New reactivity at the silicon bridge in sila[1]ferrocenophanes

We describe two new types of reactivity involving silicon-bridged [1]ferrocenophanes. In an attempt to form a [1]ferrocenophane with a bridging silyl cation, the reaction of sila[1]ferrocenophane [Fe(η-C₅H₄)₂Si(H)TMP] (12) (TMP = 2,2,6,6-tetramethylpiperidyl) towards the hydride-abstraction reagent trityl tetrakis(pentafluorophenyl)borate ([CPh₃][B(C₆F₅)₄]) was explored. This yielded the unusual dinuclear species [Fe(η-C₅H₄)₂Si(TMP·H)(η-C₅H₃)Fe(η-C₅H₄)Si(H)TMP][B(C₆F₅)₄] [13][B(C6F5)4] in low yield. The formation of [13]+ is proposed to involve abstraction of hydride from the silicon bridge in 12 with subsequent C-H bond cleavage of a cyclopentadienyl group by the resulting electrophilic transient silyl cation intermediate. We also explored the reaction of dimethylsila[1]ferrocenophane [Fe(η-C₅H₄)₂SiMe₂] (1) with the Au(i) species AuCl(PMe₃). This was found to result in addition of the Au-Cl bond across the Cp_ipso-Si bond to yield the ring-opened species [1'-(chlorodimethylsilyl)-ferrocenyl](trimethylphosphine)gold(i), [Fe(C₅H₄SiMe₂Cl){C₅H₄Au(PMe₃)}] (14). This represents the first example of ring-opening addition of a metallocenophane with a reagent possessing a transition metal-halogen bond.