Anionic group 6 transition-metal carbonyl hydrides as reducing agents. ketones, aldehydes, and epoxides

Catalytic Transfer Hydrogenation of Ketones with KHCr(CO)5/HCO2H/Et3N Systems

“…Aliquots (0.5 mL) were hydrolysed with dilute HCl (0.5 and dinuclear carbonylhydridochromates is in contrast to mL), extracted with diethyl ether (0.5 mL) and analysed by GC. what has been reported in the iron series where NaHFe 2 (CO) 8 is at least 26 times more reactive than mononuclear NaHFe(CO) 4 for the reduction of α,β-unsaturated ketones.…”

“…If the reaction of 1 with cyclohexanone is conducted for AcOH for 4 h in THF. [8] Both formic and acetic acids are too strong for the KHCr(CO) 5 base in THF, and preferenlonger reaction times (120 h), the reduction yield is not increased. After 24 h of reaction, 1 H-NMR analysis of the tially lead to KHCr 2 (CO) 10 .…”

“…[PPN] ϩ [HCr(CO) 5 ] Ϫ itself is also inactive towards ketones, but becomes an efficient reducing agent in the presence of one equivalent of acetic acid (H ϩ assistance and in situ protonolysis). [8] Two catalytic systems involving carbonylchromates and molecular hydrogen have also been reported for the hydroThere is thus a significant difference in reactivity between…”

“…Using lower (Equation 3) [9] and/or [HCr 2 (CO) 10 ] Ϫ (Equation 4). [8] amounts of 1 is also possible (10% KHCr(CO) 5 : 83% yield after 24 h; 5% KHCr(CO) 5 : 70% yield after 24 h) but complete conversion of cyclohexanone is achieved only after several days. Performing the catalytic reaction at 0°C resulted in a decrease in reaction rate.…”

“…The above system was tested for the catalytic reduction For a catalytic version, the carbonylhydridochromate of some representative ketones at room temperature ( Ϫ which has been shown to undergo a rapid As expected from literature data on the reduction of kedecarboxylation process according to Equation 6. [16] tones with hydridometallates, [8,9,19] cyclohexanones are more rapidly reduced than methyl ketones. In the case of 4-tert-butylcyclohexanone, the preponderant formation of the trans alcohol has previously been explained by the steric Formic acid itself cannot play the role of HX for the introduction of the formate moiety.…”