β‑SiH-Containing Tris(silazido) Rare-Earth Complexes as Homogeneous and Grafted Single-Site Catalyst Precursors for Hydroamination

A series of homoleptic rare-earth silazido compounds and their silica-grafted derivatives were prepared to compare spectroscopic and catalytic features under homogeneous and interfacial conditions. Trivalent tris­(silazido) compounds Ln­{N­(SiHMe2)tBu}3 (Ln = Sc (1), Y (2), Lu (3)) are prepared in high yield by salt metathesis reactions. Solution-phase and solid-state characterization of 1–3 by NMR and IR spectroscopy and X-ray diffraction reveals Ln↼H–Si interactions. These features are retained in solvent-coordinated 2·Et 2 O, 2·THF, and 3·THF. The change in spectroscopic features characterizing the secondary interactions (νSiH, 1 J SiH) from the unactivated SiH in the silazane HN­(SiHMe2)tBu follows the trend 3 > 2 > 1 ≈ 2·Et 2 O > 2·THF ≈ 3·THF. Ligand lability follows the same pattern, with Et2O readily dissociating from 2·Et 2 O while THF is displaced only during surface grafting reactions. 1 and 2·THF graft onto mesoporous silica nanoparticles (MSN) to give Ln­{N­(SiHMe2)tBu}n@MSN (Ln = Sc (1@MSN), Y (2@MSN)) along with THF and protonated silazido as HN­(SiHMe2)tBu and H2NtBu. The surface species are characterized by multinuclear and multidimensional solid-state (SS) NMR spectroscopic techniques, as well as diffuse reflectance FTIR, elemental analysis, and reaction stoichiometry. A key 1 J SiH SSNMR measurement reveals that the grafted sites most closely resemble Ln·THF adducts, suggesting that siloxane coordination occurs in grafted compounds. These species catalyze the hydroamination/bicyclization of aminodialkenes, and both solution-phase and interfacial conditions provide the bicyclized product with equivalent cis:trans ratios. Similar diastereoselectivities mediated by catalytic sites under the two conditions suggest similar effective environments.