Cobalt(I) and Nickel(II) Complexes of Bis(1,3‐diphosphacyclobutadiene) Sandwich Anions

Abstract

AbstractComplexes [(C4Me4)Co(CO)2{Co(P2C2tBu2)2}] (1, C4Me4 = tetramethylcyclobutadiene) and [CpNi{Co(P2C2tBu2)2}(PPh3)] (2, Cp = cyclopentadienyl) were synthesized by transmetalating [Tl(thf)2{Co(P2C2tBu2)2}] with [(C4Me4)Co(CO)2I] and [CpNiBr(PPh3)]. Compounds 1 and 2 were fully characterized by X‐ray crystallography, multinuclear NMR, UV/Vis, and IR spectroscopy, and elemental analysis. Their molecular structures show σ‐coordination of one phosphorus atom of the [Co(P2C2tBu2)2]– anion to the second metal atom (cobalt or nickel). Time‐dependent density functional theory (TD‐DFT) calculations were applied to gain insight into the electronic structures and the nature of the electronic transitions observed in the UV/Vis spectra. Cyclic voltammetry studies revealed the similar redox behavior of 1 and 2, which are reversibly oxidized to the corresponding monocations 1+ and 2+ with retention of the dinuclear structures. The cyclic voltammograms furthermore show that 1 and 2 decompose upon reduction with cleavage of the dinuclear structures into the free [Co(P2C2tBu2)2]– anion and further uncharacterized products.