Formation of the Imide [Ta(NMe₂)₃(μ-NSiMe₃)]₂ through an Unprecedented α-SiMe₃ Abstraction by an Amide Ligand

Abstract

Ta(NMe(2))(4)[N(SiMe(3))(2)] (1) undergoes the elimination of Me(3)Si-NMe(2) (2), converting the -N(SiMe(3))(2) ligand to the ═NSiMe(3) ligand, to give the imide "Ta(NMe(2))(3)(═NSiMe(3))" (3) observed as its dimer 4. CyN═C═NCy captures 3 to yield guanidinates Ta(NMe(2))(3-n)(═NSiMe(3))[CyNC(NMe(2))NCy](n) [n = 1 (5), 2 (6)]. The kinetic study of α-SiMe(3) abstraction in 1 gives ΔH(‡) = 21.3(1.0) kcal/mol and ΔS(‡) = -17(2) eu.

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

“…The optimized structure of D, which is shown below eqn (1), reveals an excellent correspondence to the reported X-ray diffraction structure. The computed internuclear Ta⋯Ta distance of 3.191 Å, which is slightly longer (0.028 Å) than that distance found in the solid-state structure, 27 argues against any significant bonding between the two metal centers. 38 The Wiberg index of 0.14 for the Ta-Ta vector in D underscores this assertion.…”

“…Heating Ta(NMe 2 ) 4 [N(SiMe 3 ) 2 ] in the absence of a trapping agent gives the imide-bridged dimer [Ta(NSiMe 3 )(NMe 2 ) 3 ] 2 (D) and Me 3 SiNMe 2 (C); the molecular structure of the former product has been established by X-ray diffraction analysis and presumably results from the dimerization of the intermediate imide complex Ta(NSiMe 3 )(NMe 2 ) 3 (B). 27 DFT analysis of this reaction has confirmed that the α-elimination is a concerted process and is stereospecific, insomuch as only A2 reacts to give the expected products Ta(NSiMe 3 )(NMe 2 ) 3 (B) and Me 3 SiNMe 2 (C). Species A1 and A3 do not allow the reacting amido groups to achieve the requisite orientation for the formation of the critical cyclic transition state associated with the transfer of the Me 3 Si group to the adjacent Me 2 N acceptor ligand.…”

“…The mixed amide complex Ta(NMe 2 ) 4 [N(SiMe 3 ) 2 ] is prepared from the reaction of TaCl(NMe 2 ) 4 with LiN(SiMe 3 ) 2 , and the product has been characterized by NMR spectroscopy and combustion analysis. 27 Unfortunately, the molecular structure of Ta(NMe 2 ) 4 [N(SiMe 3 ) 2 ] remains unknown due to its limited stability and the inability to grow single crystals suitable for X-ray diffraction analysis. 28 Ta(NMe 2 ) 4 [N(SiMe 3 ) 2 ] may be viewed as an ML 5 compound with a Ta(V) center.…”

“…Other tantalum-based systems that exhibit this monomer-dimer phenomenon include TaCl 2 (NMe 2 ) 3 and Ta(NMe 2 ) 4 (N 3 ). 27,28,38,40 Closely related to Ta(NSiMe 3 )(NMe 2 ) 3 is the well-known Nugent imide derivative Ta(NCMe 3 )(NMe 2 ) 3 that exists as a monomer in solution and the solid state. 23,25a,41,42 DFT calculations on Ta(NCMe 3 )(NMe 2 ) 3 (monomer and dimer) were performed to better understand the molecularity conundrum in the isostructural Ta(NEMe 3 )(NMe 2 ) 3 (where E = C, Si) compounds.…”

“…26 Xue and coworkers recently reported that the amide complex Ta(NMe 2 ) 4 [N(SiMe 3 ) 2 ] undergoes spontaneous, thermal α-SiMe 3 abstraction by an amide ligand yielding Me 3 SiNMe 2 (C) and the imide B which was observed as its dimer D (Scheme 3). 27,28 Kinetic studies of the thermal α-SiMe…”