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The reaction of the benzothiazolate-capped triosmium clusters Os 3 (CO) 9 (μ 3 ,η 2 -C 7 H 3 NSR)(μ-H) ( 1a , R = H; 1b , R = Me) with PPh 3 proceeds readily at room temperature with a μ 3 ,η 2 → μ,η 2 hapticity change in the benzothiazolate heterocycle to furnish Os 3 (CO) 9 (PPh 3 )(μ,η 2 -C 7 H 3 NSR)(μ-H) ( 2a , R = H; 2b , R = Me) in high yields. X-ray crystallography has confirmed the regiospecific nature of this reaction where the PPh 3 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 Os 3 clusters as a result of ligand isomerization, decarbonylation, and ortho metalation of the ancillary PPh 3 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 PPh 3 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 PPh 3 ligand. [ABSTRACT FROM AUTHOR]