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)

Abstract

Chloro methyl and dimethyl azatantalacyclopentene complexes [TaCp*Cl 2 - x Me x (CHCHCMe 2 NAr-κ 2 C, N )] (Cp* = η 5 -C 5 Me 5; Ar = 2,6-Me 2 C 6 H 3; x = 1, 2; 2, 3) can be prepared by reaction of [TaCp*Cl 2 (CHCHCMe 2 NAr-κ 2 C, N )] ( 1a ) with dimethylzinc and chloromethylmagnesium, respectively. Reaction of 1a with dibenzylmagnesium leads to the monoalkylated complex [TaCp*Cl(CH 2 Ph)(CHCHCMe 2 NAr-κ 2 C, N )] ( 4 ). The alkylation of [TaCp*Cl 2 {C(Ph)CHCMe 2 NAr-κ 2 C, N }] ( 1b ) with 2 equiv of chloromethylmagnesium at low temperature gave the dimethyl azatantalacyclopentene complex [TaCp*Me 2 {C(Ph)CHCMe 2 NAr-κ 2 C, N }] ( 5 ), which at room temperature decomposes, giving the dimethyl(imido) complex [TaCp*Me 2 (NAr)] ( 7 ), identified by NMR spectroscopy. Alkylation of 1b with 0.5 equiv of dibenzylmagnesium leads to the monobenzyl complex [TaCp*Cl(CH 2 Ph){C(Ph)CHCMe 2 NAr-κ 2 C, N }] ( 6 ); however treatment with 1 equiv of the alkylating reagent gave the dibenzyl(imido) [TaCp*(CH 2 Ph) 2 (NAr)] ( 8 ) in a mixture with 6 as minor component. Moreover, 1a reacts with 1 equiv of isocyanides RNC (R = 2,6-Me 2 C 6 H 3; t Bu) to give the dichloro(imido) complex [TaCp*Cl 2 (NAr)] ( 9 ), while the treatment of the chloro methyl azatantalacyclopentene 2 with 2 equiv of isocyanides RNC (R = 2,6-Me 2 C 6 H 3; t Bu) at different conditions affords the imido η 2 -iminoacyl derivatives [TaCp*Cl(NAr){η 2 -C(Me) NR}] (R = 2,6-Me 2 C 6 H 3, 12; t Bu, 13 ) in good yields with simultaneous elimination of s - trans -vinylazacumulenes R−N C CH−CH CMe 2 (R = 2,6-Me 2 C 6 H 3, 10; t Bu, 11 ). Similarly, the reaction of the dimethyl azatantalacyclopentene 3 with 1 equiv of 2,6-Me 2 C 6 H 3 NC produces the alkenylamido imido methyl derivative [TaCp*Me(NAr){η 1 -N(Ar)-C(Me) CH−CH CMe 2 }] ( 14 ), which with one additional equivalent of isocyanide gives the imido η 2 -iminoacyl methyl compound [TaCp*Me(NAr)(η 2 -C{CH(CMe NAr)(CH CMe 2 )} 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.