Syntheses and Structures of Cyclopentadienyl Arsenic (III) Compounds Part IIIa: Tetraisopropylcyclopentadienyl Arsenic (III) Dibromide and Tetraisopropyl- cyclopentadienyl Arsenic (III) Diiodide (TipCpAsBr2, TipCpAsI2)

A rsenic, A rsenic H alides, Cyclopentadienyl Arsenic Com pounds, Crystal Structure l,2 ,3 ,4-T etraisopropylcyclopenta-2,4-dien-l-yl arsenic (III) dihalides, viz. TipCpAsX2 (1 X = Br, 2 X = I), have been prepared by direct m etathesis reaction betw een the correspond­ ing arsenic (III) trihalides with one equivalent o f TipCpK at low tem perature in good yields. Alternatively, 2 has been prepared via halogen exchange reaction betw een T ipC pA sC l2 (3) and KI. N ew com pounds have been characterised by spectroscopic m ethods ( ’H, 13C NM R . EI-M S) and elem ental analyses. The crystal structures o f 1 and 2 have been determ ined by X-ray diffraction m ethods. The A sX 2-m oiety in 1 and 2 occupies an allylic position neigh­ bouring to an isopropyl substituent. The arsenic fragment is o-bound to the cyclopentadienyl ligand, indicating rem arkable jr-interactions with the diene part o f the cyclopentadienyl ring.