SYNTHESES OF NOVEL MONOMERIC 1,4,7-TRIMETHYL-1,4,7-TRIAZACYCLONONANE RUTHENIUM COMPLEXES - REACTIVITIES AND STRUCTURE OF STERICALLY ENCUMBERED CATIONIC MONOAQUARUTHENIUM(II) AND MONOOXORUTHENIUM(IV) COMPLEXES

The complexes [Ru(II)(tacn)(bipy)(OH2)]2+ 1 and [Ru(IV)(tacn)(bipy)O]2+ 2 (tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane, bipy = 2,2'-bipyridine) have been synthesised and their crystal structures determined: 1, monoclinic, space group C2/c, a = 34.093(4), b = 10.430(l), c = 17.369(2) angstrom, beta = 118.54(l)-degrees and Z = 8; 2, triclinic, space group P1BAR, a = 10.795(l), b = 11.076(2), c = 11.248(l) angstrom, alpha = 110.41 (2), beta = 90.66(l ), gamma = 94.11 (1 )-degrees and Z = 2. The structures reveal that tacn acts as a facial chelating ligand with bipy nearly perpendicular to the Ru=O and Ru-OH2 moieties. The Ru(IV)=O and Ru-OH2 distances are 1.815(6) and 2.168(3) angstrom respectively. In aqueous solution both complexes display two reversible proton-coupled one-electron redox couples corresponding to the oxidation of Ru(II) to Ru(III) and Ru(III) to Ru(IV). Complex 2 has been found to be a competent oxidant for alkene epoxidation. Preliminary kinetic studies revealed the rate law, rate = k2[Ru(IV)] [alkene] where k2 at 299 K are (1.30 +/- 0.11) x 10(-3) and (2.52 +/- 0.20) x 10(-4) dM3 mol-1 s-1 for the epoxidation of styrene and norbornene respectively. The activation parameters have been measured and are discussed.