Backbone modified small bite-angle diphosphines: Synthesis, structure, and DFT evaluation of the thermal activation products based on Os3(CO)10{μ-Ph2PC(Me)2PPh2}

Alkyne activation and polyhedral reorganization in benzothiazolate-capped osmium clusters on reaction with diethyl acetylenedicarboxylate (DEAD) and ethyl propiolate

The reactivity of the face-capped benzothiazolate clusters HOs₃(CO)₉[μ₃-C₇H₃(R)NS] (1a, R = H; 1b, R = 2-CH₃) with alkynes has been investigated. 1a reacts with DEAD at 67 °C to furnish the isomeric alkenyl clusters Os₃(CO)₉(μ-C₇H₄NS)(μ₃-EtO₂CCCHCO₂Et) (2a and 3a). X-ray crystallographic analyses of 2a and 3a have confirmed the stereoisomeric relationship of these products and the regiospecific polyhedral expansion that follows the formal transfer of the hydride to the coordinated alkyne ligand in HOs₃(CO)₉(μ-C₇H₄NS)(η²-DEAD). The significant structural differences between the two isomers, as revealed by the solid-state structures, derives from the regiospecific cleavage of one of the three Os-Os bonds in the intermediate alkenyl cluster Os₃(CO)₉(μ-C₇H₄NS)(η¹-EtO₂CCCHCO₂Et), which follows hydride transfer to the coordinated alkyne ligand in the pi compound HOs₃(CO)₉(μ-C₇H₄NS)(η²-DEAD). Control experiments confirm the reversibility of the reaction leading to the formation of 2a and 3a. Whereas heating either isomer in refluxing THF or benzene affords a binary mixture containing 2a and 3a, thermolysis in refluxing toluene leads to the activation of the alkenyl ligand and formation of the new cluster Os₃(CO)₉(μ-C₇H₄NS)(μ₃-EtO₂CCCH₂) (4). 4 was independently synthesized from 1a and ethyl propiolate at room temperature. The computed mechanisms that account for the formation of 2a and 3a are presented, along with the mechanism for the reaction of 1a with ethyl propiolate to give 4.

Catalytic applications of small bite-angle diphosphorus ligands with single-atom linkers

Diphosphorus ligands connected by a single atom (R₂PEPR₂; E = CR₂, CCR₂and NR) give chelating ligands with very small bite-angles as well as enable access to other properties such as bridging modes and hemilability. ThisPerspectivereviews the properties of diphosphorus ligands featuring a single-atom linker and their applications in catalysis, including transformations of alkenes and transfer hydrogenation and hydrogen-borrowing reactions.