Synthesis and Characterization of 2‐Mono‐ and 1,2‐Diaminocarba‐closo‐dodecaborates M[1‐R‐2‐H2N‐closo‐CB11H10] (R=H,Ph, H2N,CyHN)

The first primary 2‐aminocarba‐closo‐dodecaborates [1‐R‐2‐H₂N‐closo‐CB₁₁H₁₀]^? (R=H ( 1 ), Ph ( 2 )) have been synthesized by insertion reactions of (Me₃Si)₂NBCl₂ into the trianions [7‐R‐7‐nido‐CB₁₀H₁₀]^3?. The difunctionalized species [1,2‐(H₂N)₂‐closo‐CB₁₁H₁₀] ( 3 ) and 1‐CyHN‐2‐H₃N‐closo‐CB₁₁H₁₀ (H‐ 4 ) have been prepared analogously from (Me₃Si)₂NBCl₂ and 7‐H₃N‐7‐nido‐CB₁₀H₁₂. In addition, the preparation of [Et₄N][1‐H₂N‐2‐Ph‐closo‐CB₁₁H₁₀] ([Et₄N]‐ 5 ) starting from PhBCl₂ and 7‐H₃N‐7‐nido‐CB₁₀H₁₂ is described. Methylation of the [1‐Ph‐2‐H₂N‐closo‐CB₁₁H₁₀]^? ion ( 2 ) to produce 1‐Ph‐2‐Me₃N‐closo‐CB₁₁H₁₀ ( 6 ) is reported. The crystal structures of [Et₄N]‐ 2 , [Et₄N]‐ 5 , and 6 were determined and the geometric parameters were compared to theoretical values derived from DFT and ab initio calculations. All new compounds were studied by NMR, IR, and Raman spectroscopy, MALDI mass spectrometry, and elemental analysis. The discussion of the experimental NMR chemical shifts and of selected vibrational band positions is supported by theoretical data. The thermal properties were investigated by differential scanning calorimetry (DSC). The pK_a values of 2‐H₃N‐closo‐CB₁₁H₁₁ (H‐ 1 ), 1‐H₃N‐closo‐CB₁₁H₁₀ (H‐ 7 ), and 1,2‐(H₃N)₂‐closo‐CB₁₁H₁₀ (H₂‐ 3 ) were determined by potentiometric titration and by NMR studies. The experimental results are compared to theoretical data (DFT and ab initio). The basicities of the aminocarba‐closo‐dodecaborates agree well with the spectroscopic and structural properties.     

[1,1,2,2‐(CO)4‐1,2‐μ‐(CO)‐4,11‐(SMe2)2‐closo‐1,2‐Co2B10H8]

The title compound, 1,1,2,2‐tetra­carbonyl‐1,2‐μ‐carbonyl‐4,11‐di­methyl­sulfido‐closo‐1,2‐dicobaltadodecaborane, [Co₂(C₄H₂₀B₁₀S₂)(CO)₅], has a closo 12‐vertex {1,2‐Co₂B₁₀H₈} structure with SMe₂ ligands at the exo‐4‐ and 11‐positions. The cluster displays close structural similarities to the SEt₂ analogue.     

How to Make 8,1,2‐closo‐MC2B9 Metallacarboranes

Three examples of the rare 8,1,2‐closo‐MC₂B₉ isomeric form of an icosahedral metallacarborane have been isolated as unexpected trace products in reactions. Seeking to understand how these were formed we considered both the nature of the reactions that were being undertaken and the nature of the coproducts. This led us to propose a mechanism for the formation of the 8,1,2‐closo‐MC₂B₉ species. The mechanism was then tested, leading to the first deliberate synthesis of an example of this isomer. Thus, deboronation of 4‐(η‐C₅H₅)‐4,1,8‐closo‐CoC₂B₁₀H₁₂ selectively removes the B5 vertex to yield the dianion [nido‐(η‐C₅H₅)CoC₂B₉H₁₁]^2?, oxidative closure of which affords 8‐(η‐C₅H₅)‐8,1,2‐closo‐CoC₂B₉H₁₁ in moderate yield.     

1‐Amino‐2‐fluoromonocarba‐closo‐dodecaborates: K[1‐H2N‐2‐F‐closo‐1‐CB11H10] and [Et4N][1‐H2N‐2‐F‐closo‐1‐CB11I10]

The potassium salt of the [1‐H₂N‐2‐F‐closo‐1‐CB₁₁H₁₀]^– anion ( 1 ) was obtained from an insertion reaction of Li₃[7‐H₂N‐nido‐7‐CB₁₀H₁₀] with BF₃ · OEt₂. Anion 1 was protonated to the neutral species 1‐H₃N‐2‐F‐closo‐1‐CB₁₁H₁₀ (H 1 ) and it was iodinated with ICl to the [1‐H₂N‐2‐F‐closo‐1‐CB₁₁I₁₀]^– anion ( 2 ). All species were characterized by multinuclear NMR, IR, and Raman spectroscopy as well as by elemental analysis. The structure of H 1· (CH₃)₂CO was studied by single‐crystal X‐ray diffraction and the experimentally determined bond lengths are compared to values derived from density functional calculations.     

1,2-Carbon shifts in [C4H8O]+˙ and [C5H10O]+˙ ions

Present results demonstrate that α,β-shifts of the functional group carbon strongly dominate β,α-methyl shifts in [C₄H₈O]⁺˙ and [C₅H₁₀O]⁺˙ ions, paralleling observations of others on methyl isobutyrate ions.     

Dodecahydro‐closo‐undecaborate [B11H12]–

DFT‐calculations of the geometries of the closo‐anion [B₁₁H₁₁]^2– in its ground state and in the transition state of its skeletal rearrangement and of the protonated species [B₁₁H₁₂]^– in its ground state were performed at the B3LYP/6‐31++G(d,p) level. The corresponding NMR shifts were computed on the basis of the optimized geometry by the GIAO method at the same level. Calculated and observed NMR data are in good agreement and thus prove the structure of [B₁₁H₁₂]^–, previously deduced from 2 D‐NMR spectra. The addition of water, ethanol, and pyridine to [B₁₁H₁₂]^– at low temperature gave the nido‐species [B₁₁H₁₃(OH)]^–, [B₁₁H₁₃(OEt)]^–, and [B₁₁H₁₂(py)]^–, respectively. The structures of these anions were investigated by NMR methods and the last two of them by crystal structure analyses of appropriate salts. The course of the addition reactions can be rationalized on the basis of the structurally characterized reaction components.     

Supramolecular networks of 10‐(2‐hydroxyethyl)acridin‐9(10H)‐one and 10‐(2‐chloroethyl)acridin‐9(10H)‐one

Both 10‐(2‐hydroxyethyl)acridin‐9(10H)‐one, C₁₅H₁₃NO₂, and 10‐(2‐chloroethyl)acridin‐9(10H)‐one, C₁₅H₁₂ClNO, have monoclinic (P2₁/c) symmetry and supramolecular three‐dimensional networks. But the differences in the intermolecular interactions displayed by the hydroxy group and the chlorine substituent lead to stronger intermolecular π‐stacking interactions and hydrogen bonding, and hence a significantly higher melting point for the former.     

1,2‐Bis­(methylsulfanyl)‐1,2‐dicarba‐closo‐dodecaborane(12)

In the title compound, 1,2‐(SCH₃)₂‐1,2‐closo‐C₂B₁₀H₁₀ or C₄H₁₆B₁₀S₂, the methylsulfanyl groups are bonded to the C atoms of the 1,2‐dicarba‐closo‐dodecaborane cage. The C_cage—C_cage distance is 1.8033 (18) Å and the S—C_cage—C_cage—S torsion angle is 1.07 (13)°. The C_cage—C_cage distance is compared with those in other 1,2‐dicarba‐closo‐dodecaborane derivatives.     

2‐Methyl‐1‐phenylsulfanyl‐1,2‐dicarba‐closo‐dodecaborane(12)

In the title o‐carborane derivative, C₉H₁₈B₁₀S, the methyl and phenyl­sulfanyl groups are connected to the C atoms of the carborane cage. The C_cage—C_cage distance is 1.708 (4) Å.     

A Triple Cluster Platinaborane：[（P（2）Ph3）Pt（1）（μ2—B（11）—B（9）—OC（CH3）3—B10H10））Pt（7）（P（1）Ph3）]2

Ｉｎｒｅｃｅｎｔｙｅａｒｓｓｙｎｔｈｅｓｉｓａｎｄｃｈａｒａｃｔｅｒｉｚａｔｉｏｎｏｆｎｅｗｍｅｔａｌｌａｂｏｒａｎｅｓａｎｄｍｅｔａｌｌａｃａｒｂｏｒａｎｅｓｈａｖｅａｔｔｒａｃｔｅｄｍｕｃｈｉｎｔｅｒｅｓｔ .1 3Ａｗｉｄｅｖａｒｉｅｔｙｏｆｃｌｕｓｔｅｒｃｏｍｐｌｅｘｅｓ ,ｉｎｗｈｉｃｈｃｏｏｒｄｉｎａｔｉｏｎｃａｎｂｅｖｉａＢ—Ｈ—Ｍｏｒ (ａｎｄ)Ｂｎ—Ｍｂｏｎｄ(ｎ =1,2 ,3,4 ,5 ,6 ) ,ｈａｖｅｂｅｅｎｓｙｎｔｈｅｓｉｚｅｄａｎｄｓｔｒｕｃｔｕｒａｌｌｙｃｈａｒａｃｔｅｒｉｚｅｄ .Ｔｈｅｐｏ…     

Syntheses of Halogenated Polyhedral Phosphaboranes: Crystal Structure of conjuncto‐3,3′‐(closo‐1,2‐P2B4Br3)2

Co‐pyrolysis of B₂Br₄ with PBr₃ at 480 °C gave, in addition to the main product closo‐1,2‐P₂B₄Br₄, conjuncto‐3,3′‐(1,2‐P₂B₄Br₃)₂ ( 1 ) and the twelve‐vertex closo‐1,7‐P₂B₁₀Br₁₀ ( 2 ), both in low yields. X‐ray structure determination for 1 [triclinic, space‐group P1 with a = 7.220(2) Å, b = 7.232(2) Å, c = 8.5839(15) Å, α = 97.213(15)°, β = 96.81(2)°, γ = 94.07(2)° and Z = 1] confirmed that 1 adopts a structure consisting of two symmetrically boron–boron linked distorted octahedra with the bridging boron atoms in the 3,3′‐positions and the phosphorus atoms in the 1,2‐positions. The intercluster 2e/2c B–B bond length is 1.61(3) Å. The shortest boron–boron bond within the cluster framework is 1.68(2) Å located between the boron atoms antipodal to the phosphorus atoms. The icosahedral phosphaborane 2 was characterized by ¹¹B‐¹¹B COSY NMR spectroscopy showing cross peaks indicative for the isomer with the phosphorus atoms in 1,7‐positions. Both the X‐ray data of 1 and the NMR spectroscopic data of 1 and 2 give further evidence for the influence of an antipodal effect of heteroatoms to cross‐cage boron atoms and, vice versa, of an additional shielding of the phosphorus atoms caused by B‐Hal substitution at the boron positions trans to phosphorus.     

Undecahalo‐closo‐undecaborates [B11Hal11]2–

The closo‐undecaborate A₂[B₁₁H₁₁] (A = NBzlEt₃) can be halogenated with excess N‐chlorosuccine imide, bromine or iodine, respectively, to give the perhalo‐closo‐undecaborates A₂[B₁₁Hal₁₁] (Hal = Cl, Br, I). The chlorination in the 11 : 1 ratio of the reagents yields A₂[B₁₁HCl₁₀], whose subsequent iodination makes A₂[B₁₁Cl₁₀I] available. The three type [B₁₁Hal₁₁]^2– anions show only one and the two type [B₁₁Cl₁₀X]^2– anions (X = H, I) only two ¹¹B NMR peaks in the ratio 10 : 1, thus exhibiting the same degenerate rearrangement of the octadecahedral B₁₁ skeleton as is well‐known for [B₁₁H₁₁]^2–. The crystal structure analysis of A₂[B₁₁Br₁₁] and A₂[B₁₁I₁₁] reveals a rigid octadecahedral skeleton in the solid state, up to 330 K, whose B–B bond lengths deviate more or less from the idealized C_2v gas phase structure, but are in good accordance with the distances of A₂[B₁₁H₁₁]. Electrochemical experiments elucidate the mechanism of the known oxidation of [B₁₁H₁₁]^2– to give [B₂₂H₂₂]^2–: A first one‐electron transfer is followed by the dimerization of the [B₁₁H₁₁]^– monoanion, whereas neutral B₁₁H₁₁, a presumably most reactive species, does not play a role as an intermediate. The electrochemical oxidation of [B₁₁Hal₁₁]^2– anions also starts with a one‐electron transfer, which is perfectly reversible only in the case of Hal = Br. There is no electrochemical indication for the formation of [B₂₂Hal₂₂]^2–. The neutral species B₁₁Hal₁₁ should be a short‐lived, very reactive species.     

9,12‐Di­iodo‐1,2‐dicarba‐closo‐dodecaborane(12)

The title compound, C₂H₁₀B₁₀I₂, has a pseudo‐icosahedral cluster geometry. The crystal structure features an intermole­cular C—H⋯I—B hydrogen bond with a normalized H⋯I distance of 3.00 Å.     

1‐Oxa‐nido‐dodecaborate [OB11H12]− from the Controlled Oxidation of the closo‐Borates [B11H11]2− and [B12H12]2−

The closo‐dodecaborate [B₁₂H₁₂]^2? is degraded at room temperature by oxygen in an acidic aqueous solution in the course of several weeks to give B(OH)₃. The degradation is induced by Ag²⁺ ions, generated from Ag⁺ by the action of H₂S₂O₈. Oxa‐nido‐dodecaborate(1?) is an intermediate anion, that can be separated from the reaction mixture as [NBzlEt₃][OB₁₁H₁₂] after five days in a yield of 18 %. The action of FeCl₃ on the closo‐undecaborate [B₁₁H₁₁]^2? in an aqueous solution gives either [B₂₂H₂₂]^2? (by fusion) or nido‐B₁₁H₁₃(OH)^? (by protonation and hydration), depending on the concentration of FeCl₃. In acetonitrile, however, [B₁₁H₁₁]^2? is transformed into [OB₁₁H₁₂]^? by Fe³⁺ and oxygen. The radical anions [B₁₂H₁₂] ^{˙ ?} and [B₁₁H₁₁] ^{˙ ?} are assumed to be the primary products of the oxidation with the one‐electron oxidants Ag²⁺ and Fe³⁺, respectively. These radical anions are subsequently transformed into [OB₁₁H₁₂]^? by oxygen. The crystal structure analysis shows that the structure of [OB₁₁H₁₂]^? is derived from the hypothetical closo‐oxaborane OB₁₂H₁₂ by removal of the B3 vertex, leaving a non‐planar pentagonal aperture with a three‐coordinate O vertex, as predicted by NMR spectra and theory.     

Difunctionalized {closo‐1‐CB11} Clusters: 1‐ and 2‐Amino‐12‐ethynylcarba‐closo‐dodecaborates

Carba‐closo‐dodecaborate anions with two functional groups have been synthesized via a simple two‐step procedure starting from monoamino‐functionalized {closo‐1‐CB₁₁} clusters. Iodination at the antipodal boron atom provided access to [1‐H₂N‐12‐I‐closo‐1‐CB₁₁H₁₀]^? ( 1 a ) and [2‐H₂N‐12‐I‐closo‐1‐CB₁₁H₁₀]^? ( 2 a ), which have been transformed into the anions [1‐H₂N‐12‐RC?C‐closo‐1‐CB₁₁H₁₀]^? (R=H ( 1 b ), Ph ( 1 c ), Et₃Si ( 1 d )) and [2‐H₂N‐12‐RC?C‐closo‐1‐CB₁₁H₁₀]^? (R=H ( 2 b ), Ph ( 2 c ), Et₃Si ( 2 d )) by microwave‐assisted Kumada‐type cross‐coupling reactions. The syntheses of the inner salts 1‐Me₃N‐12‐RC?C‐closo‐1‐CB₁₁H₁₀ (R=H ( 1 e ), Et₃Si ( 1 f )) and 2‐Me₃N‐12‐RC?C‐closo‐1‐CB₁₁H₁₀ (R=H ( 2 e ), Et₃Si ( 2 f )) are the first examples for a further derivatization of the new anions. All {closo‐1‐CB₁₁} clusters have been characterized by multinuclear NMR and vibrational spectroscopy as well as by mass spectrometry. The crystal structures of Cs 1 a , [Et₄N] 2 a , K 1 b , [Et₄N] 1 c , [Et₄N] 2 c , 1 e , and [Et₄N][1‐H₂N‐2‐F‐12‐I‐closo‐1‐CB₁₁H₉]?0.5 H₂O ([Et₄N ]4 a ?0.5 H₂O) have been determined. Experimental spectroscopic data and especially spectroscopic data and bond properties derived from DFT calculations provide some information on the importance of inductive and resonance‐type effects for the transfer of electronic effects through the {closo‐1‐CB₁₁} cage.