Heteroleptic Dirhodium(II) Complexes with Redox‐Active Ferrocenyl Ligands: Synthesis, Electrochemical Properties, and Redox‐Responsive Chemoselectivity in Carbene C−H Insertion

A series of original heteroleptic dirhodium(II) complexes ( 4 a–j ) of formula [Rh 2 (OAc) 3 (L)], where L is a redox‐active ferrocenecarboxylate ligand, has been prepared. These dirhodium(II) complexes have been characterised by NMR, mass spectrometry and cyclic voltammetry. All complexes show a quasi‐reversible redox behaviour for the ferrocenyl unit. The latter can be selectively oxidised by [N(4‐C 6 H 4 Br) 3 ] + BF 4 − . Four selected heteroleptic complexes 4 a, 4 b , 4 f and 4 i , have been evaluated as catalysts for the intramolecular decomposition of a diazo compound 5 . The ratio between the aromatic substitution product 6 and the aliphatic C−H insertion product 7 increases (up to 19 % increase) when using the in situ generated oxidised form of the dirhodium(II) complexes ( 4 a + BF 4 − to 4 i + BF 4 − ). This shows that the oxidation of the ferrocenecarboxylate ligand has an effect on the chemoselectivity of the dirhodium‐catalysed diazo decomposition, and thus that the electronic properties of a complex can be tuned without exchanging ligands.