Tungsten(II) Monocarbonyl Bis(acetylacetonate): A Fourteen-Electron Docking Site for η² Four-Electron Donor Ligands

Tungsten(II) tricarbonyl bis(acetylacetonate) readily loses two equivalents of carbon monoxide upon exposure to nitrile reagents. Nitriles bind to tungsten as four-electron donors via their π-bonds, as previously reported with alkyne ligands. Imines, aldehydes, and ketones also bind to the tricarbonyl reagent as four-electron donors with two electrons originating from the π-bond and the final two electrons stemming from heteroatom lone pair donation. Experimental data suggest a high degree of double-bond character between tungsten and the heteroatom of the imine, aldehyde, or ketone. These findings are supported by DFT calculations on model complexes.