Supermolecular Assembly of Tetra- and Hexanuclear Carbonyl Clusters Using a Novel Polydentate Pyridylphosphine Ligand

The novel heterodentate ligand 2,2‘-bis(diphenylphosphino)-4,4‘-bipyridine (dpbp, 1) was
synthesized and spectroscopically characterized. The reaction of 1 with 2 equiv of [Rh6(CO)15(NCMe)] or [Ru6C(CO)17] afforded the linked double-homometallic clusters [{Rh6(CO)14}2dpbp] (2) and [{Ru6C(CO)15}2dpbp] (3), respectively, where 1 is coordinated to the hexanuclear
metal cores in a P,N bridging mode. Treatment of [Ru6C(CO)17] with an excess of dpbp results
in formation of the complex [Ru6C(CO)15dpbp] (4) to leave a phosphinopyridyl functionality
uncoordinated. The heterocluster double compounds [Ru6C(CO)15dpbpRh6(CO)14] (5) and
[Ru6C(CO)15dpbpIr4(CO)10] (7) were obtained by the reactions of 4 with [Rh6(CO)15(NCMe)]
and [Ir4(CO)11Br][NBu4]. The mixed-valence complex [{Ru6C(CO)15(dpbp)}2RhI2(CO)Cl2] (6)
was synthesized via the interaction of 2 equiv of 4 with the dimer [Rh2(CO)4Cl2]. The tri-
and tetracluster compounds {Ru6C(CO)15(dpbp)}2Ir4(CO)10 (8) and {Ru6C(CO)15(dpbp)}3Ir4(CO)8 (10) were prepared by treatment of 7 with 1 or 2 equiv of 4, respectively. Cluster 8
appears to be unstable toward loss of one CO ligand and formation of {Ru6C(CO)15(dpbp)}2Ir4(CO)9 (9), where one {Ru6C(CO)15dpbp} unit is coordinated to the tetrairidium framework
in a κ1 mode through the phosphorus atom and another {Ru6C(CO)15dpbp} fragment in a
P,N bridging mode. The structures of 2, 3, and 5 were established by X-ray crystallography
and by ESI+ mass and 1H and 31P{1H} NMR spectroscopy. The other supermolecular
complexes 4 and 6−10 were characterized by spectroscopic methods.