Synthetic and structural experiments on yttrium, cerium and magnesium trimethylsilylmethyls and their reaction products with nitriles; with a note on two cerium β-diketiminates

Abstract

The yttrium, cerium and magnesium bis(trimethylsilyl)methyls [Ln{CH(SiMe₃)₂}₃] [Ln = Y (1), Ce (2)], and the known compound Mg[CH(SiMe₃)₂]₂ (C) and [Mg(μ-Br){CH(SiMe₃)₂}(OEt₂)]₂ (D) formed the crystalline nitrile adducts [1(NCBu^t)₂] (5), [2(NCPh)] (6), [C(NCR)₂] [R = Bu^t (8), Ph (9), C₆H₃Me₂-2,6 (10)] and [Mg(μ-Br){CH(SiMe₃)₂}(NCR)]₂ [R = Bu^t (11), Ph (12), C₆H₃Me₂-2,6 (13)], rather than β-diketiminato–metal insertion products. The β-diketiminato–cerium complex [Ce{(N(SiMe₃)C(C₆H₄Bu^t-4))₂CH}{N(SiMe₃)₂}₂] (16) was obtained from [Ce{N(SiMe₃)₂}₃] and the β-diketimine H[{N(SiMe₃)C(C₆H₄Bu^t-4)}₂CH]]. The cerium alkyl 2 and [Ln{CH(SiMe₃)(SiMe₂OMe)}₃] [Ln = Y (3), Ce (4)] were obtained from the appropriate lithium alkyl precursor and [Ce(OC₆H₂Bu^t₂-2,6-Me-4)₃] or LnCl₃, respectively. Heating complex 3 with benzonitrile in toluene afforded 2,2-dimethyl-4,6-diphenyl-5-trimethylsilyl-1,3-diaza-2-silahexa-1,3-diene (7), a member of a new class of heterocycles. The X-ray structures of the crystalline compounds 1–7, D, [Mg{CH(SiMe₃)₂}₂(OEt₂)₂], the known [Ce(Cl){(N(SiMe₃)C(Ph))₂CH}₂] (E) and 16 are reported. The cerium alkyl 2 (like 1) has one close Ce⋯C contact for each ligand, attributed to a γ-C–Ce agostic interaction. The Ln alkyls 3 and 4 have a trigonal prismatic arrangement of the chelating ligands (each of the same chirality at C_α) around the metal. In an arene solution at 313 K 3 exists as two isomers, as evident from detailed NMR spectroscopic experiments.