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Orbital Analysis of Carbon‐13 Chemical Shift Tensors Reveals Patterns to Distinguish Fischer and Schrock Carbenes
Author(s) -
Yamamoto Keishi,
Gordon Christopher P.,
Liao WeiChih,
Copéret Christophe,
Raynaud Christophe,
Eisenstein Odile
Publication year - 2017
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201701537
Subject(s) - chemical shift , chemistry , paramagnetism , tensor (intrinsic definition) , carbon fibers , coupling (piping) , ligand (biochemistry) , spectroscopy , nuclear magnetic resonance spectroscopy , computational chemistry , stereochemistry , materials science , physics , biochemistry , mathematics , receptor , quantum mechanics , composite number , pure mathematics , metallurgy , composite material
Abstract Fischer and Schrock carbenes display highly deshielded carbon chemical shifts (>250 ppm), in particular Fischer carbenes (>300 ppm). Orbital analysis of the principal components of the chemical shift tensors determined by solid‐state NMR spectroscopy and calculated by a 2‐component DFT method shows specific patterns that act as fingerprints for each type of complex. The calculations highlight the role of the paramagnetic term in the shielding tensor especially in the two most deshielded components (σ 11 and σ 22 ). The paramagnetic term of σ 11 is dominated by coupling σ(M=C) with π*(M=C) through the angular momentum operator perpendicular to the σ and π M=C bonds. The highly deshielded carbon of Fischer carbenes results from the particularly low‐lying π*(M=C) associated with the CO ligand. A contribution of the coupling of π(M=C) with σ*(M=C) is found for Schrock and Ru‐based carbenes, indicating similarities between them, despite their different electronic configurations (d 0 vs. d 6 ).