Tridentate CCC-Pincer Bis(carbene)-Ligated Rare-Earth Metal Dibromides. Synthesis and Characterization

The first xylene-bridged bis(N-heterocyclic carbene) (bis(NHC))-ligated CCC-pincer rare-earth metal dibromides (PBNHC)LnBr2(THF) (PBNHC = 2,6-(2,4,6-Me3C6H2NCHCHNCCH2)2C6H3; 1: Ln = Sc; 2: Ln = Lu; 3: Ln = Sm) were prepared by in situ treatment of a THF suspension of 2,6-bis(1-mesitylimidazolium methyl)-1-bromobenzene dibromides ((PBNHC-Br)·2HBr) and lanthanide trichlorides (LnCl3) with dropwise addition of nBuLi at room temperature. The overall molecular structure of these complexes is an isostructrual monomer of a THF solvate. The monoanionic xylene-bridged bis(NHC)s bond to the central metal as a tridentate CCC-pincer moiety in a κC:κC:κC′ mode, which, in combination with the two trans-located bromo units, generates a twisted tetragonal-bipyramidal geometry.