Gerhard Lachmann

A Molecular modeling study of the changes of some steric properties of the precatalysts during the olefin metathesis reaction

The productive self‐metathesis of 1‐octene with a series of new phosphine ligated Grubbs‐type precatalysts was studied. The resulting structures were used to compare some steric properties of the new precatalysts with those of well‐known precatalysts. The possibility of α‐CC agnostic stabilization as well as the ability of the ligands to shield the metal was studied. A comparison of the obtained data, pointed to the unlikelihood that α‐CC agostic stabilization is a major contribution to the stabilization of the various metallacyclobutane rings. The similarity in the ability of the ligands to shield the metal also raised questions about the comparison of experimentally observed trends with those obtained theoretically.

A comparison of low and high activity precatalysts: do the calculated energy barriers during the self-metathesis reaction of 1-octene correlate with the precatalyst metathesis activity?

The self‐metathesis reaction of 1‐octene with several well‐known Grubbs‐type precatalysts and the new Z‐selective Grubbs precatalyst were studied with molecular modeling. The obtained Gibbs‐free energy values for all the steps during the productive metathesis of 1‐octene were compared to the values obtained for some low catalytic activity precatalysts. Determining how the Gibbs‐free energy values of highly active precatalysts compare to that of low catalytic activity precatalysts gave a deeper insight into the mechanism. The questionable correlation of the theoretically observed trends with those obtained experimentally does point to the need to be very cautious when making assumptions from theoretical results without a sufficiently large dataset.

A dual-channel gas chromatography method for the quantitation of low and high concentrations of NF3 and CF4 to study membrane separation of the two compounds

A dual-channel gas chromatographic method is described in this paper that can be conveniently used for quantitation of NF3/CF4 mixtures with a thermal conductivity detector (TCD) on one channel for the quantitation of high-concentrations, and a pulsed discharge helium ionization detector (PDHID) on a second channel for the quantitation of low concentrations. It is shown that adequate separation is achieved on both channels with this dual single-column setup in which column switching as used for NF3/CF4 analysis in industrial chromatographic methods are not required, thus yielding an effective analysis method for laboratory-scale investigations. In addition, the use of packed columns with purified divinylbenzene-styrene co-polymers as the sole stationary phase yields satisfactory resolution between NF3 and CF4 at isothermal conditions of 30°C, with elution times of less than 8min on the TCD channel and less than 4min on the PDHID channel. Consequently, this method allows for reliable, straight-forward quantitation of NF3/CF4 mixtures, which is necessary when studying the commercially important problem of NF3 and CF4 separation by different methods. Therefore, the applicability of the method to studying membrane separation of NF3 and CF4 is briefly discussed and illustrated, for which the dual-channel setup is especially beneficial.