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(PPh 2 NSiMe 3 ) 2 }) with the group 1 silanide ligand-transfer reagents MSiR 3 (M = Na, R 3 = t Bu 2 Me or t Bu 3 ; M = K, R 3 = (SiMe 3 ) 3 ) gave the yttrium methanediide silanide complexes [Y(BIPM)(Si t Bu 2 Me)(THF)] ( 1 ), [Y(BIPM)(Si t Bu 3 )(THF)] ( 2 ), and [Y(BIPM){Si(SiMe 3 ) 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 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 13 C{ 1 H} and 29 Si{ 1 H} 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. 29 Si{ 1 H} and 31 P{ 1 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(PPh 2 NSiMe 3 ) 2 [C(NCy) 2 ]-κ 4 C , N , N ', N '}{C(NCy) 2 (Si t Bu 2 Me)-κ 2 N , N '}] ( 4 ); these reactivity profiles complement and contrast with those of Y(III) BIPM alkyl complexes.