Oxidation of Alkylbenzenes with Cerium Complexes Containing a Tripodal Oxygen Ligand

The treatment of [Ce(L OEt ) 2 (NO 3 ) 2 ] (L OEt – = [Co(η 5 ‐C 5 H 5 ){P(O)(OEt) 2 } 3 ] – ) with KMnO 4 in water afforded a diamagnetic purple solid 1 , which is tentatively formulated as a Ce IV permanganate complex, “[Ce(L OEt ) 2 (MnO 4 ) 2 ]”. The Zr IV analogue, [Zr(L OEt ) 2 (MnO 4 ) 2 ] ( 2 ), has been prepared similarly from [Zr(L OEt ) 2 (NO 3 ) 2 ] and KMnO 4 . The recrystallization of 1 from CH 2 Cl 2 /hexanes at –18 °C led to the isolation of dinuclear [(CeL OEt ) 2 (μ‐L OEt ′) 2 ][MnO 4 ] 2 ( 3 ), which contains the dianionic tripodal ligand [L OEt ′] 2– ([(η 5 ‐C 5 H 5 )Co{P(O)(OEt) 2 } 2 {P(O) 2 (OEt)}] 2– ). The reactions of 1 with K[ReO 4 ] and [NH 4 ][OsO 3 N] afforded the heterodimetallic complexes [Ce(L OEt ) 2 (ReO 4 ) 2 ] ( 4 ) and [Ce(L OEt ) 2 (NOsO 3 ) 2 ] ( 5 ), respectively. The crystal structures of 3 and 5 have been determined. Freshly prepared 1 can oxidize alkylbenzenes such as toluene, ethylbenzene, and cumene at room temperature to give the corresponding ketone and/or alcohol products. Ce–L OEt complexes are efficient promoters of the aerobic oxidation of alkylbenzenes by a radical mechanism. For example, cumene in the presence of [Ce(L OEt ) 2 (H 2 O) 2 ]Cl (1 m M ) in air at 100 °C for 10 h afforded a ca. 6:1 mixture of 2‐phenyl‐2‐propanol and acetophenone with a total turnover number of 6810.