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...