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 SmI2(THF)(n) with the dilithium 1,4-diaza-1,3-diene (DAD) comp ound Li-2[(tBu)NCH=CHN(tBu)] (equivalent to Li-2(tBu-DAD); 2) prepared by r eduction of tBu-DAD by 2 equiv of lithium in THF surprisingly results in th e formation of the samarium(III) iodide complex [(THF)(2)Li(tBu-DAD)] [(THF )Li(tBu-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 Sm3+ with two Li + ions. Complex 5 and the analogous chloride complex [(THF)Li(tBu-DAD)](2)S m(mu -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(tBu)}N(tBu )]Li}(2)SmX(THF) (X=Cl (6), I(7)) in high yield. The reaction formally proc eeds 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 t he formation of a new C-C bond, and results in the formation of the novel t ripodal ligand [OC(Ph)(2)CH{CH=N(tBu)}N(tBu)](2-). X-ray structure determin ations of 6 and 7 revealed that the two tripodal ligands and the halogen at om 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 cycloaddi tion 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(tBu)}N (tBu)]Li}(2) (8). The crystal structure of 8, which is dimeric in the solid state, is reported.