2 research outputs found
Hydride Reduction of NAD(P)<sup>+</sup> Model Compounds with a Ru(II)–Hydrido Complex
In
order to better understand the regioselective hydride transfer of
metal hydrido complexes to NADÂ(P)<sup>+</sup> model compounds, reactions
of [RuÂ(tpy)Â(bpy)ÂH]<sup>+</sup> (<b>Ru-H</b>: tpy = 2,2′:6″,2″-terpyridine,
bpy = 2,2′-bipyridine) with various substituent NADÂ(P)<sup>+</sup> model compounds were investigated in detail. All of the NADÂ(P)<sup>+</sup> model compounds accepted hydride from <b>Ru-H</b>,
yielding 1:1 adducts, where the dihydro form(s) of the model compounds
coordinated with the carbamoyl group to the RuÂ(II) center of [RuÂ(tpy)Â(bpy)]<sup>2+</sup>, with very different reaction rates. Some reactions produced
the adduct with only the 1,4-dihydro structure, whereas others produced
a mixture of two adducts, with a 1,4- or 1,2-dihydro structure. In
particular, temperature-dependent adduct formation kinetics studies
provided important information on the transition state(s) of the hydride
transfer reactions and factors for determining the regioselectivity.
Most adducts were cleaved to the corresponding free dihydro product(s)
with the same distribution of the regioisomers to the adduct(s)
Formation of η<sup>2</sup>‑Coordinated Dihydropyridine–Ruthenium(II) Complexes by Hydride Transfer from Ruthenium(II) to Pyridinium Cations
Reactions
between various pyridinium cations with and without a
−CF<sub>3</sub> substituent at the 3-position and [RuÂ(tpy)Â(bpy)ÂH]<sup>+</sup> (tpy = 2,2′:6′,2″-terpyridine and bpy
= 2,2′-bipyridine) were investigated in detail. The corresponding
1,4-dihydropyridines coordinating to a RuÂ(II) complex in η<sup>2</sup> mode through a Cî—»C bond were quantitatively formed
at the initial stage. The only exception observed was in the case
of the 1-benzylpyridinium cation, where a mixture of two adducts with
1,4-dihydropyridine and 1,2-dihydropyridine was formed in the ratio
96:4. Cleavage of the Ru–(CC) bond proceeded at a slower
rate in all reactions, giving the corresponding dihydropyridine and
[RuÂ(tpy)Â(bpy)Â(NCCH<sub>3</sub>)]<sup>2+</sup> when acetonitrile was
used as a solvent. Kinetic activation parameters for the adduct formation
indicated that the 1,4-regioselectivities were induced by formation
of sterically constrained structures