Chemistry Reference
In-Depth Information
Figure 5.10 Molecular structure of the helical complex anions D,D-[Ti
2
(3)
3
]
4
(left) and
L,L-[Ti
2
(4)
3
]
4
(right).
the
ortho
-position to the amide functions is elongated, while the Ti-S bond length to the
sulfur atoms in the
meta
-position to the amide group is shorter [39]. The helical twist
angles differ significantly in [Ti
2
(
3
)
3
]
4
(12
) and [Ti
2
(
4
)
3
]
4
(60
) with the small value
for [Ti
2
(
3
)
3
]
4
possibly resulting from a tendency to reduce the electrostatic repulsion
between the double-negatively charged TiS
2
2
moieties by a maximization of the Ti
Ti
distance. The remaining lithium cation in compound Li(PNP)
3
[Ti
2
(
3
)
3
]
H
2
Ois
coordinated by two carbonyl groups of two different anions [Ti
2
(
3
)
3
]
4
plus a water and a
DMF molecule. This leads to indefinite chains Li
3DMF
[Ti
2
(
3
)
3
]
4
in the
crystal lattice. No interactions between the cations and the anion have been observed in
compound (PNP)
3
[Ti
2
(
4
)
3
]
[Ti
2
(
3
)
3
]
4
Li
3DMF.
Besides dinuclear triple-standed helicates, tetrahedral tetranuclear clusters derived
from dicatecholato ligands have been reported [23]. Such clusters have found much inter-
est owing to their ability to serve as container molecules for selected catalytic transforma-
tions [23e,f]. The factors governing the preferred formation of a tetrahedral cluster of type
[M
4
(
F
)
6
]
m
versus a triple helicate [M
2
(
F
)
3
]
n
(H
4
-
F
¼
1,5-naphthalenediamido-linked
dicatechol ligand, Scheme 5.3) starting from an identical stoichiometry M:H
4
-
F
¼
2:3
have been discussed [42]. Molecular modeling and experimental studies demonstrated
that the presence of the naphthalene spacer in H
4
-
F
causes the catechol binding units to
be offset from one another when the ligand adopts the conformation required for helicate
formation, thereby disfavoring the formation of a helicate. We have prepared the bis(ben-
zene-
o
-dithiol) ligand H
4
-
6
which also contains the 1,5-naphthalenediamido spacer
linking two benzene-
o
-dithiol groups. In spite of the identical spacers present in H
4
-
F
and
H
4
-
6
, the latter was surprisingly found to yield dinuclear complexes [Ti
2
(
6
)
3
]
4
when
reacted with [Ti(OPr)
4
] in methanol (Scheme 5.3) [43].
Three equivalents of H
4
-
6
reacted with two equivalents of [Ti(OPr)
4
] in the presence
of Na
2
CO
3
in methanol with the formation of a deep red solution, typical for the
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