BISMUTH COMPOUNDS WITH CROWDED MULTIPLY A LKYLATED CYCLOPENTADIENYL LIGANDS

Bismuth complexes of alkylated cyclopentadienyl ligands are obtained i n good yield on treating bismuth(III) halides with tetraisopropylcyclo pentadienylsodium or 1,2,4-tri-tert-butylcyclopentadienyllithium. A 1: 1 stoichiometric ratio gives the complexes [Cp4iBiCl2] (1), [CP3tBiCI 2] (2), and [Cp4iBiI2] (3) (Cp4i = C5iPr4H, Cp3t = C5H2tBu3-1,2,4). Ac cording to X-ray crystal structure analyses, 1 and 3 display dimeric s tructures with two bridging and two terminal halogeno ligands and eta3 -coordination of the cyclopentadienyl rings. With half an equivalent o f tetraisopropylcyclopentadienylsodium BiCl3 forms [Cp4iBi2Cl5] (4). A n X-ray crystal structure analysis of 3 reveals a central Bi2Cl10 core of two edge-sharing BiCl6, octahedra coordinated to two Bi(eta5-Cp4i) fragments generating a framework of two face-sharing cubes. Reaction of two equivalents of 1,2,4-tri-tert-butylcyclopentadienyllithium with BiCl3 yields deep purple [Cp23tBiCl] (5), a bent sandwich complex wit h an eta3, eta2-bonding mode of the cyclopentadienyl ligands. Attempte d formation of the octaisopropyl analogue of 5 from BiCl3 and two equi valents of tetraisopropylcyclopentadienylsodium with elimination of pr opene gives [Cp4iCp3iBiCl] (6) (Cp3i = C5H2iPr3). Use of monodeuterate d tetraisopropylcyclopentadienylsodium in the second substitution step gave pure [Cp4i([D1]Cp3i)BiCl] ([D1]6) proving the absence of ring ex change reactions under the reaction conditions employed and eliminatio n of propene from the second incoming sterically crowded tetraisopropy lcyclopentadienyl ring system. The importance of proper choice of solv ent and reaction conditions on the formation of alkylated cyclopentadi enyl bismuth derivatives is demonstrated by extensive formation of 1,1 ',3,3',5,5'-hexa-tert-butyldihydrofulvalene (7) from 1,2,4-tri-tert-bu tylcyclopentadienylsodium and BiCl3.