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# 1-Pyridine- and 1-Quinuclidine-1-boraadamantane as Models for Derivatives of 1-Borabicyclo[2.2.2]octane. Experimental and Theoretical Evaluation of the B−N Fragment as a Polar Isosteric Substitution for the C−C Group in Liquid Crystal Compounds

journal contribution

posted on 2009-02-20, 00:00 authored by Piotr Kaszynski, Serhii Pakhomov, Mikhail E. Gurskii, Sergey Yu. Erdyakov, Zoya A. Starikova, Konstantin A. Lyssenko, Mikhail Yu. Antipin, Victor G. Young, Yurii N. BubnovThe suitability of 1-borabicyclo[2.2.2]octane (

**1**) as a structural element for liquid crystals was evaluated using computational methods and experimental studies of two complexes of its close analogue 1-boraadamantane (**2**). The molecular and crystal structures for 1-pyridine-1-boraadamantane [**2-P**, C_{14}H_{20}BN,*P*2_{1}/*m*,*a*= 8.4404(13) Å,*b*= 6.8469(10) Å,*c*= 10.5269(16) Å, β = 104.712(3)°,*Z*= 2], 1-quinuclidine-1-boraadamantane [**2-Q**, C_{16}H_{28}BN,*P*2_{1}/*n*,*a*= 6.6529(3) Å,*b*= 10.6665(6) Å,*c*= 19.3817(10) Å, β = 94.689(3)°,*Z*= 4], and 1-pyridine-trimethylborane [**3-P**, C_{8}H_{14}BN,*C*_{cma},*a*= 6.9875(10) Å,*b*= 15.011(2) Å,*c*= 16.556(2) Å,*Z*= 8] were determined by X-ray crystallography and compared with the results of DFT and MP2 calculations. Gas-phase thermodynamic stabilities of complexes**1-P**,**1-Q**,**2-P**, and**2-Q**were estimated using a correlation between theoretical (MP2/6-31+G(d)//MP2/6-31G(d) with B3LYP/6-31G(p) thermodynamic corrections) and experimental data for complexes of BMe_{3}(**3**) with amines lacking N−H bonds. The analysis showed the generally higher thermodynamic stability for the quinuclidine (**Q**) complexes compared to that of the pyridine (**P**) analogues in the gas phase and an overall order of stability of**1**>**2**>**3**. This order is paralleled by high ring strain energy of**1**(SE = 27 kcal/mol) as compared to that of 1-boraadamantane (**2**, SE = 16.5 kcal/mol). The chemical stability of**2-P**and**2-Q**, with respect to hydrolytic and oxidative reagents, is high for the pyridine derivative and satisfactory for the quinuclidine complex at ambient temperature, which implies sufficiently high stability of 1-borabicyclo[2.2.2]octane complexes for materials applications. Molecular dipole moments of 6.2 ± 0.1 and 6.0 ± 0.15 D were measured for**2-Q**and**2-P**, respectively.## History

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C 8H Ccmaborabicyclomaterials applicationsanaloguechemical stabilityoxidative reagentsboraadamantaneambient temperaturePolar Isosteric Substitutionquinuclidinegas phasekcalTheoretical Evaluation16HDFTLiquid Crystal Compoundsring strain energySEcrystal structurescomplex14HB 3LYPpyridineMP 2 calculations