Metal-carbon multiple bonds: novel syntheses and reactions of aminocarbyne complexes of tungsten

Article abstract of DOI:10.1016/0022-328X(95)05483-6

Syntheses and reactions of low and high valence tugsten aminocarbyne complexes are reported.The addition of LiNⁱPr2 to W(CO)6 in Et2 O affords the imidoyl complex Li<(CO)5WC(O)NⁱPr2>, which is converted to the aminocarbyne complexes trans-X(CO)4W<*>CNⁱPr2 (X = Cl (1a) or Br (1b)) after treatment with C2O2X2.Complexex 1a and 1b react with γ-picoline (pic), 2.2'-bipyridine (bpy) and 1.10-phenanthroline (phen) to yield the CO substitution products X(CO)2L2W<*>CNⁱPr2 (3a, 3b, 5a and 6a) (L = pic (3); L2 = bpy (5); or phen (6)).Analogous reactions are also observed for the dicyclohexylaminocarbyne complexes trans- X(CO)4W<*>CNCy2 (X = Cl (2a) or Br (2b)), affording the compounds X(CO)2L2W<*>CNCy2 (4a, 7b and 8b) (L = pic (4); L2 = bpy (7) or phen (8)).Complexes 1a-8b are useful starting materials for the synthesis of a variety of low and high valence tungsten aminocarbyne complexes.Thus treatment of 1a and 1b or 3a and 3b with ^tBuNC results in the formation of the isocyanide derivatives X(CO)2(^tBuNC)2W<*>CNⁱPr2 (X = Cl (9a) or Br (9b)).Complex 9a is converted to the monocarbonyl complex Cl(CO)(^tBuNC)3W<*>CNⁱPr2 (10a), when it is treated with ^tBuNC in refluxing toluene.Complexes 3b and 4a react with NaCp and KCp^* (Cp^* = C5Me5) to give the half-sandwich aminocarbyne complexes Cp(CO)2W<*>CNR2 (R = ⁱPr (11) or Cy (12) and Cp^<*>(CO)2W<*>CNⁱPr2 (13) respectively.Similarly, 7b or 8b are converted to the dinuclear aminocarbyne complex NEt4<(CO)4Mo(μ-PPh2)2W(CO)2CNCy2> (14b), when they are treated with K2 and Br.No carbyne-carbonyl coupling is observed in these reactions.Oxidation of 1a with PhICl2 and 1b with Br2 in 1,2-dimethoxyethane (DME) affords after elimination of all CO ligands the 16-electron aminocarbyne complexes mer-X3(DME)W<*>CNⁱPr2 (X = Cl (15a) or Br (15b)).In comparison, oxidation of 11-13 with PhICl2 yields the 18-electron aminocarbyne complexes Cp(Cl)2(CO)W<*>CNR2 (R = ⁱPr (16) or Cy (17)) and Cp^*(Cl)2(CO)W<*>CNⁱPr2 (18) respectively.Restricted rotation of the amino group about the C_carbyne-N bond is observed for the first time in the complexes 16 and 17 originating from the competition of the carbyne and the carbonyl ligand for metal-ligand back bonding in these compounds.Keywords: Tungsten; Aminocarbyne complexes; Multiple bonds; Oxidation