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几种双(三甲基甲硅烷基)酰胺镱的合成和结构表征,包括无碱 [Yb{N(SiMe3)2}2(µ-Cl)]2 - 一种具有附加 Ag...
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Synthesis and Structural Characterization of Several Ytterbium Bis(trimethylsilyl)amides Including Base-free [Yb{N(SiMe3)2}2(µ-Cl)]2 - A Coordinatively Unsaturated Complex with Additional Agostic Yb···(H3C-Si) Interactions Synthesis and Structural Characterization of Several Ytterbium Bis(trimethyl- silyl)amides Including Base-free [Yb{N(SiMe3)2}2(µ-Cl)]2 2 A Coordinatively Unsaturated Complex with Additional Agostic Yb···(H3C2Si) Interactions Mark Niemeyer* Stuttgart, Institut für Anorganis
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Synthesis and Structural Characterization of Several Ytterbium Bis(trimethyl-
silyl)amides Including Base-free [Yb{N(SiMe
3
)
2
}
2
(µ-Cl)]
2
2 A Coordinatively
Unsaturated Complex with Additional Agostic Yb···(H
3
C2Si) Interactions
Mark Niemeyer*
Stuttgart, Institut für Anorganische Chemie der Universität
Received October 8th, 2001.
Abstract. The reaction of YbCl
3
with two equivalents of NaN-
(SiMe
3
)
2
has afforded a mixture of several ytterbium bis(trimethyl-
silyl)amides with the known complexes [Yb{N(SiMe
3
)
2
}2(µ-
Cl)(thf)]
2
(1) and [Yb{N(SiMe
3
)
2
}
3
](4) as the main products and
the cluster compound [Yb
3
Cl
4
O{N(SiMe
3
)
2
}
3
(thf)
3
](2) as a minor
product. Treatment of 1 and 2 with hot n-heptane gave the base-
free complex [Yb{N(SiMe
3
)
2
}
2
(µ-Cl)]
2
(3) in small yield. The struc-
tures of compounds 124 and the related peroxo complex
[Yb
2
{N(SiMe
3
)
2
}
4
(µ-O
2
)(thf)
2
](5) have been investigated by single
crystal X-ray diffraction. In the solid-state, 3 shows chlorobridged
dimers with terminal amido ligands (av. Yb2Cl 5 262.3 pm, av.
Yb2N 5 214.4 pm). Additional agostic interactions are observed
from the ytterbium atoms to four methyl carbon atoms of the bi-
Synthese und strukturelle Charakterisierung verschiedener
Ytterbiumbis(trimethylsilyl)amide darunter σ-donorfreies [Yb{N(SiMe
3
)
2
}
2
(µ-Cl)]
2
2
Ein koordinativ ungesättigter Komplex mit zusätzlichen agostischen Yb···(H
3
C-Si)
Wechselwirkungen
Inhaltsübersicht. Durch Reaktion von YbCl
3
mit zwei Äquivalenten
NaN(SiMe
3
)
2
wurde eine Mischung verschiedener Ytterbium-
bis(trimethylsilyl)amide, mit den bekannten Komplexen
[Yb{N(SiMe
3
)
2
}
2
(µ-Cl)(thf)]
2
(1) und [Yb{N(SiMe
3
)
2
}
3
](4) als
Hauptprodukte und der Clusterverbindung [Yb
3
Cl
4
O-
{N(SiMe
3
)
2
}
3
(thf)
3
](2) als Nebenprodukt, erhalten. Die Behand-
lung von 1 und 2 mit heißem n-Heptan führte in geringer Ausbeute
zur Bildung des basenfreien Komplexes [Yb{N(SiMe
3
)
2
}
2
(µ-Cl)]
2
(3). Die Strukturen der Verbindungen 124 und des verwandten
Peroxo-Komplexes [Yb
2
{N(SiMe
3
)
2
}
4
(µ-O
2
)(thf)
2
](5) wurden mit-
tels Röntgenbeugung an Einkristallen untersucht. In der Festkör-
perstruktur von 3 liegen chloridverbrückte Dimere mit terminalen
Amidliganden vor (Mittelwerte Yb2Cl 5 262,3 pm, Yb2N 5
Introduction
The homoleptic tris[bis(trimethylsilyl)amides] of the lantha-
noids Ln{N(SiMe
3
)
2
}
3
[1] are among the best characterized
* Dr. M. Niemeyer
Institut für Anorganische Chemie der Universität Stuttgart
Pfaffenwaldring 55
D-70569 Stuttgart
Fax: (49) 711 685 4241
e-mail: niemeyer@iac.uni-stuttgart.de
Z. Anorg. Allg. Chem. 2002, 628,6472657 WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002 004422313/02/628/6472657 $ 17.501.50/0
647
s(trimethylsilyl)amido groups (Yb···C 5 2842320 pm). DFT calcu-
lations have been performed on suitable model systems
([Yb
2
(NH
2
)
4
(µ-Cl)
2
(OMe
2
)
2
](1m), [Yb
2
(NH
2
)
4
(µ-Cl)
2
](3m), [Yb-
(NH
2
)
3
](4m), [Yb
2
(NH
2
)
4
(µ-O
2
)(OMe
2
)
2
](5m), [Yb{N-
(SiMe
3
)
2
}
2
Cl] (3m/2) and Ln(NH
2
)
2
NHSiMe
3
(Ln 5Yb (6m), Y
(7m)) in order to rationalize the different experimentally observed
Yb2N distances, to support the assignment of the O2O stretching
vibration (775 cm
21
) in the Raman spectrum of complex 5
and to examine the nature of the agostic-type interactions in
σ-donorfree 3.
Keywords: Agostic interactions; Bis(trimethylsilyl)amido comple-
xes; Crystal structure; DFT calculations; Ytterbium
214,4 pm). Zusätzliche agostische Wechselwirkungen werden von
den Ytterbiumatomen zu vier Methylkohlenstoffatomen der Bis-
(trimethylsilyl)amid-Gruppen beobachtet (Yb···C 5 2842320 pm).
DFT Rechnungen an geeigneten Modellsystemen ([Yb
2
(NH
2
)
4
-
(µ-Cl)
2
(OMe
2
)
2
](1m), [Yb
2
(NH
2
)
4
(µ-Cl)
2
](3m), [Yb(NH
2
)
3
](4m),
[Yb
2
(NH
2
)
4
(µ-O
2
)(OMe
2
)
2
](5m), [Yb{N(SiMe
3
)
2
}
2
Cl] (3m/2) und
Ln(NH
2
)
2
NHSiMe
3
(Ln 5Yb (6m),Y(7m)) wurden durchgeführt,
um die unterschiedlichen experimentell bestimmten Yb2N-Ab-
stände zu verstehen, die Zuordnung der O2O-Streckschwingung
(775 cm
21
) im Ramanspektrum des Komplexes 5 zu ermöglichen
und die Natur der agostischen Wechselwirkungen in σ-donorfreiem
3 zu untersuchen.
compounds of the rare earths, which is mainly attributed to
their importance as valuable starting materials [2]. In con-
trast, much less is known about bis-amido substituted com-
plexes of the composition Ln{N(SiMe
3
)
2
}
2
X(X5 halo-
gen). In 1981 Zalkin and co-workers described the in situ
synthesis of Eu{N(SiMe
3
)
2
}
2
Cl prepared from europium
trichloride and Ln{N(SiMe
3
)
2
}
3
in tetrahydrofuran solution
[3]. Some years later the isolation of the donor-stabilized
species [Ln{N(SiMe
3
)
2
}
2
(µ-Cl)(thf)]
2
was reported by Brad-
ley, Hursthouse and co-workers (Ln 5 Eu, Gd, Yb 1) [4]
and later by others (Ln 5 Nd [5], Sm [6]). The solid-state
M. Niemeyer
structures of the isostructural neodymium, samarium, ga-
dolinium, and ytterbium compounds show chloride-bridged
dimers with five-coordinate metal centers. It was found that
[Eu{N(SiMe
3
)
2
}
2
(µ-Cl)(thf)]
2
is unstable in solution with re-
spect to a dismutation reaction to EuCl
3
and
Eu{N(SiMe
3
)
2
}
3
. Removal of the donor solvent from
Y{N(SiMe
3
)
2
}
2
(Cl)(thf) [4], which was characterized by
1
H
NMR only, also leads to its fast decomposition. The insta-
bility of the [Ln{N(SiMe
3
)
2
}
2
(Cl)(thf)
x
] complexes regar-
ding ligand redistribution reactions was later confirmed by
other investigators [5, 7]. For the same reason, the hetero-
leptic iodo compounds [Ln{N(SiMe
3
)
2
}
2
(I)(thf)]
2
(Ln 5
Dy, Ho) have been used as precursors for the preparation
of ultrapure Ln
III
-tris(amides) [8]. Very recently the synthe-
sis and X-ray structure determination of the complex
[La{N(SiMe
3
)
2
}
2
(µ-I)(thf)]
2
has been reported by Collin
and co-workers [9]. In the course of our investigations on
low-coordinated σ-bonded lanthanoid organyls [10212] we
intended to use [Yb{N(SiMe
3
)
2
}
2
(µ-Cl)(thf)]
2
(1) and syn-
thesize [Yb{N(SiMe
3
)
2
}
2
(µ-Cl)]
2
(3), compounds of poten-
tial synthetic value which should allow the introduction of
organyl groups by simple metathesis reactions [13].
Results and Discussion
Synthesis
The synthesis of 1 in ca. 70 % yield from LiN(SiMe
3
)
2
and
YbCl
3
in a ratio of 2 to 1 was reported by Bradley, Hurst-
house et al. [4]. We used NaN(SiMe
3
)
2
, which is known in
the case of the trisamides to give higher yields and less pro-
duct contamination, compared to its Li analogue [2, 14].
However, in our hands the obtained yield of 1, which varied
between ca. 40 % and 50 %, was only moderate (scheme 1).
A considerable amount (total ca. 25 %) of Yb{N(SiMe
3
)
2
}
3
(4) was obtained by crystallization and sublimation (see ex-
perimental part). In addition, it was shown by X-ray cry-
stallography, Raman spectroscopy and optical microscopy
that the isolated crystalline material of 1 contained up to
5 % of the mixed ytterbium amide/chloride/oxide cluster
[Yb
3
Cl
4
O{N(SiMe
3
)
2
}
3
(thf)
3
](2). The solid-state structure
of the related cluster [Yb
3
Br
4
O{N(SiMe
3
)
2
}
3
(thf)
3
](29)was
published recently by Dehnicke and co-workers [15]. They
obtained 29 in a yield . 90 % from YbBr
3
and NaN-
(SiMe
3
)
2
although no experimental details were given. Ac-
Scheme 1 Syntheses of Compounds 125
Z. Anorg. Allg. Chem. 2002, 628, 6472657648
cording to the authors, the source of the incorporated oxide
may be attributed to reactions of the solvent tetrahydrofu-
ran with the base sodium bis(trimethylsilyl)amide. The same
explanation may account for the formation of 2 since the
used ytterbium chloride was free of oxychloride impurities
and several carefully repeated experiments always showed
the presence of this cluster.
Attempts to desolvate 1 to a thf-free species
Yb{N(SiMe
3
)
2
}
2
Cl by sublimation were unsuccessful. He-
ating a sample to 200 °C under vacuum resulted in the for-
mation of Yb{N(SiMe
3
)
2
}
3
(4), which sublimed out of the
schlenk tube. The remaining beige solid was examined by
elemental analysis which showed a low carbon and a high
chlorine content. These observations are consistent with the
analysis of 1 by mass spectrometry, in which no chlorine
containing fragments were detected. Another way to pre-
pare donorsolvent-free compounds is the toluene-reflux me-
thod [16]. It involves the treatment of the solvated complex
with hot toluene followed by exposure to a vacuum. In a
similar manner, using n-heptane as the desolvating solvent,
it was possible to isolate [Yb{N(SiMe
3
)
2
}
2
(µ-Cl)]
2
(3), al-
though the yield of 4 % was very low (scheme 1). It is nota-
ble that the related compounds Ln{N(SiMe
3
)
2
}
2
I (Ln 5
Sm, Yb) have been synthesized and characterized by IR
spectroscopy and elemental analysis, very recently [9].
The peroxo complex Yb
2
{N(SiMe
3
)
2
}
4
(µ-O
2
)(thf)
2
(5)
was obtained for the first time in a fortuitous manner by
uncontrolled oxidation of Yb{N(SiMe
3
)
2
}
2
(thf)
2
with air.
Later experiments showed that 5 can be deliberately prepa-
red by careful oxidation with a slight excess of dry oxygen
(scheme 1). Compound 5 is a rare example of a µ-η
2
:η
2
-
peroxo lanthanide complex. Despite the high oxophilicity
of the rare earth elements, there is only one previously
structurally characterized compound of this type, [(µ-η
2
:η
2
-
O
2
)La
2
{N(SiMe
3
)
2
}
4
(OPPh
3
)
2
] [17]. In addition three Ce
IV
complexes with carbonate or acetate ligands, which contain
a bis(µ-η
2
:η
2
-peroxo) fragment, have been reported [18, 19].
A weak band in the Raman spectrum of complex 5 at
775 cm
21
, which is absent in the spectra of compounds
124, may be assigned to the O2O stretching vibration.
This assignment is supported by DFT calculations on suita-
ble model systems (vide infra). Vibrational frequencies for
peroxo ligands are typically observed in the range
7902932 cm
21
[20, 21]. Bands at lower wave numbers
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