Lanthanide and Uranium Complexes with an SPS-Based Pincer Ligand

Reactions of Ln(BH4)3(THF)n and [Li(Et2O)][SPSMe], the lithium salt of an anionic SPS pincer ligand composed of
a central hypervalent λ4-phosphinine ring bearing two ortho-positioned diphenylphosphine sulfide sidearms, led to
the monosubstituted compounds [Ln(BH4)2(SPSMe)(THF)2] [Ln = Ce (1), Nd (2)], while the homoleptic complexes
[Ln(SPSMe)3] [Ln = Ce (3), Nd (4)] were obtained by treatment of LnX3 (X = I, BH4) with [K(Et2O)][SPSMe]. The
[UX2(SPSMe)2] complexes [X = Cl (5), BH4 (6)] were isolated from reactions of UX4 and the lithium or potassium
salt of the [SPSMe]- anion. The X-ray crystal structures of 1·1.5THF, 2·1.5THF, 3·2THF·2Et2O, and 5·4py reveal
that the flexible tridentate [SPSMe]- anion is bound to the metal as a tertiary phosphine with electronic delocalization
within the unsaturated parts of the ligand.