Outer-Sphere Electrophilic Fluorination of Organometallic Complexes

Abstract

Organofluorine chemistry plays a key role in materials science, pharmaceuticals, agrochemicals, and medical imaging. However, the formation of new carbon-fluorine bonds with controlled regiochemistry and functional group tolerance is synthetically challenging. The use of metal complexes to promote fluorination reactions is of great current interest, but even state-of-the-art approaches are limited in their substrate scope, often require activated substrates, or do not allow access to desirable functionality, such as alkenyl C(sp(2))-F or chiral C(sp(3))-F centers. Here, we report the formation of new alkenyl and alkyl C-F bonds in the coordination sphere of ruthenium via an unprecedented outer-sphere electrophilic fluorination mechanism. The organometallic species involved are derived from nonactivated substrates (pyridine and terminal alkynes), and C-F bond formation occurs with full regio- and diastereoselectivity. The fluorinated ligands that are formed are retained at the metal, which allows subsequent metal-mediated reactivity.

The Versatile Behavior of Platinum Alkyne Complexes towards XeF2: Formation of Fluorovinyl and Fluorido Complexes

“…[68] Examples for which af luorinated ligand remains in the coordination sphere of the metal after the CÀFb ond formation step are very rare. [70] We reported on the reactivity of platinum(0) alkyne complexes towards the electrophilic fluorinating agent NFSI yielding,f or instance, [Pt(PhC=CFPh){N(SOPh 2 ) 2 }{k 2 -(P,N)-iPr 2 PC 2 H 4 NMe 2 }],w hich bears a b-fluorovinyl ligand. [70] We reported on the reactivity of platinum(0) alkyne complexes towards the electrophilic fluorinating agent NFSI yielding,f or instance, [Pt(PhC=CFPh){N(SOPh 2 ) 2 }{k 2 -(P,N)-iPr 2 PC 2 H 4 NMe 2 }],w hich bears a b-fluorovinyl ligand.…”

Palladium‐Catalyzed Electrophilic C–H‐Bond Fluorination: Mechanistic Overview and Supporting Evidence

“…Electrophilic fluorination catalyzed by ruthenium following an “outer sphere” mechanism has also been postulated by Lynam and Slaterry groups for the formation of alkenyl and alkyl C–F bonds in the coordination sphere of ruthenium organometallic complexes …”

A Structurally Characterized Fluoroalkyne

“…We recently described how the electrophilic fluorination of alkenyl‐containing and alkynyl‐containing ligands within the coordination sphere of ruthenium may lead to the rapid and selective formation of new fluorinated ligands, including rare examples of fluorovinylidenes (Scheme a). This occurs via the novel outer‐sphere electrophilic fluorination (OSEF) mechanism.…”

“…Using OSEF methodology, the fluoroalkynyl ligand in 3 may be readily converted into a difluorovinylidene. Reaction of 3 with NFSI in THF at −78 °C resulted in formation of [Ru(η 5 ‐C 5 Me 5 )(=C=CF 2 )(dppe)][N(SO 2 Ph) 2 ], ( 4 [N(SO 2 Ph) 2 ]), Scheme , which was characterized in the same manner as 2 [N(SO 2 Ph) 2 ] and 3 , Scheme .…”