Solid state NMR had been used to determine the molecular dynamics of a series of organometallic alkylidene complexes covalently bound to amorphous silica. (F. Blanc et al J. Am. Chem. Soc. 2008, 130, 5886). The complexes have the general formula [(SiO)M(ER)(CHtBu)(R' )] (M  = Re, Ta, Mo or W; ER = CtBu, NAr or CH2tBu; R' = CH2tBu, NPh2, NC4H4). While all of these complexes are isoelectronic and isostructural, the measurement reveal different dynamic behaviors suggesting that the Mo complexes are relatively immobile while the other are mobile relative to their fixed covalent point of attachment.  Dynamic ab initio calculations of selected metal complexes covalently bonded to amorphous silica were carried out to determine these dynamics. The calculated values of the NMR CSA of the alkylidene carbon agree well with the experimental data validating the method that is used. The analysis of the dynamics of the individual complexes reveals very different behaviors that can be understood based on their electronic structures.

Mobility of alkylidene metal complexes on silica surface from a simulation of NMR Chemical Shift Anisotropy by dynamic ab initio calculations

247th National Meeting (2014)

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