Insertion of a platinum(>0>) fragment into the strained silicon–carbon bond of a silicon-bridged [1]ferrocenophane: synthesis, alkyne insertion chemistry, and catalytic reactivity of the [2]platinasilaferrocenophane Fe(η5-C5H4)2Pt(PEt3)2SiMe2

Abstract

The reaction of Pt(PEt₃)₃ with the silicon-bridged [1]ferrocenophane Fe(η⁵-C₅H₄)₂SiMe₂ 1 at 60 °C resulted in the insertion of a platinum(>0>) Pt(PEt₃)₂ fragment into the strained Si–C bond to yield the first [2]platinasilaferrocenophane Fe(η⁵-C₅H₄)₂Pt(PEt₃)₂SiMe₂ 4. Complex 4 serves as a model for the proposed intermediate during the transition metal-catalyzed ring-opening polymerization (ROP) of 1. The reactivity of 4 was illustrated by the insertion of diphenylacetylene into the Pt–Si bond at elevated temperatures to yield a [4]ferrocenophane Fe(η⁵-C₅H₄)₂Pt(PEt₃)₂C(Ph)C(Ph)SiMe₂ 5 with a cis Pt–CC–Si bridge. Both 4 and 5 were fully characterized spectroscopically and by single crystal X-ray diffraction. Despite the reactivity of the Pt–Si bond, the [2]platinasilaferrocenophane 4 was inactive as a ROP catalyst for 1 even at 95 °C. However, addition of BH₃·THF co-catalyst rendered 4 active towards the ROP of 1 at 25 °C, presumably via abstraction of one or more PEt₃ ligands, affording low molecular weight [M_n (number average molecular weight) = ca. 1720–4695; PDI (polydispersity index) = 1.51–1.73], cyclic poly(ferrocenylsilanes) 6.