Gradual Donor Stabilization of a Transient Ferrocene Bridged Bisphosphanyl Phosphenium Cation

Abstract

A transient phosphenium cation embedded into a [3]ferrocenophane scaffold was formed via chloride abstraction. The cation has been trapped with phosphane, carbene, and silylene donors resulting in stable adducts or bond activation of the ferrocenophane bridge. In the absence of donors, dimerization of the phosphenium cation to the corresponding dication is observed or P−C bond activation with migration of a substituent leading to a putative phosphoniodiphosphene. Using 1,3-di-tert-butylimidazol-2-silylene as the donor, further reaction of the initially formed chlorosilane leads to activation of a P−P bond of the ferrocenophane scaffold with ring expansion of the ansa-bridge. The donor formation and bonding situation are investigated by density functional theory calculations as well as experimental methods (e.g., NMR spectroscopy and X-ray crystallography).

Controlled Ring Opening of a Tetracyclic Tetraphosphane with Twofold Metallocene Bridging

“…When both ϕ and ψ angles simultaneously increase, [32] rigid equatorial orientations of the substituents at the P atoms get conformationally disfavored. With respect to the distortion of the cyclopentadienyl moieties from coplanarity, [33] 1 (α=3.8°) shows a slightly higher tilt angle than [Fc′ 2 P 4 t Bu 2 ] (α=0°) and other phospha[3]FCPs, [29b] but nevertheless indicates negligible ring strain of the ferrocenophane scaffold. However, both 1 and [Fc′ 2 P 4 t Bu 2 ] feature twist angles of τ=0° highlighting the directional rigidity of the linear P−P backbone [33]…”

A new entry towards diastereomeric C1,C2,C3-functionalized [3]ferrocenophanes using a solid state mediated double 1,4-Michael addition type ring closing approach

“…Hetero-atom bridged and all-carbon bridged ferrocenophanes involving saturated or unsaturated bridging components have shown their unique structural and functional features, playing a vital role as monomers in ring opening polymerization. 1–5 Functionalization opportunities at the bridging atoms have been explored extensively to obtain different types of ferrocenophanes with various functional features. Each of these functionalized ferrocenophane molecules have particular features or characteristics depending upon their functionality, number of bridging atoms, ring strain, etc.…”

Gradual Coordination and Reversible P–P Bond Activation of a P3‐Unit with Transition Metal Carbonyls

“…On top of that the anionic, cationic and electroneutral (radical) forms are known and synthetically available and the electron number varies at the central phosphorus atom (Figure 1 ). [ 6 ]…”

“… Varieties of the PPP‐[3]ferrocenophane scaffold (anionic (top left), cationic (top right) or radical (top middle)). [ 6 ] …”

“…According to recent studies, exclusive coordination at the terminal phosphorus atoms is observed for the anionic P 3 unit in 1 − (e.g., in Li ‐ 1 ), whereas the neutral radical 1 ∙ undergoes dimerization via the central phosphorus atom and the reactivity of the cationic bisphosphanyl phosphenium ion 1 + can involve both positions. [ 6 , 7 ]…”