Highly Efficient Carbonylation of Propylene Oxide into Β‐butyrolactone Catalyzed over Co‐Al Bimetallic Species

Rational designation of the catalyst for efficient atom‐economic conversion of propylene oxide (PO) and carbon monoxide (CO) into β‐butyrolactone is of current significance. By employing the O,N,O‐tridentate ligands R1,R2LH2 (1‐4), the aluminium compounds (R1,R2LAlCl)2 (R1,R2 = H,H (5), tBu,tBu (6), Cl,Cl (7), Br,Br (8)) and the derived anion‐cation pairs [H,HLAl(THF)3]+[Co(CO)4]ˉ (9) and [(R1,R2LAl)2Cl(THF)2]+[Co(CO)4]ˉ (R1,R2 = tBu,tBu (10), Cl,Cl (11), Br,Br (12)) as well as the aluminium‐cobalt bimetallic cluster compounds [(R1,R2LAl)2Cl(THF)][Co3(CO)10] (R1,R2 = tBu,tBu (13), Cl,Cl (14), Br,Br (15)) were prepared. Compounds 9‐12 efficiently catalyzed the PO carbonylation into β‐butyrolactone to achieve up 93.4‐98.9% yields while 13‐15 gained 95.2‐99.0% yields all at 25 °C and 0.1 MPa CO pressure. The Lewis acidic property of the aluminium compounds 5‐8 was investigated. The kinetic of the catalytic reaction using compound 10 was studied. The cooperatively catalytic reaction mechanism by the Co‐Al bimetallic species is proposed.