Synthesis and structural characterization of N,N′-dialkylimidazolium tetrachloroplatinate and monoaquatrichloroplatinate salts

Article abstract of DOI:10.1246/bcsj.75.1561

N,N′-Dialkylimidazolium salts, [m-C₆H₄(CH₂ImMe)₂] [PtCl₄] (Im = imidazolium) (1) and [Mes₂Im][PtCl₃(H₂O)] (Mes₂Im = N,N′-di(2,4,6-trimethylphenyl)imidazoliu

Full text of DOI:10.1246/bcsj.75.1561

c. Jpn.
Bull. Chem. Soc. Jpn., 75, 1561–1562 (2002) 1561
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When the ionic liquid [m-C6H4(CH2ImMe)2]Cl2 was treated
with K2[PtCl4] in water, a tetrachloroplatinate salt, [m-
C6H4(CH2ImMe)2][PtCl4] (1), was immediately afforded quan-
titatively as red crystals. As expected, the complex consists of
a [PtCl4]2− and [m-C6H4(CH2ImMe)2]2+ ionic pair (Eq. 1).
The X-ray crystallography of 1 reveals that the square planar
geometry of the Pt atom remains unchanged. The molecule
has a crystallographic inversion center at the platinum atom,
and thus the asymmetric unit contains a half molecule of [m-
C6H4(CH2ImMe)2][PtCl4]. The Pt–Cl bond distances (average
2.309 Å) are consistent with those of [EMIM]2[PtCl4] (EMIM
= N-ethyl-Nꢀ-methylimidazolium) (2.308 Å), which has been
described most recently.7
Synthesis and Structural Character-
ization of N,Nꢀ-Dialkylimidazolium
Tetrachloroplatinate and
Monoaquatrichloroplatinate Salts
02
61
62
SJA8
09-2673
2703
W. Chen et al.
Wanzhi Chen and Kazuko Matsumoto*
Department of Chemistry, School of Science and Engineer-
ing, Waseda University, and CREST, Japan Science and
Technology Corp. (JST), Okubo, Shinjuku-ku, Tokyo 169-
8555
The crystal packing is determined by the presence of several
weak CH≥Cl interactions, each Cl atom of the tetrachloro-
platinates being involved in such interactions with H atoms of
phenyl and imidazolate groups (Fig. 1(a)).
02
(Received January 25, 2002)
02
.2
Under the same reaction conditions as for 1, the reaction of
[Mes2Im]Cl and K2[PtCl4] in water led to the isolation of
[Mes2Im][PtCl3(H2O)] (2) as red crystals quantitatively. Unex-
pectedly, one of the chloride atoms of [PtCl4]2− is replaced by
one molecule of water (Fig. 2). The coordination geometry of
the platinum atom is thus regarded as a slightly distorted
square plane. The Pt–Cl distances (average 2.287 Å) cis to wa-
ter become shorter than those of 1, and the Pt–Cl distance
trans to water is much shorter, being 2.248(3) Å.
N,Nꢀ-Dialkylimidazolium salts, [m-C6H4(CH2ImMe)2]-
[PtCl4] (Im = imidazolium) (1) and [Mes2Im][PtCl3(H2O)]
(Mes2Im = N,Nꢀ-di(2,4,6-trimethylphenyl)imidazolium) (2),
were prepared and characterized by X-ray diffraction. Com-
pound 2 is the first structurally characterized aquatrichloro-
platinate compound.
The synthesis of N,Nꢀ-dialkylimidazolium salts (ionic liq-
uids) is currently an area of intense research activity.1–3 N,Nꢀ-
dialkylimidazolium salts can be used as non-aqueous ionic sol-
vents for many catalytic organic processes.1 A palladium/imi-
dazolium salt system catalyzes dehalogenation of aryl halides,4
and a palladium/phosphine-imidazolium system promotes
highly efficient Heck reactions of aryl bromides with n-butyl
acrylate, which have been reported very recently.5 It has re-
cently been demonstrated that ionic liquids are important alter-
natives to water as solvents for two-phase catalytic oligomer-
ization, hydroformylation, and hydrogenation of olefins by
transition metal complexes.6 N,Nꢀ-Dialkylimidazolium salts
containing transition-metal complexes, especially platinum
group metal complexes, are of great interests regarding their
potential catalytic applications. However, relatively few stud-
ies have been carried out on the use of ionic liquids for the syn-
thesis and characterization of coordination complexes.7
We report here the synthesis and structural characterization
of two novel N,Nꢀ-dialkylimidazolium chloroplatinate salts of
the type [m-C6H4(CH2ImMe)2][PtCl4] (Im = imidazolium) (1)
and [Mes2Im][PtCl3(H2O)] (Mes2Im = N,Nꢀ-di(2,4,6-trimeth-
ylphenyl)imidazolium) (2). Interestingly, compound 2 is a rare
example of an aquaplatinum complex that is probably stabi-
lized by the ionic liquid.
(2)
Platinum(II) is classified as a soft metal center which forms
stable complexes with polarizable ligands.8 It has long been
known that [PtCl3(H2O)]− ion exists in aqueous solution (Eq.
2). The hydrolysis of [PtCl4]2− is extensive at 25 ºC, and thus a
10−3 M solution of K2[PtCl4] contains only 5% of [PtCl4]2−
with 53% of mono- and 42% of diaqua species.9 However,
[PtCl3(H2O)]− compound has never been isolated and structur-
ally characterized in the solid state. In contrast, K[PtCl3-
(C2H4)], Zeise salt,10 is the most famous one, and [PtCl3-
(dmso)]−,11 [PtCl3(amine)]−,12 [PtCl3(NCR)]− and [PtCl3-
14
{HNC(OMe)R}]−,13 and [PtCl3(pyrimidine)]2−
are all
known. The [Pt(H2O)4]2+ can be obtained by interaction of
K2[PtCl4] and AgClO4 in water.9
Significantly, the crystal packing is governed by OH≥Cl
and CH≥Cl interactions, i.e., the imidazolium cations are
linked through hydrogen bonds with [PtCl3(H2O)]− (Fig. 1(b)).
These interactions make hydrogen-bond networks between im-
idazolium cations and [PtCl3(H2O)]− ion in 2. Obviously, the
network structures are stabilized by these weak interactions.
Experimental
(1)
Preparation of 1. Addition of K2[PtCl4] (100 mg, 0.24
15
mmol) in 2 mL of H2O to a solution of [m-C6H4(CH2ImMe)2]Cl2
in 3 mL of H2O resulted in an immediate precipitation of a red sol-

1562 Bull. Chem. Soc. Jpn., 75, No. 7 (2002)
© 2002 The Chemical Society of Japan
Preparation of 2. The compound was prepared as described
for [m-C6H4(CH2ImMe)2][PtCl4] by using [Mes2Im]Cl16 instead of
[m-C6H4(CH2ImMe)2]Cl2. Single crystals suitable for X-ray dif-
fraction analysis were obtained by layering K2[PtCl4] aqueous so-
lution onto [Mes2Im]Cl solution in water. Yield: 96.5%. Anal.
Calcd for C21H27Cl3N2OPt: C, 40.36; H, 4.36; N, 4.48%. Found:
C, 40.01; H, 4.48; N, 4.57%.
(a)
X-ray Structure Determination. The chosen crystals were
covered with polyfluoroether, and mounted on a glass fiber. Data
were collected on a Bruker SMART CCD diffractometer using
graphite monochromated Mo Kα radiation (λ = 0.71073 Å) at
room temperature. Crystallographic data for 1: C16H20Cl4N4Pt, fw
= 605.25, monoclinic, C2/c, a = 14.4184(12) Å, b = 10.3160(9)
Å, c = 13.8489(11) Å, β = 110.1720(10)º, V = 1933.5(3) Å3, Z
= 4, Dcalc = 2.079 Mg/m3, 5844 reflections collected, 2222 unique
(Rint = 0.0478), goodness-of-fit 0.971. R1, wR2 [I > 2σ(I)]
0.0312, 0.0788; R1, wR2 (all data) 0.0453, 0.0842. For 2:
C21H27Cl3N2OPt, fw = 624.89, orthorhombic, P212121, a =
8.5173(15) Å, b = 14.703(3) Å, c = 18.341(3) Å, V = 2296.8(7)
Å3, Z = 4, Dcalc = 1.807 Mg/m3, 13764 reflections collected, 5077
unique (Rint = 0.0777), goodness-of-fit 1.028. R1, wR2 [I > 2σ(I)]
0.0505, 0.1187; R1, wR2 (all data) 0.0658, 0.1243.
(b)
References
1
2
H. Olivier, J. Mol. Catal., 146, 285 (1999).
Recent reviews see: a) T. Walton, Chem. Rev., 99, 2071
(1999). b) D. Bourissou, O. Guerret, F. P. Gabbai, and G.
Bertrand, Chem. Rev., 100, 39 (2000).
3
T. Weskamp, V. P. W. Böhm, and W. A. Hermann, J. Orga-
nomet. Chem., 600, 12 (2000).
M. S. Viciu, G. A. Grasa, and S. P. Nolan, Organometallics,
20, 3607 (2001).
4
Fig. 1. Diagram of (a) 1 and (b) 2 showing the hydrogen
bonding interactions between imidazolium cation and
chloroplatinate anion.
5
(2001).
6
C. Yang, H. M. Lee, and S. P. Nolan, Org. Lett., 3, 1511
J. E. L. Dulius, P. A. Z. Suarez, S. Einloft, R. F. de Souza, J.
Dupont, J. Fischer, and A. De Cian, Organometallics, 17, 815
(1998).
7
M. Hasan, I. V. Kozhevnikov, M. Rafiq, H. Siddiqui, C.
Femoni, A. Steiner, and N. Winterton, Inorg. Chem., 40, 795
(2001).
8
D. M. Roundhill, in “Comprehensive Coordination Chem-
istry,” ed by. G. Wilkinson, R. D. Gillard, and J. A. McCleverty,
Pergamon (1987), Vol. 5, p. 353.
9
F. A. Cotton, G. Wilkinson, C. A. Murrillo, and M.
Bochmann, “Advanced Inorganic Chemistry,” 6th ed, Wiley-
Interscience (1999), p. 1071.
10 D. Seyferth, Organometallics, 20, 2 (2001).
11 a) Y. N. Kykushikin, Y. E. Vyazmenski, and L. I. Zorina,
Russ. J. Inorg. Chem. (Engl. Trans), 13, 1573 (1968). b) R.
Melanson and F. D. Rochon, Can. J. Chem., 53, 2371 (1975).
12 L. Nguyen, J. Kozelka, and C. Bois, Inorg. Chim. Acta,
190, 217 (1991).
Fig. 2. Molecular structure of 2. Thermal ellipsoids are
drawn at 50% probability.
13 R. Cini, P. A. Caputo, F. P. Intini, and G. Natile, Inorg.
Chem., 34, 1130 (1995).
id. It was collected by filtration and washed with H2O and ace-
tone. Single crystals suitable for X-ray diffraction analysis were
obtained by layering K2[PtCl4] aqueous solution onto [m-
C6H4(CH2ImMe)2]Cl2 solution in water. Yield: (96.0%). Anal.
Calcd for C16H20Cl4N4Pt: C, 31.75; H, 3.33; N, 9.26%. Found: C,
31.33; H, 3.14; N, 9.29%.
14 N. Nédélec and F. D. Rochon, Inorg. Chem., 40, 5236
(2001).
15 W. Chen, K. Matsumoto, J. Organomet. Chem., in press.
16 L. Jafarpour, E. D. Stevens, and S. P. Nolan, J. Organomet.
Chem., 606, 49 (2000).