Sk. Chandra et al., ELECTRON-TRANSFER .135. PENDANT CARBONYL GROUPS IN THE MEDIATION OF THE REACTIONS OF INDIUM(I) WITH BOUND RUTHENIUM(II), Inorganic chemistry, 36(21), 1997, pp. 4684-4687
Reductions using In-1(aq) and Ti-III(aq), of (NH3)(5)Ru-III derivative
s of pyridines having carbonyl-bearing substituents (-CONH2, -COOCH3,
and -COC6H5) yield the corresponding (NH3)(5)Ru-II complexes. Reaction
s with Ti-III are kinetically straightforward, exhibit only slight res
ponses to structural alteration, and give no indication of inner-spher
e mediation involving the carbonyl group. Kinetic profiles for In(I) r
eductions of the 3-CONH2, 3-COOCH3, and 3-COC6H5-substituted complexes
(in the range [H+] = 0.030-0.15 M) begin with a nearly linear section
, with rates independent of [In-1], but show curvature during the late
r stages of reaction. These profiles are consistent with a reaction se
quence in which the predominant carbonyl form of the oxidant is hydrat
ed to a more reactive gem-diol form (>C=O + H2O reversible arrow C(OH)
(2)), which undergoes reduction by In-1, yielding the observed Ru-II p
roduct and In-II. The latter is then rapidly consumed by a second unit
of Ru-III. Rate constants for the hydration step giving optimal fit t
o the experimental curves are 6 x 10(-4) s(-1) (for the 3-CONH2 comple
x) and 1.3 x 10(-3) s(-1) (for the 3-COOCH3 oxidant). Lower limits for
the rate of attack by In-1 on the active forms of the oxidants are es
timated as 10(3.3)-10(4.6) M-1 s(-1), about 10(2)-10(3) times are rapi
d as the reduction of the unsubstituted pyridine complex. Our results
suggest the utilization, by In-1, of a hydroxyl-bridged path featuring
the sequence In-1-OH-C(OH)-py in these reductions, a path which is ov
ershadowed, in the case Ti-III reactions, by a more failce outersphere
process.