Synthesis and characterization of new hydrotri(3,5-dimethyl-l-pyrazolyl) borate vanadium half sandwich complexes

Paramagnetic vanadium (III) complexes of the type Tp*VCl₂(L) were prepared by replacing the dimethylformamide ligand in Tp*VCl₂(dmf) (1) by various N-containing heterocycles. The new compounds Tp*VCl₂(L) (L = 4-substituted pyridine NC₅H₄-R(4) (R = H(3a), CH₃(3b), C₂H₅(3c), Ph(3d)), pyridazine (4), pyrimidine (5), pyrazine (6), imidazole (7a), 1-methylimidazole (7b), 1,2-dimethylimidazole (7c), and 4,4′-bipyridine (8)) were characterized by IR and mass spectroscopy, and the molecular structure of 3b was determined by X-ray crystallography. A binuclear product, Tp*Cl₂V]₂(L-L) (9), containing 4,4′-bipyridine (L-L) as bridging ligand, and the dimethyl sulfoxide complex, Tp*Cl₂(O=SMe₂) (10), were also investigated. Reactions of 1 with phenol and triethylamine in the presence of air gave Tp*V(O)(OPh)₂ (11). Other diamagnetic vanadium(V) complexes such as Tp*V(N^tBu)(SR)₂(R = Et (12a), Ph (12b) and Tp*V(N^tBu)(S₂C₆H₄) (12c)) were obtained from the tert-butylimido compound Tp*V(N^tBu)Cl₂ (2) and the appropriate thiol in the presence of the base triethylamine. The ¹H, ¹³C and ⁵¹V NMR spectra of 2, 11 and 12a-c are reported.