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Alkylation and Insertion Reactions in Dichloro Azatantalacyclopropane Complexes. X-ray Crystal Structures of [TaCpCl2{C(Ph)CHCMe2NAr-κ2C,N}] (Cp = η5-C5Me5, η5-C5H4SiMe3; Ar = 2,6-Me2C6H3)§

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journal contribution
posted on 28.02.2005, 00:00 by Mikhail V. Galakhov, Manuel Gómez, Pilar Gómez-Sal, Patricia Velasco
Dichloro azatantalacyclopropane complexes [TaCpCl2(CMe2NAr-κ2C,N)] (Ar = 2,6-Me2C6H3; Cp = η5-C5Me5, 1; η5-C5H4SiMe3, 2) can be obtained by treating TaCpCl2Me2 with 1 equiv of 2,6-dimethylphenylisocyanide. Alkylation of 1 with an excess of MgCl(CH2SiMe3) leads to [TaCp*Cl(CH2SiMe3)(CMe2NAr-κ2C,N)] (Cp* = η5-C5Me5; Ar = 2,6-Me2C6H3, 3), which in solution slowly decomposes to give [TaCp*Cl{C(Me)CH2}(NAr)] (Cp* = η5-C5Me5; Ar = 2,6-Me2C6H3, 4) with elimination of SiMe4. The same reaction with other alkylating reagents takes place with the formation of 4, although we have not observed similar intermediate monoalkyl derivatives. The complexes 1 and 2 react with ethylene to give the dichloro azatantalacyclopentane compounds [TaCpCl2(CH2CH2CMe2NAr-κ2C,N)] (Ar = 2, 6-Me2C6H3; Cp = η5-C5Me5, 5; η5-C5H4SiMe3, 6). However, benzene-d6 solutions of 5 and 6 decompose at room temperature to give a dichloro(imido) tantalum complex [TaCpCl2(NAr)] (Ar = 2,6-Me2C6H3, Cp = η5-C5Me5, 75-C5H4SiMe3, 8) with elimination of 2-methyl-2-butene (Me2CCH−Me) and 3-methyl-1-butene (H2CCH−CHMe2) (decomposition of 5) and only 2-methyl-2-butene (decomposition of 6). The complex [TaCp*Cl2{CH2CH(Me)CMe2NAr- κ2C,N}] (Cp* = η5-C5Me5; Ar = 2,6-Me2C6H3, 9) was detected by NMR spectroscopy after treatment of 1 with propylene in dichloromethane-d2. The analogous reaction of 1 or 2 with alkynes RC⋮CH (R = H, Ph, SiMe3) leads to the formation of the dichloro azatantalacyclopentene complexes [TaCpCl2(CRCHCMe2NAr-κ2C,N)] (Ar = 2,6-Me2C6H3; Cp = η5-C5Me5, R = H, 10; Ph, 11; SiMe3, 12; Cp = η5-C5H4SiMe3, R = H, 13; Ph, 14; SiMe3, 15), the process being regioselective when monosubstituted alkynes RC⋮CH (R = Ph, SiMe3) were used. All the new compounds were studied by IR and NMR spectroscopy, and the molecular structures of complexes 11 and 14 were determined by X-ray diffraction methods.