Inorganic Chemistry Communications 12 (2009) 766–768
Inorganic Chemistry Communications
Bridge-splitting of trans-[PtCl2(
and molecular structure of trans-[PtCl2(
g
2-CH2@CH2)]2 by weak nucleophiles: Crystal
g
2-CH2@CH2)(MeCN)]
a
b
Stefanus Otto a,b, , Andreas Roodt , Lars I. Elding
*
a Department of Chemistry, University of the Free State, Bloemfontein 9300, South Africa
b Department of Chemistry, Chemical Center, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden
a r t i c l e i n f o
a b s t r a c t
Bridge-splitting of trans-[PtCl2(g L -
2-CH2@CH2)]2, 1, by in dichloromethane yields trans-[PtCl2(g2
Article history:
Received 7 May 2009
Accepted 5 June 2009
Available online 11 June 2009
CH2@CH2)(L)] (L = THF, 2, or MeCN, 3) with bridge-splitting equilibrium constants of 0.0289 0.0007
and 3601 215 molꢀ1 dm3, respectively, as determined by UV/Vis measurements. The reaction of 3 in
MeCN with Clꢀ is essentially quantitative. The crystal structure of trans-[PtCl2( 2-CH2@CH2)(CH3CN)] is
g
reported.
Keywords:
Ó 2009 Elsevier B.V. All rights reserved.
Platinum
Zeise
Ethene
Equilibrium constants
Crystal structure
Zeise’s anion, [PtCl3(
dinuclear complex, trans-[PtCl2(
g
2-CH2@CH2)]ꢀ, and the chloride-bridged
2-CH2@CH2)]2, 1, represent the
shown in the inserts of Figs. 1 and 2, respectively, for THF and
MeCN.
g
earliest well documented organometallic complexes [1]. Reaction
Figs. 1 and 2 clearly illustrate the difference in coordinating
ability of the THF and MeCN ligands. Moreover, the reaction of
of 1 with ethene in acetone at ꢀ80 °C results in the formation of a
yellow unstable complex, trans-[PtCl2(
g
2-CH2@CH2)2] [2]. This spe-
trans-[PtCl2(g
2-CH2@CH2)(MeCN)] with subsequently added Clꢀ in
cies has been postulated as a short-lived intermediate in the reaction
MeCN (solution of 1 in MeCN), proceeds essentially quantitatively
to 4.
mechanism for ethene exchange at [PtCl3(
g
2-CH2@CH2)]ꢀ [3,4], and
in non-co-ordinating solvents like chloroform, it is formed as a prod-
uct of bridge-splitting of 1 by ethene. Upon standing at room tem-
perature under an ethene atmosphere the white, moderately
By comparing the bridge-splitting equilibrium constants for
trans-[PtCl2(g g
2-CH2@CH2)]2 with L, to form trans-[PtCl2( 2-CH2@
CH2)(L)], of 0.13 0.01 (MeOH) [4], 6.8 0.6 (CH2@CH2) [5],
0.0289 0.0007 (THF) and 3601 215 (MeCN) molꢀ1 dm3, the dif-
ference in the coordinating ability of the various nucleophiles to
the Pt(II) metal centre is quantitatively defined.
stable compound, cis-[PtCl2(g
2-CH2@CH2)2], can be obtained [5].
We previously reported [6] on the bridge-splitting kinetics,
equilibria and structures of the remarkably stable cyclooctene
(cot) derivatives of Zeise’s dimer. Due to the gaseous nature of eth-
ene, and the increase in reactivity, studies of 1 are considerably
more complicated. We succeeded in obtaining values for the
bridge-splitting equilibrium constants, according to Scheme 1, for
MeOH [4] and ethene [5] and now extended this work to illustrate
the quantitative experimental studies between 1 and THF and
CH3CN. These solvents are representative of weak nucleophiles en-
abling the investigation of these highly reactive systems using sim-
ple, conventional UV–Vis measurements [7].
Bridge-splitting equilibrium constants in dichloromethane at
298.2 K for the cyclooctene analogues of Zeise’s dimer, trans-
[PtCl2(cot)]2, with various nucleophiles are 0.0169 0.0015 (MeOH)
[4], 2.05 0.06 (cot) and 9.7 0.9 (MeCN) molꢀ1 dm3, while with
Clꢀ the reaction is quantitative [6]. A sequence of bridge-splitting
efficiency of MeOH < cot < MeCN < Clꢀ was established from this
study which is in agreement with the current results for the very
reactive ethene based derivatives. In the same study we also re-
ported the crystal structure of the remarkably stable trans-
[PtCl2(cot)2] obtained by bridge-splitting of trans-[PtCl(cot)]2 with
cyclooctene in dichloromethane as mentioned above. In contrast,
the ethene analogue is too reactive/unstable to be isolated, and it
The spectroscopic data were fitted [8] to appropriate equations
[9] for quantitative determination of the equilibrium constants as
isomerises to the more stable cis-[PtCl2(g
2-CH2@CH2)2] upon con-
centration of the solutions [5].
* Corresponding author. Present address: Sasol Technology Research and Devel-
opment, 1 Klasie Havenga Road, Sasolburg 1947, South Africa. Tel.: +27 16 960
4456; fax: +27 11 522 3218.
In comparison, the bridge-splitting in chloroform of the styrene
analogue of Zeise’s dimer, trans-[PtCl2(
g
2-CH2@CHC6H4)]2, with
1387-7003/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.