Novel Six-Coordinate Oxorhenium “3 + 2” Mixed-Ligand Complexes Carrying the SNS/PO Donor Atom Set: Synthesis and Characterization

Replacing the monothiolate group of the so-called “3 + 1” mixed-ligand oxorhenium(V) complexes with the
bidentate phosphinophenolate ligand produces novel “3 + 2” mixed-ligand complexes carrying the SNS/PO donor
atom set. Thus, reactions of either [ReOCl3(L)]- or [ReOCl2(L)(PPh3)] (HL = o-HOC6H4P(C6H5)2) with
aminedithiol (H2Ln) in dichloromethane methanol solutions lead to six-coordinate mixed-ligand oxo−Re(V)
complexes of the type [ReO(Ln)(L)], where H2L1 = CH3CH2N(CH2CH2SH)2 (1), H2L2 = (CH3CH2)2NCH2CH2N(CH2CH2SH)2 (2), and H2L3 = CH3CH2SCH2CH2N(CH2CH2SH)2 (3). The coordination geometry around
rhenium is distorted octahedral with the SNS donors of the aminedithiolate and the phosphorus of the
phosphinophenolate ligand defining the equatorial plane, while the apical positions are occupied by the oxo group
and the oxygen atom of the HL ligand, as shown by single-crystal X-ray analyses of 1 and 3. The strong metal−phosphorus bonds together with the chelating properties of both ligands contribute to the stability of 18-electron
[ReO(Ln)(L)] complexes. In fact, these six-coordinate species appear to be much more substitution inert than the
“3 + 1” analogous complexes vs excess thiolate, such as cysteine or glutathione, during appropriate challenge
reactions.