Synthesis of tetraphenylstannacyclopentadienes (stannoles). 1. Alkylation of 1,1-dihalostannoles leading to lithium 1,1-bis-(.eta.1-cyclopentadienyl)-1-halo-2,3,4,5-tetraphenylstannole, an [R4SnX]- anion, with pseudorotating axial- and equatorial-fluxional .eta.1-cyclopentadienyl groups