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

Abstract

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(Cpttt)2 (Cpttt is for tris-tert-butylcyclopentadienyl) led presumably to the formation of the ion pair complex [Tm(Cpttt)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.