Novel N-S bond scission and ring-opening reactions upon addition of phosphines to benzisothiazolinate zinc(II) complex

Abstract

Reaction of two equivalents of sodium benzisothiazolinate (Nabit) with one equivalent of zinc acetate in aqueous solution afford $[\text{Zn(bit)}_2(\text{H}_2\text{O})]_2$ (1). Treatment of (1) with three equivalents of triphenyl phosphine ($\text{PPh}_3$) gave $[\text{Zn}(\text{PPh}_3)_2(\kappa^1\text{-2-mbm})(\kappa^1\text{-2-mbn})]$ (2), (2-mbm = 2-mecaptobenzamide, 2-mbn = 2-mercaptobenzonitrile). Treatment of (1) with one equivalent of the bidentate diphoshine ligands (diphos), $\text{Ph}_2\text{P}(\text{CH}_2)\text{nPPh}_2$, $\text{n} = 1$, (dppm) afforded two polemerization isomers complexes $[\text{Zn}(\kappa^1\text{-dppm})(\kappa^2\text{-mbm})(\kappa^1\text{-2-mbn})]$ (3a) and $[\text{Zn}(\mu\text{-dppm})(\kappa^2\text{-2-mbm})(\kappa^1\text{-2-mbn})]_2$ (3b), when $\text{n} = 2$ (dppe), the product is $[\text{Zn}(\kappa^2\text{-2-mbm})(\mu\text{-2-mbn})]$ (4), when $\text{n} = 3$ (dppp), $\text{n} = 4$ (dppb) or $(\text{CH}_2)\text{n} = (\text{C}_5\text{H}_4)_2\text{Fe}$, bis(diphenylphosphino) ferrocene (dppf) afforded complexes of the type $[\text{Zn}(\text{diphos})(\kappa^1\text{-2-mbm})(\kappa^1\text{-2-mbn})]$ (5-7).

In all these reactions the N-S bond of the heterocyclic benzisothiazolinate ring is broken and protonated to produce the 2-mercaptobenzamide ligand (2-mbm), then the product loses $\text{H}_2\text{O}$ molecule to afford a 2-mercaptobenzonitrile (2-mbn) ligand. The synthesized complexes were characterized by elemental analysis, infrared spectra conductivity measurements and multinuclear $\text{}^1\text{H}$ and $\text{}^{31}\text{P}$ nmr spectra.