Synthesis, structure and reactivity of cis-[PtL2(1-alkenyl)2] complexes

Article abstract of DOI:10.1016/j.poly.2007.08.036

The synthesis and characterization of several new bis(1-alkenyl)platinum(II) complexes have been carried out. The structure of cis-[Pt(dppp)((CH₂)₆CH{double bond, long}CH₂)₂] has been determined by X-ray crystallography. The stability and reactivity of the compounds, cis-[PtL₂((CH₂)_nCH{double bond, long}CH₂)₂] (n = 3 or 4 and L₂ = 1,3-bis(diphenylphosphino)propane (dppp), 1,2-bis(diphenylphosphino)ethane (dppe), L = PPh₃) is strongly dependent on the nature of ligand systems. It is found that the insertion of carbon monoxide into the metal-carbon bonds of the platinum alkenyl complexes is possible. Other reactions including transmetalation, intermolecular alkenyl migrations, oxidative addition of methyl iodide are described and the thermal decomposition of the bis(alkenyl) complexes are also reported.

Full text of DOI:10.1016/j.poly.2007.08.036

Available online at www.sciencedirect.com
Polyhedron 27 (2008) 44–52
www.elsevier.com/locate/poly
Synthesis, structure and reactivity of cis-[PtL2(1-alkenyl)2] complexes
Akella Sivaramakrishna, Banothile C.E. Makhubela, Feng Zheng, Hong Su,
*
Gregory S. Smith, John R. Moss
Department of Chemistry, University of Cape Town, Rondebosch, 7701 Cape Town, South Africa
Received 10 May 2007; accepted 31 August 2007
Available online 23 October 2007
Abstract
The synthesis and characterization of several new bis(1-alkenyl)platinum(II) complexes have been carried out. The structure of cis-
[Pt(dppp)((CH2)6CH@CH2)2] has been determined by X-ray crystallography. The stability and reactivity of the compounds, cis-
[PtL2((CH2)nCH@CH2)2] (n = 3 or 4 and L2 = 1,3-bis(diphenylphosphino)propane (dppp), 1,2-bis(diphenylphosphino)ethane (dppe),
L = PPh3) is strongly dependent on the nature of ligand systems. It is found that the insertion of carbon monoxide into the metal–carbon
bonds of the platinum alkenyl complexes is possible. Other reactions including transmetalation, intermolecular alkenyl migrations, oxi-
dative addition of methyl iodide are described and the thermal decomposition of the bis(alkenyl) complexes are also reported.
ꢀ 2007 Elsevier Ltd. All rights reserved.
Keywords: Bis(alkenyl) complexes; Structure; Reactivity; Insertion reactions; Oxidative addition; Transmetalation
1. Introduction
2. Experimental
Metal–alkenyl complexes are an important class of com-
pounds. These compounds have been implicated as poten-
tial model compounds for intermediates in a number of
catalytic cycles as well as other applications [1]. Metal–
alkenyl complexes have been shown to act as precursors
for the preparation of thin metal films, which can in turn
be applied in the micro-electronics and catalysis industries
[2]. Recently we have shown that bis(1-alkenyl)platinum
2.1. Materials and methods
All manipulations were carried out under a nitrogen
atmosphere unless otherwise stated. Commercially avail-
able solvents were distilled from Na metal/benzophenone
ketyl before use.
2.1.1. Nuclear magnetic resonance spectroscopy
1H, 13C and 31P NMR spectra were recorded on a Bru-
ker DMX-400 spectrometer and all H chemical shifts are
reported relative to the residual proton resonance in deu-
terated solvents (all at 298 K, C6D6).
complexes undergo
a
novel ring closing metathesis
1
(RCM) reaction to give medium to large metallacycles
[3–5]. Selective and quantitative isomerization of cis-
[PtL2(1-alkenyl)2] to cis-[PtL2(2-alkenyl)2] complexes has
also been observed [6]. In order to explore the reactivity
pathways for these complexes, we have investigated some
novel reactions of platinum alkenyl complexes. The present
paper also explores the influence of the nature of phosphine
ligands on the reactivity aspects of the title compounds.
2.1.2. Elemental analysis
Microanalyses were conducted with a Thermo Flash
1112 Series CHNS-O Elemental Analyzer instrument.
2.1.3. GC–MS analysis
GC analyses were carried out using a Varian 3900
*
gas chromatograph equipped with an FID and
a
Corresponding author. Tel.: +27 21 650 2535; fax: +27 21 689 7499.
30 m · 0.32 mm CP-Wax 52 CB column (0.25 lm film
E-mail address: John.Moss@uct.ac.za (J.R. Moss).
0277-5387/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2007.08.036

A. Sivaramakrishna et al. / Polyhedron 27 (2008) 44–52
45
thickness). The carrier gas used was helium at 5.0 psi. The
oven was programmed to hold at 32 ꢁC for 4 min and then
to ramp to 200 ꢁC at 10 ꢁC/min and then hold for 5 min.
GC–MS analyses for peak identification were performed
using an Agilent 5973 gas chromatograph equipped with
MSD and a 60 m · 0.25 mm Rtx-1 column (0.5 lm film
thickness). The carrier gas was helium at a flow rate of
0.9 ml/min. The oven was programmed to hold at 50 ꢁC
for 2 min and then ramp to 250 ꢁC at 10 ꢁC/min and then
hold for 8 min.
a CH2Cl2/hexane mixture (3 ml: 5 ml) at À10 ꢁC for 48 h.
The pale yellow crystalline solid was separated by decant-
ing the mother liquor and dried under vacuum for 3 h.
For compound 6. Yield: 96%. M.p. 84–85 ꢁC. Anal. Calc.
for C36H42P2Pt: C, 59.09; H, 5.79. Found: C, 58.98; H,
1
5.69%. IR (mmax/cmÀ1) in CH2Cl2: 1605(m), 1636(s); H
NMR (300 MHz, CDCl3) d: 7.36–7.91 (m, 20H, Ph);
5.55–5.72 (m, 2H, @CH); 4.68–4.82 (m, 4H, @CH2);
1.96–2.22 (m, 4H, P-CH2); 1.21–1.88 (m, 12H, –CH2);13C
NMR (100 MHz, CDCl3) d: 141.01 (s, 2C);133.16–133.29
(m, 12C); 129.98 (s, 8C) 127.55–128.32 (m, 4C); 112.40 (s,
2C); 32.08–32.56 (m, 2C); 30.88 (s 2C); 29.03–29.79 (m,
2C); 22.57 (d, J = 6.67 Hz 2C) 21.60 (d, J = 6.58 Hz),
31P{1H} 45.76 (s) (JPt–P = 1641 Hz).
2.1.4. Infrared spectroscopy
Infrared spectra were recorded on a Perkin–Elmer Spec-
trum One FT-IR Spectrometer.
2.1.5. Materials
2.2.2. Carbonylation of compound 6
All chemicals were obtained commercially and
unless otherwise stated, were used as received without
further purification. 1-Alkenyl Grignard reagents (BrMg-
CH2CH2(CH2)nCH@CH2; n = 1,3,4,6) [7], Pt(COD)Cl2
[8], Pt(dppe)Cl2, [9] Pt(dppp)Cl2, [9] and Pt(PPh3)2Cl2 [9]
were prepared according to the literature procedures.
Compound 6 (262 mg, 0.358 mmol) was dissolved in tol-
uene (25 ml) of. After bubbling CO through the contents of
the flask for 5–6 min, the solution was stirred at room tem-
perature under ambient pressure of carbon monoxide (bal-
loon). After 72 h, the solvent was removed under the
reduced pressure. The residue was filtered and recrystal-
lized from a CH2Cl2/hexane mixture (2:1 v/v) to give com-
pound 10a. Yield: 62%. M.p. 118–126 ꢁC. Anal. Calc. for
C38H42O2P2Pt: C, 57.94; H, 5.37. Found: C, 58.16; H,
Bis(1-octenyl)(dppp)platinum(II)
(1),
bis(1-hexenyl)
cis- bis(triphenylphosphine)platinum(II) (2), bis(1-hexe-
nyl)(dppp)platinum(II) (3), bis(1-pentenyl)cis-bis(triphen-
ylphosphine)platinum(II) (4) and bis(1-pentenyl)(dppp)-
platinum(II) (5) were prepared as reported earlier [4].
1
5.42%. IR (mmax/cmÀ1) in CH2Cl2: 1608(m), 1680(s). H
NMR (300 MHz, CDCl3) d: 7.24–7.91 (m, 20H, Ph);
5.54–5.69 (m, 2H, CH); 4.61–4.80 (m, 4H, @CH2); 1.98–
2.40 (m, 4H, P–CH2); 1.16–1.86 (m, 12H, CH2); 13C
NMR (100 MHz, CDCl3) d: 206.78 (s, 2C); 140.92 (s,
2C); 133.21–133.58 (m, 12C); 129 (s, 8C); 126.71–128.37
(m, 4C); 112.30 (s, 2C); 31.55 (m, 2C); 30.87 (s, 2C) 25.10
(d, J = 8.66 Hz); 24.14 (d, J = 8.71 Hz) 31P{1H} 46.00 (s)
(JPt–P = 2320 Hz).
2.1.6. Crystallographic data for compound 1
Single crystals of compound 1 were obtained by
recrystallization and slow evaporation from Et2O at room
temperature. Intensity data for the compound 1 was col-
lected at 113 K on a Nonius Kappa CCD diffractometer
using graphite- monochromated Mo Ka radiation
˚
ꢀ
˚
(k = 0.71073 A). C43H56P2Pt, M = 829.91, triclinic, P1,
a = 12.59740(10), b = 12.98700(10), c = 14.5363(2) A,
2.2.3. Carbonylation of compound 1
a = 110.3300(10)ꢁ, b = 90.6480(10)ꢁ, c = 117.1230(10)ꢁ,
A similar procedure was followed by taking compound
1 (61 mg, 0.073 mmol) in a round bottom flask containing
toluene (15 ml). The reaction was carried out and worked-
up as described above to give compound 10b as colourless
crystals. Yield: 86%. M.p. 104–105 ꢁC. Anal. Calc. for
C45H56O2P2Pt: C, 61.01; H, 6.37. Found: C, 61.16; H,
V = 1943.33(3) AÀ3, Z = 2, l = 3.720 mmÀ1, unique reflec-
˚
tions = 55624/7391 [R(int) = 0.0467], R1 = 0.0210, wR2 =
0.0433 [I > 2r(I)].
2.2. Synthesis of the metal complexes
1
6.42%. IR (mmax/cmÀ1) in CH2Cl2: 1605(m), 1676(s). H
2.2.1. Preparation of bis(1-pentenyl)(dppe)platinum(II)
(6)
NMR (300 MHz, CDCl3) d: 7.21–7.97 (m. 20H, Ph);
5.40–5.70 (m, 2H, @CH); 4.63–4.73 (m, 4H @CH2); 1.99–
2.15 (m, 6H, P–CH2); 1.23–1.92 (m, 24H, CH2).
Pt(COD)Cl2 (506 mg, 1.352 mmol) in diethyl ether
(20 ml) was cooled to À78 ꢁC and of 1-pentenyl Grignard
reagent (2.8 ml, 1.34 M, 3.75 mmol) was added. The solu-
tion was warmed to 0 ꢁC and then stirred until the solution
became clear. To this, solution dppe (539 mg, 1.353 mmol)
was added and stirred for 30 h until a clear solution was
formed. The excess Grignard reagent was removed by
hydrolyzing the reaction mixture with saturated aqueous
NH4Cl (5 ml) at À78 ꢁC. The aqueous layer was washed
with dichloromethane (2 · 5 ml), dried with anhydrous
magnesium sulfate and filtered. The solvent was removed
under reduced pressure and the residue recrystallized from
2.2.4. Reaction of Pt(1-pentenyl)2 (PPh3)2 (4) with
[Cp*IrCl2]2
Compound 4 (232 mg, 0.271 mmol) and [Cp*IrCl2]2
(0.104 mg, 0.135 mmol) were transferred into a Schlenk
flask containing toluene (5 ml). The mixture was heated
for 3 h at 85–90 ꢁC. A colourless precipitate was formed
during the reaction. The solvent was removed in vacuo.
The mixture was treated with diethylether (5 ml). The insol-
uble crystalline solid was found to be a mixture of
[Pt(PPh ) Cl ] and [IrCp (PPh )Cl ]. The products 13 and
*
3 2
2
3
2

46
A. Sivaramakrishna et al. / Polyhedron 27 (2008) 44–52
14 from the solution were separated by using a p-TLC
with CH2Cl2 as an eluent. The pale yellow band was
extracted and compound 13 was obtained as a yellow
oily substance (48 mg). The oil was treated with n-hex-
ane (3 ml) and on cooling a yellow solid resulted which
was shown to be compound 13, bis(1-pentenyl)(tetra-
methylcyclopentadienyl)iridium(III)- (triphenylphosphine)
Yield: 50%. M.p. 66–68 ꢁC. Anal. Calc. for C37H46IrP:
C, 62.24; H, 6.49. Found: C, 62.43; H, 6.59%. 1H
NMR (300 MHz, CDCl3) d: 6.99–8.10 (m, 15H, Ph);
5.63–5.94 (m, 2H, @CH); 4.88–5.13 (m, 4H, @CH2);
4.19 (s, 1H, Cp*–H); 0.76–2.12 (m, 12H, CH2);
31P{1H} 25.88 (s).
2.2.6. Reaction of Pt(1-pentenyl)2 (dppp) (6) with MeI
Compound 6 (304 mg, 0.415 mmol) and 118 mg of MeI
(0.832 mmol) were taken in to of CH2Cl2 (5 ml). After stir-
ring at room temperature for 72 h, a pale yellow precipitate
was formed. The precipitate was washed with diethylether
(5 ml) and recrystallized from CH2Cl2–hexane mixture
(1:1). The product was found to be compound 9b. The
product 9a was isolated from the solution. After removing
the solvent, the compound was recrystallized from a mix-
ture of toluene (2 ml) and hexane (1 ml). The liquid prod-
uct was found to be 5-iodo-1-pentene. For compound 9a,
(1-pentenyl)(methyl)[1,2-bis-(diphenylphosphino)ethane]
platinum(II). Yield: 52%. M.p. 110–112 ꢁC. Anal. Calc. for
C32H36P2Pt: C, 56.72; H, 5.35. Found: C, 56.66; H, 5.62%.
1H NMR (300 MHz, CDCl3) d: 7.18–7.92 (m, 20H, Ph);
5.69–5.86 (m, 1H, @CH); 4.77–4.98 (m, 2H, @CH2);
1.85–2.29 (m, 4H, P–CH2); 1.15–1.67 (m, 6H, CH2);
31P{1H} d 45.96, 45.91 (d), 45.76, 45.70 (d) (1685 and
1635 Hz).
2.2.5. Reaction of Pt(1-pentenyl)2 (dppp) (5) with
[Cp*IrCl2]2
Compound 5 (202 mg, 0.272 mmol) and [Cp*IrCl2]2
(0.105 mg, 0.136 mmol) were taken in to a Schlenk flask
containing toluene (15 ml). The mixture was heated for
13 h at 85–90 ꢁC. The colourless precipitate that formed
during the reaction was found to be compound 11, (g3-
dimethylallyl)[1,3-bis(diphenyl phosphino)propane]-plati-
num(II)chloride. Yield: 68%. M.p. 144–146 ꢁC. Anal. Calc.
for C32H35P2PtCl: C, 53.97; H, 4.95. Found: C, 54.16; H,
4.88%. 1H NMR (300 MHz, CDCl3) d: 7.23–7.78 (m,
20H, Ph); 3.30–3.87 (m, 3H, allylic-H); 2.17–2.67 (m, 4H,
P–CH2); 1.09–1.17 (m, 6H, CH2); 31P{1H} À1.32 (s) (JPt–
P = 3828 Hz). All the solvent was removed from the solu-
tion and the obtained pale yellow solid was recrystallized
from 1:1 n-hexane-diethylether mixture to yield the com-
pound 12. Yield: 75%. M.p. 108–112 ꢁC. Anal. Calc. for
C14H22IrCl: C, 40.23; H, 5.31. Found: C, 40.46; H,
3. Results and discussion
3.1. Synthesis and characterization of compounds
The bis(alkenyl)–platinum complexes were prepared in
high yields by reacting the appropriate Grignard reagents
with Pt(COD)Cl2. Several derivatives of these compounds
were synthesized using various ligand systems, mainly,
PPh3, dppe and dppp (Scheme 1). All the data gathered
for compounds (1–6) are consistent with the proposed for-
1
mulations. The H NMR spectra exhibit signals which are
characteristic of species containing a vinylic functionality,
while the 31P NMR spectra showed sharp singlets with
their respective platinum satellites. Single crystals of
compound 1 were obtained by recrystallization from
Et2O at room temperature. Crystallographic data are listed
1
5.36%. H NMR (300 MHz, CDCl3) d: 4.43 (s, 1H, Cp–
H); 3.95 (m, 1H, CH); 2.95 (m, 1H, CH–CH3); 2.20 (m,
2H, –CH2), 1.81 (s, 12H, Cp–CH3), 1.52–1.61 (m, 2H,
CH2); 0.92–1.06 (m, 3H, CH3).
1-alkenyl
Grignard
Reagent
Pt
(CH2)nCH=CH2
Pt
Cl
(CH2)nCH=CH2
Cl
(CH2)nCH=CH2
L
+ L
Pt
-COD
L
(CH2)nCH=CH2
1, L2 = dppp, n = 6;
2, L = PPh3, n = 4;
3, L2 = dppp, n = 4;
4, L = PPh3, n = 3;
5, L2 = dppp, n = 3;
6, L2 = dppe, n = 3.
Scheme 1.

A. Sivaramakrishna et al. / Polyhedron 27 (2008) 44–52
47
Table 1
The interaction of metal–alkenyls with electrophilic
reagents such as acids and halogens gives the correspond-
ing hydrocarbons or 1-haloalkenes resulting from the
cleavage of metal–carbon bonds and the hydrogenation
and hydroformylation reactions of some metal alkenyl
compounds have been reported with the Lewis acid TiCl4
[1b], we explored other novel reactions with various sub-
strates. The group 10 metal-catalyzed cross-coupling reac-
tions are very important in organic synthesis through
oxidative addition, transmetallation, and reductive elimi-
nation steps [11]. Some of these reactions may have consid-
erable potential in chemical synthesis, since they provide a
method for the formation of new C–C bonds by reductive
elimination or formation of C–X bonds. The effect of the
length of the alkenyl chains, the influence of the solvent
as well as the nature of ligand systems on the reactivity
of the title compounds will be discussed.
˚
Selected bond distances (A) and angles (ꢁ) of compound 1
Bond distances
Pt(1)–C(61)
Pt(1)–C(51)
Pt(1)–P(1)
Pt(1)–P(2)
2.119 (3)
2.120 (3)
2.2766 (7)
2.2873 (7)
C(56)–C(55)
C(65)–C(66A)
C(57)–C(58)
1.526 (4)
1.5207 (7)
1.292 (5)
1.211 (7)
C(68A)–C(67A)
Bond angles
C(61)–Pt(1)–C(51)
C(61)–Pt(1)–P(2)
P(1)–Pt(1)–P(2)
85.05 (10)
91.98 (7)
92.97 (2)
C(51)–Pt(1)–P(1)
C(61)–Pt(1)–P(1)
C(51)–Pt(1)–P(2)
89.86 (8)
174.78 (7)
173.58 (7)
in Section 2, and selected bond distances and angles are
given in Table 1.
The molecular structure of compound 1 (Fig. 1) shows
square-planar coordination geometry around the platinum.
The Pt–C and Pt–P bonds of compound 1 are similar and
comparable with the literature reports of similar compounds
˚
˚
[10] (2.119(3)–2.120(3) A and 2.2766(7)–2.2873(7) A, respec-
3.3. Thermal decomposition and rearrangement reactions
tively), while the C@C distances range from 1.211(7) to
1.292(5) A. The P–Pt–P, P–Pt–C and C–Pt–C bond angles
˚
Although thermal decomposition pathways of metal–
alkenyl complexes may be similar to those of metallacycles
or metal alkyl complexes, the products formed can differ
considerably because of the pendant alkene functionality.
The thermal stability of the metal–alkenyl complexes is
dependent on the solvent system, thus halogenated
solvents readily cleave the M–C bond to form metal
halides irrespective of the ligand system. Bis(alkenyl) metal
complexes can give various products on decomposition
(Scheme 2).
in compound 1 are observed as 92.97(2), 89.86(8) to
91.98(7) and 85.05(10), respectively.
3.2. Reactivity of metal–alkenyl complexes
Generally, metal alkenyl complexes can show two dis-
tinct reaction pathways: (i) reaction at the M–C bond (ii)
coordination of the pendant alkene. It is interesting to note
that these special features impart novel chemistry to these
compounds [1a].
Fig. 1. Molecular structure and atom labeling scheme for compound 1. Displacement ellipsoids are drawn at the 40% probability level and H atoms are
shown as small spheres of arbitrary radii. Atom C67 was disordered over two positions: C67A with Site Occupancy 0.535 and C67B with Site Occupancy
0.465.

48
A. Sivaramakrishna et al. / Polyhedron 27 (2008) 44–52
L
150-250oC
n
Pt
(L2Pt)m
+
n
L
n
L = PPh3 or
L2 = dppp or dppe.
n = 2 and 4
+
n
n
Scheme 2.
Our present experiments show that the organic products
decomposition of metallacycloalkanes through b-hydride
elimination [12,13].
depend on the nature of the ligands, and this may relate to
the stability and reactivity of the metal–alkenyl compounds
in solution. Thus the triphenylphosphine complexes,
Pt(PPh3)2{(CH2)nCH@CH2}2 were found to yield an intense
red colour on decomposition which we believe to be due to
[(PPh3)2Pt]m clusters. In contrast, the PtL2[(CH2)3CH@
CH2]2 complexes (where L2 = dppp or dppe) were found
to be quite stable up to 100 ꢁC [6]. The diphosphine ligands
have generally been found to increase the thermal stability of
the complexes significantly. It is also believed that metal
alkenyl species may be important intermediates in the
Several interesting trends were noted in the products iso-
lated from the thermolysis reactions. First, all the decom-
position reactions showed the presence of 2-alkene and
cycloalkane as major components. Second, the organic
product distributions are quite dependent on the time of
heating as well as the medium of reaction whether in the
solid state or in solution (Table 2). It can be seen that there
is a significant decrease in the quantities of 1-alkene species
with increasing the time of heating, with the exception of
PPh3 derivatives, which is in agreement with earlier reports
[6]. Further thermal studies will be carried out to try and
understand the mechanistic aspects for the formation of
the organic products in these reactions.
Table 2
Thermal decomposition of bis(1-hexenyl)(dppp)platinum(II) (3), at 175 ꢁC
Medium Observed products (%)*
3.4. Oxidative addition
n-
1-
2-Hexene
Cyclohexane 1,5-
Hexadiene
The oxidative addition of organic molecules to unsatu-
rated transition metal complexes is a fundamental process
in organometallic chemistry and catalytic reactions [14].
It was found that the bis(alkenyl)platinum(II) complexes
undergo oxidative addition reactions with methyl iodide
to yield different products, depending on the experimental
conditions (Schemes 3 and 4). It is presumed that the reac-
tion proceeds via the formation of hexacoordinate plati-
num(IV) species by oxidative addition as reported earlier
Hexane Hexene (cis- + trans-
isomers)
Solid
1 h
3 h
10 h
24 h
CH2Cl2
25
2
1
0
14
8
0
0
0
0
41
63
63
71
83
14
22
18
21
3
11
12
8
8
1
By GC–MS analysis.
Ph3P
Ph3P
CH3
I
Pt
7
2 : 1,
RT; DCM
Ph3P
Ph3P
Me
Pt
I
Ph3P
Ph3P
MeI
Pt
2
Neat,
RT
[PPh3CH3]+I- + other decomposed products
8
Scheme 3.

A. Sivaramakrishna et al. / Polyhedron 27 (2008) 44–52
49
Ph2
P
products. In contrast, the presence of excess MeI showed
the quantitative formation of the known methylphosphoni-
um iodide salt (8). The decomposed products could not be
identified or isolated. The formation of the new compound
9a (15%) and known compound 9b (41%) [16] were evident
when the ligand was dppe in the presence of 1:2 MeI
(Scheme 4). The formation of 5-iodo-1-pentene (32%)
was also confirmed. It is of interest to note that the addi-
tion of MeI allowed the formation of a new metal–carbon
bond and breaking of already existing metal–carbon bond
simultaneously, this is significant. The nature of ligand sys-
tems show a marked effect in oxidative addition reactions,
which may be due to differences in steric, electronic and
chelating effects in the ligands.
Ph
P
2 Me
2MeI, DCM
Pt
Pt
I
P
P
Ph2
Ph2
5
Ph2
P
Pt
CH3
P
Ph2
9a
+
Ph2
P
I
Pt
CH3
P
Ph2
3.5. Carbonylation
9b
+
I
Carbon monoxide insertion into M-alkyl as well as M-
acyl bonds to form M-acyl as well as a-ketoacyl complexes
Scheme 4.
PPh2
[15]. The organic products were found to be 1-alkenes,
2-alkenes and a,x-dienes. Attempts to isolate these
intermediate hexacoordinate platinum(IV) species were
unsuccessful.
[Cp*MX2]2
Toluene
13 h, 85
2
+
Pt
OC
P
Ph2
M = Ir
5
X-
Surprisingly, the oxidative addition of MeI to com-
pound 2 afforded different products depending on the
experimental conditions and ligand systems (Scheme 3).
It is of interest to note that when MeI was allowed to react
with 2 in 2:1 molar ratio, a 70% of known compound
Pt(PPh3)2MeI (7) [16] was isolated. The major organic
products were found to be 1-hexene (56%), 2-hexene
(23%), 1,5-hexadiene (5%) as well as other unidentified
X-
PPh2
+
+
2
+
Pt
2
*Cp
M
P
Ph2
11
12
Scheme 6.
L
L
CO
Toluene
L
L
n
Pt
n
Pt
C
O
n
n
1, 5
n = 1, 4;
L2 = dppe or dppp
CO
O
C
L
L
n
Pt
C
O
n
10a: n =1; L2 = dppe
10b: n = 4; L2 = dppp
Scheme 5.

50
A. Sivaramakrishna et al. / Polyhedron 27 (2008) 44–52
Fig. 2. Molecular structure and atom labeling scheme for the cationic part of the compound 11, showing one of the two unique molecules (A and B) with
the atom-numbering scheme; the suffix a denotes the crystallographically independent molecule A. Displacement ellipsoids are drawn at the 25%
probability level and H atoms are shown as small spheres of arbitrary radii.
is well known in the literature [14,17]. It was found that the
reaction of carbon monoxide with the bis(pentenyl)plati-
num(II) complex L2Pt[(CH2)3CH@CH2]2 (L2 = dppe)
afforded the expected di(acyl) inserted products 10a while
the reactions with other bis(pentenyl) complexes gave
of ligand steric effects on transmetalation reactions of some
organometallic complexes [20].
The diphosphine ligand system allowed the quantitative
formation of allylic metal complexes after reaction of com-
pound 5 with the dimeric sandwich compounds of iridium
(Scheme 6). Products 11 and 12 were isolated from diethyl-
ether solution and characterized by spectroscopically.
Compound 11 was also characterized by X-ray analysis,
but the structure was not fully refined.1
1
unidentified products (L2 = COD). The H NMR spectra
of the reaction mixture (L = PPh3 and L2 = dppp) showed
very complex signals indicating the presence of the monoa-
cyl intermediate, which was identified by the characteristic
31P NMR spectrum. However, the reaction smoothly pro-
ceeds to the formation of compound 10a over time. This
was evidenced by the 13C NMR which shows a signal in
the region of d 206.8 ppm for the carbonyl carbon as well
as a signal at d 31.5 ppm corresponding to the carbon a
to the carbonyl carbon. The IR spectral analysis of the
reaction mixture also indicated the presence of bands cor-
responding to the coordinated CO, which may be due to
the replacement of PPh3 with CO ligands, when
L = PPh3. A solution of compound 1 in toluene was sub-
jected to carbonylation with carbon monoxide gas at room
temperature. This resulted in the insertion of CO into the
Pt–C r bond to afford the di-acyl product as a colourless
crystalline solid after 48 h (Scheme 5). Two strong IR
bands at 1605 cmÀ1 (C@C) and 1676 cmÀ1 (C@O) were
observed in the spectrum of compound 10b.
The Pt–P bonds of compound 11 are found to be
˚
2.261(2) and 2.265(2) A, while the Pt–C bond distances
˚
range from 2.156(10)–1.266(3) A (Fig. 2). Strikingly, the
distance between central allylic carbon (C3) and metal is
the shortest. The allylic carbon–carbon distances (C2–C3
and C3–C4), ranging from 1.349(18) to 1.427(16), showed
the nature of double bond and the other C1–C2 and C4–
C5 distances are found to be single bonds. The P–Pt–P,
P1–Pt–C2 and C–Pt–C bond angles in compound 11 are
observed as 94.69(11), 98.0(3) and 66.9(5), respectively.
In contrast, the PPh3 ligand system shows a different
trend in the reactivity by forming unexpected compounds
13 and 14 (Scheme 7). The compound can be easily
assigned in the 31P NMR, showing a signal at 26.4 ppm
1
The cationic part of the structure was completely solved, but we failed
to solve the counter anion because there were unidentified discrete solvent
molecules in this structure. However, the positions for the atoms of
cationic part of the compound 11 molecules were unambiguously placed
and refined with reasonable anisotropic displacement parameters. The
final R factor of 0.0591 is acceptable. We therefore report this structure
here. The parameters for crystal data collection and structure refinements
are in Table 1. The bond lengths, angles, torsion angles and other
molecular parameters are in Table 2–6 (see supporting information for the
tables and other details about the data collection).
3.6. Transmetalation reactions
Transmetalation is a fundamental step in cross-coupling
chemistry [11]. Various transmetalation reactions of group
10 metal halide complexes with organoboronic acid or
organometallic reagents have received recent attention
[18,19]. Clarke and Heydt have reported the importance

A. Sivaramakrishna et al. / Polyhedron 27 (2008) 44–52
51
Ph3P
Ph3P
Toluene
3h, 85-90oC
+
[Cp*IrCl2]2
2
Pt
4
*
Cp
+
+
Ir
Pt
Ph3P
13
14
+
Pt(PPh3)2Cl2
Cp*Ir(PPh3)Cl2
Scheme 7.
Ph2
P
C6D6
RT
R1R2SiCl2
+
Pt
P
Ph2
R1 = R2 = Ph or Me or Cl
6
Ph2
P
R1
Cl
+
Si
Pt
Cl
R2
P
Ph2
15
Scheme 8.
without any satellites. Pt(PPh3)2Cl2 and Cp Ir(PPh )Cl
plexes. Studies are in progress which should yield informa-
tion regarding further reactivity aspects and mechanisms of
reactions of these platinum(II) alkenyls and other metal
alkenyl compounds. Furthermore the scope of other inser-
tion reactions in the presence of, oxygen, sulphur dioxide,
carbon dioxide and elemental sulphur will be explored
which may lead to produce some interesting organic
products.
*
3
2
were also recovered from the reaction mixture as insoluble
solids from a benzene solution. All these products were iso-
lated and characterized. Data for compound 14 was in
agreement with the literature [21].
3.7. Alkenyl group migration reactions
The reaction of platinum(II)-alkenyls with halosilanes
yielded the corresponding alkenyl silane products (Scheme
8), with quantitative migration of the alkenyl chains from
the platinum to the silicon center. In all the reactions, the
products were isolated and identified. The characterization
of compound 15 is in agreement with previously reported
data [22].
Acknowledgements
We thank Anglo Platinum Corporation Ltd., Johnson
and Matthey, NRF and University of Cape Town for the
financial support.
Appendix A. Supplementary material
4. Conclusions
CCDC 631341 contains the supplementary crystallo-
graphic data for 1. These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.
html, or from the Cambridge Crystallographic Data Cen-
tre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
(+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.poly.2007.
08.036.
Various reactions of bis(alkenyl) platinum complexes
have been carried out and shown to yield interesting prod-
ucts. The chelating effect of diphosphine ligands is shown
to affect the stability as well as the reactivity aspects of
these title compounds significantly. It was also found that
these compounds decomposed in the presence of haloge-
nated solvents under light or heat. The length of alkenyl
chains did not influence the reactivity of the alkenyl com-

52
A. Sivaramakrishna et al. / Polyhedron 27 (2008) 44–52
[12] (a) R.H. Grubbs, A. Miyashita, Fundamental Res. Homogeneous
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