Reductive C–N bond cleavage of the NCCCN β-diketiminate backbone: A direct approach to azabutadienyl and alkylidene-anilide scaffolds

Tetrahydrofuran/toluene solutions of (nacnac)TiCl2 (nacnac− = [ArNC(tBu)]2CH, Ar = 2,6-iPr2C6H3) react readily with KC8 to afford the titanium imide (ArN(tBu)CCHC(tBu))TiNAr(THF)Cl (1) in 67% isolated yield. Complex 1 forms from the two-electron reductive C–N bond cleavage of the β-diketiminate ligand. Likewise, reduction of (nacnac)TiCl(NHAr) (2), prepared in 85% yield from (nacnac)TiCl2 and LiNHAr, with KC8 results in formation of the imide-anilide analogue (ArN(tBu)CCHC(tBu))TiNAr(NHAr) (3) in 88% yield. Another reductant such as LitBu (3 equiv.) reacts cleanly with the precursor (nacnac)TiCl2 to afford the alkylidene-ate complex [Li(Et2O)][(ArN(tBu)CCHC(tBu))TiNAr(Et2O)] (4), in 81% yield. Complexes 1–4 have been characterized by 1H and 13C NMR spectra as well as single-crystal X-ray diffraction analysis. Plausible mechanisms to formation of compounds 1, 3 and 4 are also presented and discussed.

Graphical abstractAzabutadienyl and alkylidene-anilide scaffolds can be readily prepared by reductive cleavage of the β-diketiminate NCCCN ring. Two-electron reduction reactions lead to C–N bond rupture and formation of the monoanionic azabutadiene framework, while a four-electron reduction results in complete CN bond rupture to form a metallacyclic alkylidene ligand.Figure optionsDownload full-size imageDownload as PowerPoint slide