Crystal structure and electrochemical behavior of Rh polypyridyl complexes

[Rh(tpy)(bpy)(Cl)](ClO4)(2) and [Rh(tpy)(phen)(Cl)](PF6)(2) (tpy; 2,2 ' ;6 ' ,2 " -terpyridine, bpy; 2,2'-bipyridine, phen; 1,10-phenanthroline) have been determined structurally. Both complexes were identified and characteri zed by spectroscopic methods. ORTEP drawings of each complex show three pyr idyl rings of the tpy ligand that are nearly coplanar, as are the two rings of bpy. The two ligands are coordinated to the metal atom through their ni trogen atoms in a mutually perpendicular fashion. The interatomic distance between chloride and rhodium atom is 2.300(12) and 2.323(2) Angstrom, respe ctively. The bond angle formed by the axially positioned nitrogen atom, the rhodium atom, and the chlorine atom is 174.96(8) and 176.32(19)degrees The oxidation of each [Rh(tpy)(bpy)(OH2](3+) or [Rh(tpy)(phen)(OH2)](3+) with two equivalents of Ce(IV) yielded the corresponding mono-ore product, [Rh-V (tpy)(bpy)(O)](ClO4)(3) and [Rh-V(tpy)(phen)(O)](ClO4)(3). A cyclic voltamm ogram of rhodium aqua complex with a scan rate of 5 mV s(-1) displays the r edox couple at - 0.81 V as reversible wave for the first oxidation from Rh( III) to Rh(IV) and the next Rh(IV)/Rh(V) wave at - 0.49 V as quasi-reversib le. Electrocatalytic oxidation of benzyl alcohol with rhodium aqua complex gave benzaldehyde as a major product with the turnover ratio of 13. (C) 200 1 Elsevier Science B.V. All rights reserved.