Rhenium(V)-Salen Complexes: Configurational Control and Ligand Exchange.

Reactions of ReO(PPh(3))(2)Cl(3) with tetradentate bis(salicylideneamine) ligands, H(2)salpd (1) and H(2)salbd (2), in different alcohols gave the novel mixed-ligand rhenium complexes ReO(sal)OAlk (OAlk = variety of alkoxy ligands). Configurational studies show that the rhenium complexes ReO(salpd)OAlk (1a-f) display either a symmetrical or a nonsymmetrical configuration, depending on the size of the alcohol and its boiling point. The rhenium complexes ReO(salbd)OAlk (2a-d) are all nonsymmetrical due to the number of carbons that bridge the imine nitrogens. In the case of the symmetrical ReO(salpd)OMe (1a) complex the methoxy ligand can be exchanged for a number of ligands of different types (OAlk, OPh, SAlk, OC(O)Alk). In the newly formed complexes the original configuration was retained except for the ReO(salpd)SAlk (1i,j) complexes which were isolated in the nonsymmetrical configuration. Starting from the nonsymmetrical ReO(salpd)OPr (2c) complex, ligand exchange led to a mixture of the symmetrical and nonsymmetrical complexes, with ratios depending on the reaction time. The crystal structures of ReO(salbd)OPr (2c), and ReO(salpd)OPhOMe (1g) have been determined. ReO(salbd)OPr crystallizes in the triclinic space group P&onemacr;, Z = 2, with a = 10.0344(16) Å, b = 10.647(2) Å, c = 11.481(2) Å, alpha = 86.551(15) degrees, beta = 86.998(14) degrees, gamma = 80.112(15) degrees, V = 1205.1(4) Å(3), and final R = 0.0460. Crystals of ReO(salpd)OPhOMe are orthorhombic, space group P2(1)2(1)2(1), Z = 4, with a = 10.6222(15) Å, b = 12.442(3) Å, c = 16.354(3) Å, V = 2161.4(7) Å(3), and final R = 0.0371. Under the influence of traces of water a number of symmetrical complexes react to a "dimeric" structure, consisting of two ReO(salpd) moieties bridged by an oxygen atom with the bridging Re-O-Re angle symmetrically imposed at 180 degrees. [ReO(salpd)](2)O (3) crystallizes in the monoclinic, space group P2(1)/c, Z = 4, with a = 14.860(2) Å, b = 12.545(2) Å, c = 16.5111(17) Å, beta = 95.030(10) degrees, V = 3066.1(7) Å(3), and final R = 0.0439.