Alkali metal phosphanides are key transfer agents in both main group and transition metal chemistry. [1] Although these species are normally represented simply as R 2 PM or RPHM, they are usually strongly associated in solution and form aggregates in the solid state through the phosphorus centers bridging two or more metal centers. [2] The structural topology of alkali metal phosphanides is mainly determined by the donor base or coordinating solvent, the radius and polarizability of the metal, and the spatial requirement of the substituents. [3] Although several conceptual approaches have been developed to prevent intermolecular interactions, [4] only a few monomeric alkali metal diorganophosphanides are known, and compounds without a metal ± phosphorus bond within a contact ion pair remain extremely scarce. [5] Moreover, despite extensive studies of the alkali metal salts of primary phosphanes, no monomeric structures and no naked monoorganylphosphanides have been described. [4d,f, 6] Here we report on the use of the bulky electron-withdrawing 2,6bis(trifluoromethyl)phenyl (Ar f ) substituent [7] for the preparation of a naked primary phosphanide anion.A commonly used synthetic strategy for the preparation of lithium phosphanides involves the treatment of primary or secondary phosphanes with n-butyllithium. [1] However, the reaction of organolithium reagents (MeLi and nBuLi) with Ar f PH 2 (1) in diethyl ether proceeds in an entirely different manner. A CÀP bond is broken, and MePH 2 and nBuPH 2 are formed as the only phosphorus-containing products after work-up. [8] It is likely that the reaction proceeds through a phosphoranide intermediate, [9] [Ar f PH 2 (R)] À Li , which subsequently undergoes a PÀC bond cleavage. Ab initio calculations [10] showed the s* PC orbital of 1 to be 0.3 eV below that of PhPH 2 , which readily explains the anomalous reactivity observed.In contrast, the reaction of the phosphane 1 with one equivalent of KH in THF at À 15 8C results in the immediate elimination of H 2 and the formation of a deep red colored solution of potassium phosphanide 2. The chemical shift of the P atom in 2 (d P À 91, 1 J P,H 173 Hz, 4 J P,F 32 Hz) is significantly deshielded relative to the phosphane precursor 1 (d P À 140, 1 J P,H 216 Hz, 4 J P,F 28 Hz). A further deshielding of the 31 P NMR signal (d P À 73, 1 J P,H 163 Hz, 4 J P,F 32 Hz) was observed by addition of one equivalent of [18]crown-6 to a solution of 2 in THF. This result is in sharp contrast to the results observed in the case of the lithium and potassium salts of MesPH 2 (Mes 2,4,6-trimethylphenyl) for which no difference in the 31 P chemical shift was observed on addition of crown ethers. [6b] Red/orange crystals suitable for an X-ray crystallographic study were isolated from a mixture of toluene and THF (4:1) at À 10 8C. The salt crystallizes as discrete units of formula [K([18]crown-6)(Ar f PH)] 3, with no close intermolecular contacts (Figure 1). [11] The phosphorus atom is Figure 1. Molecular structure of [K([18]crown-6)(Ar f PH)] ...
