Mechanism of the electronic stabilization of the 3MR and divalent carbon of bis(diisopropylamino)cyclopropenylidene

Analysis of the topology of the electron density of bis(dimethylamino)cyclopropenylidene as a model of the recently synthesized, stable bis(diisopropylamino)cyclopropenylidene with the quantum theory of atoms in molecules is used to investigate the stabilizing electronic effects at the reactive carbene site by amino substitution. This work demonstrates that the plane perpendicular lone pairs of nitrogen utilize in-plane sigma-aromaticity as a conduit to delocalize charge to the carbene carbon C2, where it is transferred preferentially back into the pi-plane at the site through sigma-pi polarization. C2 is thus stabilized relative to the parent cyclopropenylidene, c-C(3)H(2), by a very different mechanism than that suggested in the orbital view of n(pi)(N) and pi(C=C) conjugation and n(pi)(N) --> p(pi)*(C2) hyperconjugation. Validation of this premise is also found in properties of asymmetric atomic quadrupole tensors, bond path ellipticities, and diamagnetic/paramagnetic components of NMR shielding tensors.