Electron transfer in tetramethylbiphosphinine complexes of Cp∗₂Yb and Cp∗₂Sm

This article reports the synthesis and the characterization of two Cp∗₂Ln (Ln = Sm and Yb) fragments containing the tetramethylbiphosphinine (tmbp) ligand in equatorial position. The solid-state data indicate the reduction of the tmbp ligand with the decamethylsamarocene fragment along with the oxidation of the metal center, while the metrical parameters highlight a more dubious electronic structure for the tmbp adduct of the decamethylytterbocene fragment. ¹H and ³¹P NMR have been recorded for both complexes and show the unambiguous oxidation of the samarium complex. On the other hand, the NMR data for Cp∗₂Yb(tmpb) exhibit weakly shifted paramagnetic resonances along with a weak effective moment in solution; a situation that is neither in agreement with a divalent metal center and a neutral ligand, nor with an oxidized ytterbium ion and a radical tmbp ligand. In addition to these experimental data, theoretical calculations were performed on both complexes. DFT calculations highlight a large orbital contribution and an f occupation of 5.4 for the samarium complex, which is to compare to an f occupation of 13.8 and less orbital interactions in the ytterbium complex.