Two equivalents of acetylacetonate ( acac) have been successfully introduced into a monomeric tungsten( II) coordination sphere. With the tetracarbonyltriiodotungsten( II) anion as a precursor, the formation of a tungsten( II) bis( acac) tricarbonyl complex, W( CO)(3)( acac)(2), 1, has been accomplished. The addition of PMe3 or PMe2Ph to tricarbonyl complex 1 formed tungsten( II) bis( acac) dicarbonylphosphine complexes 2a and 2b, respectively. Single-crystal X-ray diffraction studies of the parent tricarbonyl complex, 1, and dicarbonyl trimethylphosphine complex 2a confirmed seven-coordinate geometries for both complexes. Variable-temperature H-1 and C-13 {H-1} NMR spectroscopy revealed fluxional behavior for these seven- coordinate molecules: rapid exchange of the three carbon monoxide ligands in 1 was observed, and movement of the phosphine ligand through a mirror plane in a C S intermediate species was observed for both 2a and 2b. Tricarbonyl complex 1 reacted readily with alkyne reagents to form bis( acac) monocarbonylmonoalkynetungsten( II) complexes 3a ( PhC CH) and 3b ( MeC CMe). Variable-temperature 1H NMR spectroscopy was used to probe rotation of the alkyne ligand in 3a and 3b. The introduction of two alkyne ligands was accomplished thermally using excess PhC CPh to form bis( alkyne) complex 4 which was characterized crystallographically, as well as by H-1 and C-13 NMR spectroscopy. The availability of W( CO)(3)( acac)(2) as a source of the W( acac)(2) d(4) moiety lies at the heart of the chemistry reported here.