A DFT study on pyridine-derived N-heterocyclic carbenes

Pyridine derived N-heterocyclic germylenes: A density functional perspective

“…A comparable result was also observed for its silylene analogue, 1H-2-silapyridine-2-ylidene, which was 9.80 kcal/mol more stable than its full-valence isomer [11,33]. These are in complete contrast to the carbene congener that was 43.4 kcal/mol less stable than pyridine [10].…”

“…On the other hand, following the pioneering work of Märkl in 1980s [7] and the theoretical calculations of Kiprof and Brown [8], Tokitoh et al reported the synthesis of the first stable germabenzene in 2002 [9]. Combining these two apparently different subjects, germanimine and germabenzene, one may reaches at germapyridines whose identification opens the gates toward the heavier congeners of our interested pyridine-derived N-heterocyclic carbenes [10] and silylenes [11]. Here, we have considered three ortho, meta, and para germapyridines none of which has been previously under experimental or theoretical investigations.…”

Pyridine-Derived N-Heterocyclic Carbenes: An Experimental and Theoretical Evaluation of the Bonding in and Reactivity of Selected Normal and Abnormal Complexes of Nickel(II) and Palladium(II)

“…24,27,28 However, the energy differences are much smaller in the complexes which can be rationalized by the calculated stronger interactions in 3-and 4-pyridylidene complexes which partly compensate the energy difference in the free pyridylidenes. The energy decomposition analysis of the metal-carbon bonds reveals increasing interaction energies (E int ) in the order 2-pyridylidene < 3-pyridylidene < 4-pyridylidene .…”

“…24,26,27 Interestingly, calculations of isodesmic reactions by Kassaee et al suggest a similar stabilization of the methylene fragment in 2-and 4-pyridylidenes. 28 Significant barriers for intramolecular interconversion allowed for detecting the co-existence of isomers I and II under high vacuum conditions. 26,27 In the condensed phase, intermolecular interconversion is more facile and pyridylidenes have thus far only been observed in complexes, i.e.…”

Stable α-heteroatom-free dialkylcarbenes: a DFT study

“…Based on our recent works on singlet carbenes [15][16][17][18], we expect that: (i) the cyclization increases the singlettriplet energy separation (DE S-T ) of the species, (ii) the cyclic structure prohibits the probability of 1,2-H shift and hence increases the kinetic stability, and (iii) the unsaturation may increase the thermodynamic stability of the species by inducing pseoudoaromaticity to the ring. In addition, in a cyclic structure two adjacent cyclopropyls necessarily orient syn toward each other which is the most stable conformer for dicyclopropylcarbene (Scheme 2) [7].…”