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