Synthesis, structure and reactivity of tungsten(IV) complexes: Development of an olefin dimerization catalyst

Two unique series of W(IV) imido complexes containing the chelating diamido ligand [o-(Me₃SiN)₂C₆H₄] have been synthesized. W(IV) arene complexes with the formulae: W(NPh)(η 4-ethylbenzene)(o-(Me₃SiN)₂C₆H ₆) (3) and W(NPh)(η4-propylbenzene)(o-(Me ₃SiN)₂C₆H₆) (4) were generated through hydrogenolysis of the W(VI) dialkyl complexes, W(NPh)(CH₂CH ₂Ph)₂(o-(Me₃SiN)₂C₆H ₄) (1) and W(NPh)(CH₂CH₂CH₂ Ph)₂(o-(Me₃SiN)₂C₆H ₄) (2). The W(IV)L₂ complexes, [W(NPh)(o-(Me ₃SiN)₂C₆H₄)(C₅H₅N) ₂] (8) and W(NPh)(o-(Me₃SiN)₂C ₆H₄)(p-C₆H₇N)₂ (9 ) were synthesized by Nao reduction of W(NPh)(o-(Me ₃SiN)₂C₆H₄)Cl₂ in the presence of pyridine or 4-picoline. These compounds have been fully characterized by NMR spectroscopy, and X-ray crystal structures of 4 and 9 have been determined.; Compounds 8 and 9 readily incorporated additional ligands, PMe₃ and CO, and undergo ligand substitution reactions with PMe₃ to give a series of six-coordinate W(IV) complexes that demonstrate the coordinative unsaturation of 8 and 9. The solid state structures of [W(NPh)(o-(Me₃SiN)₂C ₆H₄)(C₅H₅N)₂(CO)] ( 12a) and [W(NPh)(o-(Me₃SiN)₂C₆H ₄)(C₅H₅N)(PMe₃)₂] ( 14a) are described.; The reactivity of [W(NPh)(o-(Me₃SiN)₂C₆H ₄)(C₅H₅N)₂] (8) toward unsaturated substrates was examined. Compound 8 reacted with diphenylacetylene to give the metallocylopropene complex, [W(NPh)(o-(Me ₃SiN)₂C₆H₄)(PhC≡CPh)] ( 15). Likewise compound 8 also displayed reactivity towards butadienes resulting in the formation of W(NPh)[o-(Me₃SiN) ₂C₆H₄][η4-(CH₂=C(CH ₃)C(CH₃)=CH₂)] (17) and W(NPh)[o-(Me ₃SiN)₂C₆H₄](η4-CH ₂=CHCH=CH₂) (18). Reduction of the unsaturated ligands in 15 and 17 was observed in the crystal structures of these compounds.; Carbon-sulfur bond activation of thiophenes promoted by [W(NPh)(o-(Me ₃SiN)₂C₆H₄)(C₅H₅N) ₂] (8) was also studied. Reaction of 8 with thiophene, 2-methylthiophene, benzothiophene or 3-methylthiophene resulted in oxidative addition of the C-S bond to the W(IV) metal center. The solid-state structure of [o-(Me₃SiN)₂C₆H₄](NPh)W(SC ₄H₄) (22) is also discussed. Oxidation of the W(IV) center of the WL₂ complexes was also observed in their reactions with olefins. These reactions led to oxidative coupling of two olefin molecules to give a series of metallacyclopentane complexes.; Using the ability of Lewis acids such as EtAlCl₂ to decompose these metallacycles, a catalytic olefin dimerization/codimerization catalyst system was developed based o...