Synthesis, structure, and reactivity of 13-vertex carboranes and 14-vertex metallacarboranes

Syntheses, properties, and synthetic applications of 13-vertex closo- and nido-carboranes are reported. Reactions of the nido-carborane salt [(CH2)3C2B10H10]Na2 with dihaloborane reagents afforded 13-vertex closo-carboranes 1,2-(CH2)3-3-R-1,2-C2B11H10 (R = H (2), Ph (3), Z-EtCH=C(Et) (4), E-(t)BuCH=CH (5)). Treatment of the arachno-carborane salt [(CH2)3C2B10H10]Li4 with HBBr2.SMe2 gave both the 13-vertex carborane 2 and a 14-vertex closo-carborane (CH2)3C2B12H12 (8). On the other hand, the reaction of [C6H4(CH2)2C2B10H10]Li4 with HBBr2.SMe2 generated only a 13-vertex closo-carborane 1,2-C6H4(CH2)2-1,2-C2B11H11 (9). Electrophilic substitution reactions of 2 with excess MeI, Br2, or I2 in the presence of a catalytic amount of AlCl3 produced the hexa-substituted 13-vertex carboranes 8,9,10,11,12,13-X6-1,2-(CH2)3-1,2-C2B11H5 (X = Me (10), Br (11), I (12)). The halogenated products 11 and 12 displayed unexpected instability toward moisture. The 13-vertex closo-carboranes were readily reduced by groups 1 and 2 metals. Accordingly, several 13-vertex nido-carborane dianionic salts [nido-1,2-(CH2)3-1,2-C2B11H11][Li2(DME)2(THF)2] (13), [[nido-1,2-(CH2)3-1,2-C2B11H11][Na2(THF)4]]n (13a), [[nido-1,2-(CH2)3-3-Ph-1,2-C2B11H10][Na2(THF)4]]n (14), [[nido-1,2-C6H4(CH2)2-1,2-C2B11H11][Na2(THF)4]]n (15), and [nido-1,2-(CH2)3-1,2-C2B11H11][M(THF)5] (M = Mg (16), Ca (17)) were prepared in good yields. These carbon-atom-adjacent nido-carboranes were not further reduced to the corresponding arachno species by lithium metal. On the other hand, like other nido-carborane dianions, they were useful synthons for the production of super-carboranes and supra-icosahedral metallacarboranes. Interactions of 13a with HBBr2.SMe2, (dppe)NiCl2, and (dppen)NiCl2 gave the 14-vertex carborane 8 and nickelacarboranes [eta5-(CH2)3C2B11H11]Ni(dppe) (18) and [eta5-(CH2)3C2B11H11]Ni(dppen) (19), respectively. All complexes were fully characterized by various spectroscopic techniques and elemental analyses. Some were further confirmed by single-crystal X-ray diffraction studies.     

Synthesis, structural characterization, reactivity, and thermal stability of [eta(5):sigma-Me2C(C5H4)(C2B10H10)]Ti(R)(NMe2)

Reaction of [eta:(5)sigma-Me2C(C5H4)(C2B10H10)]TiCl(NMe2) (1) with 1 equiv of PhCH2K, MeMgBr, or Me3SiCH2Li gave corresponding organotitanium alkyl complexes [eta:(5)sigma-Me2C(C5H4)(C2B10H10)]Ti(R)(NMe2) (R = CH2Ph (2), CH2SiMe3 (4), or Me (5)) in good yields. Treatment of 1 with 1 equiv of n-BuLi afforded the decomposition product {[eta:(5)sigma-Me2C(C5H4)(C2B10H10)]Ti}2(mu-NMe)(mu:sigma-CH2NMe) (3). Complex 5 slowly decomposed to generate a mixed-valence dinuclear species {[eta:(5)sigma-Me2C(C5H4)(C2B10H10)]Ti}2(mu-NMe2)(mu:sigma-CH2NMe) (6). Complex 1 reacted with 1 equiv of PhNCO or 2,6-Me2C6H3NC to afford the corresponding monoinsertion product [eta:(5)sigma-Me2C(C5H4)(C2B10H10)]Ti(Cl)[eta(2)-OC(NMe2)NPh] (7) or [eta:(5)sigma-Me2C(C5H4)(C2B10H10)]Ti(Cl)[eta(2)-C(NMe2)=N(2,6-Me2C6H3)] (8). Reaction of 4 or 5 with 1 equiv of R'NC gave the titanium eta(2)-iminoacyl complexes [eta:(5)sigma-Me2C(C5H4)(C2B10H10)]Ti(NMe2)[eta(2)-C(R)=N(R')] (R = CH2SiMe3, R' = 2,6-Me2C6H3 (9) or tBu (10); R = Me, R' = 2,6-Me2C6H3 (11) or tBu (12)). The results indicated that the unsaturated molecules inserted into the Ti-N bond only in the absence of the Ti-C(alkyl) bond and that the Ti-C(cage) bond remained intact. All complexes were fully characterized by various spectroscopic techniques and elemental analyses. Molecular structures of 2, 3, 6-8, and 10-12 were further confirmed by single-crystal X-ray analyses.     

Substituted N-picolylethylenediamines of the type (ArNHCH2CH2){(2-C5H4N)CH2}NR [R = Me, 4-CH2=CH(C6H4)CH2, (2-C5H4N)CH2] and their transition metal(II) halide complexes

Alkylation of (ArNHCH2CH2){(2-C5H4N)CH2}NH with RX [RX = MeI, 4-CH2=CH(C6H4)CH2Cl) and (2-C5H5N)CH2Cl] in the presence of base has allowed access to the sterically demanding multidentate nitrogen donor ligands, {(2,4,6-Me3C6H2)NHCH2CH2}{(2-C5H4N)CH2}NMe (L1), {(2,6-Me3C6H3)NHCH2CH2}{(2-C5H4N)CH2}NCH2(C6H4)-4-CH=CH2 (L2) and (ArNHCH2CH2){(2-C5H4N)CH2}2N (Ar = 2,4-Me2C6H3 L3a, 2,6-Me2C6H3 L3b) in moderate yield. L3 can also be prepared in higher yield by the reaction of (NH2CH2CH2){(2-C5H4N)CH2}2N with the corresponding aryl bromide in the presence of base and a palladium(0) catalyst. Treatment of L1 or L2 with MCl2 [MCl2 = CoCl2.6H2O or FeCl2(THF)1.5] in THF affords the high spin complexes [(L1)MCl2](M = Co 1a, Fe 1b) and [(L2)MCl2](M = Co 2a, Fe 2b) in good yield, respectively; the molecular structure of reveals a five-coordinate metal centre with bound in a facial fashion. The six-coordinate complexes, [(L3a)MCl2](M = Co 3a, Fe 3b, Mn 3c) are accessible on treatment of tripodal L3a with MCl2. In contrast, the reaction with the more sterically encumbered leads to the pseudo-five-coordinate species [(L3b)MCl2](M = Co 4a, Fe 4b) and, in the case of manganese, dimeric [(L3b)MnCl(mu-Cl)]2 (4c); in 4a and 4b the aryl-substituted amine arm forms a partial interaction with the metal centre while in 4c the arm is pendant. The single crystal X-ray structures of , 1a, 3b.MeCN, 3c.MeCN, 4b.MeCN and 4c are described as are the solution state properties of 3b and 4b.     

Quenched gas-phase reactions of tetraborane(10), B4H10, with substituted alkynes: new nido-dicarbapentaboranes and arachno-monocarbapentaboranes

New alkyl derivatives of the nido-dicarbapentaborane, 1,2-C(2)B(3)H(7), and arachno-carbapentaborane, 1-CB(4)H(10), have been identified as the main volatile carbaborane products in quenched gas-phase reactions of tetraborane(10), B(4)H(10), with alkyl-substituted ethynes RC[triple bond]CR' (R = Me, Et, (n)Pr or (t)Bu, R' = H; R = Me or Et, R' = Me). The gaseous mixtures were heated at 70 degrees C, and monitored by gas-phase mass spectrometry. Each reaction was quenched when the ethyne was used up. The quenched gas-phase reaction of B(4)H(10) and Me(3)SiC[triple bond]CH gave a single volatile carbaborane product, 1-Me(3)Si-1,2-C(2)B(3)H(6).     

Synthesis and characterization of nickel(II) bis(alkylthio)salen complexes

NiX2(2-RSC6H4CH=NCH2CH2N=CHC6H4SR-2) (NiX2L; L = 5) (1a, X = Br, R = C6H13; 1b, X = Cl, R = C12H25) and NiX2(2-C6H13SC6H4CH2NHCH2CH2NHCH2C6H4SC6H13-2) (NiX2L; L = 6) (2a, X = Br; 2b, X = Cl; 2c, X = OClO3) were prepared from ligands 5 and 6, respectively. The 1:2 metal-ligand complex Ni(OClO3)2(2-RSC6H4CH2NHCH2CH2NHCH2C6H4SR-2)2 3, was obtained from an EtOH solution of 2c. The characterization of paramagnetic 1-3 included single-crystal X-ray diffraction studies of 1a and 3. Complex 2c converted into 3 in the presence of excess ligand 6 in CHCl3.     

Group 6 imido complexes supported by diamido-donor ligands

Reactions of the lithiated diamido-pyridine or diamido-amine ligands Li(2)N(2)N(py) or Li(2)N(2)N(am) with [W(NAr)Cl(4)(THF)] (Ar = Ph or 2,6-C(6)H(3)Me(2); THF = tetrahydrofuran) afforded the corresponding imido-dichloride complexes [W(NAr)(N(2)N(py))Cl(2)] (R = Ph, 1, or 2,6-C(6)H(3)Me(2), 2) or [W(NAr)(N(2)N(am))Cl(2)] (R = Ph, 3, or 2,6-C(6)H(3)Me(2), 4), respectively, where N(2)N(py) = MeC(2-C(5)H(4)N)(CH(2)NSiMe(3))(2) and N(2)N(am) = Me(3)SiN(CH(2)CH(2)NSiMe(3))(2). Subsequent reactions of 1 with MeMgBr or PhMgCl afforded the dimethyl or diphenyl complexes [W(NPh)(N(2)N(py))R(2)] (R = Me, 5, or Ph, 6), respectively, which have both been characterized by single crystal X-ray diffraction. Reactions of Li(2)N(2)N(py) or Li(2)N(2)N(am) with [Mo(NR)(2)Cl(2)(DME)] (R = (t)Bu or Ph; DME = 1,2-dimethoxyethane) afforded the corresponding bis(imido) complexes [Mo(NR)(2)(N(2)N(py))] (R = (t)Bu, 7, or Ph, 8) and [Mo(N(t)Bu)(2)(N(2)N(am))] (9).     

Mononuclear and dinuclear palladium and nickel complexes of phosphinimine-based tridentate ligands

The tridentate bis-phosphinimine ligands O(1,2-C(6)H(4)N=PPh(3))(2)1, HN(1,2-C(2)H(4)N=PR(3))(2) (R = Ph 2, iPr 3), MeN(1,2-C(2)H(4)N=PPh(3))(2)4 and HN(1,2-C(6)H(4)N=PPh(3))(2)5 were prepared. Employing these ligands, monometallic Pd and Ni complexes O(1,2-C(6)H(4)N=PPh(3))(2)PdCl(2)6, RN(1,2-CH(2)CH(2)N=PPh(3))(2)PdCl][Cl] (R = H 7, Me 8), [HN(1,2-CH(2)CH(2)N=PiPr(3))(2)PdCl][Cl] 9, [MeN(1,2-CH(2)CH(2)N=PPh(3))(2)PdCl][PF(6)] 10, [HN(1,2-CH(2)CH(2)N=PPh(3))(2)NiCl(2)] 11, [HN(1,2-CH(2)CH(2)N=PR(3))(2)NiCl][X] (X = Cl, R = iPr 12, X = PF(6), R = Ph 13, iPr 14), and [HN(1,2-C(6)H(4)N=PPh(3))(2)Ni(MeCN)(2)][BF(4)]Cl 15 were prepared and characterized. While the ether-bis-phosphinimine ligand 1 acts in a bidentate fashion to Pd, the amine-bis-phosphinimine ligands 2-5 act in a tridentate fashion, yielding monometallic complexes of varying geometries. In contrast, initial reaction of the amine-bis-phosphinimine ligands with base followed by treatment with NiCl(2)(DME), afforded the amide-bridged bimetallic complexes N(1,2-CH(2)CH(2)N=PR(3))(2)Ni(2)Cl(3) (R = Ph 16, iPr 17) and N(1,2-C(6)H(4)N=PPh(3))(2)Ni(2)Cl(3)18. The precise nature of a number of these complexes were crystallographically characterized.     

Low-valent chemistry of cobalt amide. Synthesis and structural characterization of cobalt(II) amido, aryloxide, and thiolate compounds

The binuclear cobalt(II) amide complex [(CoL2)2-(TMEDA)] (1) [L = N(Si(t)BuMe2)(2-C5H3N-6-Me); TMEDA = Me2NCH2CH2NMe2] has been synthesized by the reaction of anhydrous CoCl2 with 2 equiv of [Li(L)(TMEDA)]. X-ray crystallography revealed that complex 1 consists of two [CoL2] units linked by one TMEDA ligand molecule, which binds in an unusual N,N'-bridging mode. Protolysis of 1 with the bulky phenol Ar(Me)OH (Ar(Me) = 2,6-(t)Bu2-4-MeC6H2) and thiophenol ArSH (Ar = 2,4,6-(t)Bu3C6H2) gives the neutral monomeric cobalt(II) bis(aryloxide) [Co(OAr(Me))2(TMEDA)] (2) and dithiolate [Co(SAr)2(TMEDA)] (3), respectively. Complexes 1-3 have been characterized by mass spectrometry, microanalysis, magnetic moment, and melting-point measurements, in addition to X-ray crystallography.     

New and versatile routes to zirconium imido dichloride compounds

Reactions of zirconium dialkyl- or bis(amido)-dichloride complexes "[Zr(CH2SiMe3)2Cl2(Et2O)2]" or [Zr(NMe2)2Cl2(THF)2] with primary alkyl and aryl amines are described. Reaction of "[Zr(CH2SiMe3)2Cl2(Et2O)2]" with RNH2 in THF afforded dimeric [Zr2(mu-NR)2Cl4(THF)4](R=2,6-C6H3iPr2 (1), 2,6-C6H3Me2 (2) or Ph (3)), [Zr2(mu-NR)2Cl4(THF)3](R=tBu (5), iPr (6), CH2Ph (7)), or the "ate" complex [Zr2(mu-NC6F5)2Cl6(THF)2{Li(THF)3}2](4, the LiCl coming from the in situ prepared "[Zr(CH2SiMe3)2Cl2(Et2O)2]"). With [Zr(NMe2)2Cl2(THF)2] the compounds [Zr2(mu-NR)2Cl4(L)x(L')y](R=2,6-C6H3iPr2 (8), 2,6-C6H3Me2 (9), Ph (10) or C6F5 (11); (L)x(L')y=(NHMe2)3(THF), (NHMe2)2(THF)2 or undefined), [Zr2(mu-NtBu)2Cl4(NHMe2)3] (12) and insoluble [Zr(NR)Cl2(NHMe2)]x(R=iPr (13) or CH2Ph (14)) were obtained. Attempts to form monomeric terminal imido compounds by reaction of or with an excess of pyridine led, respectively, to the corresponding dimeric adducts [Zr2(mu-2,6-C6H3Me2)2Cl4(py)4] (15) and [Zr2(mu-NtBu)2Cl4(py)3] (16). The X-ray structures of 1, 2, 4, 8, 12 and 15 have been determined.     

Alkyl-eta2-alkene niobocene and tantalocene complexes with the allyldimethylsilyl-eta5-cyclopentadienyl ligand: synthesis, NMR studies and DFT calculations

Group 5 metal complexes [M(eta5-C5H5)[eta5-C5H4SiMe2(CH2-eta]2-CH=CH2)]X] (M = Nb, X = Me, CH2Ph, CH2SiMe3; M = Ta, X = Me, CH2Ph) and [Ta(eta5-C5Me5)[eta5-C5H4SiMe2(CH2-eta2-CH=CH2)]X] (X = Cl, Me, CH2Ph, CH2SiMe3) containing a chelating alkene ligand tethered to a cyclopentadienyl ring have been synthesized in high yields by reduction with Na/Hg (X = Cl) and alkylation with reductive elimination (X = alkyl) of the corresponding metal(iv) dichlorides [M(eta5-Cp)[eta5-C5H4SiMe2(CH2CH=CH2)]Cl2] (Cp = C5H5, M = Nb, Ta, Cp = C5Me5, M = Ta). These chloro- and alkyl-alkene coordinated complexes react with CO and isocyanides [CNtBu, CN(2,6-Me2C6H3)] to give the ligand-substituted metal(III) compounds [M(eta5-Cp)[eta5-C5H4SiMe2(CH2CH=CH2)]XL] (X = Cl, Me, CH2Ph, CH2SiMe3). Reaction of the chloro-alkene tantalum complex with LiNHtBu results in formation of the imido hydride derivative [Ta(eta5-C5Me5)[eta5-C5H4SiMe2(CH2CH=CH2)]H(NtBu)]. NMR studies for all of the new compounds and DFT calculations for the alkene-coordinated metal complexes are compared with those known for related group 4 metal cations.     

Preferred bonding motif for indium aminoethanethiolate complexes: structural characterization of (Me2NCH2CH2S)2InX/SR (X = Cl, I; R = 4-MeC6H4, 4-MeOC6H4)

The metathesis reaction of InCl3 with Me2NCH2CH2SNa or the redox reaction of indium metal with elemental iodine and the disulfide (Me2NCH2CH2S)2 yield the indium bis(thiolate) complexes (Me2NCH2CH2S)2InX [X = Cl (3) and I (4)], respectively. Compounds 3 and 4 may be further reacted with the appropriate sodium thiolate salts to afford the heteroleptic tris(thiolate) complexes (Me2NCH2CH2S)2InSR [R = 4-MeC6H4 (5), 4-MeOC6H4 (6), and Pr (7)]. Reaction of 2,6-Me2C6H3SNa with 4 affords (Me2NCH2CH2S)2InS(2,6-Me2C6H3) (8), while no reaction is observed with 3, suggesting a greater reactivity for 4. All isolated compounds were characterized by elemental analysis, melting point, and Fourier transform IR and 1H and 13C{1H} NMR spectroscopies. X-ray crystallographic analyses of 3-6 show a bicyclic arrangement and a distorted trigonal-bipyramidal geometry for In in all cases. The two sulfur and one halogen (3 and 4) or three sulfur (5 and 6) atoms occupy equatorial positions, while the nitrogen atoms of the chelating (dimethylamino)ethanethiolate ligands occupy the axial positions. The metric parameters of the (Me2NCH2CH2S)2In framework were found to change minimally upon variation of the X/SR ligand, while the solubility of the corresponding compounds in organic solvents varied greatly. 1H NMR studies in D2O showed that 6 and 7 react slowly with an excess of the tripeptide l-glutathione and that the rate of reaction is affected by the pendant thiolate ligand -SR.     

Half-pseudoferrocene cations from nucleophilic addition of o-carboranyl anions to the [(η6-mesitylene)2Fe](2+) dication

Reactions between the mesitylene (mes) dication [(η(6)-mes)(2)Fe](2+) (1a) [(PF(6)(-))(2) salt] and lithium o-carboranes Li[1-R-1,2-C(2)B(10)H(11)] (2) (R = H, 2a; Me, 2b; Ph, 2c) at low temperature (-60 °C, 1 h, followed by stirring for 2 h at r.t.) in THF resulted in a clean addition of the corresponding carborane anions to one of the unsubstituted arene sites in 1a, forming a series of orange monocations of general structure [(η(5)-mes-exo-6-{2-R-1,2-C(2)B(10)H(11)})Fe(η(6)-mes)](+) (3) (R = H, 3a; Me, 3b; Ph, 3c) which were isolated as PF(6)(-) salts (3PF(6)) in yields ranging 50-75%. Individual complexes were obtained on purification by LC or preparative TLC on a silica gel substrate, using MeCN-CH(2)Cl(2) mixtures as the mobile phase. Interestingly, the room-temperature reaction between 2a (threefold excess) and 1a(PF(6))(2) with a reverse order of addition of the reaction components yielded an orange salt [(η(5)-mes-exo-6-{1,2-C(2)B(10)H(11)})Fe(η(6)-mes)](+)[closo-nido-H(11)B(10)C(2)-C(2)B(10)H(12)](-) (3acCA) (cCA = conjucto-carborane anion = [closo-nido-H(11)B(10)C(2)-C(2)B(10)H(12)](-)) as a sole product in 71% yield. The formation of this conjucto anion can be taken as a strong support for the participation of a radical-chain mechanism in the ostensible nucleophilic addition which we suppose to be initiated by the formation of the [(mes)(2)Fe(+)]˙ radical cation. The structures of both 3PF(6) and 3acCA have been established by X-ray diffraction and the constitution of all compounds isolated is in agreement with elemental analyses, multinuclear NMR data, and MS spectra.     

Cyanide ion complexation by a cationic borane

While we have previously reported that [1-(Mes2B)-8-(Me3NCH2)-C10H6]+ ([2]+) complexes fluoride ions to form [1-(Mes2FB)-8-(Me3NCH2)-C10H6] (2-F), we now show that this cationic borane also complexes cyanide to form [1-(Mes2(NC)B)-8-(Me3NCH2)-C10H6] (2-CN). This reaction also occurs under biphasic conditions (H2O-CHCl3) and may serve to transport cyanide in organic phases. The zwitterionic cyanoborate 2-CN has been fully characterized and its crystal structure determined. UV-vis titration experiments carried out in THF indicate that [2]+ has a higher affinity for fluoride (K > 10(8) M(-1)) than cyanide (K = 8.0 (+/-0.5) x 10(5) M(-1)). Steric effects which impede cyanide binding to the sterically congested boron center of [2]+ are most likely at the origin of this selectivity. Finally, electrochemical studies indicate that [2]+ is significantly more electrophilic than its neutral precursor 1-(Mes2B)-8-(Me2NCH2)-(C10H6) (1). These studies also show that reduction of [2]+ is irreversible, possibly because of elimination of the NMe3 moiety under reductive conditions. In fact, [2]OTf reacts with NaBH4 to afford 1-(Mes2B)-8-(CH3)-(C10H6) (4) which has also been fully characterized.     

Synthesis, structure, reactivity, and thermal isomerization of boron-substituted 13-vertex cobaltacarboranes (eta5-Cp)Co(eta6-R2C2B10Me8H2) (R = H, Et)

Reduction of boron-substituted carboranes o-R2C2B10Me8H2 (R = H, Et), thermal isomerization, and nucleophilic reaction of the resultant 13-vertex cobaltacarboranes were studied. Reaction of o-C2B10Me8H4 (1) with excess potassium metal in tetrahydrofuran (THF) gave, after recrystallization from a THF solution of 18-crown-6 ether, [[K(18-crown-6)(THF)2][K(18-crown-6)]][[4-(18-crown-6)-2,3,5,8,9,11,12,13-Me8-4,1,6-KC2B10H4]2] (2) in 78% yield. Interaction of 1 with excess sodium or potassium metal in THF, followed by treatment with CoCl2/CpNa and then aerobatic oxidation, afforded two boron-substituted 13-vertex cobaltacarboranes, 4-Cp-2,3,5,8,9,11,12,13-Me8-4,1,6-CoC2B10Me8H4 (3) and 4-Cp-2,3,5,9,10,11,12,13-Me8-4,1,6-CoC2B10Me8H4 (4), in 15% and 8% yield, respectively. Subsequently, thermal isomerization of 3 and 4 yielded another two new isomers, 4-Cp-2,3,5,6,8,11,12,13-Me8-4,1,9-CoC2B10Me8H4 (5) and 4-Cp-2,3,5,6,7,11,12,13-Me8-4,1,9-CoC2B10Me8H4 (6). Treatment of 3 or 4 with strong bases such as nBuLi and MeLi generated unexpected nucleophilic substitution products 4-nBuCp-2,3,5,8,9,11,12,13-Me8-4,1,6-CoC2B10Me8H4 (7), 4-nBuCp-2,3,5,9,10,11,12,13-Me8-4,1,6-CoC2B10Me8H4 (8a), and 4-MeCp-2,3,5,9,10,11,12,13-Me8-4,1,6-CoC2B10Me8H4 (8b) in good yields. Under the same reaction conditions, however, only one 13-vertex cobaltacarborane, 4-Cp-1,9-Et2-2,5,6,7,8,11,12,13-Me8-4,1,9-CoC2B10Me8H4 (10), was isolated when o-Et2C2B10Me8H2 (9) was used as the starting material. Complex 10 is a thermodynamically stable product and has a substitution pattern different from that of 3-6. These results show that the substituents on either the cage carbon or boron atoms have an important effect on the formation and thermal stability of the 13-vertex metallacarboranes. The formation of these complexes can be rationalized by the diamond-square-diamond mechanism.     

Fluoride ion capture from water with a cationic borane

The reaction of the [Li(THF)4]+ salt of dimesityl-1,8-naphthalenediylborate with [Me2NCH2]I affords a borane (1-(Mes2B)-8-(Me2NCH2)-C10H6) which can be converted into a cationic borane [3]+ ([1-(Mes2B)-8-(Me3NCH2)-C10H6]+) by methylation with MeOTf. This cationic borane promptly complexes fluoride to afford the corresponding zwitterionic ammonium/fluoroborate 3-F (1-(Mes2FB)-8-(Me3NCH2)-C10H6). Cation [3]+ fails to react with chloride, bromide, and iodide indicating that fluoride complexation is selective. Structural, spectroscopic, and computational studies carried out on 3-F show the existence of an unusual C-H...F-B hydrogen bond. Remarkably, [3]+ captures fluoride from water under biphasic conditions (H2O/CHCl3) to form 3-F. The high fluoride affinity of [3]+ can be correlated to the Coulombic forces which stabilize the B-F bond against heterolysis.     

The synthesis of carboacycles derived from B,B'-bis(aryl) derivatives of icosahedral ortho-carborane

Reactions of both closo-9,12-I2-1,2-C2B10H10 and closo-9,10-I2-1,7-C2B10H10 with an excess of aryl magnesium bromide in the presence of [PdCl2(PPh3)2] afford the corresponding closo-9,12-(4-R-C6H4)2-1,2-C2B10H10 [R=H (1), Me (2), OMe (3), SMe (4), N(CH3)2 (5), Cl (6)] and closo-9,10-(4-R-C6H4)2-1,7-C2B10H10 [R'=Me (7), OMe (8), N(CH3)2 (9), Cl (10), and -C[(OCH2)2]CH3 (11)] compounds in high yields. The anisole derivatives 3 and 8 were deprotected to yield the corresponding bis-phenols 12 and 13, respectively. Structural analyses of compounds 1, 3, 6, and 12 are reported. Re-etherification of compound 12 by using gamma-bromotriethyleneglycol methyl ether provided 14 (R=(CH2CH2O)3CH3). Oxidation of 4 with ceric(IV) ammonium nitrate (CAN) generated the bis-sulfoxide 15 (R=S(O)Me). Deprotection of compound 11 led to the corresponding acetyl derivative 18 (R'=C(O)Me). Bis-anisole 3 was tethered with 1,3-dibromopropane, 1,6-dibromohexane, 1,8-dibromooctane, 4,4'-bis(iodomethyl)-1,1'-biphenyl, and alpha,alpha'-dibromo-2,6-lutidine to afford the dimers 20b, 21b, 22b, 23b, and 24b, respectively. The tetrameric carboracycles 27a and 30a, as well as the dimeric 29c were obtained through repetitive coupling of the dimeric compounds 20b, 24b, and 22b with 1,3-dibromopropane, alpha,alpha'-dibromo-2,6-lutidine, and 1,8-dibromooctane, respectively. The tetrameric carboracycle 28a was obtained upon consecutive reactions of 1 with 1,4-dibromobutane. Hexameric carboracycle 28b was identified as a byproduct. Exhaustive ether cleavage of 27a generated octaphenol 31a. Re-etherification of 31a with trimethylenesultone provided the octasulfonate 32a, the first example of a water-soluble carboracycle. Linkage of dimer 23b with alpha,alpha'-dibromolutidine yielded the cyclic tetrameric tetrapyridyl derivative 30a in low yield. The structures of the carboracycles 27a, 28a, 28b, and 30a have been confirmed by Xray crystallography. In addition, the compounds 28a,b are the first reported carboracycles that interact with solvent molecules in a host-guest fashion.     

Synthetic and structural studies on C-ethynyl- and C-bromo-carboranes

A high-yield preparation of the C-monoethynyl para-carborane, 1-Me(3)SiC[triple bond]C-1,12-C2B10H11, from C-monocopper para-carborane and 1-bromo-2-(trimethylsilyl)ethyne, BrC[triple bond]CSiMe(3) is reported. The low-yield preparation of 1,12-(Me3SiC[triple bond]C)2-1,12-C2B10H10 from the C,C'-dicopper para-carborane derivative with 1-bromo-2-(trimethylsilyl)ethyne, BrC[triple bond]CSiMe3, has been re-investigated and other products were identified including the C-monoethynyl-carborane 1-Me3SiC[triple bond]C-1,12-C2B10H11 and two-cage assemblies generated from cage-cage couplings. The contrast in the yields of the monoethynyl and diethynyl products is due to the highly unfavourable coupling process between 1-RC[triple bond]C-12-Cu-1,12-C2B10H10 and the bromoalkyne. The ethynyl group at the cage carbon C(1) strongly influences the chemical reactivity of the cage carbon at C(12)-the first example of the "antipodal effect" affecting the syntheses of para-carborane derivatives. New two-step preparations of 1-ethynyl- and 1,12-bis(ethynyl)-para-carboranes have been developed using a more readily prepared bromoethyne, 1-bromo-3-methyl-1-butyn-3-ol, BrC[triple bond]CCMe2OH. The molecular structures of the two C-monoethynyl-carboranes, 1-RC[triple bond]C-1,12-C2B10H11 (R = H and Me3Si), were experimentally determined using gas-phase electron diffraction (GED). For R = H (R(G) = 0.053) a model with C(5v) symmetry refined to give a C[triple bond]C bond distance of 1.233(5) A. For R = Me3Si (R(G) = 0.048) a model with C(s) symmetry refined to give a C[triple bond]C bond distance of 1.227(5) A. Molecular structures of 1,12-Br2-1,12-C2B10H10, 1-HC[triple bond]C-12-Br-1,12-C2B10H10 and 1,12-(Me(3)SiC[triple bond]C)2-1,12-C2B10H10 were determined by X-ray crystallography. Substituents at the cage carbon atoms on the C2B10 cage skeleton in 1-X-12-Y-1,12-C2B10H10 derivatives invariably lengthen the cage C-B bonds. However, the subtle substituent effects on the tropical B-B bond lengths in these compounds are more complex. The molecular structures of the ethynyl-ortho-carborane, 1-HC[triple bond]C-1,2-C2B10H11 and the ethene, trans-Me3SiBrC=CSiMe3Br are also reported.     

Ionic-liquid-promoted decaborane dehydrogenative alkyne-insertion reactions: a new route to o-carboranes

Unlike in conventional organic solvents, where Lewis base catalysts are required, decaborane dehydrogenative alkyne-insertion reactions proceed rapidly in biphasic ionic-liquid/toluene mixtures with a wide variety of terminal and internal alkynes, thus providing efficient, one-step routes to functional o-carborane 1-R-1,2-C2B10H11 and 1-R-2-R'-1,2-C2B10H10 derivatives, including R = C6H5- (1), C6H13- (2), HC[triple bond]C-(CH2)5- (3), (1-C2B10H11)-(CH2)5- (4), CH3CH2C(O)OCH2- (5), (C2H5)2NCH2- (6), NC-(CH2)3- (7), 3-HC[triple bond]C-C6H4- (8), (1-C2B10H11)-1,3-C6H4- (9), HC[triple bond]C-CH2-O-CH2- (10); R,R' = C2H5- (11); R = HOCH2-, R' = CH3- (12); R = BrCH2-; R' = CH3- (13); R = H2C=C(CH3)-, R' = C2H5- (14). The best results were obtained from reactions with only catalytic amounts of bmimCl (1-butyl-3-methylimidazolium chloride), where in many cases reaction times of less than 20 min were required. The experimental data for these reactions, the results observed for the reactions of B10H13(-) salts with alkynes, and the computational studies reported in the third paper in this series all support a reaction sequence involving (1) the initial ionic liquid promoted formation of the B10H13(-) anion, (2) addition of B10H13(-) to the alkyne to form an arachno-R,R'-C2B10H13(-) anion, and (3) protonation of arachno-R,R'-C2B10H13(-) to form the final neutral 1-R-2-R'-1,2-C2B10H10 product with loss of hydrogen.     

Halogenation and μH Tautomerism of 7-Benzyl-7,8-dicarba-nido-undecaborate(−1) Anion

Russian Journal of Organic Chemistry - Deboration of 1-PhCH2-1,2-C2B10H11 by heating in ethanolic potassium hydroxide afforded Me4N+ [7-PhCH2-7,8-C2B9H11]? which was treated with excess...     

Stereospecific synthesis of polysubstituted E-olefins by reaction of acyclic nitrones with free and platinum(II) coordinated organonitriles

Free nitriles NCCH2R (1a R = CO2Me, 1b R = SO2Ph, and 1c R = COPh) with an acidic alpha-methylene react with acyclic nitrones -O+N(Me)=C(H)R' (2a R' = 4-MeC6H4 and 2b R' = 2,4,6-Me3C6H2), in refluxing CH2Cl2, to afford stereoselectively the E-olefins (NC)(R)C=C(H)R' (3a-3c and 3a'-3c'), whereas, when coordinated at the platinum(II) trans-[PtCl2(NCCH2R)2] complexes (4a R = CO2Me and 4b R = Cl), they undergo cycloaddition to give the (oxadiazoline)-PtII complexes trans-[PtCl2{N=C(CH2R)ON(Me)C(H)R'}2] (R = CO2Me, Cl and R' = 4-MeC6H4, 2,4,6-Me3C6H2) (5a-5d). Upon heating in CH2Cl2, 5a affords the corresponding alkene 3a. The reactions are greatly accelerated when carried out under focused microwave irradiation, particularly in the solid phase (SiO2), without solvent, a substantial increase of the yields being also observed. The compounds were characterized by IR and 1H, 13C, and 195Pt NMR spectroscopies, FAB+-MS, elemental analyses and, in the cases of the alkene (NC)(CO2Me)C=C(H)(4-MeC6H4) 3a and of the oxadiazoline complex trans-[PtCl2{N=C(CH2Cl)ON(Me)C(H)(4-C6H4Me)}2] 5c, also by X-ray diffraction analyses.