Formation and Characterization of Stable Alkylidyne(alkene)tungsten Complexes

Reaction of the alkylidyne complexes [W(CPh)Cl(CO)₂(py)₂], [Kat][W(CR)Cl₂(CO)₂(py)], and [W-(CPh)Cl(CO)₂(tmeda)] with maleic anhydride and fumaronitrile results in substitution of carbon monoxide and affords the alkylidyne(alkene)tungsten complexes [W(CPh)Cl(CO)(η²-alkene)(py)₂] (4 and 5), [Kat][W(CR)Cl₂(CO)(η²-alkene)(py)] (6 and 7; R = Me, Kat = NEt₄; 8 and 9, R = Ph, Kat = NEt₄, PPN), and [W(CPh)Cl(CO)(η²-alkene)(tmeda)] (10 and 11), respectively. Compounds 10 and 11 can also be obtained by reaction of 4 and 5 with tmeda. The reactions are conducted in THF or CH₂Cl₂ at room temperature or slightly elevated temperatures. In all complexes the coordination site trans to the alkylidyne ligand is occupied by chloride.¹H NMR NOE difference studies show that in the anionic complexes the second chloride ligand is coordinated trans to the alkene. The fumaronitrile complexes are obtained as mixtures of diastereomers due to coordination of the two enantiotopic faces of the alkene to the asymmetric metal complex fragments. The molecular structure of 4 was determined by X-ray crystallography: space group P2₁/n, a = 11.522 (2) Å, b = 16.026 (3) Å, c = 11.680 (2) Å, β = 102.97 (1)°, Z = 4, R = 3.28%, R_w = 3.57%. Substitution of carbon monoxide in the formation of the title complexes is postulated to occur indirectly by initial substitution of pyridine or chloride and subsequent trans labilization of carbon monoxide by the alkene.