DFT examination of rare α-SiMe3 abstraction in Ta(NMe2)4[N(SiMe3)2]: formation of the imide compound Ta([double bond, length as m-dash]NSiMe3)(NMe2)3 and its trapping to give guanidinate imides.

A density functional theory (DFT) investigation on the formation of Ta([double bond, length as m-dash]NSiMe3)(NMe2)3 () and Me3SiNMe2 () from Ta(NMe2)4[N(SiMe3)2] is reported. Three different ground-state minima are computed for Ta(NMe2)4[N(SiMe3)2], and of these only the stereoisomer based on a square pyramid () with an apical N(SiMe3)2 group undergoes α-elimination to give Ta([double bond, length as m-dash]NSiMe3)(NMe2)3 () and Me3SiNMe2 (). The barrier computed for the concerted α-elimination is in agreement with the results from our earlier experimental study. The thermodynamics for the monomer-dimer equilibrium involving Ta([double bond, length as m-dash]NSiMe3)(NMe2)3 () has been computationally evaluated, and the preference for the dimeric form of the compound is discussed relative to the Nugent imide derivative Ta([double bond, length as m-dash]NCMe3)(NMe2)3, which exists as a monomer. The trapping of the intermediate by the heterocumulene MeN[double bond, length as m-dash]C[double bond, length as m-dash]NMe has been modeled, and the mechanism involved in the formation of the guanidinate-based insertion products Ta(NSiMe3)(NMe2)2[MeNC(NMe2)NMe] () and Ta(NSiMe3)(NMe2)[MeNC(NMe2)NMe]2 () is presented.