Role of torsional strain in the ring-opening polymerisation of low strain [n]nickelocenophanes

Abstract

We investigate types of ring strain responsible for the ring-opening polymerisation of [n]nickelocenophanes with carbon and silicon-based ansa bridges.

Redox Chemistry of Nickelocene-Based Monomers and Polymers

“…A stabilization effect is also observed for the disila/siloxane-bridged species within this second redox couple. The dication of the disila-bridged compound [10] 2+ exhibits a greater stabilization versus the [Ni{η 5 -C 5 H 4 (SiMe 3 )} 2 ] 2+ dication (180 mV) than that of siloxane-bridged [11] 2+ (100 mV).…”

“…Single crystals of [10][B(C 6 F 5 ) 4 ] were grown by a slow diffusion of hexanes into a dichloromethane solution of the The distortion that accounts for the structural differences between 10 and [10] + is manifested in a combination of τ (defined as the angle between the Si−Si bond of the bridge and the Cp cent −Ni−Cp′ cent plane in the nickelocene unit) and ϕ (the extent to which the Cp ligands are staggered/eclipsed within the nickelocene unit) (Figure 10).…”

“…For the neutral species 10, τ = 12.12(2)°, whereas for the cationic species [10] + , it is much larger (τ = 19.47(2)°), indicating a greater twisting of the disila bridge to allow for some of the shortening of both Ni−Cp bonds. However, there is also a greater extent of "staggering" of the upper and lower Cp rings relative to one another (quantified by the torsion angle, ϕ; Cp ipso −Cp cent −Cp′ cent −Cp′ ipso ), and this is far greater in cationic [10] + (ϕ = 12.86(15)°) than in neutral 10 (ϕ = 8.99(10)°), which contributes further to the overall twisting of the molecule upon oxidation. A very similar effect is observed in distanna [2]nickelocenophane 9 and its oxidation product [9] + , where τ increases from 12.92(4)°to 24.56(4)°and staggering of the Cp rings (ϕ) also increases significantly from 11.00(12)°to 22.3(3)°.…”

“…Single crystals of [10][B(C 6 F 5 ) 4 ] were grown by a slow diffusion of hexanes into a dichloromethane solution of the 16)°). The Si−Si bond length within the bridge is also the same within error for both species (10: 2.3638(4) Å; [10] + : 2.3636(10) Å).…”

“…One of these is disordered over the metallocene unit, the ansa bridge, and one of the C 6 F 5 rings of the tetrakis(pentafluorophenyl)borate anion. The [11] + cation shown in Figure 11 (Ni( In a similar manner to that of [10][B(C 6 F 5 ) 4 ], compound [12][B(C 6 F 5 ) 4 ] was isolated via a slow diffusion of hexanes into a dichloromethane solution of the product. [12][B(C 6 F 5 ) 4 ] crystallizes in the orthorhombic space group Pbca (Figure 12) and exhibits disorder within the ansa bridge at C(7)/C(7A) and C(8)/C(8A).…”