Evidence for a Trajectory of Hydrolytic Reactions brought about by [L3Zn−OH] Species

(Pyrazolylborato)zinc−Aldehyde Complexes

“…[14Ϫ18] We therefore hoped that in a suitable TpZn environment, aldehydes might be induced to bind to the zinc center with their CϭO functions. In order to ensure maximum protection of the substrates, we chose Tp Cum,Me as the Tp ligand with the most spacious substituents, and we used Tp Cum,Me ZnϪOH (1), [19] bearing OH as a good leaving group, [13,20] as the reagent for the aldehyde substrates.…”

“…We have elucidated a trajectory for this type of reactions of TpZnϪOH complexes by kinetic, structural and theoretical investigations. [20,21] In specific cases it corresponds to the initial stage of aldehyde hydration which is catalyzed as an abiotic process by zinc enzymes like carbonic anhydrase, [22] and which has been modeled for the catalytic hydration of acetaldehyde with zinc complexes of macrocyclic ligands. [23,24,25] The encapsulation provided by the Tp ligand and the uncharged nature of 2 and 3 renders these complexes stable and inert enough to be isolable as images of catalytic intermediates.…”

Diphosphate−Zinc Complexes with Encapsulating Tripodal Coligands

“…Both provide one point of attachment per phosphate unit, thereby activating the PϪO function, and leave coordination sites at the zinc or space in the coordination sphere for the hydrolytic nucleophile. We favor the monodentate attachment, as we have already presented preparative [15,16] and mechanistic [9,10] evidence in support of it. This paper has proved its existence in the environment of encapsulating ligands, which resembles most closely that in enzymes.…”

“…In the coordination chemistry of zinc, which is of particular interest to us, we are not aware of any studies on soluble complex species other than those of nucleotides. [4,6Ϫ8] Our aim in this field, as before, [9,10] has been to learn about function from structure. We set out to delineate all possible coordination modes between zinc ions and oligophosphate species.…”

Diphosphate−Zinc Complexes with Chelating Coligands

“…[22] Our mechanistic implications for these and similar hydrolytic reactions with ZnϪOH species [23,24] require that the substrate (e.g. the pyrophosphate) is attached to only one zinc ion through only one oxygen donor during the activation step, which is in contrast to common schemes for phosphate hydrolyses [3,8] that imply attachment of zinc to two PϪO units or the attachment of two metal ions to one phosphate entity.…”