“…[9] Furthermore, some examples were reported in which coupling reactions between CO 2 and alkenes, [10] dienes, [11] allenes, [12] or alkynes [13] in the presence of Pd, Ni, or Fe catalysts and superstoichiometric amounts of organometallic reducing agents, such as ZnR 2 , AlR 3 , Grignard reagents, and silanes, gave carboxylic acids after aqueous work up. Most notably, as early as 1978, the formation of propionic acid (38 % yield) from ethene and CO 2 was reported to occur under very drastic conditions (p = 700 bar, T = 180 8C) in the presence of [RhCl-(PPh 3 ) 3 ] and HBr, [14] but details of this transformation remain unknown.…”