An electrochemical study of chromium(0) complexes of arenes which have electronegative substituent groups

Abstract

Using cyclic voltammetry, E 1 2 values were determined for the process Cr(arene) 2 ⇄ [Cr(arene) 2] + + e (arene = C 6H 5R, for R = H, CF 3, Cl, F, OCH 3; p- and m-C 6H 4(CF 3) 2, o- and p-C 6H 4(CF 3)Cl; 1,4(CH 3) 2-2-ClC 6H 3) in acetonitrile. Compounds with electron withdrawing groups on the arene ligands have higher E 1 2 values indicating that they are more difficult to oxidize. This is in accord with a simple model in which withdrawal of electron density from the metal to ligands stabilizes the HOMO, a primarily metal orbital, in these systems. Possible correlations between E 1 2 and the Hammett substituent constants, σ m and σ p for the substituent groups on the ligands, are investigated.