IN SEARCH OF STABLE LITHIUM PENTAORGANYLSILICATES - SPECIAL ROLE OF 5PHENYL LIGANDS AND OF LIGANDS CONTAINING THE 1,4-(1,3-BUTADIENEDIYL) UNIT

Among several tetraorganylsilanes tested, only 4-6, containing the 1,4 -(1,3-butadienediyl) unit, have been found to form, by addition of a s igma-organolithium, lithium pentaorganylsilicates identifiable by char acteristic Si-29-NMR chemical shifts. Lithium silicates formed from 4 are of particular stability (and correspondingly low reactivity) and a ppear to have trigonal-bipyramidal structures that undergo stereomutat ion with Delta H-double dagger ca. 50 kJ/mol, Delta S-double dagger ca . -20 J/kmol. So far, lithium pentaphenylsilicate (3) is the only othe r lithium pentaorganylsilicate that could be identified by Si-29-NMR. (C) 1997 Elsevier Science S.A.