STERIC CONGESTION IN A CYCLOPENTADIENYL LIGAND BEARING TERT-BUTYL GROUPS ON 3 CONTIGUOUS CARBON-ATOMS - CRYSTAL AND MOLECULAR-STRUCTURE OF (ETA-5-1,2,3-TRI-TERT-BUTYLCYCLOPENTADIENYL)(ETA-5-INDENYL)RHODIUM(III) HEXAFLUOROPHOSPHATE

The (eta(5)-1,2,3-tri-tert-butylcyclopentadienyl)(eta(5)-indenyl)rhodium(III) cation is produced from (eta(5)-indenyl)(eta(4)-1,2,3-tri-tert-butylcyclopentadiene)rhodium(I) by formal hydride removal using trityl fluoroborate, oxidation using either N-bromosuccinimide or deuteriochloroform, or reaction with acetic acid. This cation contains the first example of a cyclopentadienyl ligand bearing three tert-butyl groups on contiguous carbon atoms. The structure of the hexafluorophosphate salt has been determined by a single-crystal X-ray diffraction study; this salt crystallizes in the monoclinic P2(1)/c space group, with a = 16.363 (3) angstrom, b = 9.965 (2) angstrom, c = 17.710 (2) angstrom, and beta = 117.404 (16)-degrees. The structure shows the expected sandwich arrangement, with almost parallel and eclipsed rings. Steric congestion between adjacent tert-butyl groups causes some in-plane deformations of the cyclopentadienyl ligand and its substituents but does not cause significant puckering or ring slippage of either the cyclopentadienyl or indenyl rings from eta(5)-coordination. The solution structure is shown to be unslipped using NMR spectroscopy, and counterion effects on proton and carbon chemical shifts are discussed.