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, (C 5 Me 4 XCH 2 PPh 2 )Ln(CH 2 SiMe 3 ) 2 (OC 4 H 8 )PtMe 2 ( 3a: Ln = Y, X = SiMe 2; 3b: Ln = Lu, X = SiMe 2; 4a: Ln = Y, X = CH 2; 4b: Ln = Lu, X = CH 2 ), were prepared by the reaction of (C 5 Me 4 XCH 2 PPh 2 )Ln(CH 2 SiMe 3 ) 2 (OC 4 H 8 ) with PtMe 2 (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-CH 2 SiMe 3 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-CH 2 SiMe 3 ligand in solution. These complexes underwent intramolecular C−H bond cleavage at the SiMe 3 group of the μ-CH 2 SiMe 3 ligand at elevated temperatures. In the thermolysis of 3b, a silyl-bridged bidentate alkyl Lu/Pt complex, (C 5 Me 4 SiMe 2 CH 2 PPh 2 )Lu(μ-CH 2 SiMe 2 CH 2 )(OC 4 H 8 )PtMe 2 ( 6 ), was isolated and structurally characterized. The reaction of the Y/Pt complex 3a, which bears the silylene-linked Cp-phosphine ligand, with [Ph 3 C][B(C 6 F 5 ) 4 ] or H 2 led to fragmentation (C−Si bond cleavage) of the ligand to give several unidentified products including Me 2 Si(CH 2 PPh 2 )PtMe 2 ( 5 ). In combination with [Ph 3 C][B(C 6 F 5 ) 4 ]/Al i Bu 3, 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.