Generation of low-valent tantalum species by reversible C–H activation in a cyclometallated tantalum hydride complex

Abstract

The cyclometallated tantalum(v) hydride complex {ArNC(Me)CHC(Me)N[2-(CHMeCH2)-6-(i)Pr-C6H3]}Ta(N(t)Bu)H (2) was prepared from hydrogenolysis of (BDI)TaN(t)BuMe2 (BDI = N,N'-diaryl-β-diketiminate, aryl = 2,6-(i)Pr2-C6H3). Based on mechanistic studies, formation of 2 likely proceeds through a dihydride intermediate generated from successive σ-bond metathesis steps. Compound 2 was found to undergo reductive elimination under certain conditions to form trivalent tantalum species. Coordination of DMAP to 2, followed by gentle heating under H2, gives (MAD)Ta(N(t)Bu)(NAr)(DMAP), which is produced through reductive C-N bond cleavage of the BDI ligand in a Ta(iii) intermediate. Ta(iii) dicarbonyl derivatives have been accessed by either introducing CO atmosphere to the DMAP adduct of 2 at room temperature, or by directly adding CO to 2 at low temperature.

Early/Late Heterobimetallic Tantalum/Rhodium Species Assembled Through a Novel Bifunctional NHC‐OH Ligand

“…This suggests that the Ta–NHC association might be loose and labile, and could eventually be displaced by another metal centre with a higher affinity for the NHC moiety (see below). The metrical parameters for the Ta=N t Bu moiety (Ta‐N3‐C22 angle=173.5(4)°, TaC=N3 bond length=1.753(5) Å) are typical of tantalum–imido motifs reported in the literature . The Ta−O (1.953(3) Å) and Ta−C neopentyl (Ta−C26=2.213(6) Å, Ta−C31=2.232(5) Å) bond lengths are as expected.…”

On the non-innocence of “Nacnacs”: ligand-based reactivity in β-diketiminate supported coordination compounds

“…22. 283 Interestingly, labelling experiments showed that the deuterium is exchanged not only into all of the isopropyl methyl groups, but also to a lesser extent into all of the isopropyl methine groups: this indicates that C-H activation is reversible under H 2 and occurs at both the methyl and methine positions of the i Pr aryl substituents. 283 Interestingly, labelling experiments showed that the deuterium is exchanged not only into all of the isopropyl methyl groups, but also to a lesser extent into all of the isopropyl methine groups: this indicates that C-H activation is reversible under H 2 and occurs at both the methyl and methine positions of the i Pr aryl substituents.…”

“…It is noteworthy that in the niobium case, the mono-cyclometallated hydride species is observed as an intermediate by 1 H NMR, but this undergoes facile further reactions at room temperature, from which the double-cyclometallated product could be isolated from hexane solutions and crystallized (Fig. 283 In the absence of accessible isopropyl or methyl substituents on the N-aryl groups, C sp 2-H bond activation can occur. 210 We have also shown that under CO atmosphere Scheme 72 Nucleophilic addition of nitriles and heteroallenes to the dianionic #BDI ligand in a samarium amide complex leading to substantial modification of the ligand backbone.…”

Group 5 chemistry supported by β-diketiminate ligands

“…59 This reaction proceeded entirely through Ta(V) intermediates involving multiple σ-bond metathesis steps. 59 This reaction proceeded entirely through Ta(V) intermediates involving multiple σ-bond metathesis steps.…”