Homo- and heteroleptic alkoxycarbene f-element complexes and their reactivity towards acidic N-H and C-H bonds

The reactivity of a series of organometallic rare earth and actinide complexes with hemilabile NHC-ligands towards substrates with acidic C-H and N-H bonds is described. The synthesis, characterisation and X-ray structures of the new heteroleptic mono- and bis(NHC) cyclopentadienyl complexes LnCp₂(L) 1 (Ln = Sc, Y, Ce; L = alkoxy-tethered carbene [OCMe₂CH₂(1-C{NCHCHNⁱPr})]), LnCp(L)₂(Ln = Y) 2, and the homoleptic tetrakis(NHC) complex Th(L)₄4 are described. The reactivity of these complexes, and of the homoleptic complexes Ln(L)₃(Ln = Sc 3, Ce), with E-H substrates is described, where EH = pyrrole C₄H₄NH, indole C₈H₆NH, diphenylacetone Ph₂CC(O)Me, terminal alkynes RCCH (R = Me₃Si, Ph), and cyclopentadiene C₅H₆. Complex 1-Y heterolytically cleaves and adds pyrrole and indole N-H across the metal carbene bond, whereas 1-Ce does not, although 3 and 4 form H-bonded adducts. Complexes 1-Y and 1-Sc form adducts with CpH without cleaving the acidic C-H bond, 1-Ce cleaves the Cp-H bond, but 2 reacts to form the very rare H⁺-[C₅H₅]^--H⁺motif. Complex 1-Ce cleaves alkyne C-H bonds but the products rearrange upon formation, while complex 1-Y cleaves the C-H bond in diphenylacetone forming a product which rearranges to the Y-O bonded enolate product.