Multiple Bonds between Transition Metals and Main-Group Elements. 145.1 Coordination Chemistry of Dirhenium Heptaoxide: Covalent Adducts and “Ionic Perrhenyl-Perrhe-nates”

Abstract

Dirhenium heptaoxide dissolves in donor solvents such as 1,2-dimethoxyethane, thf, and CH3CN to form adducts of the general formula O3ReOReO3·2L (L = monodentate ligand site). A strong reactivity enhancement of Re2O7 for alkylation, arylation, and similar reactions follows from this unsymmetric Lewis-base coordination. The terminal and bridging oxygens equilibrate in solution (l7O NMR). These adducts exhibit unsymmetrical bent oxygen bridges in their solid state structures, e.g. O3ReOReO3·dme (X-ray diffraction study; crystal data: space group P21/c, a = 12.162(2) Å, b = 10.830(1) Å, c = 8.195(1) Å, β = 90.80(1)°, Z = 4). With stronger, chelating N-donors L2 such as 2,2′-bipyridine, N,N′-dicyclohexyl-l,4-diazabuta-l,3-dien, and 2,2′-bis(pyrazolyl)propane the Re2O7·2L complexes have rigid asymmetric bridges even in solution (17O NMR). Thermal decomposition liberates Re2O7 (EI-MS) and the respective ligand (EI-MS, TG-MS). With tridentate ligands L3 like tris(pyrazolyl)-methane, 1,4,7-triazacyclononane (tacn), N,N′,N′′-trimethyl-l,4,7-triazacyclononane (tacn*), 1,4,7-trithiacyclononane (ttcn), the Re-O-Re bridge breaks with formation of the ionic perrhenates [ReO3L3]+[ReO4]−. An example is the ionic [Re03(tacn*)]+[ReO4]−, the structure of which compound has been determined by X-ray diffraction (crystal data: space group P1, a = 7.389(2) Å, b = 9.143(2) A, c = 1.2294(3) Å, a = 83.68(2)°, β = 77.99(2)°, γ = 89.29(2)°, Z = 2). Intermolecular hydrogen bridging plays a major role in the crystal packing of the ionic perrhenates. © 1995, American Chemical Society. All rights reserved.