Platinum and palladium bis(diphenylphosphino)ferrocene (dppf) complexes with heterocyclic N-acetamide ligands: Synthesis and molecular structures of [MCl(sac)(κ2-dppf)] (M = Pt, Pd, sac = saccharinate), [PtCl(ata)(κ2-dppf)] and [Pt(ata)2(κ 2-dppf)] (ataH = N-(2-thiazolyl)acetamide)

Article abstract of DOI:10.1016/j.ica.2012.12.010

Room temperature addition of sodium saccharinate, Na(sac), to [MCl ₂(κ²-dppf)] (M = Pd, Pt; dppf = 1,1′- bis(diphenylphosphino)ferrocene) results in the formation of [MCl(sac)(κ²-dppf)] in which the sac ligand is coordinated in a monodentate fashion through nitrogen. All attempts to coordinate a second saccharinate ligand were unsuccessful. In contrast, reaction of [PtCl ₂(κ²-dppf)] with N-(2-thiazolyl)acetamide (ataH) in the presence of KOH results in successive replacement of both chlorides affording [PtCl(ata)(κ²-dppf)] and [Pt(ata)₂(κ ²-dppf)]. Crystal structures have determined for all four complexes. In both saccharinate complexes and [PtCl(ata)(κ²-dppf)] the heterocyclic amide ligand is coordinated as expected through the amide-nitrogen. In contrast in Pt(ata)₂(κ²-dppf) both ligands are bound through the nitrogen atom of the thiazole ring. In order to understand the adoption of these different ligand binding modes, geometry optimization calculations were carried out on different isomers of both ata complexes. For [PtCl(ata)(κ²-dppf)] an energy difference of 10.5 kJ mol ^-1 was found between observed and unobserved isomers, while for [Pt(ata)₂(κ²-dppf)] the difference was 9.3 kJ mol^-1. The reasons for the adoption of these different coordination modes are not clear but steric factors are likely to be a major contributory factor.

Full text of DOI:10.1016/j.ica.2012.12.010

Inorganica Chimica Acta 398 (2013) 46–53
Contents lists available at SciVerse ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Platinum and palladium bis(diphenylphosphino)ferrocene (dppf) complexes
with heterocyclic N-acetamide ligands: Synthesis and molecular structures
of [MCl(sac)(
and [Pt(ata)2(
j j
2-dppf)] (M = Pt, Pd, sac = saccharinate), [PtCl(ata)( 2-dppf)]
j
2-dppf)] (ataH = N-(2-thiazolyl)acetamide)
a
b,
c
Subhi A. Al-Jibori a, , Amina I.A. Al-Nassiry , Graeme Hogarth , Luca Salassa
⇑
⇑
a Department of Chemistry, College of Science, University of Tikrit, Tikrit, Iraq
b Department of Chemistry, University College London, 20 Gordon Street, London WCIH OAJ, UK
c Department of Chemistry, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
a r t i c l e i n f o
a b s t r a c t
Room temperature addition of sodium saccharinate, Na(sac), to [MCl2(j2-dppf)] (M = Pd, Pt; dppf = 1,10-
bis(diphenylphosphino)ferrocene) results in the formation of [MCl(sac)(
2-dppf)] in which the sac ligand
is coordinated in a monodentate fashion through nitrogen. All attempts to coordinate a second sacchari-
nate ligand were unsuccessful. In contrast, reaction of [PtCl2(
2-dppf)] with N-(2-thiazolyl)acetamide
(ataH) in the presence of KOH results in successive replacement of both chlorides affording [PtCl(ata)
2-dppf)] and [Pt(ata)2( 2-dppf)]. Crystal structures have determined for all four complexes. In both
saccharinate complexes and [PtCl(ata)(
2-dppf)] the heterocyclic amide ligand is coordinated as expected
through the amide-nitrogen. In contrast in Pt(ata)2(
2-dppf) both ligands are bound through the nitrogen
Article history:
Received 21 September 2012
Received in revised form 6 December 2012
Accepted 7 December 2012
Available online 19 December 2012
j
j
(
j
j
Keywords:
Palladium
Platinum
Saccharinate
Acetamide
j
j
atom of the thiazole ring. In order to understand the adoption of these different ligand binding modes,
geometry optimization calculations were carried out on different isomers of both ata complexes. For
[PtCl(ata)(
isomers, while for [Pt(ata)2(
j
2-dppf)] an energy difference of 10.5 kJ molꢀ1 was found between observed and unobserved
Linkage isomerism
Diphosphane
j
2-dppf)] the difference was 9.3 kJ molꢀ1. The reasons for the adoption of these
different coordination modes are not clear but steric factors are likely to be a major contributory factor.
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
[7,8]. In this respect, platinum(II) complexes are of special interest
due to the commercial use of cis-platin and related species in
There is considerable current interest in the coordination chem-
istry of the saccharinate (sac) ligand [1–5] primarily since the
amide moiety is an important constituent of many biologically
important compounds. Acid amide ligands in general have two
potential coordination sites, the imine nitrogen and the carbonyl
oxygen, while saccharinate also has two sulfonyl oxygen groups
which can potentially coordinate to a metal [1–5]. As polyfunction-
al ligands, cyclic acetamides are able to form complexes with a
wide range of metal ions. These generally take the form of mono-
nuclear complexes, however, they are also known to form coordi-
nation polymers and in the case of bulky ligands such as sac they
sometimes act as a simple counterion remaining outside of the
coordination sphere [1,6].
chemotherapy [9]. The metal-containing diphosphane bis(diphen-
ylphosphino)ferrocene (dppf) and related derivatives are of partic-
ular interest, the high flexibility of the iron-cyclopentadienyl units
allowing bite-angle changes to occur via low-energy pathways
[10–12]. As part of our efforts to develop biologically active bifunc-
tional compounds, we have studied the incorporation of two
biologically active ligands in the same complex, for example phos-
phanes and thiones or amides [13–21]. As a continuation to this
work we report herein the preparation of platinum(II) and palla-
dium(II) bis(diphenylphosphino)ferrocene (dppf) complexes with
heterocyclic N-acetamide co-ligands, the latter being derived from
saccharine (sacH) and N-(2-thiazolyl)acetamide (ataH) (Scheme 1).
Metal complexes of bidentate phosphanes have received signif-
icant attention as a result of their potential use as antitumor agents
2. Experimental
2.1. General
⇑
Corresponding authors.
E-mail addresses: subhi_aljibori@yahoo.com (S.A. Al-Jibori), g.hogarth@ucl.ac.uk
NMR spectra were recorded on Varian Unity 500 or Gemini
200 spectrometers at the Institute for Anorganische Chemie,
(G. Hogarth).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.12.010

S.A. Al-Jibori et al. / Inorganica Chimica Acta 398 (2013) 46–53
47
washed with hexane and dried under vacuum. Crystallization from
a mixture of CHCl3/MeOH/EtOH afforded 0.08 g (ca. 65%) of a
highly crystalline orange solid consisting predominantly of orange
O
S
O
O
N
H
N
rod-like crystals of [Pt(ata)2(
small number of small yellow blocks shown to be [PtCl(ata)
2-dppf)] (3). Close inspection of crystals of 4 under a microscope
j
2-dppf)] (4) but also containing a
S
O
N
H
(j
showed that they consisted of a series of stacked thick plates. The
crystals did extinguish under plane polarized light but attempts to
get a good quality cell from preliminary X-ray data were not suc-
cessful. Careful cleavage of one of these crystals gave a thin rod
suitable for X-ray diffraction. (3) 1H NMR: 328 K d 8.5–6.9 (m,
Ar + @CH), 6.50 (br, 1H, CH), 5.72 (vbr, 1H, CH), 4.68 (s, 1H, CH),
4.52 (s, 1H, CH), 4.18 (s, 2H, CH), 3.49 (s, 2H, CH), 2.49 (brs, 3H,
Me); 31P{1H} NMR: 328 K d 14.41 (d, JPP 16.2 Hz, JPtP 4048 Hz),
4.29 (d, JPP 16.2 Hz, JPtP 3290 Hz). (4) 1H NMR: d 7.74–6.98 (m,
20H, Ph), 6.65 (d, J 4.2 Hz, 1H, @CH), 6.03 (d, J 4.2 Hz, 1H, @CH),
4.83 (s, 2H, CH), 4.44 (s, 2H, CH), 4.32 (s, 2H, CH), 4.14 (s, 2H,
sacH
ataH
Scheme 1.
Martin-Luther-Universitat, Halle, Germany or on a Bruker AMX400
spectrometer at University College London and referenced inter-
nally to the residual solvent peak (1H and 13C) or externally (31P).
All spectra were run in CDCl3. IR spectra were recorded on a Shima-
dzu FT8400 spectrometer as CsI discs. Elemental analyses were
carried out at University College London. Conductivity measure-
ments were made on a conductivity meter type Philips PW9526.
Melting points were measured on electro thermal 9300 melting
CH), 2.34 (s, 3H, Me); 31P{1H} NMR: d 3.38 (JPtP 3519 Hz); IR
m/
cmꢀ1; IR(KBr) 3086w, 2964w, 2921w, 1620s, 495s cmꢀ1; Elemental
Anal. Calc. for PtFeS2N4P2O2C44H38: C, 51.22; H, 3.71; N, 5.43.
Found: C, 51.20; H, 3.90; N, 5.70%.
point apparatus. [PdCl2(j j
2-dppf)], [PtCl2( 2-dppf)] and sodium sac-
charinate were purchased and used without further purification and
N-(2-thiazolyl)acetamide [22] was prepared according to literature
methods. All reactions were carried out in air using standard labora-
tory solvents.
2.5. X-ray crystallography
Single crystals were mounted on glass fibers and all geometric
and intensity data were taken from these samples using a Bruker
SMART APEX CCD diffractometer using graphite-monochromated
2.2. [PtCl(sac)(j
2-dppf)] (1)
Mo K
carried out with SAINT
a
radiation (k = 0.71073 Å) at 150 2 K. Data reduction was
LUS and absorption correction applied using
A warm ethanol (10 cm3) solution of sodium saccharinate
(0.096 g, 0.47 mmol) was added to a chloroform (20 cm3) solution
P
the program SADABS [23]. Structures were solved by direct-methods
and developed using alternating cycles of least-squares refinement
and difference-Fourier synthesis. All non-hydrogen atoms were re-
fined with anisotropic displacement parameters. Hydrogen atoms
were placed in calculated positions (riding model). Structure solu-
of [PtCl2(j
2-dppf)] (0.20 g, 0.23 mmol). The turbid yellow mixture
was stirred at room temperature for 3 h then filtered. The filtrate
was set aside to evaporate slowly at room temperature. The yellow
crystals of [PtCl(sac)(j
2-dppf)] (1) thus formed were filtered off
and dried under vacuum (0.17 g, 72% yield). 1H NMR: d 8.13–6.93
(m, 24H, Ar), 5.35 (s, 1H, CH), 4.89 (s, 1H, CH), 4.67 (s, 1H, CH),
4.54 (s, 1H, CH), 4.45 (s, 1H, CH), 4.38 (s, 1H, CH), 4.19 (s, 1H,
CH), 3.44 (s, 1H, CH), 3.38 (s, 1H, CH); 31P{1H} NMR: d 15.30 (JPP
tion used SHELXTL
P
LUS V6.10 program package [24].
Crystallographic data: [PtCl(sac)(
j
2-dppf)] (1): yellow block, size
0.28 mm ꢁ 0.16 mm ꢁ 0.14 mm, orthorhombic, space group
P212121, a = 10.4220(9) Å, b = 16.233(2) Å, c = 21.504(2) Å, V =
14.5, JPtP 3820 Hz), 6.01 (JPP 14.5, JPtP 3605 Hz). IR
3058w, 3016w, 2925w, 2860w, 1766s, 1587m, 1434m, 1299s,
1249s, 1161vs, 960m, 480s cmꢀ1
Elemental Anal. Calc. for
m
/cmꢀ1; IR(KBr)
3638.0(6) Å3, Z = 4, Dcalc = 1.766 g/cm3,
l
= 4.450 mmꢀ1, F(000) =
1904, final R indices [F2 > 2
(all data) R1 = 0.040, wR2 = 0.064. [PdCl(sac)(
r
] R1 = 0.039, wR2 = 0.062, R indices
2-dppf)] (2): orange
;
j
PtFeSNClP2O3C41H32: C, 50.92; H, 3.34; N, 1.45. Found: C, 51.00;
H, 3.50; N, 1.60%.
block, size 0.26 mm ꢁ 0.22 mm ꢁ 0.12 mm, orthorhombic, space
group P212121, a = 10.418(1) Å, b = 16.197(2) Å, c = 21.507(3) Å,
V = 3629.0(8) Å3, Z = 4, Dcalc = 1.608 g/cm3,
l ,
= 1.156 mmꢀ1
2.3. [PdCl(sac)(j
2-dppf)] (2)
F(000) = 1776, final R indices [F2 > 2
indices (all data) R1 = 0.051, wR2 = 0.090. [PtCl(ata)(
yellow block, size 0.08 mm ꢁ 0.08 mm ꢁ 0.07 mm, triclinic, space
r
] R1 = 0.042, wR2 = 0.087, R
j
2-dppf)] (3):
A warm ethanol (10 cm3) solution of sodium saccharinate
(0.112 g, 0.55 mmol) was added to a chloroform (20 cm3) solution
ꢀ
group P1, a = 10.389(1) Å, b = 10.558(1) Å, c = 17.298(2) Å,
77.669(2)°, b = 85.180(2)°,
= 69.840(2)°, V = 1739.9(4) Å3, Z = 2,
Dcalc = 1.768 g/cm3, = 4.697 mmꢀ1, F(000) = 912, final R indices
[F2 > 2
] R1 = 0.041, wR2 = 0.083, R indices (all data) R1 = 0.051,
wR2 = 0.088. [Pt(ata)2(
2-dppf)] (4): orange needle, size
a =
of [PdCl2(
dure to above, [PdCl(sac)(
j
2-dppf)] (0.20 g, 0.27 mmol). Following a similar proce-
c
j
2-dppf)] (2) was isolated as a red-brown
l
crystalline solid in 83% yield. 1H NMR: d 8.31–7.01 (m, 24H, Ar),
4.32 (br, 4H, CH), 3.42 (br, 4H, CH); 31P{1H} NMR: d 37.20 (d, JPP
r
j
12.7 Hz), 28.99 (d, JPP 12.7 Hz). IR m
/cmꢀ1; IR(KBr) 3058w, 3051w,
0.22 mm ꢁ 0.08 mm ꢁ 0.06 mm, monoclinic, space group P21, a =
2972w, 2918w, 1670s, 1586m, 1433m, 1294s, 1247s, 1155vs,
12.422(2) Å, b = 23.007(4) Å, c = 17.388(3) Å, b = 100.469(3)°,
962m, 482s cmꢀ1; Elemental Anal. Calc. for PdFeSNClP2O3C41H32
:
V = 4886.5(14) Å3, Z = 2, Dcalc = 1.402 g/cm3,
l ,
= 3.344 mmꢀ1
F(000) = 2048, final R indices [F2 > 2
r] R1 = 0.097, wR2 = 0.239, R
C, 56.06; H, 3.67; N, 1.59. Found: C, 56.26; H, 3.40; N, 1.70%.
indices (all data) R1 = 0.140, wR2 = 0.264.
2.4. [PtCl(ata)(j j
2-dppf)] (3) and [Pt(ata)2( 2-dppf)] (4)
2.6. Computational details
A solution of ataH (0.027 g, 0.19 mmol) in ethanol (5 cm3) and
1 cm3 of KOH in ethanol (0.19 mmol, 0.5N) was added to a yellow
Calculations were performed with the GAUSSIAN 03 (G03) pro-
gram package [25] employing the DFT method with Becke three
parameter hybrid functional [26] and Lee–Yang–Parr’s gradient
corrected correlation functional (B3LYP) [27]. Geometry optimiza-
tion was performed employing a two-layered ONIOM approach
[28]. The LanL2DZ basis set [29] and effective core potential were
solution of [PtCl2(j
2-dppf)] (0.08 g, 0.09 mmol) in chloroform
(15 cm3). The orange mixture thus formed was stirred at room
temperature for 3 h then filtered. The filtrate was reduced in vol-
ume by half and methanol (5 cm3) added. The mixture was set
aside for few days. The orange solid thus formed was filtered off

48
S.A. Al-Jibori et al. / Inorganica Chimica Acta 398 (2013) 46–53
used for the atoms in the higher-level layer, while the STO-3G basis
set was used to describe the lower-level layer. All atoms except the
carbons and hydrogens belonging to phenyl substituents were in-
cluded in the first layer. The geometry was calculated in the gas
phase. The electronic structure of all derivatives was obtained with
a single-point calculation at the B3LYP/LanL2DZ level, without
employing the ONIOM approach. NBO (natural bonding orbital)
method [30] was used in order to analyze the electronic structures.
All atoms are labeled according to X-ray schemes.
are observed. Two of these (at d 3.42 and 4.23) are very sharp, a
third at d 5.01 shows some broadening, while the final resonance
at ca. d 5.3–5.2 is broadened into the baseline. We attribute these
observations to the well-known fluxionality of the dppf ligand
[10–12]. IR spectra show the expected features for such complexes
[1,2]. Strong CO stretches were observed at 1676 and 1670 cmꢀ1
respectively shifted to a higher frequency than that of the free
ligand (1643 cmꢀ1) [1]. These higher shifts of the CO stretching fre-
quencies are indicative of an N-coordination of the saccharinate
anion. The spectra also showed strong m(SO2)asy and m(SO2)sym. at
1249, 1161 and 1247, 1154 cmꢀ1 for the platinum and palladium
complexes respectively, shifted slightly to either higher or lower
frequency from that of the free ligand indicating a non coordina-
tion of the group SO2.
3. Results and discussion
3.1. Synthesis and molecular structures of saccharinate complexes
[MCl(j
2-dppf)(sac)] (1–2)
In order to fully confirm the spectroscopic assignments, single
crystal X-ray studies were carried out on both 1 and 2 the results
of which are summarized in Fig. 1 and its caption. The two are iso-
structural both crystallizing in the orthorhombic P212121 space
group. The molecular structures are closely related to that of cis-
[PtCl(sac)(PPh3)2] reported by Henderson et al. [31]. The sac ligand
is N-bound and metal nitrogen distances are virtually identical
[2.083(4) in 1 and 2.084(3) Å in 2] being slightly longer than that
of 2.064(6) Å found in cis-[PtCl(sac)(PPh3)2]. Likewise, the metal-
chloride distance of 2.342(1) in 1 is comparable with that of
2.340(2) Å in cis-[PtCl(sac)(PPh3)2], while in 2 it is slightly shorter
[2.331(1) Å]. The two monodentate phosphanes in cis-[PtCl
(sac)(PPh3)2] subtend an angle of 99.09(8)° at the metal center
[31], while bite-angles for the dppf ligand in 1 and 2 are 99.69(5)
and 99.48(4)° respectively, showing clearly how the flexible dppf
ligand can relax to the most favorable coordination geometry.
The planar sac ligand lies orthogonal to the PtNClP2 plane (M = Pt
for 1, Pd for 2) forming dihedral angles of 64.6 and 63.7° for 1
and 2 respectively.
Saccharinate is known to bind to metal centers in a number of
different ways [1], although monodentate coordination via the
nitrogen atom is by far the most common. Thus while platinum
and palladium complexes containing both phosphanes and saccha-
rinate ligands are relatively rare [31–34] in all instances the sac-
charinate ligand is found to be N-coordinated. For the synthesis
of mixed ligand platinum(II) or palladium(II) phosphane com-
plexes, common starting materials are [MCl2(phosphane)2] since
the chlorides are labile and thus readily displaced by anionic
ligands. Using this strategy, the new complexes [MCl(sac)
(
j
2-dppf)] (1–2) were easily prepared upon addition of Na(sac) to
[MCl2(
j
2-dppf)] (M = Pt or Pd). Attempts to substitute the second
chloride upon addition of excess of Na(sac) were unsuccessful
(Scheme 2).
Both 1–2 were readily characterized by a combination of ana-
lytical and spectroscopic data. The 31P{1H} NMR spectra were par-
ticularly informative. Thus [PtCl(sac)(j
2-dppf)] (1) shows an AXZ
splitting pattern consisting of two doublets (JPP 14.5 Hz) with plat-
inum satellites (PA 15.3 ppm, JPtP 3820 Hz; PX 6.01 ppm, JPtP
3605 Hz). This clearly shows that the two phosphorus atoms are
non-equivalent suggesting that a single chloride has been substi-
tuted. We assign the higher frequency signal to the phosphorus
atom lying trans to chloride as this compares well with the re-
Over the past few years a number of other platinum and palla-
dium saccharinate complexes have been reported [37–42]. Closely
related to the work reported herein, Yilmaz and co-workers have
shown that reactions of [M(dpya)Cl2] (M = Pt, Pd; dpya = 2,20dipyr-
idylamine) with two equivalents of Na(sac) in the presence of
AgNO3 affords [M(dpya)(sac)2] in which both saccharinate ligands
are N-bound [38]. It is not immediately clear why a second chlo-
ride substitution is not observed in our case. Henderson and
co-workers have noted related behavior in the addition of Na(sac)
to [PtCl2(PPh3)2] which affords cis-[PtCl(sac)(PPh3)2] even upon
addition of excess Na(sac) and prolonged heating [31]. Interest-
ingly, the analogous palladium complex, [PdCl2(PPh3)2] reacts with
Na(sac) to afford trans-[PdCl(sac)(PPh3)2] exclusively [31]. Most
pertinent to this work, Henderson also found that addition of a
ported data for [PtCl2(
wise the high field signal compares well with that reported for
[Pt(az)2(
2-dppf)] (az = pyrazole) (7.87 ppm, JPtP 3483 Hz) [35]
suggesting that it lies trans to nitrogen. The 31P{1H} NMR spectrum
of the palladium complex [PdCl(sac)(
2-dppf)] (2) shows a similar
j
2-dppf)] (14.2 ppm, JPtP 3762 Hz) [34]. Like-
j
j
NMR pattern; a doublet at 37.2 ppm (JPP 13 Hz) is assigned to phos-
phorus trans to chloride and compares well with data for [PdCl2
(j
2-dppf)] (34.0 ppm) [36], while a second doublet at 28.99 ppm
is assigned to phosphorus trans to nitrogen of the saccharinate an-
ion. The 1H NMR spectra of both 1–2 showed signals due to the
cyclopentadienyl protons within the range d 3.38–5.30, and phenyl
protons between d 6.93 and 8.31. For 1 the 1H NMR spectrum was
quite sharp at room temperature and eight cyclopentadienyl sig-
nals could be clearly resolved. This shows that the solid-state con-
formation is maintained in solution at this temperature. For 2 the
spectrum is much broader and only four cyclopentadienyl signals
large excess of Na(sac) to [PtCl2(
j
2-dppe)] yielded only [PtCl
(sac)(j
2-dppe)], which like 1–2 is constrained to the cis-conforma-
tion [31]. Given that both cis and trans variants only result in a sin-
gle chloride substitution it is tempting to suggest that substitution
of the second chloride is sterically unfavorable, rather than being
the result of an adverse trans-effect. Henderson has also reported
that reaction of [PtCl2(
j
2-dppf)] with the sodium salt of 5,5-dieth-
Ph2
P
Ph2
P
Cl
Cl
Na(sac)
O
Fe
M
Fe
M
O
MeOH
- NaCl
S
N
Cl
P
P
Ph2
Ph2
O
1 M = Pt, 2 M = Pd
Scheme 2.

S.A. Al-Jibori et al. / Inorganica Chimica Acta 398 (2013) 46–53
49
Fig. 1. Two views of the molecular structure of [PtCl(dppf)(sac)] (1). Selected bond lengths and angles; (1) Pt(1)–Cl(1) 2.342(1), Pt(1)–N(1) 2.083(4), Pt(1)–P(1) 2.268(1),
Pt(1)–P(2) 2.263(1), P(1)–Pt(1)–P(2) 99.69(5), P(1)–Pt(1)–Cl(1) 174.42(5), P(2)–Pt(1)–N(1) 167.3(1), P(1)–Pt(1)–N(1) 90.0(1), Cl(1)–Pt(1)–N(1) 88.1(1). For isostructural
[PdCl(dppf)(sac)] (2): Pd(1)–Cl(1) 2.331(1), Pd(1)–N(2) 2.084(3), Pd(1)–P(1) 2.300(1), Pd(1)–P(2) 2.279(1), P(1)–Pd(1)–P(2) 99.48(4), P(1)–Pd(1)–Cl(1) 174.50(4), P(2)–Pd(1)–
N(2) 167.92(9), P(1)–Pd(1)–N(2) 89.6(1), Cl(1)–Pd(1)–N(2) 89.4(1).
ylbarbituric acid, Na(debarb), also leads to a single chloride
some unreacted [PtCl2(j
2-dppf)]. When two equivalents of ataH
substitution to give [PtCl(debarb)(
j
2-dppf)] even under forcing
were employed a similar mixture was isolated but this time 4 was
the major component (4:3 ca. 3:1) and there was also some unre-
acted N-(2-thiazolyl)acetamide. Crystallization of this crude prod-
uct from a mixture of CHCl3/MeOH/EtOH gave a highly crystalline
sample which was shown to consist predominantly of 4 (see below)
Careful inspection of the yellow–orange crystalline material under a
microscope showed that two crystal types were present, namely a
small number of dark yellow cubes of 3 together with mainly larger
orange rod-like crystals of 4. An X-ray diffraction study of
conditions [42], while a single 30,50-diacetylthymidine group binds
to the platinum-dppf center [43].
3.2. Synthesis and molecular structures of N-(2-thiazolyl)acetamide
complexes, [PtCl(ata)(j j
2-dppf)] (3) and [Pt(ata)2( 2-dppf)] (4)
In contrast to the well-developed chemistry of the saccharin
and saccharinate, the coordination chemistry of related N-(2-thiaz-
olyl)acetamide (ataH) (Scheme 1) has not been widely studied. An
early paper by Hughes and Rutt [22] showed that addition of ataH
to Ni(II) halides results in formation of six-coordinate complexes,
[NiX2(ataH)2] (X = Cl, Br, I), in which the N-(2-thiozole)acetamide
was proposed to bind to the metal center via the thiazole nitrogen
and the carbonyl oxygen resulting in formation of a six-membered
ring. The anionic form of the ligand, resulting from deprotonation
of the nitrogen center, appears not to have previously been studied.
[PtCl(ata)(j
2-dppf)] (3) was carried out the resultsof whichare sum-
marized in Fig. 2 and its caption.
The molecule consists of the expected square-planar platinum
center ligated by dppf, chloride and a deprotonated N-(2-thiazol-
yl)acetamide ligand being bound to platinum through the amide
nitrogen. The platinum–nitrogen bond distance of 2.092(4) Å com-
pares well with that of 2.083(4) Å in 1. Both bonds between the
coordinated nitrogen and adjacent carbon atoms [N(1)–C(1)
1.380(6) and N(1)–C(4) 1.358(7) Å] are clearly single bonds as com-
pared to the shorter C(1)–N(2) bond of 1.298(7) Å with the thiazole
ring. Platinum–chloride [Pt(1)–Cl(1) 2.340(1) Å] and platinum–
phosphorus [Pt(1)–P(1) 2.271(1) and Pt(1)–P(2) 2.257(1) Å] dis-
Addition of one equivalent of ataH to [PtCl2(
ence of NaOH afforded a yellow solid which was shown by spectros-
copy to be a mixture of [PtCl(ata)(
2-dppf)] (3) and [Pt(ata)
2-dppf)] (4) in an approximate 4:1 ratio (Scheme 3) together with
j
2-dppf)] in the pres-
j
(j
O
O
N
S
Ph2
P
Ph2
S
N
P
ataH
N
2 ataH
Fe
Pt
N
PtCl2(dppf)
Fe
Pt
P
NaOH
EtOH/CHCl3
NaOH
EtOH/CHCl3
Cl
N
Ph2
P
N
Ph2
O
S
3
4
Scheme 3.

50
S.A. Al-Jibori et al. / Inorganica Chimica Acta 398 (2013) 46–53
Fig. 2. Two views of the molecular structure of [PtCl(dppf)(ata)] (3). Selected bond lengths and angles; Pt(1)–N(1) 2.092(4), Pt(1)–Cl(1) 2.340(1), Pt(1)–P(1) 2.271(1), Pt(1)–
P(2) 2.257(1), N(1)–C(1) 1.380(6), N(1)–C(4) 1.358(7), C(1)–N(2) 1.298(7), N(2)–C(2) 1.376(6), C(2)–C(3) 1.342(8), C(3)–S(1) 1.731(6), S(1)–C(1) 1.752(5), C(4)–O(1) 1.239(6),
P(1)–Pt(1)–P(2) 97.40(5), N(1)–Pt(1)–Cl(1) 85.46(1), P(1)–Pt(1)–N(1) 172.8(1), P(2)–Pt(1)–Cl(1) 175.3(4).
Table 1
A comparison of bond lengths and angles in ataH (L) and complexes 3 and 4.
H
O
C3
S
H
C4
C2
H
C1
C5
N2
E1
H
N1
E2
H
4 N(7)
4 N(5)
4 N(3)
4 N(1)
3
L
2.08(2)
1.70(2)
1.73(2)
1.30(3)
1.40(2)
1.40(2)
1.30(2)
1.24(3)
118(2)
1.94(2)
1.73(2)
1.80(3)
1.43(2)
1.49(3)
1.43(2)
1.35(2)
1.37(3)
120(3)
2.08(1)
1.75(2)
1.66(3)
1.20(2)
1.35(2)
1.35(2)
1.34(2)
1.26(2)
120(2)
2.07(2)
1.86(2)
1.78(2)
1.30(3)
1.26(3)
1.37(2)
1.37(3)
1.29(3)
121(2)
2.092(4)
1.752(5)
1.731(6)
1.298(7)
1.380(6)
1.380(6)
1.358(7)
1.239(6)
119.6(4)
Pt–N
S–C1
S–C3
N1–C1
N2–C1
N1–C2
N2–C4
C4–O
1.733(2)/1.728(2)
1.724(2)/1.727(2)
1.311(2)/1.311(2)
1.379(2)/1.381(2)
1.385(2)/1.384(2)
1.366(2)/1.371(2)
1.221(2)/1.223(2)
123.7(2)/123.7(1)
C1–N2C4
tances are also similar to those found in 1 and the substituents on
the metal-bound nitrogen lie approximately perpendicular to the
PtP2ClN square-plane, the biggest deviation from the latter being
in the P–Pt–P bite-angle of 97.40(5)°. The molecules pack in such
a way as to generate a number of short contacts. Many of these
are between ring-bound protons and the chloride atom, but notably
there is a short contact between C(18) atoms of one of the phenyl
rings [C(18A)–C(18B) 3.226 Å].
Key metric parameters in 3 can be compared with those in the
free ligand (two molecules in the asymmetric unit) [44] and are
summarized in Table 1. Three resonance structures can be drawn
for the amide ligand (Scheme 4) with (a) dominating the structure.
It is clear from Table 1 that the metric parameters within the depro-
tonated N-(2-thiazolyl)acetamide ligand do not change markedly
upon exchange of a proton for the platinum(II) center. Bond lengths
within the thiazole ring do not vary significantly suggesting that res-
onance form (c) does not contribute significantly to the structure.
The carbon–oxygen (C4–O1) bond lengthens slightly (ca. 0.02 Å)
and there is a concomitant shortening (ca. 0.015 Å) of the nitro-
gen–carbon (C4–N2) which can be attributed to some contribution
from resonance form (b). Coordination also leads to a small change
in the bond angle at the coordinated nitrogen atom being
119.4(4)° in 3 some 4° less than in the free ligand. This change is
probably due to the steric demands of the [PtCl(j
2-dppf)] moiety.
We have not been able to obtain 3 pure and thus spectroscopic
characterization is based on data from mixtures of varying ratios
with 4. In CDCl3 at room temperature, a slightly broadened pair
of doublets are seen at 14.41 and 4.29 ppm (JPP 16.2 Hz) in the
31P{1H} NMR spectrum with platinum satellites of 4034 and
3326 Hz respectively. These broaden slightly and sharpen upon
cooling to 278 K and upon warming to 328 K. The 1H NMR spec-
trum is complicated at all temperatures and we were unable to
identify the resonances associated with the vinyl protons of the
ata ligand, presumably being masked by the aromatic resonances.
At room temperature peaks associated with the cyclopentadienyl
groups were very broad and we were unable to confidently assign
them but upon heating to 328 K a series of singlets were apparent
most of which could easily be assigned, although some were

S.A. Al-Jibori et al. / Inorganica Chimica Acta 398 (2013) 46–53
51
O
O
O
S
S
S
N
Pt
N
Pt
N
N
N
N
Pt
(b)
(a)
(c)
Scheme 4.
Fig. 3. Two views of one of the independent molecules of [Pt(dppf)(ata)2] (4). For selected bond lengths and angles see Table 1.
still quite broad. The methyl resonance was easily observed at all
temperatures appearing as a slightly broad singlet at d 2.49 (at
328 K). The temperature dependent nature of these spectra is prob-
ably a result of the well-known fluxionality of the dppf ligand [10],
however, we cannot rule out the possibility that the N-(2-thiazol-
yl)acetamide ligand has temperature-dependent mobility, espe-
cially the restricted rotation about the platinum–nitrogen bond.
From the work-up described above a relatively pure sample of
tals of 4 (see Section 2) were isolated, the molecule crystallizing
in the P21 space group with two independent molecules in the
asymmetric unit. All attempts to solve the structure in another
monoclinic space group failed. In the final refinement there were
no correlation matrix factors greater than 0.5 suggesting that the
two molecules are crystallographically different. The final data
are relatively poor and two large ghost peaks are seen near to both
independent platinum atoms. Nevertheless a clear picture of the
connectivity of the molecule can be established and some consid-
eration of the bond lengths and angles within the ata ligands is
possible. The molecular structure of one of these molecules to-
gether with important bond lengths and angles is given in Fig. 3
and its caption.
Each molecule consists of the expected square-planar platinum
core with chelating dppf and two monodentate ata ligands. Most
notable is the coordination mode of the latter, both being bound
to the metal center via the nitrogen of the thiazole ring. In such a
binding mode, a number of resonance structures need to be consid-
ered (Scheme 5). The first (a) involves an uncharged ligand, while
others (b–d) are zwitterionic and in (c–d) the aromaticity of the
thiazole ring has been retained. A comparison of some bond
lengths within the ata ligands of 4 (numbered with respect to
the metal-bound nitrogen atom) and 3 as compared to those in
the free ligand [45] is given in Table 1.
[Pt(ata)2(j
2-dppf)] (4) was obtained (Scheme 3). The elemental
analysis was consistent with the replacement of both chlorides
and concomitant addition of two ata ligands, while the molar con-
ductivity (2.3 Oꢀ1 cmꢀ1 molꢀ1) was clearly indicative of a non-io-
nic system. The 31P{1H} NMR spectrum showed only a singlet
resonance at 3.38 ppm with associated platinum satellites (JPtP
3519 Hz) indicative of the substitution of both halides and forma-
tion of a high symmetry Pt(II) center in which both ata ligands
were bound in the same fashion. The IR spectrum revealed the dis-
appearance of the m(CO) stretching vibration of the free ataH ligand
at 1666 cmꢀ1 and the appearance of a new band at 1620 cmꢀ1. The
1H NMR spectrum showed the expected methyl resonance as a sin-
glet at d 2.29 and four cyclopentadienyl environments at d 4.14,
4.32, 4.45 and 4.82. The spectrum also contained a pair of doublets
at d 5.93 and 6.60 ppm (J 3.9 Hz) attributed to the protons on the
thiazole ring near to sulfur and nitrogen respectively, being shifted
to lower frequency with respect to the free ligands (d 6.98 and
7.42 ppm).
It is clear that while three of the ata ligands in 4 are somewhat
similar the fourth (binding through N(5)) is quite different. Given
the quality of the crystallographic data only metric parameters from
the three consistent ata ligands will be considered. The Pt–N dis-
tances in the three similar ligands range from 2.07(2) to 2.08(2) Å
On the basis of spectroscopic and analytical data it was not pos-
sible to unequivocally determine the coordination mode of the
deprotonated N-(2-thiazolyl)acetamide ligands. Low quality crys-

52
S.A. Al-Jibori et al. / Inorganica Chimica Acta 398 (2013) 46–53
O
O
O
O
S
S
S
S
N
N
N
N
N
N
N
N
Pt
Pt
Pt
Pt
(b)
(a)
(d)
(c)
Scheme 5.
O4
C4
S
S
O4
C4
C1
C1
N2
N1
Pt
N1
N2
Mulliken: - 0.607
NBO: - 0.671
Mulliken: - 0.543
NBO: - 0.596
Mulliken: - 0.403
NBO: - 0.583
Pt
Mulliken: - 0.493
NBO: - 0.690
3
4
Scheme 6.
O
N
O
O
Ph2
P
O
S
N
N
N
Ph2
P
S
S
Ph2
P
Ph2
P
Fe
S
N
Pt
N
N
N
Fe
P
Pt
Fe
Fe
N
Pt
Pt
Ph2
N
P
O
N
Cl
P
P
N
Ph2
Cl
Ph2
Ph2
O
S
S
3
3(unobs)
4
4(unobs)
Scheme 7.
and compare well with that of 2.092(4) Å in 3. Carbon–oxygen bond
lengths of 1.24(3)–1.29(3) Å are indicative of a double bond, and
consequently it is clear that resonance hybrid (a) dominates in these
ligands. We have been unable to find crystallographic data for an-
other metal-bound deprotonated N-(2-thiazolyl)acetamide ligand.
Most closely related to 4 appears to be the (20-thenoyl)-2-amino-
5-nitrothiazole (tenonitrozole) complex, cis-[PtCl2(Me2SO)(tenoni-
trozole)] [45] which differs from ataH by replacement of the methyl
by a thienyl ring and the vinyl proton next to sulfur with NO2. The
Pt–N bond of 2.03(1) Å is similar to those found in 4.
significant double bond character also found between N(2)–C(1)
(1.315 Å), while in contrast N(1)–C(1) at 1.343 Å is significantly
longer. Mullikan charges of ꢀ0.543 and ꢀ0.493 on N(1) and N(2)
respectively are also in accord with this view although the NBO anal-
ysis places a higher charge on N(2). This discrepancy may be due to
the more localized nature of the NBO density. A further point of
interest in 4 is the nature of the Pt–N interaction which is character-
ized by strong back-donation from platinum to the ligand and this
may be responsible for the slightly shorter Pt–N bond calculated
for 4 versus 3 (2.040 versus 2.055 Å).
We next turned our attention to the different ligand binding
geometries adopted in 3 and 4 calculating the relative energies of
both the observed and unobserved isomeric forms (Scheme 7). In
both cases the observed isomer was shown to be the most stable.
3.3. Density functional calculations on N-(2-thiazolyl)acetamide
complexes
For the mono-amide complex
3 the energy difference was
In order to understand the adoption of the different ligand bind-
ing modes seen in 3 and 4 we have carried out geometry optimiza-
tion calculations on both using the GAUSSIAN 03 (G03) program [25]
and employing the DFT method and the PBE1PBE [46] functional.
The SDD basis set [47] and effective core potential were used for
the platinum atom and 6-31G⁄⁄+ basis set [48] were used for all
other atoms. We first considered the possible bonding modes of
the ligands in each complex using the natural bonding orbital
(NBO) method [30] to analyze the electronic structures and charges
of the calculated complexes (Scheme 6). In 3 this fully supports the
binding mode (a) (Scheme 4) as shown by the double-bond charac-
ter of the C(1)–N(1) and C(4)–O(1) bonds calculated as 1.311 and
1.225 Å respectively (see Scheme 6 for atom labels). Further, Mulli-
kan (ꢀ0.607 and ꢀ0.403) and NBO (ꢀ0.671 and ꢀ0.583) charges
calculated for N(1) and N(2) respectively are in accordance with this
ligandarrangement. For 4, the C(4)–O(1) bonds calculatedas 1.230 Å
fully supports the binding mode (a) (Scheme 5) as does the
10.5 kJ molꢀ1, while for the doubly substituted product 4 it was
9.3 kJ molꢀ1. These differences are relatively small and suggest that
the linkage isomers may be in equilibrium in solution; providing
another explanation for the relatively broad NMR spectra.
4. Summary
In this work we have shown that heterocyclic N-acetamides re-
act readily with [MCl2(dppf)] (M = Pd, Pt) to afford stable N-bound
amide complexes as a result of elimination of hydrogen chloride.
The degree of substitution appears to be highly sensitive to the nat-
ure of the acetamide used, for example with saccharinate only a
single chloride is displaced and this is tentatively attributed to ste-
ric reasons. With N-(2-thiazolyl)acetamide both mono- and disub-
stituted platinum complexes can be isolated which vary in the
linkage isomerism of the amide ligands. Thus, in the mono-substi-

S.A. Al-Jibori et al. / Inorganica Chimica Acta 398 (2013) 46–53
53
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saccharinate, while in the disubstituted complex both ligands are
bound through the nitrogen of the thiazole ring. In order to address
these differences, DFT calculations have been carried out on both
sets of linkage isomers, the results suggesting that electronic
differences between the two different binding modes are small.
This again suggests that steric effects are probably the major factor
in controlling the observed selectivity.
Acknowledgments
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Prof. Subhi A. Al-Jibori would like to thank the Department of
NMR, Institute for Anorganische Chemie, Martin-Luther-Universi-
tat, Halle, Germany for some of the NMR measurements.
Appendix A. Supplementary material
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