The triphenylphosphine cone angle and restricted rotation about the chromium–phosphorus bond in dicarbonyl(η6-hexa-alkylbenzene)(triphenyl-phosphine)chromium(0) complexes. Crystal and molecular structure of dicarbonyl(η6-hexa-n-propylbenzene)(triphenylphosphine)chromium(0)

Abstract

The variable-temperature 90.56.MHz ¹³C-{¹H} n.m.r. spectra of dicarbonyl(η⁶-benzene)(triphenylphosphine)chromium(0), (1), dicarbonyl(η⁶-hexamethylbenzene)(triphenylphosphine)chromium(0), (2), dicarbonyl(η⁶-hexaethylbenzene)(triphenylphosphine)chromium(0), (3), and dicarbonyl(η⁶-hexa-n-propylbenzene)(triphenylphosphine)chromium(0), (4), have been observed and a decoalescence in the triphenylphosphine subspectra of (2), (3), and (4), with ΔG₂₀₀^‡ca. 38 kJ mol^–1, attributed to restricted rotation about the chromium–phosphorus bond. The steric requirements for intramolecular rotations for these complexes are visualised as two cones with a common apex at the centre of the chromium atom. The crystal and molecular structure of (4) has been determined and the co-ordinated hexa-n-propylbenzene has been found to adopt an all-distal alkyl group conformation.