Alkylation, Insertion of Isocyanides, and Intramolecular Rearrangement Processes in Azatantalacyclopentene Complexes. X-ray Crystal Structure of [TaCp*Me₂(CHCHCMe₂NAr-κ²<i>C</i>,<i>N</i>)] (Cp* = η⁵-C₅Me₅; Ar = 2,6-Me₂C₆H₃)^§

Chloro methyl and dimethyl azatantalacyclopentene complexes [TaCp*Cl2-xMex(CHCHCMe2NAr-κ2C,N)] (Cp* = η5-C5Me5; Ar = 2,6-Me2C6H3; x = 1, 2; 2, 3) can be prepared by reaction of [TaCp*Cl2(CHCHCMe2NAr-κ2C,N)] (1a) with dimethylzinc and chloromethylmagnesium, respectively. Reaction of 1a with dibenzylmagnesium leads to the monoalkylated complex [TaCp*Cl(CH2Ph)(CHCHCMe2NAr-κ2C,N)] (4). The alkylation of [TaCp*Cl2{C(Ph)CHCMe2NAr-κ2C,N}] (1b) with 2 equiv of chloromethylmagnesium at low temperature gave the dimethyl azatantalacyclopentene complex [TaCp*Me2{C(Ph)CHCMe2NAr-κ2C,N}] (5), which at room temperature decomposes, giving the dimethyl(imido) complex [TaCp*Me2(NAr)] (7), identified by NMR spectroscopy. Alkylation of 1b with 0.5 equiv of dibenzylmagnesium leads to the monobenzyl complex [TaCp*Cl(CH2Ph){C(Ph)CHCMe2NAr-κ2C,N}] (6); however treatment with 1 equiv of the alkylating reagent gave the dibenzyl(imido) [TaCp*(CH2Ph)2(NAr)] (8) in a mixture with 6 as minor component. Moreover, 1a reacts with 1 equiv of isocyanides RNC (R = 2,6-Me2C6H3; tBu) to give the dichloro(imido) complex [TaCp*Cl2(NAr)] (9), while the treatment of the chloro methyl azatantalacyclopentene 2 with 2 equiv of isocyanides RNC (R = 2,6-Me2C6H3; tBu) at different conditions affords the imido η2-iminoacyl derivatives [TaCp*Cl(NAr){η2-C(Me)NR}] (R = 2,6-Me2C6H3, 12; tBu, 13) in good yields with simultaneous elimination of s-trans-vinylazacumulenes R−NCCH−CHCMe2 (R = 2,6-Me2C6H3, 10; tBu, 11). Similarly, the reaction of the dimethyl azatantalacyclopentene 3 with 1 equiv of 2,6-Me2C6H3NC produces the alkenylamido imido methyl derivative [TaCp*Me(NAr){η1-N(Ar)-C(Me)CH−CHCMe2}] (14), which with one additional equivalent of isocyanide gives the imido η2-iminoacyl methyl compound [TaCp*Me(NAr)(η2-C{CH(CMeNAr)(CHCMe2)}NAr)] (15). All compounds were studied by IR and NMR spectroscopy, and the molecular structure of complex 3 was determined by X-ray diffraction methods.