Synthesis and Characterization of 1,1′-Diphosphaplumbocenes: Oxidative Ligand Transfer Reactions with Divalent Thulium Complexes

The new 1,1′-diphosphaplumbocenes Pb(Dtp)₂ (Dtp = 2,5-di-tert-butyl-3,4-dimethylphospholyl) and Pb(Dsp)₂ (Dsp = 2,5-ditrimethylsilyl-3,4-dimethylphospholyl) have been synthesized and characterized by multinuclear NMR spectroscopy. ²⁰⁷Pb NMR spectra of both complexes, as well as for the known complex Pb(Htp)₂ (Htp = 2,5-di-tert-butylphospholyl), show that the phospholyl ligands lead to an important downfield shift compared with that of cyclopentadienyl based plumbocenes. X-ray diffraction studies of the Pb(Dtp)₂ complex revealed a structure with two slightly bent η⁵-bound ligands. This complex was employed in the oxidative ligand transfer reaction with bulky divalent thulium complexes. In the case of Tm(Dtp)₂, the first example of a monomeric trivalent tris(phospholyl)lanthanide complex Tm(Dtp)₃ was obtained. X-ray diffraction studies and low-temperature ¹H NMR studies show the η¹ coordination mode of the third Dtp ligand. In contrast, oxidation of Tm(Cp^ttt)₂ (Cp^ttt is for tris-tert-butylcyclopentadienyl) led presumably to the formation of the ion pair complex [Tm(Cp^ttt)₂][Dtp], in which no interaction between the free Dtp ligand and Tm was observed, as shown by variable temperature ¹H and ³¹P NMR studies. The new trivalent complexes could be reduced back to the original divalent complexes with potassium graphite.