The influence of remote substituent in tetrakis(μ-N,N′-diarylformamidinato)–dirhodium(II) compounds. Part 7. Linear free energy relationships in dinuclear compounds

Synthesis and characterizations are reported for the tetrakis(μ-N,N′-diarylformamidinato)dirhodium(II) compounds, where Ar is either XC6H4- with X as p-OMe (1), p-Me (2), H (3), m-OMe (4), p-Cl (5), m-Cl (6), m-CF3 (7), p-CF3 (8), or 3,4-Cl2C6H3 (9), or 3,5-Cl2C6H3 (10). The quasireversible redox couples Rh2 6+/Rh2 5+ (A), Rh2 5+/Rh2 4+ (B), and Rh2 4+/Rh2 3+ (C) were observed for all the compounds with the exception of 9. The electrode potentials are related to the Hammett constant (σ) of X by the following equation: ΔE1/2=E1/2(X)−E1/2(H)=ρ(8σ) mV with the reactivity constant ρ for the redox couples A, B, and C as 96, 98, and 97 mV, respectively. Molecular structures of compounds 4 and 10 were determined via X-ray diffraction studies.