The Taming of Redox‐Labile Phosphidotitanocene Cations. Issue 11 (29th January 2019) - Normand, Adrien T.
Abstract: Tame d 0 phosphidotitanocene cations stabilized with a pendant tertiary phosphane arm are reported. These compounds were obtained by one‐electron oxidation of d 1 precursors with [Cp2 Fe][BPh4 ]. The electronic structure of these compounds was studied experimentally (EPR, UV/Vis, and NMR spectroscopy, X‐ray diffraction analysis) and through DFT calculations. The theoretical analysis of the bonding situation by using the electron localization function (ELF) shows the presence of π‐interactions between the phosphido ligand and Ti in the d 0 complexes, whereas dπ–pπ repulsion prevents such interactions in the d 1 complexes. In addition, CH–π interactions were observed in several complexes, both in solution and in the solid state, between the phosphido ligand and the phosphane arm. The d 0 complexes were found to be light sensitive, and decompose through Ti−P bond homolysis to give Ti III species. A naked d 0 phosphidotitanocene cation has been trapped by reaction with diphenylacetylene, yielding a Ti/P frustrated Lewis pair (FLP), which was found to be less reactive than a previously reported Zr analog. Abstract : Unsubstituted phosphidotitanocene cations are fleeting species, which undergo spontaneous Ti−P bond homolysis. However, they can be stabilized with a rigid phosphane‐functionalized cyclopentadienyl (Cp) ligand, thus enabling their characterization. Experimental (XRD, NMR, UV/Vis) and theoretical (TD‐DFT, ELF) data indicate that the Ti−P interaction displays a marked double‐bond character.