NEW CHELATING SILYLAMIDO LIGANDS - SYNTHESES AND X-RAY CRYSTAL-STRUCTURES OF LITHIUM AND MAGNESIUM DERIVATIVES OF [T-BU-HN-SIME2-O-C6H4-X] (X=OME, NME2, CH2NME2, CF3)

New chelating silylamido ligands with four 'directing metalation donor groups' (DMGs), OMe, NMe2, CH2NMe2 and CF3 on aryl moieties have been synthesized. The X-ray crystal structures of the dimeric lithium deri vatives [{t-BuN-SiMe2-o-(C6H4)-DMG}Li](2) (1)(2) (OMe), (2)(2) (NMe2), (3)(2) (CH2NMe2) and (4)(2) (CF3) reveal Li-DMG contacts in all four cases and decreased lone pair-aryl conjugation for OMe and NMe2. In pl ane distortions are apparent for the alkyl and silyl substituents of t he central (LiN)(2) rings in (1)(2)-(4)(2); these give rise to short ' agostic' Li ... H3C- interactions with the t-Bu moieties. While the OM e, NMe2 and CH2NMe2 groups exhibit 'side on' lithium-heteroatom contac ts, lithium coordinates to a CF3 fluorine atom significantly more 'end on'. The ability of the chelating silylamido ligands to coordinate me tal ions other than lithium is demonstrated by the X-ray crystal struc tures of the magnesium complexes [{t-BuN-SiMe2-o-(C6H4)-OMe}(2)Mg] (9) and [{t-BuN-SiMe2-o-(C6H4)-CH2NMe2}(OMe)(2)Mg-2](10). (C) 1998 Elsevi er Science S.A.