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(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.