Chemistry Reference
In-Depth Information
Figure 4.7
Representation of the main features of the triangular supramolecules formed with
Pt(II) and Ru(II) and 9-Methyladenine or 9-Methylhypoxanthine
3
+
[
)
(
)
]
Figure 4.8
Essential skeleton of the triangle
PMe
Pt
(
1
-
MeC
H
−
(
)
3
2
3
of noncovalent processes involving p
-
p, hydrophobic and H-bonding interactions.
Formation of these trimeric structures is achieved by coordination of the purine
to metal ions as: (i) m - [ h
2
(
N7,O6
): h
1
(
N1
)] with Rh(III) and 9-ethylhypoxanthine;
(ii) m - [ h
2
(
N7,N6
): h
1
(
N1
)] with Ir(III), Rh(III) and 9-EtA, 9-MeA, respectively. It
has been found that when the 9 position of adenine is not blocked, formation of a
similar cyclic tetramer complex take places via m - [ h
2
(
N7,N6
): h
1
(
N9
)].
Pyrimidines
Preliminary
1
H,
13
C and
195
Pt NMR spectra of the products obtained by the reaction
of 1 - methylcytosine (1 - MeC) with
cis
- [(PMe
3
)
2
Pt( m - OH)]
2
(X)
2
XNOClO
(
)
3
,
in
water, suggested that single mononuclear complexes,
cis
- [(PMe
3
)
2
Pt(1 - MeC
−
)](X),
were formed. However, X-ray crystallographic analyses identifi ed the products as
the trinuclear
cis
- [(PMe
3
)
2
Pt(1 - MeC
−
)]
3
(X)
3
XNOClO
=
−
−
(
)
3
,
, formed by deproto-
nation of the exocyclic amino group of the 1-MeC. Natural abundance
15
N NMR
results are in agreement with the structural data obtained in the solid state.
9
The
initial reaction products are dinuclear complexes,
cis
- [(PMe
3
)
2
Pt(1 - MeC
−
)]
2
(X)
2
,
which rearrange to a thermodynamically more stable trinuclear species in water or
DMSO at 80 °C. The driving force for the oligomerization reaction has to be related
to a more favourable metal-ligand interaction in the trinuclear species, likely due
to the lower intramolecular repulsion of the
cis
- (PMe
3
)
2
Pt moieties. The X-ray
structure of the perchlorate complex shows three
cis
- (PMe
3
)
2
Pt units symmetrically
bridged by cytosinate anions through the N3 and N4 atoms (Figure 4.8). The
=
−
−
