Ln(ii) and Ca(ii) NCsp3N pincer type diarylmethanido complexes – promising catalysts for C–C and C–E (E = Si, P, N, S) bond formation

Abstract

Ln(II) (Ln = Yb, Sm) and Ca(II) [NC_sp³N] pincer type diarylmethanido complexes [2,2′-(4-MeC₆H₃NMe₂)₂CH]₂M (M = Yb (2), Sm (3), Ca (4)) coordinated by a tridentate diarylmethanido ligand were synthesized through salt metathesis reactions of {[2,2′-(4-MeC₆H₃NMe₂)₂CH]K(THF)}₂ and MI₂(THF)₂. X-ray analysis revealed that both diarylmethanido ligands in 2–4 are tridentate and coordinate to the metal centers via central carbon and two nitrogen atoms of NMe₂ groups resulting in [NC_sp³N] pincer coordination. In one of the five-membered MCCCN metallacycles in each tridentate diarylmethanido ligand, metal–arene interactions were detected and the coordination mode of [NC_sp³N] ligands in 2–4 can be classified as κ¹-N:η⁴-CCCN. A dynamic behavior involving the exchange between NMe₂ groups and THF molecules in the coordination sphere of the M(II) ion was detected in solution. Complexes 2–4 proved to be catalytically active in a variety of reactions of C–C and C–E (E = Si, P, N, S) bond formation. Yb(II) 2 and Ca(II) 4 complexes catalyze intermolecular hydrobenzylation of styrene with 2-methyl and 2,6-dimethyl pyridines. Complex 2 demonstrates high chemo- and regioselectivities and is the first Ln(II) catalyst for intermolecular C–C bond formation. Complexes 2–4 were found to be efficient and selective precatalysts for intermolecular hydroelementation of olefins and acetylenes with various EH substrates (E = Si, P, N, S). Complexes 2–4 have demonstrated their versatility for intermolecular C–E bond formation and allow the realization of hydroamination, hydrophosphination, hydrosilylation and hydrothiolation of styrene and phenylacetylene. Moreover, 2–4 were found to be active in the catalysis of challenging transformations such as hydrosilylation and hydrophosphination of internal double CC and triple CC bonds.