Dynamic behavior and alkyne insertion reactions of alkenyl- and thiolate-bridged diiron carbonyl complexes

The alkenyl- and thiolate-bridged diiron carbonyl complexes [Fe 2 ( & mu;-SC 6 H 4 CR 1 CH)(CO) 6 ] (R 1 = H or Me), which are derived from [Fe 3 (CO) 12 ] and benzothiophenes, reacted with alkynes (R 2 CCR 3 ) under photoirradiation conditions to form the acyl complexes [Fe 2 { & mu;-SC 6 H 4 CR 1 CHCR 2 C(R 3 )CO}(CO) 5 ]. In this reaction, an alkyne and CO are inserted into the Fe-alkenyl bond, and the bulky substituents of alkynes, including a redox active ferrocenyl group, occupy the R 3 position. To elucidate the reaction pathway, the reaction of the in situ generated acetonitrile complex [Fe 2 ( & mu;-SC 6 H 4 CHCH)(CO) 5 (NCCH 3 )] with ethynylbenzene was monitored by 1 H NMR spectroscopy. The results demonstrated that the acetonitrile complex undergoes facile insertion of the alkyne, which is followed by CO insertion to give the corresponding acyl complex [Fe 2 { & mu;-SC 6 H 4 (CH) 3 C(Ph)CO}(CO) 5 ]. The reactivity of the bridging alkenyl moiety is related to the dynamic behavior of the alkenyl-thiolate ligand (SC 6 H 4 CHCH) 2- as well as the entering alkyne. Temperature dependent 31 P NMR measurements of the dmpm-bridged complex [Fe 2 ( & mu;-SC 6 H 4 CHCH)( & mu;-dmpm)(CO) 4 ] (dmpm = bis(dimethylphosphino)methane) revealed that the activation parameters for the flip-flop motion of the alkenyl-thiolate ligand are AH & DDAG; = 46.7(7) kJ mol -1 and AS & DDAG; = -46(2) J mol -1 K -1 .& COPY; 2023 Elsevier B.V. All rights reserved.