Phosphine‐Ligated Cobalt(II) Acetylacetonate Complexes

Cobalt(II) acetylacetonate complexes bearing a phosphine ligand can be key intermediates or precursors to cobalt‐based catalysts; however, they have been rarely studied, especially from a molecular structure point of view. This work is focused on the understanding of how different phosphines react with Co(acac) 2 (acac = acetylacetonate). To do so, a variety of analytical tools, including NMR and IR spectroscopy, X‐ray crystallography, mass spectrometry, and elemental analysis, have been used to study the reactions and characterize the isolated products. These results have shown that the monodentate ligand, HPPh 2 , binds to Co(acac) 2 weakly and reversibly to produce Co 2 (acac) 4 (HPPh 2 ), whereas the bidentate ligand, 1,2‐bis(diphenylphosphino)ethane (dppe), interacts with Co(acac) 2 more strongly to yield a 1D coordination polymer of Co(acac) 2 (dppe). 2‐(Dicyclohexylphosphino)methyl‐1 H‐pyrrole ( Cy PN H ), which is a pyrrole‐tethered phosphine, forms an unusual 5‐coordinate cobalt complex, Co(acac) 2 ( Cy PN H ), in which the pyrrole moiety participates in a bifurcated hydrogen–bonding interaction with the [acac] – ligands. In contrast, another bidentate ligand, 4,5‐bis(diphenylphosphino)‐9,9‐dimethylxanthene (xantphos), fails to react with Co(acac) 2 , presumably due to its wide bite angle and difficulty in bridging two metals.