Abstract
This review summarizes the progress in organo-f-element chemistry during the year 2019. Organo-felementchemistry, including Sc, Y, the lanthanides and the actinides, has been a flourishing research areafor many years. The mainly ionic and Lewis acid character of the lanthanide metals provides a vast arrayof intriguing structural features supported by numerous organic ligands. In this year’s edition several newtypes of complexes are presented, including the first scandacyclopropene complex [Cp*(BuC(NiPr)2)Sc(g2-PhCCPh)][K(crypt)] displaying an aromatic metallacycle, the first lanthanide-aluminabenzene complexes[(1-Me-3,5-tBu2-C5H3Al)(l-Me)Ln(2,4-di-tbutylpentadienyl)] (Ln = Y, Lu) and the first scandiumphosphonioketene complex [LSc(g2-COCHPPh3)I] (L = [MeC(NDIPP)CHC(NDIPP)Me], which all showedinteresting reactivities. Furthermore, a wide range of lanthanide alkyl complexes were synthesized andstructurally characterized, including the first isolated ScMe3 derivatives [Sc(AlMe4)3(Al2Me6)0.5] and[(Me3TACN)ScMe3]. A very important finding in divalent lanthanide chemistry was the synthesis of thefirst neutral divalent Dy and Tb sandwich complexes, Ln(C5iPr5)2, which were investigated for theirmagnetic properties. The reactivity of divalent metallocenes towards transition metals precursors orAs0 provided unprecedented multimetallic complexes, for example [(Cp*2Sm)4As8], [{(Cp*)2Sm}3{(l-O4C4)(l-g2-CO)2(l-g1-CO)(CO)5Re2}SmCp*2(thf)] and [Cp*2Yb(taphen)MMe2YbCp*2] (M = Ni, Pt;taphen = 4,5,9,10-tetraazaphenanthrene). New reactivity of lanthanide complexes was unveiled, suchas the direct dinitrogen to hydrazine conversion using a low-valent Sc complex or the reduction of CS2using different divalent Yb complexes affording for the first time a CS2 2 bridging unit as shown in thecomplex [Yb2(DippForm)4(CS2)] or an intriguing acetylendithiolate bridged Yb(III) complex Yb2L4(C2S2)(L = (OtBu)3SiO). Numerous new lanthanide catalyzed homo- and co-polymerization processes involvingpolar or non-polar monomers were reported, including efficient and stereoselective polymerization of omethoxystyrene,vinylpyridine or isoprene. The regio-, diastereoselective and stereoregular cyclopolymerizationof different ether and thioether substituted 1,6-heptadienes was reported. A wide range ofhydrofunctionalization reactions were developed, among them an efficient hydrophosphinylation processof styrenes and alkynes. It was further shown that alkyllanthanide halides could undergo efficienthalogen/lanthanide exchange with arylhalides and vinylhalides providing useful organolanthanide transferreagents, for example in the stereoselective Zweifel olefination. Organolanthanide complexes havealso found new applications in material sciences, for example, Ce(C5H4iPr)3 was employed for theformation of an ultrathin CeO2 overlayer on a Pt electrode via atomic layer deposition to improve lowtemperaturesolid oxide fuel cells. An increasingly studied field is the area of endohedral metallafullerenes(EMF) which gave rise to a large number of unprecedented lanthanide compounds with unusualcages, as well as dimetalfullerenes with interesting single molecular magnet (SMM) properties andnew insights on direct Ln-Ln bonds.Hydrocarbyl complexes of the actinides continued to flourish, in spite of the challenges presented bysynthesis and characterization. The first examples of structurally-characterized uranium(IV) homolepticaryl complexes and transuranic hydrocarbyl Np(III) complex have been reported. An experimental andcomputational study has demonstrated that f-orbitals have a structure-directing role in overlap-drivencovalency in carbene-stabilised metalla-allene complexes and 13C NMR shift has be shown to be a simpleand direct probe of the actinide-carbon bond covalency in the acetylides. Small molecule activationchemistry has provided some unusual and important results, including a uranium(V) carbene complexcoordinated end-on to dinitrogen and a stable dinuclear U(IV) dihydride complex which reacted with CO2 and CO/H2 to form methoxide and ultimately methanol. New ligands and binding modes resultedfrom actinide main group chemistry, with reports of the first examples of terminal g1-cyaarside ligands(C„As), bridging diarsaallene (As = C = As)2 and trapped radical dianion of the phosphoethynolate(OCP2) ligand. The bis-CptBu2 metallocene stablised thorium phosphinidene continued to demonstratea wealth small molecule reactivity, including reductive coupling, heterocycle formation and E–H(E = P, N, C) bond activation. Two examples of U(II) complexes are reported, [K(crypt)][(C5Me4H)3U]and [K(crypt)][U(NR2)3] (R = SiMe3). The first direct assembly of a uranium tri-rhenium triple inversesandwich complex was reported, both experimental and computation data are consistent with atypicalCp-bonding, with electron density redistributed from Re(I) to U(III). Isopropyl substituted cyclopentadienylligands have enabled the synthesis, reactivity and magnetic properties of U(III) metallocenes, includingbase-free cationic species. The first example of a monomeric thorium terminal dihyrido compound(CpAr5)(Cp*)ThH2(THF) (Ar = 3,5-tBu2-C6H3) has been synthesized. The full characterisation of theorganoamericium(III) compound (C5Me4H)3Am provided a unique insight into Am-C bonding. The Th(IV)/Th(III) redox couple has been experimentally determined for a range of Th(IV) and Th(III) organometallics.The first uranium phosphaazaallene has been synthesized by reaction of a bis-phosphide complexwith tert-butyl cyanide. Actinide EMFs continued to be an active area of research; molecular structures,synthetic and purification methodologies are reported. How best to computationally model the distinctproperties of actinide EMFs was the subject of some debate. Thorium complexes have found applicationin catalysis, in the selective dihydroboration of nitriles, the hydroboration of imines and polymerizationof isoprene.