Can acyclic conformational control be achieved via a sulfur-fluorine gauche effect?

The gauche conformation of the 1,2-difluoroethane motif is known to involve stabilising hyperconjugative interactions between donor (bonding, σC-H) and acceptor (antibonding, σ*C-F) orbitals. This model rationalises the generic conformational preference of F-Cβ-Cα-X systems (φFCCX ≈ 60°), where X is an electron deficient substituent containing a Period 2 atom. Little is known about the corresponding Period 3 systems, such as sulfur and phosphorus, where multiple oxidation states are possible. Conformational analyses of β-fluorosulfides, -sulfoxides and -sulfones are disclosed here, thus extending the scope of the fluorine gauche effect to the 3rd Period (F-C-C-S(O) n ; φFCCS ≈ 60°). Synergy between experiment and computation has revealed that the gauche effect is only pronounced in structures bearing an electropositive vicinal sulfur atom (S+-O-, SO2)

Can acyclic conformational control be achieved via a sulfur-fluorine gauche effect?

The gauche conformation of the 1,2-difluoroethane motif is known to involve stabilising hyperconjugative interactions between donor (bonding, σC-H) and acceptor (antibonding, σ*C-F) orbitals. This model rationalises the generic conformational preference of F-Cβ-Cα-X systems (φFCCX ≈ 60°), where X is an electron deficient substituent containing a Period 2 atom. Little is known about the corresponding Period 3 systems, such as sulfur and phosphorus, where multiple oxidation states are possible. Conformational analyses of β-fluorosulfides, -sulfoxides and -sulfones are disclosed here, thus extending the scope of the fluorine gauche effect to the 3rd Period (F-C-C-S(O) n ; φFCCS ≈ 60°). Synergy between experiment and computation has revealed that the gauche effect is only pronounced in structures bearing an electropositive vicinal sulfur atom (S+-O-, SO2)

Deconstructing the Catalytic, <i>Vicinal</i> Difluorination of Alkenes: HF-Free Synthesis and Structural Study of <i>p</i>‑TolIF₂

Recently, contemporaneous strategies to achieve the <i>vicinal</i> difluorination of alkenes via an I­(I)/I­(III) catalysis manifold were independently reported by this laboratory and by Jacobsen and co-workers. Both strategies proceed through a transient ArI­(III)­F₂ species generated by oxidation of the ArI catalyst. Herein, an efficient synthesis of <i>p</i>-TolIF₂ from <i>p</i>-TolI and Selectfluor is presented, together with a crystallographic and spectroscopic study. To mitigate safety concerns and simplify reaction execution, an HF-free protocol was devised employing CsF as a substitute fluoride source. The study provides insight into the initial I­(I)→I­(III) oxidation stage of the catalytic protocol using Selectfluor

The Sulfur–Fluorine <i>Gauche</i> Effect in Coinage-Metal Complexes: Augmenting Conformational Equilibria by Complexation

Controlling the rotation about unhindered C­(sp³)–C­(sp³) bonds by simple structural changes has obvious benefits in molecular design. While the avoidance of nonbonding interactions remains one of the cornerstones of acyclic conformational control, stabilizing stereoelectronic effects have the added benefit that conformer populations can be fine-tuned by augmenting or diminishing the central interaction. Strategies may include adjusting the oxidation state of a substituent or reversible formation of a complex to modulate MO levels. In the case of the sulfur–fluorine <i>gauche</i> effect, the propensity of the S–C–C–F motif to adopt a <i>synclinal</i> arrangement (Φ_FCCS = 60°), the conformer population distribution of the three dominant rotamers partitioned by 120° can be biased by oxidation of the S atom. Motivated by the importance of sulfur-based ligands in main structural chemistry, the sulfur–fluorine <i>gauche</i> effect was translated to an organometallic paradigm as a potential tool to achieve structural preorganization. This would allow the influence of coinage-metal complexation on conformer population to be initially assessed. The synthesis and characterization of a model gold­(I) and silver­(I) metal complex featuring a ligand system containing a freely rotatable SCCF motif is disclosed. In both complexes, the title stereoelectronic effect manifests itself in the expected conformation, with the <i>synclinal</i>-<i>endo</i> conformer being preferred. This was corroborated by X-ray crystallography and DFT analysis, and the molar fraction of rotamers was extrapolated from a detailed solution-phase NMR spectroscopic analysis. Complexation was found to reinforce the sulfur–fluorine <i>gauche</i> effect

The Sulfur–Fluorine <i>Gauche</i> Effect in Coinage-Metal Complexes: Augmenting Conformational Equilibria by Complexation

Controlling the rotation about unhindered C­(sp³)–C­(sp³) bonds by simple structural changes has obvious benefits in molecular design. While the avoidance of nonbonding interactions remains one of the cornerstones of acyclic conformational control, stabilizing stereoelectronic effects have the added benefit that conformer populations can be fine-tuned by augmenting or diminishing the central interaction. Strategies may include adjusting the oxidation state of a substituent or reversible formation of a complex to modulate MO levels. In the case of the sulfur–fluorine <i>gauche</i> effect, the propensity of the S–C–C–F motif to adopt a <i>synclinal</i> arrangement (Φ_FCCS = 60°), the conformer population distribution of the three dominant rotamers partitioned by 120° can be biased by oxidation of the S atom. Motivated by the importance of sulfur-based ligands in main structural chemistry, the sulfur–fluorine <i>gauche</i> effect was translated to an organometallic paradigm as a potential tool to achieve structural preorganization. This would allow the influence of coinage-metal complexation on conformer population to be initially assessed. The synthesis and characterization of a model gold­(I) and silver­(I) metal complex featuring a ligand system containing a freely rotatable SCCF motif is disclosed. In both complexes, the title stereoelectronic effect manifests itself in the expected conformation, with the <i>synclinal</i>-<i>endo</i> conformer being preferred. This was corroborated by X-ray crystallography and DFT analysis, and the molar fraction of rotamers was extrapolated from a detailed solution-phase NMR spectroscopic analysis. Complexation was found to reinforce the sulfur–fluorine <i>gauche</i> effect

The Sulfur–Fluorine <i>Gauche</i> Effect in Coinage-Metal Complexes: Augmenting Conformational Equilibria by Complexation

Controlling the rotation about unhindered C­(sp³)–C­(sp³) bonds by simple structural changes has obvious benefits in molecular design. While the avoidance of nonbonding interactions remains one of the cornerstones of acyclic conformational control, stabilizing stereoelectronic effects have the added benefit that conformer populations can be fine-tuned by augmenting or diminishing the central interaction. Strategies may include adjusting the oxidation state of a substituent or reversible formation of a complex to modulate MO levels. In the case of the sulfur–fluorine <i>gauche</i> effect, the propensity of the S–C–C–F motif to adopt a <i>synclinal</i> arrangement (Φ_FCCS = 60°), the conformer population distribution of the three dominant rotamers partitioned by 120° can be biased by oxidation of the S atom. Motivated by the importance of sulfur-based ligands in main structural chemistry, the sulfur–fluorine <i>gauche</i> effect was translated to an organometallic paradigm as a potential tool to achieve structural preorganization. This would allow the influence of coinage-metal complexation on conformer population to be initially assessed. The synthesis and characterization of a model gold­(I) and silver­(I) metal complex featuring a ligand system containing a freely rotatable SCCF motif is disclosed. In both complexes, the title stereoelectronic effect manifests itself in the expected conformation, with the <i>synclinal</i>-<i>endo</i> conformer being preferred. This was corroborated by X-ray crystallography and DFT analysis, and the molar fraction of rotamers was extrapolated from a detailed solution-phase NMR spectroscopic analysis. Complexation was found to reinforce the sulfur–fluorine <i>gauche</i> effect