PI-FACE SELECTIVITY OF COORDINATED KETONES TO NUCLEOPHILIC ADDITIONS - THE IMPORTANCE OF ALUMINUM OXYGEN PI-BONDING

The interaction of AlMe(BHT)2with ketones O=CRR' yields the Lewis acid-base complexes AlMe(BHT)2(O=CRR'). The X-ray crystallographic determination of AlMe(BHT)2(O=CPh2) shows that the ketone coordinates such that the aluminum is in the nodal plane of the C=O Π-bond. The importance of the orientation of the aryl oxides toward Π-face selective nucleophilic addition to the coordinated ketone is discussed. The reaction of AlMe(BHT)2(O=CRR') with 1 equiv of MeLi, in Et2O, yields AlMe(BHT)22[OC(Me)RR']Li(OEt2), the structure of which has been confirmed by X-ray crystallography for R = R' = Ph. Addition of an excess of MeLi yields AlMe2(BHT)[OC(Me)RR']-Li(OEt2) and [Li(BHT)OEt2]2. The reaction of AlMe(BHT)2(O=CRR') with tBuLi or Li metal, in Et2O, yields AlMe(BHT)2[OC(H)RR']Li(OEt2). A possible electron-transfer mechanism for methyl and hydride addition to the coordinated ketone is presented. The compound AlMe-(BHT)2(O=CPh2) crystallizes in the monoclinic space group P21/n, a = 12.002 (2) Å, b = 24.881 (2) Å, c = 13.767 (3) Å, β = 90.573 (9)°, z = 4, observed data = 1836, R = 0.061, Rw= 0.068. The compound AlMe(BHT)2[OC(Me)Ph2]Li(OEt2) crystallizes in the monoclinic space group P21/c, a = 13.789 (1) Å, b = 19.676 (2) Å, c = 17.835 (2) Å, β = 105.389 (7)°, z = 4, observed data = 4427, R = 0.056, Rw= 0.060. © 1990, American Chemical Society. All rights reserved.