Solid-State ⁴⁵Sc NMR Studies of Cp*₂Sc–OR (R = CMe₂CF₃, CMe(CF₃)₂, C(CF₃)₃, SiPh₃) and Relationship to the Structure of Cp*₂Sc-Sites Supported on Partially Dehydroxylated Silica

Abstract

Cp*2Sc–OR (R = CMe2CF3, CMe­(CF3)2, C­(CF3)3, SiPh3) was synthesized to determine how the alkoxide affects the quadrupole coupling (CQ) obtained from solid-state 45Sc­{1H} NMR spectroscopy. These alkoxides are characterized by large (>29 MHz) CQ values, which are similar to CQ values obtained for Cp*2Sc–R (R = Me, Et, Ph) and Cp*2Sc–X (X = F, Cl, Br, I) but significantly larger than CQ values obtained for Cp*2ScX­(THF). The NMR properties from these alkoxides were used to understand the NMR properties of Cp*2Sc-supported on silica partially dehydroxylated at 700 °C. This material contains two species from the solid-state 45Sc­{1H} NMR spectra assigned to Cp*2ScOSi (5a) and Cp*2Sc­(OSi)­O­(SiO x )2 (5b). The solid-state 45Sc­{1H} NMR spectrum of 5a is considerably broader than 5b, which relates to the magnitude of the quadrupolar coupling (CQ) in these two different sites. Density functional theory (DFT) optimized structures of Cp*2Sc–OR and small cluster approximations of 5a and 5b follow similar trends as the experimental CQ values for this family of organoscandium complexes. Analysis of the origin of CQ using DFT methods shows that σ- and π-bonding orbitals from the Sc–O bond in Cp*2Sc–OR and 5a are major contributors to CQ, whereas different orbitals contribute to CQ in 5b. These studies show that quadrupolar solid-state NMR spectroscopy can distinguish between surface sites on partially dehydroxylated silica.

Observing the three-dimensional dynamics of supported metal complexes

“…Similar analyses have been done in the past to study the coordination of grafted Sc complexes. 89,90 Figure 6. 45 Sc MAS NMR spectra of the grafted complex acquired at magnetic fields of 14.1 T (top) and 9.4 T (bottom).…”

“…This last interaction has been postulated a number of times, particularly for d 0 metals such as Sc. 89,90,[92][93][94][95][96][97][98][99] As such we DFT-optimized both of these structures onto an amorphous silica surface and proceeded to calculate their structural evolutions. The first complex (4) was found to rapidly convert to 5 through the protonation of one of its amidinate ligands.…”

A Heterogeneous Palladium Catalyst for the Polymerization of Olefins Prepared by Halide Abstraction Using Surface R3Si+ Species

“…How 1 produces a bimodal molecular weight distribution is somewhat less clear. This behavior could be related to the heterogeneity of the silica surface, [20f, 35] or subtle differences in ion‐pairing that are known to affect activity in cationic Pd catalysts for polymerization reactions [36] . Evidently some of these environments prevents polymer growth, but the narrow dispersity of both the high and low molecular weight fractions indicates that all Pd−Me + sites are in well‐defined coordination environments.…”

The coordination chemistry of oxide and nanocarbon materials

“…4a. 50 The static 45 Sc NMR spectrum of κ 1 -Cp* 2 Sc-OSu and κ 2 -Cp* 2 Sc(OSiu)(uSi-O-Siu) shown in Fig. 4b was simulated as two scandium sites with quadrupolar coupling constants (C Q ) of 35.4 and 21.9 MHz, respectively.…”