Cationic iminoacyl-carbonyl tungsten complexes of the type [W(CO) (η2-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)(η2MeN=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(η 2alkyne)(η2-MeN=CR)(acac)2]+ complexes (5a-d) with a variable electron donor η2-alkyne paired with the η2-iminoacyl ligand in the W(II) coordination sphere. PMe3 adds to 1a or 5b to form [W(L)(η2-MeN=C(PMe 3)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(η2-MeC≡CMe)(η2- 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 η2-iminium complex [W(η2-MeC≡CMe)(η2-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)(η2-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 η2-iminium ligand.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry