Metal vapour synthesis and conformational analysis of bis(2-trimethylsilyl-3-methylphosphobenzene)

Reaction between chromium and 2-trimethyl-silyl-3-methylphosphobenzene {C5PH3[Si (CH3)3](CH3)} vapours using metal vapour synthesis techniques produces an extremely air-sensitive yellow oil at room temperature; after sublimation and characterization by mass spectrometry and 1H and 31P NMR spectroscopy this oil proves to be a mixture of two isomers, which various techniques failed to separate. With the impossibility of obtaining crystal structures, we have used evidence from the NMR data that one of the isomers shows a long-distance P-P interaction, and extended Huckel calculations, to access the conformations of the two isomers. The calculations show that absolute minima occur for stereochemical reasons when both trimethylsilyl groups are pointing in opposite directions.