Catalytic hydrodefluorination of fluoroaromatics with silanes as hydrogen source at a binuclear rhodium complex: Characterization of key intermediates

Activation of SO2F2 at a Rhodium PNP Pincer Complex: Ligand Supported S-F Bond Cleavage to Generate NSO2F Derivatives

The κ2-(P,N)-phosphine ligand precursor NH(CH2CH2PCy2)2 can be used for the synthesis of the rhodium(I) complex [Rh(CO){ĸ3-(P,N,P)-Cy2PC2H4NHC2H4PCy2}][Cl] (1). The deprotonated complex [Rh(CO){ĸ3-(P,N,P)-Cy2PC2H4NC2H4PCy2}] (2) shows a cooperative reactivity of the PNP ligand in the activation reaction of SO2F2 to yield the rhodium fluorido complex trans-[Rh(F)(CO){ĸ2-(P,P)-Cy2PC2H4N(SO2F)C2H4PCy2}]2 (3) by S-F bond cleavage. It is remarkable that no reaction was observed when 3 was treated with hydrogen sources e. g. dihydrogen, organosilicon compounds such as triethylsilane or TMS-CF3 and different fluorine sources such as SF4 or Selectfluor®. However, the treatment of complex 3 with XeF2 in the presence of CsF resulted in the formation of the unique fluorido rhodium(III) complex cis,trans-[Rh(F)3(CO){ĸ2-(P,P)-Cy2PC2H4N(SO2F)C2H4PCy2}]2 (4). In the presence of pyridine(HF)X or BF3 the fluorido complex 3 converted into the dicationic complexes [Rh(CO){ĸ2-(P,P)-Cy2PC2H4N(SO2F)C2H4PCy2}]2[XF]2, X=HF (5) or BF3 (6), respectively.

Organocatalyzed Fluoride Metathesis

A new organocatalyzed fluoride metathesis reaction between fluoroarenes and carbonyl derivatives is reported. The reaction exchanges fluoride (F^-) and alternate nucleophiles (OAc^-, OCO₂R^-, SR^-, Cl^-, CN^-, NCS^-). The approach provides a conceptually novel route to manipulate the fluorine content of organic molecules. When the fluorination and defluorination steps are combined into a single catalytic cycle, a byproduct free and 100% atom-efficient reaction can be achieved.

Reactivity of Binary and Ternary Sulfur Halides towards Transition-Metal Compounds

Binary sulfur fluorides exhibit an interesting reactivity towards transition metal complexes. They open up routes for the generation of sulfur‐containing building blocks. Often ligands with particular properties can be constructed. This includes their ability to transfer sulfur atoms or polysulfide units as well as fluorination reactions. This Minireview provides an insight into the reactivity of the binary and ternary sulfur halides S₂Cl₂, SCl₂, SF₄, SF₆ and SF₅Cl towards transition‐metal compounds.

C-F activation of perfluorophenazine at nickel: selectivity and mechanistic investigations

The reactivity of [Ni(cod)2] towards perfluorophenazine in the presence of phosphines is reported. When PiPr3 and PCy3 are used, an initial κ-(N) coordination of the nickel centre to the nitrogen atom of the perfluorophenazine ring occurs, forming the dark blue complexes [Ni{κ-(N)-C12N2F8}(PiPr3)2] (1) and [Ni{κ-(N)-C12N2F8}(PCy3)2] (2). Complex 1 was structurally characterized by X-ray diffraction analysis. The complexes rearranged by regioselective C-F activation of the perfluorophenazine ring in the 2-position to yield complexes trans-[NiF(2-C12N2F7)(PiPr3)2] (5) and trans-[NiF(2-C12N2F7)(PCy3)2] (6). The structure of 6 was also determined by X-ray diffraction analysis. Kinetic measurements for the decrease of 1 at different temperatures reveal a first order reaction with ΔH‡ = 19 ± 7 kcal mol-1. Initially, small amounts of an intermediate, assigned as [Ni(η2-1,2-C12N2F8)(PiPr3)2] (3), were observed, which exhibits a 1,2-η2 coordination of the perfluorophenazine. DFT calculations on the same transformation were also computed, which suggest that both a phosphine-assisted mechanism and an oxidative addition can be operating reaction pathways. The 1,2-η2 complex [Ni(η2-1,2-C12N2F8)(PEt3)2] (4) was obtained when PEt3 was used as ligand, and an unstable dark red complex trans-[NiF(2-C12N2F7)(PEt3)2] (7) formed rapidly by C-F activation. The reactivity of the perfluorophenazine was compared with those of perfluorodibenzo-p-dioxin. In this case, no prior coordination was observed and the C-F activation took place in a less selective manner forming trans-[NiF(1-C12O2F7)(PiPr3)2] (8) and trans-[NiF(2-C12O2F7)(PiPr3)2] (9), outlining the role of the nitrogen for the selectivity of the process. Treatment of two equivalents of [Ni(cod)2] and four equivalents of PiPr3 with perfluorophenazine afforded a double C-F activation to give [{trans-(PiPr3)2NiF}2(2,7-C12N2F6)] (10).

Silylation reactions on nanoporous gold via homolytic Si-H activation of silanes

We report compelling evidences that dihydrosilanes are activated in a homolytic fashion on the surface of nanoporous gold (NPG), which produces hydrogen radical and silicon moieties covalently linked to the surface of the NPG. This new reactivity has led to the development of novel silylation reactions on gold.

Si–H bond activation is an important process implicated in many useful synthetic applications including silylation and transfer hydrogenation reactions. Herein we discovered homolytic activation of Si–H bonds on the surface of nanoporous gold (NPG), forming hydrogen radicals and [Au]–[Si] intermediates. By virtue of this new reactivity, we achieved highly selective mono and sequential alcoholysis of dihydrosilane. In addition, the amphiphilic nature of the [Au]–[Si] intermediate allows for a new bis-silylation reaction of cyclic ethers. The present work showcased that the surface reactivity of nanocatalysts may provide exciting opportunity for new reaction discovery.

Constructing a Catalytic Cycle for C-F to C-X (X = O, S, N) Bond Transformation Based on Gold-Mediated Ligand Nucleophilic Attack

A tricoordinated gold(I) chloride complex, tBuXantphosAuCl, supported by a sterically bulky 9,9-dimethyl-4,5-bis(di-tert-butylphosphino)xanthene ligand (tBuXantphos) was synthesized. This complex features a remarkably longer Au-Cl bond length [2.632(1) Å] than bicoordinated linear gold complexes (2.27-2.30 Å) and tricoordinated XantphosAuCl [2.462(1) Å]. Single-crystal X-ray diffraction analysis of a cocrystal of tBuXantphosAuCl and pentafluoronitrobenzene (PFNB) and UV-vis spectroscopic titration experiments revealed the existence of an anion-π interaction between the Cl anion ligand and PFNB. Stoichiometric reaction between PFNB and tBuXantphosAuOtBu, after replacement of Cl by a more nucleophilic tBuO anion ligand, showed higher reactivity and para selectivity in the transformation of C-F to C-OtBu bond, distinctively different from that when only KOtBu was used (ortho selectivity) under the identical condition. Mechanistic studies including density functional theory calculations suggested a gold-mediated nucleophilic ligand attack of the C-F bond pathway via an SNAr process. On the basis of these results, using trimethylsilyl derivatives TMS-X (X = OMe, SEt, NEt2) as the nucleophilic ligand source and the fluorine acceptor, catalytic transformation of the C-F bond of aromatic substrates to the C-X (X = O, S, N) bond was achieved with tBuXantphosAuCl as the catalyst (up to 20 turnover numbers).

Synthesis of a rhodium(i) germyl complex: a useful tool for C–H and C–F bond activation reactions

The rhodium(i) germyl complex [Rh(GePh₃)(PEt₃)₃] is a useful tool for C–F and C–H bond activation reactions. For instance, treatment with hexafluoropropene results in the formation of two isomeric C–F activation products [Rh{(E)-CFCF(CF₃)}(PEt₃)₃] and [Rh{(Z)-CFCF(CF₃)}(PEt₃)₃] in a 3 : 1 ratio.

Synthesis and structure of rhodium(i) silyl carbonyl complexes: photochemical C-F and C-H bond activation of fluorinated aromatic compounds

The rhodium(i) silyl carbonyl complexes [Rh{Si(OEt)3}(CO)(dippp)] () and [Rh{Si(OEt)3}(CO)(dippe)] () (dippp = 1,3-bis(diisopropylphosphino)propane, dippe = 1,2-bis-(diisopropylphosphino)ethane) were synthesized on treatment of the methyl compounds [Rh(CH3)(CO)(dippp)] () or [Rh(CH3)(CO)(dippe)] () with HSi(OEt)3 at low temperature. The methyl complexes and were prepared starting from the binuclear complexes [{Rh(μ-Cl)(dippp)}2] () and [{Rh(μ-Cl)(dippe)}2] (), respectively. The silyl complexes and as well as the precursors [{Rh(μ-I)(dippp)}2] (), [Rh(X)(CO)(dippp)] (: X = CH3, : X = I) and [Rh(X)(CO)(dippe)] (: X = CH3, : X = Cl) were characterized by NMR and IR spectroscopy and the structures in the solid state were determined by X-ray crystallography. The silyl complex converts into the carbonyl-bridged complex [{Rh(μ-CO)(dippp)}2] () above temperatures of -30 °C by loss of the silyl ligand, whereas is more thermally stable and a reaction to the binuclear complex [{Rh(μ-CO)(dippe)}2] () was observed at 50 °C. The silyl complex reacted under irradiation with hexafluorobenzene and pentafluoropyridine to give the C-F activation products [Rh(C6F5)(CO)(dippe)] () and [Rh(2-C5F4N)(CO)(dippe)] (), respectively. As additional products the silyl dicarbonyl complex [Rh{Si(OEt)3}(CO)2(dippe)] () and the cationic complex [Rh2(μ-H)(μ-CO)2(dippe)2](+)[SiF5](-) () were identified. Compound was synthesized independently by treatment of with gaseous CO. In a similar manner, the dippp analogue [Rh{Si(OEt)3}(CO)2(dippp)] () was also prepared starting from . Photochemical reaction of with pentafluorobenzene and 2,3,5,6-tetrafluoropyridine resulted selectively in C-H bond activation to afford and [Rh(4-C5F4N)(CO)(dippe)] (), respectively.

Consecutive C-F bond activation and C-F bond formation of heteroaromatics at rhodium: the peculiar role of FSi(OEt)3

C-F activation of 2,3,5,6-tetrafluoropyridine at [Rh{Si(OEt)3}(PEt3)3] (1) yields [Rh{2-(3,5,6-C5F3HN)}(PEt3)3] (2) and FSi(OEt)3, but in an unprecedented consecutive reaction FSi(OEt)3 acts as a fluoride source to give [Rh(4-C5F4N)(PEt3)3] (4) by regeneration of the C-F bond and C-H activation. Analogous refluorination steps were observed for other 2-pyridyl rhodium complexes. NMR spectroscopic studies revealed a delicate balance between the feasibility for C-F bond formation accompanied by a C-H activation and the occurrence of competing reactions such as hydrodefluorinations induced by the intermediary presence of H2.

Stoichiometric and catalytic C–F bond activation by the trans-dihydride NHC complex [Ru(IEt2Me2)2(PPh3)2H2] (IEt2Me2= 1,3-diethyl-4,5-dimethylimidazol-2-ylidene)

Multiple catalytic hydrodefluorination steps take place with thetrans-dihydride complex [Ru(IEt₂Me₂)₂(PPh₃)₂H₂] (1), taking C₆F₆to tri-, di- and mono-fluorobenzenes.

Catalytic borylation of SCF₃-functionalized arenes by rhodium(I) boryl complexes: regioselective C-H activation at the ortho-position

An unprecedented reaction pathway for the borylation of SCF3-containing arenes using [Rh(Bpin)(PEt3)3] (pin=pinacolato) is reported. Catalytic processes were developed and the functionalizations proceed under mild reaction conditions. The C-H activations occur with a unique regioselectivity for the position ortho to the SCF3 group, which apparently serves as directing group. Borylated SCF3 compounds can serve as versatile building blocks.