Synthesis, characterization, and reactivity of ansa-bis(allyl) lanthanide complexes, a new class of single-component methyl methacrylate polymerization catalysts

摘要

The reaction of the dipotassium salt K-2{3-(C3H3SiMe3-1)(2)SiMe2} with LnCl(3) in THF leads to the formation of the new ansa-allyl lanthanate complexes [Ln{(eta(3)-C3H3SiMe3)(2)SiMe2}(2)-{mu-K(THF)}.nTHF](infinity) (1, Ln = La, n = 0.5; 2, Ln = Y, n = 1; 3, Ln = Sc, n = 1). Reaction of K-2{3-(C3H3SiMe3-1)(2)SiMe2} with NdI3(THF)(3.5) affords THF-free [Nd{(eta(3)-C3H3SiMe3)(2)SiMe2}(2)-(mu-K)](infinity) (4). Treatment of SMI2(THF)(2) with Li{3-(C3H3SiMe3-1)(2)SiMe2}/(KOBu)-Bu-t resulted in the samarium(III) complex [Li(OEt2)(4)][Sm{(eta(3)-C3H3SiMe3)(2)SiMe2}(2)] (5), albeit in small yield. Whereas the crystal structure of 1 shows a coordination polymer, with potassium bridging to allyl moieties of two neighboring lanthanide units and close K...CH3Si contacts, complex 5 consists of discrete ions. The complexes 1-5 are all found to be efficient catalysts for the polymerization of methyl methacrylate to high-molecular-weight polymers under a variety of conditions, with 2 at 0 degreesC giving extremely high turnovers of 86 400 mol of MMA (mol of Y)(-1) h(-1). [References: 21]