R3N → [TaCl5(NR3)] Chloride displacement reactions Tantalum pentachloride reacts at room temperature with an excess of triphenylphosphine oxide to give oxychlorides: TaCl5 + 3 OPPh3 → [TaOCl3(OPPh3)]x ... The presumed initial formation of adducts between TaCl5 and hydroxyl compounds such as alcohols, phenols and carboxylic acids is followed immediately by the elimination of hydrogen chloride and the formation of Ta–O bonds: TaCl5 + 3 HOEt → TaCl2(OEt)3 + 3 HCl In the presence of ammonia as a HCl acceptor, all five chloride ligands are displaced with formation of Ta(OEt)5. Similarly TaCl5 reacts with lithium methoxide in anhydrous methanol to form related methoxy derivatives: TaCl5 + 4 LiOMe → Ta(OMe)4Cl + 4 LiCl Ammonolysis and alcoholysis and related reactions Ammonia will displace most of the chloride ligands from TaCl5 to give a cluster. Chloride is displaced more slowly by primary or secondary amines but the replacement of all five chloride centers by amido groups has been achieved by the use of lithium dialkylamides, as illustrated by the synthesis of pentakis(dimethylamido)tantalum: TaCl5 + 5 LiNMe2 → Ta(NMe2)5 With alcohols, the pentachloride reacts to give alkoxides. As shown for the preparation of tantalum(V) ethoxide, such reactions are often conducted in the presence of base: 10 EtOH + Ta2Cl10 + 10 NH3 → Ta2(OEt)10 + 10 NH4Cl Tantalum pentachloride is reduced by nitrogen heterocycles such as pyridine. Reduction Reduction of tantalum(V) chloride gives anionic and neutral clusters including [Ta6Cl18]4− and [Ta6Cl14](H2O)4. References Further reading External links NIST Standard Reference Database Tantalum compounds Chlorides Metal halides