Hydride Dynamics in Triosmium and Triruthenium Carbonyl Clusters:Synthesis, Reactivity and Dynamics of a Trihydrido Quinoline-4-Carboxaldehyde Triosmium Cluster

摘要

An overview of the dynamical processes involving the hydrido ligand in triosmium and triruthenium carbonyl clusters is presented. The relationship between the mechanisms of hydride motions and the other ligands in the cluster are discussed for mono- di- and trihydrido-clusters. In addition, the reactivity of the electron deficient 46e~- cluster, (μ-H)(μ_3-η~2-C_9H_5N-4-CHO)Os_3(CO)_9 (1) with hydrogen is reported. The reaction gives two isomeric trihydrido clusters, H(μ-H)_2(μ_3-η~2-C_9H_5N- 4-CHO)Os_3(CO)_8 (2) and (μ-H)_3(μ_3-η~2-C_9H_5N-4-CHO)Os_3(CO)_8 (2′) in low yield along with trace amounts of other hydrido clusters. Reaction of the inseparable mixture of 2 and 2′ with triphenylphosphine at ambient temperatures gives two related addition products H(μ-H)_2(μ-η~2-C_9H_5N-4-CHO)Os_3(CO)_8PPh_3 (3) and (μ-H)_3(μ-η~2 -C_9H_5N-4-CHO)Os_3(CO)_8PPh_3 (3′) in a 5:1 ratio. These results contrast with the previously reported trihydrido-derivatives of triosmium μ_3-η~2-imidoyl clusters where only analogues of 2 and 3 are obtained. Clusters 2 and 2′ are rigid on the NMR time scale while 3 exhibits dynamical behavior in the temperature range of-50 to+25 °C. Cluster 3′ is stereochemically rigid in this temperature range. The dynamical behavior of 3 involves the exchange of the terminal and bridging hydrides coupled with tripodal motion of the phosphine substituted osmium atom, a process virtually identical to previously reported trihydrides of the μ_3-η~2-imidoyl triosmium clusters.