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)

Dichloro azatantalacyclopropane complexes [TaCpCl2(CMe2NAr-kappa(2)C,N)] (Ar = 2,6-Me2C6H3; Cp = eta(5)-C5Me5, 1; eta(5)-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-kappa(2)C,N)] (Cp* = eta(5)-C5Me5; Ar = 2,6-Me2C6H3, 3), which in solution slowly decomposes to give [TaCp*Cl{C(Me) = CH2}(NAr)] (Cp* = eta(5)-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-kappa(2)C,N)] (Ar = 2, 6-Me2C6H3; Cp = eta(5)-C5Me5, 5; eta(5)-C5H4SiMe3, 6). However, benzene-d(6) solutions of 5 and 6 decompose at room temperature to give a dichloro(imido) tantalum complex [TaCPCl2(NAr)] (Ar = 2,6-Me2C6H3, Cp = eta(5)-C5Me5, 7;eta(5)-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*Cl-2{CH2CH(Me)CMe2NAr-kappa(2)C,N}] (Cp* = eta(5)-C5Me5; Ar = 2,6-Me2C6H3, 9) was detected by NMR spectroscopy after treatment of 1 with propylene in dichloromethane-d(2). The analogous reaction of 1 or 2 with alkynes RC drop CH (R = H, Ph, SiMe3) leads to the formation of the dichloro azatantalacyclopentene complexes [TaCPCl2(CRCHCMe2NAr-kappa(2)C,N)] (Ar = 2,6-Me2C6H3; Cp = eta(5)-C5Me5, R = H, 10; Ph, 11; SiMe3, 12; Cp = eta(5)C(5)H(4)SiMe(3), R = H, 13; Ph, 14; SiMe3, 15), the process being regioselective when monosubstituted alkynes RC drop 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.