Yttrium half-sandwich complexes bearing the 2-(N,N-dimethylamino)ethyl-tetramethylcyclopentadienyl ligand

Abstract

The synthesis of bis(dimethylsilyl)amide and dimethyl half-sandwich complexes of yttrium bearing the 2-(N,N-dimethylamino)ethyl-tetramethylcyclopentadienyl ligand revealed unusual Si‒H activation reactions and ate complex formation, respectively. Protonolysis of complex Y[N(SiHMe2)2]3(thf)2 with cyclopentadiene C5Me4HCH2CH2NMe2 (HCpNMe2) at elevated temperature yielded complex CpNMe2Y[η2-SiMe2(NSiHMe2)2](thf) featuring a four-membered metallacycle. The bis(amido) ligand [η2-SiMe2(NSiHMe2)2]2− is shown to form via separation of H2SiMe2. In contrast, the salt metathesis reaction of YCl3(thf)3 with LiN(SiHMe2)2 and LiCpNMe2 in a 1/2/1 ratio at ambient temperature generated the non-activated complex CpNMe2Y[N(SiHMe2)2]2, exhibiting a distinct ligand activation at elevated temperatures, as evidenced by a comprehensive NMR spectroscopic study. Application of a sequential salt metathesis protocol involving YCl3(thf)3, LiCpNMe2, and LiMe led to the isolation of ate complexes [CpNMe2YCl2]2[LiCl(thf)2] and [CpNMe2YMe2(LiMe)]2. Aforementioned half-sandwich complexes were all characterized by X-ray structure analyses and the respective silylamido and methyl derivatives are demonstrated to produce the half-sandwich yttrium bis(tetramethylaluminate) complex [CpNMe2AlMe3Y(AlMe4)2] in the presence of excess trimethylaluminium, by NMR spectroscopic studies.