Guilty on Two Counts: Stepwise Coordination of Two Fluoride Anions to the Antimony Atom of a Noninnocent Stibine Ligand
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abstract
2015 American Chemical Society. In our efforts to investigate the coordination noninnocent behavior of transition-metal stibine complexes, we have prepared a series of platinum complexes bearing the tetradentate ligand (o-(Ph2P)C6H4)3Sb (L). Treatment of (Et2S)2PtCl2 with L affords the lantern complex (o-(Ph2P)C6H4)3SbCl)Pt(Cl) (1-Cl), which undergoes facile exchange with fluoride to form the fluorostiboranyl complex ((o-(Ph2P)C6H4)3SbF)Pt(Cl) (1-F). Starting from 1-Cl, anion exchange and abstraction reactions afford [((o-(Ph2P)C6H4)3Sb)Pt(CyNC)][SbF6]2, ([2][SbF6]2), [((o-(Ph2P)C6H4)3SbF)Pt(CyNC)][SbF6] ([3][SbF6]), and ((o-(Ph2P)C6H4)3SbF2)Pt(CyNC) (4), which are related by the formal stepwise coordination of two fluoride ligands to the antimony center. Structural studies of this series show that the Sb-Pt bond lengthens upon sequential fluoride coordination at the antimony center, consistent with the weakening of the Sb-Pt interaction. Natural bond orbital (NBO) calculations performed at the density functional theory (DFT) optimized geometries suggest that the Sb-Pt interactions become more polarized across the series, as part of a larger "spillover" of electron density from the antimony center to platinum. QTAIM analyses of the DFT-derived wave functions for this series corroborate the weakening of the Sb-Pt interaction and suggest that the Sb-Pt bonding pair becomes increasingly polarized toward platinum upon successive fluoride coordination at the antimony center. (Chemical Equation Presented).
