Compounds with pentavalent phosphorus and with tetravalent phosphorus from the reactions of trivalent phosphorus compounds with α,β-unsaturated ketones : Dipolar ions from the reactions of tertiary phosphines with 3-benzylidene-2,4-pentanedione

Abstract

The phosphorus of trialkyl phosphines, R 3P, and dialkylarylphosphines, R 2PhP, added to the β-carbon of the α,β-unsaturated ketone, 3-benzylidine-2,4-pentanedione. The crystalline 1:1 adducts had the structure of open dipolar with tetravalent phosphorus. These gave negative 31P NMR shifts relative to H 3PO 4. The 1:1 adducts from the reactions of the same unsaturated ketone with phosphite, phosphonite, and phosphinite esters, (RO) 3P, (RO) 2PhP, (RO)Ph 2P, had the structure of 5-membered cyclic oxyphosphoranes with pentavalent phosphorus. These gave positive 31P NMR shifts. These differences are attributed mainly to the higher electronegativity of oxygen than of carbon, which tends to favor the pentacovalent state of the phosphorus. The operation of steric effects is indicated by the relative instability of the adducts made from dialkylaryl-phosphines and triaryl phosphines, which tend to dissociate into the tertiary phosphine and the unsaturated ketone.