Doubly- and triply-bridging ligands derived from 2-pyridone and 2-aminopyridine. Crystal and molecular structure of the 2-pyridylamido complex [Os3H(CO)9{µ3-NC5H4(NH)}]* formed from 2-aminopyridine and dodecacarbonyltriosmium

Abstract

The bis(cyclo-octene) complex [Os₃(CO)₁₀(C₈H₁₄)₂] at room temperature or [Os₃(CO)₁₂] at elevated temperatures reacts with 2-pyridone, 2-aminopyridine, and 2-(benzylamino)pyridine. The clusters [Os₃H(CO)₁₀(µ-NC₅H₄X)](X = O, NH, or NCH₂Ph) were formed under the mildest conditions and adopt structures directly corresponding with that of the acetato-complex [Os₃H(CO)₁₀(µ-O₂CCH₃)]. Unlike the µ-acetato-complex, however, these readily decarbonylate thermally to give [Os₃H(CO)₉(µ₃-NC₅H₄X)]. The crystal and molecular structure of [Os₃H(CO)₉{µ₃-NC₅H₄(NH)}] has been determined by X-ray methods. The crystals are monoclinic, space group P2₁/n, a= 8.497(2), b= 15.019(2), c= 15.649(7)Å, β= 103.47(3)°, and Z= 4. The structure was refined to R= 0.0473 for 2 735 observed reflections. The pyridine ring is co-ordinated at one osmium atom while the NH substituent bridges the other two equivalent osmium atoms. The hydride ligand lies on the molecular plane of symmetry and bridges these equivalent osmium atoms. Decarbonylation of the decacarbonyl complex [Os₃H(CO)₁₀{µ-NC₅H₄(NCH₂Ph)}] partly occurs in the same way but also gives the ortho-metallated complex [OS₃H₂(CO)₉{µ-NC₅H₄(NCH₂C₆H₄)}], isomeric with [Os₃H(CO)₉{µ₃-NC₅H₄(NCH₂Ph)}]. Vigorous treatment of [Os₃(CO)₁₂] with an excess of the 2-substituted pyridines gives the dinuclear species, [Os₂(CO)₆(µ-NC₅H₄X)₂](X = 0 or NH), which exist as cis and trans isomers. Amphoteric behaviour is illustrated by the reversible addition of PMe₂Ph to the 2-aminopyridine derivative [OS₃H(CO)₉(µ₃-NC₅H₄X)](X = NH) and by its single and double protonations at osmium.