A new cumulene diiron complex related to the active site of Fe-only hydrogenases and its phosphine substituted derivatives: Synthesis, electrochemistry and structural characterization

Abstract

A new cumulene diiron complex related to the Fe-only hydrogenase active site [(μ-SCH 2C(S) C CH 2)Fe 2(CO) 6] ( 1) was obtained by treatment of (μ-LiS) 2Fe 2(CO) 6 with excess 1,4-dichloro-2-butyne. By controllable CO displacement of 1 with PPh 3 and bis(diphenylphosphino)methane (dppm), mono- and di-substituted complexes, namely [(μ-SCH 2C(S) C CH 2)Fe 2(CO) 5L] ( 2: L = PPh 3; 3: L = dppm) and [(μ-SCH 2C(S) C CH 2)Fe 2(CO) 4L 2] ( 4: L = PPh 3; 5: L = dppm) could be prepared in moderate yields. Treatment of 1 with bis(diphenylphosphino)ethane (dppe) afforded a double butterfly complex [(μ-SCH 2C(S) C CH 2)Fe 2(CO) 5] 2(μ-dppe) ( 7). With dppm in refluxing toluene, a dppm-bridged complex [(μ-SCH 2C(S) C CH 2)Fe 2(CO) 4(μ-dppm)] ( 6) was obtained. These model complexes were characterized by IR, 1H, 31P NMR spectra and the molecular structures of 1, 2 and 5– 7 were determined by single crystal X-ray analyses. The electrochemistry of 1– 3 was studied and the electrocatalytic property of 1 was investigated for proton reduction in the presence of HOAc.