New heterosiloxanes of bivalent Group 14 elements and their reactions with [Mo(CO)6]: crystal structures of [{M(µ-OBut)(OSiPh3)}2] (M = Ge or Sn) and [{Sn(µ-OBut)(OSiPh3)}2 Mo(CO)5]
Abstract
The protolysis of Ph
3
SiOH with a toluene solution of
[{M(OBu
t
)
2
}
n
]
(M = Ge
II
or Sn
II
,
n = 2; M = Pb
II
,
n = 3) in 1∶1 molar ratio at room
temperature via alcohol elimination facilitated the isolation
of high yields of heteroleptic alkoxosiloxides of the type
[{M(µ-OBu
t
)(OSiPh
3
)}
2
]
(M = Ge
II
1, Sn
II
2 or Pb
II
3). Crystal structural analyses
of compounds 1 and 2 revealed them to be isomorphous
and isostructural. Both the dimeric structures feature a perfect planar
M
2
O
2
(M = Sn 1 or Ge
2) core with a crystallographically imposed centre of
inversion. Each metal atom is bound to two bridging
tert-butoxide ligands and one terminal triphenylsiloxide
ligand resulting in a trigonal-pyramidal co-ordination geometry
around the metal atom. The stereochemical activity of the lone pair of
electrons present on the metal atoms of 1 and 2 is
demonstrated by their ability to form M–Mo bonds in
[{M(µ-OBu
t
)(OSiPh
3
)}
2
Mo(CO)
5
] (M = Ge 4 or Sn 5)
on their reaction with an equimolar amount of [Mo(CO)
6
] in
refluxing toluene via displacement of CO from the inner
co-ordination sphere of [Mo(CO)
6
]. The asymmetry in compound
5 was revealed by its crystal structure. The structure consists
of a four-co-ordinate tin(II) centre, bearing an
Mo(CO)
5
unit, linked via two bridging
tert-butoxide groups to another Sn
II
which exhibits
(3 + 6) co-ordination with three normal Sn–O bonds
and a weak tin(II)–arene (η
6
)
interaction originating from the orientation of a phenyl ring of the
OSiPh
3
ligand such that the tin to ring centre distance is
3.58 Å. The identity of all the compounds in solution has
been confirmed by multinuclear (
1
H,
13
C,
29
Si,
119
Sn and
207
Pb) NMR and IR
spectra and elemental analyses.
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