Synthesis and characterization of monomeric, dimeric and polymeric rare earth bis(trimethyl)silylphosphide complexes

Rare earth (RE) bis(trimethylsilyl)amide ({N(SiMe3)2} − , Nʹʹ) chemistry is well-developed, but there are few examples of RE complexes containing the analogous phosphide ligand, {P(SiMe3)2} − (Pʹʹ). Here we report the synthesis and characterization of a series of dimeric RE Pʹʹ complexes, [RE(Pʹʹ)2(μ-Pʹʹ)]2 (1-RE; RE = Y, Gd, Dy, Er) by separate protonolysis reactions between parent [RE(CH2C6H4-o-NMe2)3] and 3.3 equivalents of HPʹʹ; the synthesis of 1-Y was previously reported by a different route. The reactions of 1-RE with four equivalents of THF gave the corresponding THF-solvated monomeric RE Pʹʹ complexes [RE(Pʹʹ)3(THF)2] (2-RE; RE = Y, Gd, Dy, Er), and treatment of 1-RE with two equivalents of KPʹʹ gave the RE 'ate' coordination polymers [RE(Pʹʹ)2(μ-Pʹʹ)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, and these data were benchmarked 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 associated with the long REP bonds. For monomeric 2-RE the principal magnetic axes are also oriented between ligands, reflecting competition between three long REP bonds and two short RE-O bonds that contribute approximately equally to the crystal field anisotropy.