Rare Earth and Alkaline Earth Metal Complexes with Me₂Si‐Bridged Cyclopentadienyl‐Imidazolin‐2‐Imine Ligands and Their Use as Constrained‐Geometry Hydroamination Catalysts

Abstract

Abstract The imidazolin‐2‐imino‐functionalized tetramethylcyclopentadiene, 3 ‐H, has been prepared by the reaction of two equivalents of 1,3‐diisopropyl‐4,5‐dimethylimidazolin‐2‐imine ( 1 ) with 5‐(chlorodimethylsilyl)‐1,2,3,4‐tetramethyl‐1,3‐cyclopentadiene ( 2 ). The reactions of 3 ‐H with the trimethylsilylmethyl (neosilyl) [Ln(CH 2 SiMe 3 ) 3 (THF) 2 ] (Ln = Sc, Y, Lu) complexes afford tetramethylsilane and the constrained‐geometry [(η 5 :η 1 ‐ 3 )Ln(CH 2 SiMe 3 ) 2 ] (Ln = Sc, 4a ; Ln = Y, 4b ; Ln = Lu, 4c ) complexes, whereas the analogousbis(trimethylsilyl)amido (HMDS) calcium complex, [(η 5 :η 1 ‐ 3 )Ca(HMDS)(THF)] ( 5 ), can be obtained from 3 ‐H and [Ca(HMDS) 2 (THF) 2 ] with loss of hexamethyldisilazane, (Me 3 Si) 2 NH. The molecular structures of 4a – 4c and 5 have been established by X‐ray diffraction analyses, which confirm in all cases the formation of complexes with a chelating Me 2 Si‐bridged cyclopentadienyl‐imidazolin‐2‐imine ligand. The presence of short Ln–N and Ca–N bonds is indicative of the strong electron‐donating capacity of the imidazolin‐2‐imino nitrogen atom, which is based on the ability of the imidazolium ring to effectively stabilize a positive charge. The rare earth metal complexes 4a – 4c can be used as efficient catalysts for the hydroamination/cyclization reaction of terminal aminoalkenes and aminoalkynes.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)