A series of polyelement substituted cyclopentadienyl and indenyl boranes and arsanes containing Me3Si-, Me3Sn-was synthesised;(C5H4SiMe3) BX2 (2, X= Cl; 3, X= Br) and (C9H6SiMe3) BX2 (4, X= Cl; 5, X= Br) were obtained by Si/B exchange reaction in a low yield when X= Cl and in a moderate yield when X= Br, whereas Flu (SIMe3) 2 does not react with BBr3 at all. PhB (C5H4SiMe3) 2 (6) and PhB [C5H3 (SiMe3) 2] 2 (7) were ...