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In contrast to the reaction of vinyl(alkynyl)silanes with 9-BBN-H, leading to the quantitative formation of 5-R-4-(9-BBN)-2,3-dihydro-1H-siloles, treatment of bis(alkynyl)silanes bearing one terminal alkynyl group with 2 equiv of 9-BBN-H followed by methanolysis afforded 5-R-4-(9-BBN)-2,5-dihydro-1H-siloles with yields of 85-90% (by NMR integration). The reaction proceeds via a double 1,2-hydroboration of the terminal triple bond with the formation of the geminal diborane followed by ring closure via intramolecular 1,1-carboboration of the remaining alkynyl fragment. Depending on the nature of the substituent R in position 5, the allylic BBN group locates in position 3 (R = Ph) or position 5 (R = SiHMe2, SiMe3) to give 2,3- or 2,5-dihydrosiloles, respectively. The protodeborylation of the allylic BBN group with MeOH of both 3,4-(9-BBN)2-2,3-dihydro- and 4,5-(9-BBN)2-2,5-dihydrosiloles results in the exclusive formation of 4-(9-BBN)-2,5-dihydrosiloles. In all cases, the formation of 10-12% of 2-R-2,4-(9-BBN)2-2,3-dihydrosilole minor isomers has been observed, which occurs from vicinal diboranes formed as side products by a second hydroboration of the terminal triple bond. Similarly, treatment of the tri- and tetraalkynes containing a terminal triple bond with 2 equiv of 9-BBN-H followed by treatment with methanol resulted in the high-yield formation of 1,2,6,6a-tetrahydro-1,6-disilapentalenes and 2,6,7,7a-tetrahydro-1,6,7-trisila-1H-cyclopenta[a]pentalenes, respectively.

Methyl-camouflaged dicarbaboranes closo-1,2- and 1,10-H2C2B8Me8 have been prepared in high yields either from nido-5,6-H2C2B8H10 or closo-1,2-H2C2B8H8 via electrophilic methylation reactions and cl...

Alkylation of the [nido-5,6-R12C2B8H9]− anions (where R1 = H and Me) with alkyl halides (RX, where R = primary and secondary alkyls) in boiling tetrahydrofuran (THF) proceeds via unusual H2 elimination, followed by cage closure to give a series of the neutral closo-1,2-R12C2B8H7-3-R derivatives in ∼70–80% yields. In contrast, treatment of the unsubstituted [nido-5,6-C2B8H11]− anion with tert-butyl bromide (t-BuBr) led to the formation of the parent closo-1,2-C2B8H10 in >85% yield. The constitution of all compounds isolated has been confirmed unambiguously by multinuclear (11B, 1H, and 13C) nuclear magnetic resonance measurements and α-shift correlation assessments.

The principles of a new α-shift correlation (ASC) NMR method are demonstrated on a model series of substituted derivatives of o-carborane for which reliable NMR data are available. This graphical method revealed an acceptable linear correlation between α(11B) or α(13C) shifts and those induced by substituents in unsubstituted (u) positions of the carborane cluster. The linearity holds for all nuclei involved in skeletal bonding: Δδ(N)u = g × α (where N = 11B, 13C, and 1H). The factor g (slope of the correlation line × 102) becomes an important measure of sensitivity of a given cage position to substituent changes. The β, γ, and δ = A (= antipodal) shifts can be therefore derived from the α-shift, are linearly proportional, and reflect additive character in double substitution. The ASC method appears to be an important tool for quantitative assessment of substituent NMR effects in all exo-substituted boron-cluster systems.

Initial studies on electrophilic halogenation of the dicarbaborane closo-1,2-C2B8H10 (1) have been carried out to reveal that the substitution takes place at B7 and B10 vertexes, which are the most removed from the CH positions. The course of the halogenation is strongly dependent on the nature of the halogenation agent and reaction conditions. Individual reactions led to the isolation of the monosubstituted compounds 1,2-C2B8H9-10-X (2) (where X = F, I) and 1,2-C2B8H9-7-X (3) (where X = Cl, I). Disubstituted carboranes 1,2-C2B8H8-7,10-X2 (4) (where X = Cl, Br, I) were obtained under more forcing conditions. Individual halo derivatives were characterized by mass spectrometry and high-field NMR (11B, 1H,13C) spectroscopy combined with two-dimensional [11B–11B]-COSY, 1H{11B(selective)}, and [11B–1H]-correlation NMR techniques. All of the derivatives bearing a halogen substituent in the B10 position exhibit a remarkable antipodal 13C and 1H NMR shielding at the CH1 vertex, increasing in the order H < I < Br ...

Reported is an unusual tautomeric behavior within the [nido-5,6-C2B8H11]− (1a–) cage that has no precedence in the whole area of carborane chemistry. Isolated were two skeletal tautomers, anions [6-Ph-nido-5,6-C2B8H10-μ8,9]− (2d–) and [5,6-Me2-nido-5,6-C2B8H9-μ9,10]− (3b–), which differ in the positioning of the open-face hydrogen bridge. Their structures have been determined by X-ray diffraction analyses. The 3b–structure is stabilized by intermolecular interaction involving Et3NH+ and B8–B9 and H8 atoms in the solid phase; however, its dissolution in CD3CN causes instant conversion to the more stable [5,6-Me2-nido-5,6-C2B8H9-μ8,9]− (2b–) tautomer. The dynamic electron-correlation-based MP2/6-31G* computations suggest that the parent [nido-5,6-C2B8H11-μ8,9]− (2a–) tautomer is 3.9 kcal·mol–1 more stable than the [nido-5,6-C2B8H11-μ9,10]− (3a–) counterpart and the μ8,9 structure 2– is therefore the most stable tautomeric form in the solution, as was also demonstrated by multinuclear (1H, 11B, and 13C) NMR ...

Agostic (C−H···M) complexes [closo-3,3-(σ,η2-C8H13)-1,2-μ-(ortho-xylylene)-3,1,2-IrC2B9H9] (5) and [closo-3,3-(σ,η2-C8H13)-1,2-μ-(ortho-xylylene)-3,1,2-RhC2B9H9] (9), stable in the solid state, have been prepared via the reaction of [M(η4-COD)Cl]2 (M = Ir, Rh) with the K+ salt of the [nido-7,8-μ-(ortho-xylylene)-7,8-C2B9H10]- anion and characterized by a combination of analytical (in the case of 5) and multinuclear NMR data, including a single-crystal X-ray diffraction study of 5. The crystallographic study confirmed the agostic structure of 5 and revealed that the orientation of the σ,η2-cyclooctenyl moiety relative to the carborane ligand is substantially influenced by the specific intramolecular C−H···π interaction between the agostic hydrogen and the π-system of the cage aromatic substituent. In solution, 5 exhibited both “side-to-side” agostic hydrogen migration and reversible interconversion with [closo-3-(η3-C8H13)-1,2-μ-(ortho-xylylene)-3,1,2-IrC2B9H9] (8). The agostic rhodium complex (9), in cont...

RuCl2(PPh3)3 (1), when heated with an equimolar amount of nido-5,6-C2B8H12 (2) in toluene for a few hours, effected rather unexpected polyhedral contraction of 2 to give the new half-sandwich small ruthenacarborane closo-C2B4H6Ru(PPh3)2HCl (3) in moderate yield along with minor amounts of the two isomeric 11-vertex ruthenacarboranes [3-Cl-1-(η6-C6H5Me)-1,2,4-RuC2B8H9] (4) and [6-Cl-1-(η6-C6H5Me)-1,2,4-RuC2B8H9] (5) with open MC2B8 cluster structure. These new complexes were characterized by 1H, 13C, and 11B NMR spectroscopy and, in the case of 3 and 5, also by an X-ray crystal structure analysis.

The complex [Os3(μ-H)(CO)10(μ-η1:η2-CCCMe2)]BF4 (1) reacts with PPh3 at −78 °C to give isomeric phosphonium derivatives of the formula [Os3(μ-H)(CO)10(μ-σ:η2-C⋮CCMe2PPh3)]BF4 (2 and 3); the isomeri...

Reactions of the ruthenium chelate complex [Ru(η5:η2-C5Me4CH2OCH2CHCH2)(CO)Cl] (1) with acetylenes R1C⋮CR2 in the presence of AgBF4 give the cationic diene chelates [Ru(η5:η4-C5Me4CH2OCH2CHCHCR1CHR2)(CO)]+BF4- (2a, R1 = R2 = Ph; 3a, R1 = R2 = Me; 4a, R1 = Me, R2 = Ph; 4b, R1 = Ph, R2 = Me; 5a, R1 = H, R2 = CO2Me; 5b, R1 = CO2Me, R2 = H; 6a, R1 = H, R2 = CH2OMe) and {Ru[η5:η4-C5Me4CH2OCH2C(CH2)CHCHPh](CO)}+BF4- (7). The crystal structures of [2a‘ ‘]+PF6- and [7]+PF6- have been determined. The formation of complexes 2−6 is the result of regiospecific addition of acetylenes PhC⋮CMe, MeC⋮CMe, PhC⋮CMe, HC⋮CCO2Me, and HC⋮CCH2OMe to the terminal carbon of the allylic ether, while phenylacetylene adds to the internal carbon of the olefin. The unsymmetric acetylenes (PhC⋮CMe, HC⋮CCO2Me) give predominantly the isomers 4a and 5a, where the allylic C−H has added to the acetylenic carbon bearing the less bulky substituent. The complex [Ru(η5:η2-Me4C5CH2OCH2CHCH2)(η1-C⋮CPh)(CO)] (8) was synthesized by the reaction of 1...

The synthesis of cycloheptatrienyl(dipropyl)borane (2a) was accomplished via the exchange reaction of trimethyl(cycloheptatrienyl)tin (6) and dipropylchloroborane. Compound 2a was found by NMR spectroscopy to equilibrate with its valence tautomer 7-exo-(dipropylboryl)norcaradiene (2b). The equilibrium between 2a and 2b was studied in detail experimentally by variable temperature NMR and theoretically by ab initio calculations of size-reduced molecular systems (2a and 2b, with methyl instead of n-propyl groups) at the B3LYP/6-311+G*//B3LYP/6-31G* + ZPVE level. Experimentally determined thermodynamic parameters of the equilibrium (ΔH = 2.4 ± 0.1 kcal mol-1; ΔS = −5.5 ± 0.3 cal mol-1 K-1) and the activation barriers at 228 K (ΔG⧧228(2a→2b) = 8.2 ± 0.1 kcal mol-1, ΔG⧧228(2b→2a) = 9.4 ± 0.1 kcal mol-1) are in reasonable agreement with the computed results (ΔH = 2.0 kcal mol-1, ΔS = −3.7 cal mol-1 K-1; ΔG⧧228(2a→2b) = 3.2 kcal mol-1 and ΔG⧧228(2b→2a) = 6.7 kcal mol-1). The computations also indicate that 7-endo...

57Fe NMR spectra (11.66 MHz) of the sandwich complexes ferrocene (1), butylferrocene (2), and acetylferrocene (3) were measured at natural abundance of 57Fe by application of the polarization transfer technique (INEPT; 1H−57Fe). In contrast to previous assumptions this technique works very well, although it has to be based on rather small (∼0.3−0.7 Hz) long-range scalar 57Fe−1H couplings across two bonds. Thus, the 57Fe NMR signal of ferrocene (∼150 mg in 2 mL of CDCl3/hexane (1:1)) was observed already after 4 transients, and after 400 transients (70 min of spectrometer time) the 13C satellites (1J(57Fe,13C) = 4.7 Hz) were detected, allowing us to determine the isotope-induced chemical shift 1Δ12/13C(57Fe) = −440 ppb at natural abundance of the isotopes.

The fast sigmatropic [1,5]-Sn migration in cycloheptatrienyl(triphenyl)tin is effectively locked in the chromiumtricarbonyl complex. A much slower [1,3]-Sn + [1,2]-Cr diatropic rearrangement was detected by spin saturation transfer NMR.