SYNTHESES AND STRUCTURES OF CYCLOPENTADIENYL ARSENIC(III) COMPOUNDS PART III - TETRAISOPROPYLCYCLOPENTADIENYL ARSENIC(III) DIBROMIDE AND TETRAISOPROPYLCYCLOPENTADIENYL ARSENIC(III) DIIODIDE (TIPCPASBR(2), TIPCPASI(2))

1,2,3,4-Tetraisopropylcyclopenta-2,4-dien-1-yl arsenic (III) dihalides , viz. TipCpAsX(2) (1 X = Br, 2 X = I), have been prepared by direct m etathesis reaction between the corresponding arsenic (III) trihalides with one equivalent of TipCpK at low temperature in good yields. Alter natively, 2 has been prepared via halogen exchange reaction between Ti pCpAsCl(2) (3) and KI. New compounds have been characterised by spectr oscopic methods (H-1, (CNMR)-C-13, EI-MS) and elemental analyses. The crystal structures of 1 and 2 have been determined by X-ray diffractio n methods. The AsX2-moiety in 1 and 2 occupies an allylic position nei ghbouring to an isopropyl substituent. The arsenic fragment is sigma-b ound to the cyclopentadienyl ligand, indicating remarkable pi-interact ions with the diene part of the cyclopentadienyl ring.