Manganese(I)‐Catalyzed Chemoselective Transfer Hydrogenation of the C=C Bond in Conjugated Ketones at Room Temperature
Dipesh M. Sharma, Anand B. Shabade, Rajesh G. Gonnade, Benudhar Punji
Abstract
Abstract Chemoselective transfer hydrogenation of C=C bond in α , β ‐unsaturated ketones is demonstrated at room temperature employing a manganese(I) catalyst and half an equivalent of ammonia‐borane (H 3 N−BH 3 ). A series of mixed‐donor pincer‐ligated Mn(II) complexes, ( tBu2 PN 3 N Pyz )MnX 2 [ κ P ,κ N ,κ N ‐( N ‐(di‐ tert ‐butylphosphaneyl)‐6‐(1 H ‐pyrazol‐1‐yl)pyridin‐2‐amine)MnX 2 ] {X=Cl ( Mn2 ), X=Br ( Mn3 ), X=I ( Mn4 )} were synthesized and characterized. Amongst the Mn(II) complexes, ( Mn2 , Mn3 , Mn4 ) and Mn(I) complex, ( tBu2 PN 3 N Pyz )Mn(CO) 2 Br ( Mn1 ) screened; the Mn1 acts as an efficient catalyst for the chemoselective C=C bond reduction in α , β ‐unsaturated ketones. Various synthetically important functionalities like halides, methoxy, trifluoromethyl, benzyloxy, nitro, amine, and unconjugated alkene and alkyne groups, including heteroarenes, were compatible and provided saturated ketones in excellent yields (up to 97 %). A preliminary mechanistic study highlighted the crucial role of metal–ligand (M–L) cooperation through the dearomatization‐aromatization process in catalyst Mn1 for the chemoselective C=C bond transfer hydrogenation.