Ion-pair structure as a determinant of solvent dependence. Solvent-selective formation of tert-butylbis(indenyl)phosphine and tert-butyl(n-butyl)indenylphosphine

The reaction of tert-butyldichlorophosphine with freshly prepared lithium indene is shown to exhibit an unusual solvent dependence. In diethyl ether the reaction proceeds to the achiral tert-butylbis(3-indenyl)phosphine via a series of chiral intermediates. The reaction is catalyzed in-situ by the presence of solvent-separated indenyl ions in the solution. In toluene, tert-butyl(n-butyl)indenylphosphine is formed because of the selective precipitation of an unusual mixed indenyl-butyllithium aggregate prior to the addition of tert-butyldichlorophosphine. These mechanisms explain the solvent dependence of a range of related reactions.