Synthesis and Structural Features of Boratabenzene Rare-Earth Metal Alkyl Complexes

A series of solvent-free boratabenzene rare-earth metal alkyl complexes (C5H5BR)(2)LnCH (SiMe3)(2) (9: R = NEt2, Ln = Y; 10: R = NPh2, Ln = Y; 11: R = CH3, Ln = Y; 12: R = NPh2, Ln = Sm; 13: R = NPh2, Ln = Dy; 14: R = NEt2, Ln = Lu; 15: R = NPh2, Ln = Lu; 16: R = Me, Ln = Lu) were synthesized. The solid-state structures of 10, 13, and 15 were determined by single-crystal X-ray diffraction. The crystal structures of 10,13, and 15 feature highly unsymmetrical coordination of the alkyl ligands and short Ln-C(alkyl) distances. The diamagnetic yttrium and lutetium alkyl complexes, 9-11 and 14-16, were characterized by (H-1, C-13, B-11) NMR spectroscopy. The Ln-C alpha H alpha, (H-1 NMR: delta 0.68-0.99 ppm) and Ln-C alpha H alpha (C-13 NMR: delta 33.9-39.1 ppm) resonances of these boratabenzene rare-earth metal alkyl complexes are rather downfield in comparison with those of the bis-Cp rare-earth metal alkyl complexes. Y-89 NMR spectra of the boratabenzene yttrium alkyl complexes 9-11 and the Cp complex (C5H4Me)(2)YCH(SiMe3)(2) were recorded. The Y-89 NMR chemical shifts for 9, 10, and 11 are 176.1, 170.0, and 162.2 ppm, respectively, which are significantly downfield in comparison with that of (C5H4Me)(2)YCH(SiMe3)(2) (44.0 ppm).