The semiquinone radical anion of 1,10-phenanthroline-5,6-dione: synthesis and rare earth coordination chemistry

Reduction of 1,10-phenanthroline-5,6-dione (pd) with CoCpR2 resulted in the first molecular compounds of the pd˙− semi-quinone radical anion, [CoCpR2]+[pd]˙− (R = H, (1); R = Me4, (2)). Furthermore compounds 1 and 2 were reacted with [Y(hfac)3(thf)2] (hfac = 1,1,1-5,5,5-hexafluoroacetylacetonate) to synthesise the rare earth-transition metal heterometallic compounds, [CoCpR2]+[Y(hfac)3(N,N′-pd)]˙− (R = H, (3); R = Me4, (4))

Uranium(III) coordination chemistry and oxidation in a flexible small-cavity macrocycle

U(III) complexes of the conformationally flexible, small-cavity macrocycle trans-calix[2]benzene[2]pyrrolide (L)2–, [U(L)X] (X = O-2,6-tBu2C6H3, N(SiMe3)2), have been synthesized from [U(L)BH4] and structurally characterized. These complexes show binding of the U(III) center in the bis(arene) pocket of the macrocycle, which flexes to accommodate the increase in the steric bulk of X, resulting in long U–X bonds to the ancillary ligands. Oxidation to the cationic U(IV) complex [U(L)X][B(C6F5)4] (X = BH4) results in ligand rearrangement to bind the smaller, harder cation in the bis(pyrrolide) pocket, in a conformation that has not been previously observed for (L)2–, with X located between the two ligand arene rings

Reduction chemistry yields stable and soluble divalent lanthanide tris(pyrazolyl)borate complexes †

Reduction of the heteroleptic Ln(iii) precursors [Ln(Tp)2(OTf)] (Tp = hydrotris(1-pyrazolyl)borate; OTf = triflate) with either an aluminyl(i) anion or KC8 yielded the adduct-free homoleptic Ln(ii) complexes dimeric 1-Eu [{Eu(Tp)(μ-κ1:η5-Tp)}2] and monomeric 1-Yb [Yb(Tp)2]. Complexes 1-Ln have good solubility and stability in both non-coordinating and coordinating solvents. Reaction of 1-Ln with 2 Ph3PO yielded 1-Ln(OPPh3)2. All complexes are intensely coloured and 1-Eu is photoluminescent. The electronic absorption data show the 4f–5d electronic transitions in Ln(ii). Single-crystal X-ray diffraction data reveal first μ-κ1:η5-coordination mode of the unsubstituted Tp ligand to lanthanides in 1-Eu

New chemistry from an old reagent:Mono- and dinuclear macrocyclic uranium(III) complexes from [U(BH₄)₃(THF)₂]

A new robust and high-yielding synthesis of the valuable UIII synthon [U(BH4)3(THF)2] is reported. Reactivity in ligand exchange reactions is found to contrast significantly to that of uranium triiodide. This is exemplified by the synthesis and characterization of azamacrocyclic UIII complexes, including mononuclear [U(BH4)(L)] and dinuclear [Li(THF)4][{U(BH4)}2(μ-BH4)(LMe)] and [Na(THF)4][{U(BH4)}2(μ-BH4)(LA)(THF)2]. The structures of all complexes have been determined by single-crystal X-ray diffraction and display two new UIII2(BH4)3 motifs

Heteroleptic lanthanide(III) complexes: synthetic utility and versatility of the unsubstituted bis-scorpionate ligand framework

The unsubstituted bis-hydrotris(1-pyrazolyl)borate) (Tp) ligand framework has been used to synthesise a range of heteroleptic Ln(III) coordination complexes [Ln(Tp)2(X)]. The precursor complexes [Ln(Tp)2(OTf)] 1-Ln (Ln = Y, Eu, Gd, Yb; OTf = triflate) were synthesised by reaction of Ln(OTf)3 with two equivalents of K(Tp). The 8-coordinate β-diketonate complexes [Ln(Tp)2(hfac)] 2-Ln (Ln = Y, Eu, Yb; hfac = hexafluoroacetylacetonate) were synthesised from Ln(OTf)3 by reacting 1-Ln generated in situ with an equivalent of K(hfac). The 7-coordinate amide complexes [Ln(Tp)2(N″)] 3-Ln (Ln = Y, Yb; N″ = bis(trimethylsilyl)amide) were synthesised from 1-Ln by reaction with K(N″). Reactivity of 3-Ln towards protonolysis was demonstrated by the isolation of the hydroxide dimer [{Y(Tp)2(μ-OH)}2] 4-Y from adventitious reaction with water and the aryloxide complex [Ln(Tp)2(OAr)] 5-Ln (Ln = Y, Yb; OAr = 2,6-tBu2-4-Me-phenoxide) from reaction with H(OAr). Full characterisation data are presented for all complexes, including solid-state molecular structure determination by single-crystal X-ray diffraction

Buta- and penta-dienyl complexes of the actinides

This chapter covers the synthesis, structure and bonding, and reactivity of actinide complexes of buta-, and penta-dienyl ligands. First, the small number of homoleptic, and non-cyclopentadienyl heteroleptic hydrocarbyl actinide complexes are presented in brief. This is followed by an overview of the synthesis and reactivity of heteroleptic hydrocarbyl actinide complexes in a tris-cyclopentadienyl and bis-permethylcyclopentadienyl ancillary ligand environment. The bulk of this chapter then provides comprehensive coverage of actinide complexes with composite four-carbon ligands. First, actinide complexes containing acyclic 2-butene-1,4-diyl and 1,3-butadiene-1,4-diyl ligands. Second, the planar five-membered metallacyclic complexes, actinacyclopentadienes, actinacyclopentatrienes, and an actinacyclopentyne. The actinacyclic complexes display significant differences in bonding and reactivity depending on the level of ligand unsaturation. Third, recent developments in complexes of the cyclobutadienyl dianion are reported. Finally, a conclusion provides a summary and an outlook on future work

Expanding yttrium Bis(trimethylsilylamide) chemistry through the reaction chemistry of (N2)2–, (N2)3–, and (NO)2–complexes

The reaction chemistry of the side-on bound (N2)2–, (N2)3–, and (NO)2– complexes of the [(R2N)2Y]+ cation (R = SiMe3), namely, [(R2N)2(THF)Y]2(μ-η2:η2-N2), 1, [(R2N)2(THF)Y]2(μ-η2:η2-N2)K, 2, and [(R2N)2(THF)Y]2(μ-η2:η2-NO), 3, with oxidizing agents has been explored to search for other (E2)n−, (E = N, O), species that can be stabilized by this cation. This has led to the first examples for the [(R2N)2Y]+ cation of two fundamental classes of [(monoanion)2Ln]+ rare earth systems (Ln = Sc, Y, lanthanides), namely, oxide complexes and the tetraphenylborate salt. In addition, an unusually high yield reaction with dioxygen was found to give a peroxide complex that completes the (N2)2–, (NO)2–, (O2)2– series with 1 and 3. Specifically, the (μ-O)2– oxide-bridged bimetallic complex, [(R2N)2(THF)Y}2(μ-O), 4, is obtained as a byproduct from reactions of either the (N2)2– complex, 1, or the (N2)3– complex, 2, with NO, while the oxide formed from 2 with N2O is a polymeric species incorporating potassium, {[(R2N)2Y]2(μ-O)2K2(μ-C7H8)}n, 5. Reaction of 1 with 1 atm of O2 generates the (O2)2– bridging side-on peroxide [(R2N)2(THF)Y]2(μ-η2:η2-O2), 6. The O–O bond in 6 is cleaved by KC8 to provide an alternative synthetic route to 5. Attempts to oxidize the (NO)2– complex, 3, with AgBPh4 led to the isolation of the tetraphenylborate complex, [(R2N)2Y(THF)3][BPh4], 7, that was also synthesized from 1 and AgBPh4. Oxidation of the (N2)2– complex, 1, with the radical trap (2,2,6,6-tetramethylpiperidin-1-yl)oxyl, TEMPO, generates the (TEMPO)− anion complex, (R2N)2(THF)Y(η2-ONC5H6Me4), 8

Lanthanides and actinides: Annual survey of their organometallic chemistry covering the year 2019

This review summarizes the progress in organo-f-element chemistry during the year 2019. Organo-f-element chemistry, including Sc, Y, the lanthanides and the actinides, has been a flourishing research area for many years. The mainly ionic and Lewis acid character of the lanthanide metals provides a vast array of intriguing structural features supported by numerous organic ligands. In this year’s edition several new types of complexes are presented, including the first scandacyclopropene complex [Cp*(BuC(NiPr)2)Sc(η2-PhCCPh)][K(crypt)] displaying an aromatic metallacycle, the first lanthanide-aluminabenzene complexes [(1-Me-3,5-tBu2-C5H3Al)(μ-Me)Ln(2,4-di-tbutylpentadienyl)] (Ln = Y, Lu) and the first scandium phosphonioketene complex [LSc(η2-COCHPPh3)I] (L = [MeC(NDIPP)CHC(NDIPP)Me−], which all showed interesting reactivities. Furthermore, a wide range of lanthanide alkyl complexes were synthesized and structurally 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 the first neutral divalent Dy and Tb sandwich complexes, Ln(C5iPr5)2, which were investigated for their magnetic properties. The reactivity of divalent metallocenes towards transition metals precursors or As0 provided unprecedented multimetallic complexes, for example [(Cp*2Sm)4As8], [{(Cp*)2Sm}3{(μ-O4C4)(μ-η2-CO)2(μ-η1-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, such as the direct dinitrogen to hydrazine conversion using a low-valent Sc complex or the reduction of CS2 using different divalent Yb complexes affording for the first time a CS22− bridging unit as shown in the complex [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 involving polar or non-polar monomers were reported, including efficient and stereoselective polymerization of o-methoxystyrene, vinylpyridine or isoprene. The regio-, diastereoselective and stereoregular cyclopolymerization of different ether and thioether substituted 1,6-heptadienes was reported. A wide range of hydrofunctionalization reactions were developed, among them an efficient hydrophosphinylation process of styrenes and alkynes. It was further shown that alkyllanthanide halides could undergo efficient halogen/lanthanide exchange with arylhalides and vinylhalides providing useful organolanthanide transfer reagents, for example in the stereoselective Zweifel olefination. Organolanthanide complexes have also found new applications in material sciences, for example, Ce(C5H4iPr)3 was employed for the formation of an ultrathin CeO2 overlayer on a Pt electrode via atomic layer deposition to improve low-temperature solid 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 unusual cages, as well as dimetalfullerenes with interesting single molecular magnet (SMM) properties and new insights on direct Ln-Ln bonds. Hydrocarbyl complexes of the actinides continued to flourish, in spite of the challenges presented by synthesis and characterization. The first examples of structurally-characterized uranium(IV) homoleptic aryl complexes and transuranic hydrocarbyl Np(III) complex have been reported. An experimental and computational study has demonstrated that f-orbitals have a structure-directing role in overlap-driven covalency in carbene-stabilised metalla-allene complexes and 13C NMR shift has be shown to be a simple and direct probe of the actinide-carbon bond covalency in the acetylides. Small molecule activation chemistry has provided some unusual and important results, including a uranium(V) carbene complex coordinated 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 resulted from actinide main group chemistry, with reports of the first examples of terminal η1-cyaarside ligands (Ctriple bondAs−), bridging diarsaallene (As = C = As)2− and trapped radical dianion of the phosphoethynolate (OCP2−radical dot) ligand. The bis-CptBu2 metallocene stablised thorium phosphinidene continued to demonstrate a 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 inverse sandwich complex was reported, both experimental and computation data are consistent with atypical Cp-bonding, with electron density redistributed from Re(I) to U(III). Isopropyl substituted cyclopentadienyl ligands have enabled the synthesis, reactivity and magnetic properties of U(III) metallocenes, including base-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 the organoamericium(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 complex with 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 distinct properties of actinide EMFs was the subject of some debate. Thorium complexes have found application in catalysis, in the selective dihydroboration of nitriles, the hydroboration of imines and polymerization of isoprene

Expanding Yttrium Bis(trimethylsilylamide) Chemistry Through the Reaction Chemistry of (N₂)^2–, (N₂)^3–, and (NO)^2– Complexes

The reaction chemistry of the side-on bound (N₂)^2–, (N₂)^3–, and (NO)^2– complexes of the [(R₂N)₂Y]⁺ cation (R = SiMe₃), namely, [(R₂N)₂(THF)­Y]₂(<i>μ</i>-η²:η²-N₂), <b>1</b>, [(R₂N)₂(THF)­Y]₂(<i>μ</i>-η²:η²-N₂)­K, <b>2</b>, and [(R₂N)₂(THF)­Y]₂(<i>μ</i>-η²:η²-NO), <b>3</b>, with oxidizing agents has been explored to search for other (E₂)^<i>n</i>−, (E = N, O), species that can be stabilized by this cation. This has led to the first examples for the [(R₂N)₂Y]⁺ cation of two fundamental classes of [(monoanion)₂Ln]⁺ rare earth systems (Ln = Sc, Y, lanthanides), namely, oxide complexes and the tetraphenylborate salt. In addition, an unusually high yield reaction with dioxygen was found to give a peroxide complex that completes the (N₂)^2–, (NO)^2–, (O₂)^2– series with <b>1</b> and <b>3</b>. Specifically, the (<i><i>μ</i>-</i>O)^2– oxide-bridged bimetallic complex, [(R₂N)₂(THF)­Y}₂(<i><i>μ</i>-</i>O), <b>4</b>, is obtained as a byproduct from reactions of either the (N₂)^2– complex, <b>1</b>, or the (N₂)^3– complex, <b>2</b>, with NO, while the oxide formed from <b>2</b> with N₂O is a polymeric species incorporating potassium, {[(R₂N)₂Y]₂(<i><i>μ</i>-</i>O)₂K₂(<i><i>μ</i>-</i>C₇H₈)}_<i>n</i>, <b>5</b>. Reaction of <b>1</b> with 1 atm of O₂ generates the (O₂)^2– bridging side-on peroxide [(R₂N)₂(THF)­Y]₂(<i>μ</i>-η²:η²-O₂), <b>6</b>. The O–O bond in <b>6</b> is cleaved by KC₈ to provide an alternative synthetic route to <b>5</b>. Attempts to oxidize the (NO)^2– complex, <b>3</b>, with AgBPh₄ led to the isolation of the tetraphenylborate complex, [(R₂N)₂Y­(THF)₃]­[BPh₄], <b>7</b>, that was also synthesized from <b>1</b> and AgBPh₄. Oxidation of the (N₂)^2– complex, <b>1</b>, with the radical trap (2,2,6,6-tetramethylpiperidin-1-yl)­oxyl, TEMPO, generates the (TEMPO)⁻ anion complex, (R₂N)₂(THF)­Y­(η²-ONC₅H₆Me₄), <b>8</b>