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

Abstract

The bis(dialkylphosphino)amines R2PNHPR2 react with elemental halogens X2 in dichloromethane to produce cationic products of the general form [(R)2P(X)-N-(R)2P(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 [HCl2]− salts, while the dibromo and diiodo products have been isolated as trihalides, [X3]−. A number of these compounds have been shown to react further with methanol to produce salts containing [(R)2P(OCH3)N(R)2P(OCH3)]+ cations, some of which have also been characterized using X-ray crystallography. The conversion of [(Ph)2P(I)-N-(Ph)2P(I)][I3] to [(Ph)2P(OCH3)-N-(Ph)2P(OCH3)][I3] was monitored using 31P 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.