DFT examination of rare α-SiMe3 abstraction in Ta(NMe2)4[N(SiMe3)2]: formation of the imide compound Ta(NSiMe3)(NMe2)3 and its trapping to give guanidinate imides
A density functional theory (DFT) investigation on the formation of Ta(NSiMe3)(NMe2)3 (B) and Me3SiNMe2 (C) 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 (A2) with an apical N(SiMe3)2 group undergoes α-elimination to give Ta(NSiMe3)(NMe2)3 (B) and Me3SiNMe2 (C). 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(NSiMe3)(NMe2)3 (B) has been computationally evaluated, and the preference for the dimeric form of the compound is discussed relative to the Nugent imide derivative Ta(NCMe3)(NMe2)3, which exists as a monomer. The trapping of the intermediate B by the heterocumulene MeNCNMe has been modeled, and the mechanism involved in the formation of the guanidinate-based insertion products Ta(NSiMe3)(NMe2)2[MeNC(NMe2)NMe] (G1) and Ta(NSiMe3)(NMe2)[MeNC(NMe2)NMe]2 (I) is presented.