Syntheses and Anion Binding Capabilities of Bis(diarylboryl) Ferrocenes and Related Systems

Abstract

Isomeric diborylated ferrocenes featuring 1,1′-, 1,2-, and 1,3-substitution patterns have been targeted via a combination of electrophilic aromatic substitution and directed ortho-lithiation protocols. While none of these systems are competent for the Lewis acid chelation of fluoride, related systems featuring a mixed B/Si acceptor set capture 1 equiv of fluoride via a Si−F−B bridging motif.

A Halogen Bonding 1,3‐Disubstituted Ferrocene Receptor for Recognition and Redox Sensing of Azide

“…The rarity of 1,3‐disubstituted ferrocene derivatives arises in part from the synthetic difficulty of selectively functionalizing ferrocene at these positions on the same cyclopentadienyl ring. While such compounds have been isolated in low yields from an isomeric mixture of doubly‐substituted ferrocene derivatives,, recent methodologies have been developed allowing either direct meta ‐functionalisation of a monosubstituted ferrocene derivative or the selective elimination of the central functionality from a 1,2,3‐trisubstituted precursor . Following a recent procedure developed by Weissensteiner and co‐workers using the latter approach, we synthesized 1,3‐diiodoferrocene from commercially‐available bromoferrocene (see Supporting information).…”

Bifunctional Indenyl‐Derived Receptors for Fluoride Chelation and Detection

“…The relatively low yield reflects—at least in part—the fact that Mes 2 BF is a relatively bulky electrophile. Thus, as seen with related cyclopentadienyl nucleophiles, a major portion of the bromo(lithium)indenyl intermediate is not quenched when the temperature is raised, but protonated instead 12c,d…”

“…Thus, the mesityl rings in 7 e are aligned essentially perpendicular to the indenyl plane ( 7 e : 88.7° and 87.4°, cf. 1,2‐fc(BMes 2 )Br: 51.2° and 81.5°) and the C2‐C3‐B17 angle [126.7(2)°] is somewhat wider than expected in order to accommodate the large BMes 2 unit ortho to the bromine atom 12c,d. Additional implications of this degree of steric hindrance become apparent in the next synthetic step.…”

“…A range of reaction conditions was tested for the incorporation of the second BMes 2 unit, but in our hands these were unsuccessful. Moreover, the high degree of steric loading might in fact explain the absence of any 1,2‐(BMes 2 ) 2 benzene derivatives in the literature, with 1,2‐fc(BMes 2 ) 2 presumably being accessible due to the greater separation between ortho substituents enforced by a five (vs. six) membered carbocyclic backbone 12c,d…”

“…Such an approach, however, cannot easily be realised for 1,2‐ferrocenediyl systems;12, 13 the geometric constraints of the five‐membered ring backbone in systems such as VII enforce a B – B separation (ca. 3.68 Å) that is too wide to accommodate fluoride in a bridging position 12c,d. Given the value of the ferrocene unit as a robust electrochemical or colorimetric reporter of anion binding events,14 strategies have therefore been developed to circumvent this problem, including the incorporation of secondary Lewis acids in the 2‐position, which feature intrinsically longer EF bonds, consistent with fluoride chelation (such as the silyl groups used in VIII and IX ) 12d.…”