Reactions of P4 and I2 with Ag[Al(OC(CF3)3)4]: from elusive polyphosphorus cations to subvalent P3I6+ and phosphorus rich P5I2+

Reactions of X2 (X = Br, I), P4 and Ag(CH2Cl2)[Al(OR)4] [R = C(CF3)3] in suitable ratios to prep. naked polyphosphorus cations were carried out and led to products which suggested these elusive cations as intermediates. At temps. >-30 Deg to rt the initially formed cations decompd. the Al(OR)4- anion giving, in two cases, the more stable fluoride bridged (RO)3Al-F-Al(OR)3- anion. When Br2 was used as the oxidizing agent the proposed intermediate P cation (P5+) reacted with the solvent CDCl3 by double insertion of a P+ unit into the C-Cl bond giving Cl2P(CDCl2)2[(RO)3Al-F-Al(OR)3] (1). When I2 was used as the oxidizer the reaction led to the marginally stable P3I6[(RO)3Al-F-Al(OR)3] (2, x-ray characterization). By using very mild conditions throughout (-80 Deg) the primary product of the reaction of Ag(P4)2[Al(OR)4] and I2 was isolated: P5I2[Al(OR)4] (3) contg. the P5I2+ cation with a hitherto unknown C2v-sym. P5 cage as structural building block. P3I6[Al(OR)4] (4) was directly synthesized in quant. yield starting from P2I4, PI3 and Ag(CH2Cl2)[Al(OR)4] in CH2Cl2 soln. P3I6+ is formed through the P2I5+ stage (31P-NMR). P3I6+ (av.: P2.33) is the first subvalent P-X cation (X = H, F, Cl, Br, I). P5I2+ (av.: P0.6) is the first P-rich binary P-X cation. They are the third and fourth example of a binary P-X cation after the known PX4+ and P2X5+ cations. The obsd. reactions were fully accounted for by thermochem. Born-Haber cycles based on (RI-)MP2/TZVPP ab initio, COSMO solvation and lattice enthalpy calcns. (all phases). The gaseous enthalpies of formation of several species are (in kJ mol-1): P5+ (913), P3I6+ (694), P5I2+ (792), P2I5+ (733), Ag(P4)2+ (784). [on SciFinder (R)]