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

Synthesis and characterizations are reported for the tetrakis(mu-N,N'-diary lformamidinato)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-CF 3 (8), or 3,4-Cl2C6H3 (9), or 3,5-Cl2C6H3 (10). The quasireversible redox c ouples Rh-2(6+)/Rh-2(5+) (A), Rh-2(5+)/Rh-2(4+) (B), and Rh-2(4+)/Rh-2(3+) (C) were observed for all the compounds with the exception of 9. The electr ode potentials are related to the Hammett constant (sigma) of X by the foll owing equation: Delta E-1/2 = E-1/2(X) - E-1/2(H) = rho(8 sigma) mV with th e reactivity constant rho for the redox couples A, B, and C as 96, 98, and 97 mV, respectively. Molecular structures of compounds 4 and 10 were determ ined via X-ray diffraction studies. (C) 2000 Elsevier Science S.A. All righ ts reserved.