Chemistry Reference
In-Depth Information
N
Ge
Figure 4.16
Structure
of [EtGe
OCH
2
CH
2
3
N]
(H atoms omitted).
pyramidal three-coordinated Ge.
81
The dimeric structure is also maintained in [Ge
2
-
OBu
t
2
(OSiPh
3
2
]inwhichthe
tert
-butoxo group is preferred as the bridging ligand.
82
2.4.2
Tin
Numerous structures of Sn(
II
)andSn(
IV
) alkoxo compounds are known. In tin(
II
)
ethyleneglycollate the ligand behaves as a chelating and a bridging group giving
rise to a three-dimensional network with three-coordinated Sn.
83
The volatile [Sn
2
-
OBu
t
2
(OBu
t
2
] was shown by electron diffraction analysis to have the dimeric struc-
ture in the gas phase with three-coordinated Sn(
II
) atoms and the terminal
tert
-butoxo
in the
trans
configuration.
80
This structure was confirmed by single crystal X-ray
diffraction along with the structure of [Sn
2
-OBu
t
2
Cl
2
]
.
84
A previous structure deter-
mination of [Sn
2
-OBu
t
2
OBu
t
2
] had shown that the dimers are linked into a chain
structure by bridging weakly bonding THF molecules.
84
An interesting feature of
[M
2
-OBu
t
2
Cl
2
](MD Ge, Sn) molecules is that in the germanium compound the
chlorines are disposed
syn
with respect to the Ge
2
O
2
ring whilst in the tin compound
they are
anti
. In the dimer [Sn
2
-OBu
t
2
fN(SiMe
3
2
g
2
]
85
the bulky terminal silyl-
amido ligands also adopt the
trans
configuration. The di-anionic N-donor ligand
Me
2
Si(NBu
t
2
2
acts as a chelate to one Sn and bridges the other in the novel
dinuclear molecule [Me
2
Si(NBu
t
2
Sn
2
-OBu
t
Cl] which also contains a bridging
tert
-
butoxo group.
86
Finally it is interesting to note that [Sn
2
-OBu
t
2
OSiPh
3
2
]which
is isostructural with the germanium analogue also forms a heteronuclear complex with
Mo(CO)
5
through one tin atom acting as a donor to the molybdenum in [fSn
2
-
OBu
t
2
(OSiPh
3
2
gfMo(CO)
5
g]
.
82
A few tin(
IV
) alkoxo compounds have been structurally characterized in recent years.
It was found that the quadridentate ligand triethanolamine does not form a tin analogue
of the germatranes since only two of the three OH protons are replaced giving an octa-
hedrally coordinated tin atom in [Snf
OC
2
H
4
2
NC
2
H
4
OHg
2
]
.
86
Octahedral tin was also
found in the mixed dimer [Sn
2
-OPr
i
2
acac
2
]
.
87
The steric effects of the bulky
tert
-
butoxo ligand produced the mononuclear homoleptic alkoxide Sn(OBut)
4
with distorted
