Synthesis and Characterization of Monomeric, Dimeric, and Polymeric Rare-Earth Bis(trimethyl)silylphosphide Complexes

Rare-earth (RE) bis(trimethylsilyl)amide ({N(SiMe3)2}−, N″) chemistry is well-developed, whereas RE bis(trimethylsilyl)phosphide {P(SiMe3)2}− (P″) chemistry is immature. Here, we report a convenient protonolysis route to dimeric RE P″ complexes [RE(P″)2(μ-P″)]2 (1-RE; RE = Y, Gd, Dy, Er) from parent [RE(CH2C6H4-o-NMe2)3] and excess HP″. The reactions of 1-RE with THF gave the monomeric RE P″ complexes [RE(P″)3(THF)2] (2-RE; RE = Y, Gd, Dy, Er), and treatment of 1-RE with 2 eq. of KP″ gave the RE “ate” coordination polymers [RE(P″)2(μ-P″)2K]∞ (3-RE; Y, Gd, Dy, Er). Complexes 1-RE, 2-RE, and 3-RE were characterized by single-crystal XRD, elemental analysis, and NMR, ATR-IR, and UV–vis–NIR spectroscopy. All paramagnetic 1-RE and 2-RE were also characterized by EPR spectroscopy and SQUID magnetometry, supported by ab initio calculations. We find that weak magnetic exchange interactions persist between RE centers in dimeric 1-RE and that their principal magnetic axes are oriented between the phosphide ligands as a consequence of the diffuse crystal field (CF) associated with the long RE–P bonds. For monomeric 2-RE, the principal magnetic axes are also oriented between ligands, reflecting competition between three long RE–P bonds and two short RE–O bonds that contribute approximately equally to the crystal field anisotropy.