Rare-Earth-Metal/Platinum Heterobinuclear Complexes Containing Reactive Ln-alkyl groups (Ln = Y, Lu): Synthesis, Structural Characterization, and Reactivity

A series of Ln/Pt heterobinuclear complexes, (C₅Me₄XCH₂PPh₂)Ln(CH₂SiMe₃)₂(OC₄H₈)PtMe₂ (3a: Ln = Y, X = SiMe₂; 3b: Ln = Lu, X = SiMe₂; 4a: Ln = Y, X = CH₂; 4b: Ln = Lu, X = CH₂), were prepared by the reaction of (C₅Me₄XCH₂PPh₂)Ln(CH₂SiMe₃)₂(OC₄H₈) with PtMe₂(COD) (COD = 1,5-cyclooctadiene). Single-crystal X-ray diffraction studies revealed that these complexes possess a binuclear framework, in which the two metal centers are bridged by a μ-CH₂SiMe₃ ligand in addition to the coordination of the phoshpine side arm of the cyclopentadienyl ligand to the Pt atom. Variable-temperature NMR spectroscopic studies revealed the fluxional behavior of the μ-CH₂SiMe₃ ligand in solution. These complexes underwent intramolecular C−H bond cleavage at the SiMe₃ group of the μ-CH₂SiMe₃ ligand at elevated temperatures. In the thermolysis of 3b, a silyl-bridged bidentate alkyl Lu/Pt complex, (C₅Me₄SiMe₂CH₂PPh₂)Lu(μ-CH₂SiMe₂CH₂)(OC₄H₈)PtMe₂ (6), was isolated and structurally characterized. The reaction of the Y/Pt complex 3a, which bears the silylene-linked Cp-phosphine ligand, with [Ph₃C][B(C₆F₅)₄] or H₂ led to fragmentation (C−Si bond cleavage) of the ligand to give several unidentified products including Me₂Si(CH₂PPh₂)PtMe₂ (5). In combination with [Ph₃C][B(C₆F₅)₄]/AlⁱBu₃, the Y/Pt complex 4a, which bears the ethylene-linked Cp-phosphine ligand, showed moderate activity for the polymerization of isoprene to yield polyisoprene with isotactic-rich 3,4-microstructures.