Trimethylsilylmethyl complexes of the rare-earth metals with sterically hindered N-heterocyclic carbene ligands: Adduct formation and C-H bond activation

摘要

Tris(trimethylsilylmethyl) complexes of yttrium and lutetium [LnR _3(THF)_2] (R = CH_2SiMe_3) were treated with sterically bulky N-heterocyclic carbenes (NHC) 1,3-bis(2,6- diisopropylphenyl)imidazol-2-ylidene (IPr) and 1,3-bis(2,4,6-trimethylphenyl) imidazol-2-ylidene (IMes). IPr gave labile mono-adducts [LnR_3(NHC)], isolated as thermally robust crystals and fully characterized by NMR spectroscopy and X-ray diffraction. IMes gave a similar lutetium mono-adduct [LuR_3(IMes)] with the lutetium alkyl [LuR_3(THF) _2], whereas the yttrium alkyl [YR_3(THF)_2] resulted in the formation of an ortho-metalated product. This compound, isolated as a crystalline bis(THF) adduct, contains a strained six-membered chelate ring that has been formed by the C-H bond activation of one of the ortho-methyl groups of the mesityl group. In contrast [LuR_3(IMes)] only slowly underwent a similar C-H bond activation.