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Chemistry, Ames Laboratory

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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 13 by NMR and IR spectroscopy and X-ray diffraction reveals Ln↼H–Si interactions. These features are retained in solvent-coordinated 2·Et2O, 2·THF, and 3·THF. The change in spectroscopic features characterizing the secondary interactions (νSiH, 1JSiH) from the unactivated SiH in the silazane HN(SiHMe2)tBu follows the trend 3 > 2 > 12·Et2O > 2·THF3·THF. Ligand lability follows the same pattern, with Et2O readily dissociating from 2·Et2O 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 1JSiH 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.


This is an article from Organometallics (2017), doi: 10.1021/acs.organomet.6b00956. Posted with permission.

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American Chemical Society



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