Zirconium complexes of the tridentate bis(aryloxide)-N-heterocyclic-carbene ligand : Chloride and alkyl functionalized derivatives

Abstract The disodium salt of a bis(aryloxide)- N -heterocyclic-carbene dianionic ligand, Na 2 [L], was prepared by reaction of 1,3-bis(4,6-di- tert -butyl-2-hydroxybenzyl)imidazolium bromide [H 3 L]Br with 3 equiv. of NaN(SiMe 3 ) 2 . Reaction of ZrCl 4 (thf) 2 with 1 equiv. of Na 2 [L] gave a mixture of [L]ZrCl 2 (thf) ( 1 ) and [L] 2 Zr ( 2 ). When the amount of Na 2 [L] was increased to 2 equiv., the bis(bis(aryloxide)- N -heterocyclic-carbene) complex 2 was obtained in good yield. The dichloro complex 1 is a precursor to organometallic derivatives, and treatment with PhCH 2 MgCl or Me 3 SiCH 2 Li yielded [L]ZrR 2 [R = CH 2 Ph ( 3 ), CH 2 SiMe 3 ( 4 )]. The disodium salt of the ligand Na 2 [L] is unstable and undergoes 1,2-benzyl migration, whereas zirconium complexes of the [L] 2− ligand are found to be thermally stable in solid and solution. The X-ray crystal structures of 1 , 2 , and 3 are described.