2,2′-Pyridylpyrrolide Ligand Redistribution Following Reduction

The potential redox activity of the 2,2′-pyridylpyrrolide ligand carrying two CF<sub>3</sub> substituents (L<sup>2</sup>) is investigated. Synthesis and characterization of d<sup>6</sup> and d<sup>7</sup> species M­(L<sup>2</sup>)<sub>2</sub> for M = Fe and Co are described (both are nonplanar, but not tetrahedral), as are the Lewis acidity of each. In spite of CV evidence for quasireversible reductions to form M­(L<sup>2</sup>)<sub>2</sub><sup><i>q</i>–</sup> where <i>q</i> = 1 and 2, chemical reductants instead yield divalent metal complexes KM­(L<sup>2</sup>)<sub>3</sub>, which show attractive interactions of K<sup>+</sup> to pyrrolide, to F, and to lattice toluene π cloud. The collected evidence on these products indicates that pyridylpyrrolide is a weak field ligand here, but CO can force spin pairing in Fe­(L<sup>2</sup>)<sub>2</sub>(CO)<sub>2</sub>. Evidence is presented that the overall reductive reaction yields 33 mol % of bulk metal, which is the fate of the reducing equivalents, and a mechanism for this ligand redistribution is proposed. Analogous ligand redistribution behavior is also seen for nickel and for trimeric monovalent copper analogues; reduction of Cu­(L<sup>2</sup>)<sub>2</sub> simply forms Cu­(L<sup>2</sup>)<sub>2</sub><sup>–</sup>.