Selective hydrogenation of amides using Rh/Mo catalysts

Selective Hydrogenation of Amides using Ruthenium/ Molybdenum Catalysts

“…The results of preliminary experiments with CyCONH 2 using various Ru catalyst precursors, and two to which Mo(CO) 6 have been added, are summarised in Table 1.…”

“…35%. The co-addition of Mo(CO) 6 at an Mo:Ru atomic ratio of 0.50 (entry 3) resulted in a profound effect on catalytic behaviour, with both considerably improved amide conversion but far more importantly product selectivity, namely a complete switch in product distribution to a ca. 6:1 mixture of the desired primary amine CyCH 2 NH 2 and CyCH 2 OH, with total absence of secondary amine formation, thus representing a highly unusual feature of amide reduction chemistry.…”

“…Recently a step change in this direction has been provided by reports of a new range of bimetallic catalysts, particularly those derived from organometallic precursors such as Rh and Mo carbonyls, initially described as homogeneous, [3][4][5] and typically exemplified by the reduction of the tertiary amide N-acetylpiperidine to N-ethylpiperidine at 100 bar H 2 and 160 8C. [4] We have described details of the genesis and characterisation of such catalysts, formed in situ from Rh 6 (CO) 16 and Mo(CO) 6 , and unequivocally demonstrated that they are in fact heterogeneous. [6] Their performance in the selective hydrogenation of a representative primary amide such as cyclohexylcarboxamide to the corresponding primary amine, cyclohexanemethylamine [(Eq.…”

“…[4] We have described details of the genesis and characterisation of such catalysts, formed in situ from Rh 6 (CO) 16 and Mo(CO) 6 , and unequivocally demonstrated that they are in fact heterogeneous. [6] Their performance in the selective hydrogenation of a representative primary amide such as cyclohexylcarboxamide to the corresponding primary amine, cyclohexanemethylamine [(Eq. (1)] in up to 87% selectivity, was found to be critically dependent on the Mo:Rh composition.…”

“…Analysis of spectroscopic changes occurring during the initiation period, together with results of control experiments using, e.g., Ru 3 (CO) 12 alone, have enabled the assembly of a complete picture of the molecular species present in solution during catalyst genesis (see below). Figure 3 shows the effects, on conversion and product selectivity, of variation of Mo:Ru, from which it is evident that only very minor quantities of Mo(CO) 6 (e.g., Mo:Ru = 0.06) were necessary to initiate synergistic effects. The optimum combination of amide conversion and primary amine selectivity (typically 85% CyCH 2 NH 2 and 14% CyCH 2 OH) was found with Mo:Ru values of ca.…”