The divalent calcium and ytterbium compounds M(C(SiHMe(2))(3))(2)THF(2) contain beta-agostic SiH groups, as determined by spectroscopy and crystallography. Upon thermolysis, HC(SiHMe(2))(3) is formed. However, the SiH groups are hydridic. The compounds M(C(SiHMe(2))(3))(2)THF(2) react with 1 and 2 equiv of the Lewis acid B(C(6)F(5))(3) to form MC(SiHMe(2))(3)HB(C(6)F(5))(3))THF(2) and M(HB(C(6)F(5))(3))(2)THF(2), respectively. These species contain the anion [HB(C(6)F(5))(3)](-) from hydride abstraction rather than [(Me(2)HSi)(3)CB(C(6)F(5))(3)](-) from alkyl abstraction. The 1,3-disilacyclobutane byproduct initially suggested beta-elimination [as the dimer of the silene Me(2)Si horizontal lineC(SiHMe(2))(2)], but the other products and reaction stoichiometry rule out that pathway. Additionally, Yb(C(SiHMe(2))(3))(2)THF(2) and the weak Lewis acid BPh(3) react rapidly and also give the H-abstracted products. Despite the strong hydridic character of the SiH groups and the low-coordinate, Lewis acidic metal center in M(C(SiHMe(2))(3)THF(2) compounds, beta-elimination is not an observed reaction pathway.
A series of organometallic compounds containing the tris(dimethylsilyl)methyl ligand are described. The potassium carbanions KC(SiHMe2)3 and {KC(SiHMe2)3TMEDA}2 are synthesized by deprotonation of the hydrocarbon HC(SiHMe2)3 with potassium benzyl. {KC(SiHMe2)3TMEDA}2 crystallizes as a dimer with two types of three-center-two-electron K-H-Si interactions: side-on coordination of SiH (∠K-H-Si = 102(2)°) and more obtuse K-H-Si structures (∠K-H-Si ≈ 150°). The divalent calcium and ytterbium compounds M{C(SiHMe2)3}2L (M = Ca, Yb; L = 2THF, TMEDA) are prepared from MI2 and 2 equiv of KC(SiHMe2)3. Low 1JSiH coupling constants in the NMR spectra, low-energy νSiH bands in the IR spectra, and short M-Si distances and small M-C-Si angles in the crystal structures suggest β-agostic interactions on each C(SiHMe2)3 ligand. The IR assignments of M{C(SiHMe2)3}2L (L = 2THF, TMEDA) are supported by DFT calculations. The compounds M{C(SiHMe2)3}2L react with 1 or 2 equiv of B(C6F5)3 to give the 1,3-disilacyclobutane {Me2SiC(SiHMe2)2}2 and MC(SiHMe2)3HB(C6F5)3L or M{HB(C6F5)3}2L, respectively. In addition, M{C(SiHMe2)3}2L compounds react with BPh3 to give β-H abstracted products. The compounds M{C(SiHMe2)3}2THF2 react with SiMe3I to yield Me3SiH and disilacyclobutane as the products of β-H abstraction, while M{C(SiHMe2)3}2TMEDA and Me3SiI form a mixture of Me3SiH and the alkylation product Me3SiC(SiHMe2)3 in a 1:3 ratio.
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(SiHMe 2 )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 solventcoordinated 2·Et 2 O, 2·THF, and 3·THF. The change in spectroscopic features characterizing the secondary interactions (ν SiH , 1 J SiH ) from the unactivated SiH in the silazane HN(SiHMe 2 )tBu follows the trend 3 > 2 > 1 ≈ 2·Et 2 O > 2·THF ≈ 3· THF. Ligand lability follows the same pattern, with Et 2 O 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(SiHMe 2 )tBu} n @MSN (Ln = Sc (1@MSN), Y (2@MSN)) along with THF and protonated silazido as HN(SiHMe 2 )tBu and H 2 NtBu. 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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.