Reactions of Fe₂(<i>μ</i>‐odt)(CO)₆ (odt = 1, 3‐oxadithiolate) with small bite‐angle diphosphines to afford the monodentate, chelate, and bridge diiron complexes: Selective substitution, structures, protonation, and electrocatalytic proton reduction

Abstract

Selective substitutions of Fe 2 ( μ ‐odt)(CO) 6 (odt = 1,3‐oxadithiolate, A ) and small bite‐angle diphosphines (Ph 2 P) 2 X [X = CH 2 (dppm) or N (CH 2 CHMe 2 ) (dppa)] have been well investigated in this study. With Me 3 NO·2H 2 O in MeCN at room temperature, the reaction of A and dppm produced the monodentate complex [Fe 2 ( μ ‐odt)(CO) 5 ( κ 1 ‐dppm)] ( 1 ), whereas the similar reaction with dppa afforded the chelate complex [Fe 2 ( μ ‐odt)(CO) 4 ( κ 2 ‐dppa)] ( 2 ). Using UV irradiation in toluene emitting at 365 nm, the treatment of A and dppm rarely resulted in the formation of the bridge complex [Fe 2 ( μ ‐odt)(CO) 4 ( μ ‐dppm)] ( 3 ), whereas the similar treatment with dppa formed the chelate complex 2 . Under thermolysis condition, refluxing solution of A with dppm or dppa gave the bridge complex 3 and [Fe 2 ( μ ‐odt)(CO) 4 ( μ ‐dppa)] ( 4 ), respectively, in which the former was formed in toluene (110 °C) but the latter was produced in xylene (138 °C). All the new complexes 1 – 4 obtained above were characterized by element analysis, FT‐IR, NMR ( 1 H, 31 P) spectroscopies, and particularly for 1 – 3 by X‐ray crystallography. Furthermore, the in situ protonations of 2 with a weak acid HOAc (acetic acid) and a strong acid TFA (trifluoroacetic acid) are explored by means of FT‐IR and NMR ( 1 H, 31 P) spectra. In addition, the electrochemical behaviors of 2 – 4 are studied and compared through cyclic voltammetry (CV) in the absence and presence of a strong acid (TFA) as a proton source, indicating that they all are active for electrocatalytic proton reduction to hydrogen (H 2 ).