Electron-diffraction investigations of the molecular structures of cis- and trans-1,2-dimethyldiborane

Hedberg, Lise; Hedberg, Kenneth; Kohler, David A.; Ritter, D. M.; Schomaker, Verner

doi:10.1021/ja00530a021

Cited by 15 publications

(3 citation statements)

References 3 publications

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“…The B−C, B−H term , and B−H bridg. bond distances with average values of 1.574(4), 1.09(3), and 1.24(3) Å, respectively, are slightly shorter than those observed for [MeBH(μ-H)] 2 or [(Me 3 Si) 3 CBH(μ-H)] 2 , and the B···B separation in 4 with a value of 1.787(5) Å lies between those reported for [MeBH(μ-H)] 2 or [(Me 3 Si) 3 CBH(μ-H)] 2 . The terphenyl substituents are rotated 71.9° with respect to each other, which may be a result of steric repulsion considering that the related dimeric aluminum hydrides [2,6-Mes 2 C 6 H 3 AlH(μ-H)] 2 and [2,6-Trip 2 C 6 H 3 AlH(μ-H)] 2 (Trip = 2,4,6- i -Pr 3 C 6 H 3 ) feature an almost parallel alignment of the terphenyl substituents.…”

Section: Resultsmentioning

confidence: 49%

Unsymmetrical 9-Borafluorenes via Low-Temperature C−H Activation of m-Terphenylboranes

2002

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The reaction of 2,6-(4-t-BuC6H4)2C6H3Li and with H2ClB·SMe2 or HCl2B·SMe2 in hexane solution afforded the m-terphenyl-substituted unsymmetrical 9-borafluorene 1-(4-tert-butylphenyl)-7-tert-butyl-9-(bis-2,6-(4-tert-butylphenyl)phenyl)-9-borafluorene, 1, in good to moderate yields. The related reaction of 2,6-(3,5-Me2C6H3)2C6H3Li with BH2Cl·SMe2 or BHCl2·SMe2 in toluene solution gave 1-(3,5-dimethylphenyl)-6,8-dimethyl-9-(bis-2,6-(3,5-dimethylphenyl)phenyl)-9-borafluorene, 3. Compounds 1 and 3 are air-stable fluorescent solids. The reactions of 2,6-(2-MeC6H4)2C6H3Li or 2,6-Mes2C6H3Li (which possess either two or no o- and o‘ ‘-hydrogens) with H2ClB·SMe2 gave the primary boranes [2,6-(2-MeC6H4)2C6H3BH2]2, 4, and [2,6-Mes2C6H3BH2]2, 5, respectively. Quenching of the reaction of 2,6-(4-t-BuC6H4)2C6H3Li with H2ClB·SMe2 after 1.5 h with pyridine resulted in the isolation of the primary borane [2,6-(4-t-BuC6H4)2C6H3BH2]2, 2, as the pyridine adduct 2·py, which after thermolysis at 190 °C gave 1-(4-tert-butylphenyl)-7-tert-butyl-9-borafluorene·pyridine, 7·py. Heating a C6D6 solution of 4 to 60−70 °C led to C−H activation and formation of a 1:1 adduct of monomeric 4 and 1-(2-methylphenyl)-5-methyl-9-borafluorene, 12. Reaction of 2 equiv of 2,6-(4-t-BuC6H4)2C6H3Li with H2ClB·SMe2 in hexane solution followed by addition of THF gave the very crowded diterphenyl borate [2,6-(4-t-BuC6H4)2C6H3]2B(μ-H)2Li(THF)2]2, 11, which can be converted to 1 by simple addition of water. Prolonged exposure of 1 to concentrated aqueous HCl led to B−C bond cleavage and formation of the sterically very crowded diterphenylborinic acid [2,6-(4-t-BuC6H4)2C6H3]2BOH, 15. All compounds have been characterized by 1H, 13C, and 11B NMR spectroscopy and mass spectrometry, and compounds 1, 4, and 11 have also been characterized by single-crystal X-ray crystallography.

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Section: Resultsmentioning

confidence: 49%

Unsymmetrical 9-Borafluorenes via Low-Temperature C−H Activation of m-Terphenylboranes

2002

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“…One of the early successes in this field was Linus Pauling’s work in 1930 where it was shown that the rotational barrier function in the crystal may be presented in the first approximation as a cosine wave with a period equal to θ/ n , where θ is angle of rotational axis relative to the equilibrium position and n is the order of the symmetry axis of the molecule having the rotational axis. In the words of Dunitz and co-workers, “In a sense, one can say that spectroscopy sees the rate at which molecules cross the barrier, while diffraction sees the bottom of the potential well; we derive roughly the same barrier height as long as the potential is approximately sinusoidal.” This approach allowed us to estimate the height of the barrier of rotation based on the analysis of thermal vibrations in the X-ray structures in the framework of the theory of translation/libration/screw (TLS) in numerous papers. − As expected by the shape-conforming nature of the short-range forces responsible for close-packing interactions of molecular crystals, the rotational frequencies and activation energies for a set of crystalline rotors correlate well with the molecular symmetry of their corresponding rotational axes . Previously in our study the correlation between the environment symmetry of coronene and its rotational mobility was supposed.…”

Section: Introductionmentioning

confidence: 65%

Symmetry Influence on the Rotation of Molecules in Crystals

Islamov

Штырлин

Serov

et al. 2017

Crystal Growth & Design

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It was shown that rotational mobility of molecules in crystals is affected by the symmetry of their surroundings. A hypothesis was proposed for the discovered correlation. Three cases are possible for the location of the molecules with respect to the crystallographic symmetry elements: I – the location in a general position; II – the location in special positions without symmetry disordering; III – the location in special positions with symmetry disordering. According to the experimental data, the rotation barrier heights at the location of the molecules in cases I and III are lower than in case II. This fact is explained by the amplitude and phase shifts of the rotational energy profiles of two parts of the molecule in case I and by increasing the number of minima on the rotation barrier profile at disordering the molecules by symmetry in case III. The way is proposed for lowering the rotational barrier of molecules in crystals.

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“…Der B•••B-Abstand nimmt von 11 (1.791(2) Å), über 17 1.817(3) Å nach 18 (1.847(3) Die B-C Bindungslängen bleiben unverändert und sind vergleichbar mit literaturbekannten Verbindungen. 107,113 In 17 liegen die B-H Bindungsabstände bei B(1)-H(1A) = 1.…”

Section: Charakterisierung Von 17 Und 18unclassified

Synthese heteroatom-dotierter Phenalene

Massoth¹

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In dieser Arbeit konnte 1,8-Diborylnaphthalin (11) präparativ in einer Stufe und 65% Ausbeute aus dem literaturbekannten Boronsäureanhydrid 9 dargestellt werden. 11 ist das zweite bekannte, aromatisch verbrückte Derivat des Diborans B2H6. 11 kann als Startverbindung für eine Reihe strukturverwandter BNB-dotierter Phenalenderivate verwendet werden. Dazu werden zwei der vier Bor-gebundenen Protonen durch die Umsetzung mit einem Mesitylgrignard und Trimethylsilylchlorid substituiert. Die Umsetzung mit Wasser bzw. Aminen liefert BOB- bzw. BNB-Phenalene unter Freisetzung von elementarem Wasserstoff. Alle, auf diese Weise dargestellten Verbindungen, zeigen reversible Redoxeigenschaften und Photolumineszenz mit zum Teil besonders scharfen Emissionssignalen mit Halbhöhenbreiten von bis zu 31 nm. Zusätzlich wurden drei analoge Vertreter einer NBN-Phenalen Spezies dargestellt und charakterisiert. Die entgegengesetzte Dotierung äußert sich in einem grundlegend verschiedenem Redoxverhalten. Abschließend wurde die Reduktion des BNB-Phenalens 22 untersucht. Dabei gelang es das Radikal K[32] zu charakterisieren und seine Abbaureaktion in THF aufzuklären.

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Electron-diffraction investigations of the molecular structures of cis- and trans-1,2-dimethyldiborane

Cited by 15 publications

References 3 publications

Unsymmetrical 9-Borafluorenes via Low-Temperature C−H Activation of m-Terphenylboranes

Unsymmetrical 9-Borafluorenes via Low-Temperature C−H Activation of m-Terphenylboranes

Symmetry Influence on the Rotation of Molecules in Crystals

Synthese heteroatom-dotierter Phenalene

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