Alkyl complexes of rare-earth metals that contain a furyl-functionalized cyclopentadienyl ligand: Alkyl cation formation and unexpected ring-opening reaction of the furyl group

Rare-earth metal complexes of the type [Ln{n(5):n(1)-C5Me4SiMe2(C4H3O-2)}(CH2SiMe3)(2)(THF)] (Ln = Y, Lu) were prepared by a-bond metathesis of [Ln(CH2SiMe3)(3)(THF)(2)] with the 2-furyl-functionalized tetramethylcyclopentadiene (C5Me4H)SiMe2(C4H3O-2) and isolated as colorless crystals. Single-crystal X-ray structure analysis of the lutetium complex confirmed the coordination of the furyl group and THF to give a molecule of trigonal bipyramidal geometry with the oxygen donor atoms in the apical positions. The lability of the oxygen donor atoms results in fluxional behavior. Reaction with triphenylborane in THF gave thermally robust mono(alkyl) cations [Ln{n(5):n(1)-C5Me4SiMe2(C4H3O-2)}(CH2SiMe3)(THF)(n)](+). Unexpectedly, the reaction of [Ln(CH2SiMe3)(3)(THF)(2)] with the 5-methylfuryl-functionalized tetramethylcyclopentadiene (C5Me4H)SiMe2{(C4H2MeO-5)-2} gave yne-enolate complexes [Ln- {n(5):n(1)-C(5)Me(4)SiMe(2)CdropCCHdouble bondCMeO)}(CH2SiMe3)](2) under elimination of 2 equiv of SiMe4. Single-crystal X-ray structure analysis of the yttrium complex revealed that a ring-opening of the 5-methylfuryl group had occurred.