Reactions of Fe2(μ-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

Selective substitutions of Fe-2(mu-odt)(CO)(6) (odt = 1,3-oxadithiolate, A) and small bite-angle diphosphines (Ph2P)(2)X [X = CH2 (dppm) or N (CH2CHMe2) (dppa)] have been well investigated in this study. With Me3NO center dot 2H(2)O in MeCN at room temperature, the reaction of A and dppm produced the monodentate complex [Fe-2(mu-odt)(CO)(5)(kappa(1)-dppm)] (1), whereas the similar reaction with dppa afforded the chelate complex [Fe-2(mu-odt)(CO)(4)(kappa(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(mu-odt)(CO)(4)(mu-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(mu-odt)(CO)(4)(mu-dppa)] (4), respectively, in which the former was formed in toluene (110 degrees C) but the latter was produced in xylene (138 degrees C). All the new complexes 1-4 obtained above were characterized by element analysis, FT-IR, NMR (H-1, P-31) 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 (H-1, P-31) 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).