Solid-state NMR studies for the determination of 11B electric field-gradient tensor orientations in P/B Frustrated Lewis Pairs and related systems.
A solid state NMR method is described for measuring the angle Θ specifying the orientation of the principal component of the (11)B electric field gradient tensor relative to the (11)B(…31)P internuclear vector of (11)B-(31)P spin pairs. It is based on the anisotropic dephasing of (11)B spins in the dipolar field of (31)P nuclei via (11)B{(31)P} Rotational Echo DOuble Resonance (REDOR) experiments. The method is applied to four solid borane-phosphane compounds related to Frustrated Lewis Pair (FLP) chemistry. Results determined by numerical line shape simulations are found in excellent agreement with theoretically calculated values using advanced DFT methods. The angle Θ, which can be measured with an estimated precision of ±5°, offers a clear spectroscopic distinction between classical Lewis-acid/base adducts and active Frustrated Lewis pairs (FLPs).
Institut für Physikalische Chemie and Graduate School of Chemistry, WWU Münster, Corrensstrasse 30, D 48149 Münster, Germany.
Thomas
T
Wiegand
Institut für Physikalische Chemie and Graduate School of Chemistry, WWU Münster, Corrensstrasse 30, D 48149 Münster, Germany.
Melanie
M
Siedow
Organisch-Chemisches Institut, WWU Münster, Corrensstrasse 40, D 48149 Münster, Germany.
Olga
O
Ekkert
Organisch-Chemisches Institut, WWU Münster, Corrensstrasse 40, D 48149 Münster, Germany.
Juri
J
Möbus
Organisch-Chemisches Institut, WWU Münster, Corrensstrasse 40, D 48149 Münster, Germany.
Constantin G
CG
Daniliuc
Organisch-Chemisches Institut, WWU Münster, Corrensstrasse 40, D 48149 Münster, Germany.
Gerald
G
Kehr
Organisch-Chemisches Institut, WWU Münster, Corrensstrasse 40, D 48149 Münster, Germany. Electronic address: erker@uni-muenster.de.
Gerhard
G
Erker
Institut für Physikalische Chemie and Graduate School of Chemistry, WWU Münster, Corrensstrasse 30, D 48149 Münster, Germany. Electronic address: eckerth@uni-muenster.de.
Hellmut
H
Eckert
Dipolar interaction; Frustrated Lewis pair; Rotational echo double resonance; Tensor orientation