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

Abstract

Syntheses and reactions of low and high valence tungsten aminocarbyne complexes are reported. The addition of LiN iPr 2 to W(CO) 6 in Et 2O affords the imidoyl complex Li[(CO) 5WC(O)N iPr 2], which is converted to the aminocarbyne complexes trans-X(CO) 4W≡CN iPr 2 (X = Cl ( 1a) or Br ( 1b) react with γ-picoline (pic), 2,2′-bipyridine (bpy) and 1.10-phenanthroline (phen) to yield the CO substitution products X(CO) 2L 2W≡CN iPr 2 ( 3a, 3b, 5a, and 6a) (L = pic ( 3); L 2 = bpy ( 5); or phen ( 6)). Analogous reactions are also observed for the dicyclohexylaminocarbyne complexes trans-X(CO) 4W≡CNCy 2 (X = Cl ( 2a) or Br ( 2b)), affording the compounds X(CO) 2L 2W≡CNCy 2 ( 4a, 7b and 8b) (L = pic ( 4); L 2 = 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≡CN iPr 2 (X = Cl ( 9a) or Br ( 9b)). Complex 9a is converted to the monocarbonyl complex Cl(CO)( tBuNC) 3 W≡ CN iPr 2 ( 10a), when it is treated with tBuNC in refluxing toluene. Complexes 3b and 4a react with NaCp and KCp ∗ ( Cp ∗ = C 5 Me 5 ) to give the half-sandwich aminocarbyne complexes Cp(CO) 2 W≡ CNR 2 ( R = iPr ( 11) or Cy ( 12)) and Cp ∗( CO) 2 W≡ CN iPr 2 ( 13) respectively. Similarly, 7b or 8b are converted to the dinuclear aminocarbyne complex NEt 4[(CO) 4Mo(μ-PPh 2) 2W(CO) 2CNCy 2] ( 14b), when they are treated with K 2[ cis-Mo(CO) 4(PPh 2) 2] and [NEt 4]Br. No carbyne-carbonyl coupling is observed in these reactions. Oxidation of 1a with PhICl 2 and 1b with Br 2 in 1,2-dimenthoxyethane (DME) affords after elimination of all CO ligands the 16-electron aminocarbyne complexes mer-X 3(DME)W≡CN iPr 2 (X = Cl ( 15a) or Br ( 15b)). In comparison, oxidation of 11–13 with PhICl 2 yields the 18-electron aminocarbyne complexes Cp(Cl) 2(CO)W ≡ CNR 2 (R = iPr ( 16) or Cy ( 17)) and Cp ∗( Cl) 2 (CO)W ≡ CN iPr 2 ( 18) respectively. Restricted rotation of the amino group about the C caryneN bond is observed for the first time in the complexes 16 and 17 orignating from the competition of the carbyne and the carbonyl ligand for metal-ligand back bonding in these compounds.