Reaction of Samarium 1,4-Diaza-1,3-diene Complexes with Ketones: Generation of a New Versatile Tridentate Ligand via 1,3-Dipolar Cycloaddition

Treatment of SmI 2 (THF) n with the dilithium 1,4-diaza-1,3-diene (DAD) compound Li 2 [( t Bu)NCH CHN( t Bu)] (≡Li 2 ( t Bu-DAD); 2 ) prepared by reduction of t Bu-DAD by 2 equiv of lithium in THF surprisingly results in the formation of the samarium(III) iodide complex [(THF) 2 Li( t Bu-DAD)][(THF)Li( t Bu-DAD)]SmI ( 5 ). The characteristic structural feature of 5 is formed by two ( Z )-1,4-diaza-but-2-ene-1,4-diyl units bridging the Sm 3+ with two Li + ions. Complex 5 and the analogous chloride complex [(THF)Li( t Bu-DAD)] 2 Sm( μ -Cl) 2 Li(THF) 2 ( 4b ) react with 2 equiv of benzophenone to give the structurally very similar samarium complexes {[OC(Ph) 2 CH{CH N( t Bu)}N( t Bu)]Li} 2 SmX(THF) (X = Cl ( 6 ), I ( 7 )) in high yield. The reaction formally proceeds via a 1,3-dipolar cycloaddition of the benzophenone C O bond across a Sm−N−C fragment of the enediamide samarium complexes 4b and 5, including the formation of a new C−C bond, and results in the formation of the novel tripodal ligand [OC(Ph) 2 CH{CH N( t Bu)}N( t Bu)] 2- . X-ray structure determinations of 6 and 7 revealed that the two tripodal ligands and the halogen atom form a slightly distorted octahedral coordination geometry around the Sm 3+ ion and that the Li + ions are retained within the ligand sphere by close contacts to their N and O atoms. By controlled hydrolysis of the cycloaddition product 6, the new tripodal ligands can be separated from the samarium and isolated in the form of the lithium compound {[OC(Ph) 2 CH{CH N( t Bu)}N( t Bu)]Li} 2 ( 8 ). The crystal structure of 8, which is dimeric in the solid state, is reported.