Reduction of ketimines by samarium(II) complexes.: isolation and structural characterization of samarium(III) η1-amine/η1-ketimido and η2-ketimine complexes

The reaction of (C5Me5)(2)Sm(THF)(2) with 2 equiv of benzophenone imine (Ph2C=NH) in THF at room temperature gave the samarocene(III) amine/ketimido complex (C5Me5)(2)Sm(N=CPh2)(NH2CHPh2) (1) in 58% isolated yield. The use of 1 equiv of Ph2C=NH also afforded 1 as the only isolable product, albeit in a lower yield (ca. 20%). Deuterium-labeling experiments suggest that 1 is formed via hydrogen abstraction by the in-situ-generated imine radical anion species, followed by acid-base reaction between the resulting amido species and another molecule of Ph2C=NH. The reactions of 2 equiv of Sm(OAr)(2)(THF)(3) (Ar = (C6H2Bu2)-Bu-t-2,6-Me-4) with N-phenyl benzophenone imine (Ph2C=NPh) and N-phenyl fluorenone imine (C12H8C=NPh) yielded the Sm(III) eta(2)-imine-dianion/aryloxide complexes Sm(eta(2)-Ph-2-CNPh)(OAr)(THF)(3) (3, 65%) and Sm(eta(2)-C12H8CNPh)(OAr)(THF)(3) (4, 77%), respectively, together with the byproduct Sm(OAr)(3). The reaction of 1 equiv of Sm(OAr)(2)(THF)(3) with Ph2C=NPh also gave the imine-dianion complex 3, whereas an imine radical anion species was not observed. Similarly, the reactions of 2 equiv of SmtN(SiMe3)(2)}(2)(THF)(2) with Ph-2-C=NPh and C12H8C=NPh yielded the q2-imine-dianion/silylamido complexes Sm(eta(2)-(PhCNPh)-C-2){N(SiMe3)(2)}(THF)(3) (5, 87%) and Sm(eta(2)-C12H8CNPh){N(SiMe3)(2)}(THF)(3) (6, 71%), respectively. Complexes 3-6 represent the first examples of structurally characterized trivalent lanthanide eta(2)-imine complexes.