Improved Access to 'Butterfly' Di-Iron Dithiolates Fe₂(-SR)₂(CO)₆ and their Mono- and Bis(phosphine) Adducts

A series of Fe-2(mu-SR)(2)(CO)(6) complexes {R=Me (1(Me)), Et (1(Et)), Pr (1(Pr)), iPr (1(iPr)), tBu (1(tBu)), PhCH2 (1(Bn)) and Ph (1(Ph))} have been synthesised. Complexes 1(Me), 1(tBu), 1(Bn) and 1(Ph) were produced by addition of S2R2 to Fe-3(CO)(12), with all but 1(tBu) giving excellent yields. Two isomers of 1(Me) and 1(Ph) were isolated: the anti- and 'open' syn-products. Complexes 1(Et), 1(Pr) and 1(iPr) were synthesised by treatment of RSH with Fe-3(CO)(12); two isomers of each complex were isolated. Addition of one equivalent of PR'(3) (R'= Me, Cy, Ph) yields the corresponding mono(phosphine) adducts, whilst use of two equivalents of the phosphine (under mild condition, reflux, or irradiation using a deep blue LED depending on SR group) affords the corresponding bis(phosphine) adducts in good to excellent yield. Treatment of 1(Ph) or 1(Me) with two equivalents of PMe3 gives the corresponding bis-substituted phosphines when carried out in the absence of light but leads to oxidative cleavage to Fe(mu-SPh)(2)(PMe3)(2)(CO)(2) and Fe(mu-SMe)(2)(PMe3)(2)(CO)(2), respectively, under blue light irradiation. Treatment of 1(Pr) with two equivalents of PCy3 under blue light irradiation leads to reductive breakdown of the Fe Fe bond to yield Fe(CO)(3)(PCy3)(2), but in the dark at room temperature the desired product Fe-2(mu-SPr)(2)(PCy3)(2)(CO)(4) may be isolated. Single crystal X-ray structures were obtained for most family members of 'butterfly' {Fe2S2} cores. Cyclic voltammetry shows PMe3-containing complexes undergo irreversible oxidation, whereas both PCy3 and PPh3 complexes show one (quasi)reversible oxidation, IR of in situ protonation showed COv blue shifting around 80-100 cm(-1), while P-31{H-1} NMR spectroscopy showed shifting to low field.