Synthesis and Characterization of Novel Rhenium(V) Tetradentate N₂O₂ Schiff Base Monomer and Dimer Complexes

Several rhenium(V) oxo complexes with tetradentate N2O2 Schiff base ligands were synthesized and characterized. The general synthetic procedure involved reaction of [NBu4][ReOCl4] with a tetradentate Schiff base ligand (L1 = N,N‘-ethylenebis(acetylacetoneimine), (acac2en) or L2 = N,N‘-propylenebis(acetylacetoneimine) (acac2pn)) in ethanol solution to generate complexes of the form trans-ReOX(L) where X = Cl-, MeO-, ReO4-, or H2O. The product isolated from the reaction was found to be dependent on the reaction conditions, in particular the presence or absence of water and/or base. The μ-oxo-Re2O3(L)2 dimers were synthesized and characterized for chemical and structural comparison to the related monomers. Conversion of the monomer to its dimer analogue was followed qualitatively by spectrophotometry. The complexes were characterized by 1H and 13C NMR, UV−vis, and IR spectroscopy, elemental analysis, and single crystal X-ray diffraction. The crystallographic data reported for the structures are as follows: trans-[ReO(OH2)(acac2en)]Cl (H20C12ClN2O4Re) 1, triclinic (P1̄), a = 7.2888(6) Å, b = 9.8299(8) Å, c = 10.8195(9) Å, α = 81.7670(10)°, β = 77.1510(10)°, γ = 87.6200(10)°, V = 747.96(11) Å3, Z = 2; trans-[ReO(OReO3)(acac2en)] (H18C12N2O7Re2) 2, monoclinic (P21/c), a = 7.5547(4) Å, b = 8.7409(5) Å, c = 25.7794(13) Å, β = 92.7780(10)°, V = 1700.34(16) Å3, Z = 4; trans-[ReOCl(acac2pn)] (H20C13N2O3ClRe) 3, monoclinic (P21/c), a = 8.1628(5) Å, b = 13.0699(8) Å, c = 28.3902(17) Å, β = 97.5630(10)°, V = 3002.5(3) Å3, Z = 8; trans-[ReO(OMe)(acac2pn)] (H23C14N2O4Re) 4, monoclinic (P21/c), a = 6.7104(8) Å, b = 27.844(3) Å, c = 8.2292(9) Å, β = 92.197(2)°, V = 1536.4(3) Å3, Z = 4; trans-[μ-oxo-Re2O3(acac2en)2] (H36C24N4O7Re2) 5, monoclinic (P21/n), a = 9.0064(5) Å, b = 12.2612(7) Å, c = 12.3695(7) Å, β = 90.2853(10)°, V = 1365.94(13) Å3, Z = 2; and trans-[μ-oxo Re2O3(acac2pn)2] (H40C26N4O7Re2) 6, monoclinic (P21/n), a = 9.1190(5) Å, b = 12.2452(7) Å, c = 12.8863(8) Å, β = 92.0510(10)°, V = 1438.01(14) Å3, Z = 2.