C → N coordination bonds in (CCC) → N+ ← (L) complexes

Quantum chemical calculations were performed on a series of novel divalent N I compounds, CCC → N + ← CO ( 1 ), CCC → N + ← N 2 ( 2 ), CCC → N + ← PPh 3 ( 3 ), CCC → N + ← C(NH 2 ) 2 ( 4 ), CCC → N + ← NHC Me ( 5 ) CCC → N + ← N -methyl-4-pyridylidene ( 6 ) and CCC → N + ← Cyclopropenylidene ( 7 ), where CCC is a carbocyclic carbene (cyclohexa-2,5-diene-4-(diaminomethynyl)-1-ylidene). Complete optimization of 3D structures indicates that the chosen structures are the global minima on their respective potential energy surfaces (tautomeric alternatives are much less stable). The CCC → N + coordination bond length is in the range of 1.353–1.399 Å, supporting the C → N coordination bond character. This is also supplemented by very low CCC → N bond rotational barriers (> 8 kcal/mol). The CCC → N ← L angles are in the range of 118°–131°, suggesting that there is no heteroallene-type character at the central nitrogen atom. Electron localization function, lone pair occupancy calculations and partial charge analysis indicate the presence of excess electron density at the N + centre. The nucleophilicity of the designed compounds was further measured by calculating the proton affinity and complexation energies with various Lewis acids like BH 3 , AlCl 3 and AuCl at the N + centre. All these studies suggest the presence of divalent N I character in the designed compounds 1 – 7 .