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

Abstract

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.