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.

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