ZUSCHRIFTEN Angew. Chem. 2002, 114, Nr. 7 ¹ WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002 0044-8249/02/11407-1241 $ 20.00+.50/0 1241 The First ™Naked∫ Primary Phosphanide Anion [ArPH]  ** Valentyn L. Rudzevich, Heinz Gornitzka, Karinne Miqueu, Jean-Marc Sotiropoulos, Genevie ¡ve Pfister-Guillouzo, Vadim D. Romanenko, and Guy Bertrand* 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 polar- izability 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] More- over, 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 2,6- bis(trifluoromethyl)phenyl (Ar f ) substituent [7] for the prepa- ration 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 C P 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)]  Li  , which sub- sequently undergoes a P C bond cleavage. Ab initio calcu- lations [10] showed the s* PC orbital of 1 tobe0.3eVbelowthatof 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  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  91, 1 J P,H  173 Hz, 4 J P,F  32 Hz) is signifi- cantly deshielded relative to the phosphane precursor 1 (d P   140, 1 J P,H  216 Hz, 4 J P,F  28 Hz). A further deshielding of the 31 P NMR signal (d P  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 differ- ence 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  10 8C. The salt crystallizes as discrete units of formula [K([18]crown-6)(Ar f PH)] 3, with no close inter- molecular contacts (Figure 1). [11] The phosphorus atom is Figure 1. Molecular structure of [K([18]crown-6)(Ar f PH)] (3). Selected bond lengths [pm] and angles [8]: P1-C1 179.4(9), C1-C2 145.2(7), C2-C3 139.3(7), C3-C4 139.1(6), C4-C5 138.9(7), C5-C6 139.8(7), P1-K1 329.3(2), F1-K1 311.0(1); P1-C1-C2 120.1(2), P1-C1-C6 127.0(3), C2-C1-C6 112.9(3), C3-C4-C5 118.3(3). three-coordinate and adopts a distinctly trigonal-pyramidal configuration (sum of angles around the phosphorus atom: 345.88). The P ± K distance (329.3 pm) is comparable to those found in structurally characterized oligomeric potassium phosphanides. [6c,d] The potassium cation, in addition to being associated with the P1 atom, is encapsulated by six oxygen atoms of the crown ether, and probably interacts with one fluorine atom (K ± F: 311.0 pm). [12] A significant participation of the Ar f substituent in the delocalization of the negative charge is indicated by the relatively short P1 C1 bond (179.5 pm). To effect complete separation of the metal cation and phosphanide anion, two equivalents of [15]crown-5, which is known to form sandwich complexes with potassium cations, were added to a solution of Ar f PHK in THF that was generated in situ from Ar f PH 2 and KH. Recrystallization of the resulting precipitate from THF at  20 8C afforded extremely air and moisture sensitive deep red crystals of [K([15]crown-5) 2 ][Ar f PH] 4. Analysis by X-ray diffraction reveals that complexation of the potassium cation by two molecules of [15]crown-5 indeed occurs, thus leaving the [*] Prof. G. Bertrand, Dr. V.D. Romanenko UCR-CNRS Joint Research Chemistry Laboratory, UMR 2282 Department of Chemistry, University of California Riverside, CA 92521-0403 (USA) Fax: ( 1)909-787-2725 E-mail: gbertran@mail.ucr.edu Dr. V. L. Rudzevich, Dr. H. Gornitzka Laboratoire d×He ¬te ¬rochimie Fondamentale et Applique ¬e, UMR 5069, Universite ¬ Paul Sabatier 118, route de Narbonne, 31062 Toulouse cedex O4 (France) Dr. K. Miqueu, Dr. J.-M. Sotiropoulos, Dr. G. Pfister-Guillouzo Laboratoire de Physico-Chimie Mole ¬culaire, UMR 5624 Universite ¬ de Pau & des Pays de l×Adour Avenue de l×universite ¬, 64000 Pau (France) [**] Financial support of this work by the CNRS and UCR is gratefully acknowledged. We also thank the Institute du Developpment de Ressources en Informatique Scientifique (IDRIS, Orsay), adminis- tered by the CNRS, for the calculation facilities and the Universite ¬ Paul Sabatier for a grant to V.L.R.