Synthesis of boron-containing tyrosine derivatives based on the closo-decaborate and closo-dodecaborate anions

A series of new boron-containing tyrosine derivatives [B _n H _n?1O(CH₂)₄O-4-C₆H₄CH₂CH-(NH₃)COOH]^? and [B _n H _n?1O(CH₂CH₂)₂O-4-C₆H₄CH₂CH(NH₃)COOH]^? (n = 10, 12) were prepared by ring opening of the cyclic oxonium derivatives of the decahydro-closo-decaborate and dodecahydro-closo-dodecaborate anions, respectively, with ethyl N-trifluoroacetyl-L-tyrosinate.     

Cage complexes as a molecular scaffold for polyfunctional and polytopic systems: Synthesis of the first closo-borate iron(II) clathrochelate

The ribbed functionalization of the clathrochelate iron(II) tris-dioximates as a potential “molecular scaffold” for the synthesis of polyfunctional and polytopic complexes with closo-dodecaborate-anion substituents was performed. closo-Dodecaborate-substituted clathrochelate [FeBd₂(Cl(B₁₂H₁₁NH)Gm)(BF)₂]^2? (where Bd^2? is α-benzyldioxime dianion, Gm is glyoxime residue) dianion was prepared starting from dichloride clathrochelate FeBd₂(Cl₂Gm)(BF)₂ precursor with amino-closo-dodecaborate (NBu₄)[B₁₂H₁₁NH₃] in the presence of potassium tert-amylate. This clathrochelate dianion was isolated as a tetra-n-butylammonium salt and characterized using elemental analysis, MALDI-TOF and PD mass, IR, UV-Vis, ⁵⁷Fe Mössbauer spectra as well as by ¹H, ¹¹B and ¹³C{¹H} NMR spectra.     

New methods of preparation of hydroxy-closo-decaborates [B10H10 − n (OH) n ]2− (n = 1, 2)

New methods of preparation of hydroxy-closo-decaborates [B₁₀H_{10 ? n} (OH) _n ]^2? (n = 1, 2) that are based on the reaction of anions [B₁₀H_{10 ? n} (OAc) _n ]^2? and alkoxyethylidenoxonio-closo-decaborates [2-B₁₀H₉OC(OR)CH₃]^? with aqueous solution of hydrazine are proposed. The obtained compounds were characterized by IR, ESI/MS, and NMR (¹H, ¹¹B, ¹³C) spectroscopy.     

Practical synthesis of 1,4-dioxane derivative of the closo-dodecaborate anion and its ring opening with acetylenic alkoxides

Practical method of synthesis of the 1,4-dioxane derivative of the closo-dodecaborate anion was developed. The cleavage of the dioxonium ring in [B₁₂H₁₁O(CH₂CH₂)₂O]⁻ with acetylenic alcohols gave rise to the preparation of closo-dodecaborate derivatives with terminal acetylene group. These compounds can be introduced into click reactions with phenylazide leading to the corresponding triazoles. The structures of (Bu₄N)[B₁₂H₁₁O(CH₂CH₂)₂O] and (Bu₄N)₂[B₁₂H₁₁(OCH₂CH₂)₂OCH₂CCH] · 0.5HOCH₂CCH were determined by single-crystal X-ray diffraction.     

N-arylammonio- and N-pyridinium-substituted derivatives of dodecahydro-closo-dodecaborate(2-)

We report two methods for preparing N-arylammonio, N-pyridyl and N-arylamino dodecaborates: heating of the tetrabutylammonium salt of dodecahydro-closo-dodecaborate(2-) with aryl and pyridyl amines, or nucleophilic attack of [closo-B₁₂H₁₁NH₂]²⁻ on a strongly deactivated aromatic system. With aryl amines we obtained [1-closo-B₁₂H₁₁N(R¹)₂C₆H₅]⁻ (R¹ = H, CH₃). With 4-(dimethylamino)pyridine, [1-closo-(B₁₂H₁₁NC₅H₄)-4-N(CH₃)₂]⁻, with a bond between the boron and the pyridinium nitrogen, was obtained. A presumable mechanism for this kind of reactions is reported. By nucleophilic substitution, two products, [1-closo-(B₁₂H₁₁NHC₆H₃)-3,4-(CN)₂]²⁻ and [1-closo-(B₁₂H₁₁NHC₆H₂)-2-(NO₂)-4,5-(CN)₂]²⁻, were formed with 4-nitrophthalonitrile and 1-chloro-2,4-dinitrobenzene gave [1-closo-(B₁₂H₁₁NHC₆H₃)-2,4-(NO₂)₂]²⁻. For [1-closo-B₁₂H₁₁N(CH₃)₂C₆H₅]⁻ and [1-closo-(B₁₂H₁₁NHC₆H₃)-2,4-(NO₂)₂]²⁻ single crystal X-ray structures were obtained.     

Synthesis,characterization, X‐ray crystal structure and in vitro antitumour activity of sodium bis(2‐(3′,6′,9′‐trioxadecyl)‐1,2‐dicarba‐closo‐dodecaborane‐1‐carboxylato)triphenylstannate

Sodium bis[2‐(3′,6′,9′‐trioxadecyl)‐1,2‐dicarba‐closo‐dodecaborane‐1‐carboxylato]triphenylstannate, [(CH₃OCH₂CH₂OCH₂CH₂OCH₂CH₂)‐1,2‐C₂B₁₀H₁₀‐9‐COO)₂SnPh₃]^? Na⁺, compound 1, was synthesized by the 1:1 condensation of triphenyltin(IV) hydroxide with 2‐(3′,6′,9′‐trioxadecyl)‐1,2‐dicarba‐closo‐dodecaborane‐1‐carboxylic acid and crystallized in the presence of sodium bicarbonate. Its structure was determined by spectroscopy, elemental analysis and X‐ray diffraction. The structure of 1 consists of trigonal bipyramidal [Sn(Ph)₃(L)₂]^? anions and Na⁺ cations coordinated by oxygen atoms of polyoxaalkyl chains of different stannate anions, forming cation–anion chains elongated along the c axis. Compound 1 is significantly more active in vitro against seven tumour cell lines of human origin than 5‐fluorouracil, cis‐platin, carboplatin, and previously reported organotin carboranecarboxylates, but is less active than organotin polyoxaalkylcarboxylates. Copyright © 2004 John Wiley & Sons, Ltd.     

Ruthenium carborane complexes: a relationship between the structure, electrochemical properties, and reactivity in catalysis of polymerization processes

The ruthenacarborane complexes of the exo-nido- and closo-structure, namely, diamagnetic exo-nido-5,6,10-[RuCl(PPh₃)₂]-5,6,10-(μ-H)₃-10-H-7,8-(CH₃)₂-7,8-C₂B₉H₆, 3,3-[Ph₂P(CH₂) _n PPh₂]-3-H-3-Cl-closo-3,1,2-RuC₂B₉H₁₁ (n = 4, 5), paramagnetic 3,3-[Ph₂P(CH₂) _n PPh₂]-3-Cl-closo-3,1,2-RuC₂B₉H₁₁ (n = 2–5), and their some ortho-phenylenecycloboronated derivatives, were studied by cyclic voltammetry. All chelate closo-complexes are characterized by reversible redox transitions, while the exo-nido-complex is liable to irreversible oxidation. Shortening of the methylene link in the diphosphine ligand of closo-ruthenacarboranes and/or the introduction of ortho-phenylenecycloboronated moieties and methyl substituents to the carbon atoms of the {C₂B₉} ligand lead to a decrease in the redox potential and electron density redistribution to the metal atom. A comparison of the experimental results on methyl methacrylate polymerization in the presence of the catalytic systems based on the studied metallacarboranes with the data on their electrochemical characteristics suggests that the efficiency of using the ruthenium complexes as catalysts is mainly determined by steric factors.     

Synthesis of 12-vertex mixed ligand closo-cobaltacarborane complexes and molecular structure of [3,3-(Ph2P(CH2)2PPh2)-3-Cl-closo-3,1,2-CoC2B9H11]

A reaction of complexes CoCl₂(dppe) (dppe is the 1,2-bis(diphenylphosphino)ethane) or CoCl₂(dppp) (dppp is the 1,3-bis(diphenylphosphino)propane) with [K][7,8-nido-C₂B₉H₁₂] upon reflux in benzene led to the mixed ligand closo-cobaltacarboranes [3,3-(Ph₂P(CH₂) _n PPh₂)-3-Cl-closo-3,1,2-Co^IIIC₂B₉H₁₁] (n = 2 and 3, respectively) in moderate yields (34 and 16%). The structure of the 18-electron complexes in solution and the solid state was studied by NMR and IR spectroscopy, the structure in the case of the closo-complex with dppe-ligand was confirmed by X-ray crystallography.     

8-Dioxane ferra(III) bis(dicarbollide): A paramagnetic functional molecule as versatile building block for introduction of a Fe(III) centre into organic molecules

The synthesis of a new, paramagnetic closo-[(8-(-CH₂CH₂O)₂-1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)-3,3′-Fe]⁰ (3) is reported. This compound can serve as a versatile building block for construction of both anionic and zwitterionic derivatives, as exemplified by the synthesis of a series of compounds of general formula closo-[(8-X-(CH₂CH₂O)₂-1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)-3,3′-Fe], bearing organic end groups (X = NC₅H₅ (4), (C₆H₅)₃P (5), OH (6), and 2-O(1-CH₃O-C₆H₄) (7)) attached to the cluster by a diethyleneglycol spacer. Molecular structures of 3, 4, 5 and 7 were determined by single-crystal X-ray diffraction analysis and by the long-time neglected method of paramagnetic, high field NMR (¹H, ¹³C and ¹¹B) spectroscopy.     

A boron-boron linked large metallacarborane cluster: Characterization and X-ray structure of 8,9′-[closo-{3-Co(η-C5H5)-1,2-C2B9H10}]2

The 8,9′-[closo-{3-Co(η⁵-C₅H₅)-1,2-C₂B₉H₁₀}]₂ (1) species, in which two large closo-CoC₂B₉ sub-clusters are connected by a B-B bond, is unexpectedly obtained from the reaction of closo-[3-Co(η⁵-C₅H₅)-1,2-C₂B₉H₁₁] with sulfur in the presence of aluminium chloride under reflux conditions. The solid state conformation of 1 seems to be the result of a pair of intramolecular C-H?H-B dihydrogen bonds between the protonic H atoms of the C₅H₅ fragment of a sub-cluster and the hydridic H atoms of the C₂B₉H₁₁ fragment in the other sub-cluster in 1.     

Interaction between a Decahydro-closo-Decaborate(2–) Anion and Aliphatic Carboxylic Acids

Interaction between a closo-decaborate anion B₁₀H^2– ₁₀and carboxylic acids RCOOH (R = H, CH₃, C₂H₅, iso-C₃H₇, C₄H₉) is studied. The mono-, di- tri- and tetrasubstituted products B₁₀H_{10 – n} (OCOR)^2– _n are formed in sequence with the temperature growth. The reaction follows an essentially regioselective mechanism: only one of all possible isomers forms at every stage of the process. The respective hydroxy-closo-decaborates B₁₀H_{10 – n} (OH)^2– _n were prepared by alkaline hydrolysis in aqueous and nonaqueous solutions. All the compounds were identified by chemical analysis and ¹¹B NMR and IR spectroscopy. The crystal structure of [Pb(Bipy)(DMF)(B₁₀H₉OH)] · DMF was determined by X-ray diffraction.     

Syntheses of C-substituted icosahedral dicarbaboranes bearing the 8-dioxane-cobalt bisdicarbollide moiety

The treatment of 1,2-, 1,7- and 1,12-carbaborane lithiated isomers with [3,3′-Co-8-(CH₂CH₂O)₂-(1,2-C₂B₉H₁₀)-(1′,2′-C₂B₉H₁₁)] (1) at molar ratios 1:1 or 1:2 at room temperature in THF leads generally to the formation of a series of orange double-cluster mono and dianions. These were characterized by NMR and MS methods as [1′′-X-1′′,2′′-closo-C₂B₁₀H₁₁]⁻, [2]⁻; [1′′-X-1′′,7′′-closo-C₂B₁₀H₁₁]⁻, [3]⁻ and [1′′-X-1′′,12′′-closo-C₂B₁₀H₁₁], [4]⁻ for the monoanions, whereas [1′′,2′′-X₂-1′′,2′′-closo-C₂B₁₀H₁₀]²⁻, [2]²⁻; [1′′,7′′-X₂-1′′,7′′-closo-C₂B₁₀H₁₀]²⁻, [3]²⁻; and [1′′,12′′-X₂-1′′,12′′-closo-C₂B₁₀H₁₀]²⁻, [4]²⁻ for the dianions (where X = 3,3′-Co-8-(CH₂CH₂O)₂-(1,2-C₂B₉H₁₀)-1′,2′-(C₂B₉H₁₁)). Moreover, these borane-cage subunits can be easily modified via attaching variable substituents onto cage carbon and boron vertices, which makes these compounds structurally flexible potential candidates for BNCT of cancer and HIV-PR inhibition.     

New approaches to cluster modification in the 12-vertex metallatricarbollide series

Cluster opening of [2-Cp-9-^tBuNH-closo-2,1,7,9-FeC₃B₈H₁₀] (1) , followed by oxidation, generates complexes [2-Cp-8-^tBuNH-closo-2,1,8,10-FeC₃B₈H₁₀] (2), [2-Cp-4-^tBuNH-closo-2,1,4,12-FeC₃B₈H₁₀] (3), [2-Cp-1-^tBuNH-closo-2,1,7,10-FeC₃B₈H₁₀] (4), and [1-Cp-10-^tBuNH-closo-1,2,3,10-FeC₃B₇H₉] (5). Another variation of the syntheses led to compounds [2-Cp-closo-2,1,8,10-FeC₃B₈H₁₁] (6), [4-Cp-1-^tBuNH-closo-4,1,6,8,-FeC₃B₉H₁₁] (7) and to two isomeric, not yet fully characterized, 13-vertex compounds of general nido structure [^tBuNH-Cp-FeC₃B₉H₁₂] (8 and 9).     

Synthesis of functional derivatives of the [3,3′-Co(1,2-C2B9H11)2] anion

A series of various functional derivatives of the cobalt bis(1,2-dicarbollide) anion [8-XCH₂CH₂OCH₂CH₂O-3,3′-Co(1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)]⁻ (X=OH, NH₂, and CH(NH₂)COOH) were prepared by the ring-opening reactions of [8-O(CH₂CH₂)₂O-3,3′-Co(1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)] with different nucleophiles followed by functional group interconversion reactions. Acidic hydrolysis of [8-NCCH₂CH₂OCH₂CH₂O-3,3′-Co(1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)]⁻ resulted in the shorter-chain alcohol [8-HOCH₂CH₂O-3,3′-Co(1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)]⁻. Structures of (Bu₄N)[8-AcNHC(COOEt)₂CH₂CH₂OCH₂CH₂O-3,3′-Co(1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)] and [8-(1-C₅H₅N)CH₂CH₂OCH₂CH₂O-3,3′-Co(1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)] were determined by the single crystal X-ray diffraction method. Perspectives of application of functionalized cobalt bis(1,2-dicarbolide) derivatives in nuclear medicine are discussed.     

Synthesis and characterization of 11-vertex platinaborane compounds having nido-PtB10H12 and nido-Pt2B9H10 skeletons

The reaction of closo-[B₁₀H₁₀]²⁻ with [PtCl₂(PPh₃)₂] in MeOH at reflux affords the B-methoxy substituted 11-vertex nido-platinaborane compound [(PPh₃)₂PtB₁₀H₁₀-8-H_0.5(OCH₃)_0.5-10-(OCH₃)] (1) and the known species [(PPh₃)₂PtB₁₀H₁₁-8-(OCH₃)] (2) and 1,6-(PPh₃)₂B₁₀H₈ (3). The same reaction under solvothermal condition gives the partially degraded diplatinaborane [(PPh₃)₂(μ-PPh₂)Pt₂B₉H₇-3,9,11-(OMe)₃] (4) with a novel nido-Pt₂B₉H₁₀ skeleton. The new metallaborane compounds have been characterized by spectroscopic methods and single-crystal X-ray analyses. In particular, computational/theoretical chemistry supports the ultimate structural confirmation of 4. The structures of these metallaboranes exhibit interesting intra- and/or intermolecular C-H?O hydrogen bonding interactions.     

Cyclopentadienyl-Liganden mit hydrophilen tentakeln

Cyclopentadienyl ligands bearing hydrophilic tentacles are obtained by treating Cp′SiMe₂Cl (Cp′ Cp or C₅Me₄H) with H(OCH₂CH₂)_nOMe (n = 2 or 3) in the presence of pyridine; the products Cp′SiMe₂(OCH₂CH₂)_nOMe can be deprotonated by potassium in toluene. Reaction of the potassium salt of CpSiMe₂(OCH₂CH₂)₂OMe with Me₂SiCl₂ yields C₅H₄(SiMe₂Cl)(OCH₂CH₂)₂OMe, which can be treated with H(OCH₂CH₂)₂OMe to give C₅H₄[(OCH₂CH₂)₂OMe]₂.     

Syntheses and catalytic activities of Group 4 metal complexes derived from C(cage)-appended cyclohexyloxocarborane trianion

The reaction of Li[closo-1-Me-1,2-C₂B₁₀H₁₀] with cyclohexene oxide produced closo-1-Me-2-(2′-hydroxycyclohexyl)-1,2-C₂B₁₀H₁₀ (1) in 86% yield. Decapitation of (1) with potassium hydroxide in refluxing ethanol gave the corresponding cage-opened potassium salt of the carborane anion, [nido-1-Me-2-(2′-hydroxycyclohexyl)-1,2-C₂B₉H₁₀]⁻ (2) in 82% yield. Deprotonation of (2) with two equivalents of n-butyllithium in THF at −78 °C, followed by its further reaction with anhydrous MCl₄ · 2THF (M = Ti, Zr) produced the corresponding d⁰-half-sandwich metallacarboranes, closo-1-M(Cl)-2-Me-3-(2′-σ-O-cyclohexyl)-η⁵-2,3-C₂B₉H₉ (3 M = Zr; 4 M = Ti), in 59% and 51% yields, respectively. Reaction of Li[closo-1,2-C₂B₁₀H₁₁] with Merrifield’s peptide resin (1%) in refluxing THF gave the ortho-carborane-functionalized polymer (5) in 88% yield. The corresponding closo-1-polystyryl-2-(2′-hydroxycyclohexyl)-1,2-C₂B₁₀H₁₀ (6) was produced in 94% yield by refluxing a mixture of the lithium salt of (5) and cyclohexene oxide in THF for 2 days. Compound (6) was decapitated, deprotonated and then reacted with ZrCl₄ · 2THF to produce a polymer-supported d⁰-half-sandwich metallacarborane closo-1-Zr(Cl)-2-polystyryl-3-(2′-σ-O-cyclohexyl)-η⁵-2,3-C₂B₉H₉ (7) in 41% yield. Compounds (3) and (7), in the presence of MMAO-7 (13% ISOPAR-E), were found to catalyze the polymerization of ethylene and vinyl chloride in toluene to give high molecular weight PE (9.4 × 10³ (M_w/M_n = 1.8)) and PVC (2.1 × 10³ (M_w/M_n = 1.6)), respectively.     

A topological pattern for the understanding of the stability and aromaticity of closo-boranes: constructing closo-borane from nido-boranes

The closo-boranes B _n H _n ^2? (6????n????12) have been constructed topologically by fusing together of the two component nido-boranes B₅H₉ and B₆H₁₀. The stability and aromaticity of the closo-boranes can be regarded as inherited from the two component nido-boranes, and the closo-boranes which can be formed by two same nido-boranes through sharing a ??ring?? fragment or without sharing any BH fragment are more stable than other types of closo-boranes. It can be anticipated that the constructing method of this article can bring enlightment to the structural interpretation process of other systems.     

Synthesis of hetero-substituted derivatives of cobalt bis(1,2-dicarbollide)

A new approach to synthesis of hetero-substituted derivatives of cobalt bis(1,2-dicarbollide) was proposed. The approach involves stepwise introduction of functional groups into different dicarbollide ligands. Halogenation of the monohydroxy derivative [8-OH-3,3??-Co-(1,2-C₂B₉H₁₀)(1??,2??-C₂B₉H₁₁)]^? gave the corresponding halogen hydroxy derivatives [8-OH-8??-X-3,3??-Co(1,2-C₂B₉H₁₀)₂]^? (X = Cl, Br, and I). Reactions of 8,8??-??-iodonium-3-commo-cobaltbis(1,2-dicarba-closo-dodecaborate) [8,8??-I-3,3??-Co(1,2-C₂B₉H₁₀)₂] with chloroform and 1,2-dibromoethane yielded the mixed halides [8-Y-8??-I-3,3??-Co(1,2-C₂B₉H₁₀)₂]^? (Y = Cl and Br).     

Tetraphenylboroxinate(1-) salts of monoborate cations: Synthesis and single-crystal X-ray structures of [Ph2B{OCH2CH2N(Me)(CH2)n}2][Ph4B3O3] (n = 4, 5)

The salts, [Ph₂B{OCH₂CH₂N(Me)(CH₂)_n}₂][Ph₄B₃O₃] (n = 4, 5), were prepared in moderate yields in MeOH solution from reaction of Ph₂BOBPh₂ with [N(CH₂)_n(Me)(CH₂CH₂OH)][OH] and PhB(OH)₂ in a 1:2:4 ratio. The reactions also lead to Ph₃B₃O₃. Both salts were characterized by NMR (¹H, ¹³C, ¹¹B) IR, and single-crystal XRD studies. The salts are comprised of cationic monoborates (zwitterionic, 2N⁺ and 1B⁻) and tetraphenylboroxinate anions.