Oxorhenium(V) complexes with ketiminato ligands: coordination chemistry and epoxidation of cyclooctene.

Rhenium(V) oxo complexes of the type [ReOX(L)(2)] (1-7; X = Cl, Br) containing beta-ketiminate ligands (L = CH(3)C(O)CH(2)C(NAr)CH(3): Ar = Ph (APOH), 2-MePh (MPOH), 2,6-Me(2)Ph (DPOH), 2,6-(i)Pr(2)Ph (DiPOH)) have been prepared by reaction of [ReOX(3)(OPPh(3))(SMe(2))] (X = Cl, Br) with the lithium salts of the corresponding ligands. All compounds have been spectroscopically characterized, showing [ReOX(DiPO)(2)] (X = Cl (1), Br (5)), [ReOX(DPO)(2)] (X = Cl (2), Br (6)), and [ReOX(APO)(2)] (X = Cl (4), Br (7)) to be isomerically pure, in contrast to complex [ReOCl(MPO)(2)] (3), which exhibits a mixture of isomers. Compounds 2, 3, 5, and 7 were crystallographically characterized, showing similar octahedral coordination spheres with trans O horizontal lineRe-O and cis O horizontal lineRe-Cl bonds. However, the coordination of the nitrogen atoms vs each other is found to be cis or trans. Compounds 2 and 5 showed a trans-N,N configuration, for compound 3 both isomers (trans-N,N 3 and cis-N,N 3) were structurally characterized, and 7 gave a cis-N,N configuration. Compounds 1-6 are catalyst precursors for the epoxidation of cis-cyclooctene with 3 equiv of tert-butyl hydroperoxide (TBHP). Yields of the formed epoxide were up to 55% with all precursors, except with 2 and 6, where only up to 13% of epoxide was obtained under analogous conditions.