Intramolecular Non-covalent Interactions in Metal Complexes : Geometrical Controles and Stereoselective Reactions

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Stereoselectivities of six-coordinate complexes of 4- (l-menthyloxy) -1-phenyl-1, 3-butanedione (H (l-moba) ) and 4- (l-menthyloxy) -1-p-tolly-1, 3-butanedione (H (l-moba-Me) ) have been examined for various metal ions (Co, Cr, Mn, IIIA, IIIB, Ianthanoid). In particular the complexes of IIIA and IIIB ions were studied by means of 400 MHz H-NMR and CD spectroscopies. All the complexes showed a stereoselectivity to afford the fac-OMEGA from predominantly because of the operation of a non-covalent interaction in the from of a left-handed three-bladed propeller, comprising three interligand l-menthyl/aryl contact. The interligand contact became efficient when the central metal ion was significantly large (r>l.OA^^ﾟ).Such sterically controlled lanthanoid complexes Ln (l-moba-Me)_3 were used as Lewis acid catalysts for enantioselective reductions of ketones. Acetophenone was converted into (S) -alcohol (e e % 84) whereas butane-2-one and octane-2-one were converted into (R) -alchols.Stereose … More lectivities of tetrahedral or pseudo-tetrahedral Co (II), Cu- (II), and Zn (II) complexes of N- (l-menthyl) salicylaldimine (H (sal-ment) ) and N- (R) -alpha-methylbenzylsalicylaldimine (H (sal-Rmb) ) have been studied by single-crystal X-ray method, CD spectroscopy, and molecular mechnics Calculations. The preferred configuration was DELTA for tetrahedral [M (sal-ment)_2] (M=Co, Cu, Zn), OMEGA for tetrahedral [M (sal-Rmb)_2] (M=Co, Zn), and DELTA for pseudo-tetrahedral [Cu (sal-Rmb)_2]. The X-ray structural analyses for [M (sal-Rmb)_2] clearly demonstrated the operation of non-covalent interactions between the chiral N-substituent and the adjacent ring. The Cotton effect induced at the azomethine pi-pi^* transition was well correlated with the absolute configration about the metal center.Stereoselectivities of planar metal (II) complexes (M=Cu, Pb, Pt)) of N-substituted ethylenediamines, N- { (R) -alpha-methylbenzyl} ethylenediamine (R-mben), N- { (S) -alpha-methylbenzyl} ethylenediamine (S-mben), and N- (l-menthyl) -ethylenediamine (mten), have been examined by electronic absorption and CD spectroscopies and interpreted based on a regional rule (hexadecadalrule). The preferred conformation with respect to the ethylene chain were delta for the mten and B-mben complexes and lambda for the S-mben complexes. Less