Ultrafast Chelation Dynamics of Cyclopentadienyl Manganese Tricarbonyl Derivatives with Pendant Sulfides

The photoinduced dynamics of two new [η 5 -C 5 H 4 C(O)R]Mn(CO) 3 complexes 2 (R = CH(SCH 3 ) 2 ) and 3 (R = C(SCH 3 ) 3 ) have been investigated in n -heptane solution on the ps to μs time scale by UV-pump IR-probe transient absorption spectroscopy. Irradiation of 2 at 266 or 289 nm induces CO loss to yield two initial products in approximately equal abundance, assigned by their CO-stretching bands to be a heptane solvate of the unsaturated Mn fragment and a ring-formed product in which the pendant sulfide moiety is coordinated to the metal center. In direct analogy with the previously observed behavior of [η 5 -C 5 H 4 C(O)CH 2 (SCH 3 )]Mn(CO) 3 ( 1 ), the solvate reacts through a secondary pathway to afford the S-bound product within 200 ns. Irradiation of 3 under identical conditions yields the chelated product exclusively, with no evidence of a competing solvation pathway.