Synthesis and Characterization of Yttrium Methanediide Silanide Complexes.

The salt metathesis reactions of the yttrium methanediide iodide complex [Y(BIPM)(I)(THF)] (BIPM = {C(PPhNSiMe)}) with the group 1 silanide ligand-transfer reagents MSiR (M = Na, R = BuMe or Bu; M = K, R = (SiMe)) gave the yttrium methanediide silanide complexes [Y(BIPM)(SiBuMe)(THF)] (), [Y(BIPM)(SiBu)(THF)] (), and [Y(BIPM){Si(SiMe)}(THF)] (). Complexes provide rare examples of structurally authenticated rare earth metal-silicon bonds and were characterized by single-crystal X-ray diffraction, multinuclear NMR and ATR-IR spectroscopies, and elemental analysis. Density functional theory calculations were performed on to probe their electronic structures further, revealing predominantly ionic Y-Si bonding. The computed Y-Si bonds show lower covalency than Y═C bonds, which are in turn best represented by Y-C dipolar forms due to the strong σ-donor properties of the silanide ligands investigated; these observations are in accord with experimentally obtained C{H} and Si{H} NMR data for and related Y(III) BIPM alkyl complexes in the literature. Preliminary reactivity studies were performed, with complex treated separately with benzophenone, azobenzene, and ,'-dicyclohexyl-carbodiimide. Si{H} and P{H} NMR spectra of these reaction mixtures indicated that 1,2-migratory insertion of the unsaturated substrate into the Y-Si bond is favored, while for the latter substrate, a [2 + 2]-cycloaddition reaction also occurs at the Y═C bond to afford [Y{C(PPhNSiMe)[C(NCy)]-κ,,','}{C(NCy)(SiBuMe)-κ,'}] (); these reactivity profiles complement and contrast with those of Y(III) BIPM alkyl complexes.