2 Homometallic Alkoxides

246 Alkoxo and Aryloxo Derivatives of Metals
N
Ge
Figure 4.16 Structure
of [EtGe⊲OCH2CH2⊳3N]
(H atoms omitted).
pyramidal three-coordinated Ge. 81 The dimeric structure is also maintained in [Ge2⊲ -
OBu t ⊳2(OSiPh 3⊳2] inwhichthetert-butoxo group is preferred as the bridging ligand. 82
2.4.2 Tin
Numerous structures of Sn(II) and Sn(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 [Sn2⊲ -
OBu t ⊳2(OBu t ⊳2] was shown by electron diffraction analysis to have the dimeric structure
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 [Sn2⊲ -OBu t ⊳2Cl2]. 84 A previous structure determination
of [Sn2⊲ -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
[M2⊲ -OBu t ⊳2Cl2] (MD Ge, Sn) molecules is that in the germanium compound the
chlorines are disposed syn with respect to the Ge2O2 ring whilst in the tin compound
they are anti. In the dimer [Sn2⊲ -OBu t ⊳2fN(SiMe 3⊳2g2] 85 the bulky terminal silylamido
ligands also adopt the trans configuration. The di-anionic N-donor ligand
Me2Si(NBu t ⊳2 2 acts as a chelate to one Sn and bridges the other in the novel
dinuclear molecule [Me2Si(NBu t ⊳2Sn2⊲ -OBu t ⊳Cl] which also contains a bridging tertbutoxo
group. 86 Finally it is interesting to note that [Sn2⊲ -OBu t ⊳2⊲OSiPh3⊳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 [fSn2⊲ -
OBu t ⊳2(OSiPh 3⊳2gfMo(CO) 5g]. 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 octahedrally
coordinated tin atom in [Snf⊲OC2H4⊳2NC2H4OHg2]. 86 Octahedral tin was also
found in the mixed dimer [Sn2⊲ -OPr i ⊳2⊲acac⊳2]. 87 The steric effects of the bulky tertbutoxo
ligand produced the mononuclear homoleptic alkoxide Sn(OBut) 4 with distorted