217957-43-2Relevant academic research and scientific papers
16-electron through 19-electron complexes of the 1,5-COD and 1,3-COD isomers of (η5-C5Ph5)Rh(η4-C 8H12): Electrochemical evidence for an oxidatively induced agostic interaction
Shaw, Michael J.
, p. 5486 - 5491 (1998)
The redox properties of Cp?Rh (1,5-COD) (1) and Cp?Rh (1,3-COD) (2) (Cp? = η5-C5Ph5, COD = η4-cyclooctadiene) have been investigated by cyclic voltammetry and bulk coulometry. Both compounds display a four-membered electron-transfer series involving complexes of overall 2+, 1+, 0, and 1- charges. The 19-electron complexes [Cp?Rh(COD)]- are shortlived, rapidly releasing [C5Ph5]-. The persistent 17-electron complexes [Cp?RhCCOD)]+ have been characterized by ESR and optical spectroscopies. Complex 1+ displays an axially symmetric g-tensor, demonstrating that the 17-electon system retains the approximate Cgu symmetry of its 18-electron precursor. The oxidized forms of 2n+ (n = 1 or 2) undergo slow isomerization to those of ln+; that is, isomerization of the diolefin ligand from the 1,3- to the 1,5-isomer occurs in the higher oxidation states of [Cp?Rh(COD)]n+. The 1,3-COD ligand imparts an unexpected thermodynamic stabilization of the higher Rh oxidation states. Formation of the 17-electron and 16-electron complexes occurs at potentials ca 0.25 and 0.62 V, respectively, lower than expected. The increasing stabilization of the Rh(II) and Rh(III) complexes is ascribed to progressive formation of an agostic interaction between the metal atom and the hydrogen on carbon 5 of the 1,3-cyclooctadiene ring.
