Synthesis and Characterization of Yttrium Methanediide Silanide Complexes

The salt metathesis reactions of the yttrium methanediide iodide complex [Y(BIPM)(I)(THF)2] (BIPM = {C(PPh2NSiMe3)2}) with the group 1 silanide ligand-transfer reagents MSiR3 (M = Na, R3 = tBu2Me or tBu3; M = K, R3 = (SiMe3)3) gave the yttrium methanediide silanide complexes [Y(BIPM)(SitBu2Me)(THF)] (1), [Y(BIPM)(SitBu3)(THF)] (2), and [Y(BIPM){Si(SiMe3)3}(THF)] (3). Complexes 1–3 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 1–3 to probe their electronic structures further, revealing predominantly ionic Y–Si bonding. The computed Y–Si bonds show lower covalency than YC 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 13C{1H} and 29Si{1H} NMR data for 1–3 and related Y(III) BIPM alkyl complexes in the literature. Preliminary reactivity studies were performed, with complex 1 treated separately with benzophenone, azobenzene, and N,N′-dicyclohexyl-carbodiimide. 29Si{1H} and 31P{1H} 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 YC bond to afford [Y{C(PPh2NSiMe3)2[C(NCy)2]-κ4C,N,N′,N′}{C(NCy)2(SitBu2Me)-κ2N,N′}] (4); these reactivity profiles complement and contrast with those of Y(III) BIPM alkyl complexes