Alkylation and Insertion Reactions in Dichloro Azatantalacyclopropane Complexes. X-ray Crystal Structures of [TaCpCl₂{C(Ph)CHCMe₂NAr-κ²<i>C</i>,<i>N</i>}] (Cp = η⁵-C₅Me₅, η⁵-C₅H₄SiMe₃; Ar = 2,6-Me₂C₆H₃)

Abstract

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.