Lanthanides and actinides: Annual survey of their organometallic chemistry covering the year 2016

Abstract

This review summarizes the progress in organo-f-element chemistry during the year 2016. In some ways, the organo-f-element chemistry published in 2016 differs from that of previous years. For example, gas-phase reactions of laser-vaporized lanthanide atoms with small unsaturated organic molecules have been the subject of several interesting experimental and theoretical studies. Various unstable homoleptic and heteroleptic gas-phase species have been generated that way and studied by spectroscopic methods. Notable in this area are e.g. the methylene derivative CH2CeF2, the ceracyclopropene Ce(C2H2), the perdeuterated yttrium phenyl cation [Y(C6D5)]+, and unusual scandium carbonyl complexes such as OScCO and OCScCO3. Remarkable divalent lanthanide alkyls and carbene complexes have also been described in 2016. A continuing trend for many years which continued into 2016 was the investigation of highly reactive lanthanide alkyl complexes supported by non-cyclopentadienyl ligands (e.g. amidinates, β-diketiminates etc.). Many of these complexes found useful applications in homogeneous catalysis. Interesting reactivities have been reported e.g. for the first non-pincer-type mononuclear scandium alkylidene complexes and a series of mixed methyl/methylidene trinuclear rare-earth metal complexes. The isolation, structure and reactivity of a unique scandium boryl oxycarbene complex as well as the first molecular polyarsenides of the rare-earth elements have also been reported. Several examples of macrocyclic compounds (“giant lanthanide wheels”) have been prepared with the use of specially designed N-chelating ligands. New chemistry has been developed around “samarocene oxide”, Cp∗2Sm-O-Cp∗2 (Cp∗=pentamethylcyclopentadienyl) which is generally considered as an undesired decomposition product of the highly air-sensitive divalent samarocene Cp∗2Sm(THF)2, and novel 1,1′-diphospaplumbocenes have been synthesized and subsequently employed as phospholyl ligand transfer reagents in organothulium chemistry. Synthesis and derivative chemistry of an Yb(II) triple-decker complex with the μ-bridging naphthalene dianion have been investigated, including in formation of an unusual trinuclear Yb(II) complex with a μ-bridging P73− ligand. The cyclooctatetraenyl dianion (COT) continued to be a versatile building block for the synthesis of new half-sandwich, sandwich, and inverse sandwich complexes. Significant progress has also been made in the field of endohedral metallofullerenes, including the synthesis and characterization of an unusual non-isolated pentagon rule metallic carbide clusterfullerene containing a seven-membered ring, Sc2C2@Cs(hept)-C88. In the field of heterometallic organolanthanide complexes, novel inclusion complexes of the composition (Cp∗2Yb)2(Cp2M) (Cp=cyclopentadienyl; M=V, Cr, Fe, and Co) have been isolated in the solid state. Once again, an impressive number of interesting contributions have been published in 2016 in the field of organolanthanide catalysis, with an emphasis on Ln-catalyzed olefin and diene polymerization. Unusual new Ln-catalyzed reactions included, among others, the simultaneous chain-growth and step-growth polymerization of meta- and para-methoxystyrene, the production of Si–H-containing syndiotactic polystyrene by the direct polymerization of 4-vinylphenyldimethylsilane, the formation of poly(2-vinylpyridine) with highly isotactic and high-molecular-weight characteristics, and the C–H polyaddition of dimethoxyarenes to unconjugated dienes such as norbornadiene and 1,4-divinylbenzene. Moreover, the efficient and selective Ln-catalyzed ortho-alkylation of tertiary amines via C–H addition to alkenes has been achieved for the first time. In organoactinide chemistry, new homoleptic uranium(III) and thorium(IV) alkyl and aryl complexes have been synthesized and established as potential starting materials in organoactinide chemistry. These include e.g. U[η4-Me2NC(H)C6H5]3 and [Li(DME)3]2[Th(C6H5)6]. Novel uranium(IV)–carbene–imido complexes and a uranium(IV)-carbene-imido-amide metalla-allene have also been reported in 2016, and the chemistry of new molecular complexes of U2+ has been further developed. The thorium(III) complex Cp″3Th (Cp″=C5H3(SiMe3)2-1,3) has been reported to reacts with P4 to give (μ-η1:η1-P4)[Cp″3Th]2, which has an unprecedented cyclo-P4 binding mode. Moreover, various new and unusual transformations have been achieved using the Cp∗2Th platform, including the chemistry of the metallacyclopropene Cp∗2U[η2-C2(SiMe3)2], the generation of new phospha- and arsaazaallene thorium metallocenes, and the synthesis of the first thorium–copper heterobimetallic compounds. With the use of bulky cyclooctatetraenyl ligands, the synthesis and characterisation of novel U(V) oxo and nitrido complexes has been achieved.