Department Chemistry and Center for Materials and Advanced Materials Research (CAMBR), The University of Western University, 1151 Richmond Street, London, Ontario, N6A 5B7, Canada.
Chemistry. 2013 Aug 26;19(35):11768-75. doi: 10.1002/chem.201301003. Epub 2013 Jul 11.
The bis(phosphino)borate ligand class is used as an anionic anchor to stabilize reactive, low coordinate arsenic centers. The neutral, zwitterionic As(I) species, 2, is formed very cleanly, and isolated in good yields using cyclohexene as a halogen scavenger. The uniqueness of this heterocyclic As(I) compound is on display with the coordination to Group 6 metal centers, (2 M(CO)5; M = Cr, Mo, W). The arsenic-metal bond lengths are longer than the related AsPh3 complexes suggesting that compound 2 is a weak sigma donor. The metal complexes reveal a trigonal pyramidal arsenic atom, which provides the first experimental evidence for the presence of two "lone pairs" of electrons on the As(I) center. When more flexible and more electron-donating isopropyl substituents were used, an intermediate (compound 5) in the formation of low coordinate pnictogen compounds was crystallographically characterized. This structure, formally a base-stabilized dichloroarsenium cation, provides an alternative mechanistic proposal to the one described in the literature.
双(膦酸)硼配体被用作阴离子锚,以稳定反应性的低配位砷中心。中性、两性离子的 As(I)物种 2 非常干净地形成,并使用环己烯作为卤化物清除剂以良好的产率分离。这种杂环 As(I)化合物的独特之处在于与第 6 族金属中心配位,(2 M(CO)5;M = Cr、Mo、W)。砷-金属键长比相关的 AsPh3 配合物长,表明化合物 2 是一个弱的 sigma 给体。金属配合物显示出三角锥形砷原子,这为 As(I)中心存在两对“孤对电子”提供了第一个实验证据。当使用更灵活和更多供电子的异丙基取代基时,形成低配位的磷属元素化合物的中间体(化合物 5)在晶体学上得到了表征。该结构,形式上是一个碱基稳定的二氯代砷翁阳离子,为文献中描述的机理提供了另一种可能性。