Alkylzinc Complexes with Achiral and Chiral Monoanionic <i>N</i>,<i>N</i>,<i>O</i> Heteroscorpionate Ligands

Abstract

Abstract The synthesis of the new chiral ligand (3,5‐di‐ tert butylpyrazol‐1‐yl)(3′,5′‐dimethylpyrazol‐1‐yl)aceticacid (bpaH t Bu2,Me2 ) ( 4 ) has been achieved. Two different synthetic routes to its precursor 3,5‐di‐ tert ‐butyl‐1‐[(3,5‐dimethyl‐1 H ‐pyrazol‐1‐yl)methyl]‐1 H ‐pyrazole (bpm t Bu2,Me2 ) ( 3 ) are reported. Deprotonation at the methylene group, followed by reaction with carbon dioxide, yielded a racemic mixture of 4 . The chemical behaviour of bis(3,5‐di‐ tert ‐butylpyrazol‐1‐yl)acetic acid (bd t bpzaH) ( 2 ) and the new chiral N , N , O scorpionate ligand 4 involving their coordination to zinc ions was studied. [Zn(bpa t Bu2,Me2 )Cl] ( 5 ) was formed from a mixture of ZnCl 2 , 4 and base. Reaction of bis(3,5‐di‐ tert ‐butylpyrazol‐1‐yl)acetic acid (bd t bpzaH) ( 2 ) with Zn(CH 3 ) 2 or Zn(CH 2 CH 3 ) 2 gave the alkylzinc complexes [Zn(bd t bpza)(CH 3 )] ( 6 ) and [Zn(bd t bpza)(CH 2 CH 3 )] ( 7 ). [Zn(bpa t Bu2,Me2 )(CH 3 )] ( 8 ) was obtained from a synthesis analogous to that of 6 with 4 . The further reactions of 6 and 8 with acetic acid resulted in the acetato complexes [Zn(OAc)(bd t bpza)] ( 9 ) and [Zn(OAc)(bpa t Bu2,Me2 )] ( 10 ). The chiral methyl complex 8 may serve as a precursor for structural model complexes of the active sites of zinc enzymes, such as thermolysin or carboxypeptidase A. [Zn(bpa t Bu2,Me2 ) 2 ] ( 11 ) was formed from a side reaction. Crystal structures of 4 , 5 , 8 and 11 were obtained; 5 crystallised as the dimer [Zn(bpa t Bu2,Me2 )Cl] 2 ; 11 presents an unusual zinc binding geometry. (© Wiley‐VCH Verlag GmbH &amp; Co KGaA, 69451 Weinheim, Germany, 2003)