Stabilization of the P(CF₃)₂^- and P(C₆F₅)₂^- Ions by Coordination to Pentacarbonyl Tungsten: Structures of [18-crown-6-K]P(CF₃)₂, [18-crown-6-K][W{P(CF₃)₂}(CO)₅], and [18-crown-6-K][{W(CO)₅}₂{μ-P(C₆F₅)₂}]·THF

Abstract

The stabilization of the P(CF(3))(2)(-) ion by intermediary coordination to the very weak Lewis acid acetone gives access to single crystals of [18-crown-6-K]P(CF(3))(2). The X-ray single crystal analysis exhibits nearly isolated P(CF(3))(2)(-) ions with an unusually short P-C distance of 184(1) pm, which can be explained by negative hyperconjugation and is also found by quantum chemical hybrid DFT calculation. Coordination of the P(CF(3))(2)(-) ion to pentacarbonyl tungsten has only a minor effect on electronic and geometric properties of the P(CF(3))(2) moiety, while a strong increase in thermal stability of the dissolved species is achieved. The hitherto unknown P(C(6)F(5))(2)(-) ion is stabilized by coordination to pentacarbonyl tungsten and isolated as a stable 18-crown-6 potassium salt, [18-crown-6-K][W[P(C(6)F(5))(2)](CO)(5)], which is fully characterized. The tungstate, [W[P(C(6)F(5))(2)](CO)(5)](-), decomposes slowly in solution, while coordination of the phosphorus atom to a second pentacarbonyl tungsten moiety results in an enhanced thermal stability in solution. The single-crystal X-ray analysis of [18-crown-6-K][[W(CO)(5)](2)[mu-P(C(6)F(5))(2)]].THF exhibits a very tight arrangement of the two C(6)F(5) and two W(CO)(5) groups around the central phosphorus atom. NMR spectroscopic investigations of the [[W(CO)(5)](2)[mu-P(C(6)F(5))(2)]](-) ion exhibit a hindered rotation of both the C(6)F(5) and W(CO)(5) groups in solution.