1 research outputs found
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