Cationic iminoacyl-carbonyl tungsten complexes of the type [W(CO) (eta(2)-MeN=CR)(acaC)(2)](+) (acac = acetylacetonate; R = Ph (1a), Me (1b)) easily undergo thermal substitution of CO with two-electron donors to yield [W(L)(eta(2)-MeN=CR)(acac)(2)](+) (L tert-butylisonitrile [R = Ph (2a), Me (2b)], 2,6-dimethylphenylisonitrile [R = Me (2c)], triphenylphosphine [R Ph (3a), Me (3c)], and tricyclohexylphosphine [R = Ph (3b)]). Tricyclohexylphosphine complex 3b exhibits rapid, reversible phosphine ligand exchange at room temperature on the NMR time scale. Photolytic replacement of carbon monoxide with either phenylacetylene or 2-butyne occurs efficiently to form [W(eta(2)-alkyne)(eta(2)-MeN=CR)(acac)(2)](+) complexes (5a-d) with a variable electron donor eta(2)-alkyne paired with the eta(2)-iminoacyl ligand in the W(II) coordination sphere. PMe3 adds to 1a or 5b to form [W(L)(eta(2)-MeN=C(PMe3)Ph)(acac)(2)](+) [L = CO (4), MeC CMe (6)] via nucleophilic attack at the iminoacyl carbon. Addition of Na[HB(OMe)(3)] to 5b yields W(eta(2)-MeC CMe) (eta(2)-MeN=CHPh)(acac)(2), 8, which exhibits alkyne rotation on the NMR time scale. Addition of MeOTf to 8 places a second methyl group on the nitrogen atom to form an unusual cationic eta(2)-iminium complex [W(eta(2)-MeC CMe) (eta(2)-Me2N=CHPh)(acaC)(2)][OTf] (9[OTf], OTf = SO3CF3). X-ray structures of 2,6-dimethylphenylisonitrile complex 2c(BAr'(4)], tricyclohexylphosphine complex 3b[BAr'(4)], and phenylacetylene complex 5a[BAr'(4)] confirm replacement of CO by these ligands in the [W(L)(eta(2)-MeN=CR)(acac)(2)](+) products. X-ray structures of alkyne-imine complexes 6[BAr'(4)] and 8 show products resulting from nucleophilic addition at the iminoacyl carbon, and the X-ray structure of 9[BAr'(4)] reflects methylation at the imine nitrogen to form a rare eta(2)-iminium ligand.