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Chiral Quadridentate Ligands Derived from Amino Acids and Some Zinc Complexes Thereof
Author(s) -
Niklas Nicole,
Walter Olaf,
Alsfasser Ralf
Publication year - 2000
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/1099-0682(200008)2000:8<1723::aid-ejic1723>3.0.co;2-n
Subject(s) - chemistry , stereochemistry , substituent , zinc , transition metal , trigonal bipyramidal molecular geometry , amine gas treating , medicinal chemistry , circular dichroism , amino acid , catalysis , yield (engineering) , hydrolysis , metal , phenylalanine , diethylzinc , crystal structure , enantioselective synthesis , crystallography , organic chemistry , biochemistry , materials science , metallurgy
A series of three new quadridentate ligands was synthesized by reaction of the haloacetylated amino acid esters L ‐BrAc−Phe−OMe ( 4a ), L ‐BrAc−Lys(Z)−OMe ( 4b ), and ClAc−Gly−OEt ( 4c ), respectively, with bis(picolyl)amine (bpa, 5 ). The obtained products L ‐bpaAc−Phe−OMe ( 3a ), L ‐bpaAc−Lys(Z)−OMe ( 3b ), and bpaAc−Gly−OEt ( 3c ) were treated with Zn(OTf) 2 (OTf = CF 3 SO 3 − ) to yield the trigonal‐bipyramidal complexes [( L ‐bpaAc−Phe−OMe)ZnOTf](OTf) ( 6a ), [( L ‐bpaAc−Lys(Z)−OMe)ZnOTf](OTf) ( 6b ), and [(bpaAc−Gly−OEt)ZnOTf](OTf) ( 6c ). Crystal structures of 6c and the hydrolysis product [( L ‐bpaAc−Phe−OMe)(H 2 O)ZnOTf](OTf) 2 ( 7a ) are reported. The results suggest the formation of a chiral pocket at the metal center provided by the benzyl substituent in the L ‐phenylalanine derivative 7a . This observation is further supported by 1 H‐NMR and circular dichroism spectroscopic data. These methods indicate a significant ordering effect within the ligands upon metal coordination as well as interactions between the first coordination spheres and their chiral environments provided by the L ‐phenylalanine and L ‐lysine moieties of 3a and 3b , respectively. Our results are discussed with respect to the development of chiral building blocks for transition metal catalysts and biomimetic assemblies.