Pentafulvenes are a unique class of compounds that originally attracted attention due to their propensity to display nonbenzenoid aromaticity. Subsequently, they were recognized as valuable synthons for the construction of a wide range of compounds by virtue of their ability to display multiple cycloaddition profiles. Naturally, this area of organic chemistry has experienced rapid growth over the last five decades, fueled by elegant work showcasing the unique reactivity of pentafulvenes in a plethora of cycloaddition reactions. In this Review, we have attempted to provide a systematic account of the methods for the generation of pentafulvenes, their rich and varied cycloaddition chemistry, organometallic reactions, and theoretical studies that support their versatility. Further, we have highlighted their applications in the synthesis of a variety of complex structural frameworks. It is our conviction that this Review will be useful to a wide range of chemists, and will spur further research in this promising area.

The isolation and characterization of the first molecular complex of divalent thulium, [TmI 2 (dme) 3 ] (dme = 1,2-dimethoxyethane), [1] ten years ago, followed by the dysprosium [2] and neodymium [3] diiodides, [DyI 2 (dme) 3 ] and [NdI 2 (thf) 5

CommunicationInternational audienceReduction of bis(tri-tert-butylcyclopentadienyl)dysprosium(III) complexes by potassium/graphite in the presence of a crown ether afforded structurally characterized organodysprosium(II) ate complexes, a new class of divalent organolanthanide compounds. The organodysprosium(II) borohydride ate complex was oxidized by hexachloroethane into a structurally characterized organodysprosium(III) dichloride ate complex and was also shown to reductively couple diphenylacetylene

International audienceReaction of sodium 1,2,4-tris(trimethylsilyl)cyclopentadienide [Na(Cp' '')] with [TmI2(THF)3] afforded the divalent thulium complex [(Cp' '')2Tm(THF)]. Its crystal structure is similar to that of the previously described [(Cpttt)2Tm(THF)] (Cpttt = 1,2,4-tris(tert-butyl)cyclopentadienyl). [(Cp' '')2TmI] was prepared by reaction of TmI3 with [K(Cp' '')] and could be reduced by KC8 into a new unsolvated, homoleptic complex, [(Cp' '')2Tm], which was characterized by NMR. [(Cp' '')2Tm] gave [(Cp' '')2Tm(THF)] by interaction with THF. A convenient alternative pathway to [(Cpttt)2Tm] by reduction of [(Cpttt)2Tm(BH4)] with KC8 was found: [(Cpttt)2Tm(BH4)] derives from [Tm(BH4)3(THF)3], which can be prepared from the less expensive TmCl3. On the other hand, the dimer [{(Cptt)2TmI}2] (Cptt = 1,3-bis(tert-butyl)cyclopentadienyl), obtained by reaction of TmI3 with [Na(Cptt)], gave only intractable results by reaction with KC8. The previously described TmII complex [(Dtp)2Tm] (Dtp = 2,5-di-tert-butyl-3,4-dimethylphospholyl) and the new, homoleptic, structurally characterized TmII dimer [{(Htp)2Tm}2] (Htp = 2,5-di-tert-butylphospholyl) were prepared by KC8 reduction of [(Dtp)2TmI] and [{(Htp)2TmI}2], respectively. Reaction of [(Cpttt)2Tm] with pyridine resulted in an immediate reduction of pyridine into 1,1'-bis(1,4-dihydropyridylamide) and the formation of the structurally characterized [{(Cpttt)2Tm}2{-(NC5H5-C5H5N)}], while the reaction of [(Dtp)2Tm] with pyridine gave no isolable complexes. An NMR study suggests that initially a simple TmII adduct such as [(Dtp)2Tm(pyridine)] is formed in this reaction

The redox-transmetalation ligand-exchange reaction of ytterbium or calcium metal with 2 equiv of pentaphenylcyclopentadiene (C5Ph5H) and 1 equiv of HgPh2 in thf afforded the solvent-separated ion pairs (SSIPs) [M(thf)6][C5Ph5]2 (M = Yb, Ca), which were characterized by single-crystal X-ray analyses. Addition of toluene to the isolated SSIPs led to the precipitation of the homoleptic sandwich complexes [M(C5Ph5)2] (M = Yb, Ca). In the reaction of barium metal with C5Ph5H and HgPh2 the corresponding SSIP was observed in situ, and only the sandwich complex [Ba(C5Ph5)2] could be isolated. Single-crystal X-ray analyses were carried out for [M(C5Ph5)2] (M = Yb, Ba), which confirmed the highly symmetric structure of these complexes with two parallel cyclopentadienyl ligands. Oxidation and metal-ligand exchange reactions were investigated for the divalent ytterbium complexes.

New samarium carbene complexes have been synthesized and characterized by X-ray diffraction analysis; the carbenic nature was assessed by reactivity studies.

The new stable, neutral Tm(II) complex (Cp(ttt))2Tm [Cp(ttt) = 1,2,4-tris(tert-butyl)cyclopentadienyl] can be obtained either by direct reaction of NaCp(ttt) with TmI2 or by reduction of (Cp(ttt))2TmI in non-polar solvents; this latter route may prove itself useful for the isolation of other neutral non-classical low-valent organolanthanide species.

The introduction of a trifluoromethyl (CF ) group into an organic molecule can modify its chemical behavior and lead to changes in its physicochemical and pharmacological properties. The CF group is often chosen for its chemical inertness and stability, which are related to the strong C-F bonds. In recent years, the potential of gaining straightforward access to difluorinated compounds through selective single C-F activation in CF groups has been unveiled. This review describes the latest methodologies for the synthesis of difluoromethylated arenes, difluoroalkenes and difluorinated aldol products of potential synthetic and/or biological interest, employing low-valent metals, transition metal catalysis, FLP and Lewis acid mediated transformations as well as photoredox catalysis.