Synthesis and structural, spectroscopic, and electrochemical characterization of benzo[c]quinolizinium and its 5-aza-, 6-aza, and 5,6-diaza analogues

Four heterocyclic salts 1a-d were prepared by Ca²⁺-assisted cyclization of fluoro derivatives 3, and investigated by spectroscopic (NMR and UV), electrochemical, and computational (DFT and MP2) methods. The mechanism for the formation of the cations was investigated at the DFT level of theory. 2-D NMR spectroscopy for 1[ClO₄] in DMSOd₆ aided with DFT results permitted the assignment of ¹H and ¹³C NMR signals in cations 1. The molecular and crystal structures for 1a[ClO₄] [C₁₃H₁₀ClNO₄ triclinic, P-1, a=9.6517(12) , b=11.0470(13) , c=12.2373(15) , α=67.615(1)°, β=78.845(2)°, γ=87.559(2)°; V=1183.0(2) ³, Z=4] and 1d[ClO₄] [C₁₂H₉ClN₂O₄ triclinic, P-1, a=5.9525(6) , b=8.3141(9) , c=12.2591(13) , α=73.487(1)°, β=83.814(1)°, γ=83.456(1)°; V=576.07(10) ³, Z=2] were determined by X-ray crystallography and compared with results of DFT and MP2 calculations. Electrochemical analysis gave the reduction potential order (1b>1c∼1d>1a), which is consistent with computational results.