Preparation, characterization, and reactions of 16-electron Ta(η5-C5Me5)(η3-1-phenylallyl)2

Article abstract of DOI:10.1016/0022-328X(93)86064-O

Treatment of Cp^*TaCl4 with 4 equiv of phenylallylMgBr in THF afforded Cp^*Ta(1-phenylallyl)2 (2), whose structure was characterized by a single crystal X-ray study as 16-electron two legged piano stool with two allyl moieties in supine-supine geometry.In this reaction, the starting Ta^V complex was reduced to a Ta^III species accompanying the formation of reductive allyl-coupling products, diphenyl-1,5-hexadiene derivatives 3. ?-Donor molecules such as carbon monoxide, tert-butyl isocyanide, isocyanates and isothiocyanates induced the coupling reaction of two phenylallyl groups on tantalum to give 1,6-diphenyl-1,5-hexadiene (3a).The intermediate Cp^*Ta(tert-BuNC)2(η²,η²-1,6-diphenyl-1,5-hexadiene) (5) was characterized by 1H NMR spectroscopy.Complex 2 was the catalyst precursor for the selective dimerization of isocyanates.Oxygen donor molecules such as DMSO and pyridine-N-oxide reacted with 2 to afford 1:1 adducts.One-electron oxidation of 2 with ferrocenium cation resulted in the formation of 1-phenyl-1-propene.The Ta^IV complexes, *Ta(1-phenylallyl)2>, were obtained by the reaction of 2 with TCNQ and DDQ.