Substituent
Effects and Supramolecular Interactions
of Titanocene(III) Chloride: Implications for Catalysis in Single
Electron Steps
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Abstract
The electrochemical properties of
titanocene(III) complexes and
their stability in THF in the presence and absence of chloride additives
were studied by cyclic voltammetry (CV) and computational methods.
The anodic peak potentials of the titanocenes can be decreased by
as much as 0.47 V through the addition of an electron-withdrawing
substituent (CO<sub>2</sub>Me or CN) to the cyclopentadienyl ring
when compared with Cp<sub>2</sub>TiCl. For the first time, it is demonstrated
that under the conditions of catalytic applications low-valent titanocenes
can decompose by loss of the substituted ligand. The recently discovered
effect of stabilizing titanocene(III) catalysts by chloride additives
was analyzed by CV, kinetic, and computational studies. An unprecedented
supramolecular interaction between [(C<sub>5</sub>H<sub>4</sub>R)<sub>2</sub>TiCl<sub>2</sub>]<sup>−</sup> and hydrochloride cations
through reversible hydrogen bonding is proposed as a mechanism for
the action of the additives. This study provides the critical information
required for the rational design of titanocene-catalyzed reactions
in single electron steps