2,2′-Pyridylpyrrolide Ligand Redistribution Following Reduction

The potential redox activity of the 2,2′-pyridylpyrrolide ligand carrying two CF3 substituents (L2) is investigated. Synthesis and characterization of d6 and d7 species M­(L2)2 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(L2)2q where q = 1 and 2, chemical reductants instead yield divalent metal complexes KM­(L2)3, which show attractive interactions of K+ 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(L2)2(CO)2. 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(L2)2 simply forms Cu­(L2)2.