Isolation and electronic structures of lanthanide(II) bis(trimethylsilyl)phosphide complexes

Whilst lanthanide (Ln) silylamide chemistry is mature, the corresponding silylphosphide chemistry is underdeveloped, with [Sm{P(SiMe3)2}{μ-P(SiMe3)2}3Sm(THF)3] being the sole example of a structurally authenticated Ln(II) silylphosphide complex. Here we expand Ln(II) {P(SiMe3)2} chemistry through the synthesis and characterization of nine novel complexes. The dinuclear ‘ate’ salt-occluded complexes [{Ln[P(SiMe3)2]3(THF)}2(μ-I)K3(THF)] (1-Ln; Ln = Sm, Eu) and polymeric ‘ate’ complex [KYb{P(SiMe3)2}3{μ-K[P(SiMe3)2]}2] (2-Yb) were prepared by the respective salt metathesis reactions of parent [LnI2(THF)2] (Ln = Sm, Eu, Yb) with 2 or 3 eq. of K{P(SiMe3)2} in diethyl ether. The separate treatment of these complexes with either pyridine or 18-crown-6 led to the formation of the mononuclear solvated adducts, trans-[Ln{P(SiMe3)2}2(py)4] (3-Ln; Ln = Sm, Eu, Yb) and [Ln{P(SiMe3)2}2(18-crown-6)] (4-Ln; Ln = Sm, Eu, Yb), with concomitant loss of K{P(SiMe3)2}. The complexes were characterized by a combination of NMR, EPR, ATR-IR, electronic absorption and emission spectroscopies, elemental analysis, SQUID magnetometry, and single crystal X-ray diffraction. We find that these complexes exhibit electronic structures that contrast with those of related Ln(II) bis(trimethylsilyl)amide complexes due to differences in ligand donor atom hardness and ligand steric requirements from Ln–P bonds being longer than Ln–N bonds.