The chemistry of pyridine thiols and related ligands - 8. Synthesis, NMR spectroscopy and crystal structure of first trans-[bis(pyridine-2-thiolato-S)-bis(triphenyl phosphine) platinum(II)]

Article abstract of DOI:10.1016/S0277-5387(98)00177-6

Reaction of bis(pyridine-2-thiolato-N,S)platinum(II) (1) in acetonitrile (obtained from PtCl₂ and Na⁺C₅H₄NS^-) with two equivalents of PPh₃ forms monomeric Pt(C₅H₄NS)₂(PPh₃)₂ (2) whose X-ray structure has been determined. It crystallises from a acetonitrile-chloroform mixture and exists as a centrosymmetric square planar monomer. Pyridine-2-thiolate binds to Pt via S-atoms in a trans-configuration and the other two positions are occupied by P atoms of PPh₃. The interatomic important parameters are: Pt-S = 2.343(2), Pt-P = 2.3147(13), C-S = 1.739(6) A, bond angles P-Pt-P* and S-Pt-S* each = 180.0°, P-Pt-S, P*-Pt-S = 85.24° (acute) and P-Pt-S*, P*-Pt-S = 94.76° (obtuse). It represents the first example of a structurally characterised S-bonded pyridine-2-thiolato Pt(II) complex. The NMR data (¹H, ¹³C, ³¹P) suggest dissociation of 2 in CDCl₃ as follows: Pt(C₅H₄NS)₂(PPh₃)₂ (2)→Pt(C₅H₄NS)₂(PPh₃) (2a)+PPh₃. Both N,S- and S-bonded C₅H₄NS^- moieties are confirmed from ¹H and ¹³C NMR.

Full text of DOI:10.1016/S0277-5387(98)00177-6

Polyhedron Vol[ 06\ No[ 10\ pp[ 2642Ð2647\ 0887
Þ 0887 Elsevier Science Ltd
Pergamon
All rights reserved[ Printed in Great Britain
9166Ð4276:87 ,08[99¦9[99
\
PII] S9166!4276"87#99066!5
The chemistry of pyridine thiols and related
ligands*7[ Synthesis\ NMR spectroscopy and
crystal structure of _rst trans!ðbis"pyridine!1!
thiolato!S#!bis"triphenyl phosphine#
platinum"II#Ł
Tarlok S[ Lobana\aꢀ Renu Vermaa and Alfonso Castineirasb
aDepartment of Chemistry\ Guru Nanak Dev University\ Amritsar!032994\ Punjab\ India
bDepartamento de Quimica Inorganica\ Facultade de Farmacia\ Universidade de Santiago\ E!04695
Santiago de Compostela\ Galicia\ Spain
"Received 18 October 0886^ accepted 11 April 0887#
Abstract*Reaction of bis"pyridine!1!thiolato!N\S#platinum"II# "0# in acetonitrile "obtained from PtCl1 and
Na¦C4H3NS−# with two equivalents of PPh2 forms monomeric Pt"C4H3NS#1"PPh2#1 "1# whose X!ray structure
has been determined[ It crystallises from a acetonitrileÐchloroform mixture and exists as a centrosymmetric
square planar monomer[ Pyridine!1!thiolate binds to Pt via S!atoms in a trans!con_guration and the other two
positions are occupied by P atoms of PPh2[ The interatomic important parameters are] PtÐS ꢁ 1[232"1#\ PtÐ
P ꢁ 1[2036"02#\ CÐS ꢁ 0[628"5# Aý\ bond angles PÐPtÐPꢀ and SÐPtÐSꢀ each ꢁ 079[9>\ PÐPtÐS\ PꢀÐPtÐ
S ꢁ 74[13> "acute# and PÐPtÐSꢀ\ PꢀÐPtÐS ꢁ 83[65> "obtuse#[ It represents the _rst example of a structurally
characterised S!bonded pyridine!1!thiolato Pt"II# complex[ The NMR data "0H\ 02C\ 20P# suggest dissociation
of 1 in CDCl2 as follows] Pt"C4H3NS#1"PPh2#1 "1#:Pt"C4H3NS#1"PPh2# "1a#¦PPh2[ Both N\S! and S!bonded
0
C4H3NS− moieties are con_rmed from H and 02C NMR[ Þ 0887 Elsevier Science Ltd[ All rights reserved
Keywords] triphenyl phosphine^ pyridine!1!thione^ biochemically active chromophores^ S!bonded platinum"II#
complex^ pendant pyridyl[
———————————————————————————————————————————————
INTRODUCTION
bridging is observed in ðPt1"en#1"m!N\S!C4H3NS#1Ł
Cl1=2H1O ð03Ł\
ðPt1"m!N\S!C4H2"3!CH2#NS#1Ł04\
In recent years\ there is an upsurge in coordination
chemistry of heterocyclic thiones containing chemi!
cally active chromophores of the type] ÐN"H#Ð
C"1S#tÐN1C"ÐSH#\ because these ligands provide
several possibilities of metalÐligand interactions and
have biochemical implications ð0Ð3Ł[ Pyridine!1!
thione"C4H4NS#\ the simplest prototype of hetero!
cyclic thiones binds to a metal center in several ways]
S!bonding"h0#\ S!bridging"h1#\ N\S!chelating"h1#\ N\S!
bridging"h1#\ N\S!chelating!cum!S!bridging"h2# and
N\S!bridging!cum!S!bridging"h2# ð3Ð02Ł[ For struc!
turally characterised Pt"II or III# complexes\ N\S!
ðPt1Cl1"m!N\S!C4H3NS#3Ł=1CHCl2 ð04Ł\ and chelation
in ðPt"h1!N\S!C4H3NS#"PPh2#1Ł"PF5# ð05Ł[
As a part of our interest in coordination chemistry
of C4H4NS or its derivatives ð06Ð08Ł\ we report the
crystal structure of ðPt"C4H3NS#1"PPh2#1Ł "1# which
represents the _rst example of a platinum"II# complex
containing monodentate S!bonded C4H3NS− moiety[
The solid state behaviour of 1 is compared with its
solution phase behaviour[ In literature ð19Ł\ C4H3NS−
ligand scrambling in Pt"C4H3NS#1"PPh2# has been
mentioned[ In this investigation\ we establish both
N\S! and S!bonding modes for the species ð1a\ Pt"h1!
N\SÐC4H3NS#"h0!SÐC4H3NS#"PPh2#Ł in CHCl2 using
multinuclear NMR "0H\ 02C and 20P# spectro!
scopy and collecting massive scans for 02C NMR
spectrum[
ꢀ Author to whom correspondence should be addressed[
Fax] ¦80!072!147719^ E!mail] dcse gnduÝyahoo[com
Ð
2642

2643
T[ S[ Lobana et al[
lection were obtained by least squares re_nement of
EXPERIMENTAL
di}raction data from 14 re~ections in the range of
09[59> ³ u ³ 07[93> in a ENRAF!NONIUS MACH2
automatic di}ractometer ð12Ł[ Data were collected at
General materials
Platinum"II# dichloride was procured from M:s 182 K using MoK radiation "l ꢁ 9[60962 Aý# and the
Central Drug House Pvt "Bombay# while PPh2 from v scan technique and corrected for Lorentz and polar!
Spectrochem[ Pvt[ "Bombay#[ 1!Hydroxypyridine was isation e}ects ð13Ł[ An empirical absorption correction
procured from M:s Sisco\ Bombay[ Pyridine!1!thione! was made ð14Ł[ A summary of crystal data\ exper!
"C4H4NS# was prepared as described previously ð10\ 11Ł[ imental details and re_nement results are listed in
Sodium salt\ Na¦C4H3NS− was prepared as described ð06Ł Table 0[
for Na¦C4H3NOS−[ Acetonitrile was dried over P1O4 and
other solvents dried by usual methods[
Structure!solution and re_nement
The structure was solved by direct methods ð15Ł which
revealed the position of all non!hydrogen atoms\ and
re_ned on F1 by a full matrix least!squares procedure
using anisotropic displacement parameters for all non!
hydrogen atoms ð16Ł[ The hydrogen atoms were located
Preparation of Pt"C4H3NS#1 "0# and Pt"C4H3NS#1
"PPh2#1 "1#
Pt"C4H3NS#1 "0\ yellow# was prepared from the stoi!
chiometric reaction of PtCl1 "9[075 g\ 9[69 mmol# with
C4H3NSNa "9[194 g\ 0[43 mmol# in CH2CN "14 cm2#
under re~ux for ca[ 19 h[ The concentration of the
solution under vacuum formed a yellow coloured solid
which was treated with water to remove NaCl\ recrys!
tallised from CH2CN and dried in vacuo[ Yield\ 39)\
m[p[ ">C# × 149\ analytical data ")#\ found C\ 29[3\
H\ 1[02\ N\ 5[84^ required for C09H7N1S1Pt\ C\ 18[9\
H\ 0[82\ N\ 5[64\ IR data "cm−0#\ 0026s "nC1S#\ 315s
"nPtÐS#\ 143m "nPtÐN#[
Ä
in their calculated positions "CÐH ꢁ 9[82Ð9[85 A# and
were re_ned using a riding model[ After all shift:e[s[d
ratios were less than 9[990\ the re_nement converged
to the agreement factors listed in Table 0[ The atomic
scattering factors taken from International Tables for X!
ray Crystallography ð17Ł while molecular graphics were
prepared using ZORTEP ð18Ł[
RESULTS AND DISCUSSION
Pt"h0!SÐC4H3NS#1"PPh2#1 "1\ yellow# was prepared
by the addition of PPh2 "9[059 g\ 9[502 mmol# to
Pt"C4H3NS#1 "9[016 g\ 9[295 mmol# in CH2CN
"19 cm2# with magnetic stirring under re~ux for 1 h[
The excess solvent was removed under vacuum to get
a yellow solid which was puri_ed using diethylether and
recrystallised from CH2CN[ Yield\ 59)\ m[p[ ">C#\ 039Ð
34\ analytical data found ")#\ C\ 47[1\ H\ 2[51\ N\ 2[91\
required for C35H27N1P1S1 Pt\ C\ 47[7\ H\ 3[93\ N\ 2[99\
IR data "cm−0#\ 0009s "nC1S#\ 329m "nPtÐS#[
Description of the crystal structure of Pt"C4H3NS#1
"PPh2#1 "1#
The selected interatomic parameters are given in
Table 1 while Fig[ 0 shows the molecular structure
together with numbering scheme[ The basic structural
unit is a centrosymmetric monomer Pt"C4H3NS#1
"PPh2#1 "1#[ Two P atoms of PPh2 molecules and two
S atoms of C4H3NS− ligand coordinate to Pt atom in
a square planar geometry with trans PÐPtÐPꢀ and SÐ
PtÐSꢀ angles of 079[9>\ two acute "74[13>\ PÐPtÐS and
PꢀÐPtÐSꢀ# and two obtuse "83[65>\ PÐPtÐSꢀ and SÐ
PtÐPꢀ# angles[ Chelation in cis!ðPt"h1!N\SÐC4H3NS#
"PPh2#1Ł"PF5# "2# causes more severe distortion as
anticipated ðe[g[ trans SÐPtÐP ꢁ 054[5>^ NÐPtÐ
P ꢁ 052[7"1#Ł ð05Ł[ It is signi_cant that C4H3NS− can
modulate the geometric positions of PPh2 ligand as in
2 and 1 based on its coordination requirements[ The
PtÐP distance is normal but marginally longer than in
2 ðPtÐP ꢁ 1[184\ 1[142 AýŁ ð05Ł\ while PtÐS distance ðPtÐ
Physical measurements
The elemental analysis for C\ H and N were
obtained using a Carlo!Erba 0097 microanalyser or
from RSIC Chandigarh[ The melting points were
determined with a Gallenkamp electrically heated
apparatus[ The NMR spectra were recorded in CDCl2
using\ "i# Bruker AMX 299 spectrometer at 299[03
and 64[37 MHz probe frequencies for "0H and 02C
resonances\ respectively\ with TMS as the internal
reference# and "ii# Bruker AMX 499 spectrometer at
191[34 MHz probe frequency for 20P"0H# resonance
with 74) H2PO3 as the external reference "dP\
16[4 ppm#[
Ä
S ꢁ 1[237 AýŁ as well as PÐCPh distance ð0[721 AŁ are
nearly the same[ The SÐC"1# distance shows partial
double bond character in the usual manner[ The bite
angle of SÐC"1#ÐN"0# ð019[6"4#>Ł is typical of mono!
dentate C4H3NS− ð006[5"6#>Ł as in Hg"C4H3NS#1 ð29Ł
or is similar to the bridging C4H3NS− derivative ð011Ð
013>Ł in Pt"II# complexes ð04Ł[ Finally\ the PtÐSÐC"1#
angle is also similar to the one in dimeric complexes
X!ray data collection and reduction
The crystal of Pt"C4H3NS#1"PPh2#1 "1# was mounted ð098[9"7#>Ł[ 1 represents the _rst structurally charac!
on a glass _ber and used for data collection[ Cell terised Pt"II# 2complex containing monodentate S!
constants and an orientation matrix for data col! bonded C4H3NS− moiety[ The steric e}ect due to

The chemistry of pyridine thiols and related ligands
2644
Table 0[ Crystal data and structure re_nement for ðPt"C4H3NS#1 "PPh2#1Ł
Empirical formula
C35H27N1P1PtS1
Formula weight
828[82
Crystal system:Space group
Unit cell dimensions
Monoclinic:P10:n
a ꢁ 09[999"1# Aý^ a ꢁ 89[99"−#>
b ꢁ 04[345"2# Aý^ b ꢁ 86[93"1#>
c ꢁ 01[878"1# Aý^ g ꢁ 89[99"−#>
Volume
0881[3"6# Aý2
Z
1
Density "calculated#
Absorption coe.cient
F "999#
0[456 Mg:m2
2[631 mm−0
825
Crystal description
Crystal size
yellow prism
9[39×9[29×9[19 mm
No[ of re~ections "lattice#
u range "lattice#
u range for data collection
Index ranges
Re~ections collected
Independent
14
09[59Ð07[93>
1[53Ð15[18>
−01 ¾ h ¾ 01\ 9¾k ¾ 08\ 9¾l ¾ 05
3104
3927 ðRint ꢁ 9[9226Ł
re~ections
Re~ections observed
Criterion for observation
Data:parameters
Final R indices ðI×1s "I#Ł
1455
×1s "I#
3926:9:206
R0 ꢁ 9[9186\
wR1 ꢁ 9[9450
0[999
Goodness!of!_t on F1
Final R indices "all# R0:wR1
Largest di}[ peak and hole
Weighting scheme
9[9718:9[9565
9[503 and −9[479 eAý−2
1
w ꢁ ð0:ðS1"Fo #¦"9[9126P#1¦9[2343PŁ
where P ꢁ "Fo ¦1Fc1#:2
1
Max[ and min[ transmission
0[999 and 9[375
bulky PPh2 ðPÐPtÐP\ 86[3>Ł and short bite angle\ SÐ
The NMR spectrum shows that dissociation is not
PtÐN of 57[9> in 2 appear to favour trans!PPh2 and complete\ but is considerable[ This means that prob!
S!bonded C4H3NS− in 1[
ably 1 and 1a are in equilibrium\ however\ there was
no evidence for dissociation of both PPh2 molecules[
Since crystals of 1 were grown from CH2CN\ it is
possible that this solvent may be acting as a stabiliser
of PtÐPPh2 bonding and as shown by 20P NMR\ 1
dissociates in CHCl2 forming 1a species[ The lack of
dissociation of 1 in CH2CN could be attributed to the
coordinating properties of CH2CN presumably along
axial sites[ Alternatively CH2CN could interact with
the pendant pyridyl group via hydrogen bonding or
via delocalised p!electrons on the CN group[ This
presumably keeps C4H3NS− moiety in S!bonded form
with pendant pyridyl group[ In contrast\ in CHCl2\
this stabilisation of the pendant pyridyl group is not
available and so it coordinates to Pt"II#[ It must be
emphasised that due to bulky PPh2 groups with pen!
dant pyridyl groups in trans positions\ the ster!
eochemical requirements about the Pt"II# center
favour dissociation of a PPh2 group along with chel!
ation by NS!donor set[ Low _eld coordination shift
NMR spectral studies
Table 2 contains NMR data "0H\ 02C\ 20P# for the
compounds[ The 20P NMR spectrum of 1 "Fig[ 1#
shows the presence of dissociated PPh2 in CDCl2 solu!
tion according to the equation below[
0
"DdP\ 01[4 ppm# with JPÐPt coupling constant of
2755 Hz con_rms the coordination of PPh2 to the Pt
metal center[
The absence of 0H NMR signals due to NH in 0

2645
T[ S[ Lobana et al[
Fig[ 0[ Perspective view of ðPt"C4H3NS#1"PPh2#1Ł "1# molecule with the numbering scheme[ The thermal ellipsoids are drawn
Ä
at the 29) probability level[ The hydrogen atoms are drawn with an arbitrary radius of 9[0 A and are represented by open
circles[
Table 1[ Selected bond lengths "Aý# and angles "># for
ðPt"C4H3NS#1"PPh2#1Ł
PtÐP
PtÐS
SÐC"1#
1[2036"02#
1[232"1#
0[628"5#
0[714"5#
0[720"4#
0[730"4#
0[232"7#
0[245"7#
0[305"8#
0[237"09#
0[254"02#
0[265"01#
PÐC"20#
PÐC"10#
PÐC"00#
N"0#ÐC"1#
N"0#ÐC"5#
C"1#ÐC"2#
C"2#ÐC"3#
C"3#ÐC"4#
C"4#ÐC"5#
PÐPtÐPꢀ0
079[9
PÐPtÐSꢀ0
PÐPtÐS
Sꢀ0ÐPtÐS
83[65"4#
74[13"4#
079[9
C"1#ÐSÐPt
097[1"1#
006[3"6#
019[6"6#
019[6"4#
094[3"2#
099[4"1#
096[0"1#
008[6"1#
098[7"1#
002[3"1#0
C"1#ÐN"0#ÐC"5#
N"0#ÐC"1#ÐC"2#
N"0#ÐC"1#ÐS
C"20#ÐPÐC"10#
C"20#ÐPÐC"00#
C"10#ÐPÐC"00#
C"20#ÐPÐPt
C"10#ÐPÐPt
C"00#ÐPÐPt
Symmetry transformations used to generate equivalent
atoms] ꢀ0−x\ −y¦0\ −z[
Fig[ 1[ The 20P NMR spectrum of 1 in CDCl2[

The chemistry of pyridine thiols and related ligands
2646
Table 2[ The 0H\ 02C and 20P"0H# NMR data "d\ ppm\ J\ Hz# of compounds
H"5#
H"3#
H"2#
H"4#
0
1
8[09 d
"J4\ 5[9#
7[16 d
6[25 t
"J2\ 6[5\ J4\ 6[5#
6[21 t
6[19 d
"J3\ 7[0#
6[26 d
5[80 t
"J3\ 5[5\ J5\ 5[5#
5[71 t
set I
"J4\ 2[3#
"J2\ 6[4\ J4\ 6[4#
"J3\ 6[6#
5[57 da
"J3\ 7[1#
6[38 dt
"J3\ 4[8\ J5\ 4[8#
set II
7[98 sa
5[54 ta
5[41 sa
C4H4NSb
6[45 ddd
6[23 ddd
5[62 td
"J4\ 5[2\ J3\ 0[5\ J2\ 9[7# "J2\ 7[6\ J4\ 6[9\ J5\ 0[7# "J3\ 7[6\ J4\ 9[7\ J5\ 9[7# "J3\ 5[6\ J5\ 5[6\ J2\ 0[1#
PPh2 signals
1
PPh2
o!H
6[28 m
−
m! and p!H
6[45 m
−
free PPh2
6[03 m
6[12 m
02C NMR
1
C"1#
C"5#
C"3#
C"4#
C"2#
set Ic
065[4
053[8
064[5
035[8
031[2
026[9
025[7
024[7
024[8
013[8
013[8
021[7
004[6
004[6
002[0
set IId
C4H4NS
PPh2 signals
i!C "0JC−P
#
o!C "1JC−P
#
m!C "2JC−P
#
p!C "3JC−P
#
PPh2
1
021[4 "09[9#
017[9 "27[4#
020[5 "n[o#
023[1 "08[4#
029[6 "5[9#
021[6 "5[9#
017[8 "09[7#
016[0 "6[4#
015[8 "5[7#
018[0 "8[2#
029[4 "n[o#
018[4 "n[o#e
set I
set II
20P"0H#
dP
DdP
0JPÐPt
1
4[3f
−6[03
01[4
2755
1
PPh2
d\ doublet^ t\ triplet\ td\ triplet of doublets^ dt\ doublet of triplets^ ddd\ doublet of doublet of doublet^ s\ singlet[
aBroad[
bdNH ꢁ 02[39 nb[
cN\S!chelated C4H3NS−[
dS!bonded C4H3NS−[
en[o[\ not observed[
fIndicates free PPh2 also[
and 1 con_rms that in these compounds anionic _eld when it is S!bonded only "1\1a^ set II#[ H"2#
C4H3NS− is coordinating to the Pt"II# center[ The protons also is signi_cantly up!_eld when C4H3NS−
H"5# proton shows low!_eld shift relative to free is S!bonded only but is mildly up!_eld when it is N\S!
C4H4NS in 0 and 1[ The coordination of PPh2 to Pt"II# bonded and _nally H"4# protons are also up!_eld when
C4H3NS− is S!bonded only and down!_eld for N\S!
leads to a relative up!_eld shift in 1[ Further\ two sets
bonded moiety[
of H"5# proton "and for other protons# shows evidence
for both N\S!chelated and S!bonded C4H3NS− moi!
eties in 1a[ Since H"5#\ in the vicinity of nitrogen\ is
most sensitive to the coordination changes\ the up!
_eld shifts clearly support de!ligation of MÐN bond in
1a[ Further\ the fact that H"5# proton of N\S!chelated
C4H3NS "set I# is still up _eld relative to that of 0^
it reveals increased PtÐN back!bonding when PPh2
coordinates[ De!ligation of PtÐN bond "set II# leads to
increased aromaticity\ an usual observation in metalÐ
pyridine thiol chemistry ð20Ł[
02C NMR spectrum of 1 shows unambiguous evi!
dence for N\S!bonded "1a\ set I\ Table 2# and S!
bonded "1\1a\ set II# C4H3NS− moieties[ All pyridyl
carbons except C"4# show low!_eld shifts "relative to
free C4H4NS# for N\S!bonded C4H3NS− moiety "1a\
set I# ð20Ł[ The up_eld shift in C"1# signal with reduced
shifts in positions of C"5# supports the presence of S!
bonded C4H3NS− moiety "1\1a\ set II# ð20Ł[
Acknowled`ements*Financial assistance from the Uni!
versity Grants Commission\ Delhi ðProject No[ F[01!
36:82"SR!0#Ł[ We are thankful to Professor J[ S[ Casas\ Uni!
The H"3# proton remains nearly una}ected "0^ 1a\
set I# when C4H3NS− is N\S!bonded\ but moves up! versity of Santiago\ for instrumental facilities[

2647
T[ S[ Lobana et al[
05[ Wang\ S[\ Staples\ R[ J[\ Fackler\ J[ P[ Jr[\ Acta
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