On the Ligating Properties of Sulfonate and Perchlorate Anions Towards Zinc

Abstract

Attempts are reported to incorporate sulfonate and perchlo-Tp*Zn-OS0,R. Spectroscopic evidence for perchlorate coorrate anions as ligands in zinc complexes of tripodal ligands. dination in Tp*ZnC104 . 2 DMSO conflicts with crystallograUsing tris(benzimidazolylmethy1)amine (BIMA) only the pic evidence against it in Tp*ZnC104 . ble. Using substituted pyrazolylborates (TpY), the same three NCSH5]C1O4 were determined. sulfonate anions were found to be ligands in the complexes While the coordination chemistry of carbonates, carboxylates, nitrates or phosphates is well developed, the 0x0 anions of sulfur and of the halogens are typical representatives of the class of weakly coordinating This is inconvenient in terms of synthesis of their complexes, but it should be an advantage in terms of reactivity, because such complexes should be useful starting materials for other complexes of weakly coordinating ligands. Thus, it can be assumed that a sulfate or perchlorate ligand is less firmly bound to a metal center and hence a better leaving group than for instance a water molecule or a typical nitrogen ligand.Modern coordination chemistry gives reason to search for such complexes of easily replaceable coordinating anions. This is so because attractive substrates of metalcomplex or metalloenzyme-catalyzed reactions, e.g. C02, alcohols or aldehydes, are weakly coordinating ligands themselves and thus require the absence of better donors which would block "their" coordination sites. It is along these lines that we investigate the coordination chemistry of zinc with "bad" ligands.This paper reports our attempts to find zinc complexes with coordinated sulfonate and perchlorate anions. It was planned to limit the coordination sphere to just one available coordination site. For this purpose the neutral tripodal ligand tris(benzimidazolylmethy1)amine (BIMA) and the two anionic tripodal tris(pyrazoly1)borate ligands TpzBu,Me and TpCUm*Me were applied. We had found previously that the BIMA[4-SI and Tp* ligands[6-81 support the coordination of monodentate oxygen ligands in easily accessible LZn-X complexes. Perchlorate complexes of zinc have already been structurally characterized by other^[^*.'^] and ourselves ["]. The Cambridge Crystallographic Data Base contains quite a number of entries on zinc-coordinated sulfate ions ["], and the structures of four zinc monodentate sulfonate complexes (one of them[l31 also containing uncoordinated sulfonate) have been des~ribedI~~-'~]. BIMA BIMA ComplexesWe had already obtained a (B1MA)zinc p-toluenesulfonate, the spectra of which seemed to indicate coordination of the ~ulfonate [~]. However, this compound did not yield crystals of X-ray quality. We therefore tried to vary the preparative conditions and the organic constituents of the sulfonates. As shown below, only the aqua complexes 1 and 2 containing uncoordinated sulfonates were obtained by this approach. The starting point of the reactions was the perchlorate salt 3L4J (see below) which could not be prepared water-free. Its treatment with t...

Nucleophilic reaction by carbonic anhydrase model zinc compound: characterization of intermediates for CO2 hydration and phosphoester hydrolysis

“…The tetrahedral geometry around a zinc atom was slightly distorted, where the zinc was coordinated by three benzimidazole nitrogen atoms of and one oxygen atom of hydroxide ion with the bond angles around zinc atom 103.7(2)°-114.6(1)°( Table 2). The bond lengths of Zn-N1 2.015 (6) A, Zn-O1 2.047 (7) A are consistent with the literature data of tetrahedral zinc compounds [35,36,40,[45][46][47]. The location of the phenolic OH groups is located at two positions 5 and 6 of each benzene ring (Fig.…”

A mononuclear cobalt(II) hydroxo complex: synthesis, molecular structure, and reactivity studies

“…The kinetic experiments indicated that the rate of generation of 4-nitrophenolate ion was varied from ester to ester and TpCoOH is the kinetically active species. The hydrolysis of ester occurs via a binuclear mechanism involving the nucleophilic attack of the metal-bound hydroxide to the carbonyl group of the ester as reported by other workers also [38][39][40][41][42][43][44]. The carbonic anhydrase also promotes the hydrolysis of 4-nitrophenylacetate [45] and follows second order kinetics, involving the direct nucleophilic attack at the carbonyl group by a Zn-OH species or hydroxo of other substituted metal ions.…”

The Missing Link in COS Metabolism: A Model Study on the Reactivation of Carbonic Anhydrase from its Hydrosulfide Analogue

“…Moreover, we are currently not aware of any zinc hydrosulfide complex that binds the hydrosulfide in a monodentate manner and has an overall charge of +1. For the experimental investigation, we therefore used one example out of the only available class of model compounds for the hydrosulfide analogue of CA, the uncharged complex Tp Ph,Me ZnSH ( 5 ) 18. A slight deviation of the resulting experimental data from the calculated results must therefore be expected.…”