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-ⁱPr-C₆H₃]}Ta(N^tBu)H (2) was prepared from hydrogenolysis of (BDI)TaN^tBuMe₂ (BDI = N,N′-diaryl-β-diketiminate, aryl = 2,6-ⁱPr₂-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^tBu)(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.