Access to novel fluorovinylidene ligands via exploitation of outer-sphere electrophilic fluorination: new insights into C–F bond formation and activation

Abstract

Metal vinylidene complexes are widely encountered, or postulated, as intermediates in a range of important metal-mediated transformations of alkynes. However, fluorovinylidene complexes have rarely been described and their reactivity is largely unexplored. By making use of the novel outer-sphere electrophilic fluorination (OSEF) strategy we have developed a rapid, robust and convenient method for the preparation of fluorovinylidene and trifluoromethylvinylidene ruthenium complexes from non-fluorinated alkynes. Spectroscopic investigations (NMR and UV/Vis), coupled with TD-DFT studies, show that fluorine incorporation results in significant changes to the electronic structure of the vinylidene ligand. The reactivity of fluorovinylidene complexes shows many similarities to non-fluorinated analogues, but also some interesting differences, including a propensity to undergo unexpected C-F bond cleavage reactions. Heating fluorovinylidene complex [Ru(η(5)-C5H5)(PPh3)2(C[double bond, length as m-dash]C{F}R)][BF4] led to C-H activation of a PPh3 ligand to form an orthometallated fluorovinylphosphonium ligand. Reaction with pyridine led to nucleophilic attack at the metal-bound carbon atom of the vinylidene to form a vinyl pyridinium species, which undergoes both C-H and C-F activation to give a novel pyridylidene complex. Addition of water, in the presence of chloride, leads to anti-Markovnikov hydration of a fluorovinylidene complex to form an α-fluoroaldehyde, which slowly rearranges to its acyl fluoride isomer. Therefore, fluorovinylidenes ligands may be viewed as synthetic equivalents of 1-fluoroalkynes providing access to reactivity not possible by other routes.

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

“…In conclusion, we described electrophilic outer‐sphere fluorination reactions at platinum(0) alkyne complexes with XeF 2 , resulting in the formation of the fluoride fluorovinyl complexes [Pt(PhC=CFPh)(F){L}] [L=κ 2 ‐( P , N )‐ i Pr 2 PC 3 H 6 NMe 2 ( 3 ), κ 2 ‐( P , N )‐ i Pr 2 PC 2 H 4 NMe 2 ( 4 )]. Examples for the isolation of compounds bearing a fluorinated ligand after outer‐sphere fluorination are extremely scarce . Derivatization and reactivity studies on compound 4 did not result in any C−C coupling reactions.…”

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 .…”

A Structurally Characterized Fluoroalkyne

“…We recently described how the electrophilic fluorination of alkenyl-containing [6] and alkynyl-containing [7] ligands within the coordination sphere of ruthenium [8] mation of the vinylidene ligand was confirmed by the observation of resonances at d = 362.8 (d, 3 J CF = 43.5 Hz) and 173.9 (d, 1 J CF = 236.2 Hz) ppm in the 13 C{ 1 H} NMR spectrum and doublets at d = 7.32 and À235.8 ppm in the 1 H and 19 FNMR spectra, respectively ( 2 J FH = 80.2 Hz). Salt metathesis with NaPF 6 resulted in the formation of 2[PF 6 ] which was structurally characterized by single crystal X-ray diffraction, [9] confirming the assignments of the NMR spectra.…”