Novel cyclometallated Pd(II) and Pt(II) complexes with indole derivatives and their use as catalysts in Heck reaction

Article abstract of DOI:10.1016/j.jorganchem.2004.11.042

Several palladacycle and platinacycle complexes have been prepared from easily available or naturally occurring indole derivatives, such as gramine and related compounds. Dimeric complexes were obtained with Pd(OAc)₂, while Pt(DMSO)₂

Full text of DOI:10.1016/j.jorganchem.2004.11.042

Journal of Organometallic Chemistry 690 (2005) 2017–2026
www.elsevier.com/locate/jorganchem
Novel cyclometallated Pd(II) and Pt(II) complexes with
indole derivatives and their use as catalysts in Heck reaction
a
Giancarlo Cravotto , Francesco Demartin , Giovanni Palmisano , Andrea Penoni
b
c
c,
*
,
c
Tiziano Radice , Stefano Tollari
c,
*
a
`
Dipartimento di Scienza e Tecnologia del Farmaco, Universita degli Studi di Torino, via Giuria 9, 10125 Torino, Italy
b
`
Dipartimento di Chimica Strutturale e Stereochimica Inorganica, Universita degli Studi di Milano, Via Venezian 21, 20133 Milano, Italy
c
`
Dipartimento di Scienze Chimiche ed Ambientali, Universita degli Studi dellÕInsubria, via Valleggio 11, 22100 Como, Italy
Received 26 November 2004; accepted 26 November 2004
Abstract
Several palladacycle and platinacycle complexes have been prepared from easily available or naturally occurring indole deriva-
tives, such as gramine and related compounds. Dimeric complexes were obtained with Pd(OAc)2, while Pt(DMSO)2Cl2 mainly affor-
ded monomeric structures. A notable feature of these reactions was the formation of new M–C bonds between Pd or Pt and C-2 and
C-3 of the indole ring. With ligands like 2-(20-pyridyl)-1H-indoles, N–N metallacycles were generated instead: in fact new C–M
bonds with the C-3 position could only form if N-substituted indoles were used. The reactivity of Pd dimeric complexes with
PPh3, sym-collidine and DMAP was explored to obtain monomeric complexes. Three such compounds were prepared, one of which
was characterized by X-ray diffraction. Metathetical reactions were carried out to effect a ligand exchange replacing OAc with halide
ions, with the aim to synthesize l-Cl and l-Br bridged structures. Turning to the synthesis of hetaryl complexes, functionalization of
the C-2 position on the indole ring was achieved. These complexes were prepared by substitution reactions starting from gramine
and/or its alkylammonium salts.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Indole derivatives; Metallacycles; Palladium; Platinum; Catalysis; Heck reaction
1. Introduction
optical purity [3]. Finally, they have proved useful in
the design of molecules with promising photochemical
[4] and anticancer properties [5]. Cyclometallated com-
pounds are organometallic complexes embodying an
E–M–C connectivity of r-bonds, where E is a heterod-
onor atom of the 15- or 16-group, M a metallic atom
and C a carbon donor. They are usually classified
according to the metal, the donor atom(s) or chelate ring
size. Cyclopalladated compounds with a variety of N-
donor ligands (e.g., amines, azobenzenes, imines [6],
hydrazones [7], oximes and N-centered hetarenes) have
been extensively investigated. Whereas heteroatom-
directed cyclometallation of benzenoids and hetarenes
is well known, the chemistry of the analogous indole
derivatives remains partially unexplored [6–11]. In this
Intramolecular activation of C–H bonds through the
agency of transition metal ions (cyclometallation), first
described by Kleiman and Dubeck [1], has attracted
much interest in the last two decades. Many useful
applications of cyclometallated compounds in organic
chemistry are well established, e.g., to the synthesis of
heterocycles and of enantiomerically enriched mole-
cules, to prepare liquid crystals (metallomesogens) [2],
to the resolution of racemates and to the evaluation of
*
Corresponding
+390312386449.
E-mail address: stefano.tollari@uninsubria.it (S. Tollari).
authors.
Tel.:
+390312386471;
fax:
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.11.042

2018
G. Cravotto et al. / Journal of Organometallic Chemistry 690 (2005) 2017–2026
On the other hand, the reaction of 1 with equivalent
PPA
amounts of Pd(OAc)2 in dichloromethane at room tem-
perature (1 h) produced the dimeric acetate complex
[(L1-N,N) Pd(l-OAc)]2 4 (Scheme 3). Strong bands were
observed at 1572, 1412 cmꢀ1 due to mas (COO) and
N
N
N
H
N
N
CH3
H
1
m
s (COO), values consistent with a bridged acetate ligand;
1
Scheme 1.
in H NMR spectra the singlet resonance at 2.35 ppm
(6H) was assigned to the magnetically equivalent Me
acetate groups, in accord with a trans geometry of the
[NꢂN] cyclometallated compound 4.
L'
L
M
N
N
Complex 5 [(L1-N,N) Pd(DMAP)(OAc)] was isolated
after the addition to complex 4 of 4-dimethylaminopyri-
N
N
M=Pd, Pt
1
dine (DMAP) in CH2Cl2. The H NMR spectrum of 5
H
H
was unexceptional. Pale yellow crystals suitable for sin-
gle-crystal X-ray structure determination were obtained
by vapour diffusion of Et2O into a CH2Cl2 solution of
the crude product. 5 was then fully characterized by
X-ray diffraction. Likewise complex 4 could be reacted
with the appropriate ligating species to give 6 and 7. A
sample of 4 placed in an NMR tube was treated at room
temperature in CDCl3 with 1 equiv. of triphenylphos-
phine or 2,4,6-trimethylpyridine (sym-collidine), where-
upon an instantaneous reaction took place to give the
corresponding [(L1-N,N) Pd L(OAc)] complexes 6 and
7, respectively (Scheme 4). These complexes were iso-
lated in essentially quantitative yields by simply remov-
Scheme 2.
context we are currently studying the structures and
physico-chemical properties of 5- and 6-membered
metallacycles containing an indole subunit with a teth-
ered N-donor group [8–11]. In particular we have
focused our interest on complexes of Pt(II) and Pd(II)
with variously substituted bidentate [C, N] amines and
imines as well as tridentate [C, N, O] hydrazones. The
present work examined the formation of Pd(II) and
Pt(II) complexes with 2-(2-pyridyl)-1H-indole (HL1) 1
and their performance as precatalysts in the Heck reac-
tion between iodobenzene and tert-butylacrylate. 1 was
prepared in excellent yield by Fischer indolization [12]
of 2-acetylpyridine with phenylhydrazine in polyphos-
phoric acid (PPA) at 150 ꢁC (Scheme 1).
The juxtaposition of a pyridine and an indole system,
presenting two potential donor sets (i.e., N,N or C,N) in
a 1,4-relationship is particularly interesting. Pyridine be-
haves as a p-deficient system with Lewis basicity while
indole is a p-excessive system 10eꢀ system with a good
H-bond donor atom. When we used 1 as ligand for
the synthesis of cyclometallated compounds with the
aim to generate a new C–M bond, we found that 1 be-
haves exclusively as a nitrogen chelating agent, forming
a N–M–N coordination compound.
Ligand 1 could, in principle, behave as an ambident
nucleophile (N-1 vs. C-3) although normally indoles pre-
fer electrophilic substitution (e.g., cyclometallation) at
C-3, the 1-position being clearly less reactive. The reac-
tion in degassed EtOH of 1 with Li2[PdCl4] in the
presence of NaOAc as a proton scavenger (room tem-
perature, 2 h) afforded the orange [(L1-N,N) Pd(l-Cl)]2
complex 2 exhibiting N,N ligation, whose structure
was supported by elemental analysis and IR spectros-
copy. The absence of the two bands at 3100 and 3010
cmꢀ1 attributed to the m(N–H) mode of the ligand indi-
cated that 1 had been deprotonated and coordinated
in the amido (indolato) form (Scheme 2).
1
ing the solvent. The H NMR spectrum of 7 as well as
1H NMR and 31P NMR spectra of the complex 6
showed only one set of signals, suggesting that only
one isomer was obtained. The crystal structure of 5 evi-
denced an anti disposition of the pyridine and DMAP
moieties. By analogy we propose the same geometry
for 6 and 7 [13], as attempts to obtain single crystals
of these compounds for X-ray diffraction studies were
unsuccessful.
Metathetical reactions also occurred when complex 4
was treated with LiX (Scheme 5).
When [Pt(DMSO)2Cl2] (DMSO = dimethylsulfoxide)
was refluxed in ethanol with compound 1, the mono-
meric platinum derivative 8 was obtained (Scheme 6).
The observation of a single SMe resonance at 3.61
ppm with 195Pt satellites (3JPt–H = 25 Hz) as well as the
finding in the IR spectrum of msS–O at 1122 cmꢀ1 indi-
cated an S-bonded DMSO configuration. Compound 8
was also fully characterized by X-ray diffraction.
Following with our aim to obtain new [N–C–M] sys-
tems we turned to N-protected indoles, expecting cyclo-
metallation at C-3 to emerge. This strategy led us to
synthesize cyclometallated complexes with a new me-
tal-nitrogen bond and a new C–M bond with C-3 of
the indole derivative. In fact 1-methyl-2-(20-pyridinyl)-
1H-indole (L2) formed almost quantitatively Pd and Pt
complexes in accordance to our expectation (Scheme 7).
The substituent at the nitrogen atom should protect it
from chelation, but should not deactivate the indole
nucleus towards the electrophilic attack by the metal.
Complex 2 was uneventfully converted to the bromo-
bridged analogue, [(L1-N,N) Pd(l-Br)]2 3 by metatheti-
cal reaction with LiBr in MeOH at room temperature.

G. Cravotto et al. / Journal of Organometallic Chemistry 690 (2005) 2017–2026
2019
LiBr
Li2PdCl4
N
N
N
N
Pd
Pd
Cl
Br
2
2
2
3
N
N
H
Pd(OAc)2
CH2Cl2
N
N
Pd
AcO
2
4
Scheme 3.
N
DMAP
CH2Cl2
PPh3
CH2Cl2
N
N
Pd
OAc
N
N
N
N
Pd
OAc
Pd
Ph3P
AcO
Me2N
6
5
2
4
CH2Cl2
sym-collidine
N
N
Me
Pd
N
OAc
Me
Me
7
Scheme 4.
1-methyl-2-(20-pyridinyl)-1H-indole (L2) led to the
synthesis of several cyclometallated palladium and plat-
inum derivatives, whose reactivity was also investigated.
Reaction with Pd(OAc)2 in CH3CN yielded the dimeric,
cyclopalladated product 9 (Scheme 8).
ethanol, even in presence of AcONa, gave product 10
(Scheme 9), for which m(Pd–Cl) occurred at 277 and 254
cmꢀ1
.
Compound 10 was suspended in ethanol and carbon
monoxide was bubbled through the reaction mixture at
room temperature in the presence of NEt3 as a proton
scavenger. Metallic palladium separated out, while the
organic ligand was recovered in good yield (73%) as
3-carbethoxy-1-methyl-2-(20-pyridinyl)-1H-indole 11
(Scheme 10).
Strong bands were again observed at 1575 and 1417
cmꢀ1 due to the mas(COO) and ms(COO) stretching vibra-
tions, respectively, and in the H NMR spectrum a sin-
1
glet at 2.33 ppm, characteristic of acetate bridging [13b].
The same reaction, when carried out with Li2PdCl4 in
LiX
N
Pd
N
Pd
Pt(DMSO)2Cl2, AcONa
EtOH
N
N
N
AcO
X
EtOH
X = Cl, Br
N
N
N
Pt
Cl
H
DMSO
2
2
Scheme 5.
Scheme 6.

2020
G. Cravotto et al. / Journal of Organometallic Chemistry 690 (2005) 2017–2026
L
Cl
L
2
CO2Et
M
N
N
Pd
N
N
CO, EtOH
Et3N
M = Pd, Pt
N
N
N
N
CH3
CH3
CH3
CH3
11
Scheme 7.
Scheme 10.
The functionalization of 1-methyl-2-(20-pyridinyl)-
1H-indole at C-3 of the indole moiety was readily
achieved. Similar reactions, when conducted with sec-
ondary amines instead of ethanol, did not yield the cor-
responding carboxamide derivatives in a reproducible
manner.
tested for catalytic activity in cross-coupling reactions,
in order to discover whether they might mediate the for-
mation of new C–C bonds. Complex 12 has also been
characterized by X-ray diffraction.
1.1. Catalytic activity
As reported by some of us [8] gramine and related
compounds are good candidates and precursors for the
formation of five- and six-membered indole-fused palla-
dacycles and platinacycles. Subsequently, we investi-
gated the possibility of obtaining other palladacycles
and platinacycles by replacing the NMe2 group with
pyrazoles. The major isolated products from the reac-
tions of gramine and pyrazoles are shown in Scheme
11. In this case six-membered rings were produced, their
geometry being quite similar to that of tryptamine-like
metallacycles reported in previous papers [6,9].
In order to obtain the same kind of product when the
indole nitrogen is methylated, it is necessary to start
from the corresponding gramine methiodide (Scheme
12).
Pyrazole and 3,5-dimethylpyrazole in the presence of
Pd(OAc)2 in CH2Cl2 gave different dimeric platina- and
palladacycles as shown in Scheme 13, whereas working
with Pt(DMSO)2Cl2 monomeric Pt complexes were ob-
tained (Scheme 13).
In these instances new N–M–C bonds were formed,
affording six-membered pallada- and platinacycles.
These complexes, particularly the Pd ones, shall be
Palladacycles have been thoroughly investigated as
precatalysts in C–C bond formation reactions; one of
the most popular cross-couplings is the Heck procedure.
A wide variety of substrates has been used to design cat-
alyst precursors endowed with good activity in cross-
coupling reactions. As phosphapalladacycles [14] and
phosphine-free N-heterocyclic carbenes are air- and
moisture- sensitive they have to be handled under an in-
ert atmosphere. Recently, carbothioamide-derived palla-
dacycles were successfully used as precatalysts in Heck
and Suzuki–Miyaura reactions [15]. Gladysz and cowor-
ker [16] introduced very active catalytic systems based
on fluorous Schiff-bases palladacycle complexes as
source of palladium nanoparticles having TON values
exceeding one million. A new generation of air-stable
and highly active Pd complexes for C–C and C–N cou-
pling with aryl chlorides was introduced by Indolese and
coworkers [17]. Other remarkable results were reported
by Najera and coworkers [18] with oxime-derived palla-
R
R
N
R
N
N
H
N(CH3)2
N
2
reflux
R
AcO
toluene
N
H
N
H
Pd
N
Pd(OAc)2
CH3CN
N
HL3: R = H
HL4: R = Me
N
N
CH3
CH3
Scheme 11.
Scheme 8.
R
R
N
R
N
Cl
2
N
N(CH3)3
I
H
N
Li2PdCl4
EtOH
Pd
N
N
reflux
R
N
N
N
CH3CN
N
CH3
CH3
CH3
CH3
HL5: R = Me
HL6: R = H
10
Scheme 9.
Scheme 12.

G. Cravotto et al. / Journal of Organometallic Chemistry 690 (2005) 2017–2026
2021
R2
N
Pt(DMSO)2Cl2
EtOH
12: R1, R2 = H
13: R1 = H; R2 = Me
14: R1, R2 = Me
N
Pt
R2
Cl
N
R1
DMSO
R2
R2
N
N
Li2PdCl4
EtOH
N
N
Pd
R2
R2
15:
R
1 = H, R2 = Me
N
N
R1
Cl
R1
2
R2
N
Pd(OAc)2
CH2Cl2
16: R1= Me, R2 = H
N
Pd
Aco
R2
N
2
R1
Scheme 13.
N
N
O
O
I
Pd
O
O
X
2
+
X=OAC, Cl
Scheme 14.
dacycles that are extremely active in Sonogashira and
Glaser-type reactions. Other very active catalytic com-
plexes were used in the Heck–Mizoroki reaction [19].
Starting with the well-defined and air-stable com-
plexes 2 and 4, we tested their performance as (pre)cat-
alysts for the Heck cross-coupling reaction using
iodobenzene and tert-butyl acrylate as the alkene
(Scheme 14). In order to optimize reaction conditions,
several combinations were tried of the two precatalysts,
metal loadings, ligands, bases and solvents.
The use of THF or dioxane resulted in poor yields,
that were improved when more polar solvents were em-
ployed, such as N-methylpyrrolidone (NMP) or DMF.
Reaction conditions were subsequently optimized work-
ing in DMF at different temperatures (70, 90, 110 ꢁC
and at reflux). K3PO4, Na2CO3, NBu3, NEt3 were tried
as bases. Even PPh3 and PCy3 were tested as additive li-
gands; some trials were carried out in the absence of any
ligand.
The best results were obtained with in situ formed 1:1
4-Cy3P complex; the amount of this catalyst, initially
tried at 5% molar, was subsequently lowered down to
0.1% without affecting the yield. In order to evaluate
the stability of the catalytic system, after the reaction
of iodobenzene and tert-butyl-acrylate was completed
we made further additions of the reagents and verified
the efficiency of the catalyst after each one. Four addi-
tions of PhI and acrylate were consecutively operated
at the end of the catalytic cycle, and the uniformity of
yields demonstrated the stability and persistent activity
of 2 and 4. For latter catalyst entries 13, 15, 17 and 19
in Table 1 report the yields found at the end of the last
catalytic cycle. In preliminary work aimed to improve
the values of TON and TOF, we found in some in-
stances TON values close to 1,000,000. These experi-
ments will be repeated and further optimized in the
next future. In the reactions studied so far, preformed
complex 6 showed the same catalytic activity as its
precursors.
Data in Table 1 show that the use of organic bases
generally leads to higher yields for the coupling reaction.
The difference in yields for a simple change of base is
more marked for K3PO4/Na2CO3. 2 and 4, used to gen-
erate in situ other complexes by interaction with either
Ph3P or Cy3P, proved catalytically active in the synthesis
of (E)-tert-butyl cinnamate, albeit to different degree.
1.2. Structure of C22H22N4O2Pd (5)
A view of compound 5 is shown in Fig. 1. Selected
interatomic distances and angles are reported in Table
2. The coordination of the bidentate pyridinyl–indolyl

2022
G. Cravotto et al. / Journal of Organometallic Chemistry 690 (2005) 2017–2026
Table 1
Entry
Catalyst
Base
Ligand
Solvent
T (ꢁC)
t (h)
Yield (%)
1
4
4
4
4
4
4
4
4
4
4
4
2
2
2
2
4
4
4
4
–
–
DMF
DMF
DMF
THF
110
110
110
Reflux
Reflux
Reflux
110
110
110
110
r.t.
8
14
11
12
8
6
16
9
2
NEt3
–
–
3
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PCy3
PCy3
PPh3
PPh3
PCy3
PCy3
4
NEt3
NEt3
NEt3
NEt3
Na2CO3
K3PO4
NBu3
NEt3
NEt3
NEt3
NEt3
NEt3
NEt3
NEt3
NEt3
NEt3
31
47
82
98
22
14
88
2
5
Dioxane
NMP
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
6
5
7
2.5
7
8
9
8
10
11
12
13
14
15
16
17
18
19
5
12
10
7
70
90
46
98
31
97
54
98
25
98
70
90
14
6
70
90
12
6
70
90
10
5
Reaction conditions: catalyst 5 · 10ꢀ4 mmol, ligand 10ꢀ3 mmol, PhI 0.5 mmol, tert-butylacrylate 0.6 mmol, base 1.0 mmol in 3 ml of DMF.
ligand to the palladium atom occurs through the indole
N(1) and the pyridine N(2) atoms, and gives rise to a
pentatomic metallacycle. The square planar palladium
atom completes its coordination sphere with an acetate
anion, trans to the indole nitrogen, and with a 4-dimethyl-
aminopyridine molecule, trans to the pyridinic nitrogen.
The two Pd–N interactions are almost identical and
comparable with the average Pt–N interaction in com-
plex 8 (vide infra). The indole ligand lies essentially in
the coordination plane, whereas the acetate and 4-
dimethylaminopyridine ligands are almost perpendicu-
lar to it, as can be appreciated by the torsion angle
N(1)–Pd–N(3)–C(18) of 98.0ꢁ and from the N(1)–Pd–
O(1)–C(21) angle that is 92.4ꢁ. Such orientations are im-
posed by the need of minimising intramolecular contacts
of these two ligands with the pyridinyl–indolyl ligand.
Table 2
˚
Selected interatomic distances (A) and angles (ꢁ) for compound 5
Pd–N(1)
Pd–N(2)
2.012(3)
2.021(3)
2.021(3)
2.035(2)
1.293(5)
1.219(5)
1.371(4)
1.382(4)
1.341(5)
1.358(4)
1.345(4)
1.346(4)
1.341(4)
1.447(5)
1.460(5)
1.430(5)
1.403(5)
1.374(5)
1.444(5)
1.367(5)
1.412(5)
1.402(5)
1.357(5)
1.509(5)
Pd–N(3)
Pd–O(1)
O(1)–C(21)
O(2)–C(21)
N(1)–C(1)
N(1)–C(8)
N(2)–C(13)
N(2)–C(9)
N(3)–C(18)
N(3)–C(14)
N(4)–C(16)
N(4)–C(19)
N(4)–C(20)
C(1)–C(6)
C(6)–C(7)
C(7)–C(8)
C(8)–C(9)
C(14)–C(15)
C(15)–C(16)
C(16)–C(17)
C(17)–C(18)
C(21)–C(22)
C10
C7
C8
C5
C11
C12
C6
C9
C4
C3
C13
C1
N1
N2
C2
Pd
C14
O1
N3
C15
C16
C21
N(1)–Pd–N(2)
N(1)–Pd–N(3)
N(2)–Pd–N(3)
N(1)–Pd–O(1)
N(2)–Pd–O(1)
N(3)–Pd–O(1)
C(16)–N(4)–C(19)
C(16)–N(4)–C(20)
C(19)–N(4)–C(20)
81.14(12)
95.67(12)
176.54(12)
174.80(11)
93.66(12)
89.52(12)
122.5(3)
C18
C17
C19
O2
C22
N4
C20
121.4(3)
116.0(3)
Fig. 1. ORTEP view of compound 5. Thermal ellipsoids at 50%
probability.

G. Cravotto et al. / Journal of Organometallic Chemistry 690 (2005) 2017–2026
2023
Table 3
Selected interatomic distances (A) and angles (ꢁ) for compound 8
˚
C7
C10
C11
C12
C5
Pt–N(1)
Pt–N(2)
2.008(8)
2.043(8)
C6
C9
C8
Pt–S
Pt–Cl
2.234(3)
2.300(3)
1.478(7)
C4
C3
S–O
S–C(1S)
S–C(2S)
C13
1.776(10)
1.778(10)
1.359(12)
1.415(11)
1.350(12)
1.341(11)
1.451(13)
1.411(14)
1.405(13)
1.384(13)
1.394(13)
1.377(13)
1.374(14)
1.381(14)
N1
C1
N2
C2
N(1)–C(8)
N(1)–C(1)
N(2)–C(9)
N(2)–C(13)
C(8)–C(9)
C(1)–C(6)
C(6)–C(7)
C(7)–C(8)
C(9)–C(10)
C(10)–C(11)
C(11)–C(12)
C(12)–C(13)
Pt
S
O
Cl
C2s
C1s
Fig. 2. ORTEP view of compound 8. Thermal ellipsoids at 50%
probability.
N(1)–Pt–N(2)
N(1)–Pt–S
N(1)–Pt–Cl
N(2)–Pt–S
N(2)–Pt–Cl
S–Pt–Cl
80.1(3)
174.7(2)
95.0(2)
99.2(2)
The aminic nitrogen atom N(4) displays a planar trigo-
nal rather than a tetrahedral geometry, as predicted by
the VSEPR theory, because the lone pair is not exclu-
sively localised on the nitrogen atom but delocalised
throughout the aromatic p system. As a consequence
175.1(2)
85.72(10)
˚
the N(4)–C(16) bond length of 1.341(4) A is shorter than
the expected value for a C(sp2)–N(sp3) interaction (1.395
1.4. Structure of C14H16ClN3OPtS (12)
˚
A). The whole aromatic system is also affected by the
conjugation, with two distances, C(14)–C(15) and
C(17)–C(18), significantly shorter.
The compound crystallizes with two independent
molecules in the asymmetric unit.
Selected interatomic distances and angles are re-
ported in Table 4. A perspective view of one of the
two molecules is displayed in Fig. 3. Both molecules
contain a square planar platinum atom coordinated by
the indole ligand through one of the two atoms of the
pyrazole moiety [N(11) or N(12)] and a carbon atom
of the indole moiety [C(81) or C(82)]. A chloride anion,
trans to the carbon atom C(81) [or C(82)], and a DMSO
molecule, trans to N(11) [or N(12)], complete the coordi-
nation sphere. The six-membered metallacycle resulting
from coordination of the pirazolylindolato ligand dis-
plays a boat-type conformation. The orientation of the
DMSO molecule is determined by the presence of an
intramolecular hydrogen bond between the DMSO oxy-
gen and the indole nitrogen (Fig. 3) [ N(91)ꢁ ꢁ ꢁO(1)
1.3. Structure of C15H15ClN2OPtS (8)
A view of compound 8 is shown in Fig. 2. Selected
interatomic distances and angles are reported in Table
3. The coordination of the bidentate pyridinyl–indolyl li-
gand to the platinum atom occurs in the same way as for
the previous palladium complex. The square planar
coordination of the metal is completed by a dim-
ethylsulphoxyde (DMSO) molecule and a chloride ion,
trans to the N(1) and N(2) atoms, respectively. Maxi-
mum deviation from the average coordination plane is
˚
observed for atom N(1) 0.165(8) A; the torsion angle
N(1)–C(8)–C(9)–N(2) is 6.3ꢁ.
˚
The molecular structure of 8 can be compared
with that of r-{Pt[1H-indole-1-methyl-2-(20pyridinil-
C3,N1)]-(DMSO)Cl} [10], where the indolic moiety is
metallated through the C(8) atom. The Pt–N(2) distance
is statistically identical (within 3 times its e.s.d.) to that
found in compound r-{Pt[1H-indole-1-methyl-2-
(20pyridinil-C3,N1)]-(DMSO)Cl} and very close to the
Pt–N(1) distance. The Pt–Cl interaction is here shorter
due to different trans effect. Slightly different Pt–S
distances are observed in the two compounds, probably
owing to packing effects. All the rings of the pyridinyl–
indolyl ligand are planar within the experimental error.
2.840(7) A, N(91)–H(91)ꢁ ꢁ ꢁO(1) 121.7(4)ꢁ for the
˚
first molecule; N(92)ꢁ ꢁ ꢁO(2) 2.820(7) A, N(92)–H(92)
ꢁ ꢁ ꢁO(2) 122.6(3)ꢁ for the second molecule]. The confor-
mational and geometric parameters of both molecules
are very similar. The possibility of having missed a sym-
metry relation between the two can be ruled out by
inspection of the packing. If we consider the Ptꢁ ꢁ ꢁPt con-
tacts between adjacent molecules we realise that one of
the two molecules displays only one Ptꢁ ꢁ ꢁPt contact of
˚
5.366(1) A with related symmetry (2 ꢀ x, 1 ꢀ y, ꢀz)
whereas the other molecule displays two Ptꢁ ꢁ ꢁPt
˚
contacts of 4.891(1) and 4.953(1) A with related

2024
G. Cravotto et al. / Journal of Organometallic Chemistry 690 (2005) 2017–2026
Table 4
˚
Selected interatomic distances (A) and angles (ꢁ) for compound 12
C131
Pt(1)–C(81)
Pt(1)–N(11)
Pt(1)–S(1)
1.987(6)
2.050(5)
2.205(1)
2.397(2)
1.986(5)
2.055(4)
2.206(1)
2.397(2)
1.347(8)
1.353(6)
1.344(7)
1.349(6)
1.349(7)
1.466(7)
1.337(7)
1.460(7)
1.354(7)
1.387(7)
1.381(7)
1.385(6)
1.373(9)
1.384(9)
1.362(9)
1.397(10)
1.496(8)
1.494(7)
1.381(7)
1.427(7)
1.392(7)
1.434(7)
1.418(7)
1.413(7)
C141
C151
C121
C111
C41
Pt(1)–Cl(1)
N51
Pt(2)–C(82)
Pt(2)–N(12)
Pt(2)–S(2)
C61
C71
C101
N91
C31
Pt(2)–Cl(2)
N(11)–C(21)
N(11)–N(51)
N(12)–C(22)
N(12)–N(52)
N(51)–C(41)
N(51)–C(61)
N(52)–C(42)
N(52)–C(62)
N(91)–C(101)
N(91)–C(81)
N(92)–C(102)
N(92)–C(82)
C(21)–C(31)
C(22)–C(32)
C(31)–C(41)
C(32)–C(42)
C(61)–C(71)
C(62)–C(72)
C(71)–C(81)
C(71)–C(111)
C(72)–C(82)
C(72)–C(112)
C(101)–C(111)
C(102)–C(112)
C81
S1
C21
N11
Pt1
O1
C161
Cl1
C171
Fig. 3. ORTEP view of one of the two independent molecules of
compound 12. Thermal ellipsoids at 50% probability.
2.1. Compound 2
1
Brown-orange solid: m.p. 263 ꢁC (dec.) ; H NMR
(CDCl3, ppm): 6.46 (s, 2H), 8.10–6.70 (m, 16 H); 13C
NMR (CDCl3, ppm): 101.87, 113.51, 118.32, 119.15,
121.10, 122.24, 128.81, 132.41, 136.56, 145.02, 145.41,
152.51, 156.52. Elemental analysis (%): Calc.: C 46.60,
H 2.71, N 8.36. Found: C 46.91, H 3.02, N 8.17; IR:
C(81)–Pt(1)–N(11)
C(81)–Pt(1)–S(1)
N(11)–Pt(1)–S(1)
C(81)–Pt(1)–Cl(1)
N(11)–Pt(1)–Cl(1)
S(1)–Pt(1)–Cl(1)
C(82)–Pt(2)–N(12)
C(82)–Pt(2)–S(2)
N(12)–Pt(2)–S(2)
C(82)–Pt(2)–Cl(2)
N(12)–Pt(2)–Cl(2)
S(2)–Pt(2)–Cl(2)
86.2(2)
94.8(2)
176.7(1)
173.0(2)
88.5(1)
90.71(6)
85.8(2)
94.7(2)
177.4(1)
173.2(2)
89.0(1)
90.68(5)
307, 294 cmꢀ1
.
2.2. Compound 3
1
Brown-orange solid: m.p. 270 ꢁC (dec.); H NMR
(CDCl3, ppm): 6.45 (s, 2H), 8.15–6.85 (m, 16 H); 13C
NMR (CDCl3, ppm): 101.85, 112.93, 118.23, 119.53,
121.02, 123.10, 128.51, 134.53, 136.82, 144.81, 145.23,
152.21, 156.13. Elemental analysis (%): Calc.: C 41.14,
H 2.39, N 7.38. Found: C 41.05, H 2.41, N 7.65.
symmetries (2 ꢀ x, ꢀy, ꢀ1 ꢀ z) and (1 ꢀ x, ꢀy, ꢀ1 ꢀ z),
respectively.
2.3. Compound 4
Brown-orange solid: m.p. 255 ꢁC (dec.); IR: 1572,
1
1412 cmꢀ1, H NMR (CDCl3, ppm): 2.35 (s, 6H), 6.41
2. Experimental
(s, 2H); 8.20–6.75 (m, 16 H); 13C NMR (CDCl3, ppm):
24.16, 101.37, 113.37, 118.10, 119.03, 121.25, 122.11,
128.65, 129.76, 136.76, 144.92, 145.22, 152.41, 156.43,
185.13. Elemental analysis (%): Calc.: C 50.23, H 3.37,
N 7.81. Found: C 50.15, H 3.31, N 7.67.
Elemental analyses were carried out on a Perkin–El-
mer 2400 (series II) elemental analyzer. The IR spectra
in the 4000–200 cmꢀ1 region were performed on KBr
pellets on a Perkin–Elmer 283 spectrophotometer. The
1H, 13C and 31P NMR spectra were obtained for solu-
tion in CDCl3 or DMSO-d6 and were recorded on a
Bruker Avance 400 spectrometer. Electron-impact mass
spectra (EI-MS) were obtained on a VG 7070(EQ)
instrument.
2.4. Compound 5
1H NMR (CDCl3, ppm): 2.03 (s, 3H), 3.12 (s, 6H),
5.73 (d, 1H), 6.58 (d, 2H), 6.72 (t, 1H), 6.97 (s, 1H),

G. Cravotto et al. / Journal of Organometallic Chemistry 690 (2005) 2017–2026
2025
7.01 (t, 1H), 7.01 (t, 1H), 7.52 (d, 1H), 7.66 (d, 1H), 7.70
(t, 1H), 8.03 (d, 1H), 8.53 (d, 2H).
2H), 7.35 (dd, 1H), 7.43 (d, 1H), 7.69 (d, 1H), 8.42 (d,
1H), 9.89 (s, 1H); 13C NMR (CDCl3, ppm): 46.91,
49.52, 105.31, 106.64, 111.37, 115.65, 119.32, 120.33,
122.91, 126.62, 132.71, 136.93, 143.77.
2.5. Compound 6
1H NMR (CDCl3, ppm): 1.94 (s, 3H), 6.04 (d, 1H),
6.61 (t, 1H), 6.98 (t, 1H), 7.08 (s, 1H), 7.13 (t, 1H),
7.39 (d, 1H), 7.41–7.67 (m, 15H), 7.77 (t, 1H), 7.82 (d,
1H), 8.15 (d, 1H); 31P NMR (CDCl3, ppm): 30.30 (s).
2.12. Compound 13
1
Brown solid: m.p. 159 ꢁC (dec.); H NMR (CDCl3,
ppm): 2.41 (s, 3H), 2.60 (s 3H), 3.56 (s, 6H), 5.28 (s,
2H), 5.96 (s, 1H), 6.90 (t, 1H), 7.05 (t, 1H), 7.34 (d,
1H), 7.41 (d, 1H), 9.39 (s, 1H). 13C NMR (DMSO,
ppm): 12.22, 15.83, 41.31, 45.74, 107.79, 108.02,
115.50, 116.13, 118.92, 119.22, 127.04, 128.33, 137.48,
142.35, 151.19.
2.6. Compound 7
1H NMR (CDCl3, ppm): 1.97 (s, 3H), 2.46 (s, 3H),
3.45 (s, 6H), 5.40 (t, 1H), 6.32 (d, 1H), 6.96 (s, 1H),
7.05 (t, 1H), 7.11 (s, 2H), 7.41 (t, 1H), 7.53 (d, 1H),
7.66 (t, 1H), 7.74 (d, 1H), 8.08 (d, 1H).
2.13. Compound 14
2.7. Compound 8
Pale yellow solid: m.p. 125 ꢁC (dec.); 1H NMR
(CDCl3, ppm): 3.91 (s, 3H), 7.26 (s, 1H), 7.02 (m, 2H),
7.37 (d, 1H), 5.19 (d, 1H), 5.51 (d, 1H), 5.86 (s, 1H),
2.36 (s, 3H), 2.50 (s, 3H), 3.50 (t, 3H), 3.68 (t, 3H);
13C NMR (CDCl3, ppm): 12.23, 15.35, 35.71, 45.53,
46.18, 47.25, 107.23, 107.92, 109.79, 115.28, 119.02,
119.36, 127.09, 135.54, 138.78, 141.02, 151.34.
Orange solid: m.p. 147–148 ꢁC; IR: 1122, 328 cmꢀ1
;
1H NMR (CDCl3, ppm): 3.61 (s, 6H, JH–Pt = 25Hz),
6.95 (s, 1H); 7.00–8.70 (m, 7H), 9.49 (d, 1H, J = 5.8
Hz; JH–Pt = 43 Hz); 13C NMR (CDCl3, ppm): 44.6
(JPt–CH –S = 44 Hz), 104.17, 116.41, 119.00, 118.85,
120.51, 121.20, 129.51, 130.02, 138.61, 146.32, 147.91,
3
0
148.21 (JPt–C6 = 40 Hz), 158.13. Elemental analysis
2.14. Compound 15
(%): Calc.: C 35.90, H 3.01, N 5.58. Found: C 35.83,
H 3.15, N 5.71.
Orange solid: m.p. 270 ꢁC (dec.). Elemental analysis
(%): Calc.: C 45.92, H 3.85, N 11.48. Found: C 45.79,
H 3.90, N 11.08.
2.8. Compound 9
Orange solid: m.p. 193–195 ꢁC; IR: 1575, 1417 cmꢀ1
;
2.15. Compound 16
1H NMR (CDCl3, ppm): 2.33 (s, 6H), 3.62 (s, 6H); 7.85–
6.65 (m, 16 H); 13C NMR (CDCl3, ppm): 24.21, 32.11,
110.23, 120.13, 125.01, 125.63, 127.31, 139.02, 138.04,
141.46, 142.00, 150.93, 153.97, 155.23; Elemental analy-
sis (%): Calc.: C 51.56, H 3.79, N 7.52. Found: C 51.45,
H 3.57, N 7.59.
1H NMR (CDCl3, ppm): 1.27 (s, 6H), 3.15 (s, 6H),
4.43 (d, 2H), 6.08 (d, 2H), 6.28 (d, 2H), 6.55 (s, 2H),
7.07 (t, 2H), 7.14 (d, 2H), 7.23 (t, 2H), 7.80 (s, 2H),
7.82 (s, 2H); 13C NMR (CDCl3, ppm): 30.12, 32.15,
36.32, 76.29, 107.85, 110.82, 120.44, 124.61, 129.67,
132.82, 139.25, 140.74, 142.78, 143.51, 197.63.
2.9. Compound 10
Brown-orange solid: m.p. 205–207 ꢁC; IR: 277, 254
cmꢀ1. Elemental analysis (%): Calc.: C 48.16, H 3.18,
N 8.02. Found: C 47.79, H 3.33, N 7.91%.
3. X-ray structure determination
Numbers given in the X-Ray structures are only for
crystallographic purpose and are not relevant to the
nomenclature of heterocyclic compounds and metal-het-
erocyclic complexes.
Crystal data for C22H22N4O2Pd (5), f.w. 480.84,
monoclinic, space group P21/n, (no. 14), a =
2.10. Compound 11
1H NMR (CDCl3, ppm): 1.22 (t, 3H, J = 6.8 Hz),
3.65 (s, 3H), 4.22 (q, 2H, J = 6.8 Hz), 7.11–7.34 (m,
4H,), 7.38 (d, 1H), 7.83 (d, 1H), 8.28 (d, 1H) 8.77 (d,
1H). MS (EI) (70 eV) m/z: 280, 235, 207.
˚
A,
14.8019(11),
b = 8.4800(6),
c = 16.4163(12)
3
˚
b = 96.75(1)ꢁ, U = 2046.3(3) A , Z = 4, dcalc = 1.561
Mg mꢀ3, l = 0.932 mmꢀ1, F(0 0 0) 976, R = 0.035,
wR2 = 0.072 on 2587 reflections with I > 2r(I). 15,861
Intensity data (3914 unique) were measured at room
temperature on a Bruker Smart CCD diffractometer
2.11. Compound 12
1
Brown solid: m.p. 174 ꢁC (dec.); H NMR (CDCl3,
ppm): 3.67 (t, 6H), 5.52 (s, 2H), 6.44 (t, 1H), 7.05 (m,

2026
G. Cravotto et al. / Journal of Organometallic Chemistry 690 (2005) 2017–2026
with graphite monochromatized Mo Ka radiation
(k = 0.71073 A). An empirical absorption correction
References
˚
[1] J.P. Kleiman, M. Dubeck, J. Am. Chem. Soc. 65 (1963) 1544, for
exhaustive reviews see also:;
(
SADABS) [20] was applied to the data.
Crystal data for C15H15ClN2OPtS (8), f.w. 501.89,
(a) M.I. Bruce, Angew. Chem. Int. Ed. 16 (1977) 75;
(b) A.D. Ryabov, Synthesis (1985) 933;
monoclinic, space group P21/n, (no. 14), a = 5.884(3),
˚
b = 14.855(5), c = 17.616(6) A, b = 97.59(4)ꢁ, U =
(c) V.V. Dunina, O.A. Zalevskaja, V.M. Potapov, Russ. Chem.
Rev. 57 (1988) 250;
1526(1) A , Z = 4, dcalc = 2.184 Mg mꢀ3, l = 9.500
3
˚
mmꢀ1, F(0 0 0) 952, R = 0.034, wR2 = 0.074 on 1644
reflections with I > 2r(I). 2985 intensity data (2659
unique) were measured at room temperature on a
Enraf-Nonius CAD-4 diffractometer with graphite
(d) A.D. Ryabov, R. Van Eldik, G. Le Borgne, M. Pfeffer,
Organometallics 12 (1993) 138.
[2] (a) M. Albrecht, G. Van Koten, Angew. Chem. Int. Ed. 40 (2001)
3750;
(b) J.M. Pollino, M. Weck, Synthesis (2002) 1277.
[3] (a) J. Vicente, I. Saura-Llames, P.G. Jones, Dalton Trans. (1993)
3619;
˚
monochromatized Mo Ka radiation (k = 0.71073 A).
Data were corrected for absorption using the psi-scan
procedure [21].
Crystal data for C14H16ClN3OPtS (12), f.w. 504.90,
(b) G. Zhao, Q.G. Wang, T.C.W. Mak, Dalton Trans. (1998) 1241.
´ ´
[4] R. Ares, M. Lopez-Torres, A. Fernandez, S. Castro-Juiz, Poly-
hedron 21 (2002) 2309.
[5] F. Basuli, P. Chattopadhyay, C. Sinha, Polyhedron 15 (1996)
2439.
ꢀ
triclinic, space group P1, (no. 2), a = 9.8294(7),
˚
b = 10.6651(8), c = 15.3319(12) A, a = 83.96(1)ꢁ,
3
˚
[6] S. Tollari, S. Cenini, C. Tunice, G. Palmisano, Inorg. Chim. Acta
272 (1998) 18.
b = 82.17(1)ꢁ, c = 79.88(1)ꢁ, U = 1562.1(2) A , Z = 4,
dcalc = 2.147 Mg mꢀ3, l = 9.288 mmꢀ1, F(0 0 0) 960,
R = 0.024, wR2 = 0.066 on 5082 reflections with
I > 2r(I). 14,168 Intensity data (5972 unique) were mea-
sured at room temperature on a Bruker Smart CCD dif-
fractometer with graphite monochromatized Mo Ka
[7] S. Tollari, G. Palmisano, F. Demartin, M. Grassi, S. Magnaghi,
S. Cenini, J. Organomet. Chem. 488 (1995) 79.
[8] S. Tollari, F. Demartin, S. Cenini, G. Palmisano, P. Raimondi, J.
Organomet. Chem. 527 (1997) 93.
[9] R. Annunziata, S. Cenini, F. Demartin, G. Palmisano, S. Tollari,
J. Organomet. Chem. 496 (1995) C1.
˚
radiation (k = 0.71073 A). An empirical absorption cor-
[10] S. Tollari, S. Cenini, A. Penoni, G. Granata, G. Palmisano, F.
Demartin, J. Organomet. Chem. 608 (2000) 34.
[11] C. Crotti, S. Cenini, B. Rindone, S. Tollari, F. Demartin, J.
Chem. Soc., Chem. Commun. (1986) 784.
rection (SADABS) [20] was applied to the data. All struc-
tures were solved by Patterson and Fourier methods and
refined on F2 using SHELX-97 [22]. Non-hydrogen atoms
were refined with anisotropic thermal parameters.
Hydrogen atoms were experimentally observed and al-
lowed to ride on the pertinent atoms.
[12] (a) R.P. Thummel, W. Hegde, J. Org. Chem. 54 (1989) 1720;
(b) F. Wu, J. Hardesty, R.P. Thummel, J. Org. Chem. 63 (1998)
4055;
(c) F. Wu, C.M. Chamchoumis, R.P. Thummel, Inorg. Chem. 39
(2000) 584.
[13] (a) G.K. Anderson, R.J. Cross, Chem. Soc. Rev. 9 (1980) 185;
(b) J. Vicente, M.C. Lagunas, E. Bleuel, M.C. Ramirez de
Arellano, J. Organomet. Chem. 648 (2002) 62.
[14] J.M. Brunel, M.-H. Hirlemann, A. Heumann, G. Buono, Chem.
Commun. (2000) 1869.
4. Supplementary material
Full crystallographic data for compounds 5, 8 and 12
have been deposited with the Cambridge Crystallo-
graphic Data Centre, CCDC 101098, 253707 and
253708. Copy may be obtained free of charge from the
Director CCDC, 12 Union Road, Cambridge CB2
1EZ, UK (fax: +44 1223 336 033; e-mail:
deposit@ccdc.cam.ac.uk).
[15] Z. Xiong, N. Wang, M. Dai, A. Li, J. Chen, Z. Yang, Org. Lett. 6
(2004) 3337.
[16] C. Rocaboy, J.A. Gladysz, Org. Lett. 4 (2002) 1993.
[17] A. Schnyder, A.F. Indolese, M. Studer, H.-U. Blaser, Angew.
Chem. Int. Ed. 41 (2002) 3668.
[18] D.A. Alonso, C. Najera, M.C. Pacheco, Adv. Synth. Catal. 345
(2003) 1146.
[19] (a) C.-A. Lin, F.-T. Luo, Tetrahedron Lett. 44 (2003) 7565;
(b) C.-T. Chen, Y.-S. Chan, Y.-R. Tzeng, M.-T. Chen, Dalton
Trans. (2004) 2691.
Acknowledgements
[20] SADABS Area-Detector Absorption Correction Program, Bruker
AXS, Inc. Madison, WI, USA, 2000.
We thank Professor Cenini for helpful discussion.
The present work was supported (PRIN 2003) by the
[21] A.C.T. North, D.C. Phillips, F.S. Mathews, Acta Crystallogr. A
24 (1968) 351.
`
Italian Ministero dellÕIstruzione Universita e Ricerca
(MIUR).
[22] G.M. Sheldrick, SHELXL-93-97, Universita¨t Go¨ttingen, Germany,
1997.