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

Metathesis of Tp(Pr)MoO(2)Cl (Tp(Pr)= hydrotris(3-isopropylpyrazolyl)borate) with phenol/NEt3 or thiol/NEt3 mixtures results in the formation of air-stable, diamagnetic cis-dioxo-Mo(VI) complexes, Tp(Pr)MoO(2)X (X=(OC6H4Bu)-Bu-s-2, OC6H4R-3 (R=Me, Bu-t), OC6H4R-4 (R=Br, Et, OMe), (OC6H3Bu2)-Bu-t-3,5, (OC6H3BuMe)-Bu-t-2,4, (SBu)-Bu-n, (SBu)-Bu-s). The complexes were characterized by analytical, spectroscopic and mass spectrometric methods, which support the formulations, ligands present [IR: V(MoO2) approximately 930 and 900 cm(-1), nu(BH) 2570-2480 cm(-1), OAr 1605-1500 and 1300-1250 cm(-1)] and assigned molecular symmetries (H-1/C-13 NMR). Electrochemical studies revealed reversible or quasi-reversible (X=(OC6H3BuMe)-Bu-t-2,4), one-electron reduction processes with E-1/2 values linearly correlated with the electron donor capacity of the ligarid X (as expressed by Hammett functions). Oxygen atom transfer and comproportionation resulted in the formation of [Tp*MoO(OPh)](2)(mu-O) (Tp*=hydrotris(3,5-dimethylpyrazolyl)borate) in the reaction of Tp*MoO2(OPh) with PEt3 in toluene (in contrast to the formation of phosphine oxide complexes in the Tp(Pr) system), while hydrolysis of Tp*MoOCl2 produced [Tp*MoOCl](2)(mu-O). Reaction of Tp(Pr)MoO(2)Cl with P((OPr)-Pr-i)(3) produced [Tp(Pr)MoOCl](mu-O)[Tp(Pr)MoO(OH)]. The X-ray crystal structures of [Tp*MoOCl](2)(mu-O) and [Tp(Pr)MoOCl](mu-O)[Tp(Pr)MoO(OH)] are reported. Both compounds exhibit corner shared bioctahedral structures with a single bridging oxo ligand linking Tp(X)MoOX (X=Cl, OH) moieties. Chlorine atom transfer from Tp(Pr)MoOCl(2) to PPh3 in pyridine (py) or lutidine (lut) produces Tp(Pr)MoOCl(py) and Tp(Pr)MoOCl(lut), respectively. (C) 2002 Elsevier Science B.V. All rights reserved.