P. Bernhard et al., LIGAND DEHYDROGENATION IN RUTHENIUM-AMINE COMPLEXES - REACTIVITY OF 1,2-ETHANEDIAMINE AND 1,1,1-TRIS(AMINOMETHYL)ETHANE, Inorganic chemistry, 36(13), 1997, pp. 2804-2815
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.