Dysprosiacarboranes as Organometallic Single‐Molecule Magnets

The dicarbollide ion, nido‐C₂B₉H₁₁^2? is isoelectronic with cyclopentadienyl. Herein, we make dysprosiacarboranes, namely [(C₂B₉H₁₁)₂Ln(THF)₂][Na(THF)₅] (Ln=Dy, 1Dy ) and [(THF)₃(μ‐H)₃Li]₂[{η⁵‐C₆H₄(CH₂)₂C₂B₉H₉}Dy{η²:η⁵‐C₆H₄(CH₂)₂C₂B₉H₉}₂Li] 3Dy and show that dicarbollide ligands impose strong magnetic axiality on the central Dy^III ion. The effective energy barrier (U_eff) for the loss of magnetization can be varied by the substitution pattern on the dicarbollide. This finding is demonstrated by comparing complexes of nido‐C₂B₉H₁₁^2? and nido‐[o‐xylylene‐C₂B₉H₉]^2?, which show a U_eff of 430(5) K and 804(7) K, respectively. The blocking temperature defined by the open hysteresis temperature of 3Dy reaches 6.8 K. Moreover, the linear complex [Dy(C₂B₉H₁₁)₂]^? is predicted to have comparable properties with the linear [Dy(Cp^Me3)₂]⁺ complex. As such, carboranyl ligands and their derivatives may provide a new type of organometallic ligand for high‐performance single‐molecule magnets.     

(Indenyl)iridacarborane (η<Superscript>5</Superscript>-indenyl)Ir(η-7,8-C<Subscript>2</Subscript>B<Subscript>9</Subscript>H<Subscript>11</Subscript>): synthesis,structure, and bonding

A reaction of iodide [(η⁵-indenyl)IrI₂]_n (1) with thallium dicarbollide Tl[Tl(η-7,8-C₂B₉H₁₁)] leads to (indenyl)iridacarborane (η⁵-indenyl)Ir(η-7,8-C₂B₉H₁₁) (2) in 32% yield. The X-ray diffraction study showed that in the structure of 2, the five-membered rings C₅ and C₂B₃ have a cisoid conformation, in which the bridgehead carbon atoms of the indenyl ligand are arranged opposite to the carborane cage carbon atoms. The DFT calculations showed that the Ir—indenyl bond in compound 2 is weaker than the Ir—Cp bond in the complex (η-7,8-C₂B₉H₁₁)IrCp.     

η5‐(3)‐1‐Methyl‐1,2‐dicarbollyl‐η5‐2′,5′‐dimethylpyrrolylcobalt(III)

In the title compound, (η⁵‐2,5‐di­methyl­pyrrolyl)[(7,8,9,10,11‐η)‐7‐methyl‐7,8‐dicarba‐nido‐undecaborato]­cobalt(III), [3‐Co{η⁵‐[2,5‐(CH₃)₂‐NC₄H₂]}‐1‐CH₃‐1,2‐C₂B₉H₁₀] or [Co(C₃H₁₃B₉)(C₆H₈N)], the Co^III atom is sandwiched between the pentagonal faces of the pyrrolyl and dicarbollide ligands, resulting in a neutral mol­ecule. The C—C distance in the dicarbollide cage is 1.649 (3) Å.     

Formation of ferraboranes from pentaborane(9) or BH3 · thf and an electron-rich cyclopentadienyl iron phosphine hydride

[(η⁵-C₅R₅)Fe(PMe₃)₂H] (R = H, Me) can be made in good yields in a simple one-pot reaction between FeCl₂, PMe₃, C₅R₅H (R = H, Me) and Na/Hg in thf. Reaction of [(η⁵-C₅H₅)Fe(PMe₃)₂H] with pentaborane(9) gives the known metallaborane [(η⁵-C₅H₅)-nido-2-FeB₅H₁₀] (1) in improved yield as well as the new metallaboranes [(η-C₅H₅)-nido-2-FeB₅H₈{μ-5,6-Fe(η⁵-C₅H₅)(PMe₃)(μ-6,7-H)}] (2), [(η-C₅H₅)(PMe₃)-arachno-2-FeB₃H₈] (3), [(η⁵-C₅H₅)₂-capped-nido-2,3-Fe₂B₄H₈] (4), [(η⁵-C₅H₅)-nido-2-FeB₄H₇(PMe₃)] (5) and [(η⁵-C₅H₅)-nido-2-FeB₅H₈(PMe₃)] (6). Reaction of [(η⁵-C₅Me₅)Fe(PMe₃)₂H] with pentaborane(9) gives predominantly [(η⁵-C₅Me₅)-nido-2-FeB₅H₁₀] (7) and [(η⁵-C₅Me₅)(PMe₃)-arachno-2-FeB₃H₈] (8). Reaction of [(η⁵-C₅H₅)Fe(PMe₃)₂H] with 2 equiv. of BH₃ · thf gives low yields of ferrocene and compound 3. Compound 7 thermally isomerises to the apical isomer [(η⁵-C₅H₅)-nido-2-FeB₅H₁₀] (9) in low yield. Compounds 1 and 7 deprotonate cleanly in the presence of KH at the unique B-H-B bridge to give [(η⁵-C₅H₅)-nido-2-FeB₅H₉⁻][K⁺] (10) and [(η⁵-C₅Me₅)-nido-2-FeB₅H₉⁻][K⁺] (11) respectively, whilst 6 deprotonates more slowly at one of two equivalent B-H-B bridges to give the fluxional anion [(η⁵-C₅H₅)-nido-2-FeB₅H₇(PMe₃)⁻] (12).     

Synthesis and Structure of Lanthanide Sandwich Complexes with Mixed Cyclooctatetraenyl and Chelating Substituted‐indenyl Ligands

Two types of sandwich complexes (η⁵‐MeOCH₂CH₂C₉H₆) Ln (η⁸‐C₈H₈) (THF)_n [Ln=La (1), Nd(2), n=0; Sm(3), Dy (4) and Er (5). n = l] and (η⁵‐C₄H₇OCH₂C₉H₆)Ln(η⁸‐C₈H₈) (THF) [Ln = La (6), Nd(7). Sm(8). Dy (9) and Er (10)] were synthesized by the reactions of LnCl₃ with equivalent mole of K₂C₈H₈, followed by treatment with corresponding potassium salt of ether‐substituted indenide. The molecular structures of 3 and 8 were determined by single crystal X‐ray diffraction. (η⁵ ‐MeOCH₂CH₂C₉H₆) Sm (η⁸‐C₈H₈) (THF) (3) monoclinic. Pt₁/c, a = 1.4793(3) nm, b = 0.8716 (2) nm, c = 1.6149 (3) nm, β = 98. 17(3), V = 2.0612(7) nm³, Z = 4, R(F)=0.0362. (η⁵‐C₄H₇OCH₂C₉H₆)Sm(η⁸‐C₈H₈)(THF) (8) orthorhombic. p2₁2₁2₁. a = 0.8754(2) nm, b = 1.1000(2) nm, c = 2.3117 (5) nm, V = 2.2260(8) nm³, Z=4, R(F) =0.0497.     

Synthesis and Structure of Nido-Carboranyl Azide and Its “Click” Reactions

Novel zwitter-ionic nido-carboranyl azide 9-N₃(CH₂)₃Me₂N-nido-7,8-C₂B₉H₁₁ was prepared by the reaction of 9-Cl(CH₂)₃Me₂N-nido-7,8-C₂B₉H₁₁ with NaN₃. The solid-state molecular structure of nido-carboranyl azide was determined by single-crystal X-ray diffraction. 9-N₃(CH₂)₃Me₂N-nido-7,8-C₂B₉H₁₁ was used for the copper(I)-catalyzed azide-alkyne cycloaddition with phenylacetylene, alkynyl-3β-cholesterol and cobalt/iron bis(dicarbollide) terminal alkynes to form the target 1,2,3-triazoles. The nido-carborane-cholesterol conjugate 9-3β-Chol-O(CH₂)C-CH-N₃(CH₂)₃Me₂N-nido-7,8-C₂B₉H₁₁ with charge-compensated group in a linker can be used as a precursor for preparation of liposomes for Boron Neutron Capture Therapy (BNCT). A series of novel zwitter-ionic boron-enriched cluster compounds bearing a 1,2,3-triazol-metallacarborane-carborane conjugated system was synthesized. Prepared conjugates contain a large amount of boron atom in the biomolecule and potentially can be used for BNCT.     

Spectroscopic and Electronic Properties of Molybdacarborane Complexes with Non-innocently Acting Ligands

The molybdacarboranes [3-{L-κ²N,N}-3-(CO)₂-closo-3,1,2-MoC₂B₉H₁₁] (L=2,2′-bipyridine (2,2′-bpy, 1 a ) or 1,10-phenanthroline (1,10-phen, 1 b )) incorporating well-known potentially non-innocent ligands (CO, 2,2′-bpy, 1,10-phen) and the “non-spectator” nido-carborane ([η⁵-C₂B₉H₁₁]²⁻) ligand were prepared and fully characterised. High-resolution mass spectrometry, single-crystal X-ray diffraction methods, spectroscopy (IR, (resonance) Raman, NMR), cyclic voltammetry and spectroelectrochemistry (electrochemical properties) were supported by theoretical investigations of the electronic structure (DFT, CAS-SCF, TD-DFT).     

Synthesis and Characterization of Novel Lanthanocene Complexes with Dichalcogenolate o-Carboranyl Ligands

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Electrochemical behaviour of cobalta-dicarbollide sandwich complexes with different capping units

The redox aptitude of a series of cobalt(III) or cobalt(I) sandwich complexes bearing a charge compensated dicarbollide ligand ([9-L-7,8-C₂B₉H₁₀]⁻) as a constant unit and different counterparts (varying from classical [7,8-C₂B₉H₁₁]²⁻ to charge-compensated [9-L-7,8-C₂B₉H₁₀]⁻ dicarbollides, from cyclopentadienyl [C₅R₅]⁻ (R = Me, H) to cyclobutadiene [C₄Me₄]⁰ ligands) has been studied. All the Co(III) complexes display the reversible sequence Co(III)/Co(II)/Co(I). In contrast, the Co(I) complexes (namely, those capped by tetramethylcyclobutadiene) accede reversibly only to the Co(II) oxidation state, the passage to Co(III) being irreversible. When possible, the Co(II) intermediates have been characterized by EPR spectroscopy. The molecular structures of the monocation [Co(η-9-SMe₂-7,8-C₂B₉H₁₀)₂]⁺ in its DD/LL and meso diastereomeric forms as well as that of heteroleptic (η-7,8-C₂B₉H₁₁)Co(η-9-SMe₂-7,8-C₂B₉H₁₀) have been obtained by single-crystal diffraction. Presented at the 3rd Chianti Electrochemistry Meetings July 3−9, 2004, Certosa di Pontignano, Italy     

First cupracarborane commo-clusters based on the medium-cage nido-5,6-C2B8H12-carborane and molecular structure of [Ph3PEt][commo-9,9′-Cu(nido-7,8-C2B8H11)2]

A reaction of anhydrous CuCl₂ with Na salts of the medium-cage carborane [7-X-nido-5,6-C₂B₈H₁₀]^?(X = H or I) derivatives in THF leads to new cupracarborane commo-clusters, [commo-9,9′-Cu(nido-7,8-C₂B₈H₁₁)₂]^? and [commo-9,9′-Cu(11-I-nido-7,8-C₂B₈H₁₀)₂]^?, in moderate yields. The clusters were isolated as stable [Ph₃PEt]⁺ salts and characterized by 1H, ³¹P{¹H}, and ¹¹B/¹¹B{¹H} NMR spectroscopy and X-ray crystallography (for the unsubstituted derivative). The use in this reaction of the reducing agent Na₂SO₃ considerably increases the yields of both complexes from 25 and 18% to 74 and 68%, respectively.     

Cationic Allyl Complexes of the Rare‐Earth Metals: Synthesis,Structural Characterization,and 1,3‐Butadiene Polymerization Catalysis

Monocationic bis‐allyl complexes [Ln(η³‐C₃H₅)₂(thf)₃]⁺[B(C₆X₅)₄]^? (Ln=Y, La, Nd; X=H, F) and dicationic mono‐allyl complexes of yttrium and the early lanthanides [Ln(η³‐C₃H₅)(thf)₆]²⁺[BPh₄]₂^? (Ln=La, Nd) were prepared by protonolysis of the tris‐allyl complexes [Ln(η³‐C₃H₅)₃(diox)] (Ln=Y, La, Ce, Pr, Nd, Sm; diox=1,4‐dioxane) isolated as a 1,4‐dioxane‐bridged dimer (Ln=Ce) or THF adducts [Ln(η³‐C₃H₅)₃(thf)₂] (Ln=Ce, Pr). Allyl abstraction from the neutral tris‐allyl complex by a Lewis acid, ER₃ (Al(CH₂SiMe₃)₃, BPh₃) gave the ion pair [Ln(η³‐C₃H₅)₂(thf)₃]⁺[ER₃(η¹‐CH₂CH?CH₂)]^? (Ln=Y, La; ER₃=Al(CH₂SiMe₃)₃, BPh₃). Benzophenone inserts into the La? C_allyl bond of [La(η³‐C₃H₅)₂(thf)₃]⁺[BPh₄]^? to form the alkoxy complex [La{OCPh₂(CH₂CH?CH₂)}₂(thf)₃]⁺[BPh₄]^?. The monocationic half‐sandwich complexes [Ln(η⁵‐C₅Me₄SiMe₃)(η³‐C₃H₅)(thf)₂]⁺[B(C₆X₅)₄]^? (Ln=Y, La; X=H, F) were synthesized from the neutral precursors [Ln(η⁵‐C₅Me₄SiMe₃)(η³‐C₃H₅)₂(thf)] by protonolysis. For 1,3‐butadiene polymerization catalysis, the yttrium‐based systems were more active than the corresponding lanthanum or neodymium homologues, giving polybutadiene with approximately 90 % 1,4‐cis stereoselectivity.     

Indium monohalide insertion reactions into metal—metal bonds. Crystal structure of [InCl(THF){Mo(CO)3(η-C5H5)}2]

The reaction between InCl and [Mo₂(CO)₆(η-C₅H₅)₂] affords [InCl&{;Mo(CO)₃(η-C₅H₅)&};], 6a which has been characterised as a THF adduct [InCl(THF)&{;Mo(CO)₃(η-C₅H₅)&};₂], 10, by X-ray crystallography. An additional complex, [InCl₂&{;Mo(CO)₃(η-C₅H₅)&};₂]⁻, 11, is also formed in this reaction. Similar products are reported for reactions involving [M₂(CO)₆(η-C₅H₅)₂] (M = Cr, W). The reaction between InCl and [Fe₂(CO)₄(η-C₅H₅)₂] affords [InCl{Fe(CO)₂(η-C₅H₅)}₂], 17, and [InCl₂{Fe(CO)₂(η-C₅H₅)}], whilst that between InI and [Fe₂(CO)₄(η-C₅H₅)₂] affords [InI{Fe(CO)₂(η-C₅H₅)}₂], 19.     

New boron-containing bacteriochlorin <Emphasis Type="Italic">p</Emphasis> cycloimide conjugate

A conjugate of the bacteriochlorophyll a derivative with the cobalt bis(dicarbollide) anion [3,3′-Co(1,2-C₂B₉H₁₁)₂]⁻ was synthesized.     

Molecular Lanthanide Switches for Magnetism and Photoluminescence

Solvation of [(CNT)Ln(η⁸-COT)] (Ln=La, Ce, Nd, Tb, Er; CNT=cyclononatetraenyl, i.e., C₉H₉⁻; COT=cyclooctatetraendiid, i.e., C₈H₈²⁻) complexes with tetrahydrofuran (THF) gives rise to neutral [(η⁴-CNT)Ln(thf)₂(η⁸-COT)] (Ln=La, Ce) and ionic [Ln(thf)_x(η⁸-COT)][CNT] (x=4 (Ce, Nd, Tb), 3 (Er)) species in a solid-to-solid transformation. Due to the severe distortion of the ligand sphere upon solvation, these species act as switchable luminophores and single-molecule magnets. The desolvation of the coordinated solvents can be triggered by applying a dynamic vacuum, as well as a temperature gradient stimulus. Raman spectroscopic investigations revealed fast and fully reversible solvation and desolvation processes. Moreover, we also show that a Nd:YAG laser can induce the necessary temperature gradient for a self-sufficient switching process of the Ce(III) analogue in a spatially resolved manner.     

Organoruthenaborane Chemistry. X. The SM2-catalysed formation of [ l-(η6-C6Me6)-isocloso-RuB9H9], and some B-phenylamino derivatives. NMR and X-ray diffraction studies

The action of SMe₂ on the ten-vertex nido-ruthenaborane [6-(η⁶-C₆Me₆)RuB₉H_l3] ( 1 ) provides a high-yield route to the unsubstituted isocloso-ruthenaborane [1-(η⁶-C₆Me₆)RuB₉H₉] (2). The benzene analogue [1-(η⁶-C₆Me₆)RuB₉H₉] is prepared similarly. By contrast, reaction of (1) with PhNH₂ gives a variety of B-phenylamino isocloso derivatives, including orange crystals of [1-(η⁶-C₆Me₆)-2-(PhNH)-isocloso-1-RuB 9 H₈] ( 3 ), red-orange [1-(η⁶-C₆Me₆)-2,3-(PhNH)₂-isocloso-1-RuB₉H₇] ( 4 ) and dark-red [1-(η⁶-C₆Me₆)-5,6,7-(PhNH)₃-isocloso-1-RuB₉H₆] ( 5 ). Detailed ¹H and ¹¹B nmr properties of these various compounds are described. The structure of ( 3 ) has been established by a single-crystal X-ray diffraction study of the solvate [1-(η⁶-C₆Me₆)-2-(PhNH)-isocloso-1-RuB₉H₈] · 1/2 CH₂Cl₂; the crystals were monoclinic, space group C2/c, with a = 1895.1(3), b = 1556.6(3), c = 1716.4(3) pm, β = 104.37(1)° and z = 8.     

Electrophile‐Induced Nucleophilic Substitution of the nido‐Dicarbaundecaborate Anion nido‐7,8‐C2B9H12− by Conjugated Heterodienes

Substitution of the dicarbaundecaborate anion nido‐7,8‐C₂B₉H₁₂^? ( 1 ) by precise hydride abstraction followed by nucleophilic attack usually leads to symmetric products 10‐R‐nido‐7,8‐C₂B₉H₁₁. However, thioacetamide (MeC(S)NH₂) as nucleophile and acetone/AlCl₃ as hydride abstractor gave asymmetric 9‐[MeC(NHiPr)S]‐nido‐7,8‐C₂B₉H₁₁ ( 2 ), whereas N,N‐dimethylthioacetamide (MeC(S)NMe₂) gave the expected symmetric 10‐[MeC(NMe₂)S]‐nido‐7,8‐C₂B₉H₁₁ ( 4 ). For the formation of 2 , acetone and thioacetamide are assumed to give the intermediate MeC(S)N(CMe₂) ( 3 ), which then attacks 1 with formation of 2 . Similarly, reaction of acetyliminium chloride [MeC(O)NH(CPh₂)]Cl ( 5 ) with 1 in THF gave a mixture of 9‐ and 10‐substituted [MeC(NHCHPh₂)O]‐nido‐7,8‐C₂B₉H₁₁ ( 6 and 7 , respectively). These reactions are the first examples in which compounds (here heterodienes) that unite the functionalities of both hydride acceptor and nucleophilic site react with 1 in a bimolecular fashion. Furthermore, the analogous reaction of 1 and 5 (in an equilibrium mixture with acetyl chloride and benzophenone imine) in MeCN afforded 10‐[MeC(NCPh₂)NH]‐nido‐7,8‐C₂B₉H₁₁ ( 8 ) and MeC(O)NHCHPh₂ ( 9 ).     

Organometallic Compounds of the Lanthanides. 127 [1] Synthesis of Monomeric Bis(cyclopentadienyl)lanthanide Tetrahydroborates with Bulky Cyclopentadienyl Ligands. Single Crystal X-ray Structures of [(η5-C5Me5)2SmBH4(THF)] and [(η5-C5Me4Et)2Y(μ-H)2BH2(THF)]

The trichlorides of yttrium, samarium, and lutetium react with 2 equivalents of Na[C₅H₄ ^tBu] and 1 equivalent of NaBH₄ to give [(η⁵-C₅H₄ ^tBu)₂LnBH₄(THF)] (Ln = Y ( 1 ), Sm ( 2 ), Lu ( 3 )) or with 2 equivalents of Na[C₅Me₄R] and 1 equivalent of NaBH₄ to form [(η⁵-C₅Me₄R)₂ · LnBH₄(THF)] (R = H, Ln = Y ( 4 ), Sm ( 5 ), Lu ( 6 ); R = Me, Ln = Y ( 7 ), Sm ( 8 ), Lu ( 9 ); R = Et, Ln = Y ( 10 ), Sm ( 11 ), Lu ( 12 ); R = ⁱPr, Ln = Y ( 13 ), Sm ( 14 ), Lu ( 15 )). The new compounds have been characterized by elemental analysis, NMR spectroscopy and mass spectrometry. The crystal structures of 8 and 10 were determined by single crystal X-ray diffraction.     

Metallacarboranes and triple-decker complexes with the (C4Me4)Pt fragment

Complex Cp∗PtCl₂ (Cp∗ = η-C₄Me₄) reacts with the carborane anions [7,8-C₂B₉H₁₁]²⁻ and [9-SMe₂-7,8-C₂B₉H₁₀]⁻ giving platinacarboranes Cp∗Pt(η-7,8-C₂B₉H₁₁) (1) and [Cp∗Pt(η-9-SMe₂-7,8-C₂B₉H₁₀)]⁺ (2), respectively. Reactions of the [Cp∗Pt]²⁺ fragment (as a labile nitromethane solvate) with the sandwich compounds Cp∗Fe(η-C₅H₃Me₂BMe) and Cp∗Rh(η⁵-C₄H₄BPh) afford the triple-decker cations [Cp∗Pt(μ-η:η-C₅H₃Me₂BMe)FeCp∗]²⁺ (3) and [Cp∗Pt(μ-η⁵:η⁵-C₄H₄BPh)RhCp∗]²⁺ (4) with bridging boratabenzene and borole ligands. The structures of 1 and 3(CF₃SO₃)₂ were determined by X-ray diffraction.     

Synthese,Struktur und Reaktivität von Tris‐, Bis‐ und Mono(2,4‐dimethylpentadienyl)‐Komplexen des Neodyms,Lanthans und des Yttriums

The tris(2,4‐dimethylpentadienyl) complexes [Ln(η⁵‐Me₂C₅H₅)₃] (Ln = Nd, La, Y) are obtained analytically pure by reaction of the tribromides LnBr₃·nTHF with the potassium compound K(Me₂C₅H₅)(thf)_n in THF in good yields. The structural characterization is carried out by X‐ray crystal structure analysis and NMR‐spectroscopically. The tris complexes can be transformed into the dimeric bis(2,4‐dimethylpentadienyl) complexes [Ln₂(η⁵‐Me₂C₅H₅)₄X₂] (Ln, X: Nd, Cl, Br, I; La, Br, I; Y, Br) by reaction with the trihalides THF solvates in the molar ratio 2:1 in toluene. Structure and bonding conditions are determined for selected compounds by X‐ray crystal structure analysis and NMR‐spectroscopically in general. The dimer‐monomer equilibrium existing in solution was investigated NMR‐spectroscopically in dependence of the donor strength of the solvent and could be established also by preparation of the corresponding monomer neutral ligand complexes [Ln(η⁵‐Me₂C₅H₅)₂X(L)] (Ln, X, L: Nd, Br, py; La, Cl, thf; Br, py; Y, Br, thf). Finally the possibilities for preparation of mono(2,4‐dimethylpentadienyl)lanthanoid(III)‐dibromid complexes are shown and the hexameric structure of the lanthanum complex [La₆(η⁵‐Me₂C₅H₅)₆Br₁₂(thf)₄] is proved by X‐ray crystal structure analysis.     

New carborane-containing acids and amines

Alkylation of nido-carborane methyl sulfide derivative [9-MeS-7,8-C₂B₉H₁₁]^– was used to synthesize a series of new carborane-containing acids 9-HOOC(CH₂) _n (Me)S-7,8-C₂B₉H₁₁ (n = 1—4) and amines 9-H₂N(CH₂) _n (Me)S-7,8-C₂B₉H₁₁ (n = 2, 3). The compounds obtained can be used for the development of BNCT agents.