Multinuclear NMR Spectroscopy Research Articles

Design and Synthesis of Nitrogen-Rich Azo-Bridged Furoxanylazoles as High-Performance Energetic Materials.

A series of novel energetic materials comprising of azo-bridged furoxanylazoles enriched with energetic functionalities was designed and synthesized. These high-energy materials were thoroughly characterized by IR and multinuclear NMR (1 H, 13 C, 14 N) spectroscopy, high-resolution mass spectrometry, elemental analysis, and differential scanning calorimetry (DSC). The molecular structures of representative amino and azo oxadiazole assemblies were additionally confirmed by single-crystal X-ray diffraction and X-ray powder diffraction. A comparison of contributions of explosophoric moieties into the density of energetic materials revealed that furoxan and 1,2,4-oxadiazole rings are the densest motifs while the substitution of the azide and amino fragments on the nitro and azo ones leads to an increase of the density. Azo bridged energetic materials have high nitrogen-oxygen contents (68.8-76.9 %) and high thermal stability. The synthesized compounds exhibit good experimental densities (1.62-1.88 g cm-3 ), very high enthalpies of formation (846-1720 kJ mol-1 ), and, as a result, excellent detonation performance (detonation velocities 7.66-9.09 km s-1 and detonation pressures 25.0-37.7 GPa). From the application perspective, the detonation parameters of azo oxadiazole assemblies exceed those of the benchmark explosive RDX, while a combination of high detonation performance and acceptable friction sensitivity of azo(1,2,4-triazolylfuroxan) make it a promising potential alternative to PETN.

The Step‐Wise Synthesis of Oligomeric Phosphoramidates

AbstractIn this study, the step‐wise synthesis to a series of higher phosphoramidates was explored, affording compounds containing N−P−N, symmetric and asymmetric P−N−P and P−N−P−N−P linkages. Salt elimination and lithiation strategies were employed to create the new P−N bonds. It was found that the steric bulk and electronic contribution of the substituents on the P(V) centers were important factors to the success of the reactions. The oligomeric phosphoramidates were characterized by multinuclear NMR and IR spectroscopies as well as ESI mass spectrometry. A selection of the synthesized P−N oligomers were evaluated for their antimicrobial activity against E.coli, S.aureus, C.albicans, and A.fumigatus at varying concentrations. The results suggest their potential use as environmentally friendly fire retardants as the minimal inhibitory concentration (MIC) value for all the compounds was found to be >128 μM, indicating that the compounds do not have any detectable antimicrobial activity.

The Atomic-Level Structure of Mesoporous Hexagonal Boron Nitride Determined by High-Resolution Multinuclear Solid-State NMR Spectroscopy and DFT Calculations

The Atomic-Level Structure of Mesoporous Hexagonal Boron Nitride Determined by High-Resolution Multinuclear Solid-State NMR Spectroscopy and DFT Calculations

Synthesis and Characterization of Super Bulky β-Diketiminato Group 1 Metal Complexes

Sterically bulky β-diketiminate (or Nacnac) ligand systems have recently shown the ability to kinetically stabilize highly reactive low-oxidation state main group complexes. Metal halide precursors to such systems can be formed via salt metathesis reactions involving alkali metal complexes of these large ligand frameworks. Herein, we report the synthesis and characterization of lithium and potassium complexes of the super bulky anionic β-diketiminate ligands, known [TCHPNacnac]− and new [TCHP/DipNacnac]− (ArNacnac = [(ArNCMe)2CH]−) (Ar = 2,4,6-tricyclohexylphenyl (TCHP) or 2,6-diisopropylphenyl (Dip)). The reaction of the proteo-ligands, ArNacnacH, with nBuLi give the lithium etherate compounds, [(TCHPNacnac)Li(OEt2)] and [(TCHP/DipNacnac)Li(OEt2)], which were isolated and characterized by multinuclear NMR spectroscopy and X-ray crystallography. The unsolvated potassium salts, [{K(TCHPNacnac)}2] and [{K(TCHP/DipNacnac)}∞], were also synthesized and characterized in solution by NMR spectroscopy. In the solid state, these highly reactive potassium complexes exhibit differing alkali metal coordination modes, depending on the ligand involved. These group 1 complexes have potential as reagents for the transfer of the bulky ligand fragments to metal halides, and for the subsequent stabilization of low-oxidation state metal complexes.

Application of Multinuclear MAS NMR for the in situ Monitoring of Hydrothermal Synthesis of Zeolites.

In situ MAS NMR studies on the monitoring of hydrothermal synthesis of zeolites are reviewed. The first part of the review contains information on the experimental techniques used for the in situ NMR studies in static and MAS conditions. In the second part, the main capabilities of the in situ 1 H, 11 B, 13 C, 14 N, 19 F, 23 Na, 27 Al, 29 Si and 31 P MAS NMR for the elucidation of the mechanism of hydrothermal synthesis of zeolites are examined and the data on NMR lines identification are summarized. In the last part the main application areas of the techniques are considered and illustrated with examples taken from the mechanistic studies of zeolites A, X, MFI and BEA synthesis. A cross-reference index between the materials studied, the experimental approaches used, the mechanistic information obtained, and the corresponding literature sources is established.

Synthesis and Cu(I)/Mo(VI) Reactivity of a Bifunctional Heterodinucleating Ligand on a Xanthene Platform.

In an effort to probe the feasibility of a model of Mo-Cu CODH (CODH = carbon monoxide dehydrogenase) lacking a bridging sulfido group, the new heterodinucleating ligand LH2 was designed and its Cu(I)/Mo(VI) reactivity was investigated. LH2 ((E)-3-(((5-(bis(pyridin-2-ylmethyl)amino)-2,7-di-tert-butyl-9,9-dimethyl-9H-xanthen-4-yl)imino)methyl)benzene-1,2-diol) features two different chelating positions bridged by a xanthene linker: bis(pyridyl)amine for Cu(I) and catecholate for Mo(VI). LH2 was synthesized via the initial protection of one of the amine positions, followed by two consecutive alkylations of the second position, deprotection, and condensation to attach the catechol functionality. LH2 was found to exhibit dynamic cooperativity between two reactive sites mediated by H-bonding of the catechol protons. In the free ligand, catechol protons exhibit H-bonding with imine (intramolecular) and with pyridine (intermolecular in the solid state). The reaction of LH2 with [Cu(NCMe)4]+ led to the tetradentate coordination of Cu(I) via all nitrogen donors of the ligand, including the imine. Cu(I) complexes were characterized by multinuclear NMR spectroscopy, high-resolution mass spectrometry (HRMS), X-ray crystallography, and DFT calculations. Cu(I) coordination to the imine disrupted H-bonding and caused rotation away from the catechol arm. The reaction of the Cu(I) complex [Cu(LH2)]+ with a variety of monodentate ligands X (PPh3, Cl-, SCN-, CN-) released the metal from coordination to the imine, thereby restoring imine H-bonding with the catechol proton. The second catechol proton engages in H-bonding with Cu-X (X = Cl, CN, SCN), which can be intermolecular (XRD) or intramolecular (DFT). The reaction of LH2 with molybdate [MoO4]2- led to incorporation of [MoVIO3] at the catecholate position, producing [MoO3(L)]2-. Similarly, the reaction of [Cu(LH2)]+ with [MoO4]2- formed the heterodinuclear complex [CuMoO3(L)]-. Both complexes were characterized by multinuclear NMR, UV-vis, and HRMS. HRMS in both cases confirmed the constitution of the complexes, containing molecular ions with the expected isotopic distribution.

Preparation and Characterization of Pentafluoro‐λ6‐sulfanyldifluoromethane and Pentafluoro‐λ6‐sulfanyl‐1,1,2,2‐tetrafluoroethane

AbstractThe pentafluorosulfanyl‐λ6‐perfluoroalkyl halides SF5CF2I, SF5CF2CF2Br, and SF5CF2CF2I were prepared for use in the syntheses of other SF5‐containing compounds. For example, new, convenient syntheses were developed for the hydro compounds SF5CF2H and SF5CF2CF2H from the reduction of these iodides or bromides with either triethylborane or tributyltin hydride. Herein, more thorough spectroscopic analyses of the hydro compounds are presented, including multinuclear NMR and vibrational spectroscopy, mass spectrometry, and computational chemistry. Unfortunately, under the conditions tried, little to no evidence was obtained for potential SF5(CF2)n‐ (where n=1 or 2) transfer reagents such as SF5(CF2)nSi(CH3)3 or Cu(CF2)nSF5.

A neutral germanium/phosphorus frustrated Lewis pair: Synthesis and reactivity

A novel germinal germanium/phosphorus frustrated Lewis pair, Cl3GeCH2PtBu21, was prepared through the metathesis reaction of tBu2PCH2Li with tetrachlorogermanium. This neutral germanium-based frustrated Lewis pair 1 exhibits higher reactivity toward a series of small molecules. When 1 was treated with an excess amount of tetrachloromethane (2.3equiv) yielding a zwitterionic adduct 2, Cl4GeCH2P(Cl)tBu2. The cycloaddition of dimethyl but-2-ynedioate with 1 was took place smoothly at room temperature, and afforded a zwitterionic cyclic vinyl 3 in good yields. The reaction of 1 with furan-2,5-dione has also been performed giving the corresponding cycloaddition 4 in high yields. The additions of C=Ch (Ch = O, and S) units involving 1-isocyanato-4-methylbenzene and isothiocyanatobenzene with 1 have been also carried out at ambient temperature in which the five-membered GeCPCO(S)-ring products 5a and 5b were furnished, respectively. All these above-mentioned compounds 1-5 were fully characterized by multinuclear NMR spectroscopy, high-resolution mass spectrometry (HRMS), and the structures of 1 and 3 were also determined by single-crystal X-ray diffraction.

Synthesis of Directed, Tridentate Lewis Acids Based on a Trisilacyclohexane‐Backbone via Hydrosilylation

AbstractBased on a semiflexible trisilacyclohexane framework a series of directed, tridentate Lewis acids were synthesized by hydrosilylation using various (chloro)methylsilanes. The axial alignment of the three electron deficient functions in one spatial direction allows creating poly‐Lewis acids with chalice‐like cavities. The directed, tridentate poly‐Lewis acids were obtained in quantitative yields and characterized by multinuclear NMR spectroscopy, CHN analysis and X‐ray diffraction experiments. The Lewis acidity of the introduced silicon functions was quantified and classified using the Gutmann‐Beckett method.

Tetracarbonyl group 6B metal complexes of a N-(4-acetylphenyl)-N-(diphenylphosphino)amine ligand. Molecular structure of cis-[Cr(CO)4{4-CH3CO–C6H4-1-N(PPh2)2}]

Chemical reactions of N-(4-acetylphenyl)-N-(diphenylphosphino)amine ligand (1) with three group 6B metal hexacarbonyls produced cis-M(CO)4[1-k2P,P][ M = Cr(2), Mo(3), W(4)], respectively. The novel complexes 2–4 were isolated and their structures were elucidated by multinuclear NMR spectroscopy (1H, 13C, 31P NMR) and elemental analysis. Crystal-structure determination using single-crystal X-ray diffraction was carried out on complex 2.

New Method for Synthesis of Substituted N-Borylated Dipeptides Based on Acetonitrile Derivative of the closo-Dodecaborate Anion

A new multistage synthesis of the N-borylated dipeptide B12-PheGlyOH has been proposed. The approach is based on the reaction of nucleophilic addition of amino acid derivatives to the [B12H11NCCH3]– anion. The products of each stage have been characterized by multinuclear NMR spectroscopy, IR absorption spectroscopy, and ESI mass spectrometry.

A GAP Replacement: Improved Synthesis of 3-Azidooxetane and Its Homopolymer Based on Sulfonic Acid Esters of Oxetan-3-ol.

In the field of energetic binders, only hydroxy-terminated glycidyl azide polymer (GAP) has found widespread application and prevailed in the market. However, oxiranes such as glycidyl azide (GA) allow two ring-opening modes during polymerization and thus lead to polymers of different termination causing inhomogeneous curing results. An elegant solution is the polymerization of 3-azidooxetane as only terminating primary hydroxyl groups are formed. Beyond this, poly(3-azidooxetane) and GAP are equal in other aspects due to the similar repetition unit. Since literature methods for the preparation of 3-azidooxetane either employed toxic solvents, gave low yields or impurified product, or could not be reproduced, a new synthesis method was developed to afford pure material and satisfying yields. The syntheses of toluene- and methanesulfonic acid esters of oxetan-3-ol as precursors were also significantly improved in comparison to the literature and their molecular structures elucidated by single-crystal X-ray diffraction. The aforementioned compounds and poly(3-azidooxetane) were intensively studied by vibrational and multinuclear NMR spectroscopy (1H, 13C, 14N), differential scanning calorimetry, and elemental analysis. The key compound, 3-azidooxetane, was compared to glycidyl azide regarding performance using the EXPLO5 V6.04 thermochemical code and their sensitivity toward external stimuli like shock and friction assessed according to BAM standard procedures.

Isolation of a Cyclopentasilane from Magnesium Reduction of a Linear Hexasilane

AbstractThe reductive cyclization of two linear hexasilanes is contrasted, where a methylated precursor yielded a cyclohexasilane while the tert‐butyl‐functionalized analog unexpectedly yielded a cyclopentasilane. A comprehensive analysis using X‐ray diffraction, IR, HR, HRMS, and multinuclear (1H, 13C and 29Si) 1D and 2D NMR spectroscopy identified the 1,2‐dihydrodisilane tBuPhHSi‐SiHPhtBu as an additional product, which was interpreted as supportive of a mechanism involving silylene elimination. The results of this study may prove informative about substituent effects in the practice of complex organosilicon molecular synthesis.

Aminotroponiminates: Impact of the NO2 Functional Group on Coordination, Isomerisation, and Backbone Substitution.

Aminotroponiminate (ATI) ligands are a versatile class of redox‐active and potentially cooperative ligands with a rich coordination chemistry that have consequently found a wide range of applications in synthesis and catalysis. While backbone substitution of these ligands has been investigated in some detail, the impact of electron‐withdrawing groups on the coordination chemistry and reactivity of ATIs has been little investigated. We report here Li, Na, and K salts of an ATI ligand with a nitro‐substituent in the backbone. It is demonstrated that the NO2 group actively contributes to the coordination chemistry of these complexes, effectively competing with the N,N‐binding pocket as a coordination site. This results in an unprecedented E/Z isomerisation of an ATI imino group and culminates in the isolation of the first “naked” (i. e., without directional bonding to a metal atom) ATI anion. Reactions of sodium ATIs with silver(I) and tritylium salts gave the first N,N‐coordinated silver ATI complexes and unprecedented backbone substitution reactions. Analytical techniques applied in this work include multinuclear (VT‐)NMR spectroscopy, single‐crystal X‐ray diffraction analysis, and DFT calculations.

Nitroxy- and azidomethyl azofurazans as advanced energetic materials

Progress in the rocket industry is only possible on the basis of new, higher performance and more environmentally friendly materials compared to up-to-date propellant ingredients for liquid, solid, gelled and hybrid propellant systems. In this work, synthetic methods have been developed for the preparation of new energetic azofurazans bearing nitroxymethyl or azidomethyl groups. All prepared compounds were fully characterized by multinuclear NMR and IR spectroscopies, as well as elemental analyses. An analysis of the structural features based on the X-ray single-crystal diffraction made it possible to discuss their influence on the densities of the azofurazans of this study. Thermal decomposition and combustion of nitroxymethyl and azidomethyl azofurazans were studied using a number of complementary experimental techniques, namely thermogravimetry, differential scanning calorimetry, manometry, microthermocouple measurements in the combustion wave. The structural and physical characteristics of these new energetic analogues illustrate the extent to which the nature of the explosophoric groups can be used to tune the performace of the azofurazan framework. These azofurazans possess positive calculated enthalpy of formation and are promising candidates for new environmentally friendly energetic materials.

Crystalline Hydrogen-Bonding Networks and Mixed-Metal Framework Materials Enabled by an Electronically Differentiated Heteroditopic Isocyanide/Carboxylate Linker Group.

Mixed-metal solid-state framework materials are emerging candidates for advanced applications in catalysis and chemical separations. Traditionally, the syntheses of mixed-metal framework systems rely on postsynthetic ion exchange, metalloligands, or metal-deposition techniques for the incorporation of a second metal within a framework material. However, these methods are often incompatible with the incorporation of low-valent metal centers, which preferentially bind to electronically "soft" ligands according to the tenets of hard/soft acid/base theory. Here we present the electronically differentiated isocyanide/carboxylate heteroditopic linker ligand 1,4-CNArMes2C6H4CO2H (TIBMes2H; TIB = terphenyl isocyanide benzoate; ArMes2 = 2,6-(2,4,6-Me3C6H2)2C6H2), which is capable of selective binding of low-valent metals via the isocyano group and complexation of hard Lewis acidic metals through the carboxylate unit. This heteroditopic ligand also possesses an encumbering m-terphenyl backbone at the isocyanide function to foster coordinative unsaturation. The treatment of TIBMes2H with [Cu(NCMe)4]PF6 in a 3:1 ratio results in preferential binding of the isocyanide group to the Cu(I) center as assayed by multinuclear NMR and IR spectroscopies. IR spectroscopy also provides strong evidence for the formation of a copper(I) tris(isocyanide) complex, wherein the carboxylic acid group remains unperturbed. The addition of TIBMes2 to [Cu(NCMe)4]PF6 in a 4:1 ratio results in crystallization of the hydrogen-bonding network, [Cu(TIBMes2H)4]PF6, in which the formation of R22(8) hydrogen bonds results in a 7-fold interpenetrated diamondoid lattice structure. The preassembly of a copper(I) tris(isocyanide) complex using TIBMes2H, followed by deprotonation and the introduction of ZnCl2, generates a novel and unusual zwitterionic solid-state phase (denoted as Cu/Zn-ISOCN-5; ISOCN = isocyanide coordination network) consisting of a coordinatively unsaturated [Cu(CNR)3]+ cationic secondary building unit (SBU) and an anionic, paddlewheel-type Zn(II)-based SBU of the formulation [Cl2Zn2(O2CR)3]-. Inductively coupled plasma mass spectrometry analysis provided firm evidence for a 2:1 Zn-to-Cu ratio in the network, thereby indicating that the isocyanide and carboxylate groups selectively bind soft and hard Lewis acidic metal centers, respectively. The extended structure of Cu/Zn-ISOCN-5 is a densely packed, noninterpenetrated AB-stacked layer network with modest surface area. However, it is thermally robust, and its formation and compositional integrity validate the use of an electronically differentiated linker for the formation of mixed-metal frameworks incorporating low-valent metal centers.

Directed Syntheses of CS2- and CS3-Bridged Decaborane-14 Analogues.

To establish a procedure for single-cage cluster expansion of open cage dimetallaoctaboranes(12), we have investigated the chemistry of nido-[(Cp*M)2B6H10] (η5-C5Me5 = Cp*, 1: M = Co; 2: M = Rh), with diverse chalcogen-based borate ligands. As a result, treatment of nido-1 and nido-2 with Li[BH2E3] (E = S, Se, or Te) yielded 10-vertex nido-[(Cp*Co)2B7EH9] (3: E = S; 4: E = Se; 5: E = Te) along with known 10-vertex nido-[(Cp*M)2B6H6E2] (6: E = S, M = Co; 7: E = Se, M = Co; 8: E = Te, M = Co; 9: E = Se, M = Rh). The geometries of dimetallachalcogenaboranes, 3-9, are isostructural with decaborane(14). Thermolysis of nido-1 and nido-2 with an intermediate, generated from CS2 and [LiBH4]·THF reaction in THF, produced nido-[(Cp*M)2B6S2H4(CH2S2)] (10: M = Co; 11: M = Rh) and nido-[(Cp*M)2B6S2H4(CS3)] (12: M = Co; 13: M= Rh). Clusters 10-13 are rare species in which one of the B-B bonds is coordinated with a {CS2}2- or {CS3}2- ligand, generating di(thioborolane) {B2S2CH2} or di(thioboralane)-thione {B2CS3} moieties. To examine further the coordination chemistry of CS2-bridged decaborane(14) analogue nido-10, photolysis was carried out with {M(CO)5·THF} (M = Mo or W) that led to the isolation of [(Cp*Co)2B6S2H4(CH2S2){M(CO)5}] (14: M = Mo; 15: M = W), where the {CH2S2} moiety is coordinated with one {M(CO)5} moiety in η1-fashion. All the synthesized clusters have been characterized by ESI-mass, multinuclear NMR spectroscopy, and IR spectroscopy and structurally solved by single-crystal XRD. Furthermore, DFT calculations probe the bonding of these CS2- and CS3-bridged decaborane analogues.

Nucleophilic Addition to π-Allyl Gold(III) Complexes: Evidence for Direct and Undirect Paths.

π-Allyl complexes play a prominent role in organometallic chemistry and have attracted considerable attention, in particular the π-allyl Pd(II) complexes which are key intermediates in the Tsuji-Trost allylic substitution reaction. Despite the huge interest in π-complexes of gold, π-allyl Au(III) complexes were only authenticated very recently. Herein, we report the reactivity of (P,C)-cyclometalated Au(III) π-allyl complexes toward β-diketo enolates. Behind an apparently trivial outcome, i.e. the formation of the corresponding allylation products, meticulous NMR studies combined with DFT calculations revealed a complex and rich mechanistic picture. Nucleophilic attack can occur at the central and terminal positions of the π-allyl as well as the metal itself. All paths are observed and are actually competitive, whereas addition to the terminal positions largely prevails for Pd(II). Auracyclobutanes and π-alkene Au(I) complexes were authenticated spectroscopically and crystallographically, and Au(III) σ-allyl complexes were unambiguously characterized by multinuclear NMR spectroscopy. Nucleophilic additions to the central position of the π-allyl and to gold are reversible. Over time, the auracyclobutanes and the Au(III) σ-allyl complexes evolve into the π-alkene Au(I) complexes and release the C-allylation products. The relevance of auracyclobutanes in gold-mediated cyclopropanation was demonstrated by inducing C-C coupling with iodine. The molecular orbitals of the π-allyl Au(III) complexes were analyzed in-depth, and the reaction profiles for the addition of β-diketo enolates were thoroughly studied by DFT. Special attention was devoted to the regioselectivity of the nucleophilic attack, but C-C coupling to give the allylation products was also considered to give a complete picture of the reaction progress.

New isomeric pyridyl imine zinc(II) complexes as potential co-sensitizers for state of the Art N719 dye in DSSC

Three new isomeric Zn(II) complexes derived from pyridine based Schiff bases synthesized by condensation of pyridine-2-carboxyaldehyde and three positional isomers 2-amino pyridine (2-Py-Zn), 3- amino pyridine (3-Py-Zn) and 4-amino pyridine (4-Py-Zn). The synthesized ligands and their Zn(II) complexes have been characterized by microanalyses, FT-IR, multinuclear NMR, UV-Vis and emission spectroscopy. These newly synthesized isomeric complexes have been used as the sensitizers as well as co-sensitizers with state-of-the-art N719 dye in dye sensitized solar cells (DSSCs). Amongst all three isomeric complexes, the DSSC assembly fabricated with 4-Py-Zn/N719 dye shown best performance with an overall photon-to-current conversion efficiency (PCE) of 6.52% with IPCE of 44%. The obtained co-sensitization results are better in comparison to the DSSC fabricated using only N719 (η = 4.22%; IPCE = 45%) under identical condition.

Metalation of Bis(meta-carborane)

The first metallacarborane derivatives of 1,1′-bis(meta-carborane), specifically [1-(1′-closo-1′,7′-C2B10H11)-2-(p-cymene)-closo-2,1,7-RuC2B9H10] (2), [1-(1′-closo-1′,7′-C2B10H11)-2-(p-cymene)-6-OEt-closo-2,1,7-RuC2B9H9] (3), [1-(1′-closo-1′,7′-C2B10H11)-2-(C6Me6)-closo-2,1,7-RuC2B9H10] (4), [1-(1′-closo-1′,7′-C2B10H11)-2-(C6Me6)-6-OEt-closo-2,1,7-RuC2B9H9] (5), [1-(1′-closo-1′,7′-C2B10H11)-2-Cp-closo-2,1,7-CoC2B9H10] (6) and [1-(1′-closo-1′,7′-C2B10H11)-2-Cp*-closo-2,1,7-CoC2B9H10] (7), have been prepared by deboronation of one cage and subrogation of the {BH} fragment removed by an isolobal {Ru(arene)}, {CoCp} or {CoCp*} fragment. In the case of the {Ru(arene)} species, attack on the products 2 and 4 by EtO− resulted in derivatives 3 and 5, respectively, in which an OEt group is attached to B6 of the metallacarborane cage. All products were characterised by multinuclear NMR spectroscopy and single-crystal X-ray diffraction. All are of the form the 2,1,7-MC2B9-1′,7′-C2B10, and even though the structural studies reveal clear evidence of steric crowding between the arene or Cp/Cp* ligand on the metal and the pendant carborane cage, no isomerisation of the metallacarborane to either 2,1,8-MC2B9 or 2,1,12-MC2B9 occurs, even on heating to reflux in toluene.