Toward N,P-Doped π-Extended PAHs: A One-Pot Synthesis to Diannulated 1,4,2-Diazaphospholium Triflate Salts.

A novel method for the one-pot synthesis of diannulated 1,4,2-diazaphospholium triflate salts by a Me3SiOTf-mediated self-condensation of dichlorophosphaneyl aza-(poly)cyclic aromatic hydrocarbons (aza-(P)AHs; namely, pyridine, quinoline, phenanthridine, and benzo[d]thiazole) is reported. The diannulated 1,4,2-diazaphospholium triflate salts are characterized by multinuclear NMR spectroscopy, X-ray analysis, as well as their calculated NICS values, underlining their aromatic character. Quantum mechanical calculations shed light on the intermolecular reaction mechanism. Follow up chemistry, such as the halogenation reaction with XeF2 or SO2Cl2 with the dipyridinium derivative selectively yields the respective dihalo-σ4,λ5- and tetrahalo-σ5,λ6-diazaphospholium triflate salts. The dihalo-σ4,λ5-diazaphospholium triflate salt serves well as a surrogate for the introduction of the cationic 2-(1,2'-bipyridin)-1-iumyl ligand (1,2'-bipyl), the monocationic structural isomer of the prototypical 2,2'-bipyridine ligand (2,2'-bipy).