Dihydrogen splitting by intramolecular borane-phosphane frustrated lewis pairs: a comprehensive characterization strategy using solid state nmr and dft calculations.
KNITSCH, Robert; ÖZGÜN, Thomas; CHEN, Guo-Qiang; KEHR, Gerald; ERKER, Gerhard; HANSEN, Michael Ryan; ECKERT, Hellmut.
KNITSCH, Robert; ÖZGÜN, Thomas; CHEN, Guo-Qiang; KEHR, Gerald; ERKER, Gerhard; HANSEN, Michael Ryan; ECKERT, Hellmut.
 Abstract: Four hydrogenated intramolecular phosphane-borane frustrated Lewis pair (B/P FLP) compounds bearing unsaturated cyclic or aromatic carbon backbones have been synthesized and structurally characterized using 11B, 31P, 1H and 2H solid-state NMR spectroscopy. A comparison of the spectra with those of the corresponding free B/P FLPs shows that both 11B isotropic chemical shifts as well as nuclear electric quadrupolar coupling constants decrease significantly upon FLP hydrogenation, revealing the breakage of the partial B-P bond present in the starting materials. Likewise, the 31P isotropic chemical shift, the chemical shift anisotropy, and the asymmetry parameter decrease significantly upon FLP hydrogenation, reflecting the formation of a more symmetric, C3v-like local environment. 11B{31P} rotational echo double resonance (REDOR) experiments can be used to measure the B-P internuclear distance (about 3.2 Å) of these compounds. Observation of the hydrogen atoms bound to the Lewis centers is best accomplished via 31P{1H} and 11B{1H} cross-polarization-heteronuclear correlation experiments or by direct observation of the 2H MAS NMR signals on especially prepared FLP-D2 adducts. For accurately measuring the phosphorus-deuterium distance via 31P{2H} rotational echo adiabatic passage double resonance (REAPDOR), it is essential to take the secondary dipolar coupling of 31P with the boron-bonded 2H nuclei explicitly into consideration, by simulating a 2HP-31P-2HB three-spin system based on structural input. All of the experimental NMR interaction parameters are found in excellent agreement with values calculated by DFT methods, using the geometries obtained either by energy optimization or from single-crystal structures. | |
| ChemPhysChem |
| v. 20, n. 14, p. 1837-1849 - Ano: 2019 |
| Fator de Impacto: 3,077 |
| http://dx.doi.org/10.1002/cphc.201900406 |  @article={002955650,author = {KNITSCH, Robert; ÖZGÜN, Thomas; CHEN, Guo-Qiang; KEHR, Gerald; ERKER, Gerhard; HANSEN, Michael Ryan; ECKERT, Hellmut.},title={Dihydrogen splitting by intramolecular borane-phosphane frustrated lewis pairs: a comprehensive characterization strategy using solid state nmr and dft calculations},journal={ChemPhysChem},note={v. 20, n. 14, p. 1837-1849},year={2019}} |