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.     

Isomeric ammonio derivatives of nido-carborane 3- and 10-H3N-7,8-C2B9H11

Abstract

Structure of 3-ammonio derivative of nido-carborane 3-NH₃-7,8-C₂B₉H₁₁ was determined by single crystal X-ray diffraction. The isomeric 10-ammonio derivative 10-NH₃-7,8-C₂B₉H₁₁ was prepared by the treatment of the corresponding ethylnitrilium derivative 10-EtC≡N-7,8-C₂B₉H₁₁ with hydrazine hydrate in acetonitrile.     

Synthesis of podands with nido-carboranyl groups as a basis for construction of crown ethers with an incorporated metallacarborane moiety

The reactions of the dioxane derivative of 7,8-dicarba-nido-undecaborate anion (nido-carborane), [10-O(CH₂CH₂)₂O-nido-7,8-C₂B₉H₁₁], with a series of O,O′-dinucleophiles (pyrocatechol, resorcinol, hydroquinone, and ethylene glycol) were studied. The nido-carborane-based podand was obtained, which can be used for assembling of crown ethers with an inserted metallacarborane moiety.     

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.     

Synthesis and structure of halogen derivatives of 9-dimethylsulfonium-7,8-dicarba-nido-undecaborane [9-Me2S-7,8-C2B9H11]

Halogenation of 9-dimethylsulfonium-7,8-dicarba-nido-undecaborane [9-SMe₂-7,8-C₂B₉H₁₁] with N-chlorosuccinimide, bromine and iodine gave the expected corresponding halogen derivatives [9-SMe₂-11-X-7,8-C₂B₉H₁₀], where X = Cl (1), Br (2), I (3). In the bromination reaction, [9-SMe₂-6-Br-7,8-C₂B₉H₁₀] (4) was isolated as a minor product being the first example of substitution at a “lower” belt of the 7,8-dicarba-nido-undecaborate cage. The use of excess of bromine resulted in dibromo derivative [9-SMe₂-6,11-Br₂-7,8-C₂B₉H₉] (5). Structures of the compounds prepared were determined using ¹¹B-¹¹B COSY NMR spectroscopy (for all halogen derivatives) and single crystal X-ray diffraction (for compounds 2, 3, and 5).     

Nature of weak inter- and intramolecular interactions in crystals. 5. Interactions Na...H—B in a crystal of sodium salt of charge-compensated nido-carborane [9-SMe2-7,8-C2B9H10]−

The character of electron density distribution in the C₂B₃ open face, the influence of the SMe₂ group on the character of electron density distribution, and the nature of the sodium—anion interaction were studied based on the data of high-resolution X-ray diffraction study of crystals of the sodium salt of charge compensated nido-carborane [9-SMe₂-7,8-C₂B₉H₁₀]⁻ and quantum-chemical calculations for the Na...H—B bonded dimer, the isolated [9-SMe₂-7,8-C₂B₉H₁₀]⁻ anion, and the [7,8-C₂B₉H₁₀]²⁻ dianion. The character of electron density distribution in the C₂B₃ open face is analogous to the electron distribution in the cyclopentadienyl ligand. In nido-carborane, a substantial charge redistribution takes place compared to that observed in the closo analogs. The topological analysis of the electron density distribution function demonstrated that the cation—anion interactions are determined predominantly by Na...H—B contacts. The total energy of these contacts in the { [9-SMe₂-7,8-C₂B₉H₁₀]Na(thf)₂}₂ dimer estimated from X-ray diffraction data is 11.74 kcal mol⁻¹. Dedicated to Corresponding Member of the Russian Academy of Sciences E. P. Serebryakov on the occasion of his 70th birthday. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 911–918, April, 2005.     

Sterically-induced low temperatur polyhedral rearrangements of carbaplatinaboranes: Synthesis and crystal structures of 1-Ph-3,3-(PMe2Ph)2-3,1,2-PtC2B9H10, 1-Ph-3,3-(PMe2Ph)2-3,1,11-PtC2B9H10, 11-Ph-3,3-(PMe2Ph)2-3,1,11-PtC2B9H10 and 1,11-Ph2-3,3-(PMe2Ph)2-3,1,11-PtC2B9H9

Reaction of cis-Pt(PMe₂Ph)₂Cl₂ with Tl₂[7-Ph-7,8-nido-C₂B₉H₁₀] affords 1-Ph-3,3-(PMe₂Ph)₂-3,1,2-PtC₂B₉H₁₀, mild thermolysis (55°C) of which yields 1-Ph-3,3-(PMe₂Ph)₂-3,1,11-PtC₂B₉H₁₀ and 11-Ph-3,3-(PMe₂Ph)₂-3,1,11-PtC₂B₉H₁₀. Both of the latter compounds are produced by the microwave irradiation of a mixture of cis-Pt(PMe₂Ph)₂Cl₂ and [HNMe₃][7-Ph-7,8-nido-C₂B₉H₁₁]. When cis-Pt(PMe₂Ph)₂Cl₂ is allowed to react with Tl₂[7,8-Ph₂-7,8-nido-C₂B₉H₉] at room temperature the only isolable species is 1,11-Ph₂-3,3-(PMe₂Ph)₂-3,1,11-PtC₂B₉H₉. The generation of rearranged products with 3,1,11-PtC₂B₉ architectures is inconsistent with a diamond-square-diamond mechanism for the isomerisation of icosahedral heteroboranes.     

Synthesis of dihalo derivatives of the 7,8-dimethyldecahydro-7,8-dicarba-nido-undecaborate anion

Treatment of potassium 7,8-dimethyldecahydro-7,8-dicarba-nido-undecaborate with N-chloro-and N-bromosuccinimides in acetonitrile or with an excess of iodine in methanol gave the corresponding dihalo derivatives [9,11-X₂-7,8-Me₂-7,8-C₂B₉H₈]⁻ (X = Cl, Br, or I), which were isolated as alkylammonium salts. The compound (Me₃NH)⁺[9,11-I₂-7-Me-7,8-C₂B₉H₉]⁻ was synthesized by a reaction of K⁺[7-Me-7,8-C₂B₉H₁₁]⁻ with an excess of iodine in methanol. The compounds obtained were characterized by IR and NMR (¹H, ¹¹B, and ¹¹B-¹¹B COSY) spectroscopy. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 888–891, May, 2007.     

Solvothermal Synthesis and Characterization of Two New Nickel <Emphasis Type="Italic">Nido</Emphasis>-Carborane Diphosphine Complexes

Solvothermal synthesis method has been successfully introduced into the diphosphine carborane system, and two new nickel complexes containing nido-carborane diphosphine ligand [7,8-(PPh₂)₂-7,8-C₂B₉H₁₀]⁻ with the formula [Ni₂(μ-Cl)(μ-OOPPh₂){7,8-(PPh₂)₂-7,8-C₂B₉H₁₀}₂]·CH₂Cl₂ (1) and [H₃O][NiBr₂] {7,8-(PPh₂)₂-7,8-C₂B₉H₁₀}·C₆H₆ (2) were obtained by the reactions of 1,2-(PPh₂)₂-1,2-C₂B₁₀H₁₀ with NiCl₂·6H₂O or NiBr₂·6H₂O in CH₂Cl₂ under the solvothermal condition. Both of the two complexes have been characterized by the elemental analysis, FT-IR, ¹H and ¹³C NMR spectroscopy and single crystal X-ray diffraction. The X-ray structure analysis for these two complexes reveals the nido-nature of the carborane diphosphine ligand, indicating that the solvothermal synthesis is an efficient method for the degradation of the closo-carborane diphosphine ligand.     

Structure of 6,11-dichloro-9-dimethylthio-7,8-dicarba-nido-undecaborane [6,11-Cl2-9-SMe2-7,8-C2B9H9]

A technique is proposed for directed synthesis of 6,11-dichloro-9-dimethylthio-7,8-dicarba-nido-undecaborane [6,11-Cl₂-9-SMe₂-7,8-C₂B₉H₉]. Single-crystal X-ray diffraction is used to identify the molecular and crystal structure of the compound.     

Synthesis of binuclear rhodacarboranes from 1,4-and 1,3-C6H4(CH2-9-C2H2B9H9-7,8-nido]2 2− dianions and (Ph3P)3RhCl

1,4- and 1,3-C₆H₄(CH₂-9-C₂H₂B₉H₉-7,8-nido]₂ ^2? dianions obtained fromnido-7,8-dicarbollide ion and 1,4-bis(bromomethyl)- and 1,3-bis(bromomethyl)benzenes react with (Ph₃P)₃RhCl to give binuclear rhodacarboranes, 1,4- and 1,3-[3,3-(Ph₃P)₂-3-H-3,1,2-RhC₂B₉H₁₀-4-CH₂]₂C₆H4.     

Synthesis, isomerism, and catalytic properties of chelate ruthenium copper bimetallacarborane cluster exo-closo-(Ph3P)Cu(μ-H)Ru[Ph2P(CH2)4PPh2](η5-C2B9H11), in radical polymerization of methyl methacrylate

Chelate exo-nido-ruthenacarboranes exo-5,6,10-[RuCl(Ph₂P(CH₂)₄PPh₂)]-5,6,10-(μ-H)₃-10-H-7,8-R,R′-nido-7,8-C₂B₉H₆ (R, R′ = H, PhCH₂) were synthesized by the direct method using the reaction of Cl₂Ru(PPh₃)(Ph₂P(CH₂)₄PPh₂) with [7,8-R,R′-nido-7,8-C₂B₉H₁₀][K] in benzene. Unsubstituted exo-nido-ruthenacarborane (R, R′ = H) was used in situ for the synthesis of the dinuclear Ru-Cu exo-closo cluster of the formula exo-closo-(Ph₃P)Cu(μ-H)Ru(Ph₂P(CH₂)₄PPh₂)(η⁵-C₂B₉H₁₁). The isomerism of the complex and the crystal structure were studied by NMR spectroscopy and X-ray diffraction. The catalytic activity of the cluster in the atom transfer radical polymerization of methyl methacrylate was investigated.     

Reactions of Icosahedral Carboranes with Iminotris(dimethylamino)Phosphorane HNP(NMe2)3: a Deboronation Intermediate nido-C2B10H12·N(H)P(NMe2)3, Deboronation Reactions and Hydrogen-bonded Closo-carborane Systems

Reactions between the icosahedral carboranes 1,2-C₂B₁₀H₁₂ (1), 1,7-C₂B₁₀H₁₂ (2) and 1,12-C₂B₁₀H₁₂ (3) and the iminophosphorane HNP(NMe₂)₃ (4) are described that have afforded a variety of products whose structures have been characterised by X-ray diffraction. They include the adduct between (1) and (4), C₂B₁₀H₁₂·HNP(NMe₂)₃ (5) the 12-atom 14-skeletal pair supra-icosahedral nido structure of which illustrates an early step in the deboronation of ortho-carborane (1) by Lewis Bases, and the C–H⋯N hydrogen-bonded adducts of meta- and para-carborane with the iminophosphorane, [1,7-C₂B₁₀H₁₂⋯HNP(NMe₂)₃] _n and 1,12-C₂B₁₀H₁₂ 2HNP(NMe₂)₃. The iminophosphorane (4) readily converts ortho-carborane (1) into the nido anion [7,8-C₂B₉H₁₂]⁻ and less readily meta-carborane (2) into the nido-anion [7,9-C₂B₉H₁₂]⁻, which have been isolated from solution as salts of the cations [H₂NP(NMe₂)₃]⁺ or [{(Me₂N)₃PN}₂BNHP(NMe₂)₃]⁺, the latter evidently incorporating a boron atom removed from the carborane cage. Adventitious presence of water in the attempted recrystallization of [{(Me₂N)₃PN}₂BNHP(NMe₂)₃]⁺ [7,8-C₂B₉H₁₂]⁻ led to a salt of the cation [{(Me₂N)₃PNBN(H)P(NMe₂)₃}₂O]²⁺. Other unexpected products isolated from reactions carried out under moist air included the salt [H₂NP(NMe₂) ₃ ⁺ ]₂[CO ₃ ²⁻ ]·2B(OH)₃ (from the reaction between 2 and 4) and the salt 1,12-C₂B₁₀H₁₂·2H₂NP(NMe₂) ₃ ⁺ HCO ₃ ⁻ (from the reaction between 3 and 4).Dedicated to Prof. Brian F.G. Johnson, in recognition of his major contributions to cluster chemistry and warm friendship over the years.     

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.     

π-complexes of monoanionic carborane ligand [9-(Me2S)-7,8-C2B9H10]− with [η-C5R5Fe]+ (R=H, Me) and [η-C4Me4Co]+ cationic fragments

Compounds (η-C₅R₅)Fe[η-9-(Me₂S)-7,8-C₂B₉H₁₀] (R=H, Me) and (η-C₄Me₄)Co[η-9-(Me₂S)-7,8-C₂B₉H₁₀] were synthesized by the reactions of Na[9-(Me₂S)-7,8-C₂B₉H₁₀] with complexes [(η-C₅H₅)Fe(MeCN)₃]PF₆, [(η-C₅Me₅)Fe(MeCN)₃]BF₄, and [(η-C₄Me₄)Co(MeCN)₃]PF₆, respectively. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 177–179, January, 1999.     

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 ).     

Synthesis of metallacarborane triple-decker complexes with the bridging diborolyl ligand

Triple-decker complexes CpCo(μ-1,3-C₃B₂Me₅)M(η-7,8-C₂B₉H₁₁) (M = Rh (3), Ir (4)) were synthesized by the reaction of [CpCo(μ-1,3-C₃B₂Me₅)MBr₂]₂ (M = Rh, Ir) with Tl[TlC₂B₉H₁₁]. The structure of 3 was established by X-ray diffraction analysis.     

1,2,3,4,7-Pentamethylindenyl complex [(η5-C9H2Me5)RhI2]2 as a synthon for the [(η5-C9H2Me5)Rh]2+ fragment

The reaction of the iodide complex [(η⁵-C₉H₂Me₅)RhI₂]₂ (1) or the acetonitrile complex [(η⁵-C₉H₂Me₅)Rh(MeCN)₃]²⁺ with Tl[Tl(η-7,8-C₂B₉H₁₁)] afforded rhodacarborane (η⁵-C₉H₂Me₅)Rh(7,8-C₂B₉H₁₁) (2). The cationic triple-decker complex with the bridging boratabenzene ligand [Cp*Fe(μ-η:η-C₅H₃Me₂BMe)Rh(η⁵-C₉H₂Me₅)]²⁺ (3) was synthesized by the reaction of the nitromethane solvate [(η⁵-C₉H₂Me₅)Rh(MeNO₂)₃]²⁺ with the sandwich compound Cp*Fe(η-C₅H₃Me₂BMe). The structure of 2 was established by X-ray diffraction. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1623–1625, August, 2008.     

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     

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.