Formation and characterization of palladium ethyl 2-aminoazulene-carboxylate complexes

We tried to synthesize an intermolecular cyclic compound with ethyl 2-amino-3-bromoazulene-carboxylate (EABA) using a Buchwald-Hartwig cross-coupling reaction in the presence of palladium acetate and Cs2CO3. The consumption of EABA was confirmed; however, no target compound was produced and a palladium-EABA complex (Pd-EABA) was formed. Pd complexes with diethyl 2-aminoazulene-1,3-carboxylate (DEAA) were synthesized and characterized using single-crystal X-ray structural analysis, nuclear magnetic resonance, Fourier transform infrared (FTIR) spectroscopy, and density functional theory calculations. Oligomer composed of Pd and 2,2 '-diamino-1,1 ',3,3 '-tetrakis(ethoxycarbonyl)-6,6 '-biazulene (2DEAA) was synthesized and characterized by matrix assisted laser desorption/ionization time-of-flight mass spectrometry and FTIR. Because of the expansion of the conjugation between p-orbital of the azulenyl moiety and d-orbital of the Pd atom, Pd complexes exhibit bathochromic shifts and hyperchromic effects. When DEAA was mixed with other metal sources (Ti4+, Fe3+, Co2+, Ni2+, Cu2+, Cu+, Zn2+, and Ru3+), no coordination was observed between DEAA and the cations.