Mixed Ligated Tris(amidinate)dimolybdenum Complexes as Catalysts for Radical Addition of CCl4 to 1-Hexene: Leaving Ligand Lability Controls Catalyst Activity.

Abstract

We synthesized a series of mixed ligated tris(amidinate)dimolybdenum complexes, namely, [Mo2(DAniF)3(L)] [DAniF = N,N'-di(p-anisyl)formamidinate; L = acetate (OAc; 1a), m-diphenylphosphino benzoate (m-PPh2Bz; 1b), nicotinate (Nico; 1c), benzoate (Bz; 1d), 3-furoate (3-Furo; 1e), isonicotinate (IsoNico; 1f), and trifluoromethanesulfonate (OTf; 1g)], which served as catalysts for radical addition of CCl4 to 1-hexene to give 1,1,1,3-tetrachloroheptane. These mixed ligated complexes 1a-g afforded the higher yield of the radical addition product than a homoleptic DAniF complex, [Mo2(DAniF)4] (2). Among them, complexes 1a and 1g gave the radical addition product quantitatively after 9 h with a short induction period. When complexes 1a and 1g were treated with CCl4, we detected the mixed-valence Mo2(II/III) complex, [Mo2(DAniF)3Cl2] (4), in electrospray ionization mass spectrometry measurements, indicating that the leaving nature of the L ligands was a crucial factor for initiating the catalytic reaction: the catalytic activity of the carboxylate-bridged complex 1a and the triflate-bridged complex 1g in the initial 30 min highly depended on the ligand-exchange rate of L, as estimated by monitoring the reaction with CCl4 in pyridine, giving the pyridine adduct complex, [Mo2(DAniF)3Cl(py)] (3).