The identification of some novel four‐membered ring cyclic triphosphenium ions in solution

Abstract

The first four-membered ring cyclic triphosphenium ions with carbon substituents (methyl or cyclohexyl) on the outer phosphorus atoms have been identified in solution by31 P NMR spectroscopy. The cyclohexyl derivative in the presence of [SnCl 6 ] 2− as counterion was stable enough for methylation by methyl triflate to be carried out.

Alkyl and aryl dicationic derivatives of cyclic triphosphenium ions

“…The presence of the 'bare' P in a low oxidation state should facilitate oxidation reactions at this centre, and we have shown that direct methylation using excess methyl triflate is possible for many of these ions to form di-ium dications, as depicted in Scheme 1. 10,11 Scheme 1 Direct methylation of cyclic triphosphenium ions.…”

Protonation of some cyclic triphosphenium ions

“…Small amounts of oxidation products such as the diphosphane monoxide, which gives rise to two doublets, or the diphosphane dioxide, which gives a single resonance, were occasionally detected, particularly for diphosphanes with alkyl substituents, but these did not interfere with formation of the cyclic triphosphenium ions. These were prepared quantitatively in CH 2 Cl 2 solution as described previously [7,8,10,11], from either a 3:2 mixture of the diphosphane and PCl 3 , or a 1:1:1 mixture of the diphosphane, PCl 3 , and SnCl 2 , where the hexachlorostannate(IV) was required. The calculated quantity of a solution of AlCl 3 and t BuCl (1:1) in CH 2 Cl 2 or of triflic acid was added by microsyringe, once formation of the ring had been confirmed spectroscopically.…”

“…Protonation of the four-membered ring with cyclo-hexyl substituents 26 (described very recently by us [10]) was also attempted. In this case the ring was freshly prepared from the diphosphane, SnCl 2 , and PCl 3 ; NMR spectroscopy confirmed that it had formed (δ 31 P P B 45.4 (d) 2P, P A −216.1 (t) 1P ppm, 1 J PP 330.9 Hz).…”

“…Alkylation of the dication derived from tetraphos by a mixture of CH 2 Cl 2 and AlCl 3 was demonstrated by Schmidpeter and Lochschmidt to give a tetracation with CH 2 Cl substituents on both central phosphorus atoms [4]. Subsequently we have shown that a number of cyclic triphosphenium ions can be methylated, by using excess methyl triflate [10,11]. Schmidpeter et al also demonstrated that the cation 1 (Scheme 1) derived from bis-diphenylphosphinoethane (dppe) and the dication derived from tetraphos, (as well as several noncyclic species), could be protonated by a 1:1 mixture of t BuCl and AlCl 3 to give the corresponding triphosphane-1,3-di-ium dication 2 and tetracation respectively [4,12].…”

“…These include examples with five-, six-, or sevenmembered rings, or with two linked six-membered rings, each containing three phosphorus atoms. Very recently we have reported the first syntheses of fourmembered ring examples with carbon substituents on the outer phosphorus atoms [10]. Comparatively little investigation has been carried out into the chemistry of these species, however.…”