Synthesis and structural characterization of 10 Group metal complexes with anionic tridentate S,N,N donor Schiff bases derived from pyridylbenzothiazolines

Article abstract of DOI:10.1016/j.poly.2017.07.004

The ring opening transformation of three substituted 2-(2-pyridyl)benzothiazolines of general formula [(C₆H₄NCS)(C₅H₄?N)R] (R?=?C₅H₄N, 1; R?=?C₆H₅, 2; R?=?H, 3) was studied by their reaction with metal chlorides of Ni(II), Pd(II), and Pt(II). In these reactions, the anionic tridentate Schiff bases {Lⁿ}^? coordinated to metal ions were identified. Seven metallic complexes of type [M(Lⁿ)Cl] [M?=?Pd, n?=?1, R?=?C₅H₄N, (1a); n?=?2, R?=?C₆H₅, (2a); n?=?3, R?=?H, (3a). M?=?Pt, n?=?1, R?=?C₅H₄N, (1b); n?=?2, R?=?C₆H₅, (2b); n?=?3, R?=?H, (3b), and M?=?Ni, R?=?C₆H₅, (2c)] were characterized in solution by NMR and vibrational spectroscopy in solid state. Crystal structures of benzothiazolines 1 and 2 and complexes 1a–3a, 1b·DMSO, and 2c were analyzed by X-ray diffraction studies. In all cases, mononuclear complexes with a distorted square planar geometry were obtained. For compounds 1–3, the predominance of the benzothiazoline (ring form) over the Schiff base (open form) as well as the formation of the [Pd(Lⁿ)Cl] (n?=?1–3) complexes were studied by DFT calculations at the PBEPBE/(Def2-TZVP,SDD) level in gas phase.

Full text of DOI:10.1016/j.poly.2017.07.004

Accepted Manuscript
Synthesis and structural characterization of 10 Group Metal complexes with
anionic tridentate S,N,N donor Schiff bases derived from pyridylbenzothiazo-
lines.
Jesús-Alberto Alvarez-Hernández, Noemí Andrade-López, José G. Alvarado-
Rodríguez, José M. Vásquez-Pérez, Julián Cruz-Borbolla, Vojtech Jancik
PII:
S0277-5387(17)30486-2
DOI:
http://dx.doi.org/10.1016/j.poly.2017.07.004
POLY 12739
Reference:
To appear in:
Polyhedron
Received Date:
Revised Date:
Accepted Date:
7 June 2017
6 July 2017
6 July 2017
Please cite this article as: J-A. Alvarez-Hernández, N. Andrade-López, J.G. Alvarado-Rodríguez, J.M. Vásquez-
Pérez, J. Cruz-Borbolla, V. Jancik, Synthesis and structural characterization of 10 Group Metal complexes with
anionic tridentate S,N,N donor Schiff bases derived from pyridylbenzothiazolines., Polyhedron (2017), doi: http://
dx.doi.org/10.1016/j.poly.2017.07.004
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Synthesis and structural characterization of 10 Group Metal
complexes with anionic tridentate S,N,N donor Schiff bases
derived from pyridylbenzothiazolines.
a
a
Jesús-Alberto Alvarez-Hernández , Noemí Andrade-López *, José G. Alvarado-
a
b
a
c
Rodríguez , José M. Vásquez-Pérez , Julián Cruz-Borbolla , Vojtech Jancik .
a
Centro de Investigaciones Químicas, Universidad Autónoma del Estado de
Hidalgo. Ciudad Universitaria, Carretera Pachuca-Tulancingo km 4.5. Colonia
Carboneras, Mineral de la Reforma, Hgo. C.P. 42184, México.
b
CONACYT Research Fellow, Universidad Autónoma del Estado de Hidalgo,
Ciudad Universitaria, Carretera Pachuca-Tulancingo km 4.5. Colonia Carboneras,
Mineral de la Reforma, Hgo. C.P. 42184, México.
c
Centro Conjunto de Investigación en Química Sustentable UAEM-UNAM, km
1
4.5 Carr. Toluca-Atlacomulco, Unidad San Cayetano, C.P. 50200 Toluca, Edo. de
México, México.

Abstract
The ring opening transformation of three substituted 2-(2-pyridyl)benzothiazolines
6 4
of general formula (C H NCS)(C
5 4
H N)R] (R = C
5 4
H N, 1; R = C
6
H , 2; R = H, 3)
5
was studied by their reaction with metal chlorides of Ni(II), Pd(II), and Pt(II). In
n −
these reactions, the anionic tridentate Schiff bases {L } coordinated to metal ions
n
were identified. Seven metallic complexes of type M(L )Cl] [M = Pd, n = 1, R=
5 4
C H N, (1a); n = 2, R = C
6
H
5
, (2a); n = 3, R = H, (3a). M = Pt, n = 1, R = C
5 4
H N,
(
1b); n = 2, R = C , (2b); n = 3, R = H, (3b), and M = Ni, R = C
6
H
5
6 5
H , (2c)] were
characterized in solution by NMR and vibrational spectroscopy in solid state.
Crystal structures of benzothiazolines 1 and 2 and complexes 1a–3a, 1b·DMSO,
and 2c were analyzed by X-ray diffraction studies. In all cases, mononuclear
complexes with a distorted square planar geometry were obtained. For compounds
1
–3, the predominance of the benzothiazoline (ring form) over the Schiff base
n
(
open form) as well as the formation of the Pd(L )Cl] (n = 1–3) complexes were
studied by DFT calculations at the PBEPBE/(Def2-TZVP,SDD) level in gas phase.
Keywords: Ni(II), Pd(II), Pt(II) complexes; Benzothiazolines; NMR spectroscopy; X-
ray diffraction; DFT calculations.

1. Introduction
Benzothiazolines are heterocyclic compounds containing sulfur and nitrogen atoms
in their structure (Figure 1, left), and have been utilized for the transference of
hydrogen for the reduction of imines [[1], [2]], as well as for the synthesis of
benzothiazoles and benzothiazines used as ligands in Coordination Chemistry [[3],
[
4]]. Interestingly, the benzothiazolines can be transformed into their open form
Figure 1) by means of a tautomerization as has been observed by NMR studies in
(
solution; this open form is enhanced by the formation of intramolecular hydrogen
bonding, while the lacking of such interactions has an opposite effect [[5], [6], [7]].
Additionally, the metallic complexation of benzothiazoline compounds has been
employed to evaluate this opening along with the coordination of their
corresponding Schiff bases (Figure 1 right), which are not possible to synthesize by
condensation reactions of aldehydes or ketones with o-aminothiophenol [[8], [9]]. In

these studies, the metallic ion has been used as a template reagent, and  NS-,



N- and N S-tridentate coordination modes of the Schiff bases to the central
atom have been observed [[10], [11], [12]]. It is noteworthy that the nature of the
substituents joined to the carbon flanked by the sulfur and nitrogen atoms has a
relevant influence onto the observed isomer (ring vs. open form) [[13], [14]].
Herein we describe the reactivity of 2-pyridylbenzothiazolines with different R
groups towards metal dichlorides of the 10 Group to study the effect of the distinct
substituents such as pyridine, phenyl, or hydrogen attached to the carbon present
in the heterocyclic thiazoline ring. The benzothiazoline compounds were
transformed into their corresponding Schiff bases upon metal coordination, yielding
n
metallic complexes of general formula [M(L )Cl] (M = Ni, Pd, Pt; n = 1–3). The
benzothiazoline precursors 1–3 as well as the Ni(II), Pd(II), and Pt(II) complexes
1
13
were structurally characterized by vibrational spectroscopy, H and C NMR, and
by single crystal X-Ray diffractions studies. The tautomeric equilibria of 1–3
precursors and the formation of the Pd(II) complexes were explored by DFT
approaches.

H
N
N
R'
R
R'
R
S
SH
Ring form
Open form
Schiff base HL)
(
R, R´= H, alkyl, or aryl
Figure 1. Structure of benzothiazolines and their corresponding HL Schiff base
isomers.
2. Experimental
2
.1 General details
All the manipulations of air and moisture sensitive materials were carried out under
dinitrogen atmosphere using Schlenk techniques. Solvents such as acetonitrile
(
MeCN) and dimethylsulfoxide (DMSO) were dried according to the standard
.
methods and distilled before their use. PdCl
2
, PtCl
2
, and NiCl
2
6H O were
2
purchased from Aldrich and used as received. The [M(NCMe)
2
Cl
2
] complexes (M =
Pd, Pt) used as starting materials were prepared and isolated as reported [[15]].
Melting points were recorded on a Mel-Temp II apparatus and are reported without
correction. Elemental analyses were performed on a Perkin–Elmer Series II
CHNS/O Analyzer 2400. Infrared spectra were recorded on a FT-IR 200 Perkin–
-
1
Elmer spectrophotometer in the 4000–400 cm range using KBr pellets, CsCl, or
CHCl . NMR spectra were obtained on a Varian NMRS 400 spectrometer in
DMSO-d6 solutions at 399.78 MHz for H and 100.53 MHz for C{ H} spectra.
3
1
13
1
1
13
1
Chemicals shifts (ppm) of H and C{ H} spectra are relative to the frequency of
n
SiMe
4
. NMR assignments of compounds 1 and 2 and complexes M(L )Cl] [n = 1–
3
; M = Pd (1a–3a); Pt (1b–3b) were performed by two-dimensional heteronuclear
and mononuclear experiments (COSY, HSQC, and HMBC).
Single crystals of 1 and 2 were grown by slow evaporation of a diethylether
solution at room temperature. Crystals of 1a, 2a, 3a, and 2c were crystallized at
room temperature by slow evaporation from an acetonitrile and toluene 1:1
mixture. Crystals of 1b were grown as DMSO solvate from a supersaturated

solution of a dimethylsulfoxide solution. Intensity data were collected at 295 K on a
Gemini CCD diffractometer with either graphite-monochromated Mo-K radiation
(
 = 0.71073 Å) for 1, 2, 2a, 1b·DMSO, 2c, and 3a or Cu-K radiation ( = 1.54184
Å) for 1a. Data were integrated, scaled, sorted, and averaged using the CrysAlis
software package [[16]].
The initial structures were solved by using intrinsic phasing (SHELXT) and refined
with the ShelXTL [[17]] refinement package with the Olex2 suite [[18]] by using
2
least squares minimization against F . Anisotropic displacement parameters for
non-H atoms were refined; the positions of the hydrogen atoms were kept fixed
with a common isotropic displacement parameter at 1.2 times of all C(H) groups.
The crystal data and structure refinement details for compounds 1, 2, 1a–3a,
1
b·DMSO, and 2c are collected in Table 1.
For the DFT studies, atomic coordinates of benzothiazolines 1–3 and complexes
a–3a were obtained from X-ray crystallography while coordinates of acetonitrile
and [PdCl ] were obtained from the NIST [[19]] and COD databases [[20]]. Multiple
1
2
reaction pathways were proposed based on molecular dynamics simulations of
compounds 1–3 calculated with the DFTB+ software [[21]], and from the known
coordination modes of palladium(II) cation. Molecular structures of stable
intermediates; i.e., minima on the potential energy surface, were optimized and
used as starting points to locate the corresponding transition states by either the
double end interpolation method or scanning of reaction coordinates. Then,
intrinsic reaction coordinate (IRC) calculations were performed to ensure that every
minimum was actually connected by one transition state. All optimizations and
coordinate scans were performed with the Gaussian 09 software [[22]] at the
SVWN/SVP,SDD level of theory in gas phase, while saddle interpolations were
performed with de deMon2k software [[23]] at the SVWN/DZVP level of theory. For
the calculation of the Gibbs free energy profiles, all intermediates were
recalculated at the PBEPBE/(Def2-TZVP,SDD) level of theory in gas phase at 273
K, performing normal mode analysis and verifying that all minima and transition
states had zero and one imaginary frequencies, respectively. Activation barriers
†
∆
G for each mechanism were calculated as the energy difference between the

first step in the reaction path and the highest point along it, while free energy
changes ∆G were calculated as the energy difference between first and last steps
on the reaction path.
2.2 Synthesis of benzothiazolines 1–3
The compounds 1–3 were obtained from the reaction of o-aminothiophenol with the
corresponding aldehyde or ketone derivative, Scheme 1.
Scheme 1. Synthesis of benzothiazolines 1–3.
5 4
A mixture of the substituted 2-(pyridyl)ketone [C H NC(O)R; R = C
5
H
4
N, C
6
5
H ] with
o-aminothiophenol in a 1:1.2 ratio, catalytic amounts of sulfuric acid (three drops),
and 0.50 g of sodium sulfate anhydrous in 50 mL of toluene was refluxed for 12 h
(
1) or 72 h (2). Then, the mixture was cooled to room temperature and the sodium
sulfate was filtered off. The solution was evaporated to dryness and a yellow oil

was obtained; it was dissolved in 25 mL of dichloromethane and extracted with
water (5 × 5 mL). The organic phase was dried with sodium sulfate anhydrous,
filtered, and evaporated to give yellow solids that were identified as compounds 1
and 2. Compound 3 was synthesized as previously has been reported. [Error!
Bookmark not defined.]
2
.2.1 Compound 1
Di(2-pyridyl)ketone (1.00 g, 5.42 mmol), o-aminothiophenol (1.02 g, 8.13 mmol)
Yellow solid. Yield: 81% (1.27 g). M. p.: 140–142°C. Anal. Calc. for C17 S (%):
C, 70.08; H, 4.50; N 14.42. Found: C, 70.43; H, 4.14; N, 14.62. IR data (CsCl,
13
H N
3
−
1
1
3
cm ): 3287 (NH), 1571 (C=N). H NMR (DMSO-d6)  = 8.46 (dd, H5, 2H, J =
4
3
4
.80, J = 1.60 Hz), 7.88 (d, H2, 2H, J = 8.00 Hz), 7.84 (s, broad, NH, 1H), 7.82
3
3
4
3
3
(
ddd, H3, 2H, J = 8.00, J = 8.00, J = 1.60 Hz), 7.25 (ddd, H4, 2H, J = 7.20, J =
4
3
3
4
.60, J = 1.60 Hz), 7.02 (d, H12, 1H, J = 7.20 Hz), 6.87 (ddd, H10, 1H, J = 7.60,
3
4
3
4
J = 7.60, J = 1.60 Hz), 6.80 (dd, H9, 1H, J = 8.00, J = 1.00 Hz), 6.59 (ddd, H11,
3
3
4
13
1
1
1
1
H, J = 7.60, J = 7.20, J = 1.20 Hz). C{ H} NMR (DMSO-d6)  = 163.0 (C1),
48.6 (C5), 146.9 (C8), 136.9 (C3), 125.5 (C10), 124.0 (C7), 122.5 (C4),
21.0(C12), 120.8 (C2), 118.9 (C11), 109.6 (C9), 85.3 (C6).
2
.2.2 Compound 2
2
-benzoylpyridine (1.00 g, 5.46 mmol), o-aminothiophenol (1.023 g, 8.19 mmol).
Yellow solid. Yield: 93% (1.47 g). M. p.: 115–117°C. Anal. Calc. for C18
14
H N
2
S (%):
−
1
C, 74.45; H, 4.86; N, 9.65. Found: C, 74.42; H, 4.99; N 9.89. IR data (CsCl, cm ):
1
3
3
7
295 (NH), 1570 (C=N). H NMR (DMSO-d6)  = 8.55 (d, 1H, H5, J = 4.80 Hz),
3
3
4
.86 (ddd, 1H, H3, J = 7.83, J = 7.83, J =1.75 Hz), 7.83 (s, broad, 1H, NH), 7.78
3
4
3
(
dd, 1H, H2, J = 8.00, J = 0.80 Hz), 7.53 (d, 2H, H14, H18, J = 8.33 Hz), 7.31 (m,
3
3
3
H, H4, H15, H17), 7.22 (dd, 1H, H16, J = 7.59, J = 7.19 Hz), 7.02 (d, 1H, H12,
3
3
3
4
J = 7.44 Hz), 6.90 (ddd,1H, H10, J = 7.59, J = 7.59, J =1.20 Hz), 6.77 (d, 1H,
3
3
3
4
13
1
H9, J =7.83 Hz), 6.60 (ddd, 1H, H11, J = 7.59, J = 7.59, J = 1.20 Hz). C{ H}
NMR (DMSO-d6)  = 163.8 (C1), 149.4 (C5), 147.1 (C8), 146.1 (C13), 137.6 (C3),

1
28.5 (C15, C17), 127.8 (C16), 126.7 (C14, C18), 125.9 (C10), 124.8 (C7), 122.9
(
C4), 121.5 (C12), 120.4 (C2), 119.3 (C11), 109.5 (C9), 85.1 (C6).
2
.2.3 Compound 3
2
-pyridinecarboxaldehyde (0.30 g, 2.80 mmol), o-aminothiophenol (0.35 g, 2.80
−1
mmol). Yellow solid. Yield: 98% (0.592 g). M. p.: 93–95°C. IR data (CsCl, cm ):
1
3
3
392, 3230 (NH), 1571 (C=N). H NMR (DMSO-d6)  = 8.52 (dd, H5, 1H, J = 4.80,
3
3
3
4
J = 2.00 Hz), 7.81 (ddd, H3,1H, J = 7.80, J = 7.60, J = 2.00 Hz), 7.56 (d, H2,
3
3
3
4
1
1
7
H, J = 8.00 Hz), 7.32 (ddd, H4,1H, J = 7.60, J = 5.00, J = 1.20 Hz), 7.12 (d,
3
3
3
H, NH, J = 2.80 Hz), 7.00 (d. H12, 1H, J = 7.60 Hz), 6.92 (ddd, H10, 1H, J =
3
4
3
4
.60, J = 7.60, J = 1.20 Hz), 6.67(dd, 1H, H9, J = 7.80, J = 1.20 Hz), 6.61 (ddd,
3
3
4
3
H11, 1H, J = 7.60, J = 7.20, J = 1.20 Hz), 6.40 NH (d, H6, 1H, J = 2.80 Hz).
13
1
C{ H} NMR (DMSO-d6)  = 161.8 (C1), 149.0 (C5), 147.8 (C8), 137.3 (C3), 125.4
(
C10), 124.5 (C7), 123.0 (C4), 121.2 (C12), 119.8 (C2), 118.9 (C11), 108.9 ( C9),
9.6 (C6).
6
2.3 Synthesis of metallic complexes
2
.3.1 Synthesis of bidentate complex [Pd(1)Cl
2
]
An equimolar mixture of [Pd(NCCH Cl ] (0.080g, 0.37 mmol) in 25 mL of
3
)
2
2
acetonitrile with 1 (0.107 g, 0.37 mmol) was stirred at 0°C for 24 h. Then, the
obtained yellow solid was filtered off and dried in vacuum. The solid formed was
washed with cold acetonitrile (10 mL) and was filtered off and dried by suction.
Yield: 89% (0.090 g). Dec.: 212°C. Anal. Calc. for [Pd(C17
H
12
N
3
S)Cl
2
] (%): C,
−
1
4
3
3.66; H, 2.59; N, 8.98. Found: C, 43.94; H, 2.75; N, 8.42. IR data (KBr, cm ):
1
231 (NH), 1600 (C=N), 1580, 1471 (C=C). H NMR (DMSO-d6)  = 9.00 (dd, 1H,
3
4
3
3
H5, J = 5.69, J = 1.20 Hz), 8.82 (s, 1H, NH), 8.19 (ddd, 2H, H3, J = 8.20, J =
4
3
3
3
7
=
8
.40, J = 1.20 Hz), 7.94 (d, 2H, H2, J = 7.60 Hz), 7.58 (ddd, 2H, H4, J = 6.80, J
4
3
3
6.60, J = 1.20 Hz), 7.17 (d, 1H, H12, J = 7.60 Hz), 7.06 (ddd, 1H, H10, J =
3
4
3
3
.00, J =7.20, J = 1.20 Hz), 7.02 (d, 1H, H9, J = 8.00 Hz), 6.72 (ddd, 1H, H11, J

3
4
13
1
=
7.60, J =7.20, J = 1.20 Hz). C{ H} NMR (DMSO-d6)  = 156.3 (C5), 154.5
(
C1), 144.9 (C8), 141.4 (C3), 126.7 (C10), 125.5 (C4), 122.5 (C2), 122.2 (C7),
1
21.8 (C12), 119.9 (C11), 109.5 (C9), 83.8 (C6).
1
2
.4 Synthesis of complexes [M(L )Cl] (M = Pd, Pt).
General Procedure
An equimolar mixture of [M(NCCH
3
)
2
Cl ] (M = Pd, Pt) with the benzothiazoline 1 in
2
2
5 mL of acetonitrile was refluxed (M= Pd, 2 h; M = Pt, 18 h). The green solid
obtained was filtered off and dried in vacuum. Then, this solid was identified by
n
NMR as the mixture of complexes [Pd(1)Cl
2
] and [Pd(L )Cl] in a 20:80 ratio in the
case of M = Pd, while in the case M = Pt the mixture was observed in a 50:50 ratio
1
of [Pt(L )Cl] and an unidentified compound. Each mixture was suspended in 5 mL
of dimethylsulfoxide and heated until dissolution at 60 °C (M = Pd) and 80°C (M =
Pt) for 10 minutes. Afterward, the reaction mixture was cooling to room
temperature, the brown solid formed was filtered off and dried in vacuum.
1
2
.4.1 [Pd(L )Cl] (1a)
[
Pd(NCCH
3
)
2
)Cl
2
] (0.122 g, 0.26 mmol). Green solid. Yield: 98% (0.11 g). M. p.:
o
3
00 C. Anal. Calc. for [Pd(C17
H N
12 3
S)Cl] (CH SO (%): C, 44.71; H, 3.55; N, 8.23.
•
3 2
)
−
1
Found (%): C, 44.64; H, 3.58; N, 7.95. IR data (KBr, cm ): 1594, 1534 (C=N);
1
3
1
1
580, 1461 (C=C). H NMR (DMSO-d6)  = 8.89 (d, 1H, H5, J = 4.80 Hz), 8.70 (d,
3
3
3
4
H, H17, J = 5.20 Hz), 8.14 (ddd, 1H, H3, J = 8.00, J = 7.60, J = 1.60 Hz), 8.06
3
3
4
3
(
ddd, 1H, H15, J = 7.80, J = 7.60, J =1.60 Hz), 7.89 (d, 1H, H2, J = 8.00 Hz),
3
3
7
.76 (m, 2H, H4, H16), 7.07 (d, 1H, H14, J = 7.60 Hz), 7.02 (d, 1H, H12, J = 7.60
3
3
4
3
Hz), 6.89 (ddd, 1H, H11, J = 7.60, J = 7.20, J = 1.20 Hz), 6.38 (ddd, H10, 1H, J
3
4
3
13
1
=
8.00, J = 7.60, J =1.20 Hz), 5.63 (d, 1H, H9, J = 8.80 Hz). C{ H} NMR
DMSO-d6)  = 165.9(q, C6), 159.6 (q, C13), 155.4 (q, C7), 151.3 (C5), 150.5 (q,
C1), 148.5 (C17), 143.5(q, C8), 140.9 (C15), 138.7 (C3), 130.9 (C11), 130.0
C12), 129.5 (C14), 128.8 (C16), 126.1 (C4), 124.2 (C2), 123.3 (C9), 121.8 (C10).
(
(

1
2
.4.2 [Pt(L )Cl] (1b)
Pt(NCCH )Cl ] (0.080 g, 0.230 mmol), 1 (0.067 g, 0.230 mmol). Green solid.
Yield: 42% (0.05 g). M. p.: 245–250 °C. Anal. Calc. for [Pt(C17 S)Cl] (%): C,
[
3
)
2
2
12
H N
3
−
1
3
1
9.20; H, 2.32; N, 8.07. Found (%): C, 38.93; H, 2.28; N, 7.14. IR data (KBr, cm ):
1
595, 1520 (C=N); 1582, 1459 (C=C). H NMR (DMSO-d6)  = 8.91 (m, 2H, H5,
3
3
4
3
H17), 8.17 (ddd, 1H, H3, J = 7.60, J = 5.20, J = 1.60 Hz), 8.07 (ddd, 1H, H15, J
3
4
3
4
=
8.00, J = 7.80, J = 1.60 Hz), 7.93 (dd, 1H, H2, J = 7.60, J = 1.20 Hz), 7.82
3
3
4
3
3
(
ddd, 1H, H16, J = 7.80, J = 5.20, J = 1.20 Hz), 7.75 (ddd, 1H, H4, J = 6.60, J =
4
3
3
5
.20, J = 1.20 Hz), 7.07 (dd, 1H, H12, J = 8.00, J = 1.20 Hz), 6.93 (d, 1H, H14,
3
3
3
4
J = 8.00 Hz), 6.82 (ddd, 1H, H11, J = 8.00, J = 7.20, J = 1.20 Hz), 6.30 (ddd,
3
3
4
3
13
1
1
H, H10, J = 8.80, J = 7.20, J = 1.20 Hz), 5.54 (d, 1H, H9, J = 8.80 Hz). C{ H}
NMR (DMSO-d6)  = 171.0 (q, C6 ), 160.9 (q, C13), 156.5 (q, C7), 151.6 (C5),
1
1
50.2 (q, C1), 146.8 (C17), 145.1 (q, C8), 140.8 (C15), 138.9 (C3), 132.2 (C11),
31.2 (C14), 130.9 (C16), 130.6 (C12), 126.4 (C4), 124.7 (C2), 124.3 (C9), 121.4
(
C10).
n
2
.5 Synthesis of complexes [M(L )Cl] (n = 2, 3; M = Pd, Pt).
General Procedure
An equimolar mixture of [M(NCCH
3
)
2
Cl ] (M = Pd, Pt) with the corresponding
2
benzothiazoline (2 or 3) in 25 mL of acetonitrile was refluxed (M= Pd, 2 h; M = Pt,
h). After cooling to room temperature, the mixture reaction obtained was filtered
5
off and dried in vacuum to give a stable solid at room temperature. The solid
obtained by filtration and by evaporation of the organic phase was identified as the
n
corresponding complex of formula [M(L )Cl] (M = Pd, Pt; n = 2, 3).
2
2
.5.1 [Pd(L )Cl] (2a)
[
Pd(NCCH
3
)
2
Cl
2
] (0.080 g, 0.310 mmol), 2 (0.090 g, 0.310 mmol). Brown solid.
o
Yield: 88% (0.118 g). M. p.: 300 C. Anal. Calc. for [Pd(C18
13
H N
2
S)Cl]
•
0.5H O (%):
2
C, 49.11; H, 3.21; N, 6.36. Found (%): C, 49.37; H, 3.04; N, 5.52. IR data (KBr,

−
1
1
cm ): 1592, 1575 (C=N); 1592, 1469 (C=C). H NMR (DMSO-d6)  = 8.69 (d, 1H,
3
3
3
3
H5, J = 5.17 Hz), 8.07 (t, 1H, H3, J = 7.89 Hz), 7.76 (dd, 1H, H4, J = 5.99, J =
3
6
=
1
=
1
1
.80 Hz), 7.71 (m 3H, H15, H16, H17), 7.65 (m, 2H, H14, H18), 7.03 (d, 1H, H2, J
3
3
7.97 Hz), 7.00 (d, 1H, H12, J = 7.59 Hz), 6.88 (t, 1H, H11, J = 7.39 Hz), 6.36 (t,
3
3
13
1
H, H10, J = 7.78 Hz), 5.95 (d, 1H, H9, J = 8.68 Hz). C{ H} NMR (DMSO-d6) 
169.0 (q, C6 ), 160.9 (C1 ), 155.0 (C7 ), 148.1 (C5 ), 144.4 (C8 ), 141.0 (C3)
33.2 (C13), 131.3 (C16), 130.8 (C11), 130.5 (C15, 17), 130.2 (C12), 129.8 (C2),
28.8 (C4), 127.6 (C14, 18), 124.1 (C9), 121.7 (C10).
2
2
.5.2 [Pt(L )Cl] (2b)
[
Pt(NCCH
Yield: 56% (0.068 g). M. p.: 305-310°C. Anal. Calc. for [Pt(C18
H, 2.52; N, 5.39. Found (%): C, 40.96; H, 2.47; N, 4.35.R data (KBr, cm ): 1596,
3
)
2
Cl
2
], (0.080 g, 0.230 mmol), 2 (0.066 g, 0.230 mmol). Green solid.
H
13
N
2
S)Cl]: C, 41.58;
−1
1
3
1
577 (C=N); 1596, 1471 (C=C). H NMR (DMSO-d6)  = 8.91 (d, 1H, H5, J = 5.40
3
3
4
3
Hz), 8.06 (ddd, 1H, H3, J = 7.60, J = 7.20, J = 1.60 Hz), 7.77 (ddd, 1H, H4, J =
3
4
7
.20, J = 5.40, J = 1.20 Hz), 7.71 (m, 3H, H15, H16, H17), 7.64 (m, 2H, H14,
3
3
H18), 7.04 (d, 1H, H12, J = 9.20 Hz), 6.87 (d, 1H, H2, J = 7.60 Hz), 6.80 (ddd,
3
3
4
3
3
1
7
1
H, H11, J = 9.20, J = 7.60, J = 1.20 Hz), 6.26 (ddd, 1H, H10, J = 8.80, J =
4
3
13
1
.60, J = 1.60 Hz), 5.94 (d, 1H, H9, J = 8.80 Hz). C{ H} NMR (DMSO-d6)  =
73.9 (C6), 161.7 (C1), 156.2 (C7), 146.4 (C5), 145.6 (C8), 140.6 (C3), 132.6
(
C13), 131.7 (C11), 131.3 (C2), 131.2 (C12), 130.5 (C4,C16), 130.4 (C15, C17),
1
27.8 (C14, C18), 124.7 (C9), 121.2 (C10).
3
2
.5.3 [Pd(L )Cl] (3a)
[
Pd(NCCH
3
)
2
Cl
2
] (0.080 g, 0.310 mmol), 3 (0.066 g, 0.310 mmol). Orange solid.
o
Yield: 82% ( 0.091 g). M. p.: 318 C. Anal. Calc. for [Pd(C12
H
9
N S)Cl] (%): C,
2
−
1
3
1
2.48; H, 2.04; N, 6.31. Found (%): C, 32.32; H, 2.00; N, 5.55. IR data (KBr, cm ):
1
601, 1570 (C=N); 1583, 1475 (C=C). H NMR (DMSO-d6)  = 9.00 (s, 1H, H6 ),
3
4
3
3
8
.55 (dd, 1H, H5, J = 5.40, J = 1.60 Hz ), 8.22 (ddd, 1H, H3, J = 7.60, J = 7.80,
4
3
3
3
J = 1.60 Hz), 7.95 (d, 1H, H2, J = 8.00 Hz), 7.78 (ddd, 1H, H4, J = 8.00, J =

4
3
5
.20, J = 1.20 Hz), 7.55 (d, 1H, H9, J = 8.40 Hz), 7.07 (m, 2H, H12, H11), 6.93
3
3
4
13
1
(
ddd, 1H, H10, J = 7.60, J = 7.40, J = 1.60 Hz). C{ H} NMR (DMSO-d6) 
158.9 (C6),158.3 (C1),152.2 (C7), 148.6 (C5), 143.8 (C8), 141.2 (C3), 131.7
=
(
C11), 129.4 (C12), 129.0 (C2), 128.8 (C4), 122.8 (C10), 118.8 (C9).
3
2
.5.4 [Pt(L )Cl] (3b)
[
Pt(NCCH
3
)
2
Cl ] (0.080 g, 0.230 mmol), 3 (0.049 g, 0.230 mmol). The brown solid
2
obtained by filtration and dried in vacuum. Yield: 60 % (0.061 g). M. p.: above 330
o
C. Anal. Calc. for [Pt(C12
H
9
N S)Cl] (%): C, 32.48; H, 2.04; N, 6.31. Found (%): C,
2
−1
3
2.32; H, 2.00; N,5.55. IR data (KBr, cm ): 1605, 1568 (C=N); 1580, 1473 (C=C).
1
3
3
H NMR (DMSO-d6)  = 9.20 (s, 1H, H6, J1H-195Pt = 46.77 Hz), 8.75 (dd, 1H, H5, J
4
3
3
4
=
5.20, J = 1.00 Hz), 8.21 (ddd, 1H, H3, J = 8.00, J = 7.60, J = 1.60 Hz), 7.81
3
3
4
(
m, 2H, H2, H4), 7.51 (d, 1H, H9, J = 7.60 Hz), 7.12 (dd, 1H, H12, J = 8.40, J =
3
3
4
1
.20 Hz), 7.02 (ddd, 1H, H11, J = 8.40, J = 7.60, J = 1.20 Hz), 6.85 (ddd, 1H,
3
3
4
13
1
H10, J = 7.60, J = 7.60, J = 1.20 Hz). C{ H} NMR (DMSO-d6)  = 163.0
(
(
C6),159.3 (C1),153.3 (C7),147.1 (C5),144.8 (C8), 141.0 (C3), 132.8 (C11), 130.4
C4),130.1 (C2), 129.4 (C12), 122.3 (C10),119.5 (C9).
2
2
.6 Synthesis of complex [Ni(L )Cl] (2c)
.
2
An equimolar mixture of 0.081 g (0.345 mmol) of NiCl
6H O in 25 mL of methanol
2
with 2 (0.100 g, 0.345 mmol) was stirred at room temperature for 24 h. Then, the
mixture obtained was filtered off and dried in vacuum. A dark red solid was formed
and washed with diethylether, filtered off and dried by suction (3 x 15 mL). Deep
red crystals were obtained by evaporation of a toluene-acetonitrile mixture (1:1).
o
Yield: 69 % (0.091 g). M. p.: above 250 C. Anal. Calc. for [Ni(C18
H
13
N S)Cl] (%):
2
5
6.37% C, 3.42% H, 7.30% N. Found (%): 57.73% C, 3.07% H, 7.4% N. IR data
−1
(
KBr, cm ): 1594, 1577 (C=N); 1588, 1471 (C=C).

3. Results and discussion
n
3
.1 Synthesis of [M(L )Cl] complexes derived from 1–3.
n
Complexes of type M(L )Cl] (M = Pd, Pt; n = 1–3) (1a–3a and 1b–3b) were
obtained from the equimolar reaction of the corresponding benzothiazoline 1–3
with the complex M(NCMe)
2
Cl
2
] (M = Pd and Pt) in hot acetonitrile, whereas from
.
the reaction of 3 with the nickel salt NiCl
2
6H O in hot methanol was obtained the
2
3
complex Ni(L )Cl] (3c), Scheme 2. The scheme numbering used herein after is
also showed.
1
0
9
R
9
H
8
7
N
R
11
8
6
1
0
MCl2
N
1
6
2
+ HCl
1
2
7
1
1
1
Hot MeCN
Hot MeOH for 2c)
S
N
(
S
M
N
1
2
3
2
5
Cl
5
4
3
4
n
[
M(L )Cl]
14
15
1
6
1
3
1
1
2
3
R =
[M(L )Cl] M = Pd, (1a); M = Pt, (1b)
[
[
N
1
7
2
M(L )Cl] M = Pd, (2a); M = Pt, (2b); M = Ni, (2c)
1
4
15
3
M(L )Cl] M = Pd, (3a); M = Pt, (3b)
16
R =
1
3
18
17
R = -H
n
n −
Scheme 2. Synthesis of M(L )Cl] complexes of 10 Group containing ligand {L } .
The numbering scheme for NMR data is showed.
The reaction of 1 with Pd(NCMe)
2
Cl
2
] deserves a more detailed discussion. The
1
green solid obtained was identified as a mixture of Pd(L )Cl] and Pd(1)Cl
2
] in a
1
8
0:20 ratio by means of H NMR spectroscopy. This mixture was heated at 60 °C
1
for 5 min in dimethylsulfoxide, and the signals of Pd(1)Cl ] vanished. The H NMR
2
1
spectra just displayed signals attributable to Pd(L )Cl] (1a). We also heated the
mixture in acetonitrile; however, the ratio did not change. Moreover, our attempts to
exclusively yield 1a by means of the reaction of 1 with [Pd(NCMe)
2
Cl ] in hot
2
dimethylsulfoxide resulted in a mixture of a large number of unidentifiable
compounds.

Interestingly, when Pd(NCMe)
2
Cl ] was added to 1 at 0 °C in acetonitrile and
2
stirred for 24 h, the benzothiazoline displaced the solvent molecules and
coordinated to Pd(II) to yield the complex Pd(1)Cl ] as a yellow solid (Scheme 3).
2
1
This complex converts slowly to Pd(L )Cl] at room temperature, or quickly by
heating it either in solution or in solid state. The formation of Pd(1)Cl ] as a
2
complex of low stability at room temperature allow to appreciate the role of 1 as an
effective ligand through of the coordination of two pyridinic substituents on the
carbon atom of the thiazolidine ring, enhancing the formation of a N,N,-bidentate
complex.
1
Scheme 3. Synthesis of Pd(II) complexes derived from 1 and L .
It is noteworthy that the benzothiazolines 2 and 3 with M(NCMe)
2
Cl
2
] (M = Pd and
Pt) at 0°C as well as compound 1 with the complex Pt(NCMe)
2
Cl ] at low
2
temperature did not react.

3.2. IR Spectroscopy
IR spectra of compounds 1–3 in CsCl showed the (NH) absorptions of the amino
−
1
group in the 3340–3230 cm range. The observation of the (NH) vibration agreed
with the predominance of the benzothiazoline form in solid state; we did not
observe bands assignable to H–S groups. For 1 and 2, were observed single
−
1

(NH) absorptions at 3287 and 3295 cm , respectively. However, in the IR spectra
−
1
of 3 were displayed two (NH) absorptions at 3340 (NH free) and 3230 cm (NH
hydrogen bond). The comparison of the (NH) absorptions for 1–3 at lower
wavenumber respect to analogues containing free NH groups [[24], [25]] suggests
the presence of hydrogen bonds of type NH---N. In order to establish the nature of
the hydrogen bonds, the IR spectra of 1–3 in CHCl
3
were obtained. The (NH)
−
1
−1
−1
absorption for 1 (3300 cm ), 2 (3337 cm ) and 3 (3288 cm ) in CHCl solution
3
was displayed at high wavenumber compared to the observed in CsCl (1 at 3287,
−
1
for 2 at 3295 and, for 3 at 3230 cm ). The frequencies observed in CHCl
were attributed to the prevalence of the NH---N intramolecular hydrogen bonds for
–3.
In the complex [Pd(1)Cl
3
solution
1
−1
2
] the (NH) absorption at 3231 cm is observed; for the
n
complexes of type [M(L )Cl] it is not observed. Respect to the (C=N) absorptions,
−
1
2
for the complex [Pd(1)Cl
2
] one absorption at 1600 cm is indicative of a  N-
−
1
bidentate mode of 1, while two absorptions in the range of 1605–1592 cm and
−
1
n
1
577–1534 cm for the complexes [M(L )Cl] (1a–3a, 1b–3b, and 2c) are indicative

n −
of  NS-tridentate modes of the ligands {L } .
3.3. NMR Spectroscopy
1
13
1
H and C{ H} NMR spectra of benzothiazolines 1–3 as well as the spectra of
n
[
Pd(1)Cl
2
] and [M(L )Cl] (1a–3a and 1b–3b) complexes were obtained at room
1
13
1
temperature in DMSO-d6 solutions. The H and C{ H} NMR spectra of the nickel
compound 2c displayed very broad signals. The numbering scheme utilized for
NMR is shown in Scheme 2.
1
13
H and C NMR spectra of 1–3 displayed the frequencies of the NH proton in the
range of 7.84 to 7.12 ppm, whereas that the resonances for the C6 carbon are in

the 85.3–69.6 ppm range that has been associated with this type of quaternary
carbon atoms in benzothiazoline derivatives [Error! Bookmark not defined.].
These data also support the benzothiazoline form as the predominant tautomer in
solution, as we observed by IR spectra (vide supra).
On the other hand, the existence of hydrogen bonding interactions in DMSO-d6
1
solutions for benzothiazolines 1–3 was evaluated by means of the H NMR shift
dependence of the NH group with the temperature (/T) [[26], [27]]. Thus, the
−
3
−3
−3

/T values obtained from 363 to 295 K of −5.3×10 , −5.5×10 , and −4.4×10
ppm/K for 1, 2, and 3, respectively, suggest the presence of intermolecular
hydrogen bonding due to Me SO---HN interactions. We also analyzed the effect of
the concentration of 1, 2, and 3 in a non-polar solvent such as CDCl
2
3
onto the
−1
−3
1
chemical shift of the NH proton (1×10 and 1×10 M concentrations). H NMR
data for 1 and 2 displayed that these chemical shifts were independent of the
concentration (6.75 ppm for 1; 6.13 ppm for 2, regardless the concentration),
indicating the existence of NH---N intramolecular hydrogen bonding [[28]]. On the
other hand, in compound 3 the NH proton was observed as a very broad
−1
resonance at 5.06 ppm in a 1×10 M solution, while for the more diluted solution,
the NH resonance was not observed. The vanishing of this resonance at lower
concentration suggests that this weak NH---N interaction is in fast exchange in
CDCl
3
at room temperature.
1
In the H NMR spectrum of [Pd(1)Cl
2
] in DMSO-d6 solution, the NH proton at 8.82
ppm is displayed at higher frequencies in comparison with 1 (7.84 ppm); this
deshielding is consistent with a reinforcement of the intermolecular hydrogen bond
N–H---OSMe
protons, in a 2:1 ratio. In the complex [Pd(1)Cl
pyridine rings is attributed to the coordination of 1 toward the palladium atom in a
2
. We also observed two ABCD patterns for the pyridinic and phenyl
2
] the magnetic equivalence of both
2
1

N-bidentate mode. In the case of [Pd(L )Cl] both pyridine rings are not

equivalents and the NH proton is missing; this observation agreed with a  NS-
1
−
tridentate mode of the deprotonated Schiff base {L } . Additionally, it is noteworthy
that the pyridinic proton H5 in compounds 1–3 is observed in the 8.55 to 8.46 ppm
n
range, whereas for the [Pd(1)Cl
2
] and [M(L )Cl] complexes the data range from

9
.00 to 8.55 ppm; this shifting is attributed to the metallic bi- or tricoordination. In
general, the metallic coordination in the complexes enhances the transformation of
the ring forms of 1-3 into the open forms, i.e.; their Schiff bases, yielding the
n
[
M(L )Cl] complexes, where the NH proton has been lost.
13
1
The analysis of the C{ H} NMR data indicates that the chemical shift of the C6
2
carbon at 83.8 ppm agrees with a  N-bidentate mode of 1 in the complex
[
Pd(1)Cl
2
]; conversely, the frequencies of the carbon C6 in the range of 173.9 to

1
58.9 ppm indicate its iminic character, agreeing with a  NS-tridentate
n
coordination mode in the complexes [M(L )Cl] (1a–3a and 1b–3b).

Table 1. Selected crystallographic data for 1, 2, 1a–3a, 1b·DMSO, and 2c.
1
2
1a
SClPd
2a
SClPd
3a
Cl
1b·DMSO
OS ClPt
2c
18 13 2
C H N SClNi
Formula
C
34
H
26
N
6
S
2
C
18
H
14
N
2
S
C
17
H
12
N
3
C
18
H
13
N
2
C
24
H
18
N
4
S
2
2
Pd
2
C
19
H
18
N
3
2
Formula weight
Crystal size (mm)
Crystal system
Space group
a (Å)
582.73
290.37
432.21
431.21
710.24
599.02
383.52
0.4 × 0.4 × 0.3
Triclinic
0.6 × 0.3 × 0.3
Orthorhombic
0.5 × 0.3 × 0.1
Monoclinic
0.2 × 0.1 × 0.1
Monoclinic
0.2 × 0.1 × 0.05
Triclinic
0.4 × 0.2 × 0.1
Monoclinic
0.3 × 0.2 × 0.05
Monoclinic
P-1
P2
1
2
1
2
1
P2
1
/n
P2
1
/n
P-1
P2
1
/c
1
P2 /n
8.0990(3)
11.3297(4)
15.9625(6)
92.011(3)
9.9656(2)
10.4561(2)
13.9484(3)
90
10.3440(4)
10.9115(4)
14.9189(6)
90
12.1069(9)
7.1334(3)
19.2261(11)
90
7.0585(5)
10.6230(7)
17.4739(14)
85.169(6)
12.5796(2)
19.2841(3)
8.27730(10)
90
12.1179(5)
7.1085(2)
18.8365(6)
90
b (Å)
c (Å)



(°)
(°)
(°)
90.204(3)
90
106.102(4)
104.946(7)
80.494(7)
99.607(2)
104.617(3)
91.716(3)
1463.13(9)
2
90
90
90
70.746(7)
1219.34(17)
2
90
90
3
V (Å )
Z
1453.44(5)
4
1617.82(11)
4
1604.26(17)
4
1979.80(5)
4
1570.06(10)
4
−3

calcd (gm )
1.323
1.327
1.911
1.774
1.442
1.785
1.934
2.010
16.592
1.622
4.571
−1

(mm )
1.921
12.064
15.694
F(000)
608.0
608.0
856.0
856.0
696.0
1.161
294
1152.0
1.057
294
784
2
GOF on F
1.028
0.982
1.068
1.015
1.036
294
T (K)
294
294
295
294
2
 range (°)
7.812 to 148.964
24251
10.574 to 154.91
30691
6.73 to 52.74
27071
7.824 to 155.306
17138
8.822 to 148.988
10218
7.128 to 148.912 7.868 to 154.976
Reflections collected
Unique reflections
9715
16889
5962
3090
3306
3373
4895
4054
3310
Absorption correction
Independent reflections (Rint
multi-scan
0.0279
multi-scan
0.0376
multi-scan
0.1326
multi-scan
0.0582
multi-scan
0.0716
multi-scan
0.0303
multi-scan
0.0502
)
R
R
1
1
, wR
, wR
2
2
[I>2(I)]
0.0445, 0.1211
0.0551, 0.1327
0.38/−0.32
-
0.0358, 0.0950
0.0392, 0.0991
0.31/−0.23
0.001(6)
0.0575, 0.1399
0.0727, 0.1607
1.92/−1.62
0.0422, 0.1009
0.0690, 0.1194
1.12/−0.58
0.0946, 0.2794
0.1169, 0.2890
2.62/−0.98
0.0303, 0.0774
0.0333, 0.0807
1.35/−0.85
0.0351, 0.0851
0.0506, 0.0948
0.33/−0.23
[all data]
−3
Largest residuals (eÅ
Flack parameter
)

Table 2. Selected bond lengths [Å] and angles [°] for 1, 2, 1a–3a, 1b·DMSO, and 2c.
Compound
M
1
-
2
-
1a
2a
3a
1b·DMSO
2c
Ni
Pd
Pd
Pd
Pt
Molecule 1
Molecule 2
Molecule 1
Molecule 2
C(1)N(1)
C(6)C(1)
C(6)N(2)
C(6)S(1)
C(7)S(1)
C(8)N(2)
N(1)M
1.331(3)
1.529(3)
1.457(2)
1.8525(19)
1.765(2)
1.389(3)
1.313(3)
1.532(3)
1.456(2)
1.8543(19)
1.765(2)
1.392(3)
1.334(4)
1.526(4)
1.464(3)
1.869(2)
1.755(3)
1.384(3)
1.365(7)
1.477(7)
1.295(6)
---
1.357(6)
1.489(7)
1.287(7)
---
1.35(2)
1.50(3)
1.24(2)
---
1.34(2)
1.49(3)
1.25(2)
1.376(5)
1.477(5)
1.309(5)
---
1.358(3)
1.469(3)
1.294(3)
---
1.758(6)
1.425(6)
2.050(5)
2.013(4)
2.2301(16)
2.2974(15)
1.766(7)
1.434(7)
2.053(5)
2.001(4)
2.2369(19)
2.2949(14)
1.757(16)
1.43(2)
2.082(14)
2.012(13)
2.255(5)
2.283(5)
1.750(18)
1.41(2)
1.755(4)
1.426(5)
2.036(3)
1.980(3)
2.2545(11)
2.3039(11)
1.748(3)
1.430(3)
1.935(2)
1.8849(17)
2.1501(8)
2.1701(7)
2.082(16)
1.998(13)
2.252(5)
2.281(5)
N(2)M
MS(1)
MCl(1)
C(1)C(6)N(1)
C(8)N(2)C(6)
C(7)S(1)M
115.6(4)
129.5(4)
96.01(18)
-----
114.7(5)
128.1(4)
96.5(2)
-----
114.3(16)
127.7(16)
96.7(6)
-----
117.5(18)
125.1(16)
96.4(6)
-----
116.3(3)
127.5(3)
96.15(13)
-----
113.5(2)
126.28(19)
97.59(8)
-----
N(2)C(6)S(1)
C(8)N(2)C(6)
C(7)S(1)C(6)
N(1) MN(2)
N(1) MS(1)
N(1)MCl(1)
102.74(13)
112.81(15)
90.72(9)
102.54(13)
111.50(15)
89.50(9)
104.09(16)
115.1(2)
-----
-----
-----
-----
-----
-----
91.96(12)
-----
-----
-----
-----
-----
-----
81.66(16)
168.57(13)
96.97(13)
81.19(17)
169.36(12)
96.68(13)
80.6(6)
168.2(5)
97.3(5)
81.0(6)
168.3(4)
97.4(5)
81.28(13)
168.87(9)
96.93(9)
83.87(8)
172.88(6)
96.27(6)

3.4 X-ray crystallographic studies
Crystalline structures in solid state of 1, 2, 1a–3a, 1b, and 2c were stablished by
single-crystal X-ray diffraction analyses at room temperature. The complex 1b was
crystallized as a DMSO solvate. Crystallographic data are summarized in Table 1
and selected bond distances and angles are shown in Table 2. X-ray analyses of 1
and 3a displayed two independent molecules in the asymmetric unit.
3
.4.1 Molecular and crystalline structures of 1 and 2.
The molecular structures for compounds 1 and 2 are showed in Figure 2. The
analyses revealed that the bond lengths around the tetrahedral quaternary carbon
C(6) agree with the benzothiazoline form as the predominant one in solid state,
and are similar to other analogues where the substituents at C(6) atom are
hydrogen and phenyl groups [Error! Bookmark not defined.]. In this pair of
compounds there are several noncovalent interactions in the crystalline state
mainly due to the presence of hydrogen atoms covalently linked to electronegative
nitrogen atoms, besides to the presence of CH---S interactions and aromatic rings.
To describe the intermolecular interactions based on hydrogen bonding, we used
the graph analysis approach [[29]]. Both compounds exhibit intramolecular NH---N
and CH---S hydrogen bonds, and are described at the first level as S (5). The first
one is formed between the NH of the thiazoline ring and the pyridinic nitrogen atom
of one molecule, while the second intramolecular CH---S interaction is displayed
between the sulfur atom of the heterocyclic ring and the H2 of the pyridinic ring.
Both crystallographic different molecules in 1 also display centrosymmetric dimers
linked by intermolecular hydrogen bonds between the NH of thiazolidine ring of one
molecule and the pyridinic nitrogen of a neighboring molecule (Figure 3), described
ꢀ
by R (10). For 2, interactions of type CH [2.684 Å; interplanar angle 77.03°]
ꢀ
were observed; the molecules are related by a binary screw axis along the b
direction (Figure 3).

C11
C10
C9
C11
C10
C12
C7
C12
C9
C8
N2
C8
N2
C7
S1
C6
S1
C13
C14
C15
C6
C1
C2
N1
C15
C14
N3
C17
C16
C1
C13
C18
C5
C3
N1
C16
C4
C2
C5
C4
C3
N : S (5)
C17
1
1
2
Figure 2. Molecular drawing of benzothiazolines 1 and 2 (ORTEP 50% probability).
a
b
2.684 Å
2.684 Å
2.252 Å
2.684 Å
ꢁ
ꢁ
N
1
: R (10)
c
Figure 3. Hydrogen bonding and CH interactions in 1 and 2.
n
3
.4.2 Molecular and crystalline structures of complexes [M(L )Cl]
n
Structures of compounds of general formula [M(L )Cl] consist of neutral
mononuclear complexes with a distorted square planar local geometry for the M(II)
central cation, where the benzothiazoline compounds have been transformed to
n −
their corresponding Schiff bases, i.e., into their deprotonated open form {L }

2
(
Figure 4). In all complexes, the Schiff bases displayed a  N,S- tridentate
coordination mode, forming two five-membered chelate rings in a planar
conformation. The M-N(2) bond lengths of the iminic nitrogen atom in all
complexes are shorter than the M-N(1) lengths involving the pyridinic nitrogen
atom. These lengths are similar to those previously described for nickel, palladium,
and platinum complexes, [[30], [31], [32], [33], [34]], and they are indicative that the
iminic coordination compared to the pyridinic one is stronger, figure 5 [[35]]. In
particular, for the isostructural complexes 1a and 1b, the close similitude of the
bond distances around the metallic center (Pd or Pt) can be attributed to the
lanthanide contraction effect present in the 5d platinum(II) cation.

C16
C17
C16
C15
C14
O1
S2
C15
C14
C10
C17
N3
C9
N3
C10
C11
C13
C9
C11
C8
C6
C13
C12
C7
N2
C8
C6
C1
C2
C12
C3
C4
N2
C7
C2
C1
C3
C4
S1
N1
Pt
C5
S1
N1
Cl1
Pd
C5
Cl1
1
1
[
Pd(L )Cl] (1a)
[Pt(L )Cl]•DMSO (1b•DMSO)
C16
C16
C15
C14
C17
C17
C18
C15
C14
C10
C10
C11
C9
C18
C11
C9
C13
C13
C8
C6
C12
C6
C8
C7
N2
C12
C1
C2
C7
N2
C2
C1
C3
C4
C3
C4
S1
Pd
N1
S1
N1
Ni
C5
C5
Cl1
Cl1
2
2
[
Pd(L )Cl] (2a)
[Ni(L )Cl] (2c)
C10
C9
C11
C12
C8
C6
C7
N2
C1
C2
C3
S1
C4
Pd
N1
C5
Cl1
3
[
Pd(L )Cl] (3a)
n
Figure 4. Molecular structures of complexes [M(L )Cl] (ORTEP 50% probability).

In the crystals of 1a, 2a, 1b·DMSO, and 2c were observed dimeric
centrosymmetric M---M interactions in a head-to-tail fashion [1a, 3.5969(7) Å; 2a,
3
.6232(8) Å; 1b·DMSO of 3.6218(3) Å; 2c, 3.634(8) Å]. These M---M interactions
are larger than the van der Waals radii sum [ƩrvdW(Pd, Pd) = 3.26 Å; (Pt, Pt) = 3.44
Å] [[36]]; we adopted a less restricted criteria to analyze the intermolecular
interactions (ca. 4.0 Å) in conjunction with geometrical features. The M---M
interactions observed in our complexes are comparable to those observed in
square planar Ni(II), Pd(II), and Pt(II) complexes containing in their coordination
entity one chloro and either N,N,S- or S,S,N-tridentate ligands; the Pd---Pd lengths
in the complexes 1a and 2a are longer than the interactions described for
analogues of Pd(II) [36, [37]], whilst in 1b the Pt---Pt length is shorter than the
interaction found in the analogue complex of Pt(II) [[38]].
The compounds derived from the benzothiazoline
1
displayed both
centrosymmetric arrangements between two molecules linked by weak hydrogen
bonding (Figure 5).
3
.142 Å
3
.597 Å
3
.622 Å
2
.742 Å
1
1
[
Pd(L )Cl] (1a)
[Pt(L )Cl]∙DMSO (1b ∙DMSO)
Figure 5. Centrosymmetric dimers of 1a and 1b∙DMSO (the molecule of DMSO has
been omitted)
On the other hand, the structures of the palladium and nickel complexes 2a and 2c
are isomorphic (both crystallized in the P2 /n space group); the cell parameters are
1
shorter in the case of the smaller Ni(II) cation. Both displayed a similar
arrangement in the crystal, with CH---Cl and M---S (not showed for clarity)

interactions; in the figure 6 is showed the arrangement for the Ni(II) complex,
where the figures in parentheses are for the Pd(II) complex (2a). The difference of
2
1
a and 2c with the compounds containing a pyridinic substituent (1a and
b∙DMSO) is the presence of two CH---Cl interactions, because of the
unsubstituted phenyl group attached to C6.
3.633 Å (3.652 Å)
b
3.634 Å (3.623 Å)
a
c
2
Figure 6. Crystal packing of [Ni(L )Cl] (2c) showing some intermolecular
interactions (Ni---S, 3.353 Å; Pd---S, 3.605 Å). The data in parenthesis are for the
isomorphic compound 2a; yellow circles represent the inversion centers in the
P2
1
/n space group.
b
c
4
.825 Å
2
.988 Å
a
3
Figure 7. Crystal packing of [Pd(L )Cl] (3a) showing CH---Cl interactions; yellow
circles represent the inversion centers in the P−1 space group.

3.5. DFT studies
Several authors have mentioned the possible equilibrium between the ring (or
closed) form and the open (Schiff base) form. We study this equilibrium by DFT
methods. The proposed tautomerization mechanisms of benzothiazolines 1–3 are
shown in Figure 8 along their calculated energy profiles. Free energy changes ∆G,
†
activation barriers ∆G and equilibrium constants Keq of the ring-open form
1
2
3
conversions of compounds 1 (1→HL ), 2 (2→HL ) and 3 (3→HL ) are reported in
Table 3. The small values of the calculated equilibrium constants reveal that the
equilibria are strongly shifted towards the ring forms. These values agree with the
experimental data obtained in solution and solid state, which supports the ring form
(
benzothiazoline) as the predominant tautomer for 1–3.

†
Table 3. Free energy changes ∆G, activation barriers ∆G , and equilibrium
n
constants Keq for the tautomerization of n→HL (n = 1, 2, 3) and for the formation
of complexes 1a–3a, calculated in gas phase at 273 K at the PBEPBE/(Def2-
TZVP,SDD) level of theory.
†
−1
−1
Reaction
∆G /kcalmol
∆G/kcalmol
ꢂꢃꢄ
1
−9
−4
−6
1
2
3
1
1
2
3
→HL
→HL
→HL
30.7
27.0
32.1
22.8
21.7
23.4
24.2
31.9
23.0
10.4
4.7
4.53×10
1.89×10
1.65×10
2.5×10
2
3
7.2
1
4
4
7
7
→1a (pathway A)
→1a (pathway B)
→2a
−18.0
−18.0
−21.5
−22.0
10.2
−7.8
1
2.5×10
1.5×10
4.0×10
6.9×10
1
1
→3a
−9
[
[
Pd(1)Cl
Pd(1)Cl
2
]→1
6
2
]→1a
1.7×10
Figure 8. Free energy profile relative to the benzothiazolines 1–3 (reactants)
−1
1
(
kcalmol ) for their tautomerization process to yield Schiff bases HL (light blue)
2
3
HL (blue), and HL (dark blue), calculated in gas phase at 273 K at the
PBEPBE/(Def2-TZVP,SDD) level of theory. (Molecular structures correspond to the
1
tautomerization of 1 to HL ).

We also studied the formation of complexes of palladium 1a–3a. In this case, two
different reaction pathways are proposed (Figure 9). Mechanisms A (shown in
blue) are common to the three complexes 1a–3a and only differ in their relative
energies due to the different R groups. On the other hand, mechanism B (shown in
green) is exclusive to compound 1a. Mechanism B proceeds through the N,N-
bidentate complex [Pd(1)Cl ] and matches with mechanism A just before the final
2
−1
step. It is noteworthy that this intermediate is highly stable (10.2 kcalmol more
stable than the reactants) with backward and forward activation barriers of 31.9
−1
and 23.0 kcalmol , respectively, as shown in Table 3. Therefore, once [Pd(1)Cl ] is
2
formed, the backward reaction is unlikely because the large activation barrier, while
the forward reaction will proceed easily at room temperature. On the other hand,
−1
activation barriers at 0 ºC of mechanisms A and B are 22.8 and 21.7 kcalmol
respectively, indicating that mechanism B will be preferred at this temperature. This
result agrees with the observation of [Pd(1)Cl ] in solution by NMR. Moreover, the
2
very large equilibrium constants of the complexation reactions demonstrate that
they are irreversible.

−1
Figure 9. Free energy profiles relative to the 1–3 reactants (kcalmol ) for the formation of palladium(II) compounds 1a (red
and light blue), 2a (blue) and 3a (dark blue) calculated in gas phase at 273 K at the PBEPBE/(Def2-TZVP,SDD) level of
theory. Two different mechanisms, A (blue) and B (green) are possible for compound 1a.