Abstract
Rapid PPh 3 substitution of [Fe 3 (CO) 12 ] to give [Fe 3 (CO) 11 (PPh 3 )] occurs in tetrahydrofuran at ambient temperature. The reaction is independent of the complex concentration. An electron-transfer-catalysed mechanism is operative in this reaction, with [Fe 3 (CO) 12 ] .- as the catalytically active species. The EPR studies indicate that [Fe 3 (CO) 12 ] .- is produced rapidly at the beginning of the reaction and its concentration is maintained at a constant value during the reaction. The substitution rate is equal to k[Fe 3 (CO) 12 .- ] with k = (2.7 ± 0.1) × 10 -3 s -1 . Dissociation of a CO ligand from this radical to yield [Fe 3 (CO) 11 ] .- is the rate-limiting step for this electron catalysis. It is believed that [Fe 3 (CO) 12 ] .- is formed from a fast disproportionation of [Fe 3 (CO) 12 ] induced by an impurity in PPh 3 . The impurity is likely PPh 3 O and its concentration is proportional to that of the PPh 3 used.