Encouraged by this finding, temperature, catalyst loading and H2 sources were screened (Table ). With catalyst loadings of 1.0 and 0.5 mol% an almost quantitative formation of 1b was achieved (Table , entries 1 and 2). Further lowering of the catalyst-loading to 0.3 and 0.1mol% resulted in 73 and 1 % yield, respectively (Table , entries 3-4). Decreasing the reaction temperature from 60 °C to 45 °C and 35 °C afforded 1b in 97 and 90% yield (Table , entries 5-6). The performance of MeOH was compared to EtOH and iPrOH leading to lower yields (Table , entries 7-8). It is worth mentioning that the typical by-products from dehydrogenation of EtOH and iPrOH such as AcOEt and acetone were not observed and, thus, a transfer hydrogenation process can be ruled out. Instead, the corresponding signals of [B(OMe)4] -as a result of alcoholysis of KBH4 with MeOH were detected by 11 B NMR spectroscopy (see SI, Figures and). For comparison, when the reaction was performed in the presence of H2 (30 bar) in MeOH and toluene, respectively, E-stilbene (1b) was obtained in 13 and 99 % yields (Table , entries 9 and 10). Accordingly, in-situ formation of H2 from alcoholysis of the BH4 -anion plays the key role in this hydrogenation. Addition of water resulted in no significant change in conversion and selectivity (Table , entry 11). In the absence of catalyst, no reaction takes place (Table , entry 12).