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 R2PNHPNR2 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, t-Bu; X = Cl, Br, 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. 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 which 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.