4-Iodobenzylidyne as a precursor ligand for extended unsaturated alkylidyne ligands

Abstract

The synthesis of the 4-iodobenzylidyne and 4-bromobenzylidyne tungsten complexes [W(CC₆H₄Z-4)X(CO)₂(pic)₂] [Z = I; X = Cl, (3a), Z = I, X = Br (3b); Z = Br, X = Cl (4a)] was achieved by sequential reaction of [W(CO)₆] with Li[C₆H₄I-4] or Li[C₆H₄Br-4] in diethyl ether and C₂O₂Cl₂ or C₂O₂Br₂ and 4-picoline (pic, 4-methylpyridine) in CH₂Cl₂. The chloro ligand in 3a could be replaced by the iodo ligand to give 3c (X = I) by reaction with NaI in THF. Substitution of the picoline ligands by N,N,N′,N′-tetramethylethylenediamine (tmeda) and dppe afforded the complexes [W(CC₆H₄Z-4)X(CO)₂(L₂)] [Z = I, L₂ = tmeda, X = Cl (5a), X = Br (5b), X = I (5c); Z = Br, L₂ = tmeda, X = Cl (6a); Z = I, L₂ = dppe, X = Cl (7a), X = Br (7b), X = I (7c)]. The iodo group of the new alkylidyne complexes underwent Pd^II catalyzed cross-coupling reactions effectively. Thus coupling of complexes 5a with trimethylsilylacetylene, followed by hydrolysis, afforded the acetylide derivative [W{CC₆H₄(CCH-4)}Cl(CO)₂(tmeda)], 8. The alkynyl derivatives [W{CC₆H₄(CCC₆H₄Y)-4}Cl(CO)₂(tmeda)] (Y = H 9, CHO 10 or CN 11) were obtained by reactions of complex 5a with the respective aromatic acetylenes. The molecular structures of complexes 5a and 10 have been determined by X-ray crystallography.