-Donor/acceptor-confused ligands: the case of a chlorostibine.
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abstract
In search for new examples of -acceptor ligands, we have investigated the tridentate ligands (o-(iPr2P)C6H4)2SbPh) (L(Ph)) and (o-(iPr2P)C6H4)2SbCl) (L(Cl)) which react with (tht)AuCl (tht = tetrahydrothiophene) to afford L(Ph)AuCl (1) and L(Cl)AuCl (2), respectively. As suggested by the structure of these complexes, which confirm complexation of the SbP2 ligands to the gold chloride fragment, and in agreement with the results of the density functional theory (DFT) and natural bond orbital (NBO) calculations, the gold and antimony atom of 1 and 2 are involved in a AuSb donor-acceptor interaction. The magnitude of this interaction is higher in complex 2 which possesses a chlorinated and thus more Lewis acidic antimony center. We have also compared the strength of the AuSb interaction present in 2 with the AuBi interaction observed in the newly prepared bismuth analogue [(o-(iPr2P)C6H4)2BiCl]AuCl (3). This comparison reveals that 2 possesses a stronger AuPn bond (Pn = pnictogen), an observation reconciled by invoking the greater Lewis acidity of antimony(III) halides. Finally, complexes 1 and 2 undergo a clean antimony-centered oxidation when treated with ortho-chloranyl. These oxidation reactions afford complexes [(o-(iPr2P)C6H4)2(o-C6Cl4O2)SbPh]AuCl (5) and [(o-(iPr2P)C6H4)2(o-C6Cl4O2)SbCl]AuCl (6). Structural and computational studies of 5 show that the AuSb bond becomes shorter and more covalent upon oxidation of the antimony atom. Although the structure of 6 has not been experimentally determined, spectroscopic and computational results show a similar effect in this complex. Complex 5 and 6 constitute rare examples of metalated six coordinate antimony compounds.
