Electrophilic additions to the bimetallic silyl complexes [(OC)3{(Meo)3Si}-Fe(μ-PR2)Pt(1,5-COD)] (R = Ph, Cy). Crystal structure of [(OC)3Fe(μ-PCy2){μ-Au(PPh3)}2Pt-(1,5-COD)][PF6] (Cy = c-C6H11)