Metal complexes with an aminosubstituted tricarbollide ligand

The reaction of the tricarbollide salt Tl[7-tBuNH-7,8,9-C₃B₈H₁₀] (Tl1) with [(cod)Rh(THF)_x]⁺ gives the rhodium complex [1-(cod)-12-tBuNH-1,2,4,12-RhC₃B₈H₁₀] in almost quantitative yield. Analogous reactions of Tl1 with [(ring)M(THF)_x]²⁺ ((ring)M = Cp*Rh and (1,3,5-C₆H₃Me₃)Ru) afford the corresponding metallatricarbollides [1-(ring)-12-tBuNH-1,2,4,12-MC₃B₈H₁₀] in ca. 50% yield. Refluxing Tl1 with [Mn(CO)₃(MeCN)₃]⁺ in THF give the tricarbollide analogue of cymantrene, [1,1,1-(CO)₃-12-tBuNH-1,2,4,12-MnC₃B₈H₁₀], the structure of which was determined by single-crystal X-ray diffraction analysis. In all cases, the formation of the metallatricarbollide complexes is accompanied by polyhedral rearrangement leading to the maximum separation of the cage carbon atoms.     

Alternative syntheses and X-ray diffraction analyses of the parent tricarbaborane compounds [nido-7,8,9-C3B8H11], [nido-7,8,10-C3B8H11] and [1-(η-C5H5)-closo-1,2,4,10-FeC3B8H11]

Reaction of the neutral tricarbaborane nido-7,8,9-C₃B₈H₁₂ (1) with triethylamine in CH₂Cl₂ led to quantitative deprotonation and isolation of the corresponding Et₃NH⁺ salt of the [nido-7,8,9-C₃B₈H₁₁]⁻ anion (2). This was converted into PSH⁺ and Me₄N⁺ salts via metathetic cation exchange. Heating of the solid Me₄N⁺[7,8,9-C₃B₈H₁₁]⁻ in mineral oil at 350 °C for 2 h resulted in thermal rearrangement and isolation of the cage isomeric compound Me₄N⁺[7,8,10-C₃B₈H₁₁]⁻. Finally, compound 1 was directly complexed via reaction with [CpFe(CO)₂]₂ (Cp = η⁵-C₅H₅) to generate the ferratricarbollide sandwich [1-Cp-closo-1,2,4,10-FeC₃B₈H₁₁] (4) in 60% yield. The structures of all the generic compounds of tricarbollide chemistry, 1 (PSH⁺ salt), 2 (MePPh₃⁺salt), and 4, were established unambiguously by an X-ray diffraction analysis.     

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.     

Reaction of nido-1,2-(CpRuH)2B3H7 with ethynylferrocene to yield new metallacarboranes

Addition of ethynylferrocene to nido-1,2-(Cp^∗RuH)₂B₃H₇ (1) at ambient temperature leads to nido-1,2-(Cp^∗Ru)₂(1,5-μ-C{Fc}Me)B₃H₇ (2, 3) and closo-4-Fc-1,2-(Cp^∗RuH)₂-4,6-C₂B₂H₃ (4). Compounds 2 and 3 represent a pair of geometric isomers, nido-species in which the regiochemistry of the alkyne reduction conforms to the Markovnikoff rule. Compound 4 is an octahedral structure in which the inserted alkyne is on an open face of the closo cluster.     

Group 4 metallacarboranes of constrained geometries derived from B(cage)- and C(cage)-silylamido-substituted carborane ligands: a synthetic and structural investigation

The reactions of RNHSi(Me)₂Cl (1, R=t-Bu; 2, R=2,6-(Me₂CH)₂C₆H₃) with the carborane ligands, nido-1-Na(C₄H₈O)-2,3-(SiMe₃)₂-2,3-C₂B₄H₅ (3) and Li[closo-1-R′-1,2-C₂B₁₀H₁₀] (4), produced two kinds of neutral ligand precursors, nido-5-[Si(Me)₂N(H)R]-2,3-(SiMe₃)₂-2,3-C₂B₄H₅, (5, R=t-Bu) and closo-1-R′-2-[Si(Me)₂N(H)R]-1,2-C₂B₁₀H₁₀ (6, R=t-Bu, R′=Ph; 7, R=2,6-(Me₂CH)₂C₆H₃, R′=H), in 85, 92, and 95% yields, respectively. Treatment of closo-2-[Si(Me)₂NH(2,6-(Me₂CH)₂C₆H₃)]-1,2-C₂B₁₀H₁₁ (7) with three equivalents of freshly cut sodium metal in the presence of naphthalene produced the corresponding cage-opened sodium salt of the “carbons apart” carborane trianion, [nido-3-{Si(Me)₂N(2,6-(Me₂CH)₂C₆H₃)}-1,3-C₂B₁₀H₁₁]³⁻ (8) in almost quantitative yield. The reaction of the trianion, 8, with anhydrous MCl₄ (M=Ti and Zr) in 1:1 molar ratio in dry tetrahydrofuran (THF) at −78 °C, resulted in the formation of the corresponding half-sandwich neutral d⁰-metallacarborane, closo-1-M[(Cl)(THF)_n]-2-[1′-η¹σ-N(2,6-(Me₂CH)₂C₆H₃)(Me)₂Si]-2,4-η⁶-C₂B₁₀H₁₁ (M=Ti (9), n=0; M=Zr (10), n=1) in 47 and 36% yields, respectively. All compounds were characterized by elemental analysis, ¹H-, ¹¹B-, and ¹³C-NMR spectra and IR spectra. The carborane ligand, 7, was also characterized by single crystal X-ray diffraction. Compound 7 crystallizes in the monoclinic space group P2₁/c with a=8.2357(19) Å, b=28.686(7) Å, c=9.921(2) Å; β=93.482(4)°; V=2339.5(9) ų, and Z=4. The final refinements of 7 converged at R=0.0736; wR=0.1494; GOF=1.372 for observed reflections.     

Metal complexes of monocarbon carboranes bearing C-amine or -amino substituents

Icosahedral metal-monocarbollide complexes in which the carbon atom of the {nido-CB₁₀} fragment carries an exo-polyhedral -NR₃ or -NR₂ group have an extensive chemistry. This is illustrated with complexes of ruthenium, osmium, rhodium, molybdenum, tungsten and rhenium. Many complexes with molecular structures new to the metallacarborane field have been discovered, and it has been shown that it is possible to introduce functional groups into the {nido-CB₁₀} cage system in many different ways.     

Nano and dendritic structured carboranes and metallacarboranes: From materials to cancer therapy

An account of the current research carried out in our laboratories is presented. Included is the incorporation of several group 14 elements into charge-compensated carboranes. These species present a bonding pattern not found in other main group carboranes. In addition to our continuing studies of the syntheses and structures of organometallic compounds, the use of these compounds as catalysts and catalyst precursors has been investigated. The isotopic exchange reactions between ¹⁰B enriched boron hydrides with naturally abundant boranes catalyzed by Ru(0) nanoparticles has been studied. The Ru(0) nanoparticles were obtained by the reduction of [CpRuCp^∗RuCp^∗]PF₆ (Cp^∗ = C₅Me₅) with hydrogen and stabilized by the ionic liquid trihexyltetradecylphosphonium dodecylbenzenesulfonate [THTdP][DBS]. This was found to be an excellent, long lived catalyst for the exchange reaction of B-10 enriched diborane and naturally abundant decaborane(14). Other approaches to the production and use of nano-metal catalysts have also been explored. The reduction of the iridium carborane, (PPh₃)₂IrH(7,8-C₂B₉H₁₁) with hydrogen in the presence of trihexyltetradecylphosphonium methylsulfonate, [THTdP][MS], produced an Ir(0) nanoparticles that catalyzed the phenylborolation as did our Ir(sal = N-R = salicylaldiminato; COD = cyclooctadiene complex. Progress in the use of single wall carbon nanotubes (SWCNT) as boron delivery agents was also discussed.     

Partial incorporation of a cyclopentadienyl ligand into a molybdaborane to form a molybdacarbaborane

Reaction of the molybdaborane arachno-2-[Mo(η-C₅H₅)(η⁵:η¹-C₅H₄)B₄H₇] (I) with NEt₃ in toluene at 120 °C for 7 days gives a 90% yield of the molybdacarbaborane nido-1-[Mo(η-C₅H₅)(η³:η²-C₃H₃)C₂B₃H₅] (II). Two of the carbon atoms in the substituted cyclopentadienyl ring in I are incorporated into the metallacarbaborane cluster II. The carbaborane {C₂B₃H₅} fragment in II is attached to an allylic {C₃H₃} group and can be thought of as a new non-planar {C₅B₃H₈} ligand providing seven electrons to the molybdenum atom. Reaction of I with KH in thf at 20 °C gives the anion via deprotonation of a B-H-B bridging proton.     

Chemistry related to cluster-borane analogues of the cyclopentadienide anion and ferrocene: New developments

A review on cluster-borane analogues of the cyclopentadienide anion (Cp) and ferrocene is presented. Analogues of Cp that have been so far isolated and characterised are the 11-vertex triheteroboranes of general structure [nido-E₃B₈H₈]⁻ (where E = CH or P and their combinations), the molecules of which contain an open pentagonal face. These anions were used as effective ligands for the preparation of “half- and full-sandwich” complexes [CpFeE₃B₈H₈] and [Fe(E₃B₈H₈)₂], respectively - analogues of ferrocene. Developments in this area of cluster-borane chemistry that include recent results in the synthesis and Fe-complexation reactions of 11-vertex tricarbaboranes (tricarbollides), phosphadicarbollides, and diphosphacarbollides are the subject of this work.