Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
Inorg Chem. 2011 Dec 19;50(24):12349-58. doi: 10.1021/ic2014607. Epub 2011 Sep 6.
The Nb-P triple bond in P≡Nb(N[Np]Ar)(3) (Np = CH(2)(t)Bu; Ar = 3,5-Me(2)C(6)H(3)) has produced the first case of P(4) activation by a metal-ligand multiple bond. Treatment of P(4) with the sodium salt of the niobium phosphide complex in weakly coordinating solvents led to formation of the cyclo-P(3) anion (P(3))Nb(N[Np]Ar)(3). Treatment in tetrahydrofuran (THF) led to the formation of a cyclo-P(5) anion (Ar[Np]N)(η(4)-P(5))Nb(N[Np]Ar)(2), which represents a rare example of a substituted pentaphosphacyclopentadienyl ligand. The P(4) activation pathway was shown to depend on the dimer-monomer equilibrium of the niobium phosphide reagent, which, in turn, depends on the solvent used for the reaction. The pathway leading to the cyclo-P(3) product was shown to require a 2:1 ratio of the phosphide anion to P(4), while the cyclo-P(5) formation requires a 1:1 ratio. The cyclo-P(3) salt has been isolated in 56% yield as orange crystals of the Na(THF)(P(3))Nb(N[Np]Ar)(3) dimer or in 83% yield as an orange powder of [Na(12-crown-4)(2)][(P(3))Nb(N[Np]Ar)(3)]. A solid-state X-ray diffraction experiment on the former salt revealed that each Nb-P(3) unit exhibits pseudo-C(3) symmetry, while (31)P NMR spectroscopy showed a sharp signal at -223 ppm that splits into a doublet-triplet pair below -50 °C. It was demonstrated that this salt can serve as a P(3)(3-) source upon treatment with AsCl(3), albeit with modest yield of AsP(3). The cyclo-P(5) salt was isolated in 71% yield and structurally characterized from red crystals of [Na(THF)(6)][(Ar[Np]N)(η(4)-P(5))Nb(N[Np]Ar)(2)]. The anion in this salt can be interpreted as the product of trapping of an intermediate pentaphosphacycplopentadienyl structure through migration of one anilide ligand onto the P(5) ring. The W(CO)(5)-capped cyclo-P(3) salt was also isolated in 60% yield as [Na(THF)][(OC)(5)W(P(3))Nb(N[Np]Ar)(3)] from the activation of 0.5 equiv of P(4) with the sodium salt of the tungsten pentacarbonyl adduct of the niobium phosphide anion.
[P≡Nb(N[Np]Ar)(3)]-（Np = CH(2)(t)Bu；Ar = 3,5-Me(2)C(6)H(3)）中的 Nb-P 三重键首次实现了金属-配体多重键对 P(4)的活化。在弱配位溶剂中，将 P(4)与磷化铌复合物的钠盐进行处理，导致形成环-P(3)阴离子[(P(3))Nb(N[Np]Ar)(3)]-。在四氢呋喃（THF）中进行处理导致形成环-P(5)阴离子[(Ar[Np]N)(η(4)-P(5))Nb(N[Np]Ar)(2)]-，这代表了取代的五磷杂环戊二烯基配体的罕见实例。已经表明，P(4)的活化途径取决于磷化铌试剂的二聚体-单体平衡，而这反过来又取决于用于反应的溶剂。已经表明，生成环-P(3)产物的途径需要磷化物阴离子与 P(4)的 2:1 比，而环-P(5)的形成需要 1:1 比。环-P(3)盐已以 56%的产率分离为橙色晶体[Na(THF)]2[(P(3))Nb(N[Np]Ar)(3)]2 二聚体，或以 83%的产率分离为橙色粉末[Na(12-冠-4)(2)][(P(3))Nb(N[Np]Ar)(3)]。对前一种盐的固态 X 射线衍射实验表明，每个 Nb-P(3)单元表现出伪 C(3)对称性，而(31)P NMR 光谱在-223 ppm 处显示出尖锐信号，在低于-50°C 时分裂为双峰-三重峰对。已经表明，该盐可以作为 P(3)(3-)源，在与 AsCl(3)进行处理时，尽管产率适中的 AsP(3)。环-P(5)盐以 71%的产率分离，并从红色晶体[Na(THF)(6)][(Ar[Np]N)(η(4)-P(5))Nb(N[Np]Ar)(2)]中进行结构表征。该盐中的阴离子可以解释为通过一个苯胺配体迁移到 P(5)环上来捕获中间五磷杂环戊二烯基结构的产物。W(CO)(5)封端的环-P(3)盐也以 60%的产率分离为[Na(THF)][(OC)(5)W(P(3))Nb(N[Np]Ar)(3)]，其是通过用磷化铌阴离子的五羰基钨加合物的钠盐激活 0.5 当量的 P(4)而得到的。
