The syntheses were carried out under argon with use of Schlenk techniques and predried solvents. Cyclopentadiene (ca. 5 mL, ca. 75 mmol) was added dropwise to metallic cesium (5.90 g. 42.1 mmolj in T H F (90 mL). The blue color of the solvated electrons disappeared and the solution was slowly warmed to reflux temperature. After complete addition. the yellow solution was heated to reflux for 30 minutes. The solvent was removed under reduced pressure and the crystalline needles were dried under high vacuum for 4 h at 80 "C. This yielded CpCs as a white powder. ' H N M R (250 MHz, [DJpyridine. 2 5 T , TMS): 6 = 5.47 (s. Cp):
NMR: 6 = 106.9 (Cp). A suspension of PPh,CI (0.38 g, 1.01 mmol) in T H F (6 mL) was added to a solution of CpCs (0.40 g, 2.0 mmol) in THF (10mL). This immediately resulted in the formation a red reaction mixture from which small orange-red needles rapidly crystallized. The crystals were only slightly soluble in pyridine at room temperature. ' H N M R (250 MHr. [DJpyridine, 25 "C, TMS): 6 = 6.25 (s, Cp); 7.56-7.67 (m, PPh;), 7.78 7.82 (m. PPht). The C,H;/PPhf ratio cannot he accurately determined due to partial decomposition of C,H; (probably partial HID exchange with pyridine). Recrystallization of the needles from warm pyridine gave larger single crystals (0.29 g; 54% calculated on CpCs) with an identical NMR spectrum which are suitable for X-ray diffraction. Elemental analyses on crystals: