Homoatomic cations: From [P(5)](+) to [P(9)](+)

Recent synthetic approaches to a series of [P(9)]X salts (X = [F{Al(OR(F))(3)}(2)], [Al(OR(F))(4)], and (R(F) = C(CF(3))(3)); Ga(2)Cl(7)) overcome limitations in classical synthesis methods that proved unsuitable for phosphorus cations. These salts contain the homopolyatomic cation [P(9)](+) via (I) oxidation of P(4) with NO[F{Al(OR(F))(3)}(2)], (II) the arene-stabilized Co(I) sandwich complex [Co(arene)(2)][Al(OR(F))(4)] [arene = ortho-difluorobenzene (o-DFB) and fluorobenzene (FB)], or (III) the reduction of [P(5)Cl(2)][Ga(2)Cl(7)] with Ga[Ga(2)Cl(7)] as Ga(I) source in the presence of P(4). Quantum chemical CCSD(T) calculations suggest that [P(9)](+) formation from [Co(arene)(2)](+) occurs via the nido-type cluster [(o-DFB)CoP(4)](+), which resembles the isoelectronic, elusive [P(5)](+). Apparently, the nido-cation [P(5)](+) forms intermediately in all reactions, particularly during the Ga(I)-induced reduction of [P(5)Cl(2)](+) and the subsequent pick up of P(4) to yield the final salt [P(9)][Ga(2)Cl(7)]. The solid-state structure of [P(9)][Ga(2)Cl(7)] reveals the anticipated D(2d)-symmetric Zintl-type cage for the [P(9)](+) cation. Our approaches show great potential to bring other [P(n)](+) cations from the gas to the condensed phase.