“…For example, in a 1960 report by Haworth and Hohnstedt, pyrolysis of the reaction mixture was necessary to afford the corresponding B-functionalized borazines, when ethylmagnesium iodide or phenylmagnesium iodide was employed for the reaction. 107 In contrast substitution reactions with in situ generated Grignard reagent generated from alkyl or aryl bromides and magnesium turnings only required heating of the reaction to the reflux temperature of diethyl ether to afford the product. 106 Scheme 61 Reaction of B-trichloro-N-trimethylborazine with Grignard reagents 106 Interestingly, the reaction of B-trichloroborazine with either 1 or 2 equiv of Grignard reagent leads selectively to monoalkylated or bis(alkylated) borazines.…”
Section: Review Synthesismentioning
confidence: 99%
“…Another important type of substitution reaction of Btrichloroborazine involves the alkylation or arylation of boron by Grignard or lithium reagents. 91,106,107 These reactions provide access to various kinds of B-trialkylborazines and B-triarylborazines from B-trichloroborazines. Typically, the B-trichloroborazine reacted with freshly prepared Grignard reagent or lithium reagent (3 equiv to 4 equiv) in dry diethyl ether to give the corresponding B-functionalized borazines 117 and 82 (Schemes 61 and 62).…”
Given the wide array of current applications of borazine-based materials, synthetic access to these compounds is of importance. This review summarizes the many ways of preparing borazines and its carbo-substituted analogues. In addition, the functionalization of borazines is covered. The synthesis of molecules incorporating more than one borazine units as well as aspects of unsymmetrically substituted borazines are not included. The literature has been covered comprehensively until the end of 2020.
“…For example, in a 1960 report by Haworth and Hohnstedt, pyrolysis of the reaction mixture was necessary to afford the corresponding B-functionalized borazines, when ethylmagnesium iodide or phenylmagnesium iodide was employed for the reaction. 107 In contrast substitution reactions with in situ generated Grignard reagent generated from alkyl or aryl bromides and magnesium turnings only required heating of the reaction to the reflux temperature of diethyl ether to afford the product. 106 Scheme 61 Reaction of B-trichloro-N-trimethylborazine with Grignard reagents 106 Interestingly, the reaction of B-trichloroborazine with either 1 or 2 equiv of Grignard reagent leads selectively to monoalkylated or bis(alkylated) borazines.…”
Section: Review Synthesismentioning
confidence: 99%
“…Another important type of substitution reaction of Btrichloroborazine involves the alkylation or arylation of boron by Grignard or lithium reagents. 91,106,107 These reactions provide access to various kinds of B-trialkylborazines and B-triarylborazines from B-trichloroborazines. Typically, the B-trichloroborazine reacted with freshly prepared Grignard reagent or lithium reagent (3 equiv to 4 equiv) in dry diethyl ether to give the corresponding B-functionalized borazines 117 and 82 (Schemes 61 and 62).…”
Given the wide array of current applications of borazine-based materials, synthetic access to these compounds is of importance. This review summarizes the many ways of preparing borazines and its carbo-substituted analogues. In addition, the functionalization of borazines is covered. The synthesis of molecules incorporating more than one borazine units as well as aspects of unsymmetrically substituted borazines are not included. The literature has been covered comprehensively until the end of 2020.
“…(a) Preparation of Compounds. The synthesis of I took place in two steps using slightly modified literature procedures …”
Section: Experimental and Computational Detailsmentioning
confidence: 99%
“…Although possessing similar structural and physical properties as the prototypal carbon-based aromatic systems, borazine and its derivatives are chemically much more reactive. Past studies on borazines have focused on their electronic properties, − , aromaticity, and their syntheses − and reactivity. ,, Several studies on borazines have employed high-resolution multinuclear magnetic resonance spectroscopy in solution; ,,, however, relative to benzenes, few solid-state NMR studies have been carried out on the borazine family. , …”
Analyses of 11 B, 13 C, and 2 H NMR spectra of solid hexamethylborazine, I, provide conclusive evidence for rapid in-plane jumps of the borazine ring at room temperature. Boron-11 NMR spectra of magic-angle spinning (MAS) samples, acquired at low (4.7 T), moderate (9.4 T), and high (18.8 T) external applied magnetic field strengths, have been simulated to yield the 11 B nuclear quadrupolar coupling constant (C Q ), asymmetry parameter, and isotropic chemical shift; their values at 298 K are 2.98 ( 0.03 MHz, 0.01 ( 0.01, and 36.0 ( 0.4 ppm, respectively. Simulations of 13 C CP/MAS NMR spectra provide the carbon-boron isotropic indirect spin-spin coupling constant, J iso , the sign of C Q ( 11 B), the relative orientations of the boron electric field gradient (EFG) and the 13 C-11 B dipolar coupling tensors, and the motionally averaged 13 C-11 B dipolar coupling constant. Variable-temperature 2 H NMR spectra of a partially deuterated sample of I indicate that the in-plane jumps of the borazine ring are slow with respect to C Q ( 2 H) -1 (i.e., τ jump g 10 -4 s) at temperatures less than 130 K. Over the temperature range 180 to 128 K, 2 H NMR line shape analysis yields an activation energy of 30.1 ( 1.5 kJ mol -1 for the in-plane jumps of the borazine ring. Although a precise experimental determination of boron chemical shift anisotropy was impeded by intramolecular and intermolecular boronboron dipolar interactions and heteronuclear nitrogen-boron dipolar interactions, simulations of high-field 11 B NMR spectra of a stationary sample of I suggest a value of 55 ( 15 ppm for the motionally averaged span of the chemical shift tensor. Lastly, high-level ab initio and density functional theory calculations provide values of the boron EFG tensor and the boron and nitrogen magnetic shielding tensors for a rigid molecule of I.
“…70 1C) which was attractive due to its low mass and the low mp (5 1C) of its ultimate dehydrogenation product, N,N 0 ,N 00 -trimethylborazine. 11,12 Unfortunately, MeAB proved too volatile and exhibited insufficient thermal stability, slowly evolving hydrogen even as a solid at 25 1C. Volatility was also a problem with dimethylamine-borane (mp 37 1C).…”
Mixtures containing ammonia-borane and sec-butylamine-borane remain liquid throughout the hydrogen release process that affords tri(N-sec-butyl)borazine and polyborazylene. Concentrated solutions with metal catalysts afford >5 wt% H(2) in 1 h at 80 °C and addition of (EMIM)EtSO(4) ionic liquid co-solvent eliminates competing formation of insoluble linear poly(aminoborane) (EMIM = 1-ethyl-3-methyl-imidazolium).
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