Better characterization of surface organometallic catalysts through resolution enhancement in proton solid state NMR spectra
Delayed-acquisition methods, namely, echo and constant-time-acquisition approaches, allow a significant improvement in resolution in the proton solid state NMR spectra of surface organometallic catalysts such as [ syn-( SiO) Mo-( =NAr)( =(CHBu)-Bu-t)( (CH2Bu)-Bu-t)] and [( SiO) Re( (CBu)-Bu-t)( =(CHBu)-Bu-t)( (CH2Bu)-Bu-t)] ( syn/anti ratio) 1: 1). This enables the observation of all of the proton resonances, which is not possible with the simple proton single-pulse technique under magic-angle spinning. For example, the methylene protons of the neopentyl ligands, buried in the large peak associated with all of the methyls in the H-1 MAS spectrum, can easily be identified by recording a delayed-acquisition spectrum ( resolution enhancement of a factor of 3 is obtained). Moreover, combining constant-time acquisition with heteronuclear carbon - proton correlation spectroscopy also improves the resolution of the 2D HETCOR spectra.