Mercury(II) Complexes of the Carba-closo-dodecaboranyl Ligands
[closo-1-CB
11
X
11
]
2-
(X = H, F, Cl, Br, I)
Alexander Himmelspach,
†
Jan A. P. Sprenger,
†
Jonas Warneke,*
,‡
Manfred Za ̈ hres,
§
and Maik Finze*
,†
†
Institut fü r Anorganische Chemie, Julius-Maximilians-Universitä t Wü rzburg, Am Hubland, 97074 Wü rzburg, Germany
‡
Institut fü r Organische Chemie, Fachbereich 2 (Chemie/Biologie), Universitä t Bremen, Leobener Strasse, NW2, 28359 Bremen,
Germany
§
Institut fü r Physikalische Chemie, Universitä t Duisburg-Essen, Universitä tsstrasse 5, 45141 Essen, Germany
* S Supporting Information
ABSTRACT: Salts of the mercury(II) complexes [Hg( closo-1-
CB
11
X
11
)
2
]
2-
(X = H (1), Cl (3), Br (4)) and [PhHg(closo-1-
CB
11
X
11
)]
-
(X = H (6), Cl (8), Br (9), I (10)) were synthesized and
characterized by multi-NMR spectroscopy, mass spectrometry, elemental
analysis, and differential scanning calorimetry. Single crystals of
Cs
2
1·2Et
2
O, Cs
2
3·MeCN, Cs
2
4·4Me
2
CO, Cs9, and [Et
4
N]6·0.5Me
2
CO
were studied by X-ray diffraction, and the interpretation of the bond
properties is supported by theoretical data. In contrast to the mercury
atom of the previously published [Hg(closo-1-CB
11
F
11
)
2
]
2-
(2), which
coordinates either acetonitrile or water, the metal atom of the related
dianionic complexes 1, 3, and 4 does not reveal any further coordination.
According to results derived from DFT and ab initio calculations, this
different behavior is reasoned in the case of 1 by a reduced Lewis acidity
at mercury and in the case of 3 and 4 by the increased shielding of the central mercury atom as a result of the bulky halogenated
carba-closo-dodecaboranyl ligands [closo-1-CB
11
X
11
]
2-
(X = Cl, Br). The dianionic complex [Hg(closo-1-CB
11
I
11
)
2
]
2-
(5) with the
bulkiest carba-closo-dodecaboranyl ligand was generated via collision-induced dissociation and characterized by (-)-ESI mass
spectrometry. The fragmentation pathways of the anionic complexes [Hg(closo-1-CB
11
X
11
)
2
]
2-
(X = H, F, Cl, Br, I (1-5)) and
[PhHg(closo-1-CB
11
X
11
)]
-
(X = H, F, Cl, Br, I (6-10)) were studied by (-)-ESI mass spectrometry.
■
INTRODUCTION
Transition-metal complexes of dicarba-closo-dodecaboranyl
ligands with an exo-polyhedral metal-C
cluster
σ bond are well-
known,
1,2
and they are used in a number of applications, for
example, in catalysis. Important examples are mercury(II)
complexes with dicarba-closo-dodecaboranyl ligands,
2-4
which
have been investigated with all three isomeric clusters {closo-
1,2-C
2
B
10
}, {closo-1,7-C
2
B
10
}, and {closo-1,12-C
2
B
10
}, because
they exhibit strong similarities to Hg
II
complexes with electron-
poor perfluoroaryl ligands.
5,6
Both contain Lewis acidic
mercury atoms that can coordinate further neutral as well as
anionic ligands and are, therefore, discussed as anion receptors,
materials for gas storage, catalysis, or as buildings blocks in
supramolecular chemistry.
2,4-6
To the best of our knowledge, only a few related complexes
with carba-closo-dodecaboranyl ligands and a metal-C
cluster
σ
bond have been described, so far:
7
[ClCu(closo-1-CB
11
F
11
)]
2-
,
8
[Ag(closo-1-CB
11
I
5
Br
6
)
2
]
3-
,
9
and [PhAu(closo-1-CB
11
H
11
)]
-
.
10
Recently, we have reported on the tetraethylammonium salts of
the mercury(II) complexes [Hg(closo-1-CB
11
F
11
)
2
]
2-
(2) and
[PhHg(closo-1-CB
11
F
11
)]
-
(7) that contain a perfluorinated
carba-closo-dodecaboranyl ligand.
11
Both complexes exhibit
high thermal and chemical stability, which is similar to the
behavior of the anionic complex [Ph
3
PAu( closo -1-
CB
11
H
11
)]
-
.
10
In the case of the homoleptic complex 2, the
coordination of acetonitrile or water to the Lewis acidic
mercury center was observed, and [Et
4
N]
2
[Hg(closo-1-
CB
11
F
11
)
2
(NCMe)] ([Et
4
N]
2
[2·NCMe]) and [Et
4
N]
4
[{Hg-
(closo-1-CB
11
F
11
)
2
}
2
(OH
2
)] ([Et
4
N]
4
[2
2
·OH
2
]) were charac-
terized by vibrational spectroscopy and single-crystal X-ray
diffraction. Obviously, the fluorinated [closo-1-CB
11
F
11
]
2-
ligand results in a similar behavior of Hg
II
in 2 as found for
mercury complexes with perfluoroaryl and dicarba-closo-
dodecaboranyl ligands. This leads to the question of whether
related mercury(II) complexes with carba-closo-dodecaboranyl
ligands especially with perhalogenated clusters reveal an
analogous behavior, or not. We are interested in this topic in
connection with our study on the specific characteristics of
highly fluorinated {closo-1-CB
11
} clusters in comparison to
other halogenated and nonhalogenated {closo-1-CB
11
} deriva-
tives.
12-14
Here, we report on the synthesis of the cesium and [Et
4
N]
+
salts of the Hg
II
complexes [Hg(closo-1-CB
11
X
11
)
2
]
2-
(X = H
Special Issue: Fluorine in Organometallic Chemistry
Received: October 23, 2011
Published: December 16, 2011
Article
pubs.acs.org/Organometallics
© 2011 American Chemical Society 1566 dx.doi.org/10.1021/om201023h | Organometallics 2012, 31, 1566-1577