Synthesis, characterization and theoretical studies of new heterometallic carbonyl clusters bridged by 44′-dipyridyl unit

4,4′-Bipyridine (4,4′-bipy) reacts with the activated cluster [Os3(CO)10(NCMe)2] readily at room temperature to give a mixture of [Os3(μ-H) [Os3(μ-H)(CO)10(μ-NC5H3C5H3N)Os3(μ-H)(CO)10] (2), the composition of which depends upon the reaction conditions and the ratio of the reactants. The reactivities of the metalloligand precursor 1 with a pendant nitrogen atom towards [W(CO)5(THF)] and [Re(CO)5Cl] have been investigated, affording two new heterometallic clusters [Os3(μ-H)(CO)10(μ-NC5H3C5H4N)W (CO)5] (3) and [ReCl(CO)3{Os3(μ-H)(CO)10(μ-NC5H3C5H4N)}2] (4) in moderate to good yields. Compound 4 can also be prepared from the reaction between [Os3(CO)10(NCMe)2] and [ReCl(CO)3(4,4′-bipy)2]. The X-ray crystal structures of compounds 1-3 have been determined and molecular orbital calculations on these complexes using density functional theory (DFT) method reveal that they all have similar orbitals in the LUMO region. Clusters 1 and 2 have the Os-Os σ-bonding orbitals as their HOMO orbitals while cluster 3 has the 't2g' set orbitals of the W(CO)5fragment as the HOMO orbitals.