Atom transfer chemistry and electrochemical behavior of Mo(VI) and Mo(V) trispyrazolylborate complexes: new mononuclear and dinuclear species

Metathesis of Tp P r MoO 2 Cl (Tp P r = hydrotris(3-isopropylpyrazolyl)borate) with phenol/NEt 3 or thiol/NEt 3 mixtures results in the formation of air-stable, diamagnetic cis-dioxo-Mo(VI) complexes, Tp P r MoO 2 X (X = OC 6 H 4 sBu-2, OC 6 H 4 R-3 (R = Me, t Bu), OC 6 H 4 R-4 (R = Br, Et, OMe), OC 6 H 3 'Bu 2 -3,5, OC 6 H 3 'BuMe-2,4, S n Bu, S s Bu). The complexes were characterized by analytical, spectroscopic and mass spectrometric methods, which support the formulations, ligands present [IR: v(MoO 2 ) approximately 930 and 900 cm - 1 , v (BH) 2570-2480 cm - 1 , OAr 1605-1500 and 1300-1250 cm - 1 ] and assigned molecular symmetries ( 1 H/ 1 3 C NMR). Electrochemical studies revealed reversible or quasi-reversible (X = OC 6 H 3 'BuMe-2,4), one-electron reduction processes with E 1 / 2 values linearly correlated with the electron donor capacity of the ligand X (as expressed by Hammett functions). Oxygen atom transfer and comproportionation resulted in the formation of [Tp*MoO(OPh)] 2 (μ-O) (Tp* = hydrotris(3,5-dimethylpyrazolyl)borate) in the reaction of Tp*MoO 2 (OPh) with PEt 3 in toluene (in contrast to the formation of phosphine oxide complexes in the Tp P r system), while hydrolysis of Tp*MoOCl 2 produced [Tp*MoOCl] 2 (μ-O). Reaction of Tp P r MoO 2 Cl with P(O i Pr) 3 produced [Tp P r MoOCl](μ-O)[Tp P r MoO(OH)]. The X-ray crystal structures of [Tp*MoOCl] 2 (μ-O) and [Tp P r MoOCl](μ-O)[Tp P r MoO(OH)] are reported. Both compounds exhibit corner shared bioctahedral structures with a single bridging oxo ligand linking TpxMoOX (X = Cl, OH) moieties. Chlorine atom transfer from Tp P r MoOCl 2 to PPh 3 in pyridine (py) or lutidine (lut) produces Tp P r MoOCl(py) and Tp P r MoOCl(lut), respectively.