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 [TaCpCl 2 (CMe 2 NAr-κ 2 C,N)] (Ar = 2,6-Me 2 C 6 H 3 ; Cp = η 5 -C 5 Me 5 , 1; η 5 -C 5 H 4 SiMe 3 , 2) can be obtained by treating TaCpCl 2 Me 2 with 1 equiv of 2,6-dimethylphenylisocyanide. Alkylation of 1 with an excess of MgCl(CH 2 SiMe 3 ) leads to [TaCp*Cl(CH 2 SiMe 3 )(CMe 2 NAr-κ 2 C,N)] (Cp* = η 5 -C 5 Me 5 ; Ar = 2,6-Me 2 C 6 H 3 , 3), which in solution slowly decomposes to give [TaCp*Cl{C(Me)=CH 2 }(NAr)] (Cp* = η 5 -C 5 Me 5 ; Ar = 2,6-Me 2 C 6 H 3 , 4) with elimination of SiMe 4 . 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 [TaCpCl 2 (CH 2 CH 2 CMe 2 NAr-κ 2 C,N)] (Ar = 2, 6-Me 2 C 6 H 3 ; Cp = η 5 -C 5 Me 5 , 5; η 5 -C 5 H 4 SiMe 3 , 6). However, benzene-d 6 solutions of 5 and 6 decompose at room temperature to give a dichloro(imido) tantalum complex [TaCpCl 2 (NAr)] (Ar = 2,6-Me 2 C 6 H 3 , Cp = η 5 -C 5 Me 5 , 7;η 5 -C 5 H 4 SiMe 3 , 8) with elimination of 2-methyl-2-butene (Me 2 C=CH-Me) and 3-methyl-1-butene (H 2 C=CH-CHMe 2 ) (decomposition of 5) and only 2-methyl-2-butene (decomposition of 6). The complex [TaCp*Cl 2 {CH 2 CH(Me)CMe 2 NAr-κ 2 C,N}] (Cp* = η 5 -C 5 Me 5 ; Ar = 2,6-Me 2 C 6 H 3 , 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≡CH (R = H, Ph, SiMe 3 ) leads to the formation of the dichloro azatantalacyclopentene complexes [TaCpCl 2 (CRCHCMe 2 NAr-κ 2 C,N)] (Ar = 2,6-Me 2 C 6 H 3 ; Cp = η 5 -C 5 Me 5 , R = H, 10; Ph, 11; SiMe 3 , 12; Cp = η 5 -C 5 H 4 SiMe 3 , R = H, 13; Ph, 14; SiMe 3 , 15), the process being regioselective when monosubstituted alkynes RC≡CH (R = Ph, SiMe 3 ) 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.