Ferrous Carbonyl Dithiolates as Precursors to FeFe, FeCo, and FeMn Carbonyl Dithiolates

Reported are complexes of the formula Fe­(dithiolate)­(CO)2(diphos) and their use to prepare homo- and heterobimetallic dithiolato derivatives. The starting iron dithiolates were prepared by a one-pot reaction of FeCl2 and CO with chelating diphosphines and dithiolates, where dithiolate = S2(CH2)22– (edt2–), S2(CH2)32– (pdt2–), S2(CH2)2(C­(CH3)2)2– (Me2pdt2–) and diphos = cis-C2H2(PPh2)2 (dppv), C2H4(PPh2)2 (dppe), C6H4(PPh2)2 (dppbz), C2H4[P­(C6H11)2]2 (dcpe). The incorporation of 57Fe into such building block complexes commenced with the conversion of 57Fe into 57Fe2I4(iPrOH)4, which then was treated with K2pdt, CO, and dppe to give 57Fe­(pdt)­(CO)2(dppe). NMR and IR analyses show that these complexes exist as mixtures of all-cis and trans-CO isomers, edt2– favoring the former and pdt2– the latter. Treatment of Fe­(dithiolate)­(CO)2(diphos) with the Fe(0) reagent (benzylideneacetone)­Fe­(CO)3 gave Fe2(dithiolate)­(CO)4(diphos), thereby defining a route from simple ferrous salts to models for hydrogenase active sites. Extending the building block route to heterobimetallic complexes, treatment of Fe­(pdt)­(CO)2(dppe) with [(acenaphthene)­Mn­(CO)3]+ gave [(CO)3Mn­(pdt)­Fe­(CO)2(dppe)]+ ([3d(CO)]+). Reduction of [3d(CO)]+ with BH4– gave the Cs-symmetric μ-hydride (CO)3Mn­(pdt)­(H)­Fe­(CO)­(dppe) (H3d). Complex H3d is reversibly protonated by strong acids, the proposed site of protonation being sulfur. Treatment of Fe­(dithiolate)­(CO)2(diphos) with CpCoI2(CO) followed by reduction by Cp2Co affords CpCo­(dithiolate)­Fe­(CO)­(diphos) (4), which can also be prepared from Fe­(dithiolate)­(CO)2(diphos) and CpCo­(CO)2. Like the electronically related (CO)3Fe­(pdt)­Fe­(CO)­(diphos), these complexes undergo protonation to afford the μ-hydrido complexes [CpCo­(dithiolate)­HFe­(CO)­(diphos)]+. Low-temperature NMR studies indicate that Co is the kinetic site of protonation.