Seite - 105 - in Advanced Chemical Kinetics

and adding 10 mol% LiBF4 as additive rather than the 8.0 M KOH [16]. By doing so, an impres- sive TON of 51,000 could be reached after 94 h by using 60 ppm catalyst loading, which cor- responds to 50% yield. A >99% yield could be obtained by increasing the catalyst loading to 100 ppm (TON52h = 30,000). Based on a number of in-depth studies, including computational insights, the authors sug- gest that the Lewis acidic Li+ promotes de-coordination of formate and subsequent its dehy- drogenation as well, thereby facilitating a faster formic acid decomposition to H2 and CO2. Furthermore, they conclude that under neutral conditions, the formation of the methanediol intermediate is mediated by the catalyst as well. Interestingly, when using dry MeOH in EtOAc, methyl formate can be formed in >99% yield when otherwise similar conditions as the latter mentioned above, thus corresponding to a TON of >19,999. Recently, Beller used 0.05 mM concentration a [MnBr(PNPiPr)(CO)2] complex and additional 10 equivalents of the PNPiPr ligand in a 1:1 (v/v) mixture of 9:1 MeOH/H2O/triglyme at a applied temperature of 92°C to achieve a TON of more than 20,000 after more than a month. Thus, the system is highly stable albeit with a low turnover frequency. Moreover, the catalytic cycle was suggested to follow the general mechanism depicted in Figures 3 and 4. Fujita and Yamaguchi demonstrated in 2015 that the iridium complex shown in the catalytic cycle in Figure 12 facilitates MeOH reforming. The best conditions were found to be refluxing a 1:4 MeOH/H2O mixture containing 0.50 mol% NaOH. Employing a 5000 ppm catalyst loading afforded a 84% yield after 20 h, corresponding to a TON of 5040 and an overall TOF of 252 h−1. It was furthermore demonstrated that a system containing 1000 ppm is capable of continuously dehydrogenate MeOH. Hence, when a mixture of MeOH, H2O, and NaOH was continuously Figure 11. MeOH reforming using PNP iron catalysts. Catalyst Kinetics and Stability in Homogeneous Alcohol Acceptorless Dehydrogenation http://dx.doi.org/10.5772/intechopen.70654 105