Restricted rotation about a metal–arene bond caused by the steric effects of proximal ethyl groups; stereodynamics of some complexes of 1,3,5-triethyl-2,4,6-tris(trimethylsilylmethyl)benzene

Abstract

1,3,5-Triethyl-2,4,6-trineopentylbenzene 5 and 1,3,5-triethyl-2,4,6-tris(trimethylsilylmethyl)benzene 6 are considered as realistic role models for the intramolecular rotational behaviour of hexaethylbenzene in its metal complexes. Empirical force-field calculations are reported for the ten diastereomeric conformers of 5 and 6 which fall into four sets depending on the number of syn interactions. Variable-temperature 75.5 MHz ¹³C-{¹H} NMR spectra have been recorded for dicarbonylthiocarbonyl-, dicarbonyl(η²-cis-cycloctene- and dicarbonyl(triphenylphosphine)-[η⁶-1,3,5-triethyl-2,4,6-tris(trimethylsilymethyl)benzene]molybdenum(0). Decoalescence phenomena are observed for the three complexes and line-shape-fitting studies gave the barriers for rotation about molybdenum–arene bond.