Bifunctional Carriers of Alkali-Metal Enolates: The Use of Zirconium meso-Octaethylporphyrinogen in Aldol Condensation Reactions

The (meso-octaethylporphyrinogenato)zirconium(IV) species [(Et8N4)Zr(thf)] (1) binds the acetophenone potassium enolate [PhCOCH2K] (2) in its ion-pair form, [(η5:η1:η1:η1-Et8N4)Zr{PhC(CH2)O}K(thf)3] (3), and thus drives the aldol condensation reaction with acetophenone. The resulting aldolate, which occurs in a metallacyclic form due to the solvation of potassium by a phenyl ring, remains η1 (O)-bonded to zirconium, [(η5:η1:η1:η1-Et8N4)Zr{PhC(CH2)OC(O)C(Me)Ph}K]n (4).