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

The synthesis of the 4-iodobenzylidyne and 4-bromobenzylidyne tungsten complexes [W(CC(6)H(4)Z-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 THE Substitution of the picoline ligands by N,N,N',N'-tetramethylethylenediamine (tmeda) and dppe afforded the complexes [W(CC(6)H(4)Z-4)X(CO)(2)(L-2)] [Z = I, L-2 = tmeda, X = Cl (5a), X = Br (5b), X = I (5c); Z = Br, L-2 = tmeda, X = Cl (6a); Z = I, L, = 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.