The mechanisms of oxidative ligand dehydrogenation in high-valent ruthenium hexaamine complexes of bidentate 1,2-ethanediamine (en) and tridentate 1,1,1-tris(aminomethyl)ethane (tame) are elucidated in detail. In basic aqueous solution, [Ru(III)(tame)(2)](3+) undergoes rapid initial deprotonation (pK(III) = 10.3). This is followed by a pH-dependent disproportionation step involving either [Ru(III)(tame)(2)-H(+)](2+) + [Ru(III)(tame)(2)](3+) (k(1d) = 8300 M(-)(1) s(-)(1)) or two singly deprotonated [Ru(III)(tame)(2)-H(+)](2+) ions (k(2d) = 3900 M(-)(1) s(-)(1)). The products are [Ru(II)(tame)(2)](2+) and either the singly deprotonated species [Ru(IV)(tame)(2)-H(+)](3+) (pK(IV) = 8.2) or the doubly deprotonated [Ru(IV)(tame)(2)-2H(+)](2+). These Ru(IV) complexes undergo spontaneous dehydrogenation to give the imine [Ru(II)(imtame)(tame)](2+) (imtame = 1,1-bis(aminomethyl)-1-(iminomethyl)ethane), with first-order rate constants of k(1im) = 320 s(-)(1) and k(2im) = 1.1 s(-)(1), respectively. In the [Ru(III)(en)(3)](3+) system, the initial deprotonation (pK(III) = 10.4) is followed by the corresponding disproportionation reactions (k(1d) = 9000 M(-)(1) s(-)(1), k(2d) = 3800 M(-)(1) s(-)(1)). The complex [Ru(IV)(en)(3)-H(+)](3+) (pK(IV) = 8.9) and its deprotonated counterpart, [Ru(IV)(en)(3)-2H(+)](2+), undergo dehydrogenation to give [Ru(II)(imen)(en)(2)](2+) (imen = 2-aminoethanimine) with first-order rate constants of k(1im) = 600 s(-)(1) and k(2im) = 1.0 s(-)(1), respectively. In the light of this analysis, the disproportionation and ligand oxidation of the [Ru(III)(sar)](3+) ion are reexamined (k(1d) = 4 x 10(7) M(-)(1) s(-)(1), k(2d) >/= 2 x 10(7) M(-)(1) s(-)(1), pK(IV) = 2.0, k(1im) = 17 s(-)(1), k(2im) = 5 x 10(-)(4) s(-)(1) at 25 degrees C). While the disproportionation to Ru(II) and Ru(IV) has been recognized in such systems, the complexity of the paths has not been realized previously; the surprising variation in the rates of the intramolecular redox reaction (from days to milliseconds) is now dissected and understood. Other facets of the intramolecular redox reaction are also analyzed.

The crystal structure of [Rh(phpy)2(bpy)]PF6 (phpyH = 2-phenylpyridine, bpy = 2,2,-bipyridine) is determined and described. Crystallographic data at 100 K: chemical formula C32H24F6N4PRh, orthorhombic crystal system, space group Pbca (No. 61), Z = 8, a = 10.821 (1) A, b = 15.798 (1) A, c = 33.328 (3) A, V= 5697.4 (9) A3. There is one complex cation, i.e. two crystallographically inequivalent phpy ligands, per asymmetric unit. Polarized single-crystal absorption spectra of [Rh(phpy)2(bpy)]PF6 and excitation and site-selective luminescence spectra of [Rh(thpy)2(bpy)]+ and [Rh(thpy)(phpy)(bpy)]+ (thpyH = 2-thienylpyridine) doped into [Rh(phpy)2(bpy)]PF6 are reported and interpreted on the basis of the crystal structure of [Rh(phpy)2(bpy)]PF6. The two lowest-energy excitations of [Rh(phpy)2(bpy)]PF6, and also of [Rh(phpy)2(bpy)]BPh4, [Rh(phpy)2(en)]PF6, and [Rh(phpy)2-(en)]BPh4 (BPh4" = tetraphenylborate anion, en = ethylenediamine), are found in the region between 21 400 and 22 200 cm-1 with an energy splitting ranging from 22 to 242 cm-1. They are assigned to electronic transitions involving the phpy ligands. The third excited state of [Rh(phpy)2(bpy)]PFe lies 967 cm-1 above the first excited state and is ascribed to an analogous transition involving the bpy ligand. The polarization properties of these three lowest-energy transitions and the crystal structure of [Rh(phpy)2(bpy)]PF6 show that the transition moments are parallel to the ligand planes: The bpy transition is short-axis polarized, and the two phpy transitions are oriented approximately parallel to the respective Rh-N(phpy) bonds. It is concluded that the three lowest-energy excited states are essentially 3 * states, localized on the three ligands of the complex. They have a small admixture of the lowest-energy 'drr* excitations through spin-orbit coupling.

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