ReviewsSeveral reviews in the area of boron chemistry have been published during 2005. Chen and King have reviewed the concept of spherical aromaticity as applied to a wide range of spherical clusters such as fullerenes and more significantlycloso-borane and carbaborane systems.3Erker has reviewed the chemistry and application of a highly Lewis acidic borane, tris(pentafluorophenyl)borate, as a catalyst and stoichiometric reagent in organic and organometallic chemistry.4The chemistry of the s-, p-, d- and f-block metal sandwich complexes of the trimethylsilyl-substituted-{C2B4} carborane-cages has also been reviewed.5The chemistry of boron moieties, specifically boryl-, boride- and borylene-units, as bridging units for the formation of bimetallic species has been reviewed.6The challenging chemistries surrounding the synthesis and reactivity of the cationinic borinium (R2BL2+), borenium (R2BL+) and boronium ions (R2B+), have also been reviewed by Piers, Bourke and Conroy.7A review article providing an overview of the reaction of acetylenes and isocyanides towards metallaboranes of the general type {MB9H13} and {MB8H12} has been published.8A review of the cluster-borane analogues of the cyclopentadienide anion (Cp-) and ferrocenes has been published, focusing on the chemistry of triheteroboranes of the general structurenido-[E3B8H8]−(E = CH or P and their combinations). A special edition of theJournal of Organometallic Chemistryhas also been published celebrating the III European conference on Boron chemistry (EUROBORON 3).Polyhedral boranesDensity functional theory (DFT) has been used at the B3LYP level to investigate the polyhedral boranes [BnHn]z(n= 8 and 11,z= −2, −4 and −6) and compare them to the isolelectronic germanium clusters [Gen]z.9The aromaticity of planar boron clusters has been investigated and established in terms of topological resonance energy. The planner boron clusters in the study have been found to be highly aromatic and have large resonance energies, even if they have 4n π-electrons. Aromaticity is therefore considered to arise from unusual planar geometries.10Kennedy and co-workers have investigated the reactivity ofanti-B18H22towardstBuNC. Reaction results in the formation of the cluster 7-anti-B18H20L, in which L is the zwitterionic carbene ligand [(tBuNHCH){tBuNHC(CN)H2C:}] formed by the reductive oligomerisation oftBuCN.11The hydroxyl borane, 6-hydroxyl-nido-decaborane (6-(HO)B10H13),1, has been prepared by the reaction of [B10H10]2−with H2O in a highly acidic media.12In a related study, the diazonium-closo-decaborate cluster, [B10H9N2]−, has been shown to react with oxygen nucleophiles such as [OH]−and [OR]−(R = Me, Et,iPr, Ph) in high yielding reactions to form the hydroxyl and alkyloxy clusters [1-B10H9-OH]−and [1-B10H9-OR]−,2, respectively.13The structure of thenido-undecaborate anion [B11H14]−has been investigated in several compounds, using single crystal X-ray analysis, NMR spectroscopy and computational studies, in order to establish the position of theendo/bridging hydrides.14Thecloso-B12cluster anion, [B12H11NH2]−, containing anexo-polyhedral –NH2group has been reacted with various aldehydes to form anionic Schiff-base compounds of the general form [B12H11–N&z.dbd;C(H)–C6H4–R]−(R&z.dbd;CN, CH2&z.dbd;CH2–C6H4CN, (CH2&z.dbd;CH2–C6H4)2CN). These compounds have been investigated for their utility in two photon absorption processes.15The anion [B12H11NH2]−has also been reacted with carbodiimides, to form a series of guanidinium salts for their utility in boron neutron capture therapy.16DFT studies have been used to compare the relative stabilities and aromaticity of the mono- and dichloro-derivatives of benzene, naphthalene, [B12H12]2−, B20H16and monocarborane isomers of B20H16.17The molecular structure and the mechanism of formation of the zwitterionic phosphonium borane cluster, [B12H11(PPh3)]−, formed by the reaction of [B12H11I]2−with Pd(PPh3)4in the presence of Na2CO3in THF, has been published.18Hawthorne and co-workers have developed synthetic procedures for the alkylation ofcloso-[B12(OH)12]2−. Reaction of [B12(OH)12]2−with alky/aralkyl halides and sulfonic acid esters, yields a series of dodecaalkoxy-closo-dodecaborate products,closo-[B12(OR)12]2−.19Metallaboranes including borohydride and related complexesThe titanium complex, (Nacnac)Ti&z.dbd;CHtBu(BH4) (Nacnac&z.dbd;[Ar]NC(CH3)CHC–(CH3)N[Ar], Ar = 2,6-(CHMe2)2C6H3), has been synthesised and structurally characterised. At elevated temperatures the complex has been shown to undergo cross-metathesis with the imine functionality of the Nacac-ligand to form the imido complex (HtBuC&z.dbd;C(Me)CHC(Me)N[Ar])Ti&z.dbd;NAr(BH4) and C–H activation of two of the methane groups on the Nacac ligand affords the titanocycle Ti[2,6-(CMe2)(CHMe2)C6H3]NC(Me)CH(Me)N[2,6-(CMe2)(CHMe2)C6H3](η2-BH4), remarkably with out interaction of decomposition of [BH4]−ligand, and formation of Ti(iii) species which is common in tetrahydroborate complexes.20Reaction of H2ClB·PPh2CH2PPh2(H2ClB·dppm) with [RuCp*(NCMe)3][BArF4], ([BArF4] = [B{3,5-(CF3)2C6H3}4]−) has been reported and results in the displacement of all three acetonitrile ligands and the formation of [RuCp*(η2-H2ClB·dppm)][BArF4] which has been characterised crystallographically. Addition of CO to the metal centre results in a change in the coordination of the borane group from η2to η1of the borane ligand. The H/D exchange on the coordinatively unsaturated Ru η2-borane system has also been reported.21The reactions of Na[H2B(mt)2] (mt = methimazolyl) with [M(&z.tbd;CC6H2Me3-2,4,6)X(CO)2(L)2] (M = Mo, W; X = Cl, Br; L = pyridine, 3,5-dimethylpyrazole) have been shown to be metal dependent, providing either the alkylidyne complex [Mo(&z.tbd;CC6H2Me3-2,4,6)(CO)2{κ3-H,S,S′-H2B(mt)2}] or the bis(chelate) complex [W(CO){κ2-S,S′-H2B(mt)2}{κ3-H,S,S′-H2B(mt)2}]. The molecular structure of latter complex has been determined and shown to feature both bi- and tri-dentate coordination modes for the H2B(mt)2ligand.22In a related study Na[H2B(mt)2] has been shown to react with 1 or 2 equivalents of PtMe3I to form the complex [PtMe3{H2B(mt)2}], and sulfur-bridged dinuclear complex [Me3Pt{μ-H2B(mt)2}PtMe3I], both of which contain 3 centre -2 electron B–H⋯Pt bonds.23The phenyltrihydroborate complexes, Cp2ZrCl{(μ-H)2BHPh} and Cp2Zr{(μ-H)2BHPh}2, were prepared from the reactions of Cp2ZrCl2with one and two moles of LiBH3Ph. Reaction of the bis borate complex with the Lewis base N(C2H5)3produces (C2H5)3N·BH2Ph, while the zirconium hydride compound, Cp2ZrH{(μ-H)2BHPh}, has been prepared from the reaction of Cp2ZrHCl with LiBH3Ph. The product Cp2ZrCl{(μ-H)2B(C6F5)2} was formed in the solvent dependent reaction of Cp2ZrCl{(μ-H)2BHPh} with the Lewis acid B(C6F5). The reaction of titanocene dichloride, Cp2TiCl2, with LiBH3Ph produces the 17-electron, paramagnetic complex, Cp2Ti{(μ-H)2BHPh}.24The reaction of potassium bis(cyclooctane-1,5-diyl)dihydroborate salt, K[H2BC8H14], with the divalent lanthanide chlorides (THF)xLnCl2(Ln = Eu, Yb) yields the tetraborate complexes [K(THF)4]2[Ln{(μ-H)2BC8H14}4] irrespective of the reaction ratios. Replacement of the THF by MeTHF (2-methyltetrahydrofuran) or exchange of the potassium cation for [NMe4]+affords X-ray quality crystals of [K(THF)4]2[Ln{(μ-H)2BC8H14}4] (3) and [NMe4]2[Ln{(μ-H)2BC8H14}4].25In a related study, K[H2BC8H14] reacts with TiCl4in the donor solvents, THF or diethyl ether, in a 4∶1 reactant ratio to form the Ti(iii) compounds Ti{(μ-H)2BC8H14}3(THF)2and Ti{(μ-H)2BC8H14}3(OEt2) respectively. Reaction between K[H2BC8H14] and TiCl4in a 5∶1 ratio forms [K(OEt2)4][Ti{(μ-H)2BC8H14}4]. Displacement of the diethyl ether moiety by aniline in Ti{(μ-H)2BC8H14}3(OEt2) results in the formation of Ti{(μ-H)2BC8H14}3(PhNH2). All the compounds in this study have been characterised by single crystal X-ray diffraction analysis and show the borate ligand to be coordinated to the metal centreviabridging Ti⋯H–B bonds.26Reaction between sodium tris(2-mercapto-1-tert-butylimidazolyl)borate, Na[HB(mtBu)3], AgNO3, and (Ph3P)AuCl form the complexes [Ag{HB(mtBu)3}]2and (Ph3P)Au{HB(mtBu)3} both of which have been structurally characterised and shown to contain M⋯H–B interactions.27The manganese(i) tricarbonyl bis(mercaptoimidazolyl)borate complexes {H2BmR}Mn(CO)3(R = Me, Bz, But,p-Tol) and {Ph(H)BmMe}Mn(CO)3have been prepared by the reaction of the sodium or lithium borate salts with Mn(CO)5Br, and fully characterized. The presence of 3 centre- 2 electron Mn⋯H–B interactions in both products, in solution and in the solid state, has been investigated using a combination of IR and NMR spectroscopies and, in the case of the methyl-,tert-butyl- andpara-tolyl-substituted derivatives, by X-ray crystallography.28The structural similarities between the metalloborane clusters Cp4Co4B4H4and the organometallic cluster Cp4Fe4C4H4have been discussed.29The reaction ofnido-1,2-(η5-C5Me5Ru)2(μ-H)2B3H7,nido-2,4-(η5-C5Me5Ru)2B6H12andnido-2,3-(η5-C5Me5Ru)2B8H12with the dichloroborane BHCl2·SMe2under both mild and more forcing conditions have resulted in the formation of a range of B–Cl inserted metallaboranes products, several of which have been structurally characterised.30The air stable haxaborane analogue, 2,2,2-(Ph3P)2(CO)nido-2-OsB5H9, and its reactivity towards a series of bidentate phosphine ligands, Ph2P(CH2)nPPh2(n= 2–6), affords the complexes {(Ph3P)2(CO)OsB4H7}-3-BH2PPh(CH2)nPPh2. Intramolecular substitution reactions and reaction of the pendent-PPh2group with the organometallic fragments {(p-cym)RuX2} (X = Cl, I) have also been described.31Mild pyrolysis of (η5-C5Me5Ru)2B6H12with Fe2(CO)9yields the 12 skeletal electron pair cluster Fe2(CO)6(η5-C5Me5RuCO)(η5-C5Me5Ru)B6H10which has been structurally characterised. This compound is a novel of hybrid multiple cluster in which a {Fe2B2} tetrahedron has been fused to a {Ru2B3} ruthenaborane substrate.32Reaction of the molybdaboranearachno-2-Mo(η5-C5H5)(η5:η1C5H4)B4H7with the electron rich tungsten hydride W(PMe3)3H6gives the tungstaboranenido-2-W(PMe3)H2B7H7{Mo(η5-C5H5)(η5:η1-C5H4)H2} (4). The reaction has been followed by NMR and the product is a rare example of metal fragment exchange within a metallaborane cage.33The synthesis, using hydrothermal procedures, and the molecular structures of the 11-vertex diplatinumundecaborate clusters (Ph3P)2Pt2(μ-PPh2)B9H6Cl(OiPr) and (Ph3P)2Pt2(μ-PPh2)B9H6(OiPr)2have been reported.34Bartonet al. have reported the formation of the trimetallic cluster (Ph3P)RuB9H9{RuCl2(PPh3)2}2, which has been structurally characterised and found to have acloso-10 vertex {RuB9} core that is partially encapsulated by twoexo-polyhedral {RuCl2(PPh3)2} units that cap the {RuB2} triangular faces.35The formation of (PMe2Ph)4Pt2B10H10has been reported and its molecular structure determined. The reversible uptake of atmospheric oxygen by (PMe2Ph)4Pt2B10H10has been described. Determination of the molecular structure reveals (PMe2Ph)4(O2)Pt2B10H10(5) to contain one molecule of O2which bridges the two Pt centres. The uptake of CO and SO2by (PMe2Ph)4Pt2B10H10forms the complexes (PMe2Ph)4(μ-CO)Pt2B10H10and (PMe2Ph)4(μ-SO2)Pt2B10H10, respectively.36The thermolyses of the clusters (Me2PhP)2MB8H12(M = Pd, Pt) yields the eighteen vertex clusters (Me2PhP)3MB16H18(PMe2Ph). These clusters are structural models for precursive intermediates for more condensed macropolyhedral metallaboranes.37The seventeen-vertex macropolyhedron (Me2PhP)2PtB16H17Me has been isolated from the reaction between (Me2PhP)2PtMe2and B16H20, and has been structurally characterised revealing platination to have occurred on the {B10} subcluster. Platination of B14H18results in the formation of (Me2PhP)2PtB14H16.38Similar reaction between B16H20and RuCl2(PPh3)3results in the formation of (Ph3P)2RuB16H20which has been shown, by single crystal X-ray diffraction studies, to consist of a conventional {B10} cluster subunit fused to a 10 vertex {RuB9} unitviaa common {B3} face.39Reaction of [(p-cym)RuCl2]2withsyn-[B18H22] results in the formation of [8-{(p-cym)Ru}B17H21], the molecular structure of which has been determined crystallographically.40HeteroboranesThe synthesis, structure and DFT calculations of the small three dimentional aromatic anionic carborane clusters [CB4R5]−have been reported.41Reaction of thein situgenerated aryl- and alkyl-zinc reagents with thenido-{C4B2} carborane 1-iodo-6-phenylethynyl-2,3,4,5-tetraethyl-2,3,4,5-tetracarba-nido-hexaborane in the presence of catalytic amounts of Pd(PPh3)4results in B-halogen exchange and formation of B-aryl bonds.42The eleven-vertex diphosphacaborane,nido-7,8,9-P2CB8H10, has been synthesised along withcloso-2,1-PCB8H9andnido-7,8,9,10-P3CB7H8from the reaction ofarachno-4-CB8H14with excess PCl3and 1,8-dimethylamino naphthalene. Thermal rearrangement of the anion [nido-7,8,9-P2CB8H9]−produces [nido-7,8,10-P2CB8H9]−. DFT calculations have been used in conjunction with multinuclear NMR spectroscopy to make full assignments of all resonances.43Density functional theory calculations have been used at the B3LYP/6-311+G(d,p)//B3LYP/6-31G(d)+ZPE level to determine the relative energies of 95 phospha- and 46 aza(carba)-boranes and borates.44The ten-vertex [6-Ph-nido-6-CB9H11]−anion has been reacted with a range of two-electron donor ligands L, (L = SMe2, NH2Ph, NC5H5, NC5H4-4-CH2Ph, NC5H4-4-Ph or NC9H7)(NC9H7= quinoline) in the presence of FeCl3·6H2O and gives the neutral arachno ten-vertex monocarbaboranes compounds [6-Ph-9-L-arachno-6-CB9H12]. Prolonged treatment with FeCl3·6H2O results in oxidative cluster closure of the four pyridine based complexes, which gives the neutral closo ten-vertex monocarbaboranes [1-Ph-6-L-closo-1-CB9H8].45The anion [closo-1-CB9H8-1-COOH-10-I]−has been prepared in four steps from B10H14. The carboxylic acid is readily converted to the amine [closo-1-CB9H8-1-NH2-10-I]−using the Curtius reaction. The relative thermodynamic stabilities of each product has been assessed using DFT calculations at the MP2 level.46The molecular structures of the threecloso-carbaboranes,ortho-,meta- andpara-C2B10H12, have been experimentally determined using gas-phase electron diffraction (GED). All unique bond distances forortho-andmeta-carbaboranes have been determined experimentally for the first time.47The effect of successive methylation ofortho-carborane has been assessed using DFT at the B3LYP/6-31G level.48Computational methods have also been used to investigate the effect of electron donating and withdrawing groups on the C–C cage bond distance in the neutral and dianionic 6- and 12-vertexcloso-ortho-carboranes R2-C2BnHn(R = H, CH3, NH2, OH, F, SiH3, PH2, SH, Cl, CH2−, NH−, O−, SiH2−, PH−and S−;n= 4 or 10).49Acidic hydrolysis of N-acyl 1-methyl- and 1-phenyl-3-amino-1,2-dicarba-closo-dodecaboranes has been studied. It has been shown that acidic hydrolysis of diastereomeric amides of 1-ethyl-3-amino-1,2-dicarba-closo-dodecaborane results in the partial racemisation of the target 3-amino-1-methylcarborane.50The synthesis of 1,2-bis(o-carboranyl)benzene has been reported. Structural analysis has been performed to examine the steric effects of the two extremely bulkyo-carborane cages at adjacent positions on the planarity of the benzene ring. X-ray crystallographic analysis supported by DFT calculations reveal that the benzene ring is significantly deformed by the bulkyo-carboranyl groups.51The naphthalene substituted carborane systems 1-(1-C2B10H11)-C10H7and 2-(1-C2B10H11)-C10H7have been synthesised using several different methods.52The acetylene substitutedmetaandpara-closo-carboranes, 1,12-{4-NC4H4–C&z.tbd;C–}2C2B10H10, 1,7-{4-NC4H4–C&z.tbd;C–}2C2B10H10, 1,12-{TfOPt(PEt3)2–C&z.tbd;C–}2C2B10H10, 1,7-{TfOPt(PEt3)2–C&z.tbd;C–}2C2B10H10have been used in the synthesis and self assembly of five new supramolecular carborane complexes.53An expeditious synthetic route to a carboranyl-substituted tetrabenzoporphyrin has been reported. The X-ray structure of a Cu(ii)–carboranyl-tetrabenzoporphyrin is presented and discussed.54Gradient corrected DFT calculations have been used to explore the effects on complexation of the 1,2-diphosphino-dicarbadodecaborane system to PdCl2. The molecular structure of PdCl2(1,2-(PiPr2)2-C2B10H10) has also been reported.55The synthesis, characterisation and reactivity of dimeric carboranyl thioethers and disulfides have been reported. The carboranyl disulfide systems (1-S-2-R-C2B10H10)2(R = H Me, Ph) appear to have rather different reactivity to typical organic disulfides.56The dendritic cluster assembly, [Si{CH2CH2SiMe2(2,-Ph-1,2-C2B10H10)}4] (6) has been formed using two synthetic routes: one involving the reaction of a carbosilane with terminal Si–Cl bonds with Li[PhC2B10H11], and the second a highly selective hydrosilation reaction of tetravinyl silane with the carboranyl silane Ph(HSiMe2)C2B10H11.57,58The carborane triflates, 1-trifuoromethanesulfonylmethyl-o-carborane and 1,2-bis(trifluoromethanesulfonylmethyl)-o-carborane, have been obtained in high yields in the reactions of 1-hydroxymethyl-o-carborane or 1,2-bis(hydroxymethyl)-o-carborane with triflic anhydride (Tf2O) in CH2Cl2in the presence of pyridine. The reaction of these triflate species with nucleophiles (e.g., pyridine, potassium phthalimide, PPh3or KCN) to give the corresponding substitution products have also been described.59Xie and co-workers have described the synthetic strategies to a wide range of mono- and bis-functionalisedo-carboranes with a range of electrophiles by reaction of the lithiated dimethylaminoethyl substituted system, [Me2NCH2CH2–C2B10H10]Li with electrophiles such as MeI, MeO(CH2)2Cl, Me2N(CH2)2Cl, BrCH&z.dbd;CH2and Me2C&z.dbd;CC4H4.60The novel thiopropyl-closo-1,2-carborane ligand bearing a pendant glycerol group HS(CH2)3CB10H10CCH2–OCH(CH2OH)2has been reported. Its subsequent reaction with the labile platinum(ii) precursor [Pt(MeCN)(terpy)](OTf)2(terpy = 2,2′:6′,2″-terpyridine; OTf = trifluoromethanesulfonate) to afford the highly water soluble platinum(ii) complex [Pt{σ-S(CH2)3CB10H10CCH2–OCH(CH2OH)2}(terpy)]OTf, the first example of a metal-carborane complex functionalised with a water-solubilising glycerol group, has also been described.61Theortho-,meta- andpara-substituted bis(thiopropyl)dicarbaboranes have been used as stable scaffolds for the synthesis of platinum(ii) terpy complexes with the general formula [{(terpy)Pt–S(CH2)3–}2C2B10H10][OTf]2. Preliminary anti-cancer characteristics of the complexes have been determinedin vitro.62Weller and co-workers have reported the alkyl functionalisation of the carborane anioncloso-[CB11H12]−. Treatment of the rhodium complex (Ph3P)2Rh(CB11H12) with ethylene affords the mono-vinyl substituted system (Ph3P)2Rh(x-(C2H3)–CB11H11) (x= 12, 7), having arisen from the dehydrogenative borylation of ethylene by [CB11H12]−in the 12- or 7-positions. Treatment with H2results in the rhodium mediated hydrogenation of the vinyl group and formation of the ethyl substituted cage system, (Ph3P)2Rh(x-(C2H5)–CB11H11) (x= 12, 7). Cycling of the dehydrogenative borylation-hydrogenation process several times results in the formation of the pentaethyl substituted cage anion complex (Ph3P)2Rh((C2H5)5–CB11H7).63The decomposition products that arise from partnering [closo-1-H–CB11Me11]−with the metal fragments {Cp2ZrMe}+, {Ir(H)2(PPh3)2}+and {Pt(PiPr3)2}2+have been reported. Many of the decomposition reactions do not afford compositionally pure materials, with reaction solvent fragments (CH2Cl2or arene) being incorporated in some part into the cage.64MetallaheteroboranesThe synthesis and molecular structure of thecloso-dimetallacarbaborane 1,2-(η5-C5Me5)2-(μ-H)-1,2,3-Rh2CB4H4-3-I from the reaction of 2,5-(η5-C5Me5)2-10-Me-l-2,5-H-nido-2,5,1-Rh2CB6H8with one molar equivalent of I2in the presence of excess NMe3has been described.65A series of full- and half-sandwich metallacarboranes have been synthesised from the reaction of MCl2(M = Co, Fe) andcloso-exo-y,x-Li(L)-1-Li(L)-2,n-(SiMe3)2-2,n-C2B4H4(y= 4,x= 5, L = 2 THF,n= 3;y= 4,x= 5, L = TMEDA,n= 3;y= 5,x= 6, L = 2 THF,n= 4;y= 5,x= 6, L = TMEDA,n= 4) in 1∶1 molar ratios in benzene.66The synthesis and molecular structure of the carbons-apart from platinadicarbaborane 7,7-(Me2PhP)2-isonido-7,6,8-PtC2B6H7-6-Ph has been published.67The reaction of the carborane anionhypho-[6,7-C2B6H13]−with nickelocene in the presence of excess 1,8-bis(dimethylamino) naphthalene results in the formation of a pair of isomeric nickel clusters 6,7,8-(CpNi)3-1-CB5H6and 6,7,8-(CpNi)3-2-CB5H6.68Fehlner and co-workers have reported the reactive chemistry of the metallaboranenido-1,2-(Cp*RuH)2B3H7with phenyl acetylene to produce a wide range of metal carborane clusters which demonstrate the many ways in which metallaborane fragments can combine with alkynes.69Treatment of theclosoanion [1-CB7H8]−with Fe3(CO)12affords the cage expanded anioncloso-[{(CO)3Fe}-1-CB7H8]−(7). Further reaction with Fe3(CO)12results in an insertion of a second {Fe(CO)3} fragment to yield thecloso-[6,10-{(CO)3Fe}2-1-CB7H8]−(8) anion. Further reactions with the cationic metal ligand fragments {Cu(PPh3)}+and {Ag(PPh)3}+have also been investigated.70The mixed sandwich diphosphacarbaborane complexes [1-Cp-closo-1,2,3,4-FeP2CB8H9] and its isomer [1-Cp-closo-1,2,3,5-FeP2CB8H9], the latter of which was structurally characterised, have been synthesised by the reaction of [nido-7,8,9-P2CB8H9]Tl or [nido-7,8,10-P2CB8H9][PPh4] with [CpFe(CO)2I] in refluxing toluene, respectively.71Analogous reactions to form the ruthenium systems have also been published along with a comparative investigation into the thermally induced rearrangement of both the iron and ruthenium systems.72The metallation of the tricabollide anion, [7-tBuNH-7,8,9-C3B8H10]−, with the metal fragments {Rh(COD)}+, {Mn(CO)3}+, {CpRh}2+and {(Me3C6H3)Ru}2+has been reported and the molecular structure of the neutral manganese complex, [{Mn(CO)3-12-tBuNH-2,4,12-B8H10], determined by single crystal X-ray diffraction has described.73The metallation of thenido-carborane anion [5-I-7,8-Ph2-7,8-nido-C2B9H8]2−with {Ni(dppe)}2+and {Pt(PMe2Ph}2+to produce the neutral carborane complexes 1,2-Ph2-4,4-dppe-12-I-4,1,2-closo-NiC2B9H8, 1,8-Ph2-2,2-dppe-10-I-2,1,8-closo-NiC2B9H8, 1,8-Ph2-2,2-(PMe2Ph)2-10-I-2,1,8-closo-PtC2B9H8, 1,8-Ph2-2,2-(PMe2Ph)2-12-I-2,1,8-closo-PtC2B9H8, and 1,8-Ph2-2,2-(PMe2Ph)2-7-I-2,1,8-closo-PtC2B9H8has been reported.74Treatment of the trianionic cluster [1,3,6-{M(CO)3}-3,6-(μ-H)2-1,1,1-(CO)3-2-Ph-closo-1,2-MCB9H7]3−(M = Mo, W) with [Mn(CO)3(NCMe)3][PF6] and [(dppe)PtCl2] sequentially affords the novel hetero trimetallic clusters [1,3,6-{Mn(CO)3}-1,7-{Pt(dppe)}-3,6,7-(μ-H)3-1,1,1-(CO)3-2-Ph-closo-MCB9H6], which have been structurally characterised.75The related phenyl substituted manganese carbaborane system [{(CO)3Mn}-2-Ph-closo-1-CB9H9]−has been synthesised and its reactivity towards a range of cationic metal ligand fragments to form neutral bimetallic complexes has also been reported.76The rhenium carborane complexes [HNMe3][{(CO)2Cl2Re}-1,2-C2B9H11] and {(CO)3IRe}-1,2-C2B9H11have been formed by the reaction of [{(CO)3Re}-1,2-C2B9H11]−with the halogenating materials [N(C6H4Br-4)3][SbCl6] and I2respectively. Iodine migration, in the case of {(CO)3IRe}-1,2-C2B9H11, from the metal to a facial boron atom results in the formation of the complex anion, [{(CO)3Re}-8-I-1,2-C2B9H10]−, the structure which has been confirmed by X-ray diffraction. The luminescence and electrochemistry of these species have also been studied.77Severalortho- andmeta-rhenium tricarbonyl carborane systems with pyridine, amino, carboxylic acid, carbohydrate and aryl substituents, have been synthesised and several of the compounds structurally characterised.78The synthesis and molecular structure of theclosomercapto-functionalised ruthanacarborane system, 3-{(η6-C6H6)Ru}-8-HS-1,2-C2B9H10, have been reported, and the self-assembly through S–H⋯HB and C–H⋯S hydrogen bonds discussed.79The metallation reaction of the carborane anion [7,8-(4-MeC6H4)2-7,8-nido-C2B9H10]−with [((2,3,5,6-η4)-C7H7-2-CH2OH)RhCl]2produced two diastereomericclosocomplexes, [2,2-((2,3,8-η3):(5,6-η2)-C7H7CH2)-1,8-(4′-MeC6H4)2-2,1,8-closo-RhC2B9H9], the products of the low temperature “1,2 → 1,7” carbon atom isomerisation of a (nonisolable) [3,3-((2,3,8-η3): (5,6-η2)-C7H7CH2)-1,2-(4′-MeC6H4)2-3,1,2-closo-RhC2B9H9]. The overall architecture and stereochemistry of the diastereomers have been determined crystallographically.80The Re(iii) complex l-NHBut-{(CO)3Re}-1-CB10H10in which the carborane functions formally as an 8-electron (6π + 2σ) donor has been synthesised. Reaction of the tricarbonyl system with the ligands L in the presence of Me3NO yields the substituted products l-NHBut-{(CO)2LRe}-1-CB10H10(L = PPh3, CN-2,6-C6H3Me2, or ButC*CH).81The anion nido-[CB10H11]−has been reacted with a range of Ni0precursors to form theclosocomplex anions [{L2Ni}-1-NiCB10H11] (L = CO, PEt3, PPh3, CNBut, and CN–C6H3Me2; L2= cod).82The reactive chemistry of the charge compensated triruthenium monodicarbollide cluster {(η5-1-Me2S-CB10H8)Ru(CO)2}Ru2(CO)6towards the phosphine ligands PMe3, PCy, 1,1′(Ph2P)2-fc, and 1,2-(Ph2P)2-1,2-C2B10H10has been published. The reactivity of the triruthenium cluster towardstBu–SS–tBu andtBu–C&z.dbd;CH has also been discussed.83Reduction of the tethered carborane 1,2-(CH2)3-1,2-closo-C2B10H10followed by treatment with CoCl2/NaCp, [(p-cym)RuCl2]2(PMe2Ph)2PtCl2or (dppe)NiCl2affords the new 13-vertex metallacarboranes 1,2-(CH2)3-4-Cp-4,1,2-closo-CoC2B10H10, 1,2-(CH2)3-4-(p-cymene)-4,1,2-closo-RuC2B10H10, 1,2-(CH2)3-4,4-(PMe2Ph)2-4,1,2-closo-PtC2B10H10and 1,2-(CH2)3-4,4-(dppe)-4,1,2-closo-NiC2B10H10respectively, the molecular structures of which have been determined by single crystal X-ray diffraction.84The 13-vertex rhodacarborane [4-(COD)Rh-1,6-C2B10H12][N(PPh3)2] has been synthesised by the reaction of the Na2[C2B10H12] with [Rh(COD)Cl]2. Treatment with sources of the cation fragments {Cu(PPh3)}+, {Rh(PPh3)2}+, {Rh(COD)}+and {RuCl(PPh3)2}+results in the formation of a range of neutral bimetallic species, of which only the copper derivative has a metal–metal bond.85In a related study the rhenium and manganese carbonyl compounds [{(CO)3M}-1,6-C2B10H12]−have been synthesised and their reactivity towards I2, [NO]+and {Cu(PPh3)}+and {Au(PPh3)}+described.86Reduction ofpara-closo-C2B10H12or its C,C-dimethyl analogue with sodium in liquid ammonia followed by metallation with {CpCo}2+, {(arene)Ru}2+or {(dppe)Ni}2+fragments has afforded the first examples of 4,1,10-MC2B10species. Thermal rearrangement of these complexes results in formation of the appropriate 4,1,12-MC2B10isomers, which have hitherto been unavailable for (arene)Ru metallacarboranes.87Related studies have investigated similar reactions between {(arene)Ru}2+precursors and the anions [R2C2B10H10]2−(R = H, Ph) produced from the reaction of theortho-C2B10H12system and its diphenyl derivative with sodium metal.88The effects of bridge length and rigidity on the formation of C,C′-linked carborane anions have been studied. Reaction of 1,2-(CH2)3-1,2-C2B10H10, 1,2-(CH2CH&z.dbd;CHCH2)-1,2-C2B10H10, or 1,2-(CH2)4-1,2-C2B10H10with excess Li metal in THF gave “carbon-atoms-adjacent”arachno-carborane salt [{1,2-(CH2)3-1,2-C2B10H10}{Li4(THF)5}]2, [{1,2-(CH2CH&z.dbd;CHCH2)-1,2-C2B10H10}{Li4(THF)5}]2, or [{1,2-(CH2)4-1,2-C2B10H10}{Li4(THF)5}]2, respectively. In comparison reduction of 1,2-(CH2)5-1,2-C2B10H10or 1,2-(CH2)6-1,2-C2B10H10with excess Na metal, afforded “carbon-atoms-apart”nido-carborane salts [{1,3-(CH2)5-1,3-C2B10H10}{Na2(THF)4}]nor [{1,4-(CH2)6-1,4-C2B10H10}{Na2(THF)4}]n.89Reaction of the mono- and di-substitutedortho-carborane systems Me2NCH2CH2–C2B10H11(Me2NCH2CH2)2–C2B10H10or 1-(Me2N(CH2)2-2–(MeO(CH2)2-C2B10H10, with LnCl3(Ln = Y or Er),90Ln(NTMS2)3and LnCl(NTMS2)291in the presence of excess sodium metal results in the formation of a range of 13-vertex lanthanacarboranes.The formation and molecular structures of several fourteen vertex homo- and hetero-bimetallic metallacarboranes have been reported. Reduction of 4-(p-cymene)-4,1,12-closo-RuC2B10H12followed by metallation with {M′} fragments (M′ = {CpCo}2+, {(arene)Ru}2+or {(dppe)Ni}2+) affords the 14-vertex bimetallic 1,14,2,10-RuM9C2B10species having bicapped hexagonal antiprismatic structures.92Reaction between the tricarbaborane anion, [7-tBuNH-nido-7,8,9-C3B8H10]−, and [Cp*RuCl]4results in the formation of the ruthenatricarbollide [1-Cp*-12-tBuNH-1,2,4,12-RuC3B8H10] which is associated with extensive polyhedral rearrangement within the borane cage, and brings the carbon atoms to positions of maximum separation within the framework. DFT calculations at the B3LYP/SDD level have been used to estimate the relative stabilities of the above system with the previously reported metallacarborane structural isomers.93Exo-MetallaheteroboranesThe reactive chemistry of thehypho-dithiaborane system, [1,2-S2B6H9]−, towards the organometallic ruthenium species CpRu(PPh3)2Cl and [(p-cym)RuCl2]2to yield theexo-bound ruthenium complexes (η5-C5H5)Ru(PPh3)2{η1-1,2-S2B6H9} (9), 5-{CpRu(PPh3)}-4,6-S2B6H9(10) and 5-{(p-cym)Ru}-4,6-RuS2B6H8, has been reported.94Theansa-cyclopentadienyl-carboranyl andansa-indenyl-carboranyl ligands, [Me2C(C5H4)(C2B10H10)]Li2and [Me2C(C9H6)(C2B10H10)]Li2respectively, have been investigated as supporting ligands for titanium imido complexes. Reaction of the lithium carboranyl systems with the titanium imido complexes [Ti(NR)Cl3(py)3] results in the formation of the complexes {η5:σ-Me2C(C5H4)(C2B10H10)}Ti(&z.dbd;NR)(Py) and {η5:σ-Me2C(C9H6)(C2B10H10)}Ti(&z.dbd;NR)(Py) (R =tBu, 2,6-Me2C6H3, 2,6-iPr2C6H3). The reactivity of thetert-butyl imido systems towards Ph2CO, PhCHO, PhNCO CS2, imido exchange and the hydroamination of phenyl acetylene has also been investigated.95Theansa-indenyl-carboranyl complexes, {η5:σ-iPr2N–P(C9H6)(C2B10H10)}M(NR2)2(R = Me, M = Ti, Zr, Hf; R = Et, M = Hf) have been prepared in good yield by amine elimination reaction between the corresponding homoleptic amide precursors, M(NR2)4and the neutral phosphorous bridged protic reagentiPr2N–P(C9H7)(C2B10H11). The reactivity of these complexes towards phenyl isocyanate and acetylacetone have been explored along with the ethylene and ϵ-caprolactone polymerisation activities of the complexes in the presence of MAO.96In 2005, the chemistry of dicarba-closo-dodecaborane-1,2-dichalcogenolates (ortho-carborane dichalcogenolates) has continued to attract significant attention and their utility in the formation of heterometallic systems has continued to develop. Reaction of the 16-electron half sandwich complexes Cp*Rh(E2C2B10H10) (E = S, Se) with W(CO)3Py3in the presence of BF3·OEt2has been shown to afford the bridged dichalcogenolate complexes {Cp*Rh(E2C2B10H10)}2W(CO)2(E = S, Se), (Cp*Rh)2{S2C2B10H10}, Cp*Rh{S2C2B10H10}W(CO)2{S2C2B10H10}, and Cp*Rh(CO){Se2C2B10H10}W(CO)5. Reaction of Cp*Rh(E2C2B10H10) with Co2(CO)8afforded the trinuclear clusters Cp*Rh{E2C2B10H10}Co2(CO)5. Several of the complexes synthesised in this study have also been structurally characterised.97Similar reactions occur between the di-tert-butyl-substituted Cp-half sandwich complex Cp′Rh(E2C2B10H10) (Cp′ = 1,3-tBuC5H3) and Mo(CO)3(NC5H5)3and Ni(COD)2respectively.98The reaction between the corresponding iridium dichalocogenolato systems Cp*Ir{E2C2B10H10} (E = S, Se) with Co2(CO)8and Fe(CO)5to produce Cp*Ir{E2C2B10H10}Co2(CO)5, Cp*Ir(CO){E2C2B10H10} and Cp*Ir{E2C2B10H10}Fe(CO)3, respectively, has also been studied and the molecular structures of selected products determined.99The reactive chemistry of Cp*Ir{E2C2B10H10} with W(CO)3(py)3in the presence of BF3·OEt2has also been published.100The iridium selenide complex and its reactive chemistry towards [Rh(COD)Cl]2and Mo(CO)3(NCMe)3has been described. In the case of the Ir–Rh systems initial reaction between Cp*Ir{Se2C2B10H10} and [Rh(COD)Cl]2results in reduction of the Ir(iii) centre to Ir(ii) and the formation of thecisoid{Ir2Rh} mixed metal complex,cis-[(Cp*Ir{Se2C2B10H10})2Rh] (11). Heating of the complex in toluene results in B–H activation of one of the twoortho-carborane groups close to the iridium centres and formation of the Ir–B bonded systemtrans-[Cp*Ir{Se2C2B10H9}Rh{Se2C2B10H10}IrCp*] (12).101Four new dichalcogenolate carborane bridged binuclear rhodium(i) complexes Rh2(COD)2(μ2-E2C2B10H10) and Rh2(CO)2(μ2-E2C2B10H10) (E = S, Se) have been prepared by the reactions of the dilithium dichalcogenolate carboranes Li2E2C2B10H10with [Rh(COD)Cl]2or [Rh(CO)2Cl]2respectively. Molecular structures show strong metal–metal bonds between the two rhodium centres in all cases.102Wesemann and co-workers have described the reactivity of the anionic tin-borane cluster, [SnB11H11]−, towards the gold phosphine systems (Et3P)AuCl and (dppm)Au2Cl2, respectively, and the formation and solid state structures of the novel gold-tin clusters [Bu3NH]3[{(Et3P)Au(SnB11H11)}3] (13) and [Bu3MeN]4[{(dppm)Au2(SnB11H11)2}2] (14).1Reaction of the chloropropyl-substituted stanna-closo-dodecaborate [Cl(CH2)3–SnB11H11]−with Li[CH2PPh2] has been reported to provide the anionic phosphine ligand [Ph2P–CH2–SnB11H11]−. Reactions of the phosphine ligand with H+and sulfur to form the zwitterionic [Ph2P(H)–CH2–SnB11H11] and the phosphine sulfide [Ph2P(S)–CH2–SnB11H11]−systems have also been described, along with the reactive chemistry of the anionic phosphine towards the metal saltscis-(Ph3P)2MCl2(M = Pt, Pd) AgBF4and (Ph3P)AuCl and their subsequent products.103Boryl complexes and related systemsMain group bis-element sandwiches formed by donor–acceptor interactions of MCp and ECp (M = Li, Na, K; E = B, Al, Ga; Cp = η5-C5H5) have been studied using computational methods at the B3LYP/pVDZ theory level. The results of the calculations indicate the most stable species to be the boron-lithium containing species. Calculations also indicate that the use of Cp* (Cp* = η5-C5Me5) can enhance donor properties of the Cp*E group by 10–15 kJ mol−1.104The reaction of the nickel diphosphine hydride complexes [(R2PCH2CH2PR2)NiH]2(R = Cy,iPr,tBu) with a mixture of BEt3and super-hydride (LiHBEt3) afforded σ-borane nickel(0) compounds of the type [(R2PCH2CH2PR2)–Ni(σ-HBEt2)] with the concomitant formation of [(R2PCH2CH2PR2)2Ni2(H)3][BEt4].105The bis(dihydrogen) complex, RuH2(η2-H2)2(PCy3)2, reacts with one equivalent of either HBpin (pinicolborane) or HBcat (catchacolborane) to produce the σ-borane complexes RuH2(η2-HBpin)(η2-H2)(PCy3)2and RuH2(η2-HBcat)(η2-H2)(PCy3)2,respectively. The coordination modes of the borane have been confirmed by X-ray diffraction experiments, NMR spectroscopy and theoretical studies.106Reaction of the bromoboryl complex, Cp*Fe(CO)2{B(X)Br} (X = Br, Fc), with Pd(PCy3)2results in oxidative addition of the B–Br bond to the Pd0centre to form the borylene bridged hetrodinuclear species [Cp*(CO)Fe(μ-CO)(μ-BX)Pd(Br)(PCy3)].107Reaction of the dichloroboryl complex Cp*Fe(CO)2{BCl2} and Pd(PCy3)2results in loss of PCy3and formation of the compound [Cp*Fe(μ-CO)2{μ-B(Cl)2}Pd(PCy3)], which has been characterised by single crystal X-ray diffraction and has been shown to contain a bridging {BR2} ligand.108The photochemical reaction of Cp*Rh(η6-C6H6) with HBpin (pinicolborane) generates the complexes Cp*Rh(H)2(Bpin)2and Cp*Rh(H)(Bpin)3. X-ray diffraction, DFT calculations and NMR spectroscopy suggests weak but measurable B⋯H bonding interactions. Reaction of both Cp*Rh(H)2(Bpin)2and Cp*Rh(H)(Bpin)3with PEt3and P(p-Tol)3generates the Rh(iii) compounds Cp*Rh(PEt3)(H)(Bpin) and Cp*Rh{P(p-Tol)3}(Bpin)2and HBpin. The reaction of the rhodium-boryl hydride complexes with alkanes, and arenes have also been investigated.109The halo-borane compounds, B-chlorocatecholborane and B-bromocatecholborane undergo oxidative addition to M(PR3)3Cl (M = Rh, R = Me; M = Ir, R = Me, Et) yielding six-coordinate hetero and homo-dihalide complexes of general formulamer,cis-(PR3)3X′X″M(BO2C6H4) (X = Cl, Br).110Hill and co-workers have investigated a series of reactions between sodium tri(methimazolyl)borate, Na[HB(mt)3] (mt = methimazolyl) and metal complexes. Reaction of Na[HB(mt)3] with Rh(C6H5)Cl2(PPh3)2results in the formation of the rhodaboratrane complex RhCl(PPh3){B(mt)3}, which has been structurally characterised by single crystal X-ray diffraction, and shown to contain an unambiguous Rh → B dative bond. Formation of the complex is thought to proceedviaan intermediate complex containing a B–H–Rh agostic interaction which undergoes B–H activation and reductive elimination of benzene.111In a related study, {Rh(η4-C8H8)Cl2}2was reacted with Na[HB(mt)3] to form the boratrane complex [Rh(η4-C8H8){B(mt)3}]Cl, which undergoes further reaction with excess Na[HB(mt)3] to form the structurally characterised dirhodaboratrane [Rh2{B(mt)3}2{κ2-S,S′-HB(mt)3}]Cl, which contains two Rh → B dative bonds.112Reaction of Na[HB(mt)3] and Na[H2B(mt)2] with Ir(CO)Cl(PPh3)2results in the formation of IrH(CO)(PPh3){κ3-B,S,S′-B(mt)2R} (R = mt, H), in which both of the Ir → B bonds are supported by only two methimazolyl buttresses.113Mono-, Di- and Tri-alkyl/aryl boranes including fluorinated boranesX-ray crystal structures for the tris(tertbutyl) derivatives of boron, aluminum, gallium, and indium (M) determined at low temperatures (150–220 K) have been reported and reveal essentially monomeric molecular units throughout with consistently longer M–C bonds than in the corresponding monomeric trimethyl derivatives. Comparison of the three structures shows a significant strengthening of intermolecular M⋯β-CH3binding in the order M = B ≈ Ga < In < Al resulting in a distinctly nonplanar MC3skeleton.114The novel luminescent molecule, Mes2B(p-4,4′-biphenyl-NPh(1-naphthyl)), has been synthesised and the UV-Vis and photoluminescence spectra of the molecule have been recorded and reported.115The synthesis of the heteronuclear Lewis acid 1-pentafluorophenylmercury-8-dimesityborylnaphalene, 1-(C6F5Hg)-8-(C6H2Me3)–C10H6, has been reported and the UV-Vis spectrum recorded. The complex has been shown to act as a fluoride sensor, and coordination of F−to both the boron and mercury centre results in a strong spin–orbit coupling effect and a strong phosphorescent signalling of fluoride binding (15).116Reaction of the 4,6-dilithiodibenzofuran with dimesitylboronfluoride affords 4,6-bis(dimesitylboryl)dibenzofuran, both of which have been structurally characterised. Cyclic voltammetry shows significant electronic coupling between the two boron centres. Computational studies indicate that the two boron centres participate equally in the LUMO, and provide a rational to the observed electronic coupling.117Reaction of the ytterbium amide [Yb{N(SiMe3)2}2][BPh4] with 3,5-di-tert-butylpyrazole (tBupz) forms [Yb(tBupz){N(SiMe3)2}(THF)BPh4], the molecular structure of which reveals the η6:η6chelating mode of the [BPh4]−anion to the metal centre.118A study of the molecular structures of the mono-, di- and tetra-botylated ferrocenes Fc{BR1R2} (R1/R2= Br/Br, Br/Fc, Br/Me, Me/Me, Me/OH, OMe/OMe), 1,1′-[fc{BR1R2}2] (R1/R2= Br/Br, Br/Me, OMe/OMe), and 1,1′,3,3′-[Fe{C5H3(BMe2)2}2] reveal the boryl substituent(s) to be bent out of the Cp ring plane towards the iron centre. The corresponding dip angle, α, decreases with decreasing Lewis acidity of the boron atom and with increasing degree of borylation at the ferrocene core. DFT calculations have been used to interpret this trend.119Dinuclear and trinuclear ferrocene complexes, [Fc2BMe2]Li, [Fc-BMe2-fc-BMe2-Fc]Li, Fc2B(pyind), [Fc2B(bipy)]PF6, [Fc-B(bipy)-fc-B(bipy)-Fc][PF6]2, bearing anionic, uncharged, and cationic four-coordinate boron bridges have been synthesised (Fc = ferrocenyl; fc = 1,1′-ferrocenylene; pyind = 5-fluoro-2-(2′-pyridyl)indolyl; bipy = 2,2′-bipyridyl). The molecular structures of [Fc2BMe2][Li(12-crown-4)2], [Fc-BMe2-fc-BMe2-Fc][Li(12-crown-4)2]2, Fc2B(pyind), and [Fc2B(bipy)]PF6have been determined by X-ray crystallography. Cyclic voltammograms of the diferrocene species show two well-resolved one-electron transitions which indicate electronic interactions between the two ferrocenyl substituents. Two redox waves with an intensity ratio of 1∶2 are observed in the cyclic voltammograms of the trinuclear derivatives [Fc-BMe2-fc-BMe2-Fc]Li2and [Fc-B(bipy)-fc-B(bipy)-Fc][PF6]2.120The pentafluorophenyl esters of bis(pentafluorophenyl)borinic acid, (C6F5)2BOC6F5(16), pentafluorophenylboronic acid, C6F5B(OC6F5)2(17), and boric acid, B(OC6F5)3(18), have been prepared and characterised by multinuclear NMR and X-ray analysis. The Lewis acidity of all three esters have been compared with B(C6F5)3, using various Lewis bases. The results of these studies indicate that all these compounds are strong Lewis acids, with B(C6F5)3interacting more strongly with hard bases whereas the esters appear to bind more strongly to softer bases.121The molecular structure of the diborane salt [1,2-C6F4{B(C6F5)2}(μ-OMe)][(MeOH)3H] has been determined and its activity as a catalyst for the aqueous suspension polymerisation of isobutene determined.122The controlled hydrolysis oftBuN&z.dbd;Te(μ-NtBu)2Te&z.dbd;NtBu with one or two equivalents of the borane adduct (C6F5)3B·OH2has been reported and the molecular structures of the tellurium oxide borane adducts (C6F5)3B·O&z.dbd;Te(μ-NtBu)2Te&z.dbd;NtBu and [(C6F5)3B·O&z.dbd;Te(μ-NtBu)2Te(μ-O)]2determined.123(C6F5)3B·OH2has also been used in the controlled hydrolysis of the tantalum complexes (η5-C5Me5)TaR4(R = Cl, Me or CH2Ph) to form the borane stabilised oxo-complexes (η5-C5Me5)TaR2{OB(C6F5)3}}. DFT has been used to determine the electronic nature of the Ta–O and O–B bonds.124Lancasteret al. have reported and discussed the synthesis and solid state structure of 13 new amine–borane and amine-adducts, R′RHN·B(C6F5)3and R′RHN·Al(C6F5)3(R = H, Me, CH2Ph; R′ = Me, CH2Ph, CH(Me)Ph; RR′ =cyclo-C5H10) respectively. Each of the borane adducts shows significant intramolecular hydrogen bonding between an amino hydrogen and twoorthofluorine atoms.125Roeskey and co-workers have reported the reaction of the Al(i) species with B(C6F5)3which forms the adduct LAl·B(C6F4)3(19) (L = HC(CMeNAr)2; Ar = 2,6-C6H3(iPr)2), the molecular structure of which reveals the aluminium centre to be both Lewis acidic and Lewis basic, as indicated by the presence of both a dative Al → B bond and a secondary Al ← F interaction from one of theorthofluorine atoms.Ab-initiocalculations have also been conducted in order to understand the nature of the bonding between the aluminium and the borane.126B(C6F5)3has also been used to stabilise the organo-thallium compound [Ar′Tl] (Ar′&z.dbd;C6H3-2,6-(C6H3-2,6-Me2)2), with the thallium(i) monomer acting as a Lewis base, forming the 1∶1 adduct Ar′Tl·B(C6F5)3(20). As in the aluminium(i) adduct the thallium is stabilised further by an intramolecular F → Tl interaction.127The solid state structure of the 1,3,4,5-tetramethylimidazol-2-yl-idene-tris(pentafluorophenyl)borane adduct Me4C2N2C→B(C6F5)3showing a stabilising interaction between anorthoF-atom and the central carbene carbon of the imidazolylidene has been published.128The synthesis and molecular structures of the hydroxyl and oxide bridged borates, [(C6F4)3B(μ-OH)B(C6F5)3]−and [(C6F4)3BOB(C6F5)2]−formed in a series of reactions between (C6F4)3B·OH2and various bases has been reported.129The haloacetyl-tris(trfluromethyl)borate anions [(CF3)3B–C(O)X][R4N] and [(CF3)3B–C(O)X][Ph4P] (X = F, Cl, Br, I; R =nBu or Et) have been synthesised from the reaction of the CO borane adduct (CF3)3B·CO with the appropriate ammonium halide salts. The chemical reactivity of these compounds have been demonstrated in a series of reactions.130The isoelectronic cyano- and isocyano-borates [(CF3)3BNC]−and [(CF3)3BCN]−have been synthesised and the solid state structures of the potassium salts determined. Differential scanning calorimetry has been used to identify the decomposition pathways of both salts and to determine the enthalpy of isocyanide–cyanide rearrangement. DFT calculations have also been used to model the intramolecular rearrangement.131The activity of a series of zirconium borate systems, formed by the reaction of [H(OEt2)2][B(CF3)4], [Ph3C][(CF3)3BCN] and [Ph3C](CF3)3BNC] with Cp2ZrMe2, has been reported. The structures of several resulting complexes have been determined and the activity towards the polymerisation of propene discussed.132Boron containing heterocyclesSiebert and co workers have reported the insertion of terminal alkyne, 3-phenyl-1-propyne into the ruthanocene boracycle (η5-C5Me5)Ru(1,3-η5-C3Me3B2R2) (R = CH2SiMe3or Me) which leads to the formation of an 18-electron complex containing the η7-4-borataborepine ligand.133Reaction of the boron heterocycle, 1-ethyl-2,5-dihydro-2-phenyl-1H-12-azoborole with LDA yields the corresponding lithium borolide which has been used as the starting material for the synthesis of the silyl bridged bis(borole)dimethyl silane and cyclopentadienyl dimethyl silylborole, which have subsequently been transformed into the corresponding heterocyclic analogues ofansa-zirconocene dichloride.134Reaction of 1,1-bis(chloromethylboryl)ethane with 1,1-diisoropyl hydrazine in the presence of base results in the formation of 1,2-diisopropyldiaza-3,5-trimethyldiborolidine. Reaction with LiTMP affords the 1,2-diaza-3,5-diboryllithum complex, which upon reaction with zinc dichloride yields the bisdiorolyl zinc complex. The molecular structures of both the lithium and zinc complexes have been determined.135Pieres and co-workers have synthesised a series of boronium and borenium cations by reaction of pyridinium hydrochloride with pyridine stabilized borabenzene derivatives.136The five-membered B-N-heterocyclic carbenes: C{N(Ar)B(NMe2)}2(Ar = 2,6-C6H3Me2or 2,6-C6H3(CHMe2)2) (21) containing the diboron backbone have been reported and their adducts with {W(CO)5} structurally characterised and reported.137Bertrandet al. have developed a synthetic route to stable six-membered N-B-heterocyclic carbenes and carbocations based on borozine rings. Single crystal X-ray diffraction of the carbene and the carbocation C{N(Cy)B(NMe2)2}NMes} (22) and [HC{N(Cy)B(NMe2)}2NMes]Br (Cy = Cyclohexane, mes = 2,4,6-C6H2Me3) reveal that both ring systems have a planar skeleton with a propeller like arrangement of the susbstituents. Reactions of the carbene with [RhCl(COD)]2and [RhCl(CO)2]2have also been investigated.138The spontaneous transformation, in solution, of 1,2,4-triboracyclopentane derivatives into nonclassical 2-boryl-1,3-diboracyclcobutanes has been studied by NMR spectroscopy X-ray structural analysis and computational methods.139Density functional theory studies, comparing the energetics of [4 + 2] Diels–Alder-like cyclisations of the iminoborane (F3C)3C–B&z.dbd;NtBu, with substitutedcis-2-R-1,3-butadienes (R = CH3, NH2, CF3) have been reported. Calculations predict that some reactions will display regiospecificity derived from the transition state barrier heights. No regiospecificity is observed when R is an electronically near-neutral group (CH3). When R is an electron-donating group (NH2), the models predict a strong preference for the 5-R-1-bora-2-azacyclohexa-1,4-diene product because the R group favours proximity to the boron atom. When R is an electron withdrawing group (CF3), the models predict a preference for the 4-R-1-bora-2-azacyclohexa- 1,4-diene product with the R group in proximity to the nitrogen atom.140Boron-Chalcogen compoundsThe chainlike potassium borates K4B10O15(OH)4and KB5O7(OH)2·H2O have been synthesised under solvothermal conditions. X-ray diffraction studies reveal the two borates to have chain like structures built up by corner sharing of borate groups.141The boronic acid 4-carboxypyenyl boronic acid, and its interactions with the nitrogenous bases 4-dimethylaminopyridine, 4-acetylpyridine oxime and 2-methyl imidazole have been investigated as supramolecular synthons in crystal engineering.142The reaction between boric acid and guanidinium salts in methanolic solutions, in the presence of various bases, has been shown to produce hydrogen bonded networks containing the borate anion [B(OMe)4]−.143The hydrogen-bonding interaction energies formed between boronic acids, carboxylic acids, and carboxylate anions have been computed for a series of five homo- and hetero-dimers usingab initiomethods at the MP2/6-31G(d,p) level. The stability of these systems decreases in the following direction: RB(OH)2⋯−OOCR > RCOOH⋯−OOCR ≫ RCOOH··HOOCR > RB(OH)2⋯HOOCR > RB(OH)2⋯(HO)2BR; (R = Me, Ph). In the same study, five crystals containing boronic acids and carboxylate anions have been prepared and characterized both in solution and the solid-state using spectroscopic as well as X-ray crystallographic methods.144Lappert and co-workers have prepared and reported a series of 1,2-dipenyldioxoborylcyclopentadienyl-metal complexes with the general formulae M{η5-C5H4(BX)}Cl3(M = Ti, Zr, Hf; X = 1,2-O2C6H4, 4-tBu-1,2-O2C6H3, 3,5-tBu2-1,2-O2C6H2), M{η5-C5H4(BX)}2Cl2(M = Zr, Hf; X = 1,2-O2C6H4, 4-tBu-1,2-O2C6H3), M{(μ-η5-C5H4–BO2C6H4)2SiMe2}Cl2(M = Zr, Hf), M{η5-C5H3(BO2C6H4)2}Cl3(M = Zr, Hf), M{η5-C5H3(BO2C6H4)2}3(THF) (M = La, Ce, Yb), Sn{η5-C5H3(BO2C6H3tBu)2}Cl, Fe{η5-C5H3(BO2C6H4tBu)2}2.145Reaction of 8-hydroxyquinol and its functionalised derivatives 5-(1-napthyl)-8-hydroxyquinol, 5-(2-benzothienyl)-8-hydroxyquinol and 2-methy-8-hydroxyquinol with BPh3and B(2-benzothienyl)3result in the formation of four-coordinate boron chelated complexes of which Ph2B(5-(1-napthyl)-8-hydroxyquinolato), Ph2B(5-(2-benzothienyl)-8-hydroxyquinolato), (2-benzothienyl)2B(8-hydroxyquinolato) and (2-benzothienyl)2B(2-methyl-8-hydroxyquinolato) have been characterised by single crystal X-ray diffraction analyses. The emission spectra of the complexes has been recorded and molecular orbital calculations used to understand the electronic π-π* transitions.146Condensation of phenylboronic acid or BF3with tris(methylchloroglyoximate)iron(ii)chloride has been shown to afford the trichloro phenylboron- and fluoroboron-capped clathrochelates. Similar reaction between the iron macrocyle, FeBd2(BF2)2(NCMe)2(Bd2−= α-benzyldioximate) and methylchloroglyoxime, Me(Cl)GmH2, allows the formation of the monosubstituted clathrochelate Fe(Bd)2{Me(Cl)Gm}(BF)2. Mono- and tri-fuctionalised amine, alkylsulfide, and arylsulfide clathrochelates have also been prepared by nucleophilic substitution reactions.147In a related study boron-antimony capped iron(ii) clathrochelates have been reacted with zirconium and hafnium phthalocyanines to afford the hybrid phthalocyaninoclathrochelates. The complexes have been characterised by mass spectroscopy,57Fe Mössbauer and NMR spectroscopy, and crystallographically.148The phenylborate ester, bis(phenylboranediyl)-α-D-glucofuranose, has been produced by a condensation reaction between phenylboronic acid and D-glucose, and its molecular structure determined by single crystal X-ray analysis.149The molecular structure of the polymeric borate [Na{B(OMe)4}(HOMe)2]nhas been determined and reported.150The reaction of BEt3with the (2-dimethylaminophenyl)alcohols 1-HOX-2-NMe2C6H4(X = CPh2, CCy2, CPh2CH2) in 1∶2 and 1∶1 reaction ratios has been shown to produce a range of intramolecularly base stabilised {BEt2} and {BEt} derivatives.151Hypervalent, pentacoordinate and tetracoordinate compounds bearing an anthracene skeleton with two oxygen or nitrogen donor groups (OMe and NMe2respectively) in the 1,8-positions have been synthesised and reported. Several of the boron compounds bearing {BO2-1,2-C6H4} (23), {B(OMe)2}, {BMe2}, {BS2-1,2-C6H4}, {BF2} and {BCl2} units have been structurally characterised. DFT calculations and X-ray diffraction charge density studies have been used to verify the presence of hypervalent 3 centre-4 electron bonding.152The effect of substituents in the 2,4 positions, on the supramolecular structure and assembly of 1,4-bis(dioxaborole)-benzenes, has been explored. Analysis of the solid state structures of the hexyl, nonyl and dodecyl substituted bis-catechol borole systems reveals substitution in the 1,4 positions on the central phenyl ring to have no significant effect on the supramolecular assembly of these compounds.153Cowleyet al. have reported the synthesis and structural characterisation of the first oxobroane compound (R–B&z.dbd;O), stabilised by interaction with AlCl3. Reaction of the β-diketiminate salt [{HC(CMe)2(NC6F5)2}BCl][AlCl4] with stoichiometric amounts of H2O in CH2Cl2results in the formation of the oxoborane {HC(CMe)2(NC6F5)2}B&z.dbd;O⋯AlCl3(24). DFT calculations have been used to gain insight into the bonding.2The bis-boryloxide, O(Bpin)2(pin = OCMe2CMe2O) has been produced by the reaction of HBpin with phosphine oxides, and its molecular structure described.154The bis-boryloxides O(Bcat)2and O(B{S,S-OC(H)PhC(H)PhO})2have been investigated for their ability to bind bidentate anions such as acetate and phosphate. The 1∶1 adduct of O(Bcat)2with [PPN][O2CMe] has been structurally characterised and the binding constant determined.155Perfluoroaryl bearing bis(bora)calix[4]arenes have been synthesised by the direct reaction oftert-butylcalix[4]areneH4with (C6F5)2BF·OEt2. The reaction of BCl3withtert-butylcalix[4]areneH4produces the chloro-substituted bis(bora)calix[4]arene, which has been reacted with one and two equivalents of 2,4,6-(CF3)3C6H2Li to form the mono- and bis-substituted boracalixarenes respectively.156The selective iridium catalysed borylation of the polycyclic aromatics, naphthalene, pyrene and perylene, by B2(pin)2(pin = OCMe2CMe2O) has been reported and the molecular structures of the naphthalene-2,7-bis(pinicolboronate) and pyrene-2,7-bis(pinicolboronate) and perylene-2,5,8,11-tetra(pinicolborate) esters determined.157The same iridium catalyst [Ir(COD)OMe]2, has also been used for the regioselective borylation of porphyrins.158A series of Group 4 metal complexes supported by the boroxide anion, [OB(mes)2]−, has been reported by Coles and co-workers and their application in α-olefin polymerisation discussed. Reaction of the lithium boroxide anion with the metal chloride derivatives MCl4(M = Ti, Zr, Hf), (η5-C5H5)2MCl2(M = Ti, Zr) and (η5-C5Me4H)TiCl3, affords the complexes M{OB(mes)2}2Cl2(THF)2(M = Ti, Zr, Hf), (η5-C5H5)2M{OB(mes)2}Cl (M = Ti, Zr) and (η5-C5Me4H)Ti{OB(mes)2}Cl2respectively. Serendipitous hydrolysis of Zr{OB(mes)2}2Cl2(THF)2results in the isolation of the hydroxyl complex [Zr{OB(mes)2}3(OH)]2. Protonolysis of Ti(NEt2)4and M(CH2Ph)4(M = Ti, Hf) with HOB(mes)2results in the formation of Ti(NEt2)2{OB(mes)2}2, M(CH2Ph)2{OB(mes)2}2(M = Ti, Hf) and Hf{OB(mes)2}4, several of which have had their molecular structures determined. Several of the complexes have also been tested for ethylene polymerisation in the presence of MAO as an activator.159The reaction ofpara-substituted phenyl boronic acids or 1,4-benzene diboronic acid with a series of Schiff-bases, formed from the reaction of salicylaldehyde and aminoalcohols, provide series of heterobicyclic boronates containing N → B coordinative bonds.160The reaction of 2,6-dimethanolpyridine with the boronic acids R-B(OH)2(R = C6H4-3-COH, C6H4-3-OMe, C6H4-3-Me, C6H4-4-Br) produces a series of tetrameric compounds in good yields. Comparable reactions with 2,6-bis(1,1-diphenyl-1-ethoxy)pyridine result in the formation of monomeric species.161Boron-Pnictogen compoundsThe reaction of chloro(dimethylsulfide)gold (i) with trimethylamine-isocyanoborate, provides the adduct [(RNC)AuCl] (R = Me3NB(H)2). Treatment with KBr effects the substitution of Cl for Br to produce [(RNC)AuBr]. The structures of both adducts have been determined by single crystal X-ray diffraction analysis. Treatment with KI solution affords the unexpected compound [(RNC)2Au][AuI2].162Reaction of the phosphine–borane adducts PhRPH·BH3(R = H, Ph) with the Pt(ii)dihydride complexcis-PtH2(dcype)] (dcype = bis(dicyclohexylphosphino)ethane) has been found to produce the mono-substituted complexes PtH(PPhR·BH3)(dcype), exclusively. The reaction of Li[PPhH·BH3] withcis-PtCl2(dcype), which forms the complexcis-Pt(PPhH·BH3)2(dcype), has also been investigated.163A synthetic route to phosphorous analogues of the amino-acid proline has been developed, a key step in which is the utility of the borane adducts such as the phenylphospholane borane adduct C4H8P·BH3.164The borane adduct bis(2-pyridylmethyl)amine-borane, (2-C5H4NCH2)NH·BH3, has been synthesised and its molecular structure published.165The π-conjugated molecules,B,B′,B″-trianthryl-N,N′,N″-triarylborazine derivatives bearing various π-substituted phenyl groups (p-R-C6H4: R = hexyl,iPr, CF3, Br) on the nitrogen atoms have been designed and synthesised. The crystal structure analysis of these derivatives confirmed that the three anthryl and three phenyl groups are bundled up alternately in a C3-symmetrical gear-shaped fashion. The trianthrylborazine derivatives have been shown to form unique honeycomb like packing structures consisting of intermolecular π-stacking of the anthryl moieties. The fluorescence spectra of the trianthrylborazine derivatives show intense emissions around 390 nm and the cyclic voltammetry measurements indicate that the oxidation peak potential can be tuned by varying the substituents on the phenyl moieties. Theoretical calculations suggested that secondary through-bond/through-space interactions in the bundled structure play an important role in the tuning of these properties.166The reaction ofB,B′,B″-triphenylborazine with methyl lithium or phenyl lithium in various ratios and in the presence of nitrogen donor ligands such as TMEDA and Me3-TAC produces a series of lithiated borazine complexes which have been structurally characterised.167A variety of borylborazine-based polymers have been converted into boron nitride. Polycondensation of monomers have produced highly tractable polymers which have been easily spun into fine-diameter fibre.168The bis(dimethylamino)diborane linkedansa-zirconocene and hafnacene complexes {(η5-C5H5)2-1,2-B(NMe2)B(NMe2)}MCl2(M = Zr or Hf) and the activity of these complexes towards the α-olefin polymerisation of ethane in the presence of MAO has also been reported.169The boron-bridged half metalocenes M{η5-C5H4-B(NiPr2)NPh}(NMe2)2(M = Zr, Hf) have been prepared by the amine elimination reaction between the neutral ligand and the homoleptic amide precursor.170The reaction of the diphosphadiboretane complex 1,3-di(tert-butyl)-2,4-bis(2,2,6,6-tetramethylpiperidino)-1,3,2,4-diphosphadiboretane with AlBr3results in the synthesis and isolation of the P → Al bonded adduct, tmp&z.dbd;B&z.dbd;P(tBu)⋯AlBr3(tmp = 2,2,6,6-tetramethylpiperidino), and the more stable salt [(tmpB)2(PtBu)P]+[AlBr4]−. The molecular structures of all three complexes have been determined andab initiocalculations used to understand the unusual bonding observed.171The reaction betweenN,N′-dilithiated 1,10-bis(trimethylsilylamino)ferrocene and the boron halide adducts (HBBr2·SMe2; BF3·OEt2and BBr3·SMe2), boron halides (BCl3, BBr3, BCl2(OPh) and BCl2Ph) and 1,1-bis(dimethylamino)dichlorodiborane to give the corresponding 1,3-bis(trimethylsilyl)-1,3,2-diazabora-[3] ferrocenophanes and the 2,3-bis(dimethylamino)-1,4-bis(trimethylsilyl)-1,4,2,3-diazadibora-[4] ferrocenophane has been reported.172The 1∶1 adduct PhBCl2:CyN&z.dbd;C&z.dbd;NCy, has been isolated from the room temperature reaction between the carbodiimide and PhBCl2. Heating of the adduct in toluene results in migration of the phenyl group and formation of the amidinate {PhC(NCy)2}BCl2. DFT calculations have been used to study the overall reaction.173In a subsequent study the boron–amidinates {PhC(NSiMe3)2}BCl2, {MeC(NCy)2}BCl2, {Mes*C(NCy)2}BCl2, {MeC(NiPr)2}BCl2and {FcC(NCy)2}BBr2have also been prepared by a combination of salt metathesis and insertion reactions.174The cyano-borane adduct (η5-C5H5)Fe(CO)(PPh3)CN·BPh3has been structurally determined and reported.175Treatment of the diborane compound (Me2N)2B–B(NMe2)2with aniline or 2,6-dimethylaniline results in the formation of the primary amido compounds B2(NHR)4(R = Ph, 2,6-C6H3Me2). Treatment with butyl lithium affords the lithium imidodiborates Li4(THF)6B2(NPh4)4and Li4(THF)6B2(N-2,6-C6H3Me2)4which have been structurally characterised.176The spyrocyclic radical species [{PhB(NtBu)2}2M]&z.rad; (M = Al or Ga) containing the boraamidinate ligands {PhB(NtBu)2} have been synthesised from the corresponding anionic complexes by oxidation with stoichiomtric amounts of I2in diethyl ether. The EPR spectra and DFT calculations support the hypothesis of a spiroconjugated system in which the spin density of the single electron is equally delocalised over all four nitrogen atoms.177Reaction of the dilithium boraamidinate Li2[PhB(NtBu)2] with BF3·OEt2results in the formation of the asymmetrically substituted borazine PhF2B3N3tBu3, the molecular structure of which has been determined.178The molecular structures of dimethylamino[(dimethylboryl)methylamino]methylborane, Me2NBMeNMeBMe2, and 1,1-bis(dimethylboryl)-2,2-dimethylhydrazine, (Me2B)2NNMe2, have been determined by gas phase electron diffraction and density functional theory calculations.179Reaction of trimethylsilyl–iminophhinimides with chloro–catecholborane results in the formation of catecholboryl–phosphinimides with the general formula [(R3PN)Bcat]x(cat = O2C6H4, R = Et,n-Bu, Ph andiPr. X-ray crystallographic studies as well as solution NMR spectroscopy reveal that the species are dimeric, except for the bulkyB-phosphinimides (tBu3PN)Bcat, which is monomeric. Reaction between R3PNH (R =tBu oriPr) with pinicolborane also produces catecholboryl-phosphinimides. Computational studies have been used to understand the reactions and rationalise the reactivity.180The synthesis of 1,3,2-diazoborolidine and 2,3-dihydro-1,3,2-diazaborole derivatives, by reaction of 1,1′-bis(dibromoboryl)ferrocene, dibromoboryl–ferrocene and 1-dibromoboryl-3-methylcymantrene withtBuN&z.dbd;CH–CH&z.dbd;NtBu andtBuN(H)CH2CH2N(H)tBu, respectively has been reported. Single crystal X-ray diffraction studies and cyclic voltammetric studies have been used to characterise the resulting products.181In a related study the 2,3-dihydro-1H-1,3,2-diazaboroles {tBuNCH&z.dbd;CHNtBu}B–R (R = NH2, OMe, Me, NMe2, H, SMe, SnMe3, Br, CN) and the corresponding saturated 1,3,2-diazaborolidines have been synthesised and their oxidation potentials reported.182Boron halidesComputational studies that investigate the 1∶1 adducts formed between cytosine and BX3(X = F, Cl) have been reported. For each system three isomers have been found, with the most stable of these isomers cytosine is bound to the boron atomviathe carbonyl oxygen.183The molecular structure of trichloro(1H-imidazole)boron adduct, C3H4N2·BCl3, has been determined and reported.184The first representatives of an unknown family of organoboron compounds, the ((perfluoroorgano) ethynyl)trifluoroborate salts K[RFC&z.dbd;CBF3] (RF= CF3, C3F7, (CF3)2CF, C6F13, CF3–CF&z.dbd;CF, C4F9CF&z.dbd;CF, C6F5), have been prepared and characterized by multinuclear NMR spectroscopy (11B,13C, and19F) and reported.185The molecular structure of the halo-borane B8F12(25), has been determined by gas phase electron diffraction and computational methods, and shown to have a highly asymmetric form as observed in the solid state. Computational methods have also been used to investigate the compounds B8Cl12, B8Br12and B8I12. In the case of the iodine compound computational studies suggest a similar structure to that observed in the F, Cl and Br analogues is not the lowest energy structure, and instead a loosely associated dimmer of B{BI2}3i.e.(B{BI2}3)2(26) is preferred.186