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)A, 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.