 2H, H5,
H6), 2.60 (q, 2H, CH2CH3), 2.37 (s, 3H, CH3CO), 1.27 (t, 3H,
CH3CH2). 31P NMR: δ 43.14 ppm.
Com p ou n d s 4. NaMeO (0.34 mmol, 0.0184 g) was added
to a solution of 3 (0.34 mmol) in methanol, and the mixture
was stirred under nitrogen for 2 h at room temperature. The
solvent was removed in vacuo, and the residue was washed
with ether (2 × 10 cm3) and then dried in vacuo to give a violet
solid 4. Characterization data: 4a yield 135 mg (72%). Anal.
Calcd (found) for C27H23N2OPPd: C, 61.32 (61.1); H, 4.38 (4.4);
N, 5.30 (5.3). 1H NMR: δ 7.86-7.37 (br m, 15H, PPh3), 7.07
(d, J HH ) 7.5 Hz, 1H, H3), 6.77 (t, J HH ) 7.0 Hz, 1H, H5), 6.57
Com p ou n d s 2. A stirred suspension of PdCl2 (1.69 mmol,
0.3 g) in ethanol (30 cm3) was treated with the corresponding
hydrazone (1.69 mmol) for 3 days at room temperature. The
solid obtained was filtered, washed with ethanol (2 × 15 cm3),
and dried in vacuo to afford 2 as orange or brown solids.
Characterization data: 2a yield 445 mg (87%). Anal. Calcd
(found) for C18H18N4O2Cl2Pd2: C, 35.67 (35.8); H, 2.99 (3.0);
N, 9.24 (9.2). 1H NMR (2a + py-d5): δ 13.96 (s, 1H, NH), 8.02
(s, 1H, HCdN), 7.00 (td J HH ) 7.5, 1.0 Hz, 1H, H4), 6.70 (dd,
J HH ) 8.0, 1.0 Hz, 1H, H3), 6.12 (d, J HH ) 8.0 Hz, 1H, H6),
2.36 (s, 3H, CH3CO). 2b: yield 487 mg (91%). Anal. Calcd
(found) for C20H22N4O2Cl2Pd2: C, 37.88 (38.2); H, 3.50 (3.4);
N, 8.84 (8.8). 1H NMR (2b + py-d5): δ 14.14 (s, 1H, NH), 8.02
(s, 1H, HCdC), 6.14 (t, J HH ) 7.5 Hz, 1H, H4), 5.82 (d, J HH
)
7.5 Hz, 1H, H6), 1.95 (s, 3H, CH3CO). 31P NMR: δ 32.12 ppm.
4b: yield 114 mg (61%). Anal. Calcd (found) for C28H25N2-
OPPd: C, 61.94 (61.8); H, 4.64 (4.8); N, 5.16 (5.2). 1H NMR:
δ 7.86-7.37 (br m, 15H, PPh3), 6.58 (d, J HH ) 7.0 Hz, 1H, H4),
6.52 (s, 1H, HCdC), 6.06 (t, J HH ) 7.5 Hz, 1H, H5), 5.68 (d,
J HH ) 6.8 Hz, 1H, H6), 2.35 (s, 3H, CH3), 1.92 (s, 3H, CH3C-
O). 31P NMR: δ 32.63 ppm. 4c: yield 177 mg (95%). Anal.
Calcd (found) for C29H27N2OPPd: C, 62.54 (62.3); H, 4.88 (4.9);
N, 5.03 (5.1). 1H NMR: δ 7.86-7.37 (br m, 15H, PPh3), 6.57
(m, 2H, HCdC, H4), 6.07 (t, J HH ) 6.7 Hz, 1H, H5), 5.67 (d,
J HH ) 7.5 Hz, 1H, H6), 2.68 (q, J HH ) 7.6 Hz, 2H, CH2CH3),
1.92 (s, 3H, CH3C-O), 1.19 (t, J HH ) 7.6 Hz, 3H, CH3CH2).
31P NMR: δ 33.4 ppm.
(s, 1H, HCdN), 6.70 (d, J HH ) 7.5 Hz, 1H, H4) , 6.46 (t, J HH
)
7.5 Hz, 1H, H5), 5.84 (d, J HH ) 8.0 Hz, 1H, H6), 2.24 (s, 3H,
CH3CO), 2.15 (s, 3H, CH3). 2c: yield 466 mg (83%). Anal.
Calcd (found) for C22H26N4O2Cl2Pd2: C, 40.00 (39.9); H, 3.97
(3.8); N, 8.46 (8.4). 1H NMR (2c + py-d5): δ 14.33 (s, 1H, NH),
8.14 (s, 1H, HCdN), 6.85 (dd, J HH ) 7.5, 0.5 Hz, 1H, H4), 6.59
(t, J HH ) 7.5 Hz, 1H, H5), 5.92 (dd, J HH ) 7.5, 1.0 Hz, 1H, H6),
2.55 (q, J HH ) 7.5 Hz, 2H, CH2CH3), 2.31 (s, 3H, CH3CO), 1.20
(t, J HH ) 7.5 Hz, 3H, CH3CH2).
Ack n ow led gm en t. We thank the DGICYT (Project
No. PB 93-0804) and the Comissionat per a Universitats
i Recerca (Project No. 1995SGR 00044) for financial
support.
Com p ou n d s 3. A stirred suspension of 2 (0.3 mmol) was
treated with PPh3 (0.6 mmol, 0.157 g) in acetone (30 cm3) for
30 min at room temperature and then filtered. The filtrate
was concentrated in vacuo, and the deep orange solid obtained
after addition of ether was recrystallized from chloroform-
ether to obtain 3. Characterization data: 3a yield 361 mg
Su p p or tin g In for m a tion Ava ila ble: Tables of positional
parameters, isotropic parameters, intermolecular and in-
tramolecular bond lengths and angles, and anisotropic dis-
placement parameters for 3b and 4c (34 pages).
(14) TEXSAN: Single-Crystal Structure Analysis Software, version
5.0; Molecular Structure Corp.: The Woodlands, TX, 1989.
(15) Gonza´lez, A. Synth. Commun. 1988, 18, 1225.
OM970240W