New Fe(III)(cyclam) Complexes Bearing Axially Bound <i>geminal</i>-Diethynylethenes
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Abstract
Reported herein are the preparation
and characterization of <i>trans</i>-[Fe(cyclam)(X-<i>gem</i>-DEE)<sub>2</sub>]OTf (where cyclam = 1,4,8,11-tetraazacyclotetradecane, <i>gem</i>-DEE = σ-<i>geminal</i>-diethynylethene,
and OTf
= trifluoromethanesulfonate) compounds <b>2a</b>, <b>2b</b>, and <b>2c</b> (X = −Ph (<b>2a</b>), −Si<sup><i>i</i></sup>Pr<sub>3</sub> (<b>2b</b>), and −Fc
(<b>2c</b>)), which are the first examples of redox-active 3d
metal complexes containing <i>gem</i>-DEE ligands. These
compounds were prepared from the reaction between <i>cis</i>/<i>trans</i>-[Fe(cyclam)(OTf)<sub>2</sub>]OTf (<b>1</b>) and X-<i>gem</i>-DEE-Li. Compounds <b>2a</b>–<b>2c</b> were characterized by spectroscopic/voltammetric techniques.
The <i>trans</i>-orientation of the <i>gem</i>-DEE ligands was established from the single-crystal X-ray diffraction
study of <b>2a</b>. Furthermore, the electronic structures of
the model compounds <b>2a</b>′<sup>+</sup> and <b>2b</b>′<sup>+</sup> were analyzed with density-functional-theory
calculations, which revealed significant dπ(Fe)−π(<i>gem</i>-DEE) interactions
