Rare Earths-The Answer to Everything.

Rare earths, scandium, yttrium, and the fifteen lanthanoids from lanthanum to lutetium, are classified as critical metals because of their ubiquity in daily life. They are present in magnets in cars, especially electric cars; green electricity generating systems and computers; in steel manufacturing; in glass and light emission materials especially for safety lighting and lasers; in exhaust emission catalysts and supports; catalysts in artificial rubber production; in agriculture and animal husbandry; in health and especially cancer diagnosis and treatment; and in a variety of materials and electronic products essential to modern living. They have the potential to replace toxic chromates for corrosion inhibition, in magnetic refrigeration, a variety of new materials, and their role in agriculture may expand. This review examines their role in sustainability, the environment, recycling, corrosion inhibition, crop production, animal feedstocks, catalysis, health, and materials, as well as considering future uses.

Design and Advanced Manufacturing of NU-1000 Metal-Organic Frameworks with Future Perspectives for Environmental and Renewable Energy Applications.

Metal-organic frameworks (MOFs) represent a relatively new family of materials that attract lots of attention thanks to their unique features such as hierarchical porosity, active metal centers, versatility of linkers/metal nodes, and large surface area. Among the extended list of MOFs, Zr-based-MOFs demonstrate comparably superior chemical and thermal stabilities, making them ideal candidates for energy and environmental applications. As a Zr-MOF, NU-1000 is first synthesized at Northwestern University. A comprehensive review of various approaches to the synthesis of NU-1000 MOFs for obtaining unique surface properties (e.g., diverse surface morphologies, large surface area, and particular pore size distribution) and their applications in the catalysis (electro-, and photo-catalysis), CO2 reduction, batteries, hydrogen storage, gas storage/separation, and other environmental fields are presented. The review further outlines the current challenges in the development of NU-1000 MOFs and their derivatives in practical applications, revealing areas for future investigation.

Oxidation of the Platinum(II) Anticancer Agent [Pt{(p-BrC6F4)NCH2CH2NEt2}Cl(py)] to Platinum(IV) Complexes by Hydrogen Peroxide.

PtIV coordination complexes are of interest as prodrugs of PtII anticancer agents, as they can avoid deactivation pathways owing to their inert nature. Here, we report the oxidation of the antitumor agent [PtII(p-BrC6F4)NCH2CH2NEt2}Cl(py)], 1 (py = pyridine) to dihydroxidoplatinum(IV) solvate complexes [PtIV{(p-BrC6F4)NCH2CH2NEt2}Cl(OH)2(py)].H2O, 2·H2O with hydrogen peroxide (H2O2) at room temperature. To optimize the yield, 1 was oxidized in the presence of added lithium chloride with H2O2 in a 1:2 ratio of Pt: H2O2, in CH2Cl2 producing complex 2·H2O in higher yields in both gold and red forms. Despite the color difference, red and yellow 2·H2O have the same structure as determined by single-crystal and X-ray powder diffraction, namely, an octahedral ligand array with a chelating organoamide, pyridine and chloride ligands in the equatorial plane, and axial hydroxido ligands. When tetrabutylammonium chloride was used as a chloride source, in CH2Cl2, another solvate, [PtIV{(p-BrC6F4)NCH2CH2NEt2}Cl(OH)2(py)].0.5CH2Cl2,3·0.5CH2Cl2, was obtained. These PtIV compounds show reductive dehydration into PtII [Pt{(p-BrC6F4)NCH=CHNEt2}Cl(py)], 1H over time in the solid state, as determined by X-ray powder diffraction, and in solution, as determined by 1H and 19F NMR spectroscopy and mass spectrometry. 1H contains an oxidized coordinating ligand and was previously obtained by oxidation of 1 under more vigorous conditions. Experimental data suggest that oxidation of the ligand is favored in the presence of excess H2O2 and elevated temperatures. In contrast, a smaller amount (1Pt:2H2O2) of H2O2 at room temperature favors the oxidation of the metal and yields platinum(IV) complexes.

Syntheses, Structures, and Corrosion Inhibition of Various Alkali Metal Carboxylate Complexes.

Complexes of the alkali metals Li-Cs with 3-thiophenecarboxylate (3tpc), 2-methyl-3-furoate (2m3fur), 3-furoate (3fur), 4-hydroxycinnamate (4hocin), and 4-hydroxybenzoate (4hob) ions were prepared via neutralisation reactions, and the structures of [Li2(3tpc)2]n (1Li); [K2(3tpc)2]n (1K); [Rb(3tpc)(H2O)]n (1Rb); [Cs{H(3tpc)2}]n (1Cs); [Li2(2m3fur)2(H2O)3] (2Li); [K2(2m3fur)2(H2O)]n (2K); [Li(3fur)]n(3Li); [K(4hocin](H2O)3]n (4K); [Rb{H(4hocin)2}]n.nH2O (4Rb); [Cs(4hocin)(H2O)]n (4Cs); [Li(4hob)]n (5Li); [K(4hob)(H2O)3]n (5K); [Rb(4hob)(H2O)]n (5Rb); and [Cs(4hob)(H2O)]n (5Cs) were determined via X-ray crystallography. Bulk products were also characterised via XPD, IR, and TGA measurements. No sodium derivatives could be obtained as crystallographically suitable single crystals. All were obtained as coordination polymers with a wide variety of carboxylate-binding modes, except for dinuclear 2Li. Under conditions that normally gave coordinated carboxylate ions, the ligation of hydrogen dicarboxylate ions was observed in 1Cs and 4Rb, with short H-bonds and short O…O distances associated with the acidic hydrogen. The alkali-metal carboxylates showed corrosion inhibitor properties inferior to those of the corresponding rare-earth carboxylates.

Divalent ansa-Octaphenyllanthanocenes: Synthesis, Structures, and EuII Luminescence.

Reductive dimerization of fulvenes using low-valent metal precursors is a straightforward one-step approach to access ethylene-bridged metallocenes. This process has so far mainly been employed with fulvenes carrying one or two substituents in the exocyclic position. In this work, a new synthesis of the unsubstituted exocyclic 1,2,3,4-tetraphenylfulvene (1), its full structural characterization by NMR spectroscopy and single-crystal X-ray diffraction, as well as some photophysical properties and its first use in reductive dimerization are described. This fulvene reacted with different lanthanoid metals in thf to provide the divalent ansa-octaphenylmetallocenes [Ln(C5Ph4CH2)2(thf)n] (Ln = Sm, n = 2 (2); Ln = Eu, n = 2 (3); and Ln = Yb, n = 1 (4)). These complexes were characterized by X-ray diffraction, laser desorption/ionization time of flight mass spectrometry, and, in the case of Sm and Yb, multinuclear NMR spectroscopy, showing the influence of the ansa-bridge on solution and solid-state structures compared to previously reported unbridged metallocenes. Furthermore, the luminescence properties of the Eu ansa complex 3 were studied in solution and the solid state, revealing significant differences with the known octa- and deca-phenyleuropocenes, [Eu(C5Ph4H)2(dme)] and [Eu(C5Ph5)2].

Direct Reaction - One Step Route to Synthesize Lanthanoid-iodide Formamidinates.

This paper describes a novel and simple method - direct reaction of lanthanoid metals with equimolar amounts of iodine and a formamidine under ultrasonication as an effective, metal-based route to lanthanoid(III) diiodide formamidinates, namely I. N,N'-Bis(2,6-diisopropylphenyl)formamidinatodiiodidolanthanoid(III) complexes [Ln(DippForm)I2 (thf)3 ] (Ln=La, 1, Ce, 2, Tb, 3, Ho, 4, Er, 5, Tm, 6); II. N,N'-Bis(2,6-diethylphenyl)formamidinatodiiodidolanthanoid(III) complexes [Ln(EtForm)I2 (thf)3 ] (Ln=Ce, 7, Nd, 8, Gd, 9, Tb, 10, Dy, 11, Ho, 12, Er, 13, Lu, 14). III. N,N'-bis(2,6-dimethylphenyl)formamidinatodiiodidolanthanoid(III) complexes [Ln(XylForm)I2 (thf)3 ] (Ln=Ce, 15, Nd, 16, Gd, 17, Tm, 18, Lu 19); IV. N,N'-bis(phenyl)formamidinatodiiodidolanthanoid complexes [Ln(PhForm)I2 (thf)3 ] (Ln=Nd, 20, Gd, 21, Er, 22). Compound [Ce(XylForm)2 I(thf)2 ] (23) was also synthesized by the same method except the ratio of I2 to XylFormH was 1 : 4. Divalent N,N'-bis(2,6-diisopropylphenyl)formamidinato-iodido-lanthanoid(II) complexes [Eu(DippForm)I(thf)4 ] ⋅ thf (24), [Yb(DippForm)I(thf)3 ] ⋅ 2DippFormH (25), [Sm(DippForm)I(thf)4 ] ⋅ thf (26) have also been synthesized by direct reactions of the free metals, iodine and DippFormH. Interestingly, [Sm(DippForm)I2 (thf)3 ] (27) was obtained by the oxidation of [Sm(DippForm)I(thf)4 ] ⋅ thf (26) on exposure to air. N,N'-Bis(2,6-dimethylphenyl)formamidinatoiodidosamarium(II) [Sm(XylForm)I(thf)3 ]n (28) was also prepared by direct reaction of Sm, iodine and XylFormH (mole ratio of I2 : XylFormH=1 : 2). All products have been identified by X-ray crystallography and all the trivalent complexes [Ln(Form)n I3-n ] (n=1 or 2) are stable to rearrangement.

Pushing the Boundary of Covalency in Lanthanoid-Tellurium Bonds: Insights from the Synthesis, Molecular and Electronic Structures of Low-Coordinate, Monomeric Europium(II) and Ytterbium(II) Tellurolates.

Owing to the strict hard/soft dichotomy between the lanthanoids and tellurium atoms, and the strong affinity of lanthanoid ions for high coordination numbers, low-coordinate, monomeric lanthanoid tellurolate complexes have remained elusive as compared to the lanthanoid complexes with lighter group 16 elements (O, S, and Se). This makes the development of suitable ligand systems for low-coordinate, monomeric lanthanoid tellurolate complexes an appealing endeavor. In a first report, a series of low-coordinate, monomeric lanthanoid (Yb, Eu) tellurolate complexes were synthesized by utilizing hybrid organotellurolate ligands containing N-donor pendant arms. The reaction of bis[2-((dimethylamino)methyl)phenyl] ditelluride, 1 and 8,8'diquinolinyl ditelluride, 2 with Ln0 metals (Ln=Eu, Yb) resulted in the formation of monomeric complexes [LnII (TeR)2 (Solv)2 ] [R=C6 H4 -2-CH2 NMe2 ] [3: Ln=Eu, Solv=tetrahydrofuran; 4: Ln=Eu, Solv=acetonitrile; 5: Ln=Yb, Solv=tetrahydrofuran; 6: Ln=Yb, Solv=pyridine] and [EuII (TeNC9 H6 )2 (Solv)n ] (7: Solv=tetrahydrofuran, n=3; 8: Solv=1,2-dimethoxyethane, n=2), respectively. Complexes 3-4 and 7-8 represent the first sets of examples of monomeric europium tellurolate complexes. The molecular structures of complexes 3-8 are validated by single-crystal X-ray diffraction studies. The electronic structures of these complexes were investigated using Density Functional Theory (DFT) calculations, which revealed appreciable covalency between the tellurolate ligands and lanthanoids.

Bromobenzene Transforms Lanthanoid Pseudo-Grignard Chemistry.

Divalent lanthanoid pseudo-Grignard reagents PhLnBr (Ln=Sm, Eu and Yb) can be easily prepared by the oxidative addition of bromobenzene (PhBr) to lanthanoid metals in tetrahydrofuran (THF). PhLnBr reacts with bulky N,N'-bis(2,6-di-isopropylphenyl)formamidine (DippFormH) to generate LnII complexes, namely [Ln(DippForm)Br(thf)3 ]2 ⋅6thf (1; Sm, 2; Eu), and [Yb(DippForm)Br(thf)2 ]2 ⋅2thf (3; Yb). Samarium and europium (in 1 and 2) are seven coordinate, whereas ytterbium (in 3) is six coordinate, and all are bromine-bridged dimers. When PhLnBr reacts with 3,5-diphenylpyrazole (Ph2 pzH), both divalent (5; [Eu(Ph2 pz)2 (thf)4 ]) and trivalent (4 a; [Sm(Ph2 pz)3 (thf)3 ]⋅3thf, 4 b; [Sm(Ph2 pz)3 (dme)2 ]⋅dme) complexes are obtained. In the monomeric compounds 4(a,b), samarium is nine coordinate but europium is eight coordinate in 5. The use of PhLnBr in this work transforms the outcomes from earlier reactions of PhLnI.

Never a dull moment with praseodymium metal.

Unexpectedly, a mixture of bismuth N,N'-bis(2,6-diisopropylphenyl)formamidinates in three different oxidation states namely, [BiI2(DippForm)2] (1), [BiII2(DippForm)2(C6F5)2] (2) and [BiIII(DippForm)2(C6F5)] (3), together with [Pr(DippForm)2F(thf)]·PhMe (4), [p-HC6F4DippForm]·0.5thf (5), and a ring-opened tetrahydrofuran [o-HC6F4O(CH2)4DippForm] (6) was obtained by the reaction of an excess of praseodymium metal with tris(pentafluorophenyl)bismuth, [Bi(C6F5)3]·0.5dioxane, and bulky N,N'-bis(2,6-diisopropylphenyl)formamidine (DippFormH) in tetrahydrofuran. Similar reactions between praseodymium metal, [Bi(C6F5)3]·0.5dioxane and 3,5-diphenylpyrazole (Ph2pzH), or 3,5-di-tert-butylpyrazole (tBu2pzH), yielded the paddlewheel dibismuthanes [BiII2(Ph2pz)4]·dioxane (7) and [BiII2(tBu2pz)4] (8) respectively.

Formation of a cyclooctatetraenylsamarium(III) inverse sandwich that ring-opens tetrahydrofuran.

Reductive trapping of the cyclooctatetraenyl dianion (COT2-) by treatment of [Sm(DippForm)2(thf)2] (DippFormH = N,N'-bis(2,6-diisopropylphenyl)formamidine; thf = tetrahydrofuran) with 1,3,5,7-cyclooctatetraene (C8H8) in toluene yields an inverse sandwich dinuclear complex [Sm2(DippForm)4(COT)] (1), but [Sm(DippForm)(COT)(thf)2] (2) and [Sm(DippForm)2(O-C4H8-DippForm)(thf)] (3) in thf, and 1 yields 2 and 3 on treatment with thf.

RE(III) 3-Furoate Complexes: Synthesis, Structure, and Corrosion Inhibiting Properties.

In this study, two types of Rare Earth (RE) 3-furoate complexes were synthesized by metathesis reactions between RE chlorides or nitrates and preformed sodium 3-furoate. Two different structural motifs were identified as Type 1RE and Type 2RE. The Type 1RE monometallic complexes form 2D polymeric networks with the composition [RE(3fur)3(H2O)2]n (1RE = 1La, 1Ce, 1Pr, 1Nd, 1Gd, 1Dy, 1Ho, 1Y; 3furH = 3-furoic acid) while Type 2RE bimetallic complexes form 3D polymeric systems [NaRE(3fur)4]n (2RE = 2Ho, 2Y, 2Er, 2Yb, 2Lu). The stoichiometric mole ratio used (RE: Na(3fur) = 1:3 or 1:4) in the metathesis reaction determines whether 1RE or 2RE (RE = Ho or Y) is formed, but 2RE (RE = Er, Yb, Lu) were obtained regardless of the ratio. The corrosion inhibition behaviour of the compounds has been examined using immersion studies and electrochemical measurements on AS1020 mild steel surfaces by a 0.01 M NaCl medium. Immersion test results revealed that [Y(3fur)3(H2O)2]n has the highest corrosion inhibition capability with 90% resistance after 168 h of immersion. Potentiodynamic polarisation (PP) measurements also indicate the dominant behaviour of the 1Y compound, and the PP curves show that these rare earth carboxylate compounds act predominantly as anodic inhibitors.

Efficient synthetic route to heterobimetallic trinuclear complexes [Ln-Mn-Ln] and their single molecule magnetic properties.

A series of mononuclear lanthanoidate complexes isolated as [Bu4N][Ln(QCl4)] 1Ln (QCl = 5-chloro-8-quinolinolate; Ln = Eu, Gd, Tb, Dy, Ho, and Er) have been prepared, characterised, and used as facile precursors to obtain a series of new heterobimetallic complexes as crystalline materials. Reaction of 1Ln with manganese nitrate forms [Ln2Mn(QCl)8] (2Ln, where Ln = Tb, Dy, Er and Yb) which have been structurally characterised in the cases of 2Tb and 2Yb. The heteroleptic trinuclear complex [Dy3(QCl)8Cl(OH2)], 3, has also been obtained. Compounds 1Dy, 1Tb, and 1Er display slow relaxation of magnetisation below 10K, particularly for the prolate Er3+ ion. These results also suggest that the positive effects of the change from mononuclear to trinuclear lanthanoid complexes enhance their single molecule magnetic (SMM) behaviour, as evidenced by the well resolved frequency dependent AC out-of-phase susceptibility maxima seen in the 2Ln systems, that have been analysed quantitatively. The synthesis used here provides a promising strategy in obtaining heterobimetallic complexes with quinolinolate ligands and also constructing efficient heterobimetallic SMMs.

Reinvestigation of Reactions of HgPh2 with Eu and Yb Metal and the Synthesis of a Europium(II) Bis(tetraphenylborate).

Europium bis(tetraphenylborate) [Eu(thf)7][BPh4]2⋅thf containing a fully solvated [Eu(thf)7]2+ cation, was synthesized by protolysis of "EuPh2" (from Eu and HgPh2) with Et3NHBPh4, and the structure was determined by single-crystal X-ray diffraction. Efforts to characterize the putative "Ph2Ln" (Ln = Eu, Yb) reagents led to the synthesis of a mixed-valence complex, [(thf)3YbII(µ-Ph)3YbIII(Ph)2(thf)]⋅2thf, resulting from the reaction of Yb metal with HgPh2 at a low temperature. This mixed-valence YbII/YbIII compound was studied by 171Yb-NMR spectroscopy and single-crystal X-ray diffraction, and the oxidation states of the Yb atoms were assigned.

Selective Oxidation of a Single Metal Site of Divalent Calix[4]pyrrolide Compounds [Ln2(N4Et8)(thf)4] (Ln = Sm or Eu), Giving Mixed Valent Lanthanoid(II/III) Complexes.

The samarium(II) calix[4]pyrrolide complex [Sm2(N4Et8)(thf)4] (N4Et8 = meso-octaethylcalix[4]pyrrolide) undergoes selective oxidation of one SmII site on reaction with a range of metal carbonyls giving mixed valence Sm(II/III) complexes. Thus, reactions with TM(CO)6 (TM = Mo or Cr) entrap M2(CO)102- ions between two mixed valence hosts in [{(thf)2SmII(N4Et8)SmIII(thf)(µ-OC)TM(CO)4}2]·PhMe (TM = Mo, 1; Cr, 2), while W(CO)6 on a different stoichiometry traps W(CO)52- in [{(thf)2SmII(N4Et8)SmIII}2{(µ-OC)W(CO)4}]·PhMe 3 in which the isocarbonyl group is disordered over two sites. In contrast, [Sm2(N4Et8)(thf)4] reacts with dicobalt octacarbonyl, bis(cyclopentadienyl)tetracarbonyl diiron, and dimanganese decacarbonyl to give the mixed valence species [(thf)2SmII(N4Et8)SmIII(thf)(µ-OC)TM(CO)3]·2PhMe (TM = Co, 4; Fe, 5) and [(thf)2SmII(N4Et8)SmIII(thf)(µ-OC)Mn(CO)4]·1.5PhMe 6. However, both SmII sites of [Sm2(N4Et8)(thf)4] can be oxidized as its reaction with cyclooctatetraene (COT) yields the SmIII species [(thf)SmIII(N4Et8)SmIII(COT)] 7. The analogous EuII reagent, [Eu2(N4Et8)(thf)4] induces C-halogen activation of perfluorodecalin, hexachloroethane, and bromoethane to form the mixed oxidation state species [(thf)2EuII(N4Et8)EuIII(µ-X)]2 (X = F, 8; Cl, 9; Br, 10) despite the use of a sufficient reagent to oxidize both EuII sites. The synthetic potential of the halogenido complexes was illustrated by the reaction of 10 with sodium bis(trimethylsilyl)amide to give the mixed oxidation state [(thf)2EuII(N4Et8)EuIII(N(SiMe3)2)] 11.

Effective Dual-Functional Metal-Organic Framework (DF-MOF) as a Catalyst for the Solvent-Free Cycloaddition Reaction.

A new porous metal-organic framework, [Co (oba) (bpdh)]·(DMF) (TMU-63), containing accessible nitrogen-rich diazahexadiene groups was successfully prepared with the solvothermal assembly of 5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene (4-bpdh), 4,4'-oxybis(benzoic) acid (oba), and Co(II) ions. The combination of Lewis basic functional groups and porosity leads to high performance in CO2 adsorption and conversion in the cycloaddition reaction of epoxides under solvent-free conditions. To further enhance the catalytic efficiency of TMU-63, we introduced a highly acidic malonamide ligand into the structure via solvent-assisted ligand exchange (SALE) as a postsynthesis method. Incorporating different percentages of N1,N3-di(pyridine-4-yl) malonamide linker (4-dpm) into TMU-63 created a new porous structure. Powder X-ray diffraction (PXRD) and NMR spectroscopy confirmed that 4-bpdh was successfully replaced with 4-dpm in the daughter MOF, TMU-63S. The catalytic activity of both MOFs was confirmed by significant amounts of CO2 cycloaddition of epoxides under solvent-free conditions. The catalytic cycloaddition activities were found to be well-correlated with the Lewis base/Brønsted acid distributions of the materials examined in the TMU-63S series, showing that the concurrent presence of both acid and base sites was desirable for high catalytic activity. Furthermore, the heterogeneous catalysts could easily be separated out from the reaction mixtures and reused four times without loss of catalytic activity and with no structural deterioration.

Selective carbon-phosphorus bond cleavage: expanding the toolbox for accessing bulky divalent lanthanoid sandwich complexes.

The synthesis of two new tetra- and penta-phenycyclopentadienyldiphenylphosphine pro-ligands which readily undergo selective C-P bond cleavage has allowed for the facile synthesis of bulky divalent octa- and deca-phenylmetallocenes of europium, ytterbium and samarium.

Lanthanoid Biphenolates as a Rich Source of Lanthanoid-Main Group Heterobimetallic Complexes.

Several new trivalent dinuclear rare earth 2,2'-methylenebis(6-tert-butyl-4-methylphenolate) (mbmp2- ) complexes with the general form [Ln2 (mbmp)3 (thf)n ] (Ln=Sm 1, Tb 2 (n=3), and Ho 3, Yb 4 (n=2), and a tetravalent cerium complex [Ce(mbmp)2 (thf)2 ] (5) have been synthesised by RTP (redox transmetallation/protolysis) reactions from lanthanoid metals, Hg(C6 F5 )2 and the biphenol mbmpH2 . These new complexes and some previously reported partially protonated rare earth biphenolate complexes [Ln(mbmp)(mbmpH)(thf)n ] react with lithium, aluminium, potassium and zinc organometallic reagents to form lanthanoid-main group heterobimetallic species. When reaction mixtures containing the Ln biphenolate complexes were treated with n-butyllithium, both molecular ([Li(thf)2 Ln(mbmp)2 (thf)n ] (Ln=La 6, Pr 7 (n=2) and Er 8, Yb 9, and Lu 10 (n=1)) and charge separated ([Li(thf)4 ][Ln(mbmp)2 (thf)2 ] (Ln=Y 11, Sm 12, Dy 13, and Ho 14) complexes were isolated. Treatment with trimethylaluminium also led to isolation of molecular ([AlMe2 Ln(mbmp)2 (thf)2 ] (Ln=Pr 15, Sm 16, and Tb 17)) and ionic [La(mbmp)(thf)5 ][AlMe2 (mbmp)] (18) complexes. One gadolinium-potassium ([K(thf)3 Gd(mbmp)2 (thf)2 ] (19)), and one ytterbium-zinc species ([ZnEtYb(mbmp)2 (thf)] (20)) were isolated from treatment of reaction mixtures with potassium bis(trimethylsilyl)amide and diethylzinc respectively.

Europium is Different: Solvent and Ligand Effects on Oxidation State Outcomes and C-F Activation in Reactions Between Europium Metal and Pentafluorophenylsilver.

Unique outcomes have emerged from the redox transmetallation/ protolysis (RTP) reactions of europium metal with [Ag(C6 F5 )(py)] (py=pyridine) and pyrazoles (RR'pzH). In pyridine, a solvent not normally used for RTP reactions, the products were mainly EuII complexes, [Eu(RR'pz)2 (py)4 ] (RR'pz=3,5-diphenylpyrazolate (Ph2 pz) 1; 3-(2-thienyl)-5-trifluoromethylpyrazolate (ttfpz) 2; 3-methyl-5-phenylpyrazolate (PhMepz) 3). However, use of 3,5-di-tert-butylpyrazole (tBu2 pzH) gave trivalent [Eu(tBu2 pz)3 (py)2 ] 4, whereas the bulkier N,N'-bis(2,6-difluorophenyl)formamidine (DFFormH) gave divalent [Eu(DFForm)2 (py)3 ] 5. In tetrahydrofuran (thf), the usual solvent for RTP reactions, C-F activation was observed for the first time with [Ag(C6 F5 )(py)] in such reactions. Thus trivalent [{Eu2 (Ph2 pz)4 (py)4 (thf)2 (µ-F)2 }{Eu2 (Ph2 pz)4 (py)2 (thf)4 (µ-F)2 }] (6), [Eu2 (ttfpz)4 (py)2 (dme)2 (µ-F)2 ] (7), [Eu2 (tBu2 pz)4 (dme)2 (µ-F)2 ] (8) were obtained from the appropriate pyrazoles, the last two after crystallization from 1,2-dimethoxyethane (dme). Surprisingly 3,5-dimethylpyrazole (Me2 pzH) gave the divalent cage [Eu6 (Me2 pz)10 (thf)6 (µ-F)2 ] (9). This has a compact ovoid core held together by bridging fluoride, thf, and pyrazolate ligands, the last including the rare µ4 -1η5 (N2 C3 ): 2η2 (N,N'): 3κ(N): 4κ(N') pyrazolate binding mode. With the bulky N,N'-bis(2,6-diisopropylphenyl)formamidine (DippFormH), which often favours C-F activation in RTP reactions, neither oxidation to EuIII nor C-F activation was observed and [Eu(DippForm)2 (thf)2 ] (10) was isolated. By contrast, Eu reacted with Bi(C6 F5 )3 and Ph2 pzH or tBu2 pzH in thf without C-F activation, to give [Eu(Ph2 pz)2 (thf)4 ] (11) and [Eu(tBu2 pz)3 (thf)2 ] (12) respectively, the oxidation state outcomes corresponding to that for use of [Ag(C6 F5 )(py)] in pyridine.

Electron Delocalization in Spectroelectrochemically and Computationally Characterized [Pt{(p-BrC6F4)NCH═C(Cl)NEt2}Cl(py)]+ Formed by Electrochemical Oxidation of [PtII{(p-BrC6F4)NCH═C(Cl)NEt2}Cl(py)].

[Pt{(p-BrC6F4)NCH═C(Cl)NEt2}Cl(py)] (1Cl) is the product of the hydrogen peroxide oxidation of the PtII anticancer agent [Pt{(p-BrC6F4)NCH2CH2NEt2}Cl(py)] (1). Insights into electron delocalization and bonding in [Pt{(p-BrC6F4)NCH═C(Cl)NEt2}Cl(py)]+ (1Cl+) obtained by electrochemical oxidation of 1Cl have been gained by spectroscopic and computational studies. The 1Cl/1Cl+ process is chemically and electrochemically reversible on the short time scale of voltammetry in dichloromethane (0.10 M [Bu4N][PF6]). Substantial stability is retained on longer time scales enabling a high yield of 1Cl+ to be generated by bulk electrolysis. In situ IR and visible spectroelectrochemical studies on the oxidation of 1Cl to 1Cl+ and the reduction of 1Cl+ back to 1Cl confirm the long-term chemical reversibility. DFT calculations indicate only a minor contribution to the electron density (13%) resides on the Pt metal center in 1Cl+, indicating that the 1Cl/1Cl+ oxidation process is extensively ligand-based. Published X-ray crystallographic data show that 1Cl is present in only one structural form, while NMR data on the dissolved crystals revealed the presence of two closely related structural forms in an almost equimolar ratio. Solution-phase EPR spectra of 1Cl+ are consistent with two closely related structural forms in a ratio of about 90:10. The average g value for the frozen solution spectra (2.0567 for the major species) is significantly greater than the 2.0023 expected for a free radical. Crystal field analysis of the EPR spectra leads to an estimate of the 5d(xz) character of around 10% in 1Cl+. Analysis of X-ray absorption fine structure derived from 1Cl+ also supports the presence of a delocalized singly occupied metal molecular orbital with a spin density of approximately 17% on Pt. Accordingly, the considerably larger electron density distribution on the ligand framework (diminished PtIII character) is proposed to contribute to the increased stability of 1Cl+ compared to that of 1+.

A simple one-pot route to stable formamidinatoiodidolanthanoid(III) complexes from lanthanoid metals.

A number of formamidinatoiodidolanthanoid(III) complexes, [Ln(DFForm)2I(thf)2] and [Ln(DFForm)I2(thf)3] (DFFormH = N,N'-bis(2,6-difluorophenyl)formamidine) and [Ln(DippForm)I2(thf)3] (DippFormH = N,N'-bis(2,6-diisopropylphenyl)formamidine) have been synthesized in good yields by one-pot direct reactions of the corresponding free metals with iodine and DFFormH or DippFormH in suitable ratios and are stable to rearrangement.