Oxidative addition of phosphine-tethered thiols to iron carbonyl:: Binuclear phosphinothiolate complexes, (μ-SCH2CH2PPh2)2Fe2(CO)4, and hydride derivatives

The mononuclear complex Fe(CO)(4)(PPh2CH2CH2SH), 1, is isolated as an intermediate in the overall reaction of PPh2CH2CH2SH with [Fe-0(CO)(4)] sources to produce binuclear bridging thiolate complexes. Photolysis is required for loss of CO and subsequent S-H activation to generate the metal-metal bonded Fe-l-Fe-l complex, (mu-SCH2-CH2PPh2)(2)Fe-2(CO)4, 2. Isomeric forms of 2 derive from the apical or basal position of the P-donor ligand in the pseudo square pyramidal S2Fe(CO)(2)P coordination spheres. This position in turn is dictated by the stereochemistry of the mu-S-CH2 bond, designated as syn or anti with respect to the Fe2S2 butterfly core. Addition of strong acids engages the Fel-Fel bond density as a bridging hydride, [(mu-H)-anti-2](+)[SO3CF3](-) or [(mu-H)-syn-2](+)[SO3CF3]-, with formal oxidation to Fe-parallel to-H-Fe-parallel to. Molecular structures of anti-2, syn-2, and [(mu-H)-anti-2]+[SO3CF3](-) were determined by X-ray crystallography and show insignificant differences in distance and angle metric parameters, including the Fe-Fe bond distances which average 2.6 A. The lack of coordination sphere rearrangements is consistent with the ease with which deprotonation occurs, even with the weak base, chloride. The Fel-Fel bond, supported by bridging thiolates, therefore presents a site where a proton might be taken up and stored as a hydride without impacting the overall structure of the binuclear complex.