The Influence of C(sp³)H–Selenium Interactions on the ⁷⁷Se NMR Quantification of the π‐Accepting Properties of Carbenes

Abstract

Selenium NMR has become a standard tool for scaling the p-accepting character of carbenes. Herein, we highlight that non-classical hydrogen bonding (NCHB), likely resulting from hyperconjugation, can play a significant role in the carbene-selenium 77 Se NMR chemical shift, thus triggering a non-linear behavior of the Se-Scale.

The Influence of C(sp3)H–Selenium Interactions on the 77Se NMR Quantification of the π‐Accepting Properties of Carbenes

“…The solid-state structures of compounds 5 b-e also display short intramolecular Se-H distances, which is not the case for 5 a (Figure 8). [20] Note, that these distances (2.46-2.66 ) are well within the range of intramolecular hydrogen bonding in Silks crystalline oxazolylidene selenium adduct [Se-H 2.51-2.60 ], and in line with their proposed NCHB interactions. [16] Following geometry optimizations of 5 c and 5 d, based on the X-ray crystal structure data, [18] at the BP98/ def2tzvpp level of theory, [23] and quantum theory of atoms in molecules (QTAIM) analysis we confirmed the existence of bond paths in both compounds (Figure 9).…”

“…[19] Furthermore, the X-ray crystallographic analysis showed short intramolecular Se•••H distances for the adamantyl variants 1 c and 2 b ( Figure 5), which are not present in 1 a [12g] and 2 a. [18,20] Thus, it appears, that the same phenomenon is present in both CAACs and NHCs, although the substituent involved is attached to nitrogen for NHCs and on carbon for CAACs. To make a direct comparison, N-alkyl substituted CAACs were desirable, but until now they were hardly available using current synthetic methodologies.…”

Organoselenium ligands for heterogeneous and nanocatalytic systems: development and applications

“…It results in deshielding of the nucleus and hence its resonance is observed at a higher chemical shift value. [84][85][86] The observation also correlates the conversion obtained in a catalytic hydrogenation reaction and 77 Se chemical shift values, suggesting that there may be a link between the π-accepting properties (to which selenium chemical values are most sensitive) of the NHC ligands and the catalytic activity of the corresponding complexes. 86 In heterogeneous and/or nano-catalytic systems, similar studies have been conducted using solid state 77 Se NMR spectroscopy.…”

“…52 The catalytic cycle includes different steps 135 among which the decomposition of NaBH 4 that supplies hydrogen to the reaction mixture is very significant. This hydrogen gets adsorbed on the surface of the catalytic system (84). Nitroarene molecules are also adsorbed on the same surface by means of electrostatic attraction (85).…”

1,3‐Bis(tricyanoborane)imidazoline‐2‐ylidenate Anion—A Ditopic Dianionic N‐Heterocyclic Carbene Ligand

“…[36] Recently, intermolecular selenium-hydrogen interactions were used to rationalize deviations of d( 77 Se) from expected values. [37] The difference in d(C = Se) observed for dianion 5 in (197.9(3) pm). [38] From the structural data, the buried volume (%V bur ) [39] of the free dianionic NHC 3 was estimated to 39.9 %.…”