Reactions of the face-capped benzothiazolate-substituted clusters Os3(CO)9(μ3,η2-C7H3NSR)(μ-H) (R = H, Me) with PPh3: Kinetic formation of Os3(CO)9(PPh3)(μ,η2-C7H3NSR)(μ-H) and thermally induced ligand isomerization

Abstract

The reaction of the benzothiazolate-capped triosmium clusters Os3(CO)9(μ3,η2-C7H3NSR)(μ-H) (1a, R = H; 1b, R = Me) with PPh3 proceeds readily at room temperature with a μ3,η2 → μ,η2 hapticity change in the benzothiazolate heterocycle to furnish Os3(CO)9(PPh3)(μ,η2-C7H3NSR)(μ-H) (2a, R = H; 2b, R = Me) in high yields. X-ray crystallography has confirmed the regiospecific nature of this reaction where the PPh3 ligand is bound to the osmium atom that serves as the coordination site for the hydride and the metalated-carbon atom associated with the edge-bridged benzothiazolate ligand. The thermolysis of 2a and 2b in boiling toluene affords several new Os3 clusters as a result of ligand isomerization, decarbonylation, and ortho metalation of the ancillary PPh3 ligand. The new products have been isolated and characterized by a combination of spectroscopic methods and X-ray crystallography in the case of 3b, 4b, 5b and 6b. Clusters 3b and 4b are isomers of 2b and differ in the location of the hydride and PPh3 ligands relative to the benzothiazolate moiety. Electronic structure calculations on the isomeric clusters 2b, 3b, and 4b confirm that 2b is the kinetic product of ligand substitution, accounting for its rearrangement to the latter two isomers upon heating. Cluster 5b contains a face-capping benzothiazolate moiety and is shown by DFT calculations to derive from a site-selective loss of an axial CO group in 4b. Cluster 6a,b formed from 5a,b as a result of further decarbonylation with concomitant ortho metalation of one of the phenyl groups of the coordinated PPh3 ligand.