C–S, C–H, and N–H bond cleavage of heterocycles by a zero-valent iron complex, Fe(N 2)(depe) 2 [depe=1,2-bis(diethylphosphino)ethane

Abstract

Treatment of Fe(N 2)(depe) 2 [depe=1,2-bis(diethylphosphino)ethane] ( 1) with benzo[ b]thiophene at room temperature results in the regioselective C–S and C–H bond cleavages giving Fe(SC 6H 4CHC H)(depe) 2 ( 2a) and trans-FeH( CCHC 6H 4S )(depe) 2 ( 3a) in 72 and 19% yields, respectively. Complex 1 also reacts with thiophene, 2- and 3-acetylthiophenes and 2- and 3-methylthiophenes to give both C–S and C–H bond oxidative addition products: Fe(SCHCHCHC H)(depe) 2 ( 2b) and trans-FeH( CCHCHCHS )(depe) 2 ( 3b), Fe[SC(COMe)CHCHC H](depe) 2 ( 2c) and trans-FeH[ CCHCHC(COMe)S ](depe) 2 ( 3c), Fe[SC(Me)CHCHC H](depe) 2 ( 2d) and trans-FeH[ CCHCHC(Me)S ](depe) 2 ( 3d), and Fe[SCHC(Me)CHC H](depe) 2 ( 2e) and trans-FeH[ CCHC(Me)CHS ](depe) 2 ( 3e), respectively. On the other hand, only C–H bond cleavage takes place in the reactions of 1 with furans such as furan, benzo[ b]furan, and 2,3-dihydrofuran to give trans-FeH( CCHCHCHO )(depe) 2 ( 4a), FeH( CCHC 6H 4O )(depe) 2 ( 4b) and trans-FeH( CCHOCH 2C H 2)(depe) 2 ( 4c) and N–H bond is exclusively cleaved by the reaction of 1 with pyrroles such as pyrrole, indole and 2-acetylpyrrole to give trans-FeH( NCHCHCHC H)(depe) 2 ( 5a), trans- and cis-FeH( NCHCHC 6H 4)(depe) 2 ( 5b) and FeH[ NC(COMe)CHCHC H](η 2-depe)(η 1-depe) ( 6). Treatment of 2a with MeI results in the Fe–S bond cleavage of the thiaferracycle giving trans-FeI[( E)-CHCHC 6H 4-2-SMe](depe) 2 ( 7) whose structure is unequivocally characterized by X-ray analysis. In contrast, hydrogenolysis of 2a with H 2 (50 atm) leads to the cleavage of the Fe–C bond of the thiaferracycle to yield cis- and trans-FeH(SC 6H 4-2-Et)(depe) 2 ( 8).