Tetrahydropentalenyl-phosphazene constrained geometry complexes of rare-earth metal alkyls

Abstract

Reactions of Cp™HPPh₂ (1, diphenyl(4,4,6,6-tetramethyl-1,4,5,6-tetrahydropentalen-2-yl)phosphane) with the organic azides AdN₃ and DipN₃ (Ad = 1-adamantyl; Dip = 2,6-di-iso-propylphenyl) led to the formation of two novel CpPN ligands: P-amino-cyclopentadienylidene-phosphorane (Cp™PPh₂NHAd; L_AdH) and P-cyclopentadienyl-iminophosphorane (Cp™HPPh₂NDip; L_DipH). Both were characterized by NMR spectroscopy and X-ray structure analysis. For both compounds only one isomer was observed. Neither possesses any detectable prototropic or elementotropic isomers. Reactions of these ligands with [Lu(CH₂SiMe₃)₃(thf)₂] or with rare-earth metal halides and three equivalents of LiCH₂SiMe₃ produced the desired bis(alkyl) Cp™PN complexes: [{Cp™PN}M(CH₂SiMe₃)₂] (M = Sc (1_Ad, 1_Dip), Lu (2_Ad, 2_Dip), Y (3_Ad, 3_Dip), Sm (4_Ad), Nd (5_Ad), Pr (6_Ad), Yb (7_Ad)). These complexes were characterized by extensive NMR studies for the diamagnetic and the paramagnetic complexes with full signal assignment. An almost mirror inverted order of the paramagnetic shifts has been observed for ytterbium complex 7_Ad compared to 4_Ad, 5_Ad and 6_Ad. For the assignment of the NMR signals [{η¹ : η⁵-C₅Me₄PMe₂NAd}Yb(CH₂SiMe₃)₂] 7 was synthesized, characterized and the ¹H NMR signals were compared to 7_Ad and to other paramagnetic lanthanide complexes with the same ligand. 1_Ad, 2_Ad, 2_Dip, 3_Ad and 3_Dip were characterized by X-ray structure analysis revealing a sterically congested constrained geometry structure.