Triazolates as a Platform for Metal-Ligand Cooperative Catalysis

E-H (E= N, O, C, H, Si, etc.) bond activation represents a key mechanistic step in numerous catalytic reactions such as hydrosilylation, hydrogenation, hydroamination, hydrocarbon functionalization, etc. Non-innocent ligand systems cooperate with the metal center by undergoing reversible structural changes. E-H bond cleavage takes place by ligand (re)protonation, with the formally anionic component sequestered by the metal center.[i] Here we present a triazolate based monophosphine ligand systems, bearing negatively charged nitrogen atom, which can serve as a base in a catalytic cycle (Scheme, compound 1). Thus, a s bond coordination of E-H to relatively electrophilic metal center (Pt(II), Ru(II), Ir/Rh(III)) could follow by its deprotonation with adjacent N-anion. The resulting protonated neutral triazole remains aromatic and can be easily deprotonated (N-H pKa~10) later on to restore the active catalyst (Scheme).

Scheme. Triazolate based M=Rh(III)/Ir(III) complexes.

[i] a) C. Gunanathan, D. Milstein, Acc. Chem. Res. 2011, 44, 588- 602; b) C. Gunanathan, D. Milstein, Chem. Rev, 2014, 114, 12024-12087.