Multiple One-Electron Transfers in Bipyridine Complexes of Bis(phospholyl) Thulium

The synthesis of original neutral
bis­(phospholyl) thulium complexes,
Dtp2Tm­(L), where L is tetramethylbiphosphinine (tmbp) and
bipyridine (bipy), is reported. The electronic structures of these
complexes have been investigated and it appears that, in both cases,
an electron transfer occurs from the divalent metal to the ligand,
a consequence of the strong reduction potential of the bis­(phospholyl)
thulium fragment, Dtp2Tm. When 1 equiv of bipyridine is
added to the Dtp2Tm­(tmbp) complex, another electron transfer
occurs to form the Dtp2Tm­(bipy) complex along with free
tmbp ligand. Astonishingly, despite the apparent trivalent nature
of the thulium center, the Dtp2Tm­(bipy) complex is still
reactive toward neutral bipyridine to form a new complex in which
one phospholyl ligand is replaced by a bipyridine radical anion. An
experimental kinetic analysis is reported to rationalize this unprecedented
redox reaction with thulium and reveals an associative type of mechanism.