Synthesis of Tetraphenylstannacyclopentadienes (Stannoles). I. Alkylation of 1,1-Dihalostannoles Leading to Lithium 1,1-Di-h1-cyclopentadienyl-1-halo-2,3,4,5-tetraphenylstannole, an (R4SnX)-Anion with Pseudorotating Axial- and Equatorial-Fluxional h1-Cyclopentadienyl Groups.