SYNTHESES AND STRUCTURES OF CYCLOPENTADIENYL ARSENIC COMPOUNDS .1. PENTAMETHYLCYLOPENTADIENYL ARSENIC DIHALIDES (CP(ASTERISK)ASX(2), X=F, CL, BR, I)

Treatment of 1,2,3,4,5-pentamethylcyclopenta-2,4-dien-1-yl arsenic(III ) dichloride (II) with two equivalents of cobaltocenium fluoride or po tassium iodide affords the analogous compounds CpAsF2 (I) and Cp*AsI2 (IV) in 85% and 98% yield respectively. CpAsBr2 (III) has been synth esized by direct metathesis reaction between AsBr3 and CpLi in 70% yi eld. The new compounds have been characterized by spectroscopic method s (H-1, C-13, F-19 NMR, EI-MS) and elemental analyses, The crystal str uctures of I-IV were determined by X-ray diffraction methods. The AsX( 2)-moiety in I-IV is sigma-bound to the cyclopentadienyl ligand, indic ating remarkable pi-interaction with the diene fragment of the cyclope ntadienyl ring. In addition, weak intermolecular contacts are observed in I and IV, completing the coordination sphere around the arsenic at om to pseudo-tetrahedral.