ANCILLARY LIGAND EFFECTS ON ORGANO-F-ELEMENT REACTIVITY - ANSA-METALLOCENES WITH BRIDGE-TETHERED DONORS

The synthesis and reactivity of ansa-metallocenes based upon the new l igand system R(Me)SiCp ''(2-)(2)(Cp '' = C5Me4 and R = (CH2)(n)OMe, n = 3-5) is reported. The tethered donor functionality, which is appende d via varying chain lengths to the silicon bridge, is introduced to ex amine possible intramolecular reactivity modifications. The key step o f the ligand synthesis is the hydrosilylative fusion of the donor func tionality R to the silicon center. The complexes [R(Me)SiCp ''(2)]LnCH (SiMe3)(2) (Ln = Y, Sm) were synthesized to investigate the influence of the tethered ether group on the reactivity and catalytic properties . Catalytic reactions in which the substrate is a relatively weak dono r, such as in olefin hydrogenation, exhibit depressed turnover frequen cies, presumably reflecting competition between the substrate and dono r functionality for the empty coordination site at the metal center. I n contrast, for amino-alkene hydroamination/cyclization in which a str ong amine donor is the substrate, catalytic activity is significantly enhanced while diastereoselectivity is essentially unchanged. The mole cular structure of the precatalyst [MeO(CH2)(5)(Me)SiCp ''(2)]YCH(SiMe 3)(2) has been determined by X-ray diffraction.