Selective isomerization of cis-PtL2(1-alkenyl)2 to cis-PtL2(2-alkenyl)2 complexes

Article abstract of DOI:10.1021/om0611249

Heating the 1-alkenyl complexes cis-[Pt(1-alkenyl)₂L ₂] [alkenyl = 1-pentenyl, 1-hexenyl, 1-heptenyl, and 1-octenyl; L₂ = 1,3-bis(diphenylphosphino)propane (dppp) or 1,2- bis(diphenylphosphino)ethane (dppe)] to 100°C caused a quantitative isomerization to the corresponding 2-alkenyl complexes cis-[Pt-(2-alkenyl) ₂L₂]. This novel isomerization is strongly dependent on the length of the alkenyl chains as well as the nature of the ligand, L ₂. The new 2-alkenyl complexes were fully characterized by analytical and spectroscopic methods. An X-ray crystal structure of cis-[Pt(2-pentenyl) ₂(dppp)] confirms this isomerization. Possible reaction mechanisms are discussed.

Full text of DOI:10.1021/om0611249

5786
Organometallics 2007, 26, 5786-5790
Articles
Selective Isomerization of cis-PtL2(1-alkenyl)2 to cis-PtL2(2-alkenyl)2
Complexes
Akella Sivaramakrishna, Hong Su, and John R. Moss*
Department of Chemistry, UniVersity of Cape Town, Rondebosch 7701, Cape Town, South Africa
ReceiVed December 12, 2006
Heating the 1-alkenyl complexes cis-[Pt(1-alkenyl)2L2] [alkenyl ) 1-pentenyl, 1-hexenyl, 1-heptenyl,
and 1-octenyl; L2 ) 1,3-bis(diphenylphosphino)propane (dppp) or 1,2-bis(diphenylphosphino)ethane
(dppe)] to 100 °C caused a quantitative isomerization to the corresponding 2-alkenyl complexes cis-[Pt-
(2-alkenyl)2L2]. This novel isomerization is strongly dependent on the length of the alkenyl chains as
well as the nature of the ligand, L2. The new 2-alkenyl complexes were fully characterized by analytical
and spectroscopic methods. An X-ray crystal structure of cis-[Pt(2-pentenyl)2(dppp)] confirms this
isomerization. Possible reaction mechanisms are discussed.
Scheme 1 . Transformation of (1-Alkenyl)platinum(II) to
(2-Alkenyl)platinum(II) Complexes
Introduction
Metal-alkenyl compounds are of interest since they are key
intermediates in some catalytic reactions1 and they have been
shown to be useful for generating thin platinum films2 for
microelectronic and catalytic applications3 using the chemical
vapor deposition (CVD) method.4 Thus metal-alkenyls are an
important class of compounds with potential useful applications;5
however, their chemistry is relatively unexplored. The stability
and reactivity of metal-alkenyl compounds depends on various
factors but particularly the metal and the other ligands.5 Recently
we have shown that these bis(alkenyl) metal complexes are
novel precursors for the preparation of a range of metallacy-
cloalkenes through the ring-closing metathesis ((RCM) reac-
tion.6,7
We now find that bis(1-alkenyl)platinum(II) complexes (1-
4) undergo an irreversible and quantitative isomerization in
solution to yield the corresponding bis(2-alkenyl)platinum(II)
complexes (5-8) without prior decomposition (see Scheme 1).
This is the first example of this type of transformation to the
best of our knowledge.5 However, there are some other similar
reports in the literature about the isomerization of related
organometallic species. Thus, the acid-catalyzed reversible
isomerization of 2-methylallyliridium(III) to the corresponding
2-methylprop-1-enyl complexes has been reported8 by Deeming
et al. Also a facile transformation between parallel and
perpendicular alkyne binding modes and subsequent formation
of vinyl groups on reaction of alkynes with the heterobinuclear
complex [RhMn(CO)4(dppm)2] have been reported.9 Recently,
the isomerization of the 1-alkenyl group in disubstituted
alkenylphosphine derivatives of [Rh6(CO)16] has been ob-
served.10 This isomerization occurs within the coordination
sphere of the hexarhodium clusters to give the allyl compounds
coordinated through the double bond of the rearranged alkenyl
moieties. In a similar way, the products obtained by the reactions
of µ3-alkenyl triruthenium carbonyl clusters with alkynes yielded
vinylidene-bridging complexes at refluxing temperatures.11 The
isomerization of cyano-olefins by nickel complexes has been
found to go through the formation of an intermediate π-me-
thylallyl metal complex.12
* Corresponding author. Fax: +27 21 689-7499. Tel: +27 21 650-2535.
E-mail: John.Moss@uct.ac.za.
(1) (a) Briggs, J. R. J. Chem. Soc., Chem. Commun. 1989, 11, 674. (b)
Turner, M. L.; Marsih, N.; Mann, B. E.; Quyoum, R.; Long, H. C.; Maitlis,
P. M. J. Am. Chem. Soc. 2002, 124, 10456.
Experimental Section
(2) (a) Tagge, C. D.; Simpson, R. D.; Bergman, R. G.; Hostetler, M. J.;
Girolami, G. S.; Nuzzo, R. G. J. Am. Chem. Soc. 1996, 118, 2634. (b)
Shibli, S. M. A.; Noel, M. J. Power Sources 1993, 45, 139.
(3) Dossi, C.; Psaro, R.; Bartsch, A.; Fusi, A.; Sordelli, U. R.;
Bellatreccia, M.; Zanoni, R.; Vlaic, G. J. Catal. 1994, 145, 377.
(4) (a) Bradley, D. C. Polyhedron 1994, 13, 1111. (b) Puddephatt, R. J.
Polyhedron 1994, 13, 1233.
(5) Sivaramakrishna, A.; Clayton, H.; Kauschula, C.; Moss, J. R. Coord.
Chem. ReV. 2007, 251, 1294.
(6) Dralle, K.; Jaffa, N. L.; Roex, T. L.; Moss, J. R.; Travis, S.;
Watermayer, N. D.; Sivaramakrishna, A. Chem. Commun. 2005, 3865.
(7) Sivaramakrishna, A.; Su, H.; Moss, J. R. Angew. Chem. Int. Ed. 2007,
46, 3541-3543.
All manipulations were carried out under a nitrogen atmosphere
unless otherwise stated. The solvents were commercially available
(8) Deeming, A. J.; Shaw, B. L.; Stainbank, R. E. J. Chem. Soc. A 1971,
374-376.
(9) Wang, L. S.; Cowie, M. Can. J. Chem. 1995, 73, 1058-1071.
(10) Krupenya, D. V.; Selivanov, S. I.; Tunik, S. P.; Haukka, M.;
Pakkanen, T. A. Dalton Trans. 2004, 2541-2549.
(11) Cabeza, J. A.; del Rio, I.; Martinez-Mendez, L.; Perez-Carreno, E.
Chem.-Eur. J. 2006, 12, 7694-7705.
(12) Acosta-Ramirez, A.; Flores-Gaspar, A.; Munoz-Hernandez, M.;
Arevalo, A.; Jones, W. D.; Garcia, J. J. Organometallics 2007, 26, 1712-
1720.
10.1021/om0611249 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 10/19/2007

SelectiVe Isomerization of cis-PtL2(1-alkenyl)2
Organometallics, Vol. 26, No. 24, 2007 5787
dCHCH2-), 126.5-131.6 (m, Ph), 123.9, 124.3, 124.7 (isomers,
dCHCH3), 29.6, 27.6, 26.0, 23.2, 17.6, 14.1.
cis-[Pt(2-hexenyl)2(dppp)] (6). Compound 6 was prepared in
the same fashion as compound 5 utilizing (108 mg, 0.14 mmol) of
2 in toluene at 110 °C for 60 h. After removing the solvent, the
residue crystallized out of 10 mL of n-hexane at -10 °C and was
recrystallized from a CH2Cl2/n-hexane mixture. The yield of the
white crystalline solid was 84 mg (78%), mp 96-98 °C (dec). Anal.
Calcd for C39H48P2Pt: C, 60.53; H, 6.25. Found: C, 60.64; H, 6.17.
1H NMR: δ 6.95-7.62 (m, 20H, Ph), 5.22-5.59 (m, 4H, dCH),
1.82-2.19 (m, 6H, P-CH2), 0.73-1.79 (m, 18H, CH2 and CH3).
31P NMR: δ 3.94 (m) (1631 Hz).
and distilled from dark purple solutions of sodium/benzophenone
ketyl. 1H and 31P NMR spectra were recorded on a Bruker DMX-
400 spectrometer, and all H chemical shifts are reported relative
1
to the residual proton resonance in the deuterated solvents (all at
298 K, C6D6). Microanalyses were conducted with a Thermo Flash
1112 Series CHNS-O Analyzer instrument. GC analyses were
carried out using a Varian 3900 gas chromatograph equipped with
an FID and a 30 m × 0.32 mm CP-Wax 52 CB column (0.25 µm
film thickness). The carrier gas 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 deg/min and hold 5 min. GC-MS analyses for peak
identification were performed using an Agilent 5973 gas chromato-
graph equipped with MSD and a 60 m × 0.25 mmRtx-1 column
(0.5 µm film thickness). The carrier gas was helium at 0.9 mL/
min. The oven was programmed to hold at 50 °C for 2 min and
then ramp to 250 °C at 10 deg/min and hold 8 min. Pt(COD)Cl2,13
Pt(PPh3)2Cl2,14 Pt(dppp)Cl2,14 and 1-alkenyl Grignard reagents
(BrMgCH2CH2(CH2)nCHdCH2; n ) 1, 3, 4, 6) were prepared
according to literature procedures.15 The compounds 2-4 were
prepared in a similar way to that mentioned above7 (eq 1).
cis-[Pt(1-pentenyl)2(dppp)] (1). In a Schlenk flask, Pt(COD)-
Cl2 (406 mg, 1.085 mmol) in diethyl ether (20 mL) was cooled to
-78 °C and 1-pentenyl Grignard reagent (2.8 mL of 1.34 M, 3.75
mmol) was added. The solution was brought to ca. 0 °C and then
stirred until the solution became clear. To this dppp was added
(448 mg, 1.086 mmol) and the reaction mixture stirred for 36 h
until a clear solution was formed. The excess Grignard reagent was
removed by hydrolyzing the reaction mixture with 5 mL of saturated
aqueous NH4Cl at -78 °C. The aqueous layer was washed with 3
× 5 mL of dichloromethane before the organic layer was separated.
All the volatiles in the flask were removed under reduced pressure,
and the residue obtained was recrystallized from a CH2Cl2/hexane
mixture (5 mL:10 mL) at -10 °C for 48 h. The colorless crystalline
solid was separated by decanting the mother liquor and dried under
vacuum. For 1: mp 120-122 °C; yield 97%. Anal. Calcd for
C37H44P2Pt: C, 59.59; H, 5.95. Found: C, 59.50; H, 5.68. 1H
NMR: δ 7.22-7.60 (m, 20H, Ph), 5.48-5.62 (m, 2H, dCH);
4.67-4.77 (m, 4H, dCH2), 2.43-2.56 (m, 6H, P-CH2), 0.86-
2.08 (m, 12H, -CH2). 31P{1H} NMR: 3.59 (s) (JPt-P ) 1623 Hz).
13C{1H} NMR: 140.8 (s, CHd), 127.3-134.1 (m, Ph), 112.7 (s,
dCH2), 40.8, 32.1, 28.2, 24.5, 25.5, 25.6, 20.3.
cis-[Pt(2-heptenyl)2(dppp)] (7). Compound 7 was prepared in
the same fashion as compound 5 utilizing (125 mg, 0.156 mmol)
of 3 in toluene at 110 °C for 24 h and recrystallized as described
for compound 6. The yield was 101 mg (81%) of the white
crystalline solid, mp 88-90 °C (dec). Anal. Calcd for C41H52P2Pt:
1
C, 61.41; H, 6.54. Found: C, 61.68; H, 6.62. H NMR: δ 6.95-
7.63 (m, 20H, Ph), 5.27-5.51 (m, 4H, dCH), 2.02-2.14 (m, 6H,
P-CH2), 0.71-1.97 (m, 22H, CH2 and CH3). 31P NMR: δ 3.4 (s)
(1625 Hz).
cis-[Pt(2-octenyl)2(dppp)] (8). Compound 8 was prepared in the
same fashion as compound 5 utilizing (120 mg, 0.145 mmol) of 4
in toluene at 110 °C for 18 h and recrystallized as described for
compound 6. The yield of the white crystalline solid was 106 mg
(88%), mp 82-85 °C (dec). Anal. Calcd for C43H56P2Pt: C, 62.23;
1
H, 6.80. Found: C, 62.41; H, 6.82. H NMR: δ 6.96-7.61 (m,
20H, Ph), 5.27-5.41 (m, 4H, dCH), 2.05-2.17 (m, 6H, P-CH2),
0.75-2.04 (m, 26H, CH2 and CH3); 2.34-3.43 (m, 6H, P-CH2),
0.88-2.35 (m, 14H, CH2). 31P NMR: δ 3.66 (s) (1611 Hz). 13C-
{1H} NMR: 133.7, 133.8, 133.9 (isomers, dCHCH2-), 127.7-
132.2 (m, Ph), 123.8, 124.4, 124.8 (isomers, dCHCH3), 36.7, 33.1,
30.16, 29.6, 27.6, 26.0, 23.1, 18.1, 14.3, 13.8.
cis-[Pt(octyl)2(dppp)] (11). In a Schlenk flask, Pt(COD)Cl2 (306
mg, 0.818 mmol) in diethyl ether (15 mL) was cooled to -78 °C
and octyl Grignard reagent (4.7 mL of 0.62 M, 2.863 mmol) was
added. The solution was brought to ca. 0 °C and then stirred until
the solution became clear. To this was added dppp (338 mg, 0.819
mmol) and the reaction mixture stirred for 36 h until a clear solution
formed. The reaction mixture was worked up as described in the
preparation of compound 1. The colorless crystalline solid was
obtained from the mother liquor and dried under vacuum for few
hours. For 9: yield 94%, mp 93-95 °C. Anal. Calcd for C45H66P2-
1
Pt: C, 62.55; H, 7.70. Found: C, 62.38; H, 7.66. H NMR: δ
7.67-7.7 (m, 20H, Ph); 2.05-2.21 (m, 6H, P-CH2); 0.79-1.89
(m, 34H, -CH2). 31P{1H} NMR: δ 3.91 (s) (JPt-P ) 1619 Hz).
Results and Discussion
cis-[Pt(2-pentenyl)2(dppp)] (5). A Schlenk flask was charged
with (115 mg, 0.154 mmol) of 1 in toluene (30 mL), and the mixture
was heated at 110 °C for 125 h under reduced pressure. The reaction
Heating compounds 1-4 in toluene or benzene at 110 °C
results in quantitative isomerization of both 1-alkenyl chains
to yield the 2-alkenyl platinum(II) complexes (5-8) (Scheme
1). These reactions are completely selective, as there is no
indication of any further isomerization to 3-alkenyl species or
indeed any other organic decomposition products. All the
products 5-8 were isolated in good yields and fully character-
ized by analytical and spectroscopic methods (see Experimental
Section). These reactions can readily be followed by observing
the disappearance of the terminal dCH2 signal of 1-4 in the
1H NMR spectrum and the appearance of a new dCH signal.
Fine structure in the 31P NMR spectra for 5 and 6 (see Figure
1) was observed during the reaction,16 which we believe is due
to the presence of several alkene isomers that differ only slightly
in their 31P NMR chemical shifts, as shown in Figure 1. In
1
was monitored by H NMR. All the volatiles were removed from
the pale yellow-brown reaction mixture. The product was recrystal-
lized from a CH2Cl2/hexane mixture (3 mL:5 mL) at -10 °C for
48 h to give pure 5 as a crystalline, colorless solid. Yield: 96 mg
(84%). Mp: 143-145 °C. Anal. Calcd for C37H44P2Pt: C, 59.59;
1
H, 5.95. Found: C, 59.66; H, 5.74. H NMR: δ 6.76-7.74 (m,
20H, Ph), 5.21-5.58 (m, 4H, dCH), 1.83-2.13 (m, 6H, P-CH2),
0.68-1.77 (m, 14H, CH2 and CH3). 31P NMR: δ 3.88 (m) (JPt-P
) 1645 Hz). 13C{1H} NMR: 133.4, 133.5, 133.6 (isomers,
(13) Clark, H. C.; Manzer, L. E. J. Organomet. Chem. 1973, 59, 411-
428.
(14) (a) Slack, D. A.; Baird, M. C. Inorg. Chim. Acta 1977, 24, 277-
280. (b) Hackett, M.; Whitesides, G. M. J. Am. Chem. Soc. 1988, 110,
1449-1462.
(15) McDermott, J. X.; White, J. F.; Whitesides, G. M. J. Am. Chem.
Soc. 1976, 98, 6522.
(16) The reaction was carried out at 100 °C, and the 31P NMR spectrum
was run at room temperature.

5788 Organometallics, Vol. 26, No. 24, 2007
SiVaramakrishna et al.
Figure 1. 31P NMR spectrum for bis(2-pentenyl)platinum(II), δ 3.88 (JPt-P ) 1645 Hz).
Figure 3. Molecular structure of the major component of com-
pound 6 in the solid state, depicted at the 30% probability level.
Selected bond lengths (Å): Pt(1)-P(1) 2.2833(12); Pt(1)-P(2)
2.2877(12); Pt(1)-C(1) 2.109(5); Pt(1)-C(7) 2.104(5); C(5)-C(6)
1.4994(10); C(11)-C(12) 1.4996(10); C(4)-C(5) 1.3200(10);
C(10)-C(11) 1.3205(10). Selected bond angles (deg): P(1)-Pt-
(1)-P(2) 91.17; C(1)-Pt(1)-C(7) 86.3.
methylene hydrogens, as the signals were seen as a broad
1
multiplet in the H NMR. In a similar way, 13C NMR spectra
also showed the coupling constants in a range of 638 to 646
Hz for the 1J(195Pt13C) for both the precursors (1-4) as well as
the isomerized products (5-8). Single crystals of 2 and 6
suitable for X-ray analysis were grown from CH2Cl2/hexane
solutions. These structures confirmed that 2 is a 1-alkenyl
compound and that 6 is a 2-alkenyl compound (see Figures 2
and 3). Interestingly, it also shows that the two alkenyl chains
in 6 are different from each other, within the same molecule,
with one chain showing that the alkene H atoms are cis to each
other, whereas the other shows trans-positioned H atoms. Bond
lengths and angles of 2 and 6 are consistent with those reported
for similar compounds.17
Figure 2. Molecular structure of the major component of com-
pound 2 in the solid state, depicted at the 30% probability level.
Selected bond lengths (Å): Pt(1)-P(1) 2.2782(10); Pt(1)-P(2)
2.2805(10); Pt(1)-C(1) 2.120(4); Pt(1)-C(7) 2.118(4); C(5)-C(6)
1.271(7); C(11)-C(12) 1.315(6). Selected bond angles (deg): P(1)-
Pt(1)-P(2) 93.95; C(1)-Pt(1)-C(7) 85.03.
contrast, 31P NMR spectra of compounds 7 and 8 showed sharp
singlets at δ 3.40 and 3.66 (JPt-P ) 1620 Hz), respectively,
indicating that in these cases the presence of isomers, if they
are present, did not have any effect on the 31P NMR. The
corresponding dppp complex of bis(octyl)platinum(II) (11)
showed a similar coupling constant, JPt-P ) 1619 Hz at 3.91
ppm. This could be due to the terminal alkene moiety being
further away from the metal in 7 and 8. The range of coupling
constants, J(Pt-1H), of platinum with the hydrogen of the
adjacent methylene group was found to be 76 to 80 Hz. It was
difficult to assign the coupling constants for the rest of the
We also find that 1-alkenes such as 1-pentene, 1-hexene, and
1-octene undergo selective isomerization to their corresponding
(17) Allen, F. H.; Kennard, O.; Watson, D. G.; Taylor, R. International
Tables for Crystallography; Wilson, A. J. C., Ed.; Kluwer Academic
Publishers: Dordrecht, 1992; Vol. C.

SelectiVe Isomerization of cis-PtL2(1-alkenyl)2
Organometallics, Vol. 26, No. 24, 2007 5789
Scheme 2. Proposed Mechanism for the Internal
Isomerization Reactions of the Bis(1-alkenyl)platinum(II)
Complexes
2-alkenes in the presence of 1-4 under similar experimental
conditions (eq 2). These alkene isomerization reactions are
catalytic. In addition, we show that the incoming 1-alkene ends
up as the alkyl group in PtL2R2, suggesting that 1-alkene
insertion into a Pt-H bond is a key step in these reactions.
Also our experiments on the catalytic isomerization of
1-alkenes with bis(octyl)platinum(II) complex 11 as catalyst
suggest that the reaction proceeds through an intermolecular
interaction (eq 2). Surprisingly, the catalytic activity of metal-
alkyl complexes PtL2R2 in this regard is quite comparable with
that of compounds 1-4.
An experiment was carried out to determine if PtL2H2 species
were involved in the isomerization reaction that could have
arisen from two â-H eliminations of PtL2(1-alkenyl)2. The
PtL2H2 species could react with 1-alkene to give PtL2R2.
However, the attempted in situ generation18 of PtL2H2 and
reaction with 1-alkene did not result in the formation of a bis-
(alkyl)platinum(II) complex, as observed by the 31P NMR.
It is significant to note that this selective isomerization is
dependent on the concentration of the solution. In a dilute
solution, the isomerization is faster than in a more concentrated
one.19 This may suggest that the isomerization reaction proceeds
via an intramolecular process.
During the isomerization of compounds 1-4, the solution
changed from colorless to yellow-brown, which is a character-
istic color of Pt0 and some other nanoclusters.20 To eliminate
the possibility that Pt(0) species were catalyzing the isomer-
ization, the reactions were carried in the presence of Hg metal.
Since the reaction proceeded in the presence of mercury, we
believe that Pt(0) species are not the main species responsible
for this catalytic isomerization. The addition of free ligand
(dppp) completely retarded the isomerization reaction of 1 under
similar experimental conditions, and a new product, Pt(dppp)2
was formed with reductive elimination of 1-decene and 1,9-
decadiene (see eq 3); traces of 1-pentene and n-pentane were
also detected. As Pt(dppp)2 also did not show any isomerization
of 1-alkene, the involvement of Pt(0) species was ruled out.
diphosphine ligand, rearrangement to an allyl hydride intermedi-
ate, followed by isomerization to give the 2-alkenyl product.
In attempts to obtain support for this mechanism, we investigated
the 1H and 31P NMR spectra of 4 at high temperature. However,
these spectra did not show any peaks corresponding to the
intermediates 9 and 10, nor could any ligand dissociation be
detected even though 40% of isomerized product was formed
during the measurements.
It is possible that intermediates 9 and 10 are involved, but
they may be too short-lived to be detected. The experiments
clearly reveal that the transformation of 1-alkenes and self-
isomerization of metal bis(1-alkenyls) are possible and allylic
intermediates would seem to be most likely. Under these
experimental conditions the isomerization is favored rather than
the expected â-hydrogen elimination reaction for these com-
pounds.
We also find that the isomerizations are strongly dependent
on the length of the alkenyl chains. Thus, it was found that the
longest chain (1-heptenyl) investigated is the fastest to undergo
isomerization (see Figure 4). This could be due to strain in the
small rings when the alkenyl chains coordinate to the metal, as
in 9 in Scheme 2.
A rise in temperature (>150 °C) of benzene solutions of 1-4
led to the cleavage of the Pt-C bonds, yielding the correspond-
ing 1-alkenes, 2-alkenes, dienes, etc.
These isomerization reactions were also found to be depend-
ent on the nature of the phosphine ligand system present; thus
the chelating effect of diphosphines reduces the amount of
decomposition of the 1-alkenyl compounds, even at high
temperatures. The PPh3- and PtBu3-containing metal-alkenyl
Taking all the above into account, we suggest a possible
mechanism for these isomerizations (see Scheme 2) involving
coordination of the pendant alkene, partial dissociation of the
(18) Yoshida, T.; Yamagata, T.; Tulip, T. H.; Ibers, J. A.; Otsuka, S. J.
Am. Chem. Soc. 1978, 100, 2063.
(19) The two different concentrations of compound 2 (in 5 mL of toluene
as solvent) were taken as 7 × 10-4 and 2.8 × 10-3 M for the isomerization
reactions, and the time of reaction (product formed) was observed as 110
h (100%) and 110 h (65%), respectively.
(20) (a) Creighton, J. A.; Eadon, D. G. J. Chem. Soc., Faraday Trans.
1991, 87, 3881. (b) Finney, E. E.; Finke, R. G. Inorg. Chim. Acta 2006,
359, 2879-2887.
Figure 4. Effect of length of alkenyl chains on isomerization of
bis(alkenyl)platinum(II) complexes at 100 °C in benzene.

5790 Organometallics, Vol. 26, No. 24, 2007
SiVaramakrishna et al.
Table 1. Details of Crystallographic Data Collection and
Refinement Parameters
The molecular structures of 2 and 6 were determined by
single-crystal X-ray analysis and are illustrated in Figures 2 and
3, respectively. The structural analysis confirms that 6 is the
isomerization product of 2. The main changes in the structural
features of complexes 2 and 6 are the differences in some of
the bond angles and bond lengths. The Pt-P bonds of compound
2 are slightly shorter than for compound 6, whereas the Pt-C
bonds of 2 are slightly longer than those for 6. However these
bond distances are comparable with the literature reports17 for
related compounds (for Pt-C, 2.118(3)-2.110(3) Å, and Pt-
P, 2.263(9)-2.293(7) Å, respectively), while the CdC distances
range from 1.271(7) to 1.3200(10) Å. The internal alkene Cd
C distance in 6 is longer than in 2. The P-Pt-P and C-Pt-C
bond angles in 2 and 6 vary from 93.95(4)° to 91.17(4)° and
85.06(15)° to 86.03(2)°, respectively. Table 1 lists the pertinent
crystal data for 2 and 6 (see also the Supporting Information).
2
6
structure formula
fw
PtC39H48P2
773.80
PtC39H48P2
773.80
data collection temp (K)
113(2)
113(2)
cryst syst, space group
a (Å)
b (Å)
c (Å)
monoclinic, P21/n
14.1180(2)
14.5423(2)
18.3322(2)
90
111.156(1)
90
3510.08(8)
4
triclinic, P1h
10.0956(2)
12.8451(2)
14.5163(3)
77.775(1)
84.714(1)
70.779(1)
1736.70(6)
2
R (deg)
â (deg)
γ (deg)
volume (Å3)
Z
Dc, calcd density (g cm-3
)
1.464
4.114
1560
1.480
4.157
780
absorp coeff µ (mm-1
F(000)
)
cryst size (mm)
θ range for data collection
limiting indices
no. of reflns collected/
unique
0.08 × 0.16 × 0.18
1.84-26.74
(17; (18; -23,22
61 043/7453
0.15 × 0.17 × 0.21
3.42-25.97
-11,12; (15; (17
42 629/6749
Conclusions
The cis-[Pt(1-alkenyl)2L2] complexes undergo irreversible
selective isomerization reaction to the corresponding cis-[Pt(2-
alkenyl)2L2] complexes. The rate of isomerization is mainly
dependent on the length of the alkenyl chains, the ligand, and
the concentration. These complexes also serve as catalysts that
selectively isomerize 1-alkenes to their 2-alkene analogues.
Currently, we are exploring the interesting properties and
reactivity of these compounds. We are also investigating similar
compounds with other metal systems.
no. of params
380
353
extinction coeff
0.00062(7)
1.092
0.0002(3)
1.065
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R1 ) 0.0341
wR2 ) 0.0595
R1 ) 0.0514
wR2 ) 0.0648
1.464/-0.915
R1 ) 0.0330
wR2 ) 0.0802
R1 ) 0.0409
wR2 ) 0.0841
1.209/-2.821
R indices (all data)
largest diff peak and
hole (e Å-3
)
Acknowledgment. This work was supported by Anglo
Platinum Corporation and DST Center of Excellence in Catalysis
(C* Change). We also thank Feng Zheng for the GC analysis
and Johnson Matthey for the loan of K2PtCl4.
complexes however decompose rapidly above 80 °C; hence the
isomerization could not be detected with these ligands.
Thermal decomposition of the compounds 5-8 in dichlo-
romethane at high temperatures (150-170 °C) yielded 85% of
the corresponding 2-alkenes as the major products (with 65%
trans-2-alkene and 35% cis-2-alkene), which were analyzed by
GC-MS. These yields depended significantly on the experi-
mental conditions for decomposition, i.e., whether in solid state
or in solution.
Supporting Information Available: Tables of crystallographic
1
data and H NMR spectra for 2 and 6. This material is available
free of charge via the Internet at http://pubs.acs.org.
OM0611249