Preparation and Properties of Kinetically Stabilized Phosphaethene Derivatives Carrying the Methylsulfanyl Group

1-Methylsulfanyl-2-(2,4,6-tri-t-butylphenyl)-2-phosphaethenyllithiums, prepared from (Z)-2-bromo-2-methylsulfanyl-1-(2,4,6-tri-t-butylphenyl)-1-phosphaethene, displayed an E/Z isomerization upon warming to room temperature. The copper-mediated coupling reaction afforded (Z,Z)-2,3-bis(methylsulfanyl)-1,4diphosphabuta-1,3-diene. The reaction of the phosphaethenyllithiums with dimethyl disulfide and iodomethane gave the corresponding bis(methylsulfanyl) phosphaethene and a methylated E-isomer, respectively. On the other hand, the latter methylated Z-isomer was alternatively prepared from (Z)-2-bromo-1-(2,4,6tri-t-butylphenyl)-1-phosphapropene. Both methylated E- and Z-isomers were allowed to react with W(CO)5(thf) to give the corresponding pentacarbonyltungsten (0) complexes, either of which was deprotonated to give the 3-phospha-2-propenyllithium derivative leading to the formation of a homocoupled (Z,Z)-1,6diphosphahexa-1,5-diene complex. Some key compounds were analyzed by X-ray crystallography, revealing the effect of the methylsulfanyl group on the structures. A straightforward preparation of 1-(2,4,6-tri-t-butylphenyl)-1-phosphaallene as well as its carbonyltungsten(0) complex is also described.