Halostibines SbMeX2 and SbMe2X: Lewis Acids or Lewis Bases?

Alkylhalostibines have been shown to behave either as Lewis acids toward appropriate neutral ligands or as Lewis bases to low-valent metal fragments. The boundaries of their Lewis acid and Lewis base behavior have been determined, and the structural and spectroscopic consequences of the different behaviors probed. [SbMeX2(L–L)] (L–L = 2,2′-bipyridyl, 1,10-phenanthroline) and [SbMeX2(L)2] (L = OPMe3, OPPh3) are five-coordinate, distorted square-pyramidal monomers with the Me group axial, with the bond distances little affected by coordination. Significant changes in the bonding within the group 6 carbonyl complexes [M­(CO)5(L′)] are evident, with L′→M σ-donation decreasing across the series L′ = SbMe3 → SbMe2Br → SbMeBr2, and an increase in M→L′ π-acceptance within the same series. Intermolecular interactions are a major feature within these systems, ranging from weak, MCO···Sb interactions in [M­(CO)5(SbMe2Br)] and [M­(CO)5(SbMeBr2)] to remarkably strong O···Sb hypervalent bonds in [Mn­(CO)5(SbMe2Br)]­[CF3SO3] and [Mn­(CO)3(SbMe2Br)3]­[CF3SO3], the latter involving the triflate anions. These lead to large changes in the geometry at Sb and represent very rare examples in which the antimony exhibits significant Lewis acid and Lewis base behavior simultaneously. The coordinated alkylhalostibines are alkylated cleanly with MeLi or nBuLi.烷基卤代锑（alkylhalostibines）已被证实可兼具双重行为：既可作为路易斯酸（Lewis acids）与合适的中性配体配位，亦可作为路易斯碱（Lewis bases）与低价金属片段结合。其路易斯酸与路易斯碱行为的边界已被明确界定，且不同行为所引发的结构与光谱效应均得到了系统探究。配合物[SbMeX₂(L–L)]（其中L–L = 2,2′-联吡啶、1,10-邻菲啰啉）与[SbMeX₂(L)₂]（其中L = 三甲基氧膦（OPMe₃）、三苯基氧膦（OPPh₃））均为五配位扭曲四方锥构型的单体，甲基基团处于轴向位置，其键长几乎不受配位作用的影响。第6族羰基配合物[M(CO)₅(L′)]的成键特征发生了显著变化：随着配体L′依次为SbMe₃、SbMe₂Br、SbMeBr₂，L′→M的σ给体作用逐渐减弱，而M→L′的π受体作用则同步增强。分子间相互作用是该类体系的重要特征，相互作用强度跨度极大：从[M(CO)₅(SbMe₂Br)]与[M(CO)₅(SbMeBr₂)]中较弱的MCO···Sb相互作用，到[Mn(CO)₅(SbMe₂Br)][CF₃SO₃]与[Mn(CO)₃(SbMe₂Br)₃][CF₃SO₃]中极强的O···Sb超价键，其中后者涉及三氟甲磺酸根（triflate）阴离子。此类相互作用会使锑原子周围的几何构型发生显著改变，且是极为罕见的同时展现出显著路易斯酸与路易斯碱行为的锑基体系实例。所配位的烷基卤代锑可与甲基锂（MeLi）或正丁基锂（nBuLi）发生干净的烷基化反应。