Synthesis and Reactivity of Molybdenum(IV) Olefin Complexes Supported by a Chelating Ancillary Ligand

The reactivity of [Mo(NPh)Cl2(o-(Me3SiN)2C6H4·THF)] (1) with β-hydrogen-containing Grignard reagents was examined. Reaction of 1 with 2 equiv of RMgCl (R = CH2CH2Ph, CH2CH2CH3, CH2CH(CH3)2, CH2CH2CH2CH3, and CH(CH3)CH2CH3) gave Mo(IV) olefin complexes of the type [Mo(NPh)(η2-olefin)(o-(Me3SiN)2C6H4)] (olefin = styrene (2a), propene (2b), isobutene (2c), 1-butene (2d), and 2-butene (2e)). The crystal structure of 2a is reported. Reaction of 1 with 2 equiv of ethylmagnesium chloride afforded a mixture of metallacyclopentane [Mo(NPh)(CH2CH2CH2CH2)(o-(Me3SiN)2C6H4)] (3a) and an oligomeric molybdenum species having the empirical formula [Mo(NPh)(o-(Me3SiN)2C6H4)] x (3b). Pure 3a was obtained by reaction of 1 with 2 equiv of EtMgCl under an atmosphere of ethylene. Treatment of 3a with excess PMe3 in benzene at 80 °C afforded [Mo(NPh)(η2-ethylene)(o-(Me3SiN)2C6H4)(PMe3)2] (3c). Compounds 2c and 2a react with acetone to yield the oxametalacyclopentanes [(Mo(NPh)(C(CH3)2CH2C(CH3)2O)(o-(Me3SiN)2C6H4)] (4a) and [(Mo(NPh)(C(H)PhCH2C(CH3)2O)(o-(Me3SiN)2C6H4)] (4b), respectively. An X-ray crystallographic study on a single crystal of 4a was performed. Only one diasteriomer of 4b was formed and isolated. Its structure was assigned by NMR spectroscopy (ghmbc, ghmqc, and NOESY).