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