[82838-61-7] · C36H84O12P4Pd · Tetrakis(triisopropyl phosphite)palladium(0) · (MW 939.50)
Preparative Methods: has only been generated in situ from the reaction of Palladium(II) Acetate with 2 equiv n-Butyllithium and 4 equiv Triisopropyl Phosphite in THF.2 No reports of the characterization or isolation of [(i-PrO)3P]4Pd have appeared.
Handling, Storage, and Precautions: solutions of [(i-PrO)3P]4Pd should be generated and used under an argon or nitrogen atmosphere. Use in a fume hood.
[(i-PrO)3P]4Pd has been predominantly utilized in catalytic cycloaddition reactions which involve palladium-trimethylenemethane intermediates. The [3 + 2] cycloaddition of dimethyl 2,3-bicyclo[2.2.1]heptanedicarboxylate with 2-((trimethylsilyl)methyl)allyl iodide gave a single methylenecyclopentene isomer in 63% yield (eq 1).3 For this particular cycloaddition, [(i-PrO)3P]4Pd was reported to be the preferred reagent. Under similar conditions, pyrones undergo selective [4 + 3] cycloaddition to give methyleneoxabicyclononenones (eq 2).4
In cycloadditions which involve acyclic dienes, a competition has been observed for formation of five- and seven-membered rings. The reaction of dimethyl (E,E)-muconate with 2-((trimethylsilyl)methyl)allyl acetate in the presence of a catalytic amount of [(i-PrO)3P]4Pd gave a 1.1:1 ratio of methylenecyclopentene and methylenecycloheptene products in 89% combined yield (eq 3).1 For comparison, Tetrakis(triphenylphosphine)palladium(0) + 1,2-Bis(diphenylphosphino)ethane in dioxane gave increased selectivity for methylenecyclopentene (3.8:1). Product ratios were also found to be dependent upon diene stereochemistry. The reaction of dimethyl (Z,E)-muconate with 2-((trimethylsilyl)methyl)allyl acetate using [(i-PrO)3P]4Pd gave only cyclopentene products.
[(i-PrO)3P]4Pd has also been used as a catalyst for nucleophilic addition with high stereo- and regioselectivity. Addition of adenine to epoxides produced a single isomer in 90% yield (eq 4).1
Gregory T. Whiteker
Union Carbide Corporation, South Charleston, WV, USA