LAUSR

Abstract A series of [Ru 2 (CO) 5 (μ-SCH 2 CH 2 CH 2 S)PXS] complexes ( Ru 2 -S 2 -PXS , X = phosphine ligands, S = 1–8) have been synthesized and evaluated for their photocatalytic H 2 generation efficiencies from formic acid decomposition. The [Ru 2 (CO) 5 (μ-SCH 2 CH 2 CH 2 S)P( o -C 6 H 4 CH 3 ) 3 ] ( Ru 2 -S 2 -PX4 ) catalyst + P(CH 3 ) 3 ligand exhibited a high turnover frequency of 15,840 h −1 and turnover number of 24,536. A mechanistic investigation of the Ru 2 -S 2 -PX4  + FA/TEA catalyzed photocatalytic H 2 generation reaction using ATR-IR, EI-MS, and NMR techniques suggested that when Ru 2 -S 2 -PX4 was photoirradiated, the P( o -C 6 H 4 CH 3 ) 3 was dissociated from the complex to form a new species, [Ru 2 (CO) 5 (μ-SCH 2 CH 2 CH 2 S)]* ( I ). The free P( o -C 6 H 4 CH 3 ) 3 then attacks a second molecule of Ru 2 -S 2 -PX4 to form Ru 2 -S 2 -(PX4) 2 and release of free CO, which is then combined with species I to form Ru 2 -S 2 . Subsequent attachment of formate ion to species Ru 2 -S 2 -PX4 , Ru 2 -S 2 , and Ru 2 -S 2 -(PX4) 2 to form [Ru 2 (CO) 5 (μ-SCH 2 CH 2 CH 2 S)]-HCOO − ( II ), Ru 2 -S 2 -HCOO − ( II′ ) and Ru 2 -S 2 -PX4 -HCOO − ( II″ ), respectively. Rearrangement of complex II (or II′ or II″ ) and evolution of CO 2 generate a transient complex [Ru 2 (CO) 5 (μ-SCH 2 CH 2 CH 2 S)H] ( III ), which then undergoes a protonation process to yield complex [Ru 2 (CO) 5 (μ-SCH 2 CH 2 CH 2 S)H 2 ] ( IV ). Release of H 2 and re-incorporation of the formate anion as well as evolution of CO 2 regenerates the active complex III and the cycle begins again.