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

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(mu-Br){CH(SiMe3)(2)}(OEt2)](2) (D) formed the crystalline nitrile adducts [1(NCBut)(2)] (5), [2(NCPh)] (6), [C(NCR)(2)] [R = Bu-t (8), Ph (9), C6H3Me2- 2,6 (10)] and [Mg(mu-Br){ CH(SiMe3)(2)}(NCR)](2) [R = Bu-t (11), Ph (12), C6H3Me2-2,6 (13)], rather than beta-diketiminato-metal insertion products. The beta-diketiminato-cerium complex [Ce{(N(SiMe3) C(C6H4But- 4))(2)CH}{N(SiMe3)(2)}(2)] (16) was obtained from [Ce{N(SiMe3)(2)}(3)] and the beta-diketimine H[{N(SiMe3) C(C6H4But-4)}(2)CH]]. 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(OC6H2Bu2t- 2,6-Me-4)(3)] or LnCl(3), 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))(2)CH}(2)] (E) and 16 are reported. The cerium alkyl 2 ( like 1) has one close Ce...C contact for each ligand, attributed to a gamma-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-alpha) around the metal. In an arene solution at 313 K 3 exists as two isomers, as evident from detailed NMR spectroscopic experiments.