Reaction of bis(dialkylphosphino)amines R₂PNHPR₂ (R = i-Pr, t-Bu, Ph) with halogens X₂ (X = Cl, Br, I): different solvents – different stories

The bis(dialkylphosphino)amines R 2 PNHPR 2 react with elemental halogens X 2 in dichloromethane to produce cationic products of the general form [(R) 2 P(X)-N-(R) 2 P(X)] + (R = i-Pr, Ph, and t-Bu; X = Cl, Br, and I). All of the nine possible products have been isolated and characterized using X-ray diffraction. The dichloro compounds crystallize as [HCl 2 ] − salts, while the dibromo and diiodo products have been isolated as trihalides, [X 3 ] − . A number of these compounds have been shown to react further with methanol to produce salts containing [(R) 2 P(OCH 3 )N(R) 2 P(OCH 3 )] + cations, some of which have also been characterized using X-ray crystallography. The conversion of [(Ph) 2 P(I)-N-(Ph) 2 P(I)][I 3 ] to [(Ph) 2 P(OCH 3 )-N-(Ph) 2 P(OCH 3 )][I 3 ] was monitored using 31 P NMR spectroscopy that revealed a stepwise reaction of the former compound with methanol. The results are discussed within the context of coupled reactions; this is then used to rationalize a mechanism for the formation of a rare catenated bismuth compound we reported previously. We suggest that the formation of the weak Bi–Bi bonds is offset by a coupled or a connected reaction mechanism , involving an irreversible reaction forming strong P–OR bonds in another of the isolated products.