Activation energies for molecular tumbling and cyclopentadienyl rotation in [M(η5-C5H5)(η4-cod)](M = Rh or Ir; cod = cyclo-octa-1,5-diene) and the X-ray crystal structure of and bonding in [Rh(η5-C5H5)(η4-cod)]

Abstract

The X-ray structure of [Rh(η⁵-C₅H₅)(η⁴-cod)](cod = cyclo-octa-1,5-diene) has been determined. The cyclopentadienyl ring is distorted in a manner consistent with an ‘allyl-ene’ structure. Carbon-13 and ¹⁰³Rh n.m.r. studies have been used to determine the activation energies for molecular tumbling and cyclopentadienyl rotation in [M (η⁵-C₅H₅)(η⁴-cod)](M = Rh or Ir). Despite the ‘allyl-ene’ geometry, the activation energy for cyclopentadienyl rotation is the same as for ferrocene derivatives. The ¹³C and ¹⁰³Rh chemical shift anisotropies were also determined.