Electrophilic Fluorination of Organometallic Fragments

The electrophilic fluorination of protio-substituted ruthenium alkynyl complexes, [Ru(η5 C5Me5)(PPh3)2(C≡C-H)], [Ru(η5 C5Me5)(dppe)(C≡C-H)], and trans-[ClRu(dppe)2(C≡C H)] is reported, along with a discussion on the influence of fluorine on the spectroscopic parameters of fluorovinylidene complexes. The synthesis of the first mononuclear organometallic fluoroalkynyl complexes ([Ru(η5 C5Me5)(PPh3)2(C≡C-F)], [Ru(η5 C5Me5)(dppe)(C≡C-F)], and [ClRu(dppe)2(C≡C-F)]) is also reported. Their stability towards dimerisation and the nature of the alkynyl ligand were probed by computational and spectroscopic methods. The reactivity of the ruthenium fluoroalkynyl complexes with an electrophilic source of fluorine afforded difluorovinylidene complexes, [Ru(η5 C5Me5)(dppe)(=C=CF2)]+ and trans [ClRu(dppe)2(=C=CF2)]+. The reactivity of ruthenium fluorovinylidene complexes, [Ru(η5 C5Me5)(PPh3)2(=C=CFH)]+, [Ru(η5 C5Me5)(dppe)(=C=CFH)]+, trans-[ClRu(dppe)2(=C=CFH)]+, [Ru(η5 C5H5)(PPh3)2(=C=CFPh)]+, and [Ru(η5 C5H5)(dppe)(=C=CFPh)]+, have been explored. Attempts to liberate a fluoroalkyne were unsuccessful on addition of: carbon monoxide, dihydrogen, acetonitrile, and triphenylphosphine. Facile methods for accessing fluorinated carbene complexes (e.g. ([Ru(η5 C5H5)(dppe)(=CFCPhHF)]+) by addition of nucleophiles and acids are discussed, along with the liberation of fluorinated alkenes (e.g. FHC=CFPh) in the presence of a chloride source. The reactivity of complexes trans-[ClRu(dppe)2(C≡CR)] (R= electron-donating and electron-withdrawing groups) towards electrophilic fluorinating agents, NFSI, [FTMP]BF4, and Selectfluor, have been explored. Fluorination of trans-[ClRu(dppe)2(C≡CR)] complexes to give the corresponding trans-[ClRu(dppe)2(=C=CFR)]+ complexes was only observed with Selectfluor. One-electron oxidation of trans-[ClRu(dppe)2(C≡CR)] complexes was observed for all fluorinating agents. The mechanism of fluorination was probed by experimental and computational approaches, including radical-trap and combined UV-Vis-NMR experiments. The study revealed that oxidation and fluorination are competing pathways. The fluorination of trans-[ClRu(dppe)2(C≡CPh)], by NFSI, [FTMP]BF4, and Selectfluor, was probed through relaxed potential energy surface (PES) scans with Density Functional Theory (DFT) studies. The PES scans for both a closed-shell ‘SN2’ and open-shell single electron transfer (SET) mechanism were explored. The scans suggest that fluorination using Selectfluor occurs by a rapid ‘SET’ mechanism.