Pyridine derived N-heterocyclic germylenes: A density functional perspective

Three novel germanimines, 2-, 3-, and 4-germapyridines (1, 2, and 3, respectively) along with their isomeric germylenes, are compared and contrasted at B3LYP/AUG-cc-pVTZ//B3LYP/6-31+G^* level of theory. From a thermodynamic viewpoint, two germylenes out of a total of eight singlet minima, 1H-2-germapyridine-2-ylidene (1a) and 1H-4-germapyridine-4-ylidene (3a), are found 29.2 and 15.4 kcal/mol more stable than their corresponding aromatic germapyridine isomers, respectively. Indeed, 1a is the global minimum on the potential energy surface of cyclic C₄NGeH₅ with a singlet-triplet energy gap larger than that of Herrmann's germylene, i.e. 57.4 vs. 49.7 kcal/mol. From a kinetic viewpoint, the calculated energy barrier for 1,2-H shift of 1a to 1 is 70.8 kcal/mol compared to more prohibitive 92.5 kcal/mol for 1,4-H shift of 3a to 3. No Ge{double bond, long}Ge doubly bonded minimum structure is found as dimer for 1a. The doubly bonded dimer of 3a is 11.2 kcal/mol less stable than its two separate monomers. This study signifies the thermodynamic and kinetic stabilities of divalent 1a and 3a hoping to prompt the experimental attentions toward them.