Synthesis, characterization, and crystal structure of a quadruply bonded dimolybdenum(II) complex containing the water-soluble phosphine 1,3,5-triaza-7-phosphaadamantane (PTA)

The quadruply bonded molybdenum(II)–molybdenum(II) complex, tetrachlorotetrakis(1,3,5-triaza-7-phosphaadamantane) dimolybdenum(II), Mo2Cl4(PTA)4, was synthesized by reaction of 1,3,5-triaza-7-phosphaadamantane (PTA) with K4[Mo2Cl8] in refluxing methanol. The complex was characterized using 1H and 31P NMR, and UV–Vis spectroscopy, X-ray crystallography, and cyclic voltammetry. The Mo–Mo separation in the solid state structure is 2.13 Å, with the PTA and chloride ligands in an eclipsed arrangement with a P–Mo–Mo–Cl twist angle of 1.75(3)°. The 31P NMR spectrum contains a single peak at −62.8 ppm, and the 1H NMR spectrum exhibits two singlets of equal height at 4.60 and 4.33 ppm. The UV–Vis spectrum contains three absorbance features at 615, 363, and 231 nm, with the absorbance at 615 nm due to the δ → δ* transition. The one electron oxidation of Mo2Cl4(PTA)4 is reported at E1/2 = 0.91 V relative to Ag/Ag+ in CH2Cl2. Also discussed is the reactivity of the molybdenum complex with CN−, H2O, and HCl.