Tp* rhenium(V) oxo-halide, -hydride, -alkyl, -phenyl, and -alkoxide complexes: Syntheses and oxidations

Rhenium-oxo complexes with the hydridotris(3,5-dimethyl-1-pyrazolyl)borate (Tp*) ligand are described. Halide complexes Tp*Re(O)X(Cl) (X = Cl, I) are prepared by treatment of Tp*Re(O)(OH)Cl with HX. Reaction of Tp*Re(O)Cls (3 ) with 1 or 2 equiv of LiPh/ZnCl2 or Et2Zn produces the corresponding oxo-a ryl and oxo-alkyl complexes Tp*Re(O)(Ph)Cl, Tp*Re(O)(Ph)(2), and Tp*Re(O)(E t)Cl. Alkoxide complexes Tp*Re(O)(OR)CI and Tp*Re(O)(OR)(2) are prepared fr om 3 and ROH, PhOH, or catechol, Triflate complexes Tp*Re(O)X(OTf) (X = hal ide, H, Et, Ph, Oft, OPh) have been prepared by halide metathesis with AgOT f or by alkoxide metathesis with Me3SiOTf. Hydride complexes Tp*Re(O)(H)X ( X = Cl, H) are generated from the corresponding alkoxide complexes with BH3 . THF. Oxidation of Tp*Re(O)Ph(OTf) with Me2SO gives a phenoxide complex, a nd oxidation of Tp*Re(O)Et(OTf) with pyridine N-oxide gives acetaldehyde, B oth reactions are similar to oxidations of related Tp compounds. Tp*Re(O)H( OTf) is oxidized by either reagent to Tp*Re(O)(3), with liberation of H+; s uch a hydride complex has not been accessible in the Tp system. The Tp* lig and imparts added stability to the rhenium(V) derivatives, making preparati ons easier. Steric constraints of the Tp* ligand are illustrated by the lac k of phenyl and pyridine ligand rotation on the NMR time scale. The stabili ty and crowding of the Tp* compounds inhibits reactions with oxygen atom do nors so that heating is often required, and the resulting oxidations are mo re complex than for analogous Tp compounds.