Incorporation of [Cp*Rh] and [Cp*Ir] Species into Heterobimetallic Complexes via Protonolysis Reactivity and Dioximato Chelation

The synthesis of multimetallic compounds
can enable the placement
of two or more metals in close proximity, but efforts in this area
are often hindered by reagent incompatibilities and a lack of selectivity.
Here, we show that organometallic half-sandwich [Cp*M] (M = Rh, Ir)
fragments (where Cp* is η5-pentamethylcyclopentadienyl)
can be cleanly installed into metallomacrocyclic structures based
on the workhorse diimine–monooxime–monooximato ligand
system. Six new heterobimetallic compounds have been prepared to explore
this synthetic chemistry, which relies on in situ protonolysis reactivity
with precursor Ni­(II) or Co­(III) monometallic complexes in the presence
of suitable [Cp*M] species. Solid-state X-ray diffraction studies
confirm installation of the [Cp*M] fragments into the metallomacrocycles
via effective chelation of the Rh­(III) and Ir­(III) centers by the
nascent dioximato site. Contrasting with square-planar Ni­(II) centers,
the Co­(III) centers prefer octahedral geometry in the heterobimetallic
compounds, promoting bridging ligation of acetate across the two metals.
Spectroscopic and electrochemical studies reveal subtle influences
of the metals on each other’s properties, consistent with the
moderate M′···M distances of ca. 3.6–3.7
Å in the modular compounds. Taken together, our results show
that heterobimetallic complexes can be assembled with organometallic
[Cp*M] fragments on the diimine–dioximato platform.