2,2′‐Azobispyridine in Phosphorus Coordination Chemistry: A New Approach to 1,2,4,3‐Triazaphosphole Derivatives

Abstract

Oxidative addition of 2,2′‐azobispyridine (abpy) to PCl3 in CH2Cl2 or THF gave the 1:1 addition product, containing phosphorus in high oxidation state (+5) and a reduced form of the ligand. 2,2′‐Hydrazobispyridine (hbpy) was prepared by reduction of abpy with hydrazine‐hydrate in 63 % yield. Interaction of hbpy with PCl3 in the presence of triethylamine gave (abpy)2–PCl (2) in 25 % preparative yield. A similar reaction of hbby with (Et2N)2PCl afforded (abpy)2–PNEt2 (4) in 89 % yield. Compound 4 after work‐up with PCl3 or PBr3 gave 2 and (abpy)2–PBr (6) respectively in high yields. Diethylamino‐derivative 4 formed (κ2‐N,N) adduct with SiCl4 7 (coordination by Py and azo‐functions), while the chloro‐derivative 2 did not. Reaction of 2 with PCl5 is accompanied with liberation of PCl3 and formation of spirocyclic ate complex [(abpy)2–2P]+PCl6–. All structurally characterized compounds demonstrated short distances between pyridyl nitrogen and the phosphorus atom. However, the QTAIM analysis did not reveal the presence of appropriate bond critical points (3, –1) for the intramolecular noncovalent interactions N···P in 2, 4, and 6. We theoretically estimated values of the rotation barriers for the pyridyl and Et2N moieties in 4 using the relaxed potential energy surface scan at the B3LYP/6‐31G(d) level of theory. The values of rotation barriers are very close to each other, viz. 13.2 (pyridyl) and 13.0 (Et2N) kcal/mol.