Diamidosilylether complexes of yttrium(III) and chromium(III): Synthetic challenges and surprises

The synthesis, spectroscopic and structural characterization of a series of diamidosilylether complexes of yttrium(III) and chromium(III) are reported. Addition of one equiv. of Li2{[tBuN(SiMe2)]2O} to YCl3 in THF generates YCl(THF){[tBuN(SiMe2)]2O} (1) in high yield; 1 was crystallized as a bis-THF adduct. Alkylation of 1 proceeds cleanly with bulky LiCH(SiMe3)2 or NaC5H5 to yield Y[CH(SiMe3)2](THF){[tBuN(SiMe2)]2O} (2) and Y(η5-C5H5)(THF){[tBuN(SiMe2)]2O} (3) respectively. Complex 2 was characterized by 1H NMR spectroscopy, with the diagnostic Y-CH resonance at δ −0.84 (2JYH = 2.4 Hz), while 3 was structurally characterized and shows a diagnostic Y-C5H5 singlet at δ 6.47. Attempts to use less bulky alkylating agents resulted in a mixture of products or decomposition. Addition of two equiv. of Li2{[tBuN(SiMe2)]2O} to YCl3 in toluene with trace THF generates {Y{[tBuN(SiMe2)]2O}2}Li(THF) (4), which was structurally characterized. Complex 4 acts as a diamidosilylether ligand-transfer agent, reacting with MCl3 (M = Fe 5; Cr 6) to yield {MCl[tBuN(SiMe2)]2O}2 along with 1. Complex 6 was structurally characterized, revealing a chloride-bridged dinuclear system containing rare five-coordinate chromium(III) centres.

The addition of the diamidosilylether {Li2[tBuN(SiMe2)]2O} [NON] to YCl3 yields [NON]YCl · THF, which can only be cleanly alkylated with very bulky or multihapto groups. Addition of a 2nd equiv. of ligand to form the “ate” complex [NON]2YLi · THF only occurs cleanly in toluene solution, in which a reverse reaction with LiCl is impeded. This ligand-transfer material can be used to generate {[NON]MCl}2 systems (M = Cr, Fe).Figure optionsDownload as PowerPoint slide