Insertion of Pt into C-H and C-S bonds of thiophene derivatives. The X-ray crystal structure of a thiaplatinacycle of 3,6-dimethylthieno [3,2-b]thiophene

Article abstract of DOI:10.1016/j.jorganchem.2003.08.002

Treatment of the zerovalent platinum complex [Pt(PEt₃) ₄] with 3,6-dimethylthieno[3,2-b]thiophene leads to a six-membered, approximately planar thiaplatinacycle, which has been characterised spectroscopically and by a single crystal X-ray determination. The reaction of [Pt(PEt₃)₄] with 2,2′-bithiophene and 1-methyl-2-(2-thienyl)pyrrole produced two types of products, thiaplatinacycles resulting from C-S insertion and platinum(II) hydrides arising from C-H insertion. These complexes were characterised spectroscopically.

Full text of DOI:10.1016/j.jorganchem.2003.08.002

Journal of Organometallic Chemistry 687 (2003) 39ꢀ45
/
www.elsevier.com/locate/jorganchem
Insertion of Pt into CÃ
/
H and CÃ
/
S bonds of thiophene derivatives.
The X-ray crystal structure of a thiaplatinacycle of 3,6-
dimethylthieno[3,2-b]thiophene
Janine Chantson a,*, Helmar Gorls b, Simon Lotz a
¨
a Department of Chemistry, University of Pretoria, Hillcrest, Pretoria 0002, South Africa
b Department of Inorganic and Analytical Chemistry, University of Jena, Lessingstr. 8, 07743 Jena, Germany
Received 14 July 2003; received in revised form 12 August 2003; accepted 13 August 2003
Abstract
Treatment of the zerovalent platinum complex [Pt(PEt3)4] with 3,6-dimethylthieno[3,2-b]thiophene leads to a six-membered,
approximately planar thiaplatinacycle, which has been characterised spectroscopically and by a single crystal X-ray determination.
The reaction of [Pt(PEt3)4] with 2,2?-bithiophene and 1-methyl-2-(2-thienyl)pyrrole produced two types of products, thiaplatina-
cycles resulting from CÃ
spectroscopically.
# 2003 Elsevier B.V. All rights reserved.
/
S insertion and platinum(II) hydrides arising from CÃ
/H insertion. These complexes were characterised
Keywords: Platinum hydrides; Oxidation; CÃ
/
H activation; CÃS activation; Thiaplatinacycles; Crystal structure
/
1. Introduction
Various metallacycles [3ꢀ
which a metal fragment (e.g. Rh, Ir, Pt, Fe, W)
oxidatively inserts into the CÃS bonds of thiophenes,
benzothiophenes and dibenzothiophenes [6ꢀ13]. Thiair-
idacycles [13] and thiaplatinacycles [10,14] have both
been shown to effect HDS. This article reports on the
oxidative reactions of platinum(0) with the thiophene
derivatives 3,6-dimethylthieno[3,2-b]thiophene (1), 2,2?-
bithiophene (2) and 1-methyl-2-(2-thienyl)pyrrole (3)
/
5] have been prepared in
Hydrodesulfurisation (HDS) is an important indus-
trial process by which sulfur is removed from petroleum
feedstocks by treatment with hydrogen gas over hetero-
geneous catalysts. Despite the importance of HDS in
reducing noxious emissions, the mechanism of HDS is
not fully understood. Studies have been undertaken in
/
/
order to study CÃ
solution by organometallic complexes in order to gain
some insights into the possible reaction intermediates
/
S bond scission in homogeneous
(Scheme 1). In addition to the expected CÃ
/
S insertion
products, the competitive process of CÃH activation
/
was also found to occur to generate platinum(II)
hydrides.
and nature of kinetics on heterogeneous catalysts. CÃ
/S
bond activation is also of interest in studies of catalytic
and stoichiometric transformations of organic sulfides
[1]. For example, the Pd(0) and Pt(0) catalysed car-
bothiolation of alkynes involves the oxidative addition
2. Experimental
of the metal (M) into a CÃ
into the SÃM bond and subsequent reductive elimina-
tion [2].
/
S bond, insertion of an alkyne
2.1. General
/
All manipulations involving metal complexes were
carried out using standard Schlenk techniques under an
atmosphere of dry nitrogen [15], unless stated otherwise.
Solvents were distilled under nitrogen from appropriate
drying agents before use. The [Pt(PEt3)4] precursor was
* Corresponding author. Tel.: ꢁ
5297.
E-mail address: jchant@postino.up.ac.za (J. Chantson).
/
27-12-420-2527; fax: ꢁ27-12-362-
/
0022-328X/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2003.08.002

40
J. Chantson et al. / Journal of Organometallic Chemistry 687 (2003) 39ꢀ45
/
wR2obs
1.062, Flack-parameter ꢃ
peak and hole: 3.862/ꢃ
ꢂ
/
0.088, R1all
ꢂ
/
0.114, wR2all
ꢂ
/
0.094, GOOFꢂ
/
/
0.01(1), largest difference
ꢃ3
˚
/
1.958 e A
.
2.3. Preparation of the thiophenic substrates
Scheme 1.
prepared from K2[PtCl4] according to a literature
method [16]. 1-Methylpyrrole and N,N,N?N?-tetra-
methylethylenediamine (tmeda) were freshly distilled
2.3.1. Preparation of 3,6-dimethylthieno[3,2-
b]thiophene (1)
The ligand was prepared in a manner similar to that
described by Choi and co-workers [22]. A mixture of
2,5-dihydroxy-2,5-dimethyl-3-hexyne (17.0 g, 120 mmol)
and elemental sulfur (9.52 g, 297 mmol) and benzene
(130 ml) was sealed in an autoclave and heated over-
night at 200 8C. After cooling to room temperature
(r.t.), the autoclave was opened and the brown residue
obtained was extracted with benzene. The solvent was
removed in vacuo and the resulting residue was dis-
solved in warm hexane and filtered. Purification by
column chromatography on silica gel with hexane as the
eluent resulted in the isolation of a white solid, 1. Yield
prior to use. The dppf (where dppfꢂ1,1?-bis(diphenyl-
/
phosphanyl)ferrocene) and [PdCl2dppf] catalyst were
prepared as previously reported [17]. All other reagents
and chemicals were obtained commercially and used as
received. The 1H-, 31P{1H}- and 13C{1H}-NMR spectra
were recorded on a Bruker ARX300 spectrometer
operating at 300.133, 121.496 and 75.469 MHz for the
1
respective nuclei. Chemical shifts in H- and 13C{1H}-
NMR spectra were calibrated with reference to residual
proton signals of the deuterated solvent (7.24 and 77.0
ppm respectively for CDCl3). 31P{1H}-NMR spectra
were referenced to the deuterated lock signal, which had
previously been referenced to 85% H3PO4. Electron
impact (EI) mass spectra were recorded on a Finnigan
Mat 8200 instrument operating at 70 eV and fast atom
bombardment (FAB) mass spectra were measured on a
VG 7070-E instrument (Xe beam).
1
3.55 g (21%). H-NMR d (CDCl3): 6.949 (a-H, 2H, s),
4
2.354 (CH3, 6H, d, JHH
ꢂ
0.8 Hz). 13C-NMR d
/
(CDCl3): 140.08 (ipso-C), 130.37 (ipso-C), 121.80
(CH), 14.63 (CH3).
2.3.2. Preparation of 1-methyl-2-(2-thienyl)pyrrole (3)
Under an argon atmosphere, 1-methylpyrrole (4.02 g,
49.6 mmol) was slowly added to a Schlenk flask
containing a 1.6 M n-BuLi/hexane solution (38 ml, 60
mmol) and tmeda (8.30 ml, 55 mmol) in hexane (60 ml)
[23]. The solution was heated under reflux for 20 min.
After allowing the solution to cool to r.t., THF (40 ml)
was added. The solution was vigorously stirred as
anhydrous ZnCl2 (9.0 g, 66 mmol) was added. The
temperature of the mixture was controlled by an
external bath so that the temperature did not rise above
20 8C. 2-Bromothiophene (4.8 ml, 50 mmol) and
[PdCl2dppf] catalyst (0.54 g, 0.74 mmol) were added
and the reaction mixture was heated to reflux for 6 h.
After cooling to r.t. the solution was poured onto a 2.8
M NH4Cl (aq) solution to which a small amount of NH3
had been added. The organic layer was separated and
2.2. Crystal structure determination
The intensity data for compound 4 was collected on a
Nonius KappaCCD diffractometer, using graphite-
monochromated MoꢀKa radiation. Data were corrected
/
for Lorentz and polarisation effects, and for absorption
effects [18,19]. The structure was solved by direct
methods (SHELXS [20]) and refined by full-matrix least-
squares techniques against Fo2
(SHELXL-97 [21]). All
hydrogen atoms were included at calculated positions
with fixed thermal parameters. All non-hydrogen atoms
were refined anisotropically [21]. XP (SIEMENS Ana-
lytical X-ray Instruments, Inc.) was used for structure
representations.
2.2.1. Crystal data for 4 (see Section 5)
the aqueous phase was treated with Et2O (4ꢄ100 ml).
/
C20H38P2PtS2, Mrꢂ
prism, size 0.12ꢄ0.12ꢄ
group P212121, aꢂ9.8621(4), bꢂ
bꢂgꢂ90.008, Vꢂ
4, rcalcd
1.626 g cmꢃ3, m(Moꢀ
60.33 cmꢃ1, psi-scan, transmin: 0.4098, transmax:
0.5313, F(000)ꢂ1192, 13 153 reflections in h(ꢃ12/12),
k(ꢃ15/17), l(ꢃ24/20), measured in the range 3.015
U 527.418, completeness Umax 99.4%, 5516 indepen-
dent reflections, Rint 0.078, 4400 reflections with Foꢀ
4s(Fo), 226 parameters, 0 restraints, R1obs 0.080,
/
599.65 g molꢃ1, goldꢀ
/
yellow
0.12 mm3, orthorhombic, space
13.3149(6), cꢂ
The organic fractions were combined and dried over
anhydrous K2CO3. The solvent was removed under
reduced pressure and the product isolated by distillation
(b.p. 125 8C/15 mmHg). Yield 5.51 g (68%) slightly
/
/
/
/
/
3
˚
˚
2448.9(2) A ,
18.6497(8) A, aꢂ
Tꢂ 90 8C, Zꢂ
Ka)ꢂ
/
/
/
/
1
/
ꢃ
/
/
ꢂ
/
/
brown oil stored under Ar. H-NMR d (CDCl3): 7.244
/
(CHthienyl, 1H, dd, 3JHH
(CHthienyl, 1H, m), 7.010 (CHthienyl, 1H, dd, JHH
ꢂ
/
5.1 Hz, 4JHH
ꢂ1.3 Hz), 7.051
/
3
/
/
ꢂ
/
3.6
2.3
1.8
2.8
4
3
/
/
/
Hz, JHH
ꢂ
/
1.3 Hz), 6.687 (CHpyrrole, 1H, t, JHH
ꢂ
/
/
ꢂ
/
Hz), 6.316 (CHpyrrole, 1H, dd, 3JHH
Hz), 6.512 (CHpyrrole, 1H, dd, 3JHH
Hz), 3.703 (CH3, 3H, s) ppm.
ꢂ
/
3.6 Hz, 4JHH
3.6 Hz, 4JHH
ꢂ
/
ꢂ
/
/
ꢂ
/
ꢂ
/
ꢂ
/

J. Chantson et al. / Journal of Organometallic Chemistry 687 (2003) 39ꢀ
/45
41
2.4. Preparation of platinum(II) compounds
vacuo. FABMS: m/z 594 [Mꢁ, 17%], 537 [Mꢁ ꢃ
C2H4, 18%], 476 [Mꢁ ꢃPEt3, 5%], 431 [Mꢁ ꢃ
C9H9NS,
30%], 402 (Pt{PEt3}2ꢁ ꢃEt, 19%), 375 (Pt{PEt3}2ꢁ ꢃ
3 C2H4, 10%), 164
/
Etꢃ
/
/
/
2.4.1. Reaction of [Pt(PEt3)4] with 3,6-
dimethylthieno[3,2-b]thiophene (4)
/
/
2
C2H4, 16%), 347 (Pt{PEt3}2ꢁ ꢃ
/
Under an Ar atmosphere, [Pt(PEt3)4] (0.55 g, 0.82
mmol) was weighed into a clean, dry Schlenk flask and
dissolved in toluene (5 ml). Solid 3,6-dimethylthieno[3,2-
b]thiophene (0.278 g, 1.65 mmol) and 10 ml of toluene
were added. The mixture was heated to 80 8C under high
vacuum for 6 h and then refluxed for 3 h. Thereafter the
heat source was removed and the mixture stirred over-
night at r.t. to form an off-white solid precipitate. The
supernatant was removed and the precipitate washed
(C9H9NSHꢁ, 11%), 163 (C9H9NSꢁ, 11%), 135
(HOPEt3ꢁ, 100%), 119 (HPEt3ꢁ, 20%). Accurate mass:
594.1926 (calculated), 594.1928 (observed).
3. Results and discussion
When a twofold excess of 3,6-dimethylthieno[3,2-
b]thiophen (1) was refluxed with tetrakis(triethylpho-
sphane) platinum(0) in toluene for 3 h, a thiaplatina-
cycle complex, 4, was obtained (Scheme 2). The complex
was characterised by NMR and mass spectrometry and
the structure was confirmed by a single crystal X-ray
diffraction study.
Ivory-coloured crystals suitable for single crystal X-
ray diffraction studies were grown from a cold, satu-
rated solution of 4 in toluene/hexane. Complex 4 has an
orthorhombic crystal system and crystallised in the
space group P212121. The six-membered thiaplatina-
cycle is close to planar, while the five-membered
thiophene ring is planar (Table 1). A molecular repre-
sentation of 4 is given in Fig. 1.
with hexane (2ꢄ1 ml) and dried in vacuo. Ivory-
/
coloured crystals suitable for X-ray crystallography
studies were obtained from a saturated toluene/hexane
solution of
C20H38P2PtS2: Calc.: C, 40.06; H, 6.39. Found: C,
4
at
ꢃ20 8C. Yield 0.33 g (67%)
/
1
39.90; H, 6.42%. H-NMR d (CDCl3): 7.278 (CH, 1H,
3
dd, JP,H
unresolved), 6.785 (CH, 1H, s, long-range JPt,H
3
7.8 Hz, JP,H
4
2
ꢂ
/
ꢂ25.6 Hz, JH,H and JPt,H
/
ꢂ
ꢂ
/
9.8
0.8
4
Hz, JH,H unresolved), 2.462 (CH3, 3H, d, JH,H
4
/
4
Hz), 2.369 (CH3, 3H, d, JH,H
ꢂ1.0 Hz), 2.00 (PCH2,
/
12H, m), 1.12 (PCH2CH3, 18H, m) ppm. 13C{1H}-NMR
3
d (CDCl3): 139.04 (ipso-C, d, JP,C
ꢂ
/
7.2 Hz), 137.70
9.4
100.1 Hz, JPt,C not observed), 128.80
(ipso-C), 137.57 (ipso-C), 131.86 (CH, dd, 2JP,cis-C
ꢂ
/
2
1
Hz, JP,trans-C
(ipso-C), 116.24 (CH), 28.44 (CH3, d, JP,C
3JPt,C
59.2 Hz), 16.56 (CH3), 16.6 (PCH2, m), 8.4
ꢂ
/
The platinum atom is in a near square planar
4
ꢂ11.7 Hz,
/
coordination geometry. The bond angle P(1)Ã
/
PtÃ/P(2)
ꢂ
/
of 97.73(9)8 is considerably larger than the ideal square
planar value of 908 (Table 2), probably to allow room
for the free rotation of the phosphane ethyl substituents
(PCH2CH3, m) ppm. 31P{1H}-NMR d (CDCl3): 11.98
(P trans to S, d, 2JP,P
(P trans to C, d, 2JP,P
ꢂ
/
22.9 Hz, 1JPt,P
22.9 Hz, 1JPt,P
ꢂ
/
3140 Hz), 0.20
1696 Hz) ppm.
S2C8H8,
Et, 76%], 373 [Mꢁ ꢃ
2Et, 87%], 168 (S2C8H8ꢁ, 100%), 118 (PEt3ꢁ,
ꢂ
/
ꢂ
/
[10]. Insertion of the Pt-centre into the C(1)Ã
causes the internal angle at S(1) to increase relative to
the angle at S(2), i.e. C(6)ÃS(1)ÃPt 112.0(4)8 versus
C(4) 90.8(6)8. The remaining bond angles of
/
S(1) bond
EIMS (70 eV): m/z 599 [Mꢁ, 48%], 431 [Mꢁ ꢃ
/
76%], 402 [Mꢁ ꢃ
S2C8H8ꢃ
34%).
/
S2C8H8ꢃ
/
/
/
/
/
C(3)Ã
/
S(2)Ã
/
the thiaplatinacycle are all larger than the 1208 expected
for a delocalised six-membered ring system such as
2.4.2. Reaction of [Pt(PEt3)4] with 2,2?-bithiophene (5a
and 5b)
benzene or thiabenzene or thiaplatinabenzene. The CÃ
bond lengths in the thiaplatinacycle, show that the ring
is a non-conjugated system, where C(1)ÃC(2) is a
localised double bond, C(2)ÃC(3) a single bond and
C(3)ÃC(6) represents a bond order of between one and
two (Table 3). The PtÃP bond lengths illustrate the
difference in the trans influence of the S- and C-bound
atoms; the C-atom having a greater trans influence than
the S-atom. The bond lengths and bond angles about the
platinum centre in 4 correspond quite well with thiapla-
tinacycles of benzothiophene [10], 3-methylthiophene
/
C
Solid 2,2?-bithiophene (0.42 g 2.5 mmol) was added to
a Schlenk flask containing [Pt(PEt3)4] (1.87 g, 2.8 mmol)
in toluene (20 ml). The mixture was stirred for 5 h at
80 8C and then at r.t. overnight. The solvent was
removed in vacuo to yield a brown oil containing a
mixture of 5a and 5b (4:1 as determined by NMR).
/
/
/
/
EIMS (70 eV): m/z 597 [Mꢁ, 2%], 431 [Mꢁ ꢃ
2%], 402 [Mꢁ ꢃ Et, 3%], 373 [Mꢁ ꢃ
S2C8H6ꢃ
S2C8H6ꢃ
2Et, 3%], 166 (S2C8H6ꢁ, 100%).
/S2C8H6,
/
/
/
/
2.4.3. Reaction of [Pt(PEt3)4] with 1-methyl-2-(2-
thienyl)pyrrole (6a and 6b)
To a solution of [Pt(PEt3)4] (2.26 mmol) in 10 ml
toluene was added 1-methyl-2-(2-thienyl)pyrrole (0.56g,
3.4 mmol). The reaction mixture was stirred under reflux
for 48 h. A mixture of 6a and 6b (1:1.3 as determined by
NMR) was obtained after removal of the solvent in
Scheme 2.

42
J. Chantson et al. / Journal of Organometallic Chemistry 687 (2003) 39ꢀ45
/
Table 1
Selected torsion angles (8) of 4
such a binuclear complex were unsuccessful despite
prolonged heating of the thiaplatinacycle 4 with excess
[Pt(PEt3)4]. The formation of a thiaplatinacycle is
known to be reversible [10] and the thiaplatinacycle,
the free ligand, dissociated phosphane molecules and the
platinum(0) precursor exist in equilibrium.
C(1)Ã
S(1)ÃPtÃ
C(1)ÃC(2)Ã
S(1)ÃC(6)ÃC(3)Ã
PtÃS(1)ÃC(6)Ã
/
PtÃ
/
S(1)Ã
/
C(6)
ꢃ
ꢃ
ꢃ/
/
13.8(5) C(4)Ã
9.2(11) C(3)Ã
13.5(18) S(2)ÃC(4)Ã
3.3(17) S(2)ÃC(3)Ã
12.0(10)
/
S(2)Ã
/
C(3)Ã
C(4)Ã
C(5)Ã
C(6)Ã
/
C(6)
C(5)
C(6)
C(5)
ꢃ
/
0.5(8)
/
/
C(1)Ã
/
C(2)
/
/
S(2)Ã
/
/
1.6(10)
2.1(14)
0.6(12)
/
/
C(3)Ã
/
C(6)
C(2)
/
/
/
ꢃ
/
/
/
/
/
/
/
ꢃ/
The 31P-NMR spectrum of 4 displayed two doublets,
with accompanying 195Pt satellites, at 11.98 ppm (P
trans to S) and 0.20 ppm (P trans to C). The two non-
equivalent phosphorus atoms are coupled by a two bond
coupling of 22.9 Hz, a value typical of cis-phosphanes
/
/
/
C(3)
1
[27]. The respective JPt,P couplings of 3139 Hz (P trans
to S) and 1696 Hz (P trans to C) illustrate the large
difference in the trans influence of the S- and C-bound
groups.
Unlike [Pt(PEt3)4], the less nucleophilic [Pt(PPh3)3]
complex does not react with 3,6-dimethylthieno[3,2-
b]thiophene despite prolonged refluxing in toluene.
Instead, thermal degradation of the zerovalent metal
phosphane complex leads to the formation of dinuclear
species such as [Pt2(m-PPh2)-{m-C6H4(PPh2)-2}(PPh3)2]
[28].
In contrast to the reaction of [Pt(PEt3)4] with the
thienothiophene to give 4, the reactions of [Pt(PEt3)4]
with 2,2?-bithiophene (2) and 1-methyl-2-(2-thienyl)pyr-
role (3) led to the formation of two types of products.
Fig. 1. Ball-and-stick diagram of the molecular structure of 4.
Table 2
Selected bond angles (8) of 4
CÃ
/
S activation gave thiaplatinacycles 5a and 6a
(Scheme 2). The 31P NMR spectra of these complexes
were very similar to that obtained for 4 (Table 4).
The second type of insertion product observed was
C(1)Ã
C(1)Ã
P(2)ÃPtÃ
C(1)ÃPtÃ
P(2)ÃPtÃP(1)
S(1)ÃPtÃP(1)
C(6)ÃS(1)ÃPt
C(2)ÃC(1)Ã
C(1)ÃC(2)Ã
C(3)ÃC(6)Ã
C(6)ÃC(3)Ã
/
PtÃ
/
P(2)
85.4(4)
89.8(4)
C(3)Ã
C(6)Ã
C(4)Ã
C(3)Ã
C(5)Ã
C(1)Ã
C(3)Ã
C(2)Ã
C(5)Ã
C(4)Ã
C(6)Ã
/
S(2)Ã
C(3)Ã
C(5)Ã
C(6)Ã
C(4)Ã
C(2)Ã
C(2)Ã
C(3)Ã
C(6)Ã
C(5)Ã
C(5)Ã
/
C(4)
90.8(6)
110.(1)
111.(1)
115.(1)
114.(1)
122.(1)
115.(1)
121.(1)
119.(1)
125.(1)
124.(1)
/
PtÃ
/S(1)
/
/
S(2)
C(6)
C(5)
S(2)
C(7)
C(7)
S(2)
S(1)
C(8)
C(8)
/
/S(1)
173.7(1)
176.1(3)
97.73(9)
87.24(9)
112.0(4)
138.(1)
/
/
/
/
P(1)
/
/
hydrido platinum(II) complexes, obtained via CÃ
/
H
/
/
/
/
activation. Oxidative insertion at an unsubstituted a-
position of the thienyl rings in 2,2?-bithiophene (2) and
in 1-methyl-2-(2-thienyl)pyrrole (3) led to the formation
of 5b and 6b respectively (Scheme 3). The separation of
complexes 5a/5b and 6a/6b by column chromatography
/
/
/
/
/
/
/
/
/
/Pt
/
/
/
/
C(3)
S(1)
C(2)
123.(1)
125.8(9)
129.4(9)
/
/
/
/
/
/
/
/
/
/
1
led to decomposition. The assignments of the H-NMR
resonances for 5a/5b and 6a/6b (Table 5) were aided by
1
two-dimensional (1H, H) homonuclear chemical shift
correlation (COSY) experiments.
[24], 3-methylbenzothiophene [25], as well as 2-nitro-
and 3-chlorothiophene [14], reported in the literature.
The insertion reaction is stereoselective and the vinyl
1
The high field region of the H-NMR spectrum of 5b
showed a 1:2:1 triplet resonance at ꢃ7.30 ppm with
/
coupling to two equivalent phosphorus atoms (2JP,H
17.4 Hz) as well as coupling to platinum-195 (1JPt,H
ꢂ
/
CÃ
/
S bond rather than the aryl CÃ
/
S bond is the site of
attack [10,26]. Furthermore, the thienothiophene mole-
cule, 1, contains two thiophene moieties which allows
for the possibility of a double oxidative insertion to
form a unique dithiaplatinacycle. Attempts at preparing
ꢂ
/
713 Hz). This data is typical of hydride proton
resonances for trans HÃPtÃC(heteroaryl) type com-
plexes [29,30]. The hydride complex decomposes in
/
/
Table 3
Selected bond lengths (A) of 4
˚
PtÃ
PtÃ
PtÃ
PtÃ
/
C(1)
P(2)
S(1)
P(1)
2.04(1)
S(1)Ã
S(2)Ã
S(2)Ã
/
C(6)
C(3)
C(4)
1.75(1)
1.74(1)
1.73(2)
C(1)Ã
C(2)Ã
C(3)Ã
C(4)Ã
C(5)Ã
/
C(2)
C(3)
C(6)
C(5)
C(6)
1.29(2)
1.42(2)
1.37(2)
1.33(2)
1.43(2)
/
2.279(3)
2.290(2)
2.342(2)
/
/
/
/
/
/
/
/

J. Chantson et al. / Journal of Organometallic Chemistry 687 (2003) 39ꢀ
/45
43
Table 4
31P-NMR data for thiaplatinacycles 4, 5a and 6a
4
5a
6a
P trans to S
P trans to C
P trans to S
P trans to C
P trans to S
P trans to C
d (ppm)
1JPt,P (Hz)
2JP,P (Hz)
11.98
3140
22.9
0.20
1696
22.9
11.36
3145
22.9
0.50
1676
22.9
10.32
3094
23.4
0.93
1671
23.4
anionic ligand [31]. Similarly, the hydride proton of 6b
gives rise to a triplet pattern at ꢃ 17.5
7.24 ppm (2JP,H
/
ꢂ
/
Hz and 1JPt,H
ꢂ
713 Hz) in the 1H-NMR spectrum and a
/
singlet at 18.71 ppm (1JPt,P
ꢂ
2680 Hz) in the 31P-NMR
/
spectrum.
The 13C{1H}-NMR resonances could not be unam-
biguously assigned due to overlapping of signals and the
ipso-carbon atoms were obscured by low intensity
resonances from decomposition of the platinum(II)
complexes in solution.
In general the a-position of heteraromatic rings are
more susceptible to derivatisation than the b-position
[32]. A diplatinum complex of 2,2?-bithiophene, viz.
Scheme 3.
deuterated chloroform, presumable due to trace
amounts of hydrogen chloride in the solvent. With
1
time the H-NMR hydride resonance disappears and a
new 31P-NMR singlet resonance at 3.54 ppm (1JPt,P
ꢂ
/
3470 Hz) takes the place of the original singlet at 18.66
ppm (1JPt,P
2674 Hz). This new resonance is typical of
cis-[PtX2(PEt3)2] complexes, where Xꢂcarbon-donor
trans, trans-[Cl(PBu3)2Pt(m-2,5?-C4H2SC4H2S)Pt
(PBu3)2Cl] has been reported in the literature, however
ꢂ
/
/
Table 5
1H-NMR for 5a, 5b and 6a, 6b

44
J. Chantson et al. / Journal of Organometallic Chemistry 687 (2003) 39ꢀ45
/
no 31P-NMR data was provided [33]. The related
diplatinum thienyl derivative trans, trans-[Cl
(PBu3)2Pt(m-2,5-C4H2SPt(PBu3)2Cl] has a 31P-NMR
4. Conclusion
The reaction of 3,6-dimethylthieno[3,2-b]thiophene
with [Pt(PEt3)4] yielded a thiaplatinacycle via an oxida-
1
chemical shift of 18.91 ppm with JPt,P of 2673 Hz,
which corresponds well with the trans diphosphane
1
structure of 5b and 6b. The values of the JPt,P coupling
tive insertion into a C(vinyl)Ã
/
S bond. While the
thiophene-containing molecules 2,2?-bithiophene and
1-methyl-2-(2-thienyl)pyrrole both formed analogous
thiaplatinacycles, as deduced from NMR spectra, these
constant is characteristic of a trans-phosphane platinu-
m(II) hydrido species [29,30].
Studies of the reaction of 1-methylpyrrole with
molecules also underwent CÃ
/
H activation to generate
[Pt(PEt3)4] shows that CÃ
/
H activation on the pyrrole
ring is extremely sluggish [30], and the most likely
trans-[PtH(PEt3)2(2-thienyl)] type complexes. In the case
of 1-methyl-2-(2-thienyl)pyrrole it was concluded that
position of attack of Pt(0) on 3 is at the a-carbon of
the site of CÃ
/
H activation was at the thienyl rather than
the thienyl ring. Insertion thus occurs at a CÃ
/H bond on
the 1-methylpyrrolyl ring.
the thienyl ring rather than on the pyrrolyl ring, and this
1
is also supported by the H-NMR data. Interestingly,
insertion of the platinum centre at the C(2)Ã
which links the thienyl ring to the pyrrolyl ring did not
occur. Although CÃH activation is generally easier to
achieve than CÃC oxidative insertion [34], this bond has
been found to be readily labilised when attempting to
obtain chromium, molybdenum and tungsten carbene
derivatives of 1-methyl-2-(2-thienyl)pyrrole [35]. Upon
lithiation of the molecule with two to three equivalents
/
C(2?) bond
5. Supplementary material
/
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC no. 214446 for compound 4.
Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road,
/
Cambridge CB2 1EZ, UK (Fax.: ꢁ44-1223-336-033; e-
/
of n-butyllithium, C(2)Ã
/
C(2?) bond scission leads to the
mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
formation of two separate carbene complexes, namely 2-
butylthienyl and 1-methylpyrrolyl derivatives.
When a mixture of two equivalents of 2,2?-bithio-
phene and one equivalent of [Pt(PEt3)4] was heated for
20 h in refluxing toluene, a mixture of approximately
1:1.3 (based on NMR data) of 5a and 5b was obtained.
Increasing the reaction time to 72 h favoured the
formation of the thiaplatinacycle 5a over the hydride
Acknowledgements
This material is based upon work supported by the
National Research Foundation under Grant number
2053853.
5b. This was consistent with the conclusion that the CÃ
insertion product is thermodynamically more stable [36].
Jones and co-workers [37] have shown that both CÃ
and CÃS insertion occurs when [(C5Me5)Rh(PMe3)(H)2]
is irradiated at low temperature in the presence of
thiophene. On warming to r.t., the CÃH insertion
product [(C5Me5)Rh(PMe3)(2-thienyl)H] isomerised to
S insertion
/
S
/
H
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