Syntheses and characterization of dimolybdenum and dirhodium complexes containing 2-pyridylphosphine ligands

Reaction of dimolybdenum tetrakis(trifluoroacetate) with 2-pyridylphosphines leads to a replacement of one or two of the trifluoroacetato ligands as equatorial ligands, depending on the excess ligand used. In the product molecules, the replaced acetato ligands are found as monodentate ligands in the axial positions and the Mo-Mo quadruple bond is significantly weakened. The examined complexes are fully characterized, including two single crystal X-ray structures. Dimolybdenum tetraacetate does not react with 2-pyridylphoshpines. Dirhodium tetraacetate, in contrast, reacts readily with 2-pyridylphosphines. The 2-pyridylphosphines are attached to the product molecule in axial position by a P → Rh donor interaction, which weakens the Rh-Rh single bond. Reaction of 2-pyridylphosphines with dirhodium tetrakis(trifluoroacetate) leads to a product mixture.