Polynuclear metal complexes of nanometre size. A versatile synthetic strategy leading to luminescent and redox-active dendrimers made of an osmium(II)-based core and ruthenium(II)-based units in the branches
Abstract
A docosanuclear metal complex of nanometric size and dendritic shape
made of an osmium(ii)-based core and containing 21 ruthenium(ii)-based
units in the branches has been prepared. The key building blocks are the
[Os(2,3-dpp)
3
]
2+
‘complex ligand’, and
the [Ru(2,3-Medpp)
2
Cl
2
]
2+
and
[{Ru(bpy)
2
(µ-2,3-dpp)}
2
RuCl
2
]
4+
‘complex metals’
{2,3-dpp=2,3-bis(2-pyridyl)pyrazine;
2,3-Medpp
+
=2-[2-(1-methylpyridiniumyl)]-3-(2-pyridyl)pyrazine;
bpy=2,2′-bipyridine}. The first step of the synthesis is the
formation of the tetranuclear
[Os{(µ-2,3-dpp)Ru(2,3-Medpp)
2
}
3
]
14+
species in which the peripheral ligands
2,3-Medpp
+
are 2,3-dpp ligands with the second chelating site
inactivated (protected) by methylation. This species is obtained from the
reaction of the [Os(2,3-dpp)
3
]
2+
‘complex
ligand’ core, which contains three open chelating positions, with
three equivalents of the [Ru(2,3-Medpp)
2
Cl
2
]
2+
‘complex metal’, where the labile
Cl
-
ligands can be replaced by the chelating units of the
core. Successive demethylation (deprotection) of the tetranuclear compound
opens the six peripheral chelating sites. At this stage, the divergent
synthesis can be iterated {reaction with six equivalents of the
[Ru(2,3-Medpp)
2
Cl
2
]
2+
‘complex
metal’} with formation of the protected decanuclear compound
[Os{(µ-2,3-dpp)Ru[(µ-2,3-dpp)Ru(2,3-Medpp)
2
]
2
}
3
]
32+
. Alternatively, in a
convergent approach, the reaction of the deprotected tetranuclear species
with six equivalents of the trinuclear
[{Ru(bpy)
2
(µ-2,3-dpp)}
2
RuCl
2
]
4+
‘complex metal’ leads to the docosanuclear
[Os{(µ-2,3-dpp)Ru[(µ-2,3-dpp)Ru{(µ
-2,3-dpp)Ru(bpy)
2
}
2
]
2
}
3
]
44+
species. The absorption spectra, luminescence properties,
and electrochemical behaviour of [Os(2,3-dpp)
3
]
2+
,
[Os(µ-2,3-dpp)
3
{Ru(2,3-Medpp)
2
}
3
]
14+
,
[Os{(µ-2,3-dpp)Ru[(µ-2,3-dpp)Ru(2,3-Medpp)
2
]
2
}
3
]
32+
, and
[Os{(µ-2,3-dpp)Ru[(µ-2,3-dpp)Ru{(µ
-2,3-dpp)Ru(bpy)
2
}
2
]
2
}
3
]
44+
have been investigated.
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