Stereochemistry and stereodynamics of hexa-n-propylbenzene and of its tricarbonylchromium complex. Crystal and molecular structure of tricarbonyl(η6-hexa-n-propylbenzene)chromium(0)

Abstract

Empirical force field calculations indicate that for hexa-n-propylbenzene (1) the lowest energy ‘up-down’ stereoisomer is that with D_3d symmetry and the barrier to topomerisation of the n-propyl group is 57.7 kJ mol^–1. The crystal and molecular structure of tricarbonyl(η⁶-hexa-n-propylbenzene)-chromium(0)(3) shows that in this molecule the ground-state stereoisomer of the uncomplexed arene is retained. A decoalescence phenomenon observed in the 90.56 MHz ¹³C-{¹H} solution n.m.r. spectrum of (3) is attributed to slowed n-propyl group rotation and a barrier (ΔG₃₀₀^‡) of 49.6 kJ mol^–1 for this process has been determined from lineshape-fitting studies.