LIGAND DEHYDROGENATION IN RUTHENIUM-AMINE COMPLEXES - REACTIVITY OF 1,2-ETHANEDIAMINE AND 1,1,1-TRIS(AMINOMETHYL)ETHANE

The mechanisms of oxidative ligand dehydrogenation in high-valent ruth enium hexaamine complexes of bidentate 1,2-ethanediamine (en) and trid entate 1,1,l-tris(aminomethyl)ethane (tame) are elucidated in detail. In basic aqueous solution, [Ru-III(tame)(2)](3+) undergoes rapid initi al deprotonation (pK(III) = 10.3) This is followed by a pH-dependent d isproportionation step involving either [Ru-III(tame)(2)-H+](2+) [Ru-I II(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 ar e: [Ru-II(tame)(2)](2+) and either the singly deproronated species [R- IV(tame)(2)-H+](3+) (pK(IV) = 8.2) or the doubly deprotonated [Ru-IV(t ame)(2)-2H(+)](2+). These Ru(IV) complexes undergo spontaneous dehydro genation to give the imine [Ru-II(imtame)(tame)](2+) (imtame = 1,1-bis (aminomethyl)-1-(iminomethyl)ethane), with first-order rate constants of k(1/m) = 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) = 90 00 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+) (ime n = 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 anal ysis, 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) greater th an or equal to 2 x 10(7) M-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 R u(II) and Ru(IV) has been recognized in such systems, the complexity o f the paths has not been realized previously; the Surprising variation in the rates of the intramolecular redox reaction (from days to milli seconds) is now dissected and understood. Other facets of the intramol ecular redox reaction are also analyzed.