Proton reactivity of butterfly oxo and sulfido clusters and structural characterization of HFe3Mn(CO)10(dmpm)(μ4-O)

Phosphine substitution for CO in the butterfly oxo cluster [Fe3Mn(CO)12(μ4-O)]− (1) produces the bis-phosphine clusters [Fe3Mn(CO)10(PR3)2(μ4-O)]− (R=OCH3 (2a), CH3 (2b)) and [Fe3Mn(CO)10(dmpm)(μ4-O)]− (3). In the presence of the strong acid, HSO3CF3, the oxo cluster 1 is not protonated, 3 is protonated at the FeFe backbone of the butterfly, and [Fe3Mn(CO)12(μ4-S)]− (5) loses CO and Mn upon protonation to yield H2Fe3(CO)9(μ3-S) and a manganese containing by-product. The structure of the protonated cluster HFe3Mn(CO)10(dmpm)(μ4-O) (4), determined by single-crystal X-ray diffraction, compared with its parent, 1, compound 4, has elongated metalmetal bonds, a smaller dihedral angle (111° compared to 113°), and shorter wingtip metal-to-oxo ligand distances. Additionally, the carbonyl ligands on 4 shift to accommodate the hydride ligand on the hinge iron metals and the bidentate phosphine ligand spanning the hinge and wingtip iron atoms. The butterfly clusters were characterized by 1H NMR, variable temperature 13C NMR, 31P NMR, and infrared spectroscopy. Crystal data for 4: monoclinic (Cc), a=7.917(2), b=18.541(2), c=16.196(1) Å, β=95.41(1)°, Z=4, R (Rw)=0.022 (0.029).