Formation of a Strong Heterogeneous Aluminum Lewis Acid on Silica.

Al(OC(CF ) )(PhF) reacts with silanols present on partially dehydroxylated silica to form well-defined ≡SiOAl(OC(CF ) ) (O(Si≡) ) (1). Al NMR and DFT calculations with a small cluster model to approximate the silica surface show that the aluminum in 1 adopts a distorted trigonal bipyramidal coordination geometry by coordinating to a nearby siloxane bridge and a fluorine from the alkoxide. Fluoride ion affinity (FIA) calculations follow experimental trends and show that 1 is a stronger Lewis acid than B(C F ) and Al(OC(CF ) )(PhF) but is weaker than Al(OC(CF ) ) and Pr Si .

Solid-state B NMR studies of coinage metal complexes containing a phosphine substituted diboraanthracene ligand.

Transition metal interactions with Lewis acids (M → Z linkages) are fundamentally interesting and practically important. The most common Z-type ligands contain boron, which contains an NMR active B nucleus. We measured solid-state B{H} NMR spectra of copper, silver, and gold complexes containing a phosphine substituted 9,10-diboraanthracene ligand (BP) that contain planar boron centers and weak M → BR linkages ([(BP)M][BAr] (M = Cu (1), Ag (2), Au (3)) characterized by large quadrupolar coupling () values (4.

Origin of the Si NMR chemical shift in RSi-X and relationship to the formation of silylium (RSi) ions.

The origin in deshielding of 29Si NMR chemical shifts in R3Si-X, where X = H, OMe, Cl, OTf, [CH6B11X6], toluene, and OX (OX = surface oxygen), as well as iPr3Si+ and Mes3Si+ were studied using DFT methods. At the M06-L/6-31G(d,p) level of theory the geometry optimized structures agree well with those obtained experimentally. The trends in 29Si NMR chemical shift also reproduce experimental trends; iPr3Si-H has the most shielded 29Si NMR chemical shift and free iPr3Si+ or isolable Mes3Si+ have the most deshielded 29Si NMR chemical shift.

Al(OR) (R = C(CF)) activated silica: a well-defined weakly coordinating surface anion.

Weakly Coordinating Anions (WCAs) containing electron deficient delocalized anionic fragments that are reasonably inert allow for the isolation of strong electrophiles. Perfluorinated borates, perfluorinated aluminum alkoxides, and halogenated carborane anions are a few families of WCAs that are commonly used in synthesis. Application of similar design strategies to oxide surfaces is challenging.

Solid-state Sc NMR studies of Cp*Sc-X and Cp*ScX(THF).

Cp*Sc-X, where X is a halide, were synthesized and studied by solid-state Sc NMR to determine how the Sc-X bond affects quadrupolar NMR parameters. The experimental quadrupolar coupling constants (C) show that the fluoride has the largest coupling constant and that the iodide has the smallest coupling constant. DFT analysis of this data indicates that the C of these compounds is related to core scandium and halide orbitals, which is related to polarizability of the halide and the Sc-X distance.

The β-Agostic Structure in (C Me ) Sc(CH CH ): Solid-State NMR Studies of (C Me ) Sc-R (R=Me, Ph, Et).

Multinuclear solid-state NMR studies of Cp* Sc-R (Cp*=pentamethylcyclopentadienyl; R=Me, Ph, Et) and DFT calculations show that the Sc-Et complex contains a β-CH agostic interaction. The static central transition Sc NMR spectra show that the quadrupolar coupling constants (C ) follow the trend of Ph≈Me>Et, indicating that the Sc-R bond is different in Cp* Sc-Et compared to the methyl and phenyl complexes. Analysis of the chemical shift tensor (CST) shows that the deshielding experienced by Cβ in Sc-CH CH is related to coupling between the filled σ orbital and the vacant πSc⋯HC* orbital.