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

Synthesis of multimetallic compounds can enable placement of two or more metals in close proximity, but efforts in this area are often hindered by reagent incompatibilities and 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 metallomacrocyles 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. The [Co,Rh] complex was found to catalyze hydrogenation of p-trifluoromethylbenzaldehyde to p-trifluoromethylbenzyl alcohol more cleanly than a 1:1 mixture of the individual monometallic precursor complexes, suggesting that this family of heterobimetallic complexes could be useful in future studies of multimetallic chemistry, especially in light of the starring role of other [Cp*M] complexes in diverse catalytic systems.