4-Aminobenzylidyne: a versatile precursor for extended unsaturated alkylidyne ligands†

Abstract

The 4-aminobenzylidyne tungsten complexes [W(CC₆H₄NH₂-4)X(CO)₂(pic)₂] 1 (X = Cl a or Br b) have been prepared by sequential reaction of [W(CO)₆] with LiC₆H₄N(SiMe₃)₂-4 in diethyl ether and C₂O₂Cl₂ or C₂O₂Br₂ and 4-methylpyridine (pic) in CH₂Cl₂. Substitution of the picoline ligands by tmen (Me₂NCH₂CH₂NMe₂) and dppe (Ph₂PCH₂CH₂PPh₂) afforded the complexes [W(CC₆H₄NH₂-4)X(CO)₂(L₂)] (L₂ = tmen 2, X = Cl a or Br b; dppe 3, X = Cl a or Br b). The amino group of the new alkylidyne complexes undergoes typical functional group transformations. Treatment of complexes 2 with pyridine-2-carbaldehyde afforded the Schiff-base derivatives [W{CC₆H₄(NCHC₅H₄N-2)-4}X(CO)₂(tmen)] 5 (X = Cl a or Br b). Formylation of complexes 2 with acetic formic anhydride afforded the formamides [W(CC₆H₄NHCHO-4)X(CO)₂(tmen)] 6 (X = Cl a or Br b). The isocyanide derivatives [W(CC₆H₄NC-4)X(CO)₂(tmen)] 11 (X = Cl a or Br b) were obtained by dehydration of complexes 6 with triphosgene–NEt₃. The molecular structures of 3a, 4b, 8a, 9a and 10b were determined by X-ray crystallography.